Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 311956
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
256 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

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

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

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

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

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

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

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

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

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