Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 011934
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
234 PM CDT WED OCT 1 2014

.DISCUSSION...
328 AM CDT

A RANGE OF FALL WEATHER IS EXPECTED OVER THE NEXT WEEK WITH FAIRLY
MILD CONDITIONS TO START WITH A PERIOD OF RAIN/THUNDER USHERING IN
TEMPERATURES MUCH COLDER THAN NORMAL FOR THE WEEKEND. EARLY MORNING
WATER VAPOR IMAGERY SHOWS A CLOSED UPPER LOW SLOWLY SPINNING OVER
PENNSYLVANIA WITH A NARROW RIDGE AXIS EXTENDING OVER THE LOCAL AREA.
OF GREATER NOTE IS A BROAD LONGWAVE UPPER TROUGH OVER MUCH OF
WESTERN NORTH AMERICA. ONE CLOSED UPPER LOW IS SPINNING NORTHWARD
ACROSS THE NORTHERN PLAINS INTO THE CANADIAN PRAIRIES WITH A WEAKER
WAVE MOVING EASTWARD INTO THE CENTRAL HIGH PLAINS. ANOTHER WAVE IS
DIGGING INTO THE DESERT SOUTHWEST AND WILL BE A KEY PLAYER IN OUR
WEATHER GOING INTO THURSDAY/FRIDAY. AT THE SURFACE...HIGH PRESSURE
RIDGING IS SPREAD FROM QUEBEC SOUTHWEST INTO THE LOCAL AREA WITH A
STRONG LOW MOVING NORTHWARD INTO SOUTHERN MANITOBA.

TODAY...THE UPPER RIDGE AND ASSOCIATED SURFACE RIDGE WILL SHIFT TO
THE EAST TODAY RESULTING IN A LIGHT SOUTHEAST WIND. WINDS LOOK TO BE
LIGHT ENOUGH TO ALLOW THE LAKE TO TURN WINDS MORE EASTERLY DURING
THE AFTERNOON. SO WHILE HIGHS ACROSS THE MAJORITY OF THE AREA WILL
WARM INTO THE 70S...WARMEST WEST AND SOUTH...LAKESHORE AREAS OF NE
IL WILL LIKELY BE HELD INTO THE LOW TO MID 60S. NW INDIANA LAKEFRONT
AREAS MAY BE SPARED THE EXTRA COOLING UNLESS WINDS ARE ABLE TO TURN
NORTHEAST. STRATUS MAY BE LINGERING ACROSS THE NORTHERN COUNTIES
THROUGH MID MORNING BUT SHOULD LIFT TO THE NORTH BY LATE
MORNING/MIDDAY. MID AND HIGH CLOUDS LOOK TO THICKEN ACROSS NORTHWEST
AREAS THIS AFTERNOON.

TONIGHT...THINGS START TO BECOME MORE ACTIVE TONIGHT AS THE
NORTHERNMOST UPPER LOW LIFTS INTO CENTRAL CANADA AND A SERIES OF
WEAKER WAVES CURRENTLY MOVING ACROSS THE CENTRAL/SOUTHERN PLAINS
MOVE NORTHEAST AND ACT ON THE MID/UPPER LEVEL MOISTURE PLUME ON THE
EAST SIDE OF THE BROAD UPPER TROUGH. THIS WILL PUSH BANDS OF SHOWERS
EASTWARD INTO NORTHERN ILLINOIS. THE FORCING IS NOT TERRIBLY
COHERENT AS IT SPREADS IN EARLY THIS EVENING SO WILL KEEP POPS
LOW...BUT FORCING FOCUSES OVERNIGHT RESULTING IN BEST COVERAGE OF
SHOWERS ACROSS THE WESTERN HALF OF THE AREA...WITH LESS COVERAGE
EAST. ELEVATED INSTABILITY LOOKS TO BE LIMITED BUT STILL PRESENT
OVERNIGHT SO WILL INCLUDE THUNDER MENTION MAINLY OVERNIGHT. OVERALL
ACTIVITY LOOKS SOMEWHAT DISORGANIZED.

THURSDAY AND THURSDAY NIGHT...THIS WILL BE THE MAIN PERIOD FOR
RAIN/THUNDER AS THE UPPER WAVE NOW MOVING INTO THE DESERT SOUTHWEST
HELPS AMPLIFY THE THE LONGWAVE TROUGH AS IT MOVES INTO THE PLAINS.
THIS WILL STRENGTHEN A SURFACE LOW OVER THE SOUTHERN PLAINS WHICH
WILL TRACK NORTHEAST AND DEEPEN AS IT REACHES THE U.P. OF MICHIGAN
BY FRIDAY MORNING. THIS WILL BRING SEVERAL WAVES OF SHOWERS AND
STORMS AS A WARM FRONTAL BOUNDARY DEVELOPS AND CROSSES THE AREA
DURING THE DAY WITH A COLD FRONT CROSSING THURSDAY NIGHT. TIMING OF
WAVES WILL NEED TO BE REFINED BUT RIGHT NOW THE MAIN PERIOD FOR
ACTIVITY WILL BE FROM AFTERNOON THROUGH THE OVERNIGHT. SURFACE BASED
INSTABILITY MAY SPREAD INTO THE CWA THURSDAY AFTERNOON BUT THE WARM
SECTOR AHEAD OF THE LOW LOOKS TO BE FILLED WITH CLOUDS AND SCATTERED
PRECIP. FOCUSED FORCING LOOKS TO BE HELD BACK ACROSS
MISSOURI/OKLAHOMA/KANSAS DURING THE DAY WITH THE UPPER TROUGH AXIS
KICKING THE SURFACE LOW NORTHEAST ACROSS NW MISSOURI LATE IN THE
AFTERNOON. THIS WOULD RESULT IN A LINE OF STORMS TRACKING
NORTHEASTWARD INTO THE EVENING. WILL NEED TO KEEP AN EYE ON HOW FAR
WEST OF THE AREA THE LOW TRACKS WITH A FURTHER WEST TRACK...AS SOME
GUIDANCE IS SHOWING...LEADING TO A BETTER SEVERE THREAT ACROSS MUCH
OF THE CWA THANKS TO A MORE ROBUST WARM SECTOR AND GREATER
INSTABILITY IN PLACE TO HELP MAINTAIN AN INCOMING SQUALL LINE
DURING THE EVENING. STRONG STRAIGHT LINE WIND GUSTS WOULD BE THE MAIN
SEVERE THREAT. HEAVY RAINFALL IS A CONCERN AS PRECIPITABLE WATER
VALUES PUSH 1.6 OR 1.7 INCHES INTO THURSDAY NIGHT. WIDESPREAD
AMOUNTS OF AROUND AN INCH LOOK LIKELY WITH THE EXTENT OF STRONGER
CONVECTION DICTATING POTENTIAL FOR ISOLATED 2+ INCHES. THE LIMITING
FACTOR WOULD BE THAT THE WAVES OF PRECIP LOOK TO BE MOVING STEADILY.
HIGHS THURSDAY WILL BE TRICKY DEPENDING ON THE TIMING OF PRECIP
WAVES AND CLOUD COVER BUT WITH THE AREA GETTING INTO THE WARM SECTOR
AND COVERAGE OF PRECIP LOOKING TO BE LOWEST DURING THE DAY HIGHS MAY
WARM WELL INTO THE 70S FOR MOST AREAS.

FRIDAY AND SATURDAY...THE SURFACE LOW WILL CONTINUE NORTHEAST WITH
GUIDANCE STILL IN DISAGREEMENT ON WHERE IT WILL BE BY 12Z FRIDAY.
THE FRONT SHOULD BE EXITING THE EASTERN CWA IF NOT HAVING ALREADY
DONE SO BY FRIDAY MORNING SO SOME LINGERING CONVECTION MAY CONTINUE
EAST. A REINFORCING UPPER TROUGH WILL DIVE IN FROM CANADA AND CLOSE
OFF BEFORE DROPPING RIGHT ACROSS THE AREA LATE IN THE DAY/EVENING.
STRONG COLD ADVECTION WILL SPREAD IN AS ALL OF THIS OCCURS WITH H85
TEMPS FALLING TO NEAR 0C BY EVENING WITH A GUSTY WEST WIND. IN
ADDITION WITH THE UPPER LOW CROSSING THE AREA SHOWERS ARE A GOOD
POSSIBILITY...ESPECIALLY NORTH OF INTERSTATE 80. BETWEEN THE COLD
ADVECTION AND INCREASING SHOWER POTENTIAL HIGH TEMPS WILL PROBABLY
OCCUR EARLY THEN FALL THROUGH THE AFTERNOON. THUS EXPECT LOW TO MID
50S IF NOT COOLER BY EVENING FOR ALL AREAS...WITH LOWS FALLING TO
AROUND 40 AWAY FROM THE LAKE FRIDAY NIGHT...WITH WINDS AND CLOUD
KEEPING MAX COOLING FROM OCCURRING. SOME SHOWERS MAY LINGER IN THE
EAST SATURDAY MORNING BUT EXPECT A DRY DAY BEYOND THAT WITH A SUN
AND CLOUD MIX. HIGHS WILL LIKELY ONLY TOP OUT IN THE LOW TO MID 50S
WITH BREEZY WEST TO NORTHWEST WINDS. WEAK RIDGING WILL MOVE ACROSS
SATURDAY NIGHT BUT WITH BROAD CYCLONIC FLOW OVER THE REGION THANKS
TO WHAT WILL HAVE EVOLVED INTO A MASSIVE BROAD UPPER LOW OVER
ONTARIO...THERE WILL BE A TENDENCY FOR SHORTWAVES TO PASS ALONG WITH
BOUTS OF CLOUD COVER. AS A RESULT MAX COOLING MAY BE TEMPERED ONCE
AGAIN BUT STILL EXPECT UPPER 30S FOR MOST AREAS SATURDAY NIGHT
BRINGING AT LEAST PATCHY FROST POTENTIAL.

SUNDAY THROUGH WEDNESDAY...THE BIG UPPER TROUGH WILL BE IN PLACE
INTO AT LEAST TUESDAY AS IT WILL BE REINFORCED A FEW TIMES BY WAVES
PUSHING INTO FROM CENTRAL CANADA. THIS WILL BRING A FEW ADDITIONAL
CHANCES FOR SHOWERS WITH SOME CONSISTENCY IN A WAVE PASSING LATER
SUNDAY/SUNDAY NIGHT. EACH WAVE WILL BRING A BRIEF PUSH OF WARM
ADVECTION BUT ANY NOTABLE WARMING DOES NOT LOOK TO OCCUR UNTIL MID
WEEK WHEN UPPER RIDGING STARTS TO MOVE IN FROM THE WEST AND THE
EASTERN TROUGH STARTS TO DE-AMPLIFY. SHOULD SEE SOME TEMP MODERATION
SUNDAY AND MONDAY BUT AM WONDERING IF FORECAST HIGHS ARE A LITTLE
WARM...ESPECIALLY IF WE END UP WITH CLOUD COVER EITHER DAY. TOUGH TO
PINPOINT BEST RAIN CHANCES BUT SUNDAY AFTERNOON THROUGH SUNDAY NIGHT
LOOKS BEST RIGHT NOW.

MDB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* EAST SOUTHEAST WINDS 10 TO 15 KT THROUGH THE DAY.

* INCREASING CHANCES FOR SOME SHOWERS AND MVFR CIGS BY LATE
  TONIGHT INTO THURSDAY MORNING.

* CHANCES FOR THUNDERSTORMS INCREASE SIGNIFICANTLY DURING THE MID
  AND LATE AFTERNOON ON THURSDAY...AND CONTINUE INTO THURSDAY
  NIGHT BEYOND THE CURRENT TAF PERIOD. PERIODS OF HEAVY RAINFALL
  AND LOWER VIS LIKELY.

KJB

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

THE MAIN WEATHER CONCERNS DURING THE PERIOD WILL BE THE TIMING OF
SHOWERS AND THUNDERSTORMS...ESPECIALLY THURSDAY AFTERNOON.

A BROAD AREA OF LOW PRESSURE ACROSS THE PLAINS IS RESULTING IN A
SOUTHEASTERLY WIND COMPONENT ACROSS THE AREA THIS AFTERNOON. WIND
SPEEDS WILL GENERALLY BE AROUND 10 KT...WITH SOME OCCASIONAL GUSTS
UP AROUND 15 KT POSSIBLE.

THE BROAD AREA OF LOW PRESSURE OVER THE PLAINS WILL GRADUALLY
CONSOLIDATE AND SHIFT EAST-NORTHEASTWARD OVER THE MID AND PORTIONS
OF THE UPPER MISSISSIPPI VALLEY DURING THE DAY THURSDAY. THIS WILL
LIFT A WARM FRONTAL BOUNDARY OVER THE AREA BY EARLY THURSDAY
MORNING. THE ASSOCIATED INCREASE IN LOW LEVEL MOISTURE WITH THIS
SYSTEM COULD RESULT IN SOME LOWER MVFR CIGS AND VISBYS...ESPECIALLY
BY THURSDAY MORNING. A FEW SCATTERED SHOWERS ARE ALSO POSSIBLE
ACROSS THE AREA LATE TONIGHT INTO EARLY THURSDAY. THE THREAT FOR
THUNDER WITH THIS INITIAL ACTIVITY APPEARS TO BE LOW...BUT NOT
ZERO. MUCH BETTER CHANCES FOR SHOWERS AND THUNDERSTORMS...WITH
PERIODS OF HEAVY RAINFALL WILL BEGIN TO IMPACT THE AREA BY LATE
AFTERNOON AND EVENING ON THURSDAY...AND WILL LIKELY CONTINUE
BEYOND THE CURRENT 30 HOUR TAF PERIOD...INTO THURSDAY NIGHT.
OVERALL THE CONFIDENCE FOR THUNDERSTORMS OVER THE TERMINALS LATER
THURSDAY IS MODERATE TO HIGH...BUT CONFIDENCE ON THE EXACT TIMING
IS LOW TO MODERATE AT THIS TIME.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW WITH THUNDER POTENTIAL LATE TONIGHT AND EARLY THURSDAY
  MORNING.

* MODERATE TO HIGH WITH THUNDERSTORMS BY LATE THURSDAY
  AFTERNOON/EVENING...BUT LOW TO MODERATE ON EXACT TIMING.

* LOW TO MODERATE WITH A PERIOD OF LOWER END MVFR CIGS BY EARLY
  THURSDAY.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...PERIODS OF TSRA. MVFR LIKELY. IFR POSSIBLE.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR.

SUNDAY...CHANCE OF SHRA LATE.

MONDAY...SLIGHT CHANCE OF SHRA.

TUESDAY...SLIGHT CHANCE OF SHRA.

RODRIGUEZ

&&

.MARINE...
226 PM CDT

RELATIVELY QUIET WEATHER IS GOING TO COME TO AN END TONIGHT...AS
HIGH PRESSURE CONTINUES TO DEPART TO THE NORTHEAST WITH A STRONGER
LOW PRESSURE SYSTEM APPROACHING FROM THE SOUTHWEST. WINDS HAVE
REMAINED SOUTHEASTERLY THIS AFTERNOON...WITH A SLIGHT BUMP IN THE
GRADIENT CREATING OCCASIONAL GUSTS TO 20KT. WITH THE CONTINUED
SOUTHEAST FLOW...WAVES HAVE REMAINED ELEVATED IN THE ILLINOIS
NEARSHORE WATERS TO AROUND 2 TO 4 FT WHILE ALONG THE INDIANA
NEARSHORE WAVES ARE GENERALLY 1 TO 3 FT. AS HIGH PRESSURE DEPARTS
TONIGHT...WINDS WILL TURN SOUTHERLY AND A TIGHTENING GRADIENT IS
POISED TO INCREASE WINDS THURSDAY MORNING. AT THIS TIME WINDS ARE
EXPECTED TO REMAIN IN THE 15 TO 25 KT RANGE THRU THUR. AS THE LOW
ARRIVES OVER NORTHERN IL THUR EVENING...IT LOOKS LIKE A PERIOD OF
GALES MAY OCCUR ACROSS THE CENTRAL/SOUTHERN PORTIONS OF THE LAKE. AS
THIS LOW MOVES TO SOUTHERN ONTARIO WHILE STRENGTHENING...WITH
WINDS TO 30 KT LIKELY. A VERY TIGHT GRADIENT ON THE SOUTHERN END
OF THIS LOW PRESSURE SYSTEM AS WELL AS MUCH COLDER AIR MOVING OVER
THE LAKE WILL SUPPORT WINDS TO 30 KT FRIDAY AND FRIDAY NIGHT AS
WELL AS EVEN A PERIOD OF GALES POSSIBLE. THEN EXPECT A SLOW
DOWNWARD TREND IN SPEEDS THROUGH THE WEEKEND.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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