Friday, October 30, 2009

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.

Thursday, October 29, 2009

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.

Wednesday, October 28, 2009

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."

Tuesday, October 27, 2009

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.

Friday, October 23, 2009

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.

Thursday, October 22, 2009

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."

Tuesday, October 20, 2009

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.

Monday, October 19, 2009

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 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.


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.
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.

Sunday, October 18, 2009

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.

Saturday, October 17, 2009

From the NHC

WTPZ65 KNHC 172208
310 PM PDT SAT OCT 17 2009



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.

Thursday, October 15, 2009

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.

Monday, October 12, 2009

TS Patricia Moving Slowly Northward

Tropical Storm Patricia (see IR image from 12 UTC above) is located south of the tip of Baja and is moving slowly north-northwestward. The combined influences of Patricia and the negatively-tilted trough off California have produced a long fetch of southerly to south-southwesterly winds from the south end of Baja northward into southern Arizona. There is a strong gradient in precipitable water (see the PW time series at atmo home page), ranging from half an inch along the southern Arizona border to over 2 inches at Navajoa, Sonora. Strong morning convection is underway about half way up the Gulf of California, and a low-level cumulus field is moving northward into southern Arizona. So, there are some indications that the current moisture plume, below 500 mb, from the subtropics may affect southeastern Arizona. The morning NAM model runs indicate the deeper moisture will just clip the southeast corner of Arizona and impact mostly New Mexico; however, the NAM also forecasts a strong southerly flow at 850 mb from the GoC into southern Arizona persisting for next 24 to 36 hours. So, something to keep an eye on to the south.

Tuesday, October 06, 2009

Typhoon Melor Heads Toward Japan

Melor is now a Typhoon with sustained winds of 110 kt and gusts to 135 kt, i.e., equivalent to a high-end Cat. 3 Hurricane. The storm is forecast to hit the main island of Japan tomorrow evening. It is expected to weaken to a Cat. 1 equivalent by the time it makes landfall.

Super-Typhoon Melor

The above is an IR image of Super-Typhoon Melor on the 4th of October 2009. This was an extremely intense Typhoon - equivalent Cat. 5 relative to Hurricanes in Atlantic and east Pacific. There are numerous photos, news stories, and satellite images on the internet if one searches.

Unusual Sounding Problem

Jason Criscio sent the above photo a bit after 4 pm yesterday, asking if the NWS was trying a new procedure to be sure the upper-air sonde was reading correctly. He said the balloon (top center) had been floating above the NWS roof for about 15 minutes. However, he reported that it was still there after 7 pm and that he had seen another balloon launched.

So, Jason's photo shows one of the dangers of launching upper-air balloons from an open, exposed tub on top of a cluttered roof. The instrument package apparently snagged on the top of the tracking system dome, requiring a second sonde launch. The strange and unique launch system used at TWC (Tucson) is documented in the first part of the 21 June 2007 post titled
"Comments on the NWS Radiosonde Replacement System (RRS)" at

Friday, October 02, 2009

Very Difficult Forecast Situation

First - low temperatures: this was the first morning this Fall with a low down in the 40s - 47F - here at the house (note that it was quite a bit cooler down at the Rillito pathway). The airport (TUS) only dropped down to 59F this morning.
Second - Olaf makes for a difficult forecast situation. This morning's NAM run continues to keep the significant precipitation along and south of the border. The circultion of Olaf is quite large and the moisture shield extends far to the north of the center. It seems clear that the circulation of Olaf at and above 500 mb will shear away quickly to the east after about 24 hours. However, the NAM indicates that the large circulation below 500 mb will continue moving to the north as a remnant low and that low-level southerly winds will affect southern Arizona beginning in 24 to 36 hours (perhaps sooner given the model's tendency to be slow on moisture advection) and continue out through 72 hours. Thus, there should be a large advection of low-level moisture across the border, ahead of the digging cutoff/short-wave at 500 mb. So, the interplay among all these features will produce a significant October precipitation event and the key question for here will be how far north the event can advance. It will be interesting to see what the atmo WRF runs indicate later this morning.

Thursday, October 01, 2009


The Tropical Storm west of the tip of Baja now officially has a name - Olaf.

Evening Storms

There were a few storms across southeastern Arizona yesterday afternoon and evening. the photo above shows strongly sheared towers building south of the Rincon Mountains just after sunset. The main tower quickly developed into a 50 to 60 dBZ storm that moved rapidly eastward, just north of Benson.
All eyes now to the south, as we watch to see exactly how the very large tropical disturbance off of Baja will evolve. The NAM model also predicts very cold temperatures in the core of the next short-wave trough as it moves it south along the west coast.