FXUS63 KLOT 231146
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
546 AM CST WED DEC 23 2009
.DISCUSSION...
350 AM CST
CURRENT SATLT IMAGERY SHOWS CLOSED UPR LOW OVR 4 CORNERS MOVING
EWD. UPR AIR ANALYSIS ALSO SHOWS MUCH OF THE DYNAMICS ASSD WITH
THIS SYS HAVE ALREADY SPREAD OUT ACROSS THE SRN PLAINS WHERE UPR
FLOW HAS BECOME VERY DIFLUENT. THUNDERSTORMS HAVE INCREASED IN
COVERAGE FROM ERN KS TO NERN TX...AND HAVE DVLPD AS FAR N AS CNTRL
MO. THIS IS TESTAMENT TO HOW ENERGETIC THIS SYSTEM IS. IN
ADDITION...SFC DEW POINTS NR 60 HAVE REACHED THE RED RVR VALLEY
WITH 50 DEGREE DEW POINTS NOW NOSING INTO SERN KS. WATER VAPOR
IMAGERY ALSO SUGGESTS STRONG ISALLOBARIC COUPLET HAS ALREADY
EVOLVED FROM NRN MEXICO/BIG BEND AREA...NWD TO CNTRL PLAINS. BASED
ON THESE OBSERVATIONS...INGREDIENTS IN PLACE FOR INTENSE
CYCLOGENESIS TO TAKE PLACE OVR SRN PLAINS-OZARKS TONIGHT AND
THURSDAY...WITH THE LOW CENTER FCST TO TRACK W OF MS RVR THROUGH
THURSDAY NIGHT.
CONSIDERING STRONG DYNAMICS...COPIOUS AMOUNTS OF MOISTURE
AVAILABLE...DEEPENING OF SYSTEM...MELTING OF SNOW COVER AND FROZEN
GROUND...EXPECT THAT FLOODING WILL BE MORE OF A CONCERN WITH THIS
STORM THAN ANY WINTER WX.
STRONGEST ISENTROPIC LIFT IS EXPECTED TO BE CENTERED AROUND 6 PM
THURSDAY...WITH GFS SHOWING DEEP COLUMN OF GREATER THAN 15 MICRO
BARS OF VERTICAL MOTION DURING THIS TIME. BASED ON THIS HAVE A
FLOOD WATCH GOING FROM NOON THURSDAY TO 6 AM FRIDAY.
LIGHTER...OR MORE PERIODIC PRECIPITATION EPISODES WILL OCCUR
AHEAD OF THIS STRONGEST BAND OF PRECIPITATION...BUT WITH INDUCED
UPR RIDGING PASSING ACROSS AREA TODAY...PRECIPITATION BLOSSOMING
FROM SRN PLAINS TO SRN IL/SRN INDIANA WILL LIKELY BE SHUNTED MORE
EWD THAN NWD. WITH LESSER AMTS OF QPF EXPECTED WHILE SFC TEMPS ARE
STILL BELOW FREEZING AND SOUNDINGS STILL COOL ENOUGH TO SUPPORT
FREEZING/FROZEN PRECIP...DON'T EXPECT WINTER WARNING CRITERIA TO
BE MET. NOT THAT THINGS AREN'T GOING TO GET MESSY...STILL LOOKS
LIKE PERIOD OF FREEZING RAIN AND SLEET...POSSIBLY MIXED WITH SNOW
WILL PERSIST THROUGH TONIGHT OVER FAR NRN IL. THEREFORE HAVE OPTED
TO GO WITH A WINTER WX ADVSRY...GENLY ALONG AND N OF I-88. HAVE
KEPT ADVSRY OUT OF IMMEDIATE CHICAGO AREA XCP FOR FAR N SUBURBS
DUE TO INCREASING E WIND OFF MID 30 DEGREE LAKE WATER.
OVR NWRN INDIANA...HAVE GONE WITH A WINTER WX ADVSRY FOR TODAY AS
SFC TEMPS ARE STARTING OUT A LITTLE COLDER THAN ELSEWHERE ACROSS
FA...AND AS PRECIP TO S SLOWLY OVERSPREADS AREA...COLD ELY LLVL
WINDS WILL CONTINUE TO ADVECT TEENS AND LOW 20S DEW POINTS INTO
REGION FROM OH AND LWR MI. THIS SET UP IS MORE CONDUCIVE TO
MAINTAINING SUB FREEZING TEMPERATURES THROUGH THE DAYLIGHT HRS
TODAY. EVENTUALLY WIND WILL TURN MORE SELY ALLOWING WARMER SFC
TEMPS OVR OH VLY TO FEED INTO THIS REGION. HOWEVER...IF THIS DOES
NOT OCCUR UNTIL LATER TONIGHT...ADVSRY MAY NEED TO BE EXTENDED
BEYOND 00Z THU.
COLD AIR TO WRAP INTO REGION FROM SOUTH ON CHRISTMAS DAY AS REGION
BECOMES DRY SLOTTED AROUND 12Z FRIDAY. AS OCCLUDED FRONT LIFTS N
OF AREA LATE THURSDAY NIGHT...PRECIP WILL DIMINISH TO SOME LIGHT
RAIN OR DRIZZLE BEFORE ENDING AS DRY SLOT SUBSIDENCE ERODES CLOUD
DECK. THEREFORE WILL GO WITH A GENERALLY DRY...BUT BLUSTERY
CHRISTMAS DAY WITH TEMPERATURES FALLING BACK BELOW FREEZING IN THE
AFTN. WITH CLOSED LOW FCST TO PASS OVR AREA FRIDAY NIGHT THROUGH
SATURDAY NIGHT...PROLONGED PERIOD OF CLOUDY SKIES AND OCNL LIGHT
SNOW CAN BE EXPECTED. THEREFORE HAVE GONE WITH LIKELY POPS FOR
LIGHT SNOW MUCH OF WEEKEND.
MERZLOCK
&&
.AVIATION...
12Z TAFS...SEVERAL CONCERNS THIS PERIOD INCLUDING ONSET OF PRECIP
AND PRECIP TYPE ALONG WITH CIGS/VIS THRU THE PERIOD.
SOME FLURRIES AND POSSIBLY PATCHY FREEZING DRIZZLE AROUND THE AREA
THIS MORNING BUT EXPECT MAINLY DRY CONDITIONS UNTIL PRECIP OVER
CENTRAL IL LIFTS NORTH ACROSS THE TERMINALS LATER THIS MORNING AND
THIS AFTERNOON. LEADING EDGE EXTENDS FROM ROUGHLY PIA TO DNV. FEW
REPORTS OF MIXED PRECIP AS PRECIP STARTS BUT MOST LOCATIONS
REPORTING JUST RAIN ACROSS CENTRAL IL AS DEWPOINTS HAVE INCREASED
INTO THE MID 30S. AS THIS AREA LIFTS NORTH LATER TODAY...THERMAL
PROFILES SUPPORT A MIX OF SNOW...SLEET AND FREEZING RAIN. PERHAPS
IN THAT ORDER...THOUGH THERE WILL LIKELY BE PERIODS OF MULTIPLE
PRECIP TYPES. GOING FORECAST HAS THESE TRENDS COVERED WELL SO NO
MAJOR CHANGES. WHILE SFC TEMPS ARE HOVERING AROUND FREEZING AT
ALL OF THE TERMINALS AND TEMPS WILL LIKELY RISE A FEW DEGREES
DURING THE MORNING...AS THE PRECIP BEGINS TO FALL...EXPECT SOME
COOLING...PERHAPS BACK TO FREEZING BUT TEMPS SHOULD SLOWLY RISE
ABOVE FREEZING AGAIN BY EVENING OR THRU THE EVENING...EXCEPT AT
RFD. WARM AIR ALOFT WILL HAVE CHANGED PRECIP OVER TO RAIN BY THIS
TIME SO PRECIP TRANSITIONING TO RAIN DURING THE EARLY/MID EVENING
SEEMS REASONABLE. RFD STAYS FURTHER INTO THE COLDER AIR LONGER AND
THUS EXPECT A MIX OF PRECIP THRU THE EVENING AND POSSIBLY
OVERNIGHT...BUT EVENTUALLY PRECIP WILL SWITCH OVER TO RAIN THERE
AS WELL.
EXPECT CIGS TO BE RATHER PROBLEMATIC. GENERALLY LOW MVFR OVER THE
TERMINALS TO START BUT IFR/LIFR NOT TOO FAR AWAY TO THE SOUTH. AS
PRECIP ADVANCES NORTH...EXPECT CIGS TO LOWER INTO IFR AND REMAIN
IFR THRU MIXED PRECIP. FURTHER SOUTH...INTO THE MUCH WARMER AIR...
CIGS ARE QUITE VARIABLY BUT CERTAINLY SHOW AN IMPROVING TREND INTO
AT LEAST MVFR AND ATTEMPTED A MODEST IMPROVING TREND AS PRECIP
BEGINS TO CHANGE OVER TO RAIN.
WINDS REMAIN EASTERLY THROUGH THE PERIOD...TURNING EAST/SOUTHEAST
TONIGHT. GUSTS ALREADY 20+ KTS AND SPEEDS WILL SLOWLY INCREASE
THRU THE DAY WITH GUSTS 25-30KTS POSSIBLE BY EVENING. SUSPECT
GUSTS TO RELAX SOME IN AREAS OF HEAVIER PRECIPITATION. CMS
&&
.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 WEATHER ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
ILZ010-ILZ011-ILZ012...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.
WINTER WEATHER ADVISORY...INZ002-INZ010-INZ011 UNTIL 6 PM
WEDNESDAY.
LM...GALE WARNING...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 WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ868...4 PM THURSDAY TO NOON FRIDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL 4 AM THURSDAY.
&&
$$
