Valid 032000Z – 041200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF NEW ENGLAND AND THE NORTHERN HIGH PLAINS…
Isolated strong to severe thunderstorms remain possible this
afternoon into the evening over the northern High Plains, while a
few storms capable of producing minor wind damage will continue to
affect portions of the New England area this afternoon.
Only modest adjustments have been made to previous forecast with
primary areas of isolated strong to severe storms capable of a few
strong wind gusts and hail expected over a portion of New England
and the northern High Plains. See swomcd 1635 and 1636 for more
.PREV DISCUSSION… /ISSUED 1128 AM CDT Sat Aug 03 2019/
A broad upper ridge will persist across much of the western U.S.
today, centered over the Four Corners states. While stronger
troughing north of the ridge will remain confined to western Canada,
weak perturbations will continue progressing anticyclonically around
the periphery of the ridge — across the northern Intermountain
region/Plains states/upper Mississippi and mid/lower Missouri
Meanwhile, weak troughing will prevail over the Ohio and Tennessee
Valleys and into the Southeast, weakly phased with a stronger trough
within the main belt of midlatitude westerlies, which will cross
eastern Canada and New England today.
At the surface, a cold front is forecast to cross portions of New
York/New England ahead of the aforementioned midlatitude trough, and
will help focus a zone of scattered storms — and isolated severe
potential — across this area. Lee troughing over the northern High
Plains will also likely focus isolated storm development, and local
severe potential, this afternoon.
…Northern High Plains…
Isolated afternoon storm development is anticipated over the
northern High Plains area, near the lee trough and ahead of a weak
cool front crossing Montana. With heating/destabilization of the
relatively moist boundary layer east of the lee trough, ample CAPE
— sufficient to fuel a few vigorous updrafts — will evolve. As a
few storms initiate, updraft intensity may be supplemented by ample
shear across the region, owing in part to a belt of 35 to 40 kt
westerlies crossing Montana, within the tight height gradient
between ridging to the south, and troughing to the north. However,
relatively weak forcing/ascent across the area, and thus a tendency
for persistent capping, should limit overall convective coverage.
Therefore, will maintain 5%/MRGL risk across this area this
afternoon and early evening, before convection diurnally diminishes.
…Portions of the New England area…
Widely scattered thunderstorms are forecast to develop from portions
of Maine (ahead of the advancing cold front) south-southwestward
into southern New England and portions of eastern New York where a
moist/destabilizing airmass is present. Stronger flow aloft will be
confined to northern New England, but with weaker CAPE, only
isolated stronger storms are expected. Meanwhile, with shear
diminishing with southward extent into the more favorable
thermodynamic environment, more vigorous updrafts should likewise
remain limited in coverage. Still, with potential for a few
instances of gusty downdraft winds capable of producing minor damage
apparent, will introduce 5% wind potential/MRGL risk across portions
of New England and into parts of the Hudson Valley/Catskills for
this afternoon. Any lingering risk this evening should diminish
rapidly, in conjunction with diurnal stabilization trends.