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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made October 21, 2016

 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 Monday October 24, 2016 to Friday November 04, 2016

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT October 21 2016

Synopsis: A strong low-pressure system is forecast over southeastern Canada during the early portions of the outlook period. High pressure is forecast to build in over the Midwest, then slide eastward as an active pattern emerges over the Great Plains. A strong low-pressure system is forecast to impact the Pacific Northwest, with more troughing over the eastern Pacific setting the stage for an active period for California and the Great Basin. A potent surface low-pressure system is forecast over the Bering Sea during the middle of next week while another strong area of surface low pressure is anticipated over the Gulf of Alaska Oct 27. The predicted pattern for Week-2 favors an active pattern from the the West Coast to the High Plains, with less activity over the southeast U.S.

Hazards Detailed Summary

For Monday October 24 - Friday October 28: A strong low-pressure system is forecast over the Maritime provinces of Canada this weekend. High winds (exceeding 30 knots) are forecast over the eastern Great Lakes and Northeast through Monday. Heavy precipitation associated with this system is likely to be winding down by early next week.

High pressure and warm temperatures are likely to build in over the Great Plains. Daily high temperatures are likely to be 16-20 degrees F above normal, but high temperatures are not expected to be threatening to life or property, so no hazard is depicted.

Troughing forecast to approach the Pacific Northwest from the Gulf of Alaska is expected to cause the development of areas of surface low pressure near the region Oct 24-25. Rainfall totals are likely to approach or exceed hazardous levels across portions of western Washington, Oregon, and Northern California. Rainfall amounts during this 48 hour period could locally exceed 3 inches.

The shortwave is forecast to move from the Central Rockies to the Great Lakes, contributing to potentially heavy rains from Iowa to the Great Lakes. Rainfall totals are expected to exceed 1 inch in 24 hours for Oct 25, with lower probabilities of exceeding that same threshold on the 26th.

A second impulse is forecast to bring an extended period of wet weather to northern California on Oct 28, with rainfall totals exceeding 2 inches in 24 hours (locally higher amounts in areas where orographic effects are maximized). The continued influx of shortwaves from the Pacific also increases the odds for moderate to locally heavy snows over the higher terrain of the Northern Rockies, for the middle of next week, but uncertainty on the location of the heaviest snow precludes a depiction of a hazard.

Over the Bering Sea, a very deep trough is expected Oct 25-26. At the same time, areas of surface low pressure are anticipated over the Bering Sea and northern Gulf of Alaska. This is expected to lead to significant waves (wave heights in excess of 20 feet) Oct 25 for parts of the Aleutians and the western coast of Alaska, and high winds (winds in excess of 40 knots) Oct 25-26 for parts of western mainland Alaska and the Aleutians. Coastal flooding due to ocean encroachment along the western coast of Alaska is also possible. Localized areas of heavy precipitation are likely over western Alaska, although model guidance has backed off since yesterday with predicted precipitation totals. The risk to life and property with this predicted system is high.

As that system matures, redevelopment near the triple point, over the Gulf of Alaska, is likely during Oct 27. Heavy precipitation (snow in the higher terrain) is likely over southern Alaska and portions of the Alaska Panhandle, along with high winds (approaching 40 knots, with higher speeds at elevation). Model output indicate the potential for high winds and coastal erosion for western Alaska through Oct 29.

The tropical Pacific remains semi-active so the area will need to be monitored for possible tropical cyclone development.

For Saturday October 29 - Friday November 04: The GEFS reforecast-based calibration outputs indicated continued wet conditions for California and the Great Basin for days 8-10. Precipitation amounts are likely to be above average, but only locally over the Northern Sierras does the model indicate a slight enhancement for the odds of exceeding hazardous thresholds. Additionally, the models also indicate above average rains for the Central Great Plains and Midwest, but the odds of exceeding 2 inches in the 8-10 period are not significantly different than climatology.

Severe, or greater intensity, drought increased slightly in coverage across the CONUS during the past week. Severe drought is now covering 9.66% of the CONUS, up from 8.68% the prior week.

Forecaster: Matthew Rosencrans


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.