FXUS63 KLOT 230821
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
221 AM CST WED DEC 23 2009

.DISCUSSION...
747 PM CST

THERE IS SOME RADAR ECHOES SHOWING PRECIPITATION. SOME SURFACE REPORTS
ARE ISOLATED FREEZING DRIZZLE AND SNOW SHOWERS. WE WILL UPDATE THE
FORECAST FOR PATCHY FREEZING DRIZZLE AND SNOW SHOWERS. WE WILL
EXAMINE THE DATA DURING THE NEXT TWO HOURS FOR UPDATES ON THE
ADVISORIES.

&&

.AVIATION...
1049 PM CST

0600 UTC TAFS...NO MAJOR CHANGES ANTICIPATED FOR THE 06Z TAFS
WITH CONTINUED MAIN FORECAST ISSUES BEING MIXED PRECIPITATION
THROUGH THE PERIOD...IMPACTS OF APPROACHING STORM SYSTEM ON
CIGS/VSBYS...AND STRONG EAST WINDS.

00Z RAOB FROM DVN SHOWING A RATHER MESSY SOUNDING IN TERMS OF
PRECIPITATION TYPE WITH DEEP SATURATED LAYER UP TO ABOUT 700 HPA
WHERE TEMPS OF AROUND -8 DEG CELSIUS WERE OBSERVED WHICH
INTRODUCES QUESTION OF ICE AVAILABILITY. THROUGH TIME
TONIGHT...SHOULD SEE CONTINUED MID LEVEL DRY AIR ADVECTION WITH IN
SOUTHWESTERLY MID LEVEL FLOW. THIS SHOULD PROGRESSIVELY TRANSITION
TO WHAT HAS BEEN MAINLY LIGHT SNOW WITH OCCASIONAL FREEZING
DRIZZLE TO MAINLY MORE IN THE WAY FREEZING DRIZZLE OR LIGHT
FREEZING RAIN. WITH MOISTURE BECOMING PROGRESSIVELY MORE SHALLOW
PRECIPITATION AMOUNTS SHOULD BE LIGHT BUT SHOULD FAVOR -FZDZ OR
-FZRA. FAIRLY STRONG DRY EASTERLY LOW LEVEL FLOW DOES APPEAR TO BE
LIMITING POTENTIAL FOR IFR CIGS THIS EVENING...AND FEEL THAT THIS
TREND SHOULD CONTINUE THROUGH THE OVERNIGHT HOURS AND WILL LIKELY
STAY WITH MORE MVFR CIGS OVERNIGHT.

MAIN UPPER LOW WILL APPROACH THE SOUTHERN PLAINS TOMORROW EVENING
WITH SFC CYCLONGENESIS BEGINNING TO RAMP UP. AS THIS OCCURS SHOULD
BEGIN TO SEE LOW LEVEL WINDS VEER SLIGHTLY TO THE SOUTHEAST THAT
SHOULD ALLOW FOR MORE SUBSTANTIAL LOW LEVEL MOISTURE ADVECTION.
FORECAST SOUNDINGS CONTINUE TO SUGGEST A POTENTIAL FOR FREEZING
RAIN WEDNESDAY MORNING WITH BEST CHANCE WEDNESDAY MORNING ACROSS
RFD WHERE MOISTURE ADVECTION WILL BE STRONGER. BETTER CHANCE OF
PRECIP WILL BE WEDNESDAY AFTERNOON/WEDNESDAY NIGHT AND FOR
REMAINDER OF TERMINALS...00Z DATA STILL SUGGESTS THAT A FREEZING
RAIN/SLEET MIX STILL THE MOST LIKELY. SOME CONCERNS ABOUT
LIQUID/FREEZING PRECIP TYPE THAT WILL NEED TO BE CONSIDERED BUT
FOR NOW AM HEDGING ON IDEA OF RECENT NEW SNOW COVER HOLDING SFC
TEMPS BELOW FREEZING. DID TRANSITION BACK TO IFR CONDITIONS BY
LATE AFTERNOON WITH BETTER MOISTURE ADVECTION. EAST WINDS GUSTING
TO 20 KNOTS TONIGHT WILL INCREASE TO AROUND 25 KNOTS TOMORROW WITH
STRENGTHENING PRESSURE GRADIENT NORTH OF DEVELOPING SOUTHERN
PLAINS SFC TROUGH/LOW.

MARSILI

&&

.MARINE...

220 AM...HIGH END GALES LIKELY THURSDAY AND THURSDAY NIGHT.

OVERALL...NO MAJOR CHANGES TO GOING GRIDS/FORECASTS. MAIN CHANGE
THIS MORNING IS TO UPGRADE THE CURRENT GALE WATCH TO A GALE
WARNING. EASTERLY GRADIENT IS BEGINNING TO TIGHTEN THIS MORNING AS
THE HIGH OVER ONTARIO STRENGTHENS AND THE LOW OVER THE SOUTHERN
PLAINS BEGINS TO DEEPEN. SEVERAL MARINE LOCATIONS NOW GUSTING
20-25KTS AND AS THE GRADIENT CONTINUES TO TIGHTEN...WINDS WILL
STEADILY INCREASE WITH GUSTS TO 30KTS TODAY WITH GALES DEVELOPING
LATE TONIGHT INTO THURSDAY MORNING. STRONGEST GRADIENT MOVES
ACROSS SOUTHERN LAKE MICHIGAN THURSDAY AFTERNOON INTO THURSDAY
EVENING AND CURRENT FORECAST OF GALES TO 45KTS DURING THIS TIME 
LOOKS ON TRACK. WITH THE LOW OVER THE SOUTHERN PLAINS LIFTING
NORTH TO EASTERN IOWA AND DEEPENING TO AT LEAST 29.2 INCHES...
SOME STORM FORCE GUSTS CAN/T BE RULED OUT...BUT NOT EXPECTING
PREVAILING/FREQUENT STORM FORCE GUSTS AT THIS TIME. THE LOW WILL
BEGIN TO WEAKEN FRIDAY INTO FRIDAY NIGHT...BUT REMAIN NEARLY
STATIONARY OVER IOWA/NORTHERN ILLINOIS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ020...NOON WEDNESDAY TO NOON 
     THURSDAY.

     FLOOD WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
     ILZ032-ILZ033-ILZ039...NOON THURSDAY TO 6 AM FRIDAY.

IN...FLOOD WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...NOON THURSDAY 
     TO 6 AM FRIDAY.

LM...GALE WATCH...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878...4 AM THURSDAY TO NOON FRIDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868...4 PM THURSDAY TO NOON FRIDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM THURSDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM THURSDAY.

&&

$$