Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 300400
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1100 PM CDT TUE JUL 29 2014

.DISCUSSION...
218 PM CDT

FORECAST ISSUES CONTINUE TO FOCUS ON DAILY DIURNAL ISOLATED TO
SCATTERED SHOWER/THUNDERSTORM CHANCES...WITH VERY GRADUAL WARM UP IN
TEMPERATURES THROUGH THE FORECAST PERIOD AS LONG WAVE UPPER TROUGH
OVER EASTERN NORTH AMERICA EFFECTIVELY RETROGRADES THROUGH THE END
OF THE WEEK BEFORE FINALLY WEAKENING AND PROGRESSING OFF TO THE
NORTHEAST BY LATE WEEKEND AND EARLY NEXT WEEK.

WESTERN GREAT LAKES REGION REMAINS IN WESTERN PERIPHERY OF THIS
AFOREMENTIONED TROUGH...WITHIN REGION OF BROAD CYCLONIC CIRCULATION.
SERIES OF RELATIVELY MINOR SHORT WAVES WILL CONTINUE TO RIPPLE
SOUTH-SOUTHEAST THROUGH THE FLOW ACROSS THE AREA THROUGH THE
REMAINDER OF THE WEEK. GOES WATER VAPOR IMAGERY INDICATES A COUPLE
OF WEAK RIPPLES PASSED ACROSS THE REGION THIS MORNING...WITH A
SOMEWHAT MORE ROBUST SHORT WAVE NOTED UPSTREAM PROPAGATING SOUTH
ACROSS WESTERN ONTARIO. THESE SYSTEMS WILL TEND TO MODULATE
MID-LEVEL TEMPS AND INSTABILITY...ESPECIALLY WHEN JUXTAPOSED ATOP
AFTERNOON/EARLY EVENING DIURNAL WARMTH. FORECAST SOUNDINGS CONTINUE
TO INDICATE WEAK/SKINNY MLCAPES OF 200-300 J/KG THIS AFTERNOON...
WITH VISIBLE SATELLITE IMAGERY INDICATING CUMULUS CONGESTUS
DEVELOPMENT ALONG WEAK LOW LEVEL CONVERGENCE AXIS FROM NEAR ROCKFORD
TO THE SOUTHEAST SIDE OF CHICAGO/NORTHWEST INDIANA WHERE THE LAKE
BREEZE BOUNDARY WAS PROVIDING SOME ADDITIONAL CONVERGENCE.
CURRENT WEAK RADAR RETURNS EXPECTED TO CONTINUE TO SLOWLY GROW
THIS AFTERNOON THROUGH PEAK INSTABILITY...RESULTING IN ISOLATED TO
SCATTERED SHOWERS AND PERHAPS A FEW THUNDERSTORMS. WANING
INSTABILITY AFTER SUNSET THIS EVENING WILL ALLOW A DECREASE IN
COVERAGE. SIMILAR TREND EXPECTED TOMORROW...THOUGH ONTARIO SHORT
WAVE LOOKS TO MOVE ACROSS AREA DURING THE MORNING...AS OPPOSED TO
DURING PERIOD OF BETTER INSTABILITY LATER IN THE DAY. THIS MAY
FAVOR SOUTHEAST PARTS OF THE CWA WHERE FORCING WILL DECREASE
LAST...WHILE DAYTIME INSTABILITY DEVELOPS. THESE DIURNAL
SHOWERS/ISOLATED THUNDERSTORMS...TIED TO CONVERGENCE ZONES AS IS
THE CASE TODAY...WILL CONTINUE IN SIMILAR FASHION THURSDAY AS
WELL. OBVIOUSLY...NOT ALL AREAS WILL SEE PRECIP AND THERE WILL BE
MANY DRY HOURS EVEN IN PLACES THAT DO. BY FRIDAY...ADDITIONAL
SHORT WAVE ENERGY WILL DROP INTO THE WESTERN PORTION OF THE TROUGH
FROM THE NORTHERN PLAINS AND WILL EFFECTIVELY RETROGRADE THE LONG
WAVE TROUGH AXIS WESTWARD INTO THE WESTERN LAKES AND
MISSISSIPPI/LOWER OHIO VALLEY AREA. LARGE SCALE HEIGHT FALLS WILL
LEAD TO SLIGHTLY COOLER MID-LEVEL TEMPS WHICH MAY SUPPORT GREATER
COVERAGE IN SHOWERS/THUNDERSTORMS FRIDAY AND SATURDAY BEFORE THE
TROUGH AXIS BECOMES MORE PROGRESSIVE AND MOVES OFF TO THE EAST
SATURDAY NIGHT AND SUNDAY. THUS HAVE MAINTAINED SOMEWHAT HIGHER
CHANCE POPS WITH A GREATER AERIAL COVERAGE FOR THOSE DAYTIME
PERIODS.

SURFACE HIGH PRESSURE THEN BUILDS ACROSS THE AREA SUNDAY...BEFORE
DRIFTING TO THE SOUTHEAST MONDAY AS ANOTHER SHORT WAVE TROUGH
APPROACHES IN NORTHWEST FLOW ALOFT. THIS MID-LEVEL WAVE IS
ACCOMPANIED BY A SURFACE LOW AND COLD FRONT...WHICH RETURNS THE
SHOWER/THUNDERSTORM THREAT FOR MONDAY/TUESDAY OF NEXT WEEK.

AS FOR TEMPS...MID AND UPPER 70S BEING REACHED THIS AFTERNOON WITH
CONSIDERABLE SUNSHINE. MID-LEVEL TEMPS CONTINUE TO MODERATE VERY
SLOWLY THROUGH THE PERIOD...WITH TO SLOWLY WARMING FROM UPPER 70S TO
AROUND 80 TO LOWER 80S OUTSIDE OF LAKE BREEZE AND SHOWERS INTO THE
WEEKEND. COLD FRONTAL PASSAGE LATE MONDAY WILL ALLOW SUBTLE
COOL-DOWN FROM THE NORTH BY TUESDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* SHRA PUSHING THROUGH LATE THIS EVENING WITH CURRENT NORTHERLY
  WINDS DIMINISHING AND BECOMING MORE WEST NORTHWEST WITHIN THE
  NEXT 1-2 HOURS.

* LAKE BREEZE LIKELY FOR MDW WEDNESDAY AFTN WITH NE/E WINDS. LAKE
  BREEZE QUESTIONABLE FOR ORD.

* ISOL TO SCT SHRA TO FORM WEDNESDAY EARLY AFTN AND PERSIST
  THROUGH THE AFTN INTO THE EVENING.

DANIELSON/RODRIGUEZ

//DISCUSSION...UPDATED 00Z...

CONVECTIVELY INDUCED OUTFLOW BOUNDARY HAS MERGED WITH LAKE BREEZE
AND PUSHED EASTWARD. WINDS AT ORD AND MDW HAVE SHIFTED TO WEST AT
10 KTS. SOME LINGERING SHRA NEAR ROCKFORD AND YORKVILLE HAVE
PERSISTED BUT WITH INSTABILITY DECREASING AS THE SUN SETS THESE
WILL DISSIPATE MUCH LIKE THE REST OF THE SHRA ACTIVITY HAS IN THE
PAST HOUR. CONCERNS THEN TURN TO SHRA IN WISCONSIN WITH BETTER
COVERAGE THAN STORMS IN OUR AREA. THESE STORMS HAVE PERSISTED ON A
DECENT SURFACE TROUGH AXIS AND WEAK UPPER LEVEL SUPPORT. THIS
ACTIVITY SHOULD BEGIN TO DIMINISH BUT WILL WATCH THESE AS THEY
APPROACH THE WISCONSIN ILLINOIS BORDER. HAVE INDICATED VCSH AT RFD
FROM 02Z TO 04Z DUE TO THIS ACTIVITY.

FOCUS THEN TURNS TO SHRA ACTIVITY WEDNESDAY AND LAKE BREEZE.
CONDITIONS WILL BE SIMILAR TO TODAY WITH WEST-NORTHWEST WINDS
INCREASING IN THE MORNING HOURS. STEEP LOW LEVEL LAPSE RATES AND A
WEAK SHORTWAVE WILL PROVIDE LIFT FOR SHRA FORMING AROUND 2PM AND
LINGERING INTO THE AFTERNOON AND EARLY EVENING. HAVE INDICATED
VCSH AT 19Z FOR ALL AIRPORTS. LOW CONFIDENCE IN ANY TSRA
DEVELOPING BUT COVERAGE WILL BE MINIMAL IF IT DOES OCCUR.
INTENSITY OF THE SHRA AND WEST WINDS WILL NEED TO BE MONITORED TO
GET A BETTER GRASP ON THE LAKE BREEZE WEDNESDAY AFTN. WILL LIKELY
SEE LAKE BREEZE PUSH THROUGH GYY AND MDW. AS ELUDED TO BEFORE
CONDITIONS WILL NEED TO BE WATCHED TO SEE IF LAKE BREEZE WILL PUSH
THROUGH ORD. LAKE BREEZE UNLIKELY AT DPA. SHRA DIMINISHES
WEDNESDAY EVENING AND WINDS WEAKEN AS SUN SETS.

DANIELSON/RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE WITH SHRA TRENDS LATE THIS EVENING...MEDIUM
  CONFIDENCE WITH OVERALL TRENDS WITH WIND DIRECTION/SPEED LATE
  THIS EVENING.

* LOW CONFIDENCE FOR TIMING OF LAKE BREEZE REACHING ORD AND MDW.

* MEDIUM TO HIGH CONFIDENCE IN SCT SHRA DEVELOPMENT ACROSS THE
  AREA WEDNESDAY AFTERNOON. LOW CONFIDENCE IN TSRA DEVELOPMENT.

DANIELSON/RODRIGUEZ

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

THURSDAY...SLIGHT CHANCE TSRA IN AFTN

FRIDAY...SLIGHT CHANCE TSRA IN AFTN

SATURDAY...CHANCE TSRA

SUNDAY...VFR

MONDAY...SLIGHT CHANCE TSRA

DANIELSON/RODRIGUEZ

&&

.MARINE...
210 PM CDT

HIGH PRESSURE IN THE NORTHERN AND CENTRAL PLAINS IS EXPECTED TO
WEAKEN SOME OVER THE COMING DAYS BUT GENERALLY REMAIN STATIONARY FOR
MOST OF THE WEEK AS AN UPPER LEVEL LOW PRESSURE SYSTEMS REMAINS
PARKED OVER JAMES BAY THROUGH SATURDAY. IN THIS PATTERN WEAK LOW
PRESSURE SYSTEMS WILL GLIDE SOUTHEAST DOWN THE LAKE AT TIMES...WITH
THE FIRST EXPECTED LATER TONIGHT INTO EARLY WEDNESDAY.

IN THIS STAGNANT PATTERN THE PRESSURE GRADIENT WILL REMAIN ON THE
LIGHTER SIDE AND WILL PROMOTE THE DEVELOPMENT OF LAKE BREEZES FOR
THE NEARSHORE WATERS AND VARIABLE WINDS OVER MUCH OF THE OPEN LAKE
AND WINDS GENERALLY 15 KT OR LESS.  KMD

KMD

&&

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

$$

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