Threats Assessment Discussion

915 
FXUS21 KWNC 181909
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST February 18 2019
SYNOPSIS: An active pattern is expected during the next two weeks. High winds 
and heavy precipitation are possible across western Alaska later this week as 
low pressure moves through the Gulf of Alaska and into the Pacific Northwest. 
Some of these low pressure systems could also lead to localized areas of heavy 
snow along the Cascades. A broader area of upper-level low pressure is expected 
to keep most of the western and north-central U.S. quite cold during the next 
two weeks and temperatures could be more than 20 F below climatology. 
Meanwhile, low pressure developing in the center of the country is forecast to 
move eastward and bring significant rain and snow to much of the eastern U.S. 
by the end of the weekend.
HAZARDS
Heavy precipitation across portions of the Central Plains, the Mid-Atlantic, 
and the Ohio Valley, Sat-Mon, Feb 23-Feb 25.
Heavy rain across portions of the Mid-Atlantic and the Southeast, Fri-Sun, Feb 
22-Feb 24.
Heavy snow along the Cascades in Washington, Oregon and northern California, 
Fri-Mon, Feb 22-Feb 25.
Heavy snow across portions of interior New Mexico and southern Colorado, 
Fri-Sat, Feb 22-Feb 23.
Heavy snow across high elevation portions of Arizona, Thu-Fri, Feb 21-Feb 22.
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.
Much below normal temperatures across much of the western CONUS, Thu-Mon, Feb 
21-Feb 25.
Heavy precipitation across coastal portions of western Alaska, Sat-Sun, Feb 
23-Feb 24.
High winds across portions of western Alaska, Fri, Feb 22 and Sun-Mon, Feb 
24-Feb 25.
High significant wave heights for coastal portions of western Alaska, Fri, Feb 
22 and Sun-Mon, Feb 24-Feb 25.
Slight risk of much below normal temperatures for much of the western CONUS, 
Tue-Mon, Feb 26-Mar 4.
Moderate risk of much below normal temperatures for much of the western CONUS, 
Tue-Mon, Feb 26-Mar 4.
High risk of much below normal temperatures for much of the western CONUS, 
Tue-Sat, Feb 26-Mar 2.
Slight risk of heavy precipitation for portions of the Southeast, Tue-Wed, Feb 
26-Feb 27.
Severe Drought across the Central Plains, the Central Rockies, the Central 
Great Basin, the Southern Plains, Hawaii, the Northern Great Basin, the 
Southern Rockies, California, the Alaska Panhandle, the Pacific Northwest, and 
the Southwest.
DETAILED SUMMARY
FOR THURSDAY FEBRUARY 21 - MONDAY FEBRUARY 25: Several shortwaves will move 
through a stationary longwave trough and affect western Alaska. Each shortwave 
will carry the potential for heavy precipitation (Feb 23-25) and strong 
winds/significant waves (Feb 22 and Feb 24-25) over parts of coastal western 
Alaska. Some of the winds could exceed 45 knots and precipitation amounts could 
be up to 3 inches of liquid equivalent. Downstream along the West Coast, 
shortwave troughs are also expected to bring heavy snow (around 6-10 inches per 
day) to localized parts of the Cascades from Feb 22-25.
Anomalously cold air will overrun much of the western CONUS and daily minimum 
temperatures in some areas could be up to 20 F below normal throughout the 
week. A hazard for much below normal minimum temperatures has been posted for 
the entire forecast duration, but the cold air is expected in pulses and won't 
affect the entire region each night. The core of the cold will be centered over 
the Northern Plains and some nights the cold air will reach as far south as 
southern UT, CO, and KS and as far east as MN, MO, and IA. Heavy snow, in 
excess of 10 inches, is also possible across the high terrain in Arizona (Feb 
21-22) and New Mexico/southern Colorado (Feb 22-23). Please consult your local 
NWS forecast office for important details during the next few days.
Low pressure is expected to form over the mid-west on Wednesday and track 
eastward through the end of the week. Heavy rainfall is expected in the 
interior Southeast on Friday and some areas, especially TN, KY, and WV, could 
get more than 3 inches of rain within a 24 hour period. The region of heaviest 
precipitation will lift north as the low tracks eastward and there is the 
potential for 1-3 inches of rain over much of the mid-Atlantic and 4-8 inches 
of snow over parts of the upper Midwest and Northeast this weekend. There is 
also the potential for severe weather in the lower Mississippi and Tennessee 
Valleys on Feb 23. Interested parties are encouraged to monitor SPC forecasts 
for the latest information.
FOR TUESDAY FEBRUARY 26 - MONDAY MARCH 04: The cold air will continue to affect 
the western U.S. during Week-2. There is a slight risk of below normal minimum 
temperatures posted for much of the area, along with moderate and high risk 
hazards centered over the Northern Plains and Northern Rockies. Model guidance 
forecasts the longwave trough to slowly shift eastward during Week-2, so the 
axis of coldest air is also expected to shift eastward. By mid-week, the 
highest probabilities of cold air will be over the Dakotas, Minnesota, 
Wisconsin, and northwestern Illinois. 
There are also indications that the southeast will remain active during Week-2 
and several models suggest a slight risk of heavy precipitation Feb 26-27 over 
the interior southeast.
The U.S. Drought Monitor, valid Feb 12, indicates severe to exceptional drought 
(D2-D4) coverage throughout the CONUS decreased to 6.23 percent. Improvements 
were made across parts of Arizona, Colorado, and Utah. This is the lowest 
coverage of D2-D4 since December 2017.
FORECASTER: Kyle MacRitchie 
$$