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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0748 AM CDT Sat May 28 2022

Valid 281300Z - 291200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF SOUTH DAKOTA AND NORTHERN NEBRASKA...

...SUMMARY...
Severe thunderstorm gusts (some over 70 mph) and large hail are
expected today across parts of the central and northern Plains.  A
few severe storms may also occur across parts of the southern Plains
and in the Northeast.

...Synopsis...
A progressive, mid/upper-level synoptic pattern is forecast through
the period, as one trough leaves the eastern CONUS and another
crosses the West.  The eastern trough is devolving from an open-wave
cyclone over PA at this time, and extends south-southwestward across
the Carolinas , GA and the western FL Panhandle.  The primary
vorticity lobe and former closed circulation will move off the
coastal Mid-Atlantic and south of Long Island/southern New England
by 00Z, with the trough south-southwestward over the Outer Banks.

Out west, a broad area of cyclonic flow aloft -- with several
embedded shortwaves -- will spread across the area from the High
Plains westward, along with synoptic-scale height falls and general
cooling aloft.  The strongest shortwave trough -- now approaching
130W, west of the Pacific Northwest -- will move inland around 00Z. 
This perturbation then should dig southeastward to NV and eastern OR
by the end of the period.  Meanwhile, a weaker yet still well-
evident perturbation -- spotted in moisture-channel imagery over
northern NV -- will eject northeastward to portions of WY and
eastern MT by 0)Z, then across ND by 12Z tomorrow.

The surface analysis at 11Z showed weak lows connected by troughs
over southwestern MB, eastern SD and near SHR.  A cold front
extended from the SHR low across northern UT and southern NV.  By
00Z, the SHR low should relocate to western SD, with cold front
southwestward across WY.  Moist return flow across the lower
southern/central Plains will sharpen a dryline, expected to extend
from northern Coahuila north-northeastward to near CDS, then
northward over the extreme eastern Panhandles, western KS and the NE
Sandhills by 00Z.  By 12Z, the low should occlude and reach
northwestern ND, with a frontal triple point over southeastern ND,
warm front over central MN/WI, and cold front over central NE,
northwestern KS and south-central CO.  A separate cold front --
analyzed initially from eastern NY to the central Carolinas and
southern GA -- should move eastward over the Mid-Atlantic and New
England today.  The front is expected to reach (and decelerate over)
the eastern Carolinas around the end of the period.

...Northern Plains...
Scattered high-based thunderstorms should develop during mid/late
afternoon, in a band of maximized deep-layer ascent from north-
central/northeastern WY southeastward to the NE Sandhills.  This
activity is expected to offer severe wind (with some gusts above 65
kt possible) as it moves northeastward across eastern WY, extreme
southeastern MT, western/central SD, and west-central/north-central
NE from late afternoon into this evening.

Strengthening low-level convergence is expected amidst the mass
response to the approaching synoptic and shortwave troughs, and near
the surface low.  Storm-relative flow in the low-level/inflow layer
also should increase with time, strengthening vertical shear and
helping to organize and sustain the activity.  A limiting factor
will be lack of greater low-level moisture, though time series of
forecast soundings suggest a balance appears likely between enough
mixing/dryness to foster a deep boundary layer supporting downdraft
acceleration, and too little moisture for organized convection. 
Mixing/heating will be muted somewhat by increasing mid/high cloud
cover.  Nonetheless, with surface dew points generally in the mid
40s to low 50s F, steep low/middle-level lapse rates will support
300-800 J/kg peak/preconvective MLCAPE (locally higher in NE where
greater moisture will advect by late afternoon).  Increases of both
low-level moisture and MLCINH with time will be counterbalancing
effects across central/eastern SD and northern NE for a few hours
this evening.  Activity then should weaken late this evening into
tonight over the eastern Dakotas as it encounters progressively
more-stable boundary-layer conditions, though marginal hail/wind 
potential will persist northeastward into portions of MN.

...Northeast CONUS...
Near a prefrontal trough, a gradual increase in convective coverage
and strength should occur over the next few hours, with isolated
strong to marginally severe gusts possible by midday to early
afternoon.

This should occur behind a departing belt of morning clouds/precip,
as a sliver of favorably moist, inland warm sector destabilizes from
a co*bination of warm advection and insolation.  Meanwhile,
midlevels will destabilize slightly with increasing large-scale
ascent preceding the mid/upper trough.  The result should be around
500-1000 J/kg preconvective MLCAPE and negligible MLCINH over
southeastern NY and southern New England, with MLCAPE decreasing
northeastward to around 200-500 J/kg in a narrower, eastward-
shifting corridor across ME.  Low-level winds/shear will be modest,
but strong mid/upper flow will contribute to favorable deep shear
(e.g., 30-35-kt effective-shear magnitudes and up to about 90 kt of
cloud-layer shear) for a few organized multicell clusters, transient
supercells or small bows capable of damaging gusts.

...Southern Plains...
Isolated to widely scattered thunderstorms may initiate near the
dryline during mid/late afternoon and move into a hot, well-mixed
boundary layer with steep lapse rates and large dewpoint
depressions.  The main concern will be severe gusts.  A conditional
risk of significant-severe downburst gusts exists; however, 
uncertainties regarding overall severe-thunderstorm coverage
currently preclude a 15% unconditional wind upgrade that would allow
a 10%-sig area within.

Intense heating will boost surface temperatures along and east of
the dryline to the upper 90s to mid 100s F over the outlook area,
removing MLCINH and fostering pulses of updrafts up and down the
dryline.  MLCAPE in the 1000-2000 J/kg range should be co*mon,
locally/briefly higher, with similar magnitudes of DCAPE.  Veering
of winds with height will contribute to 30-40 kt effective-shear
magnitudes, despite lack of stronger mid/upper-level flow --
supporting some organization potential for any convection that can
survive some thermodynamic limitations.  Dry entrainment will be a
restricting factor for convective growth/maintenance, but a few
cells may mature and last long enough to produce strong to severe
gusts, before remaining activity diminishes in the cooling evening
boundary layer.

..Edwards/Mosier.. 05/28/2022