FXUS63 KLOT 241143
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
543 AM CST THU DEC 24 2009
.DISCUSSION...
357 AM CST
MAIN FOCUS OUT THE GATE THIS MORNING IS DEALING WITH WINTER
WEATHER HEADLINES DUE TO ONGOING FREEZING RAIN EVENT. ANYWHERE
BETWEEN A TENTH AND FOUR TENTHS OF AN INCH OF GLAZE HAS
ACCUMULATED THUS FAR...WITH LITTLE OR NO GLAZING REPORTED IN THE
CITY OF CHICAGO PROPER. WITH TEMPERATURES REMAINING AT OR JUST
BARELY BELOW FREEZING TO START OUT THIS MORNING...AND RADAR
SHOWING A CONTINUOUS RAIN TRAIN UPSTREAM...ALL THE WAY TO THE
GULF COAST. GFS FCST OF SFC TEMPERATURES HAS BEEN NEARLY SPOT ON
PAST 24 HRS SO HAVE USED THIS GUIDANCE FOR NON DIURNAL TEMP
TRENDS OVER THE NEXT 36-48 HRS. THIS BRINGS SFC TEMPS ABOVE
FREEZING OVER JUST ABOUT THE ENTIRE FA BY 18Z. THEREFORE...THE ICE
STORM WARNING FOR MUCH OF NRN IL AND NWRN INDIANA HAS BEEN
EXTENDED UNTIL NOON CST.
SFC ANALYSIS SHOWS EVERYTHING COMING TOGETHER AS SCHEDULED AS PER
GUIDANCE. SATLT IMAGERY SHOWS MAIN CORE OF ENERGY NOW MOVG
THROUGH WRN TX...AND BEGINNING TO INTERACT WITH CONVECTIVE PLUME
FROM SW OF HOUSTON...NWD INTO AR AS 60 DEG DEW POINTS CONTINUE TO
STREAM NWD OFF WRN GLFMEX. HAVE NOTED BLOSSOMING OF LIGHTNING
ALONG RED RVR VALLEY...AND SWD FROM SWRN AR THRU TX GULF COAST
WHERE CONVECTIVE BAND HAS BECOME SVR. MEANWHILE...INFLUX OF POLAR
AIR IS PLUNGING SWD ACROSS CNTRL HI PLAINS. THIS MIX MEANS THAT
INTENSE CYCLOGENESIS IS ABOUT TO COMMENCE OVER NERN TX. THIS DOES
NOT BODE WELL AT ALL FOR IL/WRN INDIANA IN TERMS OF FLOOD POTL.
STRONG ISENTROPIC UPGLIDE/UVM FIELD FCST TO REACH INTO SRN AND WRN
PORTIONS OF FA BY LATE THIS AFTN...THEN OVERSPREAD ENTIRE FA THIS
EVENING. QPF TOTALS OF AROUND 2 INCHES ARE EXPECTED IN GENERAL
COVERAGE...WITH SOME AREAS LIKELY TO RECEIVE UP TO 3 INCHES. IN
ADDITION TO HEAVY STRATIFORM PRECIP EVENT...WOULD NOT BE TOO
SURPRISED FOR SOME EMBEDDED THUNDER TO DVLP TONIGHT AS WELL
CONSIDERING STRONG DYNAMICS AND NOTING GFS FCST OF 150 METER H5
HGT FALLS IN THE 12 HRS ENDING AT 12Z FRI. THIS...IN COMBINATION
WITH MELTING SNOW PACK...EXPECTED TO ACCELERATE TONIGHT AS SFC DEW
POINTS RISE...AND FROZEN GROUND MAKE FLOODING OF RIVERS AND LOW
LYING AREAS EVEN MORE LIKELY. HAVE STOPPED SHORT OF UPGRADING TO
FLOOD WARNING AT THIS TIME TO SEE HOW INTENSIFYING CIRCULATION TO
SSW MAY REDISTRIBUTE RAINFALL PATTERN.
COLD AIR WRAP AROUND FCST TO CIRCULATE AROUND LOW CENTER LATE
TONIGHT...ARRIVING IN SRN CWA BY DAYBREAK CHRISTMAS MORNING. WILL
ADVECT THIS COLD AIR NWD ACROSS NRN IL/NWRN INDIANA BY NOON
CHRISTMAS DAY. HAVE MADE LTL CHG TO FCST AS THIS SCENARIO REMAINS
BASICALLY UNCHANGED FROM PREVIOUS FCST. HAVE HOWEVER BUMPED UP
POPS FROM LATE FRI NIGHT THROUGH WEEKEND AS CLOSED LOW GYRATES
OVER MID MS VLY BEFORE HEADING SLOWLY EWD ACROSS REGION. THIS WILL
LIKELY BRING IMPULSES ROTATING AROUND UPR LOW CENTER ACROSS FA
FROM TIME TO TIME THROUGH SUNDAY...INCREASING THE COVERAGE OF
LIGHT SNOW.
NO CHGS TO FCST BEYOND SUNDAY.
MERZLOCK
&&
.AVIATION...
12Z TAFS...CIGS AND PRECIP TIMING...OF MAINLY LIQUID RAIN...ARE
THE PRIMARY FORECAST CONCERNS THIS MORNING.
STILL A FEW SHOWERS/SPRINKLES ACROSS THE AREA THIS MORNING AS
TEMPS HOVER NEAR FREEZING. THIS TREND OR BREAK IN THE PRECIP IS
EXPECTED TO CONTINUE THRU THE MORNING HRS. SINCE IT WILL LIKELY
BE A FEW MORE HRS UNTIL THE THREAT OF ANYTHING FALLING NO LONGER
CAN FREEZE...OPTED TO MAINTAIN -FZRA IN A TEMPO FOR A FEW HRS.
CIGS HAVE GONE VFR ACROSS ALL OF TERMINALS EARLY THIS MORNING BUT
NOT CONFIDENT AS TO HOW LONG THIS WILL LAST. IFR/LIFR STILL VERY
CLOSE TO RFD WITH MVFR DEVELOPING OVER WEST CENTRAL IL.
SOUNDINGS/MOISTURE PROFILES WOULD SUGGEST MVFR CIGS DEVELOPING AT
SOME POINT THIS MORNING THEN HANGING ON INTO THE EVENING BEFORE
POSSIBLY LOWERING INTO IFR. CONFIDENCE ON CIGS THRU THE MORNING
IS RATHER LOW.
MODELS DIFFER ON TIMING/LOCATION OF RAIN AS IT LIFTS/DEVELOPS
NORTH LATER THIS AFTERNOON AND TONIGHT. VERTICAL MOTION FIELDS
ARE QUITE IMPRESSIVE TOWARD 06Z TONIGHT. BAND OF HEAVIEST RAINS
LIKELY TO BE SLOWLY MOVING EAST...SO INDICATED EARLIER TIMING AT
RFD AND DPA THEN INTO ORD/MDW BY LATE EVENING. THIS WILL LIKELY
NEED TO BE REFINED WITH LATER FORECASTS. THOUGHT ABOUT INCLUDING
A PERIOD OF HEAVY RAIN WHICH IS POSSIBLE BUT NOT SURE HOW ACCURATE
THAT TIMING WOULD BE FROM THIS DISTANCE. ALSO CAN/T RULE OUT A FEW
RUMBLES OF THUNDER TONIGHT BUT ANY TS THAT DO OCCUR THIS FAR NORTH
ARE LIKELY TO BE ISOLATED. RAIN WILL TRANSITION TO JUST SHOWERS
TOWARD THE END OF THE PERIOD INTO FRIDAY MORNING.
EAST WINDS WILL INCREASE THRU THE DAY STARTING WITH GUSTS TO 20
KTS OR SO...THEN INCREASING TO 25-30KTS BY EVENING AND CONTINUING
OVERNIGHT. WINDS WILL TURN MORE SOUTHEAST FRIDAY MORNING. CMS
&&
.MARINE...
218 AM...FORECAST FOCUS CONTINUES TO BE GALE FORCE WINDS THRU
FRIDAY AFTERNOON.
LOW PRESSURE OVER EASTERN TEXAS WILL MOVE NORTHEAST TO WESTERN
ILLINOIS BY FRIDAY MORNING AS IT CONTINUES TO DEEPEN. STRONG
HIGH PRESSURE OVER JAMES BAY WILL SLOWLY MOVE NORTHEAST ACROSS
NORTHERN QUEBEC TONIGHT. AS THE LOW MOVES NORTHEAST THE GRADIENT
BETWEEN THESE TWO SYSTEMS WILL CONTINUE TO TIGHTEN. CURRENT
OBSERVATIONS ACROSS SOUTHERN LAKE MICHIGAN A BIT PROBLEMATIC AS
MANY WIND SENSORS ARE READING FAR TOO LOW...LIKELY DUE TO ICE
BUILD UP FROM HRS OF FREEZING RAIN. GALE WARNING WAS SCHEDULED TO
GO INTO EFFECT AT 10Z AND WILL START IT AT 09Z WITH THIS MORNINGS
GLF. SUSPECT AT LEAST GUSTS TO LOW END GALES SOON IF NOT ALREADY
OCCURRING. GALES INCREASE TO 45KTS THIS EVENING AS THE STRONGEST
GRADIENT PASSES ACROSS SOUTHERN LAKE MICHIGAN TONIGHT. GALES
SLOWLY RELAX ON FRIDAY BUT PROBABLY NOT UNTIL AFTERNOON OR
EVENING AND HAVE EXTENDED THE GALE WARNING THRU 00Z SAT. THE LOW
WILL DRIFT NORTHEAST ACROSS IOWA FRIDAY THEN BEGIN TO WEAKEN AS
IT SLOWLY MOVES EAST ACROSS NORTHERN IL SATURDAY INTO SUNDAY. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...ICE STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ020-ILZ022-ILZ023 UNTIL 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.
WINTER WEATHER ADVISORY...ILZ014 UNTIL NOON THURSDAY.
IN...FLOOD WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...NOON THURSDAY
TO 6 AM FRIDAY.
ICE STORM WARNING...INZ001-INZ002-INZ010-INZ011 UNTIL NOON
THURSDAY.
LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878 UNTIL 6 PM FRIDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ868...4 PM THURSDAY TO 6 PM FRIDAY.
&&
$$
