Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 291925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
225 PM CDT MON JUN 29 2015

.SHORT TERM...
224 PM CDT

THROUGH TUESDAY...

TONIGHT...SHOWER/THUNDER TRENDS WILL BE THE MAIN FOCUS TONIGHT AS
ANOTHER IN A SERIES OF UPPER WAVES TRAVERSES THE AREA. LATE
AFTERNOON SHOWER/THUNDER ACTIVITY WILL FADE AS THE PRIMARY WAVE
DRIVING THE ACTIVITY SHIFTS TO THE EAST AND DAYLIGHT BEGINS TO WANE.
WATER VAPOR IMAGERY SHOWS ADDITIONAL WAVES MOVING SOUTHEAST ACROSS
MINNESOTA WITH THE MOST PRONOUNCED WAVE APPROACHING NORTHWEST
WISCONSIN. SHOWERS AND STORMS CONTINUE TO MARCH SOUTHEASTWARD WITH
THIS SECOND WAVE WHILE NEW SCATTERED ACTIVITY IS DEVELOPING TO THE
SOUTH ACROSS EXTREME SOUTHEAST MN AND SOUTHWEST WI IN CONJUNCTION
WITH THE SE MN WAVE. GUIDANCE IS MIXED ON HOW LONG ALL OF THIS
ACTIVITY WILL CONTINUE INTO THE NIGHT AND THEREFORE HOW MUCH IMPACT
THE CWA WILL SEE. BASED ON LATEST TRENDS AND NEAR TERM
GUIDANCE...SHOWERS AND STORMS COULD REACH THE NORTHWEST CWA BY MID
EVENING THEN CONTINUE ACROSS THE AREA OVERNIGHT IF THEY HOLD
TOGETHER. SOME OF THE ACTIVITY WITH THE SE MN WAVE MAY BE MORE
DIURNALLY DRIVEN SO IT MAY FADE AS IT MOVES CLOSER TO THE AREA EARLY
THIS EVENING. EXPECT THE MORE ORGANIZED NORTHERN ACTIVITY TO MAKE
BETTER PROGRESS AND HOLD TOGETHER LONGER SO WILL WORK A BAND OF LOW
LIKELY/HIGH CHANCE POPS ACROSS THE AREA FROM MID EVENING THROUGH THE
OVERNIGHT HOURS THEN EXIT THEM TO THE EAST EARLY TOMORROW MORNING.
AM A BIT CONCERNED THAT THE ARRIVAL OF POPS MAY BE JUST A BIT SLOW
SO MAY NEED TO SPEED THE PROGRESSION UP BY AN HOUR OR TWO GOING INTO
EARLY EVENING SO STAY TUNED. WOULD EXPECT ANY WIND THREAT WITH THIS
ACTIVITY TO BE DIMINISHING AS IT APPROACHES LEAVING HEAVY
DOWNPOURS/ISOLATED FLOODING AS THE PRIMARY CONCERN.

TUESDAY...ANY LEFTOVER OVERNIGHT PRECIP WILL EXIT TO THE EAST BY MID
TUESDAY MORNING AS AN UPPER TROUGH AXIS CLEARS TO THE EAST. THE MAIN
SURFACE LOW WILL LAG BEHIND THE UPPER WAVE BUT WILL DRAG A COOL
FRONTAL BOUNDARY ACROSS THE AREA THROUGH THE MORNING. THERE DOES NOT
APPEAR TO BE MUCH OF A COHERENT FOCUS FOR ADDITIONAL ORGANIZED
DEVELOPMENT THROUGH THE MORNING BUT WITH BROADER ASCENT IN PLACE
ISOLATED ACTIVITY IS POSSIBLE. HIGH PRESSURE WILL BE BUILDING ACROSS
WESTERN LAKE SUPERIOR WHILE BRINGING A STRONGER PRESSURE GRADIENT TO
NORTHERN SECTIONS OF LAKE MICHIGAN AHEAD OF IT. A SECONDARY COOL
FRONTAL BOUNDARY LOOKS TO DEVELOP AND DROP DOWN LAKE MICHIGAN
TUESDAY AFTERNOON WHICH MAY SERVE TO TRIGGER ISOLATED/SCATTERED
SHRA/TSRA DEVELOPMENT DURING THE AFTERNOON...ESPECIALLY LATER...
GIVEN THAT THE AIRMASS BEHIND THE INITIAL FRONT WILL STILL BE MOIST
AND UNSTABLE. WILL CARRY CHANCE POPS DURING THE MID/LATE AFTERNOON
INTO THE EARLY EVENING HOURS ACROSS NORTHEAST IL AND FAR NORTHWEST
IN. HIGH TEMPS WILL BE IN THE UPPER 70S TO AROUND 80 WITH LAKEFRONT
AREAS COOLING LATE IN THE DAY AS WINDS SHIFT NORTHEAST WITH THE
SECONDARY FRONTAL PASSAGE.

MDB

&&

.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 18Z...

* CIGS REMAINING MAINLY VFR THIS AFTERNOON... BRIEF LOWERING TO
  MVFR WITH SHOWERS/TSRA.
* MVFR/IFR CIGS/VSBYS PSBL AGAIN OVERNIGHT TONIGHT.
* SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THROUGH MUCH OF THE
  TAF PERIOD... BEST WINDOWS FOR THIS ARE 20-00Z THIS AFTERNOON
  AND AGAIN 09Z-13Z TUESDAY MORNING.

ED F

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

SHOWERS INCREASING IN COVERAGE AND INTENSITY PAST 1-2 HOURS SINCE
16Z... WITH ACTIVITY FOCUSING ON AREA OF LOW LEVEL CONVERGING AIR
ALONG AN INVERTED TROUGH OF LOW PRESSURE ARCING FROM THE SOUTH
SUBURBS TO THE FOX RIVER VALLEY NORTHWARD INTO SOUTH CENTRAL WI
EAST OF MSN. WITH THE ENTIRE SYSTEM DRIFTING ESE EXPECT SHOWERS TO
MOVE SE SLOWLY AWAY FROM MDW WITH A BRIEF BREAK ONLY TO BE
REPLACED BY ADDITIONAL SHOWERS AND THUNDERSTORMS LATER THIS
AFTERNOON ORD TO MDW AS THE FOX VALLEY TO S CENTRAL WISC SEGMENT
OF THIS PRECIPITATION AREA DRIFTS SLOWLY SE.

MAY SEE AN EXTENSION OF THIS RAIN PERIOD INTO THE EVENING HOURS
DEPENDING ON THE TIMING OF AN UPPER LEVEL DISTURBANCE CURRENTLY
OVER NW WISC AND WILL BE TWEAKING THE FORECAST THIS AFTERNOON
BASED ON TRENDS AND MONITORING AND MODEL PREDICTIONS OF THIS
FEATURE... WHICH HAS BEEN VERY CONSISTENT BASED ON SATELLITE AND
LIGHTNING DATA.

THEN YET ANOTHER WINDOW OF PRECIPITATION APPEARS IN THE OFFERING
LATE TONIGHT/EARLY TUESDAY AS YET ANOTHER WEAK IMPULSE DROPS SOUTH.
A WEAK COLD FRONT THEN SAGS SE ACROSS THE AREA TUESDAY
AFTERNOON... BRINGING YET ANOTHER OPPORTUNITY FOR SHOWERS IN AN
OTHERWISE CONTINUED VERY MOIST AND RELATIVELY UNSTABLE ATMOSPHERE.

ED F

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

* HIGH CONFIDENCE IN SCATTERED SHRA/ISOL TSRA THIS AFTERNOON INTO
  EVENING...LOW CONFIDENCE IN SPECIFIC TIMING AT TERMINALS.
* MEDIUM-HIGH CONFIDENCE IN WINDS STAYING AT OR BELOW 10KT.
* LOW-MEDIUM CONFIDENCE IN CIG TRENDS.
* MEDIUM CONFIDENCE IN SHOWER CHANCES LATE TONIGHT/EARLY TUESDAY
  AND AGAIN TUES AFTERNOON.

ED F

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

TUESDAY NIGHT...DRY. NE WINDS. MVFR/IFR PSBL.
WEDNESDAY...DRY. NE WINDS. MVFR/IFR PSBL.
THURSDAY...DRY. NE WINDS. MVFR/IFR PSBL.
FRIDAY...CHC SHRA/SLT CHC TSRA. NE WINDS. PRIMARILY VFR.
SATURDAY...CHC SHRA. NE WINDS. PRIMARILY VFR.
SUNDAY...SLT CHC TSRA. S WINDS. PRIMARILY VFR.

BMD

&&

.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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