US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
355 PM EDT Thu Aug 13 2020
Valid Sunday August 16 2020 - Thursday August 20 2020
- Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians,
Tue-Wed, Aug 18-Aug 19.
- Heavy rain across portions of the Mid-Atlantic, Sun, Aug 16.
- Flooding possible across portions of the Upper Mississippi Valley.
- Excessive heat across portions of California, the Lower Mississippi Valley, the Pacific
Northwest, the Northern Great Basin, and the Southern Plains, Sun, Aug 16.
- Excessive heat across portions of the Central Great Basin, California, and the Southwest,
Sun-Thu, Aug 16-Aug 20.
- Excessive heat across portions of the Lower Mississippi Valley and the Southern Plains, Sun-Mon,
Aug 16-Aug 17.
- Much above normal temperatures across portions of the Central Great Basin, the Northern Plains,
the Northern Rockies, the Central Rockies, California, the Northern Great Basin, and the Pacific
Northwest, Sun-Tue, Aug 16-Aug 18.
- Much above normal temperatures across portions of the Central Rockies and the Central Great
Basin, Sun-Wed, Aug 16-Aug 19.
- Heavy rain across portions of the Alaska Panhandle, Sun-Mon, Aug 16-Aug 17.
The expected jet stream pattern during the medium range period (Sun, Aug. 16 - Thurs, Aug. 20)
features an amplified regime with a strong ridge across the West and a corresponding trough setting
up over the East. The most commonly observed hazard is stifling heat in the Southwest and much
above normal temperatures in the Northwest. In fact, Sunday could be a scorcher in parts of the
Pacific NW with some guidance suggesting upper 90s around the Seattle metro area and near 100 in
Portland. Daily record high temps could be broken in parts of the region and thus an Excessive Heat
area was added for this Sunday. Sunday and Monday will also remain quite hot in the South Central
U.S. where heat indices look to range between 105-115 degrees. The ridge will give way to some weak
troughing in the Pacific NW early next week, but the dome of upper level high pressure remains a
fixture over the Southwest. Daytime highs exceeding 110 degrees are likely from the Great Valley of
California on south into the Desert Southwest. Sweltering conditions will also be experienced in
portions of the Intermountain West much of the period. One region's excessive heat typically means
another is much cooler; in this case, the Central Plains and Mississippi Valley where daily
temperature anomalies may range between 10 and 15 degrees below normal next week.
Precipitation-wise, the corridor with the wettest areas versus normal are most likely to occur in
the Southeast and Mid-Atlantic. Early in the period, a departing frontal system may generate areas
of moderate-to-heavy rainfall in the Mid-Atlantic. Given the antecedent rainfall and overly
saturated soil across the region, rainfall rates around 1" could lead to flash flooding. It is
worth noting there remains a considerable amount of model spread on positioning of the rainfall
axis, how much rain is observed, and timing of the storm system's departure. Meanwhile, the
longwave trough set-up across the east-central U.S. will promote a stalled front over the Southeast
and rich Gulf moisture funneling over the region. By Tues. Aug 18th, a wave of low pressure is
forecast to develop over the Southeast and promote heavy showers and storms across the region.
Portions of the Carolinas and Georgia are currently most at risk for receiving heavy rainfall in
forecast days 5-6. An upper trough may dig as far south as the Gulf Coast by days 6-7. Should this
occur, the threat for heavy rainfall could expand farther west into the Deep South and deeper into
In Alaska, a low pressure system is forecast to spin offshore of Panhandle this weekend. Moisture
inflow with this cyclone could lead to heavy rain particularly in the Panhandle where a couple
inches of rainfall are possible. Another low pressure system is currently forecast to track through
the Bering Sea next week, while another front drops southward across the northern part of the
state. There is some potential for gusty wind and heavy rain with these features in southwestern
Alaska, but large variability in model guidance persists, thus drawing hazard areas there are low
confidence at this time. Additionally, another large upper low is forecast to track through the
Gulf of Alaska by days 6-7, potentially leading to more heavy rainfall towards the middle of next
week in the Panhandle. Temperatures are expected to be warmer than average across western regions
and interior Alaska through early next week, with highs in the 70s and even nearing 80 degrees. Far
northern Alaska may begin to cool to slightly below normal levels by mid-week.
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