Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 202215
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
315 PM MST THU NOV 20 2014

.SYNOPSIS...A STORM OVER CALIFORNIA THIS AFTERNOON WILL WEAKEN AND
MOVE SOUTH INTO ARIZONA TONIGHT AND FRIDAY...JUST CLIPPING
SOUTHWEST UTAH. A STRONG NORTHWEST FLOW WILL PUSH A COLD FRONT
INTO NORTHERN UTAH SATURDAY AFTERNOON. THIS COLD MOIST NORTHWEST
FLOW WILL CONTINUE OVER THE AREA THROUGH MONDAY.

&&

.DISCUSSION...FIRST ITEM IS THE STORM OVER CALIFORNIA TODAY. ALL
MODELS TAKE THIS STORM SHARPLY SOUTHEAST INTO ARIZONA TONIGHT AND
FRIDAY. IT JUST CLIPS SOUTHWEST UTAH. 12Z GFS/NAM SHOW SOME LIGHT
RAIN SHOWERS OVER SOUTHWEST UTAH WITH THE SNOW LEVEL AROUND 7K.
12Z EC IS COMPLETELY DRY. HAVE LEFT ONLY CHANCE POPS IN FORECAST
FOR SOUTHWEST UTAH LATE TONIGHT EARLY FRIDAY.

MAIN EVENT FOR THE WEEKEND CAN BE SEEN IN SATELLITE IMAGERY AS A
VERY LONG PLUME OF MOISTURE THAT EXTENDS ACROSS NEARLY THE ENTIRE
PACIFIC OCEAN TODAY. EMBEDDED IN THIS PLUME ARE A COUPLE OF
STORMS.

THERE HAS BEEN VERY GOOD RUN TO RUN AND MODEL TO MODEL CONSISTENCY
WITH THE WEEKEND STORM SO CONFIDENCE IN THE EVENTS DESCRIBED BELOW
IS HIGHER THAN AVERAGE. YOU DON`T HEAR US SAY THAT TOO OFTEN.

THE FIRST STORM ARRIVES IN NORTHERN UTAH SATURDAY MORNING AS A
WARM FRONT. ALL NORTHERN MOUNTAINS AND VALLEYS FROM DAVIS COUNTY
NORTHWARD ARE MOST LIKELY TO SEE PRECIP FROM THE WARM FRONTAL
PORTION OF THE STORM AS LOCAL DOWNSLOPING MY LIMIT PRECIP IN SALT
LAKE VALLEY AND UTAH COUNTY SATURDAY MORNING.

COLD FRONT PUSHES SOUTH THROUGH THE FORECAST AREA SATURDAY
AFTERNOON. PASSAGE OF THE FRONT INITIATES A PROLONGED PERIOD OF
UNSTABLE NORTHWEST FLOW. TIME/HEIGHT SECTIONS FROM MODELS SHOW
DEEP INSTABILITY AND WITH MODERATE TO STRONG FLOW...MOUNTAIN AREAS
FAVORED BY NORTHWEST FLOW SHOULD GET SIGNIFICANT OROGRAPHIC
SNOWFALL.

VALLEYS WILL SEE RAIN CHANGE TO SNOW A FEW HOURS BEHIND THE
FRONTAL PASSAGE...FOR SLC THAT LOOKS TO BE IN THE 6-8PM SATURDAY TIMEFRAME.
A FEW INCHES OF SNOW ARE LIKELY BEFORE SNOW TAPERS OFF TO SHOWERS
OVERNIGHT. EAST BENCH AREAS ARE LIKELY TO SEE SOME OROGRAPHIC
ENHANCEMENT OF THE SNOW FROM SATURDAY NIGHT THROUGH MONDAY SO SNOW
TOTALS COULD BE QUITE A BIT HIGHER IN THESE BENCH AREAS.

THE DREADED LAKE EFFECT IS A WILDCARD AND COULD PRODUCE
SIGNIFICANT SNOWFALL IN SOME PARTS OF DAVIS AND/OR SALT LAKE
COUNTY. HOWEVER THIS AIRMASS IS NOT EXTREMELY COLD AND ALCOTT`S
STUDY OF THE DLE SUGGESTS ONLY ABOUT A 10-20 PERCENT CHANCE OF
OCCURRENCE GIVEN THE FORECAST TEMPERATURES. IT IS SLIGHTLY COLDER
IN THE 12Z EC THAN IN THE 12Z GFS. STILL TWO DAYS OUT...STAY
TUNED.

A BREAK IN THE ACTION SUNDAY...ALTHOUGH SHOWERS AND SOME
OROGRAPHIC SNOW LIKELY.

THE SECOND UPPER LEVEL TROUGH EMBEDDED IN THE NORTHWEST FLOW ARRIVES
SUNDAY EVENING AND SHOULD BRING ANOTHER ROUND OF WIDESPREAD
SNOWFALL...HEAVY IN THE MOUNTAINS. THIS CONTINUES INTO MONDAY
MORNING.

MONDAY/TUESDAY ARE TREATED SOMEWHAT DIFFERENTLY BY THE 12Z GFS/EC
AS RIDGING BUILDS INTO THE WEST AND A WARM FRONT MOVES OVER THE
AREA. BOTH MODELS INDICATE SOME ADDITIONAL PRECIP WITH THE WARM
FRONT BUT TIMING/DISTRIBUTION ARE DIFFERENT.

BY MIDWEEK 12Z MODELS ARE VASTLY DIFFERENT WITH ANOTHER TROUGH IN
NORTHWEST FLOW IN THE EC AND A WARM DRY RIDGE IN THE GFS.
CONTINUED TO LEAN TOWARDS THE 12Z EC SOLUTION SO KEPT CHANCE POPS
AND COOLER TEMPERATURES IN THE FORECAST.

&&

.AVIATION...ANY CIGS AT THE KSLC TERMINAL ARE EXPECTED TO REMAIN
WELL ABOVE 7000 FT AGL THROUGH TONIGHT...HOWEVER THERE IS A 20
PERCENT CHANCE THAT SCATTERED CLOUDS WEST OF THE SALT LAKE VALLEY
NEAR 7000 FT WILL BRIEFLY THICKEN ENOUGH TO FORM A CIG AS THEY CROSS
THE AIRFIELD THRU ABOUT 01Z. WINDS WILL BE LIGHT AND VARIABLE
THROUGH ABOUT 01Z THEN SHOULD BECOME PREVAILING SOUTHEASTERLY.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WATCH FROM LATE FRIDAY NIGHT THROUGH LATE MONDAY
     NIGHT FOR UTZ007>009.

WY...NONE.
&&

$$

PUBLIC...DUNN
AVIATION...WILENSKY

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)



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