000
FXUS63 KLOT 092204
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
504 PM CDT SUN MAR 9 2014

.DISCUSSION...
322 PM CDT

WARMER TEMPS IN THE NEAR TERM...AND PRECIP TYPE/SNOW POTENTIAL FOR
ESPECIALLY SOUTHERN CWA LATER TUES-WED ARE MAIN FORECAST CONCERNS
THIS AFTERNOON.

SURFACE LOW PRESSURE CONTINUED TO DEEPEN OVER ONTARIO THIS AFTERNOON
WITH A LARGE AREA OF 5+ MB THREE HOURLY PRESSURE FALLS SPREADING
ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES. STRONG WARM
ADVECTION WAS OCCURRING ALOFT...THOUGH SURFACE TEMPS HAVE BEEN SLOW
TO RISE DUE TO SHALLOW MIXING OF THIS MORNING`S STRONG INVERSION.
WINDS WILL INCREASE LATE THIS AFTERNOON AND EVENING AS GRADIENT
CONTINUES TO TIGHTEN HOWEVER...WITH TEMPS EXPECTED TO CONTINUE TO
RISE INTO THE 40S THROUGH EARLY EVENING BEFORE BECOMING STEADY OR
DROPPING OFF A FEW DEGREES LATER TONIGHT AS WINDS EASE A BIT. LOW
LEVEL THERMAL RIDGE IS PROGGED ACROSS THE FORECAST AREA MONDAY
MORNING/MID-DAY WITH H9 TEMPS AROUND +10 C...SUPPORTING MAINTENANCE
OF GOING FORECAST TEMPS ABOVE WARMEST GUIDANCE WITH HIGHS FROM THE
LOWER 50S NORTH TO THE LOW 60S WHERE LITTLE/NO SNOW COVER IMPACT
WILL EXIST. WEAK COLD FRONT SETTLES ACROSS AREA MONDAY AFTERNOON...
THOUGH WITH STILL RELATIVELY MILD AIR MASS OF WESTERLY PACIFIC
ORIGIN BEHIND THE FRONT.

ATTENTION THEN TURNS TO PRECIPITATION DEVELOPMENT TUESDAY AS
AMPLIFIED UPPER TROUGH CURRENTLY OVER THE EASTERN PACIFIC EVENTUALLY
ARRIVES AND PHASES TO SOME DEGREE WITH ANOTHER SHORT WAVE TROUGH
DIGGING FROM CENTRAL CANADA. MODELS IN GOOD AGREEMENT IN DEVELOPING
WEST-EAST BAND OF PRECIP IN ASSOCIATION WITH STRONG MID-LEVEL
FRONTOGENESIS AND BENEATH DIVERGENT RIGHT ENTRANCE OF STRONG UPPER
JET STREAK DURING THE DAY...FOCUSED MAINLY NORTH/NORTHWEST OF THE
CWA. FORECAST THERMAL PROFILES OVER THE FORECAST AREA ABOVE FREEZING
BELOW 850 MB WITH SFC TEMPS ABOVE 40 THUS RELATIVELY LOW POPS IN
PLACE ALONG THE IL/WI BORDER FOR RAIN BEFORE EVENING. SURFACE LOW
PRESSURE DEVELOPS INTO LOWER MISSOURI/OHIO VALLEY TUESDAY NIGHT WITH
LOW LEVEL NORTHEAST FLOW AND COLD ADVECTION COOLING THE COLUMN AS
PRECIP DEVELOPS ACROSS THE REGION. DECREASING LOW LEVEL THICKNESS
AND COOLING SOUNDINGS SUPPORT A CHANGE OVER TO WET SNOW TUESDAY
EVENING...WITH THE POTENTIAL FOR SOME ACCUMULATING WET SNOW
PARTICULARLY ACROSS OUR SOUTH/SOUTHEAST CWA WHERE STRONGEST FORCING
ALIGNS LATE TUESDAY NIGHT INTO WEDNESDAY MORNING. FAIRLY LOW
SNOW/LIQUID RATIO EXPECTED...THOUGH IT APPEARS THAT PERHAPS SEVERAL
INCHES POSSIBLE ACROSS OUR EAST CENTRAL IL/NORTHWEST IN COUNTIES
SOUTH OF I-80. UPPER TROUGH AXIS THEN PASSES ACROSS AREA WEDNESDAY
AS LOW CONTINUES OFF TO THE EAST THROUGH OHIO VALLEY...WITH
POTENTIAL FOR SOME LIGHT SNOW/SNOW SHOWERS CONTINUING AS CANADIAN
VORT DIGS INTO DEVELOPING EASTERN NORTH AMERICAN LONG WAVE TROUGH
INTO WEDNESDAY AFTERNOON. HEIGHT RISES/SUBSIDENCE AND SURFACE HIGH
PRESSURE RIDGE THEN BUILD QUICKLY IN FROM THE NORTHWEST WEDNESDAY
NIGHT.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* GUSTY SOUTH-SOUTHWEST (210-230 DEG) WINDS THROUGH THIS EVENING.
* LLWS DEVELOPING EARLY THIS EVENING.

RC

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

HIGH PRESSURE HAS SETTLED SOUTH OF THE TERMINALS THIS AFTERNOON WITH
AN INCREASING GRADIENT DEVELOPING ACROSS NORTHERN ILLINOIS RESULTING
IN INCREASING WINDS. WINDS WILL ALSO SHARPLY INCREASE RIGHT OFF THE
SURFACE...WITH 50+ KTS STARTING AS LOW AS 015-020. THERE WILL BE
ABOUT A 6-7 HOUR WINDOW WHERE LOW LEVEL WIND SHEAR WILL BE A
POSSIBILITY THIS EVENING. WINDS BEGIN TO RELAX OVERNIGHT AS A
FRONTAL TROUGH BEGINS TO APPROACH FROM THE NORTHWEST. BESIDES THE
WINDS AND LLWS...NO OTHER SIGNIFICANT WEATHER CONDITIONS ARE
EXPECTED WITH DRY VFR WEATHER THROUGH THE PERIOD.

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE IN WIND AND GUST TRENDS.
* HIGH CONFIDENCE IN LLWS.

RC

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

MONDAY NIGHT...VFR LIKELY.
TUESDAY...CHC OF RAIN DURING THE DAY WITH A CHC OF SNOW DURING THE
          NIGHT. IFR POSSIBLE.
WEDNESDAY...SLGT CHC OF SNOW. GUSTY NNE WINDS.
THURSDAY-SATURDAY...VFR LIKELY.

MTF

&&

.MARINE...
206 PM CDT

WINDS HAVE BEEN SLOW TO RAMP UP THIS AFTERNOON OVER THE LAKE BUT
WITH STRONGEST WINDS ALOFT FORECAST TO MOVE IN THIS EVENING AM
RELUCTANT TO BACK DOWN FROM THE FORECAST OF GALES DESPITE WHAT
APPEARS TO BE SOMEWHAT DIMINISHED CHANCES. WINDS SHOULD EASE A BIT
MONDAY AS GRADIENT GETS A BIT BAGGIER IN ADVANCE OF A COUPLE OF
COLD FRONT SLATED TO MOVE SOUTH ACROSS THE LAKE. SECONDARY FRONT
MOVES ACROSS THE LAKE TUESDAY WITH COLORADO LOW PROGGED TO DEEPEN
AS IT MOVES EAST INTO THE OHIO VALLEY TUESDAY NIGHT INTO
WEDNESDAY. RESULT SHOULD BE STRENGTHENING COLD AIR ADVECTION AND
STRONG NORTHERLY WINDS OVER THE LAKE...PROBABLY NEARING GALE FORCE
IF CURRENT MODEL PROJECTIONS OF THE STRENGTH OF THE LOW HOLD.
GIVEN ITS STILL 48-72 HOURS OUT NO GALE WATCH WILL BE ISSUED AT
THIS TIME...BUT LATER SHIFTS MAY NEED TO CONSIDER A GALE WATCH IF
CURRENT TRENDS HOLD.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868 UNTIL 9 PM SUNDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO