US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
456 PM EDT Wed Sep 08 2021
 
Valid Saturday September 11 2021 - Wednesday September 15 2021
 
Hazards:
- Heavy rain across portions of the Southeast, the Lower Mississippi Valley, and the Southern 
Plains, Mon-Wed, Sep 13-Sep 15.
- Heavy rain across portions of the Northern Plains and the Northern Rockies, Sat, Sep 11.
- Flooding occurring or imminent across portions of the Central Plains, the Middle Mississippi 
Valley, and the Mid-Atlantic.
- Flooding occurring or imminent across portions of the Middle Mississippi Valley and the 
Mid-Atlantic.
- Flooding occurring or imminent across portions of the Middle Mississippi Valley.
- Much above normal temperatures across portions of the Central Rockies, the Central Plains, the 
Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Sat-Mon, Sep 
11-Sep 13.
- Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Sep 12-Sep 13.
 
Detailed Summary:

The weather pattern during the medium range forecast period (Saturday, Sep 11 to Wednesday, Sep 15) 
is highlighted by a gradual transition to a quasi-zonal (West-East) flow pattern as a ridge of high 
pressure migrates out of the Four Corners into the Midwest over the weekend. Slight height rises 
with the eastward propagating ridge will maintain temperatures 10-15 degrees above average over the 
Central Plains, with high temperatures in the mid-upper 90's anticipated through the weekend. 
Accordingly, the Much Above Normal Temperature area was expanded further east to account for the 
warming trend in high temperatures. Temperatures for the Central U.S. finally abate to around 
seasonal after Monday, which will moderate heat indices in spite of a surge of moisture-laden Gulf 
air into the Plains by midweek.

Temperatures aside, the medium range remains fairly dry over a majority of the CONUS, and the main 
heavy rain threat falls along the western Gulf of Mexico beginning Monday ahead of a moisture-rich 
tropical disturbance emanating from the Yucatan Peninsula. Uncertainty remains high with the timing 
and evolution of this disturbance, which promotes a broad Heavy Rain area along the coast for now. 
Tropical moisture from this system will eventually lift north and interact with a front sweeping 
across the Upper Midwest and Great Lakes early next week to produce moderate rainfall, although 
timing differences with the front precludes Heavy Rain area at this time. Otherwise, shower and 
thunderstorm chances will persist over Florida through next week as a front stalls and moderates in 
the Southeast/Gulf of Mexico. Over Northwest Montana, a small Heavy Rain area was added on the 11th 
for lingering showers/thunderstorms in the region as a shortwave trough interacts with a very moist 
Pacific airmass overhead, although the threat should subside by later Saturday.

Meanwhile, Alaska will remain very wet throughout the medium range. On Sunday, a strong mean trough 
with embedded shortwaves will pivot southeast across the Aleutians and Southern Peninsula, 
propagating a series of frontal systems across the southern Alaska. As the system moves east late 
this weekend it will siphon a stream of Pacific moisture northward through the Gulf of Alaska, 
setting up another bout of heavy rain from the 12th-13th. Rainfall totals of 1-3 inches are 
possible with locally higher amounts possible in areas of favorable orographic ascent. In addition 
to the rainfall, some gusty winds are also possible through early next week over the Aleutians and 
Southern Peninsula, although they are not expected to reach hazard levels at this time. Afterwards, 
troughing will remain entrenched over Alaska through midweek, but additional precipitation is not 
expected to be hazardous.


Asherman