Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLOT 180941
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
AVIATION SECTION ISSUED BY NATIONAL WEATHER SERVICE LINCOLN IL
341 AM CST THU DEC 18 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

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

* EXTENT AND TIMING OF CLEARING MOVING IN FROM THE NORTH. DJO

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

MVFR CIGS CONTINUE TO SLOWLY ERODE FROM THE NORTH WHILE REMAINING
STEADY TO THE SOUTHWEST...RPJ/C09/IKK. CONFIDENCE REGARDING TRENDS
IS LOW BUT IF THEY CONTINUE...WILL LIKELY SEE SOME SCATTERING OF
LOW CLOUDS FROM THE NORTH OVERNIGHT...WITH CLEARING AT GYY/MDW
LIKELY TO BE LATER THIS MORNING. NORTHWEST WINDS 4-8KTS WILL
LIKELY BECOME LIGHT AND VRB WHERE CLOUDS CLEAR...WITH LIGHT
NORTHWEST WINDS THRU THE DAY AND BECOMING LIGHT AND VRB TONIGHT.
CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD. DJO

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

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE.
LIGHT AND VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...

209 AM...A LARGE AREA OF HIGH PRESSURE EXTENDING FROM ONTARIO
SOUTH TO ILLINOIS WILL VERY SLOWLY MOVE EAST ACROSS THE GREAT
LAKES TODAY AND FRIDAY...THEN ACROSS THE EASTERN LAKES AND INTO
QUEBEC SATURDAY AND SUNDAY. NORTHWESTERLY WINDS WILL GRADUALLY
DIMINISH TODAY...WITH A 36-48 HOUR PERIOD OF LIGHT WINDS...5-10
KTS...EXPECTED AS THE HIGH MOVES EAST. WINDS WILL SHIFT SOUTHERLY
SATURDAY ON THE BACK SIDE OF THE HIGH BUT STILL REMAIN LIGHT. THE
SOUTHERLY WINDS WILL BEGIN TO INCREASE SUNDAY AS THE GRADIENT
BEGINS TO TIGHTEN AHEAD OF DEVELOPING LOW PRESSURE IN THE PLAINS.
THIS LOW WILL TRACK NORTHEAST TOWARD THE WESTERN LAKES REGION BY
EARLY/MID NEXT WEEK...BUT STILL QUITE A BIT OF UNCERTAINTY
REGARDING ITS TRACK/STRENGTHEN/TIMING. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

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

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





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.