Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 240410
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
910 PM MST TUE DEC 23 2014

.SYNOPSIS...A COLD NIGHT IS IN STORE FOR SOUTHEAST ARIZONA TONIGHT
AS LOW TEMPERATURES WILL BE WELL BELOW FREEZING IN THE EASTERN
VALLEYS...AND NEAR FREEZING IN THE TUCSON METRO AREA. ALTHOUGH
CONDITIONS WILL BE DRY AND COOL WEDNESDAY...A STORM SYSTEM DIGGING
INTO THE DESERT SOUTHWEST LATE THIS WEEK WILL BRING BREEZY TO
LOCALLY WINDY CONDITIONS CHRISTMAS DAY AND A CHANCE OF VALLEY RAIN
AND MOUNTAIN SNOW THURSDAY NIGHT. THIS SHOULD BE A QUICK SHOT OF
PRECIPITATION THOUGH...ENDING IN THE EASTERN AREAS FRIDAY MORNING.
COOL AND DRY WEATHER WILL THEN RETURN THIS WEEKEND.

&&

.DISCUSSION...THE UPPER PATTERN IS DEFINED BY A HIGH AMPLITUDE
TROUGH ACROSS THE CENTRAL STATES...AND A RIDGE OF HIGH PRESSURE
BUILDING INTO THE DESERT SOUTHWEST FROM THE EASTERN PACIFIC. A
SURFACE HIGH PRESSURE AREA MOVING SE THROUGH NORTHERN ARIZONA
TODAY RESULTED IN A DRY AIRMASS ADVECTING INTO THE AREA FROM THE
N/NE BEHIND BREEZY TO LOCALLY WINDY WINDS. THE 00Z KTWC SOUNDING
DEPICTED THIS DRY AIR HAD MOVED INTO TUCSON...WITH A PRECIPITABLE
WATER VALUE OF 0.16 INCHES. IT ALSO SHOWS THE STRONGEST FLOW WAS OFF
THE SURFACE. NO SURPRISE THAT THE WINDS FOR THE MOST PART HAVE
DECOUPLED THIS EVENING...ALTHOUGH BREEZY CONDITIONS ARE STILL
OBSERVED IN THE HIGHER ELEVATIONS. GIVEN THE WEAKER FLOW IN THE
VALLEYS...FEELING MORE CONFIDENT THAT TEMPS WILL BE COLD TONIGHT.
THIS IS ALREADY REFLECTED IN THE INHERITED GRIDS. WILL MAKE SOME
MINOR TWEEKS IN DEWPOINT AND WIND GRIDS THIS EVENING TO REFLECT
CURRENT TRENDS.

&&

.PREV DISCUSSION...SHORTWAVE RIDGING ALOFT WILL BE IN CONTROL OF OUR
WEATHER ON WEDNESDAY BEFORE THE NEXT TROUGH MOVES INTO THE AREA
THURSDAY. THE 12Z ECMWF/GEM CONTINUE TO BE THE MOST AGGRESSIVE WITH
THE DIGGING TROUGH AND ASSOCIATED MOISTURE AS IT MOVES IN
THURSDAY/THURSDAY NIGHT COMPARED TO THE DRIER 12Z NAM/GFS. AS THE
TROUGH MOVES IN...EXPECT BREEZY TO LOCALLY WINDY CONDITIONS WITH
SLIGHTLY WARMER TEMPERATURES AREAWIDE ON CHRISTMAS DAY. SOME EASTERN
AREAS WILL APPROACH WIND ADVISORY THRESHOLDS. WE CAN`T RULE OUT A
SPOT OR TWO SEEING BLOWING DUST BUT WILL LEAVE OUT OF THE FORECAST
AT THIS TIME.

AS THE COLD FRONT MOVES THROUGH THURSDAY NIGHT...HAVE LEANED TOWARDS
THE WETTER SOLUTIONS AND INCREASED POPS INTO THE CHANCE CATEGORY FOR
MOST OF THE FORECAST AREA. THUS...LOOKING AT POTENTIAL QPF OF ABOUT
0.10 TO 0.30 INCHES IN THE VALLEYS WITH HIGHER AMOUNTS POSSIBLE IN
THE MOUNTAINS. SNOW LEVELS WILL START AT ABOUT 7000 FEET THURSDAY
EVENING AND DROP TO ABOUT 5000 FEET FRIDAY MORNING. 2 TO 5 INCHES OF
SNOW ARE POSSIBLE ABOVE 7000 FEET WITH AN INCH OR TWO POSSIBLE
BETWEEN 5000 AND 7000 FEET. ANY REMAINING PRECIPITATION WILL QUICKLY
DEPART EASTERN AREAS FRIDAY MORNING.

EXPECT TROUGHINESS TO LINGER ACROSS THE AREA FRIDAY WITH DRIER AIR
MOVING IN AND BELOW NORMAL TEMPERATURES. THE FIRST WIDESPREAD FREEZE
OF THE SEASON WILL BE POSSIBLE IN TUCSON ON SATURDAY MORNING.
HEIGHTS AND THICKNESSES WILL GRADUALLY RISE THIS WEEKEND WITH
TEMPERATURES REMAINING WELL BELOW NORMAL SATURDAY WITH ANOTHER
FREEZE POSSIBLE FOR SUNDAY MORNING IN TUCSON AS WELL. BY SUNDAY AND
MONDAY A GRADUAL WARMING TREND IS EXPECTED. HOWEVER...TEMPERATURES
WILL STILL BE SLIGHTLY BELOW NORMAL INTO EARLY NEXT WEEK.

&&

.AVIATION...VALID THRU 25/06Z.
EXPECT CLEAR SKIES THROUGH WEDNESDAY AFTERNOON...WITH HIGH CLOUDS
ABOVE 20K FT AGL MOVING INTO THE AREA FROM THE WEST WEDNESDAY
EVENING. SURFACE WIND WILL GENERALLY BE FROM THE EAST TO SOUTHEAST
AT 5-15 KTS TONIGHT...BRIEFLY INCREASING TO 10 TO 15 KTS BY
MID-MORNING. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...DRY CONDITIONS WILL OCCUR INTO CHRISTMAS DAY. A
LOW PRESSURE SYSTEM MOVING ACROSS THE FOUR CORNERS REGION WILL THEN
BRING A CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW THURSDAY NIGHT.
THERE IS A SLIGHT CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW EAST OF
TUCSON FRIDAY MORNING. DRY CONDITIONS WILL THEN PREVAIL FRIDAY
AFTERNOON THROUGH NEXT TUESDAY. EXPECT BREEZY TO WINDY CONDITIONS
CHRISTMAS DAY ASSOCIATED WITH THIS LOW PRESSURE SYSTEM. OCCASIONALLY
GUSTY WINDS MAY OCCUR AT OTHER TIMES...ESPECIALLY DURING THE EARLY
MORNING AND AFTERNOON HOURS.

&&

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

&&

$$

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