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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made December 19, 2014

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

Valid Monday December 22, 2014 to Friday January 02, 2015

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 19 2014

Synopsis: At the beginning of the Outlook period, a major storm system is predicted to develop across the east-central states just before Christmas, bringing a variety of hazardous weather conditions to the Great Lakes region and the Atlantic Coast states. There is also the possibility of strong to severe thunderstorms affecting the Florida peninsula, on the southern end of this expansive storm system. Another powerful storm is anticipated to move across the central Bering Sea between December 23-24, posing a significant hazard to commercial shipping. However, it does not look like hazardous conditions associated with this storm will reach the Bering Seacoast of Alaska.

Hazards Detailed Summary

For Monday December 22 - Friday December 26: An amplified 500-hPa ridge is forecast from the eastern Pacific northward across Alaska, and a deep trough is predicted downstream across the west-central CONUS. These circulation features are expected to be located 15-20 degrees longitude farther west than what was anticipated during the past few days. This will, among other things, contribute to a westward-shifted storm track through the Ohio Valley with relatively mild air across the Atlantic Coast states, and postpone the arrival of significantly colder air into the Northeast U.S.

During this period, a low pressure center is expected to move into the Upper Mississippi Valley bringing light snow to the region, while a secondary Low forms in the Lower Mississippi Valley. With time, the secondary Low is anticipated to track northward and strengthen, eventually becoming the dominant low pressure center in the vicinity of lower Michigan, or slightly farther west. This scenario is predicted by both the 00z UKMET and 06z GFS deterministic runs, with the 00z UKMET solution being about 12 hours slower. The latest GFS run (initialized at 12z) seems to split the difference, with one low pressure center moving from the middle Mississippi Valley to the central Great Lakes region. Though there are differences among the various dynamical models regarding timing and other details, the general forecast depicts low pressure over the southern or southwestern Great Lakes region by Christmas Eve. Hazards associated with this predicted storm system include the possibility of strong to severe thunderstorms across the Florida peninsula, especially on Tuesday, December 23. As of 2pm Eastern time today (Dec 19), the Storm Prediction Center in Oklahoma has not officially designated a severe weather risk area, but this may change pending the consistency of future model runs. Other hazards include heavy rain from Florida to Delaware in association with the storm's cold front, and heavy rain over New England and northern New York in association with the occluded front and possible triple-point Low. Winds of 25-35 mph are also forecast across the Great Lakes region, Ohio Valley, and Atlantic Coast states from North Carolina to Maine. By Christmas Day, as rain departs the Northeast, lake-enhanced snow squalls are expected to set up downwind of the Great Lakes, bringing localized areas of heavy snowfall.

Diminishing westerly flow across the Pacific Northwest is expected to result in significantly reduced precipitation amounts across western sections of both Washington and Oregon during the first few days of this period. The latest precipitation forecasts from the Weather Prediction Center (WPC) has significantly lowered expected precipitation amounts to 1-2 inches during December 22-23, prompting the removal of any precipitation hazards across the Northwest.

Localized areas of flooding are likely within the areas indicated on the map in southwest Washington and northwest Oregon due to the recent heavy precipitation and runoff.

A major storm system is forecast to move across the Bering Sea during Tuesday and Wednesday, December 23-24. At the storm's peak, 40-50 knot winds and 8-9 meter significant wave heights are predicted by the NOAA Wavewatch Model (initialized at 00z) for the Bering Sea, before the storm curves northwestward into extreme eastern Russia. Though this storm system poses serious hazards for commercial shipping in the Bering Sea, it appears that the West Coast of Alaska will be spared the worst of its impacts.

For Saturday December 27 - Friday January 02: Models are in agreement on a highly amplified wave pattern over North America in the Week-2 range. A highly amplified ridge is predicted from the eastern Pacific northward across Alaska, while a deep trough is expected over east-central North America. There is a slight chance of much below-normal minimum temperatures from the northern and central Rockies to the Upper Mississippi Valley during the first three days of this period. A moderate chance of much below-normal minimum temperatures is anticipated from the northern and central Rockies to the central portions of the Dakotas and Nebraska.

The most recent U.S. drought monitor, released on December 18, indicates a very slight increase in the areal coverage of severe to exceptional drought (D2 to D4) from 17.09 to 17.27 percent across the continental U.S.. Perhaps the largest and most significant change from last week's Drought Monitor is the one-class improvement (from D4 to D3) across northern California and the San Francisco area in response to the recent heavy rains in that region.

Forecaster: Anthony Artusa

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Please consult local NWS Forecast Offices for short range forecasts and region-specific information.