Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 241616 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1116 AM CDT FRI APR 24 2015

.UPDATE...
1115 AM CDT

NOT ANY SIGNIFICANT CHANGES MADE TO AFTERNOON AND EARLY EVENING
FORECAST. A MID-LEVEL SHORT WAVE ACROSS WESTERN/CENTRAL IA IS
HELPING TO FOCUS ASCENT WITHIN THE BROAD WARM ADVECTION ZONE
LEADING TO BANDS OF DBZ INCREASING ACROSS NORTHEAST IA AND
NORTHWEST IL. LITTLE OF THESE EASTERN ECHOES ARE REACHING THE
GROUND THANKS TO IMPRESSIVELY DRY AIR BELOW 6000 FT OR SO. SURFACE
DEW POINTS ARE IN THE LOWER TO MID TEENS ACROSS MOST OF THE AREA
WITH 40 DEGREE PLUS T/TD SPREADS...AND RESULTING RELATIVE HUMIDITY
VALUES UNDER 25 PERCENT. THIS SHOULD WIN OUT DURING THE DAYLIGHT
HOURS KEEPING MOST OF THE AREA DRY AND POTENTIALLY THROUGH EVEN
MID-EVENING. THE HIGH-RES GUIDANCE THAT SUPPORT THIS AND HAVE THIS
AFTERNOONS PRECIP MORE NORTH OF THE WI/IL BORDER HAVE THE MORE
ACCURATE DRIER LOW-LEVEL AIR ANALYZED. SO DO NOT FEEL INCLINED TO
SHIFT FROM CURRENT LOW POPS.

TEMPERATURES ARE GENERALLY ON TRACK. A LAKE BREEZE HAS DEVELOPED
BUT PRESENTLY IS HUGGING THE SHORE. THE DEEP MIXED BOUNDARY LAYER
DEVELOPING OVER LAND MAY HELP TO SLOW THE LAKE BREEZE PUSH INLAND
BUT AT THIS TIME STILL EXPECTED IT TO EASE INWARD BRINGING COOLING
TEMPERATURES IN LAKESIDE COUNTIES AS IT DOES.

MTF/RC

&&

.SHORT TERM...
252 AM CDT

THROUGH SATURDAY...

QUIET WEATHER ON TAP FOR MOST OF TODAY AS RIDGE AXIS CENTERED JUST
TO OUR EAST EARLY THIS MORNING SLOWLY SLIDES EAST ALLOWING RETURN
FLOW TO SPREAD MOISTURE UP ALONG WITH MISSISSIPPI RIVER VALLEY
AND INTO THE FORECAST AREA TONIGHT AHEAD OF LOW PRESSURE OVER THE
CENTRAL PLAINS. IN THE MEANTIME...EXPECT MORNING SUNSHINE TO GIVE
WAY TO INCREASING HIGH AND MID LEVEL CLOUD COVER. LIGHT WINDS IN
PLACE TODAY WILL ALLOW A LAKE BREEZE TO DEVELOP THIS AFTERNOON
ALONG THE INDIANA AND ILLINOIS SHORES. TEMPERATURES WILL WARM INTO
THE UPPER 50S TO AROUND 60 INLAND...BUT TEMPERATURES WILL LIKELY
STAY IN THE MID TO UPPER 40S ALONG THE LAKE FRONT.

CHANCES FOR PRECIP WILL INCREASE STARTING AROUND MID EVENING TONIGHT
AS SURFACE LOW MOVES INTO KS/NE AND LEADING EDGE OF MOISTURE PUSHES
INTO NORTHERN ILLINOIS ALONG WITH 850MB BAROCLINIC ZONE AND BROAD
WARM ADVECTION PROVIDING MODERATE ASCENT. DRY AIR BELOW 800MB WILL
HAVE TO BE OVERCOME BEFORE PRECIP REACHES THE SURFACE MAINLY LENDING
TO SOME UNCERTAINTY IN TIMING ONSET OF PRECIP. BY SATURDAY MORNING
EXPECT THE COLUMN TO BE SATURATED WITH DEEP MOISTURE IN PLACE AND
PWATS AROUND AN INCH. NAM INDICATES VERY MODEST INSTABILITY MAINLY
SOUTH OF A DIXON TO RENSSELAER LINE. VERY SKINNY CAPE PROFILES ARE
NOTED HOWEVER AND IT MAY BE DIFFICULT TO REALIZE THE FULL
POTENTIAL...SO WILL INTRODUCE ONLY A SLIGHT CHANCE OF THUNDER FOR
SOUTHWESTERN/SOUTHERN COUNTIES IN THE FORECAST AREA.

EXPECT RAIN ACROSS THE CWA MOST OF SATURDAY MORNING...THEN CHANCES
WILL BEGIN TO WIND DOWN THROUGH THE AFTERNOON AS THE SURFACE LOW
TRACKS ACROSS DOWNSTATE ILLINOIS AND BOUNDARY LAYER FLOW LOCALLY
COMES AROUND TO NORTHEASTERLY. PASSAGE OF THE MID LEVEL WAVE
SATURDAY EVENING AND ARRIVAL OF MID-LEVEL HEIGHT RISES SHOULD MARK
THE END OF PRECIP.

DEUBELBEISS

&&

.LONG TERM...
252 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

GENERALLY DRY CONDITIONS WITH A GRADUAL WARMING TREND IS EXPECTED TO
CLOSE OUT THE WEEKEND AND CONTINUE THROUGH MOST OF THE UPCOMING
WEEK. LOW PRESSURE THAT WILL BRING RAIN TO THE AREA FRIDAY
NIGHT/SATURDAY WILL MOVE TOWARDS THE MID ATLANTIC COAST SUNDAY WITH
HIGH PRESSURE BUILDING DOWN FROM THE CANADIAN PRAIRIES INTO THE
UPPER MIDWEST. NORTH/NORTHEAST FLOW IN THE MID-LEVELS WILL PUSH THE
BAROCLINIC ZONE BACK TO OUR SOUTH SUNDAY WITH H85 TEMPS FALLING TO
AROUND -6C TO -8C...ALBEIT BRIEFLY. THE HIGH WILL GENERALLY REMAIN
IN PLACE THROUGH MIDWEEK THOUGH WEAKENS THROUGH THIS PERIOD WITH THE
AIRMASS BECOMING INCREASINGLY MODIFIED BY LATE APRIL INSOLATION.
THIS SHOULD ALLOW TEMPS ONLY IN MID 50S SUNDAY TO GRADUALLY WARM
THROUGH THE UPCOMING WEEK WITH TEMPS PUSHING THE 70 MARK BY
THURSDAY. THE EXCEPTION THROUGH THE PERIOD WILL BE NEAR THE LAKE
FRONT WHERE ONSHORE FLOW IS EXPECTED THROUGH AT LEAST THE FIRST HALF
OF THE WEEK KEEPING CONDITIONS COOLER.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* LIKELY LAKE BREEZE PASSAGE TURNING WINDS EASTERLY AT OR OVER 10
  KT BETWEEN 19Z-21Z.
* CHANCE FOR SCATTERED LIGHT RAIN SHOWERS AS EARLY AS 22Z.
* STRONGER EASTERLY WINDS AND PERIODS OF RAIN AND IFR ON
  SATURDAY.

MTF/KJB

//DISCUSSION...UPDATED 12Z...

SURFACE HIGH PRESSURE OVER THE AREA EARLY THIS MORNING WILL SHIFT
EAST TODAY WHILE LOW PRESSURE OVER THE HIGH PLAINS BEGINS TO
CONSOLIDATE ACROSS WESTERN KANSAS BY THIS EVENING. AS THIS
OCCURS...LIGHT SOUTH-SOUTHEASTERLY WINDS THIS MORNING WILL BECOME
EASTERLY THROUGH THE AFTERNOON. WIND SPEEDS LOOK TO GENERALLY
REMAIN LIGHT THROUGH MUCH OF THE DAY. HOWEVER...SPEEDS UP AROUND
10 KT COULD DEVELOP BY MID TO LATE AFTERNOON...WITH A CONTINUED
INCREASE IN SPEEDS LIKELY TONIGHT AS THE SURFACE LOW PROGRESSES
EASTWARD TOWARDS THE LOWER AND MIDDLE MISSOURI VALLEY.

THERE WILL BE A SLIGHT CHANCE FOR SOME ISOLATED TO SCATTERED
SHOWERS LATE THIS AFTERNOON AND EVENING. HOWEVER...THE CHANCES
FOR MORE WIDESPREAD RAIN WILL GRADUALLY INCREASE ACROSS THE AREA
BY DAYBREAK SATURDAY AS THE AREA OF LOW PRESSURE APPROACHES THE
AREA. IFR CIGS...PERIODS OF LIGHT TO MODERATE RAIN AND STRONG
EASTERLY WINDS ARE EXPECTED FOR SATURDAY.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH THAT EASTERLY WINDS WILL BECOME 10KT+. MEDIUM IN TIMING OF
  20Z.
* LOW IF SHOWERS WILL OCCUR LATE THIS AFTERNOON AND EARLY THIS
  EVENING...BUT IF THEY DO MEDIUM-HIGH THAT THEY WILL BE LIGHT AND
  CONDITIONS SHOULD MAINLY BE VFR.
* HIGH FOR IFR CONDITIONS AND GUSTY EASTERLY WINDS ON SATURDAY.

MTF/KJB

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

* SATURDAY NIGHT THROUGH THURSDAY...VFR WITH PRIMARILY NORTHEASTERLY
  WINDS.

KJB

&&

.MARINE...
138 AM CDT

LIGHT AND VARIABLE WINDS EARLY THIS MORNING OVER THE LAKE WILL
BECOME EASTERLY LATER TODAY AND TONIGHT AS AN AREA OF LOW PRESSURE
CONSOLIDATES ACROSS WESTERN KANSAS. WIND SPEEDS ARE LIKELY TO
INCREASE INTO SATURDAY AS THIS AREA OF LOW PRESSURE TRACKS EASTWARD
ACROSS SOUTHERN ILLINOIS BY EARLY EVENING...THEN OVER THE OHIO
VALLEY SATURDAY NIGHT. EASTERLY WINDS OF 25 TO 30 KT LOOK LIKE A
DECENT BET ON SATURDAY...ESPECIALLY ACROSS THE SOUTHERN HALF OF THE
LAKE. THIS WILL LIKELY RESULT IN SMALL CRAFT CONDITIONS FOR ILLINOIS
AND INDIANA NEAR SHORES...WITH WAVES LIKELY TOPPING 5 FEET. WINDS
GRADUALLY SWITCH AROUND OUR OF THE NORTH FOR SUNDAY AND REMAIN GUSTY
UP TO 25 TO 30 KT AS SURFACE HIGH PRESSURE BEGINS TO BUILD BACK
SOUTHWARD ACROSS THE UPPER MIDWEST.

PERIODS OF LIGHTER WINDS...LIKELY DOMINATED MORE BY LAKE AND LAND
BREEZE INFLUENCES LOOK TO BE ON TAP FOR AT LEAST THE FIRST PORTION
OF NEXT WEEK AS SURFACE HIGH PRESSURE DOMINATES THE GREAT LAKES
REGION.

KJB

&&

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

$$

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