Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 020546
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1246 AM CDT MON MAY 2 2016

.UPDATE...

THE MORE ROBUST THUNDERSTORM DEVELOPMENT WHICH ALLOWED MANY
REPORTS OF UP TO HALF INCH HAIL ACROSS EASTERN WILL AND SOUTHERN
COOK COUNTIES HAVE SINCE DIMINISHED WHILE SHIFTING TO THE
EAST/NORTHEAST. THIS DIMINISHING TREND LIKELY OWING TO CONVECTION
OUTRUNNING INSTABILITY AXIS AND WHILE STRONGEST FORCING CONTINUES
TO LIFT TO THE NORTH. EXPECT ANY THUNDER TO BE ACROSS NORTHWEST
INDIANA OVER THE NEXT HOUR...WITH ISOLATED PEA SIZE HAIL STILL
POSSIBLE. STEADIER RAIN WILL LIKELY BE MORE PREVALENT OVER
NORTHERN ILLINOIS AT LEAST FOR THE NEXT COUPLE OF HOURS...AS THIS
PRECIP SHIELD SLOWLY PIVOTS EAST THROUGH THE REGION.

RODRIGUEZ

&&

.SHORT TERM...
234 PM CDT

THROUGH MONDAY...

FOR THE REMAINDER OF THE AFTERNOON...MAIN ISSUE WILL BE TIMING OF
NEXT ROUND OF PCPN.  THE MAIN UPPER LOW IS STILL WELL TO THE
WEST...OVER SRN IA/NRN MO...AND LATEST SATELLITE AND RADAR IMAGERY
INDICATE SLOWER EWD PROGRESSION THAN PREVIOUSLY ANTICIPATED.
SO...WHILE STILL FEEL THAT ANOTHER ROUND OF SHRA IS LIKELY FOR THE
REGION...IT COULD HOLD OFF FOR A COUPLE MORE HOURS.  THERE ALSO
CONTINUES TO BE A SLIGHT CHANCE FOR SOME ISOLD TS OVER THE FAR
SOUTHERN PORTIONS OF THE CWA...WHERE THE ISENTROPIC LIFT JUST NORTH
OF THE SFC WARM FRONT...AND CLOSER TO THE ELEVATED BOUNDARY SHOULD
BE THE MOST CONCENTRATED.  OTHERWISE...FOR THE THIS AFTERNOON AND
TONIGHT SHOULD REMAIN CLOUDY AND UNSEASONABLY COLD AS NELY FLOW
PERSISTS OFF OF THE RELATIVELY COLD LAKE MICHIGAN WATER.
TEMPERATURES TODAY SHOULD TOP OUT IN THE MIDDLE 40S NEAR THE LAKE
MICHIGAN SHORE AND REACH INTO THE LOWER 60S OVER THE FAR SOUTHERN
PORTIONS OF THE CWA.  OVERNIGHT LOWS SHOULD REMAIN UNSEASONABLY
COOL...DROPPING INTO THE LOWER 40S TOWARD THE WISCONSIN BORDER AND
THE UPPER 40S SOUTH OF THE I-80 CORRIDOR.

THE MID-LEVEL SHORTWAVE SHOULD SLOWLY PROGRESS EWD OVERNIGHT TONIGHT
AND FINALLY PUSH TO THE ERN GREAT LAKES BY EARLY MORNING.  WEAK
SHORT WAVE RIDGING BEHIND THE WAVE SHOULD HELP SHUT OFF AND RESIDUAL
PCPN CHANCES AND BRING SOME PARTIAL CLEARING FOR THE MORNING HOURS.
A SOUTHERN STREAM SHORTWAVE LIFTING OUT OF THE SRN PLAINS WILL BRING
ANOTHER CHANCE FOR SOME SHOWERS IN THE AFTERNOON...WITH THE HIGHEST
PCPN CHANCES SOUTH OF THE I-80 CORRIDOR.  AHEAD OF THE SRN STREAM
WAVE...SOME WEAK WARM ADVECTION SHOULD ALLOW FOR SOME MODERATION OF
TEMPERATURES...THOUGH WITH WINDS STILL NELY AT THE SFC...LAKEFRONT
LOCATIONS SHOULD STILL REMAIN COOLER THAN THE REMAINDER OF THE
AREA...WITH HIGHS ALONG THE LAKEFRONT ONLY IN THE LOWER 50S...WHILE
INLAND AREAS SHOULD REACH THE UPPER 50S TO AROUND 60 DEGREES.

KREIN

&&

.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...
304 PM CDT

WINDS HAVE DIMINISHED THIS AFTERNOON TO BETWEEN 15 TO 20 KT ALONG
THE SOUTHERN HALF OF LAKE MICHIGAN...WHICH HAS ALLOWED THE NEARSHORE
WATERS ALONG THE ILLINOIS SHORE TO DIMINISH AS WELL. STILL
LOOKING AT BETWEEN 3 TO 5 FT TO PERSIST THROUGH THIS EVENING...BUT
HAVE GONE AHEAD AND ENDED THE SMALL CRAFT ADVISORY EARLY TO
ACCOUNT FOR THE DIMINISHING TREND. WITH HIGH PRESSURE POSITIONED
TO THE NORTH OVER CENTRAL CANADA AND THE NORTHERN PLAINS....A LOW
PRESSURE SYSTEM WAS LIFTING NORTHEAST ACROSS THE OHIO VALLEY AND
WILL TRY TO INCREASE THE GRADIENT LATE TONIGHT FOR THE SOUTHERN
HALF OF LAKE MICHIGAN. ALTHOUGH THE WINDS LOOK TO REMAIN GENERALLY
BETWEEN 15 TO 25 KT AT THE MOST...BUT NOT LINGER VERY LONG. WINDS
WILL THEN DIMINISH AGAIN MONDAY AFTERNOON AS BROAD SURFACE HIGH
PRESSURE CENTERED OVER THE CENTRAL PLAINS INFLUENCES THE WESTERN
GREAT LAKES WITH LIGHTER WINDS THROUGH TUESDAY MORNING.

A FRONTAL BOUNDARY WILL THEN BEGIN TO SLIDE SOUTH FROM CENTRAL
CANADA TUESDAY AFTERNOON AS A LOW PRESSURE SYSTEM SLIDES EAST
BETWEEN JAMES BAY AND LAKE SUPERIOR. THIS FRONTAL BOUNDARY WILL
SLIDE SOUTH AND INCREASE THE GRADIENT OVER LAKE MICHIGAN AND TURN
WINDS NORTHERLY LATE TUESDAY...WHICH WILL ALLOW WAVES TO BUILD.
SMALL CRAFT HAZARDS WILL LIKELY DEVELOP ESPECIALLY FOR THE ILLINOIS
AND INDIANA NEARSHORE WEDNESDAY THROUGH THURSDAY.

BEACHLER

&&

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

$$

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