Area Forecast Discussion
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FXUS63 KLOT 010733
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 AM CDT MON SEP 1 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV 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 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.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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