ACUS01 KWNS 290528
SPC AC 290526
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1226 AM CDT Fri May 29 2020
Valid 291200Z - 301200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHEASTERN UNITED STATES...
Scattered thunderstorms, some severe, are possible across an area
centered over PA/NY Friday afternoon through Friday evening. A few
strong storms are also possible across the northern Rockies region.
Early-morning water-vapor imagery depicts a well-defined mid-level
vort/short-wave trough over the Mid-South lifting northeast in line
with short-range model guidance. This feature should begin to eject
quickly over the next 24hr as 500mb flow increases across the
central Appalachians this morning before translating into New
England overnight. This increase in mid-high level flow is expected
to enhance the likelihood for organized convection later today.
While mid-level lapse rates are not forecast to be particularly
steep, latest guidance suggests a corridor of strong boundary-layer
heating should develop across the Appalachians, which should result
in surface readings breaching convective temperatures around 17-18z.
Thunderstorms should develop by noon along a corridor from OH into
Upstate NY ahead of a pronounced cold front. This activity will
evolve within a strongly sheared southwesterly flow regime. While
vertical shear seems supportive of supercells, and a few may
develop, it appears thunderstorm clusters and line segments may be
the more common storm mode. Damaging winds, some hail, and perhaps a
tornado or two can be expected with pre-frontal convection as it
spreads toward New England late this afternoon.
...Northern Rockies Region...
Short-wave ridging will dominate the northern Rockies during the
day1 period; although, a strong upper low should approach the
central CA Coast by 30/12z. Prior to this upper low, diurnal heating
and orographic forcing will be the mechanisms by which scattered
convection develops across this region. A few high-based
thunderstorms are expected by late afternoon along an arcing
corridor from OR-central ID-northwestern WY. Gusty winds and
marginally severe hail are possible with the strongest convection.