Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 282255
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
355 PM MST WED JAN 28 2015

.SYNOPSIS...A STORM SYSTEM WILL BRING VALLEY RAIN AND MOUNTAIN SNOW
MAINLY THURSDAY NIGHT INTO SATURDAY. THE MOST SIGNIFICANT SNOWFALL
WILL BE ABOVE 8000 FEET OR ACROSS THE HIGHEST PEAKS. EXPECT MUCH
COOLER DAYTIME TEMPERATURES WITH THIS SYSTEM. DRY CONDITIONS WILL
RETURN EARLY NEXT WEEK ALONG WITH A WARMING TREND.

&&

.DISCUSSION...UPPER LEVEL TROUGH CONTINUES TO DEEPEN WEST OF THE SRN
CALIFORNIA/BAJA CALIFORNIA COASTS VICINITY 125W THIS AFTERNOON. IR
SATELLITE IMAGERY DEPICTED AN EXPANSIVE AREA OF COLDER CLOUD TOPS
EXTENDING FROM FAR SWRN AZ SWWD TO NEAR 20N/120W. EXPECT THICKENING
MOSTLY MID AND HIGH-LEVEL CLOUDS TONIGHT INTO THUR MORNING AHEAD OF
THE DEEPENING UPPER TROUGH. THERE IS A SLIGHT CHANCE OF SHOWERS THUR
AFTERNOON EAST AND SOUTH OF TUCSON WITH DRY CONDITIONS ELSEWHERE.

28/12Z NAM/GFS/ECMWF/CMC REMAIN CONSISTENT WITH DEPICTING WIDESPREAD
SHOWERS TO DEVELOP THUR EVENING...THEN WIDESPREAD SHOWERS SHOULD
OCCUR THUR NIGHT INTO SAT. THE MAIN ADJUSTMENT FOR THIS FORECAST
PACKAGE WAS TO INCREASE POPS VERSUS THE PREVIOUS OFFICIAL FORECAST.
OTHERWISE...QPF/S AND SNOW ACCUMULATIONS WERE LEFT ESSENTIALLY
UNCHANGED. A SLIGHT CHANCE OF THUNDERSTORMS WAS ADDED TO MUCH OF THE
AREA FRI MORNING...AND A SLIGHT CHANCE OF THUNDERSTORMS IS NOW IN
THE OFFICIAL FORECAST SAT AFTERNOON EXCEPT ACROSS THE WHITE
MOUNTAINS.

A 563 DM LOW IS PROGGED TO BE CENTERED MIDDAY FRI JUST SOUTH OF SAN
DIEGO CALIF...THEN THIS UPPER LOW IS PROGGED TO ESSENTIALLY REMAIN
QUASI-STATIONARY OVER SRN CALIFORNIA/NRN BAJA CALIFORNIA THRU MIDDAY
SAT. 28/12Z GFS TOTAL PRECIP WATER VALUE FOR THIS PERIOD IS PROGGED
TO BE ABOUT 1.20 INCHES. THIS PWAT VALUE IS NOW GREATER THAN 4
STANDARD DEVIATIONS ABOVE NORMAL. THE COMBINATION OF ABUNDANT
MOISTURE AND SYNOPTIC SCALE FORCING SHOULD PRODUCE WIDESPREAD
SIGNIFICANT RAINFALL BY MIDDAY SAT. THE UPPER LOW IS THEN PROGGED TO
FILL AND MOVE SEWD INTO SONORA MEXICO SAT NIGHT...THEN CONTINUE WELL
SOUTH OF THE AREA BY SUN EVENING. THERE APPEARS TO BE ENOUGH
RESIDUAL MOISTURE TO JUSTIFY A SLIGHT CHANCE OF SHOWERS EAST-TO-
SOUTH OF TUCSON SUN.

STORM TOTAL LIQUID AMOUNTS ARE NOW FORECAST TO GENERALLY RANGE FROM
0.50 TO 1.50 INCHES IN THE VALLEYS...WITH LOCALLY HEAVIER AMOUNTS
POSSIBLE. LIQUID AMOUNTS IN EXCESS OF 2 INCHES SHOULD OCCUR ACROSS
THE MOUNTAINS...ESPECIALLY NE OF TUCSON TO THE WHITE MOUNTAINS.

SNOW LEVELS FRI MORNING WILL BE AROUND 9000 FEET. SNOW LEVELS WILL
THEN LOWER TO AROUND 8000 FEET FRIDAY EVENING...AND CONTINUE TO
LOWER TO NEAR 7500 FEET BY MIDDAY SATURDAY. STORM TOTAL SNOW
ACCUMULATIONS SHOULD APPROACH OR EXCEED 2 FEET IN THE WHITE
MOUNTAINS ABOVE 7000 FEET...WITH 18-22 INCHES OF SNOWFALL ABOVE 7000
FEET FURTHER SWWD ACROSS THE PINALENO MOUNTAINS INCLUDING MOUNT
GRAHAM. STORM TOTAL SNOW ACCUMULATIONS ARE FORECAST TO RANGE BETWEEN
12-16 INCHES ACROSS THE CATALINA/RINCON MOUNTAINS ABOVE 7000 FEET.

DRY CONDITIONS WILL THEN PREVAIL SUN NIGHT-WED. HIGH TEMPS THUR WILL
AVERAGE ABOUT 5-10 DEGS F OR SO ABOVE NORMAL. EXPECT NEARLY 10-15
DEGS F OF COOLING FRI FOLLOWED BY AN ADDITIONAL 3-5 DEGS F OF
COOLING SAT. A WARMING TREND WILL OCCUR SUN-MON...THEN NO
SIGNIFICANT CHANGE IN DAYTIME TEMPS WILL HAPPEN TUE-WED.

&&

.AVIATION...VALID THRU 30/00Z.
EXPECT INCREASING CLOUDS MAINLY ABOVE 12K FT AGL TONIGHT FOLLOWED BY
A FEW TO SCATTERED CLOUDS AROUND 6-10K FT AGL AND OVERCAST CLOUD
DECKS ABOVE 12K FT AGL BY THURSDAY EVENING. A FEW -SHRA MAY DEVELOP
EAST AND SOUTH OF KTUS THURSDAY AFTERNOON. SURFACE WIND WILL BE LESS
THAN 10 KTS INTO THURSDAY MORNING...THEN SURFACE WIND THURSDAY
AFTERNOON WILL BE SELY/SLY AT 10-15 KTS THURSDAY AFTERNOON. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A STORM SYSTEM WILL BRING WIDESPREAD VALLEY RAIN AND
MOUNTAIN SNOW MAINLY THURSDAY NIGHT INTO SATURDAY. THE MOST
SIGNIFICANT SNOWFALL WILL OCCUR ACROSS THE HIGHEST PEAKS OF THE
WHITE MOUNTAINS...MOUNT GRAHAM AND THE CATALINA AND RINCON
MOUNTAINS. A FEW LINGERING SHOWERS WILL OCCUR MAINLY EAST TO SOUTH
OF TUCSON SUNDAY...THEN DRY CONDITIONS WILL PREVAIL MONDAY THROUGH
WEDNESDAY.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH SATURDAY
    MORNING FOR AZZ510-511-514 ABOVE 7000 FEET.

&&

$$

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FRANCIS




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