Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 220543
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1143 PM CST FRI NOV 21 2014

.UPDATE...
746 PM CST

MINOR CHANGES TO THE GOING FORECAST THIS EVENING...MAINLY SLOWING
TIMING OF PRECIP INTO THE REGION.  DEWPOINTS REMAIN PRETTY DRY
ACROSS THE REGION WITH SINGLE DIGITS STILL IN PLACE NORTH OF I-80
AND LOW/MID TEENS TO THE SOUTH. REGIONAL RADAR MOSAIC SHOWS
SCATTERED SHOWERS MOVING ACROSS NE MO/SE IA INTO WEST CENTRAL IL
THIS EVENING AND SHOULD START TO OVERSPREAD OUR SOUTHWESTERN
COUNTIES BY AROUND 04Z OR SO...AND INTO THE CHICAGO AREA CLOSER TO
THE 06-07Z HOUR. LOWERED POPS A LITTLE MAINLY DUE TO LIMITED
COVERAGE NOTED UPSTREAM. WHILE TEMPERATURES HAVE SOME DOWNWARD
POTENTIAL FROM WET BULBING THIS EVENING...CLOUDS HAVE STARTED TO
MOVE OVERHEAD WITH A FEW SITES SHOWING TEMPS REBOUNDING A DEGREE
OR TWO...WITH MID/UPPER 30S NOT TOO FAR AWAY. LATEST RAP GUIDANCE
ACTUALLY HAS AIR TEMPERATURES RISING ABOVE FREEZING AROUND THE
ONSET OF PRECIP...SO IT APPEARS THE WINDOW OF POTENTIAL FREEZING
RAIN WILL REMAIN FAIRLY SHORT. WILL MAINTAIN CURRENT ADVISORY
TIMING AS EVEN A LIGHT GLAZE OF ICE CAN BE HAZARDOUS...BUT IF
ANYTHING WE MAY BE ABLE TO LET IT GO A LITTLE EARLY.

BMD

&&

.SHORT TERM...
352 PM CST

THROUGH TONIGHT...

CONDITIONS WILL REMAIN QUIET FOR THE REMAINDER OF THE AFTERNOON
UNDER MOSTLY CLEAR SKIES.  LATEST SATELLITE IMAGERY SHOWS A DENSE
MASS OF CLOUD COVER ASSOCIATED WITH A SURGE OF MOISTURE CROSSING THE
MISSOURI VALLEY AND APPROACHING WRN IL.  AT THE SURFACE...LATEST OBS
INDICATE DEWPOINTS RAPIDLY INCREASING INTO THE 40S AND 50S WITH THE
MOISTURE SURGE...WHILE DEWPOINTS OVER NRN IL/NWRN IN UNDER THE
MOSTLY CLEAR SKIES REMAIN IN THE SINGLE DIGITS TO THE LOWER TEENS.
THE PCPN SHIELD ASSOCIATED WITH THE APPROACHING SYSTEM WILL TAKE A
LITTLE TIME TO OVERCOME THE VERY DRY AIR IN PLACE...BUT UPSTREAM
TRENDS AND THE SHORT TERM MODEL GUIDANCE ALIGN WELL WITH THE TREND
TO BRING INCREASING POPS INTO THE FAR SWRN PORTIONS OF THE CWA AFTER
SUNSET AND THEN QUICKLY SPREADING TO THE NORTH AND EAST THROUGH THE
EVENING AND OVERNIGHT.  THERE WILL BE A SLOW INCREASE IN SFC TEMPS
THROUGH THE NIGHT UNDER STRONG WARM ADVECTION DRIVEN BY A SWLY LOW
LEVEL JET TO 45KT.  AVAILABLE DEEP LAYER MOISTURE WITH SYSTEM IS
LIMITED...SO ACTUAL QPF AMOUNTS EXPECTED SHOULD BE RELATIVELY
LIGHT.  WILL MAINTAIN AND MAKE NO CHANGES TO THE GOING FREEZING RAIN
ADVISORY.  WITH LIGHT QPF AMOUNTS EXPECTED...ANY ICE ACCUMULATION
SHOULD RANGE FROM A LIGHT GLAZING TO A LITTLE OVER A TENTH OF AN
INCH.  THERE IS ALSO A CHANCE FOR SOME GLAZING AS EARLY AS 23Z-00Z
OVER THE PONTIAC AREA...WITH SOME LIGHT DRIZZLE OR LIGHT RAIN COMING
IN CONTACT WITH ROAD SURFACES AND WALKWAYS THAT ARE CURRENTLY BELOW
FREEZING DUE TO THE RECENT UNSEASONABLY COLD WEATHER.  THROUGH THE
LATE EVENING AND INTO THE OVERNIGHT HOURS...THE FREEZING PCPN WILL
GRADUALLY CHANGE OVER TO A MIX OF FREEZING OR LIQUID TO ALL LIQUID
PCPN AS THE WARMER AIR SURGES INTO THE REGION LATE THIS EVENING AND
OVERNIGHT TONIGHT.  THE FREEZING PCPN POTENTIAL SHOULD DIMINISH FROM
SOUTHWEST TO NORTHEAST AS THE WARMER AIR OVERSPREAD THE
REGION...WITH THE FREEZING PCPN POTENTIAL ENDING OVER THE FAR NERN
PORTIONS OF THE CWA...INCLUDING THE FAR NORTHERN PORTIONS OF THE
CHICAGO AREA BY DAYBREAK SATURDAY MORNING.

KREIN

&&

.LONG TERM...
352 PM CST

SATURDAY THROUGH FRIDAY...

FOR THE REMAINDER OF THE DAY ON SATURDAY...WITH LOW PRESSURE
DEEPENING OVER THE NRN PLAINS WHILE HIGH PRESSURE MOVES OFF THE
SOUTH EAST ATLANTIC COAST...THE PERSISTENT FETCH OF WARM...MOIST AIR
WILL CONTINUE TO STREAM OVER THE AREA...WITH LIGHT RAIN PERSISTING
THROUGH THE DAY.  TEMPERATURES WILL CONTINUE TO INCREASE THROUGH THE
DAY ON SATURDAY WITH HIGHS RANGING FROM AROUND 50F OVER THE PONTIAC
AREA TO THE MIDDLE 40S OVER THE REMAINDER OF THE CWA.  DEWPOINTS ARE
ALSO EXPECTED TO CONTINUE TO RISE THROUGH SATURDAY...REACHING INTO
THE MIDDLE 40S...WHICH WILL BE A STARK CONTRAST TO THE UNSEASONABLY
COLD...DRY AIR THAT HAS BEEN THE PREVAILING CONDITION FOR THE PAST
SEVERAL DAYS.  WITH THE MAIN FOCUSING MECHANISM TO MAINTAIN THE PCPN
BEING WIDESPREAD...BUT GRADUAL...ISENTROPIC LIFT...RAINFALL AMOUNTS
WILL CONTINUE TO BE RELATIVELY LIGHT THROUGH SATURDAY NIGHT...WITH
WIDESPREAD AMOUNTS OF A COUPLE TENTHS OF AN INCH.

MORE SIGNIFICANT RAINFALL IS SETTING UP FOR SUNDAY AND INTO SUNDAY
NIGHT AS A STRONG SRN STREAM SHORTWAVE LIFTS 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 OVER
SRN IL BY SUNDAY EVENING AS A NRN STREAM SHORTWAVE TRACKS ACROSS THE
NRN PLAINS TO THE WRN GREAT LAKE REGION.  THE SRN STREAM SYSTEM WILL
BE THE PRIMARY FOCUS FOR HEAVIER RAIN.  THE MODELS CONTINUE TO
INDICATE ALMOST UNPRECEDENTED LEVELS OF DEEP LAYER MOISTURE FOR LATE
NOVEMBER...WITH PWATS INCREASING TO IN EXCESS OF 1 INCH THROUGH THE
DAY ON SUNDAY.  WHILE ANY THUNDER REMAINS UNLIKELY DUE TO A LACK OF
INSOLATION UNDER PERSISTENT CLOUD COVER...THE UNUSUALLY HIGH
MOISTURE CONTENT SHOULD BRING AREAS OF FOG THROUGH SUNDAY AS WELL AS
SOME LOCALLY HEAVY RAINFALL.  WIDESPREAD RAINFALL OF 1 TO 1.5 INCHES
IS POSSIBLE FOR SUNDAY THROUGH SUNDAY NIGHT WITH LOCALIZED AREAS OF
EVEN HEAVIER RAIN POSSIBLE IS SOME CONVECTIVE ELEMENTS CAN DEVELOP.
CONDITIONS WILL REMAIN MUCH WARMER/MOISTER THAN RECENT DAYS THROUGH
SUNDAY WITH HIGHS ONCE AGAIN EXPECTED TO BE IN THE UPPER 40S TO
AROUND 50F.

THE MODELS HAVE SETTLED INTO A RELATIVELY CONSISTENT SOLUTION OF
PHASING THE NRN AND SRN STREAM SHORTWAVES OVER THE ERN GREAT LAKES
BY MONDAY MORNING WITH A SFC LOW ARND 980MB DEVELOPING.  AS THE LOW
DEEPENS FURTHER ON MONDAY...STRONG WEST WINDS WILL DEVELOP OVER THE
AREA WITH WINDS INCREASING TO ARND 25 MPH WITH 35MPH GUSTS.
CONSIDERING A POSSIBILITY THAT THE MODELS COULD EVEN BE UNDER
FORECASTING THE POTENTIAL DEEPENING OF THIS LOW...WHICH IS A
POSSIBILITY GIVEN THE LATE FALL CONTRAST OF WARM...MOIST GULF AIR
ASSOCIATED WITH THE SRN STREAM SYSTEM AND MUCH COLDER AIR WITH THE
NRN STREAM SYSTEM...THERE IS THE CHANCE THAT WIND ADVISORY CRITERIA
WINDS OF SUSTAINED 30 MPH WINDS WITH 45 MPH GUSTS MAY OCCUR ON
MONDAY.

THE DEEP SFC LOW IS EXPECTED TO LIFT OUT TO THE NORTHEAST MONDAY
NIGHT AND TUESDAY...WEAK HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
AS THE SFC WHILE BROAD UPPER TROUGHING DEVELOPS OVER THE CNTRL
CONUS.  THE UPPER LEVEL PATTERN IS EXPECTED TO BECOME MORE
AMPLIFIED...BUT SLOWLY PROGRESSIVE BY MIDWEEK THROUGH THE END OF NEXT
WEEK...THE AREA REMAINING UNDER PERSISTENT NWLY FLOW AND COLD
ADVECTION ALOFT.  SO THE WEEKEND WARMUP SHOULD COME TO AN ABRUPT END
BY MONDAY AS A STRONG COLD FRONT PASSES THROUGH THE REGION AND
TEMPERATURES DROP BACK INTO THE UPPER 30S TO ARND 40F ON MONDAY WITH
HIGHS ONLY IN THE UPPER 20S TO LOWER 30S FOR TUESDAY.  THROUGH THE
REMAINDER OF NEXT WEEK...THE TEMPERATURE TREND WILL GO BACK TO WELL
BELOW NORMAL...WITH HIGHS ON THANKSGIVING ONLY IN THE LOWER TO
MIDDLE 20S. A WEAK CLIPPER-TYPE SYSTEM DROPPING OUT OF THE NRN
ROCKIES ON TUESDAY IS EXPECTED TO DIVE INTO THE LOWER MISSISSIPPI
VALLEY BY WEDNESDAY AS ANOTHER WEAK SHORTWAVE DROPS THROUGH THE
UPPER GREAT LAKES.  THIS COULD BRING SOME LIGHT SNOW FOR
WEDNESDAY...BUT THEN STRONG HIGH PRESSURE SHOULD BUILD ACROSS THE
MIDDLE MISSISSIPPI VALLEY THROUGH THE GREAT LAKES.  THIS COULD SET
UP A WEAK PRESSURE GRADIENT PATTERN OVER THE REGION...BRINGING THE
POSSIBILITY FOR A LAKE EFFECT PLUME TO DEVELOP OVER LAKE MICHIGAN.
WHILE IT IS STILL WAY TOO EARLY TO CONSIDER THE FINER DETAILS OF
LAKE EFFECT SNOW ASSOCIATED WITH MESOSCALE BANDING OF A LAKE
PLUME...THE PATTERN WOULD BE CONDUCIVE FOR SUCH TYPE OF DEVELOPMENT.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* TEMPORARY LIGHT FZRA POSSIBLE PRIOR TO 09Z-10Z...WITH GRADUALLY
  WARMING TEMPERATURES LIKELY YIELDING TEMPORARY -SHRA AFTER THAT
  POINT THROUGH DAYBREAK.

* CIGS GRADUALLY LOWERING TO IFR BY DAYBREAK AND POTENTIALLY
  PERSISTING THROUGH THE REMAINDER OF THE TAF.

* IFR VISIBILITY IN DRIZZLE POSSIBLE SATURDAY...ESPECIALLY THE
  MORNING AND EARLY AFTERNOON.


//DISCUSSION...UPDATED 06Z...

SCATTERED SHOWERS WILL MOVE NORTHEAST OVER THE REGION THROUGH 10Z-
12Z. COVERAGE OF THESE WILL LIKELY INCREASE SOME BUT OVERALL
REMAIN SCATTERED AND GIVEN THE FORCING...WILL ALSO REMAIN MAINLY
LIGHT IN INTENSITY. SOUTHERLY WINDS ARE CONTINUING TO STEER IN
GRADUALLY WARMING TEMPERATURES AS WE PASS THE MIDNIGHT HOUR. IT IS
LIKELY MOST OF THE AIRFIELDS AIR TEMPERATURES WILL REMAIN ABOVE
FREEZING AS SHOWER INTENSITY SHOULD NOT BE ENOUGH TO BRING
TEMPERATURES DOWN TO WET BULB VALUES. HOWEVER...PAVEMENT
TEMPERATURES ARE SLIGHTLY SLOWER TO RESPOND. THIS MAY LEAD TO
LIGHT FREEZING ON SURFACES BEFORE THEY WARM TO OVER 32. BY
DAYBREAK...THE SHOWER ACTIVITY SHOULD HAVE FURTHER DIMINISHED IN
COVERAGE WITH THE PASSAGE OF AN UPPER LEVEL DISTURBANCE...HOWEVER
MOISTENING LOW-LEVELS SHOULD PROVIDE AREAS OF DRIZZLE. IN
TANDEM...CIGS WILL BE FURTHER LOWERING INTO THE IFR CATEGORY AND
VISIBILITY MAY FOLLOW. IFR CIGS MAY PERSIST THROUGH ALL OF SATURDAY
AND EVEN IF THEY DO NOT THEY ARE LIKELY TO RETURN SATURDAY NIGHT.
RAIN SHOULD BE SPREADING NORTHWARD OVER THE AREA DURING OVERNIGHT
SATURDAY NIGHT.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN LIGHT SHOWERS OCCURRING AND TIMING BUT LOW IN WHETHER IT
  WILL FREEZE AS AIR TEMPERATURES WILL LIKELY BE ABOVE 32 AND ANY
  FREEZING WILL DEPEND HEAVILY ON PAVEMENT TEMPERATURES.

* HIGH IN IFR CIGS SATURDAY MORNING AND MEDIUM IN HOW FAR THEY
  WILL DROP.

* MEDIUM IN DRIZZLE OCCURRING SATURDAY BUT LOW IN HOW FAR
  VISIBILITY WILL DROP WITH IFR POSSIBLE.


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

SUNDAY...RAIN. HEAVY AT TIMES. IFR LIKELY. GUSTY S TO SE WINDS.

MONDAY...CHANCE -RASN EARLY AND -SN LATER. MVFR CIGS POSSIBLE.
GUSTY W TO SW WINDS.

TUESDAY...CHANCE OF FLURRIES. MVFR CIGS PSBL. BREEZY WEST WINDS.

WEDNESDAY...LIGHT SNOW POSSIBLE. MVFR CIGS/VIS POSSIBLE. WEST TO
SOUTHWEST WINDS 10 KT OR LESS.

THANKSGIVING DAY...VFR LIKELY.

MTF

&&

.MARINE...

242 PM...HIGH PRESSURE OVER THE SOUTHERN LAKES AND OHIO VALLEY
WILL MOVE SOUTHEAST TONIGHT REACHING THE CAROLINA COAST ON
SATURDAY AS LOW PRESSURE MOVES ACROSS NORTHERN ONTARIO AND JAMES
BAY TONIGHT. THE GRADIENT BETWEEN THESE TWO SYSTEMS WILL STEADILY
INCREASE OVER LAKE MICHIGAN TONIGHT WITH GALE FORCE WINDS
EXPECTED...POSSIBLY GUSTING AS HIGH AS 45KTS ACROSS THE NORTHERN
PORTION OF THE LAKE. THE GRADIENT WILL BEGIN TO WEAKEN LATER
SATURDAY AFTERNOON INTO SATURDAY EVENING...BUT ANOTHER LOW MOVING
ACROSS THE NORTHERN PLAINS SATURDAY NIGHT INTO SUNDAY WILL TIGHTEN
THE SOUTHERLY GRADIENT AGAIN. THIS LOW WILL BEGIN TO WEAKEN SUNDAY
EVENING AND THEN BE ABSORBED BY ANOTHER STRONGER LOW WHICH WILL
DEVELOP OVER THE SOUTHERN PLAINS SATURDAY NIGHT INTO SUNDAY...THEN
MOVE NORTH ACROSS LAKE MICHIGAN SUNDAY NIGHT INTO MONDAY MORNING.
THIS LOW HAS BEEN FORECAST TO DEEPEN TO AS LOW AS 975MB NEAR LAKE
SUPERIOR FOR SEVERAL DAYS. IF THIS OCCURS...WESTERLY HIGH END
GALES TO 45 KTS WOULD LIKELY DEVELOP MONDAY WITH THE POTENTIAL FOR
SOME STORM FORCE WINDS OR GUSTS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FREEZING RAIN ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ020-ILZ022 UNTIL 9 AM
     SATURDAY.

     FREEZING RAIN ADVISORY...ILZ019-ILZ021-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 6 AM SATURDAY.

IN...FREEZING RAIN ADVISORY...INZ001-INZ002 UNTIL 9 AM SATURDAY.

     FREEZING RAIN ADVISORY...INZ010-INZ011-INZ019 UNTIL 6 AM
     SATURDAY.

LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM SATURDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM SATURDAY.

&&

$$

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