weather

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Mon Aug 05 2024
Valid 12Z Mon Aug 05 2024 – 12Z Wed Aug 07 2024

..Hurricane Debby is expected to cause potentially catastrophic Flash and
Urban Flooding, life-threatening storm surge, and strong winds across
portions of Florida and the Southeast…

…There’s potential for Excessive Rainfall and Severe Thunderstorms
across portions of the Upper Midwest, Lower Great Lakes and Northeast
through Tuesday…

…There are Excessive Heat Warnings over parts of Central/Southeastern
California and the Southwest and Heat Advisories over parts of the Lower
Mississippi Valley…

Hurricane Debby will make landfall this morning over Florida’s Big Bend
region, where Hurricane Warnings are in effect. Life-threatening storm
surge is possible along portions of Florida’s Gulf Coast, where Storm
Surge Warnings are in effect. Widespread thunderstorms are likely to
continue across Florida and spread into Georgia and the Southeast Coast
today. The Storm Prediction Center issued a Slight Risk of Severe
Thunderstorms (level 2/5) for portions of northern Florida through
southern/coastal Georgia and into South Carolina’s central coast, where
the chance for tornadoes is greatest. Elsewhere, Tropical Storm conditions
are are expected along Florida’s west coast including the Tampa Bay area
today.

Potentially historic heavy rainfall, associated with Hurricane Debby,
across southeast Georgia and South Carolina through Friday morning will
likely result in areas of catastrophic flooding. Heavy rainfall will
likely result in considerable flooding impacts from portions of central
and northern Florida through the Coastal Plains of the Carolinas through
Friday. There are High Risks (at least 70%) of Excessive Rainfall
stretching from Florida’s Big Bend region up through coastal Georgia and
into South Carolina’s southern coast today followed by another on Tuesday
along the Georgia–South Carolina Coastline. Anywhere between 7-15 inches
of rain, with locally higher amounts, are possible from north-central
Florida to South Carolina’s northern coast over the next 48 hours. For
more information go to hurricanes.gov.

A slow moving cold front extending from the Northern High Plains to the
Northeast will be the focus for scattered showers and thunderstorms across
the northern tier states down to the Midwest and Mid-Atlantic over the
next couple of days. Today, showers and thunderstorms are expected to
develop and potentially produce severe thunderstorms and Excessive
Rainfall over parts of the Upper Midwest and interior Northeast. Slight
Risks of Flash Flooding (at least 15%) and Severe Storms are in effect
over the aforementioned areas today. The threat for heavy rainfall shifts
into the New York Tri-State area on Tuesday where another Slight Risk of
Excessive Rainfall is in effect due to the potential involvement of
tropical moisture from Debby. A low pressure system is expected to develop
over the Northern High Plains of Montana on Tuesday and contribute to
supercell/severe thunderstorm activity that evening. Severe wind
gusts/hail will be the primary threats from these storms.

High temperatures will likely remain well below average across the
Northern Plains and Upper Midwest over the next several days, while
Excessive Heat Risk grows across the Central Gulf Coast/Lower Mississippi
Valley. Excessive Heat Warnings are in effect across the Desert Southwest
and portions of California’s southern/central Valley. Monsoonal storms are
likely to continue across the Southwest and Four Corners region this week
with a Slight Risk of Excessive rainfall over far south-central Arizona on
Tuesday.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Sun Aug 04 2024
Valid 12Z Sun Aug 04 2024 – 12Z Tue Aug 06 2024

…Tropical Storm Debby is expected to cause considerable Flash and Urban
Flooding, life-threatening storm surge, and strong winds across portions
of Florida and the Southeast Coast beginning today…

…Excessive Rainfall and Severe Thunderstorms possible from the Upper
Midwest across the Great Lakes and into the interior Northeast on Monday
and Tuesday…

Tropical Storm Debby is currently forecast to strengthen while it tracks
along Florida’s Gulf Coast today. Debby may intensify into a Hurricane
Monday morning before making landfall near Florida’s Big Bend region,
where a Hurricane Warning is in effect. Life threatening storm-surge
inundation is possible along portions of Florida’s Gulf Coast from Aripeka
to Indian Pass. Strong winds will likely cause significant damage to
unprotected infrastructure along the storm’s path. There’s a potential for
isolated tornadoes across western and northern portions of the Florida
Peninsula through Monday, which is consistent with the Storm Prediction
Center’s convective outlooks, which depict Slight Risks (level 2/5) of
Severe Thunderstorms for those days. There is a Moderate Risk (at least
40%) of Excessive Rainfall leading to Flash Flooding across portions of
northwestern Florida today where the bulk of Debby’s precip shield will
cause impacts. Debbie is forecast to slow and cause considerable to
historic Flash, Urban and river Flooding across portions of northern
Florida through southeastern Georgia and into coastal South Carolina on
Monday and Tuesday. Flood Watches are in effect for parts of coastal
Georgia and South Carolina. For more information go to hurricanes.gov

Elsewhere, a low pressure system, emerging from the Northern High Plains,
will produce scattered showers and thunderstorms across the Northern
Plains tonight before spreading storms into the Upper Midwest, Great Lakes
and interior Northeast on Monday. There’s a Slight Risk (at least 15%) of
Excessive Rainfall as well as a Slight Risk (level 2/5) of Severe
Thunderstorms over portions of the Upper Midwest/Great Lakes on Monday.
Downstream of this, the attendant stationary front draped across the
interior Northeast will be the focus for more severe storms from Lake Erie
to New England where another Slight Risk of Severe Thunderstorms is in
effect.

High temperatures will be below average across the northern tier states
this week in response to unsettled weather associated with the
aforementioned storms in the Northern Plains. Temperatures in the
Central/Southern Plains and Middle/Lower Mississippi Valley will be above
average as southerly flow persists out ahead of the descending cold front
to the north. Numerous warm overnight lows may tie or break existing
records in the Desert Southwest over the next couple of nights. Monsoonal
rain continues over portions of the Southwest and Four Corners region this
week with isolated Flash Flooding possible over vulnerable surfaces
including burn scars and slot canyons.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Sat Aug 03 2024
Valid 12Z Sat Aug 03 2024 - 12Z Mon Aug 05 2024

...A dangerous heat wave shifts from the Paciifc Northwest to the Great
Plains...

...Stormy conditions and flash flood potential across portions of the
Eastern U.S. this weekend...

...Potential Tropical Cylone Four will bring hazardous rainfall, strong
winds and life threatening storm surge inundation to portions of Florida
this weekend...

Upper-level ridging over the West will promote above average temperatures
across the region this weekend. Upper troughing over the East Pacific will
work in combination with the Western ridge to produce high temperatures in
the upper 90s to low 100s across much of the Northwest into the
Northern/Central Plains today. Warm overnight lows in the upper 60s to low
70s will represent 20-30 degree anomalies for much of the Northern Great
Basin/Rockies/High Plains tonight. The lack of overnight relief from the
heat will affect anyone without effective cooling and/or adequate
hydration. A small bit of mid-level energy will contribute to a severe
thunderstorm threat over the Northern Plains and Upper Midwest this
afternoon/evening. Damaging winds, isolated Flash Flooding and hail will
be the primary threats there. Shortwave energy spinning across the
northern periphery of a mid-level closed high pressure bubble will bring
some scattered showers, thunderstorms and cooler temperatures to the
northern tier of the country beginning on Sunday. Meanwhile, warm air
shifts into the Central Plains and Middle Mississippi Valley through early
next week.

Elsewhere, upper troughing over the Ohio/Tennessee Valley will promote
scattered thunderstorms up and down the East Coast today. Slight Risks of
Excessive Rainfall and Severe Thunderstorms are in effect from the
Tri-State area down to the Florida Panhandle. Damaging wind gusts and
Flash Flooding will be the primary concerns from these storms. Some
lingering showers and thunderstorms are expected on Sunday with only an
isolated threat of severe storms and Flash Flooding across the coastal
Mid-Atlantic/Northeast.

Tropical Depression Four is forecast to strengthen into a Tropical Storm
as it tracks west of the Florida Peninsula this weekend. Heavy rainfall,
strong winds and life threatening storm surge inundation are all possible
along the western coast of the state beginning today. Heavy rainfall,
strong winds and storm surge are also possible over northern Florida and
the Southeast U.S. Coast Sunday evening into early next week. Tropical
Storm Warnings and Storm Surge Watches are in effect along Florida's Gulf
Coast while Tropical Storm Watches extend farther out across the other
Gulf Coast states. For more information go to hurricanes.gov.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Fri Aug 02 2024
Valid 12Z Fri Aug 02 2024 – 12Z Sun Aug 04 2024

…A dangerous heat wave will impact much of the East Coast, Southeast and
Northwest through tonight…

…Excessive Rainfall concerns across portions of the Eastern U.S. this
weekend…

…Monsoonal storms continue across the Southwest/Four Corners through the
weekend…

A familiar upper-level pattern over the lower 48, with ridging in the West
and troughing over the Great Lakes and Ohio/Tennessee Valley, will support
heat waves and excessive rainfall concerns this weekend. High temperatures
in the 100s will represent a 10-15 degree positive anomaly across the
Northwest today. Some of these temperatures will tie or break records.
Overnight temperatures in the upper 60s to upper 70s will tie or break
widespread temperature records across the West tonight as well. The
combination of very hot daytime conditions and a lack of overnight relief
could harm those without adequate shelter or hydration. Cloudy conditions
will support near record breaking warmth over portions of the coastal
Northeast and Florida peninsula tonight.

Showers and thunderstorms will develop along a cold front moving through
the Midwest today and spread eastward toward the East Coast. Slight Risks
of Excessive Rainfall leading to Flash Flooding are in effect for portions
of the Lower Great Lakes, Ohio Valley and Northeast today due to the
higher rates within some of the storms that move through those areas.
Orographic lift over portions of the Central/Southern Appalachians will
promote additional Flash Flooding concerns, hence another Slight Risk area
for parts of eastern Tennessee, southeastern Kentucky, southwestern
Virginia, western North Carolina and northern Alabama/Georgia. The cold
front slows down across the Mid-Atlantic/Southeast on Saturday and becomes
the focus for additional Excessive Rainfall concerns, due in part to a
significant moisture plume from the Tropics. A Slight Risk of Excessive
Rainfall is in effect for portions of southeastern Virginia down into the
Carolina/Georgia Piedmont.

A tropical disturbance is forecast to impact the Florida Peninsula
beginning late tonight when heavy rainfall and thunderstorms are supposed
to spread across southern Florida and eventually work their way up the
peninsula on Saturday. A Slight Risk of Excessive Rainfall is in effect
for portions of southern Florida on Saturday as a result. Monsoonal
moisture is expected to continue flowing into the Southwest/Four Corners
region this weekend. Scattered showers and thunderstorms may lead to
isolated Flash Flooding across portions of the aforementioned areas,
particularly burn scars and slot canyons.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Thu Aug 01 2024
Valid 12Z Thu Aug 01 2024 – 12Z Sat Aug 03 2024

…Dangerous heat engulfs much of the country as one heatwave continues
from the Southern Plains to the Southeast/Mid-Atlantic and another begins
in the West…

…Severe weather and flash flooding expected for portions of the Midwest
Thursday…

… Locally heavy monsoonal shower and thunderstorm chances continue for
the Southwest…

Widespread, dangerous heat will unfortunately be the main weather story
for much of the country this week as one heatwave continues for the
Plains, Middle/Lower Mississippi Valley, Southeast, and Mid-Atlantic, and
another heatwave begins over portions of the West. A strong upper-level
ridge will remain in place over the southern-tier of the U.S. the next
couple days, allowing for high temperatures to reach into the low 100s
over portions of the Southern Plains/High Plains, the upper 90s to low
100s for the Lower Mississippi Valley, and the upper 90s for the Southeast
into the southern Mid-Atlantic. High humidity values for areas east of the
High Plains will bring heat indices into the 105 to 110 degree range,
potentially as high as 115 for parts of the Lower Mississippi Valley, with
many areas under heat-related advisories or warnings. The combination of
hot temperatures/high heat indices, as well as very warm morning lows only
dropping into the mid- to upper 70s, will be dangerous to anyone without
access to adequate air conditioning. Temperatures warming into the upper
80s/low 90s with periods of higher humidity will lead to some muggy,
potentially dangerous conditions for portions of New England as well,
particularly on Friday. An approaching cold front will bring relief to
northern portions of the Southern Plains and Middle Mississippi Valley on
Friday, with the expectation the heat wave will begin to wane for most
locations through the weekend.

In the West, an upper-level ridge will also begin to build northward,
sending high temperatures across much of the northern tier of the West
10-20 degrees above mid-Summer averages. Forecast highs Thursday are into
the upper 90s/low 100s for the inland Pacific Northwest/northern Great
Basin and mid- to upper 90s for the northern Rockies/High Plains.
Temperatures will get even hotter on Friday, with highs into the low to
mid-100s for most locations. Many near record-tying/breaking highs are
possible. Similar to areas further east, many heat-related advisories and
warnings have been issued as this heat will also reach dangerous levels
for the general public. Smoke from area wildfires will also continue to
plague parts of the region, resulting in hazy conditions and poor air
quality, and the risk for more wildfires will increase as the hot, dry
conditions settle in.

An upper-level low/accompanying surface frontal system traversing the
northern side of the ridge over the southern tier of the U.S. will bring
another round of showers and thunderstorms to the Midwest Thursday. High
surface moisture leading to very strong instability will support intense
thunderstorm development through the afternoon across the warm sector
ahead of an approaching cold front, with lingering outflow boundaries from
overnight convection helping to trigger individual and clusters of storms.
Sufficient shear with the passing upper-level wave will lead to the threat
of severe weather, with a Slight Risk (level 2/5) from the Storm
Prediction Center covering Illinois, Indiana, Kentucky, and southwestern
Ohio, mainly for the threat of some damaging winds. The threat for some
intense downpours given the high moisture/strong storms, and potential for
some more widespread, organized clusters of storms, will lead to some
heavier rainfall totals and the risk for flash flooding. Many of these
locations have seen recent heavy rainfall given repeated rounds of
organized storms passing through, leading to wetter antecedent conditions
more sensitive to any additional rainfall. A Slight Risk of Excessive
Rainfall (level 2/4) covers much of same region from northeastern Illinois
southeast through Indiana/western Ohio and into eastern Kentucky. Some
slow moving storms producing heavy rainfall under the passing upper-low
may also lead to some flash flooding, with the Slight Risk extending
northwest into southern Wisconsin. Some more isolated storms will be
possible further east into the Appalachians and Mid-Atlantic Thursday.
Additional storms will be possible across the region Friday as the system
shifts eastward, with a greater chance of storms spreading into the
Appalachians and the Mid-Atlantic. Some isolated severe storms and
instances of flash flooding will be possible. A lingering upper-level
weakness will lead to scattered showers and thunderstorms over Florida and
portions of the Southeast Thursday, with moderate to locally heavy
rainfall possible, especially over the Florida Peninsula. More widely
scattered storms will remain possible Friday.

Persistent Monsoonal conditions over the Southwest will continue to bring
daily shower and thunderstorm chances. Sufficient moisture across the
region will lead to the threat for some locally heavy downpours and an
isolated flash flooding, particularly over terrain sensitive areas such as
burn scars. A lingering frontal boundary will lead to some storms over
portions of the southern High Plains as well on Thursday, and a subtle
upper-level wave along the edge of the upper-ridging will bring storm
chances northwestward into portions of California Friday, particularly in
vicinity of the Sierra Nevada. Similar to areas further north, forecast
high temperatures more broadly in the region will be trending hotter and
above average, with 90s and low 100s for most locations outside of the
California Coast, and mid-100s to low 110s for the Desert Southwest.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
428 PM EDT Tue Jul 30 2024
Valid 00Z Wed Jul 31 2024 – 00Z Fri Aug 02 2024

…There is an Enhanced Risk of severe thunderstorms over parts of the
Central Plains and Middle Mississippi Valley on Tuesday evening and
Wednesday with a Slight Risk of severe thunderstorms over parts of the
Ohio Valley on Thursday…

…There is a Slight Risk of excessive rainfall over parts of the Middle
Mississippi Valley and Ohio/Tennessee Valleys on Tuesday evening and
Wednesday…

…There is a Slight Risk of excessive rainfall over parts of Northern New
England and Southwest on Wednesday and over parts of the Ohio Valley on
Thursday…

…There are Excessive Heat Watches over parts of the Pacific Northwest
and Excessive Heat Warnings/Advisories over parts of the Central/Southern
Plains, Middle/Lower Mississippi Valley, Ohio/Tennessee Valleys, and the
Southeast.

A front with a wave of low pressure over the Northern High Plains will
move slowly eastward to the Ohio Valley/Great Lakes by Thursday. The
associated boundary will aid in triggering showers and severe
thunderstorms over parts of the Central Plains, Middle Mississippi Valley,
and parts of the Ohio/Tennessee Valleys. Therefore, the SPC has issued an
Enhanced Risk (level 3/5) of severe thunderstorms over the Central Plains
and Middle Mississippi Valley through Wednesday morning. The hazards
associated with these thunderstorms are frequent lightning, severe
thunderstorm wind gusts, hail, and a few tornadoes. Also, there is a
threat of severe thunderstorm wind gust of 65 knots, or greater over parts
of the Central Plains, Middle Mississippi Valley and hail two inches, or
greater over parts of the Central Plains.

In addition, showers and thunderstorms will create heavy rain over parts
of the Middle Mississippi Valley and Ohio/Tennessee Valleys. Therefore,
the WPC has issued a Slight Risk (level 2/4) of excessive rainfall over
parts of the Middle Mississippi Valley and Ohio/Tennessee Valleys through
Wednesday morning. The associated heavy rain will create mainly localized
areas of flash flooding, with urban areas, roads, small streams, and
low-lying areas the most vulnerable.

A second area of severe thunderstorms is forecast over parts of the
Northern Plains. Therefore, the SPC has issued a Slight Risk (level 2/5)
of severe thunderstorms over parts of the Northern Plains through
Wednesday morning. The hazards associated with these thunderstorms are
frequent lightning, severe thunderstorm wind gusts, hail, and a few
tornadoes.

As the wave of low-pressure moves eastward overnight Tuesday into
Wednesday, the system will create showers and severe thunderstorms over
parts of the Middle Mississippi Valley. Therefore, the SPC has issued an
Enhanced Risk (level 3/5) of severe thunderstorms over the Middle
Mississippi Valley from Wednesday through Thursday morning. The hazards
associated with these thunderstorms are frequent lightning, severe
thunderstorm wind gusts, hail, and a few tornadoes. Moreover, there is an
increased threat of severe thunderstorms wind gust of 65 knots or greater
over parts of the Central/Southern Plains and Upper/Middle Mississippi
Valley. Additionally, there is a threat of hail two inches or greater over
parts of the Northern/Central Plains and Upper Mississippi Valley.

Furthermore, showers and thunderstorms will produce heavy rain over parts
of the Northern Plains, Upper/Middle Mississippi Valley, and Ohio Valley.
Therefore, the WPC has issued a Slight Risk (level 2/4) of excessive
rainfall over parts of these areas from Wednesday through Thursday
morning. The associated heavy rain will create mainly localized areas of
flash flooding, with urban areas, roads, small streams, and low-lying
areas the most vulnerable.

Moreover, upper-level energy and a plume of moisture moving over New
England will produce areas of heavy rain. Therefore, the WPC has issued a
Slight Risk (level 2/4) of excessive rainfall over parts of Northern New
England from Wednesday through Thursday morning. The associated heavy
rain will create mainly localized areas of flash flooding, with urban
areas, roads, small streams, and low-lying areas the most vulnerable.

Similarly, upper-level energy and a plume of moisture will create areas of
heavy rain over parts of the Southwest. Therefore, the WPC has issued a
Slight Risk (level 2/4) of excessive rainfall over parts of the Southwest
from Wednesday through Thursday morning. The associated heavy rain will
create mainly localized areas of flash flooding, with urban areas, roads,
small streams, and low-lying areas the most vulnerable.

On Thursday, the wave of low pressure continues to move eastward,
producing showers and severe thunderstorms over parts of the Ohio Valley.
Therefore, on Thursday, the SPC issued a Slight Risk (level 2/5) of severe
thunderstorms over parts of the Ohio Valley. The hazards associated with
these thunderstorms are frequent lightning, severe thunderstorm wind
gusts, hail, and a few tornadoes.

Likewise, the showers and thunderstorms will create heavy rain over parts
of the Ohio Valley/Great Lakes. Therefore, the WPC has issued a Slight
Risk (level 2/4) of excessive rainfall over parts of the Ohio Valley/Great
Lakes on Thursday. The associated heavy rain will create mainly localized
areas of flash flooding, with urban areas, roads, small streams, and
low-lying areas the most vulnerable.

Meanwhile, upper-level ridging will build over the Pacific Northwest,
spawning Excessive Heat Watches over parts of the region. The upper-level
ridging will aid in creating intense and widespread heat across portions
of the West late this week. High temperatures 10-15 degrees above normal
are expected across the Northwest and Northern High Plains later this
week, where several daily record high temperatures are forecast.

Moreover, the upper-level high will develop over the central portion of
the country, which will foster Excessive Heat Warnings/ Heat Advisories
over parts of the Central/Southern Plains, Middle/Lower Mississippi
Valley, Ohio/Tennessee Valleys, and the Southeast. The associated
dangerous heat, with high temperatures exceeding 100F and heat indices
near 110F, persists over the South-Central Plains and Mid-South through
Thursday. Multiple days of Major to Extreme HeatRisk are forecast for
portions of the southern Plains to the Southeast. These levels of heat
mean health impacts become more likely in general, and may occur in ANYONE
without adequate hydration or cooling

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Tue Jul 30 2024
Valid 12Z Tue Jul 30 2024 – 12Z Thu Aug 01 2024

…Daily scattered flash flooding and severe weather from the Mid-Atlantic
into the Northern Plains/Midwest…

…Dangerous mid-summer heat wave to expand across the Central U.S. and
Southeast; more hot weather across the West…

An active, unsettled pattern will continue across the eastern half of the
Lower 48 as an elongated frontal system with access to abundant moisture
and instability leads to repeat bouts of thunderstorms through midweek.
This will maintain a daily threat of scattered (level 2/5) flash flooding
and severe weather from the Mid-Atlantic, Ohio/Tennessee Valley, Midwest,
and Northern Plains through Thursday. Daily isolated flash flooding
chances should also continue across the Southwest tied to the monsoon.

Thunderstorms aside, heat will become the big story over the Central and
Southeast U.S. this week as an upper-level high strengthens. Forecast high
temperatures Monday and Tuesday are expected to soar into the triple
digits over the Central Plains, with upper-90s to low 100s to the west
over much of the High Plains, and mid-to upper 90s for the Middle and
Lower Mississippi Valley. High humidity values over the Mississippi Valley
and eastern portions of the plains will lead to heat indices in the
105-110 degree range, potentially as high as 115 for some locations, with
widespread Excessive Heat Warnings and Advisories in place. Warm morning
lows only dropping into the mid- to upper 70s will provide little relief
from the heat overnight. This combination of hotter temperatures to the
west, higher heat indices to the east, and the multi-day duration of this
heat wave will increase the danger not only to more sensitive groups, but
also the general public, particularly those without adequate air
conditioning.

West of the Continental Divide, a troughing pattern and associated cool
weather over the West will give way to widespread warm weather by Thursday
as a stationary Pacific front washes away beneath widespread height rises
across the region. By Friday, we can expect high temperatures in the 90’s
and triple digits across much of the West which could challenge numerous
records across the region. Unfortunately, smoke from area wildfires will
also continue to plague parts of the West, particularly over portions of
the northern Great Basin, resulting in poor air quality and areas of
reduced visibility.

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
Mon Jul 29 2024
Valid 12Z Mon Jul 29 2024 – 12Z Wed Jul 31 2024

…Flash flooding possible in the Ohio/Tennessee Valleys and
central/southern Appalachians through early this week…

…Scattered severe thunderstorms forecast across portions of the Northern
Plains Monday and Upper Midwest Tuesday…

…Dangerous mid-summer heat wave to begin expanding across the central
U.S. on Monday…

Bouts of thunderstorms are expected to continue over portions of the
Ohio/Tennessee Valleys and spread further into the central/southern
Appalachians to start off the work week. An active upper-level pattern
featuring at least a couple shortwaves and an approaching surface frontal
system from the west will help to focus storm development over the
Ohio/Tennessee Valleys and eventually into the southern Appalachians
Monday. Plentiful moisture in place will also continue to lead to the
threat of heavier rain rates, with increasing storm coverage into the
evening and potential back building/repeated rounds of storms raising the
chance for locally heavy rainfall totals. As such, a Slight Risk of
Excessive Rainfall (level 2/4) is in place for the threat of some
scattered flash flooding. In addition, sufficient instability/shear will
be in place over the Ohio Valley for a couple more intense storms, as well
as the threat for a more organized storm complex later Monday evening. The
Storm Prediction Center has included a Slight Risk (level 2/5) for severe
weather as well mainly for the threat of damaging winds. A similar pattern
will be in place on Tuesday, with the focus shifting further into the
southern and central Appalachians as the upper-level energy and surface
frontal system move eastward. Another Slight Risk of Exessive Rainfall is
in effect here for additional instances of flash flooding. Outside of the
flash flooding threat, scattered thunderstorms with moderate to locally
heavy rainfall are expected more broadly over the Midwest/Southeast
Monday, and also over portions of New England as a coastal low approaches.
Rain chances will expand over the Mid-Atlantic/Northeast as the system
approaches from the west on Tuesday. Forecast high temperatures across the
East will vary depending on cloud/storm coverage, with mostly mid-80s to
low 90s expected.

Some additional storms will be possible further west along the frontal
boundary into the Upper Midwest and Northern Plains. Embedded upper-level
energy will help to trigger one round of storms over the Northern Plains
on Monday. Stronger upper-level flow will lead to more deep-layer shear
here than further east, with another Slight Risk of severe weather for the
threat of some very large hail as well as significant damaging winds if
storms consolidate/grow upscale into an organized system later in the
evening. Another round of severe weather is possible downstream over the
Upper Midwest Tuesday as yet another upper-level impulse helps to trigger
storms along the frontal boundary. Very high moisture will lead to strong
to extreme instability, with a Slight Risk in place for the chance of more
damaging winds.

Outside of the severe weather threat, heat will become the big story more
broadly over the central U.S. over the next few days as an upper-level
high strengthens/expands over the region. Forecast high temperatures
Monday and Tuesday are expected to soar into the low to mid-100s over the
Central Plains, with upper-90s to low 100s to the west over much of the
High Plains, and mid- to upper 90s for the Middle and Lower Mississippi
Valley. High humidity values over the Mississippi Valley and eastern
portions of the plains will lead to heat indices in the 105-110 degree
range, potentially as high as 115 for some locations, with widespread
heat-related warnings/advisories in place. Warm morning lows only dropping
into the mid- to upper 70s will provide little relief from the heat
overnight. This combination of hotter temperatures to the west, higher
heat indices to the east, and the multi-day duration of this heat wave
will increase the danger not only to more sensitive groups, but also the
general public, particularly those without adequate air conditioning.

A stagnant troughing pattern over the West will keep temperatures mostly
below average across the region, especially over portions of the Pacific
Northwest and northern Great Basin/Rockies. Forecast highs Monday-Tuesday
range between the 60s and 70s along the Pacific Coast, the 70s and 80s in
the Pacific Northwest and northern Great Basin/Rockies, the 80s and 90s
for interior California and the central Great Basin/Four Corners Region,
and 100s in the Desert Southwest. A cold front passing through the Pacific
Northwest will bring some rain chances on Monday, spreading into the
northern Rockies Tuesday. Smoke from area wildfires will also continue to
plague parts of the West, particularly over portions of the northern Great
Basin, resulting in poor air quality and areas of reduced visibility.