Mesoscale Discussion 1980
NWS Storm Prediction Center Norman OK
1135 AM CDT Sun Aug 13 2023
Areas affected…eastern NH…southern and western Maine
Concerning…Severe potential…Watch possible
Valid 131635Z – 131830Z
Probability of Watch Issuance…40 percent
SUMMARY…A couple of small supercells will probably evolve this
afternoon and pose a risk for large hail (max diameter 1.25-1.75
inches) and isolated damaging gusts (peak speeds 50-65 mph). It is
uncertain whether the coverage of severe weather will warrant a
small severe thunderstorm watch.
DISCUSSION…Visible-satellite/radar mosaic shows towering cumulus
and initial thunderstorms developing across northern VT into far
western Maine as of 1230pm EDT (1630 UTC). Surface analysis
indicates cooler/less unstable conditions over the eastern half of
Maine where temperatures have been slow to warm (in the mid 60s to
lower 70s), whereas much warm conditions are observed over NH and
western Maine with temperatures ranging from the lower 80s over
southern NH to the mid-upper 70s in western Maine.
Water-vapor imagery shows a mid-level low over Quebec with a
vorticity lobe rotating through the base of the trough over the St.
Lawrence Valley. Gradual mid-level cooling over the
central-northern portions of Maine along with some additional
heating will continue to destabilize the airmass. The implied
large-scale ascent and increasing buoyancy will favor strong updraft
development. Appreciable shear through a deep layer will act to
organize updrafts. The stronger updrafts will probably evolve into
supercells with a local risk for large hail and damaging gusts.
…Please see www.spc.noaa.gov for graphic product…
LAT…LON 44547132 45297109 46926983 46736908 46236862 45116872
44136900 42977077 43137135 43447163 44547132