Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 041527
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
927 AM MDT FRI SEP 4 2015

.SYNOPSIS...AN UPPER LEVEL TROUGH WILL MOVE THROUGH THE PACIFIC
NORTHWEST TODAY...THEN PUSH A FALL COLD FRONT THROUGH THE
INTERMOUNTAIN WEST ON SATURDAY. A GENERAL DRYING AND WARMING TREND
IS EXPECTED FOR EARLY NEXT WEEK.

&&

.DISCUSSION... WATER VAPOR LOOP SHOWS A DEEP CLOSED LOW OVER THE
PACIFIC NORTHWEST...WITH TROPICAL STORM KEVIN WELL SOUTHWEST OF
BAJA. AMDAR 400-250MB WIND OBSERVATIONS SHOW A 80-120KT CYCLONIC
JET OFF THE CALIFORNIA COAST INTO THE NORTHERN ROCKIES. THERE IS
ALSO A SOUTHWEST 60-80KT JET FROM SOUTHERN CALIFORNIA INTO THE
FOUR CORNERS. GOES/GPS/RAP/12Z SLC RAOB INDICATE THE PRECIPITABLE
WATER VALUE RANGES BETWEEN 0.25" MOUNTAINS...TO 0.75"-1.00" ACROSS
THE SOUTHERN VALLEYS.

GOING FORECAST ON TRACK WITH JUST A FEW TWEAKS MADE. EXPANDED AREA
OF ISOLATED CONVECTION ACROSS THE WEST DESERT AND CACHE VALLEY THIS
AFTERNOON AS THE NEXT TROUGH BEGINS TO APPROACH. KEPT A HOLE ODGEN
SOUTH ALONG I-15 AS FEEL THREAT OF CONVECTION IS LESS THAN 20
PERCENT.

BEST MOISTURE RESIDES ALONG THE ARIZONA BORDER...EAST OF KANAB.
COULD SEE A HEAVIER DOWNPOUR THERE WITH DEWPOINTS NEAR 50F...HOWEVER
THERE IS STILL A DECENT AMOUNT OF DRY LOW LEVEL AIR TO OVERCOME AND
A SHALLOW WARM CLOUD LAYER PER RAP FORECAST SOUNDING AT PGA. STORM
MOTION IS QUITE FAST TO THE NORTHEAST SO LOW PROBABILITY OF FLASH
FLOODING. WILL HAVE TO MONITOR FOR TRAINING STORMS.

CONVECTION ESPECIALLY NORTH OF THE ARIZONA BORDER WILL BRING A
THREAT OF LOCALLY ENHANCED WINDS.

WIND ADVISORY LOOKS ON TRACK FOR MUCH OF THE WESTERN VALLEYS THIS
AFTERNOON. RAP INDICATES A DECENTLY STRONG SOUTHERN PRESSURE
GRADIENT RESIDES ACROSS THE WEST THIS AFTERNOON...WITH PRESSURE
FALLS ON THE ORDER OF 7MB BETWEEN NOON AND 6PM.

THE AFTERNOON PACKAGE WILL FOCUS ON SYNOPTIC WIND AND CONVECTIVE
TRENDS THROUGH SATURDAY EVENING.

&&

.PREVIOUS DISCUSSION... A DEEP UPPER TROF REMAINS CENTERED OVER
THE PACNW STATES EARLY THIS MORNING WITH A MODERATE TO STRONG SWLY
FLOW DOWNSTREAM FROM THIS TROF OVER THE GREAT BASIN.

MOISTURE HAS INCREASED OVER SERN UT OVERNIGHT AND THIS IS FORECAST
TO LIFT NWD TODAY. SOME OF THIS MOISTURE SEEPS INTO WRN UT BUT THE
MAJORITY WILL REMAIN OVER THE MTNS AND EAST BRINGING A THREAT OF
SCATTERED CONVECTION TO THESE AREAS.

A LEADING SURFACE TROF IS CURRENTLY STALLED ACROSS NWRN UT AND THIS
COULD ALSO ACT AS A FOCUS FOR ISOLATED CONVECTION TODAY. THIS
ACTIVITY WILL CONTINUE INTO THIS EVE AND LIMITED MOISTURE CREEPS
WEST OF I-15 BRINGING THE THREAT OF ISOLATED CONVECTION TO THE I-15
CORRIDOR MAINLY THIS EVE.

THE FLOW ALOFT IS SUFFICIENTLY STRONG TO WARRANT A WIND HIGHLIGHT
FOR THE WRN VALLEYS ONCE THESE WINDS FULLY MIX DOWN THIS AFTN. THE
PATTERN STAYS STATIC INTO SAT MORNING THEN THE COLD FRONT SURGES
INTO THE CWA IN THE AFTERNOON. EXPECT A BAND OF CONVECTION WITH THE
FRONT WITH COVERAGE MOST LIKELY REMAINING SCATTERED.

THE COOLER AIR BEHIND THE FRONT WILL SEND MAX TEMPS SUN ACROSS THE
NORTH DOWN BELOW SEASONAL NORMS WHILE THE SOUTH COOLS LESS. DRIER
STABLE AIR STAYS IN PLACE MON ALTHO THE LATEST GFS IS HINTING THE
SOME MOISTURE COULD RETURN TO SERN UT THAT DAY. CONFIDENCE IS LOW
THAT WILL WILL HAPPEN SO THERE IS NO MENTION OF PRECIP IN THE
FORECAST FOR MON AFTN/EVE AT THIS TIME.

GLOBAL MODELS HAVE COME INTO BETTER AGREEMENT WITH ANOTHER IN A
SERIES OF SHORTWAVES DROPPING OUT OF THE GULF OF ALASKA. WHILE THE
00Z GFS CONTINUES TO INDICATE THIS FEATURE WILL STRENGTHEN OVER THE
INTERMOUNTAIN REGION TUESDAY...THE 00Z EC CONTINUES TO INDICATE A
WEAKER AND MORE PROGRESSIVE SYSTEM. THE MAIN IMPACT WITH THE 00Z GFS
SOLUTION WOULD BE COOLER TEMPERATURE ACROSS AT LEAST NORTHERN UTAH
TUESDAY AND INTO WEDNESDAY. LEANED MORE TOWARD THE EC WITH THE
TEMPERATURE GRIDS FOR THE LONG TERM FORECAST AT THIS POINT AS THE EC
SEEMS TO BE A MORE REASONABLE SOLUTION.

GIVEN THE LONG RANGE PATTERN...THERE IS LITTLE CHANCE OF
PRECIPITATION ACROSS MUCH OF THE CWA FROM ROUGHLY TUESDAY THROUGH
FRIDAY.

&&

.AVIATION...SOUTHERLY WINDS WILL STEADILY INCREASE THROUGH MID
AFTERNOON...THEN REMAIN QUITE STRONG INTO EARLY EVENING.  STRONG
GRADIENT WINDS WILL PROHIBIT TYPICAL SHIFT TO A NORTHWEST LAKE
BREEZE.  OCCASIONAL VISIBILITY REDUCTIONS IN BLOWING DUST WILL BE
POSSIBLE THIS AFTERNOON INTO THIS EVENING...OTHERWISE...VFR CEILINGS
AND VISIBILITIES WILL PREVAIL.

&&

.FIRE WEATHER...RED FLAG WARNING CONTINUES THROUGH SATURDAY FOR THE
WESTERN VALLEYS. RH VALUES BETWEEN 10 AND 15 PERCENT...ALONG WITH
VERY STRONG WINDS. SOUTHERLY GUSTS UP TO 50 MPH TODAY...POTENTIALLY
STRONGER SATURDAY. A SIGNIFICANT WIND SWITCH TO THE NORTHWEST IS
FORECAST WITH THE COLD FRONT SATURDAY AFTERNOON AND EVENING. WINDS
DIMINISH SATURDAY NIGHT MOST PLACES. COOLER CONDITIONS CAN BE
EXPECTED SUNDAY.

CONVECTION APPEARS ISOLATED MOST LOCATIONS...BUT LIGHTNING AND
ENHANCED/ERRATIC WINDS WILL BE A THREAT CONCURRENT WITH THE LARGER
SCALE WIND STORM TODAY AND TOMORROW.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...RED FLAG WARNING UNTIL 10 PM MDT SATURDAY FOR UTZ478-492-495-497.

     WIND ADVISORY UNTIL 10 PM MDT THIS EVENING FOR UTZ003-005-015-
     016.

     HIGH WIND WATCH FROM SATURDAY MORNING THROUGH SATURDAY EVENING
     FOR UTZ003-005-015-016.

WY...NONE.
&&

$$

PUBLIC...ROGOWSKI/WILENSKY/KRUSE
FIRE WEATHER...ROGOWSKI
AVIATION...BARJENBRUCH

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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