US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
357 PM EDT Wed May 05 2021
 
Valid Saturday May 08 2021 - Wednesday May 12 2021
 
Hazards:
- Heavy rain across portions of the Central/Southern Plains, the Great Lakes, the Middle 
Mississippi Valley, and the Ohio Valley, Sat, May 8.
- Heavy rain across portions of the Middle/Lower Mississippi Valley, the Central/Southern 
Appalachians, the Tennessee Valley, the Southern Plains, and the Ohio Valley, Sun, May 9.
- Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Tue, May 11.
- Severe weather across portions of the Central/Southern Plains, and the Middle/Lower Mississippi 
Valley, Sat, May 8.
- Flooding occurring or imminent across portions of the Southern Plains.
- High winds across portions of California, Sat-Mon, May 8-May 10.
 
Detailed Summary:

In the medium-range forecast period, an area of strong high pressure over the Eastern Pacific (off 
the West Coast of the CONUS) and a thermal trough developing over California will create a strong 
pressure gradient over California and along as well offshore from California Coast.  With high 
pressure being semi-permanent, the area of high wind will continue from Friday to Monday. 

Meanwhile, a developing area of low pressure over the Central High Plains, on Saturday, will move 
eastward to the Middle/Lower Mississippi Valley on Sunday, pulling a front across the Southern 
Plains.  On Monday, the low will move off the Northeast Coast with a trailing front from the 
Mid-Atlantic to the Southern Plains.  The front will then become quasi-stationary, extending from 
the Southeast to the Southern Plains on Tuesday.  Then on Wednesday, a wave of low pressure over 
the Southern High Plains will move northeastward to the Tennessee Valley.   Back to Saturday, the 
SPC has issued an outlook for severe thunderstorms over parts of the Central Plains/Middle 
Mississippi Valley.  The air will become unstable in the warm sector, producing conditions that 
will allow for the development of severe thunderstorms.  Also, an area of heavy rain will develop 
along the warm front over parts of the Central Plains/Middle Mississippi Valley eastward to parts 
of the Ohio Valleys on Saturday.  As the system moves eastward with the front, on Sunday, an area 
of heavy rain will develop along the front from parts of the Ohio Valley/Central Appalachians to 
the Tennessee/Lower Mississippi Valleys.  There will be a break from the heavy rain on Monday.  
More moisture from the Western Gulf of Mexico will overrun the boundary over parts of the Southern 
Plains/Lower Mississippi Valley on Tuesday.

However, with the wave moving out of the Plains on Wednesday, the models have an uncertainty of 
where to locate the area of heavy rain. The GFS has a large area of heavy rain over eastern Texas 
and northwestern Louisiana, while the ECMWF has heavy rain over the Southeast. The MMEQPFC5KM has a 
broader area of heavy rain from the parts of the Southern Plains to The Southern Appalachians.

For Alaska, an area of low pressure will move along the Aleutians on Saturday, followed by another 
area of low pressure moving south of the Aleutians on Monday.  The parade of lows will continue 
near the Aleutians through Wednesday.  The systems will produce mostly rain, but the amounts do not 
come close to the criteria for heavy precipitation from Saturday to Wednesday.  The areas of low 
pressures have a pressure gradient associated with them.  At this point in time, the wind 
associated with the lows over the state will be below the criteria for high wind.

Ziegenfelder