FXUS63 KDVN 052038
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
238 PM CST SAT DEC 5 2009
.SYNOPSIS...
A SHARP H5 TROF REMAINED OFF THE WEST COAST WITH A POTENT S/W
DIGGING THROUGH THE GREAT BASIN THIS MORNING. ANOTHER S/W WAS
ROTATING SOUTH THROUGH SRN MANITOBA AROUND A H5 LOW NEAR LK
SUPERIOR. A WEAK SURFACE LOW WAS LOCATED OVER LK SUPERIOR WITH A COLD
FRONT EXTENDING SW THROUGH THE NW TIP OF IA INTO NWRN KS. SLY FLOW
AHEAD OF THE FRONT ALONG WITH LOTS OF SUN HAVE PUSHED TEMPS INTO THE
30S OVER TH CWFA BY EARLY AFTERNOON.
&&
.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...
THERE IS GOOD AGREEMENT AMONG THE MODELS THAT THE COLD FRONT OVER NW
IA THIS AFTERNOON WILL MOVE SE AND STALL OVER THE SERN HALF OF THE
CWFA BY SUNDAY MORNING. S/W ENERGY EJECTING OUT OF THE DEVELOPING
WRN U.S. TROF IS PROGGED TO DEVELOP A SURFACE WAVE ON THE BOUNDARY IN
ERN KS BY SUNDAY EVENING WITH THE SURFACE WAVE LIFTING NE INTO NW
IL BY MONDAY MORNING. THIS WILL RESULT IN A SWATH OF 1 TO 3 INCHES
OF SNOW SUNDAY NIGHT OVER THE NORTHERN HALF OF CWFA.
TONIGHT AND SUNDAY WILL BE QUIET AS THE COLD FRONT SLIPS INTO THE
CWFA WITH LITTLE MORE THAN SOME SCT-BKN CI ASSOCIATED WITH IT
THROUGH SUNDAY MORNING. MIN TEMPS EXPECTED TO BE CLOSE TO THE
COOLER MAV NUMBERS. THE SURFACE PRESSURE GRADIENT SHOULD RELAX
ENOUGH TONIGHT TO ALLOW WINDS TO BECOME LIGHT SOUTHERLY AND WITH
ONLY SOME THIN CI EXPECTED...WE SHOULD BE ABLE TO RADIATE OUT ENOUGH
FOR A GOOD DROP IN TEMPS
SUNDAY THE FRONT IS EXPECTED TO STALL...ROUGHLY NEAR A KFFL-KFEP
LINE BY 18Z. MID/HIGH CLOUDS WILL INCREASE BEHIND THE FRONT OVER
THE NWRN CWFA DURING THE AFTERNOON...WHICH WILL HELP HOLD TEMPS
AROUND 30. THE SOUTHEAST WILL REMAIN ON THE WARM SIDE THROUGH THE
DAY...SO WENT WITH HIGHS AROUND 40 WHICH WAS CLOSE TO BOTH THE
MAV/MET NUMBERS. THE MODELS WERE GENERATING SOME LIGHT POST FRONTAL
QPF DURING THE AFTERNOON OVER THE FAR NRN CWFA SO INCREASED POPS IN
THE AFTERNOON TO CHANCE CATEGORY. THERE WAS SOME SUPPORT FOR THIS
IN THE FORCING FIELDS IN THE FORM OF SOME WEAK LOW/MID LEVEL FGEN.
ALSO THE AREA WILL BE THE RT ENTRANCE REGION OF AN H3 JET STREAK
FROM SRN MN THROUGH NRN MI.
THE BULK OF THE ENERGY WILL MOVE THROUGH THE CWFA SUNDAY
NIGHT...PEAKING IN THE IN THE 03-09Z TIME FRAME AS THE SURFACE WAVE
MOVES THROUGH THE SERN CWFA. MODELS ALL SHOW GOOD Q-VECTOR
CONVERGENCE MOVING THROUGH DURING THIS TIME WAS WELL AS SOME WEAK
FGEN IN THE LOW TO MID LEVELS OVER THE NRN THIRD OF THE CWFA.
THERMAL PROFILES ARE COLD ENUF TO JUSTIFY SNOW AS THE PTYPE OVER
MUCH OF AREA. THERE IS SOME POTENTIAL THOUGH FOR A MIX IN THE
EXTREME SOUTH...BUT THIS WILL BE DEPENDENT ON THE TRACK OF THE
SURFACE LOW. SNOW RATIOS OF 13-15 TO 1...SUPPORTED BY SURFACE TEMPS
IN THE LOW TO MID 20S...PW'S OF .3 TO .4 INCHES AND THE MODERATE
FORCING SUGGEST A 1-3 INCH SNOWFALL OVER THE NRN THREE FOURTHS OF
THE CWFA SUNDAY NIGHT WITH AMOUNTS TAPERING OFF THE TO AROUND A HALF
INCH NEAR THE MO BORDER. THE HIGHEST AMOUNTS ARE EXPECTED NEAR
HIGHWAY 20...WEST OF THE MISSISSIPPI RIVER. WINDS SHOULD BE AROUND
10KTS OR LESS DURING THE SNOWFALL...SO BLOWING AND SIGNIFICANT
DRIFTING ARE NOT EXPECTED.
.LONG TERM...MONDAY THROUGH SATURDAY
MONDAY AND MONDAY NIGHT...THE FIRST SYSTEM SHOULD PULL RAPIDLY
NORTHEAST OUT OF THE AREA WITH LITTLE ADDITION SNOW ACCUMULATION.
THE RESPITE WILL BE BRIEF OVERNIGHT MONDAY AS THE NEXT...AND MORE
SIGNIFICANT STORM SYSTEM TAKES SHAPE ON THE WEST SLOPE OF THE
ROCKIES BY TUESDAY MORNING.
TUESDAY AND WEDNESDAY...A SIGNIFICANT WINTER STORM WILL MOVE THROUGH
THE HEART OF THE COUNTRY DURING THIS PERIOD. 00 AND 12Z MODELS
AGREE IN THE BIG PICTURE...BUT SOME IMPORTANT DETAILS ARE STILL IN
FLUX. SNOW IS EXPECTED TO DEVELOP TUESDAY...MAXIMIZE OVERNIGHT AS
WINDS INCREASE...THEN END WEDNESDAY AS WINDS PERSIST.
THUS THERE IS HIGH CONFIDENCE OF SNOW AND STRONG WINDS AND A LIKELY
EXPECTATION OF HIGHLIGHTS IN THIS TIME FRAME. EXACT SNOW AMOUNTS
REMAIN IN QUESTION DEPENDING ON THE TRACK OF THE SURFACE LOW...BUT
HEAVY SNOW SOMEWHERE IN THE CWA IS A GOOD POSSIBILITY. 12Z GFS AND
ECM HAVE TRENDED A LITTLE FURTHER NORTH WITH THE SURFACE LOW FROM
PRIOR RUNS. ALSO...THE GFS DOES NOT DEEPEN THE SURFACE LOW AS MUCH
AS THE ECM AND GEM...AND THIS WILL IMPACT JUST HOW STRONG WINDS GET
AND HOW WIDESPREAD A PROBLEM BLOWING SNOW BECOMES. BOTTOM LINE...A
DECENT WINTER STORM IS IN THE OFFING..BUT JUST HOW SIGNIFICANT IT IS
AND THE DETAILS OF HOW EXACTLY IT WILL IMPACT US AWAIT LATER MODEL
RUNS.
THURSDAY THROUGH SATURDAY...AS THE MID WEEK STORM MOVES EAST...THE
00Z GFS AND ECM DISAGREE WITH THE EVOLUTION OF THE SURFACE LOW IN
THE MIDWEST FRIDAY. THE 12Z ECM HAS NOW COME IN LINE WITH THE 00Z
AND 12Z GFS...SO THE BOTTOM LINE IS THAT SURFACE RIDGING WILL
DOMINATE THROUGH THE PERIOD WITH LITTLE CHANCE OF PRECIP.
ANTICIPATED SNOW COVER SHOULD HAVE A NOTABLE EFFECT ON TEMPS...SO
HAVE DROPPED MINS AND MODERATED THE DAYTIME RECOVERY AS A RESULT.
WOLF
&&
.AVIATION...
VFR CONDITIONS WILL BE OVER ALL TAFS SITES THROUGH 18Z SUNDAY. THROUGH
12Z ONLY SOME SCT-BKN CI EXPECTED OVER THE AREA WITH S WINDS
DIMINISHING TO 5 TO 10KTS AFTER 00Z. THE COLD FRONT WILL MOVE INTO
THE KCID/KDBQ VCNTY BETWEEN 15Z AND 18Z CAUSING WINDS TO BECOME
LIGHT NELY WITH CIGS AROUND 8-12KFT MOVING IN.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
DLF/WOLF
