Winter Storm Watch 2, NWS Tucson, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
255 AM MST WED DEC 27 2006

.SYNOPSIS...A STRONG LOW PRESSURE SYSTEM WILL MOVE ACROSS SOUTHEAST
ARIZONA TONIGHT INTO THURSDAY...BRINGING VALLEY RAIN AND MOUNTAIN
SNOW SHOWERS. BREEZY TO WINDY CONDITIONS ARE EXPECTED THIS AFTERNOON
FOLLOWED BY MUCH COLDER TEMPERATURES THURSDAY. HIGH PRESSURE ALOFT
WILL RETURN FRIDAY INTO NEW YEARS DAY...FOR DRY WEATHER WITH A
GRADUAL WARMING TREND.

&&

.DISCUSSION...DEEP UPPER TROUGH ALONG THE WEST COAST AT THIS TIME
PROGGED TO DIG SEWD TODAY AND TONIGHT. 27/00Z GFS/ECMWF/UKMET HAVE
SLOWED PROGRESSION OF SYSTEM SOMEWHAT VERSUS PREVIOUS SOLUTIONS AND
THIS SEEMS REASONABLE AND WAS ACCEPTED FOR THIS FORECAST ISSUANCE.
OPTED TO REMOVE PREVIOUS MENTION OF PRECIP FOR TODAY EXCEPT FOR A
SLIGHT CHANCE OF SHOWERS WHITE MOUNTAINS LATER THIS AFTERNOON. MAIN
IMPACT FROM APPROACHING SYSTEM TODAY WILL BE BREEZY-WINDY SWLY
SURFACE WINDS THIS AFTERNOON TUCSON VICINITY EWD. RED FLAG CRITERIA
EXPECTED TO BE MET THIS AFTERNOON ACROSS SRN FIRE ZONE 148. GFS
CONTINUED TO DEPICT AREA OF 220 METER OR SO HEIGHT FALLS CENTERED
OVER THIS FORECAST AREA VALID 28/06Z OR TONIGHT. PER COORD WITH
WFO/S PSR/FGZ OPTED TO INCREASE INHERITED QPF AND SNOW AMT GRIDDED
DATA VALUES PARTICULARLY LATE TONIGHT AND THUR. GIVEN SLOWER NATURE
OF SYSTEM CONFIDENCE FAIRLY HIGH THAT SNOW ADVISORY CRITERIA...AT
LEAST...WILL BE MET ABOVE 5000 FEET BY THUR EVENING ZONES 19/30.
THUS WILL ISSUE WINTER STORM WATCH FOR LATE TONIGHT-THUR AFTERNOON
AND DEFER SUBSEQUENT AREAL/TIMING ADJUSTMENTS TO DAYSHIFT. OPTED TO
REFLECT SLIGHTLY INCREASED POPS TUCSON VICINITY EWD THUR EVENING...
AND WILL MAINTAIN LOW GRADE POPS ERN SECTIONS LATE THUR NIGHT...AND
SLIGHT CHANCE OF SNOW SHOWERS WHITE MOUNTAINS FRI MORNING. DRY
CONDITIONS EXPECTED TO RETURN AREAWIDE FRI AFTERNOON AS FLOW ALOFT
BECOMES INCREASINGLY NWLY WITH RIDGE AMPLIFICATION AGAIN OVER THE
INTERMOUNTAIN REGION. DRY CONDITIONS TO PREVAIL THIS WEEKEND-NEW
YEARS DAY. HOWEVER CONSIDERABLE DIFFERENCES EXIST BETWEEN 27/00Z GFS
AND 27/00Z ECMWF FOR NEXT TUE. GFS DEPICTED RIDGE ALONG THE WEST
COAST WITH NWLY FLOW OVER AZ...WHILE ECMWF DEPICTED 560DM CLOSED LOW
CENTERED OVER S CENTRAL AZ VALID 03/00Z. GFS ENSEMBLES HAD 2 MEMBERS
WITH CLOSED-LOW SOLUTIONS OVER THE SWRN CONUS. AT ANY RATE CONFIDENCE
QUITE LOW WITH REGARD TO DAY 7 SCENARIO THUS WILL MAINTAIN DRY
FORECAST FOR NOW THOUGH INCREASE CLOUD COVER TO PARTLY CLOUDY. QUITE
WARM YET AGAIN TODAY WITH DAYTIME MAX TEMPS ABOUT 10-13 DEGS OR SO
ABOVE SEASONAL NORMALS. MUCH COLDER THUR WITH GENERAL DECREASE OF
ABOUT 15-20 DEGS OR SO VERSUS FORECAST MAX TEMPS TODAY. GRADUAL
WARMING BY SAT WITH WARMING TREND CONTINUING INTO NEW YEARS DAY.

&&

.AVIATION...TAFS AND TWEBS ADEQUATELY COVER ALL SIGNIFICANT WEATHER
AT KTUS.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
      RED FLAG WARNING 11AM - 5PM MST TODAY SOUTHERN FIRE ZONE 148.
      WINTER STORM WATCH LATE TONIGHT THROUGH THURSDAY AFTERNOON
        AZZ019-030 ABOVE 5000 FEET.

&&

WWW.WEATHER.GOV/TUCSON

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