Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 041600
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
900 AM MST WED MAR 4 2015

.SYNOPSIS..A WEATHER SYSTEM WILL MOVE ACROSS SONORA TODAY BRINGING A
CHANCE OF SHOWERS TO AREAS MAINLY SOUTH AND EAST OF TUCSON. A
WARMING TREND WILL BEGIN THURSDAY AND CONTINUE THROUGH THE WEEKEND
WITH GENERALLY DRY CONDITIONS.

&&

.DISCUSSION...A FEW SHOWERS OCCURRED THIS MORNING AS UPPER LEVEL
SYSTEM CONTINUES TO PUSH EAST AND RADAR STILL SHOWS A FEW LIGHT
ECHOES.  ACTUALLY EXPECT A SLIGHT UPTICK IN COVERAGE EARLY THIS
AFTERNOON ALONG THE INTERNATIONAL AND NEW MEXICO BORDERS DUE TO
UNSTABLE AIR MASS.  IN FACT MIGHT BE ENOUGH INSTABILITY FOR AN ISOLD
THUNDERSTORM. CURRENT FORECAST HANDLES THIS WELL ALONG WITH THE
BELOW NORMAL HIGH TEMPERATURES.

THEREFORE NO CHANGES NECESSARY TO CURRENT FORECAST. WILL TAKE
ANOTHER LOOK AT WEAK SYSTEM WHICH COULD AFFECT OUR WEEKEND WEATHER
AS LATEST MODELS COME IN LATER TODAY. SEE PREVIOUS FORECAST FOR MORE
DETAILS.

&&

.AVIATION...VALID THRU 05/18Z.
THERE IS A SLIGHT CHANCE OF -SHRA AND HIGHER TERRAIN -SHSN TODAY
MAINLY EAST THROUGH SOUTH OF KTUS. ENOUGH INSTABILITY WILL PROVIDE A
SLIGHT CHANCE OF -TSRA THIS AFTERNOON. OTHERWISE...CLOUD BASES WILL
MAINLY RANGE FROM 4-9K FT AGL. SURFACE WIND WILL BE LESS THAN 10 KTS
FOR MOST SECTIONS EARLY THIS MORNING THEN THIS AFTERNOON WINDS WILL
BE WLY/NWLY AT 10-20 KTS. THE STRONGEST WIND THIS AFTERNOON WILL BE
NEAR KSAD WITH GUSTS OF 25-30 KTS POSSIBLE. AVIATION DISCUSSION NOT
UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A LOW PRESSURE SYSTEM WILL MOVE EAST ACROSS SONORA
MEXICO TODAY. THERE IS A CHANCE OF SHOWERS MAINLY EAST TO SOUTH OF
TUCSON...AND ACROSS THE WHITE MOUNTAINS. A SLIGHT CHANCE OF
THUNDERSTORMS WILL ALSO EXISTS THIS AFTERNOON MAINLY FROM TUCSON
EAST AND SOUTH TO THE NEW MEXICO/INTERNATIONAL BORDERS. A SLIGHT
CHANCE OF SHOWERS CONTINUES THIS EVENING ACROSS FAR SOUTHERN AND
EASTERN COCHISE COUNTY. DRY CONDITIONS WILL THEN PREVAIL LATE
TONIGHT INTO EARLY NEXT WEEK. 20-FOOT WINDS THIS AFTERNOON WILL BE
MAINLY WEST TO NORTHWEST AT 10 TO 15 MPH. HOWEVER...20-FOOT WIND
GUSTS OF 20-25 MPH MAY OCCUR ACROSS THE UPPER GILA VALLEY INCLUDING
SAFFORD. THEREAFTER...20-FOOT WINDS THURSDAY INTO EARLY NEXT WEEK
WILL GENERALLY BE EAST AT 5-15 MPH.

&&

.PREV DISCUSSION...WATER VAPOR IMAGERY SHOWS AN UPPER LOW CURRENTLY
SWINGING ACROSS THE NORTH CENTRAL BAJA PENINSULA. IR SATELLITE
IMAGERY INDICATES THAT CLOUDINESS ASSOCIATED WITH THIS SYSTEM
CURRENTLY COVERS MUCH OF CENTRAL AND NORTH CENTRAL BAJA...THE
NORTHERN GULF OF CALIFORNIA AND EXTENDING INTO A LARGE PART OF
SOUTHEAST ARIZONA. THESE CLOUDS HAVE INCREASED OVER SOUTHERN
ARIZONA...ESPECIALLY DURING THE PAST SEVERAL HOURS WITH CLOUD DECKS
RANGING FROM AROUND 5-8K FEET.

MODELS INDICATE THAT THIS SYSTEM WILL CONTINUE TO MARCH TO THE EAST
TODAY AS IT PHASES WITH A SYSTEM FARTHER TO THE NORTH ACROSS
COLORADO AND NORTHWEST MEXICO...WITH THE TAIL END OF THIS SYSTEM
SWINGING THROUGH EXTREME SOUTHEAST ARIZONA LATE TONIGHT OR EARLY
THURSDAY. AS THIS OCCURS SOME LIGHT SHOWERS WILL DEVELOP MAINLY
ALONG THE INTERNATIONAL BORDER...BUT ALSO OVER THE MOUNTAIN TOPS OF
EAST CENTRAL ARIZONA...WHICH INCLUDE THE WHITE MOUNTAINS OF NORTHERN
GREENLEE COUNTY. MODELS AND LATEST WV IMAGERY INDICATE THAT THE LOW
IS CURRENTLY FARTHER SOUTH THAN WHAT WAS PROGGED BY THE MODELS THIS
TIME YESTERDAY. AS A RESULT...MODELS ARE SHOWING THE BULK OF THE
MOISTURE REMAINING MOSTLY SOUTH OF THE BORDER...BUT STILL CAN`T RULE
OUT ISOLATED TO OCCASIONALLY SCATTERED SHOWERS MOVING ALONG EITHER
SIDE OF THE INTERNATIONAL BORDER TODAY. COULD ALSO SEE A FEW
LIGHTNING STRIKES THIS AFTERNOON AS MODELS INDICATE THAT 850-500MB
LAPSE RATES WILL BE GREATER THAN 8 DEGS C/KM. IN ADDITION...A COLD
POOL ALOFT WILL MOVE ACROSS THE REGION HELPING TO DESTABILIZE THE
AIRMASS CONCURRENT WITH DAYTIME HEATING.

NOT EXPECTING VERY MUCH PRECIPITATION WITH THIS SYSTEM...GENERALLY
LESS THAN A TENTH OF AN INCH OF LIQUID PRECIPITATION. SNOW LEVELS
STARTING OUT AT AROUND 6-7K FEET AND EXPECTED TO DROP TO AROUND
5500-6K FEET DURING THE DAY AS THE LOW MOVES OVERHEAD. THAT SAID...
ONLY EXPECTING TO SEE SNOW AMOUNTS RANGING FROM JUST A DUSTING TO
PERHAPS UP TO AN INCH OF SNOW ACCUMULATION ABOVE 7000 FEET FOR THE
SANTA RITA...HUACHUCA AND CHIRICAHUA MOUNTAINS OF SANTA CRUZ AND
SOUTHERN COCHISE COUNTIES.

ONCE THIS SYSTEM SLIDES JUST TO THE SOUTH OF ARIZONA LATE
THURSDAY...MODELS INDICATE A WEAK CLOSED LOW WILL DEVELOP OVER
NORTHERN BAJA AND SONORA LATE IN THE WEEK AS HIGH PRESSURE DEVELOPS
OVER THE WEST COAST. THIS LOW IS PROGGED TO LINGER ACROSS NORTHERN
MEXICO AND SOUTHERN ARIZONA THROUGH LATE SATURDAY OR EARLY
SUNDAY...BUT VERY LITTLE MOISTURE TO ACCOMPANY THIS SYSTEM...SO NO
`REAL` THREAT FOR PRECIPITATION WITH THIS SYSTEM NEARLY OVERHEAD.

FOR SUNDAY AND INTO MONDAY HIGH PRESSURE WILL TRY TO BUILD IN FROM
THE WEST...BUT MODELS BEGIN TO SHOW DIFFERING SOLUTIONS THIS FAR
OUT...WITH THE GFS SHOWING A WEAKENING OF THE RIDGE INTO NEARLY
ZONAL FLOW WITH A WEAK DISTURBANCE EMBEDDED WITHIN THE FLOW TO THE
NORTH. THE ECMWF SHOWS A DRY NORTHWEST FLOW ALOFT WITH RIDGING OVER
THE WEST COAST ON TUESDAY. FOR NOW A DRY FORECAST THROUGH EARLY NEXT
WEEK.

FOR TUCSON...HIGH TEMPERATURES WELL BELOW NORMAL TODAY AND
THURSDAY...THEN NEAR NORMAL FRIDAY. HIGHS 4 TO 6 DEGS ABOVE NORMAL
FOR THE WEEKEND...THEN NEAR 10 DEGS ABOVE NORMAL FOR EARLY NEXT
WEEK. LOW TEMPS 3 TO 5 DEGS BELOW NORMAL THURSDAY MORNING...THEN
NEAR NORMAL FRIDAY AND SATURDAY...FOLLOWED BY LOWS RANGING FROM 4 TO
6 DEGS ABOVE NORMAL THROUGH TUESDAY.

&&

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

&&

$$

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

DROZD












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