AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
626 AM CDT THU OCT 20 2011
.DISCUSSION...
304 AM CDT
MAIN CONCERNS FOR THE MORNING UPDATE WILL FOCUS ON THE IMPACTS OF
THE DEEP LOW PRESSURE SYSTEM INITIALLY CENTERED OVER NWRN OHIO.
FOR THE REMAINDER OF THE NIGHT AND INTO THE MORNING HOURS...STRONG
WINDS WILL CONTINUE TO COVER NRN ILLINOIS AND NWRN INDIANA.
HOWEVER...SOME ASPECTS OF THE STORM SYSTEM HAVE NOT PANNED OUT
EXACTLY AS ANTICIPATED...WHILE OTHER IMPACTS ARE RIGHT ON TARGET.
AS PREVIOUSLY ADVERTISED...NORTHERLY STORM FORCE WINDS OVER LAKE
MICHIGAN HAVE BEEN BATTERING THE ILLINOIS AND INDIANA COASTAL
LOCATIONS...WHERE WINDS HAVE REACHED 60 MPH. ALSO...MODERATE TO
HEAVY RAIN HAS FALLEN OVER NWRN INDIANA...WITH STORM TOTAL PCPN
AMOUNTS IN EXCESS OF 2 INCHES PER LATEST RADAR ESTIMATES.
HOWEVER...THE STORM CENTER HAS NOT TAKEN A WESTERLY PATH AS
ANTICIPATED...MOVING INTO NWRN OHIO AND NOT THE MORE WESTERLY TRACK
TO NEAR FT WAYNE INDIANA. THE MAIN IMPACT OF THE MORE EASTERLY
TRACK IS THAT WINDS DID NOT GET QUITE AS STRONG AS ANTICIPATED OVER
LOCATIONS AWAY FROM THE LAKE AND THE HEAVIER PCPN WAS CONFINED TO
THE NWRN INDIANA COUNTIES. THE LOWER PCPN AMOUNT OVER NRN IL WAS
LARGELY DUE TO LOW LEVEL FLOW BEING A LITTLE WEST OF
NORTH...ADVECTING MORE DRY AIR INTO THE REGION. SO...FOR THE
REMAINDER OF THE NIGHT...WILL DROP THE WIND ADVISORY WITH THE
ISSUANCE OF THE MORNING FORECAST PACKAGE. HOWEVER...SINCE STRONG
WINDS...OF 50 TO 60 MPH...ARE STILL BEING OBSERVED OVER SRN LAKE
MICHIGAN AND AT THE ADJACENT COASTAL OBSERVING PLATFORMS...WILL LET
THE HIGH WIND WARNING CONTINUE. ALSO...AS STRONG WINDS AND HIGH
WAVES CONTINUE TO BATTER THE ILLINOIS AND INDIANA SHORES...WILL KEEP
THE COASTAL FLOOD ADVISORY IN EFFECT THROUGH LATE THIS AFTERNOON FOR
THE ILLINOIS SHORE AND INTO THE EARLY EVENING FOR THE INDIANA SHORE.
FOR THE REMAINDER OF TODAY...EXPECT THE SYSTEM TO BEGIN TO LIFT
NNEWD INTO SRN QUEBEC TONIGHT AND INTO FRIDAY MORNING. WINDS WILL
REMAIN QUITE BRISK OVER THE REGION...THOUGH SHOULD BE ON A SLOWLY
DECREASING TREND THROUGH THE DAY. PCPN SHOULD ALSO BE ON THE
DECREASE...SETTING INTO LAKE EFFECT RAIN SHOWERS OVER NWRN INDIANA
BY THIS EVENING. AS THE DEEP LOW MOVES AWAY FROM THE REGION...A
MUCH COOLER AREA OF HIGH PRESSURE WILL BUILD ACROSS THE NRN PLAINS
AND INTO THE UPPER MISSISSIPPI VALLEY. WITH FLOW REMAINING
GENERALLY NWLY...A COLD/DRY ADVECTIVE PATTERN WILL SET UP OVERNIGHT
TONIGHT. THE TREND OVERNIGHT WILL BE FOR CLEARING
SKIES...DECREASING WINDS AND TEMPERATURES. OVERNIGHT TEMPERATURES
WILL DROP INTO THE LOWER 30S FOR MUCH OF THE REGION...GENERALLY WEST
OF THE FOX VALLEY AND I-55 CORRIDOR. SO...WILL ISSUE A FROST
ADVISORY FOR THIS AREA.
CONDITIONS WILL BEGIN TO MODERATE BY FRIDAY AS THE SFC RIDGE AXIS
MOVES ACROSS THE MIDWEST AND WESTERN GREAT LAKES REGIONS...BRINGING
INCREASING SUNSHINE. HIGHS FRIDAY SHOULD REBOUND INTO THE MIDDLE
50S. THE WARMING TREND WILL CONTINUE THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK. THE NEXT CHANCE FOR PCPN WILL NOT COME UNTIL
SUNDAY AS A NRN STREAM SYSTEM TRACKS THROUGH SRN CANADA. THE MAIN
CENTER OF THE SYSTEM WILL REMAIN NORTH OF THE BORDER...BUT A
TRAILING COLD FRONT WILL SWEEP THROUGH THE NRN PLAINS AND UPPER
MIDWEST. THE SRN EXTENT OF THE FRONT SHOULD CROSS THE MISSISSIPPI
RIVER INTO NRN IL BY SUNDAY MORNING...BRINGING A CHANCE FOR RAIN AS
TI MOVES ACROSS THE REGION. HOWEVER...WITH THE MAIN FORCING OF THE
SYSTEM WELL TO THE NORTH...AND A VERY DRY AIRMASS ANTICIPATED TO SET
UP IN ADVANCE OF THE SYSTEM...WILL ONLY CARRY LOW CHANCE TO SLIGHT
CHANCE POPS. AS A WARM ADVECTIVE PATTERN SETS UP WITH SWLY WINDS
AHEAD OF THE FRONT...TEMPERATURES SHOULD REACH INTO THE MIDDLE OR
UPPER 60S FOR EARLY NEXT WEEK.
KREIN
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 12Z...
* GUSTY WINDS THROUGH THIS EVENING.
* MVFR CIGS THROUGH THIS AFTERNOON OR EVENING.
* PRECIP END TIME. BMD
//DISCUSSION...UPDATED 12Z...
EXPECT GRADUALLY IMPROVING CONDITIONS THROUGH THE PERIOD AS AREA OF
LOW PRESSURE OVER NORTHERN OHIO BEGINS TO LIFT NORTHEAST AWAY FROM
THE FORECAST AREA. A TIGHT PRESSURE GRADIENT WILL REMAIN IN PLACE
MOST OF THE DAY WITH WINDS GUSTING UPWARDS OF 30 KTS THIS
MORNING...TAPERING SOMEWHAT THIS AFTERNOON...AND FINALLY DIMINISHING
BELOW 10 KTS LATE TONIGHT. WINDS WILL BACK FROM THE NNW EARLY IN THE
PERIOD TO NW...AND EVENTUALLY WNW OVERNIGHT. CIGS HAVE BEEN TRICKY
WITH GUIDANCE GENERALLY HAVING A BAD HANDLE AND BEING TOO MOIST.
BOTH MET/MAV GUIDANCE CALLING FOR CIGS TO IMPROVE BACK TO VFR IN THE
21-00Z TIME FRAME FOR THE CHICAGO AREA...BUT SUSPECT WITH PRESSURE
RISES TAKING HOLD SHORTLY ACROSS THE AREA AND EVEN SOME DIURNAL
HELP...WILL LIFT THE ALREADY HIGH END MVFR CIGS BACK TO VFR SOONER
THAN GUIDANCE IS EXPECTING...THUS WENT MOVED THIS UP TO AROUND 18Z.
COULD BE A FEW LIGHT SHOWERS STILL AROUND THIS TIME...BUT SHOULD BE
GRADUALLY PUSHING EAST THROUGH THE DAY AND NOT CONFIDENT ENOUGH THAT
THEY WILL STILL BE CAUSING IMPACTS TO INCLUDE THEM AT THIS TIME.
ONCE THE LOW LIFTS OUT...HIGH PRESSURE WILL BEGIN TO BUILD IN FROM
THE WEST...AND SHOULD CLEAR OUT REMAINING LOW CLOUDS QUICKLY DURING
THE OVERNIGHT PERIOD. BMD
//ORD AND MDW CONFIDENCE...UPDATED 12Z...
* MEDIUM TO HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* MEDIUM TO HIGH CONFIDENCE IN MVFR CIGS THROUGH EARLY AFTERNOON.
MEDIUM CONFIDENCE IN CIGS IMPROVING TO VFR EARLY TO MID
AFTERNOON.
* LOW TO MEDIUM CONFIDENCE IN PRECIP END TIME. BMD
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
FRIDAY NIGHT...VFR.
SATURDAY...VFR.
SUNDAY...CHC SHRA.
MONDAY...VFR.
TUESDAY...CHC SHRA.
WEDNESDAY...CHC SHRA.
BMD
&&
.MARINE...
258 AM CDT
STRONG LOW PRESSURE NOW CENTERED NEAR TOLEDO IS NOT EXPECTED TO
MOVE MUCH FURTHER WEST AS IT BEGINS TO WEAKEN AND ELONGATE
NORTHEAST INTO SOUTHWEST QUEBEC BY THIS EVENING. BUT THE GRADIENT
DID TIGHTEN ENOUGH FOR STORM FORCE GUSTS ACROSS MUCH OF SOUTHERN
LAKE MICHIGAN. EVEN THOUGH THE LOW WILL BE WEAKENING...SLOWLY...
THE GRADIENT WILL STILL REMAIN QUITE STRONG THIS MORNING. THUS
WILL LET THE STORM WARNING CONTINUE. WINDS SLOWLY DIMINISH THROUGH
GALE FORCE THIS AFTERNOON INTO TONIGHT...SO ONCE THE STORM FORCE
WINDS ARE DONE...A GALE WARNING WILL BE NEEDED. WINDS SHOULD RELAX
BELOW GALE FORCE BY LATE THIS EVENING OR EARLY FRIDAY MORNING...
AND THEN CONTINUE TO STEADILY WEAKEN AS A RIDGE OF HIGH PRESSURE
MOVES ACROSS THE WESTERN LAKES FRIDAY AFTERNOON/EVENING. ANOTHER
AREA OF LOW PRESSURE IS EXPECTED TO MOVE ACROSS SOUTHERN CANADA
SATURDAY NIGHT INTO SUNDAY WHICH MAY INCREASE SOUTHWESTERLY FLOW
DURING THAT TIME. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...HIGH WIND WARNING...ILZ006-ILZ014 UNTIL 10 AM THURSDAY.
LAKESHORE FLOOD WARNING...ILZ006-ILZ014 UNTIL 4 PM THURSDAY.
FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ019-ILZ020-ILZ021-ILZ032...1 AM FRIDAY TO 9 AM
FRIDAY.
IN...HIGH WIND WARNING...INZ001-INZ002 UNTIL 10 AM THURSDAY.
LAKESHORE FLOOD WARNING...INZ001-INZ002 UNTIL 9 PM THURSDAY.
LM...STORM WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878 UNTIL 3 PM THURSDAY.
&&
$$
