Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 292219
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
519 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...
319 PM CDT

TUESDAY NIGHT THROUGH MONDAY...

THE BEGINNING OF THE PERIOD TUESDAY EVENING MAY BEGIN WITH
ISOLATED TO SCATTERED SHOWERS/THUNDERSTORMS STILL ACROSS THE
CWA...BUT EXPECT WHATEVER LINGERING DEVELOPMENT TO DIMINISH.
DEPARTING LARGE SCALE ASCENT AND A GOOD PUSH OF COOLER/DRIER AIR
ACROSS THE CWA TUESDAY NIGHT...WILL ALLOW FOR ANY FURTHER PRECIP
DEVELOPMENT ACROSS THE REGION TO REMAIN SOUTH OF THE CWA. WITH
THIS COOLER/DRIER AIRMASS IN PLACE AND WITH DIMINISHING
WINDS/CLEARING SKIES...DID LOWER LOW TEMPS TUESDAY NIGHT WITH
TEMPS DROPPING INTO THE 50S FOR MOST AREAS. ALTHOUGH NORTHWEST
FLOW ALOFT WILL PREVAIL ON WEDNESDAY...IT IS BECOMING MORE LIKELY
THAT THE BEST DEVELOPMENT FOR FURTHER PRECIP WILL BE TO THE
SOUTHWEST/SOUTH OF THE CWA. SO DID REMOVE POPS FOR MOST LOCATIONS
DURING THIS TIME BUT DID LEAVE SLIGHT CHANCE WORDING FOR THE FAR
SOUTHWEST CWA OWING TO SOME SLIGHT VARIABILITY AMONG MODEL
GUIDANCE. HOWEVER...COULD SEE THESE SLIGHT CHANCE POPS BEING
REMOVED WITH DRIER CONDITIONS THE MORE LIKELY TREND. ALSO LOWERED
SKY COVER TUESDAY NIGHT INTO WEDNESDAY WITH CLEARER SKIES BECOMING
MORE LIKELY BUT WITH SEVERAL MID LEVEL IMPULSES TRAVERSING THE
FLOW...COULD SEE SOME PERIODIC MID/HIGH LEVEL CLOUD COVER.

THE DRIER TREND WITH A MORE SOUTHWARD PLACEMENT OF BEST PRECIP
DEVELOPMENT WILL LIKELY CONTINUE WEDNESDAY NIGHT INTO
THURSDAY...WITH HIGH PRESSURE EXPANDING ACROSS MUCH OF THE REGION.
BELOW NORMAL TEMPS LOOK TO CONTINUE DURING THIS PERIOD AS WELL
WITH TEMPS FALLING TO THE 50S AGAIN. LOWERED TEMPS DURING THIS
PERIOD AND MAY NOT HAVE LOWERED ENOUGH ESPECIALLY ACROSS FAR
NORTHERN ILLINOIS WHERE TEMPS COULD FALL INTO THE 40S. WITH
STEERING FLOW KEEPING GENERAL MOVEMENT OF APPROACHING MID LEVEL
IMPULSES TO THE SOUTH AND WITH DOMINATING HIGH PRESSURE IN
PLACE...SUNNY SKIES WILL BE IN PLACE THURSDAY. HOWEVER...COOLER
AIRMASS AND ONSHORE FLOW WILL HELP KEEP TEMPS BELOW NORMAL...IN
THE 70S AND THE UPPER 60S NEAR THE LAKE. DRY CONDITIONS SHOULD
CONTINUE THURSDAY NIGHT BUT WITH CONFIDENCE LOWERING INTO
FRIDAY...AS GUIDANCE VARIES WITH A POSSIBLE SYSTEM PUSHING ACROSS
THE CWA. HAVE MAINTAINED CHANCE POPS FOR SHOWERS/THUNDERSTORMS ON
FRIDAY...BUT WILL NEED TO MONITOR THIS PERIOD FOR ANOTHER POSSIBLE
DRY DAY. GOING INTO THE WEEKEND...GUIDANCE DOES VARY BUT AT THIS
TIME...SATURDAY IS APPEARING TO BE ANOTHER DRY PERIOD FOR MOST
AREAS.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* SCATTERED SHRA/ISOLATED TSRA THRU EARLY EVENING.
* MVFR CIGS...POSSIBLE IFR CIGS OVERNIGHT/TUESDAY MORNING.
* SCATTERED SHRA LATE THIS EVENING/EARLY OVERNIGHT.
* CHANCE OF SHRA TUESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 22Z...

SCATTERED SHOWERS ALONG WITH ISOLATED THUNDERSTORMS CONTINUE TO
SLOWLY MOVE SOUTHEAST ACROSS THE AREA THIS AFTERNOON. MUCH OF THE
THUNDER ACTIVITY CURRENTLY EXTENDS WEST AND SOUTH OF THE CHICAGO
AREA TERMINALS AND SHOULD REMAIN IN THESE AREAS THRU EARLY EVENING
WHEN ACTIVITY SHOULD SLOWLY BEGIN TO DIMINISH WITH LOST OF
DAYTIME HEATING. SURFACE WINDS REMAIN QUITE LIGHT WITH VARIABLE
DIRECTIONS DUE TO OUTFLOW BOUNDARIES. STRONGER CELLS MAY PRODUCE
SOME LOCALLY HIGHER WIND SPEEDS/GUSTS. CMS

PREVIOUS 18Z DISCUSSION...

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 22Z...

* HIGH FOR SCATTERED SHRA...MEDIUM FOR COVERAGE...LOW FOR ISOLATED
  TSRA.
* MEDIUM FOR MVFR CIGS OVERNIGHT/TUESDAY MORNING.
* LOW FOR SHRA LATE THIS EVENING/EARLY OVERNIGHT AND AGAIN TUESDAY
  AFTERNOON. CMS

//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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