US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
346 PM EDT Wed Apr 28 2021
 
Valid Saturday May 01 2021 - Wednesday May 05 2021
 
Hazards:
- Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Sat-Sun, May 
1-May 2.
- Heavy rain across portions of the Central Rockies and the Central Plains, Sun-Mon, May 2-May 3.
- Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle 
Mississippi Valley, the Southern Appalachians, the Southeast, the Great Lakes, and the Ohio Valley, 
Mon-Tue, May 3-May 4.
- Flooding possible across portions of the Central Plains, the Lower Mississippi Valley, the 
Tennessee Valley, the Middle Mississippi Valley, the Southern Plains, and the Ohio Valley.
- Flooding occurring or imminent across portions of the Lower Mississippi Valley.
- Flooding likely across portions of the Lower Mississippi Valley.
- Much above normal temperatures across portions of the Central Plains, the Central Great Basin, 
the Northern Plains, the Northern Great Basin, the Central Rockies, the Middle Mississippi Valley, 
California, the Upper Mississippi Valley, and the Southwest, Sat, May 1.
 
Detailed Summary:

The overall pattern during the first several days of May will feature a mostly east-west zonal 
flow, with mid-upper ridging along/off the West Coast and in the southeastern states, while a 
series of systems moves through a broad trough in the central U.S.  While the ridge in the west 
breaks down later this week, there looks to be one more day (Saturday) with above normal 
temperatures stretching from the Upper Midwest through the north-central Plains, Great Basin and 
Desert Southwest.  Highs will range from 15-25 degrees above normal over the Plains and upper 
Midwest, which translates to temperatures well into the 80s.  Over the Southwest, expect 
triple-digit heat and near record highs for one more day before temperatures cool slightly during 
the latter half of the weekend.

Farther east, a couple of features will bring the potential for heavy rainfall to sections of the 
Gulf Coast, Tennessee and Ohio Valleys from the weekend into the early to mid part of next week.  
Over the weekend, an upper level low will tap deep Gulf of Mexico moisture as it moves slowly from 
northern Mexico across Texas and into the lower Mississippi Valley.  The moisture will interact 
with a weak frontal system and a highly unstable air mass to support heavy rainfall across parts of 
southern Texas into Louisiana.  There was still some uncertainty regarding the speed and track of 
this upper level feature, but the general consensus favored the eastern Texas Gulf Coast through 
western Louisiana and southern Arkansas.

Meanwhile, a fairly strong frontal boundary will become organized over the upper 
Midwest/north-central Plains on Sunday, then slowly progress south and eastward through the middle 
of next week.  This front will be the focus for rounds of heavy rainfall from central High Plains 
eastward through the Midwest and northern Mid-Atlantic states, and also southward through Tennessee 
Valley and southeastern states.  The challenge is pinpointing the areas most likely to receive 
significant precipitation as there are rather diverse solutions among the models.  Right now, we 
have chosen to highlight the north-central High Plains and the Ohio and Tennessee Valleys.

Over the north-central High Plains, a combination of convergence along and upslope flow behind the 
front will help to enhance the precipitation Sunday into Monday.  The actual precipitation amounts 
are only marginally heavy, but the hazard area has experienced above normal precipitation recently, 
so the rainfall may have greater impact here in terms of isolated flood risks.  From the Tennessee 
through Ohio Valleys, deep moisture from the upper level system that affects the Gulf Coast region 
earlier in the period will lift northeastward and fuel widespread showers and thunderstorms ahead 
of the slow-moving front.  Precipitation amounts across the upper Ohio Valley and lower Great Lakes 
region Tuesday-Wednesday will be enhanced by the interaction of a frontal low and an east-west 
aligned stationary boundary.  Heavy precipitation may extend into Thursday across the southeastern 
U.S., however we did not have enough confidence to draw a hazard area given the lack of agreement 
among the models.  

Across Alaska, the pattern does not favor major storm systems impacting the state.  While 
conditions will be unsettled over the Panhandle and much of the southern part of the mainland, 
nothing at this time is expected to have major impacts. 

Klein