US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
449 PM EDT Tue Mar 30 2021
 
Valid Friday April 02 2021 - Tuesday April 06 2021
 
Hazards:
- Flooding possible across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi 
Valley, and the Southern Appalachians.
- Flooding possible across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, 
and the Tennessee Valley.
- Flooding occurring or imminent across portions of the Southeast, the Lower Mississippi Valley, 
the Southern Appalachians, the Ohio Valley, and the Tennessee Valley.
- Flooding occurring or imminent across portions of the Southeast, the Lower Mississippi Valley, 
the Southern Appalachians, the Ohio Valley, and the Tennessee Valley.
- Flooding likely across portions of the Ohio Valley.
- Much below normal temperatures across portions of the Lower Mississippi Valley, the Tennessee 
Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, 
and the Ohio Valley, Fri, Apr 2.
- Heavy snow across portions of mainland Alaska, Fri-Sat, Apr 2-Apr 3.
 
Detailed Summary:
A rare moment of benign weather pattern is in store over much of the U.S. to begin April, with 
mostly calm and dry weather April 3rd - April 5th. The pattern over the CONUS at beginning of the 
forecast period (Friday, April 2nd) is characterized by an amplified closed low and associated 
frontal system departing the Northeast U.S., leaving in its wake lingering snow and mix over Maine 
on the back end of the low as it ejects northeastward; no hazardous weather is expected. On its 
heels, shortwave ridging and surface high pressure will nose into the Southern U.S., bringing 
unseasonably cool temperatures into the area and further northeast into the Mid-Atlantic. 
Temperatures will hover at or below freezing (10-15 degrees below normal) over the region. These 
sub-freezing temperatures are forecast to occur just beyond the 30 year climatological date of the 
last expected spring freeze. Thus, have added a ā€Much Below Normal Temperatureā€ hazard area as 
the late freeze may adversely affect newly planted vegetation. While areas further north of the 
ā€Much Below Normal Temperatureā€ area (such as northern Virginia and Marlyand) may see 
temperatures around freezing, stronger mean boundary layer wind may make it more difficult to reach 
a hazardous threshold. Temperatures will quickly moderate to around normal by the end of the 
weekend. 

Further west over the Plains, a building ridge is forecast to settle over the region beginning 
Saturday. Warm, dry downslope flow will take hold of the area and usher in temperatures 10-20 
degrees above average through the weekend before warm temperatures migrate east by Tuesday. 
Meanwhile, the next chance of interesting weather begins over the Gulf of Alaska April 3rd as a 
trough dives southeast along a ridge anchored in the northern Pacific. From here, deterministic 
guidance begins to differ greatly with the evolution of the system Sunday into Monday, particularly 
with a piece of energy that fractures from the main shortwave off the coast of British Columbia. 
The ECMWF amplifies this fractured energy into a closed off system off the California coast while 
the GFS continues to quickly progress the original wave inland over the Northwest. Given these are 
typical biases for the models, a solution in between the ECMWF and GFS ensemble is a reasonable 
middle ground between the two. As such, the pattern appears favorable for some snow in the Sierra 
Nevada and Cascade ranges with rain in the lower elevations; no hazardous weather is expected with 
this activity.

The aforementioned northern Pacific ridge will favor an active storm track over Alaska through the 
forecast period. A series of frontal systems will lift out of Eurasia over mainland Alaska into the 
Aleutian chain Friday into Saturday, bringing a shot of heavy blowing snow to the mainland with 
rain along the coast. Additionally, cold air behind a sweeping cold front will usher in below 
normal temperatures in the central and eastern portions of the state the 4th-6th. However, at this 
time the colder temperatures look to remain below hazardous criteria.    

Asherman