Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 010343
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
845 PM MST SAT FEB 28 2015

.SYNOPSIS...A STRONG LOW PRESSURE SYSTEM STRENGTHENING NEAR THE
CALIFORNIA COAST WILL BRING STRONG AND GUSTY WINDS AGAIN MONDAY.
PERIODS OF VALLEY RAIN AND MOUNTAIN SNOW ARE POSSIBLE THIS EVENING
AND SUNDAY MAINLY TO THE NORTH OF TUCSON...THEN BECOMING WIDESPREAD
MONDAY INTO TUESDAY TO GO ALONG WITH COOLER TEMPERATURES.
PRECIPITATION CHANCES WILL THEN DIMINISH WITH DRY CONDITIONS AND
WARMER TEMPERATURES BY THE END OF THE WEEK.

&&

.DISCUSSION...STRONG LOW DIGGING DOWN TO NEAR THE CENTRAL AND
SOUTHERN CALIFORNIA COAST NOW WITH WATER VAPOR SATELLITE IMAGERY
STILL SHOWING ADDITIONAL STRENGTHENING ROUNDING DOWN THE WEST TO
SOUTHWEST FLANK. SO, IT STILL WON`T BE IN ANY HURRY TO TURN THE
CORNER AND HEAD THIS WAY. MEANWHILE WE HAVE TO RELY ON THE STRONG
SOUTHWESTERLY GRADIENT AHEAD TO GENERATE UPSLOPE EFFECTS FOR LIGHT
TERRAIN INDUCED PRECIP. WE HAVE GOOD MOISTURE IN PLACE FOR THAT WITH
PRECIPITABLE WATER VALUES NOW UP AROUND .75 TO .80 INCHES AS PER
BLENDED SATELLITE ESTIMATES AND THE AFTERNOON KTWC SOUNDING. UNTIL
WE FINALLY GET THE MAIN SYSTEM PUSHING IN FROM THE WEST WE WILL
CONTINUE TO SEE THE SPOTTY LIGHT SHOWER ACTIVITY WITH AN EMPHASIS ON
HIGHER TERRAIN. GUSTY WIND AGAIN SUNDAY INTO MONDAY BEFORE THE
STRONGER SHOWER ACTIVITY GETS HERE BY NOON MONDAY. THIS IS REFLECTED
WELL IN OUR CURRENT FORECAST WITH SOME MINOR ADJUSTMENTS BLENDING IN
00Z MODEL DATA. PLEASE SEE THE PREVIOUS DISCUSSION BELOW FOR
ADDITIONAL DETAILS.

&&

.AVIATION...VALID THRU 02/06Z.
SCT-BKN CLOUDS 5-7KFT AGL. ISOLD -SHRA MNLY W AND N KTUS WITH MTN
TOPS OBSCD. WINDS GENERALLY EASING TO S 6-14 KTS OVERNIGHT BEFORE
INCREASING AGAIN SUNDAY. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.

&&

.FIRE WEATHER...SUSTAINED S-SW WINDS OF 10-25 MPH WITH GUSTS 20-40
MPH...HIGHER IN THE TERRAIN...WILL GRADUALLY DIMINISH OVERNIGHT.
WIND SPEEDS WILL BE A LITTLE LIGHTER ON SUNDAY BEFORE INCREASING
AGAIN ON MONDAY. THESE WINDS ARE ASSOCIATED WITH AN APPROACHING
SYSTEM CURRENTLY MOVING DOWN THE WEST COAST. A FEW LIGHT SHOWERS
WEST AND NORTH OF TUCSON...BECOMING SCATTERED IN THIS SAME AREA ON
SUNDAY. SHOWERS WILL SPREAD ACROSS 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.

&&

.PREV DISCUSSION...FOR SUNDAY...AS THE UPPER LOW CONTINUES TO DIG
SOUTH AND THE 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 WHITE MOUNTAINS
WITH ENHANCED UPSLOPE FLOW. MUCH OF THE REMAINDER OF SOUTHEAST
ARIZONA AND ESPECIALLY FROM TUCSON SOUTH AND EAST WILL STAY
COMPLETELY DRY WITH BREEZY CONDITIONS EXPECTED AGAIN SUNDAY
AFTERNOON. THE WINDS WILL NOT BE AS STRONG ON SUNDAY AND THE SNOW
LEVELS WILL REMAIN HIGH.

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 FROM THE 12Z NUMERICAL GUIDANCE DEPICT THE COLD FRONT
MOVING THROUGH MOSTLY DURING THE AFTERNOON INTO 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
HAVE BEEN LOWERED A BIT AND ARE NOW GENERALLY A QUARTER TO HALF AN
INCH. SNOW LEVELS WILL FINALLY LOWER TO 6000-7000 FEET FOLLOWING THE
FRONTAL PASSAGE. WITH LOWER QPF AND SNOW AMOUNTS AS THE MAIN CORE OF
THE PRECIPITATION MOVES THROUGH MONDAY INTO MONDAY NIGHT...IT IS
STARTING TO LOOK MORE LIKE AN ADVISORY LEVEL EVENT FOR THE MOUNTAINS
WITH 6 TO 12 INCHES DURING THIS PERIOD. WILL WAIT FOR ADDITIONAL
SHIFTS TO CONTINUE TO TWEAK THE FORECAST AND GAIN HIGHER CONFIDENCE
BEFORE ISSUING ANY WINTER WEATHER PRODUCTS. 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 PORTIONS OF THE
AREA MAY END UP BEING IN A DRY SLOT BETWEEN THE INITIAL DEPARTING
DISTURBANCE AND DIGGING SECONDARY LOW NEAR OR JUST OFF NORTHERN
BAJA. THERE ARE MORE CONSIDERABLE DIFFERENCES STARTING WEDNESDAY
WITH HOW FAST TO EJECT THE UPPER LOW EASTWARD. IN FACT...SOME OF THE
GUIDANCE IS NOW DEPICTING THE UPPER LOW TO REMAIN IN THE AREA IN A
WEAKENED STATE THROUGH THE END OF THE WEEK. WILL STILL MAINTAIN
SLIGHT CHANCE POPS ON WEDNESDAY WITH DRY CONDITIONS FOR THE END OF
THE WORK WEEK. TEMPERATURES WILL BE AT THEIR COOLEST TUESDAY INTO
WEDNESDAY WITH HIGHS ABOUT 10 DEGREES BELOW NORMAL FOR THIS TIME OF
YEAR.

&&

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

&&

$$

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MEYER/GL





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