Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 052022
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
322 PM CDT TUE MAY 5 2015

.SHORT TERM...
308 PM CDT

THROUGH WEDNESDAY...

...ISSUED A FOG ADVISORY FOR LAKE AND COOK IN ILLINOIS THROUGH MID
MORNING WEDNESDAY...

WIDELY SCATTERED THUNDERSTORMS ARE DEVELOPING ACROSS MY SOUTHERN
COUNTIES...SOUTH OF I-80 THIS AFTERNOON IN CLOSE PROXIMITY TO THE A
SURFACE FRONTAL BOUNDARY. TEMPERATURES HERE ARE IN THE MID 70S TO
NEAR 80...WITH DEWPOINTS POOLING INTO THE UPPER 60S ALONG THE
BOUNDARY. THIS IS RESULTING IN A CORRIDOR OF AROUND 1500 MLCAPES
ACROSS THESE AREAS. VAD WIND PROFILES INDICATE THAT DEEP LAYER
EFFECT SHEAR IS ON THE ORDER OF 25 TO 30 KT. WITH THIS IN MIND...IT
DOES NOT APPEAR THAT THESE STORMS WILL PRESENT A SIGNIFICANT SEVERE
THREAT. HOWEVER...IF ANY STORMS CAN MAINTAIN AN UPDRAFT LONG
ENOUGH...THERE COULD BE SOME SMALL HAIL...THOUGH RADAR TRENDS
SUGGEST THAT ONCE THE STORMS TRY TO MOVE AWAY FROM THE LOW LEVEL
CONVERGENCE ALONG THE BOUNDARY THEY DECAY DUE TO THE LACK OF ANY
GOOD LARGER SCALE FORCING FOR ASCENT. AS SUCH...IT APPEARS THESE
STORMS WILL REMAIN CONFINED TO A RELATIVELY NARROW CORRIDOR ACROSS
MY SOUTHERN COUNTIES INTO EARLY THIS EVENING...BEFORE DISSIPATING
WITH SUNSET.

THE OTHER MAIN CONCERN TONIGHT INTO WEDNESDAY WILL BE THE THREAT OF
DENSE FOG. WEBCAMS NEAR THE LAKE HAVE BEEN SOCKED IN FOG WITH THE
VERY COOL ONSHORE FLOW...AND WITH THE HIGH DEW POINT AIR...I DONT
SEE MUCH OF AN IMPROVEMENT TONIGHT. IN FACT...WE COULD ACTUALLY SEE
THE DENSE FOG BEGIN TO DEVELOP INLAND ACROSS MUCH OF NORTHERN
ILLINOIS NORTH OF THE FRONTAL BOUNDARY THIS EVENING. I ISSUED A
DENSE FOG ADVISORY FOR LAKE AND COOK COUNTIES IN ILLINOIS.
HOWEVER...I WOULD NOT BE SURPRISED IF THIS ADVISORY NEED TO BE
EXPANDED INLAND THIS EVENING. AREAS OF FOG SHOULD LIFT INLAND AREAS
BY MID TO LATE MORNING AS THE WARM FRONT BEGINS TO SHIFT NORTHWARD.
HOWEVER...AREAS NEAR THE LAKE COULD STILL SEE SOME FOG AS IT APPEARS
THAT A LAKE BREEZE WILL DEVELOP AN ONSHORE WIND AGAIN ON WEDNESDAY.
THIS LAKE BREEZE BOUNDARY COULD ALSO SPARK OFF A FEW ISOLATED
SHOWERS OR STORMS LATER WEDNESDAY AFTERNOON ACROSS THE WESTERN
SUBURBS OF CHICAGO.

TEMPERATURES ACROSS MUCH OF THE AREA AWAY FROM LAKE MICHIGAN SHOULD
WARM TO NEAR 80 TO THE MID 80S SOUTH AS THE WARM FRONT LIFTS
NORTHWARD. HOWEVER...WITH A LAKE BREEZE AND ONSHORE FLOW...MUCH
COOLER CONDITIONS ARE EXPECTED NEAR THE LAKE.


KJB

&&

.LONG TERM...
320 PM CDT

WEDNESDAY NIGHT THROUGH TUESDAY...

THE PERIOD WILL BEGIN RELATIVELY QUIET WITH DRY CONDITIONS
EXPECTED WEDNESDAY NIGHT. ANY LINGERING PRECIP AND CLOUD COVER
FROM THE AFTERNOON WILL DIMINISH EARLY IN THE EVENING WITH CLEAR
SKIES EXPECTED FOR MOST AREAS THROUGHOUT THE NIGHT.
HOWEVER...UPPER LEVEL RIDGE WILL BEGIN TO SHIFT EAST OF THE AREA
DURING THIS TIME WHILE A MID/UPPER LEVEL TROUGH LIFTS NORTHEAST
ACROSS THE CENTRAL PLAINS. AS THIS OCCURS...DO ANTICIPATE SOME
PIECES OF ENERGY TO WORK TOWARDS THE REGION WHICH WILL TRY AND
WORK ANY PRECIP TO THE WEST NEAR THE CWA. THIS PRECIP WILL LIKELY
REMAIN TO THE WEST BUT DO EXPECT INCREASING CLOUDS FOR AREAS OVER
NORTHWEST ILLINOIS LATE.

MID/UPPER LEVEL TROUGH WILL CONTINUE LIFTING NORTHEAST THROUGH
THE NORTHERN PLAINS AND UPPER MIDWEST ON THURSDAY...WITH BROAD
SOUTHWEST FLOW ALOFT IN PLACE. SURFACE LOW WILL LIFT NORTH THROUGH
THE NORTHERN PLAINS/UPPER MIDWEST DURING THIS TIME AS WELL WITH
SURFACE PRESSURE GRADIENT OVER NORTHERN ILLINOIS TIGHTENING. THIS
SOUTHERLY FLOW AND PARTLY CLOUDY SKIES WILL HELP SET THE STAGE FOR
A WARM DAY ON THURSDAY...WITH LOW TO MID 80S EXPECTED AND EVEN FOR
AREAS NEAR THE LAKE. ENERGY TO THE WEST WILL SLOWLY BEGIN TO SHIFT
EAST THURSDAY NIGHT AND ALTHOUGH CHANCES FOR PRECIP INCREASE...IT
WILL LIKELY ONLY BE FOR AREAS ACROSS THE WESTERN CWA.

MOST GUIDANCE IN GENERAL AGREEMENT WITH SHIFTING THE ACTIVITY
EAST ACROSS THE CWA ON FRIDAY...WITH SHOWERS AND THUNDERSTORMS
APPEARING TO BE MORE LIKELY DURING THIS TIME. DEWPOINTS ARE
EXPECTED TO INCREASE INTO THE LOW TO MID 60S DURING THIS TIME WITH
INSTABILITY LIKELY INCREASING AS WELL. HOWEVER...IF PRECIP WERE TO
BE ONGOING AT THE START OF THE PERIOD...I WONDER HOW MUCH
INSTABILITY WILL BE PRESENT. ALSO...FLOW REMAINS RATHER WEAK
ALOFT. SO AT THIS TIME...AM NOT OVERLY CONCERNED WITH ANY
WIDESPREAD ORGANIZED CONVECTION. SIGNIFICANT INCREASES IN MOISTURE
WILL SUPPORT HEAVY RAINFALL POTENTIAL THOUGH. WILL NEED TO
CONTINUE MONITORING THIS PERIOD AS WELL AS GOING INTO FRIDAY NIGHT
WITH UPSTREAM FORCING AND DEVELOPMENT LIKELY MOVING NORTHEAST OVER
THE AREA. WITH STRONGER FORCING...MORE ORGANIZED DEVELOPMENT COULD
OCCUR WITH ADDITIONAL HEAVY RAINFALL. ACTIVE WEATHER PATTERN LOOKS
TO REMAIN IN PLACE INTO THE WEEKEND WITH SHOWERS AND THUNDERSTORMS
LIKELY.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS AROUND 10 KT THROUGH THIS AFTERNOON.

* IFR/LIFR CIGS THROUGH THE BEGINNING OF THE MORNING RUSH
  WEDNESDAY.

* IFR/LIFR VSBYS AT ORD THROUGH EARLY TOMORROW. RETURNING TO MDW
  TONIGHT.

* SCATTERED SHOWERS AND PERHAPS A THUNDERSTORM THIS AFTN...MAINLY SOUTH
  OF MDW.

KMD

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

THE BATTLE OF THE COLD LAKE AND LOW LEVEL ONSHORE FLOW VERSUS THE
WARM MAY SUN IS UNDERWAY...MAKING FOR A CHALLENGING AFTERNOON
FORECAST ACROSS THE TERMINALS. MONITORING WEBCAMS DOWNTOWN SHOW
CLOUDS BRIEFLY ATTEMPTING TO LIFT BEFORE FILLING RIGHT BACK IN. WE
ALSO CONTINUE TO ADVECT WARMER AND MOIST AIR JUST OFF THE DECK
WHICH IS AIDING IN KEEPING THE LOW LEVEL INVERSION IN PLACE. FEEL
THAT THESE LATTER FACTORS WILL WIN OUT AND KEEP MOST OF THE TAF
SITES LOCKED IN LIFR TO IFR CONDITIONS...WHILE POINTS SOUTH WILL
LIFT TO VFR BEFORE MVFR CUMULUS FILL IN AS WELL.

THE LOW LEVEL FRONT IS NOT EXPECTED TO LIFT MUCH FARTHER
NORTH...AND THUS EXPECT THE NNE WINDS TO REMAIN IN PLACE. WITH THE
FRONT HOLDING SOUTH...EXPECT ANY CONVECTION THAT STIRS THIS
AFTERNOON TO BE FOCUSED IN THESE AREAS...SOUTH OF INTERSTATE 80.

TONIGHT WINDS SHOULD WEAKEN SOME AND EXPECT CIGS/VSBYS TO REMAIN
LOCKED IN DOWN LOW MOST OF THE NIGHT. FOG COULD BE DENSE
TONIGHT...ESPECIALLY CLOSER TO THE LAKE. LOW LEVEL FRONT GETS
SOME NORTHWARD MOVEMENT EARLY WEDS WHICH SHOULD ALLOW FOR SOME
LIFTING WEDNESDAY MORNING. PRECIP CHANCES DO EXIST TONIGHT/EARLY
WEDS BUT TOO LOW FOR A MENTION IN THE TAFS JUST YET. AT BEST SOME
ISOLATED SHOWERS AHEAD OF THE FRONT 8Z-12Z TIME FRAME FOR THE TAF
SITES.

KMD

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

* HIGH THAT EAST-NORTHEAST WINDS HOLD AROUND 10 KT THIS AFTERNOON.

* HIGH IN LIFR CIGS HOLDING AT ORD... AND IFR/LIFR CIGS RETURNING
  TO MDW. MEDIUM ON CIG HEIGHTS OVERNIGHT THOUGH LOW-MEDIUM ON
  CLEARING TIME WEDS.

* MEDIUM-LOW ON VSBYS THIS AFTERNOON AND TONIGHT. COULD BE WORSE
  VSBY OVERNIGHT.

* HIGH IN ORD REMAINING DRY THE REST OF THE DAY. MEDIUM THAT
  AFTERNOON SHOWERS/ISOLATED T-STORMS REMAIN SOUTH OF MDW. MEDIUM
  THAT TAF SITES REMAIN DRY OVERNIGHT AS WELL.

KMD

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

WEDNESDAY NIGHT...VFR. SOUTHEAST WINDS BCMG SOUTH.

THURSDAY...VFR. SOUTH WINDS.

FRIDAY...TSRA. MVFR CIGS PSBL OVERNIGHT. SOUTHWEST WINDS.

SATURDAY...SCHC TSRA DURING THE DAY AND CHC SHRA. NORTHWEST WINDS.

SUNDAY AND MONDAY...CHC TSRA. MVFR CIGS PSBL. NORTHEAST WINDS BCMG
SOUTHWEST MONDAY.

JEE

&&

.MARINE...
212 AM CDT

A STATIONARY FRONT IS OVER CENTRAL IL AND IT WILL REMAIN SOUTH OF
THE LAKE UNTIL IT LIFTS NORTH AS A WARM FRONT WEDNESDAY.
THEREFORE...NORTHEAST TO EAST WINDS WILL BECOME SOUTH WEDNESDAY
NIGHT BEHIND THE WARM FRONT.  HIGH PRESSURE CURRENTLY OVER LAKE
SUPERIOR SHIFTS EAST OF LAKE MICHIGAN WEDNESDAY AND REMAINS OVER THE
EASTERN SEABOARD THROUGH THE WEEK.  SOUTH WINDS UP TO 20 KT AT TIMES
ARE EXPECTED THROUGH FRIDAY.  THE NEXT LOW FORMS OVER THE NORTHERN
ROCKIES WEDNESDAY AND MOVES OVER ONTARIO THURSDAY NIGHT AND FRIDAY.
THE LOWS COLD FRONT SWEEPS OVER THE LAKE SATURDAY AND WINDS BECOME
NORTH BEHIND THE FRONT.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ006-ILZ014 UNTIL 11 AM WEDNESDAY.

IN...NONE.
LM...DENSE FOG ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-
     LMZ777-LMZ779 UNTIL 4 PM WEDNESDAY.

&&

$$

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