Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 030828
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
328 AM CDT SUN MAY 3 2015

.SHORT TERM...
327 AM CDT

THROUGH MONDAY NIGHT...

A POTENT SHORTWAVE IS OVER NORTHWEST IL THIS MORNING AND IT WILL
MOVE OVER CENTRAL INDIANA THIS AFTERNOON. SCATTERED SHOWERS ARE
ALIGNED WITH THE WAVE...WHILE A COUPLE OF CONVECTIVE COMPLEXES LAG
BEHIND THE WAVE OVER IOWA.  THINKING ISOLATED SHOWERS ARE POSSIBLE
THROUGH 7AM ACROSS THE CWA.  NEAR TERM GUIDANCE AGREES THAT THE BEST
FORCING FOR ADDITIONAL ISOLATED SHOWERS WILL BE ALONG AND WEST OF
THE I-55 CORRIDOR THROUGH NOON.

EARLY MORNING CLOUD COVER SHOULD DISSIPATE THIS AFTERNOON WHICH
WOULD ALLOW TEMPS TO CLIMB INTO THE LOW 80S. HAVE MEDIUM-HIGH
CONFIDENCE IN HIGHS TODAY AS A CHANGE IN CLOUD COVER WILL LEAD TO
EITHER WARMER OR COOLER TEMPERATURES.  WIND GUSTS WILL ALSO BE
DEPENDENT ON CLOUD COVER AND MIXING. BACKED OFF ON GUSTS SLIGHTLY
BUT STILL EXPECTING A FEW GUSTS UP TO 30 MPH THIS AFTERNOON.

THE SURFACE LOW THAT WILL BRING THUNDERSTORMS TO THE REGION IS
MOVING OVER HUDSON BAY THIS MORNING. ITS COLD FRONT WILL SLIDE
THROUGH THE CWA MONDAY MORNING BUT THUNDERSTORMS AHEAD OF IT WILL
INFILTRATE THE CWA FROM NORTH TO SOUTH BEGINNING LATE THIS EVENING.
HAVE MEDIUM CONFIDENCE IN THE TIMING OF THUNDERSTORMS AS GUIDANCE
TYPICALLY IS A BIT FAST WITH COLD FRONTS.  HAVE HIGH CONFIDENCE IN
THUNDERSTORMS AS THERE IS ENOUGH CAPE FOR THUNDERSTORMS AND STEEP
LAPSE RATES. SEVERE WEATHER IS NOT EXPECTED AS THE OTHER PARAMETERS
ARE NOT SUPPORTIVE OF SEVERE STORMS.  HEAVY DOWNPOURS ARE POSSIBLE
WITH THE STORMS HOWEVER AS PWAT VALUES WILL INCREASE TO 1-1.2 INCHES
OVERNIGHT.

SHOWERS AND STORMS CONTINUE THROUGHOUT THE DAY MONDAY AS THE FRONT
STALLS AT OR SOUTH OF I-80. MODELS SHOW BETTER CONSISTENCY
TODAY...BUT STILL HAVE SUBTLE DIFFERENCES AS TO WHERE THE FRONT WILL
STALL OUT.  CONVECTION WILL FIRE ALONG THE FRONT MONDAY AND THE ONLY
CONCERN I SEE IS POSSIBLE FLOODING.  PWAT VALUES INCREASE UP TO 1.5
INCHES MONDAY EVENING AND NIGHT WHICH COULD LEAD TO SOME LOCATIONS
RECEIVING OVER A HALF INCH OF RAIN IN A 24 HOUR PERIOD.

HIGHS MONDAY WILL VARY FROM THE LOW TO MID 70S NORTH OF THE
FRONT...TO THE 60S ALONG THE LAKE...TO THE MID 70S SOUTH OF THE
FRONT.

JEE

&&

.LONG TERM...
327 AM CDT

TUESDAY THROUGH SATURDAY...

THE FRONT REMAINS SOUTH OF I-80 TUESDAY AND LOOKING AT ANOTHER DAY
WITH SCATTERED TO NUMEROUS THUNDERSTORMS.  GUIDANCE SUGGESTS WE MAY
SEE A FEW DRY PERIODS BUT HAVE LOW CONFIDENCE IN WHEN AND WHERE
THOSE WOULD OCCUR SO KEPT AT LEAST A CHANCE OF THUNDER ACROSS THE
CWA.  TEMPS ON TUESDAY WILL ONCE AGAIN VARY DEPENDING ON WHICH SIDE
OF THE FRONT YOU ARE ON. AREAS NORTH OF I-80 WILL BE IN THE 60S WITH
MID TO UPPER 50S ALONG THE LAKE THANKS TO ONSHORE FLOW. SOUTH OF I-
80 AND THE FRONT...MID TO UPPER 70S.

THE FRONT LIFTS NORTH AS A WARM FRONT TUESDAY NIGHT INTO
WEDNESDAY MORNING PUSHING THE CONVECTION NORTH WITH IT LEADING TO
WHAT COULD BE A DRY WEDNESDAY. GUIDANCE SUGGESTS ISOLATED TO
SCATTERED WARM SECTOR CONVECTION IS POSSIBLE WEDNESDAY. MODEL
SOUNDINGS FEATURE A FEW HUNDRED J/KG OF CAPE WITH NO CAP SO WENT
WITH A SLIGHT CHANCE TO CHANCE OF THUNDER.  SHEAR LOOKS WEAK AT BEST
SO NOT EXPECTING SEVERE STORMS AT THIS TIME.  WARMER CONDITIONS ARE
EXPECTED SINCE WE WILL BE IN THE WARM SECTOR. CLOUD COVER WILL ONCE
AGAIN POSSIBLY BUST THE TEMP FORECAST SO WENT WITH CONSERVATIVE
NUMBERS. LOOKING AT MID 70S TO AROUND 80 AWAY FROM THE LAKE.

THE NEXT SURFACE LOW PASSES OVER ONTARIO THURSDAY NIGHT THROUGH
FRIDAY MORNING AND ITS COLD FRONT STALLS OUT NEAR THE IL/WI STATE
LINE SATURDAY MORNING.  ADDITIONAL THUNDERSTORMS ARE POSSIBLE FROM
FRIDAY ONWARD AS THE FRONT HANGS AROUND THE REGION. ONLY HAVE MEDIUM
CONFIDENCE IN THUNDERSTORM COVERAGE AT THIS TIME.  TEMPS LATE THIS
WEEK LOOK TO BE AROUND 80.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SOUTH-SOUTHWEST WINDS GUSTING 20-25 KT THIS AFTERNOON.
* CHANCE FOR SHRA/TSRA LATE SUNDAY NIGHT.

//DISCUSSION...UPDATED 06Z...

RETURNING MOIST AIR ON A LOW-LEVEL JET WILL CONTINUE TO SPRING
STORMS ACROSS IA THROUGH DAYBREAK. WITH LESS MOISTURE AND NAMELY
INSTABILITY FURTHER EAST...ISOLATED SHOWERS ARE EXPECTED ACROSS
NORTH CENTRAL AND NORTHEAST IL...WITH A LITTLE MORE COVERAGE
POSSIBLE ACROSS NORTHWEST IL DURING AND JUST AFTER DAYBREAK AS
STORMS FROM IA WEAKEN. ALL IN ALL LITTLE PRECIPITATION CONCERNS
FOR THE CHICAGO AREA TAF SITES THROUGH MOST IF NOT THIS ENTIRE
TAF...AS DRY ENOUGH AIR WILL PREVAIL TODAY. SOUTH-SOUTHWEST WINDS
WILL INCREASE TODAY WITH A TIGHTER PRESSURE GRADIENT...YIELDING
OCCASIONAL GUSTS OF 20-25 KT LATE THIS MORNING AND MORE SO THIS
AFTERNOON. THE LOW-LEVEL JET AXIS WILL BE POSITIONED MORE OVER
THE AREA SUNDAY NIGHT PROVIDING 40-45 KT WINDS SPEEDS ABOVE 1000
FT. THE NEAR-SURFACE SPEEDS SHOULD BE ENOUGH /12 KT OR SO/ NOT TO
CREATE TRUE LOW-LEVEL WIND SHEAR.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN WINDS.
* LOW ON TIMING OF SHRA/TSRA LATE SUNDAY NIGHT OR JUST BEYOND TAF
  PERIOD.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY THROUGH TUESDAY...PERIODIC SHRA/TSRA WITH MVFR AND BRIEF
IFR POSSIBLE.

WEDNESDAY THROUGH FRIDAY...PRIMARILY VFR.

MTF/IZZI

&&

.MARINE...
135 AM CDT

SOUTH-SOUTHWEST WINDS WILL INCREASE ACROSS THE GREAT LAKES REGION
TODAY AS THE PRESSURE GRADIENT TIGHTENS IN ADVANCE OF AN
APPROACHING COLD FRONT. THE OFFSHORE COMPONENT ALONG THE WESTERN
SHORE OF THE LAKE WILL BE ENOUGH TO WARRANT A SMALL CRAFT
ADVISORY FROM LATE MORNING THROUGH THE AFTERNOON.

LOW PRESSURE FAR TO THE NORTH OF THE GREAT LAKES WILL USHER THE
COLD FRONT INTO THE WESTERN LAKES REGION LATER TONIGHT. THIS FRONT
WILL EASE ITS WAY SOUTHEASTWARD ACROSS LAKE MICHIGAN BY EARLY
AFTERNOON MONDAY TURNING WINDS TO THE NORTH IN ITS WAKE. WITH THE
FRONT FORECAST TO STALL JUST SOUTH OF LAKE MICHIGAN...WINDS ACROSS
THE LAKE WILL TURN EASTERLY LATER MONDAY NIGHT AND THROUGH
TUESDAY. THE FRONT WILL THEN RETURN NORTHWARD AS A WARM FRONT
TUESDAY NIGHT AND WEDNESDAY. SOUTHERLY WINDS ARE THEN EXPECTED FOR
MUCH OF THE REST OF THE WEEK.

MTF

&&

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

&&

$$

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