360  
FXUS65 KSLC 152148  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
348 PM MDT MON OCT 15 2018  
   
SYNOPSIS
 
A MUCH COOLER AIR MASS WILL REMAIN IN PLACE TODAY.  
THE AREA WILL THEN SEE A STEADY WARMING TREND THROUGH MIDWEEK. A  
WEAK UPPER-LEVEL SYSTEM WILL MOVE INTO THE SOUTHEAST CORNER OF  
UTAH MIDWEEK.  
 

 
   
SHORT TERM (THROUGH 00Z FRIDAY)
 
 
POTENTIAL IMPACTS...  
* MONITORING POTENTIAL FOR CANYON/DOWNSLOPE WINDS ALONG THE WASATCH  
TOMORROW NIGHT  
* ACCUMULATING SNOW POSSIBLE SOUTHERN UTAH ABOVE 7KFT TOMORROW  
NIGHT AND WEDNESDAY  
 
ANTECEDENT CONDITIONS...  
EXCEPTIONAL DROUGHT IS OCCURRING NEAR THE FOUR CORNERS. EXTREME  
DROUGHT CONTINUES EAST OF THE GREAT SALT LAKE, UINTA BASIN, AND  
SOUTHEAST UTAH. SEVERE DROUGHT ELSEWHERE, EXCEPT MODERATE DROUGHT  
SOUTHWEST UTAH AND ALONG THE WYOMING BORDER.  
 
BIG PICTURE...  
DURING THE PAST 5 DAYS, THE PATTERN ACROSS THE PACIFIC REMAINS  
AMPLIFIED WITH STRONG SYSTEMS PROGRESSING INTO THE CENTRAL PACIFIC.  
A RIDGE DOMINATES THE EASTERN PACIFIC, WITH A POSITIVELY TILTED TROUGH  
FROM THE GREAT LAKES INTO THE SOUTHWEST CONUS.  
 
MDCARS 400MB-200MB AIRCRAFT OBSERVATIONS REVEAL A 75-125KT  
CYCLONIC JET SOUTHWEST OF ALASKA BECOMES ANTICYCLONIC OVER THE  
EASTERN PACIFIC AND WESTERN CANADA. THE UPPER LEVEL TROUGH AXIS  
WAS OVER UTAH AND SOUTHERN NEVADA.  
 
LOCAL OBSERVATIONS...  
12Z KSLC RAOB SHOWS A DRY AND STABLE AIRMASS, WITH SEVERAL  
SUBSIDENCE INVERSIONS ABOVE THE TOP OF THE MIX LAYER AT 740MB.  
WINDS ARE MODERATELY STRONG AND UNIFORM OUT OF THE NORTHEAST AT  
THE MID AND UPPER LEVELS.  
 
PRECIPITABLE WATER VALUES RANGE FROM 0.05"-0.10" CENTRAL AND  
SOUTHERN MOUNTAINS TO 0.20"-0.33" NORTHERN VALLEYS AND DIXIE.  
 
A 1030MB SURFACE ANTICYCLONE IS CENTERED OVER WESTERN COLORADO  
AND DOMINATES THE REGIONAL WEATHER. A SURFACE TROUGH EXTENDS UP  
THE SOUTHERN CALIFORNIA COAST. THIS IS CREATING A 6MB  
NORTHEASTERLY PRESSURE GRADIENT UTAH, SUPPORTING GUSTS UP TO 40  
MPH NEAR CANYONS AND FAVORED DOWNSLOPE AREAS OF SOUTHERN UTAH.  
 
24 HOUR TRENDS:  
* PRECIPITABLE WATER 0.10" LOWER, EXCEPT 0.10"-0.15" HIGHER  
NORTHWEST UTAH  
* TEMPERATURES ARE 5-15F WARMER  
* DEWPOINT DEPRESSIONS ARE MAINLY 5-20F HIGHER (DRIER)  
 
FORECAST...  
WEATHER DURING THE SHORT TERM PERIOD WILL LARGELY BE DICTATED BY  
THE CUTOFF LOW CURRENTLY OVER WESTERN ARIZONA, WHICH MEANDERS  
NORTH INTO UTAH WEDNESDAY, BEFORE ELONGATING AS A TROUGH AND  
EXITING TO THE EAST LATE THURSDAY.  
 
AFTER ANOTHER CHILLY NIGHT, EXPECT A GENERAL WARMING TREND DURING  
THE NEXT SEVERAL DAYS, PARTICULARLY NORTHERN UTAH WHERE CLOUD  
COVER WILL BE MORE SPARSE.  
 
SHOWERS LOOK TO INVADE SOUTHERN UTAH FROM ARIZONA LATE TOMORROW,  
BECOMING MORE WIDESPREAD LATE TUESDAY NIGHT AND WEDNESDAY. SREF  
INDICATES INSTABILITY INCREASES ACROSS SOUTHWEST UTAH WEDNESDAY,  
AND THE ENTIRE REGION THURSDAY, WHICH SHOULD SUPPORT AT LEAST  
ISOLATED COVERAGE BUILDING FURTHER WEST AND NORTH WITH TIME.  
 
SNOWLEVELS WILL GENERALLY BE 7KFT OR HIGHER, BUT MAY DIP LOWER  
UNDER HIGH INTENSITY PRECIPITATION. IMPACTS SHOULD BE SPOTTY AND  
OF SHORT DURATION AS IS THE NORM WITH CONVECTIVE SHOWERS  
ASSOCIATED WITH CLOSED LOWS.  
 
WILL NEED TO KEEP A CLOSE EYE ON WINDS ALONG THE WASATCH FRONT  
LATE TOMORROW NIGHT INTO WEDNESDAY MORNING. A 5MB EASTERLY  
PRESSURE GRADIENT IS IN PLACE FROM THE WASATCH FRONT TO ROCK  
SPRINGS, WITH ABOUT 2.5C OF COLD ADVECTION ON A 30KT EASTERLY  
700MB JET. THIS SETUP CERTAINLY SUPPORTS ENHANCED CANYON WINDS.  
 
THE QUESTION IS WHETHER OR NOT DOWNSLOPE WINDS, POTENTIALLY OF A  
HIGHER MAGNITUDE AND SCALE WILL DEVELOP. NAM BUFKIT FORECAST  
SOUNDING AT OGD DOESN'T REALLY SHOW A CRITICAL LAYER REQUIRED NEAR  
RIDGETOP LEVEL. INTERESTINGLY THE FV3 BUFKIT FORECAST SOUNDING FOR  
OGD DOES. IF THE GRADIENT, JET, OR MAGNITUDE OF COLD ADVECTION  
TREND JUST A BIT HIGHER, THIS MAY BE AN EVENT WORTHY OF A WIND  
ADVISORY.  
   
LONG TERM (AFTER 00Z FRIDAY)
 
 
AN ELONGATED UPPER LEVEL TROUGH WILL BE CENTERED OVER EASTERN  
UTAH THURSDAY NIGHT WHEN THE EXTENDED PERIOD OF THE FORECAST  
BEGINS. THIS TROUGH IS PART OF THE PREVIOUSLY MENTIONED CUTOFF LOW  
WHICH HAS FILLED INTO AN OPEN WAVE TROUGH. THE SOUTHERN EXTENT OF  
THE TROUGH WILL DIVE WELL SOUTH AS ITS ENERGY ATTACHES TO A  
SECOND UPPER LEVEL LOW ADVECTING EAST OVER THE SOCAL  
COAST...FORMING A SINGLE ELONGATED TROUGH FROM COLORADO TO THE  
PACIFIC OCEAN. THIS TROUGH WILL REMAIN TO THE SE OF UTAH THIS  
WEEKEND ALLOWING FOR RIDGING TO DOMINATE NORTHERN UTAH LATE FRIDAY  
AND SATURDAY.  
 
CONTINUING INTO THE WEEKEND, A CUTOFF LOW WILL DEVELOP ON THE  
SOUTHERN END OF THE AFOREMENTIONED TROUGH NEAR THE SOCAL COAST AND  
DEEPEN THROUGHOUT THE WEEKEND. THIS LOW WILL CREATE SOUTHERLY WINDS  
ALOFT AND ALLOW FOR MOISTURE RECOVERY TO BEGIN TAKING PLACE LATE  
SATURDAY THROUGH EARLY NEXT WEEK. GUIDANCE IS NOTORIOUSLY FAST WITH  
CUTOFF SYSTEMS, THEREFORE THE CURRENT FORECAST PACKAGE SLIGHTLY  
DELAYS THE ONSET OF PRECIPITATION COMPARED TO GUIDANCE.  
PRECIPITATION WILL BEGIN SUNDAY OVER SOUTHWEST UTAH AND SLOWLY  
ENCROACH OVER THE REMAINDER OF THE CWA INTO THE EARLY PART OF NEXT  
WEEK. THIS SYSTEM WILL BEGIN SOMEWHAT WARM WITH SNOW LEVELS AROUND  
10-11 KFT, SO THERE MAY BE CONVECTIVE POTENTIAL OVER SOUTHERN UTAH  
LATE NEXT WEEKEND AND NEXT WEEK.  
 

 
   
AVIATION
 
 
KSLC WILL CONTINUE WITH LIGHT WINDS AND MAINLY CLEAR SKIES THROUGH  
THE TAF PERIOD, WITH NO SIGNIFICANT OPERATIONAL IMPACTS EXPECTED.  
WINDS WILL FOLLOW THE DIURNAL CLIMATOLOGY THROUGH TUESDAY, WITH  
NORTHWEST WINDS TO 12 KNOTS THIS AFTERNOON DIMINISHING AND SWITCHING  
TO SOUTHEAST WINDS OF 6 KNOTS OR LESS THIS EVENING. NORTHWEST WINDS  
WILL AGAIN STRENGTHEN TUESDAY AFTERNOON.  
 

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

 
 

 
 
SHORT TERM...10  
LONG TERM...BONNETTE  
AVIATION...CHURCH/MERRILL  
 
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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