FXUS63 KDVN 020927
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
327 AM CST WED DEC 2 2009
.SYNOPSIS...
A COLD FRONT IS SLOWLY SAGGING SOUTHEAST ACROSS THE FORECAST AREA
THIS MORNING...WITH NORTHWEST FLOW BEHIND IT BRINGING IN COLDER AIR
AND BREEZY NORTHWEST WINDS BEHIND IT. THERE IS A SURFACE LOW OVER
THE UP OF MICHIGAN...MOVING NORTHEAST WITH PRETTY SIGNIFICANT
PRESSURE FALLS AHEAD OF IT. THERE IS ALSO A SURFACE LOW OVER FAR
EASTERN TEXAS...WITH EVEN STRONGER PRESSURE FALLS EAST-NORTHEAST OF
IT OVER MISSISSIPPI AND ALABAMA. AT UPPER LEVELS EACH OF THE
SURFACE LOW FEATURES IS ASSOCIATED WITH AN UPPER LEVEL LOW. THE
NORTHERN FEATURE IS A MORE OPEN WAVE...BUT WITH PRESSURE FALLS
INDICATING IT IS STILL DIGGING SOUTHEAST FROM NEAR WINNIPEG DOWN
INTO NORTHERN MINNESOTA. THE SOUTHERN UPPER LOW IS THE ONE WE HAVE
BEEN FOLLOWING ACROSS THE FAR SOUTHWEST CONUS FOR A COUPLE DAYS
NOW...AND IS FAIRLY WELL CUT OFF BUT HAS PRESSURE FALLS TO ITS EAST
SHOWING SLOW EASTWARD MOVEMENT. MOST OF THE MOISTURE AT 850MB IS OF
COURSE ASSOCIATED WITH THE SOUTHERN SYSTEM...WITH DEWPOINTS UP
AROUND 8DEG C ACROSS THE GULF COAST STATES.
&&
.SHORT TERM...TODAY AND TONIGHT...
THE SOUTHERN AND NORTHERN STREAM SYSTEM ARE GOING TO GO THROUGH
PHASING IN THE NEXT 24-48 HOURS...AND THE MAIN QUESTION WITH THIS
HAS BEEN WHETHER THE SOUTHERN STREAM SYSTEM CAN BRING PRECIPITATION
INTO THE CWA WEDNESDAY AS IT MOVES NORTHEAST ACROSS THE OHIO VALLEY
TODAY AND THIS EVENING. MODELS ARE STILL SHOWING SOME DIFFERENCES...
MAINLY IN HOW FAR NORTHWEST THE PRECIPITATION MOVES INTO THE AREA
THIS AFTERNOON AND EVENING. AN ANALYSIS OF THE EVENING
INITIALIZATION SHOWS THAT THE GFS SEEMS TO HAVE A BETTER HANDLE ON
THE 850MB DEWPOINT FIELD THAN THE NAM...WHICH IS SIGNIFICANTLY DRIER
THAN THE GFS BY LATER IN THE DAY. THIS DRY BIAS HAVING SHOT DOWN THE
NAM RUNS...HAVE GONE WITH THE WETTER SOLUTIONS PRESENTED BY NEARLY
ALL THE OTHER MODEL RUNS...WHICH BRING LIGHT PRECIPITATION INTO THE
SOUTHEAST CORNER OF THE FORECAST AREA THIS AFTERNOON AND EVENING...
WITH QPF VALUES GENERALLY LESS THAN A FIVE HUNDREDTHS OF AN INCH. WE
SHOULD GET WRAP AROUND CLOUDS CURRENTLY AFFECTING MINNESOTA IN
HERE...THE TROUBLE IS IN THE TIMING. CURRENTLY THE STRATUS IS ALREADY
OVER MINNESOTA...AND WITH FAIRLY STRONG NORTH FLOW AT 925 MB...WOULD
EXPECT THAT IT WOULD ADVECT ON DOWN HERE THIS MORNING. HOWEVER...THE
MODELS DELAY THESE LOW CLOUDS WITH SUBSIDENCE OFF THE SOUTHERN STREAM
SYSTEM UNTIL AT LEAST THIS AFTERNOON...AND THE GFS MOS GUIDANCE
DELAYS THESE 25HFT CLOUDS UNTIL THIS EVENING. THESE CLOUDS HAVE THE
POTENTIAL TO PRODUCE FLURRIES. ONCE THEY DO GET IN HERE. FOR NOW HAVE
TRIED TO GO WITH A SLIGHTLY EARLIER VERSION OF THE GUIDANCE...AND
BROUGHT THEM IN THIS EVENING TO THEN PRODUCE FLURRIES THE REST OF THE
NIGHT. TEMPERATURES TODAY AND TONIGHT WILL BE SIGNIFICANTLY COLDER
THAN YESTERDAY...AND WE MAY VERY WELL HAVE HAD OUR MAX TEMP BACK AT
MIDNIGHT...WITH ONLY A VERY SMALL RISE THIS AFTERNOON...AND THEN MUCH
COLDER TEMPERATURES TONIGHT WITH CONTINUING COLD AIR ADVECTION.
..LE..
.LONG TERM...THURSDAY THROUGH NEXT TUESDAY...
COLD CORE UPPER TROF STILL ON TRACK TO ROTATE OVERHEAD LATE THU AND
THU NIGHT. EMBEDDED VORT WILL COMBINE WITH STEEP LLVL LAPSE RATES TO
GENERATE SCTRD SNOW SHOWERS AND FLURRY ACTIVITY THU AFTERNOON WITH A
DUSTING OF ACCUMULATION POSSIBLE ALONG AND NORTH OF I80. THE STEEP
LLVL LAPSE RATES WILL MAKE FOR MIXING WINDS GUSTING OVER 20 MPH AND
ALSO MAKE THE MOST OF A COLD THERMAL PROFILE AND MIX SFC TEMPS UP
INTO THE MID 30S. FLURRIES WILL LINGER INTO THU NIGHT WITH ONGOING
CLOUD COVER AND MIXING WINDS KEEPING TEMPS FROM DIPPING MUCH BELOW
THE UPPER TEENS TO LOWER 20S.
LATEST MEDIUM RANGE SOLUTIONS CONTINUE TO DEVELOP A LARGE/BROAD
UPPER TROF OR MULTI-CENTER UPPER LOW COMPLEX ACRS THE NORTHWESTERN
GRT LKS BY FRIDAY. A FEW LINGERING FLURRIES WILL CONTINUE ON FRI BUT
NOT AS FAVORABLE AS ON THU FOR SNOW SHOWERS. BRUNT OF LLVL COLD POOL
TO BE IN PLACE ACRS THE FCST AREA FRI MORNING WITH TEMPS HAVING
TROUBLE RECOVERING BACK INTO THE LOWER 30S DESPITE RATHER DEEP MIXING
POSSIBLY UP TO H85 MB. SOME PARTIAL CLEARING WITH A BRIEF BOUT OF
LLVL RIDGING MAY MAKE FRI NIGHT THE COLDEST PERIOD OF THE FCST WITH
TEMPS DIPPING WELL DOWN INTO THE TEENS BEFORE RETURN FLOW COMMENCES.
LONGER RANGE SIGNALS OVER THE WEEKEND SUGGEST THAT GULF OF AK WAVE
ENERGY EVENTUALLY DIGGING DOWN ACRS THE NORTHERN INTERMOUNTAIN
REGION WHILE THE BRUNT OF THE GRT LKS UPPER VORTEX MIGRATES
NORTHEASTWARD AND FILLS SOME WILL COMBINE FOR A FLATTENING OUT MEAN
STEERING FLOW PATTERN ACRS THE SOUTH HALF OF THE CONUS. THIS MORE
PROGRESSIVE FLOW WOULD BRING ABOUT THERMAL MODIFICATION FOR BOTH
SAT AND SUNDAY WITH TEMPERATURES REBOUNDING BACK CLOSER TO NORMAL
WITH HIGHS IN THE UPPER 30S TO LOWER 40S. THIS SAME PROGRESSIVE FLOW
WOULD ULTIMATELY SHUTTLE AN INITIAL WAVE OUT OF THE GRT BSN THAT
GETS BOOTED OUT BY THE NEXT L/W TROF FORMATION PROCESS ACRS THE
WESTERN CONUS. BOTH THE NEW 00Z RUN GFS AND ECMWF ARE IN GOOD
AGREEMENT OF SUGGESTING A SFC WAVE AND INVERTED TROF COMPLEX OVER THE
SOUTHERN PLAINS WILL EJECT OUT ALONG AND SOUTH OF THE AREA FOR A SNOW
CHANCE SUNDAY NIGHT INTO MONDAY. FOR NOW WILL INTRODUCE SLIGHT CHC
POPS FOR SUNDAY NIGHT AND AWAIT FURTHER MODEL CONSISTENCY IN
ADDITIONAL RUNS IN HANDLING AN IMPULSE IN THE SOUTHERN STREAM AS IT
RE-ESTABLISHES IT/S DOMINANCE BY EARLY NEXT WEEK. ..12..
&&
.AVIATION...
VFR CONDITIONS TO COME TO AN END THIS AFTERNOON OR TONIGHT AS LOW
CLOUDS STREAM INTO THE AREA FROM THE NORTHWEST. THE TROUBLE IS THE
TIMING. AS DISCUSSED ABOVE...DECIDED TO BRING THEM IN FAIRLY RAPIDLY
AFTER DARK FROM 2-3KFT...AND A 4-6 HOURS LATER TO PRODUCE FLURRIES.
THE SYSTEM TO OUR SOUTHEAST SHOULD NOT AFFECT THE TAF LOCATIONS WITH
ANYTHING OTHER THAN CLOUDS ABOVE 6KFT TODAY. WINDS WILL INCREASE
OUT OF THE NORTH TODAY...AND MAY GUST TO NEAR 25 KTS. ..LE..
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
LE/12
