Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 231540
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
840 AM MST TUE DEC 23 2014

.SYNOPSIS...COOLER TEMPERATURES ESPECIALLY EAST OF TUCSON WITH SOME
BREEZY CONDITIONS TODAY. A STORM SYSTEM DIGGING INTO THE FOUR
CORNERS AREA LATE IN THE WEEK WILL BRING A FEW SHOWERS... ESPECIALLY
NEAR THE EASTERN MOUNTAINS THURSDAY NIGHT INTO FRIDAY.

&&

.DISCUSSION...LARGE SCALE PATTERN THIS MORNING HAS STRONG
NORTHWESTERLY FLOW ALOFT ACROSS ARIZONA BETWEEN A LONGWAVE TROUGH
CENTERED ACROSS THE CENTRAL US AND A STRONG RIDGE ACROSS THE EASTERN
PACIFIC. A DRY COLD FRONT MOVED THROUGH EARLY THIS MORNING WITH COLD
AIR ADVECTION UNDERWAY ACROSS THE FORECAST AREA. HIGHER ELEVATION
SITES ARE SEEING GUSTY WINDS AND AS DAYTIME HEATING/MIXING COMMENCES
IN VALLEY LOCATIONS...EXPECT BREEZY MAINLY NORTHERLY WINDS TODAY
AREAWIDE.

THE DIFFICULT FORECAST TONIGHT WILL BE FOR LOW TEMPERATURES AS LOWS
WILL APPROACH FREEZING ACROSS THE TUCSON METRO AREA. THE GRADIENT
WILL REMAIN TIGHTER THAN NORMAL ALLOWING FOR SOME AREAS TO SEE JUST
ENOUGH BREEZES TO PREVENT ELONGATED DECOUPLING. FOR THOSE LOCATIONS
IN THE TUCSON METRO THAT SEE WINDS GO NEARLY CALM...TEMPERATURES
WILL BE QUITE COLD AND LIKELY HIT FREEZING WHILE LOCATIONS THAT SEE
MORE WIND WILL SEE JUST ENOUGH MIXING TO KEEP TEMPERATURES WARMER.
THIS IS A SCENARIO WHERE THERE WILL BE LARGE VARIABILITY IN
TEMPERATURES OVER SHORT DISTANCES. ON A CLIMO RELATED NOTE...TUCSON
INTERNATIONAL AIRPORT STILL HAS YET TO SEE 32 DEGREES AND THIS
SEASON AND WILL NOW BE AT LEAST NUMBER 3 FOR LATEST FREEZE IN
TUCSON.

SHORTWAVE RIDGING ALOFT WILL BE IN CONTROL OF OUR WEATHER ON
WEDNESDAY BEFORE THE NEXT TROUGH MOVES INTO THE AREA THURSDAY.
EXPECT AN DEEP UPPER LEVEL TROUGH WITH THE BULK OF THE MOISTURE AND
DYNAMICS FROM NORTHERN ARIZONA NORTHWARD INTO THE GREAT BASIN WITH A
TRAILING SURFACE COLD FRONT THAT MOVES THROUGH AREA. THIS WILL
RESULT IN INCREASED WEST TO SOUTHWESTERLY BREEZES AREAWIDE THURSDAY
WITH SLIGHTLY WARMER TEMPERATURES. AS THE FRONT MOVES
THROUGH...EXPECT A SLIGHT CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW
SHOWERS ESPECIALLY FROM TUCSON EASTWARD. THIS SYSTEM WILL BE
SOMEWHAT MOISTURE STARVED FOR US...BUT THE LAST COUPLE OF MODEL RUNS
HAVE GENERALLY BEEN INCREASING THE MOISTURE AND RESULTANT CHANCE OF
PRECIPITATION. THUS MAY NEED TO CONTINUE THE TREND OF INCREASING THE
POPS AND WILL EVALUATE THE 12Z SUITE OF GUIDANCE.

A SECONDARY DISTURBANCE IS EXPECTED TO DIG INTO THE BASE OF THE
TROUGH ON CHRISTMAS DAY WHICH WILL KEEP THE TROUGHINESS OVER THE
DESERT SOUTHWEST AND RESIDUAL SLIGHT CHANCES FOR VALLEY RAIN AND
MOUNTAIN SNOW SHOWERS EAST OF TUCSON. MEANWHILE...COOLER
TEMPERATURES WILL MOVE IN WITH HIGHS BELOW NORMAL. THESE COOL
TEMPERATURES WILL PERSIST INTO SATURDAY WITH DRY NORTHWESTERLY FLOW
ALOFT. BY SUNDAY AND MONDAY DRY CONDTIONS WILL CONTINUE WITH
GRADUALLY WARMING TEMPERATURES.

&&

.AVIATION...VALID THRU 24/18Z.
MAINLY CLEAR SKIES THROUGH THE FORECAST PERIOD. SUSTAINED WINDS OF
10 TO 20 KTS TODAY WITH HIGHER GUSTS. THEN...A SURFACE GRADIENT WILL
SET UP TONIGHT WHICH WILL RESULT IN ENHANCED EASTERLY/NORTHEASTERLY
WINDS OF 10 TO 20 KTS DEVELOPING EARLY WEDNESDAY
MORNING...ESPECIALLY IN THE VICINITY OF THE KTUS TERMINAL. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...DRY CONDITIONS WILL PREVAIL THROUGH WEDNESDAY WITH A
SLIGHT CHANCE OF A FEW RAIN AND SNOW SHOWERS OVER THE WHITE
MOUNTAINS LATE CHRISTMAS DAY THROUGH FRIDAY. BREEZY TO LOCALLY WINDY
NORTHERLY/NORTHEASTERLY WINDS WILL DEVELOP TODAY SHORTLY AFTER
SUNRISE. ADDITIONALLY...DEW POINTS WILL DROP SIGNIFICANTLY FOLLOWING
A DRY FRONTAL PASSAGE RESULTING IN LOWERING HUMIDITY LEVELS. A
TIGHTENING SURFACE PRESSURE GRADIENT WILL DEVELOP OVERNIGHT TUESDAY
RESULTING IN INCREASING EASTERLY WINDS WEDNESDAY MORNING BEFORE
RELAXING DURING THE AFTERNOON. ANOTHER SYSTEM PASSING TO OUR
NORTHEAST WILL ONCE AGAIN BRING BREEZY TO LOCALLY WINDY CONDITIONS
TO THE REGION ON THURSDAY.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

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