Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 271940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
240 PM CDT MON OCT 27 2014

.DISCUSSION...
326 AM CDT

SHORT TERM...THROUGH MONDAY NIGHT...FOR THE REMAINDER OF THE NIGHT
AND INTO MONDAY MORNING...THE MAIN FORECAST ISSUE WILL BE ASSOCIATED
WITH A STRONG WARM FRONT LIFTING NORTH THROUGH THE REGION.  EARLY
THIS MORNING...A LINE OF ELEVATED SHOWERS AND THUNDERSTORMS ARE
MOVING THROUGH WISCONSIN...WITH THE SRN EXTENT OF THE LINE BRUSHING
THE WI/IL BORDER.  THIS IS CURRENTLY INDICATIVE THAT THE THE
STRONGEST ELEVATED INSTABILITY IS WELL NORTH OF THE SFC WARM FRONT
WHICH ROUGHLY EXTENDS FROM DBQ TO DNV.  THE SFC BOUNDARY IS MAINLY
THE LINE BETWEEN NELY WINDS AND RELATIVELY DRY AIR WITH SFC
DEWPOINTS IN THE MIDDLE 30S AND AN AREA OF WARMER/MOISTER AIR WITH
DEWPOINTS IN THE MIDDLE 50S AND SOUTHERLY WINDS.  EXPECT THE SFC
WARM FRONT TO LIFT NORTH OF THE IL/WI BORDER BY LATE MORNING....WITH
STRENGTHENING SLY WINDS...AND THE WARM/MOIST AIR OVERSPREADING THE
REGION.  THIS WILL THEN PRIME THE ATMOSPHERE FOR SHOWERS AND
THUNDERSTORMS.  THE PCPN ACTIVITY WILL LARGELY BE INVOF A COLD
FRONT...WHICH CURRENTLY EXTENDS FROM LOW PRESSURE OVER WRN
IA...SOUTHWEST TO WRN KANSAS.  THE LATEST MODEL GUIDANCE SUGGESTS
THAT THE SFC LOW WILL TRACK NEWD TO WRN WI BY THIS AFTERNOON WHILE
THE COLD FRONT MOVES INTO ERN IA.  THE COLD FRONT SHOULD STEADILY
TRACK EAST ACROSS THE CWA AS THE SFC LOW CONTINUES TO LIFT NEWD TO
THE UPPER GREAT LAKES BY EARLY TUESDAY MORNING.  ANTICIPATE A BAND
OF WIDESPREAD SHOWERS INVOF THE FRONT.  THE GUIDANCE SUGGESTS THAT
THE THUNDER POTENTIAL WILL COINCIDE WITH THE STRONGEST FORCING ALONG
THE FRONT...AIDED BY A STRONG SWLY LOW LEVEL JET OF 40-45KT.
INSTABILITY IS EXPECTED TO BE MODEST AND ELEVATED...SO ANTICIPATE
THAT THUNDERSTORM ACTIVITY WILL GENERALLY BE SCT/EMBEDDED WITHING
THE GREATER PCPN SHIELD RATHER THAN A SOLID...ORGANIZED AREA OF
CONVECTION.  FOR TIMING...CURRENTLY EXPECT THAT PCPN SHOULD MOVE
INTO THE ROCKFORD AREA BY LATE AFTERNOON AND STEADILY SPREADING EWD
THROUGH THE EVENING.  THERE IS A CHANCE FOR SOME SCT SHRA IN THE
WARM SECTOR AHEAD OF THE FRONT...BUT ANY PCPN WELL AHEAD OF THE
FRONT SHOULD BE ISOLD.

AS FOR TEMPERATURES...THIS IS AN ANOMALOUSLY STRONG SYSTEM UNDER A
HIGH AMPLITUDE PATTERN ALOFT.  THE LATEST GUIDANCE SUGGESTS THAT
TEMPS ACROSS THE REGION SHOULD BE IN THE UPPER 70S...WITH THE CHANCE
FOR LOCATIONS PEGGING 80 F...ESPECIALLY AROUND PONTIAC.  AS A FRAME
OF REFERENCE...NORMAL HIGHS FOR LATE OCTOBER ARE IN THE UPPER
50S...WITH RECORD HIGHS IN THE MIDDLE 80S.  SO TEMPERATURES TODAY
WILL BE AT LEAST 25 DEGREES ABOVE NORMAL...RECORD BREAKING
TEMPERATURES ARE NOT EXPECTED.  MUCH COOLER AIR IS EXPECTED TO
FILTER IN BEHIND THE COLD FRONT...WITH THE ROCKFORD AREA EXPECTED TO
DROP INTO THE UPPER 40S OVERNIGHT...FOLLOWING THE PASSAGE OF THE
COLD FRONT.  THE FRONT IS NOT EXPECTED TO EXIT THE FAR SERN PORTIONS
OF THE CWA UNTIL EARLY TUESDAY MORNING...SO LOWS OVER NWRN INDIANA
WILL ONLY BE IN THE UPPER 50S.

KREIN

TUESDAY THROUGH THURSDAY...
TRANSITION DAY ARRIVES TUE...WITH THE FROPA SET FOR EARLY IN THE
DAY. GUIDANCE HAS MAINTAINED A PROGRESSIVE LOOK TO THE DRY SLOT THAT
ARRIVES...WHICH SHUD BE ABLE TO BRING AN END TO THE PRECIP ARND
DAYBREAK OR SHORTLY AFTER. 500MB TROUGH AND SFC FEATURE APPEAR TO
NOT PHASE UNTIL LATER TUE EVE AND AFTER THE SYSTEM HAS LIFTED
NORTHEAST OF THE AREA. THIS SHUD HELP WITH LIFTING THE THICK CLOUD
COVER NORTHEAST AS WELL...AND POSSIBLY PROVIDE P-CLOUDY SKIES BY
LATE MORNING TUE TO THE FORECAST AREA. MUCH COOLER AIR WILL STEADILY
ADVECT INTO THE CWFA...WHICH COULD BE STRONG ENOUGH TO RESULT IN
AFTN TEMPS SLOWLY FALLING FROM THE UPR 50S/ARND 60 INTO THE LOW/MID
50S BY LATE AFTN.

ANTI-CYCLONIC FEATURE WILL SLIDE SOUTHEAST FROM THE NORTHERN PLAINS
INTO THE MID-MISSOURI VALLEY TUE NGT/EARLY WED. WRAP AROUND MOISTURE
ON THE BACKSIDE OF THE DEPARTING SFC LOW MAY CLIP THE
NORTHERN/NORTHEASTERN PORTIONS OF THE FORECAST AREA...BUT AT THIS
TIME ONLY EXPECT A FEW CLOUDS FOR THE AREA. THE THICKER
CLOUDS/PRECIP WILL BE DISPLACED WELL TO THE NORTH IN NORTHEAST
WISC/NORTHERN LOWER MICHIGAN. TUE NGT LOWS WILL BE TRICKY WITH THE
STEADY FEED OF COLD AIR ADVECTION...BUT HAVE NUDGED TEMPS DOWN A
COUPLE DEGREES INTO THE UPR 30S/ARND 40 FOR LOWS. IF WINDS CAN
DECOUPLE FURTHER...THEN IT IS POSSIBLE TEMPS COULD RADIATE FURTHER
INTO THE 30S.

BROAD RIDGE OF HIGH PRESSURE WILL DOMINATE THE REGION WED...WITH
MOSTLY SUNNY SKIES. TEMPS WILL ONLY WARM TO THE LOW 50S AS THE
REGION WILL REMAIN IN GENERALLY A NORTHWEST FLOW ALOFT. BROAD
TROUGHING REMAINS THRU THUR DESPITE THE SFC RIDGE SHIFTING
EAST/SOUTHEAST. GUIDANCE IS PAINTING A WEAK MID-LVL FEATURE TRYING
TO DEVELOP WITH A LOBE OF VORTICITY ARRIVING THUR AFTN/EVE. THIS
COULD WARRANT A LOW POP FOR LGT RAIN LATER IN THE DAY THUR. CLOUDS
WILL THICKEN THUR WITH TEMPS MAINLY IN THE LOW/MID 50S.

CONFIDENCE IN MEDIUM TERM...HIGH.

FRIDAY THROUGH THE WEEKEND...
MOTHER NATURE IS EXPECTED TO PROVIDE A TREAT FOR FRI...WITH THE
ARRIVAL OF YET ANOTHER SFC RIDGE. UNFORTUNATELY THE TRICK MAY BE ON
US AS ITS ORIGIN IS FROM CENTRAL CANADA AND WILL LIKELY KEEP TEMPS
FRI IN THE MID/UPR 40S WITH PERHAPS A FEW SITES IN THE FAR SOUTH
TOUCHING 50 DEGREES...OVERNIGHT LOWS ARE PROGGED TO DIP INTO
THE UPR 20S...AND TO ARND 30 IN THE SOUTH.

PROGRESSING INTO THE WEEKEND AND ENSEMBLES ARE DEMONSTRATING MINIMAL
SPREAD WITH RESPECT TO THE PROGRESSIVE FLOW OF THE HIGH AMPLITUDE
RIDGE OVER THE CENTRAL CONUS/CANADIAN ROCKIES...SLOWLY DRIFTING EAST
TOWARDS THE GREAT LAKES SAT/SUN AND WEAKENING. THERE IS SOME FOCUS
OF A SECONDARY TROUGH DEVELOPING ACROSS THE FOUR-CORNERS
REGION...WHICH COULD HINT AT SOMEWHAT WEAK RIDGING OVER THE GREAT
LAKES OR AT LEAST A LGT SOUTHWEST FLOW LATE IN THE WEEKEND. TEMPS
SAT WILL YET AGAIN REMAIN COOL WITH HIGHS MAINLY IN THE 40S...THEN
SLOWLY MODERATING BACK TOWARDS SEASONAL CONDS SUN.

CONFIDENCE IN EXTENDED...HIGH.

BEECHLER

&&

.AVIATION...

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

* SOUTHWEST WINDS GUSTING TO 20-25KT THROUGH LATE AFTERNOON.

* SHRA/RA LIKELY LATER THIS EVENING INTO THE OVERNIGHT WITH A
  CHANCE FOR TSRA.

* WESTERLY WIND SHIFT LATE TONIGHT FOLLOWING A COLD FRONTAL
  PASSAGE. WESTERLY WINDS GUSTY UP AROUND 27 KT DURING THE DAY
  TUESDAY.

KJB

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

SURFACE LOW PRESSURE ACROSS IOWA EARLY THIS AFTERNOON WILL SHIFT
NORTHEASTWARD ACROSS THE UPPER GREAT LAKES REGION BY TUESDAY
MORNING...WHILE DEEPENING. THIS SYSTEM WILL DRIVE A COLD FRONT
ACROSS THE TERMINALS LATER TONIGHT...LIKELY AFTER 09-10 UTC.
SOUTH-SOUTHWESTERLY WINDS WILL CONTINUE ACROSS THE AREA PRIOR TO THE
ARRIVAL OF THIS FRONTAL ZONE...WITH WIND SPEEDS LIKELY TO REMAIN
GUSTY UP INTO THE MID 20 KT RANGE DURING MUCH OF THE AFTERNOON.
STRONG GUSTY WESTERLY WINDS WILL SET UP IN THE WAKE OF THE FRONTAL
ZONE INTO TUESDAY.

SCATTERED SHOWERS ARE ALSO EXPECTED TO DEVELOP ACROSS PORTIONS OF
THE AREA DURING THE EVENING AS MOISTURE CONTINUES TO BE DRIVEN
NORTHWARD. HOWEVER...IT APPEARS THE BETTER CHANCES OF SHOWERS AND
PERHAPS A FEW THUNDERSTORMS WILL BE OVERNIGHT TONIGHT ASSOCIATED
WITH THE APPROACHING COLD FRONTAL BOUNDARY. IT APPEARS THE DURATION
OF ANY THUNDERSTORMS WILL BE SHORT (AN HOUR OR TWO). CONDITIONS
SHOULD IMPROVE BY DAYBREAK TUESDAY...WITH DRIER AIR FILTERING IN
ACROSS THE AREA...BUT GUSTY WESTERLY WINDS WILL CONTINUE FOR MUCH OF
THE DAY TUESDAY.

KJB

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

* HIGH CONFIDENCE IN WIND TRENDS.

* MEDIUM CONFIDENCE IN TIMING OF PCPN ONSET THIS EVENING.

* LOW CONFIDENCE IN TSRA DIRECTLY IMPACTING THE TERMINALS.

* MEDIUM CONFIDENCE IN CIG TRENDS.

KJB

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

TUESDAY NIGHT...VFR/WX NIL.  WEST WINDS.

WEDNESDAY...VFR/WX NIL. WEST WINDS THROUGH THE DAY...BACKING TO
SLY OVERNIGHT.

THURSDAY...VFR/WX NIL. SLY WINDS THROUGH THE DAY...VEERING NWLY
OVERNIGHT.

FRIDAY...VFR/WX NIL. NORTH TO NORTHEAST WINDS.

SATURDAY...VFR/WX NIL. NORTH TO NORTHEAST WINDS.

SUNDAY...VFR/WX NIL. SOUTHEAST WINDS.

KREIN

&&

.MARINE...
230 PM CDT

A WARM FRONT LIFTING ACROSS THE LAKE TODAY HAS PRODUCED WIDELY
VARIABLE CONDITIONS FROM ONE LOCATION TO ANOTHER...AS WELL AS
WIDESPREAD THUNDERSTORMS ACROSS THE NORTHERN END. TONIGHT THE
FRONT WILL EXIT THE NORTHERN END OF THE LAKE AND BY MORNING A
CENTER OF LOW PRESSURE WILL FOLLOW IN ITS PATH. BEHIND THE
LOW...MORE UNIFORM CONDITIONS DEVELOP TOMORROW MORNING WITH
GENERALLY WEST TO SOUTHWEST WINDS FOR THE ENTIRE LAKE. THE
TIGHTEST PRESSURE GRADIENT WILL BE LOCATED OVER THE NORTHERN HALF
WHICH IS CLOSEST TO THE DEPARTING LOW...SO A PERIOD WITH OCCASIONAL
GALE FORCE GUSTS IS POSSIBLE TOMORROW AFTERNOON INTO THE EVENING
FOR THE NORTH HALF.

WINDS REMAIN GENERALLY WESTERLY AND CONDITIONS GRADUALLY RELAX
THROUGH THE REMAINDER OF THE WEEK UNDER THE INFLUENCE OF AN
APPROACHING RIDGE UNTIL ANOTHER LOW CROSSES THE LAKE THURSDAY
NIGHT. COLD NORTHERLY FLOW THEN DEVELOPS FOR FRIDAY AND MOST OF
SATURDAY.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM TUESDAY.

&&

$$

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