488  
FXUS65 KSLC 232153  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
353 PM MDT SUN SEP 23 2018  
   
SYNOPSIS
 
A COLD FRONT MOVING INTO NORTHWESTERN UTAH AT THIS  
TIME WILL CONTINUE SOUTH AND EVENTUALLY STALL ACROSS SOUTHERN  
UTAH BY MIDDAY MONDAY. AHEAD OF THE FRONT A CHANCE OF CONVECTION  
REMAINS IN PLACE FOR CENTRAL PORTIONS THROUGH THIS EVENING. MUCH  
COOLER TEMPERATURES WILL EXIST BEHIND THE FRONT THROUGH MIDWEEK,  
BUT ANOTHER WARMING TREND IS ANTICIPATED FOR THE LATTER HALF.  
 

 
   
SHORT TERM (THROUGH 00Z THURSDAY)
 
AFTERNOON WATER VAPOR LOOP  
AND H5 ANALYSIS CONTINUE TO SHOW EAST-SOUTHEAST TRANSLATION OF THE  
UPSTREAM TROUGH, WITH AXIS NOW DRAPED FROM NORTHWESTERN MONTANA  
SOUTHWEST INTO NORTHWESTERN NEVADA. THE LEADING EDGE BAROCLINIC  
ZONE IS SHOWING SIGNS OF SHARPENING PER H7 ANALYSIS TRENDS, WHILE  
A SURFACE TROUGH CONTINUES TO DEEPEN OVER NORTHERN UTAH. EXPECTING  
THE DEVELOPING FRONTAL BOUNDARY WILL BEGIN A SOUTHERLY SURGE ALONG  
THE WASATCH FRONT OVER THE NEXT FEW HOURS, THEN CONTINUED SOUTHERN  
ADVANCEMENT TO JUST SOUTH OF THE I-70 CORRIDOR BY MIDDAY MONDAY AS  
THE UPPER TROUGH TRANSLATE ACROSS THE NORTHERN ROCKIES (LARGELY GRAZING  
THE AREA).  
 
PWATS CONTINUE TO TREND UP MEAGERLY SO, WITH VALUES TRENDING OVER  
.50 INCHES EXTENDING NORTH THROUGH CENTRAL UTAH, AND PROGS  
CONTINUE TO SUGGEST FURTHER MOISTURE ADVECTION POOLING AHEAD OF  
THE FRONT OVER CENTRAL UTAH THROUGH THIS EVENING. ALTHOUGH  
VERTICAL PROFILES/MOISTURE REMAIN SUB-PAR, SUBTLE INSTABILITY  
IS DEVELOPING AT THE MID LEVELS (H6-H4), AND COUPLED WITH THE  
MODEST FRONTAL FORCING SCATTERED SHALLOW (IN DEPTH) HIGH BASED  
(AND GUSTY) CONVECTION SHOULD DEVELOP ALONG THE BOUNDARY LARGELY  
BETWEEN 23-05Z THIS EVE. WEST- CENTRAL UTAH INTO SOUTHWEST WYOMING  
LOOKS TO BE THE FOCUS. IT'S NOT MUCH, BUT ITS SOMETHING. SUPPORT  
WILL BE LOST FOR ANY MAINTAINED CONVECTION BY EARLY MONDAY MORNING  
AS MID LEVEL BAROCLINICITY WANES AND LAPSE RATES FURTHER SLACKEN.  
 
THE MOST NOTABLE SENSIBLE CHANGE WITH THIS FRONT WILL BE THE  
MODEST CAA IN WAKE OF PASSAGE WHICH WILL DROP TEMPS TO NEAR OR  
SLIGHTLY BELOW SEASONAL NORMS THROUGH MIDWEEK. CONTINUE TO EXPECT  
LIGHT FROST FOR THE NORTHERN MOUNTAIN VALLEYS COME TUESDAY  
MORNING.  
   
LONG TERM (AFTER 00Z THURSDAY)
 
A DRY WEST TO NORTHWEST FLOW IS  
EXPECTED TO PERSIST THURSDAY INTO FRIDAY MORNING WITH THE FORECAST  
AREA IN BETWEEN A TROUGH OVER THE NORTH CENTRAL UNITED STATES AND A  
LOW OVER THE PACIFIC. THIS WILL RESULT IN A STEADY WARMING TREND IN  
TEMPERATURES WITH NO PRECIPITATION ANTICIPATED. MAXES BY FRIDAY ARE  
EXPECTED TO BE 5-7F ABOVE SEASONAL NORMALS ACROSS THE FORECAST AREA.  
 
GLOBAL MODELS INDICATE THAT THE PACIFIC LOW WILL MOVE ONSHORE AND  
EVENTUALLY GRAZE NORTHERN UTAH SATURDAY INTO SUNDAY AS IT OPENS UP  
AND WEAKENS, BRINGING ANOTHER COLD FRONT THROUGH. MODELS OVERALL ARE  
TRENDING WEAKER WITH THIS SYSTEM, THOUGH THE GFS STILL SHOWS IT AS A  
BIT STRONGER THAN THE EC. HAVE KEPT SOME POPS IN FOR SATURDAY  
AFTERNOON INTO SUNDAY, BUT OVERALL HAVE TRENDED DOWNWARD GIVEN THE  
CURRENT LOOK OF THE FORECAST MODELS.  
 

 
   
AVIATION
 
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT SLC THROUGH  
THE TAF PERIOD WILL CEILINGS REMAINING ABOVE 7K FT AND ANY STORMS  
STAYING TO THE SOUTH AND/OR EAST OF THE TERMINAL. NORTHERLY WINDS  
CURRENTLY IN PLACE ARE EXPECTED TO MAINTAIN THEMSELVES THROUGH THE  
PERIOD, AND MAY BE STRONG/GUSTY AT TIMES THIS AFTERNOON/EVENING  
BEFORE SPEEDS DIMINISH AFTER MIDNIGHT.  
 
 

 
   
FIRE WEATHER
 
MODEST MID LEVEL MOISTURE IS BECOMING  
ESTABLISHED ACROSS THE AREA IN ADVANCE OF AN APPROACHING FRONT  
THAT IS NOW MOVING INTO FAR NORTHWESTERN UTAH. A CHANCE OF SHOWERS  
AND ISOLATED STORMS REMAINS IN PLACE FROM WEST-CENTRAL UTAH INTO  
NORTHEASTERN UTAH FOCUSED BETWEEN 1700-2100 TONIGHT, BUT WITH THE  
DRY BOUNDARY LAYER IN PLACE MINIMAL RAINFALL IS EXPECTED WITH  
CELLS MORE GUSTY THAN ANYTHING. THE COLD FRONT WILL SAG INTO  
CENTRAL UTAH TONIGHT, THEN SOUTHERN UTAH MONDAY BRINGING A WIND  
SWITCH TO WEST-NORTHWEST. IN WAKE OF FRONTAL PASSAGE, GUSTY WEST  
TO NORTHWEST DOWNSLOPING WINDS ARE EXPECTED FROM THE SOUTHERN  
UINTAS SOUTH ACROSS THE UINTA BASIN AND INTO CASTLE COUNTRY.  
 
ALTHOUGH WINDS WILL BE TRENDING DOWN ACROSS THE WESTERN VALLEYS  
AND NORTHERN MOUNTAINS MONDAY, ISOLATED CRITICAL WINDS/RH REMAIN  
LIKELY IN THE BEAR RIVER VALLEY AND IS POSSIBLE IN SOME OF THE  
CANYON AREAS IN THE WASATCH.  
 
FIRE WEATHER CONCERNS WILL BECOME LIMITED BY TUESDAY...LIKELY  
THROUGH FRIDAY AS A DRY WEST-NORTHWEST FLOW BECOMES ESTABLISHED.  
COOL THROUGH MIDWEEK WITH GRADUAL WARMING LATE WEEK. THE NEXT  
POTENTIAL SIGNIFICANT FIRE WEATHER PERIOD LOOKS TO COME NEXT  
WEEKEND.  
 

 
   
SLC WATCHES/WARNINGS/ADVISORIES
 
 
UT...RED FLAG WARNING UNTIL 8 PM MDT MONDAY FOR UTZ481>484.  
 
RED FLAG WARNING UNTIL 8 PM MDT THIS EVENING FOR UTZ479-480-492.  
 
RED FLAG WARNING FROM NOON TO 8 PM MDT MONDAY FOR UTZ489.  
 
WY...RED FLAG WARNING UNTIL 8 PM MDT MONDAY FOR WYZ277.  
 

 
 
MERRILL/TRAPHAGAN/CARR  
 
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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