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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made December 02, 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 December 05, 2016 to Friday December 16, 2016

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 02 2016

Synopsis: During week-1 a surface low pressure system is forecast to lift northward through the Mississippi Valley towards the Great Lakes. Another surface low pressure may form along the Mid-Atlantic as the aforementioned system reaches the Great Lakes. Behind these disturbances arctic air is expected to spill southward due to an unseasonably strong surface high pressure expected to be positioned over the Yukon. Unsettled conditions are anticipated in the North Pacific throughout Week-1. During Week-2, mid-level high pressure is forecast along the Pacific coast with low pressure expected over the Great Lakes.

Hazards Detailed Summary

For Monday December 05 - Friday December 09: As Week-1 begins a surface low pressure system is forecast over the Lower Mississippi Valley associated with a negatively-tilted trough at 500-hPa. Dynamical model guidance continues to forecast this system to shift northward towards the Great Lakes, however, forecasts now portray a secondary coastal system developing off the Mid-Atlantic by mid-week. This secondary development would limit snow and wind potential across the northeastern quarter of the country from either system. Instead an eastward shifting heavy rain hazard (exceeding 1" in 24 h) is the most likely threat across the southeastern U.S. on Mon-Tue, Dec 5-6. The Storm Prediction Center also anticipates a 15% risk of severe weather adjacent to the Gulf of Mexico associated with this system as locally severe winds and tornadoes could be possible on Mon, Dec 5. Significant river flooding is possible associated with this system across parts of southeastern Texas on Mon-Tue, Dec 5-6.

Northerly winds are anticipated on the back side of the aforementioned low pressure system as it strengthens and moves northward. Strong surface high pressure is also forecast in the Yukon during Week-1, that will further help bring cold, arctic air southward over the CONUS. Much below-normal temperatures are possible Mon-Tue, Dec 4-5 for the Great Basin, Rocky Mountains, and Great Plains. Here minimum temperatures could be 12-20 degrees F below normal. The much below-normal temperature hazard region is expected to push eastward into the Southeast and Ohio and Tennessee Valleys for Thu-Fri, Dec 6-7.

Persistent surface low pressure is forecast in the Gulf of Alaska and North Pacific late in Week-1. This setup favors onshore flow off the Pacific for much of the West Coast. Heavy rain is possible for coastal portions of northern California and Oregon on Fri, Dec 9 as the cold front associated with this system is expected to be coming ashore.

Alaska is also forecast to be impacted by the anomalously cold weather, as polar air is forecast to wrap westward around the base of surface high pressure positioned over the Yukon. This setup results in a region of much below-normal temperatures forecast across much of Alaska for Tue-Fri, Dec 6-9 where anomalies could exceed -25 degrees F. Within this region the hazard is expected to shift eastward and southeastward over the course of Week-1. This setup also supports the potential development of easterly high winds (exceeding 50 mph) for exposed areas across the Alaska Panhandle south of Yakutat on Tue-Wed, Dec 6-7.

For Saturday December 10 - Friday December 16: The anomalous 500-hPa forecast pattern for Week-2 favors ridging along the Pacific Coast and Bering Sea, with troughing over the Great Lakes. The biggest difference among the ensemble mean fields lies in the treatment of the ridging in the Pacific, with the GEFS more amplified than the weaker European solution which keeps ridging along the Mexican border rather than extending northward into Canada. However, the GEFS is less amplified than the ECMWF ensembles in the anomalous ridge over the Bering Sea, which would result in less transport of Siberian air towards North America. The European solution results in colder air across much of North America, however both ensembles appear less bullish on the cold air potential over North America than prior runs.

Given the somewhat warmer solutions in ensemble guidance today, probabilities for much below-normal temperatures are damped relative to the previous forecast. A slight risk of much below-normal temperatures is now forecast for approximately the northwestern quarter of the CONUS for Sat-Thu, Dec 10-15. Roughly the southern two-thirds of Alaska, with the exception of most of the Aleutians, has a slight risk of much below-normal temperatures for Sat-Mon, Dec 10-12, with this risk becoming focused along the Canadian border and Alaska Panhandle over the course of the week. Within this region, parts of the Alaska Panhandle have a moderate risk of much below-normal temperatures Sat-Sun, Dec 10-11.

According to the latest U.S. Drought Monitor (USDM) valid on November 29, the coverage of severe or greater drought for the CONUS decreased nearly a half percent to 16.6%. Improvements were noted for portions of the Lower Mississippi Valley and New York state. While the most recent USDM shows deterioration of drought conditions in the Southeast, rains following the latest release may yield improvement for the next publication.

Forecaster: Daniel Harnos

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