…Flash flooding and severe weather threat forecast to stretch from the
central Plains to the Midwest over the next few days…
…Potentially dangerous heat anticipated across the southern Plains,
lower Mississippi Valley, and Gulf Coast…
…Fire weather concerns and poor air quality continues for portions of
the Pacific Northwest, Northern Rockies, and Great Basin…
A mid-August weather pattern continues this week with numerous areas of
scattered thunderstorms impacting the Nation. A quasi-stationary front
currently stretching from the Southeast to the central High Plains will be
the focus for much of this activity, with the boundary eventually forecast
to lift northeast into the Midwest by Wednesday night due to a deepening
low pressure system in the central Plains. The most likely weather hazard
over the next few days with developing thunderstorms is expected to be
associated with heavy rainfall creating instances of flash flooding, as
well as the potential for some severe weather. Specifically, three
separate areas along the front stand out today (Tuesday) as having the
greatest chances for scattered flash floods. Parts of South Carolina
remain sensitive to locally heavy rain as the area continues to contain
saturated ground conditions, leading to a continued threat for flash
flooding due to slow-moving thunderstorms, with a Slight Risk of Excessive
Rainfall (level 2/4) in effect. Further west into the Midwest/central
Plains, another organized convective system is expected Tuesday
evening/overnight, with a narrow corridor of impressive rainfall totals
expected within a few hours centered over south-central Missouri, covered
by an associated Slight Risk of Excessive Rainfall. Additionally, a Slight
Risk of Excessive Rainfall is in place for northeast Colorado with another
round of storms containing intense rainfall rates Tuesday evening as
activity forms along the leeward side of the Rockies and pushes eastward.
The Storm Prediction Center has also included a Slight Risk of severe
weather (level 2/5) mainly for some isolated damaging winds gusts.
Residents and visitors are advised to have multiple ways of receiving
warnings, have a plan should flash flooding occur, and never drive through
flooded roadways. The heavy rain and thunderstorm activity is anticipated
to gradually shift eastward into the Midwest on Wednesday along with the
strengthening low pressure system and lifting warm front. The focus for
heaviest rainfall is currently expected with ongoing storms Wednesday
morning over Missouri, and then another round of storms Wednesday
afternoon/evening along the lifting warm front in Iowa and southern
Minnesota, with a Slight Risk of Excessive Rainfall covering these
regions. Some severe weather will also be possible given strengthening
wind fields with an approaching upper-level wave, with a Slight Risk over
the Middle Missouri Valley for the threat of large hail and damaging
winds. Then, on Thursday, the system will push further eastward, with a
similar flash flooding/severe weather scenario expected. Storms over the
Middle Mississippi Valley/Great Lakes will initially pose a severe weather
threat with some large hail possible before transitioning into more of a
flash flood threat Thursday evening/overnight downstream further into the
Great Lakes and Lower Ohio Valley.
Dangerous summer heat will be confined to the southern U.S. this week as
highs into the upper 90s and triple digits span from the Southwest to the
Gulf Coast. The most anomalous and potentially dangerous heat is forecast
across the southern Plains and Gulf Coast States through the end of the
week as highs reach up to 10 degrees above the climatological average for
mid-August. Elevated humidity levels will lead to maximum heat indices up
to 110 degrees during the day and low temperatures only dipping into the
upper 70s and low 80s at night. People spending greater time or effort
outdoors, or in a building without effective cooling, are at an increased
risk of heat-related illnesses. Elsewhere, temperatures will actually be
rather pleasant for mid-August, with many locations near or below average.
Highs in the 80s (and even some 70s) will be common across the northern
tier of the country. Locations further south from the Great Basin into the
central Plains and Ohio Valley/Mid-Atlantic will tend to be warmer, with
highs in the mid-80s to low 90s.
A persistent pattern supporting fire weather concerns across much of the
central and northern Great Basin is forecast to continue today and
Wednesday with the threat of lightning with dry thunderstorms, dry
terrain, and periods of gusty winds. Red Flag Warnings remain in place
from eastern Oregon to Idaho. Ongoing wildfires also continue to spread
smoke into the atmosphere, leading to poor air quality.
Putnam/Snell
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
