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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 30, 2021 | About the Hazards Outlook

Type and PeriodTemperaturePrecipitationSnowWind
Composite Days 8-14 Map No HazardsNo HazardsNo Hazards
Probabilistic Days 8-14 Map

Composite Map
 Experimental Probabilistic Outlooks

Valid Friday January 07, 2022 to Thursday January 13, 2022

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 30 2021

Synopsis: Areas of mid-level low pressure are forecast to traverse the contiguous U.S. during week-2, with the GEFS and ECMWF differing in the evolution of the mid-level flow. While confidence is still high regarding a significant cold air outbreak over the north-central lower-48 states early in week-2, uncertainty increases toward the middle of the period. The anomalous cold is also forecast to extend back toward the Pacific Northwest and the Alaska Panhandle. Increased precipitation chances (coastal rain and high elevation snow) remain favored across the western lower-48 early in the period, but decrease thereafter as mid-level high pressure builds across the East Pacific. Enhanced frontal activity at the start of week-2 may bring increased potential for heavy precipitation (rain changing to snow) to parts of the northeastern U.S.

Hazards Detailed Summary

For Sunday January 02 - Thursday January 06: WPC Days 3-7 U.S. Hazards

For Friday January 07 - Thursday January 13: Dynamical model guidance depicts a progressive pattern during week-2, with increasing spread developing in the GEFS and ECMWF solutions toward the middle of the period. There remains high confidence regarding troughing and associated anomalously cold temperatures expanding across the north-central CONUS early in the period. Both the GEFS and ECMWF reforecast tools indicate at least a 60% chance that minimum temperatures fall below the 15th climatological percentile across parts of the Northern Plains, Upper Mississippi Valley, and western Great Lakes, and uncalibrated guidance from the GEFS and ECMWF ensembles depict minimum temperatures dropping below -10 deg F over parts of the region (below -20 deg F closer to the Canadian border), supporting a high risk for much below normal temperatures on Jan 7. The moderate risk for much below normal temperatures is posted through Jan 8, and includes parts of the Northern and Central Plains, Upper and Middle Mississippi Valley, and western Great Lakes, where both reforecast tools indicate at least a 40% chance minimum temperatures drop below the 15th climatological percentile. Subzero temperatures are increasingly likely over a large portion of the Upper Midwest, with minimum negative temperature anomalies of at least -10 deg F indicated in the uncalibrated model ensemble means across the highlighted region. The ECMWF ensemble quickly lifts out the trough, with a trend toward higher positive mid-level height anomalies depicted across much of the central and eastern CONUS favoring a moderation in temperatures. However, both models depict a renewed surge of cold air into the Midwest toward the middle and later portion of the period, with the GEFS more robust with troughing redeveloping over the central CONUS compared to the ECMWF ensemble, which is less amplified with this feature. To account for the model uncertainty, a slight risk for much below normal temperatures is posted for all of week-2 across portions of the central CONUS extending back to the Pacific Northwest, but is reduced in spatial coverage compared to yesterday. Some of the anomalous cold may shift toward the northeastern CONUS at the end of week-2, but due to the uncertainty earlier in the period, the hazard is not extended at this time.

Although the aforementioned troughing is forecast to be inland by the start of week-2, the orientation of the mid-level flow is predicted to be zonal across the West Coast of the CONUS, allowing a continuation of enhanced Pacific flow and subsequent increased chances for rounds of heavy precipitation over the Pacific Northwest and northern and central California. The GEFS and ECMWF reforecast tools indicate at least a 20% chance of 3-day precipitation amounts exceeding 1.5 inches across parts of these areas, supporting a slight risk of heavy precipitation for the region from Jan 7 to 9, with the highest potential on day-8 (Jan 7) based on uncalibrated guidance. With anomalously cold air favored to be in place, the predicted increase in moisture also supports a slight risk of heavy snow over the Cascades, Sierra Nevadas, Great Basin, and Northern and Central Rockies from Jan 7 to 9. Additionally, the GEFS and ECMWF reforecast tools depict a broad region with at least a 20% chance of wind speeds exceeding the 85th percentile and 25-mph across coastal portions of the Pacific Northwest and northern California, supporting a slight risk of high winds from Jan 7 to 9. By the middle of week-2 more ridging is forecast over the Eastern Pacific, favoring a reduction in precipitation chances.

The evolving mid-level pattern with troughing shifting further east and relatively colder air arriving across the north-central CONUS favors a cold front to move across the Eastern Seaboard early in the period. The potential for impactful weather has decreased compared to yesterday, and is ultimately tied to the strength of the troughing upstream. The GEFS reforecast tool continues to depict probabilities exceeding 20% for 3-day precipitation totals exceeding the 85th percentile along the East Coast, with the indication that the system would be exiting on day-8 (Jan 7). The ECMWF ensemble is faster with this system and would push it out of the region prior to the start of the period. Although the liquid equivalent totals are forecast to be low in terms of hazards criteria, the increased potential for a transition to snow behind the front supports having a slight risk of heavy snow posted for Jan 7 across portions of the Northeast. Increased wind speeds are also possible behind the front, although hazards criteria are not anticipated to be reached.

Across Alaska, northerly mid-level flow on the backside of the trough axis forecast over western North America favors below normal temperatures over much of Alaska at the onset of week-2. Building mid-level heights over the Bering Sea and western Mainland Alaska favors a moderation in temperatures, especially in the GEFS, with the most anomalous cold being favored over the southeastern Mainland and the Panhandle. The GEFS and ECMWF reforecast tools indicate elevated probabilities for record low temperatures and negative anomalies potentially exceeding -20 deg F. A high risk of much below normal temperatures is posted for the Alaska Panhandle for Jan 7 where the reforecast tools depict at least a 60% chance minimum temperatures drop below the lowest 10th climatological percentile. A moderate risk of much below normal temperatures continues through Jan 8, and a broader slight risk remains designated from the eastern Kenai Peninsula through the Alaska Panhandle through Jan 10.

Forecaster: Thomas Collow

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

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