Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 262155
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
255 PM MST FRI DEC 26 2014

.SYNOPSIS...WIDESPREAD FREEZING TEMPERATURES WILL OCCUR TONIGHT WITH
A HARD FREEZE FOR MANY AREAS. COLD AGAIN SATURDAY NIGHT FOLLOWED BY
A WARMING TREND SUNDAY THROUGH TUESDAY. A STRONG STORM SYSTEM WILL
THEN BRING A FEW SHOWERS WITH GUSTY WINDS WEDNESDAY. VALLEY RAIN AND
MOUNTAIN SNOW SHOULD BECOME MORE WIDESPREAD WEDNESDAY NIGHT AND NEW
YEARS DAY AS THIS SYSTEM MOVES ACROSS THE AREA.

&&

.DISCUSSION...CLEAR SKIES ACROSS MUCH OF SE AZ THIS AFTERNOON EXCEPT
FOR SCATTERED TO OCCASIONALLY BROKEN LOWER LEVEL CLOUDS ACROSS ERN
SANTA CRUZ/SRN COCHISE COUNTIES...AND IN THE WHITE MOUNTAINS. THE
AFOREMENTIONED CLOUDS WILL ONLY GRADUALLY DECREASE TONIGHT...BUT
CLEAR SKIES WILL PREVAIL ELSEWHERE. GUSTY WEST WINDS ONGOING SE OF
TUCSON WILL DIMINISH THIS EVENING. THE COMBINATION OF CLEAR SKIES OR
MOSTLY CLEAR SKIES...LIGHT WINDS AND A VERY DRY SURFACE REGIME WILL
PROVIDE EXCELLENT RADIATIONAL COOLING CONDITIONS.

A HARD FREEZE WARNING REMAINS IN EFFECT FROM MIDNIGHT TONIGHT TO 9
AM MST SATURDAY FOR THE TUCSON METRO AREA AND SOUTHEAST PINAL
COUNTY. A FREEZE WARNING CONTINUES IN EFFECT FROM MIDNIGHT TONIGHT
TO 9 AM MST SATURDAY FOR WRN PIMA COUNTY...THE TOHONO O`ODHAM
NATION...AND SOUTH CENTRAL PINAL COUNTY. WIDESPREAD FREEZING TEMPS
WILL OCCUR AGAIN SAT NIGHT INTO SUN MORNING.

OTHERWISE...DRY CONDITIONS WILL PREVAIL INTO TUE NIGHT AS NWLY FLOW
ALOFT INITIALLY BECOMES INCREASINLY WLY TUE AHEAD OF A DEEPENING LOW
PRESSURE SYSTEM OVER THE GREAT BASIN REGION. THIS LOW PRESSURE
SYSTEM IS PROGGED VIA THE 26/12Z GFS/ECMWF TO BE CENTERED NEAR LAS
VEGAS NEVADA MIDDAY WED. MEANWHILE...THE 26/12Z CMC DEPICTED A
542 DM LOW TO BE CENTERED FURTHER WEST...OR NEAR LOS ANGELES. THE
GFS/ECMWF WERE FAIRLY SIMILAR WITH THE EWD PROGRESSION OF THIS
SYSTEM ACROSS NRN/CENTRAL AZ LATE NEXT WEEK. HOWEVER...THE CMC
DEPICTED A CONSIDERABLY SLOWER EWD PROGRESSION OF THIS SYSTEM. THE
GFS/ECMWF WERE FAVORED FOR THIS FORECAST ISSUANCE IN ORDER TO HAVE
MAINTAINED CONTINUITY AND PER COORD WITH NEIGHBORING WFO/S.

AT ANY RATE...THERE IS A SLIGHT CHANCE OF VALLEY RAIN/MOUNTAIN SNOW
WED. A TIGHT MID-LEVEL GRADIENT SHOULD PRODUCE GUSTY SWLY WINDS WED
SIMILAR TO SPEEDS ACHIEVED CHRISTMAS DAY. POPS WERE INCREASED WED
NIGHT ESPECIALLY FROM TUCSON EWD TO DEPICT A CHANCE OF VALLEY RAIN/
MOUNTAIN SNOW ACROSS MUCH OF THE AREA. A SIMILAR SCENARIO EXISTS NEW
YEARS DAY...WITH CHANCE-CATEGORY POPS FROM TUCSON EWD...BUT ONLY A
SLIGHT CHANCE OF SHOWERS ACROSS WRN SECTIONS.

HAVE NOTED SOMEWHAT LOWER QPF/S PRODUCED VIA THE 26/12Z GFS/ECMWF
VERSUS THE 26/00Z SOLUTIONS. WOULD NOT BE SURPRISED TO SEE CONTINUED
QPF VARIATIONS WITH SUBSEQUENT SOLUTIONS. GIVEN THAT THIS SYSTEM IS
DEEPER/COLDER VERSUS THE MOST RECENT SYSTEM...EVENTUAL SNOW LEVELS
SHOULD BE LOWER...AND LIQUID AMOUNTS AND SNOW ACCUMULATIONS SHOULD
BE HIGHER. PRECIPITATION SHOULD GRADUALLY DECREASE FROM WEST-TO-EAST
THUR NIGHT...AND A SLIGHT CHANCE OF SHOWERS SHOULD CONTINUE ACROSS
ERN SECTIONS FRI WITH DRY CONDITIONS ELSEWHERE.

HIGH TEMPS SAT WILL BE SIMILAR TO TEMPS ACHIEVED THIS AFTERNOON...
AND WILL AVERAGE ABOUT 10-15 DEGS F BELOW NORMAL. A WARMING TREND
WILL THEN OCCUR SUN-TUE FOLLOWED BY MUCH COOLER TEMPS TO RETURN
THUR-FRI.

&&

.AVIATION...VALID THRU 28/00Z.
SCT-BKN CLOUDS AT 6-10K FT AGL SE OF KTUS AND ESPECIALLY IN THE
VICINITY OF KDUG WILL GRADUALLY BECOME SKC-FEW CLOUDS AROUND 10K FT
AGL BY SATURDAY AFTERNOON. OTHERWISE...CLEAR SKIES WILL PREVAIL
ACROSS MUCH OF SE AZ INTO SATURDAY AFTERNOON. SURFACE WIND EAST AND
SOUTH OF KTUS INTO THIS EVENING WILL BE WLY 10-18 KTS WITH GUSTS
TO AROUND 25 KTS. OTHERWISE...SURFACE WIND WILL BE LESS THAN 10 KTS.
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...DRY CONDITIONS WITH GENERALLY LIGHT TERRAIN DRIVEN
WINDS WILL PREVAIL THROUGH TUESDAY NIGHT. A DEEP LOW PRESSURE SYSTEM
WILL THEN BRING A SLIGHT CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW
WEDNESDAY. BREEZY TO WINDY CONDITIONS ARE FORECAST TO OCCUR AHEAD OF
THIS SYSTEM WEDNESDAY.  PRECIPITATION CHANCES WILL INCREASE
WEDNESDAY NIGHT AND NEW YEARS DAY AS THIS SYSTEM MOVES ACROSS THE
AREA. A SLIGHT CHANCE OF SHOWERS WILL OCCUR MAINLY NEAR THE NEW
MEXICO BORDER FRIDAY WITH DRY CONDITIONS ELSEWHERE.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    HARD FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM MST SATURDAY
      FOR AZZ504-506.

    FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM MST SATURDAY
      FOR AZZ501-502-505.

&&

$$

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FRANCIS





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