Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 192205
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
305 PM MST SUN APR 19 2015

.SYNOPSIS...A FEW SHOWERS ACROSS THE WHITE MOUNTAINS WILL END THIS
EVENING. OTHERWISE...DRY CONDITIONS WITH ABOVE NORMAL DAYTIME
TEMPERATURES WILL PREVAIL THROUGH WEDNESDAY. GUSTY WINDS SHOULD
RETURN BY WEDNESDAY AS A LOW PRESSURE SYSTEM APPROACHES FROM THE
WEST. THIS SYSTEM WILL THEN BRING A SLIGHT CHANCE OF SHOWERS AND
COOLER TEMPERATURES THURSDAY INTO FRIDAY.

&&

.DISCUSSION...FAIRLY THICK CUMULOFORM CLOUD FIELD ACROSS THE WHITE
MOUNTAINS AT THIS TIME...WITH KEMX WSR-88D DETECTING MOSTLY LESS
THAN 25 DBZ ECHOES VALID 2200Z. GIVEN THE VERY DRY NEAR-SURFACE
REGIME...THIS AREA WILL BE HARD-PRESSED TO RECEIVE MEASURABLE
RAINFALL. FOR NOW...HAVE MAINTAINED A SLIGHT CHANCE OF SHOWERS INTO
EARLY THIS EVENING. OTHERWISE...EXPECT CLEAR SKIES TO MOSTLY CLEAR
SKIES TONIGHT...WITH OTHER CUMULOFORM CLOUDS DISSIPATING WITH THE
LOSS OF DAYTIME HEATING.

UPPER RIDGE AXIS WILL EXTEND FROM SE ARIZONA NWWD INTO NRN
CALIFORNIA MON MORNING. MEANWHILE...A BROAD SRN STREAM TROUGH WILL
EXIST FROM BAJA CALIFORNIA WWD TO AROUND 130W. HAVE OPTED FOR DRY
CONDITIONS MON WITH THE BELIEF THAT ANY MEASURABLE RAINFALL WILL
REMAIN NORTH OF THIS FORECAST AREA. FLOW ALOFT WILL BECOME
INCREASINGLY SWLY TUE AS THE UPPER RIDGE MOVES NE OF THE AREA. SWLY
FLOW ALOFT WILL STRENGTHEN WED AS THE UPPER TROUGH CONTINUES TO
DEEPEN WEST TO SOUTHWEST OF THE AREA. THIS PATTERN WILL TRANSLATE
INTO CONTINUED PRECIP-FREE CONDITIONS TUE-WED...ALTHOUGH A GRADUAL
INCREASE IN AFTERNOON SURFACE WIND SPEEDS WILL OCCUR.

LOW PRESSURE ALOFT IS PROGGED TO BE CENTERED OVER NRN BAJA
CALIFORNIA MIDDAY THUR...AT LEAST ACCORDING TO THE 19/12Z ECMWF.
HOWEVER...THE 19/12Z GFS WAS DEEPER WITH THE POSITION OF THIS UPPER
LOW...CENTERED OFF THE NRN BAJA CALIFORNIA COAST NEAR 29N/119W. DUE
TO THE GFS DEPICTING A DEEPER UPPER TROUGH VERSUS THE ECMWF...THE
GFS YIELDED MORE SIGNIFICANT QPF VALUES FOR SE ARIZONA VERSUS THE
ECMWF. MEANWHILE...THE 19/12Z CMC REMAINED THE DRIEST AMONGST THESE
OPERATIONAL SOLUTIONS.

FOR THIS FORECAST PACKAGE...HAVE FAVORED THE ECMWF REGARDING PRECIP
POTENTIAL FOR THUR-FRI. HAVE CONTINUED WITH A SLIGHT CHANCE OF
SHOWERS THUR FOR MUCH OF SE ARIZONA...AND ESPECIALLY NW OF A
HANNAGAN MEADOW-TUCSON-SELLS LINE. POPS WERE THEN INCREASED INTO THE
CHANCE-CATEGORY THUR NIGHT FOR BASICALLY THE NORTHWEST HALF OF THIS
FORECAST AREA...INCLUDING THE TUCSON METRO AREA. SOME MODEST UPWARD
POP ADJUSTMENTS OCCURRED FRI...WITH CHANCE-CATEGORY POPS FOR THE
WHITE MOUNTAINS...AND A SLIGHT CHANCE OF SHOWERS EXPECTED FOR MUCH
OF THE REST OF THE AREA.

THE BULK OF THE HEAVIER PRECIPITATION ASSOCIATED WITH THIS FILLING
UPPER LOW MOVING NEWD ACROSS ARIZONA FRI SHOULD OCCUR ACROSS
CENTRAL/NRN ARIZONA. THE GFS/ECMWF WERE NEARLY IDENTICAL WITH
DEPICTING A WEAK POSITIVE-TILTED UPPER TROUGH TO APPROACH FROM THE
NORTHWEST SAT...THEN MOVE SEWD INTO SONORA SUN. HAVE DISCOUNTED THE
FEW HUNDREDTHS OF AN INCH LIQUID AMOUNTS ACROSS THE WHITE MOUNTAINS
SUN AFTERNOON AS PER THE GFS. THUS...DRY CONDITIONS TO PREVAIL FRI
NIGHT-SUN.

HIGH TEMPS MON-TUE WILL AVERAGE ABOUT 2-6 DEGS F ABOVE NORMAL.
A COOLING TREND WILL THEN OCCUR WED-FRI...WITH HIGH TEMPS FRI TO BE
NEARLY 5-10 DEGS F BELOW NORMAL. A WARMING TREND WILL PREVAIL NEXT
WEEKEND.

&&

.AVIATION...VALID THRU 21/00Z.
EXPECT SCATTERED TO BROKEN CLOUDS AROUND 6-10K FT AGL ACROSS THE
WHITE MOUNTAINS NE OF KSAD INTO EARLY THIS EVENING WITH ISOLATED
-SHRA THRU 20/04Z. OTHERWISE...CLEAR SKIES OR A FEW CLOUDS ABOVE 20K
FT AGL WILL PREVAIL THRU MONDAY. NW SURFACE WIND 8-12 KTS EASING TO
LESS THAN 10 KTS AFT 20/02Z. WIND BECOMING SW 10-15 KTS ALL AREAS
AFT 20/19Z. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A FEW SHOWERS THIS EVENING OVER THE WHITE MOUNTAINS
WITH VERY LIGHT RAINFALL AMOUNTS. THEN DRY CONDITIONS ARE EXPECTED
THROUGH WEDNESDAY AS A LOW PRESSURE SYSTEM DEVELOPS JUST OFF THE
SOUTHERN CALIFORNIA COAST. THIS LOW WILL GENERATE A SOUTH TO
SOUTHWEST GENERAL WIND ACROSS THE AREA MONDAY THROUGH WEDNESDAY WITH
WIND SPEEDS INCREASING EACH AFTERNOON. MILD WITH SEASONALLY NORMAL
RH LEVELS THROUGH WEDNESDAY.

THE LOW WILL MOVE ACROSS THE AREA THURSDAY INTO FRIDAY FOR GUSTY
WINDS...HIGHER RH LEVELS AND A CHANCE OF SHOWERS THURSDAY INTO
FRIDAY. THEN A RETURN TO DRY WEATHER WITH NEAR NORMAL TEMPERATURES
WINDS AND RH LEVELS IS EXPECTED FOR THE WEEKEND.

&&

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

&&

$$

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

DISCUSSION...FRANCIS
AVIATION/FIRE WEATHER...CERNIGLIA




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