Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 200923 RRA
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
225 AM MST SAT DEC 20 2014

.SYNOPSIS...A DRY NORTHWEST FLOW PATTERN WILL RESULT IN SOME PASSING
HIGH LEVEL CLOUDS AND NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES
THIS WEEKEND.  A FEW PATCHES OF FOG AND FREEZING FOG ARE EXPECTED
AGAIN EARLY THIS MORNING MAINLY ACROSS THE VALLEYS OF COCHISE AND
GRAHAM COUNTY.  FOR EARLY TO MID NEXT WEEK...TEMPERATURES WILL RISE
TO ABOVE NORMAL LEVELS DUE TO A PASSING UPPER LEVEL RIDGE.
UNSETTLED AND COOLER WEATHER LOOKS LIKELY FOR THE END OF NEXT WEEK.

&&

.DISCUSSION...TWO AREAS OF CONCERN FOR THIS FORECAST PERIOD...ONE
VERY SHORT TERM AND THE OTHER LONG TERM.  THE SHORT TERM CONCERN
RELATES TO THE POTENTIAL FOR FOG DEVELOPMENT EARLY THIS MORNING.  AT
THIS TIME A LARGE PORTION OF THE FORECAST AREA EAST OF TUCSON HAS
TEMP/DEWPOINTS WITHIN 3 DEGREES WITH A FEW LOCATIONS NEAR THE NEW
MEXICO BORDER WITH A ZERO SPREAD.  THUS FAR NO FOG IS INDICATED IN
ANY OBS OR SATELLITE PIX AND NOW HAVE A BAND OF RELATIVELY THICK
CIRRUS CLOUDS MOVING ACROSS THE AREA WHICH SHOULD HINDER FOG
DEVELOPMENT.  SO HAVE TWEAKED THE WORDING FROM AREAS OF FOG/FREEZING
FOG TO PATCHY.  WHATEVER FORMS WILL BURN OFF QUICKER THAN
YESTERDAY.  OTHERWISE IT WILL BE A COUPLE OF DEGREES WARMER THIS
AFTERNOON WITH CONTINUED LIGHT WINDS AND A FEW HIGH CLOUDS PASSING
BY AT TIMES.

THEN SUNDAY THROUGH WEDNESDAY THE AREA WILL HAVE A DRY NORTHWEST
FLOW OVERHEAD WITH TEMPERATURES WARMING TO A FEW DEGREES WARMER THAN
NORMAL OVERALL.  THE ONLY ITEM OF INTEREST THROUGH THIS PERIOD IS A
PASSING SHORTWAVE MONDAY NIGHT WHICH WILL TRIM TEMPERATURES BACK A
FEW DEGREES TUESDAY AFTERNOON AND NIGHT.  AT THIS POINT STILL
CARRYING A DRY FORECAST ALTHOUGH THERE COULD BE A FEW
FLURRIES/SPRINKLES ACROSS THE WHITE MOUNTAINS MONDAY NIGHT AS THE
AXIS OF THIS SYSTEM PASSES.

NOW FOR THE SECOND PERIOD OF CONCERN...CHRISTMAS DAY AND FRIDAY.  A
TROUGH IS EXPECTED TO IMPACT THE WEST COAST WEDNESDAY THEN MOVE
SOUTHEAST ACROSS THE REGION THURSDAY INTO FRIDAY.  THE BIG QUESTION
HAS BEEN THE DEPTH OF THE SYSTEM AS IT PASSES.  THIS EVENINGS 00Z
GFS OPERATIONAL RUN IS VERY FLAT WITH THIS FEATURE WITH BASICALLY NO
IMPACT ON THE AREA.  HOWEVER...LOOKING AT A PLOT OF THE 00Z GFS
ENSEMBLE MEMBERS SHOWS THIS SOLUTION TO BE ONE OF THE 5 WARM RUNS
WHILE THE OTHER 15 RUNS MORE CLOSELY RESEMBLE THE 00Z HIGH RES GFS
AND THE 00Z ECMWF WHICH IS SIMILAR TO THE PREVIOUS COUPLE OF ECMWF
RUNS...BEING A DEEPER AND SHARPER TROUGH.

THEREFORE HAVE TOSSED THE 00Z GFS AND LEANED ON THE HIGH RES GFS
WHICH IS SIMILAR TO BUT A BIT WEAKER THAN THE ECMWF.  WHAT THAT
MEANS IS A CHANCE OF A FEW SNOW/RAIN SHOWERS ACROSS THE WHITE
MOUNTAINS AND THE NE SKY ISLANDS CHRISTMAS DAY INTO FRIDAY WITH A
GOOD NORTHWEST BREEZE BOTH DAYS WITH TEMPERATURES COOLING BACK
DOWN TO OR BELOW NORMAL CHRISTMAS DAY INTO SATURDAY.  CERNIGLIA

&&

.AVIATION...VALID THRU 21/12Z.
EASTERN AREAS COULD SEE DEVELOPMENT OF PATCHY FOG OR FREEZING FOG
AFTER THROUGH AROUND 20/17Z. SCT TO LCLY BKN MOSTLY HIGH CLOUDS THRU
THIS AFTERNOON. SURFACE WIND LESS THAN 10 KTS WILL PREVAIL THROUGH
THE PERIOD. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...DRY CONDITIONS WILL PREVAIL TODAY THROUGH WEDNESDAY.
20-FT WINDS WILL GENERALLY BE LIGHT AND TERRAIN DRIVEN THROUGH THE
MIDDLE OF NEXT WEEK. HOWEVER...SOME NORTHWEST BREEZES WILL OCCUR
MONDAY AFTERNOON ACROSS THE UPPER GILA RIVER VALLEY INCLUDING
SAFFORD...AS AN UPPER LEVEL DISTURBANCE MOVES NORTHWEST TO SOUTHEAST
ACROSS THE FOUR CORNERS REGION. AT THIS TIME CONFIDENCE IS LOW
CONCERNING THE TIMING AND IMPACTS OF THE NEXT SIGNIFICANT WEATHER
MAKER WHICH MAY AFFECT THE REGION LATE NEXT WEEK. A SLIGHT CHANCE
FOR VALLEY RAIN AND MOUNTAIN SNOW ARE POSSIBLE...ALONG WITH AN
INCREASE IN WINDS ON THURSDAY...MAINLY FOR AREAS SOUTH AND EAST OF
TUCSON TOWARD THE INTERNATIONAL BORDER AS WELL AS THE BORDER WITH
NEW MEXICO.

&&

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

&&

$$

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