SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0252 PM CDT Thu Sep 12 2024
Valid 122000Z - 131200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
MONTANA AND WESTERN NORTH DAKOTA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
SOUTHEAST...
...SUMMARY...
A few tornadoes are possible today from northern Florida to
north-central Alabama. Scattered large hail and severe wind gusts
(some significant) are expected across eastern Montana into western
North Dakota this afternoon through early/mid-evening.
...20z...
The D1 Convective Outlook remains on track with no updates needed.
A narrow corridor of tornado risk associated with Tropical
Depression Francine and the mid/upper low across the southeast will
continue across central/southern Alabama this afternoon and evening.
See MCD#2061 for more information.
Across the northern Great Plains, potential for significant damaging
winds will increase through the afternoon and evening as ongoing
convection across Montana and Wyoming increases in coverage and tend
to grow upscale through the evening. See previous discussion for
more information on this threat.
..Thornton.. 09/12/2024
.PREV DISCUSSION... /ISSUED 1138 AM CDT Thu Sep 12 2024/
...Northern Great Plains including eastern MT/western ND...
Have upgraded portions of eastern Montana and western North Dakota
for a heightened/focused potential for severe storms capable of
large hail and potentially significant-caliber severe wind gusts
later this afternoon through around mid-evening.
Strong-severe thunderstorms are expected, along and behind the
front, as early as early/mid-afternoon, with the most probable
severe potential arising from activity moving north-northeastward
from northern Wyoming and far southern Montana. High-based
supercells and multicells are possible, offering large hail and
severe wind gusts. These storms may aggregate and grow upscale into
one or two bowing clusters, racing north-northeastward accompanied
by a swath of better-organized, potentially significant (65+ kt)
gust potential.
This scenario will be supported by trough-related cooling mid-level
temperatures and steep low/mid-level rates atop a modestly moist
boundary layer, as the exit region of a strong upper-level jet
overspreads the region. MLCAPE of 500-1200 J/kg and 45-55 kt
effective-shear magnitudes will support the severe potential
including fast-moving and relatively long-lived storms into western
North Dakota. The near-surface airmass over the central Dakotas
should stabilize with time and eastward extent tonight, limiting
duration and eastward shift of the threat.
...Southeast...
Current Tropical Depression Francine is forecast to continue moving
generally northward over Mississippi, and to lose definition as it
interacts more closely with the mid/upper-level low. Associated
deep-layer winds will continue to weaken, but low-level shear will
remain favorable through most of the day, well to the east-southeast
of its center. A destabilizing airmass along and south of the
warm/marine front will support a continued, slow inland shift of
supercell potential amid enlarged hodographs. The favorable
environment will be bounded on the west by a dry slot and veering
low-level flow, on the northeast by more stable air in heavy precip
north of the front, and on the south by a gradual weakening of
low-level winds and shear as the cyclone center pulls away and
fills. In the favorable corridor, where inflow parcels are
surface-based, expect effective SRH in the 200-500 m2/s2 range, very
rich moisture, low LCL, and weak MLCINH. In the shorter term, a
tornado threat may persist this afternoon across northern Florida,
while potentially increasing later this afternoon through early
evening near the warm front across southern into central Alabama.
Read more
