Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 201742
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1142 AM CST SAT DEC 20 2014

.SYNOPSIS...
ISSUED AT 324 AM CST SAT DEC 20 2014

LATEST SFC ANALYSIS WAS INDICATING HIGH PRESSURE COMPLEX CONTINUING
TO SLOWLY MIGRATE EASTWARD ACRS THE WESTERN GRT LKS...WITH SOUTH TO
SOUTHEAST RETURN FLOW CONTINUING TO ORGANIZE TO THE WEST OF THE MS
RVR VALLEY. ALOFT...WAVE ANALYSIS ON CURRENT WATER VAPOR LOOP WAS
INDICATING A WEAK VORT EXITING THE AREA ACRS EASTERN IL WHILE A MUCH
STRONGER VORT MAX WAS SEEN DIGGING EAST-SOUTHEASTWARD ACRS EASTERN
NEB INTO WESTERN IA WITH EYES OF ROLLING ACRS THE IA/MO BORDER
REGION THIS MORNING. AREAS OF MAINLY LIGHT FLURRIES WHERE BEING
PICKED UP ON RADAR MOVING EASTWARD ACRS THE NORTHEAST HALF OF THE
DVN CWA ATTM...WITH THE SOUTHWESTERN IA VORT MAX KICKING UP ANOTHER
AREA OF LIGHT PRECIP ACRS MUCH OF CENTRAL IA...OBS AND REPORTS OUT
THERE SUGGEST A MIX OF FLURRIES WHERE SEEDER-FEEDER PROCESSES ARE
GOING ON...AND FREEZING DRIZZLE ACRS NORTH CENTRAL IA OUT OF LOW
STRATUS DECK.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 324 AM CST SAT DEC 20 2014

TODAY...WITH THE ABOVE VORT MAX AND FORCING ON ITS GRADIENT ROLL
TOWARD AND ACRS THE AREA THIS MORNING BUT CONTINUED RATHER SHALLOW
SATURATED LAYER UNDER H8 MB...WILL KEEP FLURRIES GOING ON ACRS THE
EAST HALF OF THE CWA THOUGH 15Z WHERE SOME LINGERING MID LEVEL SEEDER
FEEDER PROCESSES GOING ON...BUT KEEP A MIX OF FLURRIES AND FREEZING
DRIZZLE ACRS THE WEST WHERE UPSTREAM LOWER STRATUS WILL LOOK TO SEEP
ACRS THE AREA FROM THE WEST. SFC TEMPS WILL BE WARMING TO OR ABOVE
FREEZING BY MID MORNING IN THE SOUTHWESTERN THIRD OR MORE OF THE CWA
LIMITING GLAZE POTENTIAL IN THOSE AREAS...BUT UNTIL THEN WILL HAVE TO
WATCH SFC OBS AND REPORTS FOR POSSIBLE SPECIAL WX STATEMENTS. AS
THE VORT MAX MOVES TO THE EAST ACRS CENTRAL IL BY LATE MORNING...
INCOMING SUBSIDENCE SHOULD SHUT DOWN ANY LIGHT PRECIP MAKING
PROCESSES FROM WEST TO EAST BY MIDDAY. AS THE LOWER CLOUD DECK MOVES
IN FROM THE WEST...THERE MAY BE SOME FOG THIS MORNING AS WELL BUT DO
NOT THINK ANY WORSE THAN 1-3 MILE VSBYS SO NOT ZONE MENTION
WORTHY. CLOUDY BUT MAINLY PRECIP-FREE AFTERNOON...ONGOING WARM AIR
ADVECTION TO MAKE FOR A MILDER DAY IN THE MID 30S FOR MUCH OF THE
FCST AREA WITH SOME AREAS IN THE SOUTH PUSHING THE UPPER 30S BY LATE
AFTERNOON.

TONIGHT...MOST 00Z RUN MODEL SOLUTIONS SUGGEST ANOTHER WEAK VORT TO
ARRIVE FROM THE WEST ACRS IA FROM LATE EVENING INTO THE EARLY SUNDAY
MORNING PERIOD. THIS COMBINED WITH LOWER LEVEL WARM AIR ADVECTION/
TYPE OF WARM FRONTAL FORCING MAY PRODUCE ANOTHER ROUND OF LIGHT
PRECIP FROM LATE EVENING ACRS THE WEST AND CENTRAL CWA...AND
EXPANDING TO THE NORTH ESPECIALLY AFTER MIDNIGHT. WITH ONGOING
BLANKETING LLVL STRATUS...HIGHER SFC DPTS IN THE LOWER 30S FEEL SFC
TEMPS TO HOLD AT OR EVEN JUST ABOVE FREEZING ACRS MUCH OF THE
SOUTHERN HALF OR MORE OF THE CWA OVERNIGHT SO WILL JUST MENTION
DRIZZLE. BY THE TIME THE DRIZZLE GETS WIDESPREAD TO THE NORTH OF
I80 AFTER MIDNIGHT...EVEN MANY AREAS UP THERE MAY BE MARGINAL FOR
MUCH OF ANY FREEZING DRIZZLE TROUBLE OR SLIPPERY GLAZE. BUT WILL
KEEP MAINLY FREEZING DRIZZLE WORDING AND RAISE POPS FOR POSSIBLE
MEASURE OF AT LEAST A HUNDREDTH ALONG AND NORTH OF THE HWY 30
CORRIDOR AFTER MIDNIGHT IN MAIN LLVL FRONTOGENETICAL FORCING
SWATH.    ..12..

.LONG TERM...(SUNDAY THROUGH NEXT FRIDAY)
ISSUED AT 324 AM CST SAT DEC 20 2014

CONFIDENCE ON A CLOUDY FORECAST APPEARS ABOUT AS HIGH AS IT GETS
THROUGH WEDNESDAY...AS OUR COMPLICATED STORM SYSTEM OFFERS UP ONE
CERTAINTY...STRATUS.  THE FORECAST REMAINS A PROLONGED PERIOD OF
STRATUS...DRIZZLE...LIGHT RAIN AND EVENTUALLY TUESDAY A MIX TO SNOW.
THIS ALL OCCURS AS WE SEE A PHASING OF NORTHERN AND SOUTHERN ENERGY
INTO A VERY POTENT STORM SYSTEM BY TUESDAY IN THE GREAT LAKES OR
OHIO VALLEY. THE EVOLUTION OF THIS SYSTEM REMAINS POORLY CONFIDENT...
BUT IT DOES CONTINUE TO APPEAR OUR CWA WILL BE BRUSHED BY ANY OF
THE SIGNIFICANT AFFECTS ON THE 00Z DATA SET. THE OPERATIONAL GFS
IS NOW ONE OF THE FARTHEST NORTHWEST TRACKS OF THE SURFACE LOW
TUESDAY...AND IS MUCH MORE VARIABLE RUN TO RUN COMPARED TO THE
ECMWF WHICH CONTINUE TO SUPPORT A MORE EASTERLY SOLUTION TO THIS
LOW. ALL MODEL OUTPUT CONTINUES TO INDICATE LIGHT SNOW TUESDAY
AFTERNOON THROUGH WEDNESDAY...WITH SOME LOW ACCUMULATIONS POSSIBLE
ALONG WITH STRONG WINDS OF 20 TO 30 MPH...GUSTS TO 40 POSSIBLY.

PRECEDING THIS...SUNDAY THROUGH SUNDAY NIGHT SHOULD BE RELATIVELY
MILD...AND DAMP. MEASURABLE RAIN CHANCES SHOULD RAMP UP CONSIDERABLY
AFTER MIDNIGHT SUNDAY NIGHT...AS THE STRONG MID LEVEL FORCING WITH
THE NORTHERN WAVE ARRIVES. THIS SLOWLY SHIFTS THROUGH THE CWA
THROUGH MONDAY EVENING...WITH TEMPERATURES ALOFT CONTINUING TO
INDICATE A COLD RAIN THE MOST LIKELY P-TYPE.  I HAVE DELAYED ANY
TRANSITION TO SNOW MIX SLOWER MODELS...AS WE SHOULD HAVE VERY MUCH
SATURATED LOW LEVELS...AND WITHOUT STRONG CAA...THIS WILL HAVE A
TOUGH TIME COOLING BELOW FREEZING WITH THE MAIN LIFT WELL ABOVE THAT
LAYER. RAINFALL AMOUNTS OF 0.15 TO 0.35 SEEM MOST ON TARGET FOR THE
PERIOD OF SUNDAY NIGHT THROUGH MONDAY NIGHT.

WEDNESDAY AND THROUGH CHRISTMAS MORNING WILL BE WINDY AND RAW...NO
DOUBT ABOUT THAT...AND PROBABLY CLOUDY AS WELL WITH SNOW SHOWERS IN
CAA. TEMPERATURE SHOULD BE COOL...BUT NOT OVERLY COLD AS THE SYSTEM
IS NOT EXPECTED TO TAP MUCH ARCTIC AIR.

THURSDAY EVENING INTO FRIDAY...MODELS ARE GREATLY DIVERGENT BUT
INTERNALLY CONSISTENT TONIGHT. THE GFS REMAINS FOCUSED ON A SHORT
WAVELENGTH BETWEEN UPPER TROFS...AND INDICATES A WEAK LOW PRESSURE
SWEEPING EAST THROUGH THE PLAINS AND MISSISSIPPI VALLEY THURSDAY
NIGHT AND EARLY FRIDAY WITH SOME LIGHT SNOW. THE EC AND UKMET SHOW A
LONGER WAVELENGTH OF UPPER TROFS...ALLOWING FOR MORE RIDGING IN
BETWEEN. THIS ALLOWS FOR STRONGER CYCLOGENESIS IN THE PLAINS THURSDAY
AS THE UPPER WAVE DIGS SOUTHWARD BEFORE EJECTING EAST. THE ECMWF
CONTINUES TO THEN CREATE A SIGNIFICANT LOW PRESSURE IN THE PLAINS
THROUGH FRIDAY.

ERVIN

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1138 AM CST SAT DEC 20 2014

GENERALLY IFR CONDITIONS WITH PERIODS OF LOWER END MVFR AND LIFR CONDITIONS
AT ALL TERMINALS NEXT 24 HOURS AS TRAPPED LOW LEVEL MOISTURE TO PRODUCE
LOW CLOUDS AND LIGHT FOG. AN APPROACHING UPPER DISTURBANCE TO INTENSIFY
LEE SIDE PLAINS TROUGH FROM THE PACIFIC NORTHWEST...THIS MAY PRODUCE
LIGHT DRIZZLE LATER TONIGHT AND INTO SUNDAY AFTERNOON WHICH ARE LEFT
OUT OF THE TAFS DUE TO SPOTTY NATURE AND LOW CONFIDENCE. WINDS WILL
BE SOUTH TO SOUTHEASTERLY AT 5 TO 10 KTS.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.

&&

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...ERVIN
AVIATION...NICHOLS






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