Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 241619
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
920 AM MST THU APR 24 2014

.SYNOPSIS...EXPECT A WARM DAY WITH LESS WIND...THEN WINDS WILL
INCREASE FRIDAY AND BECOME STRONG AND GUSTY SATURDAY AS A STRONG
SYSTEM MOVES ACROSS THE REGION.  THERE WILL BE A CHANCE OF VALLEY
RAIN AND HIGH ELEVATION SNOW SHOWERS SATURDAY INTO SATURDAY NIGHT.
DRY AND WARMER WEATHER IS ON TAP FOR NEXT WEEK.

&&

.DISCUSSION...SOUTHEAST AZ WILL BE UNDER A LIGHT WESTERLY FLOW ALOFT
WITH A WARM AIR MASS OVER THE REGION.  THIS WILL ALLOW FOR A
RELATIVELY CALM DAY WITH ABOVE NORMAL TEMPERATURES...THE CALM BEFORE
THE STORM.

MODELS 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.
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 RAIN.  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 SATURDAY EVENING.

HOWEVER...THE MOST IMPORTANT FEATURE OF THIS STORM WILL 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 LOCAL 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 AND LIKELY
EXCEEDING WIND ADVISORY FOR PARTS OF THE AREA...MAINLY EAST OF
TUCSON...WHICH WE WILL ADDRESS THIS AFTERNOON.  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.  CERNIGLIA

THIS SYSTEM WILL EXIT THE REGION BY EARLY SUNDAY WITH RIDGING
BEGINNING TO BUILD IN FROM THE WEST INTO EARLY NEXT WEEK.  BOTH THE
GFS AND ECMWF ARE INDICATING THAT A VORT LOBE DROPPING DOWN THE BACK
SIDE OF THIS EXITING LOW PRESSURE SYSTEM WILL MOVE THROUGH THE FOUR
CORNERS AREA LATE TUESDAY AND THEN MOVE THROUGH PORTIONS OF THE
STATE IN SOME FORM OR FASHION THROUGH WEDNESDAY.  IF THIS OCCURS WE
COULD SEE A SLIGHT LOWERING OF TEMPERATURES DURING THAT TIME AND
PERHAPS A THREAT OF PRECIPITATION...MAINLY FOR THE MOUNTAINS.  FOR
NOW THE THREAT IS NOT GREAT ENOUGH...NOR IS CONFIDENCE HIGH ENOUGH
TO MENTION ANY PRECIPITATION AT THIS TIME.

HIGHS GENERALLY 3 TO 4 DEGS ABOVE NORMAL TODAY AND FRIDAY...THEN
AROUND 10 DEGS BELOW NORMAL THIS WEEKEND...THEN ABOUT 2 TO 4 DEGS
BELOW NORMAL FOR MONDAY.  THEREAFTER...HIGHS ABOUT 2 TO 3 DEGS ABOVE
NORMAL.  LOW TEMPERATURES ABOUT 3 TO 5 DEGS ABOVE NORMAL FRIDAY AND
SATURDAY MORNINGS...THEN 5 TO 10 DEGS BELOW NORMAL SUNDAY AND MONDAY
MORNINGS...BUT THE COOLEST MORNING WILL OCCUR ON SUNDAY WHEN LOWS
WILL BE NEARLY 10 DEGS BELOW NORMAL.  FOR TUESDAY AND WEDNESDAY LOWS
SLIGHTLY ABOVE NORMAL.  MOLLERE

&&

.AVIATION...VALID THRU 25/18Z.  WESTERLY FLOW ALOFT WITH MOSTLY
CLEAR SKIES OTHER THAN SOME CIRRUS PASSING BY AT TIMES MAINLY NORTH
OF TUCSON.  SFC WINDS ARE EXPECTED TO REMAIN BELOW 12 KTS AT ALL
TERMINALS THRU 25/15Z THEN SOUTHWEST WINDS WILL BEGIN TO INCREASE TO
13-18 KTS 25/18Z.  THE AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.  CERNIGLIA

&&

.FIRE WEATHER...GENERALLY LIGHT WINDS AND DRY CONDITIONS TODAY AHEAD
OF ANOTHER PACIFIC SYSTEM.  THIS SYSTEM WILL DIG SOUTHWARD INTO THE
REGION FRIDAY RESULTING IN A TIGHTENING OF THE PRESSURE GRADIENT.
BY FRIDAY AFTERNOON THE AREA SHOULD EXPERIENCE SOME BREEZY WIND
CONDITIONS.  THIS COMBINED WITH THE PREVAILING DRY CONDITIONS COULD
SEE A FEW LOCATIONS HIT RED FLAG CRITERIA.  A FIRE WEATHER WATCH IS
IN EFFECT FRIDAY LATE AFTERNOON TO EARLY EVENING FOR AREAS ACROSS
SOUTHERN ZONE 152 AND SOUTHEASTERN ZONE 151...WHERE WINDS WILL BE
THE STRONGEST.

THE FORECAST TRACK OF THIS SYSTEM AS IT COMES ACROSS THE AREA ON
SATURDAY IS FAVORABLE FOR MOISTURE ADVECTION INTO THE AREA.  THIS
WILL RESULT IN SOME VALLEY RAIN AND MOUNTAIN SNOW DURING THE DAY
SATURDAY.  SATURDAY WILL HAVE THE STRONGEST WINDS AS THE MAIN JET
CORE PUSHES THROUGH.  THE INCREASED MOISTURE AND CLOUD COVER SHOULD
HELP KEEP RED FLAG CONDITIONS AT BAY FOR MOST...BUT NOT ALL AREAS.
THE BEST AREA FOR RED FLAG CONDITIONS LOOKS TO BE EAST OF THE
SAFFORD TO DOUGLAS LINE...OR THE EASTERN HALF OF ZONE 152...AS
MOISTURE WILL BE A LITTLE SLOWER TO REACH THESE LOCATIONS.  A FIRE
WEATHER WATCH IS IN EFFECT FOR THIS AREA...MINUS THE CHIRICAHUA
MOUNTAINS FOR SATURDAY AFTERNOON AND EARLY EVENING.  MORE DETAILS
EXPECTED THIS AFTERNOON.

SUNDAY THE FLOW ALOFT SHIFTS TO MORE NORTHWESTERLY AS THE SYSTEM
EXITS AND GIVEN THE LINGERING PRESSURE GRADIENT...AREAS EAST OF
TUCSON COULD SEE SOME BREEZY NORTHWEST WINDS.  WINDS WILL BEGIN TO
TAPPER OFF MONDAY...THOUGH WEDNESDAY HAS THE POTENTIAL FOR AN
EASTERLY GRADIENT INDUCED WINDS FROM TUCSON EAST.  HUMPHREYS/MEADOWS

&&

.TWC WATCHES/WARNINGS/ADVISORIES...FIRE WEATHER WATCH FROM FRIDAY
AFTERNOON THROUGH FRIDAY EVENING FOR AZZ151-152.

FIRE WEATHER WATCH FROM SATURDAY MORNING THROUGH SATURDAY EVENING
FOR AZZ152.

&&

$$

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