Valid Sunday December 21, 2014 to Thursday January 01, 2015
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST December 18 2014Synopsis
: At the beginning of this Outlook
period, the focus of unsettled weather is expected to be the Pacific Northwest
and northern Rockies. A weak area of low pressure moving across the Carolinas
is forecast to head out to sea. A more significant storm is predicted to
develop across the east-central states just before Christmas, affecting
primarily the Great Lakes region and the Atlantic Coast states. A strong storm
system is anticipated to move across the Bering Sea providing only a glancing
blow to the Bering Seacoast of Alaska between December 23-25.
Detailed Summary For
Sunday December 21 - Thursday December 25:
- Heavy precipitation (low elevation rain and
mountain snow) in western portions of Washington and Oregon, Sun-Mon, Dec 21-22.
- Heavy precipitation (low elevation rain and mountain snow) in the northern
and central Rockies, Sun-Mon, Dec 21-22.
- Periods of heavy rain for northern and central Florida, Sun-Wed, Dec 21-24.
- Heavy rain from the southernmost Appalachian Mountains northeast across the
mid-Atlantic region and New England, Tue-Wed, Dec 23-24.
- Heavy snow downwind of the Great Lakes, Thu-Fri, Dec 25-26.
- High winds over much of the eastern CONUS, as far west as the northern and
central Great Plains, and as far south as northern Georgia, Wed-Thu, Dec 24-25.
- Possible flooding in southwest Washington and northwest Oregon, Sun-Mon,
- Slight risk of much below-normal temperatures from eastern Montana to the
mid-Atlantic region, Fri-Mon, Dec 26-29.
- Moderate risk of much below-normal temperatures for the Upper Mississippi
Valley, Fri-Mon, Dec 26-29.
- Severe drought for the Central and Southern Great Plains, Southwest,
Southeast, Lower Mississippi Valley, Pacific Northwest, Great Basin, and
*** Hazards Outlook will be
updated by late afternoon Eastern time ***
A weak low pressure system is forecast to move from the central Gulf Coast
region to the Carolinas. High pressure over Quebec could prevent the
disturbance from tracking farther north, instead diverting it out to sea.
However, some light precipitation may overspread the southern mid-Atlantic
region. Temperatures appear to be marginally cold enough to support a period of
light snow in the interior, and light rain for coastal areas. The trailing cold
front is forecast to bring heavy rain (1.0-1.5 inches) to far southern Georgia
and much of northern Florida. Meanwhile, fast westerly flow across the Pacific
Northwest and northern Rockies (in-between a low pressure center over the
northern Gulf of Alaska, and a high pressure center off the central California
coast) is expected to maintain stormy conditions across the region. The
expected passage of several storm systems during this period may result in
precipitation totals of 5-10 inches (liquid equivalent) in the Cascades of
Washington and Oregon, and 2-4 inches in the northern Rockies. Once this energy
passes the northern Rockies, a deepening 500-hPa trough across the Central
CONUS is anticipated to steer the flow southeastward from the northern Great
Plains towards the middle Mississippi Valley. Winds of 25-35 mph are predicted
across this area, as the trough deepens. A significant storm system is then
expected to develop across the Midwest and Ohio Valley towards the end of this
By this time, uncertainty increases rapidly regarding the future evolution
of this storm system. If the latest GFS model run (initialized at 12z) is
correct, two low pressure centers will consolidate into one center over the
Ohio Valley. The 12z GFS run predicts this consolidated Low will gradually arc
in a counter- clockwise motion first northward across far western New York, and
then westward into the central Great Lakes region. At the same time, the
central pressure of this Low is forecast to fall rapidly to a minimum of
960-965 hPa during Christmas Day. In addition, locally intense lake-enhanced
snow bands can be anticipated downwind of the Great Lakes. It is too early to
specify which areas may be hardest hit with these squalls. If the 12z GFS is
correct, areas along the southern shore of Lake Superior, and areas northeast
of Lakes Erie and Ontario would be particularly vulnerable. Another
consideration with this potential winter storm is the latest GFS run does not
predict a clear transfer of energy from the primary Low to a coastal Low near
the mid-Atlantic coast with this storm system, as is frequently the case.
However, if one does develop off the Delmarva Peninsula, enhanced precipitation
would be favored across eastern Long Island and eastern New England.
Interestingly, the 12z operational GFS and the 00z operational ECMWF both
forecast relatively mild temperatures with this system, supporting mostly a
rain event (especially for coastal areas), with snow favored on the rear-side
of the storm as it departs the region. For the time being, this potential storm
is being highlighted only in the text, and not on the map, given all the
uncertainty in the details.
In Alaska, a fairly strong low pressure system just off the south-central
coast is forecast to bring high winds and waves from near Prince William Sound
eastward and southward along the coastal areas to Ketchikan in the southern
Panhandle. Another strong cyclonic system is expected to affect the Bering Sea
and western Alaska by the middle of next week. However, no hazardous areas
associated with this second storm are designated on the map at this time, given
too much uncertainty a week out. For Friday December 26 -
Thursday January 01:
*** Hazards Outlook will be updated by late afternoon
Eastern time ***
Models are in agreement on a highly amplified wave pattern over North
America in the Week-2 range. A highly amplified ridge is predicted over Alaska
and the Gulf of Alaska, while a deep trough is expected over east-central North
America. There is a slight chance of much below-normal minimum temperatures
from eastern Montana southeastward into the Ohio Valley during the first four
days of this period. A moderate chance of much below-normal minimum
temperatures is anticipated over portions of the Dakotas and Minnesota for the
The most recent U.S. drought monitor, released on December 11, indicates a
very slight increase in the areal coverage of severe to exceptional drought (D2
to D4) from 16.90 to 17.09 percent across the continental
Forecaster: Anthony Artusa
Click here to see a display of the GFS Ensemble Forecasts
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.