Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Saturday December 07, 2024 to Friday December 13, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 29 2024

Synopsis: A reinforcing shot of cold air is likely to move into the eastern contiguous U.S. (CONUS) near the start of the week-2 period with deepening mid-level low pressure. The additional cold air advection into the northeastern CONUS may continue to promote lake effect snow off the Great Lakes. Meanwhile in southeastern Alaska, repeated chances for heavy precipitation are possible throughout week-2.

Hazards

• Slight risk of much below normal temperatures for interior New England, Sat-Tue, Dec 7-10.
• Slight risk of episodic heavy snow for favored lake effect snow belts and along the Allegheny Front, Sat-Tue, Dec 7-10.
• Slight risk of periodic heavy precipitation for portions of south-central and southeast Mainland Alaska and Southeast Alaska, Fri-Thu, Dec 7-13.

Detailed Summary

For Monday December 02 - Friday December 06: WPC Days 3-7 U.S. Hazards

For Saturday December 07 - Friday December 13: Negative 500-hPa height anomalies and troughing continue to be forecast for the eastern CONUS during much of the week-1 and 2 period. This trough will be reinforced with another round of negative height anomalies moving south from the Arctic at the start of week-2 and bring enhanced chances for much below-normal temperatures to portions of the Northeast. Minimum temperatures from the raw ECENS are forecast to be near 0 deg F. Similarly, the GEFS Probabilistic Extremes Tool (PET) indicates 20-40% chances for temperatures falling below 10 deg F and below the 15th climatological percentile. Therefore, a slight risk of much below-normal temperatures is posted for Dec 7-10 across the interior portions of New England.

The broad mid-level trough across the northeastern CONUS continues to bring chances for lake effect snow off the Great Lakes. While the environment does not appear to be as favorable for heavy lake effect into week-2 as in the coming week, there continues to be some signals for shortwave troughs to move through the region that may promote additional snow chances. A slight risk of episodic heavy snow is posted for downwind of the Great Lakes and across the Allegheny Front for Dec 7-10.

In the south-central CONUS some tools show enhanced chances for heavy precipitation during week-2. At this time there is considerable uncertainty about this potential, and even the most aggressive tools are not remarkably wetter than hazards thresholds, so for now, no associated hazard is posted.

Model guidance remains fairly robust with the potential for a series of strong low pressure systems to track across or near the Gulf of Alaska. The timing, strength, and track of individual storm systems is highly uncertain, but a large-scale pattern favorable for periods of stormy weather is expected along parts of the southern tier of Alaska throughout week-2. For this reason, a slight risk of periodic heavy precipitation is posted for south-central and southeastern Alaska for the entirety of the period. Above-normal temperatures are favored in much of southern Alaska, therefore, snow levels may be at higher elevations than normal leading to the potential for rain on snow, increasing hazardous risks. In addition, high winds will be possible at times across the entire southern tier of the state, including parts of the Aleutians. Right now, however, it appears that high winds will primarily affect offshore areas, so no high wind hazard is posted, but this situation will need to be closely monitored for increasing signals of higher winds occurring inland.

Forecaster: Ryan Bolt

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts