SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Thu Aug 08 2019
Valid 082000Z - 091200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHEAST...MID-ATLANITC...AND OHIO VALLEY...
...SUMMARY...
Strong to severe storms should continue to produce isolated damaging
wind gusts across parts of the Northeast into the Mid-Atlantic and
mid/upper Ohio Valley through this evening.
...20Z Update...
A bowing line segment producing wind damage and isolated measured
severe wind gusts will continue moving eastward across parts of
central/eastern NY this afternoon. This convection is occurring on
the nose of a mid-level jet, and there is potential for strong to
severe storms to persist into parts of western New England late this
afternoon and early evening where weak instability exists.
Therefore, have expanded wind probabilities eastward across this
region. Behind the line of ongoing storms, severe probabilities have
been reduced across western NY/PA and northern OH.
A few storms have formed across parts of southwestern/central NE
along a weak front. Even though large-scale forcing for ascent will
remain weak across this region owing to upper ridging remaining
centered over the Rockies, modestly enhanced mid-level winds and a
veering wind profile are resulting in enough shear to support
organized updrafts. Isolated strong to severe storms may occur
through the early evening along/south of the boundary, with both
large hail and severe wind gusts possible. Accordingly, have
expanded the Marginal Risk to include this area.
Across the southern Plains into the lower MS Valley, severe
probabilities have been confined to a narrow corridor along and
south of a convectively reinforced surface boundary. A weak
mid-level perturbation associated with prior convection is present
over north-central OK this afternoon per water vapor satellite
imagery. Some short-term guidance suggests that a couple storms may
strengthen across parts of central/eastern OK and then spread into
western/central AR through the early evening. Strong diurnal heating
has occurred to the south of the front, and isolated strong/gusty
winds and perhaps some hail could occur with any robust storms that
can form and then move southeastward along this boundary.
Persistent cloud cover has hampered diurnal heating across parts of
northern UT into far southern ID. The Marginal Risk has been
adjusted slightly in NV/UT based on radar trends and where low-level
lapse rates have been able to steepen this afternoon. With modest
instability and shear noted, isolated strong/gusty winds will
continue to be the main threat.
..Gleason.. 08/08/2019
.PREV DISCUSSION... /ISSUED 1121 AM CDT Thu Aug 08 2019/
...Synopsis...
A large trough will continue moving across eastern Canada and the
eastern U.S. today, with another large trough surrounding a very
slow-moving upper low over the eastern Pacific. In between, ridging
will continue to prevail over the Rockies and south-central U.S.
through tonight.
At the surface, a weak pressure field prevails. A subtle cool front
will continue crossing the lower Great Lakes/Ohio Valley today,
while remnants of a prior/weak front linger from the southeastern
U.S. west-northwestward into the Oklahoma vicinity. These two
boundaries, and weak disturbances aloft crossing the Great Basin
area ahead of the Pacific low/trough, will support showers and
thunderstorm activity, along with limited/local severe risk.
...NY/PA/OH/WV vicinity...
Showers and thunderstorms are ongoing across western New York and
adjacent northwest Pennsylvania, near a very weak cool front moving
across the region. As heating continues into the afternoon,
resulting in additional/modest destabilization, an increase in
convective coverage is expected, along with some uptick in intensity
-- aided by moderate westerly/west-northwesterly flow through a deep
layer. With this flow promoting rather quick eastward storm motion,
stronger convective elements will be capable of producing
gusty/damaging winds, that may reach severe levels locally. Risk
should continue through the afternoon, diminishing with the onset of
diurnal cooling early this evening. For additional short-term
information, please refer to SWOMCD #1674.
...Southern KS/OK east-southeast to northern MS...
A large area of weak convection is ongoing from the southern Plains,
east across the Ozarks to the northern Mississippi Vicinity. An
outflow boundary is observed from Oklahoma southeast to northern
Mississippi, on the southern fringe of a stronger west-northwest to
east-southeast band of storms. Some intensification of storms
within this band, and/or new convective development near the
aforementioned outflow, may -- given the favorably moist/gradually
destabilizing airmass away from active convection -- intensify to
occasionally severe levels. Gusty/locally damaging winds may occur
with the strongest storms, along with some risk for large hail.
Storms -- and possibly some severe risk -- will continue into the
overnight hours, as a south-southwesterly low-level jet develops
across the southern Plains, aiding continued storm
development/sustenance.
...Central and southern high Plains...
Daytime heating of a seasonally moist boundary layer across the high
Plains region will permit afternoon destabilization, supporting
development of scattered to isolated thunderstorms. Mid-level flow
is not particularly strong across the region (generally 20 to 30 kt
from the west), a weak easterly component to the low-level flow will
help to provide both ample shear for a few organized storms, as well
as some tendency for storms to progress southeastward off the higher
terrain. The strongest storms/storm clusters may be capable of
producing gusty/damaging winds, along with some hail risk. Severe
risk should gradually decrease through the evening, as convection
weakens.
...Parts of the Great Basin and vicinity...
A relatively moist low-level airmass resides across the Great Basin
vicinity, with dewpoints in the low 50s. Showers and isolated
thunderstorms are ongoing across parts of the region -- partly in
response to several disturbances aloft moving across the area,
embedded within cyclonic upper flow surrounding the eastern Pacific
upper low. Clearing is noted in morning visible imagery across
parts of Nevada away from ongoing convection, which will aid in
afternoon destabilization, and an associated increase in convective
coverage. Given moderate deep-layer southwesterly flow supporting
semi-organized cells/clusters, potential for locally damaging winds
will exist with a few of the strongest storms, before convection
weakens this evening.
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