Winter storm watch
A Winter Storm Watch is issued by the National Weather Service of the United States when there is a possibility of heavy snow or potential of significant ice accumulations. The watch is typically issued 12 to 48 hours before the storm's arrival in the given area. The criteria for this watch can vary from place to place, which is true with other winter weather warning and advisories.
As the event of the storm draws nearer in time and confidence in the occurrence of significant winter weather conditions is increased, the weather watch will be upgraded to a Winter Storm Warning or Blizzard Warning, depending on whether blizzard conditions will be met. If there is considerable confidence in significant ice accumulations with little to no snow, the watch will be upgraded to an Ice Storm Warning. When confidence increases in the occurrence of winter like conditions that are not expected to reach warning criteria, a Winter Weather Advisory will be issued instead. A watch could be discontinued altogether if neither warning nor advisory-level conditions are expected to be met. Generally, a watch is not issued when only advisory-level conditions are expected. Watches generally go into effect when the chance of meeting warning criteria ranges from 50% to 80% of snow.
Example of a Winter Storm Watch
918
WWUS43 KLOT 301126
WSWLOT
URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE CHICAGO IL
526 AM CST SUN JAN 30 2011
...SIGNIFICANT WINTER STORM TO AFFECT THE SOUTHERN GREAT LAKES
REGION TUESDAY INTO WEDNESDAY...
.A PERIOD OF WINTRY WEATHER IS EXPECTED TO AFFECT NORTHERN
ILLINOIS AND NORTHWEST INDIANA THE FIRST HALF OF THE WORK WEEK.
SIGNIFICANT AMOUNTS OF SNOW ARE EXPECTED TO ACCUMULATE BETWEEN
MONDAY MORNING AND WEDNESDAY EVENING...WITH SNOWFALL TOTALS OF 12
OR MORE INCHES QUITE POSSIBLE IN NORTHEAST ILLINOIS AND NORTHWEST
INDIANA BY WEDNESDAY NIGHT.
THE FIRST ACCUMULATING SNOW IS EXPECTED TO SPREAD ACROSS THE AREA
MONDAY MORNING. SNOWFALL IS EXPECTED TO INTENSIFY FOR MONDAY
AFTERNOON AND EVENING...THEN LIGHTEN UP AGAIN LATE MONDAY NIGHT
INTO TUESDAY MORNING. ACCUMULATIONS OF 2 TO 4 INCHES CAN BE
EXPECTED BY MIDDAY TUESDAY. HOWEVER...THIS WILL ONLY BE THE
PRELIMINARY ROUND OF SNOW AS AN INTENSE WINTER STORM WILL BE
TRACKING FROM ARKANSAS NORTHEASTWARD UP THE OHIO VALLEY TUESDAY
AFTERNOON THROUGH WEDNESDAY MORNING. THIS STORM SYSTEM WILL
LIKELY PRODUCE AN BAND OF VERY HEAVY SNOW ALONG AND TO THE NORTH
OF ITS TRACK. THIS PUTS THE ENTIRE AREA UNDER THE GUN FOR A MAJOR
SNOWFALL EVENT.
AS THE LOW PRESSURE CENTER REACHES THE UPPER OHIO VALLEY BY LATE
WEDNESDAY MORNING A STRONG FLOW OF COLD AIR WILL BE MOVING ACROSS
SOUTHERN LAKE MICHIGAN...WITH LAKE EFFECT SNOW DEVELOPING ON THE
ILLINOIS SIDE OF THE LAKE. AS THE DAY PROGRESSES WEDNESDAY THE
STRONG LOW LEVEL FLOW WILL BECOME MORE NORTHERLY AND THE LAKE
EFFECT SNOW WILL SHIFT TO FAR NORTHWEST INDIANA.
BY LATER WEDNESDAY THE SNOW FROM THE DEPARTING WINTER STORM WILL
BE WINDING DOWN ACROSS THE AREA BUT A BAND OF SIGNIFICANT LAKE
EFFECT SNOW IS EXPECTED IN NORTHWEST INDIANA WHERE SEVERAL
ADDITIONAL INCHES OF SNOW ARE POSSIBLE BEFORE THE LAKE EFFECT
SHIFTS FURTHER OFF TO THE EAST INTO SOUTHWESTERN LOWER MICHIGAN
AND NORTH CENTRAL INDIANA.
BETWEEN THE INITIAL LIGHTER SNOW MONDAY INTO TUESDAY
MORNING...THE HEAVY SNOWFALL FROM THE MAJOR WINTER STORM DURING
TUESDAY AFTERNOON THROUGH WEDNESDAY MORNING...AND THE INCREASINGLY
INTENSE LAKE EFFECT SNOW DEVELOPING DURING WEDNESDAY...A FOOT OR
MORE OF SNOW WILL NOT BE UNCOMMON OVER MUCH OF NORTHEAST ILLINOIS
AND FAR NORTHWEST INDIANA.
THE STORM SYSTEM WILL BE AFFECTING A LARGE PORTION OF THE
SOUTHERN GREAT LAKES...MIDWEST AND OHIO VALLEY REGIONS. ANYONE
WITH TRAVEL PLANS TUESDAY AND WEDNESDAY...INCLUDING THOSE
TRAVELING THROUGH CHICAGO OHARE AND MIDWAY AIRPORTS...SHOULD
CONTINUE TO MONITOR LATER FORECASTS REGARDING THE DEVELOPMENT OF
THIS WINTER STORM.
ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
301930-
/O.NEW.KLOT.WS.A.0001.110201T1800Z-110203T0000Z/
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DUPAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
INCLUDING THE CITIES OF...ROCKFORD...BELVIDERE...WOODSTOCK...
WAUKEGAN...OREGON...DIXON...DEKALB...AURORA...WHEATON...CHICAGO...
OTTAWA...OSWEGO...MORRIS...JOLIET...KANKAKEE...PONTIAC...
WATSEKA...PAXTON...GARY...VALPARAISO...MOROCCO...RENSSELAER...
FOWLER
526 AM CST SUN JAN 30 2011 /626 AM EST SUN JAN 30 2011/
...WINTER STORM WATCH IN EFFECT FROM TUESDAY AFTERNOON THROUGH
WEDNESDAY AFTERNOON...
THE NATIONAL WEATHER SERVICE IN CHICAGO HAS ISSUED A WINTER STORM
WATCH...WHICH IS IN EFFECT FROM TUESDAY AFTERNOON THROUGH
WEDNESDAY AFTERNOON.
- TIMING...HEAVY SNOWFALL WILL SPREAD NORTHEASTWARD ACROSS THE
SNOWFALL FROM THE STORM SYSTEM STARTS TO WIND DOWN DURING
WEDNESDAY MORNING AND EARLY AFTERNOON...LAKE EFFECT SNOW WILL
HAVE DEVELOPED ON THE ILLINOIS SIDE OF THE LAKE. INCREASINGLY
HEAVY AND MORE CONCENTRATED LAKE EFFECT SNOW WILL SHIFT INTO FAR
NORTHWEST INDIANA DURING WEDNESDAY AFTERNOON AND PERSIST INTO
WEDNESDAY EVENING BEFORE SHIFTING FURTHER OFF TO THE EAST INTO
SOUTHWEST LOWER MICHIGAN AND NORTH CENTRAL INDIANA.
- ACCUMULATIONS...TOTAL ACCUMULATIONS FROM MONDAY MORNING THROUGH
NORTH CENTRAL ILLINOIS...AND IN EXCESS OF 12 INCHES OVER
NORTHEAST AND EAST CENTRAL ILLINOIS...AS WELL AS NORTHWEST
INDIANA. LOCAL AMOUNTS IN EXCESS OF 18 INCHES ARE POSSIBLE IN
FAR NORTHWEST INDIANA...DEPENDING ON EXACTLY WHERE THE LAKE
EFFECT SNOW BAND SETS UP AND HOW PERSISTENT IT IS OVER ANY ONE
LOCATION.
- HAZARDS...HEAVY SNOWFALL AS WELL AS BLOWING AND DRIFTING SNOW.
- IMPACTS...VERY DIFFICULT TO NEAR IMPOSSIBLE TRAVEL CONDITIONS AS
SNOW STORM TUESDAY AFTERNOON AND NIGHT. HEAVY LAKE EFFECT SNOW
IN NORTHWEST INDIANA LATER WEDNESDAY AND WEDNESDAY EVENING WILL
CONTINUE TO HAMPER TRAVEL THERE.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
A WINTER STORM WATCH MEANS THERE IS A POTENTIAL FOR SIGNIFICANT
SNOW...SLEET...OR ICE ACCUMULATIONS THAT MAY IMPACT TRAVEL.
CONTINUE TO MONITOR THE LATEST FORECASTS.
&&
$$