US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
516 PM EDT Fri May 15 2020
 
Valid Monday May 18 2020 - Friday May 22 2020
 
Hazards:
- Heavy precipitation across portions of California, Mon, May 18.
- Heavy rain across portions of the Northern Rockies, and the Northern Great Basin, Mon-Wed, May 
18-May 20.
- Heavy rain across portions of the Northeast, the Central Appalachians, and the Mid-Atlantic, 
Mon-Wed, May 18-May 20.
- Flooding possible across portions of the Southern Plains, the Northern Rockies, the Middle 
Mississippi Valley, the Northern Great Basin, the Upper Mississippi Valley, and the Great Lakes.
- Flooding occurring or imminent across portions of the Middle Mississippi Valley, the Lower 
Mississippi Valley, and the Northern Plains.
- Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the 
Southern Plains.
- Much above normal temperatures across portions of the Northern/Central Plains, the Rockies, and 
the Upper Mississippi Valley, Mon-Thu, May 18-May 21.
- Enhanced wildfire risk across portions of the the Southern Rockies, the Central Rockies, the 
Central Great Basin, and the Southwest, Mon-Tue, May 18-May 19.
- Heavy precipitation across portions of mainland Alaska, Tue, May 19 and Thu, May 21.
 
Detailed Summary:

A highly amplified synoptic pattern will be the theme during the medium range period (Monday 5/18 
to Friday 5/22). Models are in excellent agreement that a relatively flat upper-level pattern 
across the U.S. during the weekend will dramatically amplify into an omega block pattern, with a 
pronounced ridge sandwiched in between two major cut-off lows impacting both the West Coast and 
East Coast. Models dig down an upper trough quickly and aggressively from the Great Lakes into the 
eastern U.S. The current assessment of the situation calls for heavy rain to occur from the 
interior Northeast and Mid-Atlantic into the Central Appalachians next Monday through Wednesday.

Prior to the formation of this anomalous upper low over the East Coast, a threat of heavy rain is 
expected to impact areas from the lower Great Lakes eastward across the central Appalachians into 
parts of New England ahead of a pair of well-developed frontal boundaries and a low pressure 
system. This will be in stark contrast with a pronounced ridge of high pressure forecast to develop 
over the Great Plains. This ridge will ensure a significant warming trend across the northern and 
central Plains for early to middle of next week with afternoon temperatures likely reaching well up 
into the 80s to possibly the lower 90s.

Models continue to indicate the formation of a low pressure system fairly near the east coast of 
Florida this weekend. The National Hurricane Center continues to monitor this area for the 
potential of subtropical cyclogenesis. Impacts associated with this system are expected to remain 
largely offshore. However, with the major shift toward a major closed low developing over the 
eastern U.S., there is a possibility for the offshore subtropical system to mutually interact with 
the deep upper low over the East Coast and thus spreading moisture toward the eastern U.S.

Over the West Coast, a deepening upper-level trough is forecast to produce heavy rain across lower 
elevation portions of northern/central California on Monday. Meanwhile, heavy wet snow is expected 
for the higher elevations of the central Sierra Nevada next Monday into Tuesday as the upper trough 
digs further into California.

Over the Pacific Northwest, a frontal system moving onshore is expected to arrive, bringing 
localized areas of heavy rainfall to the Northern Great Basin/Rockies Monday through Wednesday. By 
Tuesday and Wednesday, the threat of heavy rain is forecast to spread from northern Idaho into 
western Montana ahead of a low pressure system. By Thursday, the heavy rain threat should linger 
across central Montana as the low pressure system begins to interact with a cold front arriving 
from western Canada. Wet snow can also be expected over the highest elevations in these areas.

Over Alaska, a pair of low pressure systems moving across the southern portion of the state could 
result in heavy precipitation along the southern coastal areas later on Monday into Tuesday as well 
as Wednesday into Thursday, respectively. Above normal temperatures are forecast to continue over 
the western and much of the southern portions of the state, in contrast with colder than normal 
temperatures over the north and northeast portions of the state.

Kebede/Kong