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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made December 18, 2014

 Days 3-7Days 8-14Prob. Days 8-14
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Categorical OutlooksDay 3-7Day 8-14
8-14 Day Probabilistic OutlooksTemperature HazardsPrecipitation Hazards

Valid Sunday December 21, 2014 to Thursday January 01, 2015

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 18 2014

Synopsis: 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.

Hazards Detailed Summary

For Sunday December 21 - Thursday December 25: *** 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 period.

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 same period.

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 U.S.

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.