Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 180942
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
240 AM MST FRI APR 18 2014

.SYNOPSIS...A PACIFIC LOW PRESSURE SYSTEM WILL BRING A CHANCE OF
SHOWERS AND THUNDERSTORMS LATER THIS AFTERNOON INTO SATURDAY. COOLER
TEMPERATURES WILL ALSO OCCUR TODAY FOLLOWED BY A WARMING TREND EARLY
NEXT WEEK. GUSTY WINDS WILL RETURN TO THE AREA NEXT TUESDAY AND
WEDNESDAY.

&&

.DISCUSSION...SATELLITE IMAGERY THIS MORNING SHOWED EXTENSIVE CLOUD
COVER OVER SRN AZ IN ADVANCE OF UPPER LOW THAT WAS OFF SRN CA/NRN
BAJA CST. PRECIPITABLE WATER VALUES ACROSS THE AREA THIS MORNING
WERE AROUND 0.40" WITH HIGHER VALUES NEAR 0.65" OVER SRN CA AND SRN
SONORA MEXICO WITH EVEN HIGHER VALUES UP TO 1" OFF BAJA SPUR. AS PW
VALUES INCREASE TODAY...THE ATMOSPHERE WILL BE MOISTENING FROM TOP
DOWN. SO LOTS OF VIRGA THIS AFTERNOON WITH A CHANCE FOR MEASURABLE
RAIN IN THE HIGHER TERRAIN. INVERTED V SOUNDINGS THIS AFTERNOON WILL
LEAD TO GUSTY AND ERRATIC WINDS NEAR VIRGA SHAFTS.
HIGHS TODAY UNDER THE THICK CLOUD COVER WILL BE 7-12 DEGREES COOLER
THAN THURSDAY.

TONIGHT INTO SATURDAY...UPPER TROF AXIS WILL MOVE INTO WRN AZ LATER
TONIGHT THEN ACROSS THE STATE ON SATURDAY. PW VALUES ACROSS THE AREA
ARE FORECAST TO BE BETWEEN 0.60" AND 0.85" WHICH IS ALMOST 2
STANDARD DEVIATION ABOVE NORMAL FOR APRIL. MADE SOME SLIGHT
ADJUSTMENTS TO AREAL POPS THIS EVENING INTO SATURDAY MORNING. WITH
THE TROF AXIS OVER THE AREA SATURDAY...HAVE SIGNIFICANTLY INCREASED
POPS IN THE MOUNTAINS....WITH SMALLER INCREASES ACROSS LOWER
ELEVATIONS. I BASED THIS ON LATEST RUNS OF LOCAL WRF MODEL WHICH
HITS SATURDAY AFTERNOON PRETTY HARD WITH LOCALIZED HEAVY
RAINERS/ISOLATED THUNDERSTORMS. ALSO INCREASED QPF VALUES IN THE
MOUNTAINS BUT THIS WILL LIKELY CHANGE WITH LATER MODEL GUIDANCE.

LINGERING SHOWERS SATURDAY NIGHT ACROSS EASTERN AREAS AS TROF AXIS
PUSHES ON EAST. WITH PLENTY OF MID-LEVEL MOISTURE AROUND ON
SUNDAY...COULD SEE HEAT OF THE DAY SHOWERS DEVELOP OVER THE HIGHER
TERRAIN. OTHERWISE IT WILL BE WARMER SUNDAY WITH ADDITIONAL WARMING
MONDAY WITH UPPER RIDGE AXIS OVER THE STATE.

TUESDAY AND WEDNESDAY...BREEZY TO WINDY CONDITIONS AS STRONG UPPER
TROF MOVES THROUGH THE INTERMOUNTAIN WEST WITH TIMING ISSUES BETWEEN
GFS/ECMWF. WILL MAINTAIN CONTINUITY WITH PREVIOUS FORECAST AND HAVE
WEDNESDAY BEING THE WINDIEST DAY. FIRE WEATHER CONCERNS ARE
ADDRESSED IN THE FIRE WEATHER SECTION BELOW.

&&

.AVIATION...VALID THRU 19/06Z.
A WEAK UPPER LEVEL LOW PRESSURE SYSTEM NEAR THE SOUTHERN CALIFORNIA
COAST WILL MOVE INTO THE AREA TODAY. EXPECT OVERCAST CLOUD DECKS
MOSTLY ABOVE 12K FT AGL TODAY. ISOLD-SCT -SHRA SHOULD DEVELOP THIS
AFTERNOON. SURFACE WIND THIS MORNING WILL BE MOSTLY LESS THAN 10 KTS
WITH WINDS BECOMING SLY/SWLY 15-20 KTS WITH GUSTS TO NEAR 30 KTS
THIS AFTERNOON. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A WEAK UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE
EAST ACROSS THE AREA THROUGH SATURDAY. THERE APPEARS TO BE ENOUGH
MOISTURE TO JUSTIFY ISOLATED TO SCATTERED SHOWERS THIS AFTERNOON
THROUGH SATURDAY. THERE ALSO APPEARS TO BE ENOUGH INSTABILITY TO
SUPPORT A SLIGHT CHANCE OF THUNDERSTORMS MAINLY ON SATURDAY...BUT
CAN`T COMPLETELY RULE IT OUR FOR TODAY...THOUGH THUNDER SEEMS MORE
LIKELY TO OUR EAST TODAY. RAINFALL AMOUNTS ARE EXPECTED TO BE RATHER
LIGHT FOR VALLEY/DESERT LOCATIONS TODAY AND SATURDAY...BUT COULD SEE
WIDESPREAD AMOUNTS AROUND A HALF INCH OR MORE FOR MOUNTAIN LOCATIONS
ON SATURDAY. HOWEVER...THE MAIN CONCERN WILL BE FOR THE POTENTIAL OF
GUSTY AND ERRATIC WINDS ASSOCIATED WITH ANY THUNDERSTORMS THAT
OCCUR.

DRY CONDITIONS WILL THEN PREVAIL SATURDAY NIGHT THROUGH WEDNESDAY.
EXPECT NORMAL DIURNAL WIND TRENDS SUNDAY AND MONDAY...WITH
OCCASIONAL GUSTS DURING THE AFTERNOON HOURS DUE TO DAYTIME HEATING.

CRITICAL FIRE WEATHER CONDITIONS MAY RETURN AS EARLY AS TUESDAY...
THOUGH MORE LIKELY NEXT WEDNESDAY WHEN STRONGER WINDS ARE FORECAST
TO OCCUR. THE STRONGEST WINDS WILL BE ACROSS GREENLEE...GRAHAM AND
COCHISE COUNTIES EAST OF TUCSON.

&&

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

&&

$$

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