158
FXUS65 KSLC 131048
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
348 AM MST MON JAN 13 2025
SYNOPSIS
A COLD AIRMASS WILL REMAIN IN PLACE ACROSS THE REGION
THROUGH AT LEAST MIDWEEK WHEN HIGH PRESSURE WILL MOVE IN, BRINGING
DRY, STABLE CONDITIONS. THE NEXT WEATHER SYSTEM AND ASSOCIATED
COLD FRONT IS POISED TO MOVE INTO THE REGION IN THE LATE FRIDAY TO
SATURDAY TIMEFRAME, POTENTIALLY BRINGING THE COLDEST AIR SO FAR
THIS SEASON TO THE REGION BY NEXT WEEKEND.
SHORT TERM (THROUGH 12Z/5AM FRIDAY)
EARLY MONDAY MORNING
ANALYSIS REVEALED A WEAKENING POSITIVELY-TILTED TROUGH EXTENDING
FROM EAST-CENTRAL UTAH THROUGH SOUTHWEST UTAH, WHILE DRY, COLD
NORTHERLY MID-LEVEL FLOW WAS IN PLACE ACROSS NORTHERN UTAH AND SW
WYOMING. AN UPSTREAM SHORTWAVE COULD BE SEEN NEAR THE
MONTANA/CANADIAN BORDER. MODEL CONSENSUS DROPS THIS FAST-MOVING
SHORTWAVE SOUTHWARD, REACHING NORTHEAST UTAH AND SW WYOMING THIS
EVENING, BEFORE EXITING INTO ARIZONA TUESDAY MORNING. THIS
SHORTWAVE IS LACKING BOTH DEEP-LAYER MOISTURE AND ANY NOTABLE
TEMPERATURE ADVECTION. HOWEVER, DESPITE THE LACK OF DEEP-LAYER
MOISTURE, THE SHORTWAVE IS FORECAST TO BE ACCOMPANIED BY A SUBTLE
INCREASE IN LOW TO MID-LEVEL MOISTURE AS WELL AS PROVIDING A
SLIGHT BOOST TO LOW TO MID-LEVEL LAPSE RATES LATE THIS AFTERNOON
AND EVENING. THE QUESTION THEN BECOMES, WILL THERE BE ENOUGH
FORCING AND MOISTURE TO PROVIDE SNOW? THE ANSWER IS MUDDLED,
PARTICULARLY IN NORTHERN VALLEYS, AS CAMS RUN THE GAMUT FROM NO
PRECIPITATION TO A TRACE TO 1 OR 2" DOWNSTREAM OF THE GREAT SALT
LAKE. ON THE EXTREME END OF THE ENVELOPE, A HIGH-END SCENARIO
(LESS THAN A 10% CHANCE OF OCCURRENCE) SHOWS A NARROW RIBBON OF
3-6" OF LAKE-EFFECT SNOW FROM THE SOUTH ARM OF THE LAKE SSE ACROSS
LAKE POINT AND THE OQUIRRHS. AN EXAMINATION OF FORECAST SOUNDINGS
SUGGESTS A MOST LIKELY SCENARIO IS A FEW, ISOLATED SNOW SHOWERS
IN THIS AREA, GENERALLY BETWEEN 6PM AND 12AM. DURING THIS WINDOW,
FORECAST TIME HEIGHTS DO INDICATE MODEST MOISTENING IN THE DGZ.
FOR MOUNTAINS, MOST LIKELY SNOWFALL RANGES ANYWHERE FROM A TRACE
TO 1-3" INCHES, WITH THE NORTH SLOPE OF THE UINTAS FAVORED, THANKS
TO THE OROGRAPHIC BOOST ASSOCIATED WITH THE NORTHERLY FLOW. AFTER
MIDNIGHT TONIGHT, MOISTURE AND ATTENDANT SNOWFALL CHANCES
GRADUALLY WANE, LEAVING DRY CONDITIONS FOR TUESDAY INTO LATE IN
THE WORKWEEK.
OTHERWISE, SEASONABLY COLD TEMPERATURES HAVE SETTLED INTO THE
REGION EARLY THIS WEEK. IN NORTHERN VALLEYS, APPARENT TEMPERATURE
FORECAST BOTTOMS OUT IN THE 15F-20F RANGE MONDAY, TUESDAY AND
WEDNESDAY MORNINGS, POTENTIALLY HAZARDOUS FOR THE UNSHELTERED,
VULNERABLE POPULATION. TEMPERATURES WILL MODERATE BY MID TO LATE
IN THE WORKWEEK, WITH HIGH TEMPERATURES FORECAST TO RISE TO 5F-10F
ABOVE NORMAL BY THURSDAY, AND POTENTIALLY INTO FRIDAY, DEPENDING
ON THE TIMING OF AN INCOMING COLD FRONT. MORE ON THAT BELOW.
AS WE HEAD INTO MIDWEEK, A REX BLOCK IS FORECAST TO SET UP ACROSS
THE WESTERN CONUS, AS A RIDGE OF HIGH PRESSURE NOSES IN FROM THE
WEST, WHILE A CLOSED LOW RETROGRADES OFF OF THE SOCAL COAST. AS
THE RIDGE BUILDS INTO THE AREA, MODEST VALLEY INVERSION CONDITIONS
WILL BEGIN TO SET UP BY WEDNESDAY, AND THESE ARE FORECAST TO
LINGER INTO FRIDAY. THIS DURATION OF INVERSION CONDITIONS WILL
LIKELY BE LONG ENOUGH FOR SOME HAZE TO FORM ACROSS NORTHERN
VALLEYS, BUT CONDITIONS ARE NOT FORECAST TO RIVAL THOSE OBSERVED
DURING THE EARLY DECEMBER INVERSION PERIOD. CHECK UTAH DEQ FOR
THE LATEST AIR QUALITY CONDITIONS AND FORECASTS.
LONG TERM (AFTER 12Z/5AM FRIDAY)
THE REX BLOCK PATTERN
THROUGH MUCH OF THE WEEK WILL BREAK DOWN LATE IN THE WEEK INTO THE
WEEKEND. HIGH PRESSURE WILL BE POSITIONED OFF THE WEST COAST OF
THE U.S. THE CLOSED LOW THAT WAS PART OF THE BLOCKING PATTERN WILL
EJECT INLAND. IT WILL LIKELY TRACK INTO SOUTHERN CALIFORNIA AND
ARIZONA. LIMITED MOISTURE AND FORCING WILL PUSH INTO UTAH, WITH
ISOLATED SNOW SHOWERS FOR THE SOUTHERN MOUNTAINS.
WITH THE REX BLOCK DIMINISHING, SOUTHWEST WYOMING AND UTAH WILL BE
MORE LIKELY TO GET INFLUENCE FROM TROUGHS THAT DIG NEAR THE EASTERN
PERIPHERY OF THE RIDGE OFF THE WEST COAST. ENSEMBLES ARE IN GOOD
AGREEMENT ON A TROUGH FRIDAY INTO THE WEEKEND, BUT SIGNIFICANT
DIFFERENCES IN THE STORM TRACK AND TIMING MAKE FOR LOWER CONFIDENCE
ON DETAILS. THE MAIN DIFFERENCES WITH ENSEMBLE MEMBERS ARE ON
WESTWARD EXTENT OF THE TROUGH. MOST CANADIAN ENSEMBLE MEMBERS BRING
THE TROUGH FURTHER WEST, WITH MUCH COLDER CONDITIONS INTO SOUTHWEST
WYOMING AND UTAH. MOST GEFS MEMBERS TRACK THE TROUGH MORE SIMILAR TO
A MORE COMMON TRACK, WHERE THE COLDEST CONDITIONS ARE EAST OF THE
ROCKIES. EPS MEMBERS ARE GENERALLY BETWEEN THOSE ENSEMBLES, BUT A
LEAN TOWARD MOST GEFS MEMBERS.
THE TROUGH WILL BE RATHER DRY, BUT WILL BRING A RELATIVELY STRONG
BAROCLINC ZONE, MOST LIKELY FRIDAY INTO SATURDAY. IT WILL BE LIMITED
WITH MOISTURE, BUT THE COLD CONDITIONS WILL ALLOW FOR HIGH SNOW
RATIOS WHERE ACCUMULATION COULD STACK UP QUICKLY IN THE MOUNTAINS
WITH LOWER WATER CONTENT.
AVIATION...KSLC
MOSTLY CLEAR CONDITIONS WILL LAST THROUGH AROUND
19Z. THERE IS A LOW CHANCE FOR SNOW, BUT CLOUDS IN VFR RANGE WILL
INCREASE AS ISOLATED TO SCATTERED MOUNTAIN SNOW SHOWERS ARE LIKELY
AFTER 18Z. LIGHT NORTHWEST WINDS WILL PREVAIL.
REST OF UTAH AND SOUTHWEST WYOMING
ISOLATED TO SCATTERED SNOW
SHOWERS ARE LIKELY FROM AROUND 19-03Z FOR THE NORTHERN MOUNTAINS.
FOR NORTHERN VALLEY LOCATIONS, THERE WILL BE AN INCREASE IN CLOUDS,
WITH VFR CONDITIONS LIKELY. WINDS WILL BE RELATIVELY LIGHT FROM THE
NORTHWEST. DRY CONDITIONS WILL PREVAIL THROUGHOUT SOUTHERN UTAH WITH
FEWER CLOUDS AND SLIGHTLY STRONGER NORTH WINDS, WITH GUSTS AROUND 20
KNOTS AFTER 19Z.
SLC WATCHES/WARNINGS/ADVISORIES
UT...NONE.
WY...NONE.
ADESMET/WILSON
FOR MORE INFORMATION FROM NOAA'S NATIONAL WEATHER SERVICE
VISIT... HTTP://WEATHER.GOV/SALTLAKECITY
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