Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 240545
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1145 PM CST TUE DEC 23 2014

.UPDATE...
ISSUED AT 943 PM CST TUE DEC 23 2014

BAND OF SNOW CONTINUES FROM PORTIONS OF NORTHEAST-CENTRAL-SOUTHWEST
IA WITHIN ZONE OF WEAK ISENTROPIC LIFT ON BACKSIDE OF UPPER TROUGH
AXIS. THIS LIFT DEPICTED WELL ON 295K SFC OF NAM AND RAP MODELS
AND IS SHOWN TO GRADUALLY WEAKEN OVERNIGHT REMAINING MAINLY WEST OF
CWA ALTHOUGH POSSIBLY BRUSHING FAR WEST SECTIONS... ALONG/W OF
IIB-VTI-OOA LINE WITH FLURRIES OR VERY LIGHT SNOW. OTHERWISE...SOME
PATCHY DRIZZLE WAS NOTED ALONG MISSISSIPPI RIVER AHEAD OF FRONT
AND THIS MAY CONTINUE NEXT FEW HOURS BEFORE SHIFTING EAST WITH THE
FRONT... THEN ASIDE FROM FAR WESTERN CWA REST OF THE NIGHT APPEARS
TO BE MAINLY DRY. AS RESULT... HAVE UPDATED TO REMOVE ANY MEASURABLE
POPS REST OF TONIGHT. ALSO...WITH CONSIDERABLE CLOUDS AND FAIRLY
WEAK COLD ADVECTION HAVE NUDGED UP MINS WITH MOST AREAS STAYING AT
OR ABOVE 32F.

AS FOR TOMORROW /CHRISTMAS EVE/ SYSTEM... SOME OF THE LATEST MODEL
GUIDANCE OF RAP...NAM AND GFS MODELS TAKE THE STORM SLIGHTLY
FURTHER EAST AND SUGGEST MAY NOT EVEN SEE FAR EAST BRUSHED BY ANY
SNOW. MAY SEE SOME FLURRIES AND POSSIBLY FEW SNOW SHOWERS IF
SUFFICIENT MOISTURE DEPTH BUT ASIDE FROM BRIEF REDUCTION IN VSBY
(SHOULD THE SNOW SHOWERS OCCUR) NO IMPACTS EXPECTED WITH TEMPS ABOVE
32F. HAVING SAID THAT... ANYONE WITH TRAVEL INTERESTS TO OUR EAST
TOMORROW WILL WANT TO STAY UPDATED AS POSSIBILITY OF IMPACTS TO TRAVEL
FROM WET/SLUSHY ROADS AND LIMITED VISBILITIES AT TIMES.

&&

.SYNOPSIS...
ISSUED AT 312 PM CST TUE DEC 23 2014

SYNOPSIS...AT 3 PM CST..A WEAK COLD FRONT BISECTED THE DVN CWA.
THICK OVERCAST WAS OBSERVED TO THE NW OF THE BOUNDARY WITH TEMPS
IN THE MID TO UPPER 30S. TO THE SE...IN A SOUTHWEST SFC WIND FLOW
SKIES WERE SCT TO BKN AND TEMPS WERE IN THE LOWER TO MIDDLE
40S...AND A LIGHT RAIN SHOWERS WAS LOCATED NEAR IOWA CITY. A
DEVELOPING SFC LOW PRESSURE SYSTEM WILL MOVE NORTHEASTWARD ON
WEDNESDAY AFTN AND NIGHT...BUT WILL REMAIN WELL EAST OF E IOWA AND
W ILLINOIS. THERE IS A CHANCE FOR LIGHT SNOW ACCUMULATIONS ACROSS
THE FAR EASTERN CWA WITH THIS SYSTEM. HOWEVER HIGH TEMPS IN THE
MID 30S SHOULD LIMIT THE OVERALL IMPACT FROM ANY SNOW THAT FALLS.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 312 PM CST TUE DEC 23 2014

TONIGHT...AS THE COLD FRONT SLIDES EAST OF THE AREA AFTER MIDNIGHT
SFC WINDS WILL VEER FROM THE SW TO THE NW AND THE STRATUS WILL
OVERSPREAD THE ENTIRE CWA. NAM FORECAST SFC DEWPOINT DEPRESSIONS ARE
NEAR 1-2 F OVERNIGHT BUT NW FLOW WILL LEAD TO SLOWLY DECREASING
MOISTURE THROUGH THE NIGHT SO NOT EXPECTING MUCH FOR FOG. A FEW
LIGHT RAIN/SNOW SHOWERS WILL BE POSSIBLE AS THE 850 MB TROUGH AXIS
SWINGS THROUGH BUT MANY AREAS WILL REMAIN DRY. NO SNOW ACCUMULATION
IS EXPECTED.

WEDNESDAY...PROMINENT LONGWAVE TROUGH ACROSS THE CENTRAL U.S.
DIPPING ALL THE WAY DOWN TO THE GULF OF MEXICO ALONG WITH A
STRENGTHENING JET STREAK ON ITS EASTERN FLANK AND BURGEONING
CONVECTION ACROSS THE SOUTHERN U.S. WILL INDUCE AN AREA OF
CYCLOGENESIS IN THE WESTERN OHIO VALLEY/GREAT LAKES. THE SFC LOW
IS FORECAST TO TRACK FROM N LOUISIANA TO N LOWER MICHIGAN.

MODEL DISCREPANCIES...12.23/12Z NAM AND GFS WERE THE FURTHEST WEST
WITH THE LOW TRACK FROM NE INDIANA TO NE LOWER MICHIGAN AND HAVE
THE GREATEST POTENTIAL FOR A PERIOD OF SNOW IN MY EASTERN CWA. THE
ECMWF AND GEM ARE FURTHER EAST WITH THE TRACK AND BRING VERY LIGHT
SNOW POTENTIAL WITH LESS THAN 0.10 INCHES OF QPF IN MY EASTERN
COUNTIES. THE HI-RES WRF-NMM HAS THE STEADY PRECIP DEFORMATION
BAND AFFECTING EASTERN BUREAU AND ALL OF PUTNAM COUNTY WITH STRONG
700-500 MB FRONTOGENESIS. THE 18Z NAM HAS NOW SHIFTED SLIGHTLY
EAST SO MODELS OVERALL IN FAIRLY GOOD AGREEMENT AT THIS POINT.

CWA IMPACTS...BEST CHANCES FOR ACCUMULATING SNOW WILL BE IN BUREAU
AND PUTNAM COUNTIES. A FEW FACTORS TO CONSIDER ARE THE RELATIVELY
WARM GROUND WITH THE PROLONGED PERIOD OF TEMPS IN THE 40S THE LAST
FEW DAYS AND FORECAST MAX TEMPS ABOVE FREEZING TOMORROW AFTN.
SINCE THERE IS NO COLD AIR IN PLACE...DYNAMIC COOLING IS NECESSARY
FOR SNOW TO OCCUR. BEST FORECAST AT THIS TIME IS FOR PERIOD OF
LIGHT SNOW TO IMPACT THE FAR EAST DURING THE AFTN WITH
ACCUMULATIONS POSSIBLY UP TO AN INCH OR TWO OF WET SNOW WITH SLRS
AT 9:1 OR SLIGHTLY LOWER...AND FLURRIES OR SCT SNOW SHOWERS
POSSIBLE ELSEWHERE.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 245 PM CST TUE DEC 23 2014

MAIN FORECAST CONCERN IN THE EXTENDED PERIOD IS THE NEXT SYSTEM
THAT WILL AFFECT THE AREA ON FRIDAY AND INTO SATURDAY MORNING.
THIS SYSTEM LOOKS TO BRING US A CHANCE OF RAIN AND SNOW MIXED IN
FOR FRIDAY NIGHT INTO SATURDAY.

CHRISTMAS DAY IS A DRY DAY BETWEEN TWO STORM SYSTEMS.  UNFORTUNATELY
AT THIS TIME...IT LOOKS LIKE WE WILL HAVE A BROWN CHRISTMAS AND IT
DOES NOT LOOK LIKE WE WILL HAVE ANY APPRECIABLE SNOW IN THE
EXTENDED. WE COULD SEE THE SUN LATER IN THE DAY ON CHRISTMAS EVE.
USED CONSRAW AS A STARTING POINT FOR TEMPERATURES SINCE BOI VERIFY
SUGGESTED IT HAS VERIFIED THE BEST RECENTLY.

FRIDAY...WARM AIR RETURNS TO THE AREA AS A LOW PRESSURE SYSTEM
PASSES TO OUR NORTH.  TEMPERATURES SHOULD BE IN THE HIGH 40S. CLOUDS
RETURN LATER IN THE DAY ON FRIDAY AS ANOTHER STORM SYSTEM MAKES ITS
WAY INTO THE AREA. MODELS DIFFER ON THE TIMING OF PRECIP.  THE GFS
HAS PRECIP ENTER THE CWA BEFORE 00Z SATURDAY.  THE GFS APPEARS TO BE
FASTER THAN ALL OF THE MODELS...THIS IS THE CASE IN RESPECT TO THE
GEFS AS WELL.  THE GEM AND ECMWF ARE CLOSER TO THE GEFS MEANS.  SO
DECIDED TO EXCLUDE THE GFS FORECAST FOR PRECIP DURING THIS TIME.
LOOKS LIKE PRECIP MAKES ITS WAY IN AS A COLD FRONT APPROACHES THE
AREA. H92 TEMPS AND MODEL SOUNDINGS FROM THE GFS SUGGEST SNOW AT 03Z
ACROSS THE AREA...HOWEVER THE ECMWF WHICH HAS A MORE REASONABLE
SOLUTION SUGGESTS RAIN ACROSS EASTERN PORTIONS OF THE CWA FROM 00Z
TO 03Z WITH A RASN LINE MOVING EAST THROUGH THAT TIME.  BY 12Z MOST
OF THE PRECIP WILL BE SNOW...WITH A FEW AREAS IN FAR EASTERN ZONES
STILL A RASN MIX.

LOOKING TOWARDS THE END OF THE EXTENDED PERIOD.  A POLAR AIRMASS IS
FORECAST TO OCCUPY THE AREA TOWARDS NEW YEARS EVE.  MODELS AGREE
THAT FLOW WILL BE OUT OF THE NW...SO TEMPS SHOULD BE COOLER THE

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1135 PM CST TUE DEC 23 2014

ANTICIPATE WIDESPREAD IFR TO LIFR CONDITIONS OVERNIGHT INTO WED AM
WITH ARRIVAL OF COLDER AIR AND ABUNDANT LOW LEVEL MOISTURE. SOME
IMPROVEMENT TO MVFR EXPECTED WED PM AND POSSIBLY INTO VFR WEST OF
THE MISSISSIPPI RIVER WED EVE. AN UPPER LEVEL TROUGH WILL MOVE
ACROSS THE REGION ON WED AND MAY BRING FLURRIES AND A FEW SNOW
SHOWERS TO THE AREA... BUT ENOUGH UNCERTAINTY WITH MOISTURE DEPTH
AND FORCING DUE TO DEEPENING LOW PASSING WELL EAST OF THE TERMINALS
PRECLUDES ANY MENTION MORE THAN JUST FEW FLURRIES ATTIM. TIGHTENING
PRESSURE GRADIENT WILL RESULT IN INCREASING NORTHWEST WINDS 10-15+
KTS AND GUSTY BY WED PM.

&&

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

$$

UPDATE...05
SYNOPSIS...UTTECH
SHORT TERM...UTTECH
LONG TERM...GIBBS
AVIATION...05




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