497  
FXUS65 KSLC 141044  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
344 AM MST THU DEC 14 2017  
   
SYNOPSIS
 
NORTHERLY FLOW WILL PREVAIL ACROSS THE REGION TODAY  
IN THE WAKE OF A DEPARTING STORM SYSTEM. A STRONGER SYSTEM WILL  
CROSS THE AREA SATURDAY, SWEEPING OUT VALLEY INVERSIONS AND  
BRINGING A CHANCE OF SNOW TO TO NORTHERN AND WESTERN UTAH.  
 

 
   
SHORT TERM (THROUGH 00Z MONDAY)
 
EARLY MORNING SATELLITE IMAGERY  
AND OBJECTIVE ANALYSIS DEPICT AN UPPER RIDGE CENTERED OFF THE  
PACIFIC COAST NEAR 130W, WITH NORTHERLY FLOW EXTENDING DOWNSTREAM  
ACROSS THE GREAT BASIN. A SHORTWAVE TROUGH WHICH PASSED THROUGH  
THE FORECAST AREA WEDNESDAY EVENING INTO THE OVERNIGHT HOURS IS  
CURRENTLY LOCATED NEAR THE FOUR CORNERS REGION AND WILL CONTINUE  
MOVING AWAY FROM THE AREA TODAY. THIS FEATURE BROUGHT A BIT OF  
LIGHT SNOW, BUT MORE IMPORTANTLY HAS COOLED TEMPERATURES ALOFT AND  
SIGNIFICANTLY WEAKENED VALLEY INVERSIONS ACROSS NORTHERN UTAH.  
700MB TEMPS ARE ANALYZED BY THE RAP AT NEAR -5C THIS MORNING, AND  
THIS COUPLED WITH 700MB FLOW NEAR 30 KTS AND A BIT OF A NORTHERLY  
SURFACE GRADIENT HAS BOTH ERODED THE FOG/LOW STRATUS BANK WHICH  
HAS PLAGUED NORTHERN UTAH OVER THE PAST FEW DAYS, AS WELL AS  
IMPROVED AIR QUALITY BASED ON DEQ SENSORS AROUND THE WASATCH  
FRONT. AS SUCH HAVE REMOVED FOG/STRATUS FROM THE FORECAST FOR  
TODAY AS WELL AS BUMPED VALLEY TEMPERATURES A BIT, ALTHOUGH HAVE  
RETAINED HAZE AS THE AIRMASS HAS NOT FULLY MIXED OUT OVERNIGHT,  
AND MAY SEE THE INVERSIONS STRENGTHEN A BIT TODAY AS TEMPERATURES  
WARM ALOFT.  
 
FURTHER SOUTH, A NORTHERLY GRADIENT COUPLED WITH STRONG 700MB COLD  
ADVECTION IS RESULTING IN STRONG GUSTY WINDS ALONG THE I-15  
CORRIDOR BETWEEN CEDAR CITY AND ST GEORGE, AS WELL AS OTHER WIND  
PRONE AREAS OF WASHINGTON COUNTY. WILL MAINTAIN THE GOING HIGH  
WIND WARNING THROUGH THE MORNING HOURS WHERE GUSTS TO 60 MPH WILL  
REMAIN POSSIBLE.  
 
SHORTWAVE RIDGING WILL TEMPORARILY BUILD ACROSS THE REGION TONIGHT  
THROUGH FRIDAY BRINGING WARMING TEMPERATURES ALOFT, AND LIKELY  
ALLOW VALLEY INVERSIONS TO STRENGTHEN A BIT. HAVE INCLUDED A  
MENTION OF PATCHY FOG FOR LATE TONIGHT THROUGH FRIDAY ACROSS THESE  
AREAS.  
 
THE MODELS REMAIN IN GOOD AGREEMENT DIGGING A SPLITTING SHORTWAVE  
THROUGH THE GREAT BASIN LATE FRIDAY NIGHT INTO SATURDAY. ALTHOUGH  
THIS WAVE WILL BE SPLITTING, THE COLD FRONT COUPLED WITH 700MB  
TEMPS FALLING BELOW -10C AND A NORTHERLY GRADIENT SHOULD SWEEP OUT  
LINGERING INVERSIONS FROM NORTHERN UTAH SATURDAY MORNING.  
 
THE BAROCLINIC ZONE COUPLED WITH THE PASSAGE OF THE TRAILING MID  
LEVEL TROUGH SHOULD BE SUFFICIENT TO BRING A FEW INCHES OF SNOW TO  
THE HIGHER TERRAIN ALTHOUGH THIS SYSTEM DOES NOT LOOK LIKE A  
MAJOR SNOW PRODUCER. THE FRONTAL BAND WILL SHIFT SOUTH INTO  
SOUTHWEST UTAH BY SATURDAY AFTERNOON BRINGING A CHANCE OF SNOW AS  
FAR SOUTH AS CEDAR CITY. FOR NOW HAVE INCREASED POPS INTO THE  
70-80 PERCENT RANGE ACROSS THE NORTHERN MOUNTAINS WHILE LEAVING  
THE VALLEYS OF NORTHERN AND WESTERN UTAH IN THE CHANCE CATEGORY  
FOR NOW. THIS TROUGH WILL GRADUALLY EXIT THE REGION SATURDAY NIGHT  
WHICH SHOULD LEAVE A DRYING TREND FOR SUNDAY AS SHORTWAVE RIDGING  
BUILDS INTO THE REGION.  
   
LONG RANGE (AFTER 00Z MONDAY)
 
HEADING INTO EARLY NEXT WEEK,  
SHORTWAVE RIDGING WILL BUILD IN BUT EXTENDED MODELS ALL POINT TO A  
SHORT DURATION RIDGING WITH VERY WEAK (IF ANY) WARMING ALOFT. THE  
BIG PICTURE WEATHER PATTERN DOES CONTINUE TO POINT TO AN  
UNSETTLED DISTURBANCE SLIDING THROUGH THE WESTERN CONUS AND THE  
GREAT BASIN BY MID-WEEK. A NICE CHANGE IN THE PATTERN AS THE RIDGE  
OF HIGH PRESSURE SEEMS TO RETROGRADE AND WEAKEN A BIT.  
 
LONG RANGE MODELS ARE POINTING TO A COLD WEATHER DISTURBANCE BY  
MID- LATE WEEK, AND MODELS ARE PRETTY CLOSE IN TIMING SO THAT  
HELPS CONFIDENCE A BIT. HOWEVER, WITH THE HISTORY OF SHORTWAVE  
ENERGY WEAKENING AT THE LAST MINUTE, HAVE LOW CONFIDENCE IN THE  
FINER DETAILS OF THIS SYSTEM. AM FEELING MORE COMFORTABLE ABOUT  
THE FACT THAT INVERSIONS WILL STRUGGLE TO REDEVELOP AFTER THE  
STORM SYSTEM THE PREVIOUS WEEKEND, AND WITH TEMPERATURES AT 700MB  
OF -13C TO -17C BEING ADVERTISED, HAVE HIGHER CONFIDENCE THIS WILL  
CONTINUE TO KEEP VALLEYS MIXED OUT.  
 
THE SHORTWAVE TROUGH MODELS ARE ADVERTISING FOR THURSDAY ARE IN  
DECENT AGREEMENT AT THIS TIME AND EVEN ADVERTISING A DECENT AMOUNT  
(COMPARED TO RECENT EVENTS) OF MOISTURE. WON'T GET TOO EXCITED AT  
THIS TIME IN THE PROSPECT OF MOISTURE/PRECIPITATION CHANCES, BUT  
WITH THE FLOW PATTERN AND NATURE OF THE TROUGH, WE MAY SEE SOME  
WINTER PRECIPITATION BEFORE THE END OF 2017 AFTER ALL.  
 

 
   
AVIATION
 
LOW STRATUS AND HAZE WILL CONTINUE TO BE THE PRIMARY  
OPERATIONAL WEATHER CONCERN AT KSLC TODAY. MVFR/IFR VISIBILITIES  
AND CEILINGS WILL PERSIST THROUGH THE DAY. A 20 PERCENT CHANCE  
THAT CONDITIONS WILL DROP INTO LIFR IN FOG. LIGHT WINDS WILL  
PREVAIL WITH A NORTHWEST DIRECTION UNTIL 03Z OR SO THIS EVENING  
WHEN A SWITCH BACK TO THE SOUTHEAST TAKES PLACE. A 30 PERCENT  
CHANCE THAT LOW IFR CONDITIONS SET UP AFTER 00Z THIS EVENING IN  
FOG AND HAZE.  
 

 
   
SLC WATCHES/WARNINGS/ADVISORIES
 
 
UT...HIGH WIND WARNING UNTIL 9 AM MST THIS MORNING FOR UTZ019.  
 
WY...NONE.  

 
 

 
 
SEAMAN/DEWEY  
 
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