Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 162215
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
415 PM MDT TUE SEP 16 2014

.SYNOPSIS...HIGH PRESSURE ALOFT CENTERED ACROSS UTAH WILL SHIFT
EAST OF THE STATE LATE WEDNESDAY. MOISTURE CURRENTLY OVER ARIZONA
WILL SPREAD INTO SOUTHERN UTAH WEDNESDAY NIGHT AND THEN OVER MUCH
OF UTAH THURSDAY THROUGH THURSDAY NIGHT.



&&

.DISCUSSION...A BROAD UPPER LEVEL RIDGE REMAINS OVER THE ROCKY
MOUNTAINS THIS AFTERNOON...HELPING TO BRING WARM AND STABLE
CONDITIONS TO UTAH AND SOUTHWEST WYOMING. ENOUGH MOISTURE IS
LINGERING UNDER THE RIDGE TO PRODUCE ISOLATED SHOWERS AND
THUNDERSTORMS ALONG THE HIGHER TERRAIN...BUT MOST OF THESE STORMS
ARE STRUGGLING TO GET MUCH HEIGHT OR LONGEVITY.

WEDNESDAY SHOULD BE A FAIRLY SIMILAR DAY TO TODAY...WITH ONE
POSSIBLE EXCEPTION OF INCREASED SHOWERS AND THUNDERSTORMS ALONG
THE UTAH/ARIZONA BORDER...AS ADDITIONAL MOISTURE MOVES IN FROM THE
SOUTH. THAT SAID...THE BEST MOISTURE LOOKS TO REMAIN SOUTH OF THE
AREA THROUGH AT LEAST 00Z THURSDAY...WITH ONE INCH PRECIPITABLE
WATER VALUES FORECAST TO BARELY MOVE OVER UTAH. OTHER THAN
HELPING TO ESTABLISH THIS MODERATE MOISTURE IN NORTHERN
ARIZONA...TROPICAL STORM ODILE HAS BASICALLY BECOME A NON-FACTOR
FOR THE UTAH WEATHER...AS IT IS EXPECTED TO CONTINUE TRACKING
EASTWARD NEAR THE MEXICAN BORDER AND REMAIN WELL SOUTH AND EAST
OF THE CWA.

A DEEP PACIFIC TROUGH WILL MOVE INTO THE GREAT BASIN ON WEDNESDAY
NIGHT AND THROUGH THURSDAY...AND THE SOUTHERLY FLOW AHEAD OF IT
WILL DRAW PW VALUES OF 1.0 TO 1.1 INCHES OVER PRETTY MUCH THE
ENTIRE CWA. THE PRIMARY FORCING FROM THIS TROUGH AND ITS
ASSOCIATED COLD FRONT WILL IMPACT THE NORTHERN HALF OF THE CWA
THURSDAY AFTERNOON THROUGH THURSDAY NIGHT...AND COMBINED WITH GOOD
SHEAR COULD ALLOW SOME SEVERE THUNDERSTORMS TO DEVELOP THROUGH THE
LATTER HALF OF THURSDAY. PERHAPS THE BIGGEST CHANGE IN THE
FORECAST IS THAT THE MODELS ARE PRODUCING VERY LITTLE QPF OVER
THE SOUTHERN HALF OF UTAH...AS ALL OF THE FORCING REMAINS IN THE
NORTH. HAVE REDUCED POPS FOR THE SOUTH FOR MOST OF THE EVENT...BUT
STILL KEPT THEM AROUND 40-60 PERCENT FOR THE PEAK OF THE
STORM...AS ENOUGH MOISTURE SHOULD BE IN PLACE FOR AT LEAST TYPICAL
DIURNAL ACTIVITY.

THE PROGRESSIVE NORTHERN BRANCH OF THE TROUGH HELPS TO PUSH DRIER
AIR INTO THE CWA FROM THE NORTHWEST THROUGH THE DAY
FRIDAY...DECREASING THE COVERAGE OF PRECIPITATION HEADING INTO
FRIDAY NIGHT. THE SOUTHERN PART OF THE TROUGH IS PROGGED TO CUT
OFF INTO A CLOSED LOW OVER SOUTHERN CALIFORNIA LATE FRIDAY.

MODELS OVER THE PAST FEW DAYS HAVE STRUGGLED ON WHAT TO DO WITH
THIS LOW AFTER IT CUTS OFF...BUT THE 12Z RUNS OF THE GFS AND ECMWF
HAVE FINALLY COME INTO SOME AGREEMENT...AND THEIR CURRENT SOLUTION
WILL NOT BE GOOD NEWS FOR THOSE WHO WERE HOPING FOR A DRY WEEKEND.
BOTH MODELS KEEP THE LOW OVER SOUTHERN CALIFORNIA AND NEVADA
SATURDAY AND SUNDAY...WHICH DRAWS MOISTURE BACK NORTHWARD INTO
UTAH. THIS MOISTURE REACHES SOUTHWEST UTAH SATURDAY
AFTERNOON OR EVENING...AND THEN INTO MUCH OF THE REST OF THE
STATE SATURDAY NIGHT AND SUNDAY. PRECIPITATION ALSO CONTINUES INTO
MONDAY AS THE LOW TRACKS DIRECTLY ACROSS UTAH. HAVE BEGUN
INCREASING POPS FOR THIS SATURDAY THROUGH MONDAY TIMEFRAME...AND
POPS WILL HAVE TO BE INCREASED EVEN MORE OVER THE NEXT FEW SHIFTS
IF THE MODELS HOLD ONTO THIS SOLUTION.


&&

.AVIATION...VFR CONDITIONS ARE EXPECTED THROUGH THE TAF
PERIOD AT THE KSLC TERMINAL. LIGHT NORTHWEST WINDS THIS AFTERNOON
WILL SWITCH TO THE SOUTHEAST BETWEEN 0200 UTC AND 0400 UTC.

&&

.FIRE WEATHER...ABOVE-NORMAL TEMPERATURES WILL CONTINUE STATEWIDE
THROUGH WEDNESDAY AS A HIGH PRESSURE RIDGE CONTINUES TO ENVELOP THE
REGION. WEDNESDAY AFTERNOON EXPECT ISOLATED THUNDERSTORMS TO DEVELOP
AGAIN OVER SOUTHERN AND CENTRAL UTAH MOUNTAINS...WHILE MINIMUM
RELATIVE HUMIDITIES IN THE TEENS WILL BE MORE CONFINED TO THE
CENTRAL AND NORTHERN WEST DESERT AREAS. A SIGNIFICANT MOISTURE SURGE
WILL INFILTRATE SOUTHERN UTAH WEDNESDAY EVENING AND SPREAD NORTHWARD
BY THURSDAY... CATAPULTING RH VALUES AND DELIVERING A SOLID CHANCE
OF WETTING RAINS TO MUCH OF THE FORECAST AREA THURSDAY INTO
FRIDAY.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&

$$

PUBLIC...SCHOENING
FIRE WEATHER...VERZELLA
AVIATION...GRAHAM

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)


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