Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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 191748
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1148 AM CST WED NOV 19 2014

.SHORT TERM...
335 AM CST

TODAY THROUGH FRIDAY...

MAIN FOCUS IN NEAR TERM IS WITH CLIPPER-TYPE SYSTEM MOVING THROUGH
THE REGION THIS MORNING...AND THE POTENTIAL FOR SOME LIGHT
ACCUMULATING SNOW MAINLY ACROSS FAR NORTHERN/NORTHEAST IL. OTHER
HIGHLIGHTS...OR LOW LIGHTS AS THE CASE MAY BE...THROUGH FRIDAY ARE
CONTINUED SUB-NORMAL CHILLY TEMPERATURES AND THE POTENTIAL FOR SOME
LIGHT FREEZING RAIN FRIDAY NIGHT INTO EARLY SATURDAY MORNING AHEAD
OF A SYSTEM WHICH WILL BRING RAIN AND WARMER WEATHER OVER THE
WEEKEND.

EARLY MORNING WATER VAPOR IMAGERY DEPICTS A SHORT-WAVE DIGGING
SOUTHEAST ACROSS THE UPPER MISSISSIPPI VALLEY AND APPROACHING WI/IL
AT 0830Z. SURFACE TROUGH REFLECTION WAS OVER SOUTHERN MN/EAST
CENTRAL IA...WITH FAIRLY IMPRESSIVE SURFACE PRESSURE FALLS SPREADING
INTO SOUTHERN WI/IL AND BACKING WINDS TO THE SOUTH AND RAISING
TEMPS. RADAR RETURNS FROM MID-LEVEL CLOUDS HAVE DEVELOPED SOUTHEAST
FROM TWIN CITIES AREA...THOUGH DRY LOW LEVEL AIR SO FAR HAS SLOWED
DEVELOPMENT OF SNOW AT THE SURFACE. TRACK OF SYSTEM...RADAR TRENDS
AND HIGH-RES HRRR GUIDANCE ALL INDICATE BEST POTENTIAL FOR
MEASURABLE SNOW THROUGH THE EARLY MORNING HOURS WILL BE ALONG A
ROUGHLY MSP-MKE CORRIDOR...WITH GENERALLY LIGHT AMOUNTS OF AN INCH
OR LESS EXPECTED ACROSS FAR NORTHEAST IL AND PARTS OF NORTHERN IN.
FORECAST SOUNDINGS INDICATE DRY AIR ARRIVING IN MID-LEVELS BY
MID-LATE MORNING AND LIMITING BEST FORCING FOR SNOW TO A ONLY A FEW
HOURS THIS AM. SURFACE TROUGH PASSES MID-DAY...WITH RENEWED COLD
ADVECTION AND EXTENSIVE UPSTREAM CLOUDINESS SUPPORTING SCATTERED
FLURRIES THIS AFTERNOON AS LOW-LEVEL THERMAL PROFILES COOL AGAIN.
MOISTURE BECOMES VERY SHALLOW TONIGHT AND THURSDAY...DECREASING
POTENTIAL FOR FLURRIES DESPITE ANOTHER DIGGING SHORT WAVE ACROSS THE
WESTERN LAKES. THE MAIN LARGE-SCALE UPPER TROUGH AXIS THEN SHIFTS
EAST THURSDAY NIGHT...ALLOWING SURFACE HIGH PRESSURE TO SPREAD EAST
ACROSS THE AREA BY FRIDAY MORNING.

TEMPERATURES WERE RISING INTO THE 20S WITH THE SOUTH WINDS THIS
MORNING...WITH HIGHS EXPECTED TO TOP OUT IN THE MID 20S TO LOW 30S
TODAY WITH THE MILDEST TEMPS ACROSS THE FAR EAST/SOUTHEAST CWA.
COLDER TEMPS AGAIN TONIGHT AND THURSDAY...WITH THE COLDEST EXPECTED
EARLY FRIDAY MORNING IN THE VICINITY OF THE SURFACE RIDGE AXIS. LOWS
IN THE SINGLE DIGITS TO LOWER TEENS ARE LIKELY FRIDAY MORNING WITH
LIGHT WINDS AND MOSTLY CLEAR SKIES.

MUCH-TOUTED CHANGE IN THE UPPER PATTERN WILL BE UNDERWAY FRIDAY...
AS FLOW DE-AMPLIFIES AND UPPER TROUGH MOVES ACROSS THE SOUTHWESTERN
STATES AND ACROSS THE CENTRAL AND SOUTHERN ROCKIES FRIDAY NIGHT.
ALONG WITH A DISTURBANCE MOVING ACROSS CENTRAL CANADA...THIS WILL
SET UP SOUTHERLY RETURN FLOW INTO THE REGION FRIDAY NIGHT WITH
ASSOCIATED WARM/MOIST ADVECTION. MODELS CONTINUE TO INDICATE
DEVELOPMENT OF SOME LIGHT PRECIP OVERNIGHT...WITH FORECAST SOUNDINGS
INDICATING ELEVATED WARM LAYER TEMPS APPROACHING +5C WHILE SFC TEMPS
ARE BELOW FREEZING. THIS SUPPORTS THE POTENTIAL FOR SOME LIGHT
FREEZING RAIN OR SLEET FRIDAY NIGHT...BEFORE WARM ADVECTION
EVENTUALLY RAISES SURFACE TEMPS ABOVE FREEZING ON SATURDAY. MODELS
HAVE TRENDED A LITTLE SLOWER WITH ARRIVAL OF LIGHT PRECIP...THOUGH
ALSO SOMEWHAT COLDER INITIALLY AT THE SURFACE. WILL CONTINUE TO
MENTION POTENTIAL FOR FREEZING RAIN/SLEET AND WILL HAVE TO MONITOR
TRENDS FOR THE POTENTIAL OF SOME LIGHT ICE ACCUMULATION LATER FRIDAY
NIGHT INTO EARLY SATURDAY.

RATZER

&&

.LONG TERM...
335 AM CST

SATURDAY THROUGH TUESDAY...

LONGER RANGE MODEL SOLUTIONS CONTINUE TO LIFT SOUTHWESTERN TROUGH
TOWARD THE AREA OVER THE WEEKEND...WITH LOW LEVELS QUICKLY WARMING
ABOVE FREEZING SATURDAY MORNING AND CHANGING ANY MIXED PRECIP OVER
TO RAIN. 00Z GFS/ECMWF HAVE COME INTO BETTER AGREEMENT IN TIMING THE
NEGATIVELY-TILTED SOUTHWESTERN SHORT WAVE AND DEEPENING SURFACE LOW
TO LIFT ACROSS THE FORECAST AREA SUNDAY AFTERNOON/EVENING...WITH
TEMPS RISING INTO THE BALMY 45-50 RANGE. SOME DIFFERENCES REMAIN
WITH THE DETAILS OF PHASING THIS SYSTEM WITH A NORTHERN STREAM
DEVELOPING CLOSED UPPER LOW OVER THE REGION SUNDAY NIGHT INTO
MONDAY...THOUGH REASONABLY SIMILAR IN THE IDEA OF MILD WITH
RAIN/SHOWERS EVENTUALLY GIVING WAY TO LIGHTER RAIN/SNOW TRANSITION
MONDAY-MONDAY NIGHT AND TO LINGERING SNOW SHOWERS TUESDAY AS WE
SHIFT BACK TO A DEEP EASTERN CONUS UPPER TROUGH AND COLDER WEATHER
EARLY NEXT WEEK.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LIGHT SNOW SHOWERS MIDDAY INTO EARLY AFTERNOON WITH MVFR CIGS/VSBY.

* CIGS TRENDING TO MVFR THIS AFTERNOON.

* GUSTY WEST WINDS RETURN LATE THIS MORNING WITH PEAK GUSTS ARND
  25-28 KT THIS AFTN.

KMD

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

SNOW SHOWERS IN SOUTHWEST WISCONSIN HAVE A HISTORY OF 2-5SM
VISIBILITY FOR A 2-3 HOUR PERIOD AT MOST. THE FORCING ASSOCIATED
WITH THIS ACTIVITY COMES THROUGH NORTHERN ILLINOIS MIDDAY INTO
EARLY AFTERNOON. IT DOES WEAKEN SOMEWHAT AS IT PROGRESSES SOUTH
AND EAST...BUT WE WILL HAVE MORE UNSTABLE LOW LEVELS WHICH WILL
SUPPORT SOME LIGHT SNOW SHOWERS. MUCH OF THIS ACTIVITY WILL BE
LIGHT AND NON ACCUMULATING WITH NO SIGNFICIANT VSBY
REDUCTION...BUT THERE COULD BE A BRIEF DUSTING WITH ANY OF THE
HEAVIER SNOW SHOWERS.

CIGS TREND BACK TO VFR TONIGHT WITH SOME CLEARING POSSIBLE. WINDS
REMAIN WESTERLY THROUGH THE PERIOD...STRONGEST THIS
AFTERNOON.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH IN A PERIOD OF LIGHT AND GENERALLY NON ACCUMULATING SNOW
  SHOWERS THIS AFTERNOON. MEDIUM ON HOW LONG VISIBLITIES WILL BE
  REDUCED TO MVFR AND LOW ON WHETHER CIGS WILL DROP BELOW 2000 FT.

* HIGH FOR PERIODS OF MVFR CIGS THIS AFTERNOON.

* HIGH FOR WIND TRENDS.

KMD

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

THURSDAY NIGHT...VFR.

FRIDAY...CHANCE OF A WINTRY MIX OVERNIGHT. IFR LIKELY OVERNIGHT.

SATURDAY...WINTRY MIX BCMG RAIN. IFR LIKELY.

SUNDAY...RAIN AND IFR LIKELY.

MONDAY...CHC -RASN BCMG -SN. MVFR TO IFR CIGS.

TUESDAY...VFR.

JEE

&&

.MARINE...
210 AM CST

HEADLINES...DID NOT MAKE ANY CHANGES TO THE SMALL CRAFT ADVISORY BUT
DID UPGRADE THE OPEN WATER GALE WATCH TO A WARNING. MAY SEE WINDS
DIMINISH TO BELOW GALES FASTER THAN THE WARNING WOULD INDICATE...BUT
HAVE LIMITED CONFIDENCE IN HOW LONG GALES WILL LAST SO LEFT THE END
TIME AS IS.

A TROUGH OF LOW PRESSURE MOVES OVER THE LAKE THIS AFTERNOON WITH
WEST WINDS BECOMING SOUTH OVER THE NEXT FEW HOURS. WINDS RETURN TO
WEST BEHIND THE TROUGH THIS AFTERNOON AND INCREASE TO GALES BY THE
LATE AFTERNOON. GALES CONTINUE OVERNIGHT INTO THURSDAY MORNING...BUT
THEY MAY COME DOWN BELOW GALE FORCE SOONER THAN THE WARNING
INDICATES.  NW WINDS TO 30 KT BECOME WEST 10-20 KT BY FRIDAY
MORNING. HIGH PRESSURE PASSES SOUTH OF THE LAKE LATE THURSDAY NIGHT
AND FRIDAY MORNING WITH LIGHT WINDS BECOMING SOUTH TO SOUTHWEST TO
20 KT BY FRIDAY EVENING. WINDS INCREASE TO 30 KT FRIDAY NIGHT AS THE
GRADIENT TIGHTENS BETWEEN THE DEPARTING HIGH AND A LOW OVER NORTHERN
QUEBEC.  SOUTH WINDS PERSIST THROUGH SATURDAY NIGHT BEFORE BECOMING
SOUTHEAST SUNDAY AHEAD OF THE NEXT LOW. GUIDANCE DIFFERS ON STRONG
THE LOW WILL BE AND ITS EXACT PATH BUT GUIDANCE MEMBERS DO AGREE
THAT THE LAKE WILL MOVE OVER THE LAKE AT SOME POINT SUNDAY NIGHT.

JEE

&&

.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...3 PM WEDNESDAY TO 9 AM
     THURSDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 2 PM FRIDAY.

&&

$$

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.