Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 020848
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
348 AM CDT MON MAY 2 2016

.SHORT TERM...
348 AM CDT

TODAY THROUGH WEDNESDAY NIGHT...

SOMEWHAT UNSETTLED WEATHER PATTERN WILL CONTINUE ACROSS THE AREA
THROUGH MID-WEEK...AS A LONG WAVE UPPER TROUGH EVOLVES ACROSS
EASTERN NORTH AMERICA. MOSTLY CLOUDY...COOL AND OCCASIONALLY
SHOWERY CONDITIONS WILL PLAGUE THE REGION TODAY AND AGAIN
WEDNESDAY... INTERRUPTED BRIEFLY TUESDAY AS WARMER WESTERLY FLOW
DEVELOPS IN ADVANCE OF STRONG DIGGING SHORT WAVE AND SURFACE COLD
FRONT RESPONSIBLE FOR CARVING OUT THE AFOREMENTIONED LARGE SCALE
EASTERN TROUGH.

IN THE NEAR TERM...MID-LEVEL WAVE AND ASSOCIATED SURFACE LOW
WHICH PROVIDED OUR RAINY WEEKEND WERE MOVING OFF TO THE EAST OF
THE AREA EARLY THIS MORNING...WITH ONLY A FEW SPRINKLES AND PATCHY
DRIZZLE LINGERING MAINLY ACROSS OUR NORTHWEST INDIANA COUNTIES AS
OF 3 AM. LOW LEVEL WINDS BACKING MORE NORTHERLY THIS MORNING WILL
BRING MODEST DRYING WHICH SHOULD SHUT OFF ANY LINGERING LIGHT
PRECIP...AND THIN OUT SOME OF THE EXTENSIVE CLOUD COVER ESPECIALLY
OVER FAR NORTHERN IL. SIGNIFICANT CLEARING IS NOT EXPECTED
HOWEVER...AS ANOTHER STRONG MID-LEVEL WAVE DROPPING SOUTHEAST INTO
THE DAKOTAS EARLY THIS MORNING APPROACHES THE AREA THIS AFTERNOON.
ASSOCIATED HEIGHT FALLS AND COOLING MID-LEVEL TEMPS SHOULD SUPPORT
STRATOCU DEVELOPMENT AND MAY SUPPORT A FEW SPRINKLES MAINLY
WEST/NORTHWEST OF THE CWA BY AFTERNOON. HIGH-RES GUIDANCE ALSO
CONTINUES TO DEPICT SOME LIGHT QPF ACROSS OUR FAR SOUTHEAST
COUNTIES WHERE LOW LEVEL MOISTURE WILL LINGER INTO TONIGHT IN THE
VICINITY OF WEAK SURFACE TROUGH LEFT BEHIND DEPARTING LOW
PRESSURE. NORTHEAST WINDS OFF OF THE LAKE COMBINED WITH
CONSIDERABLE CLOUD COVER AND RELATIVELY COOL TEMPS ALOFT WILL
LIMIT HIGH TEMPS TO THE 50S IN MOST AREAS TODAY...WITH UPPER 40S
LIKELY ALONG THE IMMEDIATE LAKE MICHIGAN SHORE. FAR NORTHWEST
COUNTIES MAY TAG 60 BRIEFLY WELL INLAND OF MAIN LAKE COOLING PUSH
AND WHERE SOME PEAKS OF SUN MAY BE POSSIBLE AT TIMES.

NORTHERN PLAINS SHORT WAVE PUSHES SOUTHEAST ACROSS THE AREA
OVERNIGHT AND THEN DRIFTS OFF TO OUR SOUTHEAST ON TUESDAY...WITH A
BRIEF PERIOD OF SUBSIDENCE AND A WEAK SURFACE HIGH PRESSURE RIDGE
OVER THE AREA DURING THE DAY. LOW LEVEL WINDS WILL BACK TO THE
WEST AS THIS RIDGE MOVES OFF TO THE SOUTHEAST IN THE
AFTERNOON...AND IN RESPONSE TO LOW PRESSURE DEVELOPING OVER THE
NORTHERN LAKES IN ASSOCIATION WITH ANOTHER DEEP UPPER LOW DIGGING
SOUTHEAST ACROSS THE REGION. THE GOOD NEWS IS THAT WE BRIEFLY WARM
UP TUESDAY AHEAD OF THIS NEXT SYSTEM... WITH HIGHS IN THE MID-
UPPER 60S EXPECTED. WEST WINDS AHEAD OF THE APPROACHING COLD FRONT
SHOULD LIMIT ANY LAKE COOLING PRIMARILY TO THE SOUTH SHORE OF THE
LAKE IN LAKE/PORTER COUNTIES. RAIN CHANCES RAMP UP QUICKLY AGAIN
TUESDAY EVENING AS THE STRONG MID-LEVEL WAVE AND SURFACE COLD
FRONT APPROACH. GIVEN CONSISTENT SIGNAL IN MODEL RUNS HAVE GONE
WITH LIKELY POPS TUESDAY NIGHT ESPECIALLY ACROSS THE EASTERN HALF
OR SO OF THE CWA...AND INCLUDED SLGT CHANCE MENTION OF THUNDER
GIVEN COOL TEMPS ALOFT WITHIN THE UPPER TROUGH. THE COLD FRONT
CLEARS THE AREA BY WEDNESDAY MORNING...THOUGH PRECIP WILL LIKELY
LINGER DURING THE DAY AS INSTABILITY SHOWERS DEVELOP BY AFTERNOON.
RENEWED PUSH OF COOLER AIR ON BLUSTERY NORTH WINDS WILL LIMIT
TEMPS ONCE AGAIN. HIGHS WEDNESDAY MAY NOT GET OUT OF THE 40S ALONG
THE INDIANA IMMEDIATE LAKE SHORE...THOUGH INLAND PARTS OF NORTHERN
IL MAY REACH 60. PRECIP THREAT DWINDLES WEDNESDAY NIGHT WITH
DIURNAL STABILIZATION. DECREASING WINDS AND CLEARING SKIES LOOK TO
PRODUCE A CHILLY NIGHT FOR EARLY MAY...WITH LOWS DIPPING INTO THE
UPPER 30S IN SOME SPOTS.

RATZER

&&

.LONG TERM...
203 PM CDT

MONDAY NIGHT THROUGH SUNDAY...

MONDAY NIGHT THROUGH TUESDAY...
ELONGATED MID-LVL TROUGH WILL FINALLY DEPART THE REGION LATE MON
NIGHT...HEADED FOR THE EASTERN GREAT LAKES. THIS WILL ALLOW A BROAD
SFC RIDGE TO SLIDE SOUTH FROM ONTARIO ACROSS THE WESTERN GREAT LAKES
AND ALSO STEADILY ERODE CLOUD COVER/PRECIP...HOWEVER THE FAR
SOUTHERN CWFA COULD SEE AN ISOLATED SHOWER EARLY MON EVE BEFORE
QUICKLY ENDING. WINDS WILL BE TURNING NORTHERLY BUT WITH THE WEAK
GRADIENT SPEEDS WILL NOT BE VERY HIGH...SO EXPECT THE EROSION OF
CLOUD COVER TO BE SLOW. TEMPS WILL FALL INTO THE LOW/MID 40S...BUT A
FEW AREAS IN FAR NORTHERN IL COULD DIP INTO THE UPPER 30S. THERE
DOES APPEAR TO BE ENOUGH MIXING TO PREVENT FROST FROM FORMING...SO
WILL HOLD OFF AT THIS TIME FROM INCLUDING ANY MENTION OF FROST MON
NGT.

TUE WILL BE HEAVILY INFLUENCED BY THE BROAD SFC RIDGE CENTERED OVER
THE CENTRAL ROCKIES THAT WILL EXTEND EAST THROUGH THE MID-MISSOURI
VALLEY...HOWEVER GUIDANCE IS INDICATING THAT WITH THE HIGH AMPLITUDE
MID-LVL RIDGE LIFTING INTO WESTERN CANADA A LOBE OF VORTICITY WILL
DRIVE SOUTH ACROSS LAKE SUPERIOR TUE AFTN. THIS SHORTWAVE WILL BE
ASSOCIATED WITH A DEVELOPING TROUGH THAT WILL SLIDE SOUTH OVER THE
WESTERN GREAT LAKES LATE TUE NGT...WITH MOISTURE POOLING ALONG THE
FRONTAL BOUNDARY AS IT SLIDES SOUTH LATE TUE. LAPSE RATES WILL
QUICKLY STEEPEN AS THE 850MB THERMAL GRADIENT DEVELOPS AND SFC TEMPS
TUE AFTN WILL WARM INTO THE 60S. EXPECT INSTABILITY TO REMAIN
MARGINAL...HOWEVER ENOUGH FORCING WILL BE PRESENT THAT A SLIGHT
CHANCE FOR THUNDER COULD OCCUR LATE TUE/EARLY WED. HAVE PUSHED POPS
UP TO LIKELY TUE EVE THROUGH THE OVERNIGHT HOURS.

FORTUNATELY ENSEMBLES AND OPERATIONAL SOLUTIONS CONTINUE TO BE
PROGRESSIVE AND PUSH THE HIGH AMPLITUDE RIDGE FURTHER EAST BY EARLY
WED...WHICH SHOULD HELP EJECT THE TROUGH AXIS EAST OVER LOWER
MICHIGAN WED MORNING AND BRING A RETURN TO DRY WEATHER FOR THE
FORECAST AREA BY WED EVE...WITH THE POTENTIAL THAT DRIER AIR COULD
ARRIVE BY EARLY WED AFTN. BUT WITH THE NORTHERLY FLOW TEMPS WILL
STRUGGLE TO WARM BEYOND THE 50S...AND AREAS ADJACENT TO LAKE
MICHIGAN WILL REMAIN IN THE UPPER 40S WED AFTN. WED NGT ANTI-
CYCLONIC FLOW ARRIVES WITH A WEAKENING PRESSURE GRADIENT AND MUCH
COLDER TEMPS...FALLING INTO THE MID/UPR 30S. AT THIS TIME HAVE
HELD OFF ON MENTION OF FROST BUT IF CLOUDS ERODE QUICKER WED EVE
THEN THE DEVELOPMENT OF FROST IS PLAUSIBLE FOR AREAS AWAY FROM
LAKE MICHIGAN AND NORTH OF I-80.

THURSDAY THROUGH SUNDAY... LATEST ENSEMBLES CONTINUE TO BE IN GOOD
AGREEMENT WITH THE HIGH AMPLITUDE RIDGE SLIDING EAST ACROSS THE
CENTRAL PLAINS AND GREAT LAKES THURSDAY INTO FRIDAY. AS THIS FEATURE
SLIDES EAST...THE RIDGE WILL BEGIN TO WEAKEN WITH THE FOCUS TURNING
TOWARDS THE MID-LVL TROUGH PROGGED TO SLIDE INTO THE SOUTHWEST CONUS
SAT/SUN. SIMULTANEOUSLY A SHORTWAVE IS EXPECTED TO SLIDE EAST ACROSS
ONTARIO...AND COULD LAYOUT A BOUNDARY OVER THE GREAT LAKES REGION
FOR THE WEEKEND WHICH COULD BECOME A FOCAL POINT FOR
SHOWERS/THUNDERSTORMS LATER IN THE WEEKEND.

TEMPS THROUGHOUT THE EXTENDED PERIODS WILL QUICKLY MODERATE FROM THE
60S TO PERHAPS LOW 70S FRIDAY AND SATURDAY...THEN DEPENDING ON A
FRONTAL BOUNDARY PLACEMENT SUN COULD SEE TEMPS BACK IN THE 60S.

BEACHLER

&&

.AVIATION...
FOR THE 06Z TAFS...

AN UPPER LOW IS OVER SOUTHERN MICHIGAN LATE THIS EVENING AND WILL
CONTINUE TO MOVE AWAY FROM THE REGION WITH A FEW LINGERING LIGHT
SHOWERS OR DRIZZLE IN PLACE FOR ANOTHER HOUR OR SO...THEN DRY
CONDITIONS EXPECTED THROUGH THE REMAINDER OF THE TAF PERIOD. MAIN
FORECAST CHALLENGE WILL BE CIGS OVERNIGHT INTO MONDAY. GUIDANCE IS
ALL OVER THE PLACE WITH TRENDS...SOME SUGGESTING IMPROVEMENT WHILE
OTHERS SUGGEST DETERIORATING CONDITIONS OVERNIGHT. LIKEWISE...
REGIONAL OBS OVER THE LAST FEW HOURS HAVE ALSO REVEALED MIXED
TRENDS. WITH LOW CONFIDENCE IN THE FORECAST...OPTED TO NOT MAKE
ANY SIGNIFICANT CHANGES WITH THE LATEST TAF. THINKING THERE WILL
BE MODEST IMPROVEMENT BACK TO LOW END MVFR AT SOME POINT
OVERNIGHT...THEN CONDITIONS RETURN TO VFR MONDAY MORNING. IF
ANYTHING...MAY OPT TO EXTEND THE MVFR CONDITIONS LATER INTO THE
DAY MONDAY...BUT WILL WAIT UNTIL THE 09Z TAFS TO MAKE THAT
DECISION. NORTHEAST WINDS WILL PREVAIL THROUGH THE OVERNIGHT HOURS
AND THROUGH MOST OF THE DAY MONDAY...THEN APPROACHING HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH MONDAY EVENING WITH WIND
DIRECTION BACKING TO THE NORTH/NORTHWEST OR BECOMING VARIABLE IN
SOME LOCATIONS.

BMD

&&

.MARINE...
300 AM CDT

LOW PRESSURE IS DEPARTING THE REGION EARLY THIS MORNING WITH SOME
LINGERING 15 TO 20 KT WINDS STILL IN PLACE ACROSS SOUTHERN LAKE
MICHIGAN...BUT PROGGED TO CONTINUE TO DIMINISH THROUGH THE
MORNING. HIGH PRESSURE WILL BUILD ACROSS LAKE MICHIGAN THIS
EVENING AND TONIGHT...THEN SOUTHWESTERLY FLOW WILL DEVELOP ON
TUESDAY AS LOW PRESSURE MOVES ACROSS ONTARIO. THE LOW WILL MOVE
SOUTHEAST TO THE EASTERN GREAT LAKES REGION BY WEDNESDAY...BUT A
TRAILING COLD FRONT IS PROGGED TO MOVE SOUTH ACROSS LAKE MICHIGAN
TUESDAY NIGHT. NORTH WINDS GUSTING TO 30 KT ARE EXPECTED TO
DEVELOP BEHIND THE FRONT LATE TUESDAY NIGHT AND CONTINUE THROUGH
THE DAY WEDNESDAY. WINDS SHOULD BEGIN TO DIMINISH THURSDAY AS
ANOTHER RIDGE APPROACHES THE REGION.

BMD

&&

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

$$

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