Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 160304
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1004 PM CDT MON SEP 15 2014

.DISCUSSION...
221 PM CDT

TONIGHT...
FRONTAL BOUNDARY THIS AFTERNOON CONTINUES TO SLIDE SOUTHEAST ACROSS
THE FORECAST AREA. VISIBLE IMAGERY ALONG AND JUST AHEAD OF THE
BOUNDARY INDICATED SOME VERTICAL GROWTH TO THE CLOUDS...SUGGESTIVE
OF SOME INSTABILITY. THERE HAS BEEN SOME SPOTTY CONVECTION ACROSS
NORTHEAST MO STRETCHING EAST THROUGH IL/CENTRAL IN BUT SOUTH OF THE
CWFA. DESPITE CONSIDERABLE SOLAR SHIELDING HAS BEEN ABLE TO KEEP
TEMPS IN THE 50S...WITH A FEW LOCATIONS BEING ABLE TO NUDGE TO ARND
60. WINDS WILL SHIFT NORTHWEST/NORTH BEHIND THE BOUNDARY WITH MUCH
DRIER/COOLER AIR STEADILY FILTERING INTO THE REGION OVERNIGHT.
PRECIP WILL COME TO AN END LATER THIS AFTN/EARLY EVE...WITH JUST A
FEW LINGERING SHOWERS ALONG AND EAST OF GIBSON CITY TO FOWLER. TEMPS
OVERNIGHT WILL COOL INTO THE LOW/MID 40S...WITH A FEW OF THE
TRADITIONALLY COOL SPOTS POSSIBLY DIPPING INTO THE UPR 30S BEFORE
DAYBREAK TUE. MEANWHILE CLOSER TO DOWNTOWN CHICAGO...THE URBAN HEAT
ISLAND SHUD AID IN KEEPING TEMPS IN THE UPR 40S TO ARND 50. THE ONLY
WILDCARD FOR OVERNIGHT LOWS WILL BE SKY COVER/WINDS...WHICH WITH
HIGH PRESSURE BUILDING IN SHUD ERODE/DIMINISH.

THERE IS ALSO SOME CONCERN THAT WITH THE LACK MIXING THIS AFTN AND
EXPECTED TEMPS BEING COOLER THAN AFTN DEW PTS...COUPLED WITH LIGHT
WINDS...COULD POINT TOWARDS PATCHY FOG DEVELOPING AWAY FROM THE
METRO AREA.

TUESDAY THROUGH THURSDAY...
RATHER BENIGN PATTERN FOR A GOOD PORTION OF THE WEEK. BROAD
ANTI-CYCLONIC FLOW WILL BUILD INTO THE REGION TUESDAY...WITH THE
MID-LVL TROUGH PIVOTING EAST. THE LONGWAVE PATTERN WILL LIKELY KEEP
THE REGION IN A CONTINUED NORTHWEST FLOW AS MID-LVL RIDGING RETURNS
TO THE WESTERN CONUS. GUIDANCE SUGGESTS THE SFC RIDGE THAT ARRIVES
TUE WILL SHIFT EAST...HOWEVER ANOTHER DOME OF HIGH PRESSURE FROM
CANADA IS THEN POISED TO SLIDE SOUTH AND CONTINUE THE DRY/COOL
WEATHER WED/THUR. TEMPS WILL GENERALLY REMAIN IN THE MID/UPR
60S...BUT POSSIBLY REACH 70 DEG IN SEVERAL AREAS FOR THUR. ABUNDANT
SUNSHINE IS EXPECTED EACH OF THE NEXT SEVERAL DAYS AS WELL.
OVERNIGHT LOWS WILL ALSO DIP INTO THE 40S TUE NGT/WED NGT...THEN
WITH THE SFC RIDGE BEGINNING TO PUSH EAST THUR NGT TEMPS COULD HOLD
ARND 50.

CONFIDENCE...HIGH.

FRIDAY THROUGH SUNDAY...
WITH THE SFC RIDGE POISED TO PUSH EAST OF THE REGION FRI...FLOW WILL
BE TURNING SOUTHERLY AND THE MID-LVL WAVE STARTING TO FLATTEN.
ENSEMBLES CONTINUE TO SHOW CONSIDERABLE SPREAD ON TIMING OF
PRECIP/MOISTURE RETURNING...WITH MOST MEMBERS POINTING TOWARDS FRI
NGT. THE ATMOSPHERE WILL MODERATE BY FRI/SAT WITH TEMPS IN THE
MID/UPR 70S...OR MORE SEASONAL. SAT APPEARS TO BE THE MOST FAVORABLE
PERIOD TO SEE SPOTTY SHOWERS/THUNDERSTORMS AS A MID-LVL TROUGH
DEVELOPS OVER THE CENTRAL PLAINS AND NEARS THE REGION SAT AFTN/EVE.
THEN FOR THE SECOND HALF OF THE WEEKEND SFC RIDGING IS PROGGED TO
RETURN TO THE REGION.

CONFIDENCE...MEDIUM/HIGH.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* LIGHT WEST TO NORTHWEST WINDS TUESDAY. LAKE BREEZE EXPECTED TO
  STAY TO THE EAST.

MDB

//DISCUSSION...UPDATED 03Z...

CLOUDS CONTINUE TO EXIT TO THE SOUTH WITH SKIES AT GYY BEING THE
MAIN CHALLENGE OVERNIGHT. SATELLITE DOES SHOW A NARROW BAND OF
LAKE STRATUS OFF THE SE WI AND NE IL SHORE LINE. WILL CONTINUE
WITH MVFR CIGS AT GYY INTO THE OVERNIGHT WITH THE IDEA THAT THE
CLOUD BAND WOULD SHIFT JUST TO THE EAST OVERNIGHT. CLOUD BASE
HEIGHT MAY NEED ADJUSTMENT AS WELL BUT TEMP-DEWPOINT SPREADS OVER
THE LAKE AND FORECAST SOUNDINGS SUGGEST 1500-2000 FT. NOT OVERLY
CONFIDENT IN THE DURATION OF CIGS THOUGH. THE OTHER CHALLENGE WILL
BE PATCHY FOG POTENTIAL OVERNIGHT...ESPECIALLY AT RFD/DPA. WILL
CONTINUE WITH BCFG AND TEMPO MVFR VSBY FOR NOW.

FROM 00Z...

FRONTAL BOUNDARY IS NOW APPROACHING MDW AND WILL PASS GYY EARLY
THIS EVENING TURNING WINDS NORTHERLY WITH AN INITIAL INCREASE IN
SPEED TO 10-15 KT. SPEEDS WILL SETTLE UNDER 10 KT THROUGH EARLY
EVENING BEHIND THE FRONT THOUGH GYY MAY KEEP SPEEDS ABOVE 10 KT
INTO MID EVENING. SATELLITE SHOWS THE BACK EDGE OF THE MAIN CLOUD
SHIELD MOVING QUICKLY SOUTHEAST WITH THE DIURNAL STRATO CU TO THE
NORTHWEST QUICKLY DISSIPATING. EXPECT SKIES TO CLEAR BY MID
EVENING ACROSS THE IL TERMINALS WITH LAKE EFFECT PROCESSES
POTENTIALLY KEEPING MVFR CLOUDS AT GYY INTO THE OVERNIGHT. SOME
RESIDUAL LOW LEVEL MOISTURE MAY ALLOW FOR SOME PATCHY OR SHALLOW
FOG OVERNIGHT AT RFD/DPA AS WINDS DIMINISH. NORTHWEST WINDS WILL
BECOME WESTERLY UNDER 10 KT AT THE IL TERMINALS TUESDAY. A LAKE
BREEZE WILL LIKELY DEVELOP BY MIDDAY BRINGING NE WINDS TO GYY BUT
THE INLAND PUSH LOOKS TO BE SLOW GIVEN THE MINIMAL LAKE-LAND TEMP
DIFFERENCE SO WILL KEEP IT EAST OF ORD/MDW FOR NOW. SOME SCATTERED
STRATO CU IS EXPECTED TO DEVELOP LATE MORNING THEN LIFT/DISSIPATE
THROUGH THE AFTERNOON.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN WEST TO NORTHWEST WINDS TUESDAY. MEDIUM-HIGH
  CONFIDENCE ANY LAKE BREEZE WILL REMAIN EAST.

MDB

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

WEDNESDAY...VFR. LIGHT WEST WINDS. LAKE BREEZE POSSIBLE.

THURSDAY...VFR. EAST WINDS.

FRIDAY...VFR. BREEZY SOUTH WINDS.

SATURDAY...CHANCE TSRA. MVFR POSSIBLE. BREEZY SOUTHWEST WINDS.

SUNDAY...SLIGHT CHANCE TSRA. VFR. WEST WINDS.

MDB

&&

.MARINE...
246 PM CDT

WEAK LOW PRESSURE WILL PUSH EAST THROUGH THE OHIO VALLEY AND
DISSIPATE THIS EVENING AS HIGH PRESSURE MOVES INTO THE MID
MISSOURI VALLEY TONIGHT. AHEAD OF THE HIGH A WEAK COLD FRONT WILL
SPREAD DOWN THE REMAINDER OF THE LAKE THIS EVENING AND BRIEFLY
INCREASE NORTH WINDS TO NEAR 20 KT THE HIGH WILL WEAKEN AND MOVE
OVER LAKE MICHIGAN ON TUESDAY. LOW PRESSURE OVER HUDSON BAY WILL
SPREAD INTO QUEBEC ON WEDNESDAY AS HIGH PRESSURE PUSHES SOUTH OUT
OF NORTHERN MANITOBA. AHEAD OF THE HIGH THE SOUTHWEST GRADIENT
INCREASES WITH WINDS 15 TO 25 KT FOR THE NORTH HALF OF THE LAKE. THE
HIGH REACHES LAKE SUPERIOR THURSDAY EVENING AND WILL PUSH A COLD
FRONT DOWN THE LAKE THURSDAY NIGHT. THIS HIGH WILL THEN MOVE TO
THE EASTERN LAKES BY LATE THURSDAY INTO FRIDAY AS SEVERAL LOWS
ORGANIZE IN THE CENTRAL PLAINS AND CANADIAN PRAIRIES.

KMD

&&

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

$$

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