190  
FXUS65 KSLC 261505  
AFDSLC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SALT LAKE CITY UT  
905 AM MDT WED APR 26 2017  
   
SYNOPSIS
 
A SERIES OF PROGRESSIVELY COLDER SYSTEMS WILL CROSS  
THE REGION THROUGH SATURDAY, WITH HIGH PRESSURE RETURNING LATE IN  
THE WEEKEND.  
 

 
   
DISCUSSION
 
 
WATER VAPOR LOOP SHOWS A STRONG ZONAL FLOW ACROSS THE PACIFIC WITH  
ATOP A RIDGE. AMDAR 400MB-200MB WIND OBSERVATIONS REVEAL A  
130KT-145KT ANTICYCLONIC JET FROM OREGON INTO UTAH. GOES/HRRR/12Z  
KSLC RAOB INDICATE PRECIPITABLE WATER VALUES RANGE FROM  
0.10"-0.20" MOUNTAINS TO 0.35"-0.50" MOST VALLEYS. BLENDED  
PRECIPITABLE WATER PRODUCT SHOWS AN ATMOSPHERIC RIVER WITH ORIGINS  
NORTHWEST OF HAWAII PENETRATING THE WESTERN GREAT BASIN.  
 
WARM ADVECTION PATTERN TODAY WITH THE NOSE OF A STRONG JET MOVING  
INTO THE REGION. STRONGEST WARM ADVECTION IS EXPECTED THIS  
AFTERNOON, SUPPORTING AN INCREASE IN PRECIPITATION COVERAGE ACROSS  
THE NORTH AND SOME CENTRAL UTAH LOCATIONS. SNOW LEVELS INITIALLY  
NEAR 6000FT THIS MORNING WILL CLIMB TO BETWEEN 7500FT AND 9000FT  
BY LATE AFTERNOON. KEPT THE SLIGHT CHANCE OF THUNDER FOR THE  
WESTERN TWO THIRDS OF THE FORECAST AREA PER SREF GUIDANCE AS  
STRONGER DYNAMICS ARRIVE.  
 
SOUTHWEST WINDS BECOME GUSTY ACROSS WEST CENTRAL AND SOUTHWEST  
UTAH THIS AFTERNOON DUE TO THE COMBINATION OF 5MB-6MB/3HR  
PRESSURE FALLS AND 700MB FLOW NEAR 30KTS.  
 
FORECAST IN GREAT SHAPE. DID LOWER POPS A BIT ACROSS THE SALT LAKE  
VALLEY THIS AFTERNOON GIVEN SOME SHADOWING WITH SOUTHWEST 700MB  
FLOW IN PLACE. NEVERTHELESS THE PROBABILITY OF MEASURING IS FAIRLY  
HIGH THIS AFTERNOON. SOME UTAH COUNTY LOCATIONS AS WELL AS OGDEN  
NORTHWARD STAND A HIGHER CHANCE OF PRECIPITATION IN THIS WARM  
ADVECTIVE REGIME.  
 

 
   
PREVIOUS DISCUSSION
 
 
THE NEXT SHORTWAVE TROUGH TO IMPACT THE FORECAST AREA IS  
CURRENTLY MOVING ONSHORE ALONG THE PACIFIC NORTHWEST COAST, AND  
WILL QUICKLY TRANSLATE SOUTHEAST THROUGH THE NORTHERN GREAT BASIN  
TODAY, BEFORE CROSSING THE FORECAST AREA TONIGHT. THIS FEATURE IS  
ALONG THE NOSE OF A STRONG PACIFIC JET, WHICH IS ASSOCIATED WITH  
AN ATMOSPHERIC RIVER EXTENDING ACROSS MUCH OF THE PACIFIC. WARM  
ADVECTION AHEAD OF THIS WAVE IS CURRENTLY OVERSPREADING NORTHERN  
UTAH RESULTING IN A FEW SHOWERS ALONG THE IDAHO BORDER. AS THIS  
WAVE APPROACHES TODAY, THE FLOW IS EXPECTED TO BACK WHICH WILL  
STRENGTHEN WARM ADVECTION, AND RESULT IN AN INCREASE IN VALLEY  
RAIN/MOUNTAIN SNOW ACROSS NORTHERN AND EVENTUALLY CENTRAL UTAH.  
 
THE COLD FRONT ASSOCIATED WITH THIS WAVE IS EXPECTED TO SWEEP FROM  
WEST TO EAST ACROSS THE FORECAST AREA THIS EVENING, LIKELY  
ENHANCING PRECIPITATION FOR A TIME, AS WELL AS SPREADING THIS  
PRECIP SOUTH INTO SOUTHERN UTAH, WITH PRECIPITATION BECOMING MORE  
OROGRAPHIC IN NATURE FROM LATE EVENING INTO THE OVERNIGHT HOURS  
 
A RELATIVE LULL IN PRECIPITATION IS EXPECTED THURSDAY ASIDE FROM  
PERHAPS SOME LIGHT OROGRAPHIC SNOW ALONG THE HIGHER TERRAIN, WITH  
A COLDER WAVE DROPPING IN FROM THE NORTH THURSDAY NIGHT INTO  
FRIDAY. THIS WAVE LOOKS TO BE ASSOCIATED WITH A CONTINENTAL  
AIRMASS AND THUS CONSIDERABLY DRIER, BUT WILL ALSO DROP SNOW  
LEVELS TO MOST VALLEY FLOORS LATE THURSDAY NIGHT INTO FRIDAY  
MORNING, WITH SOME VALLEY ACCUMULATION NOT OUT OF THE QUESTION ON  
ELEVATED/GRASSY SURFACES. A COLD NORTHERLY FLOW WILL LINGER INTO  
THE DAY SATURDAY, AND WITH THE COLD POOL ALOFT STILL OVERHEAD  
COULD CERTAINLY SEE SNOW SHOWERS CONTINUE INTO SATURDAY BEFORE THE  
TROUGH BEGINS TO PULL OFF TO THE EAST LATE IN THE DAY.  
 
AS THE TROUGH CONTINUES TO EXIT TO THE EAST ON SATURDAY NIGHT, A  
WEAK RIDGE WILL BUILD OVER THE GREAT BASIN, WITH CLEARING SKIES  
AND ANOTHER COLD MORNING SUNDAY. THE RIDGE FLATTENS AND STRONGER  
NORTHWEST FLOW RETURNS THROUGH THE DAY SUNDAY, AS ANOTHER TROUGH  
PUSHES ACROSS IDAHO AND MONTANA. FOR SUNDAY AND MONDAY, AT LEAST,  
UTAH AND SOUTHWEST WYOMING WILL REMAIN ON THE SOUTHERN FRINGES OF  
THIS TROUGH. THIS SHOULD LEAVE MOST OF THE FORECAST AREA DRY,  
THOUGH SOME STRAY SHOWERS ARE POSSIBLE ACROSS THE NORTH.  
 
THE TROUGH INTENSIFIES AND DIGS SOUTH LATE MONDAY INTO TUESDAY,  
THOUGH THERE IS STILL SOME DISCREPANCY ABOUT WHETHER THE BRUNT OF  
THE STORM WILL PRIMARILY IMPACT COLORADO, OR WHETHER IT WILL MAKE  
A PIT STOP IN UTAH ON THE WAY THERE. FOR NOW THE FORECAST IS A  
COMPROMISE BETWEEN THE COLDER/WETTER SOLUTIONS IN THE GFS AND  
CANADIAN, AND THE SOMEWHAT WARMER/DRIER ECMWF SOLUTION.  
 
EITHER WAY, SHOWERS LOOK TO DECREASE IN COVERAGE ACROSS THE AREA  
WEDNESDAY AS THE TROUGH MOVES TOWARD THE FOUR CORNERS. LOOKING  
AHEAD TO DAYS 8-10 (THURSDAY-SATURDAY), MODELS ARE HINTING AT WHAT  
HAS BECOME A RARE PHENOMENON: A HIGH AMPLITUDE RIDGE OVER THE  
INTERMOUNTAIN WEST. DON'T GET TOO EXCITED YET, OR YOU MIGHT JUST  
SCARE IT AWAY.  
 

 
   
AVIATION
 
 
VFR CONDITIONS ARE EXPECTED AT THE SLC TERMINAL FOR THE REST OF  
THE MORNING. CIGS ARE EXPECTED TO DROP TO OR BELOW 6000 FEET BY  
18Z AS SHOWERS DEVELOP IN THE VICINITY OF THE TERMINAL, WITH  
CONDITIONS DROPPING TO MVFR AT TIMES DURING THE AFTERNOON IN  
HEAVIER RAIN SHOWERS. WINDS ARE EXPECTED TO REMAIN SOUTHERLY  
DURING THE AFTERNOON HOURS, BUT ERRATIC WINDS ARE POSSIBLE IN THE  
VICINITY OF SHOWERS.  
 

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

 
 

 
 
PUBLIC...ROGOWSKI  
AVIATION...TRAPHAGAN  
 
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  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab UT Page
The Nexlab ID Page
The Nexlab WY Page Main Text Page