644  
FXUS65 KSLC 210910  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
310 AM MDT THU OCT 21 2021  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL BUILD INTO THE REGION THROUGH FRIDAY. A WEAK  
DISTURBANCE WILL CLIP NORTHERN UTAH SATURDAY WITH A MORE  
SIGNIFICANT STORM TO IMPACT THE ENTIRE AREA LATE SUNDAY INTO EARLY  
NEXT WEEK.  
 

 
   
SHORT TERM (THROUGH 12Z/6AM SUNDAY)
 
 
EARLY THIS MORNING A WEAK WAVE ROUNDING THE TOP OF A LONGWAVE  
RIDGE OVER THE SOUTHWEST IS PUSHING A BAND OF MID AND HIGH LEVEL  
CLOUD COVER ACROSS THE STATE. THIS WAVE WILL PUSH TO OUR EAST  
TODAY, WHILE THE RIDGE AXIS AMPLIFIES OVER UTAH. THUS MORNING  
CLOUDS ARE EXPECTED TO SWEEP SOUTHEASTWARD WITH CLEARING SKIES  
ACROSS THE NORTHERN 2/3RDS OF UTAH TODAY, WHILE SOME CLOUD COVER  
LINGERS NEAR THE ARIZONA BORDER THROUGH THE AFTERNOON.  
TEMPERATURES WILL MODERATE WITH DRY CONDITIONS ACROSS THE STATE  
UNDER THE RIDGE, WITH HIGHS NEAR TO SLIGHTLY ABOVE NORMAL.  
 
SOUTHWESTERLY FLOW WILL INCREASE ACROSS WESTERN UTAH ON FRIDAY AS  
A TROUGH MOVES IN ALONG THE PACIFIC NORTHWEST COAST AND A  
SHORTWAVE EJECTS FROM NORTHERN CALIFORNIA TO WESTERN MONTANA. THE  
THERMAL RIDGE AXIS WILL SHIFT EASTWARD OVER UTAH, AND WHEN  
COMBINED WITH BETTER MIXING OVER WESTERN UTAH WILL BRING HIGH  
TEMPERATURES RUNNING 5-10 DEGREES ABOVE AVERAGE. HOWEVER, A LACK  
OF MIXING IN EASTERN BASINS WILL MAINTAIN ONLY NEAR NORMAL  
TEMPERATURES.  
 
BY SATURDAY, THE MEAN TROUGH WILL SETTLE IN PLACE OVER THE PACIFIC  
NORTHWEST AND NORTHERN ROCKIES, PLACING UTAH UNDER ACTIVE ZONAL  
FLOW WITH DISORGANIZED EMBEDDED SHORTWAVES. THIS WILL DRIVE  
SHOWERS MAINLY OVER NORTHERN UTAH, BUT WITH SCATTERED ACTIVITY  
REACHING SOUTHWARD INTO CENTRAL UTAH AS WELL. THIS MILD PACIFIC  
FLOW WILL MAINTAIN FAIRLY HIGH SNOW LEVELS DURING THIS EVENT,  
GENERALLY ABOVE 7500 FEET IN NORTHERN UTAH AND 8500 FEET INTO  
CENTRAL UTAH. PRECIPITATION TOTALS WILL BE ON THE LIGHT SIDE FROM  
THIS INITIAL STORM SYSTEM, WITH NORTHERN UTAH VALLEYS SEEING  
AROUND 0.1 TO 0.3 INCHES OF WATER, WHILE NORTHERN MOUNTAINS WILL  
GENERALLY SEE AROUND 0.2 TO 0.4 INCHES OF WATER WITH LOCALLY  
HIGHER AMOUNTS.  
   
LONG TERM (AFTER 12Z/6AM SUNDAY)
 
 
CLUSTER MODEL FORECASTS ARE GENERALLY CONFIDENT IN THE WEATHER  
FORECAST SUNDAY WITH PERHAPS SLIGHT UNCERTAINTIES REGARDING  
STRENGTH OF A WEAK SHORTWAVE TROUGH EXITING NORTHERN UTAH.  
LINGERING MOISTURE MAY ALLOW FOR AREAS OF VALLEY RAIN AND MOUNTAIN  
SNOW. UTAH WILL THEN BE IN THE WARM SECTOR OF THE NEXT  
APPROACHING WEATHER SYSTEM THE REMAINDER OF THE DAY AND INTO  
MONDAY.  
 
IMPACTFUL WEATHER CONDITIONS REMAIN FORECAST INTO TUESDAY WITH THE  
ARRIVAL OF A DEEP AREA UPPER LEVEL TROUGH FROM THE WEST. CLUSTER  
MODEL FORECAST INDICATE UNCERTAINTIES IN THE STRENGTH OF THIS  
APPROACHING TROUGH BUT ARE MORE CONFIDENT IN ITS POSITION OVER THE  
WEST COAST AT THE START OF THE UPCOMING WORK WEEK. AT ATMOSPHERIC  
RIVER REMAINS IN THE FORECAST ACROSS THE WEST COAST, WITH THE GEFS  
ENSEMBLE MEAN IWVT INDICATING AT LEAST 450 KG / MS ACROSS WESTERN  
UTAH. PRECIP CHANCES WILL INCREASE FROM WEST TO EAST PRIMARILY IN  
THE FORM OF RAIN. SNOW LEVELS AT THIS POINT ARE EXPECTED TO BE  
AROUND 10,000 FT. A CHANCE OF THUNDER ALSO CAN'T BE RULED OUT MONDAY  
EVENING. A COLD FRONT IS EXPECTED TO PASS THROUGH THE REGION MONDAY  
INTO TUESDAY MORNING WITH SNOW LEVELS DROPPING THROUGH THE DAY. THIS  
WOULD ALLOW FOR ADDITIONAL AREAS FOR SNOW SHOWERS AT THAT TIME WITH  
ACCUMULATING SNOW ABOVE 7,000 FT.  
 
THE WIND FORECAST ALONE IS CERTAINLY ONE TO KEEP AN EYE ON. A 60+ KT  
700 MB JET WILL FORM ACROSS WESTERN UTAH EARLY MONDAY AND PLANT  
ITSELF THERE THROUGH TUESDAY MORNING BEFORE THE ARRIVAL OF A COLD  
FRONT. SEVERAL MODELS ARE INDICATING THIS EVENT WILL BE AN ANOMALOUS  
ONE AND ONE THAT WILL SURELY LEAD TO LEAD A WIND HEADLINE OF SOME  
SORT (WIND OR HIGH WIND). FOR EXAMPLE, THE ECMWF STANDARDIZED MODELS  
INDICATE VALUES OF 3 TO 5 (AN ANOMALOUS EVENT INDEED), PEAKING  
MONDAY EVENING. INTERESTINGLY THOUGH, SHIFT OF TAILS IS NOT  
NECESSARILY INDICATING THIS EVENT AS MUCH OF AN ANOMALOUS ONE AT  
THIS TIME. THESE WINDS WOULD BE FROM THE SOUTH OR SOUTH-SOUTHWEST  
WHICH WOULD MAKE TRAVEL MOST IMPACTED ALONG EAST-WEST ORIENTED  
ROUTES. THIS WOULD PARTICULARLY IMPACT I-80 FROM WENDOVER TO SALT  
LAKE CITY AND US-50 WEST OF DELTA.  
 
BY WEDNESDAY, THE SYSTEM LOOKS TO EXIT TO THE EAST WHILE HIGH  
PRESSURE BUILDS IN FROM THE WEST THROUGH THURSDAY.  
 

 
   
AVIATION
 
 
KSLC...HIGH PRESSURE TODAY WILL BRING LIGHT SOUTHEAST WINDS THIS  
MORNING, SHIFTING NORTHWEST THIS AFTERNOON AND EVENING BEFORE  
SWITCHING OVER AGAIN FROM THE SOUTHEAST AROUND 3Z. VFR CEILING AND  
VISIBILITIES ARE FORECAST WITH ONLY HIGH LAYER CLOUD DECKS.  
 
REST OF UTAH AND SOUTHWEST WYOMING...VFR CEILING AND VISIBILITIES  
ARE FORECAST THIS PERIOD WITH OCCASIONAL HIGH BASED CLOUD DECKS.  
LIGHT WINDS ARE GENERALLY ANTICIPATED TODAY RESULTING FROM HIGH  
PRESSURE ACROSS THE REGION.  
 

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

 
 

 
 
SHORT TERM...CHURCH  
LONG TERM...NDESMET  
AVIATION...NDESMET  
 
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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