SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 PM CDT Tue Jul 05 2022
Valid 052000Z - 061200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
SOUTH DAKOTA INTO SOUTHWEST MINNESOTA AND NORTHWEST IOWA...
...SUMMARY...
A derecho with embedded gusts over 80 mph will spread across
southeast South Dakota, parts of southwest Minnesota and northern
Iowa through evening. Severe winds may persist tonight as far east
as southern Wisconsin.
...SD/MN/IA region...
A derecho is currently producing gusts over 90 mph as it moves
across southeast SD, and the threat of particularly damaging winds
should impact the I-29 corridor by 21Z.
A zone of very strong instability exists along a stationary front,
with MLCAPE of 3000-4000 J/kg from southeast SD all the way into
northern IL. GPS precipitable water measurements are averaging 1.75
to 2.00" across the length of the front, confirming boundary layer
moisture quality. As such, the derecho, or at least a severe MCS, is
expected to impact the corridor extending well east across southern
MN, northern IA, and southern WI.
..Jewell.. 07/05/2022
.PREV DISCUSSION... /ISSUED 1151 AM CDT Tue Jul 05 2022/
...SD to IA and southern MN...
An intense cluster over central SD will likely persist
east-southeast across southeast SD. This should evolve into a
forward-propagating linear MCS, expanding in latitudinal extent as
MLCIN further diminishes ahead of it. A large MLCAPE reservoir in
excess of 3000 J/kg across southern SD/MN and northern IA will
support potential for embedded significant severe wind gusts
exceeding 75 kts. While the majority of CAM guidance appears to be
egregiously poor (especially the HRW-FV3) with handling the
conceptual model for this event, the 12Z HRW-ARW and NSSL are in the
ballpark and suggest bowing linear segments will be maintained into
southern MN and northern IA before weakening this evening.
...Central/eastern MT to western ND...
Air mass recovery is underway across central to eastern MT in the
wake of the intense MCS over northwest SD. Residual 50s to low 60s
surface dew points in conjunction with pockets of pronounced
boundary-layer heating will yield MLCAPE of 1000-1500 J/kg. With
45-55 kt effective bulk shear, at least a few supercells are
expected from central to northeast MT during the late afternoon and
evening with large hail and isolated severe wind gusts as the
primary threats. Some of these cells should consolidate into a
cluster that spreads into western ND during the evening. Overall
intensity should decrease as activity impinges on the more stable
air mass left in the wake of the SD MCS.
...Mid-Atlantic to Midwest...
Poor mid-level lapse rates were evident in 12Z observed soundings
east of the Appalachians and this will be the main limiting factor
to more intense convective development. An MCV over western PA will
move east towards the NJ coast, with scattered thunderstorms near
and to its south. With 30-40 kt 700-mb westerlies impinging on the
region attendant to this MCV and the boundary-layer destabilizing
from south to north, an increase in strong gust potential should
occur from VA into the Lower DE Valley.
Arcing convective bands extend west of the lead MCV across WV and
OH/IN. This activity will likely persist through the rest of the
afternoon into this evening, building south-southwest in time
towards large buoyancy centered on the Lower OH Valley. Moderate
deep-layer shear will be further offset as this process occurs,
suggesting that loosely organized clusters will dominate with strong
to isolated severe gusts as the primary threat. Additional multicell
clusters will probably form northwest along the baroclinic zone near
the IA/IL/WI border area during the late afternoon into the evening.
These will similarly pose a threat for scattered damaging winds and
isolated severe hail, although the spatial extent of this threat
will likely be limited by this morning's stabilization in OH.
Read more CHECK UPDATE ZOOM GRAPHIC
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