Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Fri May 17 2024
Valid 171200Z - 181200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
INTO TONIGHT ACROSS PARTS OF SOUTHEASTERN MONTANA...NORTHWESTERN
SOUTH DAKOTA...MUCH OF NORTH DAKOTA...SOUTHEASTERN
LOUISIANA...SOUTHERN MISSISSIPPI...SOUTHERN ALABAMA...SOUTHWESTERN
GEORGIA AND THE WESTERN FLORIDA PANHANDLE...
...SUMMARY...
Severe thunderstorms may impact parts of the central into eastern
Gulf Coast states and portions of the northern Great Plains this
afternoon through tonight.
...Synopsis...
A belt of seasonably strong west-southwesterly mid/upper flow will
continue to gradually overspread the Gulf Coast states today. Near
the leading edge of this regime, models suggest that a convectively
augmented perturbation will weaken while progressing east of the
central Gulf coast/lower Mississippi Valley vicinity into the
Southeast this morning. This will be trailed by at least a couple
of additional perturbations emanating from shearing larger-scale
troughing emerging from the Southwest.
By 12Z this morning, a lower/mid-tropospheric baroclinic zone,
demarcating the northern periphery of warmer and more strongly
capping elevated mixed-layer air, may be roughly aligned with the
northwestern/north central Gulf coast after having been suppressed
southward. Preceding the primary remnant upstream troughing, it
appears that the warmer air aloft may return east-northeastward
across southeastern Louisiana through the eastern Gulf states during
the day. Although perhaps initially slowed by convective outflow
still advancing southward into the northeastern Gulf this morning,
boundary-layer moistening beneath this regime across southeastern
Louisiana through much of southern Mississippi and Alabama may
contribute to a corridor of moderately large mixed-layer CAPE by
late this afternoon.
Meanwhile, in higher latitudes, models indicate that a seasonably
strong belt of westerlies emerging from the northern mid-latitude
Pacific will continue to nose eastward across the northern Rockies
and Great Plains today through tonight. Significant cyclogenesis is
already underway to the lee of the Canadian and northern U.S.
Rockies. While the initial cyclone may deepen further across
Saskatchewan, models indicate that a notable secondary surface
cyclone may form east-northeast of the Bighorn Basin through the
northern Great Plains Red River Valley later today through tonight.
Despite strengthening southerly low-level wind fields ahead of an
associated cold front, low-level moisture content likely will remain
seasonably low across much of the northern Great Plains, but
steepening lapse rates may still contribute to weak/modest
boundary-layer destabilization.
...Central/Eastern Gulf States...
In the wake of the weakening convective perturbation, the most
favorable mid/upper support for renewed convective development may
not begin impacting the region until mid/late evening. However, it
appears that the environment across much of southeastern Louisiana
through southern Mississippi/Alabama, southwestern Georgia and
western Florida will become at least conditionally supportive of
severe storm development, including supercells, by late this
afternoon. While potential convective evolution remains uncertain,
isolated to widely scattered thunderstorm initiation seems possible
late this afternoon into this evening, before a more notable
increase in thunderstorm development and upscale growth occurs this
evening into the overnight hours. Stronger storms will pose an
initial risk for large hail, locally damaging wind gusts and perhaps
a couple of tornadoes, before potentially damaging wind gusts
becomes the more prominent potential hazard tonight.
...Northern Great Plains...
Although there is spread within/among the various model output,
guidance (particularly the latest NAM) is suggestive that increasing
high-based thunderstorm development along the higher terrain of
southeastern Montana may generate a significant
northeastward/eastward propagating cold pool by late this afternoon.
Forecast soundings suggest that a deeply mixed boundary layer will
contribute to sub-cloud evaporative cooling and potential for severe
surface gusts. As this advances across portions of the western
Dakotas, it may encounter at least somewhat more unstable
boundary-layer air and contribute to further intensification. In
the presence of strengthening deep-layer shear, an increasingly
organized convective system may evolve and progress across the
middle Missouri into Red River Valley, accompanied by a risk for
severe hail and continuing risk for severe wind before weakening
overnight.
..Kerr/Bentley.. 05/17/2024
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