FXUS65 KSLC 111718
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
1018 AM MST FRI DEC 11 2009

.SYNOPSIS...A SERIES OF MOIST BUT RELATIVELY MILD PACIFIC STORM 
SYSTEMS WILL IMPACT THE REGION THROUGH THE WEEKEND. HIGH PRESSURE
WILL THEN DEVELOP OVER THE AREA THROUGH THE MIDDLE PART OF NEXT
WEEK.

&&

.DISCUSSION...SURFACE HIGH PRESSURE REMAINED IN PLACE ACROSS MUCH
OF THE FORECAST AREA OVERNIGHT INTO EARLY THIS MORNING...ALLOWING
FOR ANOTHER COLD START ACROSS MOST VALLEY LOCATIONS. 12Z KSLC
SOUNDING SHOWED CONSIDERABLE WARMING ALOFT OVER THE PAST 24 HOURS
WITHIN THE 800-650MB LAYER. THIS WILL ALLOW FOR WARMER MAX TEMPS
ACROSS THE HIGHER TERRAIN TODAY...HOWEVER SHALLOW COLD AIR WILL
REMAIN TRAPPED ACROSS MOST VALLEY LOCATIONS AGAIN TODAY. 

AN ACTIVE WESTERLY FLOW WITH SEVERAL EMBEDDED SHORTWAVE TROUGHS
WILL IMPACT THE FORECAST AREA THROUGH THE UPCOMING WEEKEND. THE
FIRST IN THIS SERIES OF WAVES IS CURRENTLY MOVING THROUGH THE
SOUTHERN GREAT BASIN. LIGHT SNOW HAS BEEN REPORTED ACROSS PORTIONS
OF WESTERN AND SOUTHERN NV WITH THIS WAVE...WHILE DOWNSTREAM AN
ARC OF PRIMARILY VIRGA IS NOTED EXTENDING ACROSS SOUTHWEST UT
WITHIN PLUME OF MOISTURE ADVECTION. 

AS THIS WAVE CONTINUES EAST TODAY INTO TONIGHT ANTICIPATE SNOWFALL
TO DEVELOP ACROSS THE HIGHER TERRAIN OF SOUTHERN AND CENTRAL UT
THIS AFTERNOON...AND SPREAD INTO THE NORTHERN MOUNTAINS OVERNIGHT.
MODEL TIME-HT SECTIONS SHOW VERY WEAK OMEGA ACROSS NORTHERN UT
LATE TONIGHT INTO EARLY SATURDAY...AND WITH VERY DRY BOUNDARY
LAYER IT MAY TAKE SOME TIME FOR AIRMASS TO SATURATE SUFFICIENTLY
TO ALLOW FOR SNOW DOWN TO THE VALLEY FLOORS. HOWEVER...CURRENT
THINKING IS THERE WILL BE A FAVORABLE WINDOW FROM ROUGHLY 10Z
TONIGHT THROUGH SUNRISE SATURDAY FOR LIGHT SNOW ACROSS THE
NORTHERN AND CENTRAL VALLEYS. ANY ACCUMULATION WOULD LIKELY REMAIN
AN INCH OR LESS...HOWEVER GIVEN VERY COLD SURFACE TEMPS ANY SNOW
WHICH FALLS WOULD ACCUMULATE ALONG UNTREATED SURFACES. WILL LIKELY
BUMP POPS FOR OVERNIGHT/EARLY SATURDAY PERIOD WITH AFTERNOON
PACKAGE. 

SECONDARY WAVE ON THE HEELS OF THE FIRST IS EXPECTED TO SPREAD
INTO SOUTHERN AND CENTRAL UT SATURDAY...ALLOWING FOR FAIRLY
WIDESPREAD SNOWFALL ABOVE ROUGHLY 4500 FT. MAY NEED TO UPGRADE
GOING WATCH FOR THESE AREAS WITH AFTERNOON PACKAGE AS WELL.

OTHERWISE 12Z MODELS CONTINUE TO BRING STRONG AND MOIST SHORTWAVE
THROUGH THE REGION SUNDAY...WITH STRENGTHENING SOUTHERLY FLOW
AHEAD OF THIS SYSTEM SATURDAY NIGHT. THIS FLOW SHOULD EFFECTIVELY
SCOUR OUT REMAINING VALLEY INVERSIONS EXCEPT PERHAPS ACROSS THE
CACHE VALLEY AND UINTA BASIN...WITH MANY VALLEYS REALIZING MAX
TEMPERATURES AFTER SUNSET SATURDAY. 

BEST LARGE SCALE ASCENT OVERSPREADS MUCH OF UTAH SUNDAY...WITH
WIDESPREAD AND POTENTIALLY HEAVY SNOWFALL ACROSS MOST LOCATIONS
EXCLUDING UTAHS DIXIE AND LAKE POWELL. ALTHOUGH WET-BULB ZERO
LEVELS WOULD SUGGEST SNOW LEVELS MAY REMAIN ABOVE THE VALLEY
FLOORS THROUGH AT LEAST SUNDAY MORNING...PRECIS INTENSITY MAY
SUFFICIENT FOR ALL SNOW THROUGH THE DURATION OF THE EVENT. IN
ADDITION TO POSSIBLY UPGRADING SOUTHERN/CENTRAL MOUNTAINS...MAY
NEED TO EXPAND WATCH INTO REMAINING NORTHERN AND CENTRAL VALLEYS
FOR LATE SATURDAY NIGHT THROUGH SUNDAY. SNOWFALL WITHIN POST
FRONTAL ENVIRONMENT LOOKS TO PERSIST ACROSS THE HIGHER TERRAIN OF
NORTHERN UT INTO MONDAY...WITH LOCALLY UP TO 3 FEET POSSIBLE.

WILL UPDATE ZONES/GRIDS TO REMOVE MORNING FOG ALONG WITH OTHER
MINOR ADJUSTMENTS. WILL HOLD OFF ON ANY SIGNIFICANT CHANGES TO
WEEKEND TIMEFRAME UNTIL THIS AFTERNOON...AND ALLOW FOR THE 12Z
ECMWF ALONG WITH 18Z MODEL RUNS. 

&&

.AVIATION...VFR CONDITIONS ARE EXPECTED TO PREVAIL AT THE SLC 
TERMINAL THROUGH THE DAY TODAY. CEILINGS ARE EXPECTED TO REMAIN 
ABOVE 7000FT AGL THROUGH EARLY THIS EVENING THEN LOWER BELOW 6000 FT 
BETWEEN 02-04Z. CIGS SHOULD LOWER INTO MVFR RANGE BETWEEN 08-10Z AND 
THERE WILL BE A CHANCE OF LIGHT SNOW STARTING AROUND 10Z. THERE IS A 
30 PERCENT CHANCE OF IFR VSBYS IN LIGHT SNOW AFTER 10-11Z CONTINUING 
THRU ABOUT 18Z SAT. WINDS WILL BE LIGHT AND VARIABLE BECOMING LIGHT 
NORTHERLY BY 18Z. WINDS SHOULD SHIFT BACK TO SOUTHEASTERLY BETWEEN 
01-03Z AND REMAIN THAT WAY INTO SAT.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WATCH FROM 5 PM SATURDAY TO 11 PM SUNDAY FOR UTZ001-
     UTZ002-UTZ004-UTZ006-UTZ016-UTZ518.

     WINTER STORM WATCH FROM 5 PM SATURDAY TO 9 AM MONDAY FOR UTZ007-
     UTZ008-UTZ009-UTZ010-UTZ517.

WY...NONE.

&&

$$

SEAMAN/WILENSKY

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)