Winter storm warning
A Winter Storm Warning (SAME code: WSW) is a statement made by the National Weather Service of the United States which means a winter storm is occurring or is about to occur in the area, usually within 36 hours. Generally, a Winter Storm Warning is issued if at least the criteria—usually between 4 inches (10 cm) to 7 inches (18 cm) or more of snow or usually 3 inches (7.6 cm) or more of snow with a large accumulation of ice is forecast. In the Southern United States, where severe winter weather is much less common and any snow is a more significant event, warning criteria are lower, as low as 2 inches (5.1 cm) in the southernmost areas. (Thus, as you go from south to north the necessary accumulations get higher.) A warning can also be issued during high impact events of lesser amounts, usually early or very late in the season when trees have leaves and damage can result. Winter Storm Warnings are issued when winds are less than 35mph, but if the storm has winds above this wind speed, it becomes a Blizzard Warning.
Usually, a large accumulation of ice alone with little to no snow will result in an Ice Storm Warning, or in the case of light freezing rain, a Winter Weather Advisory, a Freezing Rain Advisory, or Drizzle Advisory.
Prior to the 2008-09 winter storm season, there was the Heavy Snow Warning, specific for when only a heavy amount of snow was expected in the warned area. The Winter Storm Warning for Heavy Snow has since replaced it.
Because of the changes with the 2008-09 winter storm season, several varieties have been noted throughout the US.
- Winter Storm Warning for Heavy Snow (Replaced the Heavy Snow Warning)
- Winter Storm Warning for Heavy Wet Snow (same as above, except when the snow will also be wet)
- Winter Storm Warning for Heavy Snow and Blowing Snow (When the criteria for both a WSW for Heavy snow and a winter weather advisory for Snow and Blowing Snow are met [near-blizzard conditions])
- Winter Storm Warning for Heavy Sleet (Replaced the Sleet Warning)
- Winter Storm Warning for Heavy Snow and Ice (When both the criteria for a WSW for heavy snow and an Ice Storm Warning are met) 
- Winter Storm Warning for Snow and Ice (When both the criteria for a Winter Weather Advisory for Snow and an Ice Storm Warning are met)
- Winter Storm Warning for Sleet and Freezing Rain (When both the criteria for a Winter Weather Advisory for Sleet and an Ice Storm Warning are met)
Additionally, all of the above may also include "Strong Winds" in their title if strong winds are expected as well (ex. Winter Storm Warning for Heavy Wet Snow and Strong Winds).
- Also, the generic term, Winter Storm Warning, may be used on its own, typically to indicate that all three winter precipitation types are expected in high amounts; however, it may be used on its own as just a generic term at the forecaster's discretion regardless of whether or not this condition is met.
Example of a Winter Storm Warning
URGENT - WINTER WEATHER MESSAGE NATIONAL WEATHER SERVICE NORTHERN INDIANA 236 PM EST MON JAN 31 2011 ...POWERFUL WINTER STORM TO AFFECT THE REGION... AN INTENSE WINTER STORM WILL MOVE THROUGH THE AREA IN TWO PHASES BEGINNING TONIGHT AND ENDING WEDNESDAY EVENING WITH A LULL TUESDAY MORNING. SNOW WILL DEVELOP ACROSS THE AREA EARLY THIS EVENING WITH A MIX OF SLEET AND SNOW EXPECTED MAINLY SOUTH OF HIGHWAY 24. SNOW ACCUMULATIONS TONIGHT WILL BE GENERALLY 2 TO 5 INCHES...WITH LESSER AMOUNTS WHERE THE MIX OCCURS AND IN THE FAR NORTH. WINDS WILL INCREASE EARLY TUESDAY WITH BLOWING AND DRIFTING SNOW...ALTHOUGH THERE WILL LIKELY BE A LULL WITH THE FALLING SNOW TUESDAY MORNING AND EARLY TUESDAY AFTERNOON. HEAVY SNOW WITH SIGNIFICANT BLOWING AND DRIFTING IS LIKELY BY LATE TUESDAY AFTERNOON. VERY HEAVY SNOW WILL CONTINUE TUESDAY NIGHT INTO WEDNESDAY MORNING...ENDING BY WEDNESDAY EVENING. SNOWFALL RATES OF 1 TO 2 INCHES PER HOUR ARE EXPECTED TUESDAY NIGHT. SNOW MAY MIX WITH OR CHANGE TO SLEET OR FREEZING RAIN SOUTH OF ROUTE 24...WITH SIGNIFICANT ICING POSSIBLE. ICE ACCUMULATIONS WILL LIKELY BE BETWEEN ONE QUARTER AND ONE HALF INCH...WITH HIGHEST ICING POTENTIAL NEAR AND SOUTH OF A LINE FROM MARION INDIANA TO OTTAWA OHIO. SNOWFALL AMOUNTS OF UP TO 18 INCHES WILL BE POSSIBLE WITH THIS SYSTEM...WITH LOCALLY HIGHER AMOUNTS OF OVER 20 INCHES NOT OUT OF THE REALM OF POSSIBILITY. THESE HIGHER SNOWFALL AMOUNTS WILL BE ACROSS FAR NORTHERN INDIANA AND SOUTHWEST LOWER MICHIGAN. SUSTAINED WINDS OF 15 TO 30 MPH WITH HIGHER GUSTS...WOULD SUPPORT WIDESPREAD BLOWING AND DRIFTING SNOW...WITH DRIFTS POTENTIALLY REACHING SEVERAL FEET IN SOME LOCATIONS. BLIZZARD TO NEAR BLIZZARD CONDITIONS ARE ALSO POSSIBLE IN MANY AREAS...ESPECIALLY ACROSS FAR NORTHWESTERN INDIANA AND SOUTHWEST LOWER MICHIGAN. VISIBILITIES COULD BE DOWN TO ZERO AT TIMES TUESDAY NIGHT AND WEDNESDAY MORNING. TRAVEL WILL LIKELY BE DIFFICULT TO IMPOSSIBLE IN MANY AREAS...WITH ROAD CLOSURES POSSIBLE. LISTEN TO NOAA WEATHER RADIO OR YOUR LOCAL MEDIA FOR UPDATES ON THIS DANGEROUS WINTER STORM...ESPECIALLY IF YOU ARE PLANNING TRAVEL IN THE REGION. INZ017-018-022>027-032>034-OHZ004-005-015-016-024-025-010400- /O.UPG.KIWX.WS.A.0001.110201T0000Z-110203T0000Z/ /O.NEW.KIWX.WS.W.0001.110201T0000Z-110203T0000Z/ WHITLEY-ALLEN IN-CASS IN-MIAMI-WABASH-HUNTINGTON-WELLS-ADAMS- GRANT-BLACKFORD-JAY-DEFIANCE-HENRY-PAULDING-PUTNAM-VAN WERT- ALLEN OH- INCLUDING THE CITIES OF...COLUMBIA CITY...TRI-LAKES... SOUTH WHITLEY...FORT WAYNE...NEW HAVEN...LOGANSPORT... ROYAL CENTER...PERU...GRISSOM AFB...MEXICO...WABASH... NORTH MANCHESTER...HUNTINGTON...ROANOKE...BLUFFTON...OSSIAN... DECATUR...BERNE...MARION...GAS CITY...UPLAND...HARTFORD CITY... MONTPELIER...PORTLAND...DUNKIRK...DEFIANCE...SHERWOOD... HICKSVILLE...NAPOLEON...DESHLER...LIBERTY CENTER...PAULDING... ANTWERP...MELROSE...OTTAWA...PANDORA...KALIDA...FORT JENNINGS... VAN WERT...DELPHOS...OHIO CITY...LIMA...SPENCERVILLE 236 PM EST MON JAN 31 2011 ...WINTER STORM WARNING IN EFFECT FROM 7 PM THIS EVENING TO 7 PM EST WEDNESDAY... THE NATIONAL WEATHER SERVICE IN NORTHERN INDIANA HAS ISSUED A WINTER STORM WARNING FOR A MIX OF SNOW...SLEET AND FREEZING RAIN...WHICH IS IN EFFECT FROM 7 PM THIS EVENING TO 7 PM EST WEDNESDAY. THE WINTER STORM WATCH IS NO LONGER IN EFFECT. * TIMING...SNOW WILL DEVELOP TONIGHT. AFTER A SHORT LULL IN THE SNOW TUESDAY MORNING...THE SNOW WILL EXPAND IN COVERAGE AND INTENSITY LATE TUESDAY. SNOW MAY MIX WITH OR CHANGE TO FREEZING RAIN AND SLEET LATE TUESDAY NIGHT INTO WEDNESDAY MORNING. SNOW WILL CONTINUE INTO WEDNESDAY AFTERNOON...ENDING WEDNESDAY EVENING. * MAIN IMPACT...2 TO 5 INCHES OF SNOW WILL BE POSSIBLE BY TUESDAY MORNING. ADDITIONAL HEAVY SNOW AND SLEET ACCUMULATIONS OF 4 TO 8 INCHES ARE POSSIBLE TUESDAY AFTERNOON THROUGH WEDNESDAY. IF PRECIPITATION CHANGES TO FREEZING RAIN OR SLEET...MUCH LOWER SNOWFALL AMOUNTS WOULD BE EXPECTED BUT SIGNIFICANT ICING WOULD BE POSSIBLE WITH EXTENDED POWER OUTAGES. ONE QUARTER TO ONE HALF INCH OF ICE ACCUMULATION IS POSSIBLE. * OTHER IMPACTS...SUSTAINED WINDS OF 15 TO 30 MPH WITH HIGHER GUSTS WOULD SUPPORT WIDESPREAD BLOWING AND DRIFTING SNOW... HIGHLY IMPACTING TRAVEL. THESE WINDS WOULD ALSO CAUSE TREE LIMBS AND POWER LINES TO FALL IF SIGNIFICANT ICING OCCURS. PRECAUTIONARY/PREPAREDNESS ACTIONS... A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW... SLEET...AND ICE ARE EXPECTED OR OCCURRING. STRONG WINDS ARE ALSO POSSIBLE. THIS WILL MAKE TRAVEL VERY HAZARDOUS OR IMPOSSIBLE. && $$