Area Forecast Discussion
Issued by NWS Chicago, IL

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124
FXUS63 KLOT 031122
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
622 AM CDT TUE MAY 3 2016

.SHORT TERM...
322 AM CDT

TODAY THROUGH WEDNESDAY NIGHT...

FORECAST FOCUS IS ON BRIEF WARM-UP TODAY...SHOWERS AND A FEW
THUNDERSTORMS TONIGHT WITH COLD FRONT PUSHING THROUGH THE
AREA...AND A RETURN TO COOL AND SHOWERY WEATHER WEDNESDAY.

BAGGY UPPER TROUGH REMAINS STUBBORNLY ACROSS THE MIDWEST THIS
MORNING...THOUGH THE WFO LOT CWA IS POSITIONED BETWEEN ONE SHORT
WAVE MOVING AWAY TO THE EAST ACROSS INDIANA AND OHIO...AND A
DEEPER WAVE WELL TO OUR NORTH ACROSS MANITOBA AND WESTERN ONTARIO.
WEAK HIGH PRESSURE RIDGING WAS AT THE SURFACE BETWEEN THESE TWO
FEATURES EARLY THIS MORNING. THIS RIDGE WILL DRIFT SOUTH OF THE
AREA TODAY ALLOWING WINDS TO BACK TO THE WEST...EVENTUALLY
BECOMING BREEZY AT 15-20 MPH THIS AFTERNOON IN RESPONSE TO
TIGHTENING OF THE SURFACE PRESSURE GRADIENT AHEAD OF THE SURFACE
LOW/COLD FRONTAL TROUGH ASSOCIATED WITH THE CANADIAN SHORT WAVE.
FORECAST SOUNDINGS FROM VARIOUS MODELS INDICATE FAIRLY DEEP MIXING
OF RELATIVELY DRY AIR MASS THIS AFTERNOON WHICH WILL BOOST TEMPS
INTO THE MID-UPPER 60S ACROSS THE AREA AND PERHAPS A 70 OR TWO
OVER NORTHWEST/NORTH CENTRAL IL. LIGHT WINDS EARLY IN THE DAY MAY
ALLOW A WEAK LAKE BREEZE TO DEVELOP RIGHT ALONG THE SHORE OF LAKE
MICHIGAN BY MID-DAY...THOUGH WOULD EXPECT GRADUALLY INCREASING
WEST WINDS THIS AFTERNOON TO PUSH THE BOUNDARY BACK OVER THE WATER
ESPECIALLY ALONG THE IL LAKE SHORE. DEEP MIXING SEEN IN WRF AND
GFS SOUNDINGS DOES GENERATE SOME WEAK CAPE...THOUGH SURFACE DEW
POINTS IN THE LOW 40S LOOK A BIT OVER-DONE AND ANTICIPATE A HIGH
BASED SCT-BKN CU/SC DECK WITHOUT PRECIP THROUGH THE AFTERNOON
HOURS.

THE CANADIAN SHORT WAVE DIGS QUICKLY ACROSS THE UPPER MIDWEST BY
EVENING...AND ACROSS THE FORECAST AREA OVERNIGHT WITH STRONG
FORCING ALOFT COINCIDENT WITH APPROACH OF SHARP SURFACE COLD
FRONT. RAPID HEIGHT FALLS AND MID-LEVEL COOLING YIELDS 700-500 MB
LAPSE RATES OF 7-7.5 C/KM WHICH YIELDS 200-300 J/KG OF MUCAPE PER
00Z WRF SOUNDINGS WHICH SHOULD SUPPORT EMBEDDED THUNDER
CONSIDERING STRONG FORCING AIDED BY JUXTAPOSITION OF DIVERGENT
LEFT EXIT REGION OF UPPER JET. TIMING VARIES A BIT BETWEEN VARIOUS
GUIDANCE MEMBERS...THOUGH SHOWERS/STORMS SHOULD BE MOVING INTO THE
AREA BY MID-LATE EVENING AND CLEARING THE SOUTHEAST PART OF THE
CWA BEFORE/NEAR SUNRISE WEDNESDAY MORNING. BEHIND THE
FRONT...WINDS WILL QUICKLY VEER NORTH AND BECOME GUSTY 25-30 MPH
WITH TEMPS DROPPING INTO THE 40S.

SHORT WAVE ENERGY WORKS TO CARVE OUT A DEEP UPPER TROUGH ACROSS
EASTERN NORTH AMERICA WEDNESDAY...WITH ANOTHER CLOSED UPPER LOW
DEVELOPING OVER THE WESTERN GREAT LAKES. CYCLONIC FLOW AND COOL
AIR ALOFT WILL SUPPORT MOSTLY CLOUDY/SHOWERY CONDITIONS THROUGH
THE DAY AS SEVERAL SMALLER VORTS ROTATE SOUTHWARD AROUND THE MAIN
MID-LEVEL CIRCULATION TO OUR EAST. THESE SHOWERS...EXTENSIVE CLOUD
COVER AND COOL...BLUSTERY NORTH WINDS WILL MAKE FOR ANOTHER CHILLY
SPRING DAY. TEMPS WILL LIKELY STRUGGLE TO EXCEED 50 DEGREES ALONG
THE LAKE MICHIGAN SHORE AND DOWNWIND INTO NORTHWEST INDIANA...AND
WILL LIKELY ONLY BE IN THE UPPER 50S/NEAR 60 FARTHER WEST ACROSS
NORTH CENTRAL IL. THE GOOD NEWS IS THAT THE UPPER FLOW PATTERN
WILL BE AMPLIFYING ACROSS THE CONTINENT...WITH STRONG UPPER
RIDGING DEVELOPING OVER THE CENTRAL CONUS HELPING TO NUDGE THE
DOWNSTREAM EASTERN TROUGH AND UPPER LOW AWAY FROM THE AREA BY THE
END OF THE SHORT TERM PERIOD. THIS ALLOWS WEAK SURFACE HIGH
PRESSURE TO SPREAD INTO THE MISSISSIPPI VALLEY AND WESTERN GREAT
LAKES REGION LATER WEDNESDAY NIGHT...WITH SHOWERS
ENDING...DECREASING CLOUDS AND DIMINISHING WINDS. THIS WILL
SUPPORT CHILLY OVERNIGHT TEMPS ESPECIALLY ACROSS NORTH CENTRAL AND
FAR NORTHERN IL...WHERE MINS IN THE MID-UPPER 30S ARE PROGGED BY
SUNRISE THURSDAY. HAVE ADDED A MENTION OF PATCHY FROST FOR THE
NORTHERN COUPLE OF TIERS OF ILLINOIS COUNTIES AWAY FROM THE CORE
OF THE CHICAGO METRO HEAT ISLAND TO THE PRE-DAWN HOURS OF THURSDAY
MORNING.

RATZER

&&

.LONG TERM...
322 AM CDT

THURSDAY THROUGH MONDAY...

THE EXTENDED PORTION OF THE FORECAST FEATURES A LATE-WEEK WARM-UP
FRIDAY INTO THE WEEKEND...THOUGH ANOTHER COLD FRONT WILL SAG
ACROSS THE AREA SATURDAY. THIS WILL TEMPER THE WARM-UP ALONG LAKE
MICHIGAN AND ACROSS FAR NORTHERN IL SUNDAY AND MONDAY AS WINDS
TURN OFF THE LAKE...AND WILL ALSO PRESENT THE POTENTIAL FOR
PERIODIC SHOWERS AND THUNDERSTORMS.

SURFACE HIGH PRESSURE RIDGING WILL SPREAD EAST INTO THE MIDWEST
ON THURSDAY AS THE UPPER TROUGH OVER THE EASTERN CONUS DRIFTS AWAY
TO THE EAST. NORTHERLY FLOW WILL INITIALLY MAINTAIN COOL
TEMPERATURES ESPECIALLY NEAR AND DOWNWIND OF LAKE MICHIGAN INTO
NORTHWEST INDIANA. SUNSHINE WILL RETURN HOWEVER...AS DRY/SINKING
AIR HELPS TO CLEAR OUT ANY LINGERING CLOUDS. AFTERNOON TEMPS
THURSDAY SHOULD CLIMB TO THE LOW-MID 60S ACROSS NORTHERN IL AWAY
FROM THE LAKE...WHILE HOLDING IN THE 50S ACROSS NORTHWEST INDIANA.
BETTER THINGS ARE IN STORE HOWEVER AS THE UPPER RIDGE OVER THE
CENTRAL CONUS BUILDS EAST THURSDAY NIGHT INTO FRIDAY...ALLOWING
TEMPERATURES TO SURGE WELL INTO THE 70S AND POSSIBLY TO THE 80
DEGREE MARK IN A FEW SPOTS ON FRIDAY. MODEST WEST TO SOUTHWEST
WINDS WILL LIKELY ALLOW A WEAK LAKE BREEZE TO DEVELOP BY
AFTERNOON...COOLING IMMEDIATE SHORE AREAS A BIT.

GUIDANCE HAS TRENDED FASTER WITH A SHORT WAVE TROUGH WHICH TOPS
THE RIDGE FRIDAY NIGHT INTO SATURDAY...INDUCING A SURFACE LOW
WHICH MOVES ACROSS THE NORTHERN LAKES AND TRAILS A COLD FRONT INTO
THE CWA DURING THE DAT SATURDAY. THUS WHILE TEMPS WILL ONCE AGAIN
REACH THE MID-UPPER 70S ACROSS WESTERN AND SOUTHERN PARTS OF THE
CWA SATURDAY...IT APPEARS THAT THE COLD FRONT WILL SHIFT WINDS
ONSHORE NEAR THE LAKE. WITH THIS SCENARIO IN MIND HAVE LIMITED
TEMPS TO THE MID-UPPER 60S ALONG THE IL SHORE AND MAY SEE FALLING
TEMPS NEAR THE LAKE SATURDAY AFTERNOON. INCREASED CLOUD COVER AND
SCATTERED SHOWERS AND THUNDERSTORMS WILL ALSO LIKELY ACCOMPANY THE
FRONT WHICH PUSHES INTO DOWNSTATE IL/IN SATURDAY NIGHT BEFORE
BECOMING STATIONARY. WEAK HIGH PRESSURE SPREADS ACROSS THE GREAT
LAKES NORTH OF THE FRONT AND PRODUCES COOLER ONSHORE WINDS SUNDAY
AND MONDAY...WITH THE ELEVATED BAROCLINIC ZONE NORTH OF THE
SURFACE FRONT CONTINUING TO BE A FOCUS FOR INCREASED CLOUD COVER
AND POTENTIAL SHOWERS/THUNDERSTORMS. BOTH DAYS WILL FEATURE A
CONTRAST IN TEMPERATURES FROM NEAR 60 UP NEAR WAUKEGAN TO THE LOW-
MID 70S ACROSS THE FAR SOUTHERN PARTS OF THE CWA. SUNDAY COULD BE
RELATIVELY DRY WITH THE FRONT WELL TO THE SOUTH... WITH POPS
INCREASING MONDAY AS THE FRONT BEGINS TO LIFT BACK NORTH AS A WARM
FRONT.

RATZER

&&

.AVIATION...
FOR THE 12Z TAFS...

RIDGE AXIS IN PLACE ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA
EARLY THIS MORNING WILL SHIFT SOUTH TODAY ALLOWING WESTERLY
WINDS TO PICK UP THROUGH THE DAY. GUSTS TO NEAR 20 KT ARE POSSIBLE
DURING THE AFTERNOON HOURS AS THE GRADIENT TIGHTENS AHEAD OF AN
APPROACHING COLD FRONT. EXPECT VFR CONDITIONS WITH MAINLY MID/HIGH
LEVEL CLOUD COVER TODAY. LATE THIS EVENING INTO THE EARLY
OVERNIGHT HOURS...A COLD FRONT WILL SWEEP ACROSS THE REGION.
EXPECT SCATTERED SHOWERS AND A PERHAPS A FEW THUNDERSTORMS TO BE
IN PLACE AHEAD OF THE FRONT LATE THIS EVENING. GIVEN THE OVERNIGHT
TIMING OF THE FRONT AND VERY WEAK INSTABILITY NOTED IN FORECAST
SOUNDINGS THIS EVENING...WILL NOT MENTION THUNDER IN THE TAFS FOR
NOW...THOUGH THEY REMAIN A SMALL POSSIBILITY. ONCE THE FRONT
SWEEPS THROUGH...PRECIP SHOULD TAPER AND LOW MVFR OR EVEN IFR CIGS
ALONG WITH STRONG NORTHERLY WINDS ARE EXPECTED TO OVERSPREAD THE
TERMINALS. GUSTS INTO THE LOW TO MID 20 KT RANGE ARE POSSIBLE LATE
TONIGHT AND THROUGH MUCH OF THE DAY WEDNESDAY. CIGS SHOULD LIFT
DURING THE DAY WEDNESDAY AS WE HEAT UP...AND BY WEDNESDAY
AFTERNOON...ADDITIONAL SCATTERED SHOWERS ARE POSSIBLE.

BMD

&&

.MARINE...
221 AM CDT

HIGH PRESSURE IS OVER THE REGION EARLY THIS MORNING PROVIDING
LIGHT FLOW ACROSS LAKE MICHIGAN...HOWEVER A COLD FRONT IS EXPECTED
TO MOVE SOUTH ACROSS LAKE MICHIGAN LATE THIS EVENING AND OVERNIGHT
BRINGING NEAR GALE FORCE NORTHERLY WINDS. SOUTHWEST FLOW WILL
INCREASE THROUGH THE DAY TODAY AHEAD OF THE FRONT. SHOWERS AND A
FEW THUNDERSTORMS ARE ALSO EXPECTED TO OCCUR IMMEDIATELY ALONG AND
AHEAD OF THE FRONT...THEN WINDS WILL TURN NORTHERLY AND INCREASE
WITH GUSTS TO AROUND 30 KT EXPECTED BEHIND THE FRONT. WINDS WILL
REMAIN STRONG THROUGH THE DAY WEDNESDAY...THEN GRADUALLY COME DOWN
THROUGH THE DAY THURSDAY. A SMALL CRAFT ADVISORY WILL LIKELY BE
NEEDED FOR THE ILLINOIS AND INDIANA NEARSHORE WATERS THROUGH THIS
TIMEFRAME. WINDS DIMINISH ENOUGH FOR LAKE BREEZES BY LATE THURSDAY
AFTERNOON AS HIGH PRESSURE ONCE AGAIN MOVES OVERHEAD...THEN
SOUTHWESTERLY FLOW RETURNS THURSDAY NIGHT AS THE RIDGE AXIS SAGS
SOUTHEAST OF THE LAKE. ANOTHER COLD FRONT IS EXPECTED TO PUSH
ACROSS LAKE MICHIGAN OVER THE WEEKEND.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...7 AM WEDNESDAY TO
     10 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...7 AM WEDNESDAY TO
     3 PM THURSDAY.

&&

$$

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