Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLOT 050936
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
436 AM CDT SAT SEP 5 2015

.SHORT TERM...
249 AM CDT

THROUGH SUNDAY...

SKIES HAVE REMAINED MAINLY CLEAR EARLY THIS MORNING...WITH THE
EXCEPTION OF A WARM AIR ADVECTION WING THAT WAS SLOWLY SLIDING EAST
ACROSS FAR NORTHWEST IL. THERE REMAINS VERY WEAK INSTABILITY TO
ALLOW A FEW ISOLATED SHOWERS/THUNDERSTORMS TO BUBBLE UP THIS
MORNING. THE FORCING WITHIN THE COLUMN DOES NOT SUPPORT GROWTH OR
MORE ORGANZITION TO THE PRECIP/CONVECTION...OTHER THAN A FEW STORMS.
THERE WAS A LOBE OF VORTICITY PIVOTING SOUTHEAST ACROSS SOUTHWEST
WISC...HOWEVER THIS APPEARS TO BE SLOWING AS IT BUMPS UP AGAINST THE
MID-LVL SHORTWAVE THAT WAS ROTATING OVER THE GREAT LAKES.

TEMPERATURES HAVE GENERALLY FALLEN TO ARND 70 DEG...WITH MINIMAL
SPREAD IN THE DEW POINTS. THIS COUPLED WITH A VERY LIGHT GRADIENT
AND MINIMAL CLOUDS HAS ALLOWED PATCHY FOG TO DEVELOP. CLOUDS WILL
THICKEN FROM WEST TO EAST EARLY THIS MORNING...WITH THE WARM AIR
ADVECTION WING...WHICH SHOULD HELP INHIBIT THE FOG THAT DEVELOPS.
THEN CLOUDS SHOULD ERODE BY LATE MORNING...OR WITH JUST FEW/SCT
COVERAGE. DEW POINTS WILL HOVER IN THE MID/UPR 60S AGAIN
TODAY...WITH A LIGHT SOUTHWESTERLY TO SOUTHERLY FLOW. WINDS ABOVE
THE SFC WILL REMAIN LIGHT...WHICH SHOULD ALLOW WINDS TO TURN ONSHORE
LATER THIS AFTERNOON.

THE FOCUS THEN TURNS TOWARDS ADDITIONAL ISOLATED
SHOWERS/THUNDERSTORMS EARLY THIS AFTERNOON THROUGH TONIGHT. SEVERAL
CAMS CONTINUE TO INDICATE THAT ARND 19Z CONVECTION MAY BEGIN TO
BUBBLE UP. WINDS ALOFT REMAIN EQUALLY LIGHT...AS ANY SHEAR WOULD BE
LESS THAN 15KT AND NOT CONDUCIVE OF ANY STRONGER/SEVERE STORMS THIS
AFTERNOON. MID-LVL HEIGHTS WILL BEGIN TO RISE ALONG THE WESTERN
CWFA...AS THE DOWNSTREAM TROUGH BEGINS TO WEAKEN BY LATE AFTERNOON.
THUS EXPECT WHATEVER SHOWERS/THUNDERSTORMS BUBBLE UP...WILL BE
DIURNALLY DRIVEN AND SHOULD DISSIPATE AROUND SUNSET. HIGHS TODAY
WILL AGAIN BE UNSEASONABLY WARM...TOPPING OUT ARND 90 TO THE LOW 90S
IN A FEW LOCATIONS. DEPENDING ON THE TIMING OF A LAKE BREEZE/ONSHORE
FLOW...AREAS ADJACENT TO LAKE MICHIGAN MAY STRUGGLE TO WARM BEYOND
THE MID 80S.

MID-LVL TROUGH OVER THE REGION WILL FINALLY DISSIPATE LATE THIS
EVENING...WITH HEIGHTS HOLDING IN PLACE AND PROVIDING SOME WEAK
DIFFLUENT FLOW. COULD SEE FOG DEVELOPING GIVEN HOW MOIST THE
ATMOSPERE WILL BECOME WITH DEW PTS LINGERING IN THE UPR 60S AND
PERHAPS ONLY A FEW DEGREE SPREAD AGAINST TEMPS.

SUNDAY... UNSEASONABLY WARM/HUMID CONDITIONS WILL PERSIST AGAIN
SUN...WITH MID-LVL RIDGING HOLDING IN PLACE ACROSS THE REGION. SFC
WINDS MAY BE JUST STRONG ENOUGH TO CONFINE THE LAKE BREEZE TO THE
NEARSHORE...OR PERHAPS WITHIN A MILE OR TWO OF THE SHORELINE. EXPECT
FOG TO STEADILY LIFT AFTER DAYBREAK SUN...BUT COULD SEE SOME HAZE
LINGERING THRU MID/LATE MORNING. THERMAL RIDGE ALOFT WILL SUPPORT
TEMPS EARILY WARMING TO 90 ACROSS THE BULK OF THE FORECAST
AREA...WITH SEVERAL HI-RES GUIDANCE MEMBERS LEANING TOWARDS THE LOW
90S SUN AFTN. THIS COUPLED WITH DEW POINTS IN THE MID/UPR
60S...COULD LEAD TO HEAT INDEX READINGS OF 95-98 DEG SUN AFTERNOON.

BEACHLER

&&

.LONG TERM...
324 AM CDT

SUNDAY NIGHT THROUGH FRIDAY...

AN UPPER LEVEL LOW MOVES INTO SOUTH CENTRAL CANADA EARLY NEXT WEEK
AND THE PERSISTENT UPPER LEVEL RIDGE OVER THE MIDWEST IS REPLACED BY
A TROUGH LATE NEXT WEEK. TWO SURFACE LOWS WILL BE OVER SOUTHERN
CANADA EARLY NEXT WEEK WITH THE EASTERN ONE QUICKLY SHIFTING OVER
THE ATLANTIC WHILE THE WESTERN LOW REACHES HUDSON BAY BY MID WEEK.

HOT AND HUMID CONDITIONS WILL CONTINUE THROUGH SUNDAY NIGHT WITH
LOWS AROUND 70.  THE WESTERN LOWS COLD FRONT APPROACHES THE REGION
MONDAY WITH SHOWERS AND THUNDERSTORMS MAINLY WEST OF I-55 MONDAY
MORNING. GUIDANCE CONTINUES TO INDICATE THAT PRECIP WILL WEAKEN
DURING THE DAY MONDAY AS THE FRONT STALLS AND THE VORT STREAMER
ASSOCIATED WITH IT CONTINUES EAST.  AS SUCH ONLY HAVE A CHANCE OF
SHOWERS AND STORMS MONDAY AFTERNOON.

A SECOND VORT STREAMER MOVES OVERHEAD MONDAY NIGHT INTO TUESDAY SO
RAISED PRECIP CHANCES TO LIKELY THROUGH THIS PERIOD.  PWAT VALUES
WILL TOP OUT AT AROUND 2 INCHES TUESDAY SO HEAVY RAIN IS VERY
POSSIBLE. WITH THE STALLED FRONT AND SLOWLY MOVING STORMS...FLOODING
MAY OCCUR.  PRECIP THEN SHIFTS ALONG AND WEST OF I-55 TUESDAY NIGHT
WITH A STRONGER COLD FRONT SWINGING THROUGH THURSDAY.  ADDITIONAL
RAIN IS POSSIBLE WITH THE SECOND FRONT.

THE BIGGER STORY WILL BE TEMPERATURES. MONDAY WILL ONCE AGAIN BE
WARM AND HUMID WITH HIGHS RANGING FROM THE LOW 80S ALONG THE IL/WI
STATE LINE TO THE LOW 90S SOUTH OF I-80. HAVE LOW CONFIDENCE IN
TEMPS MONDAY AS CLOUD COVER AND RAIN COULD LEAD TO COOLER TEMPS
SOUTH OF I-80.  WE BEGIN A COOLING TREND TUESDAY WITH HIGHS IN THE
LOW 70S ALONG THE IL/WI STATE LINE BUT IN THE UPPER 80S OVER EAST
CENTRAL IL AND NW INDIANA.  DEWPOINTS WILL STILL BE IN THE 70S
ACROSS THE REGION SO TUESDAY WILL STILL BE MUGGY.   LESS HUMID
CONDITIONS AND MUCH COOLER TEMPS MOVE IN BEHIND THE FRONT LATE NEXT
WEEK WITH HIGH TEMPERATURES FRIDAY ONLY IN THE 70S. A FEW LOCATIONS
MAY STRUGGLE TO GET OUT OF THE 60S.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* POSSIBLE PATCHY FOG EARLY THIS MORNING...MAY REDUCE VSBYS.
  MAINLY WEST OF ORD/MDW.

* ISOLATED STORMS POSSIBLE EARLY THIS AFTERNOON...COVERAGE WILL
  REMAIN LOW.

* LIGHT SOUTHWEST TO SOUTH WINDS...MAY ALLOW WINDS TO TURN
  SOUTHEAST FROM A LAKE BREEZE CLOSER TO MDW AND POSSIBLY ORD
  LATE IN THE AFTN.

BEACHLER

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

UPPER LEVEL SYSTEM CONTINUES TO ROTATE OVER THE GREAT LAKES
REGION...WITH A VERY LIGHT GRADIENT. THIS HAS ALLOWED WARM/HUMID
AIR TO FLOW NORTH. WITH LIGHT WINDS EARLY THIS MORNING AND VERY
MOIST ENVIRONMENT...PATCHY FOG MAY BEGIN TO DEVELOP. VSBYS COULD
BECOME REDUCED TO ARND 3-4SM...AND POSSIBLY FURTHER REDUCTIONS
WELL WEST OF THE METRO AREA.

A WEAK AREA OF FORCING WILL FLOAT OVERHEAD AFTER DAYBREAK AND
COULD TOUCH OFF AN ISOLATED SHOWER/THUNDERSTORM FOR FAR
WEST/NORTHWEST IL THRU MID-MORNING. THEN THIS AREA WILL
WEAKEN...WITH SEVERAL HI-RESOLUTION GUIDANCE INDICATING ADDITIONAL
ISOLATED SHOWERS OR STORMS DEVELOPING AFTER 18Z. SINCE COVERAGE IS
EXPECTED TO BE SO LOW AND EVEN THE CONFIDENCE IS LOW THAT IT WOULD
IMPACT THE AIRFIELDS...HAVE OPTED TO PULL THE PROB30 GROUP AND
LIMIT WITH A VCSH. THIS MAY NEED TO BE REVISED LATER THIS MORNING
AS CONFIDENCE COULD INCREASE WITH RESPECT TO TIMING/COVERAGE.

WINDS WILL GENERALLY REMAIN LIGHT OR LESS THAN 8KT FROM THE
SOUTHWEST...THEN BEGIN TO TURN SOUTHERLY LATER THIS MORNING. THE
GRADIENT SHOULD REMAIN LIGHT ENOUGH TO ALLOW WINDS TO TURN
SOUTHEAST AND COULD BECOME ONSHORE LATE THIS AFTERNOON FOR
MDW/ORD FROM A LAKE BREEZE.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE IN WIND DIR/SPEED...MEDIUM CONFIDENCE IN LAKE
  BREEZE DEVELOPING.

* HIGH CONFIDENCE IN ISOLATED SHOWERS/THUNDERSTORMS
  DEVELOPING...BUT VERY LOW CONFIDENCE IN TIMING/COVERAGE.

* MEDIUM CONFIDENCE IN EARLY MORNING VSBY FORECAST.

BEACHLER

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

SUNDAY...VFR LIKELY. SOUTH WINDS.
MONDAY...CHANCE OF TSRA. SOUTHWEST WINDS.
TUESDAY...TSRA LIKELY. SOUTHWEST WINDS.
WEDNESDAY...CHANCE OF TSRA. NORTHEAST WINDS.
THURSDAY...SLIGHT CHANCE OF SHRA. NORTH WINDS.

MTF

&&

.MARINE...
249 AM CDT

HIGH PRESSURE WILL REMAIN CENTERED OVER THE MID-ATLANTIC
REGION...WITH A LIGHT GRADIENT AND SOUTHWEST TO SOUTH FLOW OVER
LAKE MICHIGAN. HIGH PRESSURE WILL BEGIN TO DRIFT EAST...WITH A
LARGE TROUGH OF LOW PRESSURE OVER THE NORTHERN PLAINS PIVOTING
EAST AND STRENGTHENING. THE GRADIENT WILL BECOME MORE EVIDENT
SUNDAY AS THE WINDS INCREASE OVER THE NORTHERN PORTION OF THE
LAKE...WITH SPEEDS BETWEEN 15-25KT EXPECTED FROM THE SOUTHWEST.
LOW PRESSURE WILL LIFT NORTH INTO MANITOBA AND WEAKEN...WITH A
TRAILING FRONTAL BOUNDARY STALLING ACROSS THE NORTHERN PORTIONS OF
LAKE MICHIGAN MONDAY AFTERNOON/EVENING. THEN A SERIES OF WEAK LOW
PRESSURES WILL RIDE ALONG THIS WEAK FRONTAL BOUNDARY...HELPING TO
SLOWLY PUSH THE FRONT TO THE EAST/SOUTHEAST BY THE MIDDLE OF NEXT
WEEK. HIGH PRESSURE WILL ARRIVE FOR THE CENTRAL/NORTHERN PORTIONS
OF THE LAKE TUESDAY NIGHT/WEDNESDAY...WITH WINDS TURNING
NORTHEAST. CONFIDENCE IN TIMING OF THE FRONTAL BOUNDARY CLEARING
LAKE MICHIGAN REMAINS LOW.

BEACHLER

&&

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

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.