SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0249 PM CDT Tue Aug 13 2024
Valid 132000Z - 141200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST CO
INTO SOUTHWEST NE AND FAR NORTHWEST KS...
...SUMMARY...
Severe thunderstorms are possible this afternoon and evening from
northeast Colorado into southwest Nebraska and far northwest Kansas.
Strong to isolated severe thunderstorms are also possible this
afternoon and evening across parts of the eastern Great
Basin/northern Intermountain region into the northern/central High
Plains and central Great Plains, as well as South Carolina.
...20z Update...
Adjustments were made to the Day 1 Outlook to remove portions of the
Marginal Risk South Carolina behind an ongoing convective line and
to introduce 2% tornado probabilities within the Slight Risk across
northeast Colorado, southwest Nebraska, and northwest Kansas.
Initial cellular development is ongoing across portions of Colorado
and Wyoming this afternoon, with potential for strong to severe
gusts and large hail. Through the afternoon/evening, evolution of a
more organized convective line is expected across northeast
Colorado. This line will propagate eastward into NE/KS through the
evening. Lee cyclogenesis and mass response will support a
strengthening low-level jet and resulting strengthening of low-level
shear. The primary threat will be for damaging wind as this line
continues eastward into the central Plains overnight.
A Marginal Risk continues across the Intermountain West and Northern
High Plains, where scattered thunderstorm development is ongoing.
Strong to severe gusts and instances of severe hail will possible.
..Thornton/Mosier.. 08/13/2024
.PREV DISCUSSION... /ISSUED 1126 AM CDT Tue Aug 13 2024/
...Central High Plains into the Central Plains...
Low-amplitude shortwave trough currently moving through the Four
Corners vicinity is expected to continue northeastward, helping to
support afternoon thunderstorms across the central Rockies.
Favorable low-level moisture will exist within the airmass
downstream across the central High Plains, characterized by late
afternoon dewpoints in the low to mid 60s. Ongoing cloud covered may
delay heating a bit, but temperatures are still expected to reach
the mid 80s by the late afternoon. These low-level thermodynamic
conditions will help remove convective inhibition while also
supporting moderate buoyancy. The westerly/southwesterly flow aloft
should remain relatively modest (i.e. 20 to 30 kt at 500 mb), but
the veering wind profiles expected to be in place will still result
in moderate vertical shear. Current expectation is for 0-6 km bulk
shear to range from 25 to 35 kt, with the highest values located
over northeast CO into western NE.
A predominantly multicellular mode is anticipated, with isolated
large hail and a damaging gusts possible. The stronger shear over
northeast CO suggests a more organized mode is possible here, with
the development of a forward-propagating convective line
anticipated. Strong gusts will be possible within this line. This
line may continue eastward into the central Plains overnight,
supported by a moderate low-level jet.
...Lower MO Valley into southeast NE...
Ongoing convective complex moving through southwest MO is expected
to continue southeastward while gradually weakening. Some
re-development is possible during the evening, beginning across
southwest MO, as warm-air advection occurs along the remnant
outflow. Thunderstorm development should then expand northwestward
into northeast KS, northwest MO, and southeast NE as the low-level
jet continues to strengthen. Some isolated hail is possible within
the strongest storms. Additionally, despite their elevated
character, downdrafts could become strong enough to penetrate any
low-level stability, with some damaging gusts possible.
...Intermountain West into the northern High Plains...
Early-day satellite imagery shows upper ridging centered over the
southern Plains and upper troughing from Pacific Northwest into
central CA. Moderately enhanced southwesterly flow aloft is in place
between these two features, from the Great Basin across much of the
Intermountain West and into the northern High Plains. A shortwave
trough currently moving through the western Great Basin is expected
to progress through this southwesterly flow, reaching the northern
High Plains by early Wednesday morning. Favorable moisture is in
place ahead of this wave, as evidence by PWATs around 1" sampled by
the 12Z soundings at SLC and GJT, with near 0.9" at BOI as well.
Scattered to numerous thunderstorms are expected across the region,
as northeastward-progressing shortwave trough interacts with this
favorable moisture.
Ongoing cloud cover and filtered daytime heating is expected to keep
temperatures in the upper 70s across much of the region, with
slightly warmer temperatures possible across eastern ID and
northeastern UT. These temperatures combined with the mid-level
moisture already in place will support moderate buoyancy, with the
enhanced mid-level flow supporting moderate vertical shear as well.
As a result, a largely multicellular mode is anticipated, but a few
more organized storms are possible, with occasional bowing segments
capable of producing strong gusts. The only exception is across the
eastern ID/northeast UT vicinity, where slightly better buoyancy and
shear could result in a few supercells. Anticipated isolated
coverage currently precludes the need for higher severe
probabilities.
...South Carolina...
A weak surface low is near the southern SC coast this morning.
Modest low-level convergence from this low northwestward into
western SC/northeast GA is helping support showers and occasional
thunderstorms. This convergence will likely persist throughout the
day, with the showers and thunderstorms progressing gradually
eastward. A very moist airmass is in place, as evidenced by 16.7
g/kg lowest 100-mb mean mixing ratio on the 12Z CHS sounding, and
will diurnally destabilize today. Moderate west-northwesterlies
(around 30 kt at 500 mb) may aid in some multicellular organization.
Isolated gusts 50-60 mph capable of wind damage will be the primary
concern with the stronger storms.
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