Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 061927
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
227 PM CDT WED MAY 6 2015

.SHORT TERM...
224 PM CDT

THROUGH FRIDAY...

MUCH OF THE AREA IS GETTING OUT OF THE HAZE/FOG EARLY THIS
AFTERNOON...WITH FOG EVEN LIFTING IN DOWNTOWN CHICAGO. AT 2
PM...THERE WAS A 29 DEGREE DIFFERENCE IN TEMPERATURE BETWEEN
MIDWAY AIRPORT (81) AND NORTHERLY ISLAND (52). THE STATIONARY
FRONT THAT WAS PARKED OVER CENTRAL ILLINOIS YESTERDAY IS MARCHING
NORTHWARD AND ALL BUT FAR NORTHEAST ILLINOIS...INCLUDING NORTHERN
COOK AND LAKE COUNTIES...IS FEELING THE WARMTH BEHIND THIS FRONT
AS TEMPERATURES QUICKLY WARMED TO AROUND 80 ELSEWHERE. AN
EXTENSIVE CUMULUS FIELD IS FILLING IN IN THE WARM SECTOR. IN
ADDITION TO THIS FUN...THE LAKE BREEZE IS NOW MOVING THROUGH COOK
COUNTY WHICH WILL LIMIT THE NORTHEASTWARD MOVEMENT OF THE FRONT.
MEANWHILE ALOFT...SHORTWAVE ENERGY IS ROTATING NORTHWARD AHEAD OF
AN UPPER LOW IN THE PLAINS. SHOWERS AND THUNDERSTORMS REMAIN
CONFINED EAST OF THE MISSISSIPPI.

FOR THE REST OF THIS AFTERNOON/EARLY EVENING...WEAK SHORTWAVE ENERGY
CONTINUES NORTH WITH THE WARM FRONT. HIGH RES GUIDANCE SUGGESTS THAT
ANY SHOWERS/TSTORMS THAT FORM THIS FAR EAST WOULD BE ISOLATED IN
NATURE AT BEST AS THE UPPER LEVEL HEIGHT FALLS ARE MAINLY OFF INTO
IOWA. MODELS SUGGEST THE WARM FRONT WILL STALL ITS NORTHWARD
MOVEMENT...AND THEREFORE WITH THE MOIST AIRMASS IN PLACE...EXPECT
SOME FOG/HAZE TO REFORM THIS EVENING. NOT QUITE SURE HOW THICK OR
WIDESPREAD IT WILL BE...BUT NOT LIKE IT WAS THIS MORNING. EXPECT
FOG TO REFORM OVER THE LAKE...SO IT COULD BECOME DENSE AGAIN ALONG
THE LAKESHORE AREAS. THROUGH THE NIGHT WE WILL ALSO SEE SOME HIGH
CLOUD OUT AHEAD OF CONVECTION TO OUR WEST.

ON THURSDAY...PRONOUNCED SOUTHERLY FLOW SHOULD FINALLY ALLOW THE
ENTIRE AREA TO HAVE A TASTE OF SUMMER WARMTH. SLIGHT SE FLOW AT THE
SURFACE AT THE LAKE WILL PROVIDE SOME COOLING FROM CHICAGO NORTHWARD
INTO AREAS NEAR THE LAKE IN LAKE COUNTY ILLINOIS AFTER WARMING
THROUGH EARLY AFTERNOON. WIDESPREAD 80S ARE STILL ANTICIPATED WITH
850/925 TEMPS A TOUCH HIGHER THAN TODAY WHERE WE WERE EASILY ABLE TO
QUICKLY REACH THE UPPER 70S TO LOW 80S ALREADY TODAY. THE UPPER LOW
IN THE PLAINS ONLY INCHES EASTWARD...BUT SOME WEAK HEIGHT FALLS IN
THE AFTERNOON MAY ALLOW A FEW SHOWERS/T-STORMS TO PUSH INTO AREAS
ALONG AND EAST OF I-39...BUT MORE ORGANIZED ACTIVITY DURING THE DAY
WILL REMAIN CLOSER TO A COLD FRONT EXTENDING FROM THE UPPER MIDWEST
INTO THE CENTRAL PLAINS.

KMD

&&

.LONG TERM...
345 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

A DIGGING OF THE NORTHERN STREAM JET ALONG WITH AN INTENSIFYING
SUBTROPICAL JET INTO THE SOUTHWEST U.S. WILL CARVE A BROAD
LONGWAVE TROUGH WITH LIKELY EMBEDDED UPPER LOW ACROSS THE WESTERN
PART OF THE COUNTRY. THIS WILL ESTABLISH SOUTHWEST FLOW ALOFT AND
AN INCREASING SUBTROPICAL MOISTURE PLUME INTO THE MIDWEST/CORN
BELT REGION GOING INTO FRIDAY AND THE WEEKEND. SEVERAL MID-LEVEL
IMPULSES ARE EVIDENT IN MODEL GUIDANCE AND WOULD BE EXPECTED IN
SUCH A PATTERN. UNFORTUNATELY THAT PROVIDES LOW PREDICTABILITY OF
SHOWER AND STORM TIMING...EVEN WITHIN A GIVEN 12-HR PERIOD.

LOOKING AT RUN-TO-RUN CONSISTENCY IN MODEL GUIDANCE...THERE IS
GOOD AGREEMENT IN MOISTURE TRANSPORT AND FOCUSED WARM ADVECTION
ALOFT THURSDAY NIGHT TO THE POINT WHERE SOME STORMS IN THE REGION
ARE PROBABLE. FRIDAY AFTERNOON/EVENING IS ALSO A PRONOUNCED
OVERLAP IN GUIDANCE OF A SHORT WAVE TRAVERSING THE EASTERN EDGE
OF THE LONG WAVE TROUGH. HAVE LIKELY POPS IN THAT TIME PERIOD.

THE TEMPERATURE FORECAST IS ALSO A NOTEWORTHY CHALLENGE GIVEN THE
PROBABLE SHOWERS AT TIMES...BUT ALSO A NORTHERN STREAM SURFACE
TROUGH INCHING INTO THE AREA. THIS LOOKS TO ALMOST MIRROR THE
SURFACE SETUP WE ARE IN NOW...WITH THE BOUNDARY DRAPING INTO THE
AREA OR JUST SOUTH DURING THE WEEKEND. IF THIS PANS OUT THIS WILL
COOL NORTHERN AREAS CONSIDERABLY...ESPECIALLY NEAR THE LAKE SHORE.
CONTINUE TO LEAN THAT ROUTE. CONFIDENCE IS REALLY LOW ON
TEMPERATURES GOING INTO MONDAY AS THE FRONTAL PLACEMENT VARIES
GREATLY ON LONG RANGE GUIDANCE. THERE WILL ALSO ONCE AGAIN BE
POTENTIAL FOR FOG IN SUCH A SETUP.

THE CHANCES FOR SEVERE STORMS MAY SLOWLY INCREASE IN THE LONG
RANGE PART OF THE FORECAST BUT LIKELY VERY SLOWLY. IT WOULD
APPEAR A MORE FAVORED SYNOPTIC PATTERN IS PRESENT SUNDAY NIGHT
INTO MONDAY WHEN SHARPER HEIGHT FALLS ARE AGREED UPON IN CURRENT
GLOBAL GUIDANCE TO OVERSPREAD THE AREA. VERY LOW CONFIDENCE THOUGH
AT THIS TIME.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LAKE BREEZE TURNING WINDS FROM SELY TO ELY/ENELY EARLY
  AFTERNOON.

* WIND SPEED LESS THAN 8 KT BEFORE AND AFTER LAKE BREEZE
  PASSAGE...THOUGH AN OCCASIONAL GUST TO 10-12KT IS POSSIBLE
  THROUGH AROUND 20Z WITH THE INITIAL PUSH OF COOLER AIR BEHIND
  THE LAKE BREEZE BOUNDARY.

* CHANCE MVFR HZ/BR THIS EVENING.

KREIN

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

HIGH PRESSURE EXTENDS FROM THE UPPER GREAT LAKES THROUGH NEW
ENGLAND WHILE LONG WAVE TROUGHING DEVELOPS OVER THE WESTERN
PLAINS. A WEAK WARM FRONT IS SLOWLY MOVING NWD THROUGH IL/IN AND
IS CURRENTLY ALONG THE ILLINOIS/KANKAKEE RIVERS. NORTH OF THE
FRONT...THE MORNING FOG AND STRATUS HAS DISSIPATED AND LIGHT SELY
WINDS HAVE SET UP. A WEAK LAKE BREEZE IS BEGINNING TO MOVE INLAND
AND SHOULD PUSH THROUGH THE ORD/MDW AREA BY AROUND 20Z.
HOWEVER...THE BOUNDARY IS VERY FAINT ON RADAR SO TIMING IS LOW
CONFIDENCE RIGHT NOW. CONFIDENCE IS HIGHER THAT WIND SPEED SHOULD
REMAIN LESS THAN 8KT BEFORE AND AFTER THE LAKE BREEZE PASSAGE.

THE WARM FRONT IS EXPECTED TO BE SOUTH OF THE TERMINALS THROUGH
THE EVENING HOURS...SO WITH SOME RESIDUAL LOW LEVEL MOISTURE AND
LIGHT SELY WINDS OFF OF LAKE MICHIGAN...THERE IS A CHANCE FOR SOME
VIS RESTRICTION THIS EVENING. THIS IS ALSO A LOW CONFIDENCE
FORECAST...BUT IF ANY HZ/BR DOES DEVELOP...IT VIS SHOULD ONLY DROP
TO MVFR LEVELS.

LATEST MODEL GUIDANCE SUGGESTS THAT THE WARM FRONT SHOULD PUSH
NORTH OF THE TERMINALS BY ARND 06Z WITH WINDS SHIFTING TO
SOUTHERLY. INITIALLY WIND SPEED SHOULD BE LESS THAN 10KT FOR THE
OVERNIGHT AND EARLY MORNING HOURS...BUT BY LATE MORNING...DEEP
LAYER MIXING SHOULD BE ABLE TO TAP THE STRONGER WINDS ALOFT WITH
SLY GUSTS OF 20-25KT FROM LATE MORNING THROUGH THE AFTERNOON.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND SPEED THIS AFTERNOON THROUGH EARLY
  TOMORROW MORNING.

* MEDIUM-HIGH CONFIDENCE IN SOUTHERLY WINDS GUSTING TO 20-25KT
  LATE TOMORROW MORNING THROUGH THE AFTERNOON.

* MEDIUM CONFIDENCE IN MVFR VIS THIS EVENING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

THURSDAY NIGHT...CHC TSRA. VFR. SOUTH WINDS.

FRIDAY...SHRA LIKELY...CHC TSRA. MVFR PSBL OVERNIGHT. SOUTHWEST
WINDS.

SATURDAY...CHC SHRA. MVFR PSBL. NORTH WINDS BCMG NORTHEAST.

SUNDAY...CHC SHRA/TSRA. MVFR PSBL. NORTHEAST TO EAST WINDS.

MONDAY...TSRA LIKELY. MVFR PSBL. SOUTH WINDS BCMG NORTHWEST
OVERNIGHT.

TUESDAY...SCHC SHRA. MVFR PSBL. NORTHWEST WINDS.

JEE

&&

.MARINE...
223 AM CDT

THE STATIONARY FRONT IS OVER CENTRAL ILLINOIS AND IT WILL LIFT AS A
WARM FRONT THROUGH TONIGHT. HAVE MEDIUM CONFIDENCE IN HOW QUICKLY IT
WILL ADVANCE AND HAVE MEDIUM-HIGH CONFIDENCE THAT THE DENSE FOG WILL
STAY PUT UNTIL THE WARM FRONT MOVES THROUGH. THEREFORE EXTENDED THE
DENSE FOG ADVSY THROUGH 10PM CDT THIS EVENING. IF THE FRONT IS
SLOWER THAN FORECAST...THE DENSE FOG COULD ALSO PERSIST LONGER. EAST
WINDS BECOME SOUTH BEHIND THE FRONT TONIGHT AND INCREASE TO 15-25 KT
OVER THE NORTHERN HALF OF THE LAKE THURSDAY NIGHT.  A LOW OVER
NORTHEAST CANADA DRAGS A COLD FRONT ACROSS THE LAKE FRIDAY NIGHT
INTO SATURDAY. WINDS BECOME NORTH TO 20 KT BEHIND THE FRONT.  THE
NEXT LOW PRESSURE SYSTEM MOVES OVER THE LAKE EARLY NEXT WEEK BUT
GUIDANCE DIFFERS ON IF THE LOW WILL MOVE OVER THE LAKE OR SOUTH OF
THE LAKE.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-
     LMZ777-LMZ779 UNTIL 11 PM WEDNESDAY.

&&

$$

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