Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 240341
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
845 PM MST FRI JAN 23 2015

.SYNOPSIS...GUSTY EAST WINDS SATURDAY WITH WARMER AFTERNOON HIGHS
THROUGH THE WEEKEND. A DISTURBANCE JUST WEST OF THE BAJA PENINSULA
WILL GUIDE MOISTURE NORTH AND BRING SHOWERS TO SOUTHERN ARIZONA
MONDAY INTO EARLY TUESDAY.

&&

.DISCUSSION...A WEAK IMPULSE IS HELPING TO ACCENTUATE THE CIRRUS
LEVEL MOISTURE OVER SOUTHERN ARIZONA ON THE FAR NORTHERN FRINGE OF A
SUBTROPICAL MOISTURE BAND JUST SOUTH OF THE AREA. LOWER LEVELS STILL
ON THE DRY SIDE WITH .22 INCH PRECIPITABLE WATER ON THE 00Z KTWC
SOUNDING AND SURFACE DEW POINTS IN THE TEENS AND 20S.

THIS IMPULSE IS STILL EXPECTED TO SPIN UP A BIT AND DEEPEN JUST WEST
OF BAJA AND GUIDE MOISTURE INTO SOUTHERN ARIZONA BY MONDAY. IT
RE-ENGAGES WITH HIGHER LATITUDE SUPPORT AS THIS HAPPENS AND LIFTS
THROUGH SOUTHERN CALIFORNIA AND ARIZONA LATE MONDAY INTO TUESDAY.
CURRENT FORECAST HAS VERY GOOD TRENDS WITH SHOWERS LIKELY AREA-WIDE
BY LATE MONDAY AND MONDAY NIGHT. PLEASE SEE THE PREVIOUS DISCUSSION
FOR ADDITIONAL DETAILS.

&&

.AVIATION...VALID THRU 25/06Z.
HIGH PRESSURE AND VFR CONDITIONS WILL BE THE RULE THROUGH THE
WEEKEND. HIGH CLOUDS WILL BE ON THE INCREASE OVER THE NEXT 24 HOURS
AS AN AREA OF LOW PRESSURE DEVELOPS TO THE SOUTHWEST OVER THE
PACIFIC. WET WEATHER AND PERHAPS WORSENING CONDITIONS ARE POSSIBLE
FOR EARLY NEXT WEEK. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.

&&

.FIRE WEATHER...GUSTY EAST TO SOUTHEAST WINDS WILL BE PRESENT FOR
MUCH OF THE AREA OVER THE NEXT DAY OR SO. WINDS WILL BE STRONGEST IN
AREAS WHERE TERRAIN FOCUSES WINDS FROM AN EASTERLY COMPONENT. IT
WILL REMAIN DRY THROUGH THE WEEKEND.

MOISTURE AND THE POTENTIAL FOR SHOWERS WILL BE ON THE INCREASE EARLY
NEXT WEEK AS LOW PRESSURE OFF THE BAJA COAST LIFTS NORTH. THE BEST
CHANCE FOR SHOWERS WILL OCCUR MONDAY AND MONDAY NIGHT.

&&

.PREV DISCUSSION...UNSETTLED AND WET WEATHER LIES AHEAD IN THE NEXT
SEVEN DAYS. INITIALLY...WARMING AND DRY CONDITIONS WILL PERSIST INTO
THE WEEKEND. A FEW HIGH CLOUDS WILL BE PRESENT...BUT THEY SHOULD
HAVE LITTLE IMPACT ON SURFACE TEMPERATURES. HIGH TEMPERATURES WILL
RISE TO NEAR AVERAGE ON SATURDAY...THEN HOVER AT OR SLIGHTLY ABOVE
AVERAGE FOR THE REMAINDER OF THE WEEK.

A SHORT WAVE TROUGH WILL DIG SOUTH TOWARD ARIZONA AS A LARGE WAVE
HIGHLY AMPLIFIED UPPER RIDGE BUILDS OVER THE WESTERN UNITED STATES.
BY SATURDAY AFTERNOON...THE SHORT WAVE TROUGH WILL DEEPEN INTO A CUT
OFF LOW JUST WEST OF THE BAJA PENINSULA. THE LOW WILL CHURN FOR A
DAY OR SO BEFORE EJECTING NORTH TOWARD SOUTHERN CALIFORNIA.

AS THE LOW MOVES NORTH SUNDAY INTO MONDAY...MOIST AIR WILL MOVE INTO
SOUTHERN ARIZONA. PRECIPITABLE WATER VALUES...DEPENDING ON THE
MODEL...SHOULD INCREASE INTO THE 0.80 TO 1.10 INCH RANGE. VALUES
THIS HIGH ARE FAIRLY ANOMALOUS FOR LATE JANUARY AND ONLY OCCUR ONCE
IN ABOUT FIVE YEARS. NOW WILL THAT TRANSLATE TO WIDESPREAD HEAVY
RAIN...THAT DEPENDS ON THE FORCING. CURRENTLY...THE MODELS ARE
SHOWING LIMITED SURFACE FORCING...BUT THERE IS SOME DIFFLUENCE ALOFT
SINCE ARIZONA WILL SIT IN THE NORTHWEST QUADRANT OF THE UPPER LOW.

BASED ON PRIOR ANALOG EVENTS FROM THE GOOD FOLKS AT CIPS...THERE IS
SOME CONCERN PRECIPITATION VALUES COULD RAMP UP TO AROUND ONE HALF
INCH WITH LOCALIZED VALUES CLOSER TO ONE INCH. THIS SEEMS A BIT HIGH
BASED ON CURRENT MODEL DATA...SO I HAVE TRENDED CLOSER TO A HIGH
POTENTIAL BUT A GENERALLY LOW PRECIPITATION EVENT. AS SUCH...THE
CHANCE OF PRECIP FORECAST HAS INCREASED ON MONDAY EVENING INTO
TUESDAY MORNING. THE GFS...SREF AND NAM ARE HINTING THAT MONDAY WILL
EXPERIENCE THE MOST PRECIP...SO WE CAN FINE TUNE THE DETAILS OVER
THE NEXT FEW SHIFTS.

THE OTHER ISSUE WITH THIS EVENT IS THE SNOW LEVELS...OR RATHER...THE
NON ISSUE. SNOW LEVELS SHOULD BE AROUND 9000 FEET OR HIGHER SO WE
ARE EXPECTING MINIMAL IMPACTS FROM SNOW.

A BRIEF TRANSITION PHASE ENSUES ON WEDNESDAY THROUGH THURSDAY AND
THEN YET ANOTHER REX BLOCK SCENARIO SHOULD DEVELOP LATE NEXT WEEK.
THIS MEANS PRECIPITATION CHANCES WILL AGAIN INCREASE SOMETIME NEXT
WEEKEND. THIS HAPPENS TO COINCIDE WITH A FAIRLY WELL ATTENDED
SPORTING EVENT IN THE PHOENIX AREA THAT MAY ATTRACT FANS FROM THE
TUCSON AREA. THUS...WE WILL NEED TO KEEP A CLOSE EYE ON THE EXTENDED
FORECAST AS TRAVEL CONDITIONS MAY DETERIORATE IF WE EXPERIENCE
MODERATE OR HEAVY RAIN. ONCE AGAIN THOUGH...SNOW LEVELS WILL BE
HIGH.

JJB

&&

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

&&

$$

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

MEYER




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