Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 222102
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
302 PM CST SAT NOV 22 2014

.SHORT TERM...THIS AFTERNOON AND TONIGHT...
258 PM CST

FOR THE REMAINDER OF THIS AFTERNOON AND THROUGH TONIGHT...AN
INFLUX OF WARM...MOIST AIR WILL CONTINUE TO STREAM INTO THE UPPER
MIDWEST. LATEST SFC ANALYSIS SHOWS DEWPOINTS IN THE 50S OVER
MISSOURI WHILE DEWPOINTS ACROSS NRN IL. NWRN IN HAVE CLIMBED INTO
THE MIDDLE TO UPPER 40S. TEMPERATURES HAVE ALSO BEEN ON THE RISE
THROUGH THE DAY WITH TEMPERATURES AT OR IN EXCESS OF 50F AS FAR
NORTH AS MIDWAY AIRPORT AND AURORA AS OF 230PM CST. TEMPERATURES
ARE EXPECTED TO CONTINUE TO RISE INTO THE EARLY EVENING UNDER THE
PERSISTENT WARM...MOIST ADVECTION UNDER A STRONG SWLY LOW LEVEL
JET WITH 850MB WINDS UP TO 45KT...TEMPERATURES WILL LIKELY HOVER
AROUND THE 50 DEGREE MARK THROUGH THE NIGHT. ADDITIONAL LIGHT RAIN
OR DRIZZLE WILL PERSIST THROUGH THE EVENING AND OVERNIGHT...WITH
AREAS OF FOG POSSIBLE.

KREIN

&&

.LONG TERM...SUNDAY THROUGH FRIDAY...
258 PM CST

MORE SIGNIFICANT RAINFALL IS SETTING UP FOR SUNDAY AND INTO
SUNDAY NIGHT AS A STRONG SRN STREAM SHORTWAVE LIFTING OUT OF THE
SOUTH HIGH PLAINS PHASES WITH ANOTHER SHORTWAVE LIFTING FROM THE
SOUTHWEST GULF COAST REGION. THESE SYSTEM WILL RESULT IN A
DEEPENING SFC LOW OF 984MB NEAR ST LOUIS BY SUNDAY EVENING. THE
MODELS CONTINUE TO ADVERTISE PWAT VALUES AROUND 1.2 INCHES...WHICH
IS AT THE 99TH PERCENTILE FOR PWATS FOR THE REGION. THIS PHASING
OF THE TWO SRN STREAM SYSTEMS COMBINED WITH THE UNUSUALLY HIGH
PWAT AIRMASS WILL COMBINE TO FOCUS STEADY RAINFALL ACROSS THE
REGION THROUGH THE DAY ON SUNDAY AND INTO SUNDAY EVENING...WITH A
CORRIDOR OF THE HEAVIEST RAIN OVER THE NWRN PORTIONS OF THE
CWA...GENERALLY NORTH OF A LINE FROM PERU TO MCHENRY...WHERE
UPWARDS OF A HALF INCH PER 3 HOUR PERIOD IS POSSIBLE. LATER SUNDAY
NIGHT...THE PHASED SRN STREAM SYSTEM WILL BEGIN TO PHASE WITH A
NRN STREAM SHORTWAVE...WITH LOW PRESSURE RAPIDLY DEEPENING AS IT
LIFTS THROUGH THE UPPER GREAT LAKES. WHILE THE GUIDANCE IS
RELATIVELY CONSISTENT ON THE TRACK AND TIMING OF THE DEEPENING
LOW...THE GFS IS A MUCH STRONGER OUTLIER IN THE GUIDANCE
ENVELOPE...DEEPENING THE CENTRAL PRESSURE TO ARND 966MB BY MIDDAY
MONDAY...WHILE MUCH OF THE OTHER GUIDANCE ONLY DEEPENS THE LOW TO
ARND 980MB. WHILE THE GFS SOLUTION MAY BE TOO DEEP...LIKELY
DRAWING COLDER AIR INTO THE SYSTEM FASTER THAN THE OTHER
MODELS...OR TAPPING MORE NRN STREAM ENERGY...THERE WILL STILL
LIKELY BE A DEEP LOW DEVELOPING OVER THE UPPER GREAT LAKES SUNDAY
NIGHT INTO MONDAY...WHOSE CIRCULATION PATTERN WILL COVER A LARGE
EXPANSE FROM THE EAST-CENTRAL PLAINS TO NERN QUEBEC. A STRONG WLY-
NWLY GRADIENT WILL SET UP ON THE SWRN PERIPHERY OF THE
SYSTEM...LEADING TO STRONG...GUSTY WINDS ACROSS THE CWA FROM EARLY
MONDAY MORNING THROUGH LATE MONDAY EVENING. THE STRONGEST WINDS
SHOULD OCCUR FROM LATE MORNING THROUGH LATE EVENING...WITH
SUSTAINED WINDS OF 25-30 MPH AND PEAK GUSTS OF 35-40 MPH.
HOWEVER...IF THE SYSTEM EVOLVES A LITTLE DEEPER THAT THE CONSENSUS
GUIDANCE AND DEEPENS CLOSER TO THE OUTLIER GFS SOLUTION...WINDS
ACROSS THE AREA COULD REACH WIND ADVISORY LEVELS OF SUSTAINED
WINDS OF 30 MPH OR HIGHER OR GUSTS OF 45 MPH OR GREATER.

ALSO...AS THE SFC LOW BEGINS TO LIFT OUT TO THE NORTHEAST MONDAY
AFTERNOON...MUCH COOLER AIR WILL BEGIN TO FILTER ACROSS THE REGION.
AS THE PATTERN TRANSITIONS FROM ONE OF STRONG WARM ADVECTION SUNDAY
NIGHT TO STRONG COLD ADVECTION BY MONDAY MORNING...FOLLOWING THE
PASSAGE OF A STRONG ASSOCIATED COLD FRONT...LINGERING PCPN WILL
BEGIN TO TRANSITION FROM RAIN TO SNOW.  SINCE THE COLD AIR SHOULD
EXTEND THROUGH THE ENTIRE ATMOSPHERE...THERE SHOULD BE A MORE
STRAIGHTFORWARD TRANSITION FROM RAIN TO SNOW WITH LITTLE CHANCE FOR
ANY FREEZING RAIN OR SLEET.  THERE COLD BE SOME ISSUES WITH WATER
FLASH FREEZING ON ELEVATED SURFACES AS SUB-FREEZING AIR QUICKLY
FILTERS ACROSS THE REGION BY LATE MONDAY AFTERNOON.

THE STRONG COLD ADVECTION WILL PERSIST THROUGH THE NIGHT WITH
TEMPERATURES DROPPING TO THE LOWER TO MIDDLE 20S BY DAYBREAK TUESDAY
MORNING.  THE PERSISTENT COLD ADVECTION WILL ALLOW FOR LITTLE
DIURNAL WARMING WITH HIGHS ON TUESDAY EXPECTED TO BE IN THE UPPER
20S TO ARND 30F OVER THE FAR SERN PORTIONS OF THE CWA. THERE BE SOME
MODERATION TO TEMPERATURES ON WEDNESDAY AS WEAK SFC RIDGING CROSSES
THE AREA ALLOWING TEMPERATURES TO RISE INTO THE MIDDLE 30S.
WEDNESDAY SHOULD BE THE WARMEST OF THE EXTENDED PERIOD.  A SERIES OF
STRONG NORTHERN STREAM SHORTWAVES IS EXPECTED TO CARVE OUT A BROAD
LONGWAVE TROUGH OVER ERN CONUS FROM THE MISSISSIPPI VALLEY TO THE
EAST COAST.  THE UPPER LEVEL PATTERN SHOULD DECREASE IN AMPLITUDE
THROUGH THE EXTENDED PERIOD...BUT THE LOCAL AREA IS EXPECTED TO
REMAIN UNDER GENERAL NWLY FLOW ALOFT...KEEPING A PERSISTENT FETCH OF
COLD AIR ACROSS THE AREA. BY LATE NEXT WEEK...HIGH TEMPERATURES WILL
STRUGGLE INTO THE LOWER TO MIDDLE 20S...WHILE OVERNIGHT LOWS DROP
INTO THE LOWER TO MIDDLE TEENS...WITH THE POSSIBILITY OF THE NWRN
PORTIONS OF THE CWA...INCLUDING THE ROCKFORD AREA DROPPING INTO THE
SINGLE DIGITS FRIDAY AND SATURDAY MORNING.  THE SERIES OF SHORTWAVES
RIPPLING THROUGH THE NORTHWEST FLOW SHOULD BRING PERIODIC CHANCES
FOR SOME LIGHT SNOW...BUT CONFIDENCE IS LOW ON THE EXACT TIMING.
CONFIDENCE IS A LITTLE HIGHER THAT ANY SNOW THAT DOES OCCUR SHOULD
BE LIGHT AS THERE WILL BE LITTLE ENVIRONMENTAL MOISTURE OR SFC
FORCING.  ANY SNOW GENERATION WILL HAVE TO RELY ON MID-LEVEL FORCING
AND MEAGER MOISTURE CONTENT.

KREIN

&&

.AVIATION...

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

* PATCHY IFR CIGS...TO LOW END MVFR CIGS THIS AFTN. LIKELY
  TRENDING BACK TOWARDS IFR OVERNIGHT THRU SUN MORNING.

* VSBY WILL HOVER BETWEEN 3-6SM THIS AFTN...POSSIBLY FALLING TO
  JUST UNDER 3SM OVERNIGHT THRU SUN MORNING.

* LOW-LEVEL WIND SHEAR DEVELOPING TONIGHT. ARND 2KFT AGL FROM THE
  SOUTHWEST NEARING 45KT.

* RAIN SHOWERS DEVELOPING EARLY SUN MORNING...INCREASING IN
  COVERAGE CLOSER TO MIDDAY.

BEACHLER

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

VERY MOIST AIR MASS CONTINUES TO FEED NORTHEAST ACROSS NORTHERN
IL/NORTHWEST IN AIRFIELDS THIS AFTERNOON. LITTLE IMPROVEMENT TO
THE CIGS IS EXPECTED...AS A RESULT HAVE HELD CIGS DOWN ARND LOW
END MVFR THIS AFTN AND WILL LIKELY TREND BACK TOWARDS IFR CONDS
OVERNIGHT. GENERALLY EXPECT CIGS ARND 500-900FT AGL THRU THE
OVERNIGHT HOURS. WIND DIR WILL NOT CHANGE MUCH THIS
AFTN/EVE/OVERNIGHT...MAINLY FROM THE SOUTH WITH SPEEDS ALSO NOT
CHANGING MUCH ARND 10-12KT. GIVEN HOW MOIST THE ATMOSPHERE
IS...PERIODIC ROUNDS OF DRIZZLE CAN BE EXPECTED THRU THIS
AFTN/EARLY EVE WILL A LULL LATE THIS EVE. WIND SHEAR IS ALSO
POISED TO DEVELOP THIS EVENING...WITH WINDS ARND 2KFT AGL FROM THE
SOUTHWEST INCREASING TO 40-45KT.

GUIDANCE HAS CONTINUED TO SUGGEST DEVELOPING RAIN SHOWERS AFT
MIDNIGHT/EARLY SUN...SO HAVE HELD ONTO THE MENTION OF LGT RAIN
EARLY SUN. THEN IT APPEARS THE BETER COVERAGE FOR PERHAPS MORE
STEADY RAIN WILL OCCUR LATE SUN MORNING...AND COULD PERSIST THRU
SUN AFTN.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS HOLDING AT LOW END MVFR...AND MEDIUM
  CONFIDENCE ON TIMING CIGS TRENDING BACK TOWARDS IFR.

* HIGH CONFIDENCE IN WIND DIR/SPEED.

* MEDIUM CONFIDENCE IN LOW-LEVEL WIND SHEAR.

* HIGH CONFIDENCE IN DRIZZLE THRU THIS AFTN...THEN MEDIUM
  CONFIDENCE IN TIMING OF ENDING THE MENTION OF DRIZZLE.

* HIGH CONFIDENCE IN LIGHT RAIN DEVELOPING EARLY SUN WITH BETTER
  COVERAGE LATE SUN MORNING/AFTN. MEDIUM CONFIDENCE IN PRECISE
  TIMING OF RAIN IMPACTING TAF SITES.

BEACHLER

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

SUNDAY NIGHT...RAIN AND IFR PROBABLE. SOUTHERLY WINDS.
MONDAY...CHANCE OF RAIN AND SNOW. STRONG WEST TO SOUTHWEST WINDS.
TUESDAY...MVFR CIGS POSSIBLE. WESTERLY WINDS.
WEDNESDAY...CHANCE OF SNOW AND MVFR. SOUTHWEST WINDS.
THURSDAY...FLURRIES AND MVFR POSSIBLE. NORTHWEST WINDS.
FRIDAY...VFR PROBABLE. SOUTHWEST WINDS.

MTF

&&

.MARINE...

231 PM...STRONG LOW PRESSURE WILL MOVE ALONG THE U.S. CANADIAN
BORDER TONIGHT AND BEGIN TO WEAKEN AS IT REACHES WESTERN LAKE
SUPERIOR SUNDAY AFTERNOON. ANOTHER LOW WILL DEVELOP OVER THE
SOUTHERN PLAINS TONIGHT AND MOVE NORTH TO SOUTHERN LAKE MICHIGAN
AS IT DEEPENS AND ABSORBS THE LOW OVER WESTERN LAKE SUPERIOR. THIS
LOW WILL THEN DEEPEN FURTHER AS IT REACHES EASTERN LAKE SUPERIOR
MONDAY MORNING. THERE STILL REMAINS SOME DIFFERENCES AMONG THE
MODELS REGARDING HOW STRONG THIS LOW WILL BECOME. THE DEEPEST OF
THE MODELS HAS A PRESSURE OF 28.5 INCHES MIDDAY MONDAY. CONFIDENCE
IS INCREASING FOR MID/HIGH END GALES SO WILL BE GOING WITH A GALE
WATCH FOR MONDAY AND MONDAY NIGHT. STORM FORCE GUSTS OR PREVAILING
WINDS ALSO REMAIN POSSIBLE. WINDS STEADILY DIMINISH TUESDAY AS
HIGH PRESSURE MOVES ACROSS THE SOUTHERN LAKES AND OHIO VALLEY.
ANOTHER LOW IS EXPECTED TO MOVE ACROSS THE LAKES REGION WEDNESDAY
INTO THURSDAY...BRINGING NORTHWEST WINDS TO 30KT ON THURSDAY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM SATURDAY.

     GALE WATCH...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878...6 AM MONDAY TO 3 AM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868...NOON MONDAY TO 3 AM TUESDAY.

&&

$$

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