US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
255 PM EDT Thu May 20 2021
 
Valid Sunday May 23 2021 - Thursday May 27 2021
 
Hazards:
- Heavy rain across portions of the Northern High Plains, Sun-Mon, May 23-May 24.
- Flooding possible across portions of the Central Plains, the Middle Mississippi Valley, the Lower 
Mississippi Valley, and the Southern Plains.
- Flooding occurring or imminent across portions of the Middle Mississippi Valley, the Lower 
Mississippi Valley, and the Southern Plains.
- Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, the Lower 
Mississippi Valley, and the Southern Plains.
- Much above normal temperatures across portions of the Upper Ohio Valley and Great Lakes, Sun-Tue, 
May 23-May 25.
- Much above normal temperatures across portions of the Southeast, Sun-Wed, May 23-May 26.
 
Detailed Summary:

A strong upper level low initially over the Great Basin to begin the medium range period on Sunday 
will lift into the Northern Rockies/High Plains. Moderate to heavy precipitation is expected to 
accompany this system on Sunday into Monday across portions of the Northern Rockies and High 
Plains. Accumulating snowfall appears likely in the higher terrain, but does not look heavy enough 
to reach criteria for an area on the outlook for today. Did go ahead though and introduce a heavy 
rain area for the lower elevation areas of central into eastern Montana where several pieces of 
guidance are indicating rainfall in excess of an inch each day. The attendant cold front with this 
system will shift into the Central Plains and Upper Midwest early next week, with convection likely 
to break out ahead of and along the front. Heavy rainfall is possible, especially within mesoscale 
convective complexes, but there remains enough uncertainty on exactly where any MCSs may form so 
it's difficult to pinpoint an outlook heavy rain area at this time. The only other mention for 
heavy rainfall across the CONUS next week is along portions of the already very saturated central 
Texas Gulf Coast. Gulf of Mexico moisture will be funneled into the region this weekend in between 
Western U.S. troughing and Eastern U.S. ridging, but rainfall amounts are marginal for reaching 
criteria and the area of concern is too localized. As a result, the small area highlighted on 
yesterdays forecast was removed today.

In terms of temperatures across the nation during the extended range, there are two regions of 
concern for consecutive days of much above normal temperatures. The first is across portions of the 
upper Ohio Valley/Great Lakes where daytime highs approaching 90 degrees (10 to 20 degrees above 
average) will continue from this weekend into early next week with near record highs possible for 
some locations, especially Sunday. Into the East, parts of the interior Southeast (from Georgia to 
South Carolina) will also be much above normal through most of next week, where the first heat wave 
of the season will bring temperatures into the upper 90s, with many locations forecast to reach or 
exceed record highs for this time of the year. Above normal temperatures may expand into parts of 
the Mid-Atlantic as well, but a back door cold front should keep values in check early into the 
week. As warmer air moves in Wednesday, a brief period of temperatures 10-20 degrees above normal 
are possible, but should cool back towards normal by Thursday so for this reason a hazards area was 
excluded for the Mid-Atlantic region (but continued from yesterday for the Southeast).

Finally in Alaska, a system is expected to affect the Aleutians into the Alaskan peninsula this 
weekend into next week, but any associated wind and rainfall hazards should remain below criteria. 
As such, no significant hazards were added in Alaska.

Santorelli