FXUS65 KSLC 232233
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
333 PM MST WED DEC 23 2009
.SYNOPSIS...A COLD AND GENERALLY DRY NORTHWEST FLOW ALOFT WILL BE
OVER THE AREA THE NEXT TWO DAYS.
&&
.DISCUSSION...SHORT TERM...LOW TO MID LEVEL NORTHWEST FLOW IS
PRODUCING STRATUS OVER AND UPSTREAM OF TERRAIN WHERE UPSLOPE
CONDITIONS ARE CREATED. SNOW FLURRIES WILL PERSIST IN THESE
REGIONS INTO THIS EVENING. SNOW COVERED VALLEYS WITHOUT CLOUD
COVER OR WIND ARE LIKELY TO SEE PATCHY FOG DEVELOP OVERNIGHT. 700
MB TEMPERATURES ARE NOT LOOKING AS COLD IN THE LATEST MODELS AS
THEY HAVE LOOKED EARLIER IN THE WEEK...SO ALTHOUGH ANY PLACE WITH
SNOW COVER AND CLEAR SKIES WILL SEE COLD MORNING TEMPERATURES...IT
WILL NOT BE AS COLD AS EARLIER FORECASTS INDICATED.
DOWNSLOPE AND GAP WINDS JUST BELOW ADVISORY LEVEL EXPECTED TO
CONTINUE OVERNIGHT IN PORTIONS OF WASHINGTON COUNTY. WINDS WILL
DECREASE THURSDAY.
LONGER TERM...ALL MODELS IN VERY GOOD AGREEMENT IN PATTERN
EVOLUTION AS AN UPPER RIDGE DEVELOPS ALONG THE WEST COAST AND
SLOWLY MOVES INLAND. BUT BEFORE IT REACHES THE GREAT BASIN THE
RIDGE PINCHES OFF INTO A CLOSED HIGH AND MIGRATES NORTH INTO
SOUTHERN CANADA. WESTERLY FLOW UNDERCUTS THIS RIDGE TO SUCH AN
EXTENT THAT THE STORM TRACK ENDS UP GOING THROUGH AZ/NM WITH UTAH
IN A REGION OF LIGHT FLOW BEGINNING THIS WEEKEND. SOME REMNANT
MOISTURE FROM THE PASSING STORMS WORKS INTO THE NO FLOW REGION AND
THERE IS SOME CHANCE OF LIGHT SNOW FROM LATE SUNDAY ON INTO NEXT
WEEK...BUT TIME/HEIGHT SECTIONS SHOW THAT ALTHOUGH THE MOISTURE
EXISTS THROUGH A DEEP LAYER...THERE IS NO ASCENT AND WITH NO WIND
THERE WILL BE NO OROGRAPHIC LIFT EITHER.
BY THE MIDDLE OF NEXT WEEK ALL MODELS INDICATE FLOW MAY BEGIN TO
CONSOLIDATE BUT DETAILS DIFFER SIGNIFICANTLY FROM MODEL TO MODEL
AND RUN TO RUN.
A KEY ELEMENT OF THE PATTERN EVOLUTION DESCRIBED ABOVE IS THAT THE
UPPER RIDGE AND ASSOCIATED WARM AIR ALOFT NEVER MAKES IT TO UTAH.
RESULTING 700 MB TEMPERATURES REMAIN AROUND MINUS 10 THROUGH THE
PERIOD. SO ALTHOUGH THE AIRMASS WILL BE STABLE...IT ALREADY IS
STABLE...WE SHOULD NOT DEVELOP A KILLER INVERSION LIKE WE HAD THIS
PAST WEEKEND AND MONDAY OVER THE NORTHERN VALLEYS. THERE WILL BE
HAZE AND VALLEY FOG...BUT THERE IS A BETTER CHANCE OF SOME MIXING
WITHIN THE STABLE LAYER WITH THIS SITUATION SINCE THE AIR ALOFT IS
NOT AS WARM.
&&
.AVIATION...CEILINGS STRUGGLING TO IMPROVE BEYOND MVFR EARLY THIS
AFTERNOON...WILL MOST LIKELY SCATTER DURING THE LATE AFTERNOON OR
AROUND SUNSET. WITH LOW LEVEL MOISTURE REMAINING IN THE
AREA...WILL HAVE TO WATCH FOR THE FOG POTENTIAL TONIGHT. FOG
POTENTIAL WILL HINGE ON HOW MUCH CLEARING CAN TAKE PLACE THIS
EVENING. SURFACE WIND DIRECTION SHOULD REMAIN LIGHT OUT OF THE
NORTHWEST THROUGH THE REMAINDER OF THE DAY...BEFORE BECOMING
VARIABLE DURING THE EVENING. SOUTHEASTERLY DRAINAGE WINDS DEVELOP
LATER TONIGHT.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&
$$
PUBLIC...DUNN
AVIATION...ROGOWSKI
FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
