Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 290835
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CDT FRI MAY 29 2015

.UPDATE...
840 PM CDT

FOR EVENING UPDATE...

NO REAL CHANGES TO GOING FORECAST THIS EVENING...OTHER THAN ADD
DETAIL TO WIND GRIDS FOR LAKE BREEZE LOCATION PER METAR/RADAR OBS.
18Z NAM AND RECENT RAP/HRRR HIGH RES GUIDANCE DEVELOP SOME ISOLATED
SHOWERS ACROSS PARTS OF THE EASTERN CWA/CHICAGO METRO SHORTLY AFTER
MIDNIGHT...THOUGH FORCING APPEARS PRETTY WEAK PER 00Z RAOB AND RAP
ANALYSIS OTHER THAN SURFACE WARM FRONT PROPAGATING NORTHWARD LATE
TONIGHT. ISOLATED SFC/NEAR SFC BASED SHRA/TSRA WHICH DEVELOPED ALONG
THE WARM SIDE OF THE SURFACE WARM FRONT THIS AFTERNOON WERE QUICKLY
DISSIPATING WITH LOSS OF DIURNAL INSTABILITY. STILL APPEARS THAT THE
GREATER PROSPECTS FOR PRECIP STILL APPEAR TO HOLD OFF UNTIL MUCH
LATER TONIGHT...WITH STRONGER THETA-E ADVECTION AND MOISTURE
TRANSPORT AXIS OVER MO/IA/MISSISSIPPI VALLEY GRADUALLY SHIFTING
EASTWARD INTO WESTERN IL...INCLUDING NORTHWEST AND PARTS OF NORTH
CENTRAL IL...AHEAD OF THE SHORT WAVE CURRENTLY OVER WESTERN MO/AR
PER GOES VAPOR IMAGERY. GOING FORECAST HAS POPS INCREASING MAINLY
ACROSS WESTERN CWA 09-12Z...AND ACROSS THE EASTERN CWA BY/AFTER
12Z...AND THIS STILL LOOKS REASONABLE BASED ON CURRENT DATA.

RATZER

&&

.SHORT TERM...
225 PM CDT

THROUGH TONIGHT...

THE FORECAST AREA FINDS ITSELF BETWEEN TWO STATIONARY FRONTS
THIS AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE SANDWICHED IN
BETWEEN DIRECTLY OVER THE AREA. THIS RIDGE HAS ALLOWED A LAKE
BREEZE WITH LAKESIDE COOLING AT THE CHICAGO SHORE ABOUT 14
DEGREES COOLER THAN INLAND AT ORD/MDW AS OF 200 PM. THE FRONT OF
INTEREST FOR OUR AREA TONIGHT WILL BE THE ONE TO THE SOUTH WHICH
WILL LIFT NORTH AS A WARM FRONT...BRINGING A RETURN TO MUGGY AIR
BY DAYBREAK...AS WELL AS KEEP NIGHTTIME TEMPERATURES MILD...EVEN
INCREASING THEM LATE TONIGHT ALONG THE LAKE SHORE AREAS.

MULTIPLE MID-LEVEL DISTURBANCES...SOME LIKELY CONVECTIVELY
ENHANCED...ARE NOTED ON WATER VAPOR AND RADAR MOSAIC IMAGERY ACROSS
THE CENTRAL PLAINS THIS AFTERNOON. ONE OF THESE JUST NORTH OF KANSAS
CITY AS OF 200 PM IS WELL ANALYZED BY THE LATEST RAP AND THIS IS
EXPECTED TO PROPAGATE INTO WISCONSIN OVERNIGHT...WITH ONE OR TWO
WEAKER IMPULSES TO ITS SOUTH APPROACHING THE AREA. WITH A 25-30 KT
LOW-LEVEL JET AHEAD OF THESE AND INCREASING MOISTURE AT THAT
HEIGHT...THERE WILL LIKELY BE SCATTERED SHOWERS OR STORMS FROM
SOUTHWEST WISCONSIN INTO NORTHWEST AND POSSIBLY NORTH CENTRAL
ILLINOIS OVERNIGHT.

MTF

&&

.LONG TERM...
314 PM CDT

FRIDAY THROUGH THURSDAY...

MAIN FORECAST CONCERNS/CHALLENGES DURING THE PERIOD ARE WITH
SHOWER/THUNDERSTORM CHANCES FRIDAY INTO SATURDAY...AND THEN WITH
MUCH COOLER AIR TO PUSH ACROSS THE AREA SATURDAY.

SOME UNCERTAINTY AS TO HOW THE PERIOD WILL BEGIN...DUE TO HOW
PRECIP DEVELOPMENT WILL EVOLVE LATE TONIGHT INTO FRIDAY MORNING.
THE CURRENT UPSTREAM MID LEVEL TROUGH OVER THE CENTRAL PLAINS WILL
CONTINUE MOVING NORTHEAST THROUGH THE CWA FRIDAY MORNING...WITH
LINGERING PRECIP FROM THE OVERNIGHT STILL LIKELY TO AFFECT
PRIMARILY THE WESTERN HALF OF THE CWA IN NORTH CENTRAL ILLINOIS.
LIKELY SCENARIO WILL BE FOR THIS DEVELOPMENT TO CONTINUE EAST
THROUGH THE MORNING. CONFIDENCE WITH OVERALL COVERAGE DURING
FRIDAY MORNING IS LOW...AND HAVE THUS CAPPED POPS AT LIKELYS.
MORNING PRECIP AND EVEN CLOUD COVER SHOULD EXIT THROUGH LATE
MORNING AND MIDDAY...WITH SKIES BECOMING MORE PARTLY CLOUDY/PARTLY
SUNNY. THIS WILL HELP WITH EARLY DESTABILIZATION WITH LITTLE TO NO
INHIBITION AND WITH MID LEVEL ENERGY RETURNING DURING THIS
TIME...THINK DEVELOPMENT WILL ONCE AGAIN BE POSSIBLE IN THE
AFTERNOON. WITH A LACK OF GOOD FOCUS AT THE SURFACE...THINK BEST
DEVELOPMENT WILL STILL BE ACROSS NORTH CENTRAL ILLINOIS WHERE
BETTER LARGE SCALE ASCENT WILL RESIDE. WEAK MID/UPPER LEVEL FLOW
WILL BE A LIMITING FACTOR WITH HOW ORGANIZED ANY STORM WILL BE AND
ALTHOUGH I DONT THINK THERE WILL BE ANY WIDESPREAD SEVERE
THREAT...AN ISOLATED STRONG TO SEVERE STORM WILL STILL BE POSSIBLE
WITH STRONG WINDS AND HEAVY RAINFALL THE MAIN HAZARDS DUE TO
INCREASING INSTABILITY AND MOISTURE. 80 DEGREE WEATHER WILL BE
LIKELY FRIDAY...BUT WITH TEMPS LIKELY BEING LIMITED IN ANY AREA
THAT OBSERVES MORE PRECIP/CLOUD COVER.

STILL THINK THAT THE BEST CHANCES FOR WIDESPREAD
SHOWER/THUNDERSTORM DEVELOPMENT WILL BE FRIDAY NIGHT INTO SATURDAY
MORNING. HOWEVER...GUIDANCE IS VARYING WITH REGARDS TO HOW THE
NIGHT WILL EVOLVE. THIS IS LIKELY DUE TO LARGER TROUGH OVER
SOUTHERN CANADA AND NORTHERN PLAINS MOVING EAST/SOUTHEAST...WHILE
A SEPARATE TROUGH AND SEVERAL IMPULSES WORKS EAST THROUGH THE
PLAINS. NONETHELESS...BEST LOW/MID LEVEL COVERAGE WILL PUSH
THROUGH THE CWA DURING THIS TIME WHILE LARGE SCALE FORCING ALSO
INCREASES. SO DO THINK PRECIP WILL PUSH THROUGH THE CWA...BUT WITH
COVERAGE AND DURATION POSSIBLY LOWER IN SOME LOCATIONS. THUNDER
SHOULD BE DECREASING IN COVERAGE THROUGHOUT THE NIGHT AND
ESPECIALLY INTO SATURDAY MORNING AS THE INSTABILITY AXIS SHIFTS
SOUTH...WITH HEAVY RAINFALL THE MAIN HAZARD DURING THIS TIME. ANY
LINGERING PRECIP WILL CONTINUE SOUTH OF THE CWA THROUGH MIDDAY
SATURDAY AS SURFACE TROUGH AND FRONT PUSH THROUGH THE REGION.
CLOUD COVER WILL LIKELY LINGER THROUGH MUCH OF SATURDAY WHILE
WINDS/GUSTS INCREASE THROUGHOUT THE DAY. HIGH TEMPS WILL LIKELY
OCCUR EARLY SATURDAY MORNING WITH TEMPS FALLING THROUGH THE
DAY...WITH 40 DEGREE WEATHER LIKELY FOR MOST LOCATIONS IN FAR
NORTHEAST ILLINOIS AND NORTHWEST INDIANA FOR MUCH OF THE DAY.

RODRIGUEZ

&&

.AVIATION...

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

* SCATTERED TSRA LATE MORNING THRU MID AFTERNOON.
* SCATTERED SHRA/TSRA LATE TONIGHT/SATURDAY MORNING.
* GUSTY SOUTHERLY WINDS MID MORNING THRU LATE AFTERNOON. CMS

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

A WARM FRONT WILL MOVE NORTH ACROSS THE AREA LATER THIS MORNING.
EAST/SOUTHEAST WINDS UNDER 10KT EARLY THIS MORNING WILL GRADUALLY
TURN MORE SOUTHERLY BY MID MORNING AND BEGIN TO INCREASE INTO THE
10-12KT RANGE WITH HIGHER GUSTS POSSIBLE.

WHILE AN ISOLATED SHOWER IS POSSIBLE TOWARD DAYBREAK...THE BEST
CHANCES APPEAR TO BE WEST OF THE CHICAGO AREA TERMINALS AND
INCLUDED VICINITY MENTION AT RFD...BUT OVERALL CONFIDENCE IS
FAIRLY LOW FOR ANY PRECIP THRU MID MORNING. GUIDANCE APPEARS MORE
FOCUSED ON A WAVE LIFTING NORTHEAST ACROSS THE AREA LATE THIS
MORNING THRU MID AFTERNOON AND THIS APPEARS THE BEST CHANCE FOR
SCATTERED THUNDERSTORMS TO AFFECT THE AREA THOUGH CONFIDENCE FOR
COVERAGE/DURATION IS STILL SOMEWHAT LOW. ASSUMING THIS ACTIVITY
DOES MATERIALIZE...WOULD EXPECT A BIT OF LULL FROM LATE AFTERNOON
INTO THIS EVENING AS THE WAVE DEPARTS.

A COLD FRONT WILL MOVE ACROSS THE AREA AFTER MIDNIGHT AND MORE
LIKELY CLOSER TO DAYBREAK SATURDAY. ADDITIONAL SHOWERS AND
THUNDERSTORMS WILL LIKELY OCCUR BUT CONFIDENCE ON TIMING IS STILL
LOW...AS IT APPEARS MUCH OF THE PRECIP COULD BE POST FRONTAL INTO
SATURDAY MORNING. ADDED VICINITY MENTION IN THE 30 HOUR ORD TAF
FOR NOW.

WINDS/GUSTS COULD INCREASE SOME MID/LATE AFTERNOON ONCE PRECIP
ENDS AND CLOUDS SCATTER BUT WINDS SHOULD QUICKLY DIMINISH WITH
SUNSET. CMS

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

* MEDIUM FOR TSRA LATE MORNING THRU MID AFTERNOON.
* MEDIUM FOR SHRA/TSRA LATE TONIGHT/SATURDAY MORNING.
* MEDIUM FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY....CHANCE SHRA EARLY. MVFR POSSIBLE. STRONG NORTH-
NORTHEAST WINDS.

SUNDAY...VFR/WX NIL. NORTHEAST WINDS.

MONDAY...VFR/WX NIL. EAST WINDS.

TUESDAY...VFR/WX NIL. SOUTHEAST WINDS.

WEDNESDAY...SLIGHT CHANCE TSRA. SOUTH WINDS.

KJB

&&

.MARINE...

335 AM...A STRONG COLD FRONT WILL MOVE ACROSS NORTHERN LAKE
MICHIGAN EARLY SATURDAY MORNING...THEN PUSH SOUTH OF THE LAKE BY
EARLY SATURDAY AFTERNOON. STRONG HIGH PRESSURE WILL BUILD ACROSS
THE NORTHERN PLAINS AND UPPER MIDWEST SATURDAY INTO SATURDAY
NIGHT...WHICH WILL STRENGTHEN THE GRADIENT BEHIND THE FRONT. WINDS
WILL SHIFT NORTHERLY AND INCREASE TO 30 KT WITH SOME GALE GUSTS
POSSIBLE. COULD BE A PERIOD OF LOW END GALES OVER THE SOUTHERN
PORTION OF THE LAKE FROM LATE SATURDAY MORNING THRU MID AFTERNOON
BUT CONFIDENCE TOO LOW TO INCLUDE PREVAILING GALES. WINDS WILL
TURN MORE NORTHEASTERLY SATURDAY NIGHT INTO SUNDAY...BUT THE
GRADIENT WILL BE SLOW TO RELAX ACROSS THE SOUTHERN PORTION OF THE
LAKE...SO A PROLONGED PERIOD OF 15-25KT IS POSSIBLE INTO SUNDAY
NIGHT. THE HIGH WILL SHIFT EAST INTO QUEBEC MONDAY...LEAVING A
WEAKER RIDGE OF HIGH PRESSURE ACROSS THE WESTERN LAKES INTO
TUESDAY. CMS

&&

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

$$

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