US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
503 PM EDT Fri Apr 30 2021
 
Valid Monday May 03 2021 - Friday May 07 2021
 
Hazards:
- Flooding possible across portions of the the Middle Mississippi Valley and the Southern Plains.
- Flooding occurring or imminent across portions of the Middle/Lower Mississippi Valley and the 
Southern Plains.
- Flooding likely across portions of the Lower Mississippi Valley.
- Heavy rain across portions of the Middle/Lower Mississippi Valley, the Central/Southern 
Appalachians, the Tennessee Valley, the Southeast, the Southern Plains, and the Ohio Valley, 
Mon-Wed, May 3-May 5.
- Heavy snow across portions of the Central Rockies, Mon, May 3.
- Severe weather across portions of the Central/Southern Plains and the Middle/Lower Mississippi 
Valley, Mon, May 3.
- Much above normal temperatures across portions of California, the Northern/Central Great Basin, 
and the Pacific Northwest, Tue-Thu, May 4-May 6.
 
Detailed Summary:

During the medium range period (Monday, May 3rd - Friday, May 7th) upper-level troughing will 
dominate the lower 48 for the first half of the week, priming the atmosphere for active weather, 
particularly in the Lower Mississippi Valley and Southeast where multiple rounds of heavy rain are 
likely. The first of these is expected to occur Sunday into early Monday, when a warm front with an 
anomalously high moisture content, fueled by a northerly surge of moisture from the Gulf of Mexico 
via a strong low-level jet, passes northeastward through the Ark-La-Tex region. Convective 
precipitation along the warm front's path is forecast to deposit 1 to 2 inches of rain from eastern 
Texas to western Mississippi through Monday night. In addition to the heavy rainfall, which is 
hazardous enough on its own, the antecedent highly saturated soils in Louisiana and Mississippi 
will serve to exacerbate the flash flooding concerns associated with this event. While the warm 
front marches through the South, spreading showers and thunderstorms through the Appalachians, a 
long frontal boundary consisting of a cold front over the Great Plains/Midwest and a stationary 
front extending from the Great Lakes to the Northeast will concurrently be producing widespread 
showers and thunderstorms of its own. As highlighted by the Storm Prediction Center, moderate to 
strong instability accompanying the cold front segment may lead to the development of severe 
weather from the Southern Plains to the Ozark Plateau Monday evening. 

Tuesday through Thursday morning the long frontal boundary is forecast to slowly move southeast 
through the eastern US, during which time a second influx of Gulf of Mexico moisture is expected to 
occur. Strong frontogentical forcing along the slow-moving boundary interacting with the 
anomalously moist air will likely result in a two-day heavy rain event extending from the Southern 
Plains through the Ohio and Tennessee Valleys, where accumulations of 1 to 2+ inches in 24 hours 
will be possible. Additionally, as with the preceding period of heavy rain, already saturated soils 
throughout the affected areas will likely amplify flash flooding concerns.

Elsewhere, cool air residing over the Colorado Rockies due to a passing cold front is expected to 
interact with upslope convergence behind a low pressure system over the Four Corners region Monday, 
likely resulting in the development of wet heavy snow along the Front Range. To the northwest, a 
frontal system dropping southeast from British Columbia on Tuesday may also bring snow to the 
Absaroka Range in Wyoming. Throughout the latter half of the period strong and persistent ridging 
over the West will pave the way for temperatures to rise 10 to 15 degrees above normal over 
portions of California, Oregon, and the Central Great Basin before moderating on Friday with the 
passing of a cold front.

Throughout the medium range period no hazards are expected for Alaska, however, two systems are 
forecast to pass through the western part of the state next week, both of which have the potential 
to create some unsettled weather. On Monday, a low pressure/frontal system passing through the 
Aleutians may produce gusty winds over the eastern islands before bringing moderate rain to the 
Alaskan Peninsula and Kodiak Island into Tuesday. During the latter half of the week a second 
system may also bring rain to the same area, but the models are currently in disagreement as to how 
much. Due to the high uncertainty surrounding this rain event a hazard area has not been drawn at 
this time. In regards to temperature, highs and lows across the state are expected to remain at or 
close to normal.

Zavadoff