US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
238 PM EST Fri Nov 13 2020
 
Valid Monday November 16 2020 - Friday November 20 2020
 
Hazards:
- Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great 
Basin, Tue-Fri, Nov 17-Nov 20.
- Heavy rain across portions of California and the Pacific Northwest, Tue-Thu, Nov 17-Nov 19.
- Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Mon-Fri, Nov 
16-Nov 20.
- Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Tue-Fri, Nov 
17-Nov 20.
- Heavy snow across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, 
and the Northern Great Basin, Wed-Fri, Nov 18-Nov 20.
- Heavy snow across portions of the Central Rockies and the Central Plains, Fri, Nov 20.
- Flooding possible across portions of the Mid-Atlantic and the Central Appalachians.
- Flooding occurring or imminent across portions of the Southeast and the Mid-Atlantic.
- Flooding likely across portions of the Mid-Atlantic.
- High winds across portions of the Pacific Northwest, Mon-Tue, Nov 16-Nov 17.
 
Detailed Summary:

The upper level pattern during the medium range can be summarized with a large long-wave trough 
situated over the northeast Pacific, a strengthening ridge over the Southwest and Great Plains, and 
a trough over the Northeast the first half of the week. Warm air advection and large scale upper 
level divergence supports a wet and active pattern over the Pacific Northwest. The most prominent 
storm system is a strong surface low forecast to take aim at the west coast of Washington and 
British Columbia late Monday into Tuesday. Along with heavy coastal/valley rain and mountain snow, 
the immediate coastline could be subjected to strong winds. The persistent moist onshore flow will 
keep mountain snow and valley rainfall in the forecast from northern California to the 
International border most of the period. By mid-late week, Pacific moisture will reach the northern 
and central Rockies which leads to the opportunity for heavy mountain snow.

Temperature hazards appear to be short of reaching any thresholds but it is worth noting the medium 
range can expect 5-day temperature anomalies of 8-12 degrees above normal in parts of the Southwest 
and Plains. These temps are quite warm for this time of year but not to levels that could be deemed 
"hazardous". Meanwhile, portions of the Ohio Valley and Mid-Atlantic may witness their first freeze 
of the season Wednesday and/or Thursday morning. However, the cold shot is a glancing one and not 
overly-frigid for mid-November, so no below normal temperature area has been issued at this time.

Over Alaska, a cold surface high pressure dominates the mainland with temperatures remaining below 
normal into the middle of the week. By the second half of the week, a big warm-up over northern 
Alaska and along the western coast leads to the return of above normal temperatures. The next 
notable low pressure system should be moving through the Aleutians by midweek. As that storm 
occludes, a new low may form near Kodiak Island and drift east. Expect wet conditions from the 
Aleutians and along the southern mainland coast Wednesday and Thursday to potentially reach the 
Panhandle late week. At this time, precipitation totals and confidence in the storm's timing/track 
are not high enough to include a heavy rain/precipitation area at this time.

Mullinax