000
FXUS65 KSLC 211012
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
412 AM MDT TUE MAY 21 2013

.SYNOPSIS...HIGH PRESSURE WILL BUILD ACROSS THE REGION TODAY AND OVER
EASTERN COLORADO BY WEDNESDAY AND FOR THE REMAINDER OF THE WEEK.
MEANWHILE...A LARGE LOW PRESSURE SYSTEM WILL TAKE UP RESIDENCE
OVER THE PACIFIC NORTHWEST RESULTING IN A MAINLY DRY AND WARM
SOUTHWEST FLOW ACROSS THE REGION INTO THE WEEKEND. A COUPLE OF DRY
COLD FRONTS WILL PENETRATE INTO NORTHERN UTAH AND THEN RETREAT
THROUGH FRIDAY.


&&

.DISCUSSION...A MID LEVEL RIDGE AXIS WILL MOVE ACROSS THE CWA EARLY
TODAY WITH A WARM SOUTHWEST FLOW FOLLOWING IN ITS WAKE. DEPENDING
ON THE THICKNESS OF HIGH CLOUDS THIS AFTERNOON...TEMPERATURES
SHOULD REBOUND RAPIDLY THIS AFTERNOON AS SOUTH WINDS INCREASE OVER
WESTERN VALLEYS. MAXIMUM TEMPERATURES ARE NOT LIKELY TO OCCUR UNTIL
BETWEEN 6 AND 7 PM. THE SOUTH WINDS ARE IN RESPONSE TO A LARGE
UPPER LOW MOVING INTO THE PACIFIC NORTHWEST FOR THE NEXT SEVERAL
DAYS. AS THIS LOW SPINS AROUND SEVERAL LOBES OF ENERGY WILL BRUSH
BY NORTHWESTERN UTAH DURING THE NEXT SEVERAL DAYS. AS EACH ONE OF
THESE LOBES MOVES BY AN ASSOCIATED SURFACE COLD FRONT WILL UNDERCUT
THE WARM SOUTHWEST FLOW ALOFT TO ROUGHLY AN EVANSTON WYOMING TO
DELTA LINE. THE FIRST OF THESE COLD FRONTS IS EXPECTED TO MOVE
ACROSS NORTHERN UTAH AROUND MIDDAY WEDNESDAY ACCORDING TO THE NMM...EC
AND NAM12. HOWEVER...THE GFS AND LOCAL MODELS HOLD OFF PASSAGE AT
SLC UNTIL WEDNESDAY EVENING. THIS MAKES THE MAX TEMPERATURE
FORECAST DIFFICULT FOR THE WASATCH DUE TO THE TIMING DIFFERENCES.
HAVE GONE WITH THE EC AND NAM SOLUTION OF LOW LEVEL COOLER AIR
MAKING IT TO SLC BY NOON RESULTING IN MAX TEMPS IN THE MID 70S
VERSES LOW TO MID 80S BY OTHER MODELS THAT DELAY THE PASSAGE.

DUE TO A LITTLE RESIDUAL MOISTURE OVER THE NORTHEAST MOUNTAINS AND
A WEAK THETA-E RIDGE OVER THIS AREA LATE TODAY HAVE KEPT THE
SLIGHT THREAT OF THUNDERSTORMS IN FOR THE HIGHER TERRAIN FROM THE
TAVAPUTS TO THE UINTAS. BY LATE WEDNESDAY THIS THETA-E RIDGE WILL
COINCIDE WITH THE CONVERGENCE ZONE OF THE COOL FRONT FOR SLIGHT
CHANCE OF THUNDERSTORMS ONCE AGAIN OVER THE HIGHER TERRAIN.
ANOTHER WEAK AREA OF INSTABILITY IS POSSIBLE OVER THE HIGHER
TERRAIN OF EXTREME NORTHWEST UTAH AS WELL WEDNESDAY AFTERNOON AND
EVENING.

THE TEMPERATURE FORECAST REMAINS TROUBLESOME FOR THURSDAY AS THE
ARW4G INDICATES SOUTHERLY SURFACE WINDS ACROSS NEARLY THE ENTIRE
WASATCH FRONT AND WESTERN GREAT SALT LAKE DESERT BY THURSDAY
AFTERNOON. HOWEVER...THE SURFACE GRADIENT WOULD ARGUE THAT A BOUNDARY STILL
REMAINS IN PLACE JUST TO THE SOUTH OF SALT LAKE CITY RESULTING IN
A SHALLOW NORTHERLY WIND. HAVE LEANED TOWARDS THE COOL AIR
REMAINING IN PLACE AND NOT GETTING ERODED AWAY WHICH THE EC...NAM
AND GFS ALL AGREE ON. UTAH COUNTY SHOULD REMAIN IN THE WARM SECTOR
TO THE SOUTH OF THIS FRONT. ANOTHER COOL FRONT REINFORCES THE
COOL POCKET ACROSS THE NORTHWEST QUARTER OF THE STATE THURSDAY
NIGHT RESULTING IN LITTLE CHANGE IN TEMPERATURES FOR FRIDAY.

FARTHER SOUTH AND EAST...BREEZY/WINDY CONDITIONS ARE FORECAST EACH
AFTERNOON FROM WEDNESDAY THROUGH SUNDAY...WITH THURSDAY LIKELY
BEING THE WINDIEST. THIS MAY BECOME A FIRE WEATHER CONCERN AS SOME
FUELS ACROSS SOUTHERN UTAH ARE NEARING CRITICALLY DRY STAGE.

BY SATURDAY THE UPPER LEVEL LOW OF THE PACIFIC NORTHWEST LIFTS
FARTHER NORTH AND ALLOWS THE SOUTHWEST FLOW TO SET BACK UP ACROSS
THE ENTIRE REGION FOR WARMER TEMPS THROUGH THE WEEKEND. THE EC AND
GFS DIFFER IN THE TIMING AND STRENGTH OF ADDITIONAL LOBES OF
ENERGY SWEEPING ACROSS THE GREAT BASIN BY MONDAY AND TUESDAY.
OVERALL STILL EXPECT A WARM...DRY AND BREEZY PERIOD TO PREVAIL
SATURDAY THROUGH MONDAY AND POSSIBLY TUESDAY.


&&

.AVIATION...THE SLC TERMINAL WILL SEE VFR CONDITIONS THROUGHOUT THE
DAY WITH MOSTLY CLEAR SKIES. SOUTHEAST WINDS ARE EXPECTED DURING THE
DAY...BECOMING GUSTY THIS AFTERNOON. THERE IS A 20 PERCENT CHANCE OF
A LATE SWITCH TO THE NORTHWEST BETWEEN 21Z AND 23Z.

&&

.FIRE WEATHER...HIGH PRESSURE WILL MOVE OVER THE DISTRICT
TODAY...RESULTING IN A WARMING AND DRYING TREND. THE RIDGE WILL
SHIFT EAST BY WEDNESDAY AS A PACIFIC NORTHWEST STORM SYSTEM
APPROACHES THE AREA. THIS SYSTEM WILL RESULT IN BREEZY SOUTHERLY
WINDS FOR AT LEAST THE SOUTHERN HALF OF THE DISTRICT FOR MUCH OF THE
REMAINDER OF THE WEEK. A COLD FRONT WILL CROSS NORTHERN UTAH
WEDNESDAY NIGHT AND THURSDAY...COOLING TEMPERATURES SOME AND KEEPING
WINDS FROM GETTING TOO STRONG THERE. THE SYSTEM LOOKS TO EXIT THE
AREA BY FRIDAY...BUT A SECOND APPROACHING STORM SYSTEM MAY KEEP
SOUTHERLY WINDS ELEVATED THROUGH THE WEEKEND. LOW RELATIVE
HUMIDITY VALUES WILL ACCOMPANY THESE WINDS SO FUELS MAY SUDDENLY
BECOME PERCEPTIBLE TO BURNING...ESPECIALLY AFTER SEVERAL DAYS OF
WIND AND LOW RH.

&&

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

$$

PUBLIC...STRUTHWOLF
FIRE WEATHER...TRAPHAGAN
AVIATION...TRAPHAGAN

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)