Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 182157
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
357 PM MDT THU SEP 18 2014

.SYNOPSIS...AN UPPER TROUGH WILL SLOWLY ADVANCE INTO THE WESTERN
GREAT BASIN TODAY THROUGH TONIGHT THEN FORM A CLOSED LOW OFF THE
SOUTHERN CALIFORNIA COAST BY LATE FRIDAY. MOISTURE WILL INCREASE
ACROSS UTAH TODAY AHEAD OF THIS TROUGH AND REMAIN INTO FRIDAY.



&&

.DISCUSSION...A PACIFIC TROUGH HAS MOVED INTO THE GREAT BASIN THIS
AFTERNOON...AND HAS BEGUN IMPACTING NORTHERN UTAH. THUNDERSTORMS
IN THE FAR NORTHWEST CORNER OF UTAH HAVE BEEN INCREASING IN
INTENSITY THROUGH THE AFTERNOON...WITH AT LEAST ONE STORM
APPEARING SEVERE WITH STRONG ROTATION. A FEW ISOLATED STORMS HAVE
POPPED UP IN THE WARM SECTOR AHEAD OF THE TROUGH...BUT FOR THE
MOST PART CONVECTION ACROSS THE STATE HAS BEEN SURPRISINGLY
SUPPRESSED...DESPITE GOOD MOISTURE IN PLACE. HAVE MAINTAINED
SLIGHT CHANCE POPS IN THE SOUTHERN AND EASTERN VALLEYS THROUGH THE
00Z TO 12Z TIMEFRAME...BUT THE CHANCE FOR ANY SIGNIFICANT
CONVECTION IN THE SOUTHERN HALF OF THE CWA IS LOOKING SLIMMER BY
THE MINUTE.

ALSO DECREASING IN CONFIDENCE IS THE RAIN THAT IS EXPECTED TO MOVE
ACROSS THE WASATCH FRONT AND INTO SOUTHWEST WYOMING THIS EVENING
AND OVERNIGHT. STILL THINK RAINFALL IS LIKELY...BUT QPF OVER THE
LAST 36 HOURS HAS DECREASED AND BECOME MORE MOTH-EATEN IN VARIOUS
MODELS...SO IT IS NOT THE SLAM DUNK THAT IT LOOKED LIKE A COUPLE
DAYS AGO. PART OF THE REASON FOR THIS IS THAT THE LOW IS CUTTING
OFF MORE QUICKLY...PUSHING SOME OF THE DYNAMICS FURTHER SOUTH AND
WEST...AS WELL AS THE FACT THAT THE NORTHERN BRANCH OF THE TROUGH
IS PRIMARILY REMAINING NORTH OF THE AREA.

SHOWERS ARE GENERALLY EXPECTED TO DECREASE IN COVERAGE THROUGH
THE DAY FRIDAY...AS DRIER AIR FILTERS INTO THE CWA. THIS DRYING
WILL BE SHORT-LIVED...AS THE CLOSED LOW OVER SOUTHERN CALIFORNIA
PUSHES MOISTURE BACK INTO UTAH FROM THE SOUTH LATE SATURDAY.
PRECIPITATION ASSOCIATED WITH THE EASTERN EDGE OF THIS LOW IS
PROGGED TO MOVE INTO CENTRAL AND NORTHERN UTAH SATURDAY NIGHT AND
SUNDAY...WITH SHOWERS POTENTIALLY LINGERING INTO MONDAY AS THE LOW
IS OVERHEAD...BEFORE THE LOW EVENTUALLY EXITS INTO WYOMING. HAVE
CONTINUED TO INCREASE POPS FOR THIS SYSTEM...ESPECIALLY SATURDAY
NIGHT AND SUNDAY.

BEHIND THE LOW...HIGH PRESSURE WILL BUILD OVER THE GREAT BASIN
TUESDAY AND WEDNESDAY...BRINGING A WARMING AND DRYING TREND TO THE
AREA. BOTH THE ECMWF AND GFS BRING A LARGE TROUGH INTO THE WEST
COAST WEDNESDAY AND THURSDAY...BUT RECENT MODEL RUNS HAVE SLOWED
THE EASTWARD PROGRESSION OF THIS SYSTEM...LEAVING THE
INTERMOUNTAIN WEST IN THE WARM SECTOR THROUGH AT LEAST THURSDAY
AND POSSIBLY INTO FRIDAY. HAVE WARMED TEMPERATURES FOR WEDNESDAY
AND THURSDAY TO ACCOUNT FOR THIS SLOWER SOLUTION...WITH A WARM
AIRMASS AND INCREASINGLY STRONG SOUTHERLY FLOW HEADING INTO THE
END OF THE WORK WEEK.

&&

.AVIATION...GUSTY SOUTH WINDS THIS AFTERNOON ARE EXPECTED TO
PERSIST INTO THE EVENING HOURS. HOWEVER...THERE IS A 20 PERCENT
CHANCE THAT A SWITCH TO NORTHWEST WINDS ASSOCIATED WITH THE LAKE
BREEZE WILL OCCUR BETWEEN 2300 UTC AND 0100 UTC. THERE IS 40 PERCENT
CHANCE THAT A THUNDERSTORM WILL IMPACT THE TERMINAL BETWEEN 2300 UTC
AND 0400 UTC. HOWEVER...THERE IS A GREATER LIKELIHOOD THAT GUSTY
ERRATIC WINDS FROM NEARBY CONVECTION WILL IMPACT THE TERMINAL.

&&

.FIRE WEATHER...MOISTURE IN PLACE ACROSS NORTHERN AND CENTRAL UTAH
WILL MAINTAIN A THREAT FOR SHOWERS AND THUNDERSTORMS CAPABLE OF
PRODUCING WETTING RAINS THROUGH FRIDAY MORNING. HIGH PRESSURE
WILL BRING A BRIEF DRYING TREND LATER FRIDAY INTO SATURDAY. A
LOW PRESSURE SYSTEM WILL CROSS THE REGION DURING THE LATTER HALF
OF THE WEEKEND INTO EARLY NEXT WEEK BRINGING ANOTHER CHANCE FOR
SHOWERS AND THUNDERSTORMS CAPABLE OF PRODUCING WETTING RAINS.

&&

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

$$

PUBLIC...SCHOENING
FIRE WEATHER...SEAMAN
AVIATION...GRAHAM

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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