Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 160814
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 AM CDT TUE SEP 16 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 06Z...

* FOG POTENTIAL EARLY TUESDAY.
* LAKE BREEZE POTENTIAL TUESDAY AFTERNOON.

BMD

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

HIGH PRESSURE WILL BUILD TO THE SOUTH OF THE TERMINALS TONIGHT
KEEPING WINDS VERY LIGHT AND ALLOWING CONDITIONS TO REMAIN
GENERALLY VFR OUTSIDE OF SOME FOG THIS MORNING. PATCHY FOG HAS
ALREADY DEVELOPED IN SOME AREAS AND WILL MOST LIKELY IMPACT
RFD/DPA WITH CONFIDENCE TOO LOW AT ORD/MDW/GYY AT THIS TIME TO
INCLUDE ANY MENTION IN THE TAF. WINDS WILL REMAIN LIGHT GENERALLY
4-7 KT THROUGH THE DAY TUESDAY OUT OF THE NORTHWEST THOUGH THERE
MAY BE SOME VARIABILITY IN DIRECTION DUE TO THE LIGHT MAGNITUDE.
WILL ALSO HAVE TO MONITOR A LAKE BREEZE MONDAY AFTERNOON. FOR NOW
EXPECT A LAKE BREEZE TO DEVELOP BUT STAY NEAR THE SHORE.

BMD

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

* LOW CONFIDENCE IN FOG IMPACTING TERMINALS.
* LOW CONFIDENCE THAT A LAKE BREEZE WILL PUSH FAR INLAND.
* HIGH CONFIDENCE IN VFR CONDITIONS AND WINDS LESS THAN 10 KT
  THROUGH PERIOD.

BMD

//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...
314 AM CDT

HIGH PRESSURE WILL BUILD ACROSS SOUTHERN LAKE MICHIGAN TODAY
ALLOWING WINDS TO DIMINISH...HOWEVER NORTHERN LAKE MICHIGAN WILL
SEE SOUTHWEST FLOW FRESHEN UP AHEAD OF THE NEXT COLD FRONT. THE
FRONT WILL SAG SOUTH ACROSS THE LAKE WEDNESDAY WITH HIGH PRESSURE
QUICKLY BUILDING IN BEHIND CAUSING A SHARP INCREASE IN WINDS
BEHIND THE FRONT INTO THE 20 TO 25 KT RANGE OUT OF THE NORTHEAST
WEDNESDAY EVENING. WINDS WILL VEER BACK AROUND TO THE SOUTHEAST
THURSDAY AND THURSDAY NIGHT DIMINISHING...THEN SOUTH TO SOUTHWEST
FRIDAY INCREASING BACK INTO THE 20 TO 25 KT RANGE...POSSIBLY 30 KT
AS BROAD LOW DEVELOPS OVER THE PLAINS AND CANADIAN PRAIRIES.

BMD

&&

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

$$

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