Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 261221 CCA
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
520 AM MST FRI DEC 26 2014

.SYNOPSIS...THE UPPER LEVEL LOW PRESSURE SYSTEM OVER UTAH WILL
SETTLE INTO THE FOUR CORNERS REGION THIS MORNING...THEN EXIT THE
REGION TONIGHT. A NEW ROUND OF UNSETTLED WEATHER WILL DEVELOP LATE
IN THE WEEKEND AND REMAIN THROUGH THE FIRST HALF OF NEXT WEEK.

&&

.SHORT TERM (THROUGH 12Z MONDAY)...STORM SYSTEM WITH CLOSED LOW
EVIDENT ON WATER VAPOR IMAGERY CENTERED JUST SOUTH OF LAKE POWELL IS
CONTINUING TO SLOWLY TRACK EAST. IN THE MEANTIME...THE NORTHERLY
FLOW ACROSS WESTERN UTAH ON THE BACKSIDE OF THE TROUGH STILL
FAVORABLE FOR PRODUCING SNOW ALONG UPSLOPE REGIONS OF THE CENTRAL
AND SOUTHERN MOUNTAINS AND ADJACENT VALLEYS. OBS INDICATE SNOW STILL
OCCURRING AT SITES SUCH AS FILLMORE...MILFORD AND BEAVER. AS
SUCH...HAVE LEFT WINTER STORM WARNINGS IN PLACE ACROSS
SOUTHERN/CENTRAL ZONES FOR THE REMAINDER OF THE MORNING.

ACROSS NORTHERN UTAH...THE EASTERLY COMPONENT TO THE FLOW HAS SHUT
DOWN PRECIPITATION MARKEDLY FOR THE WASATCH FRONT AND EVEN MANY OF
THE NORTHERN MOUNTAINS. SOME SNOW IS STILL OCCURRING ACROSS PORTIONS
OF SOUTHWEST WYOMING AND LIKELY THE NORTH SLOPE OF THE UINTAS...AND
RADAR SUGGESTS SOME LIGHT SNOW ALSO IN THE VICINITY OF THE STANSBURY
AND CEDAR MOUNTAINS. ALTHOUGH ADDITIONAL PRECIPITATION IS STILL
POSSIBLE ACROSS NORTHERN ZONES THROUGH THIS AFTERNOON AS MOISTURE
CONTINUES TO WRAP BACK INTO THE AREA IN THE NORTH-NORTHEAST
FLOW...ANY ADDITIONAL ACCUMULATIONS SHOULD REMAIN LIGHT AT THIS
POINT. WINTER WEATHER HIGHLIGHTS HAVE BEEN CANCELLED FOR NORTHERN
UTAH AND SOUTHWEST WYOMING. THIS CANCELLATION INCLUDES THE BLOWING
SNOW ADVISORY FOR THE NORTHERN WASATCH FRONT. THE EASTERLY WINDS
SHOULD HAVE ALREADY PEAKED PER THE PRESSURE TRENDS AND THEY HAVE NOT
BEEN PARTICULARLY STRONG OVERNIGHT...SO ADDITIONAL IMPACTS ARE
MINIMAL.

THE STORM WILL EXIT THE AREA LATE TONIGHT WITH HIGH PRESSURE
BUILDING BACK INTO UTAH. OVERNIGHT MINS TONIGHT ARE EXPECTED TO BE
QUITE COLD DUE TO CLEARING SKIES...SNOW COVER...AND 700MB
TEMPERATURES OF -16C OVER SLC BY 12Z. WARM ADVECTION AT 700MB
STRENGTHENS TOMORROW WITH INCREASING MID AND HIGH CLOUDS FOR
NORTHERN UTAH. HOWEVER...THE STABLE AIRMASS WILL TRAP COLD AIR IN
THE VALLEYS...WITH ALL AREAS EXCEPT THE FAR SOUTH EXPECTED TO STAY
NEAR OR BELOW FREEZING THROUGH THE DAY.

THE NEXT STORM SYSTEM WILL SAG SOUTH FROM THE PACIFIC NORTHWEST INTO
NORTHERN UTAH TOMORROW NIGHT. PRECIPITATION IS EXPECTED TO BEGIN
FILLING IN ALONG THE IDAHO BORDER IN THE WARM SECTOR BEFORE A COLD
FRONT PUSHES MORE WIDESPREAD AND HEAVIER PRECIPITATION THROUGHOUT
NORTHERN UTAH DURING THE DAY SUNDAY. THE FRONT WILL THEN CONTINUE
THROUGH CENTRAL UTAH THROUGH THE EVENING HOURS WITH PRECIPITATION TO
FOLLOW. THE HEAVIEST SNOW IS EXPECTED TO COME IN A RELATIVELY QUICK
BURST ALONG THE FRONTAL BOUNDARY. ALTHOUGH QPF IS NOT PARTICULARLY
IMPRESSIVE...THE COLD AIRMASS COULD LEAD TO HIGHER SNOW RATIOS...AND
COMBINED WITH COLD SURFACE TEMPERATURES THERE IS A
POTENTIAL FOR SIGNIFICANT ACCUMULATIONS.

&&

.LONG TERM (AFTER 12Z MONDAY)...HIGHLY AMPLIFIED RIDGE OFF THE WEST
COAST AND A SHORTWAVE DROPPING DOWN THE EAST SIDE OF THE RIDGE EARLY
MONDAY WILL HELP TO DEVELOP A BROAD LONGWAVE TROUGH OVER THE WESTERN
UNITED STATES EARLY NEXT WEEK. MODELS CONTINUE TO BE IN DECENT
AGREEMENT WITH THE EVOLUTION OF THIS PATTERN WITH MINOR TIMING
DIFFERENCES NOTED BETWEEN THE 00Z EC AND THE 00Z GFS.

BOTH SOLUTIONS BRING VERY COLD 700MB TEMPERATURES TO THE CWA BY
TUESDAY AFTERNOON...WITH 700MB TEMPERATURES AROUND -14 TO -16C
ACROSS NORTHERN UTAH. THIS WILL BRING A PERIOD OF BELOW NORMAL
TEMPERATURES TO MUCH OF THE STATE TUESDAY INTO WEDNESDAY.

PERHAPS THE BIGGEST POSSIBLE IMPACT IN THE LONG TERM FORECAST PERIOD
CONTINUES TO BE THE POSSIBILITY OF A DOWNSLOPE WIND EVENT ACROSS THE
NORTHERN/CENTRAL WASATCH FRONT MONDAY EVENING THROUGH WEDNESDAY
MORNING. GLOBAL MODELS CONTINUE TO INDICATE FAIRLY SIGNIFICANT COLD
AIR ADVECTION ALONG WITH EASTERLY FLOW ACROSS THE AREA. TROUGH
ORIENTATION ACROSS THE WEST VARIES ENOUGH BETWEEN THE 00Z GFS AND
THE 00Z EC AND IS HIGHLY VARIED IN THE 00Z ENSEMBLE
GUIDANCE...KEEPING CONFIDENCE LIMITED AS TO THE POSSIBLE STRENGTH OF
THE DOWNSLOPE WIND EVENT. STARTED INCREASING THE WINDS A BIT ABOVE
THE LAST FORECAST PACKAGE GIVEN THE SIMILARITIES BETWEEN THE 00Z
OPERATIONAL MODELS...BUT DONT HAVE THE CONFIDENCE TO INCREASE THEM
AS HIGH AS SOME OF THE GUIDANCE WOULD INDICATE. CONTINUE TO MONITOR
THE FORECAST AS CONFIDENCE IN THE STRENGTH OF THE EVENT SHOULD
INCREASE OVER THE NEXT FEW DAYS.

AS THE TROUGH CUTS OFF TUESDAY INTO WEDNESDAY...EXPECT PRECIPITATION
NEAR THE BAROCLINIC ZONE STRETCHED ACROSS SOUTHERN UTAH/NORTHERN
ARIZONA TUESDAY. PRECIPITATION WILL CONTINUE INTO WEDNESDAY AS THE
LOW BEGINS TO EJECT EASTWARD AND THE BAROCLINIC ZONE SHIFTS SOUTH.
MAY BE LOOKING AT A LONG PERIOD OF LIGHT PRECIPITATION GIVEN THE
CONTINENTAL NATURE OF THE AIRMASS TUESDAY THROUGH THURSDAY ACROSS
THE SOUTHERN THIRD OF UTAH.

&&

.AVIATION...LIGHT AND VARIABLE WINDS AT THE SLC TERMINAL EARLY THIS
MORNING ARE EXPECTED TO BECOME PREDOMINANTLY NORTH TO NORTHWEST
BETWEEN 15-16Z AND REMAIN NORTHERLY FOR THE REMAINDER OF THE DAY.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING UNTIL NOON MST TODAY FOR UTZ014>016-517-518.

WY...NONE.

&&

$$

CHENG/KRUSE

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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