Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 261633
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
932 AM MST THU FEB 26 2015

.SYNOPSIS...DRY CONDITIONS WITH ABOVE NORMAL DAYTIME TEMPERATURES
WILL OCCUR THROUGH FRIDAY. A STRONG LOW PRESSURE SYSTEM WILL THEN
BRING GUSTY WINDS SATURDAY FOLLOWED BY A GOOD CHANCE OF VALLEY RAIN
AND MOUNTAIN SNOW EARLY NEXT WEEK. LINGERING SHOWERS WITH WELL BELOW
NORMAL TEMPERATURES WILL CONTINUE TUESDAY INTO WEDNESDAY.

&&

.DISCUSSION...A WEAK SHORTWAVE TROUGH EMBEDDED IN THE NORTHWESTERLY
FLOW ALOFT WILL BRUSH THROUGH NORTHEAST ARIZONA TODAY INTO TONIGHT.
THIS FEATURE COULD TRACK FAR ENOUGH SOUTH TO BRING A CHANCE OF
SHOWERS TO THE WHITE MOUNTAINS LATER THIS EVENING AND TONIGHT. RIGHT
NOW...THOSE CHANCES APPEARED TO BE RATHER SLIM. THUS...WILL KEEP THE
MENTION OF SHOWERS OUT OF THE FORECAST. OTHERWISE...DRY CONDITIONS
CAN BE EXPECTED THROUGH FRIDAY. THEREAFTER...GUSTY WINDS SATURDAY
FOLLOWED BY PERIODS OF VALLEY RAIN AND MOUNTAIN SNOW CAN BE
ANTICIPATED. FOR MORE DETAILS ON THE UPCOMING UNSETTLED
WEATHER...PLEASE REFER TO THE ADDITIONAL SECTIONS IN THIS PRODUCT.

&&

.AVIATION...VALID THRU 27/18Z.
VFR CONDITIONS WILL PREVAIL WITH A FEW TO BROKEN CLOUDS ABOVE 20K FT
AGL. SURFACE WIND EAST AND SOUTH OF KTUS THIS AFTERNOON AND EARLY
THIS EVENING WILL BE SWLY-NWLY AT 12-18 KTS WITH GUSTS OF 20-25 KTS.
OTHERWISE...SURFACE WIND WILL BE LESS THAN 10 KTS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...DRY CONDITIONS WILL CONTINUE THROUGH FRIDAY. A
STRENGTHENING STORM SYSTEM WEST OF THE AREA FRIDAY WILL PRODUCE
GUSTY WINDS IN EXCESS OF 20 MPH...ESPECIALLY ACROSS THE HIGHER
TERRAIN. FRIDAY WILL ALSO BE THE WARMEST DAY DURING THE NEXT 7
DAYS...WITH MINIMUM RH VALUES IN THE TEENS. EXPECT STRONGER WINDS
SATURDAY...WITH 20-FOOT WIND SPEEDS GENERALLY FROM THE SOUTHWEST AT
15-25 MPH. STRONGER SPEEDS WILL OCCUR ACROSS HIGHER ELEVATIONS.
PRECIPITATION CHANCES WILL INCREASE ACROSS THE AREA SATURDAY
FOLLOWED BY WIDESPREAD VALLEY RAIN AND MOUNTAIN SNOW EARLY NEXT
WEEK. ISOLATED TO SCATTERED VALLEY RAIN AND MOUNTAIN SNOW SHOWERS
WILL CONTINUE TUESDAY AND WEDNESDAY...WITH THE BEST CHANCE OF
PRECIPITATION TO OCCUR EAST OF TUCSON. DAYTIME TEMPERATURES WILL BE
WELL BELOW NORMAL MONDAY THROUGH WEDNESDAY.

&&

.PREV DISCUSSION...NWLY FLOW ALOFT WILL OCCUR TODAY IN RESPONSE TO
UPPER RIDGE NEAR 140W AND AN UPPER TROUGH OVER THE ERN CONUS. A
SERIES OF IMPULSES EMBEDDED WITHIN THIS FLOW WILL BRING A CHANCE OF
SHOWERS TO THE FOUR CORNERS REGION TONIGHT-FRI. THUS...DRY
CONDITIONS WILL PREVAIL ACROSS SE AZ INTO FRI WITH ANY MEASURABLE
PRECIP REMAINING NORTH OF THIS FORECAST AREA. THE FLOW ALOFT WILL
BECOME INCREASINGLY WLY FRI NIGHT AS THE UPPER RIDGE RETROGRADES TO
NEAR 145W...AND A TROUGH DEEPENS OVER THE PACIFIC NW/NRN ROCKIES.

26/00Z GFS/ECMWF REMAINED IN GOOD AGREEMENT THAT THE UPPER TROUGH
WILL CONTINUE TO DEEPEN OVER THE GREAT BASIN REGION SAT. THERE IS AT
LEAST A SLIGHT CHANCE OF SHOWERS ACROSS MUCH OF THE AREA SAT. THE
BEST CHANCE OF PRECIP SAT WILL BE ACROSS THE WHITE MOUNTAINS. THE
MAIN IMPACT SAT WILL LIKELY BE STRONG AND GUSTY SOUTHWEST WINDS IN
RESPONSE TO A TIGHTENING MID-LEVEL GRADIENT. HAVE NOTED THAT THE
26/00Z NAM/GFS MOS GUIDANCE SPEEDS HAVE DECREASED A FEW MPH VERSUS
PREVIOUS SOLUTIONS. THUS...THE PROSPECT OF ACHIEVING WIND ADVISORY
CRITERIA PARTICULARLY SE OF TUCSON HAS BEEN REDUCED.

PRECIP CHANCES WILL INCREASE SAT NIGHT INTO MON AS THE UPPER TROUGH
CONTINUES TO DEEPEN OVER THE SWRN CONUS. 26/00Z GFS/ECMWF WERE
SIMILAR VERSUS PREVIOUS SOLUTIONS WITH DEPICTING THE HIGHEST POPS/
QPFS SUN TO OCCUR ACROSS WRN SECTIONS. AT THIS TIME...APPEARS THAT
THE TIMING FOR THE BEST CHANCE OF SIGNIFICANT PRECIP FOR THE TUCSON
METRO AREA WILL BE SUN NIGHT INTO MON. THE GRIDDED DATA POP VALUES
WERE MODIFIED TO REFLECT THIS SCENARIO.

THE LONGWAVE UPPER TROUGH OVER THE WRN CONUS WILL MAINTAIN ISOLATED
TO SCATTERED VALLEY RAIN/MOUNTAIN SNOW SHOWERS TUE AND TUE NIGHT.
PRECIPITATION CHANCES WILL THEN BEGIN TO DECREASE FROM SOUTHWEST
TO NORTHEAST NEXT WED AS THE TROUGH AXIS MOVES EWD ACROSS THE AREA.
THERE WILL BE ENOUGH MOISTURE TO JUSTIFY CHANCE-CATEGORY POPS ACROSS
THE HIGHER TERRAIN NE OF TUCSON WED...AND A SLIGHT CHANCE OF SHOWERS
ELSEWHERE.

TOTAL RAINFALL AMOUNTS FOR SATURDAY THRU NEXT WEDNESDAY IN THE
VALLEYS WILL GENERALLY RANGE FROM 0.50 INCH TO 1.50 INCHES...WITH
LOCALLY HEAVIER AMOUNTS IN EXCESS OF 2 INCHES POSSIBLE. TOTAL
SNOWFALL ACCUMULATIONS FOR SATURDAY THROUGH NEXT WEDNESDAY WILL
GENERALLY BE AROUND 12 INCHES ACROSS THE CATALINA/RINCON MOUNTAINS
ABOVE 6500 FEET. TOTAL SNOW ACCUMULATIONS WILL RANGE FROM 12-30
INCHES ACROSS THE PINALENO AND WHITE MOUNTAINS ABOVE 6500 FEET.

A POINT OF EMPHASIS HERE...THESE RAINFALL AMOUNTS AND SNOW
ACCUMULATIONS DEPICT A VERY PRELIMINARY ESTIMATE. THESE AMOUNTS AND
ACCUMULATIONS WILL BE REFINED VIA SUBSEQUENT FORECAST ISSUANCES
DURING THE NEXT FEW DAYS.

HIGH TEMPS THIS AFTERNOON WILL BE NEARLY 5 DEGS F WARMER ACROSS ERN
SECTIONS VERSUS WED. HIGH TEMPS THIS AFTERNOON FROM TUCSON WWD WILL
BE ABOUT 6-10 DEGS WARMER VERSUS WED. EXPECT ANOTHER 2-3 DEGS F OR
SO OF WARMING FRI. A COOLING TREND WILL COMMENCE SAT FOLLOWED BY
MARKEDLY COOLER TEMPS SUN. THERE ARE NO SIGNIFICANT DAILY TEMP
VARIATIONS EXPECTED PRESENTLY FOR MON-WED...AND THESE TEMPS WILL
AVERAGE ABOUT 6-10 DEGS F BELOW NORMAL FOR MUCH OF THE AREA.

&&

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

&&

$$

VISIT US ON FACEBOOK...TWITTER...YOUTUBE...AND AT WEATHER.GOV/TUCSON

PREV DISCUSSION...FRANCIS
AVIATION/FIRE WEATHER...HUMPHREYS












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