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Categorical Outlooks Day 3-7 Day 8-14

Experimental Probabilistic Outlooks (Information) Temperature Hazards Precipitation Hazards

Valid Monday February 25, 2019 to Friday March 08, 2019

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST February 22 2019

Synopsis: Intense surface low pressure is forecast to be moving northeastward over Atlantic Canada, allowing surface high pressure to build over the eastern U.S. A predominately west to east mid-level flow across the country is forecast to result in relatively quiet conditions in most places with the exception being the western U.S. and Pacific coast, where increased Pacific flow favors a transition to a wetter pattern. Mid level low pressure centered over central Canada favors continued cold air surges into the northern and central U.S. which are forecast to continue into week-2.


Hazards

• Heavy precipitation across portions of California and Oregon, Mon-Tue, Feb 25-Feb 26. and Fri, Mar 1.
• Heavy snow across portions of the Great Basin and the Northern Rockies, Mon-Tue, Feb 25-Feb 26.
• Heavy snow across portions of the Cascades and the Sierra Nevadas, Mon-Tue, Feb 25-Feb 26.
• Flooding possible across portions of the Central Plains, the Middle and Lower Mississippi Valley, the Central and Southern Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southeast, and the Ohio Valley.
• Flooding occurring or imminent across portions of the Middle and Lower Mississippi Valley, the Ohio Valley, and the Tennessee Valley.
• Flooding likely across portions of the Ohio Valley.
• High winds across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Ohio Valley, Mon, Feb 25.
• High winds across portions of the Plains and the Mississippi Valley, Fri, Mar 1.
• Much below normal temperatures across portions of the Northern and Central Plains, the Northern Rockies, the Upper and Middle Mississippi Valley, the Northern Great Basin, and the Western Great Lakes, Mon-Fri, Feb 25-Mar 1.
• High winds across portions of the Aleutians, Mon-Thu, Feb 25-Feb 28.
• High significant wave heights for the Aleutians, Mon-Thu, Feb 25-Feb 28.
• Slight risk of much below normal temperatures for much of the northern half of the CONUS, Sat-Fri, Mar 2-Mar 8.
• Moderate risk of much below normal temperatures for portions of the Plains, the Mississippi Valley, the Great Lakes, the Northern and Central Rockies, the Northern Great Basin, and the Ohio Valley, Sat-Wed, Mar 2-Mar 6.
• High risk of much below normal temperatures for portions of the Northern and Central Plains, the Upper and Middle Mississippi Valley, and the Great Lakes, Sat-Mon, Mar 2-Mar 4.
• Slight risk of heavy precipitation for portions of eastern New England, Sat-Sun, Mar 2-Mar 3.
• Slight risk of heavy precipitation for portions of California, Nevada, and southern Oregon, Sat-Fri, Mar 2-Mar 8.
• Severe Drought across the Central and Southern Plains, the Central and Southern Rockies, the Great Basin, Hawaii, California, the Alaska Panhandle, the Pacific Northwest, and the Southwest.

Detailed Summary

For Monday February 25 - Friday March 01: As intense surface low pressure exits through Atlantic Canada and surface high pressure begins to move into the eastern CONUS, a tight pressure gradient is forecast to be in place over the northeast. While the strongest winds are forecast on 2/24, before the start of the period, lingering high winds are still probable on 2/25 (sustained 20-30 knots, gusts over 40 knots). High wind watches and warnings have been posted by local Weather Forecast Offices for parts of the northeast and the Ohio Valley. Please refer to the latest updates from your local weather forecast office through the weekend regarding this developing threat.

Troughing moving southward from Alaska is forecast to become elongated over western Canada and direct surface low pressure into the west coast with associated impacts anticipated on 2/25 and 2/26. Liquid precipitation totals of 2-5 inches are possible through the 2-day period based on ensemble guidance from the GEFS and ECMWF. Heavy snow (6-12 inches per day, locally up to 18 inches) is also favored for the Cascades and the Sierra Nevadas and well as parts of Idaho and Wyoming. On 2/27 and 2/28, precipitation is still favored along the west coast but is projected to not be as heavy with lower totals (generally less than 1 inch). Therefore these days were not included in the hazard. On March 1, heavy precipitation chances along the west coast increase once again as an atmospheric river event is forecast to approach the West Coast.

Troughing in place over the Bering Sea and ridging over eastern Alaska is forecast to direct multiple surface low pressure systems near the Aleutians throughout the period. The primary threats are strong southerly winds (greater than 40-knots) and significant wave heights.

Anomalously cold air is forecast over the north central CONUS and extending back to the Pacific northwest throughout the period. Minimum temperatures 15-30 degrees below average are possible. Anomalies are forecast to weaken slightly as the period progresses with a reinforcing surge of Arctic air forecast near the end of the period and lasting into week-2. High winds are possible across parts of the Plains on 3/1 as this new cold surge of air ejects south and east.

Due to critical weather day declarations, the transition of the day 3-7 hazards outlook to the Weather Prediction Center has been delayed until Monday February 25. After the transition has taken place, the Climate Prediction Center will continue to issue the week-2 hazards outlook.

For Saturday March 02 - Friday March 08: Overall pattern in week-2 is forecast to be tranquil, with cold air forecast over much of the northern half of the CONUS and increased precipitation chances along the west coast.

A high risk (60%) of much below normal temperatures is posted for parts of the northern Plains into the Great Lakes for 3/1-3/4 where the reforecast tool from the GEFS has the highest probabilities for below normal temperatures. After 3/4, much below normal temperature probabilities begin to decrease. A moderate risk (40%) extends back to the Pacific northwest and is valid through through 3/6. A slight risk (20%) covers a large region of the northern CONUS and expands into parts of the northeast, and is valid for the entire week-2 period as weak mid-level troughing is forecast to remain in place.

A slight risk (20%) of heavy precipitation is posted for parts of central and northern California along with surrounding areas due to increased Pacific flow. The ECMWF reforecast tool favors the entire period having chances for heavy precipitation, with the GEFS tool forecasting drier conditions in the second half of week-2. For continuity, the slight risk remains posted for the entire period given the same mean mid-level height pattern in both models, and integrated water vapor transport along the coast remaining elevated throughout the period in the GEFS.

A slight risk (20%) of heavy precipitation is posted for parts of eastern New England on 3/2 and 3/3 as several ensembles of the GFS and ECMWF indicate possible development of surface low pressure off the New England coast in this time frame.

The U.S. Drought Monitor, valid Feb 19, indicates severe to exceptional drought (D2-D4) coverage throughout the CONUS decreased to 5.79 percent. Improvements were made across parts of Oregon and Idaho. This is the lowest coverage of D2-D4 since December 2017.

Forecaster: Thomas Collow

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts