Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 011904
AFDLOT

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

.UPDATE...1044 AM CDT

UNFORTUNATELY IT APPEARS MOTHER NATURE HAS OPTED TO HIT THE PAUSE
BUTTON...KEEPING MUCH OF NORTHERN ILLINOIS AND NORTHWEST INDIANA
STUCK IN A COOL/CLOUDY PATTERN. AS HAS BEEN THE CASE FOR THE PAST
FEW DAYS...CLOUDS WILL BLOCK MUCH OF THE SUN AGAIN TODAY AND KEEP
TEMPERATURES GENERALLY IN THE 50S ALONG AND SOUTH OF I-80. PERHAPS
A FEW SITES MAY TOUCH 60 DEGREES IN THE FAR SOUTHERN FORECAST
AREA. ELSEWHERE THE CONTINUED NORTHEAST/NORTH FLOW WILL KEEP THE
NORTHERN COUNTIES OF ILLINOIS IN THE UPPER 40S TO LOW 50S...AND
AREAS ADJACENT TO LAKE MICHIGAN WILL HAVE THE COOL MARINE AIR
KEEPING TEMPERATURES IN THE MIDDLE TO UPPER 40S.

AS THE UPPER LEVEL VORT MAX BEGINS TO LIFT NORTHEAST THIS
AFTERNOON FROM SOUTHERN IOWA/NORTHERN MISSOURI...A WEAKER SFC LOW
WILL BE SIMULTANEOUSLY LIFTING NORTHEAST ACROSS CENTRAL IL INTO
CENTRAL IN. THIS WILL HELP TO PROVIDE A MORE FORCED ENVIRONMENT
OVER THE FORECAST AREA LATER THIS AFTERNOON THAT SHOWERS WILL ONCE
AGAIN DEVELOP...WITH A SLIGHT CHANCE FOR A FEW EMBEDDED
THUNDERSTORMS MAINLY ALONG AND SOUTH OF THE KANKAKEE VALLEY.

BEACHLER

&&

.SHORT TERM...
248 AM CDT

THROUGH TONIGHT...

A CLOUDY AND DREARY DAY IS ON TAP TODAY ACROSS NORTHERN ILLINOIS
AND NORTHWEST INDIANA. AN ELONGATED AREA OF LOW PRESSURE IS
DRAPED ACROSS CENTRAL ILLINOIS AND INDIANA WITH LOW
CLOUDS...PATCHY FOG...AND DRIZZLE IN PLACE ACROSS THE LOCAL
FORECAST AREA EARLY THIS MORNING. MEANWHILE...AN UPPER LOW OVER
NEBRASKA EARLY THIS MORNING IS PROGGED TO MOVE EAST ACROSS IOWA
THIS AFTERNOON AND INTO NORTHERN ILLINOIS THIS EVENING. SCATTERED
SHOWERS ARE EXPECTED TO REDEVELOP OUT AHEAD OF THIS LOW MAINLY
DURING THE AFTERNOON AND EVENING HOURS FOR NORTHERN ILLINOIS AND
NORTHWEST INDIANA. MODELS CONTINUE TO INDICATE MODEST ELEVATED
INSTABILITY...SO CANNOT RULE OUT AN ISOLATED THUNDERSTORM MAINLY
SOUTH OF I-80 NEAR THE SURFACE FRONT...BUT THE OVERALL LIKELIHOOD
OF THUNDER IS LOW. THE UPPER LOW WILL EXIT TO OUR EAST AROUND
MIDNIGHT OR SO WITH PRECIP CHANCES QUICKLY TAPERING THEREAFTER.
BUMPED DOWN TEMPERATURES SOME FOR TODAY AND EXPECT FAIRLY SIMILAR
CONDITIONS TO YESTERDAY WITH NO REAL CHANGE IN AIRMASS. LESS
PRECIP TODAY MIGHT HELP US WARM A LITTLE MORE BUT OVERCAST SKIES
AND MORNING FOG WILL INHIBIT INSOLATION AND MODELS HAVE BEEN TOO
WARM THE LAST COUPLE OF DAYS. THE FAR SOUTHERN TIER OF COUNTIES
WOULD HAVE THE BEST CHANCE FOR BREAKING OUT OF THE LOW CLOUDS AND
SEEING A LITTLE SUNSHINE THUS EXCEEDING TEMPERATURE PROJECTIONS
BUT LEANING AGAINST THAT SCENARIO FOR NOW.

DEUBELBEISS

&&

.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 18Z TAFS...

PRIMARY CONCERNS...

-IFR CIGS THROUGH MUCH OF THE PERIOD...POSSIBLY DROPPING TO LIFR
AGAIN OVERNIGHT.

-PERIOD OF SHRA EXPECTED LATE AFTN/EVE.

CIGS REMAINING IN IFR RANGE EARLY THIS AFERNOON...WITH LIFR CIGS
PERSISTING NEAR LAKE MICHIGAN...ESPECIALLY AFFECTING KGYY. WITH
SOME WEAK MIXING AND A LITTLE DIURNAL WARMING...VIS HAS GENERALLY
IMPROVED TO VFR OR HIGHER END MVFR LEVELS ACROSS THE AREA. EXPECT
THAT CIGS WILL GRADUALLY IMPROVE THROUGH THE AFTERNOON...LIFTING
TO HIGHER END IFR OR LOWER END MVFR. HOWEVER...SINCE THE REGION
SHOULD REMAIN UNDER PERSISTENT NELY FLOW AND WELL NORTH OF A SFC
WARM FRONT EXTENDING ACROSS SRN IL/IN...DO NOT EXPECT SIGNIFICANT
IMPROVEMENT IN CONDITIONS UNTIL LATE TOMORROW WHEN THE SFC LOW
CURRENTLY OVER NRN MO FINALLY MOVES OFF TO THE EAST AND SOME DRIER
AIR CAN MOVE INTO THE REGION. UNTIL THEN...EXPECT THAT WINDS WILL
REMAIN PREVAILING NELY. CIGS/VIS SHOULD DROP AGAIN LATE THIS
AFTERNOON OR EARLY THIS EVENING AS SHRA/RA SPREADS FROM WEST TO
EAST ACROSS THE AREA AS THE SCF LOW TRACKS SLOWLY EWD. WITH THE
PCPN FALLING THROUGH THE STRATUS DECK...EXPECT THAT CIGS SHOULD
LOWER TO LIFR AGAIN OVERNIGHT TONIGHT.

KREIN

&&

.MARINE...
253 AM CDT

A PERIOD OF MODERATELY STRONG NORTHEAST WINDS GUSTING 20-25 KT
WILL PERSIST ACROSS LAKE MICHIGAN TODAY...EVENTUALLY BACKING MORE
NORTHERLY AND DIMINISHING AS LOW PRESSURE MOVES EAST ACROSS
ILLINOIS AND INDIANA AND REACHES THE UPPER OHIO VALLEY EARLY
MONDAY. WEAK HIGH PRESSURE RIDGING WILL THEN SETTLE SOUTH ACROSS
THE GREAT LAKES REGION MONDAY AND MONDAY EVENING...BEFORE AN AREA
OF LOW PRESSURE APPROACHES FROM ONTARIO. THIS LOW...AND ITS
ACCOMPANYING COLD FRONTAL TROUGH... WILL PUSH SOUTHEAST ACROSS
THE LAKE TUESDAY AND TUESDAY NIGHT. LIGHT WINDS WILL SHIFT TO THE
SOUTHWEST AND INCREASE TO 15-25 KTS INITIALLY AS THE TROUGH AND
LOW APPROACH TUESDAY...SHIFTING NORTH-NORTHWEST BEHIND THE FRONT
EARLY WEDNESDAY WITH SPEEDS 25-30 KT AND PERSISTING INTO THURSDAY
BEFORE DIMINISHING THURSDAY NIGHT/EARLY FRIDAY AS HIGH PRESSURE
RIDGING BUILDS IN FROM THE NORTHWEST. ON THE SOUTH END OF THE
LAKE...MARGINAL SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED TO
CONTINUE THROUGH THE DAY. WILL MONITOR AS WE MAY BE ABLE TO CANCEL
EARLIER THAN CURRENT EXPIRATION THROUGH THIS EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 1 AM
     MONDAY.

&&

$$

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