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Current Winter Storm Watches, Warnings and Advisories

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Wind Chill Information

New Wind Chill Chart

On November 1, 2001, the National Weather Service (NWS) implemented a replacement Wind Chill Temperature (WCT) index for the 2001/2002 winter season. The new WCT index:

  • uses calculated wind speed at an average height of five feet (typical height of an adult human face) based on readings from the national standard height of 33 feet (typical height of an anemometer)
  • is based on a human face model; incorporates modern heat transfer theory (heat loss from the body to its surroundings, during cold and breezy/windy days);
  • lowers the calm wind threshold to 3 mph;
  • uses a consistent standard for skin tissue resistance; and assumes no impact from the sun (i.e. clear night sky).

El Niño and La Niña Effects on Philadelphia Winters
SNOWFALL BY ENSO STATE
1949-50 THROUGH 2009-2010 WINTER
AVG 21.9
STRONG NINA - 6 WINTERS 15.9
MODERATE NINA - 7 WINTERS 13.8
WEAK NINA - 7 WINTERS 23.1
ENSO NEUTRAL - 22 WINTERS 22
WEAK NINO - 5 WINTERS 28.1
MODERATE NINO - 8 WINTERS 24.3
STRONG NINO - 6 WINTERS 27
NUMBER OF SIGNIFICANT SNOWFALL EVENTS
AT PHL BY ENSO STATE
>/= 6" >/= 10"
STRONG NINA - 6 WINTERS 3 0
MODERATE NINA - 7 WINTERS 1 0
WEAK NINA - 7 WINTERS 4 1
ENSO NEUTRAL - 22 WINTERS 21 8
WEAK NINO - 5 WINTERS 5 3
MODERATE NINO - 8 WINTERS 8 1
STRONG NINO - 6 WINTERS 8 6
Typical La Nina conditions

Terminology & Watch/Warning/Advisory Criteria
  • Warnings:
    A warning is issued to alert the public to imminent dangerous winter weather. Normally a warning is issued after a winter storm watch has been in effect. A winter storm watch may not precede a warning if winter weather develops quickly and unexpectedly. A Winter Storm Warning is issued when heavy snow, significant freezing rain, or heavy sleet is expected to occur. Usually issued 6 to 18 hours in advance of the winter weather. A Blizzard Warning is issued when sustained or gusty winds of 35 mph or more are expected to reduce visibility at or below a quarter of a mile due to falling and/or blowing snow for at least three hours. Wind Chill Warnings are issued when wind chills are expected to be below -24 degrees fahrenheit.
  • Watches:
    A watch is issued to alert the public to the potential for dangerous winter weather. A Winter Storm Watch is issued when conditions exist for the possible occurrence of dangerous winter weather such as a blizzard, heavy snow, significant freezing rain or heavy sleet. Usually issued 12 to 36 hours in advance of the winter weather.
  • Advisories:
    A less severe winter weather event will prompt the issuance of an advisory. An advisory is named specific to the weather event expected and is issued when the event is expected to be widespread. Travel by foot or vehicle may be dangerous during an advisory even if the winter weather is not expected to reach winter storm criteria.
Criteria Maps for Watches and Warnings
12 Hour Snow
Mt. Holly County Warning Area Eastern Region
24 Hour Snow
Mt. Holly County Warning Area Eastern Region
Freezing Rain
Mt. Holly County Warning Area Eastern Region
Wind Chill
Mt. Holly County Warning Area Eastern Region
Criteria Maps for Advisories
12 Hour Snow
Mt. Holly County Warning Area Eastern Region
Freezing Rain
Mt. Holly County Warning Area Eastern Region
Wind Chill
Mt. Holly County Warning Area Eastern Region

Gradient high wind outlooks, watches, warnings, and wind advisories shall be issued using the following wind speed values
Product Type Sustained Wind ( 1 Hr) Any duration gust
High Wind Outlook >= 40 MPH (35 KTS) >= 58 MPH (50 KTS)
High Wind Watch >= 40 MPH (35 KTS) >= 58 MPH (50 KTS)
High Wind Warning >= 40 MPH (35 KTS) >= 58 MPH (50 KTS)
Wind Advisory (land) 31-39 MPH (27-34 KTS) 46-57 MPH (40-49 KTS)
Wind Advisory for area lakes 25-30 MPH (22-26 KTS) 40-45 MPH (35-39 KTS)

Previous Winters

Seasonal Snowfall Totals (through last winter) for:

Top Snowstorms for Philadelphia (unofficial):

  1. 30.7" on January 7-8, 1996
  2. 21.3" on February 11-2, 1983
  3. 21.0" on December 25-26, 1909
  4. 19.4" on April 3-4, 1915
  5. 18.9" on February 12-14, 1899
  6. 16.7" on January 22-24, 1935
  7. 15.1" on February 28-March 1, 1941

Storm Archives

Winter Weather Awareness and Safety