779  
FXUS65 KSLC 182205  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
405 PM MDT FRI SEP 18 2020  
   
SYNOPSIS
 
AN UPPER LEVEL TROUGH MOVING EAST THROUGH THE NORTHERN  
ROCKIES WILL BRING SHOWERS AND ISOLATED THUNDERSTORMS TO NORTHERN  
UTAH LATE TONIGHT THROUGH SATURDAY. COOLER, MORE SEASONAL  
TEMPERATURES ARE EXPECTED THROUGH THE WEEKEND. A WARMING TREND  
WILL ONCE AGAIN OCCUR NEXT WEEK.  
 

 
   
SHORT TERM (THROUGH 12Z MONDAY)
 
LATEST H5 ANALYSIS INDICATES  
THE UPSTREAM TROUGH IS TRENDING TO OPEN WHILST PHASING SLIGHTLY  
NEGATIVELY TILTED AS EXPECTED. DOWNSTREAM OF THE TROUGH AND  
LOCALLY A BROAD AREA OF UPPER DIFFLUENCE REMAINS IN PLACE ACROSS  
THE EASTERN GREAT BASIN, THIS MAINTAINING A WIDESPREAD MID/UPPER  
CLOUD SHIELD ACROSS WESTERN PORTIONS OF THE FORECAST AREA. A VERY  
DRY SUB CLOUD LAYER REMAINS PRESENT, AND LACK OF INSTABILITY  
PRECLUDES AND POTENTIAL FOR PRECIP UNTIL FRONTAL PASSAGE LATE  
TONIGHT, AND LARGELY, SATURDAY MORNING.  
 
NOT MUCH HAS CHANGED REGARDING TIMING OR SIGNIFICANCE OF THE  
FRONTAL PASSAGE, OUTSIDE OF A SLIGHT TREND IN MODELS LIFTING THE  
CORE OF UPPER SUPPORT (COINCIDENT WITH THE INCREASINGLY NEGATIVE  
TILTED TROUGH) NORTH A BIT FASTER TOMORROW MORNING. WITH THIS  
HAVE SLIGHTLY LOWERED POPS/QPF ACROSS THE CENTRAL WASATCH AND  
POINTS SOUTH A SKOSH. THE MAIN FOCUS FOR PRECIP POTENTIAL REMAINS  
ACROSS THE NW, UT/ID BORDER REGION, AND NORTHERN MOUNTAINS WHERE  
WETTING CONDITIONS REMAIN LIKELY.  
 
AN ADDITIONAL NOTE FOR SATURDAY, MID LEVEL LAPSE RATES ACROSS THE  
UT/ID BORDER WILL STEEPEN ENOUGH FOR MODEST INSTABILITY DURING  
THE MIDDAY AND AFTERNOON HOURS. CAN'T RULE OUT ISOLATED BUT SEMI-  
ORGANIZED CONVECTION IN THIS AREA, THOUGH THE MOST LIKELY SCENARIO  
IS THAT THIS WILL REMAIN JUST NORTH OF THE BORDER PER BULK OF CAMS.  
 
AREAS SOUTH AND EAST OF THE FRONT SATURDAY WILL REMAIN WARM, DRY  
AND BREEZY. THIS ESPECIALLY HOLDS TRUE FOR THE SOUTHEAST WHERE  
CRITICAL FIRE WEATHER CONDITIONS ARE ANTICIPATED ONCE AGAIN. SEE  
THE FIRE WEATHER DISCUSSION AND LATEST RFW FOR ADDITIONAL INFO ON  
THIS.  
 
HEIGHTS WILL BEGIN TO BUILD IN RAPIDLY FROM THE WEST SATURDAY  
AFTERNOON/EVE AS THE UPPER TROUGH LIFTS MORE TO THE NORTHEAST AND  
DEEPER INTO THE NORTHER ROCKIES REGION. WITH THIS, RAPID  
DRYING/CLEARING IS EXPECTED FROM WEST TO EAST. SENSIBLY, IT SHOULD  
BE QUITE PLEASANT LATER SATURDAY, WITH TEMPS TRENDING DOWN SOME 5  
DEGREES BELOW NORMAL UNDER CLEARING SKIES. THIS WILL HOLD TRUE  
FOR SUNDAY AS WELL, THOUGH TEMPS SHOULD REBOUND A BIT MORE TOWARDS  
SEASONAL NORMS.  
   
LONG TERM (AFTER 12Z MONDAY)
 
AN UPSTREAM TROUGH OVER THE PACIFIC  
NORTHWEST WILL INCREASE SOUTHWEST FLOW AND DRAW MOISTURE INTO THE  
REGION MONDAY. THE DRIEST CONDITIONS, WITH RH VALUES AROUND 15-20%  
WILL BE THROUGH FAR WESTERN UTAH. THAT'S ALSO WHERE INCREASED WIND  
GUSTS TO AROUND 30 KTS ARE EXPECTED. MOST MOISTURE, SHOWN  
CONSISTENTLY BY GUIDANCE, HAS HIGHER PWAT VALUES INCREASING TO  
ROUGHLY 0.75" MONDAY EVENING MAINLY OVER CENTRAL TO EASTERN UTAH.  
THERE'S NOT MUCH TO WORK WITH BESIDES THAT, AS LOW LEVELS WILL BE  
DRY AND THERE'S NOT MUCH DYNAMIC SUPPORT AT THAT TIME FOR MUCH  
RAINFALL.  
 
AS RIDGING BUILDS IN TUESDAY, EXPECT DRIER CONDITIONS, BUT ALSO  
LIGHTER WINDS THROUGH THE WESTERN PART OF UTAH. THE STRONGER GUSTS  
WILL BE TOWARDS CENTRAL AND EASTERN UTAH, WHERE THE MOISTURE FROM  
MONDAY WILL BE LINGERING. THE BEST CHANCES FOR RAIN MOVE INTO THE  
UINTAS AND EAST.  
 
HIGH PRESSURE SETTLING IN BY THE MIDDLE OF THE WEEK WILL INHIBIT  
POP'S AND CLOUD COVER. DRIER CONDITIONS WILL BRING DAYTIME HIGHS  
INTO THE LOW TO MID 80S WEDNESDAY AND THURSDAY.  
 
MODELS BRING IN A SIMILAR SETUP TO THIS WEEKEND BY NEXT WEEKEND,  
LIKELY PROVIDING COOLER CONDITIONS AND ADDED MOISTURE.  
 
 

 
   
AVIATION
 
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD.  
PERIODIC GUSTY SOUTH WINDS WILL PERSIST UNTIL 02Z-03Z AND REMAIN  
PREDOMINANTLY OUT OF THE SOUTH UP TO 15 KNOTS UNTIL A COLD FRONT  
PASSAGE AROUND 09Z. BEHIND THE FRONT EXPECT SCATTERED SHOWERS AND  
WEST TO NORTHWEST WINDS THROUGH THE END OF THE TAF PERIOD.  
 

 
   
FIRE WEATHER
 
JUST NOW SEEING THE STRONGER SOUTHWESTERLY FLOW ALOFT  
SPREADING EAST ACROSS THE AREA THIS AFTERNOON, AND HAVE NOTED THE  
ANTICIPATED UPTICK IN WIND GUSTS MEETING CRITICAL THRESHOLDS  
ACROSS MUCH OF THE WESTERN HALF OF UTAH. WINDS WILL CONTINUE TO  
INCREASE INTO THIS EVENING. WIDESPREAD RED FLAGS REMAIN IN PLACE  
THROUGH 9PM THIS EVENING.  
 
SIGNIFICANT MID/UPPER CLOUD COVER RESIDES ACROSS MUCH OF THE  
DISTRICT THIS AFTERNOON, WHILE THE ANTICIPATED COLD FRONT  
CONTINUES TO TAKE FORM OVER THE CENTRAL GREAT BASIN. NOT MUCH HAS  
CHANGED IN REGARDS TO THIS FRONT, WITH PASSAGE ACROSS THE NORTH  
LATER TONIGHT INTO SATURDAY MORNING, THEN AN EXPECTED STALLING  
ACROSS CENTRAL PORTIONS MID/LATE SATURDAY. BEHIND AND NORTH OF  
THIS FRONT TEMPS WILL BE MUCH COOLER, AND WETTING RAIN POTENTIAL  
REMAINS (LARGELY NORTH OF I-80 AND IN THE UINTA MOUNTAINS). SOUTH  
AND EAST OF THIS FRONT WARM, DRY, AND BREEZY WILL BE MAINTAINED  
THROUGH SATURDAY PRIOR TO ANY COOL DOWN (NAMELY SUNDAY) AND A  
RED FLAG REMAINS IN PLACE THROUGH THAT TIME ACROSS THE SOUTHEAST.  
 
DO NOT FORESEE ANY CRITICAL FIRE WEATHER CONDITIONS ON SUNDAY.  
EARLY NEXT WEEK THE POTENTIAL WILL AGAIN CLIMB ACROSS WESTERN  
PORTIONS AS YET ANOTHER MODEST BELT OF SOUTHWESTERLY FLOW ALOFT  
WILL SPREAD IN. WILL HAVE TO WATCH THE NET DRYING AFTER DECENT RH  
RECOVERY LATE WEEKEND, BUT WINDS SHOULD BE THERE FOR SOME WESTERN  
AREAS. WILL KEEP YOU POSTED MOVING FORWARD.  
 

 
   
SLC WATCHES/WARNINGS/ADVISORIES
 
 
UT...RED FLAG WARNING UNTIL 9 PM MDT SATURDAY FOR UTZ489-494-498.  
 
RED FLAG WARNING UNTIL 9 PM MDT THIS EVENING FOR UTZ478-479-483-  
484-488-492-493-495>497.  
 
WY...NONE.  

 
 

 
 
MERRILL/WILSON  
 
FOR MORE INFORMATION FROM NOAA'S NATIONAL WEATHER SERVICE VISIT...  
HTTP://WEATHER.GOV/SALTLAKECITY  
 
FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION  
VISIT...  
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP  
 
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