Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 291950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CDT FRI MAY 29 2015

.SHORT TERM...
248 PM CDT

THROUGH SATURDAY EVENING...

MESSY WEATHER PATTERN IN PLACE REST OF TODAY AND TONIGHT AS THE
REGION FALLS IN THE WARM SECTOR AHEAD OF A COLD FRONT DROPPING
ACROSS THE UPPER MIDWEST AND PLAINS THIS AFTERNOON. EXPECT
UNCAPPED MODEST INSTABILITY TO BE IN PLACE THROUGH LATE THIS
EVENING TONIGHT THOUGH FORCING IS FAIRLY WEAK RESULTING IN
UNFOCUSED ISOLATED TO WIDELY SCATTERED SHOWER ACTIVITY. MID LEVEL
LAPSE RATES CONTINUE TO BE WEAK IN THE 5-6 C/KM RANGE OVERNIGHT SO
DONT SEE A SIGNIFICANT INCREASE IN THE THUNDER CHANCES THROUGH
EARLY OVERNIGHT...AND SEVERE THREAT IS FAIRLY MINIMAL WITH AN
ISOLATED WET MICROBURST BEING THE MAIN CONCERN. THE COMBINATION OF
POOR LAPSE RATES...INCREASING MOISTURE AND RELATIVELY HIGH MELTING
LEVELS WILL GREATLY LIMIT THE HAIL THREAT DESPITE DEEP LAYER SHEAR
INCREASING THROUGH THE EVENING.

SYNOPTICALLY...WE ARE NOT UNDER A FAVORABLE AREA OF FORCING MOST
OF THE EVENING AND EARLY OVERNIGHT HOURS HOWEVER MODELS DO
CONTINUE TO DEVELOP CONVECTION OVER THE AREA. UNDERCUT MODEL POPS
THROUGH THE EARLY OVERNIGHT HOURS LEAVING ABOUT A 30-40 POP CWA-
WIDE...THINKING A LOT OF THE MODEL VORTICITY THAT IS GENERATED IS
A RESULT OF CONVECTIVE FEEDBACK. A MORE ROBUST UPPER LEVEL WAVE IS
PROGGED TO LIFT ACROSS THE MID-MISSISSIPPI VALLEY EARLY SATURDAY
MORNING AND THE COLD FRONT APPROACHES FROM THE NORTHWEST...SO DO
GRADUALLY INCREASE POPS THROUGH THE PREDAWN HOURS. THE COLD FRONT
SHOULD BE NEAR THE IL/WI STATE-LINE AROUND SUNRISE TOMORROW
MORNING. BUMPED UP LOWS FOR THE NORTHERN HALF OF THE CWA WITH A
SLOWER THAN EXPECTED ARRIVAL OF THE FRONT.

COLD FRONT SHOULD CLEAR THE SOUTHERN COUNTIES OF THE CWA BY EARLY
TO MID AFTERNOON. NORTHERN COUNTIES WILL HAVE EARLY MORNING
HIGHS THEN TEMPERATURES FALLING THROUGH THE DAY AS AN UNSEASONABLY
STRONG COLD FRONT PUSHES THROUGH. 30 KT WINDS COMING DOWN BEHIND
THE FRONT OVER A MOSTLY STABLE LAKE MICHIGAN ARE EXPECTED TO
INCREASE IN THE WARMER NEARSHORE WATERS. WINDS GUSTING TO AROUND
40 MPH ARE EXPECTED TO BLEED INLAND...WITH GUSTS OF 30 TO 35 MPH
EXPECTED FARTHER INLAND. STRONG WINDS AND THE ONSHORE COMPONENT
WILL DRIVE WAVES INTO THE 8 TO 12 FOOT RANGE SO THERE IS THE
POSSIBILITY OF FLOODING ALONG THE BIKE PATH IN CHICAGO AND OTHER
TYPICALLY FLOOD PRONE AREAS ALONG THE SOUTH END OF THE LAKE
MAINLY EARLY AFTERNOON THROUGH THE EVENING.

INSTABILITY DOES HAVE A LITTLE TIME TO BUILD IN THE SOUTHERN TWO
THIRDS TO HALF OF THE CWA AHEAD OF THE FRONT BY MID MORNING...SO
THERE MAY BE BETTER CHANCES FOR THUNDERSTORMS DURING THE DAY
TOMORROW AHEAD OF THE FRONT. INSTABILITY QUICKLY DIMINISHES
BEHIND THE FRONT AND SOME MODELS /ESPECIALLY GFS/ SHOW A STABLE
WAVE DEVELOPING ALONG THE FRONT WITH RAIN CONTINUING BEHIND THE
FRONT AS AN F-GEN BAND DEVELOPS. EXPECT A LOT OF THE FORECAST AREA
TO FALL INTO THE UPPER 40S BY MID TO LATE TOMORROW AFTERNOON...AND
SITES ALONG THE LAKE EXPERIENCING WIND CHILLS IN THE MID TO UPPER
30S...ONLY TWO DAYS BEFORE METEOROLOGICAL SUMMER BEGINS.

DEUBELBEISS

&&

.LONG TERM...
356 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

THE EXTENDED PERIOD IS SHAPING UP TO BE A BIT QUIETER...AND
CERTAINLY INITIALLY MUCH COOLER. SUNDAY WILL FEATURE PLENTY OF
SUNSHINE...AND WILL ALSO FEATURE A SIGNIFICANT TEMPERATURE GRADIENT
FROM NEAR LAKE AREAS ONLY IN THE 50S TO NEAR 70 IN THE FAR
SOUTHWEST. COOLER CONDITIONS MAKE LITTLE HEADWAY OUT OF THE AREA AS
AN UPPER TROUGH SLIDES BY TO OUR NORTH. SURFACE HIGH PRESSURE
REMAINS OFF THE NORTHEAST MAINTAING AN ONSHORE FLOW AS WELL. UPPER
LEVEL RIDGING WILL BUILD TUESDAY THROUGH THURSDAY. SURFACE HIGH
PRESSURE WILL BE SLOWLY PUSHING EASTWARD WHICH WILL ALLOW ONSHORE
WINDS TO TURN MORE SOUTHEASTERLY AND A WARMING AIR MASS EACH DAY.
LAKE BREEZES CAN BE EXPECTED EACH DAY AS WELL...KEEPING LAKE AREAS
ON THE COOL SIDE FOR EARLY JUNE.

KMD

&&

.AVIATION...

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

* ISOLATED TO SCATTERED SHRA AND ISOLATED TSRA POSSIBLE THIS
  AFTERNOON AND AGAIN OVERNIGHT.

* WIND SHIFT TO STRONG/GUSTY NORTH-NORTHEAST ON SATURDAY MORNING
  AND CONTINUING THROUGH THE DAY.

* IFR CIGS/POSSIBLY LIFR/DEVELOPING SATURDAY MORNING.

* PERIODS OF RAIN AND VSBY RESTRICTIONS SATURDAY MORNING THROUGH
  THE AFTERNOON.

RC

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

LATEST RADAR SHOWS ISOLATED-SCATTERED SHRA ACTIVITY OVER THE
REGION AND TRENDS SUGGEST THIS GENERAL REGIME WILL CONTINUE
THROUGH AT LEAST MID AFTERNOON. DUE TO GENERALLY WEAK
INSTABILITY...NONE OF THE SHOWERS HAS BEEN ABLE TO PRODUCE
LIGHTNING OVER IL AND IN. THERE MAY BE A WINDOW THIS AFTERNOON
WHERE ENOUGH INSTABILITY COULD BUILD TO ALLOW FOR SOME ISOLATED
TSRA...BUT CONFIDENCE IN DIRECT TERMINAL IMPACTS REMAINS LOW.
AN UPPER DISTURBANCE IS EXPECTED TO CLIP NORTHWEST/NORTH CENTRAL
IL THIS EVENING...WITH SOME POTENTIAL FOR ISOLATED-SCATTERED
SHRA/TSRA. WINDS WILL BE OCCASIONALLY GUSTY OUT OF THE SOUTH-
SOUTHWEST THROUGH THE AFTERNOON THEN LIGHTER SW THIS EVENING.

A BETTER CHANCE FOR MORE WIDESPREAD SHOWERS LOOKS TO
ARRIVE WITH THE APPROACH OF A STRONG COLD FRONT TOWARD DAYBREAK.
HOWEVER GIVEN UNFAVORABLE TIMING WOULD NOT EXPECT ANYTHING MORE
THAN VERY ISOLATED TSRA SO HAVE PULLED THUNDER MENTION. AS WIND
SHIFT FROM LIGHT SOUTHWEST TO STRONG/GUSTY NORTH- NORTHEAST WINDS
OCCURS MID- SATURDAY MORNING...MARINE AIRMASS DRIVEN SOUTHWARD
WILL BE CONDUCIVE FOR IFR TO POSSIBLY LIFR CIGS...ESPECIALLY NEAR
LAKE MICHIGAN. IN ADDITION...A STOUT UPPER DISTURBANCE MOVING OVER
THE AREA WILL GENERATE STEADY/OCCASIONALLY MODERATE TO EVEN HEAVY
RAIN THAT WILL TAPER OFF LATE IN THE AFTERNOON. WINDS WILL BE
SUSTAINED IN THE 15-20 KT RANGE AFTER THE WIND SHIFT...WITH GUSTS
UP TO ABOUT 30 KT FOR THE EASTERN TERMINALS.

RC

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

* HIGH IN ISOLATED TO SCATTERED SHRA OVER REGION THROUGH MID
  AFTERNOON...LOW IN DIRECT TERMINAL IMPACTS...LOW IN TSRA.

* LOW IN SHRA/TSRA TRENDS THIS EVENING AND OVERNIGHT.

* HIGH IN WIND SHIFT ON SATURDAY TO STRONG NORTH-NORTHEAST
  WINDS...MEDIUM IN TIMING AND SPEEDS.

* HIGH IN IFR CIGS DEVELOPING SATURDAY MORNING...MEDIUM IN
  TIMING...LOW IN LIFR.

* HIGH IN PERIODS OF RAIN ON SATURDAY...LOW-MEDIUM IN SPECIFIC
  VSBY IMPACTS.

RC

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

* SATURDAY NIGHT AND SUNDAY...DRY/VFR. GUSTY NORTHEAST WINDS.
* MONDAY AND TUESDAY...DRY/VFR. EAST WINDS.
* WEDNESDAY...SLIGHT CHANCE OF TSRA. SOUTHEAST WINDS.
* THURSDAY...CHANCE OF TSRA. SOUTH WINDS.

&&

.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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