FXUS63 KDVN 300908
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
305 AM CST MON NOV 30 2009
.SYNOPSIS...
LATEST SFC ANALYSIS WAS INDICATING A RATHER SUBSTANTIAL RIDGE AXIS
EXTENDING FROM JUST NORTH OF LK HURON...SOUTHWESTWARD ALL THE WAY
DOWN ACRS THE TX PANHANDLE. SOME PRESSURE FALLS AND A SFC TROF WAS
NOTED ON THE NORTH SIDE OF THIS SYSTEM ACRS THE EASTERN DAKOTAS.
ALOFT...W/V IMAGERY LOOP WAS INDICATING A SERIES OF VORT COMPLEXES
RIDGE-RIDING OFF THE PACIFIC NORTHWEST AND ACRS CENTRAL/NORTHERN
ALBERTA AND SASKATCHEWAN.
&&
.SHORT TERM...TODAY AND TONIGHT...
EXTRAPOLATING THE WESTERN EDGE/CLEARING LINE OF THE STRATUS
OVERHEAD...THE CLEARING SHOULD BE INTO THE WESTERN CWA BY 12-13Z...
WITH THIS PROCESS THEN ACCELERATING EASTWARD OR EVEN MIXING OUT
DIURNALLY THROUGH MIDDAY. OTHER SUBSIDENCE HOLES WILL MAKE IT INTO
NORTHWEST IL OUT OF WI THIS MORNING AS WELL. THUS A MOSTLY SUNNY
FCST EXPECTED BY AFTERNOON IF NOT SOONER. AS THE ABOVE MENTIONED
CANADIAN WAVE COMPLEX CLIPPERS IT/S WAY DOWN ACRS NORTHEAST MN...WI
AND LOWER MI THROUGH THIS EVENING...BACKING LLVL FLOW TO THE SOUTH
OF IT WILL WAA AND MIXING JUST TO H95 MB SUGGEST ONGOING FCST HIGHS
ON TARGET AND WILL GENERALLY MAINTAIN. A BIT DEEPER MIXING ABOVE
H95 MB BY MID AFTERNOON WOULD SUPPORT THE WARMER MAV HIGHS WITH
WIDESPREAD MID TO UPPER 40S...BUT FOR NOW LEAVE THE CURRENTLY
ADVERTISED HIGHS MORE IN THE 43-46 DEGREE RANGE WITH A FEW SITES IN
THE FAR SOUTHWEST INDEED REACHING THE UPPER 40S. ELEVATED CLOUD
SHIELD OFF THE PASSING CLIPPER TO THE NORTH AND NORTHEAST MAY SKIRT
ACRS THE FAR NORTHERN AND NORTHEASTERN CWA BY LATE AFTERNOON AND
ESPECIALLY DURING THE EVENING.
TONIGHT...AS THE CLIPPER AND ITS ASSOCIATED SNOWS PASSES OFF TO THE
NORTHEAST OF THE DVN CWA THIS EVENING AND OVERNIGHT...A BOUT OF
UPPER RIDGING UNDULATES UP ACRS THE NORTHERN PLAINS AND UPPER MS
RVR VALLEY IN THE WAKE OF IT...SIGNALING A TEMPORARY SUBSIDENCE
REGIME RIGHT DOWN ACRS THE REGION BY 06Z. LLVL FLOW THAT VEERED IN
RESPONSE TO THE PASSING WAVE TO THE NORTH WILL START TO BACK
AGAIN LATE TONIGHT AND BEGIN YET ANOTHER ELEVATED WAA REGIME AHEAD
OF THE NEXT UPSTREAM WAVE IN ACTIVE NORTHERN STREAM. BUT THE NET
RESULT MAY ONLY BE SOME LATE NIGHT AC MAINLY ACRS THE NORTHERN THIRD
OF THE FCST AREA. ANY SFC WIND DECOUPLE TONIGHT BEFORE THE BACKING
SFC WINDS START TO INCREASE TOWARD SUNRISE WOULD FOSTER SUB-GUIDANCE
LOW TEMPS DOWN INTO THE 20S AGAIN EVEN THOUGH THE BULK OF GUIDANCE
HAS LOWS IN THE LOWER OR EVEN MID 30S. ..12..
.LONG TERM...TUESDAY THROUGH NEXT SUNDAY...
TUESDAY WILL BE THE WARMEST DAY OF THE FORECAST...WITH A NEW UPPER
LEVEL WAVE APPROACHING US FROM THE NORTHWEST CAUSING WARM AIR
ADVECTION UP OVER THE AREA DURING THE DAY...AND BRINGING IN 850MB
TEMPS UP AROUND 6-8 DEG C. HAVE WARMED UP THE MAX TEMP FOR TUESDAY
OVER PREVIOUS FORECAST. STRICT MIX-DOWN TECHNIQUES TO 925-950MB
WOULD ONLY PRODUCE PERHAPS MID 50S ACROSS THE SOUTH...AND AROUND 50
NORTH. HOWEVER...COMPARING TO LAST SATURDAY WHEN WE HAD A SIMILAR
AIRMASS AND SIMILAR SUNSHINE...WE GOT UP INTO THE LOW 50S NORTH...
AND 60-65 SOUTH. MODELS WERE A GOOD 5-8 DEGREES TOO COOL AT KBRL...
AND HAVE DECIDED TO BASE MY FORECAST BASED MORE ON THESE BIASES THAN
ON THE MIX-DOWN TECHNIQUE. WE WILL BE 3-5 DEGREES COOLER AT 925-
950MB... AND HAVE TRENDED BACK A FEW DEGREES FROM SATURDAYS MAX TEMP
VALUES BASED ON THAT.
AFTER TUESDAY WE DROP INTO A MUCH COLDER REGIME. TUESDAY NIGHT THE
COLD FRONT DROPS SOUTHEAST THROUGH THE AREA...USHERING IN COLDER
AIR. OF CONCERN FOR THIS TIME RANGE HAS BEEN A STRONG CUT OFF UPPER
LOW CURRENTLY POSITIONED OVER BAJA CALIFORNIA...WHICH WILL MOVE
SLOWLY EAST OVER THE NEXT COUPLE DAYS. THE MAIN FORECAST CONCERN
RECENTLY HAS BEEN IF OR WHEN THIS LOW WILL BECOME PHASED WITH THE
MORE ACTIVE NORTHERN STREAM...AND WHAT EFFECTS IT WILL HAVE ON THE
FORECAST AREA. ONLY THE NAM AND UKMET ARE INDICATING PRECIPITATION
MOVING UP OVER OUR SOUTHEASTERN COUNTIES WEDNESDAY...WITH ALL OF THE
OTHER AVAILABLE MODELS...INCLUDING THE GFS...GFS ENSEMBLE MEAN...
ECMWF...AND CANADIAN GEM KEEPING THIS SYSTEM FARTHER SOUTHEAST AND
ALL PRECIPITATION OUT OF THE AREA. THIS HAS BEEN CONSISTENT ON MODEL
RUNS FOR THE PAST 24-36 HOURS...SO FEEL FAIRLY CONFIDENT IN KEEPING
THE FORECAST DRY THROUGH WEDNESDAY. THE UPPER LEVEL LOW IN THE
NORTHERN STREAM...MOVING ACROSS MINNESOTA SHOULD PUSH ENOUGH COLD
AIR...COLD AIR INSTABILITY AND SOME ACCOMPANYING SHORTWAVE IN THE
CYCLONIC UPPER LEVEL FLOW TO GENERATE SOME SNOW SHOWERS WEDNESDAY
NIGHT AND THURSDAY. DUE TO THE INCREASED CLOUD COVER I EXPECT WITH
THIS ACTIVITY...HAVE NOT DROPPED TEMPERATURES AS MUCH AS THE HPC
GUIDANCE HAS INDICATED...BUT THURSDAY NIGHT WE SHOULD GET SOME
CLEARING IN HERE AND HAVE GONE WITH TEENS TO AROUND 20 ACROSS THE
AREA. FRIDAY AND SATURDAY SHOULD REMAIN CHILLY...THOUGH A GRADUAL
WARMING/MODERATING TREND SHOULD BEGIN.
A QUESTION FOR THE FRIDAY THROUGH SUNDAY TIME FRAME HAS TO DO WITH A
NEW UPPER LEVEL WAVE THAT MOVES ON SHORE OVER BRITISH COLUMBIA
SOMETIME BETWEEN THURSDAY AND SATURDAY...WITH SIGNIFICANT DIFFERENCES
BETWEEN THE MODELS ON THE HANDLING OF THIS SYSTEM. BASED ON MODEL
TENDENCIES...DISTRUST THE RAPID MOVEMENT OF THE GFS...AND THE SLOWER
ECMWF SOLUTION IS PREFERRED. HAVE CONTINUED THE DRY AND COLD
FORECAST WE ARE CURRENTLY CARRYING...THOUGH WE MAY NEED TO ADD SNOW
SHOWERS TO THE FRIDAY FORECAST IF THIS TREND CONTINUES. ..LE..
&&
.AVIATION...
HIGHER LEVEL MVFR TO VFR STRATUS DECK SHOULD CLEAR FROM THE WEST AT
CID BY 13Z...AND IF IT KEEP IT/S CURRENT PACE CLEAR THE MS RVR
INCLUDING THE DBQ/MLI/BRL TERMINALS BETWEEN 15Z-16Z. DO EXPECT SOME
DIURNAL ACCELERATION AND MIX-ERODING WHICH MAY BRING CLEAR BEFORE
THAT WINDOW. OTHERWISE A VFR TAF CYCLE THROUGH 12Z TUE WITH SFC
WINDS BACKING TO THE SOUTHWEST AND INCREASING TO 12-18 KTS WITH
SOMEWHAT HIGHER GUSTS AFTER 18Z. SOME EVENING CI OR EVEN AC POSSIBLE
OVER DBQ THIS EVENING SOUTH OF WI CLIPPER...BUT AGAIN THIS ALL VFR
AND A NONE FACTOR WITH DRY LLVLS. ..12..
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
12/LE
