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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 February 21, 2024 | About the Hazards Outlook

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Type and Period Temperature Precipitation Snow Wind Rapid Onset
Drought
Composite Days 8-14 Map No HazardsNo Hazards
Probabilistic Days 8-14 Map

Composite Map
Experimental Probabilistic Outlooks

Valid Thursday February 29, 2024 to Wednesday March 06, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST February 21 2024

Synopsis: Model guidance favors a more amplified mid-level low pressure over the North Pacific compared to yesterday, supporting increased likelihood of heavy precipitation to the West Coast. An increased potential for heavy snow in higher elevations of the Northern Rockies, and high winds continues across much of the western contiguous U.S. (CONUS). There is decreasing confidence in the hazards outlook by the middle of week-2 due to increasing model divergence. A series of surface lows tracking across the northeastern CONUS may support localized high winds and enhanced precipitation at the beginning of the period, although there is significant uncertainty regarding these possible storms. Over Alaska, Arctic high pressure over the northern parts of the state may help to promote much below normal temperatures and gap winds across the southern Mainland.

Hazards Detailed Summary

For Saturday February 24 - Wednesday February 28: WPC Days 3-7 U.S. Hazards

For Thursday February 29 - Wednesday March 06: Multiple dynamical model ensemble means show a more amplified mean week-2 500-hPa height pattern across much of the U.S. compared to yesterday, but continue to be in fairly large disagreement. The ECENS indicates a more amplified mid-level trough over the North Pacific compared to the GEFS at the beginning of the period. By the middle of the period,, there are increasing differences among the models regarding the evolution of this feature. The GEFS maintains this feature near the West Coast until the end of week-2, with mid-level shortwave troughs moving across the central CONUS whereas the ECENS indicates the North Pacific mid-level trough shifting eastward to the central CONUS, weakening throughout week-2. These model differences translate to decreasing confidence in associated hazards by the middle of the period.

The increased amplification of the mid-level trough over the North Pacific translates to increased heavy precipitation signals for the West Coast, especially at the beginning of week-2. A moderate risk (at least a 40% chance) of heavy precipitation is posted across parts of the northern of California, Feb 29-Mar 1, based on increasing enhanced integrated vapor transport (IVT) signals in the GEFS, and the ECENS (GEFS) Probabilistic Extremes Tool (PET) which show at least a 40% (30%) chance of 3-day liquid equivalent totals exceeding the 85th percentile climatologically and one inch in this area. An associated moderate risk of high elevation snow is designated for the Klamath and portions of the Sierra Nevada Mountains, Feb 29-Mar 1. A broader area of slight risk (>20% chance) is continued for periods of heavy precipitation for much of California and the Pacific Northwest with a slight risk of heavy snow for the higher elevations of the Sierra Nevada, Klamath and Cascade Mountains, Feb 29- Mar 4. Shallow landslides and rock falls are always possible in California during periods of heavy rainfall in winter.

As this mid-level trough moves inland, raw and calibrated guidance supports a slight risk of periods of heavy snow across the higher elevations of the Northern Rockies south through the northern Wasatch Range of Utah, Feb 29-Mar 4. A slight chance of high winds for much of the western CONUS, Feb 28-Mar 3, is expanded to include southern California and more of the Southwest compared to yesterday associated with the increased deepening of the mid-level trough favored in the North Pacific.

A series of surface lows are predicted to track across the northeastern CONUS at the beginning of the period. However, there is significant model uncertainty regarding the evolution of these potential storms and associated impacts. There may be increased potential for localized heavy snow across parts of the Great Lakes region, Ohio Valley, Appalachians, and Northeast, although there is too much uncertainty at this time to designate an associated hazard at this time. A slight risk of high winds is highlighted for parts of the northeastern CONUS, Feb 29-Mar 1, based on the potential for tight pressure gradient associated with these storms, and support from the PETs indicating at least a 20% chance of wind speeds exceeding the 85th percentile and 20 mph.

In Alaska, an area of Arctic high pressure is forecast across the northern parts of the state and the Yukon, with surface low-pressure over the Gulf of Alaska. This pattern favors increased chances of gap winds over much of the southern Alaska coastline throughout the week-2 period. Thus, a slight risk of high winds is maintained for Feb 29-Mar 2 across the area. The PETs show noticeably increased probabilities for much below normal temperatures relative to previous guidance, and indicate at least a 40% chance of minimum temperatures falling to the lowest 5th percentile climatologically across the southwestern Mainland and Alaska Peninsula on day 8 (Feb 29). A moderate risk of much below normal temperatures is designated for parts of southern Alaska south of the Interior Basin, Feb 29-Mar 1. A broader area of slight risk is highlighted across southern Alaska, Feb 29-Mar 4. High winds across the southern coast of Alaska could contribute to anomalously low wind chill values.

Forecaster: Melissa Ou

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts