FXUS63 KDVN 222141
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
341 PM CST TUE DEC 22 2009
.SYNOPSIS...
12Z UA ANALYSIS HAD A WEAK H85 LOW OVER EASTERN NEBRASKA WITH
ANOTHER BETWEEN KAMA AND KMAF. AN H85 STATIONARY FRONT RAN FROM THEN
NORTHERN PLAINS ACROSS THE GREAT LAKES AND INTO THE MID ATLANTIC
STATES. SATELLITE SHOWED PLENTY OF LOW LEVEL STRATUS WITH AC ABOVE
IT ACROSS THE MIDWEST. RADAR RETURNS INDICATED SOME -SN CONTINUED
ACROSS NORTHEAST ILLINOIS THROUGH MID AFTERNOON. 18Z SFC ANALYSIS
HAD A WEAK LOW NEAR KMCI WITH A WARM FRONT RUNNING ACROSS MISSOURI
INTO THE OHIO VALLEY. A COLD FRONT RAN FROM THE LOW SOUTHWEST INTO
ANOTHER LOW IN SOUTHWEST OKLAHOMA. DEW POINTS WERE IN THE MID 20S TO
LOWER 30S ACROSS THE MID MISSISSIPPI VALLEY WITH 40 AND 50 DEW
POINTS ADVECTING NORTH INTO KANSAS AND SOUTHERN MISSOURI.
&&
.SHORT TERM...TONIGHT AND WEDNESDAY...
COMPARING 12Z UA TO 00Z MODEL RUNS AND 12Z MODEL INITIALIZATION
SHOWS ALL MODELS ARE TOO COLD WITH THE WARM AIR AT H85 ACROSS THE
SOUTHERN PLAINS. THIS WARMER AIR HAS SIGNIFICANT CONSEQUENCES TO THE
OVERALL FCST FOR THE AREA.
WEAK TO MINIMAL FORCING WILL BE SEEN ACROSS THE AREA TONIGHT WITH
ESSENTIALLY NO VORTICITY ADVECTION. FCST SOUNDINGS ALSO POINT TO
FZDZ/DZ DEPENDING UPON LOCATION. GLOBAL GEM MODEL IS VERIFYING THE
BEST WITH THE LOW LEVEL MOISTURE AND WILL FOLLOW ITS INPUT REGARDING
PTYPE. THEREFORE...EXPECT DZ TO OCCUR ACROSS THE SOUTHERN THIRD OF
THE CWFA TONIGHT WITH SOME RA DEVELOPING JUST PRIOR TO DAWN. THE
NORTHERN TWO THIRDS OF THE CWFA SHOULD SEE PATCHY FZDZ.
LIFT INCREASES ON WEDNESDAY WITH THE FIRST PIECE OF ENERGY. RAIN
WILL BE SEEN ACROSS THE SOUTHERN THIRD OF THE CWFA ALL DAY. THE
NORTHERN TWO THIRDS OF THE CWFA WILL SEE A MIX OF PRECIPITATION WITH
THE I-80 CORRIDOR CHANGING OVER TO ALL RAIN DURING THE AFTERNOON.
SOME -SN WILL BE SEEN DURING THE MORNING BEFORE THE LOWER ATMOSPHERE
SATURATES TO THE MID LEVELS. THE BEST CHANCES FOR ICE ACCUMULATION
WILL BE ACROSS THE NORTH THIRD WITH ONE OR TWO TENTHS OF AN INCH.
THE I-80 CORRIDOR SHOULD SEE MINIMAL ICE ACCUMULATION.
THE QUESTION NOW IS WHAT TO DO WITH HEADLINES. THE CURRENT PLAN IS
TO GO WITH A WINTER WEATHER ADVISORY OVER THE WATCH AREA AND INCLUDE
THE I-80 COUNTIES IN ILLINOIS. THE I-80 CORRIDOR PART OF THE
ADVISORY WILL EXPIRE WEDNESDAY EVENING WHILE THE NORTH THIRD
CONTINUES INTO WEDNESDAY NIGHT.
...08...
.LONG TERM...WEDNESDAY NIGHT THROUGH NEXT TUESDAY...
FOCUS REMAINS ON THE LARGE WINTER STORM THAT WILL HAVE IMPACTS ON
THE CWA WELL INTO THE HOLIDAY WEEKEND. LATEST MODELS HAVE TRENDED
TOWARD A STRONGER...DEEPER SURFACE AND UPPER LOW THAT CONSENSUS NOW
HAS REMAINING ON A TRACK WEST OF THE FORECAST AREA. THIS WILL KEEP
THE AREA ON THE WARM ADVECTION SIDE OF THE STORM THROUGH AT LEAST
THU NIGHT...AND HAVE MADE SIGNIFICANT ADJUSTMENTS OF PRECIPITATION
TYPES ACCORDINGLY. THE POTENTIAL FOR SIGNIFICANT SNOW OR ICE
ACCUMULATIONS HAS DECREASED...WHILE A GREATER THREAT LOOKS TO BE
FLOODING POTENTIAL DUE TO EXTENDED PERIODS OF RAIN OVER FROZEN
GROUND AND SNOW COVER.
12Z MODELS DEPICT THE OCCLUDING SURFACE LOW OVER CENTRAL IA...OR AS
FAR EAST AS E CENTRAL IA AS SHOWN BY THE NAM...BY 12Z FRI. A MUCH
LARGER SPREAD CONTINUES WITH THE PHASING AND EVOLUTION OF THE H5 LOW
OVER THE REGION ON FRI. ECMWF AND THE GEM ARE IN DECENT AGREEMENT
AND HAVE GOOD CONTINUITY IN SURFACE FEATURES THE PAST FEW RUNS AND
GENERALLY FOLLOWED.
RESULTING STRONG SOUTH TO SERLY LOW LEVEL JET AND FEED OF GULF
MOISTURE...INCREASING TO 50 TO 55 KTS BY THU NIGHT...WILL FOCUS
NEARLY DIRECTLY INTO THE AREA...OVERWHELMING ANY SHALLOW COLD AIR AT
THE SURFACE. THIS WILL CAUSE TEMPERATURES TO RISE TO WELL ABOVE
FREEZING WED NIGHT...CHANGING ANY INITIAL MIXED PRECIPITATION TYPES
IN THE FAR NORTH TO ALL RAIN BY SUNRISE THU. HAVE LEFT A POTENTIAL
FOR PERIODS OF SLEET IN THE FAR NW AS SOME MODELS SUGGEST A
POSSIBILITY FOR A LINGERING LAYER BELOW FREEZING ALOFT. ON
THU...STRONG UPPER LEVEL FORCING AND LOW LEVEL ISENTROPIC LIFT AHEAD
OF THE PHASING UPPER LOW OVER THE PLAINS WILL PROVIDE PERIODS OF
LIGHT TO MODERATE RAIN. THE AMOUNT OF FORCING...ALONG WITH STEEP MID
LEVEL LAPSE RATES...COULD LEAD TO THUNDERSTORMS...BUT WILL LEAVE OUT
FOR NOW DUE TO ALREADY COMPLEX FORECAST. WITH THE SEVERAL PERIODS OF
PRECIP...THERE WILL BE A POTENTIAL FOR FLOODING AND HAVE ADDRESSED
THIS WITH A FLOOD WATCH OUTLINED IN THE SEPARATE HYDRO SECTION.
THU NIGHT OR CHRISTMAS EVE...THE SURFACE LOW IS SHOWN OCCLUDING AND
SHIFTING N TO NW FROM CENTRAL MO INTO CENTRAL IA. A SEPARATE WEAK
TRIPLE POINT IS SUGGESTED LIFTING NORTHEAST INTO N CENTRAL
IL...FOLLOWED BY COLD AIR WRAPPING AROUND THE SURFACE AND UPPER LOW
OVER CENTRAL INTO SE IA. FORECAST SOUNDINGS SUPPORT A CHANGE IN THE
PRECIPITATION OVER TO SNOW FROM W-SW TO E-NE BY MORNING WITH LIGHT
ACCUMULATIONS POSSIBLE. FAR SE IA AND NW IL ARE SHOWN GETTING INTO A
DRY SECTOR OVERNIGHT WITH PRECIP BECOMING VERY LIGHT AND FOG POSSIBLE.
FORECAST SOUNDINGS SUPPORT SNOW FOR PRECIP TYPE CHRISTMAS DAY
ONWARD...AND MAY STILL HAVE MAINLY LIGHT ACCUMULATING SNOWS GOING
THROUGH CHRISTMAS NIGHT...INTO SAT AS UPPER LOW HANGS JUST N TO NE
OF THE CWA.
BEYOND...THE UPPER LOW MAY FINALLY EXIT TO THE EAST BY SUN
NIGHT...KEEPING POTENTIAL FOR AT LEAST FLURRIES GOING. SURFACE AND
UPPER UPPER LEVEL RIDGING DEVELOPS BY MON AND TUE...PROVIDING BELOW
NORMAL TEMPERATURES AND A BREAK FROM PRECIPITATION.
..SHEETS..
&&
.AVIATION...IFR TO MVFR CIGS WILL BECOME ALL IFR CIGS AFT 00Z/23. MOISTURE
TRAPPING INVERSION TO KEEP CLOUDS AROUND. FORCING IS NOT GREAT AND
FCST SOUNDINGS SUGGEST DZ/FZDZ THROUGH 12Z/23. CIGS SHOULD
EVENTUALLY DROP TO LIFR AFT 12Z/23 FOR ALL TAF SITES. PATCHY FZDZ
SHOULD BE SEEN THROUGH 12Z/23 FOR KCID/KDBQ/KMLI WITH DZ AT KBRL.
APPROACHING VORT MAX INCREASES LIFT ARND 12Z/23 WHICH WILL ALLOW
FZRA AND PL TO DEVELOP AT KCID/KDBQ/KMLI 12Z-18Z/23. KBRL MAY SEE A
VERY BRIEF PERIOD OF FZRA ARND 12Z/23 BUT WILL QUICKLY CHANGE TO RA.
...08...
&&
.HYDROLOGY...
AN EXTENDED PERIOD OF LIGHT TO MODERATE RAIN...FROM WED THROUGH THU
NIGHT...WILL LIKELY RESULT IN WIDESPREAD 1 TO 2 INCH RAINFALL OVER
THE CWA. 40 TO 55 KT LOW LEVEL JET WILL FEED AIRMASS WITH PW VALUES
OF 150 TO 250 PERCENT OF NORMAL WILL FEED INTO THE REGION ESPECIALLY
THU INTO THU EVENING BEFORE WARM CONVEYOR BELT AXIS SHIFTS NE AS THE
SURFACE AND UPPER LOWS BECOME STACKED AND OCCLUDED TO THE WEST.
MODEL RUN QPF THROUGH FRI IS WELL INTO THE 1.5 TO 2.5 INCH RANGE
ACROSS THE CWA. WHILE THE DEEP SNOW COVER IN THE NORTH MAY INITIALLY
ABSORB MUCH OF THIS...THERE WILL STILL BE A POTENTIAL FOR PRIMARILY
URBAN PONDING AND INUNDATION FLOODING DUE TO BLOCKED DRAINAGE
SYSTEMS IN THE RESULTING SLUSHY MESS. IN THE CENTRAL AND
SOUTH...ABOVE 32 DEWPOINTS AND AT LEAST 2 DAYS OF TEMPERATURES ABOVE
FREEZING WILL MELT MUCH OF THE SNOWCOVER. IN THESE AREAS...FROZEN
GROUND WILL LEAD TO RUNOFF INTO STREAMS AND RIVERS THAT ARE ALREADY
RUNNING 70 TO 90 PERCENT ABOVE DECEMBER NORMALS. THUS...HAVE ISSUED
A FLOOD WATCH FROM 18Z WED THROUGH 12Z FRI.
..SHEETS..
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE THURSDAY NIGHT
FOR BENTON-BUCHANAN-CEDAR-CLINTON-DELAWARE-DES MOINES-
DUBUQUE-HENRY IA-IOWA-JACKSON-JEFFERSON-JOHNSON-JONES-
KEOKUK-LEE-LINN-LOUISA-MUSCATINE-SCOTT-VAN BUREN-WASHINGTON.
WINTER WEATHER ADVISORY FROM 6 AM WEDNESDAY TO 6 AM CST THURSDAY
FOR BENTON-BUCHANAN-DELAWARE-DUBUQUE-JACKSON-JONES-LINN.
WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
AFTERNOON FOR BENTON-BUCHANAN-DELAWARE-DUBUQUE-JACKSON-
JONES-LINN.
WINTER WEATHER ADVISORY FROM 6 AM TO 6 PM CST WEDNESDAY FOR
CEDAR-CLINTON-IOWA-JOHNSON-MUSCATINE-SCOTT.
IL...FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE THURSDAY NIGHT
FOR BUREAU-CARROLL-HANCOCK-HENDERSON-HENRY IL-JO DAVIESS-
MCDONOUGH-MERCER-PUTNAM-ROCK ISLAND-STEPHENSON-WARREN-
WHITESIDE.
WINTER WEATHER ADVISORY FROM 6 AM WEDNESDAY TO 6 AM CST THURSDAY
FOR CARROLL-JO DAVIESS-STEPHENSON.
WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
AFTERNOON FOR JO DAVIESS.
WINTER WEATHER ADVISORY FROM 6 AM TO 6 PM CST WEDNESDAY FOR
BUREAU-HENRY IL-PUTNAM-ROCK ISLAND-WHITESIDE.
MO...FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE THURSDAY NIGHT
FOR CLARK-SCOTLAND.
&&
$$
SHEETS/08
