Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 200832
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
332 AM CDT WED AUG 20 2014

.DISCUSSION...
320 AM CDT

SHORT TERM...THROUGH WEDNESDAY NIGHT...

FOR THE REMAINDER OF THE OVERNIGHT HOURS...CONDITIONS WILL REMAIN
QUIET WITH HIGH PRESSURE OVERHEAD AND THE PESKY UPPER LOW LIFTING
INTO THE UPPER GREAT LAKES AND ANY ASSOCIATED CONVECTION MOVING WELL
TO THE EAST.  UNDER CLEAR SKIES AND LIGHT WINDS...EXPECT THAT SOME
LOCATIONS COULD SEE SOME FOG DEVELOPMENT...MAINLY LOW LYING AND
SHELTERED AREAS.  DO NOT EXPECT WIDESPREAD DENSE FOG  AS DEWPOINT
DEPRESSIONS ARE STILL 3-5 DEGREES IN MANY PLACES.  CONDITIONS WILL
REMAIN QUIET INTO WEDNESDAY BUT UPPER RIDGING BUILDING OVER THE
CENTRAL PLAINS AND ACROSS THE MIDDLE AND UPPER MISSISSIPPI VALLEY
WHILE THE UPPER LOW CONTINUES TO LIFT TO THE NORTHEAST IS SIGNALING
THE BEGINNING OF A SIGNIFICANT WARMING TREND...MORE LIKE THE TRUE
DOG DAYS OF SUMMER THAT THE UNSEASONABLY COOL WEATHER THAT THE AREA
HAS SEE FOR MUCH OF THIS SUMMER.  ACCOMPANYING THE UPPER RIDGING AND
INCREASING TEMPERATURES ALOFT WILL BE AN INCREASE OF LOW LEVEL
MOISTURE.  THE BERMUDA HIGH IS IN PLACE OVER THE ERN GLFMEX WHILE
A TROUGH OF LOW PRESSURE IS DEVELOPING OVER THE CENTRAL PLAINS.
THIS IS SETTING UP A RETURN FLOW OF MOISTURE FROM A WIDE OPEN GULF
OF MEXICO...WITH 20-30KT 850MB WINDS WITH TRAJECTORIES OFF OF THE
WESTERN GLFMEX POINTING RIGHT INTO THE MIDWEST. UNDER AMPLE SUNSHINE
FOR MOST OF THE DAY TODAY...THERE SHOULD BE LITTLE TROUBLE MIXING
DOWN THE WARMER AIR ALOFT...WHERE 850MB TEMPS SHOULD BE ARND
18-20C.  SO...THE AREA WILL SEE HIGHS TODAY IN THE MIDDLE TO UPPER
80S.  WITH DEWPOINTS IN THE MIDDLE TO UPPER 60S...THE MAX HEAT INDEX
TODAY SHOULD BE IN THE UPPER 80S TO LOWER 90S.  WHILE THESE HEAT
INDEX VALUES ARE NOT ANYWHERE NEAR HEADLINE LEVELS...THEY ARE
CERTAINLY MUCH HIGHER THAN HAS BEEN SEEN FOR THE BULK OF THE
SUMMER.

SHOWERS AND THUNDERSTORMS WILL BECOME AN INCREASING CONCERN THROUGH
THE AFTERNOON AND INTO WEDNESDAY NIGHT.  EARLY THIS MORNING...THERE
IS ONGOING CONVECTION OVER THE UPPER MISSOURI VALLEY ASSOCIATED WITH
A SHORTWAVE OVER TOPPING THE UPPER RIDGE.  EXPECT THAT THIS ACTIVITY
SHOULD SLIDE SOUTHEAST OF THE CWA THIS MORNING...MOVING THROUGH SRN
IA/NRN MO AND INTO CNTRL/SRN IL.  THE MODELS ARE CONSISTENT IN
DEVELOPING A WARM FRONT EXTENDING EAST FROM A DEEPENING LOW OVER THE
DAKOTAS THROUGH THE MIDDLE MISSISSIPPI VALLEY BY EARLY WEDNESDAY
EVENING.  THIS SHOULD BE THE FOCUS FOR SHRA/TSRA SPREADING INTO THE
REGION FROM SOUTHWEST TO NORTHEAST THROUGH THE EVENING AND OVERNIGHT
HOURS WEDNESDAY NIGHT.  HAVE MAINTAINED A MORE BROADBRUSHED
APPEARANCE TO THE WX/POP/QPF GRIDS FOR WEDNESDAY NIGHT DUE TO SOME
CONCERN WITH TIMING OF THE PCPN SPREADING NWD AS THERE IS STILL SOME
UNCERTAINTY IN THE MODELS AS FAR AS TIMING THE LEADING EDGE OF THE
PCPN...BUT HAVE GONE WITH LIKELY POPS AS CONFIDENCE IS HIGHER IN THE
POTENTIAL FOR PCPN.  CONFIDENCE IS JUST A LITTLE LOWER IN THE ONSET
TIME.  WHILE THE SEVERE POTENTIAL WILL BE LOW...A GREATER CONCERN
WILL BE LOCALLY HEAVY RAINFALL.  AS SWLY FLOW AND WARM/MOIST
ADVECTION INCREASES THROUGH WEDNESDAY NIGHT...THE MODEL GUIDANCE IS
INDICATING PWATS AROUND 2 INCHES OVER THE AREA.  WITH UPPER LEVEL
WINDS FROM JUST ABOVE THE SURFACE THROUGH THE COLUMN EXPECTED TO BE
ARND 25-30KT...THE THUNDERSTORM ACTIVITY SHOULD BE PROGRESSIVE.
SO...WHILE LOCALLY HEAVY RAINFALL IS QUITE POSSIBLE...WIDESPREAD
FLOODING IS NOT ANTICIPATED THOUGH LOCALIZED URBAN AND SMALL STREAM
ADVISORY TYPE FLOODING REMAINS A POSSIBILITY.

KREIN

THURSDAY THROUGH SUNDAY...
MAIN CONCERN IN THE MEDIUM TERM WILL RESIDE ON THE
PLACEMENT/STRENGTH OF THE 500MB RIDGE POISED TO SETUP ACROSS THE
OZARKS. GUIDANCE HAS BEEN CONSISTENTLY SUGGESTING AN ATMOSPHERIC
RIVER DEVELOPING ACROSS THE NORTHERN PLAINS AND BECOMING ORIENTED
ALONG THE NORTHERN PERIPHERY OF THE MID-LVL RIDGE...THEN TURNING
SOUTHEAST ACROSS THE ALLEGHENIES IN PENNSYLVANIA. CONCERN DOES ARISE
WITH THE FACT THAT MEDIUM RANGE GUIDANCE HAS DEMONSTRATED A REDUCED
LEVEL OF CONFIDENCE WITH SPREAD IN HOW AMPLIFIED THE RIDGE WILL
BECOME...WHICH COULD BE STARTING TO HINT THAT THE ACTIVE RING-O-FIRE
MAY END UP CLOSER TO THE FORECAST AREA THUR NGT/FRI. AT THIS TIME
HAVE ONLY MADE MINOR ADJUSTMENTS WITH THE POPS...AND EXPECT A
CHANNEL OF LIKELY POPS TO BE LIFTING NORTH THUR MIDDAY INTO WISC BY
THUR NGT. CURRENT OPER SOLUTIONS STILL FAVOR THIS SCENARIO...PLUS
850MB TEMPS WILL BE STEADILY WARMING AND SHUD LIMIT THE COVERAGE OF
CONVECTION/PRECIP.

THEN INTO FRI SOLUTIONS SUGGEST THE TOP OF THE RIDGE MAY BEGIN TO
FLATTEN. LOCAL ARW8KM ALSO HINTS THAT THE ACTIVE ZONE MAY BE
DRIFTING SOUTH AND COULD BE OVER THE FORECAST AREA FRI AFTN/EVE.
THEN FOR SAT RIDGE REMAINS OVERHEAD...BUT IT STILL LOOKS POSSIBLE
FOR CHC POPS TO START THE WEEKEND. THE ONE CONSISTENCY THROUGH THE
THUR-SAT TIMEFRAME...THE HEAT/HUMIDITY. WHILE PWAT VALUES CONTINUE
TO HOVER IN THE 1.6-1.8" RANGE...THE FORECAST DEW PTS ARE EXPECTED
TO LINGER IN THE LOW TO PERHAPS MID 70S FOR MANY LOCATIONS THUR-SAT.
SFC TEMPS ARE PROGGED TO PUSH WELL INTO THE 80S...AND PERHAPS WARMER
YET DEPENDING ON CLOUD COVER/PRECIP. THE COMBINATION OF ANOMALOUSLY
HIGH DEW PTS AND SFC TEMPS IN THE UPR 80S/NEAR 90 WOULD SIGNAL HEAT
INDEX VALUES IN THE MID/UPR 90S TO PERHAPS THE LOW 100S SOUTH OF
I-80...MAINLY FRI-SUN.

EARLY NEXT WEEK...
ENSEMBLES AND OPER SOLUTIONS CONTINUE TO POINT TOWARDS THE HOT/HUMID
AIRMASS BREAKING DOWN AND TRANSITIONING BACK TO A MID CONUS/GREAT
LAKES TROUGH. MON WILL LIKELY STILL BE A HOT/HUMID DAY. GUIDANCE HAS
DEMONSTRATED SOME CONFIDENCE/CONSISTENCY IN A FRONTAL BOUNDARY
APPROACHING THE REGION MON NGT/TUE...WITH MUCH COOLER AIR BEGINNING
TO DRIVE SOUTH ACROSS THE NORTHERN PLAINS TUE...AND ARRIVING ACROSS
THE CWFA TOWARDS THE MIDDLE OF NEXT WEEK.

BEACHLER

&&

.AVIATION...

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

* CHANCE MVFR VIS OVERNIGHT INTO EARLY WEDNESDAY MORNING.

* POSSIBLE LAKE BREEZE LATE WEDNESDAY AFTERNOON/EARLY EVENING.

KREIN

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

ALL CONVECTIVE ACTIVITY HAS MOVED OUT OF NRN IL/NWRN IN AND SKIES
HAVE BECOME MOSTLY CLEAR WITH CALM TO LIGHT WEST WINDS. CLEAR
SKIES LIGHT WINDS AND DEWPOINTS IN THE 60S SHOULD ALLOW FOR SOME
FG/BR DEVELOPMENT AS TEMPERATURES RADIATE DOWN CLOSE TO THE IN
SITU DEWPOINTS. WILL CARRY MVFR VIS AT ALL TERMINAL EXCEPT ORD/MDW
WHERE URBAN HEAT ISLAND EFFECTS COULD KEEP TEMPS A LITTLE
HIGHER...AND SATURATION WOULD BE LESS LIKELY. A FEW ISOLD POCKETS
OF IFR VIA ARE POSSIBLE IN LOW LYING...SHELTERED LOCATIONS.

WESTERLY WINDS INCREASE BY MID TO LATE MORNING WEDNESDAY WITH
MODEL FORECAST SOUNDINGS SUGGESTING PREVAILING WINDS AROUND 10
KT...ESPECIALLY DURG THE LATE MORNING HOURS. WINDS ARE EXPECTED TO
WEAKEN DURG BY THE LATE AFTERNOON HOURS AS A WEAK RIDGE AXIS
DEVELOPS FROM WISCONSIN...THROUGH NERN IL/NWRN IN INTO THE LOWER
OHIO VALLEY. A LAKE BREEZE IS EXPECTED TO DEVELOP NEAR THE LAKE
AND EVENTUALLY MOVE INLAND...BUT LIKELY NOT REACHING ORD/MDW UNTIL
LATE AFTERNOON OR EARLY EVENING. WINDS AT ORD/MDW SHOULD TURN
ESELY WITH THE PASSAGE OF THE LAKE BREEZE...BUT THERE WILL ONLY BE
A WEAK PUSH TO THE LAKE BREEZE AND THE SSELY WINDS SHOULD ONLY BE
ARND 5KT OR SO AT ORD/MDW. WINDS WILL THE SETTLE INTO A SSELY TO
SLY DIRECTION THROUGH THE LATE EVENING HOURS. ANOTHER MID LEVEL
IMPULSE IS EXPECTED TO DROP OUT OF THE UPPER MISSISSIPPI VALLEY
LATE WEDNESDAY NIGHT...BRINGING A CHANCE FOR MORE SHOWERS AND
THUNDERSTORMS TO THE REGION.

KREIN

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

*  HIGH CONFIDENCE IN WIND TRENDS THROUGH THE PERIOD...BUT A
   LITTLE LOWER CONFIDENCE IN THE EXACT TIMING OF LAKE BREEZE
   PASSAGE.

*  MEDIUM TO HIGH CONFIDENCE THAT VIS WILL DROP TO MVFR WITH ISOLD
   IFR ACROSS THE REGION...AND MEDIUM CONFIDENCE THAT VIS AT
   ORD/MDW WILL REMAIN 6SM OR HIGHER.

*  LOW CONFIDENCE IN TIMING AND COVERAGE OF SHRA/TSRA WEDNESDAY
   NIGHT.

KREIN

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

* THURSDAY THROUGH SATURDAY...CHANCE OF TSRA.
* SUNDAY...SLIGHT CHANCE OF TSRA.
* MONDAY...DRY/VFR.

&&

.MARINE...
314 AM CDT

SFC LOW PRESSURE CONTINUES TO MEANDER AROUND NORTHERN LOWER
MICHIGAN THIS MORNING...ALTHOUGH HAS BEEN WEAKENING. THIS LOW IS
EXPECTED TO DRIFT SOUTHEAST AND REACH THE EASTERN GREAT LAKES
EARLY THURSDAY. OVER THE NEXT SEVERAL DAYS THE GRADIENT IS
EXPECTED TO BE VERY WEAK...SO MOST OF THE WINDS WILL BE LESS THAN
15KT. THIS WILL ALSO RESULT IN WAVES REMAINING LOW...OR GENERALLY
LESS THAN 3 FT IN MOST AREAS. WITH THUNDERSTORMS CHANCES OVER THE
NEXT SEVERAL DAYS...WINDS/WAVES WILL LIKELY BE ELEVATED IN AND
AROUND STORMS. OTHERWISE A SERIES OF WEAK LOW PRESSURE SYSTEMS
WILL MOVE FROM THE CENTRAL PLAINS NORTHEAST TO THE UPPER MIDWEST
INTO WESTERN ONTARIO.

BEACHLER

&&

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

$$

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