566
ACUS01 KWNS 161949
SWODY1
SPC AC 161948

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0248 PM CDT Mon Sep 16 2024

Valid 162000Z - 171200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTH
DAKOTA INTO NORTHWEST MINNESOTA AND PARTS OF COASTAL NORTH
CAROLINA...

...SUMMARY...
The threat for a few tornadoes will continue this afternoon and
evening over eastern North Carolina and vicinity. Thunderstorms
capable of producing severe gusts and large hail should occur today
in parts of the northern Plains. Isolated severe wind and hail also
appears possible across parts of the Great Basin to Four Corners.

...Four Corners/Arizona...
The primary adjustment was to expand the Marginal risk area
southward into eastern AZ. Dewpoints in the upper 50s to low 60s are
supporting MLCAPE values upwards of 1000 J/kg with negligible
inhibition based on latest RAP mesoanalysis estimates. A deepening
and expansive cumulus field across the region (including a few early
attempts at convective initiation) corroborate these estimates,
suggesting that adequate buoyancy resides across the region for
robust convection. Regional VWPs are sampling 30-40 knot winds
around 2-3 km AGL with stronger flow analyzed aloft in recent
upper-air analyses. Consequently, adequate deep-layer wind shear
appears to be in place to support organized convection, including a
supercell or two with an attendant severe hail/wind threat, though
storm coverage should remain somewhat limited due to modest forcing
for ascent (largely driven by orographic lift). For additional
information regarding near-term convective trends further north
across the Four Corners see MCD #2072.

...North Dakota...
The forecast largely remains on track across ND with only some
northwestward expansion of the Slight risk/15% hail probability
line. Latest high-res solutions continue to suggest that robust
convection will most likely develop near the vorticity maximum
(noted just to the west/southwest of Minot, ND as of 19 UTC) and
propagate northeast along the warm front. This scenario aligns well
with recent satellite trends with gradual convective development
observed ahead of the vort max and along the front amid continued
diurnal destabilization. This alignment of observed trends and
recent guidance yields sufficiently high confidence to warrant
adjusting the risk probabilities.

Elsewhere, the previous forecast remains on track. See the prior
discussion (below) or MCDs #2071 and #2073 for the latest details
regarding convective trends across coastal North Carolina and
portions of the Great Basin, respectively.

..Moore.. 09/16/2024

.PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Sep 16 2024/

...North Dakota into Northwest Minnesota...
Elevated thunderstorms which have produced sporadic, marginally
severe hail earlier this morning across parts of ND into northwest
MN have generally remained sub-severe over the past couple of hours
as a southerly low-level jet has gradually weakened. In the wake of
this activity, a surface low should consolidate over the northern
High Plains, with a front and convectively reinforced outflow
expected to lift slowly northward across ND this afternoon/evening
as an effective warm front. Airmass recovery is expected along/south
of this boundary, with steepening mid-level lapse rates, moistening
at low-levels, and daytime heating all contributing to moderate
instability by later this afternoon. While low/mid-level flow will
not be overly strong for most of the day, strengthening low-level
southerly flow is expected again this evening as a low-level jet
strengthens across the northern/central Plains.

Current expectations are for robust thunderstorms to develop
along/near the front late this afternoon and early evening. Enough
deep-layer shear should be present to support a threat of large hail
with any supercells initially. With time, some clustering should
occur. A potentially greater wind threat may exist through the
evening as activity spreads east-northeastward across
central/eastern ND into northwest MN. A tornado or two also appears
possible with any surface-based convection along/south of the front,
especially this evening as 0-1 km shear increases with the
strengthening low-level jet.

...Eastern North Carolina and Vicinity...
The surface low off the NC/SC Coast (Potential Tropical Cyclone 8)
is forecast by NHC to move northwest and inland across parts of SC
through this evening. A surface trough/weak baroclinic zone extends
northeastward from the low just off the NC Coast/Outer Banks. As the
system moves inland, enhanced low-level flow should turn more
east-southeasterly. Various NAM/RAP forecast soundings suggest that
as low 70s surface dewpoints advance inland along the coastal plain
of eastern NC, then only modest/filtered daytime heating will be
needed to support weak boundary-layer destabilization. Sufficiently
enlarged low-level hodographs should support a threat for a few
tornadoes with any low-topped supercells that can form offshore and
be sustained inland across coastal portions of eastern NC. The
Slight Risk for this region has been maintained with only small
adjustments based on recent observations and 12Z guidance.

...Great Basin into the Four Corners...
A deep, closed upper low centered over CA this morning will advance
slowly eastward across parts of the Great Basin through the period.
An attendant south-southwesterly mid-level jet will overspread
eastern portions of the Great Basin into the Four Corners region
this afternoon and evening. Although cloud cover remains prevalent
across parts of these areas, some daytime heating will encourage the
development of weak instability by mid to late afternoon. Stronger
mid-level flow and related deep-layer shear are forecast across the
Four Corners vicinity, where marginal supercell structures could
pose an isolated hail threat. Even though instability should
generally remain weak owing to limited low-level moisture,
occasional strong to severe wind gusts should be the main threat
with various small clusters that can form/consolidate and
subsequently spread north-northeastward through the early evening.
This wind threat will be locally maximized where filtered diurnal
heating can help steepen low-level lapse rates.

...Central High Plains...
Relatively high-based thunderstorms may develop this afternoon
across parts of the central High Plains, generally along/east of a
weak surface trough. This region will be mostly displaced to the
east of large-scale ascent associated with the upper low over the
West. Even so, a narrow zone of weak to moderate instability should
be in place across parts of central NE into western KS by peak
afternoon heating. Although flow through low/mid levels should
remain modest for much of the afternoon, a veering wind profile with
height should foster around 25-35 kt of deep-layer shear, sufficient
for some updraft organization. The primary uncertainty regarding any
isolated severe hail/wind threat remains whether convection will
initiate or not. Have therefore not added a Marginal Risk across
parts of the central High Plains with this update, but trends will
continue to be monitored.

$$