Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 141955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT MON APR 14 2014

.DISCUSSION...
1205 PM CDT

CHALLENGING FORECAST CONTINUES THROUGH THE EVENING WITH PRECIP
COVERAGE...INTENSITY...AND TYPE BEING THE MAIN FOCUS. LARGE SCALE
UPPER TROUGH COVERING THE MID SECTION OF THE COUNTRY CONTINUES TO
PIVOT EASTWARD PUSHING COLDER AIR INTO THE REGION. SUBTLE WAVES
TRAVERSING THE FLOW CONTINUE TO WORK WITH COLD ADVECTION TO BRING
PRECIP DEVELOPMENT. SURFACE TEMPS HAVE WARMED CENTRAL AND
SOUTHEAST WHICH IS SUPPORTIVE OF MORE RAIN BUT TEMPERATURES WILL
LIKELY COOL INTO THE AFTERNOON FROM THE NORTHWEST.
THEREFORE...PRECIP TYPE THROUGH EARLY AFTERNOON WILL LIKELY BE
RAIN OR SNOW EXCEPT FOR FAR SOUTHEAST AREAS THAT WOULD SEE
RAIN...THOUGH PRECIP CHANCES ARE LOWER THERE. WATER VAPOR SHOWS A
MORE ORGANIZED SHORTWAVE STARTING TO EJECT NORTHEAST FROM
SOUTHWEST MISSOURI AND EASTERN OKLAHOMA AND KANSAS. THIS WAVE WILL
LIFT INTO THE AREA LATE THIS AFTERNOON INTO THE EARLY EVENING AND
TIGHTEN THE MID LEVEL BAROCLINIC ZONE RESULTING IN INTENSIFYING
FRONTOGENESIS. RADAR MOSAIC SHOWS BANDS OF PRECIP DEVELOPING
NORTHEASTWARD IN CONJUNCTION WITH THIS FEATURE. WILL CONTINUE WITH
THE IDEA OF A MORE FOCUSED PERIOD OF PRECIPITATION LATE THIS
AFTERNOON INTO THE EVENING BUT HAVE TRIED TO REFINE DETAILS. WHILE
PRECIP WILL CONTINUE ON AND OFF THROUGH THE AFTERNOON...HAVE
SLOWED THE PERIOD OF BETTER COVERAGE/INTENSITY SLIGHTLY. FORECAST
SOUNDINGS/CONCEPTUAL MODELS SUPPORT ALL SNOW WITHIN THE MOST
INTENSE BAND THANKS TO WELL ALIGNED ASCENT WITHIN THE SNOW GROWTH
ZONE AND COOLING LOW LEVEL TEMP PROFILES. EXPECT THAT THERE WILL
BE A CORRIDOR OF MODERATE SNOW WITHIN A LARGER AREA OF LESS
INTENSE PRECIP THAT WILL DEVELOP NORTHWARD ALONG A LINE FROM
ROUGHLY CHICAGO TO MENDOTA...THEN PIVOT EASTWARD INTO THE EVENING.
MUCH OF THE EVENING RUSH HOUR IN THE CHICAGO METRO LOOKS TO FALL
INTO THE PERIOD OF MORE INTENSE SNOWFALL...WHICH MAY LAST A FEW
HOURS. THE VORT MAX LIFTS NORTHEAST WHICH MAY BRING A LULL IN THE
PRECIP EARLY THIS EVENING BUT LARGER SCALE FORCING INCREASES TO
THE EAST SO THERE MAY BE RE-INTENSIFICATION OVER NORTHWEST INDIANA
BY MID EVENING BEFORE PRECIP EXITS LATE EVENING. TEMPERATURES
WILL LIKELY COOL INTO THE MID 30S LATER TODAY AND SNOW SHOULD FALL
AT AN INTENSE ENOUGH RATE TO PROVIDE FOR ACCUMULATION ON GRASSY
SURFACES AND SLUSHY ACCUMULATION ON ROADS. WILL CONTINUE WITH THE
IDEA OF AROUND AN INCH OF ACCUMULATION.

MDB

//PREV 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...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

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

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

MTF

&&

.AVIATION...

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

* MVFR CEILINGS...LOWERING BACK TOWARDS LOW END MVFR LATER THIS
  AFTERNOON.

* GUSTY NORTH/NORTHWEST WINDS.

* RAIN/SNOW MIX...WITH BETTER SNOW DEVELOPMENT MOVING OVER THE
  TERMINAL LATE THIS AFTERNOON INTO THE EARLY EVENING.

* POSSIBLE LAKE EFFECT SNOW SHOWERS LINGERING INTO THE LATE
  EVENING.

RODRIGUEZ

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

COMPLEX FORECAST THIS PERIOD AS A WINTRY MIX IS LIKELY THIS
AFTERNOON INTO THE EVENING. LATEST RADAR IMAGERY DEPICTING
CONTINUED LIGHT DEVELOPMENT AT THIS HOUR WITH ALL SNOW BEING
REPORTED ACROSS NORTH/NORTHWEST ILLINOIS...AND THEN A RAIN SNOW
MIX BEING REPORTED OVER AREAS IN NORTHEAST ILLINOIS. THIS LIGHTER
DEVELOPMENT WILL LIKELY CONTINUE THROUGH MID AFTERNOON BEFORE A
HEAVIER/STEADIER BAND OF LIGHT TO MODERATE SNOW MOVES THROUGH LATE
THIS AFTERNOON INTO THE EARL EVENING...WITH ANY AREAS OBSERVING A
RAIN/SNOW MIX OBSERVING A QUICK TRANSITION TO ALL SNOW. VIS AND
CEILINGS WILL LIKELY LOWER UNDER THIS BETTER DEVELOPMENT...WITH
IFR VIS AND LOW END MVFR CEILINGS LIKELY. THIS STEADIER SNOW
SHOULD BEGIN TO SHIFT EAST OF THE TERMINALS LATER THIS
EVENING...BUT WITH LAKE EFFECT DEVELOPMENT POSSIBLY LINGERING
THROUGH THE MIDNIGHT TIME FRAME. CONFIDENCE IS LOW WITH REGARDS TO
LAKE EFFECT SNOW DEVELOPMENT THIS EVENING/TONIGHT...AND WILL NEED
TO MONITOR THIS POSSIBLE DEVELOPMENT. AREAS WILL THEN OBSERVE A
CLEARING TREND OVERNIGHT...WITH VFR CONDITIONS THEN LIKELY
TUESDAY. NORTHERLY WINDS MAY CONTINUE TO VARY BETWEEN NNW AND NNE
OVER THE NEXT SEVERAL HOURS...BUT WITH A TREND TOWARDS NNW. HAVE
CONTINUED TO LOWER SPEEDS/GUSTS THIS AFTERNOON WITH THE HIGHEST
GUSTS OF AROUND 21KT NOW LIKELY EARLY THIS AFTERNOON. NORTHWEST
WINDS WILL PREVAIL TONIGHT INTO TUESDAY...WITH SPEEDS DIMINISHING.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH CEILING TRENDS.

* MEDIUM HIGH CONFIDENCE IN WIND DIRECTION/SPEED.

* MEDIUM HIGH CONFIDENCE WITH RAIN/SNOW AND ALL SNOW TRENDS AND
  TIMING.

* LOW CONFIDENCE WITH LAKE EFFECT SNOW SHOWERS.

RODRIGUEZ

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.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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