US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
343 PM EDT Fri May 14 2021
 
Valid Monday May 17 2021 - Friday May 21 2021
 
Hazards:
- Heavy rain across portions of the Lower/Middle Mississippi Valley into the Midwest, Mon, May 17.
- Heavy rain across portions of the central/southern Plains into the Lower/Middle Mississippi 
Valley, Mon-Wed, May 17-May 19.
- Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Tue-Fri, May 
18-May 21.
- Flooding possible across portions of the Central Plains and the Northern Great Basin.
- Flooding occurring or imminent across portions of the Lower Mississippi Valley.
- Much above normal temperatures across portions of the Northern High Plains to the Upper 
Mississippi Valley, Mon-Tue, May 17-May 18.
 
Detailed Summary:

The main weather hazard during the medium-range forecast period (Monday, May 17 - Friday, May 21) 
will be heavy rainfall from the southern Plains to parts of the lower Mississippi Valley and the 
Midwest. This is in response to very moist return flow out of the Gulf of Mexico ahead of an 
initial southern Plains upper low then western U.S. mean troughing along with a quasi-stationary 
surface boundary draped from the Midwest to the Plains through next week. With this setup, a 
multi-day period of heavy to possibly significant rainfall (and some threat of strong to severe 
thunderstorms) is expected. At this time, the best chance for heavy rainfall should focus along the 
surface front from Oklahoma into the Midwest on Monday. By Tuesday and beyond, the main activity 
may shift more west and south into central and eastern Texas, Oklahoma, and parts of the lower 
Mississippi Valley. Exact locations and magnitude of heaviest rainfall will likely vary on a 
day-to-day basis with specific details hard to resolve at these longer lead times. Regardless, 
models have been consistent in showing a signal for a very wet pattern for parts of the southern 
and central U.S. over a region which is already very saturated due to well above normal 
precipitation in the past several weeks. This may increase the flood and flash flood threat for 
some locations.

Elsewhere, a small heavy rain area across parts of eastern Colorado was added today to the outlook 
due to upslope flow into the Colorado Rockies and a somewhat marginal threat for heavy to excessive 
rainfall. Given WPC does not issue this medium range hazards outlook over the weekend, felt an area 
was warranted for Monday even though there is some looming uncertainties in this. In Florida, 
increased moisture across southern parts of the Sunshine state may support some organized heavy 
rainfall later next week but uncertainty in amounts and location was too high at this time to 
include an outlook area. In terms of temperatures across the CONUS, the only notable region was an 
area of much above normal temperatures stretching across parts of the far northern tier and so an 
area was added to the graphic today given the potential for +10-20F temperatures early next week 
ahead of a Pacific cold front.

For Alaska, much of the area should remain relatively quiet through the greater part of next week. 
A potent storm system may impact the Aleutians on Tuesday and Wednesday, but models continue to 
show increasing uncertainty in the overall pattern and exact specifics. At this time, any 
associated weather threats (wind and rain) appear below hazards thresholds.

Santorelli