Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 261032
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
432 AM MDT WED AUG 26 2015

.SYNOPSIS...A LOW PRESSURE SYSTEM WILL CROSS THE REGION FROM SOUTH
TO NORTH TODAY. HIGH PRESSURE WILL RETURN FOR THE LATTER HALF OF
THE WEEK INTO THE UPCOMING WEEKEND.

&&

.SHORT TERM (THROUGH 06Z SUNDAY)...A MID LEVEL RIDGE CENTERED OVER
THE CENTRAL ROCKIES COUPLED WITH AN UPPER LOW SPINNING OFF THE
PACIFIC COAST IS ALLOWING FOR A DEEP FETCH OF SOUTHERLY FLOW
ACROSS THE DESERT SOUTHWEST/INTERMOUNTAIN WEST REGION THIS
MORNING. A WELL DEFINED WAVE EMBEDDED WITHIN THIS FLOW IS
CURRENTLY LIFTING NORTH FROM NORTHWEST AZ INTO SOUTHWEST UT...AND
IS FORECAST TO CONTINUE ON ITS NORTHWARD TRAJECTORY ACROSS THE
FORECAST AREA THIS MORNING INTO EARLY AFTERNOON. AMPLE BOUNDARY
LAYER MOISTURE HAS ADVECTED ACROSS SOUTHERN AND CENTRAL UT...AND
WILL INCREASE ACROSS THE NORTH THROUGH THE MORNING HOURS. ALREADY
SEEING NUMEROUS SHOWERS ACROSS MUCH OF THE FORECAST AREA...AND
EXPECT THIS TO CONTINUE INTO THE MORNING HOURS...BECOMING MORE
FOCUSED OVER THE NORTH WITH TIME. AS IS OFTEN THE CASE IN THESE
SITUATIONS...EXTENSIVE CLOUD COVER AND PRECIPITATION COUPLED WITH
MODEST MID LEVEL LAPSE RATES WILL SIGNIFICANTLY LIMIT INSTABILITY
THROUGH THE DAY...THUS ALTHOUGH LOCALLY HEAVY RAINFALL CANT BE
RULED OUT THE THREAT IS LOW ENOUGH TO PRECLUDE ANY SORT OF
WATCH...AND HAVE GONE WITH MODERATES FOR THE FLASH FLOOD
POTENTIAL. WITH THE EXTENSIVE CLOUD COVER AND PRECIP MAX
TEMPERATURES SHOULD BE HELD WELL BELOW SEASONAL NORMS.

ANTICIPATE SHOWERS TO WIND DOWN ACROSS THE SOUTH DURING THE
MORNING HOURS...AND ACROSS THE NORTH DURING THE MID TO LATE
AFTERNOON. A NUMBER OF HI-RES MODELS INCLUDING MOST MEMBERS OF
THE NCAR ENSEMBLE REGENERATE CONVECTION IN THE WAKE OF THIS WAVE
ACROSS SOUTHERN UT THIS AFTERNOON...HOWEVER GIVEN THE STABLE
AIRMASS LEFT IN PLACE AND LARGE SCALE SUBSIDENCE IN THE WAKE OF
THE DEPARTING WAVE THIS SEEMS RATHER UNLIKELY. HAVE HELD ONTO
CHANCE POPS FOR NOW OVER THE SOUTH HOWEVER THIS MAY BE A BIT
OVERDONE.

SHORTWAVE RIDGING IN THE WAKE OF TODAYS TROUGH WILL BUILD ACROSS
THE FORECAST AREA THURSDAY. THE MODELS HAVE TRENDED TOWARD
RETAINING MORE BOUNDARY LAYER MOISTURE THURSDAY WHICH WOULD
SUPPORT A BETTER CHANCE FOR AFTERNOON CONVECTION...HOWEVER THIS
MOISTURE/INSTABILITY WILL HAVE TO OVERCOME LARGE SCALE SUBSIDENCE
ASSOCIATED WITH THE BUILDING RIDGE. IT APPEARS THE BEST CHANCE FOR
CONVECTION WILL COME ACROSS THE TERRAIN OF SOUTHWEST AND SOUTH
CENTRAL UT WHERE SUBSIDENCE IS EXPECTED TO BE WEAKER. HAVE
INCLUDED CHANCE POPS IN THE TERRAIN AND SLIGHT CHANCE IN THE
ADJACENT VALLEYS ACROSS THIS AREA...AS WELL AS SLIGHT CHANCE POPS
ACROSS THE UINTAS AND WASATCH PLATEAU. BUILDING HEIGHTS WILL ALSO
ALLOW MAX TEMPERATURES TO QUICKLY REBOUND NEAR CLIMO.

THIS RIDGE AXIS WILL SLOWLY SHIFT EAST FRIDAY INTO SATURDAY
ALLOWING A DRYING SOUTHWESTERLY FLOW TO OVERSPREAD THE EASTERN
GREAT BASIN. AS A RESULT HAVE MAINTAINED A DRYING TREND AREAWIDE
ALONG WITH AN UPTICK IN TEMPERATURES INTO THE UPCOMING WEEKEND. A
SHORTWAVE TROUGH EXPECTED TO LIFT THROUGH THE PACIFIC NORTHWEST
DURING THE DAY SATURDAY MAY RESULT IN LOCALLY BREEZY WINDS ACROSS
WESTERN UT SATURDAY AFTERNOON.

.LONG TERM (AFTER 06Z SUNDAY)...THE GFS SHOWS A WEAK AND DIFFUSE
LOOKING PLUME OF MOISTURE BETWEEN 850 AND 500 MB SUNDAY OVER THE
SPINE OF THE MOUNTAINS SO THROUGH IN SOME LOW POPS. THE EC EJECTS A
SLIGHTLY STRONGER LOOKING SHORTWAVE ACROSS THE NORTHERN ROCKIES
WHICH PUSHES A COLD FRONT INTO NORTHERN UTAH WHILE THE GFS IS ABOUT
12 HRS SLOWER AND SOMEWHAT WEAKER WITH THIS SHORTWAVE. THE GFS
ENSEMBLE IS ABOUT 8 HRS SLOWER. HAVE LEANED TOWARD THE ENSEMBLE
FORECAST WHICH ALLOWS THE COLD FRONT TO MOVE INTO UTAH BUT NOT BE AS
STRONG. USED A BLEND OF MOS GUIDANCE FOR MAX TEMPERATURES ON MONDAY.
IGNORED THE QPF THAT THE EC FORECASTS FOR THE NORTHWEST CORNER
MONDAY SINCE THE 00Z GFS DID NOT SHOW IT. HOWEVER...AT THE TIME OF
WRITING THIS DISCUSSION THE NEW 06Z GFS SHOWS THAT THE COLD FRONT
HAS SPED UP AND THAT SOME SHOWERS ARE POSSIBLE OVER THE NORTHWEST
CORNER OF UTAH. WILL LEAVE FORECAST AS IS BUT NEXT SHIFT MAY HAVE TO
INCLUDE SOME LOW POPS. A DRY SOUTHWEST FLOW IS EXPECTED TO PREVAIL
TUESDAY AND WEDNESDAY.


&&

.FIRE WEATHER...A DISTURBANCE EMBEDDED WITHIN A MONSOONAL SURGE
WILL MOVE NORTHWARD ACROSS THE REGION TODAY CREATING WIDESPREAD
SHOWERS AND SCATTERED THUNDERSTORMS. INSTABILITY SHOWERS AND
THUNDERSTORMS WILL CONTINUE INTO THURSDAY...BUT MAINLY OVER THE
HIGHER TERRAIN AND BY FRIDAY AND SATURDAY ONLY ISOLATED MOUNTAIN
THUNDERSTORMS ARE EXPECTED. A STRONG TROUGH IS EXPECTED TO REMAIN
OFF THE PACIFIC NORTHWEST COAST THIS WEEKEND WHICH WILL CAUSE A
MAINLY DRY AND BREEZY SOUTHWEST FLOW TO PREVAIL ACROSS UTAH. THE
TROUGH WEAKENS MONDAY AS SOME ENERGY EJECTS NORTHEAST ACROSS THE
NORTHERN ROCKIES WHICH WILL PUSH A COLD FRONT INTO NORTHERN UTAH.
HOWEVER...A BROAD TROUGH WILL REMAIN OVER THE PACIFIC NORTHWEST
AND NORTHERN ROCKIES THROUGH MIDWEEK WHICH WILL KEEP UTAH UNDER A
DRY AND BREEZY REGIME.

&&

.AVIATION...SHOWERS WITH ISOLATED THUNDERSTORMS ARE EXPECTED AT
THE SLC TERMINAL THROUGH EARLY THIS EVENING. WINDS WILL LIKELY BE
SOUTHERLY UNTIL ABOUT 20Z WITH GUSTS TO 20 MPH POSSIBLE.
HOWEVER...WINDS WILL BE ERRATIC IN AND AROUND ANY
SHOWERS/THUNDERSTORMS. A WIND SHIFT IS EXPECTED THIS AFTERNOON BUT
THERE IS A 30 PERCENT CHANCE THAT THE WINDS WILL REMAIN SOUTHERLY.

&&

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

$$

SEAMAN/STRUTHWOLF

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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