FXUS65 KSLC 100435
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
935 PM MST WED DEC 9 2009
.SYNOPSIS...A VERY COLD AND STABLE NORTHERLY FLOW ALOFT WILL
EXIST ACROSS THE AREA TONIGHT. GENERALLY DRY AND COLD CONDITIONS
WILL EXIST THROUGH THE REMAINDER OF THE WEEK. A MOIST WESTERLY
FLOW OFF THE PACIFIC WILL ENTER THE GREAT BASIN LATE FRIDAY...AND
REMAIN THROUGH THE WEEKEND.
&&
.DISCUSSION...WATER VAPOR LOOP SHOWS A DISTURBANCE MOVING ACROSS THE
CENTRAL ROCKIES. A SERIES OF WEAK DISTURBANCES WERE ROTATING AROUND
40N/140W...WEST OF A WEAKNESS IN THE EASTERN PACIFIC RIDGE.
400-250MB ACARS WIND OBSERVATIONS SHOWS A CONFLUENCE ZONE
ALOFT...WITH A SINGLE 140-185KT JET FROM THE SOUTHERN ROCKIES INTO
THE MID ATLANTIC. 00Z 700MB ANALYSIS SHOWS THE TIGHT HEIGHT GRADIENT
IS SHIFTING EAST AS THE CYCLONE RACES ACROSS THE GREAT LAKES. WARM
ADVECTION CONTINUES WITH -19C REPORTED AT KSLC AND -15C UPSTREAM AT
KLKN. 00Z KSLC RAOB INDICATES 3-5C OF WARMING IN THE COLUMN DURING
THE PAST 24 HOURS...WITH THE STRONGEST WARMING ALOFT.
GOES/RUC PRECIPITABLE WATER INDICATE VALUES REMAIN AT A TENTH OF AN
INCH ACROSS THE FORECAST AREA.
MAIN FORECAST CHALLENGE TONIGHT IS THE LOW TEMPERATURE FORECAST.
STARTED WITH THE OVERNIGHT LOWS LAST NIGHT SINCE THE SNOWPACK HAS
NOT CHANGED MUCH. WITH WARMING OCCURRING ALOFT...NUDGED HIGHER
ELEVATIONS A BIT WARMER ESPECIALLY ACROSS THE SOUTH. 24 HOUR
TEMPERATURE CHANGE IS 2-9F WARMER ACROSS THE NORTH DUE TO
COMBINATION OF EARLIER CLOUDS AND WINDS...5-13F COOLER ACROSS THE
SOUTHERN VALLEYS. WARMED UP FORECAST TO VALUES SLIGHTLY WARMER THAN
LAST NIGHT ACROSS THE SALT LAKE VALLEY...NORTHERN WASATCH FRONT AND
SOUTHWEST WYOMING DUE TO PRESENCE OF DRAINAGE/GRADIENT WINDS.
UNDERCUT LOWS LAST NIGHT ACROSS SOUTHERN VALLEYS DUE TO TEMPERATURE
TRENDS AND CURRENT READINGS...WHILE ALLOWING WARMING IN THE HIGHER
TERRAIN.
SKIES CONTINUE TO CLEAR OUT ACROSS FAR NORTHERN UTAH AND SOUTHWEST
WYOMING AS THE DISTURBANCE EXITS EAST. HAVE ADJUSTED SKY GRIDS TO
REFLECT THE CLEAR SKIES ELSEWHERE ACROSS THE STATE. ALSO NUDGED
WINDS TO THE LATEST GUIDANCE.
PREVIOUS DISCUSSION BELOW...
A PATTERN CHANGE WILL FINALLY ALLOW THE WESTERLIES TO PUNCH THROUGH
THE COAST AND INTO THE INTERIOR WEST BY LATE FRIDAY. INTERESTING
SITUATION SETTING UP FOR FRIDAY NIGHT/SATURDAY WITH A DOME OF VERY
COLD AIR IN THE VALLEYS BECOMING OVERRUN WITH A RELATIVELY WARM AND
MOIST AIRMASS. COULD SEE A SITUATION WHERE LIGHT SNOW PRECIP
DEVELOPS OVER THE WRN VALLEYS BY SATURDAY...WITH A LITTLE HEAVIER
PRECIP ALONG THE WEST SLOPES OF THE MOUNTAINS. THE BEST THREAT FOR
ORGANIZED PRECIP WILL COME SATURDAY NIGHT/SUNDAY WHEN A FAIRLY WELL
DEVELOPED TROUGH RACES THROUGH THE REGION. THIS FEATURE WILL HAVE
PLENTY OF MOISTURE AVAILABLE FOR WHAT LOOKS TO BE MODEST DYNAMIC
LIFT...A WEAK SURFACE FEATURE...AND DECENT COLD AIR ALOFT. THIS
FEATURE...BESIDES THE PRECIP IT PRODUCES...SHOULD HAVE ENOUGH KICK
TO SCOURER OUT THE COLD AIR IN THE WRN VALLEYS. THE ERN VALLEYS MAY
BE A BIT MORE OF A CHALLENGE AS THE PRECIP PROBABLY WONT BE AS
EXTENSIVE AND THE SURFACE WINDS SOMEWHAT LESS OWING TO THE WEAK
NATURE OF THE SURFACE FRONT.
HIGH PRESSURE ALOFT WILL RETURN FOR THE EARLY PORTION OF THE WEEK.
THE CORE OF THE MOIST WESTERLIES WILL SKIRT ALONG THE UT/ID BORDER
REGION...POSSIBLE PRODUCING LIGHT PRECIP OVER THE FAR NRN ZONES.
EXTENSIVE SNOW COVER OUTSIDE OF THE LOWEST VALLEYS WILL INHIBIT
AN WARMING...SO WILL KEEP READINGS A AT OR BELOW SEASONAL NORMS IN
THE EXTENDED PERIOD.
&&
.AVIATION...WINDS AT THE SLC TERMINAL ARE EXPECTED STAY FROM THE
SOUTHEAST OVERNIGHT. THERE IS ONLY A 10 PERCENT CHANCE THAT FOG
COULD DROP VISIBILITIES INTO THE IFR TO MVFR RANGE BETWEEN 10Z AND
14Z...DEPENDING ON HOW STRONG THE SURFACE WINDS REMAIN THROUGH THE
NIGHT.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&
$$
PUBLIC...ROGOWSKI/CONGER
AVIATION...SCHOENING
FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
