SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0256 PM CDT Thu Aug 15 2024
Valid 152000Z - 161200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL OK TO
THE MID MS VALLEY...
...SUMMARY...
Scattered severe thunderstorms are possible across parts of the
Midwest through tonight. Severe gusts capable of wind damage and
large hail are the primary risks with the stronger thunderstorms.
A cluster of storms is ongoing across eastern Nebraska and will move
into an increasingly unstable environment across Iowa later this
afternoon and this evening. Have expanded the slight risk farther
north into Iowa to account for this threat. See MCD #1907 for more
discussion of this threat.
Elsewhere, the forecast remains on track. Thunderstorm development
appears imminent along a frontal boundary in Oklahoma within the
next 1 to 2 hours. A somewhat similar environment exists farther
southwest across portions of northwest Texas and the Texas
Panhandle. However, slightly warmer temperatures around 500mb may
limit updraft intensity somewhat and thus mitigate a greater severe
weather threat.
A few storms have developed over the higher terrain in central Idaho
and southwest Montana. These storms may pose some severe wind threat
as they move northeast. However, instability is quite weak (100-250
J/kg MLCAPE) and should keep any threat mostly isolated.
A few large hail and severe wind gusts have occurred across New
Hampshire this afternoon and a few additional strong to severe
storms may develop in the region, in addition to the ongoing cluster
now in northern Massachusetts. This threat should persist through
early evening before waning near or shortly after sunset.
..Bentley.. 08/15/2024
.PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Aug 15 2024/
...Mid MS Valley this afternoon/evening...
The remnants of overnight convection, and an associated/lead
shortwave trough, are moving across southern MO/IL. Though these
storms will likely weaken through midday, a diffuse
outflow/differential heating zone may help focus additional
thunderstorm development this afternoon. Southern MO to southern IL
will be along the southern fringe of the stronger midlevel flow,
where a mix of multicell clusters and possibly a supercell or two
capable of producing damaging winds (60-70 mph) and isolated large
hail (1-1.5 inches in diameter) will be possible later this
afternoon/evening.
The primary midlevel shortwave trough will progress eastward from
NE/SD toward the upper MS Valley by tonight, in conjunction with a
surface cold front. Weak, ongoing convection across north central
and northeast NE reflects the zone of ascent spreading
east-southeastward through the afternoon, toward the destabilizing
warm sector in the wake of overnight convection across northern
MO/southern IA. Though timing is still a bit uncertain,
thunderstorm development appears probable late this afternoon or
this evening across eastern NE and especially near the MO/IA border.
Relatively long/straight hodographs, midlevel lapse rates near 7.5
C/km and MLCAPE in excess of 2000 J/kg will support supercells
capable of producing large hail (1-2 inches in diameter) and
damaging gusts (60-75 mph). Some upscale growth into a cluster may
also occur as the storms spread east-southeastward toward IL
tonight.
...OK this afternoon/evening...
Strong surface heating is ongoing across central OK along a weak
pre-frontal trough. Mid-upper flow will be weak this far southwest,
but deep mixing with surface heating will contribute to steep
low-level lapse rates and MLCAPE of 1500 J/kg or greater with
minimal convective inhibition. Scattered thunderstorms are expected
along this trough by mid-late afternoon, when isolated damaging
downburst winds (60-75 mph) will be possible.
...New England this afternoon...
To the west of a closed low over Nova Scotia, an embedded shortwave
trough is rotating southward over New England with ongoing
convection in southwest ME and NH. Surface heating/destabilization
on the western/southern fringes of the ongoing storms will likely
contribute to additional thunderstorm development this afternoon.
Moderate buoyancy and steepening low-level lapse rates, as well as
cool midlevel temperatures (-14 to -15 C at 500 mb), will support
the potential for isolated wind damage with 45-60 mph gusts and
isolated hail approaching 1 inch in diameter with multicell
clusters. See MD #1557 for additional information.
...Northern Rockies this afternoon/evening...
A midlevel trough will eject east-northeastward over ID/southwest
MT/extreme northwest WY through this evening. Steep lapse rates and
modest PW (near or less than 0.75 inches) will support high-based
thunderstorm development this afternoon in the zone of ascent
preceding the midlevel trough. Strong outflow gusts (50-60 mph)
will be the main concern.
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