Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 271958
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
258 PM CDT WED MAY 27 2015

.SHORT TERM...
304 AM CDT

THROUGH WEDNESDAY NIGHT...

FOR THE REMAINDER OF THE OVERNIGHT HOURS...LATEST RADAR IMAGERY
INDICATES SCT SHRA LIFTING THROUGH CNTRL IL ASSOCIATED WITH A
SHORTWAVE RIPPLING THROUGH FAST SWLY FLOW ALOFT ON THE SERN
PERIPHERY OF A LONG WAVE TROUGH MOVING THROUGH THE WESTERN GREAT
LAKES REGION.  TRAJECTORIES OF THE PCPN ASSOCIATED WITH THE SRN
SHORTWAVE SUGGEST THAT THE PCPN WILL REMAIN SOUTH OF THE CWA THROUGH
THE REMAINDER OF THE OVERNIGHT HOURS...BUT THERE IS STILL A CHANCE
FOR A FEW ROGUE SHOWERS TO CLIP THE FAR SRN PORTIONS OF THE CWA.
PCPN ASSOCIATED WITH THE MAIN LONGWAVE TROUGH TO THE NORTH WILL ALSO
REMAIN NORTH OF THE CWA...IN WISCONSIN.  OTHERWISE...THE ONLY SGFNT
WX EXPECTED FOR THE REMAINDER OF THE NIGHT WILL BE BREEZY SWLY WINDS
AND INCREASING LOWER LEVEL CLOUD COVER IN THE WARM...MOIST ADVECTIVE
PATTERN AHEAD OF THE UPPER TROUGH AND ASSOCIATED SFC COLD FRONT.

AS THE UPPER TROUGH LIFTS NEWD THROUGH THE DAY TODAY...THE
ASSOCIATED SFC LOW AND COLD FRONT WILL ALSO TRACK EWD...WITH THE
COLD FRONT CROSSING THE CWA THROUGH THE DAY.  THE COLD FRONT IS A
FAIRLY DIFFUSE BOUNDARY AND ONLY EXPECT A GRADUAL WIND SHIFT TO WLY
AND A SLIGHT CHANCE FOR SOME SHOWERS.  BY LATE AFTERNOON...SFC HIGH
PRESSURE WILL BUILD ACROSS THE REGION...WITH THE SFC RIDGE AXIS
EXTENDING FROM THE SERN CONUS...THROUGH THE UPPER MISSISSIPPI
VALLEY.  WITH CLOUD COVER EXPECTED TO DIMINISH THROUGH THE AFTERNOON
AND A LACK OF ANY SIGNIFICANT COLD ADVECTION FOLLOWING THE
FROPA...STILL EXPECT THAT TEMPS SHOULD REBOUND INTO THE MIDDLE TO
UPPER 70S...WITH THE PONTIAC METRO AREA POSSIBLY HITTING 80F.  A
WEAKENING PRESSURE GRADIENT AND DIFFERENTIAL HEATING BETWEEN WARMER
LAND AND RELATIVELY COOLER LAKE MICHIGAN WATER COULD SET UP A LAKE
BREEZE LATE THIS AFTERNOON.  HOWEVER...CONFIDENCE IS LOW IN THE LAKE
BREEZE FORMATION SINCE LOW LEVEL WINDS SHOULD BE WLY AND IN EXCESS
OF 10KT WELL INTO THE AFTERNOON.  WHILE THE LATEST HIGH RES MODEL
GUIDANCE SUGGESTS THAT SFC WINDS SHOULD DROP OFF TO 5KT OR LESS BY
ARND 21-22Z...MODEL SOUNDING INDICATE THAT WINDS FROM 925MB-850 MB
SHOULD BE 10-15KT.  MODEL SOUNDINGS ALSO SUGGEST THAT THE BOUNDARY
LAYER COULD REMAIN WELL MIXED INTO THE LATE AFTERNOON...KEEPING SFC
WINDS MORE WLY AND NOT DROPPING BLW 10 KT.  SO...SOME INDICATORS
SUGGEST THAT A LAKE BREEZE IS POSSIBLE WHILE OTHERS WOULD SUGGEST
THAT A LAKE BREEZE IS LESS LIKELY.  SO...WILL GO WITH FORECAST
DETAILS INDICATIVE OF NO LAKE BREEZE...WITH TEMPS IN THE MIDDLE 70S
UP TO THE LAKEFRONT...AND EVEN IF A LAKE BREEZE DOES FORM AND PUSH
INLAND...IT WOULD LIKELY BE AFTER THE TIME OF MAX HEATING.  THE ONLY
REAL IMPACT WOULD BE THAT TEMPS ALONG THE COOK/LAKE COUNTY SHORE
WOULD COOL OFF QUICKER THAN THE REMAINDER OF THE AREA.

FOR TONIGHT...CONDITIONS SHOULD BE QUIET ACROSS THE REGION AS WEAK
RIDGING ALOFT MOVES ACROSS THE AREA...BRINGING MOSTLY CLEAR
SKIES...LIGHT SLY WINDS AND OVERNIGHT LOW TEMPS IN THE UPPER 50S TO
AROUND 60F.  FOLLOWING THE FRONTAL PASSAGE EARLIER IN THE
DAY...DRIER AIR SHOULD OVERSPREAD THE AREA...WITH DEWPOINTS DROPPING
FROM THE LOWER 60S THIS MORNING TO THE MIDDLE 50S OVERNIGHT TONIGHT.

KREIN

&&

.LONG TERM...
226 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

THURSDAY...
THUR CONTINUES TO SHAPE UP TO BE A DRY DAY...WITH THE MID-LVL FLOW
REMAINING RELATIVELY PROGRESSIVE AND EJECTING THE TROUGH AXIS TO THE
EAST BY EARLY THUR MORNING. WEAK SFC RIDGING WILL QUICKLY ARRIVE
EARLY THUR...UNFORTUNATELY THE SEMI-ZONAL FLOW WILL NOT ALLOW THIS
FEATURE TO LINGER. BY THUR AFTN SFC FLOW WILL BE TURNING
SOUTHERLY...AS THE MOIST CHANNEL POSITIONED ACROSS THE CENTRAL CONUS
BEGINS TO NUDGE EAST.

HEIGHTS BEGIN TO FALL LATE THUR NGT...AS A LOBE OF MID-LVL VORTICITY
PUSHES EAST OF THE ROCKIES. THIS WILL ALLOW A SFC LOW TO DEVELOP AND
RIDE NORTHEAST ALONG THE SLOW MOVING FRONTAL BOUNDARY. DOWNSTREAM
RIDGING CENTERED OVER THE SOUTHEAST CONUS WILL SEND RETURN FLOW
MOISTURE NORTH THROUGH THE OZARKS INTO THE MID-MISSOURI VALLEY LATE
THUR. THIS WILL LIKELY BRING CLOUDS AND PRECIP CHANCES BACK TO THE
WESTERN CWFA BY LATE THUR NGT.

PRIOR TO CLOUDS AND PRECIP RETURNING...TEMPS SHUD EASILY WARM INTO
THE LOW 80S FOR MUCH OF THE FORECAST AREA. THE GRADIENT MAY BE WEAK
ENOUGH TO ALLOW AN ONSHORE FLOW TO DEVELOP FOR FAR NORTHEAST IL
PRIOR TO THE SOUTHERLY WINDS RETURNING IN THE AFTN HOURS. SO TEMPS
ACROSS FAR NORTHEAST IL MAY BE SEVERAL DEGREES COOLER IF THE ONSHORE
FLOW IS MORE PRONOUNCED AND DEVELOPS EARLIER IN THE DAY.

CONSIDERABLE SOLAR SHIELDING COUPLED WITH MOIST SOUTHERLY FLOW WILL
LIMIT HOW COOL TEMPS ARE OVERNIGHT INTO FRI. GENERALLY EXPECT TEMPS
TO BOTTOM OUT IN THE LOW/MID 60S WITH DEW POINTS POSSIBLY NUDGING UP
A DEGREE OR TWO FROM THE UPR 50S TO LOW 60S OVERNIGHT.
4
FRIDAY THROUGH EARLY NEXT WEEK... HIGH AMPLITUDE RIDGING CONTINUES
TO HOLD ACROSS ALASKA...WITH A SEMI-ZONAL FLOW DEVELOPING DOWNSTREAM
ACROSS THE CENTRAL CONUS AND GREAT LAKES REGION FOR THE WEEKEND INTO
EARLY NEXT WEEK. OPER SOLUTIONS CONTINUE TO PROG A ROBUST MID-LVL
VORT DROPPING SOUTH FROM CENTRAL CANADA FRI AND CLIPPING THE UPPER
MIDWEST SAT. ALONG THE LEE-SIDE OF THIS FEATURE A STRENGTHENING
FRONTAL BOUNDARY WILL BE ORIENTED FROM THE SOUTHERN PLAINS
STRETCHING NORTHEAST THROUGH THE GREAT LAKES TO ONTARIO/QUEBEC. A
SERIES OF SFC WAVES WILL RIDE ALONG THIS QUASI-STATIONARY BOUNDARY
FRI. THEN A STOUT SFC RIDGE WILL BEGIN TO DROP SOUTH FRI NGT INTO
THE NORTHERN PLAINS.

THE LARGEST CONCERN CONTINUES TO BE PRECIP FRI INTO SAT MORNING.
THIS SETUP IS IDEAL FOR THE DEVELOPMENT OF AN ATMOSPHERIC RIVER WITH
ABUNDANT LOW LEVEL MOISTURE AND EFFICIENT PRECIP PRODUCING
CONVECTION. THE BOUNDARY SHOULD SLIDE EAST WITH WINDS QUICKLY
VEERING NORTH/NORTHEAST FOR SAT AND USHERING IN MUCH COOLER AND
DRIER AIR TO THE REGION. DRIER AIR WILL PUSH PRECIP SOUTH BY MIDDAY
SAT.

CURRENT INDICATIONS ARE THAT HIGHS SAT MAY STRUGGLE TO WARM BEYOND
THE UPR 50S ACROSS NORTHEAST IL/NORTHWEST IN...WITH ONLY LOW 60S
ELSEWHERE. STRONG SFC RIDGE WILL REMAIN NORTH OF THE REGION...SO THE
PRIOR FRONTAL BOUNDARY MAY BECOME QUASI-STATIONARY FOR THE WEEKEND
ALONG THE OHIO VALLEY AND CONTINUE TO FEED PRECIP CHANCES TO THE
SOUTHERN CWFA.

BEACHLER

&&

.AVIATION...

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

* VCSH ACROSS THE TERMINALS.

* LOW CHANCE OF MVFR CEILINGS EARLY THIS AFTERNOON.

* WINDS SHIFTING EASTERLY UNDER 10KT AROUND 23Z.

MM

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

A COLD FRONT TRAVERSING THE AREA TODAY IS PROVIDING THE FOCUS FOR
THUNDERSTORMS WELL SOUTHEAST OF THE TERMINALS TODAY. SOME REMNANT
MOISTURE ASSOCIATED WITH THE FRONT WILL CONTINUE TO ALLOW SOME
ISOLATED SHOWER ACTIVITY ACROSS THE AREA. A LINE OF SHOWERS
EXITING MDW ATTM WILL CONTINUE EASTWARD AND MAY HIT GYY...BUT JUST
A VCSH MENTION IN THE TAFS AS THE LINE WORKS INTO SOME DRY AIR AND
AN UNFAVORABLE TRAJECTORY SHOULD HAVE THE LINE SKIRT NORTH.

ORD MAY STAY CLEAR OF THE VCSH...BUT PROXIMITY OF THE NEXT BATCH
FROM THE NORTH WILL KEEP THE THREAT ACTIVE. AFTER 20Z...THE POST
FRONTAL AIRMASS REALLY KICKS IN AND SCOURS OUT THE MOISTURE. THIS
WILL LEAD TO JUST SCT-SKC CONDITIONS FOR THE FOLLOWING 24 HOURS.

WINDS BECOME QUITE VARIABLE TONIGHT AS SURFACE HIGH PRESSURE
CENTERS ITSELF NEAR CHICAGO. THE LOSS OF WEST FLOW WILL ALLOW THE
LAKE TO DICTATE WIND DIRECTION...WITH MOST GUIDANCE SUGGESTING
SPEEDS OF JUST 5 KT. FOLLOWING THE OVERNIGHT HOURS...WINDS WILL BE
LIGHT FROM THE SOUTHEAST...INCREASING TO ABOUT 12KT DURING THE
DAYTIME.

MM

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

* MEDIUM CONFIDENCE IN VCSH.

* MEDIUM CONFIDENCE IN CEILINGS EARLY THIS AFTERNOON...HIGH
  CONFIDENCE FROM THIS EVENING ONWARD.

* LOW TO MEDIUM CONFIDENCE IN LAKE BREEZE DEVELOPING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

MM

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

THURSDAY NIGHT...MAINLY VFR WITH CHANCE SHRA/TSRA LATE NIGHT. EAST
WINDS.

FRIDAY...PERIODIC SHRA/TSRA. MVFR POSSIBLE. SOUTHWEST WINDS.

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

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

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

TUESDAY...VFR/WX NIL. SOUTH WINDS.

KREIN

&&

.MARINE...
225 PM CDT

GENERALLY LIGHT TO MODERATE SOUTHERLY FLOW EXPECTED THROUGH TOMORROW
NIGHT WITH SOUTHERLY WINDS INCREASING SOME FRIDAY IN ADVANCE OF
APPROACHING COLD FRONT. COLD FRONT WILL DROP DOWN THE LAKE FRIDAY
NIGHT WITH AN UNSEASONABLY STRONG CANADIAN HIGH BUILDING INTO THE
REGION IN ITS WAKE. A HEALTHY LATE SEASON SHOT OF CHILLY AIR ALONG
WITH THE TIGHT GRADIENT SHOULD SET THE STAGE FOR A PERIOD OF STRONG
FULL FETCH NORTH WINDS DOWN THE LAKE SATURDAY INTO SATURDAY NIGHT.
FORECAST SOUNDINGS SUGGEST THE MIXED LAYER WILL BE SHALLOW BUT DO
SHOW GALE FORCE WINDS WITHIN THE MIXED LAYER THAT SHOULD BE
TRANSPORTED TO THE SURFACE...ESPECIALLY CLOSE TO THE SHORE WHERE
WATER TEMPS ARE WARMER AND CONDITIONS LIKELY TO BE MORE UNSTABLE.
WHILE WIND AND GUST GRIDS DONT REFLECT THIS...THE STRONGEST WINDS
SHOULD OCCUR WITHIN ABOUT 5-8MI OF THE SHORE OVER SOUTHERN THIRD OF
THE LAKE. A LITTLE EARLY TO HOIST A GALE WATCH AT THIS POINT...BUT
CERTAINLY SOMETHING THAT MAY NEED TO BE CONSIDERED SOON.

&&

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

$$

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