Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 140931
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
406 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
400 AM CDT

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

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

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD

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

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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