349 AM CDT
THE MAIN FORECAST CONCERN FOR THE MORNING UPDATE WILL FOCUS ON THE
DEVELOPING SYSTEM TO LIFT FROM THE SOUTH AND BRING AN EXTENDED
PERIOD OR WIDESPREAD RAIN TO NORTHERN ILLINOIS AND NORTHWEST INDIANA.
HOWEVER...BEFORE THE RAIN MOVES INTO THE AREA...THE REMAINDER OF THE
NIGHT AND THE EARLY MORNING HOURS WILL BE QUIET. THE MAIN ISSUE HAS
BEEN OVER NORTHERN ILLINOIS WHERE TEMPERATURES HAVE DROPPED INTO THE
UPPER 30S. THE LATEST SATELLITE IMAGERY INDICATES INCREASING CLOUD
COVER OVER THE AREA...SO DO NOT EXPECT TEMPERATURES TO DROP MUCH
LOWER THAN THE CURRENT VALUES. SO...THERE WILL STILL BE THE
POTENTIAL FOR SOME ISOLATED AREAS OF PATCHY FROST THIS MORNING.
FOR THE REST OF TODAY...THE FOCUS OF THE FORECAST WILL SHIFT TO THE
DEVELOPING PCPN SITUATION. AS THE DEEP UPPER LOW THAT HAS BEEN
SITTING OVER THE JAMES BAY AREA LIFTS OUT TO THE EAST THIS
MORNING...A DEEPENING SOUTHERN STREAM SHORTWAVE WILL LIFT FROM THE
LOWER MISSISSIPPI VALLEY AND INTO THE OHIO VALLEY. A STRENGTHENING
BAROCLINIC ZONE JUST NORTH AND WEST OF THE MAIN SFC LOW WILL SHIFT
OVER THE FAR SERN PORTIONS OF THE CWA BY LATE MORNING...SIGNALING
THE BEGINNING OF A WIDESPREAD PCPN EVENT FOR THE AREA. THE TREND OF
THE MODEL GUIDANCE HAS BEEN TO SHIFT THE TRACK OF THE SYSTEM A
LITTLE MORE TO THE WEST...SO HAVE BEEFED UP POPS AND PCPN AMOUNTS
OVER THE AREA. AS THE SYSTEM TRACKS NEWD...A NRN STREAM SHORTWAVE
DROPPING OUT OF THE NRN PLAINS WILL PHASE WITH THE SRN STREAM
LOW...HELPING CARVE OUT A FULL LATITUDE TROUGH OVER THE MISSISSIPPI
VALLEY. AS THIS OCCURS...THE ASSOCIATED PCPN SHIELD WILL SPREAD
FROM SOUTHEAST TO NORTHWEST ACROSS THE CWA...REACHING THE ROCKFORD
AREA BY THIS EVENING. A SERIES OF NRN STREAM SHORTWAVES WILL DROP
OUT OF CANADA...REINFORCING THE UPPER TROUGH AND EVENTUALLY A CLOSED
UPPER LOW WILL DEVELOP OVER THE LOWER OHIO VALLEY BY WEDNESDAY
AFTERNOON. A COMPLICATING FACTOR WITH THIS DEVELOPING SITUATION
WILL BE THE INTERACTION OF A TROPICAL SYSTEM LIFTING OUT OF THE ERN
GULF OF MEXICO. THE MODELS HAVE NOT BEEN VERY CONSISTENT ON THE
EVOLUTION AND INTERACTION OF THIS SYSTEM...WHICH WOULD ADD A BIT OF
UNCERTAINTY TO THE FORECAST.
THE LATEST GUIDANCE SUGGESTS THAT THE MID-LATITUDE AND
TROPICAL-SOURCED SYSTEMS SHOULD MERGE OVER THE UPPER OHIO VALLEY
WITH A DEEP SFC LOW DEVELOPING BY WEDNESDAY MORNING. AT THE SAME
TIME...STRONG HIGH PRESSURE WILL SETTLE OVER SOUTHCENTRAL CANADA.
BETWEEN A 1030MB HIGH TO OUR NORTHWEST AND A 991MB LOW TO OUR
SOUTHEAST...A VERY STRONG NELY-NLY PRESSURE GRADIENT WILL SET
UP...WITH THE STRONGEST GRADIENT FOCUSED OVER LAKE MICHIGAN AND
IL/SERN WI/NWRN INDIANA. WINDS WILL INCREASE RAPIDLY THROUGH THE
DAY WEDNESDAY. IN ADDITIONS TO THE STORM-FORCE WINDS EXPECTED TO
DEVELOP OVER LAKE MICHIGAN ON WEDNESDAY...WIND GUSTS WILL APPROACH
35MPH OVER THE CWA. THE WIND FORECAST WILL REQUIRE CLOSE
EXAMINATION FOR THE NEXT MODEL RUNS SINCE WIND SPEEDS WILL BE
APPROACHING WIND ADVISORY CRITERIA. WILL HOLD OFF ON ISSUING A WIND
ADVISORY AT THIS POINT...BUT IF THE 12Z RUNS AND THE OBSERVED SFC
PATTERN INDICATES GREATER STRENGTHENING OF THE PRESSURE GRADIENT OVER
THE AREA...A WIND ADVISORY MAY BE REQUIRED FOR WEDNESDAY AFTERNOON
THROUGH THURSDAY AFTERNOON.
THE OTHER CONCERN WILL BE FOR RAINFALL AMOUNTS. SINCE THIS SYSTEM
WILL BE VERY DYNAMIC BOTH AT THE SFC AND ALOFT...RELATIVELY HEAVY
RAINFALL AMOUNTS ARE LIKELY. HAVE GENERALLY BUMPED UP POPS AND QPF
OVER THE AREA OVER PREVIOUS FORECASTS. WITH THE ADDED INFLUENCE OF
THE SYSTEM LIFTING OUT OF THE ERN GLFMEX...THE ERN PORTIONS OF THE
CWA SHOULD SEE THE HEAVIEST PCPN AMOUNTS. THE LATEST FORECAST
UPDATE WILL CARRY STORM TOTAL QPF RANGING FROM AROUND A QUARTER INCH
OF RAIN OVER THE I-39 CORRIDOR TO ABOUT 1 INCH OVER CHICAGO AND THE
I-57 CORRIDOR. THE HEAVIEST AMOUNTS SHOULD BE OVER THE NWRN INDIANA
COUNTIES...WHERE STORM TOTAL QPF SHOULD APPROACH 1.5 INCHES. SINCE
THE AREA HAS NOT RECEIVED MUCH RAIN RECENTLY...AREA RIVERS SHOULD
HAVE ADEQUATE CAPACITY TO HANDLE THE RAINFALL...BUT THE WRN PORTIONS
OF THE KANKAKEE RIVE WILL NEED TO BE CLOSELY MONITORED FOR
SIGNIFICANT RISES.
FOR THE LONGER TERM FORECAST PERIOD...THE SYSTEM SHOULD FINALLY
BEGIN TO QUICKLY LIFT OUT TO THE NORTHEAST BY THURSDAY NIGHT AND ALL
PCPN SHOULD FINALLY COME TO AN END OVERNIGHT THURSDAY NIGHT. BY
FRIDAY MORNING...A MUCH COOLER AIRMASS WILL SETTLE OVER THE REGION
AND TEMPERATURES WILL ONCE AGAIN BECOME A CONCERN. THE LATEST
EXTENDED GUIDANCE SUGGESTS THAT TEMPERATURES SHOULD DROP INTO THE
LOWER 30S WEST OF THE FOX VALLEY...WHILE THE REMAINDER OF THE
AREA...AWAY FROM THE LAKE FRONT AND THE HIGHLY URBANIZED AREAS OF
THE CHICAGO METRO AREA SHOULD SEE TEMPERATURES DROP INTO THE MIDDLE
TO UPPER 30S. THIS WOULD MEAN WIDESPREAD FROST FOR THE AREA...AND
TEMPERATURES TO OR JUST BELOW FREEZING. SO...THE GENERAL TREND FOR
THE EXTENDED FORECAST PERIOD...FROM FRIDAY THROUGH MONDAY...SHOULD
SEE TEMPERATURES START OUT AT BELOW NORMAL LEVELS AND MODERATE
THROUGH THE WEEKEND. THE PCPN FORECAST IS A LITTLE MORE UNCERTAIN
DUE TO DIFFERENCES IN HOW THE MODELS HANDLE THE FINER SCALE
DETAILS. SO...WILL CARRY A DRY FORECAST THROUGH THE LATTER PORTIONS
OF THE WEEK AND THE WEEKEND.
KREIN
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* PRECIPITATION CHANCES AND COVERAGE TONIGHT AND ON WEDNESDAY.
* CIG TRENDS TONIGHT AND ON WEDNESDAY.
* TIMING/MAGNITUDE OF STRONG NORTHERLY WIND GUSTS TONIGHT AND
WEDNESDAY.
KJB
//DISCUSSION...UPDATED 18Z...
A STORM SYSTEM ACROSS THE CENTRAL AND LOWER MISSISSIPPI RIVER VALLEY
WILL QUICKLY STRENGTHEN TONIGHT INTO WEDNESDAY AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY. THIS SYSTEM WILL PRODUCE SEVERAL MAJOR
WEATHER IMPACTS ACROSS THE TERMINALS BY EARLY WEDNESDAY MORNING.
THESE CONCERNS INCLUDE: WINDS...CIG AND VIS TRENDS AND TIMING OF
RAINFALL.
STRONG NORTH TO NORTHEAST WINDS WILL QUICKLY DEVELOP DURING THE
EARLY MORNING HOURS AS THE DEEPENING SURFACE LOW PRODUCES A STRONG
PRESSURE GRADIENT ACROSS THE AREA. THE WINDS WILL CONTINUE TO
INCREASE DURING THE DAY AS THE LOW LIFTS NORTHWARD. I EXPECTED
NORTHERLY WINDS AROUND 25 KT WITH GUSTS FROM 35 TO 40 KT DURING
THE AFTERNOON.
CIGS SHOULD FALL INTO THE MVFR CATEGORY TONIGHT. HOWEVER...IFR
CONDITIONS ARE POSSIBLE AS EARLY AS LATE WEDNESDAY AFTERNOON...BUT
MORE LIKELY BY WEDNESDAY EVENING. RAINFALL SHOULD BEGIN TO DEVELOP
ACROSS NORTHEASTERN ILLINOIS LATE TONIGHT AS THE FLOW INCREASES OFF
THE LAKE. IT MAY BE MORE SHOWERY IN NATURE DUE TO SOME LAKE
ENHANCEMENT. HOWEVER...MORE WIDESPREAD RAIN WILL ARRIVE DURING THE
DAY ON WEDNESDAY. IT APPEARS THAT THE BEST CHANCES FOR HEAVY
RAINFALL WILL NOT BE UNTIL LATE WEDNESDAY AFTERNOON AND WEDNESDAY
NIGHT. THIS IS THE TIMING IN WHICH STRONG MID LEVEL FORCING FOR
ASCENT INCREASES IN RESPONSE TO A DEVELOPING TROWAL. BECAUSE OF
THIS...I SCALED BACK ON THE LOWER VISIBILITIES IN RAIN THAT WERE
PREVIOUSLY ADVERTISED EARLY WEDNESDAY MORNING. ANY PROLONGED MVFR OR
LOWER VIS IN RAIN LOOKS TO OCCUR AFTER 20 UTC TOMORROW AFTERNOON.
KJB
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
* LOW TO MEDIUM CONFIDENCE IN PRECIP TIMING/COVERAGE TONIGHT.
* MEDIUM CONFIDENCE IN CIGS DROPPING TO MVFR OVERNIGHT.
* LOW CONFIDENCE ON IFR CIGS ON WEDNESDAY.
* HIGH CONFIDENCE IN WIND GUSTS IN EXCESS OF 30 KT BEGINNING
WEDNESDAY MORNING.
KJB
//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...
WEDNESDAY NIGHT...SHOWERS LIKELY...IFR POSSIBLE. STRONG WINDS.
THURSDAY...CHANCE OF SHOWERS...IFR POSSIBLE.
FRIDAY THROUGH MONDAY...VFR.
BMD
&&
.MARINE...
844 AM CDT
...GALES DEVELOPING WEDNESDAY AND INCREASING TO STORM FORCE
WEDNESDAY AFTERNOON/EVENING...
COMPONENTS CONTRIBUTING TO THE EXPECTED STORM COMING TOGETHER THIS
MORNING WITH AN UPPER TROUGH APPROACHING THE MID MISSISSIPPI RIVER
VALLEY STARTING TO STRENGTHEN AS AN UPPER LEVEL JET DIGS SOUTHWARD
ACROSS THE HIGH PLAINS. SURFACE LOW PRESSURE OVER THE GULF COAST
STATES WILL START TO INTENSIFY AND MOVE NORTHWARD INTO THE OHIO
VALLEY BY THIS EVENING. NORTHWEST WINDS TODAY WILL TURN NORTH THEN
NORTHEAST THIS EVENING AND TONIGHT WITH SPEEDS STEADILY INCREASING
TO GALE FORCE BY WEDNESDAY MORNING. LOW TRACK HAS BEEN SHIFTING
WESTWARD WITH TIME AND IS NOW EXPECTED TO MOVE INTO NORTHEAST
INDIANA/NORTHWEST OHIO BY WEDNESDAY EVENING THEN POSSIBLY SHIFT A
BIT WEST OF THERE. THIS SHOULD RESULT IN A RAPID INCREASE FROM
GALES TO STORM FORCE WINDS ACROSS AT LEAST THE SOUTHERN HALF TO
TWO-THIRDS OF THE LAKE LATE WEDNESDAY AFTERNOON. WILL NEED TO
CONSIDER INCREASING WINDS SLIGHTLY ACROSS THE SOUTHERN PART OF THE
LAKE WITH POTENTIAL FOR 55-60 KT GUSTS. POTENTIAL LIMITING FACTOR
FOR THESE HIGHER WINDS WILL BE THE FAIRLY COOL ATMOSPHERE IN
PLACE OVER THE LAKE AND THE LACK OF A SIGNIFICANT COLD PUSH OF
AIR...STILL RESULTING IN UNSTABLE CONDITIONS OVER THE LAKE... BUT
POSSIBLY LIMITING THE DEEPEST MIXING AND THEREFORE LIMITING THE
MAXIMUM GUST POTENTIAL. SHOULD NOT BE A PROBLEM ACHIEVING 50 KT
STORM FORCE WINDS...ITS MORE OF A MATTER OF THE CHANCES OF HAVING
GUSTS HIGHER THAN THAT. CONFIDENCE IS GROWING IN NEEDING TO
INCREASE SLIGHTLY BUT NOT HIGH ENOUGH TO MAKE CHANGES WITH THE
MORNING UPDATE. THE LOW WILL THEN BEGIN TO FILL AND MOVE NORTHEAST
THURSDAY. MAY SEE SOME STORM FORCE WINDS CONTINUE THURSDAY MORNING
BUT EXPECT WINDS TO EASE BACK TO GALE FORCE BY AFTERNOON THEN
BELOW GALES SOME TIME THURSDAY EVENING.
MDB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...5 AM WEDNESDAY TO 4 PM
WEDNESDAY.
STORM WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 PM WEDNESDAY TO 3 PM
THURSDAY.
GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...10 AM
WEDNESDAY TO 10 PM THURSDAY.
&&
$$
