US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
339 PM EDT Mon May 18 2020
 
Valid Thursday May 21 2020 - Monday May 25 2020
 
Hazards:
- Heavy rain across portions of the Plains and the Mississippi Valley, Thu-Mon, May 21-May 25.
- Heavy rain across portions of the Southern Appalachians, the Mid-Atlantic, and the Central 
Appalachians, Thu, May 21.
- Flooding possible across portions of the Central/Southern Appalachians, the Northern Rockies, the 
Middle Mississippi Valley, the Mid-Atlantic, the Northern Great Basin, the Great Lakes, and the 
Ohio Valley.
- Flooding occurring or imminent across portions of the Mississippi Valley, the Great Lakes, and 
the Northern Plains.
- Flooding likely across portions of the Middle Mississippi Valley, the Northern Rockies, and the 
Northern Great Basin.
- Heavy precipitation across portions of mainland Alaska, Thu-Sat, May 21-May 23.
 
Detailed Summary:

The medium range period will begin on Thursday 5/21 with a cutoff upper-level low continuing to 
meander over the Tennessee and Ohio Valleys. Due to this low, heavy rainfall should persist into 
Thursday over portions of the Appalachians and Mid-Atlantic, with several inches of rainfall 
expected to accumulate from the short range period through Thursday night. The upper-level low is 
forecast to move eastward and offshore over the weekend. 

The western half of the U.S. should see a general upper-level trough pattern through the weekend, 
with a couple rounds of shortwave energy enhancing the trough. Underneath, some precipitation is 
forecast to continue across the Northern Great Basin to Northern Rockies late in the week, and some 
snow is expected in higher elevations. But the broader concern is ahead of this trough. Moisture 
inflow could interact with a series of frontal boundaries traversing the Plains and Mississippi 
Valley through early next week, leading to the potential for heavy rain and thunderstorms in those 
regions. At this point, model guidance varies quite a bit on position and timing of heavy rainfall, 
and it seems some areas could see multiple rounds of rainfall. So the broad Heavy Rain hazard area 
may be refined spatially and temporally over the coming days as model guidance hopefully becomes 
more consistent and in better agreement. Severe weather is also a possibility, and its potential is 
being monitored by the Storm Prediction Center.

The trough in the West will lead to maximum temperatures of 10 to 15 degrees below normal over the 
Northwest through the end of the week, though minimum temperatures should not be considerably below 
average. Farther east, somewhat warmer than average temperatures are expected for parts of the 
Plains to Great Lakes region through early next week.

Over Alaska, there is a good signal for heavy precipitation through the end of the week for eastern 
portions of the Alaska and Kenai Peninsulas. Then, there is some potential for precipitation over 
the weekend and early next week for parts of the Panhandle, but model guidance has not settled on a 
consistent signal for precipitation there. Ice jam flooding will be a concern over the North Slope 
as rivers have not yet broken up, while minor snowmelt flooding is a possibility in central and 
southern parts of the mainland. No significant temperature anomalies are expected, but southern 
parts of the mainland will generally see below average high temperatures, with warmer than average 
temperatures in central and parts of the northern mainland. 

Tate