Valid 310100Z – 311200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN HIGH PLAINS AND NORTHEAST…
A few severe thunderstorms will be possible across parts of the
northern High Plains this evening. A few storms capable of
marginally severe wind gusts will be possible in the Northeast and
across southern and central Arizona.
…Northern High Plains…
Latest water vapor imagery shows an upper-level ridge in place
across the northern High Plains. At the surface, a corridor of
maximized low-level moisture exists from southwest South Dakota into
eastern Montana, along which the RAP is analyzing moderate
instability with MLCAPE in the 1500 to 2500 J/kg range. In spite of
the presence of the ridge aloft, scattered thunderstorms have
developed early this evening in far eastern Montana and near the
Black Hills in South Dakota. These storms should be sustained over
the next few hours. The moderate instability combined with
directional shear in the low to mid-levels and steep mid-level lapse
rates should result in a threat for hail and damaging wind gusts.
The slight risk area has been expanded northward into eastern
Montana to account for WW 546.
Southwest mid-level flow is evident on water vapor imagery across
the Northeast with a plume of moisture extending northeastward from
the Central Appalachians into western New England. At the surface, a
moist airmass is located across much of the Northeast with surface
dewpoints in the mid to upper 60s F. Moderate instability is
analyzed by the RAP across southeast New York and western New
England where MLCAPE values are estimated to be in the 1000 to 2000
J/kg range. Although deep-layer shear is relatively weak, the
instability and steep low-level lapse rates should be enough for a
marginal wind damage threat for another hour or two this evening.
Scattered thunderstorms associated with the western monsoon are
currently ongoing across central and southeastern Arizona. The RAP
is analyzing moderate instability across much of the southern half
of Arizona with MLCAPE in the 1500 to 2500 J/kg range. The
instability combined with steep low-level lapse rates will be
sufficient for a few marginally severe wind gusts with the stronger
multicells over the next hour or two.