304  
FXUS65 KSLC 220319  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
919 PM MDT SAT APR 21 2018  
   
SYNOPSIS
 
HIGH PRESSURE ALOFT WILL MAINTAIN WARM AND DRY  
CONDITIONS ACROSS UTAH THROUGH THE DAY SUNDAY. A WEAK WEATHER  
DISTURBANCE WILL BRING SHOWERS TO NORTHERN UTAH AND SOUTHWEST  
WYOMING EARLY IN THE UPCOMING WEEK.  
 

 
   
DISCUSSION
 
 
ANTECEDENT CONDITIONS...  
EXTREME DROUGHT IS OCCURRING FROM PROVO SOUTH TO CEDAR CITY AND  
TO THE SOUTHEAST. SEVERE DROUGHT IS OCCURRING SURROUNDING THE  
EXTREME DROUGHT, IN AREAS SOUTH OF OGDEN AND DUCHESNE TO THE  
ARIZONA BORDER. DROUGHT CONDITIONS SCALE DOWN TO ABNORMALLY DRY  
ALONG THE IDAHO AND WYOMING BORDER.  
 
BIG PICTURE...  
DURING THE PAST 5 DAYS, THE AMPLIFIED PATTERN OVER THE PACIFIC HAS  
SHIFTED TOWARD BEING MORE ZONAL AS THE MAGNITUDE OF THE JET HAS  
SIGNIFICANTLY DECREASED.  
 
WATER VAPOR SATELLITE SHOWS A DEEP CLOSED LOW HAS PROGRESSED EAST  
TO THE OKLAHOMA, WITH RIDGING EXTENDING FROM THE SOUTHERN PACIFIC  
INTO THE GREAT BASIN. 400-250 MDCARS WIND OBSERVATIONS SHOW A  
NORTHWESTERLY 110-140KT JET FROM SOUTHEAST OF THE FOUR CORNERS  
INTO NORTHWEST TEXAS.  
 
LOCAL OBSERVATIONS AND TRENDS...  
00Z KSLC RAOB SHOWS A DRY AIRMASS WITH LIGHT FLOW. 700-500MB LAPSE  
RATES ARE DECENTLY STEEP. PRECIPITABLE WATER VALUES RANGE FROM  
0.10"-0.20" MOUNTAINS, TO TO 0.33"-0.55" MOST VALLEYS.  
 
A 1018MB SURFACE ANTICYCLONE HAS CENTERED ACROSS NORTHWEST UTAH,  
CREATING A 5MB NORTHEASTERLY PRESSURE GRADIENT TO FAR SOUTHWEST  
UTAH.  
 
24 HOUR TRENDS INCLUDE 10-20F WARMER SOUTH OF SALT LAKE CITY, 5F  
WARMER ACROSS THE NORTH. DEWPOINTS DEPRESSION HAVE INCREASED  
(DRIED) 15-35F EXCEPT 5-10F LOWER (MOISTENED) ACROSS THE  
NORTHWEST.  
 
FORECAST...  
INHERITED FORECAST IN GREAT SHAPE, WITH NO REASON TO UPDATE THIS  
EVENING. BEAUTIFUL WEATHER UNDER A RIDGE OF HIGH PRESSURE TODAY,  
WITH EVEN THE VALLEYS ACHIEVING STRONG WARMING COMPARED TO THE  
WINTER IN THIS PATTERN, DUE TO THE HIGHER SUN ANGLE THIS TIME OF  
YEAR.  
 
RETURN FLOW WILL BRING AN INCREASE IN MID LEVEL MOISTURE  
TOMORROW, SUPPORTING DIURNAL INSTABILITY FROM THE UINTA MOUNTAINS  
SOUTH TO BOULDER SUMMIT. WITH VERY STEEP 700-500MB LAPSE RATES  
ACROSS THE REGION, ISOLATED CONVECTION IS LIKELY IN THE  
AFOREMENTIONED AREAS.  
 

 
   
PREVIOUS DISCUSSION
 
 
THE WEAK DIFFLUENT WESTERLY FLOW ALOFT ACROSS THE GREAT BASIN  
WILL MAINTAIN DRY CONDITIONS AND BRING SOMEWHAT WARMER TEMPS TO  
THE FORECAST AREA ON SUNDAY. A SHORTWAVE MOVING INTO THE PACIFIC  
NORTHWEST EARLY SUNDAY WILL CONTINUE SLOWLY EAST ACROSS THE  
NORTHERN ROCKIES/NORTHERN GREAT BASIN LATE SUNDAY NIGHT THROUGH  
EARLY TUESDAY.  
 
THE INITIAL PUSH OF THE MID-LEVEL TROUGH INTO NORTHWEST UTAH  
SHOULD BRING CONVECTION TO NORTHERN UTAH THROUGH MONDAY MORNING.  
MODEST, BUT FAIRLY DEEP COLD ADVECTION ALONG WITH DYNAMIC SUPPORT  
FROM THE UPPER TROUGH AND ADEQUATE MOISTURE SHOULD BE SUFFICIENT  
TO GENERATE SCATTERED CONVECTIVE PRECIP. INCREASE JET SUPPORT  
DURING THE DAY MONDAY COULD LEAD TO A THUNDERSTORM OR TWO LATE  
MONDAY MORNING THROUGH THE AFTERNOON.  
 
BOTH THE GFS AND ECMWF ARE SHOWING THE DEVELOPMENT OF A MID-LEVEL  
CIRCULATION CENTER WITHIN THE THE TROUGH ACROSS THE NORTHERN  
ROCKIES LATE MONDAY AFTERNOON OR EVENING. THE RESULT OF THIS  
DEVELOPMENT WILL LEAD TO A CYCLONIC NORTHWEST FLOW ACROSS FAR  
NORTHERN UTAH/SOUTHWEST WYOMING LATE MONDAY NIGHT THROUGH TUESDAY.  
ANY PRECIP WILL LIKELY STAY CLOSE TO THE COLDER AIR ALOFT WHICH  
WILL REMAIN PRIMARILY OVER SOUTHWEST WYOMING. RAPID WARMING ALOFT  
TUESDAY AFTERNOON SHOULD BRING AN END TO ANY LINGERING SHOWERS UP  
NORTH DURING THE AFTERNOON.  
 
WILL HAVE TO KEEP AN EYE ON POSSIBLE ISOLATED CONVECTION OVER THE  
HIGHER TERRAIN OF CENTRAL/SOUTHERN UTAH TUESDAY. THE GLOBAL MODELS  
DO SHOW A NARROW BAND OF MOISTURE CONCENTRATED ALONG THE OLD LOW-  
LEVEL BAROCLINIC ZONE STALLED OUT OVER THE SOUTHERN HALF OF THE  
STATE. ANTICIPATING JUST ISOLATED COVERAGE OF ANY CONVECTION THAT  
DEVELOPS, AND THEN MAINLY OVER THE HIGHER TERRAIN THROUGH EARLY  
EVENING.  
 
AN OFFSHORE LOW REMAINS OUT TO SEA BY MID-WEEK WITH HIGH PRESSURE  
RIDGING DEVELOPING AND CONTINUING ACROSS THE EASTERN GREAT BASIN.  
DRY AND WARMING CONDITIONS WILL SETTLE IN AND PERSIST FOR THE  
FORECAST AREA OF UTAH AND SOUTHWEST WYOMING FOR WEDNESDAY.  
 
MODELS BEGIN TO DIFFER IN A SOLUTION FOR THURSDAY, WITH A BRUSH-  
BY TROUGH SWEEPING THROUGH WYOMING AND DOWN THE FRONT RANGE OF  
COLORADO AS ONE MODEL SUGGESTS. THE COLD AIR LOOKS TO REMAIN WELL  
TO THE EAST OF OUR AREA, SO KEPT VERY MINOR MENTION OF ANY  
PRECIPITATION CONFINED TO THAT AREA. HEIGHTS AND UPPER LEVEL  
TEMPERATURES STILL REMAIN WARM, SO WENT WITH A WARM BIAS ON THE  
TEMPERATURE FORECAST FOR FRIDAY AND SATURDAY.  
 
HEADING INTO THE WEEKEND, WENT WITH SOME SLIGHT CHANCE MENTION IN  
THE MOUNTAINS AND HIGHER TERRAIN OF NORTHEAST UTAH AND THE CENTRAL  
SPINE MOUNTAINS AS THE UPPER LEVEL LOW BEGINS AN INLAND TRAJECTORY  
WITH INCREASING SOUTHWEST FLOW. CONFIDENCE IS STILL SOMEWHAT LOW  
WITH THIS FEATURE, BEING THE FAR EXTENDED TIME PERIOD AND GIVEN THE  
LACK ON CONSISTENT SOLUTIONS.  
 

 
   
AVIATION
 
 
BENIGN WEATHER FOR THE KSLC TERMINAL DURING THE VALID TAF PERIOD.  
AN EASTERLY PRESSURE GRADIENT SHOULD CAUSE THE TYPICAL SOUTHEAST  
DRAINAGE TO BACK MORE EASTERLY THAN NORMAL.  
 

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

 
 

 
 
PUBLIC...10/CONGER/DEWEY  
AVIATION...10  
 
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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