US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
257 PM EST Mon Feb 18 2019
 
Valid Thursday February 21 2019 - Monday February 25 2019
 
Hazards:
Heavy rain across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee 
Valley, the Great Lakes, the Middle Mississippi Valley, the Mid-Atlantic, the Southern 
Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Thu-Sat, Feb 21-Feb 23.
Heavy snow across portions of the Central Plains, the Northern Plains, the Great Lakes, the 
Northern Great Basin, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Pacific 
Northwest, Fri-Sun, Feb 22-Feb 24.
Heavy snow across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, 
and the Southwest, Thu-Fri, Feb 21-Feb 22.
Heavy snow across portions of the Northeast, Sun, Feb 24.
Severe weather across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the 
Southern Plains, the Ohio Valley, and the Tennessee Valley, Sat, Feb 23.
Flooding possible across portions of the Lower Mississippi Valley, the Tennessee Valley, the 
Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley.
Flooding occurring or imminent across portions of the Middle Mississippi Valley, the Lower 
Mississippi Valley, the Ohio Valley, and the Tennessee Valley.
Flooding likely across portions of the Lower Mississippi Valley, the Ohio Valley, and the Tennessee 
Valley.
High winds across portions of the Southern Rockies and the Southern Plains, Sat, Feb 23.
Much below normal temperatures across portions of the Central Plains, the Central Rockies, the 
Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, California, 
the Northern Great Basin, the Upper Mississippi Valley, the Pacific Northwest, and the Southwest, 
Thu-Mon, Feb 21-Feb 25.
High winds across portions of the Aleutians, Thu-Fri, Feb 21-Feb 22.
and Sun-Mon, Feb 24-Feb 25.
High significant wave heights for coastal portions of the Aleutians, Thu-Mon, Feb 21-Feb 25.
 
Detailed Summary:

The medium range period begins with a low pressure system moving across the Southwest U.S. late 
this week. The guidance continues to show the potential for heavy snowfall across mainly the 
terrain of the Four Corners states. Snow levels in these regions will be lower than usual, and 
upwards of a foot of snow is forecast in some of the highest elevations. High winds may also 
develop on the backside of this system on Saturday across parts of New Mexico and west Texas.

As this system exits the Southwest this weekend, it is forecast to develop into a potentially 
significant system as it tracks towards the Upper Great Lakes by Sunday. There is a good signal for 
heavy snowfall to the north and west of the low center moving from west to east from the Central 
Plains/Upper Mississippi Valley on the 23rd, into the Upper Great Lakes by the 24th. There is 
likely to be a region of gusty winds within the heavy snow area which may lead to blizzard 
conditions for some locations, but a high wind hazard was not included on today's chart due to 
model spread in the strength of the low pressure system. Stay tuned for additional details as the 
forecast evolves. The low moves into eastern Canada by the end of the weekend, but may also clip 
parts of western Maine with heavy snows as well.

The warm side of this system features a heavy rainfall signal along a stationary front draped 
across the Tennessee Valley into the lower Ohio Valley. Heavy rainfall may linger for several days 
(from the 21st to the 23rd) across these regions, with upwards of an inch of rain in a 24-hour 
period expected for some places. This is likely to lead to a flash flood threat, especially given 
heavy rainfall expected over these same areas during the short range period as well. The Storm 
Prediction Center has also highlighted an area from the lower/middle Mississippi Valley to the 
western Tennessee Valley within a chance for severe thunderstorms on Saturday, the 23rd.

Cold surface high pressure and mid-level troughing will sustain below to much below normal 
temperatures through the medium range period across much of the West and into the Northern Plains. 
While a hazard was posted for the entire valid period, the cold air will come in waves and so the 
whole region may not meet criteria each day. The core of the cold air looks to focus over Montana 
and the Dakotas, but some days may reach as far south as the Southwest or as far west as California.

Elsewhere, several systems/shortwaves affect Alaska during the medium range period resulting in 
periods of high winds and significant waves for much of the Aleutian island chain. Locally heavy 
precipitation is also likely to accompany these systems as well, but may not be significant enough 
to include a hazard on the chart at this time. Downstream, these shortwaves are also expected to 
produce heavy snowfall in the Cascade range of Oregon/Washington during the upcoming weekend.

Santorelli