Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 240920
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
320 AM CST WED DEC 24 2014

.SYNOPSIS...
ISSUED AT 319 AM CST WED DEC 24 2014

SANDWICHED BETWEEN TWO WIDESPREAD PCPN EVENTS EASTERN IOWA AND
WESTERN ILLINOIS HAVE BEEN CLOUDY OVERNIGHT. LIGHT SNOW IS FALLING
IN DEFORMATION ZONE PROCESSES FROM SOUTHWEST TO NORTH CENTRAL
IOWA...AND ARE IN A DISSIPATION STAGE SINCE MIDNIGHT. FARTHER
EAST...THE POTENT DYNAMICS OF THE STORM DEVELOPING NEAR TENNESSEE
ARE SPREADING RAINS ACROSS EASTERN ILLINOIS. AS OF 2 AM...WET BULB
TEMPERATURES AT LOW LEVELS CONTINUE TO BE WELL ABOVE FREEZING OVER
ALL OF EASTERN IOWA AND ILLINOIS. THIS MAY BE A SIGN OF GREAT
DIFFICULTY IN GETTING ANY ACCUMULATING SNOW TODAY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 319 AM CST WED DEC 24 2014

MUCH LIKE YESTERDAY...TODAY WILL MAINLY JUST BE A CLOUDY DAY.  WITH
FORECASTS THAT NEED TO EXTEND FROM A DECAYING SNOW EVENT IN CENTRAL
IOWA WHICH SHOULD NOT IMPACT EASTERN IOWA GREATLY...TO A RAIN/SNOW
EVENT IN ILLINOIS WHICH SHOULD NOT IMPACT OUR ILLINOIS COUNTIES
GREATLY...WE DO HAVE POPS ON THE WESTERN AND EASTERN BORDER. BOTH
LOCATIONS CAN BE ADJUSTED AS NEEDED WITH TIMELY MORNING UPDATES.
WITH THE DRY SLOT STILL OVERHEAD...AND WEAKENING DYNAMICS FROM THE
DECAYING DEFORMATION ZONE ARRIVING TODAY...WE ARE JUST IN THE WRONG
SPOT TO GET MUCH MEASURABLE RAIN OR SNOW. IN FACT...THE STRONG
SYSTEM EXPECTED TO MOVE EAST OF CHICAGO SHOULD OFFER SUM SUBSIDENCE
ON ITS WEST SIDE AS WELL...THUS AM THINKING TODAY WILL SEE ONLY
INTERMITTENT FLURRIES...OR EVEN SOME DRIZZLE. WE SHOULD SEE LESS AND
LESS DEEP SATURATION THROUGH THE DAY...AND PATCHY DRIZZLE MAY BE THE
RESULT OF THIS. LOW CLOUDS ARE A CERTAINTY...AS THIS CLOUDY DECK
EXTENDS WELL INTO CANADA. BASED ON THE EXTENT...AND MODELS USUALLY
OVERDOING CLEARING OF STRATUS BEHIND SYSTEMS LACKING A PUSH OF
ACRTIC AIR...I AM KEEPING OUR FORECAST CLOUDY THROUGH TONIGHT.

THIS WILL MODERATE BOTH TEMPEATURES TODAY AND TONIGHT...WITH HIGHS
TODAY ONLY A FEW DEGREES WARMER THAN MORNING LOWS...OR IN THE MID TO
UPPER 30S. TONIGHT...MID TO UPPER 20S ARE SET BY THE GUIDANCE
BLEND...WHICH SEEMS TO FIT NICELY WITH THE MODEST COLD ADVECTION.
WINDS TODAY WILL NOT BE OVERLY STRONG...AS THE OLD OCCLUSION REMAINS
IN THE SURFACE WIND FIELD IN OUR NORTHEAST CWA THIS MORNING.  WINDS
OVER THE CENTRAL AND SOUTH WILL BE 10 TO 15 MPH...WITH SOME GUSTS TO
AROUND 20 THROUGH THE DAY.
ERVIN

.LONG TERM...(THURSDAY THROUGH NEXT TUESDAY)
ISSUED AT 319 AM CST WED DEC 24 2014

THURSDAY...MOST OF 00Z RUN MODELS SUGGEST THAT DECENT LLVL SOUTH TO
SOUTHWESTERLY FLOW BEHIND PASSING SFC RIDGE LOBE TO MAKE FOR A NICE
WARM UP AND SEASONABLY MILD CHRISTMAS DAY...HIGHS IN MUCH OF THE CWA
RANGING FROM 40-45 WITH AT LEAST PARTIAL SUNSHINE AND MAYBE SOME
PERIODS OF MOSTLY SUNNY BEFORE CIRRUS PLUME/WAA MID DECK EMBEDDED IN
AMPLIFYING SOUTH-WESTERLIES STREAMS UP ACRS THE REGION LATER IN THE
DAY AND INTO THE NIGHT. SOUTHERLY SFC FLOW TO KEEP TEMPS UP IN THE
30S OVERNIGHT INTO FRI MORNING...POSSIBLY MID TO UPPER 30S ALONG AND
SOUTH OF I80.

FRIDAY AND SATURDAY...AS THE NEXT WAVE ORGANIZES ACRS THE
SOUTHWESTERN PLAINS...CONTINUED LLVL WARM AIR ADVECTION/WAA/
PROCESSES COULD BOOST FRI TEMPS IN THE UPPER 40S TO LOW 50S ACRS MUCH
OF THE SOUTHERN 2/3S OF THE CWA EVEN WITH INCREASING WAA CLOUD COVER.
DO NOT BUY THE WET BIAS GFS OF LIGHT PRECIP BREAKING OUT FRI
AFTERNOON AND WILL KEEP THE FCST DRY THRU 00Z SAT. THEN THE VARIOUS
00Z RUN MEDIUM RANGE MODELS START TO VARY ON HANDLING OF LLVL NE-TO-
SW ORIENTED BAROCLINICITY/FRONT AS IT SLIDES EASTWARD THRU THE REGION
FRI NIGHT. THE ECMWF HAS A WEAK SFC WAVE SLIDE TO THE NORTH WHILE A
BIT STRONG ONE ORGANIZES ACRS THE SOUTHEASTERN PLAINS SLOWING THE
FRONT ALONG AND EAST OF THE CWA BY SAT MORNING...STILL WITH SOME
LIGHT ISENTROPIC PRECIP PROBABLY IN THE FORM OF LIGHT RAIN OR DRIZZLE
MAKING IT ACRS THE SOUTHEASTERN HALF OF THE CWA MAINLY AFTER
MIDNIGHT. THE 00Z GFS ROLLS A STRONGER WAVE ALONG THE FRONT ACRS THE
EASTERN CWA FRI EVENING MAKING FOR MORE OF A RAIN SHOWER REGIME UNTIL
THE LOW PASSES...ALLOWING FOR IN-WRAPPING COLD CONVEYOR TO MAKE A
SWITCH OVER TO SNOW OR RAIN-SNOW MIX NW-TO-SE AS THE FRI OVERNIGHT
PROGRESSES INTO SAT MORNING. THE 00Z RUN GEM SIDES WITH THE EURO AND
MAY TAILOR THE FCST THAT WAY FOR NOW. BUT THEN THIS/A SIDING WITH THE
GEM-ECMWF/ SUGGESTS THAT SAT MAY BE MORE MESSY AS THE SOUTHEASTERN
PLAINS WAVE ROLLS UP THE OH RVR VALLEY AND PRODUCES AN OVERRUNNING
SNOW EVENT FOR MUCH OF THE CWA SAT INTO SAT EVENING. THE SOUTHEAST
MAY HAVE LINGERING RAIN-SNOW MIX FOR PART OF SAT MORNING. THE ECMWF
SUGGESTS THE PRECIP TO BE ON THE LIGHT SIDE WITH ONLY AN INCH OR TWO
AT THE MOST OF SNOW ACCUM BY SAT EVENING WITH MOISTURE SOURCE
INTERRUPTION BY MAIN STORM TO THE SOUTH...THE GEM LOOKS OVERDONE WITH
SEVERAL INCHES OF SNOW POSSIBLE ACRS THE CENTRAL INTO THE
NORTHWESTERN CWA...WHILE IT HOLDS ON TO A RAIN/SNOW MIX OR EVEN ALL
RAIN LONGER IN THE SOUTHEAST. THE GFS IS MAINLY DRY SAT WITH THE MAIN
ENERGY/WAVE LIFTING OUT MUCH SOONER DURING FRI NIGHT. AGAIN FEEL THE
CONSISTENT ECMWF PROBABLY THE MODEL THAT WILL VERIFY...WILL KEEP LOW
TO MODERATE CHC POPS FRI NIGHT INTO SAT FOR NOW. THE 00Z UKMET THE
OUTLIER WITH MAIN WAVE ENERGY SURGE INTO A MAJOR STORM LIFTING OUT
LATE SAT NIGHT INTO SUNDAY TOWARD SOUTHERN CHICAGOLAND AREA.

SUNDAY THROUGH NEXT TUESDAY...WILL PLAY IT COLDER AND DRIER SUNDAY
INTO MONDAY WITH THE CWA PROBABLY IN-BETWEEN LIKELY STORM PATHS/MAIN
STORM TRACK WELL TO THE SOUTH. INCREASING COLD CORE L/W TROF
ADVANCEMENT AND CONTINUED STORM GENERATION IN THE SOUTHERN PLAINS
TOWARD THE OH RVR VALLEY MAY INDUCE SECONDARY ELEVATED PRECIP BANDS
OF LIGHT SNOW TOWARD OR INTO THE LOCAL FCST AREA MON NIGH INTO TUE...
WITH A POTENTIALLY VERY COLD/ARCTIC SOURCE AIRMASS DUMP ACRS THE
UPPER MIDWEST TOWARD THE MID WEEK NEW YEARS EVE PERIOD.   ..12..

&&

.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.
&&

$$

SYNOPSIS...ERVIN
SHORT TERM...ERVIN
LONG TERM...12
AVIATION...05






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