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ACUS02 KWNS 300559
SWODY2
SPC AC 300558

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 AM CDT Tue Jul 30 2019

Valid 311200Z - 011200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS AND NORTHEAST/MID-ATLANTIC...

...SUMMARY...
Isolated strong to severe thunderstorms may occur Wednesday across
parts of the northern Plains and Northeast/Mid-Atlantic.

...Synopsis...
Upper ridging will remain prominent over much of the western and
central CONUS on Wednesday. An upper trough will advance eastward
across the Appalachians to the Northeast and Mid-Atlantic through
the period. At the surface, a cold front should move slowly across
much of the eastern CONUS, with scattered to numerous storms
expected along/ahead of it. High pressure will likely be centered
over the Great Lakes, with a corridor of 60s surface dewpoints
extending from the southern into central/northern Plains.

...Northern Plains...
Heights are forecast to slowly rise across the northern Plains
through the period. A surface trough/dryline should mix eastward
across eastern MT/WY by late Wednesday afternoon. Moderate to
locally strong instability will likely develop ahead of this surface
trough across the western Dakotas as ample boundary-layer heating
occurs and mid-level lapse rates gradually steepen. Most guidance
suggests isolated thunderstorms will develop along/ahead of the
surface trough in far eastern MT and western ND by peak diurnal
heating as the cap weakens. Modest ascent associated with a subtle
mid-level perturbation may also assist convective development.

Although low-level winds will remain modest, strengthening
mid/upper-level west-northwesterly flow should support updraft
organization in any storms that can remain sustained. Long,
generally straight hodographs above 3 km suggest splitting
supercells may occur, with a related large hail threat. Severe wind
gusts will also be possible given a well-mixed boundary layer with
steep low-level lapse rates present. Main uncertainty is overall
coverage of storms given the weak/subtle forcing mechanisms and
generally rising heights across this region.

...Northeast and Mid-Atlantic...
Ample diurnal heating will occur ahead of a surface trough extending
from the Northeast through the Mid-Atlantic. Convective development
will likely occur by early Wednesday afternoon along this surface
trough, with weak to moderate instability forecast across the warm
sector. Around 20-30 kt of mid-level southwesterly flow associated
with the upper trough may be sufficient to loosely organize storms
into clusters as they spread eastward through the afternoon and
early evening. Although mid-level lapse rates are expected to remain
poor, steepening low-level lapse rates combined with the modestly
enhanced mid-level flow and high precipitable water values may
support strong/gusty downdraft winds capable of producing occasional
damage.

...Central Plains into the Ozarks...
A weak surface low may gradually deepen across parts of the central
High Plains beneath the upper ridge. Isolated storms might form
along a baroclinic zone extending eastward from the low across KS by
late afternoon. Even if convection develops, shear should remain
weak across this region. But, strong instability and steep low-level
lapse rates will be present along/south of the boundary, and very
isolated strong/gusty winds cannot be ruled out. The potential for
convective development appears too conditional to include any
probabilities at this time.

A south-southwesterly low-level jet should slowly strengthen across
the central Plains Wednesday evening/night. Elevated storms will
probably form across eastern NE into northwestern MO by late
Wednesday evening. There are substantial differences in guidance
regarding the amount of MUCAPE that will be available to these
storms, with the 00Z NAM suggesting enough elevated instability and
cloud-bearing shear to support some hail risk with initial
development. However, this threat appears too uncertain to introduce
5% severe probabilities for now.

...MAXIMUM RISK BY HAZARD...
Tornado:  <2%     - None
Wind:      5%     - Marginal
Hail:      5%     - Marginal

..Gleason.. 07/30/2019

$$


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