Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 010900
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
400 AM 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 09Z...

* MVFR CEILINGS DEPARTING WITHIN THE NEXT HOUR.

* EAST SOUTHEAST WINDS THROUGH PERIOD...AROUND 10 KT TODAY.

* INCREASING CHANCES FOR PRECIP VERY LATE IN THE PERIOD.

RODRIGUEZ

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

SATELLITE IMAGERY SHOWING MVFR CEILINGS SLOWLY DEPARTING TO THE
NORTH...WHILE AN EXTENSION OF THESE CLOUDS ALSO PUSHING TOWARDS
THE TERMINALS. WITH THE POSSIBILITY FOR A LONGER DURATION OF THESE
CEILINGS BASED ON LATEST TRENDS...DID PUSH BACK TIMING OF
SCATTERING 1-2 HOURS. THESE CEILINGS AROUND 2KFT MAY FALL SOME
OVER THE NEXT COUPLE OF HOURS BUT EXPECT THEM TO STAY ABOVE
1500FT...BEFORE THEY CONTINUE NORTH OF ALL THE TERMINALS TOWARDS
THE 11-12Z TIME FRAME. VFR CONDITIONS WILL THEN PREVAIL ON
WEDNESDAY AS THE CURRENT EAST WINDS TURN MORE TO THE
SOUTHEAST...WHILE INCREASING TO AROUND 10 KT LATER THIS MORNING.
THERE COULD BE SOME LAKE INFLUENCE LATER THIS AFTERNOON...BUT THIS
WOULD BE NO MORE TO TAKE THEM TO MORE OF AN EAST SOUTHEAST
COMPONENT. DIMINISHING WINDS AND INCREASING VFR CEILINGS WILL
OCCUR WEDNESDAY NIGHT...AS THE NEXT SYSTEM DRAWS NEAR AND HELPS
STEER PRECIP TOWARDS THE TERMINALS LATE IN THE FORECAST PERIOD.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS AND TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* MEDIUM CONFIDENCE WITH PRECIP TRENDS.

RODRIGUEZ

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

* THURSDAY...TSRA LIKELY. MVFR POSSIBLE. GUSTY SOUTHERLY WINDS
  POSSIBLE.
* THURSDAY NIGHT...PERIODS OF TSRA. MVFR LIKELY. IFR POSSIBLE.
  GUSTY SOUTHERLY WINDS POSSIBLE.
* FRIDAY...SLIGHT CHANCE OF PM SHRA. STRONG/GUSTY WEST WINDS.
* FRIDAY NIGHT...CHANCE OF SHRA. MVFR POSSIBLE. GUSTY WESTERLY
  WINDS.
* SATURDAY...DRY/VFR. WESTERLY WINDS.
* SUNDAY...SLIGHT CHANCE OF SHRA. WESTERLY WINDS.
* MONDAY...DRY/VFR. WESTERLY WINDS.

&&

.MARINE...
306 AM CDT

BOTH WINDS AND WAVES HAVE CONTINUED TO DIMINISH/SUBSIDE EARLY THIS
MORNING...AS THE SURFACE FIELD HAS RELAXED WITH HIGH PRESSURE
SPANNING FROM THE UPPER MIDWEST NORTHEAST TO QUEBEC. THIS HIGH
PRESSURE WILL SHIFT EAST TOWARDS THE EASTERN GREAT LAKES TODAY
WHILE LOW PRESSURE OVER THE NORTHERN PLAINS LIFTS NORTH INTO
CANADA...AND WHILE A SEPARATE AREA OF LOW PRESSURE REMAINS
SITUATED OVER THE CENTRAL PLAINS. SURFACE PATTERN OVER THE LAKE
DURING THIS TIME WILL TRY AND TIGHTEN UP THROUGH THE DAY BUT WILL
ONLY RESULT IN AN INCREASE IN SPEEDS MORE TOWARDS 10 TO 20 KT...AS
SOUTHEAST WINDS BECOME MORE SOUTH LATER TODAY INTO TONIGHT. THIS
SPEED AND DIRECTION WILL CONTINUE INTO THURSDAY AS THE LOW
PRESSURE OVER THE CENTRAL PLAINS LIFTS NORTHEAST REACHING THE
UPPER MISSISSIPPI VALLEY BY THURSDAY NIGHT. WINDS WILL LIKELY RAMP
UP QUICKLY THURSDAY NIGHT 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.

RODRIGUEZ

&&

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

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
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.