Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 210515
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
1015 PM MST SAT DEC 20 2014

.SYNOPSIS...A VERY WARM AND MOIST STREAM OF PACIFIC AIR EXTENDS
FROM THE PACIFIC NORTHWEST INTO NORTHERN UTAH. THIS WILL CONTINUE
INTO MONDAY. A COLD FRONT WILL MOVE THROUGH THE AREA FROM NORTH
TO SOUTH ON MONDAY BRINGING A COOLER BUT DRIER AIRMASS.

&&

.DISCUSSION...AN ANOMALOUSLY MOIST AIRMASS OWING TO AN ATMOSPHERIC
RIVER PENETRATING THE PACIFIC NORTHWEST AND TAKING AIM AT NORTHERN
UTAH IS STILL ON TRACK TO PROVIDE COPIOUS PRECIPITATION TO MUCH OF
NORTHERN UTAH AND THE CENTRAL UTAH MOUNTAINS. PRECIPITATION IS
BEGINNING TO FILL IN OVER NORTHERN UTAH THIS EVENING AS WARM
ADVECTION BEGINS. HEAVIER PRECIPITATION IS EXPECTED LATE TONIGHT
INTO TOMORROW MORNING AS WARM ADVECTION MAXES OUT...THEN CONTINUE IN
EARNEST THROUGH EARLY TOMORROW EVENING AS MOISTURE CONTINUES TO
INCREASE AS A STRONG UPPER JET NOSES INTO NORTHERN UTAH.
PRECIPITATION WILL LINGER TOMORROW NIGHT BEFORE DRIER AIR SPREADS
INTO THE AREA BEHIND A COLD FRONT MONDAY. MODELS ARE A BIT FASTER
WITH THE DRIER AIR WHICH COULD SHUT OFF THE PRECIPITATION ACROSS
NORTHERN UTAH A BIT EARLIER THAN EXPECTED. HOWEVER...SOME OF THE
MOISTURE WILL GET SHUNTED OFF TO THE SOUTH SO CENTRAL UTAH COULD BE
ACTIVE THROUGH THE DAY MONDAY.

MODELS ARE STILL INDICATING STORM TOTAL QPF OVER 2 INCHES FOR THE
NORTHERN MOUNTAINS WHICH EVEN WITH HIGH-DENSITY SNOW WOULD STILL
LEAD TO SIGNIFICANT ACCUMULATIONS. SNOW LEVELS WILL BE FAIRLY HIGH
FOR MUCH OF THE STORM...KEEPING ACCUMULATING SNOW LIMITED TO THE
HIGH ELEVATIONS. TEMPERATURES TONIGHT SHOULD PRETTY MUCH FLATLINE OR
PERHAPS RISE A BIT THROUGH THE REST OF THE NIGHT ACROSS THE NORTH
DUE TO THICKENING CLOUDS. ALTHOUGH OVERNIGHT MINS ACROSS THE LOWER
VALLEYS OF NORTHERN UTAH ARE FORECAST TO REMAIN ABOVE
FREEZING...CONCERNED THAT WITH SOME BELOW OR NEAR-FREEZING
DEWPOINTS...THERE IS STILL A CHANCE FOR SNOW IN A FEW SPOTS TONIGHT.
ELKO NV MANAGED SO SNOW BRIEFLY AND NAM BUFR SOUNDINGS INDICATE SNOW
FOR MUCH OF THE NIGHT AT LOGAN...ALTHOUGH THIS IS LIKELY OVERDONE.
STILL...HAVE ADJUSTED THE FORECAST TO BRING SNOW WORDING TO A FEW
ZONES TONIGHT. SNOW LEVELS WILL ALSO LOWER ON MONDAY BEHIND THE
FRONT...WITH A POTENTIAL FOR BRIEF VALLEY SNOW AT THE TAIL END OF
THE EVENT.

BESIDES PRECIPITATION...WIND WILL ALSO BE A MAJOR PLAYER IN THIS
EVENT. STRONGEST WINDS WILL BE ACROSS THE HIGHER ELEVATIONS...WHICH
WILL LEAD TO REDUCED VISIBILITIES IN BLOWING SNOW. WINDS AT 700MB
MAX OUT TOMORROW AROUND 50KT TOMORROW...NEAR 60KT ACROSS SOUTHWEST
WYOMING. HOWEVER...500MB WINDS CONTINUE TO INCREASE THROUGH MONDAY
WITH GFS AND NAM SHOWING A RELATIVELY LARGE SWATH OF 100KT OVER
UTAH. EXPOSED AREAS ALONG THE HIGH PEAKS COULD SEE VERY STRONG GUSTS
LATE SUNDAY NIGHT INTO MONDAY AS A RESULT.

EXISTING WINTER STORM AND HIGH WIND WARNINGS REMAIN IN EFFECT.

&&

.AVIATION...CEILINGS AT THE SLC TERMINAL WILL REMAIN AT OR BELOW
6000FT AGL THROUGH THE NIGHT AS RAIN DEVELOPS ACROSS THE AREA. EXPECT
MOSTLY VFR CONDITIONS BUT PERIODIC MVFR CONDITIONS IN HEAVIER RAIN
ARE EXPECTED TO DEVELOP AFTER 10Z AND CONTINUE THROUGH MUCH OF
SUNDAY. SOUTHERLY SURFACE WINDS ARE EXPECTED TO INCREASE THROUGH THE
NIGHT.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING UNTIL 6 PM MST MONDAY FOR UTZ007>010-517.

WY...HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY FOR WYZ021.

&&

$$

CHENG

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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