Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 231956
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
156 PM CST SUN NOV 23 2014

.SHORT TERM...
312 AM CST

THROUGH TONIGHT

WHAT A DIFFERENCE 48 HOURS MAKES! BRISK SOUTHERLY WINDS ARE
TRANSPORTING AN UNSEASONABLY MILD AND MOIST AIR MASS INTO THE REGION
WITH OVERNIGHT TEMPS IN THE UPPER 40S/LOWER 50S. COMPLEX PATTERN
ALOFT WITH STRONG CLOSED MID LEVEL LOW TRACKING EASTWARD JUST NORTH
OF THE CANADIAN BORDER WHILE A POWERFUL PACIFIC JET NOSES INTO THE
SOUTHERN ROCKIES AT THE BASE OF A STRONG SOUTHERN STREAM SHORTWAVE.

IN THE NEAR TERM...MORE SUBTLE SHORTWAVE EVIDENT ON WATER VAPOR
IMAGERY OVER NE OK/SE KS TRACKING NORTHEASTWARD HAS RESULTED IN A
RECENT BLOSSOMING OF RAIN OVER NORTHERN MISSOURI. SHORT RANGE
GUIDANCE AGREES THAT AS THE SHORTWAVE CONTINUES NE THIS MORNING THAT
THIS AREA OF RAIN WILL DEVELOP EASTWARD WHILE MOVE NORTHEAST AND
SPREAD INTO MAINLY WESTERN AND NORTHERN PORTIONS OF OUR CWA. THIS
RAIN SHOULD LIFT NORTH THROUGH THE MORNING AND AS IT LOOKS NOW THERE
WILL BE A SEVERAL HOUR LONG BREAK IN THE RAIN OVER MUCH OF THE AREA
THIS AFTERNOON IN THE WAKE OF THIS SHORTWAVE AND PRIOR TO THE
HEAVIER AND MORE WIDESPREAD RAIN ASSOCIATED WITH THE STRENGTHENING
SOUTHERN STREAM SHORTWAVE SPREADS ACROSS THE CWA LATE THIS AFTERNOON
AND ESPECIALLY THIS EVENING. HIGH PWATS AND STRONG FORCING SHOULD
RESULT IN HEALTHY RAINFALL TOTALS AND PERIODIC MODERATE TO NEARLY
HEAVY RAIN WITHIN THE WARM CONVEYOR BELT THIS EVENING. STILL LOOKS
LIKELY THAT MOST OF THE AREA WILL PICK UP IN THE NEIGHBORHOOD OF AN
INCH OF RAIN THIS AFTERNOON INTO TONIGHT.

STEADY STREAM OF MID-UPPER 40 DEWPOINTS ADVECTING NORTH INTO THE
AREA SHOULD ALLOW TEMPS TO FALL VERY LITTLE EARLY THIS MORNING.
WHILE CLOUD COVER WILL BE EXTENSIVE TODAY...THE ANTICIPATE BREAK IN
THE PRECIP SHOULD BE ENOUGH TO ALLOW TEMPS TO INCH UP INTO THE
MID-UPPER 50S ACROSS THE MAJORITY OF THE CWA...ONE EXCEPTION
POTENTIALLY BEING FAR NORTHWEST WHERE RAIN COULD LINGER LONGER INTO
MIDDAY. TONGUE OF 50 DEGREE DEWPOINTS SHOULD POKE UP INTO THE AREA
TONIGHT AHEAD OF THE STRONG COLD FRONT AND ANTICIPATE TEMPS TONIGHT
TO HOLD IN THE 50S WITH THE RAIN THE MAJORITY OF THE NIGHT WITH LOWS
OCCURRING JUST PAST SUNRISE.

IZZI

&&

.LONG TERM...
312 AM CST

MONDAY ONWARD...

STILL SEEING SOME NON-TRIVIAL DIFFERENCES IN THE MODELS WITH RESPECT
TO THE DETAILS MONDAY...LIKELY DUE TO THEIR TENDENCY TO STRUGGLE
WITH PHASING SYSTEMS. ALL GUIDANCE SWEEPS A STRONG COLD FRONT ACROSS
THE AREA MONDAY MORNING WITH FALLING TEMPERATURES AND STRONG
WESTERLY WINDS LIKELY MONDAY INTO MONDAY EVENING. THE BIGGEST
DIFFERENCE IN THE SOLUTIONS FOR OUR AREA IS AN INCREASING LARGE CAMP
OF MODEL GUIDANCE IS SHOWING A FAIRLY STRONG NORTHERN STREAM
SHORTWAVE LAGGING BEHIND AND ENHANCING ASCENT IN THE DEFORMATION
ZONE ACROSS OUR CWA MONDAY AFTERNOON AND EVENING. BY THIS POINT
THERMAL PROFILES WOULD SUPPORT ALL SNOW. LATEST GFS/ECMWF/PARALLEL
13KM GFS ALL SHOWING AN ACCUMULATING SNOWFALL ACROSS OUR CWA MONDAY
AFTERNOON AND EVENING...ESPECIALLY NORTHERN 1/2 TO 2/3 OF THE AREA.
THE LACK OF RUN-TO-RUN CONSISTENCY AND KNOWN ISSUES GUIDANCE HAS
WITH PHASING SYSTEMS LEADS TO LOWER THAN AVERAGE CONFIDENCE BUT HAVE
BUMPED UP POPS TO LIKELY IN THIS TIME FRAME AND CARRIED A COUPLE
INCHES OF ACCUMULATION IN THE GRIDS FOR THIS TIME FRAME.

IF THE LATEST GFS/ECMWF QPF ENDS UP BEING IN THE BALL PARK OF WHAT
HAPPENS THEN WE COULD BE LOOKING AT A FAIRLY HIGH IMPACT EVENT WITH
SEVERAL INCHES OF ACCUMULATION POSSIBLE. IN ADDITION...VERY STRONG
WINDS WILL FURTHER RESULT IN A FURTHER DETERIORATION IN CONDITIONS.
FORECAST SOUNDINGS DON`T FAVOR HIGH SNOW:LIQUID RATIO SNOWFALL WITH
DEEP ISOTHERMAL LAYER WARMER THAN -10C...RATHER LARGER AGGREGATE
FLAKES WOULD BE FAVORED WITH A WETTER SNOW AND LOWER VSBYS. WILL
BEGIN TO ADVERTISE THIS THREAT IN THE HWO BUT FAR TOO EARLY TO
CONSIDER ANY HEADLINES AT THIS POINT.

YET ANOTHER SURGE OF ARCTIC AIR SPILLS INTO THE REGION TUESDAY IN
THE WAKE OF THIS SYSTEM. FAST ON ITS HEELS OF THIS SYSTEM LOOKS TO
BE A FAIRLY ENERGETIC CLIPPER DIVING INTO THE REGION WEDNESDAY. THE
00Z GFS HAS BACKED OFF ON THE INTENSITY OF THIS WAVE...WHILE THE
ECMWF HAS TRENDED STRONGER AND LOOKS MORE IN LINE WITH THE 84 HOUR
WRF-NAM. IN ADDITION...THE 13KM PARALLEL GFS IS MORE IN THE STRONGER
NAM/ECMWF CAMP SO FELT COMFORTABLE RAISING POPS ABOVE THE SUPERBLEND
INITIALIZATION AS POTENTIAL LOOKS TO BE GROWING FOR A HIGHER
PROBABILITY/LOWER QPF SNOW EVENT IN THE REGION WEDNESDAY. IT SHOULD
COME AS NO SURPRISE THAT MORE ARCTIC LOOKS TO SPILL INTO THE REGION
BEHIND THIS SYSTEM IN TIME FOR THE THANKSGIVING HOLIDAY WEEKEND.

IZZI

&&

.AVIATION...

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

* IFR CIGS WITH INCREASING SHRA COVERAGE THROUGH THE AFTERNOON.

* MORE WIDESPREAD RAIN BEGINNING LATE AFTERNOON THROUGH THE
  EVENING. IFR CIGS/VIS LIKELY. LIGHTER RAIN OR DRIZZLE PERSISTING
  THROUGH THE NIGHT WITH IFR CONDITIONS CONTINUING.

* WINDS BACKING FROM SOUTH TO SOUTHEAST AND INCREASING TO 12-15 KT
  DURG THE AFTERNOON.

* WINDS VEERING SOUTHWEST TO WEST BY LATE TOMORROW MORNING AND
  INCREASING TO 20G30KT BY AROUND NOON WITH OCCASIONAL HIGHER
  GUSTS POSSIBLE.

* RAIN WILL TRANSITION TO SNOW DURG THE LATE MORNING TO EARLY
  AFTERNOON HOURS...WITH LIGHT SNOW CONTINUING THROUGH THE
  AFTERNOON.

KREIN

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

LATEST RADAR IMAGERY SHOWING AN AREA OF WIDESPREAD RAIN MOVING NWRN
ALG THE MISSISSIPPI RIVER AND OVER NWRN IL...WITH MORE SHOWERY
PCPN OVER NERN IL AND INTO NWRN IN. RFD WILL LIKELY SEE THE STEADY
RAIN INITIALLY...BUT BASED ON THE LATEST RADAR TRENDS...THE MORE
WIDESPREAD...STEADY RAIN SHOULD MOVE INTO THE CHICAGO AREA
TERMINALS THROUGH THE EARLY AFTERNOON HOURS. CIGS HAVE ALREADY
DROPPED TO MVFR AND ANTICIPATE THAT CIGS SHOULD CONTINUE TO LOWER
AS RAIN FALLS THROUGH THE STRATUS LAYER...SATURATING BASES
DOWNWARD AND ALLOWING CIGS TO DROP INTO IFR LEVELS THROUGH THE
AFTERNOON. AS THE STEADIER RAIN AND HIGHER DEWPOINTS CONTINUE TO
STREAM NEWD...VIS WILL BEGIN TO DROP S WELL...INITIALLY TO MVFR
LEVELS THROUGH THE EARLY AFTERNOON AND THEN TO IFR LEVELS BY LATE
AFTERNOON. IFR CONDITIONS SHOULD THEN PERSIST THROUGH THE EVENING
AND OVERNIGHT...AND POSSIBLE EVEN EXTEND THROUGH TOMORROW MORNING.

WINDS WILL START OUT SLY AT THE INITIAL TIME...BUT EXPECT
DIRECTION TO BECOME SELY BY LATE AFTERNOON AS A MID LEVEL IMPULSE
TRACKS NWD AND SFC LOW PRESSURE DEVELOPS OVER MISSOURI LATE
AFTERNOON INTO EARLY EVENING. THE LOW IS EXPECTED TO TRACK INTO
LOWER MICHIGAN BY MONDAY MORNING...CAUSING WINDS TO VEER TO SWLY
DURG THE MORNING HOURS. AN ASSOCIATED COLD FRONT SHOULD PASS
ACROSS THE REGION AS THE SFC LOW MOVES INTO LOWER MICHIGAN...AND
COLDER AIR WILL BEING TO FILTER ACROSS THE REGION THROUGH THE
MORNING AS WINDS CONTINUE TO VEER TO WLY BY EARLY AFTERNOON. THE
INFLUX OF COLDER AIR WILL CAUSE PCPN TO GRADUALLY SHIFT OVER TO A
RAIN/SNOW MIX BY LATE MORNING AND THEN CHANGE OVER TO ALL SNOW BY
ARND NOON. PCPN RATES WILL DECREASE FOLLOWING THE PASSAGE OF THE
COLD FRONT...BUT WINDS WILL QUICKLY INCREASE WITH GUSTS TO 30 KT
OR OR BY AROUND NOON AS WELL. THE COMBINATION OF LIGHT SNOW AND
STRONG WINDS WILL KEEP VIS RESTRICTED TO IFR LEVELS THROUGH MUCH
OF THE DAY TOMORROW.

KREIN

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

* MEDIUM TO HIGH CONFIDENCE IN CIG/VIS TRENDS...BUT LOWER
  CONFIDENCE IN THE EXACT TIMING OF THE TRANSITION FROM MVFR TO
  IFR.

* HIGH CONFIDENCE IN PCPN TRENDS...BUT MEDIUM CONFIDENCE IN THE
  TIMING OF THE TRANSITION FROM PREVAILING RAIN TO PREVAILING
  SNOW.

* HIGH CONFIDENCE IN WIND TRENDS...BUT HAVE SOME CONCERN FOR GUSTS
  HIGHER THAN 30-32KT TOMORROW AFTERNOON.

KREIN

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

MONDAY NIGHT...SNOW SHOWERS LIKELY. GUSTY BUT DIMINISHING WEST WINDS.

TUESDAY...MVFR CIGS POSSIBLE WITH A FEW FLURRIES IN THE MORNING.
NORTHWEST WINDS.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR PSBL. SSE WINDS TURNING WEST.

THURSDAY...SCHC SNOW...OTHERWISE VFR. BREEZY NORTHWEST WINDS.

FRIDAY...SCHC SNOW.

SATURDAY...VFR.

KMD

&&

.MARINE...
252 AM CST

LOW PRESSURE MOVING EAST FROM THE CANADIAN PRAIRIES EARLY THIS
MORNING WILL CONTINUE TO FILL AS IT TRACKS ALONG THE CANADIAN BORDER
TODAY AND REACHES LAKE SUPERIOR LATE THIS AFTERNOON. THIS LOW WILL
MERGE WITH LOW PRESSURE CURRENTLY EMERGING OUT OF THE SOUTHERN HIGH
PLAINS REGION. THE HIGH PLAINS LOW WILL ABSORB THE NORTHERN LOW OVER
LAKE MICHIGAN TONIGHT THEN CONTINUE TO DEEPEN AS IT TRACKS OVER/EAST
OF LAKE MICHIGAN MONDAY MORNING...THEN DEEPENS MORE MONDAY NIGHT AS
IT CONTINUES EAST OF JAMES BAY.  HAVE NOT MADE CHANGES TO THE
HEADLINES AT THIS MOMENT. CONFIDENCE ON GALES FOR THE SOUTHERN HALF
OF THE LAKE IS HIGH THOUGH STILL SOME ISSUES WITH TIMING. IT LOOKS
LIKE GALES BEGIN TO SPREAD OVER THE SOUTHERN TIP OF THE LAKE NEAR OR
SHORTLY AFTER DAYBREAK MONDAY.  CONFIDENCE FOR GALES ON THE NORTH
HALF OF THE LAKE IS A BIT LESS BUT STILL MEDIUM-HIGH GIVEN
DIFFERENCES IN HOW QUICKLY MODELS MOVE THE LOW OVER THE LAKE MONDAY
INTO MONDAY NIGHT. DEPENDING ON HOW QUICKLY THE LOW KICKS
NORTHEAST...THE GALE WATCH END TIME FOR THE FAR NORTHERN PORTION OF
THE LAKE MAY BE A BIT TOO SHORT. WEAK HIGH PRESSSURE PASSES OVER THE
LAKE TUESDAY. THIS WILL BE FOLLOWED ON WEDNESDAY ON A CLIPPER-TYPE
LOW COMING OUT OF THE DAKOTAS TUESDAY. THIS LOW PUSHES EAST OF THE
LAKE WEDNESDAY NIGHT AS STRONGER HIGH PRESSURE BUILDS IN TO THE
CENTER OF THE COUNTRY THURSDAY AND LINGERS FOR A FEW DAYS. KMD

&&

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

     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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