Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 242039
AFDLOT

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

.SHORT TERM...
209 PM CDT

THROUGH TONIGHT...

VERY SHARP WARM FRONT HAS BEEN GRADUALLY LIFTING NORTHWARD THROUGH
THE AFTERNOON HOURS. TEMPERATURES HAVE SOARED INTO THE 80S BEHIND
THE FRONT...WITH MUGGY MID 60S DEWPOINTS AS WELL. MEANWHILE FAR
NORTHERN ILLINOIS IS HOLDING ONTO THE 70S WITH TEMPS HOLDING AROUND
60 AT THE LAKE WITH ONSHORE WINDS.  ALOFT... A DEEP AND CLOSED UPPER
LOW IS SPINNING OVER NORTHERN COLORADO. A NEGATIVELY TILTED TROUGH
AXIS OUT AHEAD OF THE LOW INTO NORTHERN TEXAS WITH A MODESTLY STRONG
SHORTWAVE ALONG AND AHEAD OF IT. SHOWERS AND THUNDERSTORMS CONTINUE
AHEAD OF THIS FEATURE. CLOSER TO HOME...UPPER LEVEL RIDGING IS IN
PLACE ACROSS THE EASTERN HALF OF THE AREA...AND NO NOTABLE
SHORTWAVES OTHER THAN SOME WEAKER WAVES ARE FOUND IN SW FLOW ALOFT
ACROSS FAR WESTERN ILLINOIS. MORE ORGANIZED SHOWER ACTIVITY FROM
I-39 WESTWARD ASSOCIATED WITH THIS...BUT MUCH OF THE AREA REMAINS
IN BROAD AND MOIST SW FLOW. THEREFORE SCATTERED SHOWERS CONTINUE
TO FESTER FARTHER EASTWARD THOUGH THE ARE STRUGGLING A BIT MORE IN
THE LESS FAVORABLE ENVIRONMENT.

EXPECT AS THE AFTERNOON CONTINUES THAT SHOWERS REMAIN LIKELY IN OUR
WESTERN AREAS...WHILE MUCH OF ILLINOIS WILL BE SUSCEPTIBLE TO
SCATTERED SHOWERS THROUGH THE AFTERNOON PERIOD AS WELL. THE SHOWERS
PUT DOWN NEARLY TWO TENTHS OF AN INCH IN AN HOUR AT PEORIA...AND
WITH PW VALUES ON THE RISE...SOME BRIEF DOWNPOURS REMAIN POSSIBLE.
INSTABILITY IS MODEST AND FOCUSED ALONG AND WELL SOUTH OF I-80 WHERE
AN ISOLATED MENTION HAS BEEN HELD...BUT WE DO HAVE SOME STRIKES IN
LASALLE COUNTY AS OF THIS WRITING.

LOOKING FARTHER DOWNSTATE BEHIND THIS BATCH OF SHOWERS CUMULUS FIELD
IS FAIRLY TEMPERED WITH MORE AGITATED CLOUDS IN MISSOURI...AND MORE
SO FARTHER SOUTH IN THE ARKLATEX REGION. HAVE TRIED TO SHOW SOMEWHAT
OF A DOWNWARD TREND IN CHANCES FOR PRECIPITATION ACROSS NE ILLINOIS
TONIGHT IN BETWEEN THE CURRENT ACTIVITY BEFORE THE TROUGH AXIS
BEGINS PIVOTING NORTHWARD. MOIST ISENTROPIC LIFT REMAINS A BIT MORE
ROBUST ALONG AND WEST OF I-39 WHERE OCCASIONAL SHOWERS WILL CONTINUE
EVEN THIS EVENING AND HELD ONTO LIKELY POPS LONGER IN THESE AREAS.

OVERNIGHT IS WHEN THINGS WILL RAMP UP ACROSS OUR LOCAL AREA. THE
NEGATIVELY TILTED TROUGH AXIS GETS SHUNTED NORTHEASTWARD ON A
POTENT MID/UPPER LEVEL JET. LOW LEVEL MOISTURE ADVECTION INCREASES
WHICH WILL BRING THE MOST ORGANIZED PERIOD OF SHOWERS AND
ISOLATED/SCATTERED THUNDERSTORMS ACROSS THE AREA...AFTER MIDNIGHT
AND INTO THE MORNING OF MEMORIAL DAY. WITH A VERY STRONG LOW LEVEL
WIND FIELD AND AND CLOSED SURFACE LOW PASSING ACROSS EASTERN
IOWA...SOUTHERLY WINDS WILL BE RAMPING UP CONSIDERABLY LATE
TONIGHT INTO MEMORIAL DAY MORNING.

MORE ON THE WINDS TOMORROW AND THE LONG TERM DISCUSSION SOON...

KMD

&&

.LONG TERM...
302 PM CDT

MONDAY THROUGH SUNDAY...

SCATTERED SHOWERS AND STORMS WILL LIKELY START THE MEMORIAL DAY
HOLIDAY BUT SHOULD BE MOVING QUICKLY NORTHEAST IN TANDEM WITH
DEEPENING LOW PRESSURE ADVANCING FROM NORTHEAST IA EARLY IN THE
MORNING TO NORTHERN WI BY MIDDAY. SHOWERS SHOULD END FROM SOUTHWEST
TO NORTHEAST BETWEEN 8 AM AND 11 AM FOR MOST LOCATIONS. THE BIGGER
STORY ON THE HOLIDAY WILL BE THE GUSTY WINDS ASSOCIATED WITH THIS
LOW...AS WELL AS WARMTH...WITH SOME LOCATIONS POSSIBLY REACHING
UPPER 80S.

THE SYNOPTIC SETUP IS IN PLACE FOR A THREE-FOUR HOUR PERIOD OF
STRONG WINDS MONDAY MORNING...WITH GLOBAL AND HIGH-RES MODELS
INDICATING 1.) SYSTEM DRY SLOT NOSE ADVANCING OVER THE
AREA...2.)STRONG SURFACE PRESSURE FALL/RISE COUPLET QUICKLY MOVING
THROUGH IN THE MORNING...AND 3.) STEEP LOW/LEVEL LAPSE RATES AND Q-
VECTOR DIVERGENCE INDICATING A PORTION OF THE LOW-LEVEL JET WINDS
WILL BE MIXED DOWN IN GUSTS. THE STRONGEST SOUTHWEST WINDS GUSTING
TO 40 TO 45 MPH WITH A POSSIBLE 1-2 HOUR TIME OF 50+ MPH GUSTS LOOK
TO BE BETWEEN 9 AM AND 2 PM. THIS IS IN THE IMMEDIATE WAKE OF THE
SHOWERS...THOUGH SOME OF THE LAST SHOWERS/STORMS COULD TAP SOME
OF THESE HIGHER WINDS WITH ISOLATED STRONG GUSTS BEFORE ENDING.
RIGHT NOW THE WIND FORECAST IS A LITTLE BELOW WIND ADVISORY
CRITERIA...BUT EVENING AND OVERNIGHT SHIFTS WILL HAVE TO CONSIDER
THIS POSSIBILITY LOOKING AT FURTHER GUIDANCE REGARDING MAGNITUDE AND
DURATION OF THESE WINDS...AS WELL AS TAKING INTO ACCOUNT THE HOLIDAY
AND AMOUNT OF OUTDOOR ACTIVITIES/PARADES.

THESE WINDS WILL TRANSPORT A STRONG THERMAL RIDGE INTO THE AREA.
SUBSIDENCE WITHIN THE DRY SLOT WILL LIKELY AID IN SCATTERING CLOUDS
BY EARLY AFTERNOON. SO SUN SHOULD FURTHER HEATING ON TOP OF THE LOW-
LEVEL WARM ADVECTION. GIVEN A MILD LOW TONIGHT...EXPECTING HIGHS TO
EASILY BE ABLE TO GET INTO THE 80S AREAWIDE. WITH SOME CENTRAL IL
LOCATIONS KNOCKING ON THE DOOR OF UPPER 80S TODAY...COULD ENVISION
THESE TYPE OF READINGS AND EVEN A 90 OR TWO SPREADING OVER
MUCH OF NORTHERN IL AND NORTHWEST IN ON MEMORIAL DAY...ALTHOUGH THE
INCREASED DEW POINTS ARE EXPECTED TO LIMIT THAT UPPER THRESHOLD.

WITH A VERY BROAD LONGWAVE TROUGH ACROSS THE WESTERN AND CENTRAL
U.S. GRADUALLY DEAMPLIFYING MIDWEEK...A GENERALLY UNSETTLED WEATHER
PATTERN CONTINUES THROUGH TUESDAY AND TUESDAY NIGHT. HEIGHT FALLS
AND JUST MORE FAVORABLE JET SUPPORT FOR LIFT WILL SPREAD OVER ON
TUESDAY. A SHORT WAVE TROUGH WITH A SLIGHT NEGATIVE TILT WILL BE IN
LINE WITH THIS...AND SUPPORT FOR SHOWERS AND AT LEAST SCATTERED
STORMS IS AGREED WELL UPON IN GUIDANCE. HAVE CONTINUED THE UPWARD
TREND WITH POPS. WITH THE RAIN AROUND...TEMPERATURES ON TUESDAY
LOOK TO BE AROUND 10 DEGREES COOLER THAN MONDAY.

BEYOND...THE MAIN REFINEMENTS WERE TO TRY TO INDICATE ANY TIMES
WHERE POPS MAY NOT NEED TO BE MENTIONED. WEDNESDAY AFTERNOON
THROUGH THURSDAY...AND POSSIBLY A LITTLE LONGER...LOOK TO BE A
PERIOD OF BUILDING HEIGHTS FOR MUCH OF THE AREA AND WOULD BE THE
WINDOW WHERE CHANCES OF RAIN WOULD SEEM SMALL. THE CHANCES FOR
PRECIPITATION INCREASE IN GLOBAL ENSEMBLES AS WE ENTER NEXT
WEEKEND...WITH THE 12Z GFS PARTICULARLY WET. AT THIS TIME...WPC
DOES HAVE AROUND AN INCH IN THEIR DETERMINISTIC DAY 6-7 GUIDANCE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

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

* SCT SHRA AND POSSIBLY AN ISOLD TSRA EXPECTED INTO LATE
  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 20Z...

A NARROW CORRIDOR OF SHOWERS AND SOME ISOLD TS HAS DEVELOPED FROM
RPJ SOUTH TO NEAR PNT AND IS LIFTING NNE. TS MAY BECOME LESS
PREVALENT AS IT MOVES FURTHER NORTH BUT HAVE ADDED TEMP SHRA WITH
VSBY RESTRICTION IN DOWNPOUR TO ORD/MDW/DPA FOR A FEW HOURS.
OTHERWISE WARM FRONT CONTINUES TO LIFT NORTH AND WILL BRING A
SHIFT TO SOUTH WINDS AS IT MOVES ACROSS THE TERMINALS LATE THIS
AFTERNOON/EARLY THIS EVENING.

FROM 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 20Z...

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

* HIGH CONFIDENCE SOME SHRA AND POSSIBLY BRIEF TSRA WILL AFFECT
  THE TERMINALS INTO LATE AFTERNOON. MEDIUM-HIGH CONFIDENCE IN
  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...
330 PM CDT

A WARM FRONT WILL LIFT NORTHWARD INTO THE SOUTHERN PART OF THE
LAKE THIS EVENING...OR POSSIBLY NOT UNTIL OVERNIGHT...BUT EITHER
WAY WINDS WILL TURN SOUTHERLY DURING THE NIGHT. HIGHER DEW POINT
AIR WILL ADVECT NORTHWARD ON THESE SOUTHERLY WINDS ALLOWING FOR
POTENTIAL FOG DEVELOPMENT. AS LOW PRESSURE LIFTS NORTH THROUGH
WISCONSIN ON MEMORIAL DAY MORNING....SOUTH TO SOUTHWEST WINDS
WILL ENCOMPASS THE ENTIRE LAKE. ALSO...WIND SPEEDS WILL RAPIDLY
INCREASE IN THE ILLINOIS AND INDIANA NEARSHORE WATERS...WITH
OFFSHORE WINDS REACHING GALE CRITERIA DURING THE MORNING AND
LASTING INTO AT LEAST EARLY AFTERNOON. OVER MUCH OF THE OPEN
WATERS...STABLE AIR WILL LIKELY KEEP THE STRONGEST WINDS FROM THE
SURFACE...ALTHOUGH STILL 20 TO 30 KT WINDS ARE EXPECTED AND
LASTING INTO MONDAY NIGHT.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM MONDAY TO 9 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...9 AM
     MONDAY TO 3 PM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...3 PM MONDAY TO 4 AM TUESDAY.

&&

$$

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