Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 022006
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
306 PM CDT SUN AUG 2 2015

.SHORT TERM...
151 PM CDT

.THROUGH TONIGHT...

A FEW ISOLATED SHOWERS/STORMS ARE WORKING THERE WAY EASTWARD ACROSS THE
AREA. THESE STORMS ARE HOLDING TOGETHER TO SOME DEGREE AS
INSTABILITY IS FAVORABLE. THE STORM IN DEKALB COUNTY HAS PRODUCED
SOME HAIL OF NICKEL TO QUARTER SIZE. THIS STORM WILL CONTINUE TO
PROPAGATE SOUTHEASTWARD ALONG THE INTERSTATE 88 CORRIDOR. SHEAR IS
WEAKER CLOSER TO THE LAKE...SO A DOWNWARD TREND IS POSSIBLE...BUT
IT WILL LIKELY HOLD ITS OWN FOR A BIT LONGER. THERE IS QUITE A BIT
OF INTER-CLOUD LIGHTNING WITH THIS STORM...WITH OCCASIONAL/FREQUENT
CLOUD TO GROUND LIGHTNING AS WELL.

WE DO STILL EXPECT AFTERNOON ACTIVITY TO REMAIN ISOLATED AS WATER VAPOR
IMAGERY SUGGESTS THE BETTER SHORTWAVE ENERGY IS PASSING THROUGH
CENTRAL ILLINOIS...AND EVEN MORE SO ACROSS WISCONSIN. STILL...WEAK
ENERGY IN THE NORTHWEST FLOW PATTERN KEEPS THE ISOLATED/WIDELY
SCATTERED STORM CHANCE IN PLACE IN AN UNCAPPED ATMOSPHERE. SHEAR
IS STILL LOW THIS AFTERNOON...SO THE SEVERE THREAT AT LEAST
THROUGH MID AFTERNOON APPEARS ON THE LOW SIDE...THOUGH THESE
STORMS COULD LOCALLY ENHANCE THE ALREADY SYNOPTICALLY MODEST WIND
FIELD AND MAY HAVE SOME MARGINALLY SEVERE HAIL.

FOR THE REST OF THE AREA...JUST WARM AND BREEZY CONDITIONS REMAIN
IN PLACE ACROSS THE AREA AND READINGS IN UPPER 80S/LOW 90S.
AFTERNOON MIXING IS KEEPING DEWPOINTS FROM GETTING OUT OF THE LOW
TO MID 60S...EXCEPT IN FAVORED OUTLYING AREAS WHERE AIDED
EVAPOTRANSPIRATION LOCALLY ENHANCES THE MOISTURE READINGS.

MORE ORGANIZED THUNDERSTORMS ARE EXPECTED TO SPREAD SOUTH AND EASTWARD
TOWARD THE AREA AHEAD OF BETTER HEIGHT FALLS AND A MODEST COLD
FRONT. STILL SOME CONCERNS OVER HOW WIDESPREAD THE CONVECTIVE
COVERAGE WILL BE THIS EVENING. BEST FORCING IS TIED TO THE COLD
FRONT WHICH WILL BE COMING THROUGH THE AREA JUST AFTER PEAK
HEATING TIME. FOR STORMS THAT DO FORM...AMPLE SHEAR AND
INSTABILITY WILL BE PRESENT FOR STORMS TO QUICKLY BECOME
SEVERE...AND OUTFLOW BOUNDARIES FROM STORMS TO OUR NORTH COUPLED
WITH THE COLD FRONTAL PUSH WILL COMPLICATE MATTERS. AIDED
CONVERGENCE/LIFT CAN POTENTIALLY BE ENHANCED CLOSER TO THE LAKE
WHERE ADDITIONAL MOMENTUM MAY KEEP THE HIGHER CHANCES FOR STORMS
NORTH AND EAST CLOSER TO THE LAKE...AND POTENTIALLY IN OUR
SOUTHWEST ZONES WHERE DEWPOINTS/INSTABILITY MAY BE A LITTLE
HIGHER. CONVECTIVE ALLOWING MODELS PAINTING QUITE A RANGE OF
SOLUTIONS FROM A FORWARD PROPAGATING MCS IN OUR SOUTHWEST AREAS
AND VERY LITTLE CLOSER TO CHICAGO...WITH ALTERNATE SOLUTIONS
SUGGESTING THE FORMER SCENARIO WITH LAKE ADJACENT COUNTIES
FAVORED. THE COLD FRONT WILL PUSH SOUTHEASTWARD THROUGH THE AREA
TONIGHT...WITH THUNDERSTORMS EXITING TO THE SOUTHEAST.

KMD

&&

.LONG TERM...
310 AM CDT

MONDAY NIGHT THROUGH SATURDAY...

THE PERIOD WILL BEGIN WITH THE TRANSITION TO A MUCH DRIER
AIRMASS MONDAY NIGHT AS A SURFACE RIDGE OF HIGH PRESSURE SETS UP
FROM CENTRAL CANADA...EAST-SOUTHEASTWARD ACROSS MUCH OF THE CENTRAL
CONUS. THIS SHOULD SET UP A DECENTLY COOL NIGHT ACROSS MUCH OF NORTH
CENTRAL ILLINOIS. LIGHT WINDS AND MAINLY CLEAR SKIES LOOK TO ALLOW
TEMPERATURES TO POSSIBLY DROP INTO THE MIDDLE TO UPPER
50S...ESPECIALLY OUTSIDE URBAN AREAS. CONDITIONS DURING THE DAY
TUESDAY LOOK GREAT...WITH HIGHS MAINLY NEAR 80 WITH LOW HUMIDITY.
THE MAIN CORRIDOR FOR ANY SHOWERS AND THUNDERSTORMS LOOKS TO BE
SOUTH AND WEST OF THE AREA...SO DRY CONDITIONS ARE EXPECTED TUESDAY.

HOWEVER...WITH TIME THROUGH THE MID TO LATER PORTION OF THE
WEEK...THE CHANCES FOR A PERIOD OR TWO OF MORE PRECIPITATION LOOK TO
INCREASE. THE MAIN UPPER LOW...CENTERED NEAR THE JAMES BAY...IS
EXPECTED TO SHIFT EAST-NORTHWARD...ESSENTIALLY ALLOWING THE
MID/UPPER LEVEL FLOW OVER THE REGION TO STEER ADDITIONAL SHORT WAVE
DISTURBANCES RIGHT ACROSS THE AREA. OVERALL...IT APPEARS THE BEST
CHANCES FOR MORE RAIN WILL COME INTO THE PICTURE ON WEDNESDAY NIGHT
INTO THURSDAY. AT THIS TIME IT APPEARS THE THREAT FOR THUNDER WILL
BE WITH THIS ACTIVITY OVER NORTHERN ILLINOIS WILL BE LOW...AS THE
AREA LOOKS TO REMAIN IN A FAIRLY STABLE AND COOL EAST-NORTHEASTERLY
LOW LEVEL FLOW PATTERN. TEMPERATURES DURING THE MID TO LATER PORTION
OF THE WEEK LOOK TO MAINLY REMAIN IN THE 70S.


KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY SOUTHWEST WINDS TO AROUND 30 KT AT TIMES THIS AFTERNOON
  INTO THE EVENING.
* THUNDERSTORM CHANCES INCREASING THIS EVENING...ESPECIALLY AFTER
  00Z.

BMD

//DISCUSSION...UPDATED 18Z...

A COLD FRONT STRETCHES FROM NORTHERN WISCONSIN SOUTHWEST INTO
IOWA AND NEBRASKA THIS AFTERNOON. STRONG SOUTHWEST WINDS ARE IN
PLACE AHEAD OF THE FRONT...WITH GUSTS TO AROUND 30 KT EXPECTED
THROUGH THE AFTERNOON INTO THE EVENING. PRIMARILY DRY WEATHER IS
EXPECTED THROUGH EARLY AFTERNOON...THOUGH CANNOT RULE OUT AN
ISOLATED THUNDERSTORM DEVELOPING...ESPECIALLY WITHIN A PREFRONTAL
CONVERGENCE ZONE THAT CURRENTLY STRETCHES FROM SOUTHERN WI ACROSS
FAR NW IL AND INTO EASTERN IA. A FEW SHOWERS/THUNDERSTORMS HAVE
BEEN TRYING TO DEVELOP WITHIN THIS CORRIDOR THROUGH THE MORNING
BUT SO FAR A CAPPING INVERSION HAS KEPT MORE WIDESPREAD CONVECTION
FROM DEVELOPING. THUNDERSTORM CHANCES WILL INCREASE AHEAD OF THE
MAIN FRONT THIS EVENING AS IT PUSHES ACROSS NORTHERN ILLINOIS
STARTING AROUND 00Z. STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE
THIS EVENING. CONDITIONS SHOULD DRY OUT BEHIND THE FRONT LATE THIS
EVENING AND OVERNIGHT WITH WINDS TURNING TO THE NORTHWEST. MORE
BENIGN WEATHER IS EXPECTED MONDAY WITH A MODEST NORTHWEST BREEZE
AND VFR CONDITIONS.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WINDS.
* MEDIUM CONFIDENCE IN SCATTERED OR GREATER THUNDERSTORM
  COVERAGE/GENERAL TIMING AT TERMINALS.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT THROUGH TUESDAY...VFR. NORTHWEST WINDS.
WEDNESDAY...MAINLY VFR. CHANCE OF SHOWERS LATE.
THURSDAY...VFR. CHANCE OF SHRA/SLIGHT CHANCE OF TSRA.
FRIDAY...VFR.
SATURDAY...VFR.

BEACHLER

&&

.MARINE...
313 AM CDT

SMALL CRAFT ADVISORY CONDITIONS WILL DEVELOP ACROSS THE NEAR
SHORE WATERS THIS MORNING. STRONG GUSTY WEST-SOUTHWESTERLY WINDS
UP TO 30 KT CAN BE EXPECTED THROUGH THE AFTERNOON. ALSO...WE CANT
RULE OUT SOME GALE FORCE GUSTS AT TIMES LATER THIS AFTERNOON.

THE THREAT FOR SEVERE THUNDERSTORMS WILL BE THE OTHER SIGNIFICANT
ISSUE OVER THE LAKE THIS AFTERNOON INTO THE EARLY EVENING. A
RATHER POTENT FRONTAL TROUGH OF LOW PRESSURE IS EXPECTED TO FOCUS
THE DEVELOPMENT OF THESE STORMS. STRONG WIND GUSTS IN EXCESS OF 50
KT AND HAIL WILL BE POSSIBLE WITH THESE STORMS.

FOLLOWING THIS FRONTAL PASSAGE TONIGHT...IT APPEARS CONDITIONS
WILL BE FAIRLY QUIET OVER THE LAKE FOR A COUPLE DAYS AS A LARGE
EXPANSIVE RIDGE OF HIGH PRESSURE BUILDS OVER THE CENTRAL CONUS.
THE NEXT CONCERN FOR STRONGER WINDS AND HIGH WAVES LOOKS TO BE
LATER THIS WEEK. DURING THIS TIME...ANOTHER AREA OF LOW PRESSURE
COULD SET THE STAGE FOR A PERIOD OF 15 TO 25 KT EAST-NORTHEASTERLY
WINDS OVER PORTIONS OF LAKE MICHIGAN. THESE WINDS COULD RESULT IN
4+ FOOT WAVES AND SMALL CRAFT ADVISORY CONDITIONS OVER SOUTHERN
LAKE MICHIGAN THURSDAY.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 PM SUNDAY.

&&

$$

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