644
FXUS65 KSLC 210910
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
310 AM MDT THU OCT 21 2021
SYNOPSIS
HIGH PRESSURE WILL BUILD INTO THE REGION THROUGH FRIDAY. A WEAK
DISTURBANCE WILL CLIP NORTHERN UTAH SATURDAY WITH A MORE
SIGNIFICANT STORM TO IMPACT THE ENTIRE AREA LATE SUNDAY INTO EARLY
NEXT WEEK.
SHORT TERM (THROUGH 12Z/6AM SUNDAY)
EARLY THIS MORNING A WEAK WAVE ROUNDING THE TOP OF A LONGWAVE
RIDGE OVER THE SOUTHWEST IS PUSHING A BAND OF MID AND HIGH LEVEL
CLOUD COVER ACROSS THE STATE. THIS WAVE WILL PUSH TO OUR EAST
TODAY, WHILE THE RIDGE AXIS AMPLIFIES OVER UTAH. THUS MORNING
CLOUDS ARE EXPECTED TO SWEEP SOUTHEASTWARD WITH CLEARING SKIES
ACROSS THE NORTHERN 2/3RDS OF UTAH TODAY, WHILE SOME CLOUD COVER
LINGERS NEAR THE ARIZONA BORDER THROUGH THE AFTERNOON.
TEMPERATURES WILL MODERATE WITH DRY CONDITIONS ACROSS THE STATE
UNDER THE RIDGE, WITH HIGHS NEAR TO SLIGHTLY ABOVE NORMAL.
SOUTHWESTERLY FLOW WILL INCREASE ACROSS WESTERN UTAH ON FRIDAY AS
A TROUGH MOVES IN ALONG THE PACIFIC NORTHWEST COAST AND A
SHORTWAVE EJECTS FROM NORTHERN CALIFORNIA TO WESTERN MONTANA. THE
THERMAL RIDGE AXIS WILL SHIFT EASTWARD OVER UTAH, AND WHEN
COMBINED WITH BETTER MIXING OVER WESTERN UTAH WILL BRING HIGH
TEMPERATURES RUNNING 5-10 DEGREES ABOVE AVERAGE. HOWEVER, A LACK
OF MIXING IN EASTERN BASINS WILL MAINTAIN ONLY NEAR NORMAL
TEMPERATURES.
BY SATURDAY, THE MEAN TROUGH WILL SETTLE IN PLACE OVER THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES, PLACING UTAH UNDER ACTIVE ZONAL
FLOW WITH DISORGANIZED EMBEDDED SHORTWAVES. THIS WILL DRIVE
SHOWERS MAINLY OVER NORTHERN UTAH, BUT WITH SCATTERED ACTIVITY
REACHING SOUTHWARD INTO CENTRAL UTAH AS WELL. THIS MILD PACIFIC
FLOW WILL MAINTAIN FAIRLY HIGH SNOW LEVELS DURING THIS EVENT,
GENERALLY ABOVE 7500 FEET IN NORTHERN UTAH AND 8500 FEET INTO
CENTRAL UTAH. PRECIPITATION TOTALS WILL BE ON THE LIGHT SIDE FROM
THIS INITIAL STORM SYSTEM, WITH NORTHERN UTAH VALLEYS SEEING
AROUND 0.1 TO 0.3 INCHES OF WATER, WHILE NORTHERN MOUNTAINS WILL
GENERALLY SEE AROUND 0.2 TO 0.4 INCHES OF WATER WITH LOCALLY
HIGHER AMOUNTS.
LONG TERM (AFTER 12Z/6AM SUNDAY)
CLUSTER MODEL FORECASTS ARE GENERALLY CONFIDENT IN THE WEATHER
FORECAST SUNDAY WITH PERHAPS SLIGHT UNCERTAINTIES REGARDING
STRENGTH OF A WEAK SHORTWAVE TROUGH EXITING NORTHERN UTAH.
LINGERING MOISTURE MAY ALLOW FOR AREAS OF VALLEY RAIN AND MOUNTAIN
SNOW. UTAH WILL THEN BE IN THE WARM SECTOR OF THE NEXT
APPROACHING WEATHER SYSTEM THE REMAINDER OF THE DAY AND INTO
MONDAY.
IMPACTFUL WEATHER CONDITIONS REMAIN FORECAST INTO TUESDAY WITH THE
ARRIVAL OF A DEEP AREA UPPER LEVEL TROUGH FROM THE WEST. CLUSTER
MODEL FORECAST INDICATE UNCERTAINTIES IN THE STRENGTH OF THIS
APPROACHING TROUGH BUT ARE MORE CONFIDENT IN ITS POSITION OVER THE
WEST COAST AT THE START OF THE UPCOMING WORK WEEK. AT ATMOSPHERIC
RIVER REMAINS IN THE FORECAST ACROSS THE WEST COAST, WITH THE GEFS
ENSEMBLE MEAN IWVT INDICATING AT LEAST 450 KG / MS ACROSS WESTERN
UTAH. PRECIP CHANCES WILL INCREASE FROM WEST TO EAST PRIMARILY IN
THE FORM OF RAIN. SNOW LEVELS AT THIS POINT ARE EXPECTED TO BE
AROUND 10,000 FT. A CHANCE OF THUNDER ALSO CAN'T BE RULED OUT MONDAY
EVENING. A COLD FRONT IS EXPECTED TO PASS THROUGH THE REGION MONDAY
INTO TUESDAY MORNING WITH SNOW LEVELS DROPPING THROUGH THE DAY. THIS
WOULD ALLOW FOR ADDITIONAL AREAS FOR SNOW SHOWERS AT THAT TIME WITH
ACCUMULATING SNOW ABOVE 7,000 FT.
THE WIND FORECAST ALONE IS CERTAINLY ONE TO KEEP AN EYE ON. A 60+ KT
700 MB JET WILL FORM ACROSS WESTERN UTAH EARLY MONDAY AND PLANT
ITSELF THERE THROUGH TUESDAY MORNING BEFORE THE ARRIVAL OF A COLD
FRONT. SEVERAL MODELS ARE INDICATING THIS EVENT WILL BE AN ANOMALOUS
ONE AND ONE THAT WILL SURELY LEAD TO LEAD A WIND HEADLINE OF SOME
SORT (WIND OR HIGH WIND). FOR EXAMPLE, THE ECMWF STANDARDIZED MODELS
INDICATE VALUES OF 3 TO 5 (AN ANOMALOUS EVENT INDEED), PEAKING
MONDAY EVENING. INTERESTINGLY THOUGH, SHIFT OF TAILS IS NOT
NECESSARILY INDICATING THIS EVENT AS MUCH OF AN ANOMALOUS ONE AT
THIS TIME. THESE WINDS WOULD BE FROM THE SOUTH OR SOUTH-SOUTHWEST
WHICH WOULD MAKE TRAVEL MOST IMPACTED ALONG EAST-WEST ORIENTED
ROUTES. THIS WOULD PARTICULARLY IMPACT I-80 FROM WENDOVER TO SALT
LAKE CITY AND US-50 WEST OF DELTA.
BY WEDNESDAY, THE SYSTEM LOOKS TO EXIT TO THE EAST WHILE HIGH
PRESSURE BUILDS IN FROM THE WEST THROUGH THURSDAY.
AVIATION
KSLC...HIGH PRESSURE TODAY WILL BRING LIGHT SOUTHEAST WINDS THIS
MORNING, SHIFTING NORTHWEST THIS AFTERNOON AND EVENING BEFORE
SWITCHING OVER AGAIN FROM THE SOUTHEAST AROUND 3Z. VFR CEILING AND
VISIBILITIES ARE FORECAST WITH ONLY HIGH LAYER CLOUD DECKS.
REST OF UTAH AND SOUTHWEST WYOMING...VFR CEILING AND VISIBILITIES
ARE FORECAST THIS PERIOD WITH OCCASIONAL HIGH BASED CLOUD DECKS.
LIGHT WINDS ARE GENERALLY ANTICIPATED TODAY RESULTING FROM HIGH
PRESSURE ACROSS THE REGION.
SLC WATCHES/WARNINGS/ADVISORIES
UT...NONE.
WY...NONE.
SHORT TERM...CHURCH
LONG TERM...NDESMET
AVIATION...NDESMET
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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