Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 232204
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
404 PM MDT THU OCT 23 2014

.SYNOPSIS...HIGH PRESSURE ALOFT BUILDING TO THE EAST OF UTAH WILL
BRING A WARMING TREND TO THE AREA THROUGH SATURDAY. A COLD FRONT
APPROACHING FROM THE WEST WILL GENERATE WINDY CONDITIONS ON
SATURDAY...FOLLOWED BY PRECIPITATION ACROSS NORTHERN UTAH AND
MUCH COLDER TEMPERATURES STATEWIDE LATE IN THE WEEKEND.

&&

.SHORT TERM (UNTIL 12Z SUNDAY)...HIGH PRESSURE ALOFT BUILDING
NORTHWARD FROM THE DESERT SOUTHWEST/SOUTHERN ROCKIES WILL GENERATE
A WARMING TREND THE NEXT COUPLE OF DAYS. THE MAIN SHORT TERM
CONCERNS THE NEXT COUPLE OF DAYS WILL FOCUS ON THE POTENTIAL FOR
RECORD TEMPERATURES AND STRONG WINDS SATURDAY.

THE VORTICITY LOBE CURRENTLY ROTATING THROUGH THE SOUTHWEST FLANK
OF THE VORTEX OVER THE GULF OF ALASKA WILL REACH THE PACIFIC
NORTHWEST COAST EARLY SATURDAY. COLD AIR ASSOCIATED WITH THIS
FEATURE WILL WORK EASTWARD INTO THE GREAT BASIN...WITH THE SURFACE
COLD FRONT BECOMING BETTER DEFINED AS IT CROSSES NEVADA SATURDAY
AFTERNOON. THIS ADVANCING SURFACE FRONT COMBINED WITH GOOD MIXING
IN THE STRONG SOUTHWEST FLOW OVER THE BASIN SHOULD CREATE STRONG
SOUTHERLY WINDS AND TEMPERATURES HOVERING AROUND RECORD LEVELS.

CONVECTIVE PRECIP NOT EXPECTED TO BE AN ISSUE AHEAD OF THE SURFACE
FRONT AS THE DEEP LAYER INSTABILITY WILL LAG BACK WITH THE COLD
AIR ALOFT OVER WESTERN IDAHO/NORTHWEST NEVADA. THE FIRST THREAT OF
ORGANIZED CONVECTION MAY HOLD OFF UNTIL LATE SATURDAY NIGHT. A
SHORTWAVE ROTATING NORTHEAST BEHIND THE FRONT WILL DRAG ENOUGH
COLD AIR IN AT THE MID-LEVELS TO SUPPORT DEEP INSTABILITY AND
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ACROSS THE FAR NORTHERN
ZONES LATE SATURDAY NIGHT/EARLY SUNDAY.

&&

.LONG TERM (AFTER 12Z SUNDAY)...THE COLD FRONT IS EXPECTED TO BE
RIGHT ON THE DOORSTEP OF UTAH EARLY SUNDAY MORNING...THOUGH TIMING
DIFFERENCES STILL REMAIN AMONG THE MODEL SOLUTIONS. THE ECMWF IS
STILL ABOUT 6 HOURS FASTER THAN THE GFS WITH THE TIMING OF THE
BOUNDARY AND ONSET OF PRECIP ACROSS MUCH OF THE NORTHERN THIRD OF
THE CWA...WITH THE FRONTAL PASSAGE EARLY SUNDAY MORNING...COMPARED
TO SUNDAY AFTERNOON IN THE GFS. HAVE CONTINUED TO INCREASE POPS
DURING THE DAY SUNDAY...AS MODELS ARE PRODUCING AT LEAST SOME
PRECIPITATION AS THE FRONT PUSHES THROUGH THE AREA...THOUGH NOT WITH
PARTICULARLY HIGH QPF VALUES.

HAVE ALSO INCREASED WIND SPEEDS FOR SUNDAY AFTERNOON AND EVENING
POST-FRONTALLY...AS THERE LOOKS TO BE A GOOD MSLP GRADIENT AND
DECENT WINDS ALOFT BEHIND THE FRONT. ONE OF THE LARGER UNCERTAINTIES
IN THE FORECAST IS HOW LONG SHOWERS WILL CONTINUE ACROSS NORTHERN
UTAH SUNDAY NIGHT AND MONDAY...AS A SECOND PIECE OF THE TROUGH MOVES
OVER THE AREA. IT IS WITH THIS WAVE THAT 700MB TEMPERATURES DROP TO
-8 CELSIUS IN THE NORTH...BUT IT IS LESS CERTAIN WHETHER THE 500MB
COLD POOL WILL MOVE OVER THE AREA...OR REMAIN NORTH OVER IDAHO AND
WYOMING. FOR NOW...HAVE KEPT A 20 PERCENT POP ACROSS THE NORTHERN
VALLEYS THROUGH THE DAY MONDAY TO ACCOUNT FOR THE POSSIBILITY OF
LINGERING SHOWERS.

THE TROUGH IS PROGGED TO EXIT THE REGION THROUGH THE LATTER HALF OF
MONDAY...WITH SHORTWAVE RIDGING BUILDING FOR MONDAY NIGHT. ONE
SIGNIFICANT DIFFERENCE IN THE 12Z GFS IS THAT IT NOW CLEARS THE
SKIES MONDAY NIGHT...AS OPPOSED TO BRINGING IN SOME ADDITIONAL CLOUD
COVER IN THE ZONAL FLOW AS IT DID YESTERDAY. THIS COULD LEAD TO A
COLDER NIGHT IN THE VALLEYS AND BASINS OF UTAH...AS THAT COLDEST
AIRMASS OF THE SEASON SO FAR REMAINS BEHIND IN THE LOWEST LEVELS.
HAVE LOWERED TEMPERATURES FOR MONDAY NIGHT/TUESDAY MORNING IN THE
FORECAST...AND THERE IS A CHANCE THESE STILL ARE NOT COLD
ENOUGH...AS THE GUIDANCE HAS YET TO SEE A GOOD COLD FRONT LIKE THIS
ONE SO FAR THIS SEASON.

FOR TUESDAY...BOTH THE GFS AND ECMWF BUILD A RIDGE OVER THE WEST
COAST...PUTTING THE CWA IN A COOL WEST-NORTHWEST FLOW ALOFT. ONE
DIFFERENCE BETWEEN THEM IS THE LOCATION OF THE NORTHERN STORM TRACK.
THE EC KEEPS IT SOMEWHAT FURTHER NORTH AND AWAY FROM THE
AREA...WHILE THE GFS DRAGS SOME MOISTURE AND INSTABILITY DOWN TO FAR
NORTHERN UTAH...POTENTIALLY PRODUCING SOME SHOWERS AND CLOUD COVER.
HAVE INTRODUCED SOME SLIGHT CHANCE POPS FOR THE CACHE VALLEY ON
TUESDAY NIGHT AND WEDNESDAY TO ACCOUNT FOR THIS THREAT. EITHER
WAY...BOTH GLOBAL MODELS SHIFT THE RIDGE OVER THE GREAT BASIN
THROUGH THE DAY WEDNESDAY...LEADING TO DRYING AND WARMING CONDITIONS
FOR THE LATTER HALF OF THE WEEK.

&&

.AVIATION...WINDS AT THE SLC TERMINAL SHOULD SWITCH BACK TO THE
SOUTHEAST BETWEEN 02Z AND 04Z...WITH A SLIGHT CHANCE THAT THE SWITCH
OCCURS AS EARLY AS 01Z. VFR CONDITIONS WILL PREVAIL THROUGH TONIGHT
UNDER CLEARING SKIES.

&&

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