294
FXUS65 KSLC 180948
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
348 AM MDT THU SEP 18 2025
SYNOPSIS
DRY AND WARM CONDITIONS CAN BE EXPECTED OVER THE AREA
TODAY. MOISTURE RETURNS TO THE AREA TONIGHT INTO THE WEEKEND,
WITH INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS.
SHORT TERM (THROUGH 12Z SATURDAY)
THE MEAN UPPER LOW CENTERED
OVER THE NORTHERN PLAINS WILL CONTINUE TO SHIFT EAST TODAY, ALLOWING
FOR A SHORTWAVE RIDGE TO BUILD INTO UTAH. THIS RIDGE WILL RESULT IN
WARMER AND DRY CONDITIONS ACROSS THE AREA TODAY WITH GENERALLY LIGHT
WINDS. AFTERNOON MAX TEMPERATURES ARE EXPECTED TO TREND NEAR TO JUST
SLIGHTLY ABOVE CLIMATOLOGICAL NORMALS. MEANWHILE, UPSTREAM, A STORM
SYSTEM THAT HAS INGESTED TROPICAL SYSTEM REMNANTS IS CHURNING OFF
THE SOCAL COAST.
AS THE SHORTWAVE RIDGE SHIFTS EASTWARD TONIGHT, SOUTH TO
SOUTHWESTERLY FLOW DEVELOPING OVER UTAH WILL DRAW MOISTURE FROM THE
UPSTREAM SYSTEM INTO THE AREA. MODELS SHOW PWATS INCREASING FAIRLY
RAPIDLY THIS EVENING. FOR EXAMPLE, ACROSS THE SOUTHWEST CORNER OF
UTAH, ENSEMBLE MEAN PWATS FROM THE HREF IS FORECAST TO RISE FROM
BETWEEN 0.4-0.5 INCHES AROUND 18Z TO 0.9-1.0+ INCHES BY 06Z. THIS
MOISTURE, COUPLED WITH INCREASED FORCING FROM THE APPROACHING STORM
SHOULD BRING SHOWERS TO THE AREA BEGINNING WITH SOUTHWEST UTAH
TONIGHT BEFORE SPREADING INTO AT LEAST CENTRAL UTAH AND POTENTIALLY
FARTHER NORTH THROUGH THE DAY FRIDAY. THE INITIAL ROUND OF SHOWERS
ARE LIKELY TO REMAIN HIGH-BASED AND PRODUCE GUSTY MICROBURST WINDS.
THEN, AS THE LOWER LEVELS CONTINUE TO MOISTEN, HEAVIER RAIN MAY
BECOME MORE LIKELY WITH THE STRONGER STORMS.
MODEL SPREAD IS MAKING THE TIMING OF THE ONSET OF SHOWERS AS WELL AS
THE LOCATION OF ANY STRONGER STORMS DIFFICULT AT THIS POINT.
FURTHERMORE, SOME HREF MEMBERS INSIST THAT OVERNIGHT AND EARLY
MORNING SHOWERS ACROSS SOUTHWEST UTAH WILL LEAVE THAT AREA LARGELY
SUPPRESSED BY PEAK DAYTIME HEATING FRIDAY AFTERNOON, DESPITE MEAN
HREF SBCAPE VALUES OF 250-750J/KG. WPC HAS AN EXCESSIVE RAINFALL
OUTLOOK OF MARGINAL ACROSS SOUTHWEST UTAH FOR FRIDAY, WHICH IS NOT
UNREASONABLE, BUT IS CONDITIONAL ON HAVING SHOWERS IN THE FIRST
PLACE.
LONG TERM (AFTER 12Z/6AM SATURDAY)
ABOVE-NORMAL MOISTURE WILL BE
IN PLACE AT THE START OF THE LONG-TERM PERIOD, REACHING UP TO 200%
OF NORMAL ACROSS WESTERN UTAH (150% ACROSS EASTERN UTAH/SOUTHWEST
WYOMING). MID-LEVEL FLOW WILL BE LARGELY ZONAL ON SATURDAY, THOUGH
WEAK SYNOPTIC DYNAMICS FROM A 80-90KT JET STREAK AND SUBTLE
SHORTWAVE TROUGH WILL HELP SCATTERED SHOWERS AND THUNDERSTORMS TO
DEVELOP ACROSS THE FORECAST AREA BY SATURDAY AFTERNOON. DESPITE
APPRECIABLE COLUMN MOISTURE, MODEL SOUNDINGS ACTUALLY SUGGEST THAT
DRIER AIR WILL MOVE INTO THE MID LEVELS ACROSS THE STATE,
POTENTIALLY LIMITING CONVECTIVE DEVELOPMENT AND FLASH FLOOD
POTENTIAL. BY SUNDAY, THIS TREND WILL CONTINUE, WITH MOST CONVECTION
EXPECTED ACROSS NORTHERN UTAH AND PRIMARILY OVER HIGHER TERRAIN
GIVEN AN OVERALL LACK OF SYNOPTIC LIFT.
BY LATE SUNDAY, A GRAZING TROUGH WILL ADVECT MUCH DRIER AIR INTO THE
REGION, WITH PWATS DIPPING DOWN TO 50% OF NORMAL BY LATE MONDAY.
INTERESTINGLY, THERE ARE STILL ROUGHLY 20% OF ENSEMBLE MEMBERS THAT
ACTUALLY FAVOR A STRONGER TROUGH OVERHEAD INSTEAD OF JUST GRAZING
OUR AREA; THIS COULD PRODUCE COOLER AND WETTER CONDITIONS TO START
THE WORK WEEK, IF THIS SCENARIO WERE TO PAN OUT. HIGH PRESSURE WILL
THEN BUILD OVER UTAH BEHIND THIS TROUGH, THOUGH FORECAST CONFIDENCE
DECREASES SIGNIFICANTLY AFTER TUESDAY. MODELS CAN AGREE ON THE
DEVELOPMENT OF A CUTOFF LOW OVER SOCAL, BUT THEY DIVERGE GREATLY
WITH REGARDS TO WHERE/WHEN THIS LOW MOVES BY MID-WEEK. ULTIMATELY,
THIS WILL IMPACT HOW LONG HIGH PRESSURE RESIDES OVER OUR AREA. BY
DAY 7/THURSDAY, NOW 61% OF ENSEMBLE MEMBERS FAVOR HIGH PRESSURE
STILL OVERHEAD, WITH OR WITHOUT AN STRONG UPSTREAM TROUGH. ANOTHER
23% FAVOR A WEAK TROUGH, WHILE THE REMAINING 16% ARE STILL HANGING
ONTO A POTENT TROUGH OVER THE WESTERN US...LOWER THAN WHERE CHANCES
WERE YESTERDAY.
AVIATION...KSLC
LIGHT, SOUTHEASTERLY WINDS WILL CONTINUE THROUGH
THE MORNING, LIKELY TRANSITIONING TO NORTHWESTERLY AROUND ~20-21Z,
WITH A LOW CHANCE OF OCCURRING AS EARLY AS 19Z. VFR CONDITIONS WILL
PREVAIL WITH CLEAR SKIES. HIGH CLOUDS WILL BEGIN TO MOVE INTO THE
AREA BY THURSDAY EVENING.
REST OF UTAH AND SOUTHWEST WYOMING
WINDS WILL REMAIN LARGELY
LIGHT AND TERRAIN-DRIVEN THROUGH THE VALID TAF PERIOD, THE EXCEPTION
BEING AN INCREASE IN WESTERLY WINDS NEAR KSGU THURSDAY EVENING AHEAD
OF SOME RAIN SHOWERS. WHILE MOST LOCATIONS WILL BE DRY WITH CLEAR
SKIES, HIGH-BASED SHOWERS COULD MOVE INTO KSGU AS EARLY AS 23Z AND
KCDC AS EARLY AS 02Z, WITH GUSTY OUTFLOW WINDS BEING THE MAIN THREAT.
FIRE WEATHER
HIGH PRESSURE OVER THE AREA TODAY WILL RESULT IN
WARMER AND DRY CONDITIONS ACROSS THE AREA. AS THIS HIGH PRESSURE
MOVES EAST OF THE AREA, SOUTH TO SOUTHWEST FLOW WILL DRAW MOISTURE
INTO THE AREA BEGINNING TONIGHT AND INTO THE WEEKEND. EXPECT SHOWERS
AND THUNDERSTORMS TO BE POSSIBLE ACROSS SOUTHWEST UTAH TONIGHT,
SPREADING INTO CENTRAL AND POTENTIALLY PORTIONS OF NORTHERN UTAH
DURING THE DAY FRIDAY. SHOWERS NEAR THE LEADING EDGE OF THE MOISTURE
SURGE WILL MORE LIKELY RESULT IN ISOLATED DRY LIGHTNING AND GUSTY
MICROBURST WINDS. WITH SURFACE HUMIDITIES INCREASING, WETTING RAIN
CHANCES WILL GRADUALLY INCREASE THROUGH THE DAY. BY SATURDAY AND
SUNDAY, PRECIPITATION CHANCES WILL BECOME INCREASINGLY FOCUSED OVER
NORTHERN UTAH. DRIER AIR WILL THEN SPREAD BACK INTO UTAH EARLY NEXT
WEEK. ANOTHER ROUND OF MOISTURE WILL BE POSSIBLE BY THE MIDDLE OF
NEXT WEEK, BUT WITH SIGNIFICANT MODEL SPREAD, CONFIDENCE REMAINS ON
THE LOW SIDE FOR NOW.
SLC WATCHES/WARNINGS/ADVISORIES
UT...NONE.
WY...NONE.
CHENG/CUNNINGHAM
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