Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 291130
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
630 AM CDT FRI APR 29 2016

.SHORT TERM...
254 AM CDT

TODAY THROUGH TONIGHT...

WEAKENING CLOSED LOW OVER SOUTHERN WI/LAKE MICHIGAN WILL SHEAR
EASTWARD ACROSS THE GREAT LAKES REGION THIS MORNING...ALONG WITH
ASSOCIATED WEAK SURFACE LOW. SUBSIDENCE IN THE WAKE OF THIS
FEATURE IS INDICATED BY RISING HEIGHTS AND DRYING/WARMING OF THE
COLUMN FROM MID-MORNING INTO THIS EVENING. THIS SHOULD BRING AN
END TO ANY LINGERING LIGHT RAIN/DRIZZLE EARLY IN THE DAY. LIGHT
ANTICYCLONIC SFC WINDS WILL MAINTAIN COOL NORTHEAST FLOW...THROUGH
FORECAST SOUNDINGS DO INDICATE THAT SOME THINNING/EROSION OF LOW
CLOUDS IS POSSIBLE LATE IN THE DAY. ANY BRIEF PEAKS OF SUN WILL
NOT DO MUCH TO BOOST TEMPS HOWEVER. LOW LEVEL THERMAL FIELDS IN
GOOD AGREEMENT WITH GUIDANCE NUMBERS FOR AFTERNOON HIGHS...RANGING
FROM THE 40S AT THE LAKE SHORE TO THE MID/UPPER 50S ACROSS NORTH
CENTRAL IL...AND LOW/MID 60S FAR SOUTH COUNTIES.

WFO LOT FORECAST AREA BRIEFLY FINDS ITSELF BENEATH SHORT WAVE
RIDGE AXIS TONIGHT...ALTHOUGH INFLUENCE OF THE NEXT UPPER LOW
EMERGING FROM THE CENTRAL/SOUTHERN ROCKIES BEGINS OVERNIGHT
PRIMARILY IN THE FORM OF STRENGTHENING COOL EASTERLY WINDS ACROSS
THE CWA AND REDEVELOPMENT AND THICKENING OF CLOUD COVER AS THE
STATIONARY FRONTAL BOUNDARY CURRENTLY OVER THE SOUTHERN PLAINS AND
LOWER MISSISSIPPI VALLEY DEVELOPS NORTHWARD AS A WARM FRONT. SOME
OF THE AVAILABLE GUIDANCE SPREADS PRECIP INTO THE FAR SOUTHERN
COUNTIES OF THE CWA PRIOR TO SATURDAY MORNING...AND WHILE THE 00Z
WRF/21Z SREF MIGHT BE A BIT TOO FAR NORTH GIVEN THE SPREAD IN
MODEL OUTPUT...AT LEAST SOME LOW CHANCE POPS REMAIN APPROPRIATE
ACROSS THE SOUTH AFTER MIDNIGHT TONIGHT.

RATZER

&&

.LONG TERM...
254 AM CDT

SATURDAY THROUGH THURSDAY...

MAIN FORECAST FOCUS IS ON CONTINUATION OF COOL/WET WEATHER
THROUGH THE WEEKEND...AS PLAINS UPPER EVENTUALLY IS ABSORBED BY
EASTERN NORTH AMERICAN UPPER TROUGH.

UPPER LOW IS PROGGED TO BE OVER THE CENTRAL HIGH PLAINS SATURDAY
MORNING WITH SURFACE LOW PRESSURE OVER EASTERN KANSAS. MID-LEVEL
SHORT WAVE ENERGY IS DEPICTED ROTATING NORTHEASTWARD AROUND THE
UPPER LOW AND INTO THE REGION DURING THE DAY...AS 30-40 KT 850 MB
WINDS WORK TO LIFT THE ELEVATED WARM FRONTAL ZONE ACROSS CENTRAL
AND NORTHERN IL/IN. PERIOD OF INCREASED MOISTURE
CONVERGENCE/MOISTURE FLUX ON THE NOSE OF 1+ INCH PWAT AXIS
SUPPORTS HIGHEST POPS DURING THE DAY SATURDAY. PLUME OF 7-7.5 C/KM
700-500 MB LAPSE RATES AND WEAK COUPLED JET STRUCTURE ALOFT ALSO
POINT TO EMBEDDED ELEVATED THUNDER POTENTIAL ESPECIALLY ACROSS THE
SOUTHERN HALF OF THE CWA. GUIDANCE VARIES A BIT WITH PLACEMENT AND
AMOUNTS...THOUGH A GENERAL 0.90-1.25 INCH QPF AXIS IS NOTED ACROSS
THE CENTRAL/SOUTHERN PARTS OF THE CWA BY MIDNIGHT SATURDAY NIGHT.
PRECIP THREAT CONTINUES SATURDAY NIGHT AND INTO SUNDAY AS UPPER
LOW CIRCULATION SHEARS EASTWARD ALONG NEARLY STATIONARY ELEVATED
BAROCLINIC ZONE...THOUGH LIGHTER AMOUNTS AND COVERAGE ARE
ANTICIPATED AS OVERALL DYNAMICS WEAKEN AND DRIER AIR IS ENTRAINED
IN MID-LEVELS PER FORECAST SOUNDINGS. THE WEAKENING UPPER LOW
CIRCULATION EVENTUALLY IS ABSORBED INTO UPPER TROUGH OVER
NORTHEASTERN NORTH AMERICA SUNDAY NIGHT WITH DEEPER DRYING NOTED.
THICKER CLOUD COVER... PRECIP AND PERSISTENT EAST TO NORTHEAST LOW
LEVEL WINDS WILL KEEP TEMPERATURES BELOW NORMAL THROUGH THE
WEEKEND. LOW LEVEL THERMAL FIELDS SUPPORT GENERAL GUIDANCE TRENDS
OF HIGHS FROM THE 40S (NEAR THE LAKE) AND LOWER 50S ACROSS THE
NORTHERN CWA SATURDAY...WITH UPPER 50S IN THE SOUTH. 925-950 TEMPS
ARE ACTUALLY A LITTLE WARMER SUNDAY NORTH AND WITH POTENTIAL FOR
SOME PARTIAL CLEARING IN THE AFTERNOON HIGHS IN THE UPPER
50S/AROUND 60 APPEAR REASONABLE AWAY FROM COOL NORTHEAST FLOW OFF
THE LAKE.

FOR DAYS 4-7...MONDAY THROUGH THURSDAY...TROUGHING OVER EASTERN
NORTH AMERICA REMAINS DOMINANT THROUGH THE PERIOD WITH GENERAL
MODEL AGREEMENT IN BRINGING A RELATIVELY STRONG MID-LEVEL SHORT
WAVE AND ASSOCIATED SURFACE TROUGH ACROSS THE REGION IN NORTH-
NORTHWEST FLOW IN THE WEDNESDAY TIME FRAME. SLIGHTLY BELOW NORMAL
TEMPS LOOK TO PERSIST OUTSIDE OF TUESDAY-WEDNESDAY PERIOD WITH THE
APPROACH OF THE COLD FRONT...WITH THE TUESDAY NIGHT/WEDNESDAY
PERIOD ALSO HAVING THE BEST CHANCE FOR SOME SCATTERED SHOWERS WITH
FROPA. MAINTAINED A BLENDED GUIDANCE APPROACH WITH
TEMPS...GENERALLY LOW-MID 60S AWAY FROM LAKE MICHIGAN AND LOW-MID
50S NEAR THE LAKE WITH UPPER 60S/AROUND 70 TUESDAY-WEDNESDAY.

RATZER

&&

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

LOW CEILINGS AND PATCHY FOG CONTINUE TO BE THE MAIN FORECAST
CHALLENGES THIS MORNING. IFR STRATUS DECK STRETCHES FROM CENTRAL
IL/IN NORTH TO NEAR CENTRAL WI EARLY THIS MORNING...WITH CLOUD BASES
ACROSS THE CHICAGO/ROCKFORD TERMINALS RANGING FROM 004-009. THERE IS
AN OFF CHANCE WE MAY LOSE ANOTHER HUNDRED FEET OR SO OVER THE NEXT 1-
2 HOURS BUT WITH SUNRISE AND DAYTIME HEATING EXPECT A GRADUAL
INCREASE IN CIGS WITH MVFR CONDITIONS RETURNING MID TO LATE THIS
MORNING...THEN SCATTERING TO VFR AT SOME POINT THIS AFTERNOON THOUGH
CONFIDENCE REMAINS LOW-MEDIUM IN SPECIFICS. LIGHT N/NNW WINDS EARLY
THIS MORNING WILL VEER TO THE NORTHEAST THROUGH THE MORNING HOURS
AND PICK UP TO AROUND 10 KT WHERE THEY SHOULD REMAIN THROUGH MOST OF
THE DAY. LOW PRESSURE LIFTING ACROSS THE PLAINS THIS EVENING AND
TONIGHT WILL CAUSE WINDS TO VEER FURTHER TO THE EAST LATE THIS
EVENING AND OVERNIGHT WITH INCREASINGLY GUSTY CONDITIONS EXPECTED ON
SATURDAY. SHOWERS WILL OVERSPREAD THE REGION ON SATURDAY...THOUGH
THE BEST CHANCES APPEAR TO BE BEYOND THE CURRENT TAF PERIOD.

BMD

&&

.MARINE...
246 AM CDT

HIGH PRESSURE WILL REMAIN JUST NORTH OF LAKE MICHIGAN TODAY
ALLOWING LIGHT FLOW ONCE AGAIN AND AFTERNOON LAKE BREEZES TO
DEVELOP. LOW PRESSURE IS PROGGED TO DEEPEN OVER THE PLAINS TONIGHT
INTO SATURDAY ALLOWING NORTHEAST WINDS TO PICK BACK UP INTO THE 15
TO 25 KT RANGE BY SATURDAY EVENING...WITH 30 KT WINDS NOT OUT OF
THE REALM OF POSSIBILITY. THE STRONG NORTHEAST BREEZE WILL PERSIST
INTO SUNDAY...THEN SHOULD DIMINISH AGAIN SUNDAY NIGHT INTO MONDAY
AS THE LOW DEPARTS EAST AND HIGH PRESSURE BUILDS BACK ACROSS THE
REGION. THE RIDGE AXIS WILL MOVE EAST OF LAKE MICHIGAN MONDAY
NIGHT AS ANOTHER LOW PRESSURE SYSTEM DEVELOPS OVER HUDSON BAY
ALLOWING WINDS TO TURN SOUTH TO SOUTHWESTERLY. THE LOW WILL DRIVE
A COLD FRONT ACROSS LAKE MICHIGAN AROUND MIDWEEK.

BMD

&&

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

$$

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