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    HOME> Expert Assessments>Hazards Outlook

    For 3-7 day hazards see Weather Prediction Center's: WPC 3-7 Day Hazards

    U.S. Week-2 Hazards Outlook - Made December 06, 2019 | About the Hazards Outlook

     Days 8-14Probabilistic Days 8-14
    TemperatureNo Hazards
    PrecipitationNo Hazards
    SnowNo Hazards
    WindNo Hazards

    Categorical Outlooks
    Experimental Probabilistic Outlooks

    Valid Saturday December 14, 2019 to Friday December 20, 2019

    US Hazards Outlook
    NWS Climate Prediction Center College Park MD
    300 PM EST December 06 2019

    Synopsis: Mid-level low pressure is predicted over eastern North America and the Aleutians/Bering Sea region during week-2, with mid-level high pressure forecast over portions of western North America. Although these higher-level circulation features appear to be fairly persistent, even slight variations in the strength or location of these features will have a noticeable impact on storm tracks and temperature patterns near the surface.

    Hazards Detailed Summary

    For Monday December 09 - Friday December 13: WPC Days 3-7 U.S. Hazards

    For Saturday December 14 - Friday December 20: Two low pressure systems are predicted to bring significant precipitation to portions of the eastern CONUS during week-2. The first storm system is forecast to bring heavy precipitation (1-inch or greater per 24-hour period) to the Atlantic Coast states during the first few days of week-2. Today's model runs generally depict precipitation mostly in the form of rain, with mixed or frozen precipitation possible over the interior portions of the Mid-Atlantic and Northeast. This potential event is still at least a week away so the details regarding precipitation type, storm track, and timing may all change substantially. The 12z GEFS predicts a second storm system will develop somewhere near the Central Gulf Coast states before bringing another round of precipitation to the Southeast, Mid-Atlantic, and Northeast later in week-2. Therefore, a slight risk (20%) area of heavy precipitation is posted from the Central Gulf Coast region eastward and northeastward to include most of the East Coast during week-2.

    Over the western CONUS, the expected deamplification of the mid-level ridge should allow for increased onshore flow across western sections of both Washington and Oregon. The 0z ECMWF ensemble solution is more robust regarding precipitation amounts during the week-2 period than the GEFS, with the ECMWF ensemble favoring liquid equivalent values of at least 2 inches, associated with multiple storm systems. If correct, heavy snow can be expected over the higher elevations of the Cascades and Coastal Ranges of the Pacific Northwest. Due to significant differences between the various ensemble means and the deterministic model runs, only a slight risk of heavy precipitation is posted for the area. A slight risk of heavy snow is indicated for the southern coast of Alaska, from about Kodiak Island to the northern half of the Alaska Panhandle, where 1.5-2.0 inches of precipitation (liquid equivalent) is generally expected in advance of the 500-hPa trough over the Bering Sea and Aleutians. The 0z ECMWF ensemble and the 12 GEFS forecast temperatures below freezing not only for mountainous regions, but the coastal lowlands as well. As is the case with the other noted precipitation hazards, the combination of multiple storm systems and differences in timing necessitate the hazard to be broadly designated for the entire week-2 period.

    Today's hazardous temperature map features a slight risk of much below normal temperatures only over the east-central CONUS, from Dec 14-18. The GEFS is generally colder than the ECMWF ensemble, and the exact placement of the coldest temperature anomalies is uncertain; hence the designation of only a slight risk area on the map. Analysis of the deterministic 12z ECMWF run suggests that a mean trough develops over the northern and central Rockies beginning before the start of week-2, and raises 500-hPa heights across the Gulf Coast and Lower Mississippi Valley late in Week-2.

    Across the northern and central Plains, conditions are likely to change rapidly, as an early arctic air outbreak and related upslope flow transitions to warmer, downslope flow several days later. A slight risk of high winds (at or above the 85th percentile, and 25 mph or greater) is posted for this region from Dec 14-16.

    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

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