Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 201144
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
644 AM CDT MON OCT 20 2014

.DISCUSSION...
557 AM CDT

WE ARE SEEING SCATTERED SHOWERS SPARK NEAR CHICAGO AS OF 555 AM
AHEAD OF THE UPPER DISTURBANCE MENTIONED IN THE PREVIOUS
DISCUSSION. THIS DISTURBANCE HAS A POCKET OF STEEP LAPSE RATES
ALOFT /500MB-750MB/ OF 8C/KM AND GREATER AND THAT IS AIDING SOME
OF THESE SHOWER UPDRAFTS. THIS IS INDICATED BY A COUPLE LIGHTNING
STRIKES OVER LAKE MI AND THE OBSERVERS AT ORD AND MDW REPORTING
INTRA-CLOUD AND CLOUD-TO-AIR LIGHTNING. THE GOOD NEWS IS THIS
UPPER WAVE AND ITS FORCING IS MOVING ABOUT 35-40 MPH SO NOT
EXPECTING THESE TO STICK AROUND THE CHICAGO AREA AFTER 7 AM.
CONTINUE THE SHOWER CHANCES THIS MORNING AS IS IN NORTHWEST
INDIANA AND HAVE ADDED A SLIGHT CHANCE OF THUNDER FOR AREAS NEAR
THE I-80/I-90 CORRIDOR.

MTF

//PREV DISCUSSION...
319 AM CDT

A QUIET WEATHER PATTERN WILL REMAIN IN PLACE IN TERMS OF LACK OF
PRECIPITATION CHANCES AND ANY HIGH IMPACT WEATHER THROUGH NEXT
WEEKEND...THOUGH STILL SEVERAL LITTLE INTERESTS TO TACKLE. THESE
INCLUDED HOW WIDESPREAD CLOUDS WILL REACH LATER TODAY THROUGH
TUESDAY AS WELL AS LAKE EFFECT SHOWER POTENTIAL DURING THAT TIME.
THEN LOOKING AT WHEN AND HOW QUICKLY OF A WARM-UP OCCURS LATE IN
THE WEEK INTO THE WEEKEND.

TODAY THROUGH TUESDAY...
THE CONTINUED AMPLIFIED BUT PROGRESSIVE FLOW OVER CANADA AND THE
NORTHERN CONUS CONTINUES FOR A LITTLE LONGER WITH A PACIFIC/CLIPPER
HYBRID SYSTEM MOVING SOUTHEASTWARD FROM THE CENTRAL GREAT LAKES.
AROUND THIS A WELL-DEFINED SHORT WAVE ON GOES WATER VAPOR IMAGERY IS
MOVING INTO NORTHERN IL EARLY THIS MORNING. THIS IS FAIRLY MOISTURE
STARVED BUT CANNOT RULE OUT A FEW SHOWERS THIS MORNING MAINLY IN
NORTHWEST INDIANA. THIS SHORT WAVE ALSO BEGINS TO BREAK DOWN THE
LOW-LEVEL THERMAL RIDGE OVER THE AREA...WITH CLOUDS LIKELY TO
ADVECT/DEVELOP SOUTHWARD INTO THE FORECAST AREA THIS AFTERNOON. IN
ADDITION...TEMPERATURES MAY ALSO PEAK EARLY IN THE AFTERNOON AND
THEN EXPERIENCE A SLOW DROP. TEMPERATURES SHOULD STILL PEAK AROUND
CLIMATOLOGICAL NORMAL /60 TO 65/ WITH THE MORNING SUN. THE CYCLONIC
FLOW OVER THE REGION AND RAPIDLY COOLING 850-925MB TEMPERATURES LOOK
TO SUPPORT CLOUDS OVER MUCH OF THE AREA BY EARLY THIS EVENING AND
UPSTREAM OBSERVATIONAL TRENDS SUPPORT THIS. HAVE GONE WELL ABOVE
MOST GUIDANCE IN SKY COVER FROM LATE TODAY ALL THE WAY THROUGH
TUESDAY MORNING AS HIGH-RESOLUTION MODEL CONDENSATE /SUCH AS THE
4KM SPC WRF/ SEEMS TO WORK BETTER IN SUCH A PATTERN WITH THIN BUT
PROBABLY BROKEN-OVERCAST CLOUD COVER. THE CLOUDS AND NORTH-
NORTHEAST WINDS ON TUESDAY MORNING SHOULD LIMIT WARMING BY QUITE A
BIT WITH SOME LOCATIONS POSSIBLY NOT REACHING 50.

AS THE COOLER AIR AT OR AROUND 0C AT 850MB EXPANDS SOUTHWARD DOWN
THE LAKE LATER TODAY FORESEE DEEPENING LAKE EFFECT CLOUDS AND
SOME SHOWERS DEVELOPING. THESE SHOWERS LOOK TO BE NOT PARTICULARLY
CONCENTRATED WITH LIMITED CONVERGENCE AND MAINLY LIGHT IN
INTENSITY WITH LAKE-INDUCED EQUILIBRIUM LEVELS FORECAST BY THE
NAM OF AROUND 5000 FT. THE BOUNDARY LAYER FLOW FETCH SHOULD FAVOR
NORTHWEST INDIANA FOR THESE SHOWERS TONIGHT INTO EARLY
TUESDAY...THOUGH SOME VEERING TOWARD THE IL/IN STATE LINE AND EVEN
POTENTIALLY CHICAGO TUESDAY MORNING COULD SUPPORT SOME LIGHT
SHOWER ACTIVITY TUESDAY MORNING IN THOSE PLACES. THE HOPWRF-TS
SUPPORTS SUCH A GENERAL EVOLUTION WITH ITS RECENTLY ADDED EXTENDED
HIGH-RES OUTPUT.

TUESDAY NIGHT THROUGH THURSDAY...
SURFACE HIGH PRESSURE WILL BUILD OVER THE AREA FROM THE NORTH DURING
THIS TIME AS THE OVERALL UPPER PATTERN SLOWS THANKS TO AMPLIFICATION
OF A TROUGH ALONG THE WEST COAST OF NORTH AMERICA. OVERALL BENIGN
WEATHER LOOKS TO BE THE RULE WITH TEMPS SLIGHTLY BELOW NORMAL THOUGH
GRADUALLY MODIFYING. MODEL GUIDANCE DOES INDICATE AN ELONGATED SHORT
WAVE TO MOVE INTO THE UPPER MISSISSIPPI VALLEY DURING OR AROUND
THURSDAY NIGHT THOUGH THIS WILL BE MOVING INTO AN UNFAVORABLE
UPPER LEVEL AND MOISTURE SUPPORTIVE PATTERN. SO CONTINUE THE DRY
FORECAST.

FRIDAY INTO NEXT WEEKEND...
THE ONLY CHANGE WITH THIS PORTION OF THE FORECAST WAS TO INCREASE
TEMPERATURES...MAINLY ON SATURDAY. IF CLOUD COVER CAN REMAIN LIMITED
WITH THE PATTERN FORECAST...THE 850MB-925MB TEMPERATURES WOULD
SUPPORT TEMPERATURES POTENTIALLY IN THE 70S WITH A THERMAL RIDGE
STEERED IN FROM THE WEST-SOUTHWEST.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* WEST/SOUTHWEST WINDS BECOMING NORTHWEST LATE MORNING/EARLY THIS
  AFTERNOON...THEN NORTH/NORTHEAST LATE THIS AFTERNOON.
* POSSIBLE MVFR CIGS THIS AFTERNOON AND EVENING. CMS

//DISCUSSION...UPDATED 12Z...

LINE OF SHRA/TSRA DEVELOPED OVER FAR NORTHEAST IL IN THE PAST HOUR
OR SO AHEAD OF AN UPPER LEVEL WAVE. THIS ACTIVITY WILL CONTINUE TO
MOVE EAST...AFFECTING GYY SHORTLY. THE SURFACE COLD FRONT WILL
MOVE ACROSS THE TERMINALS THIS MORNING SHIFTING WEST/SOUTHWEST
WINDS TO THE NORTHWEST. WINDS WILL CONTINUE TO SLOWLY TURN MORE
NORTH/NORTHWEST BY MID/LATE AFTERNOON. THE GRADIENT IS THEN
EXPECTED TO WEAKEN ENOUGH FOR WIND DIRECTIONS TO SHIFT TO THE
NORTH/NORTHEAST EITHER LATE THIS AFTERNOON OR EARLY THIS EVENING
WITH PREVAILING SPEEDS AT THAT TIME LIKELY UNDER 10KTS. WINDS WILL
TURN BACK TO THE NORTH/NORTHWEST OVERNIGHT.

LOW VFR/HIGH MVFR CIGS ACROSS NORTHERN WI WILL MOVE SOUTH THIS
MORNING REACHING THE TERMINALS LATE THIS MORNING OR EARLY THIS
AFTERNOON. CONFIDENCE REGARDING SPECIFIC CIG HEIGHTS IS FAIRLY LOW
WITH CIGS POSSIBLE DIPPING INTO HIGH MVFR FROM MID AFTERNOON INTO
THE EVENING HOURS.

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH FOR WINDS THRU MID MORNING...THEN MEDIUM FOR DIRECTION AND
  TIMING CHANGES THIS AFTERNOON/EVENING.
* LOW FOR MVFR CIGS THIS AFTERNOON AND EVENING. CMS

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

* TUESDAY NIGHT...DRY/VFR.
* WEDNESDAY...DRY/VFR. EAST/NORTHEAST WINDS.
* THURSDAY...DRY/VFR. SOUTH WINDS.
* FRIDAY...DRY/VFR. SOUTHWEST WINDS.
* SATURDAY...DRY/VFR. WEST WINDS.
* SUNDAY...DRY/VFR. SOUTH WINDS.

&&

.MARINE...

309 AM...LOW PRESSURE OVER THE UPPER PENINSULA OF MICHIGAN WILL
MOVE SOUTHEAST TODAY AND TONIGHT REACHING THE MID ATLANTIC ON
TUESDAY. A TRAILING COLD FRONT WILL MOVE ACROSS LAKE MICHIGAN THIS
MORNING. SOUTHWEST WINDS WILL TURN NORTHWEST THIS MORNING THEN
NORTH THIS EVENING. THE GRADIENT REMAINS FAIRLY TIGHT ACROSS THE
SOUTHERN THIRD OR SO OF THE LAKE...WITH GUSTS TO 30KT POSSIBLE FOR
A FEW MORE HOURS. HIGH PRESSURE WILL BUILD ACROSS ONTARIO TODAY
AND TONIGHT AS IT STRENGTHENS. WHILE THE CENTER OF THIS HIGH WILL
MOVE EAST INTO QUEBEC TUESDAY NIGHT...A RIDGE WILL EXTEND SOUTH
ACROSS THE WESTERN LAKES TONIGHT AND TUESDAY...THEN MOVE ACROSS
THE LAKE WEDNESDAY. THE GRADIENT WILL TIGHTEN BETWEEN THIS
APPROACHING RIDGE AND THE DEPARTING LOW WITH NORTHERLY WINDS
INCREASING TO 30 KT THIS EVENING AND REMAINING THERE UNTIL TUESDAY
AFTERNOON...AS THE RIDGE SLOWLY WORKS EAST. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL 7 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 PM MONDAY TO 7 AM WEDNESDAY.

&&

$$

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.