Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 241759
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1259 PM CDT SUN MAY 24 2015

.UPDATE...

VERY SHARP WARM FRONT HAS SET UP ACROSS THE AREA THIS AFTERNOON
AND LOOKS TO HOLD TIGHT THROUGH MID TO LATE AFTERNOON. LIGHT RAIN
ACROSS NORTHERN AND WESTERN PORTIONS OF THE AREA WILL DRIFT
THROUGH IN THE COMING HOURS. MEANWHILE...NO REAL STRONG SHORTWAVE
IS EXPECTED TO MOVE THROUGH THE REMAINDER OF TODAY...BUT WE DO
HAVE MOIST LOW LEVEL SOUTHWEST FLOW THAT WILL CONTRIBUTE TO
SCATTERED SHOWER DEVELOPMENT THROUGH THE AFTERNOON HOURS...WHICH
IS ONGOING ALREADY ONGOING WEST OF I-39 AND ALONG THE I-55
CORRIDOR IN MCLEAN COUNTY...JUST SOUTHWEST OF FORD/LIVINGSTON.
ILLINOIS WILL BE THE FAVORED AREA FOR SCATTERED SHOWERS...WITH THE
MOST LIKELY AREAS BEING IN THE VICINITY OF THE I-39 CORRIDOR.
ISOLATED THUNDERSTORMS WILL REMAIN CONFINED SOUTH OF THE WARM
FRONT WHICH WILL BE INCHING ITS WAY NORTHWARD TO THE SOUTHERN
CHICAGOLAND COUNTIES.

WE ALSO INCREASED WINDS FOR MONDAY MORNING. THERE LOOKS TO BE A
SURGE OF STRONGER WIND GUSTS DURING THE MORNING HOURS WHERE GUSTS
TO 40 MPH ARE LIKELY...WITH LOCALIZED HIGHER GUSTS. MONDAY WILL BE
A WINDY DAY...BUT EXPECT WINDS TO COME DOWN SOME IN THE AFTERNOON.

KMD

&&

.SHORT TERM...
310 AM CDT

SUNDAY AND SUNDAY NIGHT...

MAIN ISSUES FOR THE SHORT TERM FORECAST PERIOD WILL BE RAMPING UP
PCPN CHANCES AS WELL AS HIGH TEMPS FOR TODAY...ESPECIALLY ALONG THE
ILLINOIS LAKE MICHIGAN SHORE.  A LARGE AREA OF HIGH PRESSURE
CONTINUES TO SLOWLY SLIDE OFF THE MID ATLANTIC COAST WITH A RIDGE
AXIS EXTENDING BACK THROUGH THE UPPER MISSISSIPPI VALLEY.
MEANWHILE...LEE CYCLOGENESIS SLOWLY PERSISTS OVER ERN CO/NM. A
RETURN FLOW OF MOISTURE IS SETTING UP OVER THE CNTRL CONUS IN
GENERALLY SELY-SLY AROUND THE WRN PERIPHERY OF THE DEPARTING HIGH.
ALSO...A WEAK WARM FRONT/TROUGH APPEARS TO BE SEEING UP ACROSS THE
OHIO VALLEY WEST THROUGH SRN MO.  WINDS TO THE NORTH OF THE BOUNDARY
ARE PREVAILING SELY WITH PREVAILING SLY WINDS TO THE SOUTH. THE SELY
WINDS WILL CONTINUE TO KEEP THE IL SHORE OF LAKE MICHIGAN A BIT
COOLER THAN INLAND LOCATIONS.  HOWEVER...THE BOUNDARY IS EXPECTED TO
MOVE NORTH THROUGH THE DAY...PUTTING THE ENTIRE REGION UNDER SLY
FLOW EVENTUALLY.  THE MAIN IMPACT WILL BE ON TEMPERATURES.  WITH
LITTLE CHANGE TO THE OVERALL PATTERN...ANOTHER WARM DAY IS EXPECTED
FOR TODAY...THOUGH MORE EXTENSIVE CLOUD COVER COULD KEEP MAX TEMPS
LOWER BY A DEGREE OR 2.  DO NOT EXPECT A LAKE BREEZE TO
FORM...ESPECIALLY WITH STRENGTHENING WINDS OF 10-15 MPH...BUT RATHER
WITH SYNOPTICALLY SOUTHEAST FLOW PERSISTING INTO THE EARLY
AFTERNOON...THE ILLINOIS SHORE SHOULD BE COOLER THAN WELL
INLAND...BUT AS WINDS TURN SLY BY EARLY AFTERNOON OVER THE COOK
COUNTY SHORE...TEMPS SHOULD REBOUND INTO THE LOW 70S.  LAKE COUNTY
IL WILL REMAIN UNDER THE COOLER SELY FLOW A BIT LONGER...KEEPING THE
WAUKEGAN AREA COOLER THROUGH THE DAY...WITH HIGHS ONLY IN THE
LOWER 60S. LOCATIONS WELL INLAND SHOULD SEE MAX TEMPS TODAY RISING
INTO THE MIDDLE TO UPPER 70S...WITH THE PONTIAC METRO AREA HITTING
CLOSE TO 80F.

PCPN CHANCES FOR TODAY WILL BE A BIT TRICKY.  A WAVE OF SCT SHOWERS
IS MOVING NWD THROUGH WRN IL...ASSOCIATED WITH A WEAK SHORTWAVE
TRACKING UP THE WRN SIDE OF THE UPPER RIDGE WHICH IS ORIENTED FROM
THE SERN CONUS THROUGH THE UPPER MISSISSIPPI VALLEY.  THERE IS A
CHANCE FOR SOME OF THESE SHOWERS TO BRING SOME LIGHT RAIN TO THE
NWRN PORTIONS OF THE CWA...ALONG AND WEST OF THE I-39
CORRIDOR...INCLUDING THE ROCKFORD AREA.  OTHERWISE...THE GREATER
PCPN CHANCES WILL HAVE TO WAIT FOR A MUCH STRONGER SHORTWAVE
EXPECTED TO LIFT OUT OF THE SOUTH HIGH PLAINS LATER THIS MORNING.
THIS WAVE WILL TRACK NNELY TO THE UPPER MISSOURI VALLEY BY EARLY
THIS EVENING AND THEN AS THE UPPER RIDGE IS FORCES EWD...WILL THEN
TURN MORE NELY...REACHING THE MIDDLE MISSISSIPPI VALLEY LATE
TONIGHT.  THE MODEL GUIDANCE INDICATES A FEW STRONG LOW LEVEL JET OF
50-55KT DIRECTED INTO NRN IL LATE TONIGHT AS WELL.  THE STRONG LOW
LEVEL JET WILL HELP PUMP UP DEEP LAYER MOISTURE OVER THE REGION WITH
PWATS CLIMBING TO ARND 1.8 INCHES THIS EVENING.  THE TRICKER PARTS
TO THE WX/POP FORECAST HAS BEEN WHERE TO FOCUS THE CATEGORICAL POPS
AND HOW FAR EAST TO SPREAD THE HIGHER POPS AND HOW MUCH THUNDER TO
INDICATE WITHING THE WX.  HAVE LARGELY CONFINED THE CATEGORICAL POPS
TO THE VCNTY OF THE UPPER SHORTWAVE...OVER NWRN IL...INCLUDING THE
ROCKFORD AREA...BUT HAVE DROPPED OFF POPS TO THE SOUTHEAST...AWAY
FROM THE STRONGEST UPPER FORCING.  WHILE CURRENT THINKING IS THAT
MUCH OF THE CWA SHOULD SEE SOME MEASURABLE PCPN AT SOME POINT...IT
IS MOST LIKELY THAT THE ERN PORTIONS OF THE CWA...INCLUDING THE
CHICAGO METRO AREA AND NWRN INDIANA WILL LIKELY NOT SEE THE PCPN
UNTIL LATE TONIGHT OR EARLY TOMORROW MORNING.  THE OTHER CONCERN IS
THE THUNDER CHANCES.  FEEL THAT THE GREATER CHANCES WILL ALSO BE
CLOSER TO THE UPPER FORCING...OVER THE WRN PORTIONS OF THE CWA...BUT
THERE IS A CHANCE THAT THE ERN PORTIONS OF THE CWA COULD SEE SOME
ISOLD-SCT TS AS WELL LATE TONIGHT.  CURRENTLY...THE GREATEST
SENSIBLE WEATHER THREAT FROM THIS SYSTEM WILL BE LOCALLY HEAVY
RAINFALL DUE TO THE ANOMALOUSLY HIGH PWATS.  PER THE DVN PWAT
CLIMATOLOGY FOR MID TO LATE MAY...THE EXPECTED 1.75 INCH PWAT
FORECAST IS NEAR THE 99TH PERCENTILE.  SO...SOME OF THE STRONGER
SHRA/TSRA THAT DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE LOCALLY
HEAVY RAINFALL.

KREIN

&&

.LONG TERM...
229 AM CDT

MONDAY THROUGH SATURDAY...

FOR MEMORIAL DAY...LARGEST CONCERN FOR THE DAY WILL BE ON PRECIP
TIMING/COVERAGE. GUIDANCE HAS BEEN RELATIVELY CONSISTENT THAT A
LOBE OF VORTICITY WILL BE LIFTING NORTH ACROSS THE MID-MISSOURI
VALLEY EARLY MON...WITH A SFC WAVE PROGGED TO BE OVER CENTRAL IOWA
BY DAYBREAK MON. THE CHANNEL OF NEARLY 2.00 INCHES OF PWAT AND
ANOMALOUSLY STRONG 850MB V-WIND OR MOISTURE TRANSPORT...WILL BE
STEADILY SHIFTING EAST/NORTHEAST ACROSS THE FORECAST AREA SHORTLY
AFT DAYBREAK. BY MID-MORNING THE MOIST PLUME WILL BE DEPARTING THE
WESTERN CWFA AND BY MIDDAY OR SHORTLY BEFORE...THE REMAINDER OF
THE FORECAST AREA COULD BE DRY. IN ADDITION TO THE PRECIP ENDING
BY MIDDAY...CLOUD COVER SHOULD QUICKLY ERODE WITH ONLY A FEW
CLOUDS LINGERING IN THE AFTERNOON HOURS. UNFORTUNATELY THE TRADE
OFF FOR A DRY HOLIDAY AFTERNOON WILL BE THE BREEZY CONDITIONS.
MIXING WILL BE MAXIMIZED GIVEN THE LACK OF CLOUD COVER...SO EXPECT
GUSTS TO NEAR 35 MPH AND POSSIBLY FLIRT WITH 40MPH FOR A FEW
HOURS. HAVE ALSO NUDGED TEMPS UP A DEGREE...WITH GENERALLY 80 TO
84 DEG EXPECTED.

THE WARM/MOIST AIR WILL CONTINUE TO ADVECT ACROSS THE REGION MON NGT
INTO TUE...WITH YET ANOTHER VERY MILD OVERNIGHT. HAVE TEMPS MAINLY
IN THE MID 60S BUT COULD SEE THIS NOT BEING WARM ENOUGH. THE
WILDCARD WILL BE CLOUD COVER...WHICH IS CLOUDS HOLD OFF
LONGER...TEMPS COULD STILL DIP INTO THE LOW/MID 60S. THE DEW POINTS
HOLDING IN THE 60S WOULD LIKELY SLOW THE RATE OF FALL OVERNIGHT.

TUESDAY THROUGH SATURDAY... 500MB TROUGH AXIS WILL REMAIN IN A
SLIGHTLY NEGATIVE ORIENTATION ACROSS THE CENTRAL CONUS...WITH A WEAK
SFC FEATURE LIFTING NORTH ACROSS THE MID-MISSOURI VALLEY TUE
MORNING. BROAD MID-LVL RIDGING WILL REMAIN OVER THE SOUTHEAST
CONUS...MEANWHILE HIGH-AMPLITUDE RIDGING CONTINUES ACROSS WESTERN
CANADA/ALASKA. THIS WILL MAINTAIN A RELATIVELY ACTIVE SOUTHWEST FLOW
PATTERN FOR THE CENTRAL CONUS/GREAT LAKES REGION THROUGH THUR/FRI.

LATER IN THE WEEK ENSEMBLES BEGIN TO NUDGE A 500MB VORT SOUTH FROM
CENTRAL CANADA WITH A SFC FEATURE PROGGED TO DEVELOP ALONG THE LEE-
SIDE OR THE NORTHERN PLAINS. CLOSER TO FRI/SAT...OPER SOLUTIONS
DEVELOP THIS SFC FEATURE WITH A FRONTAL BOUNDARY SLIDING SOUTH FROM
CANADA. CONFIDENCE REMAINS LOW ON HOW THINGS WILL EVOLVE LATER IN
THE WEEK...ALTHOUGH ENSEMBLES ARE DEMONSTRATING MINIMAL SPREAD THAT
THE UPSTREAM RIDGE WILL BEGIN TO FLATTEN WITH A SEMI-ZONAL
ORIENTATION DEVELOPING.

WILL CONTINUE TO CARRY PERIODIC CHANCES FOR SHOWERS/STORMS...AND
TEMPS GENERALLY SEASONAL TO SLIGHTLY ABOVE SEASONAL THROUGH THE BULK
OF THE EXTENDED.

BEACHLER

&&

.AVIATION...

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

* EASTERLY WINDS TURNING SOUTH AND BECOMING BREEZY LATE THIS
  AFTERNOON.

* ISOLD-SCT SHRA POSSIBLE THROUGH THE AFTERNOON WITH A LESSER
  CHANCE THIS EVENING. PERIOD OF SHRA/TSRA EXPECTED LATE TONIGHT.

* SOUTH WINDS INCREASE EARLY MONDAY MORNING WITH 30 KT GUSTS
  LIKELY AND 35+KT GUSTS POSSIBLE. DIRECTION TURNS SOUTHWEST
  TOWARD MID MORNING. SPEEDS EASE MID-LATE MONDAY AFTERNOON.

MDB

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

SHRA COVERAGE CONTINUES TO SLOWLY INCREASE ACROSS CENTRAL AND
WESTERN IL AND LIFT NNE. EXPECT ISOLD-SCT COVERAGE THROUGH THE
AFTERNOON WITH MOST FREQUENT SHRA OCCURRENCE AT RFD AND LEAST AT
GYY. WARM FRONTAL BOUNDARY IS STILL SOUTH OF THE TERMINALS AND
HAVE SEEN A SHARPER EAST COMPONENT TO THE WINDS OVER THE LAST FEW
HOURS NORTH OF THE FRONT. DO EXPECT A SHIFT TO SOUTH OR SSE WINDS
LATER THIS AFTERNOON AND TIMING IN TAF MAY NEED TWEAKING. ONCE
WINDS TURN SOUTH SHOULD SEE SOME INCREASE IN SPEED AS WELL AS
MORE FREQUENT GUSTS TOWARDS 20 KT. SHRA COVERAGE LOOKS TO WANE A
BIT THIS EVENING THOUGH THERE MAY BE A SLIGHTLY BETTER CHANCE FOR
SOME TS TO OCCUR WITH ANY SHRA. COVERAGE WILL LIKELY INCREASE FROM
WEST TO EAST OVERNIGHT WITH A BAND OF SHRA/TSRA EXPECTED TO MOVE
ACROSS THE TERMINALS LATE TONIGHT INTO FIRST THING MONDAY MORNING.
HAVE INCLUDED TEMPO TSRA FOR THE MOST LIKELY PERIOD OF OCCURRENCE.
A PERIOD OF MVFR CIGS IS ALSO EXPECTED LATE TONIGHT AND EARLY
MONDAY MORNING.

WINDS JUST ABOVE THE SURFACE WILL INCREASE OVERNIGHT WITH SPEEDS
NEAR 50 KT BY 2000 FT. SURFACE WINDS WILL PICK UP THROUGH THE
OVERNIGHT WHICH MAY NEGATE LOW LEVEL WIND SHEAR SO WILL NOT
INCLUDE A MENTION FOR NOW...BUT WILL CONTINUE TO MONITOR. SURFACE
WINDS WILL MARKEDLY INCREASE AFTER DAYBREAK MONDAY MORNING AS A
SURFACE LOW PASSES WEST OF THE TERMINALS. SOUTH WINDS JUST EITHER
SIDE OF 180 DEGREES WILL RAMP UP AND GUST 30-35 KT THEN TURN
SOUTHWEST TOWARD 230 DEGREES OR SO BY MID MORNING. THERE IS SOME
SUGGESTION THAT THERE COULD BE A SHORT 1-2 HR WINDOW WHERE GUSTS
COULD BE HIGHER EARLY IN THE MORNING BUT THE LIKELIHOOD OF THAT IS
NOT CLEAR AT THIS POINT SO WILL CAP GUSTS AT 35 KT OR LESS FOR
NOW. WINDS LOOK TO REMAIN SOUTHWEST INTO THE AFTERNOON...THOUGH
RFD MAY TURN MORE WESTERLY...AND SPEEDS SHOULD GRADUALLY EASE MID/LATE
AFTERNOON.

MDB

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

* HIGH CONFIDENCE IN WIND TRENDS THROUGH THE EVENING. MEDIUM
  CONFIDENCE IN TIMING OF A SHIFT TO SOUTHERLY WINDS.

* MEDIUM CONFIDENCE THAT SHRA COVERAGE WILL BE ISOLD-SCT THROUGH
  THE AFTERNOON WITH LESSER COVERAGE THIS EVENING. MEDIUM-HIGH
  CONFIDENCE IN SHRA-TSRA OCCURRING LATE TONIGHT.

* HIGH CONFIDENCE IN WIND GUSTS REACHING 30KT AND MEDIUM-HIGH
  CONFIDENCE IN 35KT MONDAY MORNING. MEDIUM-HIGH CONFIDENCE IN
  SOUTH DIRECTION TURNING SOUTHWEST MID MORNING WHILE SPEEDS
  REMAIN STRONG. MEDIUM CONFIDENCE IN SPEEDS EASING MID-LATE
  MONDAY AFTERNOON.

MDB

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

MONDAY NIGHT...CHANCE OF SHRA/TSRA. MVFR POSSIBLE. GUSTY
SOUTHWEST WINDS.

TUESDAY...SHRA LIKELY/CHANCE TSRA. GUSTY SOUTHWEST WINDS.

WEDNESDAY...CHANCE OF SHRA/TSRA EARLY. WEST WINDS TURNING EAST.

THURSDAY...CHANCE SHRA/SLIGHT CHANCE TSRA. SOUTHEAST WINDS.

FRIDAY...CHANCE SHRA/SLIGHT CHANCE TSRA. SOUTHWEST WINDS.

SATURDAY...CHANCE SHRA. EAST WINDS.

KREIN

&&

.MARINE...
244 AM CDT

WARM/MOIST AIR WILL BE STEADILY LIFTING NORTH OVER THE
LAKE LATER TODAY AND CONTINUE THROUGH EARLY NEXT WEEK. THIS WILL
LIKELY ALLOW AREAS OF FOG TO DEVELOP...AND COULD BECOME DENSE AT
TIMES.

THE GRADIENT QUICKLY INCREASES LATE TONIGHT FROM THE
SOUTHWEST/SOUTH...WITH GUSTS NEARING 25-30KT FOR THE NEARSHORE
WATERS OF IL/IN THROUGH MON NIGHT. AS A RESULT HAVE HOISTED A SMALL
CRAFT ADVISORY FOR MON/MON NIGHT. WITH GUIDANCE TRENDING UP ON
GUSTS...IT IS POSSIBLE WE MAY SEE A GALE FORCE GUSTS OR TWO OCCUR
MON AFTERNOON IN THE IL/IN NEARSHORE WATERS. THEN ANOTHER WAVE WILL
LIFT NORTH TUE AND COULD BRING GUSTY WINDS YET AGAIN TO THE
NEARSHORE WATERS. EXPECT THE GUSTS NOT TO PUSH OUT FAR OVER THE OPEN
WATERS AS THE WATER REMAINS MUCH COLDER...WHICH WILL LIKELY ALLOW A
STABLE MARINE LAYER TO DEVELOP AND LIMIT HOW MUCH MIXING CAN OCCUR
FROM THE WINDS ALOFT TO THE SFC. IN ADDITION THIS WILL LIKELY LIMIT
HOW LARGE THE WATERS WILL BUILD.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM MONDAY TO 4 AM TUESDAY.

&&

$$

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