Have been away the last day and a half or so and will do a brief overview this morning, since there is a feature of interest over west-central Mexico.
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Top IR image for US shows only one small cluster of deep convection over land this early morning - that being in west Texas. Rest of country is fairly dry and under the influence of a large ridge aloft - see the 200 mb analysis for this morning from NCAR RAP (middle image). Note that the streamline analysis indicates an inverted trough across west-central Mexico. this feature is quite distinct in the water vapor imagery (bottom image) and WV loops indicate that it is currently moving to the north-northwest. The ECMWF has been indicating for several days now that this feature would affect Arizona and New Mexico, as it approaches the border and then swings northeastward across New Mexico in the forecast. This morning's NAM seems to forecast that it will fragment into various components - a piece at 500 mb strings northward into Arizona; a piece of the upper-level trough seems to escape across New Mexico, etc.
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Remains very dry at lower-levels and PW is not very great; however, in far southeast Arizona PW has definitely been increasing. Higher values of around an inch and a half appear to be within striking distance south of the border. So, a bit of "weather" to watch as a new week begins.
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I found that the early morning Forecast Discussion from Phoenix covered the situation quite nicely and I'm just going to lift it and paste it below:
EARLY MORNING WATER VAPOR AND IR SATELLITE IMAGERY REVEALS
INCREASING CLOUD COVER ACROSS THE DESERT SOUTHWEST AHEAD OF AN UPPER
LOW OVER CENTRAL MEXICO. SOME PRECIPITATION WAS ASSOCIATED WITH THIS
LOW WELL SOUTH OF THE INTERNATIONAL BORDER BUT CONDITIONS ACROSS
ARIZONA WERE DRY. DEWPOINTS AT THE SURFACE REMAINED LOW...GENERALLY
IN THE 20S AND 30S ACROSS THE FORECAST AREA. NOT MANY CHANGES TO THE
FORECAST TODAY...THE MAIN FEATURE OVER THE NEXT SEVEN DAYS WILL BE
THE LOW PRESENTLY OVER MEXICO.
THE MODELS DID A GOOD JOB INITIALIZING THE POSITION OF THE LOW AT
00Z SUN...BUT SEEM TO BE UNDER-FORECASTING THE AMOUNT OF MOISTURE IN
THE MID AND UPPER LEVELS OF THE ATMOSPHERE BASED ON GFS/NAM BUFR
SOUNDINGS. WILL GET A BETTER HANDLE ON THINGS WITH THE 12Z
PHOENIX/TUCSON SOUNDINGS BUT MY INITIAL THOUGHTS ARE THAT THE MODELS
MAY BE A BIT TOO DRY WITH THIS SYSTEM. REGARDLESS...THE MAIN FORCING
WITH THIS SYSTEM WILL BE EAST OF THE FORECAST AREA ALONG THE AZ/NM
BORDER AND I STILL THINK THAT A 10-15 PERCENT CHANCE OF
THUNDERSTORMS EAST OF PHOENIX IS FEASIBLE.
INCREASING CLOUD COVER ACROSS THE DESERT SOUTHWEST AHEAD OF AN UPPER
LOW OVER CENTRAL MEXICO. SOME PRECIPITATION WAS ASSOCIATED WITH THIS
LOW WELL SOUTH OF THE INTERNATIONAL BORDER BUT CONDITIONS ACROSS
ARIZONA WERE DRY. DEWPOINTS AT THE SURFACE REMAINED LOW...GENERALLY
IN THE 20S AND 30S ACROSS THE FORECAST AREA. NOT MANY CHANGES TO THE
FORECAST TODAY...THE MAIN FEATURE OVER THE NEXT SEVEN DAYS WILL BE
THE LOW PRESENTLY OVER MEXICO.
THE MODELS DID A GOOD JOB INITIALIZING THE POSITION OF THE LOW AT
00Z SUN...BUT SEEM TO BE UNDER-FORECASTING THE AMOUNT OF MOISTURE IN
THE MID AND UPPER LEVELS OF THE ATMOSPHERE BASED ON GFS/NAM BUFR
SOUNDINGS. WILL GET A BETTER HANDLE ON THINGS WITH THE 12Z
PHOENIX/TUCSON SOUNDINGS BUT MY INITIAL THOUGHTS ARE THAT THE MODELS
MAY BE A BIT TOO DRY WITH THIS SYSTEM. REGARDLESS...THE MAIN FORCING
WITH THIS SYSTEM WILL BE EAST OF THE FORECAST AREA ALONG THE AZ/NM
BORDER AND I STILL THINK THAT A 10-15 PERCENT CHANCE OF
THUNDERSTORMS EAST OF PHOENIX IS FEASIBLE.
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