Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 280000
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
700 PM CDT WED AUG 27 2014

.DISCUSSION...
330 PM CDT

SHORT TERM...WEDNESDAY AFTERNOON THROUGH SATURDAY...

FOR THE REMAINDER OF THE AFTERNOON SHOULD REMAIN QUIET AS THE OLD
STATIONARY BOUNDARY REMAINS WELL TO THE SOUTH ACROSS SRN IL AND THE
OHIO VALLEY.  HAVE MAINTAINED SLIGHT CHANCE POPS ACROSS THE VERY FAR
SOUTH OF THE CWA...A LITTLE NORTH OF THE BOUNDARY IN DEFERENCE TO
THE PROXIMITY TO THE BOUNDARY TO THE SOUTH AND A WARM AND VERY MOIST
AIRMASS...WITH DEWPOINTS STILL IN THE LOW 70S...ACROSS THE AREA.
THROUGH THE LATE EVENING AND INTO THE OVERNIGHT HOURS...ANTICIPATE
INCREASING POPS SPREADING FROM SOUTHWEST TO NORTHEAST AS LOW
PRESSURE OVER THE CENTRAL PLAINS LIFTS NEWD...DRAGGING THE OLD
STATIONARY BOUNDARY BACK NORTH AS A WARM FRONT.  WITH UPPER RIDGING
BUILDING ALOFT WITH THE RIDGE AXIS EXTENDING JUST EAST OF THE
MISSISSIPPI RIVER BY EARLY THURSDAY MORNING...ANTICIPATE THAT SWLY
FLOW ALOFT SHOULD HELP KEEP THE HIGHEST PCPN CHANCES OVER LOCATIONS
WEST OF A LINE FROM ROCKFORD TO WATSEKA.

THROUGH THURSDAY AND THURSDAY NIGHT...THE UPPER RIDGE WILL SLOWLY
BUILD  EAST AS SHORTWAVE ENERGY OVERTOPS THE RIDGE.  THE SHORT RANGE
MODELS ARE RELATIVELY CONSISTENT ON ADVERTISING THIS SCENARIO...SO
ANTICIPATE INCREASING POPS OVER THE WRN PORTIONS OF THE CWA THROUGH
THE EVENING AND THEN THE NORTHERN PORTIONS OF THE CWA THROUGH THE
NIGHT...BUT WITH THE TRACK OF THE MAIN UPPER SHORTWAVE TO THE WEST
AND NORTH OF THE CWA...THE STRONGER UPPER FORCING SHOULD BE OVER
IOWA AND INTO WISCONSIN...SO HAVE LIMITED POPS OVER THE CWA TO
CHANCE LEVELS.  THE LOCAL AREA SHOULD BEGIN TO SEE POPS INCREASING
THROUGH THE DAY FRIDAY AND ESPECIALLY LATER FRIDAY NIGHT AS A STRONG
SHORTWAVE LIFTING OUT OF THE GREAT BASIN TONIGHT SLOWLY TRACKS EAST
ACROSS THE CENTRAL PLAINS AND REACHES THE MIDDLE AND UPPER
MISSISSIPPI VALLEY FRIDAY NIGHT.  WILL INCREASE POPS THROUGH FRIDAY
EVENING WITH LIKELY POPS SPREADING INTO THE WRN PORTIONS OF THE CWA
AFTER MIDNIGHT FRIDAY NIGHT AND EAST ACROSS THE REMAINDER OF THE
AREA THROUGH SATURDAY AND INTO SATURDAY EVENING.

FORM TEMPERATURES...WITH SFC HIGH PRESSURE SLOWLY SLIDING ACROSS THE
GREAT LAKES REGION...THE WARMEST AND MOST HUMID CONDITIONS WILL BE
CONFINED TO THE FAR SOUTHERN PORTIONS OF THE CWA...THOUGH EVEN
LOCATIONS NORTH OF THE I-80 CORRIDOR HAVE SEEN TEMPS CLIMB INTO THE
LOWER 80S EVEN WITH PERSISTENT NELY FLOW AT THE LOWER LEVELS.  THE
HIGH WILL STILL HAVE A MAJOR INFLUENCE ON TEMPS THROUGH
THURSDAY...KEEPING THE NORTHERN PORTIONS OF THE CWA...INCLUDING THE
LAKEFRONT...ON THE COOLER SIDE WITH HIGHS IN THE UPPER 70S TO AROUND
80...WHILE THE SRN LOCATIONS SHOULD WARM INTO THE LOWER 80S.  AS THE
UPPER RIDGE BUILDS ACROSS THE AREA ON FRIDAY AND THE WARM FRONT
LIFTS WELL TO THE NORTH INTO WISCONSIN...EXPECT THAT TEMPS SHOULD
RETURN TO THE MIDDLE TO UPPER 80S WITH DEWPOINTS IN THE LOWER 70S.
THIS COMBINATION OF WARMTH AND MOISTURE SHOULD DRIVE HEAT INDEX
VALUES BACK INTO THE LOWER 90S.  BY FRIDAY NIGHT OR EARLY
SATURDAY...A WEAK COLD FRONT IS EXPECTED TO SWEEP ACROSS THE
AREA...BUT LITTLE SIGNIFICANT AIRMASS CHANGE IS EXPECTED AS THERE
SHOULD BE LITTLE INFLUX OF SIGNIFICANTLY COOLER/DRIER AIR INTO THE
REGION AS SFC HIGH PRESSURE BUILDS ACROSS SRN CANADA AND THE REGION
ONLY EXPERIENCES A BRIEF PERIOD OF LIGHT AND VARIABLE WINDS UNDER
VERY WEAK SFC TROUGHING ASSOCIATED WITH THE COLD FRONT.  BY
SATURDAY...SOUTHERLY FLOW SHOULD RETURN AS A COLD FRONT AND SFC
TROUGH MOVES OUT OVER THE NRN/CNTRL PLAINS AND AND THE BERMUDA HIGH
BUILDS BACK ACROSS THE GULF COAST.

FOR THE LONGER TERM...FROM SUNDAY THROUGH WEDNESDAY...UNSETTLED
WEATHER WILL CONTINUE ACROSS THE REGION FOR SUNDAY AND MONDAY.  THE
LONGER RANGE GUIDANCE IN IN RELATIVELY GOOD AGREEMENT ON A LONG WAVE
TROUGH MOVING ACROSS THE ROCKIES WITH WEAK RIDGING OVER THE ERN
CONUS.  THIS WILL PUT THE UPPER MIDWEST UNDER BROAD SWLY FLOW WITH A
SERIES OF WEAK SRN STREAM SHORT WAVES TRACKING ACROSS THE AREA.  IN
GENERAL...THE UPPER LEVEL PATTERN WILL BE FAIRLY LOW AMPLITUDE...SO
TIMING AND STRENGTH OF INDIVIDUAL WAVES WILL BE QUESTIONABLE...BUT
THE GENERAL TREND SHOULD BE FOR MORE PERIODIC SHOWERS AND
THUNDERSTORMS...THOUGH CONFIDENCE IN TIMING WILL BE LOW.  BY TUESDAY
AND WEDNESDAY...THE LONGER RANGE GUIDANCE IS INDICATING THAT THE
UPPER TROUGH SHOULD BEGIN TO MOVE EAST OF THE AREA...WITH HIGH
PRESSURE SETTLING OVER THE UPPER MISSISSIPPI VALLEY AND WESTERN
GREAT LAKES REGION.  THIS WOULD LEAD TO A PERIOD OF DRIER CONDITIONS
SO HAVE REMOVED POPS FOR TUESDAY AND WEDNESDAY.  UNDER RELATIVELY
LOW AMPLITUDE FLOW ALOFT...THERE SHOULD BE LITTLE DAY TO DAY
TEMPERATURE SWINGS WITH HIGHS GENERALLY IN THE LOWER 80S AND
OVERNIGHT LOWS IN THE 60S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* EAST WINDS AROUND 10 KT THROUGH THE EARLY EVENING...THEN
  INCREASING AGAIN TO AROUND 10 KT THURSDAY AFTERNOON.

* SHRA/ISOLATED TSRA THURSDAY AFTERNOON/EVENING

KMD

//DISCUSSION...UPDATED 00Z...
EAST WINDS STILL HOVERING AROUND 10 KT...AND EXPECT THAT TO
CONTINUE UNTIL A LITTLE AFTER SUNSET. HIGH PRESSURE REMAINS IN
CONTROL TONIGHT FOR PASSING HIGH CLOUDS AND LIGHTER EAST
WINDS...THEN CLOUDS INCREASE ON THURSDAY AHEAD OF A WARM FRONT.
DRIER EAST WINDS KEEP MOST AREAS DRY...THOUGH KRFD HAS THE BEST
CHANCE FOR A SHOWER IN THE AFTERNOON. THE WARM FRONT LIFTS THROUGH
THURSDAY EVENING WHICH IS THE BEST CHANCE FOR ANY SHOWERS ACROSS
THE TERMINALS. INSTABILITY PARAMETERS ARE WEAK AND THUS EXPECT
THUNDER ACTIVITY TO BE ISOLATED AND THEREFORE KEPT THE KORD TAF
LIMITED TO SHOWERS FOR NOW. HIGHEST IMPACTS FOR THE AIRSPACE WILL
BE FOR AREAS NORTH AND WEST.

KMD


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH IN WINDS AT OR ABOVE 10 KT THROUGH 1Z. MEDIUM THAT EAST
  WINDS WILL REACH 10 KT OR HIGHER TOMORROW AFTERNOON AND MEDIUM
  ON TIMING.

* MEDIUM THAT SHRA REMAIN WEST OF ORD/MDW THROUGH 0Z. MEDIUM IN
  SHRA THURSDAY EVENING. MEDIUM THAT ANY TSRA WOULD BE ISOLATED
  THROUGH 6Z.

KMD

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

FRIDAY...CHANCE TSRA.

SATURDAY...TSRA LIKELY.

SUNDAY AND MONDAY...CHANCE TSRA.

TUESDAY...SLIGHT CHANCE TSRA.

KMD

&&

.MARINE...
205 PM CDT

HIGH PRESSURE WILL CONTINUE TO BE OVERHEAD OF LAKE
MICHIGAN...LIKELY LINGERING THROUGH DAYBREAK THURSDAY BEFORE
MOVING EAST TOWARDS LAKE ERIE TOMORROW NIGHT. AS THE HIGH DRIFTS
EAST...WINDS WILL SLOWLY TURN SOUTHEASTERLY THEN SOUTHERLY.
GUIDANCE IS EXPECTING A LOW PRESSURE SYSTEM TO LIFT NORTHEAST
ACROSS THE CENTRAL PLAINS INTO THE UPPER MIDWEST THURSDAY
AFTERNOON. THIS WILL RESULT IN A TIGHTENING GRADIENT FROM SOUTH TO
NORTH ACROSS THE LAKE. AT THIS TIME IT IS POSSIBLE THAT WINDS
COULD HOVER IN THE 15 TO 25 KT RANGE THURSDAY NIGHT INTO FRIDAY.
THEN AS THE LOW PRESSURE LIFTS NORTHEAST OF LAKE MICHIGAN AND A
RIDGE OF HIGH PRESSURE SLIDES SOUTH FROM CENTRAL CANADA INTO THE
UPPER MIDWEST FRIDAY EVENING...A FRONTAL BOUNDARY WILL SAG SOUTH
AND TURN WINDS NORTHERLY FOR THE NORTHERN HALF OF THE LAKE.
MEANWHILE IT DOES APPEAR THE BOUNDARY GETS HUNG UP ACROSS THE
CENTRAL PORTION OF THE LAKE FRIDAY NIGHT/EARLY SATURDAY...WHICH
WILL KEEP SOUTHERLY WINDS FOR THE SOUTHERN HALF OF THE LAKE. THEN
YET ANOTHER AREA OF LOW PRESSURE IS FORECAST TO DEVELOP ACROSS THE
NORTHERN PLAINS SATURDAY AFTERNOON AND DEEPEN AS IT MOVES
NORTHEAST INTO WESTERN ONTARIO. THIS WILL LIKELY CREATE A TIGHT
GRADIENT ACROSS THE LAKE SUNDAY WITH YET ANOTHER PERIOD OF WINDS
NEARING 20-25KT.

BEACHLER

&&

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

$$

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