Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 242144
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
245 PM MST THU APR 24 2014

.SYNOPSIS...A STRONG STORM SYSTEM WILL MOVE ACROSS THE STATE
SATURDAY. GUSTY WINDS WILL BEGIN TO PICK UP ACROSS THE AREA FRIDAY
AFTERNOON WITH AREAS OF BLOWING DUST POSSIBLE. THE WIND WILL BECOME
STRONGER SATURDAY AS THE SYSTEM PASSES AND WILL ALSO BRING A THREAT
OF SHOWERS...THUNDERSTORMS AND HIGH ELEVATION SNOWS TO PORTIONS OF
THE AREA. DRY AND WARMER WEATHER IS ON TAP FOR NEXT WEEK.

&&

.DISCUSSION...MODELS REMAIN IN VERY GOOD AGREEMENT WITH THE
SIGNIFICANT STORM SYSTEM THAT WILL AFFECT THE REGION FRIDAY INTO THE
WEEKEND.  SEVERAL ASPECTS OF THIS SYSTEM THAT ARE RATHER
INTERESTING.  FIRST IS THE MOISTURE WITH THE SYSTEM WHICH HAS A TAP
INTO SOME DECENT WATER VAPOR OFF THE PACIFIC.  FORECAST PRECIPITABLE
WATER VALUES (WATER VAPOR THROUGH A DEEP LAYER IN THE ATMOSPHERE)
WILL PEAK ABOUT 2 STANDARD DEVIATIONS ABOVE NORMAL JUST IN ADVANCE
OF THE SYSTEM.  THIS AMOUNT OF MOISTURE ALONG WITH THE EXPECTED
DYNAMICS ARE ENOUGH TO JUSTIFY A THREAT OF SHOWERS FOR DESERT/VALLEY
LOCATIONS AND GREATER THREAT OVER THE MOUNTAINS SATURDAY INTO
SATURDAY EVENING.  ALTHOUGH INSTABILITY IS NOT ALL THAT GREAT...THE
DYNAMICS WITH THIS SYSTEM SHOULD BE ENOUGH THAT A SLIGHT CHANCE OF
THUNDERSTORMS IS POSSIBLE MAINLY ACROSS NORTHERN AREAS.  THE
PRECIPITATION THREAT WILL QUICKLY DIMINISH EARLY SATURDAY EVENING
FOR ALL AREAS OUTSIDE OF THE WHITE MOUNTAINS.

HOWEVER...THE MAIN IMPACT PRECIPITATION WISE WILL BE OVER THE WHITE
MOUNTAINS WHERE THE HIGHEST PEAKS COULD SEE A COUPLE OF INCHES OR SO
OF SNOW MIXED WITH A FAIR AMOUNT OF RAIN.  I RAISED POPS THIS AREA
FOR SATURDAY AFTERNOON.  WITH THE RATHER COOL CONDITIONS THAT WILL
ACCOMPANY THIS SYSTEM...SNOW LEVELS WILL BE UNCHARACTERISTICALLY LOW
FOR THIS TIME OF YEAR...DROPPING DOWN TO AROUND 6500 FT NEAR THE END
OF THE PRECIPITATION SOMETIME SATURDAY EVENING.

HOWEVER...THE PRIMARY CONCERN WITH THIS STORM CONTINUES TO BE THE
WINDS THAT WILL BE GENERATED FRIDAY AND SATURDAY WHICH WILL RESULT
IN FIRE WEATHER CONCERNS BOTH DAYS. (SEE FIRE WEATHER SECTION BELOW
FOR MORE DETAILS).

WINDS ARE EXPECTED TO PICK UP FRIDAY AFTERNOON WELL IN ADVANCE OF
THE STORM WITH THE POTENTIAL FOR AREAS OF BLOWING DUST.  WINDS WILL
EASE SOME DURING THE EVENING ACROSS LOWER ELEVATIONS...HOWEVER IT
WILL REMAIN WINDY ACROSS THE RIDGES AND MOUNTAIN TOPS.  FOR
SATURDAY...THE WINDS ARE EXPECTED TO BE EVEN STRONGER ACROSS MOST OF
THE AREA.  AS A RESULT...A WIND ADVISORY HAS BEEN ISSUED FROM THE
TUCSON AREA EASTWARD.  THIS IS A RATHER STRONG SYSTEM...EVEN FOR
APRIL...WITH UPPER LEVEL WINDS EXCEEDING THE 99TH PERCENTILE AND
DEPENDING ON CLOUD COVER THE SURFACE WINDS SHOULD AT LEAST EXCEED
THE 90TH PERCENTILE RANGE OVER PORTIONS OF THE FORECAST AREA.

BY SUNDAY THE SYSTEM WILL BE WELL TO THE EAST WITH A DECENT NW
GRADIENT REMAINING ACROSS THE REGION FOR BREEZY CONDITIONS
ESPECIALLY THE GILA VALLEY AND ALONG THE NEW MEXICO BORDER.  IT WILL
BE A DRY DAY WITH COOL TEMPERATURES CONTINUING...ROUGHLY 8-10
DEGREES COOLER THAN NORMAL.  HIGH PRESSURE IS THEN EXPECTED TO
DEVELOP ALONG THE WEST COAST FOR WARMING TEMPERATURES EARLY IN THE
WEEK...BACK UP TO NORMAL LEVELS.

BEYOND TUESDAY...THE LONG RANGE OPERATIONAL MODELS HAVE SIGNIFICANT
DIFFERENCES IN HOW THEY HANDLE A SYSTEM SLIDING SOUTH ON THE BACK
SIDE OF A DEEP LOW PRESSURE SYSTEM OVER THE CENTRAL PLAINS.  AT THIS
POINT IN TIME THEY ARE BOTH DRY WITH THE POSSIBLE EXCEPTION OF THE
WHITE MOUNTAINS WITH VARYING DEGREES OF WIND.  FOR NOW HAVE LEFT THE
EXTENDED FORECAST ALONE UNTIL GREATER AGREEMENT IN THE VARIOUS
SOLUTIONS BEGINS TO DEVELOP.  CERNIGLIA

&&

.AVIATION...VALID THRU 26/00Z. WESTERLY FLOW ALOFT WITH SOME HIGH
LEVEL CIRRUS CLOUDS PASSING BY AT TIMES...WITH THICKENING HIGH
CLOUDS DURING THE DAY FRIDAY. SOUTHWEST SURFACE WINDS 13-18 KTS WITH
OCCASIONAL GUSTS TO 25 MPH THIS AFTERNOON THRU 25/02Z...THEN DIURNAL
TERRAIN DRIVEN WINDS LESS THAN 12 KTS OVERNIGHT. SOUTHWEST WINDS
WILL THEN PICK UP BY THE MID-MORNING HOURS FRIDAY AND RANGE BETWEEN
17-22 KTS WITH GUSTS TO 35 MPH. THE STRONGEST WINDS WILL BE ACROSS
SANTA CRUZ AND COCHISE COUNTIES.

THE AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A PACIFIC STORM SYSTEM MOVING INTO CALIFORNIA FRIDAY
WILL RESULT IN BREEZY TO LOCALLY WINDY CONDITIONS ACROSS SOUTHEAST
ARIZONA...ESPECIALLY SANTA CRUZ AND COCHISE COUNTIES. THESE WINDS
COMBINED WITH THE PREVAILING DRY AIRMASS/LOW HUMIDITIES SHOULD
RESULT IN SOME SPOTS MEETING AND EXCEEDING RED FLAG CRITERIA...
ESPECIALLY ACROSS EASTERN SANTA CRUZ AND SOUTHERN COCHISE COUNTIES.
THEREFORE...A RED FLAG WARNING IS IN EFFECT FROM 2 PM TO 7 PM MST
FRIDAY FOR AREAS ACROSS SOUTHERN FIRE ZONE 152 AND SOUTHEASTERN FIRE
ZONE 151.

THIS STORM SYSTEM WILL THEN MOVE ACROSS ARIZONA SATURDAY RESULTING
IN WINDY CONDITIONS ACROSS THE MAJORITY OF SOUTHEAST ARIZONA. THIS
SYSTEM WILL IMPORT DEEPER MOISTURE...RESULTING IN SOME VALLEY RAIN
AND MOUNTAIN SNOW SATURDAY AFTERNOON AND EARLY EVENING. ALTHOUGH THE
INCREASED MOISTURE AND CLOUD COVER SHOULD HELP KEEP RED FLAG
CONDITIONS AT BAY FOR MOST AREA...MOISTURE WILL BE SLOW TO REACH
LOCATIONS ACROSS EASTERN COCHISE...SOUTHEAST GRAHAM AND SOUTHERN
GREENLEE COUNTIES. THEREFORE...A RED FLAG WARNING IS IN EFFECT FROM
11 AM TO 7 PM MST SATURDAY FOR THE EASTERN HALF OF FIRE ZONE 152.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...RED FLAG WARNING FROM FRIDAY
AFTERNOON THROUGH FRIDAY EVENING FOR AZZ151-152.

RED FLAG WARNING FROM SATURDAY MORNING THROUGH SATURDAY EVENING
FOR AZZ152.

&&

$$

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