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 routinely
produces 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.
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:
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
Beginning with the 2013-14 season, all of the probabilistic
forecasts are generated automatically based on the WPC Winter Weather
Desk forecasts of 24-h accumulations of snow and ice. Therefore, the
forecasts depicted here are usually not edited directly by the
forecaster. Please see the PWPF description for more information on how the probabilistic
forecasts are generated.
To gain further insight into this forecast, please read the Heavy
Snow Discussion (HSD) that accompanies these graphical products.
LOW TRACKS GRAPHIC
depict 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 position
and track forecast by the NCEP WPC meteorologist in black.
Each low is accompanied by a forecast central pressure.
Additionally, low positions from a multi-model ensemble are depicted
with symbols. The typical constituency of the ensemble is:
In each case, the latest available model run is utilized to extract the low positions.
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.
- 1 NCEP North American Mesoscale (NAM) run
- 1 NCEP Global Forecast System (GFS) run
- 1 European Centre for Medium-Range Weather Forecasts (ECMWF) run
- 1 Canadian Global Model (CMC) run
- 1 Naval Research Lab (NAVGEM) run
- 1 United Kingdom Met Office (UKMET) run
- 21 NCEP Short-Range Ensemble Forecast (SREF) members
- 1 NCEP SREF ensemble mean
- 1 NCEP SREF bias-corrected ensemble mean
- 20 NCEP Global Ensemble Forecast System (GEFS) members
- 1 NCEP GEFS ensemble mean
- 1 NCEP GEFS bias-corrected ensemble mean
- 1 ECMWF ensemble mean
- 1 mean of the NAM and GFS runs
- 1 mean of the GFS and ECMWF runs
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.