Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 241036
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
335 AM MST TUE FEB 24 2015

.SYNOPSIS...EXPECT SCATTERED VALLEY RAIN AND MOUNTAIN SNOW SHOWERS
MAINLY FROM TUCSON NORTHWARD AND EASTWARD TODAY. MUCH COOLER
TEMPERATURES WILL ALSO PREVAIL TODAY...WITH GUSTY WEST TO NORTHWEST
WINDS THIS AFTERNOON. COLDER LOW TEMPERATURES TONIGHT...THEN DRY
CONDITIONS WITH A WARMING TREND WEDNESDAY INTO FRIDAY. A DEEPENING
LOW PRESSURE SYSTEM THIS WEEKEND WILL BRING A CHANCE OF VALLEY RAIN
AND MOUNTAIN SNOW SHOWERS...COOLER TEMPERATURES AND GUSTY WINDS.

&&

.DISCUSSION...LOW PRESSURE ALOFT WAS CENTERED OVER NWRN ARIZONA
EARLY THIS MORNING. THIS LOW PRESSURE SYSTEM WILL MOVE SEWD TO NEAR
THE WHITE MOUNTAINS THIS AFTERNOON...THEN WEAKEN AND MOVE RAPIDLY
SEWD INTO CENTRAL TEXAS EARLY WED. SCATTERED SHOWERS SHOULD OCCUR
FROM TUCSON NEWD TO THE WHITE MOUNTAINS THIS MORNING. ISOLATED TO
SCATTERED SHOWERS WILL CONTINUE THIS AFTERNOON FROM TUCSON EWD TO
THE NEW MEXICO BORDER.

GIVEN THE AMOUNT OF MID-LEVEL COOLING ASSOCIATED WITH THIS SYSTEM...
CANNOT RULE OUT THE POSSIBILITY OF A FEW LIGHTNING STRIKES MAINLY
THIS AFTERNOON NE OF TUCSON. HOWEVER...GIVEN THE LOW CONFIDENCE OF
THIS OCCURRENCE...HAVE OPTED TO NOT INCLUDE WITH THIS FORECAST
ISSUANCE. THERE IS A CHANCE OF SNOW SHOWERS ACROSS THE WHITE
MOUNTAINS THIS EVENING. PRECIP-FREE CONDITIONS WILL RETURN AREA-WIDE
LATE TONIGHT UNDER CLEARING SKIES.

STORM TOTAL RAINFALL AMOUNTS ARE EXPECTED TO RANGE GENERALLY FROM A
FEW HUNDREDTHS OF AN INCH TO ONE THIRD OF AN INCH. THE HIGHEST
AMOUNTS SHOULD BE NE OF TUCSON. SNOW LEVELS THIS AFTERNOON WILL FALL
TO AROUND 6500 FEET. STORM TOTAL SNOW ACCUMULATIONS WILL BE QUITE
LIGHT...WITH PERHAPS 1 TO 4 INCHES OF SNOW ABOVE 7000 FEET. THE
GREATEST SNOW ACCUMULATIONS SHOULD OCCUR ACROSS THE SOUTHERN WHITE
MOUNTAINS.

GUSTY WEST TO NORTHWEST WINDS WILL PREVAIL THIS AFTERNOON ESPECIALLY
FROM TUCSON EASTWARD TO THE NEW MEXICO BORDER. GIVEN THE ORIENTATION
OF THE MID-LEVEL PRESSURE GRADIENT...THE STRONGEST WINDS THIS
AFTERNOON SHOULD BE ACROSS THE UPPER GILA RIVER VALLEY INCLUDING
SAFFORD. BASED ON THE 24/00Z NAM/GFS MOS GUIDANCE...WIND SPEEDS ARE
FORECAST TO REMAIN JUST BELOW ADVISORY CRITERIA ACROSS THE UPPER
GILA RIVER VALLEY THIS AFTERNOON.

A SERIES OF IMPULSES EMBEDDED WITHIN NWLY FLOW ALOFT WILL BRING SOME
SHOWERS TO THE FOUR CORNERS REGION WED-THUR. DRY CONDITIONS WILL
OCCUR ACROSS SE AZ...AND DRY CONDITIONS WILL CONTINUE INTO FRI AS
THE FLOW ALOFT BECOMES INCREASINGLY WLY AHEAD OF A DEEPENING TROUGH
OVER THE NWRN CONUS. 24/00Z GFS/ECMWF WERE IN GOOD AGREEMENT THAT
THIS UPPER TROUGH WILL DEEPEN OVER THE GREAT BASIN REGION SAT...AND
CONTINUE TO DEEPEN OVER THE SWRN CONUS SUN.

THERE IS A SLIGHT CHANCE OF SNOW SHOWERS ACROSS THE WHITE MTNS FRI
NIGHT...THEN PRECIP CHANCES WILL GRADUALLY INCREASE ACROSS THE AREA
SAT AND SAT NIGHT. GUSTY SOUTHWEST WINDS WILL ACCOMPANY THE
DEEPENING TROUGH ON SAT. AT THIS TIME...APPEARS THAT THE TIMING FOR
THE BEST CHANCE OF WIDESPREAD AND SIGNIFICANT PRECIP TO OCCUR IS
SUN. THEREAFTER...DEEPER MOISTURE IS PROGGED TO BE SHUNTED EWD INTO
THE SRN ROCKIES BY MON. LINGERING MOISTURE SHOULD STILL PROVIDE AT
LEAST A SLIGHT CHANCE OF VALLEY RAIN/MOUNTAIN SNOW SHOWERS NEXT MON.

MUCH COOLER TEMPS WILL OCCUR TODAY...WITH HIGH TEMPS FORECAST TO BE
ABOUT 10-15 DEGS F COOLER VERSUS MON. A WARMING TREND WILL OCCUR
WED-FRI...AND HIGH TEMPS THUR-FRI WILL AVERAGE NEARLY 2-5 DEGS F
ABOVE NORMAL. MUCH COOLER TEMPS WILL PREVAIL BY SUN.

&&

.AVIATION...VALID THRU 25/12Z.
A LOW PRESSURE SYSTEM WILL MOVE EASTWARD ACROSS NORTHERN ARIZONA
TODAY. THIS SYSTEM WILL BRING SCATTERED -SHRA AND HIGHER TERRAIN
-SHSN MAINLY FROM KTUS VICINITY NEWD TO THE WHITE MOUNTAINS. THESE
SHOWERS MAY BRING MVFR CONDITIONS...ESPECIALLY ACROSS THE HIGHER
TERRAIN. A FEW -TSRA MAY ALSO OCCUR NE OF KTUS TODAY. HOWEVER...
FORECAST CONFIDENCE IS VERY LOW FOR THIS OCCURRENCE. CLOUD BASES
WILL MAINLY RANGE FROM 4-8K FT AGL TODAY. A FEW LINGERING -SHRA/
-SHSN WILL OCCUR THIS EVENING MAINLY NEAR THE NEW MEXICO BORDER AS
THE UPPER LOW MOVES INTO FAR WEST TEXAS. DECREASING CLOUDS TONIGHT
WITH CLEAR SKIES TO MOSTLY CLEAR SKIES BY DAYBREAK WEDNESDAY.
SURFACE WIND THIS AFTERNOON WILL BE WLY/NWLY AT 12-25 KTS WITH GUSTS
OF 25-35 KTS. THE STRONGEST WIND WILL BE EAST OF KTUS...AND
ESPECIALLY IN THE VICINITY OF KSAD. AVIATION DISCUSSION NOT UPDATED
FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A STORM SYSTEM MOVING ACROSS NORTHERN ARIZONA WILL
BRING SCATTERED VALLEY RAIN AND MOUNTAIN SNOW SHOWERS MAINLY FROM
TUCSON EASTWARD TO THE NEW MEXICO BORDER TODAY. LIQUID AMOUNTS WILL
GENERALLY BE LESS THAN ONE QUARTER OF AN INCH. THE BEST CHANCE FOR
SNOW ACCUMULATIONS WILL BE ABOVE THE WHITE MOUNTAINS ABOVE 7000
FEET...WITH AMOUNTS MAINLY LESS THAN 5 INCHES. 20-FOOT WINDS THIS
AFTERNOON WILL BE WEST TO NORTHWEST AT 10-25 MPH...WITH THE
STRONGEST WINDS ACROSS THE UPPER GILA VALLEY INCLUDING SAFFORD. A
FEW LINGERING SNOW SHOWERS ACROSS THE WHITE MOUNTAINS THIS EVENING...
THEN DRY CONDITIONS WEDNESDAY THROUGH FRIDAY. A CHANCE OF VALLEY
RAIN AND MOUNTAIN SNOW WILL OCCUR THIS WEEKEND AS THE NEXT STORM
SYSTEM DEVELOPS ACROSS THE REGION. GUSTY WINDS WILL ACCOMPANY THIS
SYSTEM...ESPECIALLY ON SATURDAY.

&&

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

&&

$$

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FRANCIS




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