Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 230921
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
321 AM 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 09Z...

* MVFR CIGS THROUGH THIS MORNING. IFR POSSIBLE LATE SUNDAY
  MORNING AND LIKELY BY LATE AFTERNOON.

* VFR VSBY EXPECTED OUTSIDE OF ANY SHOWERS THROUGH SUNDAY
  MORNING.

* ISOLATED-SCATTERED SHOWER CHANCES INCREASE BRIEFLY THIS MORNING
  AND AGAIN BY MID AFTERNOON. STEADIEST RAIN BY EVENING.

* SOUTH WINDS BECOMING GUSTY SUNDAY MORNING. SHOULD TURN SOUTHEAST
  SUNDAY AFTERNOON THEN BACK SOUTH SUNDAY EVENING.

* LOW LEVEL WIND SHEAR FOR A FEW MORE HOURS WITH 40 KT WINDS AT
  2000 FT AGL.

KMD

//DISCUSSION...UPDATED 09Z...

QUITE A GRADIENT IN CONDITIONS ACROSS THE AREA EARLY THIS
MORNING...FROM LIFR CONDITIONS NEAR KRFD TO VFR FROM KMDW AND
AREAS SOUTH AND EAST. SLIGHTLY DRIER AIR IS MOVING IN FROM THE
SOUTH THAT WILL ALLOW CIGS TO IMPROVE SOME OVER THE COMING HOURS.
LOOKS LIKE ORD WILL LIFT HERE PRETTY SOON TO AT LEAST HIGHER MVFR
AND PROBABLY VFR FOR A TIME. EVEN EXPECT SOME IMPROVEMENT WEST
TOWARDS KRFD BACK TO AT LEAST MVFR FOR A TIME AS WELL.

PREV DISCUSSION FROM 06Z...

CIGS CONTINUE TO DETERIORATE FROM WEST TO EAST EARLY THIS
MORNING...WITH LOWER MVFR CIGS KNOCKING AT THE DOOR CLOSER TO
KRFD...WHILE SOUTHEAST OF KIKK TO KGYY CIGS WILL CONTINUE VARY
WITH VFR DOMINATING AND OCCASIONAL MVFR THROUGH THE OVERNIGHT
HOURS. IFR CONDITIONS MAY SNEAK INTO OUR WESTERN AREAS OVERNIGHT
BUT NOT SEEING MUCH BELOW 1000 FT CIGS YET. LOW LEVEL WIND SHEAR
IS ALSO POSSIBLE FOR THE COMING HOURS.

HAVE NOT MADE MAJOR CHANGES TO THE CURRENT TAF THEME. EXPECT A
WAVE OF RAIN THIS MORNING BETWEEN 12Z AND 18Z FROM SOUTH TO
NORTH...WITH ACTIVITY MORE SCATTERED IN NATURE IN THE MAIN
CHICAGOLAND TERMINALS AND POINTS EAST...WHILE AREAS WEST HOLD A
BETTER CHANCE OF MODERATE RAIN AND IFR CONDITIONS. EXPECT MVFR TO
HOLD ELSEWHERE. THE MAIN FORCING FOR PRECIPITATION BEST COINCIDES
WITH DEEPER MOISTURE IN THE 22Z-6Z TIME FRAME WHERE CIGS AND
VISIBILITIES SHOULD EASILY FALL TO IFR/LIFR. WINDS WILL ALSO SHIFT TO A
SOUTHEASTERLY DIRECTION THROUGH THE AFTERNOON AND EARLY EVENING. AFTER
6Z WINDS WILL SHIFT MORE SOUTHERLY AND RAIN WILL EASE SOMEWHAT.
THAT SAID CIGS WILL GENERALLY REMAIN IN IFR/LIFR WITH A PERIOD OF
LIGHTER RAIN/DRIZZLE WITH AN ADDITIONAL PERIOD OF SHOWERS TOWARD
MONDAY MORNING.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN MVFR LIFTING TO VFR IN THE COMING HOURS. LOW- MEDIUM
  CONFIDENCE IN FALLING TO IFR BEFORE SUNDAY AFTERNOON. HIGH THAT
  IFR/LIFR WILL PREVAIL FROM LATE AFTERNOON THROUGH EARLY MONDAY
  MORNING.

* MEDIUM-HIGH IN VFR VSBY OUTSIDE OF ANY SHOWERS OVERNIGHT/SUNDAY
  MORNING.

* HIGH THAT COVERAGE OF SHOWERS WILL INCREASE FOR A SHORT TIME
  THIS MORNING THEN AGAIN ESPECIALLY LATER THIS AFTERNOON.

* HIGH IN WIND TRENDS THROUGH SUNDAY MORNING. MEDIUM CONFIDENCE
  SUNDAY AFTERNOON/EVENING.

* MEDIUM IN LLWS.

KMD

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

MONDAY...CHANCE OF RAIN AND SNOW. STRONG WEST TO SOUTHWEST WINDS.
TUESDAY...MVFR CIGS POSSIBLE. WESTERLY WINDS.
WEDNESDAY...CHANCE OF SNOW AND MVFR. SOUTH TO SOUTHWEST WINDS.
THURSDAY...SNOW SHOWERS AND MVFR POSSIBLE. NORTHWEST WINDS.
FRIDAY...VFR PROBABLE. WEST TO SOUTHWEST WINDS.

MDB

&&

.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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