779
FXUS65 KSLC 182205
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
405 PM MDT FRI SEP 18 2020
SYNOPSIS
AN UPPER LEVEL TROUGH MOVING EAST THROUGH THE NORTHERN
ROCKIES WILL BRING SHOWERS AND ISOLATED THUNDERSTORMS TO NORTHERN
UTAH LATE TONIGHT THROUGH SATURDAY. COOLER, MORE SEASONAL
TEMPERATURES ARE EXPECTED THROUGH THE WEEKEND. A WARMING TREND
WILL ONCE AGAIN OCCUR NEXT WEEK.
SHORT TERM (THROUGH 12Z MONDAY)
LATEST H5 ANALYSIS INDICATES
THE UPSTREAM TROUGH IS TRENDING TO OPEN WHILST PHASING SLIGHTLY
NEGATIVELY TILTED AS EXPECTED. DOWNSTREAM OF THE TROUGH AND
LOCALLY A BROAD AREA OF UPPER DIFFLUENCE REMAINS IN PLACE ACROSS
THE EASTERN GREAT BASIN, THIS MAINTAINING A WIDESPREAD MID/UPPER
CLOUD SHIELD ACROSS WESTERN PORTIONS OF THE FORECAST AREA. A VERY
DRY SUB CLOUD LAYER REMAINS PRESENT, AND LACK OF INSTABILITY
PRECLUDES AND POTENTIAL FOR PRECIP UNTIL FRONTAL PASSAGE LATE
TONIGHT, AND LARGELY, SATURDAY MORNING.
NOT MUCH HAS CHANGED REGARDING TIMING OR SIGNIFICANCE OF THE
FRONTAL PASSAGE, OUTSIDE OF A SLIGHT TREND IN MODELS LIFTING THE
CORE OF UPPER SUPPORT (COINCIDENT WITH THE INCREASINGLY NEGATIVE
TILTED TROUGH) NORTH A BIT FASTER TOMORROW MORNING. WITH THIS
HAVE SLIGHTLY LOWERED POPS/QPF ACROSS THE CENTRAL WASATCH AND
POINTS SOUTH A SKOSH. THE MAIN FOCUS FOR PRECIP POTENTIAL REMAINS
ACROSS THE NW, UT/ID BORDER REGION, AND NORTHERN MOUNTAINS WHERE
WETTING CONDITIONS REMAIN LIKELY.
AN ADDITIONAL NOTE FOR SATURDAY, MID LEVEL LAPSE RATES ACROSS THE
UT/ID BORDER WILL STEEPEN ENOUGH FOR MODEST INSTABILITY DURING
THE MIDDAY AND AFTERNOON HOURS. CAN'T RULE OUT ISOLATED BUT SEMI-
ORGANIZED CONVECTION IN THIS AREA, THOUGH THE MOST LIKELY SCENARIO
IS THAT THIS WILL REMAIN JUST NORTH OF THE BORDER PER BULK OF CAMS.
AREAS SOUTH AND EAST OF THE FRONT SATURDAY WILL REMAIN WARM, DRY
AND BREEZY. THIS ESPECIALLY HOLDS TRUE FOR THE SOUTHEAST WHERE
CRITICAL FIRE WEATHER CONDITIONS ARE ANTICIPATED ONCE AGAIN. SEE
THE FIRE WEATHER DISCUSSION AND LATEST RFW FOR ADDITIONAL INFO ON
THIS.
HEIGHTS WILL BEGIN TO BUILD IN RAPIDLY FROM THE WEST SATURDAY
AFTERNOON/EVE AS THE UPPER TROUGH LIFTS MORE TO THE NORTHEAST AND
DEEPER INTO THE NORTHER ROCKIES REGION. WITH THIS, RAPID
DRYING/CLEARING IS EXPECTED FROM WEST TO EAST. SENSIBLY, IT SHOULD
BE QUITE PLEASANT LATER SATURDAY, WITH TEMPS TRENDING DOWN SOME 5
DEGREES BELOW NORMAL UNDER CLEARING SKIES. THIS WILL HOLD TRUE
FOR SUNDAY AS WELL, THOUGH TEMPS SHOULD REBOUND A BIT MORE TOWARDS
SEASONAL NORMS.
LONG TERM (AFTER 12Z MONDAY)
AN UPSTREAM TROUGH OVER THE PACIFIC
NORTHWEST WILL INCREASE SOUTHWEST FLOW AND DRAW MOISTURE INTO THE
REGION MONDAY. THE DRIEST CONDITIONS, WITH RH VALUES AROUND 15-20%
WILL BE THROUGH FAR WESTERN UTAH. THAT'S ALSO WHERE INCREASED WIND
GUSTS TO AROUND 30 KTS ARE EXPECTED. MOST MOISTURE, SHOWN
CONSISTENTLY BY GUIDANCE, HAS HIGHER PWAT VALUES INCREASING TO
ROUGHLY 0.75" MONDAY EVENING MAINLY OVER CENTRAL TO EASTERN UTAH.
THERE'S NOT MUCH TO WORK WITH BESIDES THAT, AS LOW LEVELS WILL BE
DRY AND THERE'S NOT MUCH DYNAMIC SUPPORT AT THAT TIME FOR MUCH
RAINFALL.
AS RIDGING BUILDS IN TUESDAY, EXPECT DRIER CONDITIONS, BUT ALSO
LIGHTER WINDS THROUGH THE WESTERN PART OF UTAH. THE STRONGER GUSTS
WILL BE TOWARDS CENTRAL AND EASTERN UTAH, WHERE THE MOISTURE FROM
MONDAY WILL BE LINGERING. THE BEST CHANCES FOR RAIN MOVE INTO THE
UINTAS AND EAST.
HIGH PRESSURE SETTLING IN BY THE MIDDLE OF THE WEEK WILL INHIBIT
POP'S AND CLOUD COVER. DRIER CONDITIONS WILL BRING DAYTIME HIGHS
INTO THE LOW TO MID 80S WEDNESDAY AND THURSDAY.
MODELS BRING IN A SIMILAR SETUP TO THIS WEEKEND BY NEXT WEEKEND,
LIKELY PROVIDING COOLER CONDITIONS AND ADDED MOISTURE.
AVIATION
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD.
PERIODIC GUSTY SOUTH WINDS WILL PERSIST UNTIL 02Z-03Z AND REMAIN
PREDOMINANTLY OUT OF THE SOUTH UP TO 15 KNOTS UNTIL A COLD FRONT
PASSAGE AROUND 09Z. BEHIND THE FRONT EXPECT SCATTERED SHOWERS AND
WEST TO NORTHWEST WINDS THROUGH THE END OF THE TAF PERIOD.
FIRE WEATHER
JUST NOW SEEING THE STRONGER SOUTHWESTERLY FLOW ALOFT
SPREADING EAST ACROSS THE AREA THIS AFTERNOON, AND HAVE NOTED THE
ANTICIPATED UPTICK IN WIND GUSTS MEETING CRITICAL THRESHOLDS
ACROSS MUCH OF THE WESTERN HALF OF UTAH. WINDS WILL CONTINUE TO
INCREASE INTO THIS EVENING. WIDESPREAD RED FLAGS REMAIN IN PLACE
THROUGH 9PM THIS EVENING.
SIGNIFICANT MID/UPPER CLOUD COVER RESIDES ACROSS MUCH OF THE
DISTRICT THIS AFTERNOON, WHILE THE ANTICIPATED COLD FRONT
CONTINUES TO TAKE FORM OVER THE CENTRAL GREAT BASIN. NOT MUCH HAS
CHANGED IN REGARDS TO THIS FRONT, WITH PASSAGE ACROSS THE NORTH
LATER TONIGHT INTO SATURDAY MORNING, THEN AN EXPECTED STALLING
ACROSS CENTRAL PORTIONS MID/LATE SATURDAY. BEHIND AND NORTH OF
THIS FRONT TEMPS WILL BE MUCH COOLER, AND WETTING RAIN POTENTIAL
REMAINS (LARGELY NORTH OF I-80 AND IN THE UINTA MOUNTAINS). SOUTH
AND EAST OF THIS FRONT WARM, DRY, AND BREEZY WILL BE MAINTAINED
THROUGH SATURDAY PRIOR TO ANY COOL DOWN (NAMELY SUNDAY) AND A
RED FLAG REMAINS IN PLACE THROUGH THAT TIME ACROSS THE SOUTHEAST.
DO NOT FORESEE ANY CRITICAL FIRE WEATHER CONDITIONS ON SUNDAY.
EARLY NEXT WEEK THE POTENTIAL WILL AGAIN CLIMB ACROSS WESTERN
PORTIONS AS YET ANOTHER MODEST BELT OF SOUTHWESTERLY FLOW ALOFT
WILL SPREAD IN. WILL HAVE TO WATCH THE NET DRYING AFTER DECENT RH
RECOVERY LATE WEEKEND, BUT WINDS SHOULD BE THERE FOR SOME WESTERN
AREAS. WILL KEEP YOU POSTED MOVING FORWARD.
SLC WATCHES/WARNINGS/ADVISORIES
UT...RED FLAG WARNING UNTIL 9 PM MDT SATURDAY FOR UTZ489-494-498.
RED FLAG WARNING UNTIL 9 PM MDT THIS EVENING FOR UTZ478-479-483-
484-488-492-493-495>497.
WY...NONE.
MERRILL/WILSON
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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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