The WPC Winter Weather Desk (WWD) is staffed two shifts a day
from Sept. 15 through May 15.

The WWD forecaster routinely releases updated forecasts twice daily
at 0900Z and 2100Z (4am/pm EST or 5am/pm EDT respectively).

Forecasts may be updated if warranted by rapidly changing situations.

These graphics indicate the probability (potential) for a location to receive specific thresholds of accumulated snow or ice. 

• Snowfall - closed lines represent the probability (slight, moderate, and high) that enclosed areas will receive equal to or greater than a specific threshold accumulation (4", 8" or 12") of snowfall in a 24 hour period.

• Freezing Rain - depicts the probability in the same manner and time period as snowfall, but with an accumulation threshold of .25" (one quarter of an inch) of  freezing rain.

Note the 4" threshold on the Snowfall Probability Graphic is drawn only for elevations less than 7,500 feet.  Elevation criteria is not imparted for the 8" and 12" thresholds. 


CAUTION ! The probability contours may appear to inordinately expand, contract or "jump" geographically after a scheduled update.  This is partially due to the frequency which the products are updated.  The "new" 24 hour period covers the last 12 hours of the previous issuance AND the next 12 hours. Additionally two model cycles have passed since the last scheduled issuance.

Specific (deterministic) accumulations for a particular location in the United States can be obtained via the National Weather Service home page. Note, at this site you will have to click the GRAPHICAL FORECAST tab prior to clicking a location on the map.

The probabilistic graphics combined with the deterministic forecasts provide a user both the most likely amount expected from an event and the potential the event will produce accumulations in excess of specific thresholds.

The probability thresholds used are defined as follows:

• SLGT - 10% to 40% chance of occurrence within the outlined area.
• MODERATE (MDT) - 40% to 70% chance of occurrence within the outlined area.
• HIGH - 70% chance or greater of occurrence within the outlined area.

To gain further insight into this forecast, please read the Heavy Snow Discussion (HSD) that accompanies these graphical products.

• The non-technical version depicts the low position and track forecast by the NCEP WPC meteorologist in white.  Each low position is accompanied by a lead time (Eastern Time).  The circle around each low represents a 75% probability the observed low will be located within the circle. Note: The probability is derived using previous season's verification data. For reference, existing surface lows are depicted with a red marker without yellow circles. 

• The technical version depicts the low position and track forecast by the NCEP WPC meteorologist in black.  Each low is accompanied by a forecast central pressure. Additionally there are no less than 35 different computer model forecasts of low position for a given lead time available to the WPC forecaster - these are depicted with symbols.  Both the central pressure and computer model forecasts are color coded according to lead time (Universal Time).  Together, the WPC forecast position of the low and computer generated position provide a user both the preferred position and track of the low and a sense of the uncertainty with the forecast.

• For reference, existing surface lows are depicted with a red marker.  Surface lows can also be found on the WPC Surface Analysis. One can see the current location surface lows and the forecast path of both existing surface lows and surface lows expected to develop within three days time.