Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 291935
AFDLOT

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

.SHORT TERM...
204 PM CDT

THROUGH SATURDAY...

COOL CLOUDY CONDITIONS HAVE PERSISTED AGAIN THIS AFTERNOON...WITH
THE LACK OF FORCING TO SCOUR THE CLOUDS FROM THE WEAK MID-LVL
HEIGHT RISES AND LACK OF PRESSURE GRADIENT. THIS HAS KEPT CLOUD
IMPROVEMENTS TO A MINIMUM AS WELL...AND THE NORTH/NORTHEAST SFC
FLOW HELD TEMPS ALONG THE IMMEDIATE LAKESHORE IN THE MID/UPR 40S.
FURTHER INLAND TEMPS HAVE SLOWLY WARMED INTO THE LOW/MID 50S.

THROUGH THIS EVENING AND MUCH OF THE OVERNIGHT HOURS MID-LVL
HEIGHTS WILL REMAIN SLIGHTLY ELEVATED...WHICH SHOULD MAINTAIN THE
DRY FORECAST THROUGH AT LEAST 9Z. LOW LEVEL MOISTURE WILL BE
STEADILY ADVECTING NORTH AS A FRONTAL BOUNDARY DRIFTS NORTH AHEAD
OF THE SHORTWAVE PRESENTLY POSITIONED OVER THE CENTRAL PLAINS. THE
CONTINUED NORTHEAST/EAST SFC WINDS WILL HELP TO DELAY THE ONSET
OF PRECIP ALONG AND NORTH OF I-80 UNTIL JUST AFTER DAYBREAK...BUT
EXPECT STEADY MOISTENING THROUGH THE COLUMN TO OCCUR WITH POPS
APPROACHING CATEGORICAL BY EARLY AFTERNOON.

VERY MOIST SAT AFTN IS IN STORE...AS PWAT VALUES ARE PROGGED TO
APPROACH 1 INCH AND PERHAPS ALONG THE SOUTHERN HALF OF THE
FORECAST AREA NEARLY 1.2 INCHES. WITH THE MOIST AXIS OVERHEAD SAT
AFTN AND ISENTROPIC ASCENT TO PARCELS COUPLED WITH A LOW LEVEL JET
AROUND 30-40KT...THE POTENTIAL FOR MODERATE RAIN TO OCCUR
THROUGHOUT THE AFTERNOON APPEARS FAVORABLE...ALONG WITH SOME
EMBEDDED THUNDER FROM MODEST INSTABILITY IN THE SOUTHERN CWFA.
TEMPS SAT WILL SLOWLY WARM INTO THE LOW/MID 50S...HOWEVER FOR
AREAS ADJACENT TO LAKE MICHIGAN IN FAR NORTHEAST IL THE NORTHEAST
WINDS WILL LIKELY KEEP TEMPS IN THE UPR 40S.

BEACHLER

&&

.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 18Z TAFS...

MVFR CIGS ACROSS THE AREA WILL PERSIST INTO MID AFTERNOON BUT
THERE ARE HINTS OF SCATTERING OR AT LEAST LIFTING TOWARD HIGHER
MVFR OR VFR. WINDS FROM THE NORTHEAST QUADRANT ALSO WILL PREVAIL
THROUGH THE TAF PERIOD. THERE IS SOME UNCERTAINTY IN THE TIMING
OF PRECIP TOMORROW BUT THE MOST FAVORABLE PERIOD WOULD BE
AFTERNOON. IT ALSO IS NOT CLEAR HOW LOW CIGS/VSBYS MIGHT GO AS THE
RAIN BECOMES MORE PERSISTENT...BUT ANOTHER PERIOD OF IFR APPEARS
POSSIBLE OR LIKELY LATER IN THE DAY...TOWARD MID TO LATE
AFTERNOON.

LENNING

&&

.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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