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Categorical Outlooks Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Tuesday February 04, 2020 to Monday February 10, 2020

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST January 27 2020

Synopsis: A very broad area of mid-level low pressure is predicted over much of Alaska and the CONUS during week-2, with the exception of southern Alaska and the far western CONUS where mid-level high pressure is forecast. There is significant uncertainty among the various computer models regarding the predicted movement and intensity of individual storm systems during the week-2 period.

Hazards

• Slight chance of much below normal temperatures over northern Alaska, Tue-Sat, Feb 4-8.
• Slight chance of much below normal temperatures over the vicinity of the Upper Mississippi Valley and Upper Great Lakes region, Tue-Wed, Feb 4-5.
• Slight chance of heavy precipitation from the eastern part of the southern Plains to the southern Appalachians and Southeast, Tue-Thu, Feb 4-6, and Sun-Mon, Feb 9-10.
• Slight chance of heavy snow along the southern coast of Alaska from about Kodiak Island to the southern tip of the Panhandle, Tue-Mon, Feb 4-10.
• Slight chance of high winds for the northern and central Great Plains, Tue-Sat, Feb 4-8.
• Slight chance of high winds for the southern coast of Alaska, Tue-Mon, Feb 4-10.

Detailed Summary

For Thursday January 30 - Monday February 03: WPC Days 3-7 U.S. Hazards

For Tuesday February 04 - Monday February 10: A slight risk (20% or greater) for much below normal minimum temperatures (falling to or below the 15th percentile) exists for two areas during portions of week-2; northern Alaska (Feb 4-8), and the Upper Mississippi Valley/Upper Great Lakes region (Feb 4-5). For the first region, the GFS and ECMWF ensembles predict a subsiding of the cold snap over Alaska, in terms of its magnitude and spatial coverage, with the best odds for much below normal temperatures confined to the northern half of the state (Feb 4-8). This is associated with a predicted 500-hPa trough and below normal heights. This trough is actually one (minor) lobe of the expansive polar vortex, with another (major) lobe extending across Canada and most of the CONUS east of the Continental Divide. This second lobe of the polar vortex, and accompanying well below-normal heights, is responsible for the second slight risk area across the Upper Mississippi Valley/Upper Great Lakes region on Feb 4-5.

Multiple surface low pressure systems are forecast to bring widespread precipitation from the eastern part of the southern Plains eastward to the vicinity of the southern Appalachians and Southeast, from Feb 4-6 and from Feb 9-10. Between 1.0-1.5 inches of rain are forecast for each event by the GFS and ECMWF ensemble probabilistic extremes tools. Towards the end of week-2, temperatures along the northern edge of this precipitation area may be cold enough to support freezing or frozen precipitation, but confidence this far out in time is low.

The rear-side of the trough is expected to be located over the eastern CONUS, supporting a slight risk of high winds (values at or exceeding the 85th percentile, and 25 mph or greater) across the northern and central Great Plains, Feb 4-8. This is due to several disturbances forecast to move southeastward out of the Canadian Prairies and accompanying upslope flow.

Several cyclonic systems are expected to affect the southern coast of Alaska during week-2. Therefore, a slight risk for heavy snowfall (18 inches or more in orographically favored regions) is warranted from about Kodiak Island eastward to the southern tip of the Panhandle region. Low-level (850-hPa) temperatures from the ECMWF model are forecast to be subfreezing even for immediate coastal areas, which would be supportive of snow. A slight risk for high winds (35 mph or greater) is posted for the entire southern coast during this period.

Forecaster: Anthony Artusa

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts