650  
FXUS65 KSLC 170951  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
351 AM MDT WED OCT 17 2018  
   
SYNOPSIS
 
AN UPPER LEVEL LOW OVER NORTHERN ARIZONA WILL MOVE  
SLOWLY NORTH ACROSS UTAH THROUGH THURSDAY. HIGH PRESSURE ALOFT  
WILL BUILD IN BEHIND THE EXITING LOW PRESSURE FRIDAY THROUGH THE  
UPCOMING WEEKEND.  
 

 
   
SHORT TERM (UNTIL 00Z SUNDAY)
 
THE UPPER LOW CURRENTLY  
POSITIONED OVER NORTHERN ARIZONA WILL TAKE A SLOW NORTH-NORTHEAST  
TRACK ACROSS UTAH THROUGH THURSDAY. A COUPLE OF VORTICITY LOBES  
ROTATING AROUND THE LOW ALONG WITH FAVORABLE THERMAL ADVECTION  
WILL LEAD TO SUFFICIENT SYNOPTIC-SCALE LIFT AND WIDESPREAD PRECIP  
ALONG THE NORTHERN AND EASTERN FLANKS OF THE LOW AS IT MOVES  
THROUGH THE STATE.  
 
A VORTICITY LOBE ROTATING WEST-NORTHWEST ACROSS SOUTHERN UTAH  
ALONG WITH WEAK LOW-LEVEL WARM ADVECTION HAS SPAWNED AREAS OF  
LIGHT PRECIP OVERNIGHT. THIS FIRST SURGE OF PRECIP WILL LIKELY  
REMAIN ON THE LIGHT SIDE BEFORE DISSIPATING AS THE VORTICITY LOBE  
MOVES OUT OF THE STATE.  
 
THE BAROCLINIC STRUCTURE OF THE ADVANCING LOW WILL BECOME MUCH  
IMPROVED THIS AFTERNOON/EVENING. INCREASING LOW AND MID-LEVEL WARM  
ADVECTION IN THE EASTERN/NORTHERN FLANKS OF THE LOW ALONG WITH  
INCREASING DYNAMIC SUPPORT FOR LIFT SHOULD PRODUCE WIDESPREAD  
LIGHT/MODERATE PRECIP ACROSS MAINLY CENTRAL/EASTERN UTAH THIS  
AFTERNOON THROUGH THE OVERNIGHT HOURS. CAN NOT RULE OUT EMBEDDED  
CONVECTION WITH BRIEF HEAVY PRECIP NEAR THE MID-LEVEL COLD POOL  
AT THE CENTER OF THE LOW LATE THIS AFTERNOON THROUGH THIS EVENING.  
 
HEADING INTO THURSDAY THE UPPER LOW WILL BEGIN TO WIND DOWN AS IT  
DRIFTS INTO NORTHEAST UTAH. THERMAL ADVECTION LOOKS TO BE LESS OF  
DRIVING FORCE FOR LIFT AS IT TOO WEAKENS DURING THE MORNING.  
SUSPECT THAT PRECIP WILL BEGIN TO TAKE ON A MORE CONVECTIVE NATURE  
AS COLD AIR INSTABILITY NEAR THE CENTER REMAINS A FACTOR. BY LATE  
AFTERNOON/EVENING THE REMNANT OF THE UPPER LOW BEGINS TO SHEAR TO  
THE EAST AS IT BECOME ABSORBED BY THE FAIRLY STRONG SHORTWAVE  
DIVING SOUTHEAST INTO THE NORTHERN PLAINS STATES LATE THURSDAYS  
NIGHT/FRIDAY.  
 
THE REX BLOCK SETTING UP ALONG THE WEST COAST FRIDAY WILL LEAVE  
MOST OF UTAH UNDER DRY/STABLE CONDITIONS THROUGH SATURDAY. THE  
BLOCKING PATTERN LOOKS TO BE SHORT-LIVED AS THE RIDGE SHIFTS INTO  
THE INTERIOR WEST LATE SATURDAY AND THE LOW PORTION OF THE OLD  
BLOCK GRADUALLY STRENGTHENS ALONG THE CALIFORNIA COAST. THIS LOW  
COULD PUMP SOME MOISTURE NORTH INTO SOUTHWEST UTAH, LEADING TO A  
FEW CONVECTIVE SHOWERS LATE IN THE DAY SATURDAY.  
   
LONG TERM (AFTER 00Z SUNDAY)
 
GLOBAL MODELS HAVE ALL TRENDED  
TOWARD A MUCH MORE ACTIVE SOLUTION WITH THE 00Z RUNS FOR THE LONG  
TERM FORECAST PERIOD. A RELATIVELY WEAK BUT SLOW MOVING UPPER LEVEL  
LOW WILL BE LOCATED OFF THE SOUTHERN CALIFORNIA COAST SATURDAY  
EVENING. DIFFLUENT FLOW AHEAD OF THIS LOW COMBINED WITH A DECENT  
MOISTURE TAP SHOULD PROVIDE AN IMPETUS FOR PRECIPITATION ACROSS THE  
DESERT SOUTHWEST THROUGH THE TIME THIS LOW...AND THEN OPEN WAVE  
CROSS THE INTERIOR WEST (THROUGH LATE TUESDAY, EARLY WEDNESDAY).  
 
MUCH OF THE GLOBAL MODEL GUIDANCE FOCUS ON A PERIOD OF MODERATE RAIN  
ACROSS SOUTHWEST UTAH AS EARLY AS SUNDAY MORNING, WITH PRECIPITATION  
CONTINUING TO MOVE NORTH AND EAST INTO MUCH OF THE REST OF THE STATE  
THROUGH THE DAY SUNDAY INTO MONDAY. IT SHOULD BE NOTED THAT MUCH OF  
YESTERDAY'S GUIDANCE WAS FAR LESS BULLISH WITH THIS SYSTEM. STARTED  
MARKEDLY INCREASING POPS THROUGH THE LONG TERM FORECAST PERIOD, BUT  
REMAIN BEHIND WHAT THE 00Z GLOBAL MODEL CONSENSUS WOULD SUGGEST DUE  
TO A NOTORIOUSLY POOR PERFORMANCE IN CLOSED LOW/EJECTING LOW ACROSS  
THE SOUTHWESTERN UNITED STATES.  
 
BOTTOM LINE: WIDESPREAD PRECIPITATION IS POSSIBLE LATE THIS WEEKEND  
INTO EARLY NEXT WEEK. THIS SYSTEM WOULD BE RELATIVELY WARM...WITH  
HIGH SNOW LEVELS AND NEAR NORMAL TEMPERATURES ACROSS THE STATE.  
 

 
   
AVIATION
 
EXPECT SOUTHERLY WINDS TO CONTINUE AT THE SLC TERMINAL  
INTO THE MORNING...WITH A NORTHERLY WIND DEVELOPING BETWEEN 18-19Z.  
 

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

 
 

 
 
SHORT TERM...CONGER  
LONG TERM/AVIATION...KRUSE  
 
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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