Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 051657
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1157 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 ORGANIZATION 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
ATMOSPHERE 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 BARELY 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 18Z...

* LOW CHANCES FOR ADDITIONAL SHRA/TSRA THIS AFTERNOON.
* WIND DIRECTION REST OF TODAY.

BMD

//DISCUSSION...UPDATED 18Z...

SHOWERS AND THUNDERSTORMS HAVE BECOME FOCUSED ALONG AND SOUTH OF
THE I-80 CORRIDOR WHERE THEY SHOULD REMAIN THROUGH THE REMAINDER
OF THE AFTERNOON...WITH ONLY SLIGHT CHANCE FOR ISOLATED
DEVELOPMENT FARTHER NORTH. UPPER LEVEL WAVE WILL PIVOT ACROSS THE
REGION THIS AFTERNOON WITH RIDGING BUILDING IN BEHIND WHICH SHOULD
ALLOW CONVECTIVE ACTIVITY TO DIMINISH STARTING AROUND MID
AFTERNOON...WITH CHANCES FURTHER DECREASING AS WE NEAR SUNSET AND
LOSE DAYTIME HEATING.

WINDS THIS MORNING HAVE BACKED TO THE SSE WITH STABILIZATION OF
THE BOUNDARY LAYER BEHIND THE THUNDERSTORMS...HOWEVER EXPECT
WINDS SHOULD SHIFT BACK TO THE SSW/SW EARLY THIS AFTERNOON AS WE
START TO SEE A FEW PEEKS OF SUNSHINE ALLOWING FOR BETTER MIXING.
WILL HAVE TO MONITOR FOR THE DEVELOPMENT OF A LAKE BREEZE THIS
AFTERNOON...BUT FOR NOW DO NOT HAVE ANY WIND SHIFTS INCLUDED AT
THE TERMINALS FROM A LAKE BREEZE.

OVERNIGHT...WINDS SHOULD DIMINISH TO 5 KT OR LESS...HOWEVER EXPECT
TO KEEP MID AND HIGH CLOUDS IN MUCH OF THE NIGHT. WITH DEW
POINTS IN THE LOW 70S THIS AFTERNOON...FOG IS A CONCERN OVERNIGHT
HOWEVER MODELS NOT REALLY HITTING IT HARD AND DONT EXPECT OPTIMAL
RADIATING CONDITIONS. FOR NOW WILL ONLY INCLUDE MENTION AT
DPA/RFD. IF SKIES CLEAR OUT MORE THAN EXPECTED THEN THE FOG THREAT
WILL INCREASE.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH CONFIDENCE IN DRY CONDITIONS AT THE TERMINALS
  THROUGH THE TAF PERIOD.
* MEDIUM CONFIDENCE IN WIND TRENDS...LOW CONFIDENCE THAT A LAKE
  BREEZE WILL PASS ACROSS THE TERMINALS.
* LOW CONFIDENCE IN FOG TONIGHT.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. SLIGHT CHANCE OF TSRA LATE.
MONDAY...CHANCE OF TSRA. SOUTHWEST WINDS.
TUESDAY...TSRA LIKELY. SOUTHWEST WINDS.
WEDNESDAY...CHANCE OF TSRA. NORTHEAST WINDS.
THURSDAY...SLIGHT CHANCE OF SHRA. NORTH WINDS.
FRIDAY...SLIGHT CHANCE OF TSRA/SHRA.

BEACHLER

&&

.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.
&&

$$

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