National Weather Service Forecast for: Peotone IL Issued by: National Weather Service Chicago, IL

Updated: 3:26 am CDT Jul 31, 2010

Overnight Chance Showers Saturday Chance Showers Saturday Night Partly Cloudy Sunday Mostly Sunny Sunday Night Partly Cloudy Monday Mostly Sunny Monday Night Chance Tstms Tuesday Chance Tstms Tuesday Night Chance Tstms Lo 64 °F Hi 80 °F Lo 65 °F Hi 86 °F Lo 66 °F Hi 92 °F Lo 75 °F Hi 90 °F Lo 70 °F

Forecast from NOAA-NWS for Peotone IL.

000
FXUS63 KLOT 310802
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
302 AM CDT SAT JUL 31 2010

.DISCUSSION...
302 AM CDT

A PROGRESSIVE AND SOMEWHAT ACTIVE PATTERN LIES AHEAD INTO THE MIDDLE
OF NEXT WEEK WITH THE UPPER FLOW PATTERN GOING THROUGH SEVERAL
CONFIGURATION CHANGES. EARLY MORNING WATER VAPOR IMAGERY SHOWS A
BROAD LARGE SCALE TROUGH OVER MUCH OF EASTERN CANADA AND THE EASTERN
U.S. SEVERAL BETTER DEFINED TROUGH AXES ARE EVIDENT WITH ONE
CROSSING THE GULF OF ST. LAWRENCE AND ANOTHER EXTENDING FROM NEAR
JAMES BAY SOUTHWESTWARD INTO SOUTHERN MN. SEVERAL WEAKER WAVES ARE
EMBEDDED IN THE FLOW AROUND THE BROAD TROUGH. FURTHER WEST...UPPER
RIDGING CONTINUES TO AMPLIFY OVER THE NORTHERN ROCKIES IN RESPONSE
TO A DEEP TROUGH OVER THE COAST OF THE PACIFIC NORTHWEST. THE
AMPLIFICATION OF THE RIDGE SEEMS TO BE SOMEWHAT INHIBITED BY A
SMALLER SCALE UPPER LOW MOVING EASTWARD ACROSS NORTHERN ALBERTA. AT
THE SFC...OBSERVED WIND FIELD AND PRESSURE CHANGE ANALYSIS SHOW LOW
PRESSURE MOVING SOUTHEASTWARD ACROSS SOUTHEASTERN IOWA INTO FAR WEST
CENTRAL ILLINOIS.

MAIN FORECAST CONCERN IN THE SHORT TERM IS POPS TODAY. CURRENT ROUND
OF SHOWERS AND THUNDERSTORMS IS ASSOCIATED WITH MID LEVEL
SHORTWAVE TROUGH AND ALIGNED WELL WITH A BAND OF FRONTOGENETICAL
FORCING IN THE 850-700 MB LAYER. THIS BAND OF PRECIP WILL SHIFT TO
THE EAST THROUGH DAYBREAK RESULTING IN ISOLATED TO SCATTERED
PRECIP COVERAGE ACROSS THE CWA FOR THE REMAINDER OF THE MORNING
WITH WATER VAPOR IMAGERY AND UPSTREAM SOUNDINGS SHOWING
SIGNIFICANT DRYING IN THE MID AND UPPER LEVELS. ANOTHER UPPER
LEVEL TROUGH CONTINUES TO MOVE EAST-SOUTHEAST ACROSS THE WESTERN
U.P. OF MICHIGAN AND NORTHERN WISCONSIN. A TROUGH AXIS DOES EXTEND
FURTHER SOUTHWESTWARD ACROSS SOUTHERN MINNESOTA WHICH WILL CROSS
THE AREA EARLY THIS AFTERNOON. THE SFC LOW ACROSS SOUTHEAST IOWA
WILL DRIFT SOUTHEASTWARD WITH AN INVERTED TROUGH AXIS EXTENDING
NORTHWARD AND MOVING ACROSS THE AREA INTO EARLY AFTERNOON WHILE
BECOMING LESS DEFINED. THE CLOUD SHIELD OVERHEAD EXTENDS WELL
BEYOND THE FORECAST AREA AND WILL LIKELY STAY IN PLACE INTO THE
AFTERNOON. GIVEN THE DEGREE OF DRYING AND THE EXPECTED CLOUD COVER
LIMITING INSTABILITY EXPECT THAT THE TROUGH WILL CROSS THE AREA
DRY BUT CANNOT COMPLETELY ELIMINATE THE POSSIBILITY OF A FEW
ISOLATED SHOWERS DEVELOPING THIS AFTERNOON GIVEN THE ASSOCIATED
ASCENT AND ENHANCED SFC CONVERGENCE PROVIDED BY THE SFC TROUGH.
WILL KEEP MINIMAL SLIGHT POPS GOING FOR ALL BUT THE FAR NORTHWEST
THIS AFTERNOON. WILL NEED TO WATCH CLOUD COVER THROUGH THE MORNING
SINCE AN EARLY SCATTERING WOULD LEAD TO SOME MINIMAL SFC BASED
INSTABILITY WHICH WOULD SLIGHTLY INCREASE THE THREAT FOR A SHOWER.

HIGHS TODAY WILL BE TRICKY BECAUSE OF THE CLOUD COVER BUT
GENERALLY EXPECT HIGHS TO BE ABLE TO WARM TO AROUND 80 WITH
WESTERN AREAS HAVING THE BEST CHANCE FOR SEEING LOW 80S. SOME
LOCATIONS ACROSS THE EASTERN HALF OF THE CWA MAY STRUGGLE TO REACH
80. HIGH PRESSURE SETTLES SOUTHWARD ACROSS WI AND IA TONIGHT WITH
THE PRESSURE GRADIENT BEING WEAK ENOUGH TO ALLOW WINDS TO BECOME
CALM OR LIGHT AND VARIABLE. WILL INCLUDE PATCHY FOG OVERNIGHT
ACROSS MUCH OF THE CWA WITH AREAS OF FOG ACROSS THE
NORTHERN/NORTHWESTERN QUARTER OF THE AREA OR SO GIVEN THE RAINFALL
FROM THIS MORNING. HIGH PRESSURE WILL BE IN PLACE SUNDAY KEEPING
DRY CONDITIONS IN PLACE.

THE NORTHWEST FLOW ALOFT WILL CONTINUE OVERHEAD OF THE LOCAL AREA
INTO EARLY NEXT WEEK BUT THE UPPER RIDGE CURRENTLY OFF TO THE WEST
WILL PUSH EASTWARD TOWARDS THE AREA AND DAMPEN AT THE SAME TIME.
UPPER RIDGING IS FORECAST TO MAKE IT TO THE AREA FOR MONDAY BRINGING
A SURGE IN TEMPERATURES AS AN AXIS OF WARMER MID LEVEL AIR NOSES IN
LATE MONDAY AND TUESDAY. THIS WILL RESULT IN TEMPERATURES RETURNING
TO THE LOWER 90S. THE TROUGH CURRENTLY OVER THE PAC NW COAST WILL
MOVE LITTLE INTO MONDAY AND A TROUGH WILL EJECT EAST-NORTHEASTWARD
ALONG THE NORTHWESTERN FRINGE OF THE UPPER RIDGE AND ATTEMPT TO
PHASE WITH A TROUGH DROPPING SOUTHEASTWARD ACROSS CENTRAL ALBERTA
AND SASKATCHEWAN. THE TROUGH WILL THEN MOVE EASTWARD ACROSS THE
CANADIAN PRAIRIES PUSHING SFC LOW PRESSURE EASTWARD WITH IT WHICH
WILL IN TURN SEND A FRONTAL BOUNDARY TOWARDS THE AREA INTO TUESDAY.
LARGER SCALE TROUGHING WILL FOLLOW THIS INITIAL SHORTWAVE AND
TRANSITION THE FLATTENED RIDGE TO A BROAD TROUGH BY LATE WEDNESDAY.
THIS TRANSITION MAY TAKE SOME TIME WHICH COULD LEAD TO THE FRONTAL
BOUNDARY TAKING ITS TIME MOVING SOUTHEAST OF THE AREA TUESDAY INTO
WEDNESDAY. SLIGHT TROUGHING MOVING OVER THE CENTRAL U.S. ROCKIES
WILL SUPPORT A SFC LOW DEVELOPING ACROSS THE SOUTHERN/CENTRAL PLAINS
AND TRACKING ALONG THE BOUNDARY INTO WEDNESDAY. WILL CONTINUE WITH
POPS FROM MONDAY NIGHT THROUGH TUESDAY NIGHT. THE DETAILS ARE YET
TO BE DETERMINED BUT GIVEN THE VERY MOIST AIRMASS EXPECTED TO BE
IN PLACE HEAVY RAINFALL WOULD BE POSSIBLE WITH ANY CONVECTION.
WILL KEEP MONDAY AS THE WARMEST DAY WITH LOW 90S WITH THE
EXPECTATION THAT PRECIPITATION MAY KEEP TEMPS DOWN AT LEAST A FEW
DEGREES TUESDAY BUT STILL EXPECT HIGHS AROUND 90. SFC HIGH
PRESSURE WILL BUILD IN AS THE FRONT PUSHES TO THE SOUTH AS THE
UPPER FLOW TRANSITIONS BACK TO A NORTHWESTERLY ORIENTATION
OVERHEAD WEDNESDAY.

MDB

&&

.AVIATION...

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

*CHANCE OF SHRA AND VERY SMALL CHANCE OF A BRIEF TSRA OVERNIGHT
 THROUGH SUNRISE.
*CIGS SHOULD BUILD DOWN TO MVFR TOWARD SUNRISE WITH LINGERING
 MVFR CIGS INTO DAY SAT BEFORE GRADUAL IMPROVEMENT.

IZZI

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

SUBTLE SHORTWAVE PROPAGATING THROUGH THE NORTHWEST FLOW WILL
PROVIDE FOR SCT SHRA AND POSSIBLY A TSRA OVERNIGHT. CURRENT RADAR
TRENDS SUGGEST HIGHEST PROBABILITIES OF PRECIP WILL BE NEAR AND
GENERALLY NORTH OF CHGO METRO TERMINALS AND HAVE ONLY INCLUDED
VCSH FOR NOW AND WILL PROACTIVELY AMEND SHOULD SHRA COVERAGE
INCREASE FARTHER SOUTHWARD. AT RFD OCNL SHRA WITH A CHC OF TSRA
WILL CONTINUE FOR A LEAST A COUPLE/FEW MORE HOURS. PRECIP CHANCES
SHOULD BEGIN TO DECREASE TOWARD SUNRISE AND ESPECIALLY BY MID/LATE
MORNING SATURDAY.

MVFR CIGS OVER NW IL APPEAR TO BE EXPANDING EASTWARD WITH RFD/RPJ
NOW DOWN TO MVFR. OBJECTIVE GUIDANCE SUGGESTS THIS TREND SHOULD
CONTINUE OVERNIGHT WITH CIGS BUILDING DOWN TO MVFR IN CHGO METRO
AREA TOWARD SUNRISE. SOME SPOTTY IFR CIGS HAVE DEVELOPED OVER EC
IA INTO SW WI WHERE RAINFALL WAS MORE CONCENTRATED...WHICH DOES
RAISE SOME CONCERNS THAT RFD COULD FALL TO IFR TOWARD SUNRISE AS
SHRA THIN OUT. THIS APPEARS TO BE A LOWER PROBABILITY OF
OCCURRENCE SO JUST BROUGHT TAF DOWN TO LOWER END MVFR FOR NOW.
CIGS SHOULD SLOWLY LIFT DURING THE DAY SATURDAY AND EXPECT VFR
CONDITIONS AGAIN BY AFTERNOON...THOUGH COULD MAINTAIN A BKN VFR
DECK INTO THE EARLY EVENING.

IZZI

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

* MEDIUM CONFIDENCE IN SHRA OCCURRING
* HIGH CONFIDENCE IN PROBABILITY OF TSRA AT TERMINALS REMAINING
  VERY LOW
* MEDIUM-HIGH CONFIDENCE IN CIGS BUILDING DOWN TO MVFR
* LOW CONFIDENCE ON TIME OF ARRIVAL OF MVFR CIGS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 06Z...

SUNDAY...POSS MVFR VSBY IN AM...OTHERWISE VFR.
MONDAY...CHC OF TSRA AT NIGHT...OTHERWISE VFR.
TUESDAY...CHC OF TSRA...OTHERWISE VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.

IZZI

&&

.MARINE...
143 AM CDT

A WEAK TROUGH OF LOW PRESSURE WILL MOVE ACROSS THE WESTERN LAKES
TODAY WITH HIGH PRESSURE BUILDING INTO THE REGION TONIGHT INTO
SUNDAY. THIS HIGH WILL MOVE SLOWLY EAST WITH INCREASING SOUTHERLY
WINDS OVER THE LAKE...PARTICULARLY NORTHERN PORTIONS OF THE
LAKE...MONDAY INTO TUESDAY AS GRADIENT TIGHTENS A BIT BETWEEN
DEPARTING HIGH AND APPROACHING LOW PRESSURE AND ASSOCIATED COLD
FRONT. NEXT COLD FRONT SHOULD MOVE ACROSS THE LAKE TUESDAY INTO
TUESDAY NIGHT WITH ANOTHER HIGH PRESSURE BUILDING IN BRINGING
LIGHT WINDS AGAIN BY MIDWEEK.

IZZI

&&

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

$$

NWS LOT Office Area Forecast Discussion