Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | 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 212008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
308 PM CDT THU MAY 21 2015

.SHORT TERM...
247 PM CDT

THROUGH SATURDAY...

HIGH PRESSURE IS OVER THE PLAINS AND SPREADING ACROSS CENTRAL AND
SOUTHERN IL.  EARLY MORNING CLOUDS HAVE CLEARED NICELY AND
TEMPERATURES ROSE QUICKLY IN RESPONSE TO THE AMPLE SUNSHINE.  A WEAK
LOW PRESSURE TROUGH AND COLD FRONT ARE OVER THE NORTHERN END OF LAKE
MICHIGAN AND THE FRONT WILL SLIDE DOWN THE LAKE OVERNIGHT. WHILE A
FEW LIGHT RAIN SHOWERS ARE EXPECTED WITH FRONT OVER THE
LAKE...THINKING IT WILL BE TOO DRY FOR PRECIP TO FALL OVER THE LAND
BASED CWA.  WINDS BECOME NORTH BEHIND THE FRONT LATE TONIGHT INTO
FRIDAY MORNING.

WINDS DROP OFF QUICKLY AS HIGH PRESSURE BUILDS OVERHEAD. FLOW WILL
BE OFF THE LAKE AND EXPECTING WINDS AROUND 10 MPH ALONG THE LAKE
FRIDAY.  AREAS WELL AWAY FROM THE LAKE WILL GET INTO THE MID 60S TO
AROUND 70...WHILE AREAS ALONG THE LAKE WILL ONLY BE IN THE 50S TO
LOW 60S.  OUTSIDE OF CHILLIER TEMPS ALONG THE LAKE...EXPECTING A
BEAUTIFULLY SUNNY DAY. OVERNIGHT LOWS WILL VARY FROM THE LOW 40S TO
AROUND 50.

THE HIGH SHIFTS EAST SATURDAY BUT EXPECTING ANOTHER DRY DAY WITH
INCREASING CLOUD COVER.  THE NEXT LOW FORMS OVER THE CENTRAL PLAINS
TOMORROW BUT THE UPPER LEVEL RIDGE REMAINS OVER THE MIDWEST.
THINKING THE DRY AIR WILL KEEP THE REGION PRECIP FREE THROUGH
SATURDAY AFTERNOON. SOUTH WINDS ARE EXPECTED AND A WEAK LAKE BREEZE
IS POSSIBLE. THINKING THE LAKE BREEZE WILL HUG THE SHORE AND
PROBABLY ONLY PUSH OVER LAND OVER LAKE COUNTY IL.  AS SUCH KEPT
DAYTIME HIGH TEMPS IN THE 60S ALONG THE LAKE BUT EXPECTING ALL OTHER
REGIONS TO CLIMB INTO THE MID 70S. IF CLOUD COVER IS SLOWER THAN
FORECAST...COULD SEE A FEW SITES REACH 80...BUT DECIDED TO GO THE
SAFER ROUTE AND BET ON INCREASING CLOUD COVER. HAVE MEDIUM-HIGH
CONFIDENCE IN HIGH TEMPS FOR SATURDAY.

JEE

&&

.LONG TERM...
307 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

PRETTY BIG MODEL DISCREPANCIES CREEPING IN WITH RESPECT TO THE
PATTERN EVOLUTION ON SATURDAY NIGHT AND ESPECIALLY SUNDAY AS
WESTERN TROUGH OPENS UP AND OUR AREA ON WESTERN PERIPHERY OF
EASTERN RIDGE. MUCH OF SATURDAY NIGHT NOW APPEARING IT COULD BE
DRY...ESPECIALLY PER GFS/GEFS/GEM/NAM BUT DID KEEP SLIGHT POPS IN
FAR WEST AFTER MIDNIGHT. ON SUNDAY...MODELS SHOW BEST FORCING FROM
AN UPPER WAVE FOCUSING INTO NORTHWEST IL AND SOUTHERN
WISCONSIN...BUT THE SIGNIFICANT DIFFERENCES BETWEEN GFS AND ECMWF
ARISE BECAUSE GFS FIRMLY ENTRENCHES US IN THE WARM SECTOR WHILE
ECMWF FOCUSES WIDESPREAD SHOWERS ON CONVERGENCE NOSE OF 850 MB
JET. FORECAST IS A BIT OF A MIDDLE GROUND...WITH LIKELY POPS IN
WESTERN HALF OF CWA CLOSER TO UPPER WAVE FORCING AND CHANCE POPS
TO THE EAST. DUE TO POOR MIDLEVEL LAPSE RATES ON ALL THE GUIDANCE
HAVE ONLY INCLUDED A SLIGHT CHANCE FOR TSRA. IF LESS CLOUDS/PRECIP
OCCUR...THEN LOWER-MID 70S TEMPS FORECAST FROM IL SHORE WOULD
LIKELY BE TOO COOL...WHILE ON OTHER HAND...MUCH COOLER TEMPS WOULD
RESULT FROM A EC LIKE EVOLUTION. CONFIDENCE IS LOW IN THE SUNDAY
FORECAST.

FOR MEMORIAL DAY THROUGH WEDNESDAY...MULTIPLE DISTURBANCES RIDE
INTO AREA IN WEST-SOUTHWEST FLOW ALOFT...SO HAVE POPS THE ENTIRE
PERIOD. HOWEVER...IT DOES NOT APPEAR ANY DAY WOULD BE A WASHOUT.
WE DO GET INTO BETTER INSTABILITY DUE TO MIDLEVEL LAPSE RATES AND
60S DEWPOINTS ALONG WITH MODERATE MIDLEVEL FLOW. A SURFACE LOW
LOOKS TO LIFT NORTHEAST ON MONDAY...BUT BIG VARIANCE IN HOW CLOSE
TO THE AREA IT WILL GET. ANOTHER DISTURBANCE COULD THEN LIFT
TOWARD THE REGION TUESDAY INTO WEDNESDAY. CONFIDENCE IS AGAIN LOW
GIVEN HOW DIFFICULT IT IS FOR GUIDANCE TO HANDLE TIMING/ETC OF
DISTURBANCES IN ACTIVE WSW FLOW PATTERN. THERMAL PROGS ARE QUITE
WARM WITH 850 MB TEMPS IN MID TEENS CELSIUS AND 925 MB TEMPS IN
HIGH TEENS CELSIUS...SO AGAIN TEMPERATURES COULD END UP WARMER
THAN CURRENTLY FORECAST IF MORE SUN IF OBSERVED. STILL WILL LIKELY
BE A MUGGY PERIOD GIVEN HIGHER DEWPOINTS AND ABOVE SEASONAL TEMPS.
THEN BY THURSDAY...LATEST ECMWF KEEPS US IN SOUTHERLY SFC FLOW AND
SIMILAR UPPER PATTERN WHILE OPERATIONAL GFS BRINGS DOWN HIGH
PRESSURE BEHIND WEDNESDAY SYSTEM. STAYED CLOSE TO CONSENSUS BLEND
DUE TO LARGE UNCERTAINTY.

RC

&&

.AVIATION...

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

* NE WINDS GREATER THAN 10 KT ON FRIDAY MORNING.

MM

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

SOME DAYTIME HEATING DRIVEN CUMULUS FORMING AHEAD OF AN UPPER
LEVEL SHORTWAVE IN WISCONSIN. THIS WAVE COMES THROUGH THIS EVENING
WHICH IS NOT A FAVORED TIME FOR ANY SHOWER ACTIVITY...THOUGH WILL
SEE A SCT AND POSSIBLY BROKEN VFR DECK 6-9K FT WITH IT. EXPECT
WEST WINDS WITH GUSTS TO 20 KT THIS AFTERNOON BEFORE EASING THIS
EVENING. FOCUS IS THEN ON THE BACKDOOR COLD FRONT CURRENTLY
REACHING NORTHERN LAKE MICHIGAN. THIS FRONT IS SLATED TO MOVE
INTO THE TERMINALS DURING THE EARLY MORNING HOURS. EXPECT A RAPID
SHIFT TO NORTHEAST WINDS WITH THE FRONT AND SPEEDS/GUSTS ABOVE 10
KT AT LEAST INTO THE START OF THE FRIDAY MORNING RUSH. EXPECT
WINDS TO TURN MORE EASTERLY DURING THE DAY WITH LIGHTER SPEEDS.

KMD

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

* MEDIUM-HIGH ON NE WIND TIMING AND MEDIUM ON SPEEDS.

MM

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

* FRIDAY NIGHT...DRY/VFR. SOUTHEAST WINDS.
* SATURDAY...DRY/VFR. SOUTH WINDS.
* SUNDAY...SHRA LIKELY. CHANCE OF TSRA. MAINLY VFR. SOUTHEAST WINDS.
* MONDAY...SHRA/TSRA LIKELY. MVFR POSSIBLE. GUSTY SOUTHWEST WINDS.
* TUESDAY...CHANCE OF SHRA/TSRA. MVFR POSSIBLE. GUSTY SOUTHWEST
  WINDS.
* WEDNESDAY...CHANCE OF SHRA/TSRA. MAINLY VFR. SOUTHWEST WINDS.

BMD

&&

.MARINE...
247 PM CDT

A COLD FRONT IS OVER THE NORTHERN END OF THE LAKE AND IT WILL SINK
SOUTH ACROSS THE LAKE. EXPECTING IT TO CLEAR THE SOUTHERN END OF THE
LAKE EARLY FRIDAY MORNING...WITH WINDS BECOMING NORTH BEHIND THE
FRONT.  COULD SEE A FEW GUSTS TO 20-25 KT IMMEDIATELY BEHIND THE
FRONT. WINDS DIMINISH TO 5 TO 10 KT FRIDAY MORNING AS A SURFACE HIGH
SPREADS OVER THE REGION.  EXPECTING ONSHORE FLOW ACROSS THE LAKE
FRIDAY AFTERNOON WITH GUSTS ARND 15 KT PSBL. SOUTH WINDS SET UP
BEHIND THE HIGH FRIDAY NIGHT AND SATURDAY. COULD SEE GUSTS TO 25 KT
OVER THE NORTHERN HALF OF THE LAKE SATURDAY. A WEAK LAKE BREEZE IS
ALSO PSBL ALONG THE IL SHORE SATURDAY AND MAYBE SUNDAY.  HAVE HIGHER
CONFIDENCE IN SATURDAY/S LAKE BREEZE THAN SUNDAY/S. SOUTH WINDS ARE
EXPECTED THROUGH AT LEAST MONDAY WITH SPEEDS UP TO 20 KT.

JEE

&&

.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.