Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 141717
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
1117 AM MDT TUE APR 14 2015

.SYNOPSIS...A COLD UPPER LEVEL TROUGH WILL SETTLE INTO THE GREAT
BASIN TODAY...THEN REMAIN OVER THE REGION THROUGH EARLY THURSDAY.
HIGH PRESSURE WILL RETURN FOR LATE IN THE WEEK.

&&

.SHORT TERM (THROUGH 00Z SATURDAY)...MORNING WATER VAPOR AND H5
ANALYSIS IDENTIFY A POTENT TROUGH WITH UPPER LEVEL CIRCULATION
CURRENTLY OVER CENTRAL NEVADA. THE ASSOCIATED COLD FRONT IS IN A
PERIOD OF DISCRETE PROPAGATION AT THIS TIME...AS THE MSLP SURFACE
TROUGH REMAINS STATIONARY OVER FAR NORTHWESTERN UTAH...AND THE
UPPER SUPPORT AND MSLP HEIGHT RISES REMAIN TO THE WEST OVER
NORTHEASTERN NEVADA PER MSAS. OVER THE NEXT FEW HOURS A RAPID
TRANSITION TO FRONTOGENESIS WILL OCCUR ALONG AND BEHIND THE
SURFACE TROUGH...WITH UPPER SUPPORT DRIVING THE FRONT EAST QUITE
RAPIDLY THIS AFTERNOON THROUGH THIS EVENING. THREE PRIMARY
IMPACTS TO FOCUS ON IN THE SHORT TERM...VERY STRONG
WINDS...THUNDERSTORMS AND SNOW.

WINDS...SOUTHERLY WINDS CONTINUE TO RAMP UP AHEAD OF THE SURFACE
TROUGH THIS MORNING WITH PEAK GUSTS (PER MESOWEST AND SPOTTERS) IN
EXCESS OF 50 MPH ACROSS THE WESTERN VALLEYS ALREADY OCCURRING.
EXPECTING THESE SPEEDS TO CONTINUE TO INCREASE AND MOVE INTO THE
WASATCH FRONT THROUGH EARLY AFTERNOON AS THE FRONT BEGINS ITS
EASTWARD PUSH...AND DEEPER LAYER MIXING OF H7 WINDS ON THE ORDER
OF 40 TO 50 KNOTS OCCURS. FURTHER SOUTH AND EAST...SPECIFICALLY
THE SOUTHEASTERN VALLEYS...SOUTHWESTERLY WINDS WILL CONTINUE TO
INCREASE MORE GRADUALLY THROUGH THIS AFTERNOON BUT BECOME VERY
STRONG LATE THIS AFTERNOON WITH FURTHER ENCROACHMENT OF THE FRONT.
LATEST FRONTAL PASSAGE TIMING HAS SLOWED A FEW HOURS IN 12Z HI-RES
GUIDANCE AND NOW LOOKS TO OCCUR BETWEEN 2PM AND 3 PM AT KSLC...5PM TO
6 PM KCDC AND BETWEEN 7PM AND 9 PM IN THE SOUTHEASTERN VALLEYS.
BEHIND THE FRONT WINDS WILL SNAP TO THE NORTHWEST...WITH SPEEDS
LIKELY INCREASING FOR A 1 TO 2 HOUR PERIOD. GUSTS TO 70 MPH CAN
NOT BE RULED OUT DURING FRONTAL PASSAGE...ESPECIALLY ACROSS THE
WESTERN DESERTS AND PORTIONS OF SOUTHERN SALT LAKE AND NORTHERN
UTAH COUNTIES. VISIBILITIES WILL BE ON THE DECLINE AS WELL WITH A
SIGNIFICANT BLOWING DUST THREAT LIKELY WITH FRONTAL PASSAGE.
CURRENT SUITE OF HIGH WIND WARNINGS REMAIN ON TRACK...THOUGH LOOK
MOST SOLIDLY SO ACROSS THE WESTERN VALLEYS.

THUNDERSTORMS...EXPECTING SCATTERED DEVELOPMENT ALONG AND JUST
BEHIND THE SURFACE FRONT THIS AFTERNOON INTO THE EVENING HOURS.
MUCAPE VALLEYS PROGGED TO INCREASE TO NEAR 500 J/KG WITHIN THE
FRONTOGENIC ENVIRONMENT...THIS ENVIRONMENT DRIVING A RAPID
STEEPENING OF LAPSE RATES...WILL LIKELY SPARK A BROKEN SQUALL LINE
BY MID AFTERNOON AND CONTINUING INTO THE EVENING HOURS. ISOLATED
SEVERE LEVEL CONVECTIVE WIND GUSTS REMAIN A THREAT ON TOP OF THE
SYNOPTIC WINDS DISCUSSED PREVIOUSLY.

SNOW...WITH ENCROACHMENT OF UPPER SUPPORT THE
BAROCLINICITY/THERMAL PACKING ALONG THE FRONT WILL CONTINUE TO
TIGHTEN THIS AFTERNOON. H7 TEMPS AT KSLC REMAIN PROGGED TO DROP
FROM +5 C (CURRENT ESTIMATE) AT KSLC TO -10 C BY 00Z. IMPRESSIVE
NEEDLESS TO SAY. DYNAMIC LIFT ASSOCIATED WITH THE LEFT EXIT
REGION OF A 100+ KNOT UPPER JET COUPLED WITH FRONTAL LIFT AND POST
FRONTAL COLD CORE MOVING THROUGH NORTHERN/CENTRAL UTAH THIS
EVENING WILL GENERATE IMPRESSIVE LIFT OWING TO WIDESPREAD MODERATE
TO HEAVY PRECIP POTENTIAL THIS EVENING. POST FRONTAL TEMP TRENDS
NOTED ABOVE WILL ALLOW FOR A NEAR INSTANTANEOUS TRANSITION TO
SNOW IN THE MOUNTAINS/MOUNTAIN VALLEYS IN THE NORTH BY LATE
THIS AFTERNOON...VALLEY FLOORS BY THIS EVENING. OPTED TO ISSUE A
WINTER WEATHER ADVISORY FOR THE WASATCH MOUNTAIN VALLEYS AND
SOUTHWEST WYOMING BEGINNING AT 4 PM THIS AFTERNOON AS INTENSITY OF
SNOW AND WINDS IS EXPECTED TO IMPAIR TRAVEL WITH AT LEAST ROAD
SLUSH AND REDUCED VISIBILITIES THIS EVENING AND OVERNIGHT. WILL
ADDRESS ANY POTENTIAL FOR VALLEY HIGHLIGHTS ALONG THE WASATCH
FRONT FOR THE AFTERNOON PACKAGE...BUT RIGHT NOW IMPACTS LOOKS MORE
NEGLIGIBLE. EASTWARD PROGRESSION OF THE UPPER TROUGH LATE TONIGHT
THROUGH TOMORROW WILL TRANSITION THE NORTHERN/CENTRAL PORTIONS OF
THE STATE INTO A DEEPLY UNSTABLE WRAP AROUND ENVIRONMENT WITH MORE
SHOWERY SNOW EXPECTED. MOUNTAIN WARNINGS FOR VERY STRONG WINDS AND
HEAVY SNOWFALL REMAIN ON TRACK THROUGH TOMORROW...THOUGH
INTENSITIES AND AREAL OF EXTENT OF SNOWFALL LOOKS TO DECLINE AT
TIMES LATE TONIGHT AND TOMORROW.

NOT MUCH SIGNIFICANT TO NOTE FOR THU/FRI. THE UPPER LOW WILL
GRADUALLY TRACK AND CLOSE OFF OVER THE 4-CORNERS REGION ALLOWING
AN UPPER RIDGE TO NOSE IN FROM THE WEST/SOUTHWEST. DRYING
CONDITIONS AND WARMING TEMPS ARE EXPECTED...ESPECIALLY BY FRI.

&&

.LONG TERM (AFTER 00Z SATURDAY)...THE GENERAL TREND OF THE GLOBAL
MODEL SOLUTIONS FOR THE TROUGH FORECAST TO MOVE THROUGH NORTHERN
UTAH SATURDAY NIGHT HAS BEEN WEAKER AND WEAKER AS THE HEART OF THE
TROUGH MOVES ACROSS MONTANA INTO THE HIGH PLAINS RATHER THE NORTHERN
ROCKIES. THE 700MB TEMPERATURES COOL BY MAYBE ONE DEGREE CELSIUS
OVER NORTHERN UTAH BETWEEN SATURDAY AND SUNDAY. BUT SINCE THE TREND
IS FOR THIS TROUGH TO BECOME LESS AND LESS OF A PLAYER HAVE NOT
COOLED THE SURFACE TEMPERATURES EXCEPT RIGHT ALONG THE IDAHO AND
WYOMING BORDERS BY A COUPLE OF DEGREES OR LESS.

AS FAR AS SEEING ANY PRECIPITATION IT IS HIGHLY UNLIKELY WITH THE
COLD AIR ALOFT REMAIN WELL TO OUR NORTH. ONCE AGAIN THE GFS AND EC
PRODUCE SOME SPURIOUS LOOKING QPF OVER THE REGION SUNDAY...MONDAY
AND TUESDAY WITH NO EVIDENCE OF SUPPORT. HAVE MAINTAINED THE POP
FREE FORECAST THROUGH THE EXTENDED. A TROUGH MOVING TOWARD THE
CALIFORNIA COAST TUESDAY WILL CENTER THE RIDGE OVER THE FAR EASTERN
GREAT BASIN TUESDAY FOR SOME SOUTHERLY WINDS INCREASING OVER WESTERN
VALLEYS AS WELL AS TEMPERATURES WARMING SEVERAL DEGREES.


&&

.AVIATION...SOUTHERLY WINDS WILL CONTINUE TO RAMP UP AT THE SLC
TERMINAL AS THE COLD FRONT APPROACHES...WITH SOUTHERLY WIND GUSTS IN
EXCESS OF 50 MPH POSSIBLE BETWEEN 17Z AND 19Z JUST AHEAD OF THE
FRONT. WINDS ARE EXPECTED TO SHIFT RATHER ABRUPTLY TO THE NORTHWEST
AROUND 19-20Z...WITH A 20 PERCENT CHANCE OF A DELAY TILL 21Z....WITH
GUSTS POSSIBLE IN EXCESS OF 55 MPH.

VISIBILITIES WILL LIKELY LOWER IN BLOWING DUST BOTH AHEAD OF AND
BEHIND THE FRONT...WITH A 40 PERCENT CHANCE OF OCCASIONAL MVFR
CONDITIONS. THERE IS A 40 PERCENT CHANCE OF THUNDERSTORMS AND
SQUALLS ALONG THE COLD FRONT...NOT ENOUGH CONFIDENCE OF PROXIMITY TO
THE TERMINAL TO ADD MENTION YET IN THE TAF.

RAIN/SNOW MIX EXPECTED TO BEGIN BETWEEN 23-01Z...THEN ALL SNOW
LIKELY BY SUNDOWN. PERIODIC HIGH INTENSITY SNOWFALL COULD ALLOW SOME
ACCUMULATED SLUSH INTO THE EVENING HOURS.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...HIGH WIND WARNING UNTIL 11 AM MDT WEDNESDAY FOR UTZ011>013-
     019>021-518.

     WINTER STORM WARNING UNTIL 4 PM MDT WEDNESDAY FOR UTZ007>010-517.

     HIGH WIND WARNING UNTIL 10 PM MDT THIS EVENING FOR UTZ001>006-
     014>016.

     WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM MDT
     WEDNESDAY FOR UTZ006.

WY...HIGH WIND WARNING UNTIL 10 PM MDT THIS EVENING FOR WYZ021.

     WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM MDT
     WEDNESDAY FOR WYZ021.

&&

$$

MERRILL/VERZELLA/STRUTHWOLF


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VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)



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