Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 242301
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
401 PM MST WED DEC 24 2014

.SYNOPSIS...A WINTER STORM MOVING OUT OF THE PACIFIC NORTHWEST
WILL IMPACT UTAH LATE TONIGHT THROUGH FRIDAY. UNSETTLED WEATHER
WILL DEVELOP AGAIN FOR LATE IN THE WEEKEND THROUGH EARLY NEXT
WEEK.

&&

.SHORT TERM (UNTIL 00Z SUNDAY)...THE UPPER TROUGH CURRENTLY ALONG
THE PACIFIC NORTHWEST/NORTHERN CALIFORNIA COAST WILL CONTINUE
SOUTHEAST INTO THE WESTERN GREAT BASIN AS AN OPEN TROUGH THIS
EVENING. FROM THERE THIS TROUGH WILL GAIN A CLOSED CIRCULATION
LATE TONIGHT...WITH THIS CENTER DRIFTING SOUTH-SOUTHEAST TO THE
FOUR CORNERS REGION BY EARLY FRIDAY MORNING.

THE ASSOCIATED SURFACE COLD FRONT BASED ON MSAS DATA EXTENDS FROM
WEST-CENTRAL MONTANA THROUGH NORTHERN CALIFORNIA LATE THIS
AFTERNOON. SOLID PRESSURE FALLS ACROSS THE GREAT BASIN THIS
AFTERNOON SUGGEST THIS FRONT IS STRENGTHENING AS EXPECTED.
CURRENT TIMING WOULD PUT THE FRONT INTO EXTREME NORTHWEST UTAH
AROUND EARLY TO MID EVENING...THEN THROUGH THE URBAN CORRIDOR
BETWEEN 06Z TO 10Z.

MOIST WARM ADVECTION AHEAD OF THE FRONT WILL LIKELY GENERATE SOME
LIGHT PRE-FRONTAL PRECIP THIS EVENING. PRECIP WILL RAPIDLY
INCREASE IN AREAL COVERAGE AND INTENSITY WITH THE FRONT ACROSS
NORTHERN/WESTERN UTAH DUE TO THE STRONG DYNAMIC LIFT AND GOOD
BAROCLINIC STRUCTURE TO THIS STORM. PRECIP WILL REMAIN FAIRLY
ACTIVE NEAR THE FRONT ACROSS SOUTHERN AND EASTERN UTAH LATE
TONIGHT/EARLY FRIDAY...THOUGH LIKELY NOT AS INTENSE AS THE FRONT
WILL SHOW MODEST WEAKENING AS IT PRESSES INTO SOUTHEAST UTAH.

SNOW WILL PERSIST ACROSS THE FORECAST AREA AS THE OPEN TROUGH
CLOSES OFF OVER THE AREA. SYNOPTIC-SCALE LIFT ASSOCIATED WITH THIS
FEATURE SHOULD PROMOTE WIDESPREAD SNOW...WITH WARM ADVECTION WRAP
AROUND ALONG THE NORTHERN AND WESTERN FLANKS OF THE UPPER LOW THE
AREAS OF HEAVIEST PRECIP.

SNOW WILL BEGIN TO WIND DOWN FRIDAY AS THE UPPER LOW SETTLES INTO
THE FOUR CORNERS REGION. THE COLD AND UNSTABLE AIR MASS TRAILING
THE EXITING LOW WILL CONCENTRATE ADDITIONAL SNOWS ACROSS THE
CENTRAL AND SOUTHERN MOUNTAINS...AS WELL AS ALONG THE I-15/I-70
CORRIDORS OF CENTRAL AND SOUTHWEST UTAH. HAVE BOOSTED SNOW TOTALS
SUBSTANTIALLY IN THOSE AREAS TO ACCOUNT FOR THE FAVORABLE SNOW
CONDITIONS.

CONDITIONS SHOULD STABILIZED FAIRLY QUICKLY AS AN ANTICYCLONIC
NORTH-NORTHWEST FLOW ALOFT DEVELOPS BEHIND THE EXITING LOW.
OVERRUNNING MOISTURE WILL RETURN AGAIN LATE SATURDAY AHEAD OFT HE
NEXT STORM SYSTEM SCHEDULED FOR LATE IN THE WEEKEND.

&&

.LONG TERM (AFTER 00Z SUNDAY)...12Z GLOBAL RUNS IN BETTER AGREEMENT
REGARDING THE INITIAL STAGES OF THE NEXT TROUGH TO IMPACT THE
EASTERN GREAT BASIN SUNDAY THROUGH TUESDAY. RAPID AMPLIFICATION OF
THE WEST COAST RIDGE WILL ALLOW A STRONG SHORT WAVE TO CARVE ALMOST
DUE SOUTH THROUGH EASTERN WA/OR SATURDAY NIGHT SETTING UP DECENT
NEAR H7 BAROCLINICITY ACROSS SOUTHERN IDAHO AT THAT TIME. THE
ASSOCIATED SURFACE COLD FRONT IS EXPECTED TO TRANSITION SOUTH ACROSS
THE AREA SUNDAY NIGHT BRINGING STRONG LOW LEVEL COLD ADVECTION AND
FAIRLY WIDESPREAD LIGHT SNOW TO AT LEAST NORTHERN UTAH. THE MORE
WESTERN/AMPLIFIED SOLUTIONS OF PREVIOUS MODEL RUNS SEEMS TO HAVE WON
OUT.

THE AIRMASS TAPPED UPSTREAM WILL HAVE A STRONG CONTINENTAL
FLAVOR...AND A VERY COLD AND FAIRLY DRY ARCTIC AIRMASS ASSOCIATED.
H7 TEMPS AT KSLC FORECAST TO BE -15 TO -20 C DEPENDING ON MODEL OF
CHOICE. MODEL QPF REMAINS QUITE LOW WITH AND BEHIND THE FRONT BUT
EXPECTING HIGH SNOW RATIOS WITH ANY PRECIPITATION THAT DOES FALL.

MODEL CONFIDENCE WANES ON TROUGH EVOLUTION MONDAY ON AS EXTENT OF
CONTINUED UPSTREAM RIDGE AMPLIFICATION VARIES. 12Z GFS NEARLY CUTS
THE TROUGH OFF IN THE VICINITY OF THE 4-CORNERS MIDWEEK WHILE 12Z
ECMWF IS A FAIR BIT PROGRESSIVE. BOTTOM LINE...LOW CONFIDENCE IN
TROUGH EVOLUTION AT TIME...BUT RATHER HIGH CONFIDENCE EXISTS
REGARDING A SIGNIFICANT COOL DOWN AND A BIT OF LOW DENSITY SNOW
DOWN TO VALLEY LEVELS EARLY NEXT WEEK.

&&

.AVIATION...A SIGNIFICANT WINTER STORM WILL IMPACT THE SLC TERMINAL
EARLY CHRISTMAS MORNING INTO FRIDAY MORNING. A STRONG COLD FRONT IS
EXPECTED TO CROSS THE TERMINAL BETWEEN 08-09Z TONIGHT...BRINGING
GUSTY NORTHWEST WINDS...ACCUMULATING SNOW AND LIFR CONDITIONS FOR
THE REMAINDER OF THE MORNING. SNOWFALL INTENSITIES ARE EXPECTED TO
DECREASE THURSDAY AFTERNOON BUT PERIODIC IFR/LIFR CONDITIONS ARE
EXPECTED TO CONTINUE INTO THE OVERNIGHT HOURS. 2 TO 5 INCHES OF SNOW
ACCUMULATION IS EXPECTED ON UNTREATED SURFACES.

A 40 PERCENT CHANCE EXISTS THAT SOUTHERLY WIND GUSTS AHEAD OF THE
FRONT WILL EXCEED 30 MPH AT TIMES AFTER 00Z THIS EVENING.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING FROM 2 AM THURSDAY TO NOON MST FRIDAY FOR
     UTZ001>004-006>010-014>016-517-518.

     WINTER WEATHER ADVISORY FROM 2 AM THURSDAY TO NOON MST FRIDAY
     FOR UTZ005.

WY...WINTER STORM WARNING FROM 2 AM THURSDAY TO NOON MST FRIDAY FOR
     WYZ021.

&&

$$

SHORT TERM...CONGER
LONG TERM/AVIATION...MERRILL

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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