Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 290802
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
302 AM CDT MON JUN 29 2015

.SHORT TERM...
253 AM CDT

THROUGH TONIGHT...

IR IMAGERY EARLY THIS MORNING HAS THICKER CLOUD COVER STRETCHING
FROM CENTRAL/EASTERN WISC SOUTHEAST ACROSS NORTHEAST IL INTO CENTRAL
IN. SFC ANALYSIS HAS A WEAK LOW CENTERED OVER CENTRAL IL...AND WILL
EVENTUALLY LIFT NORTHEAST ACROSS CENTRAL IN LATER THIS AFTN. THE
NOTABLE FEATURE IS THE LACK OF A GRADIENT WITH THIS WAVE...AS
WINDS ACROSS THE REGION EARLY THIS MORNING ARE GENERALLY LESS THAN
10KT. SOME CLEARING HAS TAKEN PLACE IN THE CLOUD SHIELD ALONG THE
WESTERN PORTIONS OF THE CWFA...WHICH COUPLED WITH THE DEW PTS IN
THE LOW 60S HAS ALLOWED FOG TO PATCHY DENSE FOG TO DEVELOP. EXPECT
FOG TO LINGER A COUPLE HOURS AFTER DAYBREAK GIVEN THE LACK OF
MIXING...BUT BY MID- MORNING THE FOG SHUD ERODE. CLOUDS ARE POISED
TO THICKEN YET AGAIN...WITH MARGINAL INSTABILITY LATE MORNING THRU
THE AFTN/EVE. HAVE OPTED TO HOLD THE MENTION OF THUNDER THRU THE
MORNING...THEN HAVE GONE WITH JUST A SLIGHT CHANCE OF THUNDER. THE
COVERAGE FROM SHOWERS/THUNDER WILL NOT BE GREAT...SO ONLY MINOR
ADJUSTMENTS TO THE GOING POPS.

TEMPS WILL HINGE ON CLOUD COVER AND WIND DIR...ESPECIALLY TRUE FOR
AREAS ADJACENT TO LAKE MICHIGAN. GUIDANCE HAS CONTINUED TO POINT
TOWARDS A NORTHEAST WIND OFF OF THE LAKE...WHICH WILL LIKELY HOLD
TEMPS IN THE UPR 60S TO LOW 70S. ELSEWHERE THE INLAND AREAS SHUD
SLOWLY WARM GIVEN THE BUOYANT ATMOSPHERE INTO THE LOW/MID 70S.

LATER THIS EVENING WITH THE 500MB TROUGH AXIS STILL
OVERHEAD...ANOTHER LOBE OF MID-LVL VORTICITY IS POISED TO DROP SOUTH
FROM THE UPPER MIDWEST ACROSS THE WESTERN GREAT LAKES. THIS SHUD
PROVIDE A BRIEF LULL IN SHOWERS/THUNDER THIS EVE...BEFORE
SHOWERS/THUNDER REDEVELOP LATE TONIGHT AS THE VORT MAX ARRIVES. WITH
DEW POINTS REMAINING IN THE LOW/MID 60S OVERNIGHT...AS THE NEXT SFC
LOW DEVELOPS TONIGHT...SOME OF THE PRECIP COULD BE BRIEF DOWNPOURS
AND SLOW MOVING. THIS COULD RESULT IN RENEWED FLOODING CONCERNS FOR
AREAS THAT CONTINUE TO SEE NEARLY SATURATED SOILS.

BEACHLER

&&

.LONG TERM...
253 AM CDT

TUESDAY THROUGH SUNDAY...
500MB TROUGH AXIS WILL BE SLOWLY PIVOTING EAST...WITH GUIDANCE
SUGGESTING MID-LVL HEIGHTS MAY TRY TO RISE AND ALLOW FOR A BREAK
IN THE PRECIP TUE AFTN/EVE. ADDITIONALLY A QUASI- STATIONARY
BOUNDARY WILL BECOME ORIENTED FROM THE OHIO RIVER STRETCHING
WEST/NORTHWEST TO EASTERN NEBRASKA. THIS BOUNDARY WILL BECOME A
FOCAL POINT MID-WEEK AS A LOW ACROSS THE PLAINS WILL RIDE ALONG
THE BOUNDARY AND MAY BUCKLE NORTH TOWARDS THE SOUTHERN CWFA. PRIOR
TO THIS SCENARIO...AN AREA OF ANTI- CYCLONIC FLOW WILL TRY TO DROP
SOUTH FROM ONTARIO AND PUSH A BACKDOOR FRONT SOUTH ACROSS THE LAKE
TUE NGT/EARLY WED. THIS WILL SHARPEN THE BAROCLINIC ZONE WED...BUT
SHUD STILL REMAIN WELL SOUTH OF THE FORECAST AREA. TEMPS TUE PRIOR
TO THE FRONT MAY BE ABLE TO WARM INTO THE UPR 70S OR NEAR 80...BUT
THEN A NORTH/NORTHEAST LLVL FLOW WED WILL KEEP TEMPS IN THE UPR
60S TO NEAR 70 FOR AREAS ADJACENT TO LAKE MI. FURTHER INLAND
CLOUDS WILL THICKEN WED WITH TEMPS GENERALLY IN THE LOW/MID 70S.

THERE IS SOME DISCREPANCIES AMONGST THE GUIDANCE MEMBERS FOR
WED...WHICH INDICATE THE SFC LOW PATCH AND BOUNDARY MAY BE FURTHER
SOUTH AS A RESULT OF A SLIGHTLY STRONGER SFC RIDGE DROPPING SOUTH
FROM ONTARIO. THIS WILL ALSO DRIVE PRECIP PLACEMENT WED
NGT/THUR...ALONG WITH TEMPS THUR. HAVE NUDGED POPS DRIER FOR THE
NORTHERN CWFA BOTH WED/THUR. TEMPS THUR WILL CONTINUE TO BE IN THE
70S...WITH LIKELY THE UPR 60S FOR AREAS ADJACENT TO LAKE MICHIGAN.

FRIDAY THROUGH SUNDAY... WESTERN CONUS HIGH AMPLITUDE RIDGE WILL
REMAIN THROUGH SAT WITH THE DOWNSTREAM TROUGH OVER THE GREAT LAKES
SLOWLY WEAKENING OVER THE WEEKEND. SIMULTANEOUSLY HEIGHTS WILL BEGIN
TO RISE ACROSS THE SOUTHEASTERN CONUS...WHICH COULD HELP TO PUSH
WARMER TEMPS BACK NORTH ACROSS THE CENTRAL STATES LATE IN THE
WEEKEND INTO EARLY NEXT WEEK. OPER GUIDANCE SUGGESTS THE MID-LVL
RIDGE MAY RELAX EARLIER IN THE WEEKEND...WITH A QUASI-NORTHWEST FLOW
INTO THE GREAT LAKES BY SUN. SO PERIODIC CHANCES FOR
SHOWERS/THUNDERSTORMS MAY RETURN FOR THE SECOND HALF OF THE HOLIDAY
WEEKEND INTO EARLY NEXT WEEK. TEMPS WILL RETURN TO MORE SEASONAL
CONDS BY THE END OF THE WEEKEND INTO EARLY NEXT WEEK.

BEACHLER

&&

.AVIATION...

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

* LOWERING CIGS OVERNIGHT WITH MVFR/IFR POSSIBLE BY EARLY MONDAY
  MORNING...AND THEN AGAIN EARLY TUESDAY MORNING.
* PERIODIC CHANCES FOR SHOWERS MUCH OF THE TAF PERIOD.

BMD

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

FIRST AREA OF LOW PRESSURE IS CENTERED NEAR WEST CENTRAL ILLINOIS
TONIGHT WITH SYNOPTICALLY E/SE FLOW ACROSS NORTHERN ILLINOIS AND
NORTHWEST INDIANA. A FEW LIGHTS SHOWERS PERSIST ACROSS THE AREA
THOUGH COVERAGE IS LOW ENOUGH WILL JUST CONTINUE TO CARRY VCSH AT
THE TERMINALS. THE SURFACE LOW HAS TRACKED A LITTLE FARTHER SOUTH
THAN EXPECTED WHICH LOWERS THE PROSPECTS OF LOW CIGS ACROSS THE
TERMINALS. WHILE IFR IS POSSIBLE...CONFIDENCE IN WANING. THE BEST
CHANCE WILL BE AT RFD NEAR THE EDGE OF THE CLOUD SHIELD WHERE
LOWER STRATUS AND FOG ARE FORMING JUST TO THE WEST. SURFACE LOW
WILL TRACK EAST ACROSS INDIANA MONDAY WITH WINDS CONTINUING TO
BACK TO THE NORTHEAST. SHOWERS REMAIN POSSIBLE THROUGH MUCH OF THE
DAY BUT ESPECIALLY IN THE AFTERNOON AS INSTABILITY BUILDS
DIURNALLY. WEAK/SUBTLE FORCING WILL MAKE IT DIFFICULT TO PIN DOWN
TIMING DETAILS HOWEVER. ANOTHER WEAK SURFACE LOW IS PROGGED TO
DROP INTO NORTHERN ILLINOIS LATE MONDAY NIGHT INTO TUESDAY MORNING
ONCE AGAIN RESULTING IN INCREASED PRECIP CHANCES AND LOWERING
CIGS.

BMD

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

* MEDIUM-HIGH CONFIDENCE IN SCATTERED SHOWERS AROUND THE
  TERMINALS MUCH OF THE TAF PERIOD...BUT LOW CONFIDENCE ON
  SPECIFIC TIMING OF IMPACTS AT THE TERMINALS.
* LOW CONFIDENCE IN IFR TONIGHT...MEDIUM CONFIDENCE IN IFR MONDAY
  NIGHT/TUESDAY MORNING.

BMD

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

* TUESDAY...CHANCE OF TSRA. NORTHWEST WINDS.
* WEDNESDAY...DRY/VFR. NORTHEAST WINDS.
* THURSDAY...SLIGHT CHANCE OF SHRA. NORTHEAST WINDS.
* FRIDAY...CHANCE OF TSRA. NORTHEAST WINDS.
* SATURDAY...CHANCE OF SHRA/TSRA. WESTERLY WINDS.

&&

.MARINE...
301 AM CDT

EXPECT A WEAK GRADIENT MUCH OF THE UPCOMING WEEK WITH THE
EXCEPTION OF TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. EXPECT
GENERALLY LIGHT WINDS TODAY AND TONIGHT AS LAKE MICHIGAN LIES
BETWEEN TWO AREAS OF LOW PRESSURE WHICH WILL EVENTUALLY MERGE OVER
THE EASTERN GREAT LAKES LATER ON TUESDAY. WINDS BRIEFLY PICK UP
MAINLY IN THE 15 TO 20 KT OCCASIONALLY 25 KT RANGE OUT OF THE
NORTH BEHIND THE DEPARTING LOW AND AHEAD OF A RIDGE BUILDING SOUTH
INTO THE REGION. EXPECT LIGHT WINDS TO RETURN TO CLOSE OUT THE
WEEK AND CONTINUE INTO THE WEEKEND.

BMD

&&

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

$$

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