Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 292225
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
425 PM MDT FRI APR 29 2016

.SYNOPSIS...THE NEXT PACIFIC STORM SYSTEM WILL SETTLE INTO THE
ARIZONA THIS WEEKEND AND IMPACT MUCH OF SOUTHERN AND EASTERN UTAH
INTO EARLY NEXT WEEK. HIGH PRESSURE ALOFT WILL RETURN TO THE
INTERIOR WEST BY THE MIDDLE OF NEXT WEEK.

&&

.SHORT TERM (UNTIL 00Z TUESDAY)...A STILL MOIST AND SOMEWHAT
UNSTABLE AIR MASS SUPPORTED BY A WEAK SHORTWAVE MOVING SOUTHEAST
THROUGH NORTHWEST UTAH WILL GENERATE SCATTERED CONVECTION THROUGH
EARLY THIS EVENING. MUCH OF THIS CONVECTION WILL DISSIPATED EARLY
THIS EVENING...WITH LINGERING ACTIVITY REMAINING NEAR THE PASSING
SHORTWAVE.

THE NEXT SHORTWAVE MOVING SOUTHEAST THROUGH WESTERN OREGON LATE
THIS AFTERNOON WILL DEVELOP INTO A CLOSED CIRCULATION OVER
SOUTHERN NEVADA LATE TONIGHT...THEN CONTINUE SOUTHEAST INTO
ARIZONA SATURDAY. CONVECTION ASSOCIATED WITH THIS FEATURE WILL
EXPAND ACROSS NEVADA THIS EVENING...WITH SOME SPILL OVER INTO FAR
WESTERN UTAH LATE TONIGHT. NOT ANTICIPATING AN EASTWARD EXPANSION
OF THE CONVECTION ACROSS UTAH OVERNIGHT AS THE TRAJECTORY OF THE
UPPER LOW REMAIN OUTSIDE OF UTAH. ONCE THE UPPER LOW SETTLES IN
ARIZONA SATURDAY THE BROAD AREA OF SYNOPTIC-SCALE LIFT AND
AVAILABLE MOISTURE WILL GENERATE AN INCREASE IN PRECIP ACROSS THE
SOUTHERN UTAH AND THROUGH THE CENTRAL MOUNTAINS. THE UPPER LOW
WILL GRADUALLY WEAKEN AS IT DRIFT NORTH TOWARD THE FOUR CORNERS
SUNDAY. THE ASSOCIATE PRECIP WILL REMAIN CLOSE TO THE RESIDUAL LOW
CENTER OVER SOUTH-CENTRAL THROUGH EAST-CENTRAL UTAH SUNDAY
AFTERNOON AND EVENING. RESIDUAL SHOWERS WILL PERSIST INTO
MONDAY...THOUGH THIS ACTIVITY WILL BE CONFINED TO THE
EASTERN/CENTRAL MOUNTAINS AND LARGELY DRIVEN BY DIFFERENTIAL
HEATING.

THE BIG ISSUE IN THE SHORT TERM REMAINS THE POTENTIAL FOR
DOWNSLOPE WIND EVENT ACROSS FAR NORTHERN UTAH LATE SATURDAY NIGHT
THROUGH SUNDAY. THE UPPER LEVEL PATTERN OF HIGH PRESSURE CENTERED
ACROSS SOUTH-CENTRAL CANADA AND THE UPPER LOW OVER THE CENTRAL
PLAINS STATES WILL CREATE A DEEP LAYER EASTERLY FLOW ACROSS
WYOMING AND BACK INTO FAR NORTHERN UTAH THIS WEEKEND. EAST WINDS
BETWEEN 40 AND 50 KTS NEAR 700 MB WITH STRONG COLD ADVECTION AND A
FAVORABLE NORTHEAST SURFACE PRESSURE GRADIENT BOTH POINT TOWARDS
HIGH WINDS FOR THE NORTHERN WASATCH FRONT AND CACHE VALLEY LATE
SATURDAY NIGHT THROUGH SUNDAY.

THE PATTERN SETTING UP DOES HAVE ITS PLUSES AND MINUSES WHEN IT
COMES TO A DOWNSLOPE HIGH WIND EVENT. ON THE PLUS SIDE THERE IS A
GOOD STABLE LAYER FORECAST TO BE ABOVE THE TERRAIN WITH FAIRLY
STRONG UPSTREAM COLD ADVECTION TAKING PLACE. THE SURFACE PRESSURE
GRADIENT OF 8-10 MB BETWEEN CENTRAL WYOMING AND NORTHERN UTAH IS
ADEQUATE TO SUPPORT HIGH WINDS. ON THE MINUS SIDE THE SURFACE
PRESSURE IS JUST ADEQUATE.

THE EVENT WILL LARGELY DEPEND ON THE UPPER LEVEL PATTERN REMAINING
FAVORABLE OVER THE WEEKEND. INITIALLY THE EASTERLY FLOW IS
SUPPORTED BY THE HIGH PRESSURE OVER SOUTH-CENTRAL CANADA AND THE
UPPER LOW MOVING INTO THE CENTRAL PLAINS. BY THE BEGINNING OF THE
EVENT THE CANADIAN HIGH SHIFTS WEST TO THE NORTHERN ROCKIES AND
THE ARIZONA LOW DRIFTS NORTH TO SUSTAIN THE DEEP EASTERLY FLOW
ALOFT. IF THIS PATTERN TRANSITION FAILS TO MATERIALIZE...THE HIGH
WIND EVENT COULD FIZZLE. AT THIS POINT CONFIDENCE THAT THE HIGH
WIND EVENT WILL OCCUR IS REASONABLY HIGH BASED ON RUN-TO-RUN
CONSISTENCY OF THE GLOBAL MODEL THE PAST SEVERAL RUNS. HAVE ISSUED
AN HIGH WIND WATCH FOR LATE SATURDAY NIGHT THROUGH SUNDAY FOR THE
NORTHERN WASATCH FRONT AND CACHE VALLEY. POINTS TO THE SOUTH ALONG
THE URBAN CORRIDOR MAY SEE MORE OF A CANYON WIND EVENT...WITH WIND
GUSTS GENERALLY EXPECTED TO REMAIN NEAR OR BELOW WHAT WOULD MEET
WIND ADVISORY CRITERIA.

.LONG TERM (AFTER 00Z TUESDAY)...THE BROAD...DISSIPATING TROUGH IS
EXITING THE REGION TO THE EAST LATE MONDAY...WITH DRIER AIR
GENERALLY WORKING INTO UTAH FROM THE WEST. HOWEVER...MODELS ALREADY
HAVE MAJOR DISCREPANCIES HEADING INTO TUESDAY...AS THE GFS AND
CANADIAN SLOWLY BUT SURELY BUILD HIGH PRESSURE OVER THE
REGION...WHILE THE ECMWF BRINGS A CLOSED LOW INTO SOUTHWEST WYOMING
AND NORTHERN UTAH FROM THE NORTHEAST MONDAY NIGHT THROUGH WEDNESDAY.

THE ECMWF DEFINITELY SEEMS TO BE AN OUTLIER...BUT CANNOT RULE IT
OUT...ESPECIALLY SINCE IT HAS HAD THE SAME SOLUTION AT LEAST A
COUPLE RUNS IN A ROW. HAVE MAINTAINED SOME LOW-END POPS AND CLOUD
COVER IN THE NORTHEASTERN PORTIONS OF THE CWA TUESDAY AFTERNOON TO
ACCOUNT FOR THE EC...BUT HAVE GENERALLY KEPT THE TEMPERATURES
SOMEWHAT CLOSER TO THE GFS/CANADIAN SUGGESTED VALUES.

MODELS CONVERGE ONCE AGAIN ON THURSDAY...WITH SIGNIFICANTLY
WARMER HIGH PRESSURE OVER THE INTERMOUNTAIN WEST...AND INCREASING
SOUTHERLY FLOW AHEAD OF A LARGE PACIFIC TROUGH. THAT TROUGH LOOKS
TO MOVE INTO THE CWA LATE FRIDAY INTO SATURDAY...SO HAVE RAISED
POPS AND LOWERED TEMPS A BIT FOR THIS PERIOD. THIS TROUGH LOOKS TO
BE THE DOMINANT WEATHER FEATURE THROUGH AT LEAST SATURDAY AND
POSSIBLY THROUGH SUNDAY NEXT WEEKEND.

&&

.AVIATION...THERE IS A 30 PERCENT CHANCE THAT SHOWERS WILL IMPACT
THE SLC TERMINAL THROUGH TONIGHT...AND AN EVEN LOWER CHANCE THAT A
THUNDERSTORM COULD DIRECTLY IMPACT THE AREA. MOST LIKELY IMPACTS
WOULD BE BRIEF ERRATIC WINDS AND CEILINGS BELOW 7000FT.
OTHERWISE...EXPECT WINDS TO SWITCH TO THE SOUTHEAST AROUND 02-04Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY
     AFTERNOON FOR UTZ001-002.

WY...NONE.
&&

$$

SHORT TERM...CONGER
LONG TERM/AVIATION...SCHOENING

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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