FXUS65 KSLC 080400
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
900 PM MST MON DEC 7 2009

.SYNOPSIS..UNNECESSARY TRAVEL IS DISCOURAGED TONIGHT ALONG ALL OF 
INTERSTATE 70 AND INTERSTATE 15 FROM SANTAQUIN SOUTH TO ST GEORGE. A
STORM SYSTEM WILL EXIT CALIFORNIA THIS EVENING AND MOVE EAST
ACROSS THE GREAT BASIN LATE TONIGHT THROUGH TUESDAY. A VERY COLD
NORTHERLY FLOW ALOFT WILL DEVELOP MIDWEEK...PRODUCING BITTERLY
COLD TEMPERATURES THROUGH THE END OF THE WEEK.

&&

.DISCUSSION...UNNECESSARY TRAVEL IS DISCOURAGED TONIGHT ALONG ALL OF 
INTERSTATE 70 AND INTERSTATE 15 FROM SANTAQUIN SOUTH TO ST GEORGE.

WATER VAPOR LOOP SHOWS AN UPPER TROUGH APPROACHING FROM THE WESTERN 
GREAT BASIN. A TRAILING WAVE IS SINKING THROUGH BRITISH COLUMBIA. A 
RIDGE DOMINATED THE EASTERN PACIFIC WITH AN UPPER LOW SPINNING OVER 
43N/152W. 400-250MB ACARS WIND OBSERVATIONS SHOWS THE UPPER TROUGH 
OVER WESTERN NEVADA AND SOUTHERN CALIFORNIA...WITH A 100-140KT JET 
ROUNDING THE BASE OF THE TROUGH AND EXTENDING THROUGH THE NORTH 
CENTRAL CONUS AND NEW ENGLAND. 00Z 700MB ANALYSIS SHOWS A CYCLONE 
OVER WESTERN NEVADA. ADVECTION IS TURNING NEUTRAL WITH -10C REPORTED 
AT KSLC AND UPSTREAM AT KDRA. 00Z KSLC RAOB INDICATES 5-7C OF 
WARMING ABOVE 750MB DURING THE PAST 24 HOURS. A STRONG VEERING 
SIGNATURE WAS PRESENT INDICATIVE OF WARM ADVECTION. AN INVERSION WAS 
LOCATED BELOW 750MB.

GOES/RUC PRECIPITABLE WATER INDICATE VALUES RANGE FROM A QUARTER 
INCH ACROSS NORTHERN UTAH TO A HALF INCH ACROSS SOUTHERN UTAH.

BLENDED TOTAL PRECIPITABLE WATER LOOP INDICATES NOSE OF RICH 
MOISTURE (VALUES > 1") WRAPPING NORTHWARD ACROSS SOUTHERN CALIFORNIA 
WITH AIM AT SOUTHERN NEVADA AND NORTHERN ARIZONA. RADAR RETURNS 
ACROSS SOUTHERN UTAH HAVE INCREASED AS A RESULT DURING THE PAST 
SEVERAL HOURS. IR SATELLITE SHOWS COOLING CLOUD TOPS FROM SOUTHWEST 
UTAH NORTHWARD ALONG THE NEVADA BORDER...APPROACHING THE BAROCLINIC 
ZONE WHICH IS MARCHING ACROSS EASTERN NEVADA PER RUC ANALYSIS.

IT APPEARS THAT THIS MARKS THE BEGINNING OF THE TRANSITION FROM PURE 
WARM ADVECTION PRECIPITATION WITH AREAS FAVORED BY SOUTHWEST 
OROGRAPHIC FLOW TO THE PASSAGE OF THE BAROCLINIC ZONE WHICH THEN 
SHIFTS HEAVIER PRECIPITATION TO AREAS FAVORED BY NORTHWEST FLOW IN 
ITS WAKE TOMORROW MORNING.   

WENT AHEAD AND RAISED POPS ACROSS WESTERN AND NORTHERN ZONES TO 
ACCOUNT FOR A BETTER CHANCE OF SNOWFALL WITH THE PASSAGE OF THE
700MB COLD FRONT FROM THE WEST OVERNIGHT. OTHERWISE TWEAKED
OVERNIGHT TEMPERATURES BASED ON LATEST OBSERVATIONS AND GUIDANCE.

LOOKING AHEAD TO TOMORROW MORNING WHEN NORTHWESTERLY FLOW SETS 
UP...700MB TEMPERATURES FALL FROM -15C TO -20C DURING THE DAYTIME. 
18Z NAM BUFKIT FORECAST SOUNDING FOR KSLC SUGGESTS WITH LAKE 
TEMPERATURES AT +5C...THAT LAKE INDUCED CAPE WILL BE ABOUT 500 
J/KG...WITH EQUILIBRIUM LEVELS BETWEEN 10KFT AND 12KFT. ENOUGH 
INSTABILITY EXISTS FOR SNOW SHOWERS OFF THE LAKE AS COLDER AIRMASS 
FILTERS IN THE REGION TUESDAY.

PREVIOUS DISCUSSION BELOW...

THIS STORM WILL LIKELY MAINTAIN GOOD BAROCLINIC STRUCTURE AS IT 
MOVES THROUGH THE BASIN...PRODUCING HEAVY SNOW ACROSS MUCH OF 
SRN/ERN UTAH INTO EARLY TUESDAY. NRN UTAH WILL COME UP A BIT ON THE 
LOW SIDE...WITH MOST OF THE PRECIP ASSOCIATED WITH THE TROUGH 
PASSAGE AND IN THE COLD ADVECTION THAT FOLLOWS ON TUESDAY. 
OROGRAPHICS WILL BE IN PLAY WITH AREAS FAVORING SW FLOW GETTING THE 
HEAVY PRECIP THIS EVENING...AND THOSE FAVORING NW FLOW LATE 
TONIGHT/TUESDAY MORNING. THE NUMEROUS WINTER WEATHER HIGHLIGHTS IN 
EFFECT WERE LEFT IN PLACE AS ISSUED EARLIER.

THE COLD CYCLONIC NORTHERLY FLOW TO FOLLOW ON WEDNESDAY SHOULD
OFFER UP THE COLDEST TEMPERATURES OF THE SEASON SO FAR. THIS
CONTINENTAL POLAR AIRMASS WILL FOR THE MOST PART REMAIN EAST OF
THE DIVIDE...THOUGH PLENTY WILL FILTER INTO NRN UTAH MIDWEEK. THE
REMAINDER OF UTAH WILL LIKELY HAVE EXTENSIVE SNOW COVER AND
GENERALLY CLEAR SKIES TO DRIVE TEMPS DOWN SHARPLY MIDWEEK.

THE DEVELOPMENT OF A MOIST WESTERLY FLOW BY THE WEEKEND WILL OFFER
UP ANOTHER ROUND OF SNOW HEADING INTO EARLY NEXT WEEK. OVERRUNNING
PRECIP A GOOD BET WITH COLD AIR DOMED INTO THE VALLEYS AND
OROGRAPHIC INFLUENCES IN THE MOUNTAINS. EMBEDDED SHORTWAVES WILL
ENHANCE PRECIP AS THEY PASS THROUGH THE REGION...WITH THE
STRONGEST OF THESE SCHEDULED TO ARRIVE LATE THIS WEEKEND. PRECIP
TYPE WILL LIKELY BE SNOW EVERYWHERE SAVE THE UT/AZ BORDER REGION
WHERE TEMPS MAY WARM ENOUGH KEEP RAIN OVER SNOW.

&&

.AVIATION...MVFR CEILINGS ARE EXPECTED TO CONTINUE THROUGH THE 
NIGHT AT THE KSLC TERMINAL...WITH LIGHT SNOW SHOWERS ESPECIALLY 
OVER THE SURROUNDING TERRAIN. A 30 PERCENT CHANCE EXISTS THAT IFR 
VISIBILITIES WILL OCCUR IN HEAVIER SNOW SHOWERS UNTIL MIDNIGHT THEN 
BECOME MORE WIDESPREAD. SNOW WILL THEN CONTINUE THROUGH THE DAY 
TUESDAY. TOTAL ACCUMULATIONS OF 1 TO 3 INCHES ARE POSSIBLE AT THE 
TERMINAL. LIGHT SOUTHWESTERLY WINDS WILL TURN NORTHWEST AROUND 03Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING UNTIL 4 PM TUESDAY FOR UTZ008-UTZ009-UTZ010-
     UTZ517-UTZ518.

     WINTER STORM WARNING UNTIL NOON TUESDAY FOR UTZ014-UTZ015-UTZ016.

     WINTER STORM WARNING UNTIL 6 AM TUESDAY FOR UTZ011-UTZ012-UTZ013-
     UTZ019-UTZ020-UTZ021.

     WINTER WEATHER ADVISORY UNTIL 4 PM TUESDAY FOR UTZ003-UTZ004-
     UTZ006.

WY...NONE.

&&

$$

PUBLIC...ROGOWSKI/CONGER
AVIATION...YOUNG

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