WRF model 850 mb Prog

From Mike Leuthold - the high-res WRF forecast of 850 mb winds and Td valid 1 pm on Thursday the 21st. Very impressive - looks like a Southern Plains situation setting up out here in the desert! So far, even with all the clouds and two rain bands passing by, I can only report 0.02" of rain sprinkles. Hopefully, more in later reports.

RE 17 January 2010 Post

Mike Leuthold writes:

Bob,
That precip amount is way out of line. The regional WRF forecast has Tucson in the precip hole again with amounts around 1/2 inch. See this graphic for total precip to see what I mean.

http://www.atmo.arizona.edu/products/models/forecasts/wrf_disc_html_m38aa2520.jpg

Light Rain Showers at Sunrise

A rain band, aligned along I-10 and zipping rapidly to the east, has produced the first rain sprinkles of the past 25 days here at the house. Light showers at sunrise and a Trace at 7 am MST. Very nice to smell rain in the air. Heavy cloud clover kept the morning low at a mild 43F. The big weather change has indeed begun - quite amazing long-term numerical forecasts from several hundred hours ago!

Serious Outlooks and Forecasts For Next Seven Days

A number of forecasts and outlooks have indicated serious amounts of rainfall and snow for the Southwest during the coming week. The radar chart above indicates that the rainy week is already underway in southern, coastal California.
-----------------------------------------------------
From the NWS at San Diego on Friday the 15th -

HYDROLOGIC OUTLOOK

 1220 PM PST FRI JAN 15 2010

 
 ...EXTENDED PERIOD OF SIGNIFICANT RAIN AND MOUNTAIN SNOW NEXT WEEK
 FOR SOUTHERN CALIFORNIA...

 A STORMY PATTERN IS SETTING UP ACROSS THE EASTERN PACIFIC OCEAN THAT
 WILL BRING PERIODS OF MODERATE TO HEAVY RAIN AND MOUNTAIN SNOW TO
 SOUTHERN CALIFORNIA MOST OF NEXT WEEK AND POSSIBLY INTO THE
 FOLLOWING WEEK.

 BASED ON HISTORIC PATTERNS...THIS WEEK-LONG EVENT HAS THE POTENTIAL
 TO GENERATE RAINFALL OF 5 TO 8 INCHES NEAR THE COAST...TO 20 OR
 MORE INCHES ON THE COASTAL MOUNTAIN SLOPES. TYPICALLY WETTER
 LOCATIONS ON THE COASTAL MOUNTAINS SLOPES COULD RECEIVE 30 OR MORE
 INCHES OF RAINFALL. AT HIGHER ELEVATIONS IN THE SAN BERNARDINO
 MOUNTAINS... MOSTLY ABOVE 6000 FEET...4 OR MORE FEET OF SNOWFALL IS
 POSSIBLE.
 ---------------------------------------

Steve Mullen reports that a local weathercaster last evening called for

up to 1" of rainfall in Tucson on Tuesday and up to 1 3/4" on Friday

with snow amounts in the Catalinas up to 5 feet.

This afternoon's NWS forecast indicates POPs of 100% for Tuesday night

and Thursday night - the highest POPs out at 48-hours and beyond that

I can recall since I moved here.

Quite a change from the last 3 weeks of no weather - better clean the

crud out of my rain gauge!

Strong, Zonal Pacific Jet Now in Place!

The 300 mb GFS analysis from 1200 UTC this morning (Saturday Jan. 16, 2010) shows an extremely strong (>150 kt core), zonal jetstream across most of the Pacific. The development of this feature has been consistently forecast by both GFS and ECMWF models for about 10 days now. Simply quite amazing. We will now see what the next 10 days bring to us in the Southwest.

Morning Showers

It is a cool morning in Tucson with 500 mb S/W nearly overhead and a smell of moisture in the air. No showers at house but a heavy snow shower has been moving across the Catalina mountains. Photo from Computer Science Building on campus, above, shows the shower at right side (east half of mountains) of the view.

Heavy Clouds over Catalinas

Heavy clouds moving in from the northwest over the Catalina Mountains this morning, with some sun peeking in beneath the clouds. Some virga around as the first in a series of S/Ws aproaches. This first S/W is digging in down the coast, but the next several are forecast to come into the Southwest more directly off the Pacific. Thus, the much advertised pattern change is just about to get started.

GFS Forecasts

Jack wrote: Bob.. Looks a little thin for our part of AZ...near Tucson with just a tenth of an inch! Lets hope for more this far south! - Jack

Of course this far out, the model "answers" depend on what product and what model(s) one looks at. From this morning's operational GFS run the forecasted precipitation totals from 180 to 240 hours is shown above. This would be quite a nice change for Tucson and then the next 60 hours' forecast has purple contours over southeastern Arizona. All very enticing but sometimes the GFS-world is much different than the real world - so we'll have to wait this all out.

More on Pattern Change for the West

Chris Smallcomb, of Reno, had an interesting post to SUNY map weather talk list yesterday about the forecasted change to a wet pattern for the West. He used a number of nice graphics and I've shown one above. This is GFS 240-hour accumulated precipitation for the 240 hours ending at 0600 UTC 21 January 2010. Quite something, and I for one am certainly hoping that precipitation along these lines is coming our way.

Long-term GFS Forecasts Very Wet

While I usually focus on the shorter-term numerical forecasts, I have noticed for several days now that the GFS longer-range forecasts are indicating the development of a very wet pattern for the Southwest. In the near-term, several S/Ws break under/thru the western North America ridge. But, by 228 hours (see above) from the 12 UTC initialization this morning (Sunday January 10th) the GFS forecasts six consecutive 12 hour periods of significant rainfall over Arizona - i.e., from Tuesday afternoon of the 19th right through Friday the 22nd. This would be the rainiest period over AZ in many months - IF it were actually to occur in the physical world. While I show the operational GFS forecast above, the GFS ensemble members are all quite consistent in forecasting this 72-hour period of substantial rains. Something very interesting to keep an eye on as the month progresses!

First Day This Year With No Rain!

The new year is off to a clear and dry beginning, starting off much like most of 2009. The photo above is from September 6, 2009 - a day on which 0.10" of rain fell here at house from the dissipating Cb.

Brief overview of 2009 observations from our backyard:

*December precipitation - 0.61"

*Annual precipitation for 2009 - 7.95" which was quite dry but considerably better than the airport (TUS) did (only 5.67" making 2009 the fourth driest year ever at that location).

Two months I measured over an inch of rain - July 2.63" and August 1.06" Note that 8 days during July 2009 had storms and rain that produced 33% of the year's total precipitation.

*Three months had a tenth of an inch or less - June, October, and November

*Here at the house the low temperature was in the 20's on 36 days - with December 26 and 27 being the coldest days at 20F. The location here, very near the Rillito Wash, is very cold relative to the airport - for example, the low here this morning was 24F while the airport's low was a balmy 42F (calm here and breezy at the airport).

*For the first time since I started my weather log at this location there was not a single severe thunderstorm during the year, and there was no day with a rain amount of an inch or more ( heaviest 24-hour rainfall 0.77" on July 3/4).

*So a very benign and dry year here - here's hoping for a better weather year in 2010!

Happy New Year to all - Bob

Details on Christmas Eve Blizzard in Oklahoma

For details on the Christmas Eve blizzard in Oklahoma, see Roger Edward's photo above and his blog writeup at http://stormeyes.org/wp/

Cold Christmas

The Christmas Holiday has been quite cold here at the house with morning lows of:

Dec. 24 25F

Dec. 25 21F

Dec. 26 20F

Dec. 27 20F

This morning's low (on 26th) of 20F is the coldest since Dec. 28 2008 - when the low was also 20F. Very chilly for the desert but much warmer than many experienced the last several days!

Winter in the Desert

BEST OF THE HOLIDAY SEASON TO ALL WHO DROP-IN HERE! Bob

Second Strong Storm of December Across Arizona

As was well advertised by both the short and long-range models, a strong storm pushed across Arizona yesterday and during the night. There is some snow lingering in the far southeast portions of the state. The subtropical moisture plume mentioned in Sunday's post did come across southern Arizona briefly (mainly as high and middle clouds with some virga, mammatus, and sprinkles - trace here at house midday yesterday) but was shunted east and south before the strong PVA moved into southern Arizona. The storm blew into the Tucson area yesterday afternoon with gusty winds and plenty of blowing dust, as shown above.

Highlights from the observations this morning:

It is difficult to assess the Pima County ALERT gauges this morning since higher elevation sites experienced a snow event and those gauges are registering "0". It does appear that the coverage was nearly a 100%, although a couple of sites in the far west part of the network might have stayed dry. Amounts ranged from around a 1/10" to a bit more than 1/2" - once again well-predicted by the models. Here at the house we had 0.32" and atmo had 0.51". Winds gusted at most southern Arizona stations to around 40 to 50 mph, not nearly as strong as with the event of December 7/8. I did note that Gutherie recorded 64 mph, Horse Camp Canyon had winds to 72 mph, and the atmo anemometer (75 ft above ground level) had several gusts around 65 mph.

Other observations of interest: snow occurred this early morning at Nogales, Ft. Huachuca, and Douglas, and during the night at Kingman. Phoenix and Scotssdale reported thunderstorms yesterday afternoon, and Prescott had thunder with snow. The models continue to predict that this S/W will will produce a blizzard-like storm for parts of the central and northern Plains on Christmas day.

More on Tuesday Night/Wednesday AM Storm

Shown above is an Eastern Pacific IR image from 1400 UTC Sunday morning. At the present time there is a long plume of tropical and subtropical moisture extending northward into the S/W that will be digging down the coast. Thus, there is a nice "pineapple" connection in place. However, the NAM does not pick this plume up as the S/W digs. Rather, the NAM indicates that westerly flow around the base of the trough will shunt the low-latitude moisture off to the east and into Mexico. This connection should be monitored closely the next two days, since it has the potential to bring a more significant precip event to the Southwest than the model currently is predicting.

Interesting Weather Situation Developing for Southwest

After the huge snow storm in the East, attention for the next strong storm event will shift to the Southwest. This morning's (Sunday 20 Dec 09) NAM 500 mb forecast valid on Wednesday morning indicates very strong PVA across southern Arizona. Thicknesses (1000 - 500 mb) around Tucson are very near 534 dm, indicating quite low snow levels with this storm. All the models are very consistent and indicate that this strong S/W will swing rapidly into the Central Plains, producing a Christmas Eve blizzard. Thus, a very interesting event is unfolding for Southwest and Central Plains as Christmas approaches.

Strong Winds in Southern New Mexico

From Mike Hardiman in El Paso regarding the strong winds that impacted much of the state yesterday (Mike asks a good question below concerning the possible roll of the N-S Franklin Mountains in the localized occrrence of very strong winds east of the mountains).

Quite the wind event in the El Paso CWA today (Tuesday, December 8, 2009). Widespread damage in the Sacramento Mountains with 70 mph wind gusts at an APRS mesonet site in High Rolls, NM (elev ~6250) and 55 mph at a WxUnderground site in Cloudcroft, NM (elev 8850). Both were recorded before 9am and were the last obs reported before apparent power outages stopped the data flow. Lots of trees and powerlines down, some falling into homes.


The 12z RAOB from EPZ showed a strong inversion just above the mountaintop level of the Franklin Mountains which bisect the city of El Paso. Wind Gusts on the east (leeward) side of town topped out at 79 mph at an AWS site, which was well supported by 75 and 78 mph gusts at other mesonet stations. Wind blew down the signature canopy at Cohen Stadium (which looks eerily like Denver Int'l Airport), roofs blown off structures, debris breaking car windows, trees down, etc. Also, the Transmountain highway was shut down due to high winds blowing rocks into the road. Lots of residents reported a "tornado" despite just scattered flat Cu at 6000 feet. Interestingly, a plot of all the "mesonet" sites on the East Side shows one site reporting a SE wind much of the morning (everyone else was SW), before turning due West with that 79 mph gust, after which it remained SW. Don't really trust the siting of all these stations (combination of AWS Schoolnet, APRS, WxUnderground, etc), but the one site in question hasn't been noted to have wind direction issues in lighter winds. Can't help but wonder if a rotor or some sort of lee-side eddy wasn't at work here and may have aided in the damaging winds -- the worst damage was sort of clustered in the area of this cock-eyed wind ob.


A notoriously windy site at Aguirre Springs, NM, on the east slopes of the Organ Mountains near Las Cruces has a 97 mph recorded gust which destroyed a well-built hay barn. Widespread wind damage also occurred at White Sands Missle Range Main Base, 'de-roofing' the Police Station there, knocking out powerlines, injuring 2 people, and finally sending workers home early. WSMR's mesonet includes a station at San Augustin Pass (elev ~5700), through which US-70 links WSMR with Las Cruces. Peak Gust 116 mph. Hurricane force winds there are common in WSW high-wind events, but 100+ mph is still quite notable.

See:

http://www.uswx.com/us/stn/KELP/?code=c

Rapid Deepening of the Upper-Midwest Cyclone

The cyclone bringing the blizzard and severe winter storm to the central US deepened rapidly during the night. At 00Z last evening it had a central pressure of ~994 mb. This morning it has moved to near Milwaukee (see above) and deepened to ~978 mb. Thus, the storm has been deepening at more than a mb an hour - very impressive.

Weather Watchers

Cows in southeast Nebraska watching and waiting for the blizzard to arrive.

Big Storm Blows into Central Plains

Very late post today.

Brief summary of various aspects of the overnight storm event.



Precipitation - at 7 am this morning about 75% of the Alert gauges in Pima County had measured precipitation in past 24 hours. Those that had not had rain were generally in the southern portions of eastern Pima County and most of those had light rainfall after 7 am. We had
0.24" in the gauge at 7 am here at house and had 0.02" more in the next hour or so. Heaviest rainfall report I noted at 7 am was 1.65" at CDO and Coronado (i.e. up on the northwest flanks of the Catalinas).

Snows were quite heavy at high elevations in the mountains and the photo above shows a bit of snow on higher peaks of the Catalinas at right side of photo.

However, the main aspect of the storm was the very strong wind gusts that swept across most of state - many areas in almost all parts of state had winds of 50 to 60 mph and max gusts were considerably higher. For example, the Gutherie RAWS station reported winds of 79 mph, Horse Camp Canyon had 73 mph, and the anemometer on the roof of the Atmo building on campus also had 73 mph. The only station that reported thunder was apparently Phoenix and the SPC storm reports map indicates a number of severe thunderstorm reports in Arizona last evening. This was a "sneaky" severe storm situation in that the severe winds were produced by the extreme synoptic pressure gradients and the thunderstorms were along for the ride!

The most interesting thing about the photo above is that there is considerable dust hanging in the air, even after widespread precipitation. This gives an erie cast to the photo and as the preciptation areas moved to the east they had a distinct brownish cast to them. Very strange morning reflecting the power of the windstorm.


The strong S/W that produced th overnight weather in Arizona has swept eastward very quickly and is now bringing a very major snow event to the Central Plains and upper Midwest, in addition to widespread blizzard conditions tonight as the low intensifies.

Not Quite as Cold This Morning

Considerably high-level cloudiness moved into southern Arizona overnight helping keep temperatures a bit warmer last night. Low here at house was 24F. Low at TUS NWS observation site was only 35F this morning, in contrast to 32F yesterday. The exception was far southeast Arizona, where Douglas dropped to a low of 20F this morning, in contrast to their low yesterday's of 27F.

Difficult forecast situation for next week as fast, low-latitude flow will bring several S/Ws across Arizona with at least some moisture from Pacific. Situation is complicated by the strong, cold S/W trough to the north - making timing, exact locations, and possible amounts of precipitation hard to anticipate precisely. Pattern for next couple of weeks certainly looks el nino-ish!

Cold Morning Here at House

It was quite cold here this morning - coldest of the winter so far with a low of 23F. I noticed a lot of readings down in the 20s this morning across southeast Arizona. The coldest I saw at lower elevations was 21F at Sasabe. This was 14th freeze this winter here at house and 7th day down in the 20s.



Snow photo above is from Mike Hardiman in El Paso. he has taken a lot of nice shots of the snowfall produced in the New Mexico and big bend borderlands by the storm earlier this week (see below) and these can be viewed at

http://www.flickr.com/photos/33443072@N04/sets/72157622802834945/

Jim Means reports from

Alpine, CA at 1270', 32.83N 116.81W and are Alpine 3W on the hourly roundups out of San Diego

Hi Bob,
We had an under-predicted storm here on Saturday. I got 0.70" at my house with pea-sized hail, and some places nearby had over an inch of rain, with 5 inches of snow at Mt. Laguna.
Nice start to the winter season--things are less flammable now (a prime concern at my house).
Jim

-----------------------------------------

I tried to find recent photos from the snow event across southern New Mexico and the Big Bend country this morning but with no luck. The photo above shows heavy snow falling in El Paso yesterday (Mon Nov. 30th).

Yesterday 5% of the Pima County alert gauges had light precipitation and these were all in the Catalina and Rincon Mountains.

Clear and cool this morning with a low here at house of 31F. Fall (September, October, and November) closes out with only a total of 0.63" inches of rain here at the house.

Cold Winds but Not Much Rain

The intrusion of a strong cold front from New Mexico into southeastern Arionza around 4 am this morning brought an end to the precipitation at lower elevations in eastern Pima County. Strong downslope east winds continue here at the house with gusts estimated 30 to 35 mph. For the 24 hours ending at 7 am 90% of the Pima County alert gauges had measured rain but, even though the event was widespread, amounts were light with the highest amount only 0.47". Here at the house the entire, even with several periods of lightning and thunder, event produced only 0.10". Earlier this morning the strong east winds across the Rincon Mountains produced a sky that reminded me of Colorado - lenticular clouds, a cap cloud sitting on the mountains and a couple of rotor clouds to the west of the mountains. Regardless of the sad amounts of rain, it's nice to have some weather again after so long.

More on the Southwest Cutoff

Photo above shows early morning rainbow today, Sunday the 29th, to the northwest of the house.

As the 500 mb cutoff dug southward across southern California yesterday, strong and gusty winds deloped in south-central Arizona around mid to late morning on Saturday, November 28th. The winds caused a serious dust storm between Tucson and Phoenix that resulted in wrecks and fatalities on I-10.

-----------------------------------------------------

CASA GRANDE, Ariz. - Two people are dead after their small sport utility vehicle crashed into a commercial vehicle during a dust storm in south-central Arizona.

The state Department of Public Safety began warning travelers Saturday morning to avoid Interstate 10 near Casa Grande until the dust settled. The wind slowed down by the afternoon, but Public Safety spokesman Harold Sanders said visibility along the interstate from mile post 190 to 216 remained poor.

Sanders says officers are investigating five separate collisions in the area that resulted from Saturday's dust storms, including the one involving the two fatalities. He did not have details on the other collisions.

-----------------------------------------------------

Finally Some Weather in the Southwest!

A strong and cold cutoff at 500 mb has dug into the Southwest during the last 36 hours, bringing clouds and thunderstorms to the Tucson area. Photo above shows clouds hanging on the west flanks of the Catalina Mountains at sunrise on November 29, 2009. At 7 am I measured only 0.01" but saw some in-cloud flashes and heard rumbles of thunder. This is the first rainfall since October 3rd. Just the smell of moisture in the air is very much welcome!

Low temperatures last several mornings

As the photo above shows, we've had another night with clear skies and strong radiational cooling here in Tucson. The low temperatures here at the house (near the Rillito Wash on the north side of Tucson) for the last three mornings have been: Monday Nov. 16 - 26F (39F); Tuesday Nov. 17 - 27F (53F); and Nov. 18 - 36F (48F). The temperatures in parens are the official NWS observed morning lows at Tucson International Airport (TUS). The winds has kept things warmer down south at the airport; whereas, each morning here at the house it has been calm. The remarkable 26F difference between here and the airport on Tuesday morning is the largest that I've observed - beating the previous record of 23F! I also suspect that the temperature down at the Rillito was several degrees cooler than here at the house - so there's the low down.

No measureable rain here since October 2/3 but it does appear there was a sprinkle trace on Saturday the 14th. It did rain on Saturday where we were, 5 NW of Sonoita, as I suspected it would. The orographic forcing there is quite good with S to SW low-level winds.

Showers on the Catalinas

Early morning view looking north to the Catalinas, where the montain tops were also in the clouds. The two 500 mb S/Ws affecting the western US have pulled substantial moisture into Arizona - a nice change from past days this week. Could actually smell moisture when I walked this morning. Showers now obscuring parts of the mountains, where the current POPs of 20 to 30% are not high enough. Will be interesting to see what happens down at lower elevations. We'll be down NW of Sonoita this afternoon through tomorrow and there'll be an excellent chance that we'll finally see a bit of rain (probably 70% chance or greater based on my experiences down there).

Finally a Bit of Weather

Web cam view on Kitt peak showing that the mountain is in the clouds this morning.

Slight Bit of Weather in Tucson

It has been very dry and mostly tranquil here in Tucson during most of October and early November. October was exceedingly dry with rain at house on only one day (late on the 2nd) that amounted to only 0.05". A weak, upper-level short-wave came by off the Pacific yesterday and produced an afternoon with thick heavy cloud, and some virga and mammatus. A quite dreary afternoon actually.

This morning there are puffy Cu floating around and a few mini-Cbs, as in the photo above. Note the classic Cb structure for this tiny cloud - a clearly distinct updraft area with darkened, flat cloud base, anvil, and snow-crystal virga falling out of the down-shear side of the cloud. Quite an amazing little Cb. That's not a drifting weather balloon above the Cb, but is rather the waning, 3/4 moon. Photo was taken at 8 am this morning (Thursday Nov. 5th, 2009) looking to the west.

Whoops - How did the Seven Day Forecasts Verify?

I have completely redone this post. Paul Iniguez posted a Comment that linked to a nice looping tool for the model forecasts. I was browsing this tool and noticed that I posted the wrong verifying analysis in the original post! Twelve hours can make quite a difference!

Back on October 23rd I posted the 168 hour forecasts (from 23/12Z observations) of the operational versions of the ECMWF and the GFS. These 500 mb forecasts verified at 12Z this morning (30 October). They are posted below and if interested one can scroll down and assess how well the forecasts did wrt the verifying analysis at 500 mb (posted above).

You'll see that the models were each off about a quater of a wavelength for the deep trough over the central US. The ECMWF was too slow, especially for the southwestern end of the trough. Whereas, the GFS was too fast. Both models had troubles with the following trough off the Pacific coast.

A quick scan of the verifying analysis heights vs the forecast heights indicates that the GFS had heights too low by about 450 m off the northwest WA coast and the ECMWF had heights about 250 m too low over southern Arizona.

But, all-in-all, model performance at 5 to 7 days was just amazingly good from my old-timer perspective!

Snow Event in Northern Mexico

From Mike Hardiman - El Paso

You've probably already seen this, but vis satellite this morning shows snow fell over the higher terrain deep into Chihuahua, Mexico overnight. In fact, the observation from Chihuahua City this morning was carrying Snow Grains, Temp of 32F. Snow coated the Franklin Mountains here in El Paso, down to about 4500' elevation. A few flakes fell even in the valley locations (~3600') yesterday.

Tough Sledding on The Plains

Web cam view of I-70 at Bennett, CO, at 2:30 pm 29 October 2009. The storm in Colorado has dumped about 1 to 3 feet+ of snow along the Front Range from Colorado Springs north to Cheyenne. Heaviest snow and blizzard conditions have shifted eastward onto the Plains this afternoon.

Back here in Tucson, we had the coldest morning at the house since February 11, 2009 with a morning low of 26F.

Very Rare Occurrence

How often does the coldest 500 mb temperature in continental US and southern Canada occur at Tucson, Arizona?

Storm Heads Toward Denver

View of the State Capital in Denver this morning (October 28, 2009) as the snow storm begins to ramp up in Colorado.

Here in southeast Arizona we had mostly dust and wind yesterday afternoon and during the night. Temperatures have been falling since around midnight. Very little precipitation except at higher elevations. The Pima County ALERT network data show that 8 of the mountain sites reported measurable rainfall. Amounts were light except at Davidson Canyon which reported 0.24" - the Carr RAWS station reported 0.21". So this event, which materialized much more quickly than the long range models had been forecasting 5 or so days ago, brings us wind and winter-like temperatures. Winds were mostly in the 30 to 45 mph range as the cold front swept through, but there were some reports of higher maximum gusts at the RAWS stations in southeast Arizona: Mt. Hopkins 50 mph, Horse Camp 53 mph, Chiricahua NM Headquarters 55 mph, and the highest I found this morning - Gutherie 60 mph. So, words for the day are "bundle up and keep warm."

Dust Laden Skies

Evening view looking north toward Catalinas as winds of 30 to 40 miles per hour bring in dust and grit from western Arizona. Ugh.

Coldest Morning of Fall

Morning web cam shot of sky this morning as strong short wave digs southward toward Arizona. Interestingly, this morning has been the coldest here at the house of the Fall, with a low of 38F.
The first low temperature in the 30s this Fall has occurred about two weeks later than last year when it was 36F on the 12th and 29F on the 13th. The lows here have been very steady during the past week with readings of 42, 42, 42, 42, 41, 40 and 38. It appears that the low at TUS airport this morning was 49 or 50F.

Big Changes in Pattern Likely Part 3

Above is the GFS North Pacific surface forecast for 96 hours from this morning's data (1200 UTC 23 October 2009). The GFS forecasts a tremendously strong surface low to develop in the west Pacific, while a strong low over the central Pacific is weakening and splitting into north and south components. The west Pacific low appears to be related to the extra-tropical transition of once Super Typhoon Lupit, which has been looping and wandering around the area east of Luzon. Definitely a difficult forecast situation. the central Pacific system appears to be interacting with the remnants of former Hurricane Neki, which developed south of Hawaii and is now west of the islands and moving northwardas a Tropical Storm - another complex forecast situation. So, the forecast pattern changes over the U.S. are related to the model forecast, upstream solutions for the very complex situation over the North Pacific. The flip-flopping of forecasts in the two models compared here probably results from both their initializations and the way they forecast the interactions between the tropics and the higher latitudes to evolve over the next few days.

Big Changes in Pattern Likely Part 2

The ECMWF 168 hour 500 mb forecast, valid at the same time as the GFS forecast below is quite different. It predicts a strong cutoff still lingering over the Southwest while the digging S/W is further off the northwest coast. So, the two models indicate a change to an amplified pattern but with the weather outcomes for next Friday being considerably different for much of the country. The ECMWF has been fairly consistent the last two forecast cycles but was much different than the GFS in yesterday morning's forecasts. So, the question is what's causing this large, longer term variance in the two models. See Part 3 above for some possiblities.

Big Changes in Pattern Likely Part 1

The above GFS 500 mb forecast is at 196 hours, valid next Friday at 1200 UTC. Note that the morning run of the GFS was markedly different than the runs from 12 and 24 hours ago in that the strong S/W over the Mississippi Valley is now forecast to be progressive. A new and powerful S/W is now forecast to be digging down the West Coast. See Part 2 above for a comparison with the ECMWF.

More Chaff "Rain"

It has been a perfectly clear day across southwestern Arizona. However, the WSR-88D precipitation algorithm data are indicating that there has been precipitation along the Borderlands and southeast of San Diego (see storm total precipitation product above). One small area along the border is indicated to have received more than 0.60" of rain this afternoon. A bit of the "rain" is due to ground clutter echo, but most of it is due to military chaff releases. Unfortunately, the chaff contamination problem has never been addressed by the WSR-88D agency partners (NOAA-NWS, FAA, and DoD) and these kind of erroneous rainfall products go right into the level 3 archives and lurk there waiting to confound researchers of the future.

David Blanchard commented on the previous chaff post as per:

"A few months ago I noticed chaff streaks in Mexico. What was interesting was they were oriented roughly north-south and were moving to the north.

These streaks had not drifted into Mexico from US military bases and I was left wondering about their origins."

Chaff Streaks in Northern Mexico

The KEMX (Tucson) radar composite image this evening indicates a couple of thunderstorms out in far eastern Arizona and New Mexico. The streamer-like echoes along the border and in northern Mexico are not weather echoes. Rather, they are indeed long streamers of chaff being advected southeastward, by the strong winds aloft, from the USAF training ranges near Ajo. These chaff plumes are extending far into Mexico. The radar's automated rainfall alogrithm has interpreted these as areas of rainfall and has accumulated light swaths of precipitation along the swaths. So it goes - user beware.

Mostly Wind and Dust Here at House

The Kitt Peak web cam, looking south toward Baboquivari Peak, view at 5:30 pm MST this evening shows clear skies but with a dusty boundary layer. The strong afternoon winds of 30 to 40 mph brought in lots of dust late in the day from the west and northwest. Some fast moving thunderstorms occurred over the southeast corner of Arizona this afternoon, but we just had wind and dust here at house.

Should be an Interesting Day

Lots of cumulus scudding to the north-northeast this morning with clouds on most of the mountains. View above was at 7 am looking north from Kitt Peak. Low-level moisture increasing, at least briefly, as strong, short-wave, trough at 500 mb approaches from the northwest part of state. This is not a particularly cold S/W, with coldest temps at 500 mb around -20C, but positive vorticity advection will be fairly strong this afternoon and we should see a nice mix of weather elements: showers, some thunder, wind, dust and falling temperatures.

Art Douglas Reports from Ash Canyon

10 pm MST radar last night from NCAR RAP web site - see second note below

Two nights of thunderstorms here in Ash Canyon (SE Huachucas) with T and 0.01 on the rain amounts..........but spectacular lightning SW to S to SE and East. Heavy rainshafts in Mexico to my SSE much of the evening which got illuminated by the cloud to ground strikes. Saturday's line was active 10PM to midnight and yesterday afternoon Cananea area started popping early and by 7PM to Midnight great lightning display with a good number of leaders coming out of the mid layer of the CBs cloud and back in at 20,000 to 30,000'. Even more spectacular were the positive strokes...very orange and red......one blinded me for a few seconds and the thunder afterwards was incredible. Clouds topping the ridges now with dew point 54F. Models show nothing! No Guaymas sounding since October 17 and Tucson must have failed this morning. LAP MZT and CHIH all have pretty light winds up to about 400mb........not like with Jimena or Olaf. Rick might need a little ventilation to compensate for the drier air from the NW. ECMWF and NAM don't recurve Rick......and it looks like the lower layer system is still moving NW while the upper deck is moving NNE.

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Note that Art mentions the fact that the NWS operational models shear out some of Rick's middle-level vorticity but keep the circulation in the lower half of troposphere drifting slowly around near the south end of Baja. This alternate scenario is mentioned in this morning's 8am NHC discussion, but the official forecasts remain that Rick will turn the corner and accelerate rapidly inland over west-central Mexico.

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Note 2 - The NCAR RAP web site provides easy access to NWS radar reflectivity plots but, because the base scan data are used for both the site and regional displays, the products are seriously flawed across the western US. This is because of severe terrain blockage problems around most sites. The Tucson base scan figure above illustrates the many sectors that are completely blocked. This is why one should always try to examine composite reflectivity products for western US radars.

Precipitable Water Increasing

Precipitable water has been increasing slowly the past 24 to 48 hours as Hurricane Rick's influence has inched the boundary between dry continental air and the subtropical air in Mexico northward. Values have reached around an inch over southeast Arizona and may help fuel additional storms today - particularly if the warm layer of air above 500 mb cools as the strong S/W over the Pacific begins to move toward Arizona. Unfortunately, there is no morning upper-air sounding available from Tucson this morning. Regardless a slight bit of local weather to keep up our interest.

Isolated Thunderstorms Yesterday

There were isolated thunderstorms around southeast Arizona at dusk yesterday, as the 02Z regional radar above shows. The storms were quite pretty, especially to the southeast with very clear skies and the setting sun highlighting them.

Meanwhile At The Other Side of the North Pacific Ocean

Super Typhoon Lupit is spinning away with sustained winds of 135 kts.

Hurricane Rick Still Cat 5 Storm

Hurricane Rick, spinning along over the eastern north Pacific remains a Category 5 Hurricane this afternoon with sustained winds of 140 kts.

From the NHC

WTPZ65 KNHC 172208
TCUEP5
HURRICANE RICK TROPICAL CYCLONE UPDATE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP202009
310 PM PDT SAT OCT 17 2009


...RICK BECOMES A CATEGORY FIVE HURRICANE...

SATELLITE IMAGERY INDICATES THAT RICK HAS BECOME A CATEGORY FIVE
HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE WITH MAXIMUM
SUSTAINED WINDS OF 160 MPH...260 KM/HR.

Rick Continues to Strengthen

Hurricane Rick is now evaluated to be a Category 4 Hurricane after continuing to intensify rapidly. The long range models are indicating that it may have a mid-week landfall on southern Baja.

Rick Develops Rapidly

Apparently Tropical Storm Rick has formed very quickly today (Thursday October 15, 2009) and is currently spinning off the coast of far south Mexico - see above visible satellite image. The models forecast Rick to intensify rapidly and that it will become a major hurricane as it moves to the northwest. Current indications are that it may threaten southern Baja, as have several other storms this season.