Quick Look At Morning Forecasts

It has been a dreary, very dry (currently 82F at airport with -8F dewpoint giving RH of 3%), day this Sunday with gray and dirty skies. Looks like more dust coming by tomorrow and perhaps some showers late in day. The U of A Atmo WRF-GFS forecast from 12 UTC this morning, top, continues to forecast precipitation through 11 pm Monday night to occur mostly on the mountains, with no rainfall right in the metro area. The model forecasts a slight touch of snowfall at only the very highest elevations. The coarser resolution NAM forecast (bottom) for same period has the precipitation smeared out spatially, but with this considered, the two forecasts are quite similar for southeast Arizona, indicating another event much like that of 27 February (the last rainfall here).

Strong Surface Low Spins Up West Of San Francisco

Yesterday afternoon (Saturday March 19th 2011) a surface low began developing over the eastern Pacific to the south of the upper cut-off. This low intensified dramatically west of San Francisco and moved rapidly northeastward during the night. The top water vapor image shows the feature at 0115 UTC west of San Francisco. The lower image is a 20 March,10 UTC surface plot from NCAR RAP and indicates surface pressures near 987 mb north of San Francisco - indicating falls of 20 mb or more since the 00 UTC observations. The NAM model forecasts at 12 UTC yesterday morning hinted at this development, the 18 UTC NAM had a deeper low forecast along the coast (but weaker than what actually occurred), and the 00 UTC NAM more or less caught up with the intense cyclogenesis, but in what was essentally a diagnostic time frame. Thus, a challenging situation for forecasters in the Bay area, who were following rapidly changing, short-term observations due to the not so stellar model forecasts. The Forecast Discussion from the San Francisco NWS office this morning provides a brief summary of the events during the night:
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.DISCUSSION...AS OF 4:30 AM SUNDAY...A VERY DEEP SURFACE LOW
DEVELOPED RIGHT OFF OUR COAST LAST EVENING. THE LOW IS CURRENTLY
CENTERED NEAR POINT ARENA AND ITS CENTRAL PRESSURE IS DOWN AROUND
984 MB...AND PROBABLY A BIT LOWER. SUCH A DEEP LOW IN CLOSE
PROXIMITY TO OUR COAST GENERATED VERY STRONG WINDS OVERNIGHT...
BEGINNING IN THE SOUTHERN COASTAL WATERS EARLY IN THE EVENING AND
SPREADING EAST AND NORTH AS THE NIGHT WORE ON. STRONGEST WIND GUSTS
OCCURRED LATE LAST EVENING THROUGH ABOUT MIDNIGHT. WIND GUSTS IN
EXCESS OF 60 MPH WERE REPORTED IN THE NORTH BAY AND THE SAN FRANCISCO
AIRPORT HAD A PEAK WIND GUST OF 53 MPH. WINDS HAVE BEEN GRADUALLY
SUBSIDING SINCE ABOUT 1 AM BUT ARE STILL QUITE STRONG.

WRF Versus NAM For Next Event

The model forecast runs from midnight last night are compared above for the WRF-GFS (Atmo high-resolution version) of the WRF model and the midnight run of the NAM model. The WRF forecast (top - total precipitation for period) indicates that the event is over by midnight on Monday night and predicts precipitation only at the higher elevations of southeast Arizona. The midnight run of the NAM model (bottom) is quite similar, although about 6 to 12 hours slower than the WRF, predicting precipitation mainly northward from the Catalinas. Neither model indicates much happening across the Tucson metro area, except for a strong frontal passage Monday afternoon or evening. But of note - the GFS ensemble members' (except for the operational member) forecasts are more agressive, with 11 of 12 forecasts indicating a frontal band of showers moving across southeastern Arizona late Monday into early Tuesday. The ECMWF forecasts a very strong frontal passage across southern Arizona (I don't have access to ECMWF precipitation forecasts). So, even though the event is only a couple days away, the forecast for metro Tucson remains very difficult. I will note that when the GFS ensembles have indicated 90 to 100% of the members' forecasting precipitation, we have almost always had measureable rain here at the house. So, I'm hopeful that we'll have at least a light rainfall here.

Strong Cutoff Spinning West Of Washington State

The system that will affect Arizona at the start of next week is currently spinning away over the Pacific to the west of Washington state (see WV image at 4 pm MST top). The NAM 300 mb 12-hour forecast valid at 5 pm MST this afternoon (middle) has forecast the system to be further north and east of where it appears to be, at least in the WV imagery. A strong 300 mb jetstream is forecast to be approaching the cutoff from the northwest, i.e., the feature that will help the system dig down the coast. The current water vapor loop shows the cutoff to be moving slowly southeastward at this time. The NAM 60-hour forecast for 500 mb (bottom) indicates that the system will dig nearly due south and be off the northern California coast at 5 pm MST on Sunday (March 20th) afternoon with central heights lower than 5220 m. Thus, a very impressive system. However, after 60 hours the models forecast the system to weaken, become an open trough and move rapidly eastward. The GFS ensemble forecast from this morning shows that most of the members forecast a frontal band of precipitation to move eastward across southern Arizona Monday night, quite like what happened with the last system in February. However, most significant precipitation remains to the north. There is another large plume of subtropical moisture over the eastern Pacific that may be pulled into the digging cutoff. So it is yet another sittion that we'll have to watch evolve as it approches the Southwest.

Strong Capping Inversion Over Southern Plains

Srong return flow from the Gulf of Mexico has brought cool and moist mT air north across the southern Plains during the past 24 to 36 hours. Weaker flow aloft has advected a cT, elevated mixed layer eastward over the mT air mass. Thus, the soundings above (DRT to FWD to TOP bottom to top) all illustrate classic capping inversions (or Lid structures), with an mT boundary layer topped with a deep, high-lapse rate, old boundary layer. All these soundings are fairly stable this morning and the mT air will need some serious heating before there's much CAPE available.

Cluster Of Soundings With Superadiabatic Layers Aloft

Just a reminder that the problems with the RRS sondes have not gone away. There are a number of eastern US soundings this evening with superadiabatic layers aloft, at the top of a moist layer. The sounding from IAD is shown above. Soundings with similar problems were taken at PIT, RNK, GSO, MHK, and even at WAL. I'm not sure what sonde is being flown at WAL, but it too suffered from a wetted temperature sensor and subsequent evaporative cooling..

Gradual Pattern Change In The Southwest

It appears that several short waves at 500 mb will kick out of the developing trough along the west coast this week. These will bring more moutain snows to much of the West but stay north of Arizona. However, by 5 am next Monday morning both the GFS (top) and ECMWF (middle) operational models forecast a stong system to be over southern California. At this time the ECMWF is a bit deeper with this short wave/cutoff, but the interesting aspect of the forecasts is that the ECMWF forecasts a strong negative tilt that provides significant forcing for vertical motion over the Southwest. The GFS forecasts a positive tilt to the trough and tends to move it east-northeastward further north than does the ECMWF. The spaghetti chart for the GFS ensemble at 144-hours (bottom) indicates that the operational member is an outlier, lagging behind the other members that have the system further east. As usual, I expect that the ECMWF will perform better at 144-hours than will the GFS. At least something to watch for out on the horizon.
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Strange precipitation quirk - I was just looking back through my weather log and note that no month since October 2010 has had any precipitaion (not even a Trace) here at the house during its first half - and March has fit right into this pattern.

Disasters In Japan

Found this map while reading of the various disasters unfolding in Japan - posting it for those who wish to see where the places being referred to in the news reports are.      Bob

Tucson Festival Of Books

Tucson Festival of Books going on today - Saturday March 12th and tomorrow. Many activities and book signings involving hundreds of authors. Elmore Leonard, Jim Harrison, Leslie Marmon Silko, Martin Cruz Smith, Robert Crais and many, many others. On the Mall at the University of Arizona; head on over for an interesting day!

Clear And Dry With Large Temperature Swings

Perfectly clear skies this morning. The surface dewpoint fell to -3F yesterday afternoon giving an RH of 3%. Yesterday morning's low was 32F at the house (versus 46F at the airport) - the airport's high of 87F means a diurnal temperature range here at house of about 55F! This morning (Friday March 11th) the low here was 38F versus a balmy 50F at the airport. Even the long-range model forecasts don't indicate much to get excited about until way out toward 10 days - which is too far out to pay much attention to. Very dry, so I need to water the plants that survived the great February freeze.

Weak Short-Wave Ridges And Troughs

From the afternoon NWS FD by Tucson: MAIN INFLECTION OF RIDGE AXIS PHASES THROUGH TODAY BUT RELATIVE  HEIGHT AND THICKNESS VALUES REMAIN HIGH AS A LARGER SCALE RIDGE FROM  THE EASTERN PACIFIC THROUGH CENTRAL MEXICO REMAINS IN CONTROL

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My attempt at translation (see the 500 mb NAM analysis top and the 12 hour forecast valid at 5 pm MST this afternoon - 10 March 2011): The weak southern portion of a ridge that extends northward into Canada was overhead this morning and will move slowly eastward today. There is a persistent 500 mb high located from the eastern Pacific into central Mexico (actually, I don't see this feature at all in the NAM or GFS forecasts, and it appears that the Gulf of Alaska cyclone and short-wave troughs along the northwest coast are the dominant features impacting western North America next few days - regardless, not much to write about down here).

Stormy Weather On Fat Tuesday

New Orleans had a rainy Mardi gras on Tuesday - above is photo of part of the parade from the Times-Picayune slide show of the festivities.

Heavy rains with some severe thunderstorms spread from central Louisiana northeastward across Mississippi and northern Alabama. Rainfall map is for 24-hours ending at 12 UTC yesterday morning (Wednesday      
                                    March 9th). Reds and violet indicat 3 to 6+ inches of rainfall.
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Remaining parts of my two lost posts are too old now to be very relevant; so they've gone to the Recycle Bin.

A Test

Hummingbird trying to get attention by ringing a Paolo Soleri wind chime.

Problems

I have had problems the last several times I have tried to post to the madweather blog - apparently something is goofed up in my settings and I can not post images. Will return as soon as I can get things working again.   Bob

More On Early February Freeze Damage

There have been some headlines, mostly focused on "expect large price increases for produce," about the extensive crop damage that occurred in Sinaloa and Sonora, Mexico, during the extreme early February freeze over southwestern North America. However, the above photos (circulated from Dept. of Agriculture at U of A) of the crop destruction are quite graphic. Corn field at top and tomato field bottom after the freeze (location is either southern Sonora or very north part of Sinaloa).

All Quiet On The Southwestern Front

Chamber of Commerce weather continues in Tucson and the Southwest this weekend. I did note this morning that a very long plume of tropical moisture has again formed over the Pacific. It extends from near 10 degrees north, southwest of Hawaii, northeastward to California and Oregon. Shown above are IR and PW graphics from early this morning - Saturday March 5th. Enjoy the weekend.
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Spoke too soon - east winds kicked in and now (a bit after 9 am) are gusting 25 to 35 mph here near the Rillito wash.

A Mild Morning

It is a mild morning (Thursday March 3rd 2011) here in Tucson, with the low temperature at the house of 44F. There is a noticeable touch of humidity in the air under hazy, chatotic skies with high and middle clouds(see top image). This is mostly due to the long west-to-east plume of precipitable water that extends from west of Hawaii into the Southwest (bottom image). Also of interest is the curl of higher PW extending from south of Cuba into a weak surface low over the central Gulf of Mexico. This feature may help feed strong thunderstorms tomorrow - see the SPC outlook for Friday.

Victims Of the February Cold Snap

The two photos above are looking north from backyard toward the Catalinas. It appears that 80% or so of the palm trees in this part of town have been killed by the severe freezes the first week of February. Some deciduous trees also appear to have fallen victim to the cold snap, but not to the degree that the palms did.

January and February 2011 - Quick Overview

Here is a quick overview of the first two months of 2011 at my "observation" site here in north part of City of Tucson.
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JANUARY
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Precipitation 0.76" - all on the 31st with almost all falling in less than an hour during a heavy convective shower.
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Temperature - low in the teens on 2 days (17 and 17F); low in the twenties 21 days; low in the thirties 8 days.
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FEBRUARY
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Precipitation 0.29" - most on the 27th during a brief 3-hour period, including some very light snowfall with no accumulation in this part of town.
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Temperature - low in the teens on 3 consecutive days (18, 14, 11F); low in the twenties on 12 days; low in the thirties on 9 days. Much tree and shrub damage in this part of town, with large percentage of palms apparently falling victim to the three day cold snap. Art Douglas reports much damage in the Sierra Vista area that sounds even more widespread than up here.

Winter Severe Thunderstorms in Middle Mississippi Valley

There were many severe thunderstorm reports yesterday from northern Oklahoma east-northeastward to Ohio. The SPC outlooks were similar during the day - the 20Z product is shown at the top. The current plot of yesterday's reported severe thunderstorm events is shown at bottom. The north half of the slight risk area caught most of the severe reports, but the south half of this area was mostly devoid of storm reports. The moderate area outlooked at 20 UTC also remained mostly devoid of severe storm reports.
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A quick look indicates that most of the severe storms occurred along and north of the strong west-east frontal zone, with a large number of the storms being elevated and not rooted in the surface BL. The extreme eastward push of cT air - reported by Bosart on the MAPS chatboard - apparently lead to a rapid intensification of a capping layer above the BL across the south half of the outlooked severe area (the soundings taken at Little Rock, Arkansas, at 00, 03, and 06 UTC captured this capping process). The 500 mb S/W also took on a positive tilt during the day and slowed considerably, weakening forcing for vertical motion in the warm sector - thus, a missed short-term outlook worthy of more detailed examination.