Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 281613
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
912 AM MST SAT FEB 28 2015

.SYNOPSIS...A STRONG LOW PRESSURE SYSTEM DEVELOPING ALONG THE WEST
COAST WILL BRING STRONG AND GUSTY WINDS TO THE AREA TODAY AND AGAIN
MONDAY. THIS WIND WILL BE FOLLOWED BY PERIODS OF VALLEY RAIN AND
MOUNTAIN SNOW LATER THIS WEEKEND INTO THE MIDDLE OF NEXT WEEK. THE
BEST CHANCE FOR PRECIPITATION WILL BE MONDAY AND MONDAY NIGHT. AS
THIS OCCURS...A WARM WEEKEND WILL GIVE WAY TO COOLER TEMPERATURES
THE FIRST HALF OF NEXT WEEK.

&&

.DISCUSSION...LATEST IR/WV SATELLITE IMAGERY SHOWS CLOSED UPPER LOW
NOW MOVING SOUTHWARD ACROSS FAR NRN CALIFORNIA. CLOSER TO
HOME...STRONG WESTERLY FLOW ALOFT WITH CONSIDERABLE MID AND HIGH
LEVEL CLOUDINESS...ESPECIALLY ACROSS THE NORTHERN PORTIONS OF THE
AREA AS WEAK EMBEDDED DISTURBANCES IN THE FLOW MOVE THROUGH. CLOSER
TO THE SURFACE...A STRONG SOUTH TO SOUTHWEST GRADIENT HAS SETUP
ADVECTING LOWER LEVEL MOISTURE INTO THE AREA. 12Z KTWC SOUNDING HAS
PWAT VALUES AT 2/3RDS OF AN INCH WITH 20-25KT WINDS JUST OFF THE
DECK. BREEZY TO WINDY CONDITIONS AREA WIDE ARE EXPECTED THROUGH
 AFTERNOON WITH DEEP MIXING. THE STRONGEST WINDS WILL REMAIN TO THE
SOUTH AND EAST OF TUCSON. HOWEVER...WINDS ARE GENERALLY EXPECTED TO
REMAIN BELOW ADVISORY THRESHOLDS. LATEST SHORT TERM HIGH RESOLUTION
GUIDANCE MATCHES WELL WITH ONGOING FORECAST KEEPING PRECIPITATION
CHANCES MAINLY TO THE NORTH OF TUCSON AND ACROSS THE FAVORED HIGHER
TERRAIN DUE TO UPSLOPE FLOW INTO THIS EVENING. SNOW LEVELS WILL
REMAIN FAIRLY HIGH THROUGH TONIGHT AT ABOUT 8000-9000 FEET BUT
SEVERAL INCHES OF SNOW ARE POSSIBLE FOR THE WHITE MOUNTAINS.

FOR SUNDAY...AS THE UPPER LOW CONTINUES TO DIG SOUTH AND TROUGH AXIS
TAKES ON A MORE NORTH-SOUTH ORIENTATION...THAT WILL LIKELY FOCUS THE
DEEP MOISTURE PLUME TO THE NORTH AND WEST OF THE AREA WITH HEIGHTS
ACTUALLY SLIGHTLY INCREASING ACROSS SOUTHEAST ARIZONA DUE TO THE
AMPLIFICATION OF THE TROUGH. THE BEST PRECIPITATION CHANCES WILL
REMAIN ACROSS THE MOUNTAINS WITH ENHANCED UPSLOPE FLOW AS MUCH OF
SOUTHEAST ARIZONA STAYS DRY WITH BREEZY CONDITIONS EXPECTED AGAIN
SUNDAY AFTERNOON. THE MIDNIGHT SHIFT ALREADY MADE SOME ADJUSTMENTS
TO ACCOUNT FOR LATEST PRECIPITATION TRENDS SUNDAY...BUT WILL LIKELY
MAKE SOME MORE TWEAKS TO ACCOUNT FOR LATEST TRENDS IN THE AFTERNOON
PACKAGE. SNOW LEVELS WILL REMAIN HIGH ON SUNDAY.

ON MONDAY...THE TROUGH AXIS...ASSOCIATED COLD FRONT AND DEEP LAYER
ASCENT WILL GRADUALLY SHIFT FROM WEST TO EAST BRINGING THE BEST
CHANCE OF RAIN AND MOUNTAIN SNOW TO SOUTHEAST ARIZONA. THE LATEST
TRENDS HAVE CONTINUED TO SLOW THE SYSTEM DOWN WITH THE FRONT MOVING
THROUGH MOSTLY DURING THE AFTERNOON THROUGH THE EVENING. HAVE NOTED
THAT THE HIGHEST QPF WILL REMAIN ACROSS THE NORTHERN HALF OF THE
STATE INCLUDING THE MOGOLLON RIM CLOSEST TO THE STRONGEST JET
DYNAMICS AS THE TROUGH SHIFTS EAST WITH LESSER AMOUNTS IN OUR
FORECAST AREA. THE MOUNTAINS WILL CONTINUE TO SEE FAVORABLE UPSLOPE
FLOW ENHANCING PRECIPITATION TOTALS FOR THOSE AREAS BUT VALLEY QPFS
OF MOSTLY A QUARTER TO HALF AN INCH LOOK ON TARGET. SNOW LEVELS WILL
FINALLY LOWER TO 6000-7000 FEET FOLLOWING THE FRONTAL PASSAGE. WILL
CONTINUE TO EVALUATE THE POSSIBILITY OF WINTER WEATHER HEADLINES FOR
THE MOUNTAINS...BUT CONFIDENCE ON TIMING AND SNOW AMOUNTS IS STILL
TOO LOW AT THIS TIME. THE OTHER BIG STORY ON MONDAY WILL BE THE
GUSTY WINDS...ESPECIALLY SOUTH AND EAST OF TUCSON. WITH THE SYSTEM
BEING A BIT SLOWER...THIS WILL ALLOW DEEPER MIXING ESPECIALLY TO THE
SOUTH AND EAST OF TUCSON. SOME OF THESE AREAS MIGHT SEE WINDS
EXCEEDING ADVISORY THRESHOLDS.

THERE WILL REMAIN A CHANCE OF SHOWERS AND MOUNTAIN SNOW SHOWERS ON
TUESDAY INTO TUESDAY NIGHT  AS A SECONDARY TROUGH AXIS SHIFTS SOUTH
AND EAST. HOWEVER...CONFIDENCE REMAINS QUITE LOW AS THE AREA MAY END
UP BEING IN A DRY SLOT SIMILAR TO THE 12Z NAM SOLUTION IF THE UPPER
LOW
ON THE BACKSIDE OF THIS SYSTEM DIGS FARTHER SOUTH AND IS STRONGER
THAN EXPECTED. TEMPERATURES WILL BE QUITE A BIT COOLER ON TUESDAY AS
WELL. ANY RESIDUAL SHOWERS SHOULD COME TO AN END BY WEDNESDAY OR
WEDNESDAY EVENING AS THE TROUGH FINALLY EJECTS EAST OF THE AREA AND
NORTHWESTERLY FLOW ALOFT MOVES IN WITH DRIER AIR TO END THE WEEK.

&&

.AVIATION...VALID THRU 01/18Z.
CLOUDS GENERALLY INCREASING TODAY WITH SCT TO OCCASIONALLY BKN
CLOUDS AOA 20K FT AGL WITH INCREASING SCT-BKN CLOUDS 5-7K FT THIS
AFTERNOON.  AS THE LOWER CLOUDS DEVELOP THERE IS ALSO A SLIGHT CHC
OF -SHRA INTO SUNDAY MORNING TO THE NORTH AND WEST OF KTUS AS WELL
AS OVER THE MOUNTAINS.  WINDS GENERALLY SOUTH AT 8-15 KTS BECOMING
SWLY AND INCREASING TO 15-25 KTS WITH GUSTS TO 35 KTS THROUGH 01/02Z
THEN EASING TO SOUTH 6-14 KTS OVERNIGHT.  AVIATION DISCUSSION NOT
UPDATED FOR TAF AMENDMENTS.  CERNIGLIA

&&

.FIRE WEATHER...A STRENGTHENING STORM SYSTEM WEST OF THE AREA WILL
PRODUCE GUSTY WINDS TODAY MAINLY SOUTH OF I-10...GENERALLY AROUND 5
MPH STRONGER THAN YESTERDAY AND WITH HIGHER GUSTS.  EXPECT SUSTAINED
WINDS TO PEAK AROUND 18-28 MPH THIS AFTERNOON WITH GUSTS 40+ MPH
SOUTH OF I-10 AND ACROSS HIGHER TERRAIN.  WINDS WILL BE SOMEWHAT
LIGHTER SUNDAY THEN INCREASE AGAIN ON MONDAY...POTENTIALLY BEING THE
WINDIEST DAY OF THIS STRETCH.

AS THE SYSTEM APPROACHES...ISOLATED SHOWERS ARE EXPECTED TODAY NORTH
AND WEST OF TUCSON...THEN SCATTERED SHOWERS ACROSS THE SAME AREA
TONIGHT AND SUNDAY.  THE THREAT OF SHOWERS WILL SPREAD TO ALL AREAS
SUNDAY NIGHT THROUGH TUESDAY BEFORE DIMINISHING WEDNESDAY WITH DRY
CONDITIONS THEREAFTER.  THE SHOWERS WILL BE SNOW ABOVE 8000 FT
THROUGH MONDAY THEN DROPPING TO AROUND 6000 FEET LATE MONDAY THROUGH
WEDNESDAY.  CERNIGLIA

&&

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

&&

$$

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GL





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