FXUS65 KSLC 070413
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
913 PM MST SUN DEC 6 2009
.SYNOPSIS..A STORM SYSTEM DEVELOPING ALONG THE WEST COAST
OVERNIGHT WILL TURN EAST TOWARDS THE GREAT BASIN MONDAY. THIS
STORM WILL RAPIDLY GAIN STRENGTH AS IT MOVES ACROSS THE BASIN
MONDAY NIGHT THROUGH TUESDAY. COLD TEMPERATURES AND LINGERING SHOWERS
ARE EXPECTED MIDWEEK.
&&
.DISCUSSION...WATER VAPOR LOOP SHOWS AN UPPER LOW SINKING INTO
NORTHERN CALIFORNIA AS A WEAKER DISTURBANCE LIFTS INTO THE NORTHERN
ROCKIES. A RIDGE DOMINATED OFF THE BRITISH COLUMBIA COAST...AS A
DISTURBANCE IS ABSORBED EAST FROM 38N/136W. 400-250MB ACARS WIND
OBSERVATIONS SHOWS A WESTERLY 125-150KT JET ACROSS THE GREAT BASIN
AND INTO THE CENTRAL ROCKIES. 00Z 700MB ANALYSIS SHOWS A CYCLONE
OVER FAR NORTHERN CALIFORNIA. WARM ADVECTION IS INITIATING LOCALLY
WITH -18C AT KSLC WITH -9C UPSTREAM AT KFGZ. 00Z KSLC RAOB INDICATES
3C OF COOLING ABOVE 700MB AND SLIGHT COOLING IN THE LOWER LEVELS
DURING THE PAST 24 HOURS.
GOES/RUC PRECIPITABLE WATER INDICATE VALUES RANGE FROM A TENTH OF AN
INCH ACROSS NORTHERN UTAH TO A QUARTER OF AN INCH ACROSS SOUTHERN
UTAH.
STRONG WARM ADVECTION IS ONGOING...WITH RUC ANALYSIS INDICATING A
10C TEMPERATURE GRADIENT BETWEEN LAS VEGAS AND SALT LAKE CITY.
FAVORED CORRIDOR OF ISENTROPIC UPGLIDE CAN BE TRACKED VIA IR
SATELLITE...SHOWING COOLING CLOUD TOPS FROM NORTH CENTRAL NEVADA
INTO NORTHWEST UTAH. ITS BEEN SNOWING AT ELKO NOW FOR MORE THAN 3
HOURS.
ALWAYS A CHALLENGE FORECASTING ONSET TIMING OF PRECIPITATION DURING
BOUTS OF STRONG WARM ADVECTION. ITS USUALLY BEST TO GO WITH A START
TIME SEVERAL HOURS BEFORE GUIDANCE WOULD SUGGEST. HAVE BUMPED POPS
UP ACROSS NORTHERN UTAH OVERNIGHT FOR THIS REASON. IT WILL BE
INITIALLY DIFFICULT FOR PRECIPITATION TO REACH THE VALLEY FLOOR
OWING TO A DRY AIRMASS IN PLACE. HOWEVER VISIBILITY DID GO FROM 9
MILES TO 1 IN A SPAN OF LESS THAN AN HOUR AT ELKO.
AM CONCERNED THAT EVEN A LIGHT SNOW OVERNIGHT MAY SET THE STAGE FOR
SLICK ROADWAYS...AS PAVEMENT TEMPERATURES ACROSS THE AREA ARE
CURRENTLY RANGING FROM THE UPPER TEENS TO THE LOWER 20S.
GUSTY CANYON WINDS ARE CURRENTLY ONGOING ACROSS NORTHERN UTAH...WITH
A STRONG PRESSURE GRADIENT IN PLACE FROM NORTHERN UTAH INTO WYOMING.
GUSTS ARE ON THE ORDER OF 25 TO 35 MPH...AND SHOULD DIMINISH AS
MONDAY MORNING PROGRESSES.
ACROSS SOUTHERN UTAH...THINGS STILL LOOK ON TRACK TO GET GOING
OVERNIGHT. AS A PACIFIC WAVE BECOMES ABSORBED INTO THE TROUGH OVER
CALIFORNIA TONIGHT...THE STORM SYSTEM WILL INHERIT DEEP LAYER
MOISTURE NECESSARY FOR THE PRODUCTION OF HEAVY PRECIPITATION
DURING THE NEXT COUPLE OF DAYS.
PREVIOUS DISCUSSION BELOW...
THE WEST-TO-EAST COLD CORE UPPER TROUGH ALONG THE
OREGON/CALIFORNIA BORDER WILL CONTINUE TO ELONGATE WEST-TO-EAST
OVERNIGHT...THEN TURN EAST INTO THE WRN GREAT BASIN MONDAY. THE
INGREDIENTS ARE THERE TO MAKE THIS A SIGNIFICANT WINTER STORM FOR
MONDAY NIGHT/TUESDAY...ESPECIALLY ACROSS SRN/CNTRL UTAH. COLD
TEMPERATURES AND LINGERING SHOWERS WILL REMAIN MIDWEEK IN THE WAKE
OF THE TROUGH....WITH A MOIST WESTERLY FLOW ALOFT PUNCHING INTO
THE BASIN BY NEXT WEEKEND.
THE APPROACHING SYSTEM WILL BRING GOOD DYNAMIC LIFT/MOISTURE/COLD
AIR ALOFT ALONG WITH A STRONG UPPER JET ACROSS ARIZONA MONDAY
NIGHT. THE RAPID INTENSIFICATION OF THE LEE SIDE SURFACE LOW OFF
THE CNTRL SIERRAS MONDAY INDICATIVE OF THE STRONG LIFT GENERATED
BY THIS STORM. HEAVY SNOW EXPECTED ACROSS MUCH OF THE SRN HALF OF
UTAH...WITH EVEN THE LOWEST ELEVATIONS NEAR THE ARIZONA BORDER
PICKING UP MEASURABLE SNOW. NRN UTAH WILL SEE MOST OF ITS SNOW
GENERATED IN THE MOIST SW FLOW ALOFT...FOLLOWED BY A PERIOD OF
INSTABILITY SNOWS IN THE WAKE OF THE TROUGH. AMOUNTS ARE EXPECTED
TO BE LESS THAN DOWN SOUTH DUE IN PART TO LESS FAVORABLE DYNAMICS
AND A SHORTER DURATION OF HEAVY PRECIP.
CYCLONIC NORTHERLY FLOW ALOFT MIDWEEK WILL KEEPS TEMPS VERY COLD
WITH SPOTTY LIGHT PRECIP POSSIBLE OVER THE FAR NORTH. EXTREME COLD
POSSIBLE WHERE DEEP SNOW COVER EXISTS. THE WESTERLIES WILL FINALLY
CUT UNDER THE ERN PACIFIC RIDGE AND RACE ACROSS THE CONUS BY NEXT
WEEKEND. THE WESTERLIES DO LOOK TO BE MOIST...WITH AN INCREASING
THREAT OF SNOW AND SPOTTY LOWER VALLEY RAIN LATE IN THE FORECAST
PERIOD.
&&
.AVIATION...LIGHT SOUTHEAST WINDS ARE EXPECTED TO CONTINUE THROUGH
THE NIGHT. INCREASING AND LOWERING CLOUDS WILL BE THE RULE OVERNIGHT
AS LIGHT SNOW FLURRIES TURN TO SNOW SHOWERS AFTER 06Z. A 40 PERCENT
CHANCE OF MVFR OR HIGH END IFR CONDITIONS ARE POSSIBLE AFTER 09Z.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING UNTIL 4 PM TUESDAY FOR UTZ517-UTZ518.
WINTER STORM WARNING FROM 3 AM MONDAY TO NOON TUESDAY FOR UTZ014-
UTZ015-UTZ016.
WINTER STORM WARNING FROM 6 AM MONDAY TO 6 AM TUESDAY FOR UTZ011-
UTZ012-UTZ013-UTZ019-UTZ020-UTZ021.
WINTER STORM WARNING FROM MIDNIGHT MONDAY TO 4 PM TUESDAY FOR
UTZ008-UTZ009-UTZ010.
WINTER WEATHER ADVISORY FROM 6 AM MONDAY TO 4 PM TUESDAY FOR
UTZ003-UTZ004-UTZ006.
WY...NONE.
&&
$$
PUBLIC...ROGOWSKI/CONGER
AVIATION...YOUNG
FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
