…Record heat relents over the Southern Plains as the heat shifts
northward into the central/northern Plains and Midwest…
…Severe storms and isolated flash flooding possible for the Northern
Plains/Upper Midwest Sunday-Monday…
…Daily monsoonal thunderstorms continue across the Four Corners region,
shifting eastward into the southern Rockies/High Plains…
As the cool upper trough pushes farther inland across the western U.S.,
the heatwave over portions of the Southern Plains will gradually relent
during the next couple of days. Meanwhile, deep southerly flow ahead of
the upper trough will direct the heat farther north into the central and
northern Plains today before spreading into the Midwest on Monday, then
reaching into the Great Lakes on Tuesday. The area of major HeatRisk
today will expand well to the north across much of the central and
northern Plains into the upper Midwest. By Monday into Tuesday, extreme
HeatRisk is forecast to overspread the Midwest and toward lower Michigan
where maximum heat indices are forecast to reach well into the 90s to the
mid-100s in the afternoon, prompting widespread heat-related advisories
and warnings. Extra caution should be observed by those without effective
air conditioning and anyone who must be outdoors should remain adequately
hydrated.
A cold front marking the leading edge of a large dome of cool air over the
western U.S. will reach into the Northern Plains on Monday, bringing
relief to the heat into the region. However, the cold front will also
bring a period of inclement weather across the northern Plains on Monday,
followed by the possibility of severe thunderstorms by Monday night into
Tuesday toward the upper Midwest. This is in response to strong
upper-level dynamics ahead of the upper trough interacting with a low
pressure system that is forecast to form along the cold front over the
northern Plains. The Storm Prediction Center highlighted an area of
enhanced risk for severe weather across the northern Plains toward the
upper Midwest from Monday into early Tuesday, with a chance for
potentially larger hail and significant damaging winds. Some locally
heavy rainfall and isolated flash flooding will also be possible. By
early Tuesday, the severe weather threat is forecast to shift east into
the Great Lakes with areas of heavy rain farther north from the upper
Midwest to the upper Great Lakes as the low pressure system passes to the
south.
Across the Southwest, daily monsoonal thunderstorm chances will continue,
initially focusing over the Four Corners region today before shifting east
to mainly across the southern Rockies for Monday and Tuesday. Deep
moisture and moderate instability will lead to some more intense
thunderstorms with locally heavy downpours along with some isolated flash
flooding especially for terrain sensitive areas such as burn scars.
Besides the rainfall, the big story across the West the next few days will
be the much below average temperatures expected behind a strong cold
front. Widespread high temperatures in the 60s and 70s will be common
across the Pacific Northwest, northern Rockies, Great Basin, and northern
California, with near record low maximum values for some locations. Lows
are dipping into the 40s and even 30s this morning for much of the
interior Pacific Northwest and Great Basin where Frost Advisories are in
effect in portions of Nevada. Some post-frontal showers and storms over
portions of the Great Basin will expand across the northern Rockies into
the northern High Plains tonight into Monday, and then across the northern
Plains later on Monday into early Tuesday. Elsewhere, some showers and
storms with moderate to locally heavy rainfall will be possible Monday
into Tuesday over New England when a back-door upper-level wave passes
over the region. Daily showers and thunderstorms will also be possible for
Florida and along the Gulf Coast with a lingering frontal boundary in the
region. Over the Pacific Northwest, showers associated with the next
system from the Pacific are forecast to arrive Monday night into early
Tuesday.
Kong/Putnam
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
