360
FXUS65 KSLC 152148
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
348 PM MDT MON OCT 15 2018
SYNOPSIS
A MUCH COOLER AIR MASS WILL REMAIN IN PLACE TODAY.
THE AREA WILL THEN SEE A STEADY WARMING TREND THROUGH MIDWEEK. A
WEAK UPPER-LEVEL SYSTEM WILL MOVE INTO THE SOUTHEAST CORNER OF
UTAH MIDWEEK.
SHORT TERM (THROUGH 00Z FRIDAY)
POTENTIAL IMPACTS...
* MONITORING POTENTIAL FOR CANYON/DOWNSLOPE WINDS ALONG THE WASATCH
TOMORROW NIGHT
* ACCUMULATING SNOW POSSIBLE SOUTHERN UTAH ABOVE 7KFT TOMORROW
NIGHT AND WEDNESDAY
ANTECEDENT CONDITIONS...
EXCEPTIONAL DROUGHT IS OCCURRING NEAR THE FOUR CORNERS. EXTREME
DROUGHT CONTINUES EAST OF THE GREAT SALT LAKE, UINTA BASIN, AND
SOUTHEAST UTAH. SEVERE DROUGHT ELSEWHERE, EXCEPT MODERATE DROUGHT
SOUTHWEST UTAH AND ALONG THE WYOMING BORDER.
BIG PICTURE...
DURING THE PAST 5 DAYS, THE PATTERN ACROSS THE PACIFIC REMAINS
AMPLIFIED WITH STRONG SYSTEMS PROGRESSING INTO THE CENTRAL PACIFIC.
A RIDGE DOMINATES THE EASTERN PACIFIC, WITH A POSITIVELY TILTED TROUGH
FROM THE GREAT LAKES INTO THE SOUTHWEST CONUS.
MDCARS 400MB-200MB AIRCRAFT OBSERVATIONS REVEAL A 75-125KT
CYCLONIC JET SOUTHWEST OF ALASKA BECOMES ANTICYCLONIC OVER THE
EASTERN PACIFIC AND WESTERN CANADA. THE UPPER LEVEL TROUGH AXIS
WAS OVER UTAH AND SOUTHERN NEVADA.
LOCAL OBSERVATIONS...
12Z KSLC RAOB SHOWS A DRY AND STABLE AIRMASS, WITH SEVERAL
SUBSIDENCE INVERSIONS ABOVE THE TOP OF THE MIX LAYER AT 740MB.
WINDS ARE MODERATELY STRONG AND UNIFORM OUT OF THE NORTHEAST AT
THE MID AND UPPER LEVELS.
PRECIPITABLE WATER VALUES RANGE FROM 0.05"-0.10" CENTRAL AND
SOUTHERN MOUNTAINS TO 0.20"-0.33" NORTHERN VALLEYS AND DIXIE.
A 1030MB SURFACE ANTICYCLONE IS CENTERED OVER WESTERN COLORADO
AND DOMINATES THE REGIONAL WEATHER. A SURFACE TROUGH EXTENDS UP
THE SOUTHERN CALIFORNIA COAST. THIS IS CREATING A 6MB
NORTHEASTERLY PRESSURE GRADIENT UTAH, SUPPORTING GUSTS UP TO 40
MPH NEAR CANYONS AND FAVORED DOWNSLOPE AREAS OF SOUTHERN UTAH.
24 HOUR TRENDS:
* PRECIPITABLE WATER 0.10" LOWER, EXCEPT 0.10"-0.15" HIGHER
NORTHWEST UTAH
* TEMPERATURES ARE 5-15F WARMER
* DEWPOINT DEPRESSIONS ARE MAINLY 5-20F HIGHER (DRIER)
FORECAST...
WEATHER DURING THE SHORT TERM PERIOD WILL LARGELY BE DICTATED BY
THE CUTOFF LOW CURRENTLY OVER WESTERN ARIZONA, WHICH MEANDERS
NORTH INTO UTAH WEDNESDAY, BEFORE ELONGATING AS A TROUGH AND
EXITING TO THE EAST LATE THURSDAY.
AFTER ANOTHER CHILLY NIGHT, EXPECT A GENERAL WARMING TREND DURING
THE NEXT SEVERAL DAYS, PARTICULARLY NORTHERN UTAH WHERE CLOUD
COVER WILL BE MORE SPARSE.
SHOWERS LOOK TO INVADE SOUTHERN UTAH FROM ARIZONA LATE TOMORROW,
BECOMING MORE WIDESPREAD LATE TUESDAY NIGHT AND WEDNESDAY. SREF
INDICATES INSTABILITY INCREASES ACROSS SOUTHWEST UTAH WEDNESDAY,
AND THE ENTIRE REGION THURSDAY, WHICH SHOULD SUPPORT AT LEAST
ISOLATED COVERAGE BUILDING FURTHER WEST AND NORTH WITH TIME.
SNOWLEVELS WILL GENERALLY BE 7KFT OR HIGHER, BUT MAY DIP LOWER
UNDER HIGH INTENSITY PRECIPITATION. IMPACTS SHOULD BE SPOTTY AND
OF SHORT DURATION AS IS THE NORM WITH CONVECTIVE SHOWERS
ASSOCIATED WITH CLOSED LOWS.
WILL NEED TO KEEP A CLOSE EYE ON WINDS ALONG THE WASATCH FRONT
LATE TOMORROW NIGHT INTO WEDNESDAY MORNING. A 5MB EASTERLY
PRESSURE GRADIENT IS IN PLACE FROM THE WASATCH FRONT TO ROCK
SPRINGS, WITH ABOUT 2.5C OF COLD ADVECTION ON A 30KT EASTERLY
700MB JET. THIS SETUP CERTAINLY SUPPORTS ENHANCED CANYON WINDS.
THE QUESTION IS WHETHER OR NOT DOWNSLOPE WINDS, POTENTIALLY OF A
HIGHER MAGNITUDE AND SCALE WILL DEVELOP. NAM BUFKIT FORECAST
SOUNDING AT OGD DOESN'T REALLY SHOW A CRITICAL LAYER REQUIRED NEAR
RIDGETOP LEVEL. INTERESTINGLY THE FV3 BUFKIT FORECAST SOUNDING FOR
OGD DOES. IF THE GRADIENT, JET, OR MAGNITUDE OF COLD ADVECTION
TREND JUST A BIT HIGHER, THIS MAY BE AN EVENT WORTHY OF A WIND
ADVISORY.
LONG TERM (AFTER 00Z FRIDAY)
AN ELONGATED UPPER LEVEL TROUGH WILL BE CENTERED OVER EASTERN
UTAH THURSDAY NIGHT WHEN THE EXTENDED PERIOD OF THE FORECAST
BEGINS. THIS TROUGH IS PART OF THE PREVIOUSLY MENTIONED CUTOFF LOW
WHICH HAS FILLED INTO AN OPEN WAVE TROUGH. THE SOUTHERN EXTENT OF
THE TROUGH WILL DIVE WELL SOUTH AS ITS ENERGY ATTACHES TO A
SECOND UPPER LEVEL LOW ADVECTING EAST OVER THE SOCAL
COAST...FORMING A SINGLE ELONGATED TROUGH FROM COLORADO TO THE
PACIFIC OCEAN. THIS TROUGH WILL REMAIN TO THE SE OF UTAH THIS
WEEKEND ALLOWING FOR RIDGING TO DOMINATE NORTHERN UTAH LATE FRIDAY
AND SATURDAY.
CONTINUING INTO THE WEEKEND, A CUTOFF LOW WILL DEVELOP ON THE
SOUTHERN END OF THE AFOREMENTIONED TROUGH NEAR THE SOCAL COAST AND
DEEPEN THROUGHOUT THE WEEKEND. THIS LOW WILL CREATE SOUTHERLY WINDS
ALOFT AND ALLOW FOR MOISTURE RECOVERY TO BEGIN TAKING PLACE LATE
SATURDAY THROUGH EARLY NEXT WEEK. GUIDANCE IS NOTORIOUSLY FAST WITH
CUTOFF SYSTEMS, THEREFORE THE CURRENT FORECAST PACKAGE SLIGHTLY
DELAYS THE ONSET OF PRECIPITATION COMPARED TO GUIDANCE.
PRECIPITATION WILL BEGIN SUNDAY OVER SOUTHWEST UTAH AND SLOWLY
ENCROACH OVER THE REMAINDER OF THE CWA INTO THE EARLY PART OF NEXT
WEEK. THIS SYSTEM WILL BEGIN SOMEWHAT WARM WITH SNOW LEVELS AROUND
10-11 KFT, SO THERE MAY BE CONVECTIVE POTENTIAL OVER SOUTHERN UTAH
LATE NEXT WEEKEND AND NEXT WEEK.
AVIATION
KSLC WILL CONTINUE WITH LIGHT WINDS AND MAINLY CLEAR SKIES THROUGH
THE TAF PERIOD, WITH NO SIGNIFICANT OPERATIONAL IMPACTS EXPECTED.
WINDS WILL FOLLOW THE DIURNAL CLIMATOLOGY THROUGH TUESDAY, WITH
NORTHWEST WINDS TO 12 KNOTS THIS AFTERNOON DIMINISHING AND SWITCHING
TO SOUTHEAST WINDS OF 6 KNOTS OR LESS THIS EVENING. NORTHWEST WINDS
WILL AGAIN STRENGTHEN TUESDAY AFTERNOON.
SLC WATCHES/WARNINGS/ADVISORIES
UT...NONE.
WY...NONE.
SHORT TERM...10
LONG TERM...BONNETTE
AVIATION...CHURCH/MERRILL
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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