Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 012346
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
646 PM CDT SUN MAY 1 2016

.UPDATE...611 PM CDT

MONITORING LOW POTENTIAL FOR AN ISOLATED STRONGER THUNDERSTORM
OVER THE NEXT COUPLE OF HOURS PRIMARILY ACROSS THE FAR SOUTHERN
TIER OF COUNTIES OF THE CWA...SOUTH OF A FAIRBURY IL TO
RENSSELAER IN LINE. IN AND AROUND SURFACE LOW JUST TO THE SOUTH OF
THE CWA IN 60 DEG DEWPOINT AIR...STEEPENING LOW LEVEL LAPSE RATES
HAVE ALLOWED FOR AN INCREASE IN SURFACE BASED INSTABILITY.
ALTHOUGH THE AXIS OF HIGHEST INSTABILITY IS JUST TO THE SOUTH OF
THE CWA...THIS HIGHER DEWPOINT AND MORE UNSTABLE AIR IS RIGHT NEAR
THE CWA LINE. LARGE SCALE ASCENT ASSOCIATED WITH UPPER LEVEL
TROUGH OVER THE REGION WILL ALLOW PRECIP TO FURTHER BLOSSOM OVER
THE COUPLE OF HOURS...WHILE EFFECTIVE BULK SHEAR IN THE AREA OF
INTEREST COULD ALSO SUPPORT AN ISOLATED MORE ROBUST STORM. EXPECT
A HIGHER THREAT OF A MORE ORGANIZED STORM TO THE SOUTH OF THE
CWA...BUT ONCE AGAIN...AN ISOLATED STRONGER STORM CLIPPING THE CWA
WITHIN THE NEXT 1-2 HOURS IS NOT OUT OF THE QUESTION.

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 AJACENT 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 00Z TAFS...

CONCERNS FOR THE 0Z TAFS

- DEVELOPING SHOWERS WITH EMBEDDED TSRA IN THE FIRST FEW HOURS OF
THE TAF CYCLE
- CIGS LOWERING BACK TO LIFR IN THE SHOWERS WITH ISOLATED IFR VSBY
- TIMING THE LIFTING OF CIGS LATE TONIGHT INTO MONDAY
- CONTINUED ENE WINDS GREATER THAN 10 KT

SHOWERS AND EMBEDDED THUNDERSTORMS WILL INCREASE IN COVERAGE IN
RESPONSE TO THE UPPER LEVEL LOW MOVING THROUGH NORTHERN ILLINOIS
IN THE COMING HOURS. CHANGES IN THIS TAF CYCLE WERE TO INCLUDE
VCTS FOR THE CHICAGOLAND TERMINALS. RAP ELEVATED INSTABILITY AXIS
WILL SLIDE RIGHT THROUGH THE AREA BETWEN NOW AND 3Z. SINCE
INSTABILTY LEVELS ARE LOW HAVE JUST GONE VCTS AS COVERAGE AT THIS
POINT DOES NOT APPEAR TO BE WIDESPREAD.

CIGS ARE HOLDING GENERALLY AT OR ABOVE 1000 FT. AS RAIN FALLS INTO
THE MOIST LOW LAYERS EXPECT THAT CIGS WILL TREND TOWARD IFR.
CONFIDENCE IS NOT SUPER HIGH EXACTLY WHEN CIGS WILL FALL BELOW THE
800 FT THRESHOLD OF CONCERN FOR ORD ON THE CURRENT EAST FLOW
PLAYBOOK GIVEN THAT SHOWERS AND STORMS WILL FORM OVERHEAD BUT
LATEST TRENDS FROM THE LAMP/RAP/HRRR SUGGEST THE MAIN WINDOW WILL
BE BETWEEN 2Z-6Z...STARTING AS EARLY AS 1Z.

SHOWERS AND STORMS WILL EXIT EAST AFTER 4Z...THOUGH CIGS APPEAR TO
HOLD AT LIFR FOR A FEW MORE HOURS BEFORE A LIFTING TREND SHOULD
OCCUR. MOST GUIDANCE LIFTS CIGS ABOVE IFR LEVELS FOR THE MONDAY
MORNING RUSH...THOUGH CONFIDENCE ON SPECIFIC TRANSITION TIMES
LATER TONIGHT INTO MONDAY ARE NOT SUPER HIGH. OTHERWISE MONDAY
SHOULD BE A BETTER DAY WITH CIGS LIFTING THROUGH MVFR TO
VFR...THOUGH EAST-NORTHEAST WINDS WILL CONTINUE AT OR ABOVE 10 KT
MOST OF THE DAY.

KMD

&&

.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 DIMINSH 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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