Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 022323 AAA
AFDLOT

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

.MESOSCALE DISCUSSION...
620 PM CDT

WE CONTINUE TO MONITOR SEVERE STORM POTENTIAL FOR THIS EVENING.
LATEST HAND ANALYSIS INDICATED AN ANOMALOUSLY DEEP LOW AT 998 MB
NEAR SHEBOYGAN WI MOVING SOUTHEAST WITH A COLD FRONT/AXIS OF
CONVERGENCE EXTENDING BACK TO THE SOUTHWEST. THIS FRONT HAS SOME
ACCAS AND SOME CU ALONG IT IN EASTERN IA AND SOUTHERN WI...WITH
CONVECTION BACK IN SOUTHERN IA AS WELL. SO CANNOT RULE OUT A STORM
OR TWO GOING NOT FAR NORTHWEST OF ROCKFORD IN THE NEXT 60-90
MINUTES...ALTHOUGH MAIN FOCUS IS LIKELY WITH STORMS IN EASTERN
WISCONSIN AND PROGRESSION OF OR DEVELOP OFF OF THESE. SOUTHWEST
WINDS GUSTING TO 25-35 MPH IN THE NORTHERN END OF THE WARM SECTOR
LIKELY WILL DROP OFF SOME EARLY THIS EVENING...ALTHOUGH PRESSURE
FALLS WILL SUPPORT A CONTINUED DRAW OF LOW-MID 70S DEW POINTS
AHEAD OF THE FRONT.

HOW MUCH THE STORMS FILL IN ALONG THE BOUNDARY IS SOMEWHAT
UNCERTAIN GIVEN THE CAP STILL PRESENT ON ASCENDING 00Z DVN
WEATHER BALLOON...WITH ABOUT A 1C CAP ROUGHLY 600 FT DEEP NEAR
830MB. HOWEVER...AT LEAST SOME STORM DEVELOPMENT FURTHER WEST-
SOUTHWEST OF ONGOING ACTIVITY IN EASTERN WI IS LIKELY GIVEN THE
FORCING FROM INCOMING UPPER WAVE AND THE AFOREMENTIONED LOW-LEVEL
AIR MASS. THIS IS SUPPORTED BY MOST CONVECTIVE ALLOWING MODELS
/CAMS/...ESPECIALLY THE THEME OF FAR NORTHEAST ILLINOIS /INCLUDING
CHICAGO/ SEEING BETTER STORM COVERAGE IN THE 8-10 PM WINDOW. THE
SEGMENT OF STORMS IN EAST CENTRAL WISCONSIN HAVE PRODUCED OUTFLOW
THAT IF ABOUT 30 MILES AHEAD OF THEM...WHICH IS A BIT CONCERNING
THAT THEY MAY SHOW A GRADUAL WEAKENING. AT LEAST SOME STORM
DEVELOPMENT IS SEEN ON RADAR ALONG THIS OUTFLOW THOUGH. THIS
OUTFLOW...AS WELL AS ANY THAT MAY SURGE DOWN THE LAKE AND INTO
NEARSHORE AREAS OF SOUTHEAST WI AND NORTHEAST IL WOULD BE FAVORED
TO SUPPORT NEW STORM DEVELOPMENT AS WELL GIVEN THE LIMITED CAP IN
PLACE.

STEEP MID-LEVEL LAPSE RATES SUPPORTING HIGH CAPE WILL CONTINUE THE
LARGE HAIL THREAT IN THE STRONGEST OF STORMS THIS EVENING. ANY
SEGMENTS WILL BE CAPABLE OF SEVERE WINDS WITH STRONG AMBIENT
FLOW AND JUST THE BEHAVIOR SEEN ALREADY UPSTREAM AND LOCALLY IN
THE AREA FROM EARLIER STORM...AND THIS WILL LIKELY BE THE GREATER
THREAT AFTER SUNDOWN IF STORMS INDEED MOVE INTO NORTHEAST
IL/NORTHWEST IND.

MTF

&&

.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...
344 PM CDT

MONDAY THROUGH SUNDAY...

PERIOD WILL BEGIN WITH SURFACE TROUGH/FRONTAL BOUNDARY DEPARTING
TO THE EAST...WITH ASSOCIATED PRECIP LIKEWISE DEPARTING TO THE
EAST. COOLER AND DRIER CONDITIONS STILL APPEAR LIKELY FOR THE
BEGINNING OF THIS UPCOMING WEEK AS LARGE UPPER LEVEL LOW SETTLES
INTO SOUTHERN CANADA AND THE NORTHEAST CONUS. NO PRECIP EXPECTED
MONDAY INTO TUESDAY...WITH TEMPS IN THE LOW 80S LIKELY BOTH DAYS.
MODELS QUICKLY DIVERGE WITH APPROACHING SYSTEM BY MIDWEEK...WITH
THE GFS THE OUTLIER BRINGING STRONGER/MORE DEFINED LOW CLOSER TO
THE CWA. THIS WOULD PROVIDE A FURTHER NORTHWARD PUSH OF PRECIP
AXIS ESPECIALLY DURING THE WEDNESDAY TIME FRAME. WITH UNCERTAINTY
IN PLACE AND WITH SOME GUIDANCE KEEPING THE CWA DRY...HAVE MADE
LITTLE CHANGES TO THE GOING FORECAST AND KEPT LOW CHANCE POPS FOR
THE SOUTHERN HALF OF THE CWA. AFTER THIS POSSIBLE PRECIP...A DRIER
TREND IS LOOKING LIKELY TOWARDS THE END OF THE WORK WEEK WHILE
BELOW NORMAL TEMPS OCCUR.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* 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 22Z...

* 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...
440 PM CDT

STRONG SOUTHWEST WINDS WILL CONTINUE LATE THIS AFTERNOON INTO THE
EVENING ACROSS MUCH OF THE LAKE INCLUDING THE NEARSHORE AREAS...AS
STRONG LOW PRESSURE MOVES THROUGH THE GREAT LAKES REGION. HIGHEST
SPEEDS ARE OCCURRING ACROSS THE SOUTHERN HALF OF THE LAKE AND
ESPECIALLY ALONG THE NEARSHORE WHERE A FEW GALE FORCE GUSTS ARE
ALSO POSSIBLE. THIS WILL PERSIST BEFORE WINDS DIMINISH LATE THIS
EVENING AND INTO THE OVERNIGHT HOURS AS THIS LOW EXITS TO THE
EAST...WITH WINDS BECOMING MORE WEST NORTHWEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL
     10 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.