439  
FXUS65 KSLC 180245  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
845 PM MDT TUE OCT 17 2017  
   
SYNOPSIS
 
A WARMING TREND WILL CONTINUE THROUGH THE MIDDLE PORTION  
OF THE WEEK. A WEAK STORM SYSTEM IS FORECAST TO CROSS THE AREA  
FRIDAY, BRINGING COOLER TEMPERATURES AND MOUNTAIN SHOWERS.  
 

 
   
DISCUSSION
 
 
WATER VAPOR SATELLITE SHOWS A TROUGH CROSSING THE NORTHERN  
ROCKIES, TRANSITIONING TO A SHEAR AXIS FROM CENTRAL CALIFORNIA  
INTO A CLOSED LOW OVER THE SOUTHERN PACIFIC. 400-200MB MDCARS WIND  
OBSERVATIONS PLACE A 120-135KT CYCLONIC JET OVER THE PACIFIC  
NORTHWEST WHICH BECOMES ANTICYCLONIC OVER CENTRAL CANADA. GOES/SLC  
00Z RAOB/HRRR INDICATE THAT PRECIPITABLE WATER VALUES VARY FROM  
0.10"-0.20" MOST LOCATIONS, UP TO 0.25" OVER NORTHWEST UTAH.  
 
WITH THE RIDGE FLATTENING OUT, CIRRUS ASSOCIATED FROM THE CENTRAL  
CALIFORNIA SHORTWAVE AND SUBTROPICAL JET OVER THE SOUTHERN  
PACIFIC CONTINUES TO INCREASE. DID BUMP UP SKY COVER TO PARTLY  
CLOUDY FOR MANY AREAS FOR AT LEAST PART OF THE NIGHT PER WEBCAMS  
AND LATEST SATELLITE IMAGERY.  
 
IT WILL BE A WARMER NIGHT DUE TO INCREASING 850-700MB THICKNESS,  
CIRRUS AND SOUTHWESTERLY FLOW. STILL DUE TO THE DRY AIRMASS IN  
PLACE OUTLYING AREAS MAY DIP A FEW EXTRA DEGREES.  
 
GOING FORECAST IN GREAT SHAPE. UPDATED DIURNAL T/RH CURVE BASED ON  
LATEST OBSERVATIONS AND GUIDANCE.  
 

 
   
PREVIOUS DISCUSSION
 
 
MOSTLY BENIGN WESTERLY FLOW ALOFT WILL CONTINUE THROUGH EARLY  
FRIDAY, BRINGING GENERALLY QUIET WEATHER CONDITIONS TO UTAH AND  
SOUTHWEST WYOMING. A RIDGE AXIS CURRENTLY OVERHEAD PER LATEST  
WATER VAPOR IMAGERY WILL SLIDE EAST OF THE AREA TONIGHT, WHILE A  
VERY WEAK SHORTWAVE CURRENTLY IN WESTERN NEVADA WILL PUSH THROUGH  
CENTRAL UTAH. THE ONLY EFFECT OF THIS WAVE WILL BE A FEW MID LEVEL  
CLOUDS IN CENTRAL/SOUTHERN UTAH TONIGHT.  
 
A STRONGER SHORTWAVE TROUGH IS FORECASTED TO LIFT NORTHEASTWARD  
FROM LAS VEGAS AREA ACROSS CENTRAL AND EASTERN UTAH LATE TOMORROW  
INTO THURSDAY. A FEW MODELS ARE WRINGING OUT LIGHT PRECIP OVER THE  
CENTRAL UTAH MOUNTAINS FROM THIS DISTURBANCE. GIVEN THE VERY DRY  
LOW-LEVEL PROFILES, IT WILL BE TOUGH TO GET ANYTHING OTHER THAN  
SPRINKLES OUTSIDE OF THE HIGH TERRAIN. OTHERWISE, WEDNESDAY WILL  
BE ANOTHER PLEASANT DAY FOR MOST AREAS WITH TEMPERATURES 5-10  
DEGREES ABOVE NORMAL.  
 
SOUTHWEST FLOW ALOFT INCREASES OVER THE GREAT BASIN THURSDAY IN  
ADVANCE OF A DEVELOPING LONGWAVE TROUGH STRETCHING FROM NORCAL TO  
THE PACIFIC NW. STRONGER MIXING SHOULD ALLOW FOR THE WARMEST  
TEMPERATURES OF THE WEEK, WITH MOST UTAH VALLEYS REACHING THE 70S  
OR AROUND 10 DEGREES ABOVE NORMAL.  
 
THE TROUGH PUSHES INLAND THURSDAY, REACHING UTAH BY MID-DAY  
FRIDAY AND PUSHING A COLD FRONT THROUGH NORTHERN UTAH AND  
SOUTHWEST WYOMING DURING THE DAY. BREEZY CONDITIONS CAN BE  
EXPECTED BY FRIDAY AFTERNOON, ESPECIALLY OVER THE WESTERN DESERTS.  
MODELS ARE IN GENERAL AGREEMENT WITH KEEPING THE CORE OF COLD AIR  
AT 500MB TO OUR NORTH, WITH A SHALLOWER FRONT FROM THE SURFACE TO  
AROUND 700MB THAT PUSHES THROUGH ALL OF OUR AREA EXCEPT FAR  
SOUTHERN UTAH BY FRIDAY NIGHT. AS HAS BEEN THE TREND WITH RECENT  
TROUGHS, THIS SYSTEM WILL BE LACKING MOISTURE, AND THUS THE BEST  
CHANCE OF LIGHT PRECIP WILL BE OVER THE HIGHER TERRAIN FROM AROUND  
UTAH COUNTY NORTHWARD, PARTICULARLY OVER THE UINTAS. SNOW LEVELS  
WILL APPROACH VALLEY FLOORS, BUT NOT EXPECTING TO SEE ANYTHING IN  
THE WASATCH FRONT GIVEN THE MOSTLY DRY NATURE OF THE SYSTEM. THE  
MOST NOTICEABLE ASPECT WILL BE A ~20 DEGREE DROP IN TEMPERATURES  
FROM THURSDAY'S HIGHS TO SATURDAY'S HIGHS.  
 
TEMPERATURES QUICKLY REBOUND ACROSS THE AREA SUNDAY AS A DRY  
NORTHWEST FLOW ALOFT SETS IN AND HEIGHTS BUILD IN THE WAKE OF  
SATURDAY'S TROUGH PASSAGE.  
 
LOOKING AHEAD TO NEXT WEEK, GLOBAL MODELS ARE IN AGREEMENT IN  
BUILDING A STRONG RIDGE OVER THE WESTERN US. THIS RIDGE IS QUITE  
PERSISTENT AND ACTUALLY STRENGTHENS FURTHER INTO THE WEEK. THIS  
WILL LIKELY BRING AN EXTENDED PERIOD OF WARMER-THAN-NORMAL  
TEMPERATURES AND DRY CONDITIONS FOR OUR AREA.  
 

 
   
AVIATION
 
THE DRY/STABLE WESTERLY FLOW ALOFT ACROSS NORTHERN UTAH  
WILL MAINTAIN VFR CONDITIONS UNDER MOSTLY CLEAR SKIES THROUGH THE  
TAF PERIOD. CALM WINDS WILL BECOME LIGHT OUT OF THE SOUTHEAST  
AROUND 04Z THIS EVENING.  
 

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

 
 

 
 
PUBLIC...ROGOWSKI/VAN CLEAVE  
AVIATION...ROGOWSKI  
 
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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