Valid Thursday, February 28, 2019 to Monday, March 11, 2019

Summary of Forecasts and Hazards

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST March 07 2026

Synopsis: During week-2, heavy precipitation is possible for parts of the Mid-Atlantic and Northeast, heavy snow remains possible for higher elevations of the interior Northeast and into the Great Lakes, and high winds may occur across the northeastern contiguous U.S. (CONUS). Flooding is also possible for portions of the Ohio Valley as a result of antecedent precipitation. Strong pressure gradients bring a possibility for high winds across the Northern Intermountain region and the Northern and Central Rockies. Enhanced onshore flow across the Pacific Northwest and Northern Rockies elevates the chances of heavy precipitation and wind over the Pacific Northwest, and heavy snowfall over most of the Cascades and Northern Rockies. Over portions of southern and western Alaska, hazards are posted for much below-normal temperatures and high winds.

Hazards

• Slight risk of heavy precipitation for the Pacific Northwest, Sun-Wed, Mar 15-18.
• Slight risk of heavy precipitation for portions of the Mid-Atlantic and Northeast, Sun-Tue, Mar 15-17.
• Slight risk of heavy snow over most of the Cascades, Sun-Wed, Mar 15-18.
• Slight risk of heavy snow over the Northern Rockies, Sun-Mon, Mar 15-16.
• Slight risk of heavy snow for portions of the interior Northeast, Sat-Mon, Mar 14-16.
• Slight risk of high winds for portions of the coast of Washington and northwest Oregon, Sun-Wed, Mar 15-18.
• Slight risk of high winds over most of the Northern Intermountain region, and the Northern and Central Rockies, Sun-Mon, Mar 15-16.
• Slight risk of high winds for portions of the Northeast and Mid-Atlantic, Sun-Tue, Mar 15-17.
• Slight risk of much below normal temperatures over Southeast Alaska and southeastern to southcentral Mainland Alaska, Sun, Mar 15.
• Slight risk of much below normal temperatures over much of southern and western Alaska, Sun-Sat, Mar 15-21.
• Slight risk of high winds over the southern coast of Alaska and Southeast Alaska, Sun-Sat, Mar 15-21.
• Possible flooding for portions of the lower Ohio Valley

Detailed Summary

For Tuesday March 10 - Saturday March 14: WPC Days 3-7 U.S. Hazards

For Sunday March 15 - Saturday March 21: Negative 500-hPa height anomalies are forecast across northern North America with positive height anomalies across the southern tier of the CONUS at the end of week-1. A mid-level trough is forecast to dig into the central and eastern CONUS from this pool of negative anomalies over northern North America early in week-2. This trough will likely linger over the eastern CONUS through the end of week-2. In the West, positive 500-hPa height anomalies will build across much of the western CONUS into the Plains through the period.

A strong ridge forecast over the West and troughing in Gulf of Alaska will promote onshore flow into the northern Pacific Northwest and British Columbia during week-2, with the highest confidence early in the period. Probabilistic Extremes Tools (PETs) from the GEFS and ECENS both highlight the potential for precipitation to exceed the 85th percentile into the middle of week-2. The Integrated Water Vapor Transport (IVT) tools also highlight elevated chances for an atmospheric river type precipitation event into western North America. Therefore, a slight risk of heavy precipitation is posted for March 15-18 for parts of western Oregon and Washington. A slight risk of heavy snow is forecast for portions of the Cascades for the same period. Further inland, a slight risk of heavy snow is forecast for March 15-16, before the snow shifts north into Canada. Along the immediate coast, a slight risk of high winds is forecast for Mar 15-18. The enhanced Pacific flow into the Rockies may bring enhanced chances for episodes of high winds across downslope regions of the Northern and Central Rockies into the high Plains. Therefore, a slight risk of high winds is posted for this region for Mar 15-16.

East of the Rockies, a mid-level trough is forecast to dig into the central CONUS, initially amplifying positive 500-hPa height anomalies over the eastern CONUS early in the period. During the period, the trough will progress towards the Eastern Seaboard. As the trough progresses east, surface low pressure and associated frontal system is forecast. This system brings elevated chances for heavy snow across portions of the Great Lakes and interior Northeast, Mar 15-16. Along the immediate Northeast and Mid-Atlantic coast there is an elevated chance of 3 day precipitation amounts exceeding the 85th percentile and 1 inch. An associated slight risk of heavy precipitation is posted for Mar 15-17. Finally, as the front moves through, cold air advection is favored and high winds are possible. Therefore, a slight risk of high winds is posted for Mar 15-17.

Following the warm up during the first half of March over the Northeast, a shot of cold air is forecast to build back into the East for the 3rd week of March. The European based tools would bring this colder than normal air in by day 9 while the GEFS is slower waiting to bring elevated chances of temperatures falling below the 15th percentile until the end of week-2. At this time, temperatures are unlikely to be hazardous but a freeze is possible into parts of the Southeast where plants may begin greening up by this period.

A flooding possible hazard remains in place across portions of the Lower Ohio Valley for the period as a result of antecedent precipitation. More than 5 inches of precipitation has fallen over parts of Ohio and Indiana in the past 5 days and the Weather Prediction Center's Day 1-7 QPF is forecasting another 2-3 inches over this region during week-1. However, the flooding possible shape has been reduced from prior forecasts over the upper Ohio and Lower and Middle Mississippi Valleys.

Surface low pressure over the Gulf of Alaska and high pressure over interior Alaska and the Yukon is favored to enhance gap winds along the southern coast of Alaska, as well as maintain cold flow over the state. Forecast wind speeds are marginally hazardous, but there is also the continuing concern of freezing spray in this region. Therefore, a slight risk of high winds indicated from Mar 15-21. This pattern is favored to bring anomalously cold air to much of the state during week-1 and week-2. A slight risk of much below-normal temperatures remains posted for much of southwestern Mainland Alaska (including the Alaska Peninsula), valid Mar 15-21. A slight risk of much below normal temperatures continues for Southeast Alaska and southeastern Mainland for Mar 15 before temperatures warm across this region. Associated with this risk is a chance for enhanced snowfall over Southeast with onshore flow aloft and low pressure in the Gulf of Alaska. The Probabilistic Extremes Tools (PETs) for minimum temperatures reintensify chances for much below normal temperature chances over southwestern Mainland through much of week-2. Deterministic guidance would support a broader slight risk over much of interior Alaska but PETs are not quite as supportive at this time, but will be monitored.

Over the Central Pacific, a mid-level trough and associated surface low are expected to bring heavy rainfall to the Hawaiian Islands during week-1. However, these chances have fallen relative to yesterday early in the week-2 period. Nevertheless, the GEFS and ECENS PETs still predict at least a 20 percent chance of precipitation totals exceeding the 85th climatological percentile statewide during the first 3 days of week-2.

Forecaster: Ryan Bolt

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