About WPC Winter Weather
PRODUCT DELIVERY SCHEDULE
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.
Provide feedback on these products using our
PROBABILITY GRAPHICS FOR SNOW
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
threshold accumulation (4", 8" or 12") of snowfall in a 24 hour period.
Freezing Rain - depicts the probability in the same manner and time
as snowfall, but with an accumulation threshold of .25" (one quarter of
an inch) of freezing rain.
Note the 4" threshold on the
Graphic is drawn only for elevations less than 7,500 feet.
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.
for a particular location in the United States can be obtained via the
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
the deterministic forecasts provide a user both the most likely amount
expected from an event and the potential the event will produce
in excess of specific thresholds.
The probability thresholds used are defined as follows:
At times the forecasters may use only one or two isolines for the
This simply implies slight or slight to moderate probability for the
SLGT - 10% to 40% chance of occurrence within the
MODERATE (MDT) - 40% to 70% chance of occurrence
within the outlined
HIGH - 70% chance or greater of occurrence within the
To gain further insight into this forecast, please read the Heavy
Snow Discussion (HSD) that accompanies these graphical products.
LOW TRACKS GRAPHIC
depicts the forecast location of significant surface lows impacting the
48 contiguous United
States in 12 hour increments out to 72 hours into the future. It
is provided in two formats, non-technical and technical.
- 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
and track forecast by the NCEP WPC meteorologist in black.
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
position and track of the low and a sense of the
with the forecast.
Note - winter weather is
not always associated with significant surface lows.
- 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.