Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281715
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1215 PM CDT SUN JUN 28 2015

.UPDATE...
1215 PM CDT

THE FORECAST IS GENERALLY ON TRACK FOR INCREASING CHANCES OF
SHOWERS AN THUNDERSTORMS AS A SHORTWAVES DROPS THROUGH THE MIDDLE
MISSISSIPPI VALLEY. LATEST RADAR IMAGERY INDICATES MORE BROCKEN
COVERAGE TO THE PCPN ASSOCIATED WITH THE SHORTWAVE...BUT AS THE
SHORTWAVE CONTINUES ACROS NRN AND CNTRL IL...IT WILL MOVE INTO A
MORE UNSTABLE...MOIST AIRMASS WITH DEWPOINTS RISING INTO THE LOWER
TO MIDDLE 60S AND SFC BASED CAPE OF 500-1500 J/KG...WITH THE
GREATEST INSTABILITY OVER THE SWRN PORTIONS OF THE CWA. EXPECT
THAT THE AREAL COVERAGE OF PCPN WILL INCREASE THROUGH THE
AFTERNOON...AS THE SHORTWAVE INTERACTS WITH THE HIGHER MOISTURE
AND INSTABILITY. THE LATEST SPC DAY1 CONVECTIVE OUTLOOK MAINTAINS
A MARGINAL RISK OF SEVERE WEATHER OVER PORTIONS OF THE AREA SOUTH
AND WEST OF A LINE FROM DIXON TO PAXTON...WITH THE MAIN THREATS
BEING STRONG WINDS AND LARGE HAIL. ALSO...PWATS ACROSS THE REGION
HAVE REBOUNDED BACK TO AROUND 1.4 INCHES...SO LOCALLY HEAVY
RAINFALL WILL ALSO BE POSSIBLE WITH SOME OF THE STRONGER STORMS.

KREIN

&&

.SHORT TERM...
309 AM CDT

THROUGH TONIGHT...

WEAK SFC RIDGING OVERHEAD HAS PROVIDED NEAR CLOUDLESS SKIES WITH
LIGHT TO VARIABLE WINDS...AND SFC TEMPS IN THE MID/UPR 50S. THE
NORTHWEST FLOW WILL REMAIN PROGRESSIVE AND PUSH THE SFC RIDGE EAST
BY MIDDAY WITH WINDS TURNING SOUTHERLY ACROSS THE FORECAST AREA. IR
IMAGERY SHOWS THE MID-LVL WAVE DIVING SOUTHEAST ACROSS THE UPPER
MIDWEST...AND IT PROGGED TO ARRIVE LATER THIS MORNING ACROSS THE
WESTERN CWFA.

PRIOR TO ARRIVAL TEMPS SHUD QUICKLY WARM INTO THE LOW/MID 70S BY
MIDDAY...WITH STEADILY THICKENING CLOUD COVER. GUIDANCE CONTINUES TO
SUGGEST MARGINAL INSTABILITY WITH THIS WAVE AS IT ARRIVES...WITH
MLCAPE GENERALLY ARND 300-600J/KG. WITH SOME INCREASED ASCENT ALONG
THE FRONT-SIDE OF THE WAVE...SOME EMBEDDED THUNDERSTORMS LOOKS
FAVORABLE. IN ADDITION THE LOW WILL BE SLOWLY DEEPENING AS IT
ARRIVES THIS EVENING...WHICH COULD ENHANCE THE PRECIP COVERAGE AND
POSSIBLY THE INTENSITY OVERNIGHT INTO EARLY MON. THE PATH OF THE LOW
IS CURRENTLY TO SLIDE ACROSS THE QUAD-CITIES ARND DAYBREAK
MON...THEN SLOWLY LIFT NORTHEAST LATE MON ACROSS LOWER MICHIGAN.

WITH CONSIDERABLE CLOUD COVER TONIGHT...TEMPS WILL BE CHALLENGING.
HAVE NUDGED TEMPS UP SLIGHTLY IN A FEW LOCATIONS INTO THE LOW 60S
BUT COULD SEE A FEW LOCATIONS REMAINING IN THE MID 60S.

BEACHLER

&&

.LONG TERM...
309 AM CDT

MONDAY THROUGH SATURDAY...
RIDGING WILL CONTINUE TO STRENGTHEN ACROSS THE ROCKIES...WITH THE
TROUGHING DIGGING INTO THE GREAT LAKES REGION. SFC WAVE WILL BE
SLOW TO DEPART THE GREAT LAKES REGION MON...AND LIKELY CONTINUE TO
PROVIDE SOME SHOWERS AND SCATTERED THUNDERSTORMS THRU AT LEAST TUE
MORNING. THEN ANOTHER LOBE OF VORTICITY IN THE MID-LVLS WILL SLIDE
SOUTHEAST ACROSS THE WESTERN GREAT LAKES TUE AFTN...AND HELP TO
FURTHER KICK EAST THE STUBBORN LOW. TEMPS TUE MAY BE ABLE TO
APPROACH 80...HOWEVER IT WILL HINGE ON CLOUD COVER IN THE AFTN.
OTHERWISE EXPECT BOTH MON AND TUE TO REMAIN GENERALLY IN THE 70S.

HEIGHTS SHUD BE ABLE TO INCREASE WED AND PROVIDE POSSIBLY A PERIOD
OR TWO OF DRY WEATHER TUE NGT INTO WED. GUIDANCE CONTINUES TO POINT
TOWARDS THE DEVELOPMENT OF A BACKDOOR COLD FRONT THAT WILL SLIDE
SOUTH ACROSS THE LAKE TUE NGT...AS A SFC RIDGE DROPS SOUTH FROM
CENTRAL ONTARIO WED. THIS WILL LIKELY REINFORCE COOLER AIR...WITH
HIGHS STRUGGLING TO WARM BEYOND THE LOW/MID 70S AND POSSIBLY
REMAINING IN THE MID 60S FOR AREAS ADJACENT TO LAKE MICHIGAN FROM A
NORTH/NORTHEAST SFC FLOW.

THE FRONTAL BOUNDARY SHUD EVENTUALLY PUSH FURTHER SOUTH...HOWEVER
WITH ANOTHER WAVE DEVELOPING OVER THE CENTRAL PLAINS AND SLIDING
EAST WED NGT...THE BOUNDARY MAY BUCKLE BACK NORTH.

THURSDAY THROUGH SATURDAY... ENSEMBLES MAINTAIN THE RIDGING WEST
THEME WITH TROUGH OVER THE GREAT LAKES REGION. MINIMAL SPREAD IS
DEMONSTRATED IN THE LONGWAVE PATTERN...WHICH SUGGESTS TEMPS WILL
CONTINUE TO BE SLIGHTLY ON THE COOLER THAN NORMAL SIDE. IN ADDITION
OPER GUIDANCE FEATURES PERIODIC CHANCES FOR SHOWERS...AND POSSIBLY A
FEW THUNDERSTORMS FROM DIFFERENTIAL HEATING.

BEACHLER

&&

.AVIATION...

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

* PERIODS OF SHOWERS BEGINNING EARLY THIS EVENING AND CONTINUING
  INTO THE OVERNIGHT HOURS.

* SMALL CHANCE OF A FEW EMBEDDED THUNDERSTORMS...MAINLY MID TO
  LATE THIS EVENING.
* LIGHT SW WINDS THIS MORNING GRADUALLY BACKING TO THE SOUTHEAST
  THROUGHOUT THE DAY.
* LOWERING CIGS THIS EVENING/OVERNIGHT...MVFR TO IFR LIKELY BY
  LATE TONIGHT EARLY MONDAY MORNING.

BMD/KB

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

LOW PRESSURE WILL DIG FROM SOUTHERN MINNESOTA THIS MORNING INTO
FAR EASTERN IOWA THIS EVENING...THEN TO CENTRAL ILLINOIS
OVERNIGHT. SHOWERS AND THUNDERSTORMS ARE ALREADY OCCURRING TO OUR
WEST AND NORTHWEST THIS MORNING AND EXPECT THESE TO CONTINUE
SPREADING SOUTHEAST THROUGH THE DAY...REACHING THE TERMINALS THIS
AFTERNOON. INITIAL LINE OF SHOWERS MAY BE IN A WEAKENING STATE AS
IT REACHING THE CHICAGO AREA EARLY TO MID AFTERNOON DUE TO FAIRLY
MARGINAL INSTABILITY...HOWEVER INSTABILITY IS PROGGED TO INCREASE
AHEAD OF THE SURFACE LOW MID TO LATE AFTERNOON AND PERSIST THROUGH
THE EVENING AS FORCING FROM THE MAIN UPPER WAVE DROPS INTO
NORTHERN ILLINOIS. COVERAGE SHOULD BE SOMEWHAT SCATTERED LATER
TODAY MAKING IT HARD TO PIN DOWN SPECIFIC TIMING. DEEPER MOISTURE
AND MORE PERSISTENT FORCING WILL OVERSPREAD THE AREA LATE THIS
EVENING AND OVERNIGHT BRINGING WHAT SHOULD BE A BETTER CHANCE FOR
SHOWERS WITH EMBEDDED THUNDERSTORMS. WINDS THIS MORNING SHOULD
START OUT SW/SSW AND GRADUALLY BACK TO THE SOUTHEAST THROUGH THE
DAY...AND EVENTUALLY EAST/NORTHEAST BY TOMORROW.

BMD

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

* HIGH WITH SHRA CHANCES THIS EVENING INTO THE OVERNIGHT.
* LOW-MEDIUM WITH THE CHANCES OF A THUNDERSTORM IMPACTING THE
  TERMINALS THIS EVENING.
* MEDIUM-HIGH WITH GENERAL WIND TRENDS BACKING THROUGH DAY.
* HIGH WITH MVFR CIGS DEVELOPING LATE THIS EVENING OR
  TONIGHT...MEDIUM IN IFR CIGS OVERNIGHT.

BMD/KB

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

MONDAY NIGHT...CHC SHRA/SLT CHC TSRA. LIGHT WINDS.
TUESDAY...CHC SHRA/SLT CHC TSRA. NW/N WINDS.
WEDNESDAY...DRY. NE WINDS.
THURSDAY...DRY. NE WINDS.
FRIDAY...SLT CHC TSRA. LIGHT WINDS.
SATURDAY...SLT CHC TSRA. SW WINDS.

BMD

&&

.MARINE...
242 AM CDT

HIGH PRESSURE IS RESULTING IN LIGHT WINDS ACROSS LAKE MICHIGAN
TONIGHT...HOWEVER LOW PRESSURE FORMING OVER THE MID AND UPPER
MISSISSIPPI VALLEY TODAY WILL ALLOW THE PRESSURE GRADIENT TO
TIGHTEN...PARTICULARLY OVER THE SOUTH END OF THE LAKE. WINDS WILL
BECOME SOUTHEASTERLY AND INCREASE INTO THE 10 TO 20 KT RANGE THIS
EVENING AND OVERNIGHT ACROSS THE SOUTH HALF...THEN SHOULD BEGIN TO
TAPER AGAIN MONDAY. ANOTHER PERIOD OF MODERATE NORTH WINDS IS
POSSIBLE ON THE BACK EDGE OF THIS SYSTEM TUESDAY NIGHT WHEN WINDS
WILL INCREASE INTO THE 15 TO 25 KT RANGE.

BMD

&&

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

$$

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