Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 251634
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
935 AM MST WED FEB 25 2015

.SYNOPSIS...EXPECT DRY CONDITIONS WITH A WARMING TREND THROUGH
FRIDAY. A STRONG LOW PRESSURE SYSTEM WILL BRING GUSTY WINDS SATURDAY
FOLLOWED BY A GOOD CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW EARLY
NEXT WEEK. MUCH COOLER TEMPERATURES WILL OCCUR SUNDAY AND MONDAY.

&&

.DISCUSSION...CHILLY START TO THE DAY...A NICE CHANGE FROM THE
EXTENDED PERIOD OF ABOVE NORMAL LOW TEMPERATURES FOR MOST OF THE
AREA. BAND OF HIGH CLOUDS OVER THE SOUTHERN ZONES WILL CONTINUE TO
MOVE E-SE TODAY. WARMER TODAY IN WAKE OF YESTERDAYS STORM.

DRY FOR THE REMAINDER OF THE WORK WEEK AND INTO THE FIRST HALF OF
THE WEEKEND. THE NEXT WINTER STORM WILL START TO IMPACT THE AREA ON
SATURDAY WITH STRONG GUSTY WINDS...WITH SOME AREAS APPROACHING WIND
ADVISORY CRITERIA. STILL LOOKING AT A VERY GOOD CHANCE OF WIDESPREAD
VALLEY RAIN AND MOUNTAIN SNOW SUNDAY INTO MONDAY. FOR DETAILS ABOUT
THIS CHECK OUT THE PREVIOUS DISCUSSION BELOW.

&&

.AVIATION...VALID THRU 26/18Z.
BAND OF HIGH CLOUDS ACROSS PIMA...SANTA CRUZ AND COCHISE COUNTIES
INTO THE AFTERNOON HOURS. OTHERWISE SKC. EXPECT LIGHT WINDS THROUGH
25/19Z THEN NW WINDS 10-15 KTS EXCEPT TO 20 KTS NEAR KSAD. WIND
BECOMING LIGHT AGAIN AFTER 26/02Z. AVIATION DISCUSSION NOT UPDATED
FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...MOSTLY CLEAR AND DRY TODAY AND THURSDAY WITH
WESTERLY AFTERNOON BREEZES OF 10 TO 20 MPH...STRONGEST EAST OF
TUCSON TODAY AND SOUTHERN AREAS THURSDAY. AN APPROACHING DEEP STORM
SYSTEM WILL BEGIN TO AFFECT THE REGION FRIDAY WITH INCREASING WINDS
LOCALLY IN EXCESS OF 20 MPH...ESPECIALLY ACROSS HIGHER TERRAIN.
FRIDAY WILL ALSO BE A WARM AND DRY DAY WITH MINIMUM RH VALUES IN THE
TEENS. WINDS WILL BECOME EVEN STRONGER SATURDAY...GENERALLY 20-30
MPH WITH STRONGER WINDS AT HIGHER ELEVATIONS. CLOUDS WILL OVERSPREAD
THE REGION WITH SHOWERS DEVELOPING MAINLY WEST AND NORTH. SUNDAY
THROUGH MONDAY WILL BE A COOL AND WET PERIOD WITH HIGH ELEVATION
SNOWFALL. DRIER CONDITIONS ARE EXPECTED TUESDAY WITH THE POTENTIAL
FOR ANOTHER WET WEATHER SYSTEM THE MIDDLE TO LATTER PART OF NEXT
WEEK.

&&

.PREV DISCUSSION...FAIRLY STRONG NWLY FLOW ALOFT REGIME TO PREVAIL
INTO THUR IN RESPONSE TO UPPER RIDGE NEAR 140W AND UPPER TROUGH OVER
THE ERN CONUS. FLOW ALOFT WILL BECOME INCREASINGLY WLY FRI AS THE
UPPER RIDGE RETROGRADES TO NEAR 145W...AND A TROUGH DEEPENS OVER THE
PACIFIC NW/NRN ROCKIES. HAVE OPTED FOR DRY CONDITIONS AREA-WIDE INTO
FRI WITH THE BELIEF BASED ON VARIOUS 25/00Z NWP MODELS THAT ANY
MEASURABLE PRECIP WILL REMAIN NORTH OF THIS FORECAST AREA.

25/00Z GFS/ECMWF/CMC REMAINED IN GOOD AGREEMENT THAT THE UPPER
TROUGH WILL DEEPEN OVER THE GREAT BASIN REGION SAT...AND CONTINUE TO
DEEPEN OVER THE SWRN CONUS SUN. THESE SOLUTIONS SUGGESTED THAT THE
ONSET OF PRECIP FOR SE AZ...AS WELL AS THE TIMING FOR WHEN THE MOST
SIGNIFICANT PRECIP WOULD OCCUR...HAS BEEN DELAYED ABOUT 12 HOURS OR
SO VERSUS PREVIOUS NWP SOLUTIONS. THUS...POPS WERE ADJUSTED TO
REFLECT THIS SCENARIO.

THERE IS A SLIGHT CHANCE OF SNOW SHOWERS ACROSS THE WHITE MTNS FRI
NIGHT WITH DRY CONDITIONS ELSEWHERE. PRECIP CHANCES WILL GRADUALLY
INCREASE ACROSS THE AREA SAT. THE MAIN IMPACT SAT WILL LIKELY BE
STRONG AND GUSTY SOUTHWEST WINDS AS THE MID-LEVEL GRADIENT TIGHTENS
CONSIDERABLY ACROSS THE AREA. WIND ADVISORY CRITERIA SPEEDS SHOULD
BE APPROACHED ACROSS SANTA CRUZ/SRN COCHISE COUNTIES. A CHANCE OF
SHOWERS THEN EXISTS FOR MUCH OF SE AZ SAT NIGHT. A PRELIMINARY
ESTIMATE FOR SNOW LEVELS SAT NIGHT WILL RANGE FROM 7500-8000 FEET.

A 549 DM LOW IS PROGGED TO BE CENTERED JUST WEST OF LOS ANGELES
MIDDAY SUN WITH STRONG SWLY FLOW ALOFT OVER SE AZ. THE UPPER LOW IS
PROGGED TO DIG TO JUST WEST OF SAN DIEGO LATE SUN NIGHT. THUS...
BASED ON THESE 25/00Z NWP SOLUTIONS...THE MOST SIGNIFICANT RAINFALL
SUN SHOULD OCCUR ACROSS WRN SECTIONS. POPS WERE THEN RAISED TO
DEPICT THE BEST CHANCE OF RAINFALL SUN NIGHT TO OCCUR GENERALLY FROM
NOGALES TO TUCSON NEWD INTO THE WHITE MOUNTAINS.

THE UPPER TROUGH IS THEN PROGGED TO FILL AND MOVED EWD ACROSS THE
AREA MON. CHANCE-CATEGORY POPS EXISTS MON FROM TUCSON EWD TO THE NEW
MEXICO BORDER...AND A SLIGHT CHANCE OF SHOWERS CONTINUES ACROSS WRN
SECTIONS. THE FLOW ALOFT IS THEN DEPICTED TO BECOME INCREASINGLY WLY
LATE MON NIGHT-TUE. THIS FLOW REGIME SHOULD ADVECT DRIER AIR EWD
ACROSS MUCH OF THE AREA. THUS...POPS WERE REDUCED TO DEPICT A SLIGHT
CHANCE OF VALLEY RAIN/MOUNTAIN SNOW SHOWERS MAINLY NE OF TUCSON MON
NIGHT-TUE.

THERE WILL BE REFINEMENT TO THIS PRECIP SCENARIO. STILL TOO EARLY TO
GIVE EXACT RAINFALL AMOUNTS AND SNOWFALL ACCUMULATIONS. HOWEVER...
AMOUNTS AND ACCUMULATIONS SHOULD BE CONSIDERABLY HIGHER VERSUS
AMOUNTS/ACCUMS THAT WERE PRODUCED TUESDAY.

THE WARMING TREND WILL CONTINUE THUR-FRI... AND HIGH TEMPS WILL
AVERAGE NEARLY 2-5 DEGS F ABOVE NORMAL. EXPECT ABOUT 5 DEGS F OR SO
OF COOLING SAT FOLLOWED BY MUCH COOLER TEMPS SUN-MON. MODEST WARMING
IS ON TAP NEXT TUE...BUT HIGH TEMPS AT THIS TIME APPEAR TO REMAIN
SEVERAL DEGS BELOW NORMAL.

&&

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

&&

$$

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