Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 021140
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
640 AM CDT SUN AUG 2 2015

.SHORT TERM...
258 AM CDT

THIS MORNING THROUGH THIS EVENING...
REGIONAL IR IMAGERY SHOWS A COUPLE AREAS OF SHOWERS/THUNDERSTORMS
ACROSS THE UPPER MIDWEST...AND A SECOND IN NORTHEAST WISC. CURRENT
EXPECTIONS ARE THAT THIS AREA OF CONVECTION WILL CONTINUE TO
REMAIN NORTH OF NORTHERN IL/NORTHWEST IN. A ROBUST THERMAL RIDGE
AT 925MB EXISTS THIS MORNING...AND STRETCHES ACROSS IOWA NORTHEAST
INTO CENTRAL WISC WHICH HAS MAINTAINED SFC TEMPS IN THE MID 70S
ACROSS THOSE AREAS. MEANWHILE NORTHERN IL REMAINS SOUTH OF THIS
THERMAL RIBBON...WITH SFC TEMPS IN THE UPR 60S FOR THE MOST PART.
THE EXCEPTION IS THE URBAN HEAT ISLAND OF DOWNTOWN CHICAGO...WHERE
TEMPS REMAIN IN THE 70S.

LLVL MOISTURE HAS BEEN SLOW TO REBOUND...WITH MANY AREAS SEEING DEW
POINTS REMAIN IN THE MID 60S. HOWEVER AS THE DAY PROGRESSES MOISTURE
SHOULD POOL NORTH ACROSS THE REGION. MIXING WILL BE STRONG AGAIN
TODAY...WITH MIX-HGTS NEARING 3500FT AGL AND FILTERING TO THE SFC
30KT. EXPECT FREQUENT GUSTS IN THE 30-35MPH RANGE FROM LATE MORNING
THROUGH THIS EVENING...PRIOR TO THE EXPECTED THUNDERSTORMS. HOWEVER
WHAT COULD POSE SOME CHALLENGES TO THE GUSTY WINDS MAY BE SOME
LINGERING CLOUD COVER. THIS MAY LIMIT HOW HIGH THE MIXING MAY OCCUR.

THE 500MB TROUGH WILL BE PIVOTING SOUTH ACROSS THE UPPER
MIDWEST...ALONG WITH A DEEPENING SFC WAVE. THIS WILL ALLOW THE
FRONTAL BOUNDARY THAT WILL BE ACROSS THE CANADIAN BORDER EARLY THIS
MORNING TO DROP SOUTH ACROSS WISC THIS EVENING. THE CHALLENGE FOR
THIS EVENING REMAINS ON TIMING AND COVERAGE OF THUNDERSTORMS FOR
NORTHERN IL/NORTHWEST IN.

CONSIDERABLE DIFFERENCES REMAIN AMONGST THE CONVECTIVE ALLOWING
MODELS...WITH TIMING RANGING FROM LATE THIS AFTERNOON TO THIS
EVENING FOR NORTHERN IL. THE DRIVING CHALLENGE WILL BE WHAT
TRANSPIRES THIS AFTERNOON UPSTREAM ACROSS WISC. GUIDANCE HAS BEEN
KEYING IN ON A COMPLEX OF STORMS DEVELOPING THIS AFTERNOON ACROSS
CENTRAL/EASTERN WISC...WHICH MAY SEND AN OUTFLOW SOUTH TOWARDS
NORTHERN IL. MEANWHILE OTHER GUIDANCE SUGGESTS THE BEST FORCING WILL
BE MORE FOCUSED FURTHER EAST ACROSS LOWER MICHIGAN...WHICH NOW WILL
BE CLOSER TO THE SFC WAVE. THE MOST REALISTIC APPROACH WOULD BE THAT
AS AN OUTFLOW PUSHES SOUTH ACROSS NORTHERN IL THAT THIS WILL SERVE
AS THE TRIGGER FOR A STEADY GROWTH OF CONVECTION ACROSS THE FORECAST
AREA LATE THIS AFTN AND MORE LIKELY JUST AFTER 00Z. HIGHS THIS
AFTERNOON WILL EASILY WARM INTO THE UPR 80S TO ARND 90...AND WITH
THE WARM RIBBON OVERHEAD AND JUST NORTH A FEW LOCATIONS IN THE
NORTHERN CWFA MAY WARM FURTHER TO 91-93 DEG.

THE ATMOSPHERE WILL BE PRIMED WITH CONSIDERABLE INSTABILITY THIS
AFTERNOON/EVENING...ALONG WITH AMPLE DEEP LAYER SHEAR OF AROUND
40KT. SO ONCE CONVECTION DEVELOPS UPSTREAM THIS AFTERNOON...IT SEEMS
FAVORABLE THAT A STEADY GROWTH IN COVERAGE/INTENSITY WILL OCCUR AS
IT ARRIVES ACROSS THE FORECAST AREA. THE CURRENT DAY 1 OUTLOOK FROM
THE SPC HAS MUCH OF NORTHERN IL/NORTHWEST IN OUTLINED FOR AN
ENHANCED RISK OF SEVERE STORMS...WHILE SOUTH OF A ROCKFORD TO
KANKAKEE LINE IN A SLIGHT RISK. THE MAIN HAZARDS FROM
STRONG/SEVERE STORMS FOR OUR AREA WILL BE DAMAGING WIND
GUSTS...AND LARGE HAIL GIVEN THE STEEPENING MID-LVL LAPSE RATES.

TONIGHT THROUGH MONDAY...
BY LATE TONIGHT THE LINE OF STORMS SHOULD BE RELATIVELY
PROGRESSIVE AND SLIDING EAST/SOUTH. CONVECTION WILL BE COMING TO
AN END BY 9Z MON...WITH THE MID-LVL VORT LOBE PIVOTING EAST. WITH
FRONTAL PASSAGE POISED FOR 9-12Z MON...WINDS WILL SHIFT TO
NORTHWEST/NORTH WITH THE MUCH COOLER AIR ARRIVING. MOISTURE
QUICKLY PEELS EAST...AND MAY PROVIDE MOSTLY CLEAR SKIES FOR EARLY
MON. ENOUGH DIFFLUENT FLOW MAY LINGER TO ALLOW SKIES TO REMAIN
MOSTLY SUNNY THRU MON AFTN. TEMPS MON WILL BE MUCH COOLER WITH
HIGHS MAINLY AROUND 80 TO PERHAPS THE LOW 80S.

BEACHLER

&&

.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 12Z...

* SOUTHWEST WINDS AROUND 10KT WILL QUICKLY INCREASE BY 15-16Z TO
  AROUND 15KT AND GUSTING TO NEAR 30KT. A FEW GUSTS MAY EXCEED
  30KT EARLY IN THE AFTERNOON.

* THUNDERSTORMS WILL BEGIN TO DEVELOP LATE THIS AFTERNOON...BEST
  TIMING WILL BE AFTER 2Z.

* WINDS WILL VEER FROM SOUTHWEST TO NORTHWEST AFTER THUNDERSTORMS
  END...WITH SPEEDS DECREASING TO AROUND 10-12KT.

BEACHLER

//DISCUSSION...UPDATED 12Z...

ISOLATED THUNDERSTORMS HAVE DEVELOPED EARLY THIS MORNING ACROSS
NORTHERN WISCONSIN...BUT SHOULD REMAIN WELL NORTH OF THE TAF
SITES THIS MORNING. WINDS FROM 220-240 DIRECTION WILL REMAIN
TODAY...BUT AS MIXING INCREASES THE SPEEDS WILL QUICKLY INCREASE
TO AROUND 15KT AND GUSTS WILL APPROACH 30KT. A FEW GUSTS MIDDAY
AND EARLY THIS AFTERNOON MAY EXCEED 30KT TO NEAR 35KT. THEN THE
FOCUS TURNS TOWARDS TIMING OF THUNDERSTORMS...WHICH MOST HI-RES
GUIDANCE HAS NARROWED THE TIMING DOWN TO AFTER 23Z. THEN THE
BETTER COVERAGE AND STRONGEST STORMS LOOK TO BE CLOSER TO 2-4Z
ARRIVAL INTO NORTHERN IL/NORTHWEST IN. A FRONTAL BOUNDARY WILL BE
IMMEDIATELY FOLLOWING THE LINE OF THUNDERSTORMS...WHICH SHOULD
ALLOW FOR THUNDERSTORMS TO QUICKLY PUSH EAST/SOUTH OF THE TAF
SITES BY 6Z. WINDS WILL ALSO BE SHIFTING FROM SOUTHWEST TO
NORTHWEST WITH FRONTAL PASSAGE. A FEW OF THE THUNDERSTORMS COULD
BECOME SEVERE...AND PRODUCE BRIEF WIND GUSTS IN EXCESS OF 60KT.
THE BEST TIMING FOR SEVERE STORMS CONTINUES TO BE BETWEEN 2-5Z.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH CONFIDENCE IN WIND DIR/SPEED/GUSTS.

* HIGH CONFIDENCE IN THUNDERSTORMS DEVELOPING LATE
  AFTERNOON...MEDIUM CONFIDENCE IN PRECISE TIMING.

* HIGH CONFIDENCE IN THUNDERSTORMS ENDING BEFORE 6Z MON.

BEACHLER

//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.

&&

$$

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.