Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 240549
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1249 AM CDT THU APR 24 2014

.DISCUSSION...
931 PM CDT

SHOWERS CONTINUE TO MOVE/DEVELOP EASTWARD ACROSS NORTHERN ILLINOIS
EARLY THIS EVENING WITHIN A ZONE OF INCREASING ISENTROPIC ASCENT
ALONG THE WESTERN PERIPHERY OF A SURFACE RIDGE OF HIGH PRESSURE. THIS
ACTIVITY IS EXPECTED TO CONTINUE MOVING EASTWARD ACROSS NORTHERN
ILLINOIS LATE THIS EVENING...AND LIKELY ENDING PRIOR TO DAYBREAK
THURSDAY AS THE BETTER FORCING AND MOISTENING SHIFTS TO THE NORTH
AND EAST OF THE REGION. THEREFORE...NO BIG CHANGES ARE NEEDED TO THE
GOING FORECAST FOR TONIGHT.

THURSDAY IS SHAPING UP TO BE A BREEZY AND A MILDER DAY ACROSS THE
AREA AS SOUTHEASTERLY FLOW RAMPS UP IN RESPONSE TO AN AREA OF LOW
PRESSURE APPROACHING WESTERN ILLINOIS DURING THE AFTERNOON. IT
APPEARS THAT IN SPITE OF THE SOUTH-SOUTHEASTERLY WIND
COMPONENT...THAT WINDS COULD BE VERY GUSTY...UP IN THE 30 TO 35 KT
RANGE...DURING THE AFTERNOON. ALSO...IT APPEARS THAT THESE
SOUTHEASTERLY WINDS WILL TRANSPORT A DRIER LOWER LEVEL AIR MASS IN
ACROSS THE AREA DURING THE DAY...AND THIS COULD LEAD TO LOWER
SURFACE DEW POINTS THAN CURRENTLY FORECAST...ESPECIALLY ACROSS THE
EASTERN HALF OF THE AREA. WITH THIS IN MIND...I HAVE BACKED OFF ON
POPS DURING THE AFTERNOON THURSDAY...WITH A LIKELY SLOWER EVOLUTION
OF THE PRECIPITATION. IT APPEARS THE MAIN FORCING AND MOISTURE WILL
NOT ARRIVE ACROSS THE AREA UNTIL THURSDAY EVENING. AT THIS TIME I
HAVE LEFT SOME LOW END POPS IN DURING THE AFTERNOON...BUT IF THESE
TRENDS CONTINUE...WE MAY BE ABLE TO GO DRY ALL AFTERNOON ON
THURSDAY...ESPECIALLY ACROSS THE EASTERN HALF OF THE AREA. PERIODS
OF RAIN STILL APPEAR TO BE A GOOD BET THURSDAY NIGHT.

KJB

//PREV DISCUSSION...
310 PM CDT

SYNOPSIS...ANOTHER PLEASANT DAY TODAY...BUT SHOWERS MOVE IN FROM THE
WEST THIS EVENING. SHOWERS AND STORMS ARE EXPECTED TOMORROW
AFTERNOON AND EVENING WITH A DRY AND WARM END TO THE WORK WEEK.
THIS WEEKEND LOOKS TO HAVE BELOW NORMAL TEMPERATURES WITH SHOWERS
AND PERHAPS SOME THUNDERSTORMS ALONG AND SOUTH OF I-80 FOR THE FIRST
HALF OF NEXT WEEK.

REST OF TODAY AND TONIGHT...
A LARGE UPPER LEVEL RIDGE IS OVER THE CENTRAL PLAINS WHILE A SURFACE
HIGH IS CENTERED OVER LAKE MICHIGAN. THE RIDGE PASSES OVERHEAD
TONIGHT WHILE THE SURFACE HIGH PUSHES EAST TO THE NORTHERN OHIO
VALLEY THROUGH EASTERN QUEBEC.

A WEAK SHORTWAVE IS OVER EASTERN NEBRASKA AND WESTERN IOWA WITH
SHOWERS OVER WESTERN IOWA.  THE SHOWERS WILL CONTINUE TO PUSH
EAST...BUT WITH DEWPOINT DEPRESSIONS AT 20+ DEGREES...THINKING THE
SHOWERS WILL DISSIPATE A BIT BEFORE MOVING INTO CENTRAL IL. AS SUCH
THINKING THE FIRST SHOWERS WILL ENTER THE FAR EASTERN CWA AFTER 5PM
CST.  USED THE LOCAL ARW...RAP...AND HRRR TO CREATE THE POPS FOR THE
REST OF TODAY AND TONIGHT. THINKING A BAND OF SCATTERED SHOWERS WILL
SLOWLY CROSS NORTHERN IL THIS EVENING IN ASSOCIATION WITH AN UPPER
LEVEL VORTICITY STREAMER. THE BEST COVERAGE WILL BE BETWEEN MIDNIGHT
AND 4 AM CST WITH A CHANCE OF LIGHT RAIN SHOWERS NORTH OF I-80. THE
BAND THEN LIFTS NORTH EARLY THURSDAY MORNING AS THE RIDGE MOVES
DIRECTLY OVERHEAD. NOT EXPECTING ANY SIGNIFICANT PRECIP
ACCUMULATIONS.

CLOUD COVER WILL INCREASE THROUGH THIS AFTERNOON AND LOOKING AT MIN
TEMPS IN THE UPPER 30S TO MID 40S ACROSS THE CWA.

TOMORROW AND TOMORROW NIGHT...
AN UPPER LEVEL TROUGH MOVES OVER THE PLAINS TOMORROW MORNING AND THE
TROUGH PASSES OVER THE REGION TOMORROW NIGHT. THE UPPER LEVEL LOW
ASSOCIATED WITH THE TROUGH PASSES FARTHER NORTH...ALONG THE
US/CANADA BORDER.  THE SURFACE LOW ALSO BEGINS OVER THE PLAINS
THURSDAY MORNING AND THEN MOVES OVER IL THURSDAY EVENING. GUIDANCE
HAS THE LOW PROGRESSING A BIT SLOWER AND MADE THE NECESSARY
ADJUSTMENTS.

RAIN AND SOME STORMS MOVE IN FROM THE WEST THROUGH THE MORNING AND
EARLY AFTERNOON.  INSTABILITY IS NOT EXTREMELY IMPRESSIVE WITH THE
SYSTEM SO KEPT ONLY A CHANCE OF THUNDER. QPF AMOUNTS ON THE OTHER
HAND COULD BE IMPRESSIVE WITH TOTALS AROUND A HALF INCH OF RAIN.

WINDS WILL ALSO BE SHIFTING FROM SOUTHEAST IN THE MORNING TO OUT OF
THE WEST OVERNIGHT BEHIND THE LOW.  LOOKING AT A BREEZY AFTERNOON
WITH SOUTH WINDS GUSTING TO 35 MPH.  THE AMPLE WAA WILL LEAD TO MAX
TEMPS FROM AROUND 60 ALONG THE IL/WI BORDER TO THE UPPER 60S IF NOT
70 IN THE SOUTHERN CWA.

FRIDAY AND SATURDAY...
THE UPPER LEVEL LOW CONTINUES TO SHIFT EAST REACHING NEW ENGLAND BY
SATURDAY AFTERNOON/EVENING.  THE SURFACE LOW SHIFTS EAST AND
EXPECTING PRECIP TO COME TO AN END EARLY FRIDAY MORNING.  WEST WINDS
WILL BE GUSTING TO ARND 30 MPH FRIDAY AND AM THINKING THERE COULD BE
SOME DRY AIR MIXING DOWN TO THE SURFACE SO LOWERED DEWPOINTS A BIT.

THE AIR BEHIND THE COLD FRONT IS NOT REALLY ALL THAT COLD SINCE MAX
TEMPS ON FRIDAY LOOK TO BE AROUND 70 DEGREES.  A BACK DOOR COLD
FRONT SLIDES DOWN FROM THE NORTH IN THE EVENING. SOME GUIDANCE
MEMBERS FEATURE A BAND OF PRECIP FORMING AHEAD OF THE FRONT OVER FAR
NORTHERN IL AND NW INDIANA. PUT IN A CHANCE OF PRECIP SINCE FORCING
LOOKS GOOD...BUT HAVE LOW CONFIDENCE IN THE BAND OF PRECIP ACTUALLY
FORMING. AS SUCH KEPT POPS IN THE CHANCE RANGE.  WINDS TURN
NORTHEAST BEHIND THE FRONT AND OVERNIGHT LOWS WILL BE IN THE UPPER
30S TO MID 40S.

SOME GUIDANCE MEMBERS KEEP A BAND OF PRECIP OVER THE REGION SATURDAY
MORNING...BUT WITH HIGH PRESSURE MOVING OVER THE REGION HAVE LOW
CONFIDENCE AND WENT WITH A DRY FORECAST SATURDAY.  SKIES WILL CLEAR
BUT THE COOLER AIR OFF THE LAKE WILL RESULT IN HIGHS IN THE UPPER
40S TO MID 50S ALONG THE LAKE...AND THEN IN THE LOW TO MID 60S IN
THE OUTLYING AREAS.

GUIDANCE FEATURES PRECIP MOVING IN AHEAD OF THE NEXT LOW SATURDAY
NIGHT. HAVE LOW CONFIDENCE IN THIS ROUND OF PRECIP AS WELL...BUT
LEFT A CHANCE OF RAIN IN THE FORECAST.  OVERNIGHT LOWS WILL RANGE
FROM THE UPPER 30S TO THE MID 40S.

EXTENDED...SUNDAY THROUGH TUESDAY...
AN UPPER LEVEL CLOSED LOW SHIFTS OVER THE GREAT PLAINS SUNDAY
EVENING/NIGHT. GUIDANCE DIFFERS ON ITS EXACT PATH EARLY NEXT WEEK
BUT DOES HAVE THE UPPER LEVEL LOW OVER THE REGION THROUGH AT LEAST
MID WEEK.  ITS ASSOCIATED SURFACE LOW MOVES OVER THE PLAINS LATE
SUNDAY NIGHT/MONDAY MORNING AND SLIDES SOUTH OF THE CWA MONDAY
NIGHT. THE 12Z GUIDANCE AGREED A BIT MORE ABOUT THE SURFACE LOWS
PATH...AND HAVE IT MOVING THROUGH SOUTHERN IL TUESDAY.

IN TWO WORDS EARLY NEXT WEEK LOOKS CHILLY AND WET.  A BOUNDARY OVER
NORTHERN IL BRINGS THE LIFT FOR THE FIRST WAVE OF PRECIP EARLY ON
SUNDAY...BUT THEN MULTIPLE VORTICITY STREAMERS PASS THROUGH THE
REGION AS THE LOW SLOWLY SHIFTS EAST. THIS WILL RESULT IN A CHANCE
OF PRECIP THROUGHOUT THE EXTENDED. WILL INCLUDE A SLIGHT CHANCE OF
THUNDER ALONG AND SOUTH OF I-80 WHERE THERE WILL BE LIMITED ELEVATED
INSTABILITY BUT ENOUGH TO PERHAPS SUPPORT A COUPLE OF THUNDERSTORMS
SUNDAY NIGHT AND MONDAY. THE UPPER LEVEL JET DIPS FAR SOUTH THROUGH
TEXAS ALLOWING COOL AIR TO SPREAD ACROSS THE REGION. AS SUCH HIGHS
WILL VARY BETWEEN THE LOW 50S NORTH TO MID 60S SOUTH WITH A COOLING
TREND THROUGH TUESDAY.  LUCKILY OVERNIGHT LOWS LOOK LIKE THEY WILL
REMAIN ABOVE FREEZING.

JEE

&&

.AVIATION...

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

* PERIODS OF LIGHT RAIN THROUGH EARLY THIS MORNING.

* STRONG/GUSTY SOUTHEAST WINDS TODAY.

* SHRA LATER THIS EVENING W/ ISOL TSRA.

* POSSIBLE LOW END MVFR CEILINGS LATE IN THE FORECAST PERIOD.

RODRIGUEZ

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

TERMINALS REMAIN ON EASTERN FRINGE OF PERSISTENT SHOWER
DEVELOPMENT AT THIS HOUR...AND NOW EXPECT THIS TO CONTINUE OVER
THE NEXT COUPLE OF HOURS BEFORE THIS PRECIP SHIELD ALL LIFTS TO
THE NORTH OF THE TERMINALS LATER THIS MORNING. ALTHOUGH...STILL
CONFIDENT THIS WILL REMAIN LIGHT WITH VFR CONDITIONS CONTINUING.
A LULL IN THE ACTIVITY AS WELL AS CLOUD COVER WILL LIKELY OCCUR
FOR THE REMAINDER OF THE DAY BEFORE THE NEXT SYSTEM CURRENTLY WELL
WEST OF THE TERMINALS SLOWLY APPROACHES. VFR CEILINGS WILL RETURN
LATE THIS AFTERNOON INTO THE EVENING AS WELL AS
SHOWER/THUNDERSTORM CHANCES. MAINTAINED JUST SHOWERS IN THE TAFS
WITH LOW CONFIDENCE OF TSRA AT THIS TIME...WITH EVEN SOME
POSSIBILITY OF DELAYING THE ONSET OF VCSH/-SHAR WITH LATER
FORECASTS. SOUTHEAST WINDS WILL RAMP UP RATHER QUICKLY LATER THIS
MORNING WITH STRONG GUSTS TO AROUND 30 KT LIKELY BEFORE A SLOW
DOWNWARD TREND OCCURS LATER THIS AFTERNOON. WITH CONFIDENCE LOWER
WITH REGARDS TO OVERALL TIMING OF THIS SYSTEM...HAVE LEFT OUT ANY
MENTION OF WIND SHIFT TO THE NORTHWEST AND POSSIBLE LOW END MVFR
CEILINGS VERY LATE IN THE FORECAST PERIOD FOR ORD.

RODRIGUEZ


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

* HIGH CONFIDENCE WITH RAIN AND VFR CONDITIONS.

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH SHOWERS LATER THIS EVENING...WITH LOW
  MEDIUM CONFIDENCE ON EXACT TIMING AND TSRA.

* LOW CONFIDENCE WITH LOW END MVFR CEILING CHANCES.

RODRIGUEZ

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

* FRIDAY AND SATURDAY...DRY/VFR.
* SUNDAY THROUGH TUESDAY...CHANCE OF SHRA. MVFR POSSIBLE.

&&

.MARINE...
219 PM CDT

PROGRESSIVE FLOW WILL CONTINUE THROUGH FRIDAY BEFORE A MUCH MORE
AMPLIFIED AND LOCKED PATTERN WILL SET UP FOR THE WEEKEND THROUGH THE
MIDDLE OF NEXT WEEK. THE HIGH PRESSURE PRESENTLY OVER THE LAKE WILL
BE SCOOTED EASTWARD EARLY FRIDAY AS LOW PRESSURE FROM THE CENTRAL
PLAINS BOOKS EASTWARD INTO NORTHERN INDIANA. DURING THURSDAY THIS
WILL PROVIDE STRONG SOUTHERLY FLOW. A FAIRLY STOUT INVERSION SHOULD
BE PRESENT OVER THE LAKE...BUT STRONG OFFSHORE WINDS IN NEARSHORE
AREAS SHOULD LEAD TO 25 TO POSSIBLE 30 KT GUSTS. AS A DEEP TROUGH
SETS UP ACROSS THE WESTERN U.S. AND SLOWLY MOVES EAST THROUGH THE
WEEKEND AND EARLY NEXT WEEK...SURFACE HIGH PRESSURE WILL GET
LOCKED OVER THE CENTRAL GREAT LAKES. A TIGHTENING PRESSURE
GRADIENT ON ITS SOUTHERN AND WESTERN SIDES WILL PROVIDE CONTINUOUS
EAST TO NORTHEAST SURFACE WINDS. THIS LOOKS LIKE A POTENTIAL
PROLONGED PERIOD OF SMALL CRAFT ADVISORY CRITERIA.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM THURSDAY TO 10 PM THURSDAY.

&&

$$

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