224  
FXUS65 KSLC 202232  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
432 PM MDT WED OCT 20 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 MDT SATURDAY)
 
 
SCATTERED TO BROKEN MID / HIGH CLOUDS CONTINUE TO STREAM IN FROM THE  
WEST THIS AFTERNOON. EXPECT THESE CLOUDS TO CONTINUE INCREASING  
OVERNIGHT, LEADING TO SLIGHTLY WARMER OVERNIGHT TEMPERATURES. SKIES  
LOOK TO CLEAR AGAIN THROUGH THE LATE MORNING HOURS AS HIGH PRESSURE  
CONTINUES TO BUILD ACROSS THE AREA AND WILL DOMINATE AGAIN ON  
THURSDAY. ON FRIDAY, FLOW TURNS TOWARD THE SOUTHWEST AHEAD OF AN  
APPROACHING TROUGH OVER THE WEST CONUS COAST. MODELS SHOW THIS  
TROUGH AXIS PASSING THROUGH THE FORECAST AREA ON FRIDAY EVENING.  
THANKS TO THIS DISTURBANCE, PRECIPITATION CHANCES INCREASE SLIGHTLY  
STARTING ON FRIDAY UP NORTH. AS THE LARGE PARENT MID LEVEL LOW GETS  
CLOSER TO THE PACIFIC NW, PRECIPITATION CHANCES CONTINUE TO  
GRADUALLY INCREASE ACROSS NORTHWEST UTAH AS MOISTURE BECOMES MORE  
PRONOUNCED OVER THE FORECAST AREA THROUGH FRIDAY NIGHT.  
   
LONG TERM (AFTER 12Z/6AM MDT SATURDAY)
 
 
LOW PRESSURE SPINNING OFF THE GULF OF ALASKA WILL BE DRIVING AN  
UNSETTLED WEATHER PATTERN THROUGH THE LONG TERM. THE FIRST TROUGH  
EJECTED FROM SAID LOW WILL CLIP THE NORTHWEST CORNER OF UTAH BY  
SATURDAY MORNING, SHIFTING THE RIDGE OF HIGH PRESSURE EAST AND  
TRANSITIONING MID-LEVEL FLOW FROM THE SOUTHWEST TO MORE ZONAL.  
STRONG WESTERLY WINDS ACROSS NORTHERN UTAH WILL TRANSPORT LEFT OVER  
MOISTURE FROM AN ATMOSPHERIC RIVER (AR) EVENT ACROSS THE NORTHERN  
WASATCH SATURDAY INTO SUNDAY. VARIABILITY WITH THIS FIRST PULL OF  
MOISTURE IS EVEN APPARENT IN CLUSTER ANALYSES ON DAY 3, WHICH WOULD  
ATTRIBUTE TO NOTABLE DIFFERENCES DETECTED IN DETERMINISTIC GUIDANCE.  
THE 00Z/ECMWF, FOR INSTANCE, PULLS MORE MOISTURE ACROSS THE REGION  
SATURDAY AFTERNOON, AND DRAGS PRECIPITATION AND COOLER AIR FURTHER  
SOUTH THAN WHAT’S DEPICTED BY THE 12Z/GFS. THUS, SOME UNCERTAINTY  
STILL LIES WITH THE EVOLUTION OF THIS FIRST SYSTEM WITH REGARD TO  
TIMING AND TOTAL QPF THROUGH SUNDAY MORNING.  
 
HOWEVER, BY THIS TIME, A DEEPER AND ANOMALOUSLY LOWER TROUGH WILL BE  
PRIMING THE PUMP FOR ANOTHER SURGE OF MOISTURE, AS THE NEXT LOW DIPS  
SOUTH ALONG THE PACIFIC NORTHWEST. EVEN THOUGH DISCREPANCIES PERSIST  
WITH THE DEPTH AND TIMING OF THE APPROACHING SYSTEM, THERE IS HIGHER  
CONFIDENCE IN A STRONG AR IMPACTING THE REGION EARLY NEXT WEEK.  
PRECIPITABLE WATER VALUES ARE ESTIMATED TO INCREASE BY 200 TO 300  
PERCENT OF NORMAL BY MONDAY NIGHT, RESULTING IN WIDESPREAD  
PRECIPITATION CONTINUING INTO TUESDAY NIGHT. TOTAL QPF VALUES RANGE  
FROM 1.5 TO 2.0 INCHES OVER THE CENTRAL NORTHERN WASATCH AND WESTERN  
UINTAS BY THE TIME THIS SYSTEM EXITS ON WEDNESDAY. IN ADDITION,  
EXPECT COLDER AIR ASSOCIATED WITH THE SECOND SYSTEM, DROPPING DAILY  
HIGHS 5 TO 10 DEGREES BY MID-WEEK. DESPITE TIMING DIFFERENCES EARLY  
ON IN THE LONG TERM PERIOD, FORECAST GUIDANCE AND ENSEMBLE MEANS  
CONTINUE TO FAVOR A WET PERIOD FROM DAY 5 THROUGH DAY 7.  
 

 
   
AVIATION...KSLC
 
CONTINUED VFR CONDITIONS ARE EXPECTED FOR THE  
DURATION OF THE VALID TAF PERIOD. MID AND HIGH CLOUD COVER WILL  
REMAIN FOR THE MAJORITY OF THE DAY AND OVERNIGHT. GENERALLY LIGHT  
WINDS ARE EXPECTED WITH A BRIEF PERIOD OF NORTHWEST FLOW THIS  
EVENING BEFORE RETURNING TO A SOUTHEAST DRAINAGE FLOW OVERNIGHT.  
 
REST OF UTAH AND SOUTHWEST WYOMING...LINGERING FOG AND LOW STRATUS  
SHOULD CLEAR FROM VALLEY LOCATIONS STATEWIDE. MID LEVEL CLOUD DECKS  
WILL REMAIN ACROSS MUCH OF THE FORECAST AREA, WITH PATCHY MOUNTAIN  
OBSCURATION POSSIBLE, ESPECIALLY EARLY IN THE AFTERNOON BUT THINNING  
INTO THE EVENING. GENERALLY LIGHT WINDS ARE EXPECTED AT ALL  
TERMINALS THROUGHOUT THE DAY AND OVERNIGHT.  
 

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

 
 

 
 
STEARNS/WALTER/WESSLER  
 
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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