ACUS02 KWNS 041734
SWODY2
SPC AC 041733

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1233 PM CDT Sun Aug 04 2024

Valid 051200Z - 061200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHERN FL
INTO EASTERN GA AND SOUTHERN SC...ACROSS PORTIONS OF THE UPPER
MIDWEST...AND FROM THE UPPER OH VALLEY INTO NEW ENGLAND...

...SUMMARY...
A few severe thunderstorms are possible Monday into Monday night
from the Upper Ohio Valley into New England, across portions of the
Upper Midwest, and from northern Florida into southern Georgia and
southeast South Carolina.

...Synopsis...
A belt of enhanced westerlies is forecast to extend across the
length US/Canada border, from the Pacific Northwest through the
northern Plains/Upper Midwest and Northeast. Several shortwave
troughs will be embedded within these westerlies, the most prominent
of which is a wave that is forecast to progress quickly from central
Ontario through southern Quebec and northern ME. Another,
low-amplitude shortwave trough is expected to move through the
northern Plains, Upper Midwest, and Upper Great Lakes.

Expansive upper ridging is expected to remain centered over the Four
Corners,  extending from the southern Great Basin vicinity through
the lower MS Valley. Tropical Cyclone Debby is expected to move
between the eastern periphery of the Four Corners ridge and
subtropical ridging over the western Atlantic, progressing across
northern FL and reaching the southeast GA/southern SC vicinity by
early Tuesday morning.

Surface pattern early Monday is expected to feature a low over the
central SD/NE border vicinity, with a stationary front extending
eastward from this low across central IA, northern IL, and southern
Lower MI before arcing more northeastward along the St. Lawrence
Valley to another low over New Brunswick. Eastern portion of this
front is expected to progress southeastward across the Northeast
throughout the day, while the portion of the front closer to the
SD/NE surface low transitions to a warm front amid southerly
low-level flow ahead of the low.

A cold front will extend westward from the SD/NE surface low into
eastern WY, where it intersects lee troughing extending across the
northern and central High Plains. This front is expected to push
southward across the central Plains as the low progresses
eastward/southeastward through IA.

...Northern FL into southern GA and far southern SC...
Tropical cyclone Debby is forecast to progress across northern FL
throughout the day, reaching the southeast GA/southern SC vicinity
by early Tuesday morning. Strong low-level flow attendant to this
system will support the potential for tornadoes within deeper, more
persistent updrafts. These updrafts are most likely in the areas
where dewpoints exceed 74/75 deg F. This appears most likely across
northern FL and southeast GA. However, a more westerly track would
allow this more favorable low-level moisture to penetrate inland
more of southern GA and perhaps even southern SC. 5-percent tornado
probabilities were adjusted northward to account for this
possibility.

...Northern OH Valley through the Northeast/New England...
Thunderstorm development is anticipated Monday afternoon along the
length of the cold front extending from ME into northern IN/OH.
Dewpoints ranging from the mid 60s across central ME to the low 70s
across IN/OH will support moderate buoyancy, with the strongest
buoyancy across the OH Valley where greater low-level moisture
exists. Moderate mid-level flow will extend across the region as
well, with the stronger flow and greater vertical shear expected
across New England. While there is some displacement between the
strongest shear and greatest buoyancy, there is still enough overlap
to support scattered strong to severe storms, including even some
supercells across New England. Damaging gusts will be the primary
severe hazard.

...Upper Midwest...
Late afternoon/evening thunderstorm development is expected near the
surface low and associated warm front moving across IA. The airmass
will be very unstable, supported by temperatures in the upper
80s/low 90s and dewpoints in the mid 70s. Even so, there is some
question whether true warm sector storms will initiate, given the
potential for significant mixing and warm mid-level temperatures.
Storms north of the warm front could still pose a severe risk, with
large hail and damaging gusts as the primary threats. A
surface-based, warm sector storm would have these threat as well,
but with an added potential for very large hail and potentially even
a tornado or two, given the potential for a supercellular mode.
After the initial cellular mode, a quick transition to a more
linear/forward-propagating mode is expected.

...Northern Rockies...
A low-amplitude shortwave trough is forecast to move through the
northern periphery of the ridge across the northern Rockies Monday
afternoon. Ascent and increased mid-level moisture attendant to this
wave combined with orographic ascent and deep boundary-layer mixing
will help support afternoon/evening thunderstorms. Deep-layer
vertical shear is strong enough to some organized, more persistent
updrafts. High storm bases and steep low-level lapse rates will help
support damaging gusts with the strongest storms.

..Mosier.. 08/04/2024

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