A Long, Thin Red Line

There was a very long, but quite thin, squall in the Southeast last evening and night. The top image shows the 0328 UTC radar mosaic (from the CoD page) with echoes of 50 dBZ or greater extending from western Kentucky southwestward to Louisiana. The middle image is from the NWS radar in northeast Mississippi (GWX) and shows a portion of the narrow squall line from a more detailed perspective, with stratiform precipitation trailing along quite a distance to the west. The length-to-width (or vice versa) aspect ratio of the radar squall line of strong storm echoes (>50 dBZ) is truly amazing.
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The bottom figure shows SPC severe thunderstorm and tornado reports from yesterday afternoon, evening and night. The preliminary reports indicate two, extended,  nearly west-to-east swaths of severe reports with a long void between the swaths. It is interesting that the swaths of dense storm reports are oriented nearly orthogonal to that of the squall line. Interesting questions: if real, why the long gap from southwest Arkansas to eastern Kentucky without severe storms? When, if ever, will we be able to anticipate, on time frames of several hours to a day, such strange structures?

Widespread Weather Across US As We Head Toward Weekend

As the 500 mb short-wave trough over New Mexico heads eastward and the strong, cold system over the Northwest digs south today, the country is nearly covered this morning with NWS watches and warnings and special weather statements! See above - range is from a severe thunderstorm watch (TX and OK) to a blizzard warning (ID and WA).

The WRF-GFS run at Atmo at midnight, and the other forecast models, are forecasting gusty winds ahead of the Pacific Coast storm event. Above is WRF-GFS surface forecast for 4 pm Saturday afternoon. Looks like for second straight Saturday the air could be dirty with serious blowing dust and other sundry substances (see post for last Saturday morning down below). Also note above the warm temps with low dwpoints.

Finally, the NWS GFS continues to be the most agressive of the models for the weekend storm across southeast Arizona. The GFS operational member forecast for noon (from 00 UTC run last evening) on Sunday is shown above. All 12 GFS ensemble members now forecast a nice precipitation event for Saturday night. The forecast thicknesses appear cold enough for some flakes here at house, and would likely bring a covering of white to the Dove Mountain course for the finals of the Match Play golf tournament! We''ll keep watching as this event unfolds.

Apparently February 2011 Will End With Its Second Very Cold Weather Event

The forecast models have now been in reasonable agreement for several days (although the NAM seems to be holding with a different alignment of the west coast, short-wave at 500 mb) and indicate another very cold weather system will dig into the Southwest this weekend (500 mb temperatures within this developing wave were colder than -40C last evening over much of Alaska and northwestern Canada). Thus, it appears that February 2011 will exit just as it began, with unusually cold temperatures and perhaps a better chance of precipitation this time (snow right in town?). This event will likely garner more attention - the Tucson Rodeo is underway and runs through Sunday. The big dollar, PGA Match Play Championship comes to Dove Moutain just north of Tucson beginning this morning and running through Sunday afternoon. The most important matches are scheduled for the weekend, and there will be substantial national TV coverage of the event - could be quite interesting!

The two graphics above compare the operational member 500 mb forecasts from last evening's ECMWF and GFS model runs. Note the runs are very similar and forecast 500 mb heights to fall below 540 dm over the Southwest by Saturday afternoon. The ECMWF is about 6 to 12 hours slower than the GFS, but both models are forecasting a very cold weather system across Arizona over the weekend.

The two panels above show the operational GFS forecasts for midnight on Saturday night. Although the GFS height contours at 500 mb indicate a cutoff, the model winds indicate a strong open wave with excellent forcing for upward vertical motion. The operational member of the GFS forecasts 1000-500 mb thicknesses falling toward 528 dm during the Saturday night. If the thickness falls this low, with precipitation occurring (as the model forecast indicates), then the snow levels would drop right into metro Tucson. Note that all 12 GFS ensmble members forecast precipitation across southeast Arizona for the 12-hours ending Sunday morning at 5 am, and 9 of the members forecast precipitation for the 12-hours ending 5 pm Saturday afternoon. February 2011 could end up having record-setting storms twice during the month! Our visitors to Tucson (with expensive match play tickets) could leave shaking their heads, wondering why the PGA picked this cold locale for one of their biggest tournaments - keep tuned (matches will get lots of coverage on NBC).

Light Showers In Parts of Tucson Last Evening

Light showers moved across the Tucson area late yesterday afternoon and evening. Above image shows light showers on the Catalinas and north part of town at 5 pm yesterday. The very tail end of the weekend event left 30 of the 93 ALERT gauges in eastern Pima County with light precipitation, measured at 6 am for the past 24 hours (remember that the highest elevation stations may have had snow that was not recorded). Here at the house we had 0.04" between 5 and 7 pm. Six ALERT stations had 0.10" or more and highest amount was 0.31" up on the north slopes of the Catalinas. So, we now have a tiny bit of rainfall for February. Low temperature this morning at the house was 31F.

The NAM 500 mb analysis at 12 UTC this morning (top chart) shows a trailing cutoff low off the Oregon coast. This feature is forecast by the model to drop rapidly southward over the Pacific and then to turn inland and weaken across Arizona and northern Mexico on Wednesday afternoon and night (60 hour forecast shown in bottom panel). At this time the models forecast some middle-level moisture and clouds to come across Arizona with this short wave, but only precipitation forecast is for northeastern portions of the state.

ECMWF vs GFS Forecasts For Saturday February 27th

The operational member forecasts for 500 mb (valid at 144 hours from last evening or 5 pm Saturday February 27th) are shown above for ECMWF (top) and GFS (middle). There is quite a bit of difference between the two forecasts. Both forecasts have cold heights (lower than 534 dm) over the western US but the ECMWF system is impacting the Southwest, while the GFS system is impacting the Northwest. Note that ECMWF forecast 500 mb heights are MORE than 300 m lower than those forecast by GFS near San Diego. The ECMWF has been doing much better than the GFS last several winters (my subjective feel is that at longer ranges for the western US it is more accurate for significant events than the GFS 8 or 9 times out of 10). So, something to watch as the week progresses.
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The bottom figure is the GFS spaghetti plots and ensenble average for 500 mb forecasts valid at the same time. In this situation the GFS operational member seems to be a significant outlier over western North America and the eastern Pacific, with many of the ensemble members having a forecast considerably more similar to that of the ECMWF (see the right panel).

Saturday - Mostly Wind And Dust For Southeast Arizona

Weekend weather event has so far been mostly wind and dust across southeast Arizona. No precipitation recorded in the ALERT network at 6 pm yesterday evening, and only 8 stations in the Catalina mountains had recorded light precipitation by 6 am this morning (note that snow only might have occurred at some high elevations gauges). So POPs of 60% yesterday and last night were too high, as were the models' forecasts of precipitation coverage down here. However, the winds picked up and exceeded expectations with gusts of 40 to 50 mph common. Highest gusts I found were at Guthrie RAWS site with 70 mph - time series there seems to support this observation. Lots of ugly dust, as reported in previous post.

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Further north in the Phoenix area things were a bit more active. The above two graphics show time series of surface conditions at Sky Harbor Airport with strong frontal passage indicated around noon yesterday (Saturday February 19th). Showers with and behind the front produced 0.33" inches of rainfall at Sky Harbor.

Dirty Skies

Winds have been gusting from the south-southwest since midmorning - some gusts over 45 mph at TUS. When I drove down to the south side to go to the main Post Office before noon, I could see large clouds of dust blowing off the tailing piles at the copper mines to the south toward Green Valley. The densest of these were extending north to the Rincons and the east side of the Catalinas. Above two images show the dirty skies toward the Catalinas at noon, and an aerial view of the copper mines south-southwest of Tucson on the west side of I-19. I shudder to think of what all we might be breathing today!

Mild Morning As Stormy Weather Remains To West So Far

The large Pacific trough remains offshore west of California this morning. Rain and snow is falling over much of the northwest half of Arizona at sunrise and heavy rains and some thunderstorms continue in extreme southern California. Here in Tucson it is another mild morning - lows so far: airport 56F, Atmo 59F, here at house 48F. The top image shows middle cloud overhead and to the north. The second image shows eastern Pacific PW at 1200 UTC this morning (Saturday February 19th) and indicates that the Pacific trough has pulled a plume of higher PW back into the Southwest. So far not much to report from this part of the state. No precipitation measured across the eastern Pima County ALERT network during past 24 hours. I see that Kingman has had 0.72" of rain so far and that Flagstaff has had a sloppy mix of rain and snow that has totalled 0.70" so far.

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Models continue to forecast that this event will affect mostly the higher elevations of southeast Arizona with perhaps a tenth of an inch possible by 5 pm tomorrow afternoon in the Tucson area. The WRF-GFS midnight forecast for period ending at 5 pm on Sunday is shown in third panel, with most precipitation indicated over the Catalinas. The WRF forecast of composite radar reflectivity at 5 pm today is shown in bottom panel. This indicates some deep convection and perhaps thunderstorms moving across the metro area this afternoon and evening - so some spots might get considerably more rainfall, as we did here at house with the brief storm at the end of January.

Still A Complex And Confusing Situation

The above is the NAM analysis of 500 mb heights and vorticity at 1200 UTC this morning - Friday, February 18th. The model analyzes numerous vorticity streamers and maxima within the west-coast trough eastward to the Great Lakes. The strongest maximum is analyzed far west of central California. The way that this feature moves into the bottom of the trough and then eastward will play a strong role in what happens here in southeastern Arizona. This morning the models continue to forecast that most precipitation, through Sunday, will be to the west and north of the Tucson area. However, both the NAM and this morning's early WRF now indicate QPFs in metro Tucson of about a tenth of an inch.
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Yesterday 2 ALERT gauges up in the Catalinas had very light precipitation, with no rainfall measured through the remainder of the network.

Models Not Forecasting Much For Southeast Arizona At This Time

 Heavy clouds hanging on the Catalinas this morning Thursday 17 February 2011). Cloud cover during the night kept the morning low at a very mild 54F - the warmest morning low here at the house since last October or early November!

Situation at 500 mb is very complex over the Pacific and western North America - GFS analysis at 1200 UTC is shown above. The sytem out near Hawaii has produced another long plume of high PW that curves eastward to northern Baja. What is not clear at this time is whether the short-wave trough/cutoff forecast to affect the Southwest this weekend will be able to pull this richer moisture northward. There is a massive 500 mb ridge extending northward across the Bering Sea and one stream of vorticity is digging south along the eastern side of the ridge, while several other vorticity maxima are along the west coast, having had their origins in the large, cold cyclone over Canada. It's not clear how well the models will do forecasting the details of the evolution of the current plethora of vorticity maxima - we'll have to watch as all this sorts itself out over the next couple of days.

The two precitation forecasts above are from the midnight run of the Atmo WRF-GFS and and this morning's 12 UTC run of the NWS NAM model. The WRF (top) forecasts no precipitation in the metro Tucson area through 11 am Sunday morning, keeping the event confined higher elevations. The NAM (bottom) forecasts no precipitation over southeast Arizona through 5 pm Sunday afternoon, keeping the significant precipitation amounts over the Rim country and northwest mountains.

Interesting Difference Between Models This Morning

After an interruption of several days, I am now able to get back to the blog.

The large 500 mb trough that is off the west coast this morning has a very complex structure, with a number of distinct short waves embedded within the larger-scale feature. One short wave is forecast by this morning's NAM to be ejected across the Great Basin today and tonight with little amplitude. Although precipitation covers most of California this morning, all the way south to San Diego, both the NAM and the WRF-GFS run at midnight last night forecast only a bit of precipitation in far northern Arizona. By the weekend however a much sharper trough is forecast to approach the Southwest, and this wave may bring enough moisture with it for a precipitation event across much of Arizona. (Note that February to date has been rain-free and almost cloud-free here in Tucson.) The top graphic shows total precipitation forecast by the Atmo version of the WRF-GFS for the period ending at 10 am Saturday morning (February 19th) and indicates a large band of rainfall and high elevation snowfall moving into southeast Arizona. The NAM however is slower (bottom graphic shows its prcipitation forecast for the 60 hours ending at 5 pm Saturday), and keeps the precipitation over northern portions of Arizona through early Saturday night. Regardless, finally a possible weather event for the Southwest!

Extreme Cold This Morning In Oklahoma

Rodger Edwards reports: I'm about ready for such a change (re previous post about the predicted pattern change) after the last two weeks, some of the coldest and snowiest in recent memory in OK (including *the* coldest temperature in state history this morning at BVO: -28 deg F). That, and my geothermal heat pump quit working sometime last month thanks to a worn-out condenser coil that leaked refrigerant like a sieve, leading to a doubling of my electric bill and a 4-figure repair cost for a part that hasn't arrived yet. Supercell observation season cannot come soon enough, nor can a different longwave pattern than this!
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Addendum: The OK Mesonet shows two sites colder than BVO, including Nowata at -31 deg F! Nasty...


Here is the link to the image (now shown above - perishable, so you may want to grab and save it if using it):

http://www.mesonet.org/data/public/mesonet/maps/realtime/today.TAIR.min.grad.png

Hemispheric Pattern Change

Shown above are the GFS ensemble, 500 mb, means from 00 UTC last evening for: 24, 84, 144, and 240 hours (from top to bottom). The models continue to indicate a pattern change in the Northern hemisphere, especially over the Pacific and North America. The strong ridge that has been persistent over the eastern Pacific finally shifts eastward over the continent, allowing a trough to develop and perist for a week or more along the west coast of the US. Also of note is the forecast deepening of the near-polar cyclone over Alaska and the redevlopment of a weak trough west of Hawaii - as per earlier in the winter. So, perhaps we will finally see a bit more weather possiblities here in the Southwest during the next couple of weeks.

Tremendous Damage In Southeast Arizona From Extreme Cold

The extreme cold of late last week left tremendous damage across much of southeast Arizona. The most serious damage being frozen and broken water lines. Today (Monday February 7th) when I was out running errands, I encountered several places where water is still running into the streets from ruptured pipes. The top photo is from Jim Toth (who lives a couple of miles away in the foothills where the local microclimate is warmer than here at the house). It shows bougainvillea encrusted in ice after a drip irrigation line froze and ruptured spraying water onto the plant. Interestingly, here on our circle the bougainvillea had been dead and brown since December, when the cold killed them back to their roots. Jim has more details at:

http://weatherwilderness.blogspot.com/

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The lower photo is of fallen prickly pear limbs and pads - I have piles and piles of these, probably at least 1000 pounds worth, and I figure it will take me about a month to get it all cleaned up. The morning low temperatures here at the house during the first week of February have been: 27F; 18F; 14F; 11F; 20F; 24F; and 26F. Easily the coldest week since I started keeping low temperature records here. We were quite lucky not to have frozen pipes, as several neighbors on the circle did. Art Douglas reports two nights with 0F at his place in Ash Canyon and much damage in the Sierra Vista area.

Lot Of Strange Soundings In Northeast Last Evening

Many of the RRS soundings at 00 UTC 6 February 2011 from the Northeast US appeared to have problems. There were many smal layers aloft with super-adiabatic lapse rates - too many to show them all. I've posted three soundings above (from the Univ. of Wyoming upper-air page).
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Albany data (top) have a super layer just above 700 mb and a deep layer below that exhibits absolute, moist instability. An unstable layer was definitely present, since the observations indicated thunder and snow and graupel and/or hail.
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The data at Pittsburgh (middle) indicate a VERY low tropopause - I can't rule this out - but the sounding seems very strange wrt all of its neighbors.
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Sterling (bottom) has a number of shallow super layers aloft, a layer below 700 mb with noise in the RH data, and then extremely low depoints for rest of sounding above 700 mb.
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No need to ask where the most interesting weather in the country was last evening!

After The Blizzard



I have not been able to find time to post last several days but hope that things will be back to normal tomorrow. Above photo shows my sister's little dogs heading out along a special snow route into the back yard after the Great Chicago Blizzard earlier this week. Sister lives in Batavia, Illinois, and she said they had about 20" or so at their house - much too much for the little dogs to deal with on their own!

Cold Forecast By ECMWF Definitely More Accurate Than GFS!

Chicago Lake Shore Drive during "rush" hour last evening - credit: Brian Cassella, Chicago Tribune.

Photo at top just one of many from the Midwest last evening and this morning of the show-stopping blizzard.
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Last Saturday I noted in a post that the ECMWF 120-hour forecast for 1200 UTC tomorrow morning was much different than, and VERY much colder than, the NWS GFS forecast for same time. That ECMWF forecast is playing out to have been much more accurate, perhaps even a bit conservative, as very cold air overs the West this morning (Wednesday February 2nd). It looks as if the 120-hour GFS forecast may have missed the 1000-500 mb thickness near Tucson for tomorrow morning by around 250m! The middle two panels show the NCAR RAP analyses of the 1200 UTC observations at 500 mb and 850 mb this morning. The 500 mb height analysis indicates a closed low near the Four Corners, while the observed winds indicate an open short-wave still, with temps of -38C near Grand Junction (note the very cold surface temperatures in northwest Colorado). The 850 mb analysis captures the extreme temperature gradients over the Southwest. Coldest arctic air remains east of the Continental Divide, but it is also spilling southward from the Great Basin. A weak inverted trough still extends south-to-north just along and west of the Continental Divide. The weakening, blizzard cyclone in the Midwest is now centered near Detroit.
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The 7 am surface data plot from NCAR RAP is the bottom graphic - one of the more wintery charts I've ever seen for Aziona and New Mexico. Observations of note: Guadalupe Pass, Texas, -2F with snow and east-northeast wind gusts to 41 mph; El Paso and Deming, New Mexico, both 9F with snow; Nogales, Arizona, 17F; here at house 7 am temperature was 20F (looks like low was 19F a bit after 7 - airport was still dropping at 8 am with 26F). Will tomorrow morning bring all time record lows?

Helicopter Crash Near Tucson Yesterday

Yesterday around 11:30 am a Sheriff's Dept. helicopter crashed at the north end of the Tucson mountains. Three were injured and, sadly, the pilot was killed. The storms that I reported in preceeding post had developed over the Tucson Mountains, apparently just before the copter went down. The top image shows NWS Tucson radar, base reflectivity, right before 11 am local time - the strong cell of 50+ dBZ produced abundant graupel, and perhaps hail, and was the storm that produced strong outflow winds that came all the way east past the house.
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As today's blizzard batters the Midwest, an intense arctic front has rapidly moved south down the Front Range of the Rockies. The U of A WRF model forecasts very COLD temperatures with this front tomorrow and especially Thursday morning. The WRF forecasted surface winds and temperatures valid at 7 am Thursday are shown in the middle figure. The temperatures are all the more remarkable given the strong downslope winds forecasted. See Mike Leuthold's special WRF discussion from this morning:

http://www.atmo.arizona.edu/products/models/forecasts/wrf_disc.html
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The surface data plot from an hour ago, bottom, indicates a battle between a Pacific front and the arctic front, centered over western New Mexico. Note the 10F temperature at Guadalupe Pass, Texas, with 43 mph wind gusts from the east-northeast and ice needles. To the west, Deming, New Mexico, was holding at 50F with west winds gusting to 30 mph - an amazing convergence zone. Will be interesting to see how long it takes before the arctic air dominates and comes west across the Continental Divide.