Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 290544
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1244 AM CDT TUE JUL 29 2014

.DISCUSSION...
244 PM CDT

MAIN FOCUS THROUGH THE FORECAST PERIOD REMAINS ON COOLER THAN NORMAL
WEATHER FOR LATE JULY AND EARLY AUGUST...AND LOW CHANCE POPS FOR
DAILY DIURNAL SHOWER/THUNDERSTORM POTENTIAL.

MORNING UPPER AIR ANALYSIS DEPICTS ANOMALOUSLY DEEP EASTERN NORTH
AMERICAN UPPER TROUGH WITH AN UPPER LOW OVER CENTRAL QUEBEC. THIS
FEATURE IS PROGGED TO SLOWLY RETROGRADE WESTWARD TOWARD JAMES BAY
THROUGH FRIDAY BEFORE EVENTUALLY OPENING UP AND LIFTING OUT TO THE
NORTHEAST OVER THE WEEKEND. THIS PERSISTENT UPPER AIR PATTERN WILL
KEEP THE WESTERN GREAT LAKES REGION IN PERSISTENT COOL NORTHWEST
FLOW ALOFT...WITH SERIES OF SHEARED MID-LEVEL SHORT WAVE FEATURES
ROTATING THROUGH THE WESTERN PERIPHERY OF THE UPPER LOW. THIS
PRESENTS A DAILY THREAT OF ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS DURING THE AFTERNOON/EVENING DIURNALLY FAVORED
INSTABILITY MAXIMA...WITH COVERAGE LIKELY LIMITED SOMEWHAT AND
TIED TO LOCALIZED BOUNDARY LAYER CONVERGENCE LINES. CURRENT
AFTERNOON GOES WATER VAPOR IMAGERY DEPICTS A WEAK MID-LEVEL SHORT
WAVE FEATURE DROPPING SOUTHWARD ACROSS WESTERN ONTARIO WHICH SHOULD
ARRIVE OVER THE AREA TUESDAY MORNING...AND MODELS INDICATE ANOTHER
SUCH FEATURE PASSING THROUGH WEDNESDAY. STRONGER HEIGHT FALLS OCCUR
FRIDAY INTO AS UPPER TROUGH RETROGRADES. GIVEN THESE CONTINUED
GUIDANCE TRENDS HAVE MAINTAINED GENERALLY LOW CHANCE POPS MAINLY FOR
AFTERNOON/EARLY EVENING PERIODS TUESDAY-THURSDAY...WITH SLIGHTLY
HIGHER POPS FRIDAY-SATURDAY WITH TROUGH OVERHEAD. TROUGH AXIS DRIFTS
OFF TO THE EAST SATURDAY NIGHT INTO SUNDAY INDICATING A RESPITE FROM
PRECIP THREAT BEFORE ANOTHER SHORT WAVE DIGS IN FROM THE NORTHWEST
ON MONDAY.

HIGH TEMPS HAVE STRUGGLED TO TOP 70 ACROSS NORTHEASTERN PARTS OF THE
FORECAST AREA TODAY...AND EVEN TO REACH THE MID 60S ALONG THE
INDIANA LAKE SHORE WITH STRONG GUSTY NORTH WINDS. DIMINISHING WINDS
AND A VERY GRADUAL MODERATION IN TEMPS ALOFT WILL HELP NUDGE TEMPS
INTO THE MID AND UPPER 70S OVER THE NEXT FEW DAYS. MORE OF A
NORTHWEST COMPONENT TO WIND TUESDAY SHOULD KEEP LAKE COOLING MAINLY
IN NORTHWEST INDIANA...AND WEAKER LAKE BREEZES OVER THE NEXT FEW
DAYS SHOULD ALLOW SHORE AREAS TO PEAK IN THE 70-75 DEGREE RANGE
MID-LATE WEEK. TEMPS NEAR 80 BY SUNDAY/MONDAY WILL AT LEAST BE ONLY
A FEW DEGREES FROM EARLY AUGUST NORMALS.

RATZER

&&

.AVIATION...

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

* LAKE BREEZE PSBL THIS AFTN WITH WINDS SHIFTING TO NE OR E
  BEHIND IT. BEST CHANCE OF LAKE BREEZE AT MDW.

* CHANCE OF ISOL/SCT SHRA OR TSRA LATE THIS AFTN INTO THE EARLY
  EVENING.

JEE

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

WE REMAIN BETWEEN SYSTEMS WITH A LOW OVER MAINE AND HIGH PRESSURE
ACROSS THE PLAINS. WEAK FLOW WILL STAY WITH US THROUGH THE PERIOD
RESULTING IN VARIABLE TO CALM WINDS TONIGHT. PATCHY VFR CLOUDS WILL
PASS OVER THE TERMINALS WITH PERIODS OF BKN TO OVC VFR CIGS.

A LAKE BREEZE IS EXPECTED...BUT HAVE MEDIUM CONFIDENCE IN HOW FAR
WEST THE LAKE BREEZE WILL TRAVEL. BASED ON SHORT TERM
GUIDANCE...THINKING THE LAKE BREEZE WILL IMPACT MDW AND GYY BUT
STALL BEFORE REACHING ORD. SHRA AND PERHAPS A FEW THUNDERSTORMS
 WILL FORM ALONG THE LAKE BREEZE AND AHEAD OF AN UPPER LEVEL WAVE
THAT ROTATES THROUGH THE REGION. HAVE SOME DOUBTS ABOUT
COVERAGE AND IF THE ISOL TO SCT SHRA/TSRA WILL MOVE DIRECTLY OVER
THE TERMINALS. WINDS BACK TO WNW THIS EVENING AND EXPECTING VFR
CONDITIONS.

JEE


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

* MEDIUM CONFIDENCE IN TIMING AND EASTERN PUSH OF LAKE BREEZE.

* MEDIUM CONFIDENCE IN PRECIP DEVELOPING THIS AFTN AND
  TIMING...LOW CONFIDENCE IN COVERAGE/IMPACTING TERMINALS...LOW
  CONFIDENCE IN TSRA DEVELOPMENT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY THROUGH SUNDAY...PREDOMINANTLY VFR...THOUGH A BRIEF
SHRA/TSRA CANNOT BE RULE OUT (MAINLY AFTERNOON/EARLY EVENING)

IZZI

&&

.MARINE...
124 PM CDT

NORTHERLY WINDS CONTINUE UP AROUND 25 KT ACROSS THE SOUTHERN HALF OF
THE LAKE EARLY THIS AFTERNOON...AND THIS IS CONTINUING TO RESULT IN
BUOY OBSERVATIONS OF 8 TO 10 FOOT WAVES. THESE WINDS WILL GRADUALLY
EASE LATE THIS AFTERNOON AND EVENING...AND EVEN BECOME WESTERLY
TONIGHT AS THE GRADIENT WEAKENS. HOWEVER...WAVE HEIGHTS WILL BE SLOW
TO SUBSIDE...WITH 4+ FOOTERS EXPECTED ACROSS SOUTHERN LAKE MICHIGAN
THROUGH MUCH OF TONIGHT. NO CHANGES ARE PLANNED TO THE CURRENT
ENDING TIMES OF THE SMALL CRAFT ADVISORIES.

FOLLOWING TODAY`S WIND AND WAVE EVENT...IT APPEARS THE WEATHER WILL
BE SOMEWHAT QUIET ACROSS THE LAKE DURING THE WEEK. AN UPPER LEVEL
LOW OVER QUEBEC WILL CONTINUE TO LEAD TO A WEST NORTHWESTERLY FLOW
PATTERN...ALBEIT LIGHT...ACROSS THE LAKE THROUGH MUCH OF THE PERIOD
AS A COUPLE OF WEAK COLD FRONTAL BOUNDARIES DROP SOUTHWARD OVER THE
LAKE.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ014 UNTIL 4 AM TUESDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 4 AM TUESDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE NORTHERLY IS TO MICHIGAN CITY IN UNTIL 4 AM
     TUESDAY.

&&

$$

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