Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 171611
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
910 AM MST FRI OCT 17 2014

.SYNOPSIS...A WEAK DISTURBANCE WILL BRING SOME SPRINKLES OR A FEW
SHOWERS TODAY. EXPECT DRY CONDITIONS TO OCCUR SATURDAY. A SERIES OF
WEAK LOW PRESSURE SYSTEMS WILL THEN BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS MAINLY EAST OF TUCSON SUNDAY THROUGH WEDNESDAY.

&&

.DISCUSSION...KEMX WSR-88D DETECTED SCATTERED 30-40 DBZ ECHOES
MOSTLY FROM JUST WEST OF THE TUCSON METRO AREA WESTWARD ACROSS THE
TOHONO O`ODHAM NATION AT THIS TIME. GIVEN THE VERY DRY SURFACE-
600 MB LAYER AS PER THE 17/12Z KTWC SOUNDING...THESE ECHOES ARE
LIKELY PRODUCING VIRGA AS WELL AS SOME SPRINKLES. HOWEVER...WOULD
NOT BE SURPRISED TO SEE A FEW HUNDREDTHS OF AN INCH OF RAINFALL
EVENTUALLY OCCUR ACROSS PORTIONS OF THE AREA BY THIS EVENING.

A WEAK UPPER LEVEL LOW PRESSURE SYSTEM OVER THE NRN GULF OF
CALIFORNIA WILL MOVE NEWD ACROSS THE AREA INTO THIS EVENING. THE
BEST CHANCE FOR MEASURABLE RAINFALL TO OCCUR LATER TODAY AND THIS
EVENING WILL BE ACROSS THE MOUNTAINS. WILL ALSO MAINTAIN THE
DEPICTION AND MENTION OF SPRINKLES ACROSS THE LOWER ELEVATIONS.
CLEARING SKIES SHOULD OCCUR FROM SOUTHWEST-TO-NORTHEAST LATE TONIGHT
FOLLOWED BY MOSTLY SUNNY SKIES TO PARTLY CLOUDY SKIES SAT.

HIGH TEMPS THIS AFTERNOON WILL GENERALLY BE ABOUT 3-8 DEGS F OR SO
COOLER VERSUS THUR. THERE WILL ONLY BE A FEW MINOR ADJUSTMENTS MADE
TO THE INHERITED GRIDDED DATA SKY/POP/WEATHER FIELDS TODAY.
OTHERWISE...PLEASE REFER TO THE ADDITIONAL SECTIONS FOR FURTHER
DETAIL.

&&

.AVIATION...VALID THRU 18/18Z.
A WEAK IMPULSE WILL MOVE NORTHEASTWARD ACROSS THE AREA INTO THIS
EVENING. THIS SYSTEM WILL BRING ISOLATED -SHRA AND PERHAPS -TSRA...
AND CLOUD DECKS MOSTLY ABOVE 8K FT AGL. DECREASING CLOUDINESS WILL
THEN OCCUR FOR MOST SECTIONS LATE TONIGHT AS THE UPPER SYSTEM MOVES
NORTHEAST OF THE AREA. EXPECT A FEW-SCT CLOUDS SATURDAY MORNING
AROUND 10-15K FT AGL. SURFACE WIND THRU SATURDAY MORNING WILL
EXHIBIT NORMAL DIURNAL WIND TRENDS GENERALLY LESS THAN 10 KTS.
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A WEAK DISTURBANCE WILL BRING CLOUDS AND A FEW
SPRINKLES AND LIGHT SHOWERS TODAY. DRY CONDITIONS WILL OCCUR
SATURDAY. A SERIES OF STORM SYSTEMS WILL THEN MOVE THROUGH THE
INTERMOUNTAIN WEST SUNDAY THROUGH WEDNESDAY. THESE SYSTEMS IN
COMBINATION WITH ADEQUATE MOISTURE WILL RESULT IN A CHANCE OF
SHOWERS AND THUNDERSTORMS...MAINLY EAST OF TUCSON. 20-FOOT WINDS
WILL BE DIURNAL IN NATURE AND GENERALLY LESS THAN 15 MPH.

&&

.PREV DISCUSSION...ANOTHER IMPULSE UNDERCUTS THE LARGER SCALE MEAN
RIDGE POSITION SUNDAY. MODELS GENERALLY HANDLING THINGS SIMILARLY
WITH A FAIRLY EVEN COMPROMISE BETWEEN 00Z NAM/GFS/ECMWF HANDLING THE
RESIDUAL ENERGY AS IT QUICKLY LOSES HIGHER LATITUDE SUPPORT. BEST
AVAILABLE MOISTURE FIELDS DRAWN IN THROUGH NEW MEXICO WITH EAST
BORDER AREAS SEEING THE MOST ACTION IN OUR CWA...GENERALLY EAST OF
TUCSON.

THAT ENERGY WILL PROBABLY SIT AND FILL A BIT MONDAY INTO AT LEAST
EARLY TUESDAY BEFORE A STRONGER AND DEEPER TROUGH PUSHES IN FROM THE
COAST AROUND LATE TUESDAY INTO WEDNESDAY. PLENTY OF UNCERTAINTY
ABOUT AMPLITUDE...HOWEVER CONSIDERING THE PROGRESSIVE DEEPER SYSTEM
WELL DOWNSTREAM AND WEAKER PATTERN THROUGH WESTERN STATES AND
OCTOBER CLIMATOLOGY...WOULD TEND TO FAVOR FLATTER GFS. FOR NOW WE
WILL STICK WITH A BLEND OF ECMWF/GFS RESOLUTIONS...AGAIN WITH BEST
AVAILABLE MOISTURE IMMEDIATELY DOWNSTREAM IN NEW MEXICO. A RATHER
UNSETTLED WEEK THAT COULD SEE LINGERING ENERGY AND MOISTURE NEAR
EASTERN BORDER AREAS LONGER THAN WE ARE CURRENTLY ADVERTISING.

&&

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

$$

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

FRANCIS/MEYER





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