Mesoscale Discussion 1160
NWS Storm Prediction Center Norman OK
1100 AM CDT Tue Jun 27 2017
Areas affected...Portions of central and southern New England
Concerning...Severe potential...Watch possible
Valid 271600Z - 271800Z
Probability of Watch Issuance...40 percent
SUMMARY...Thunderstorms are expected to develop/increase in coverage
through the afternoon. Hail up to an inch in diameter and isolated
thunderstorm wind damage may occur with the strongest thunderstorms.
A watch is currently not anticipated, but conditions will continue
to be monitored.
DISCUSSION...A shortwave trough moving across the eastern Great
Lakes will continue to move east across New England this afternoon.
Ahead of this trough, widespread cloud cover across New England has
kept surface temperatures from quickly warming this morning. These
relatively cool temperatures (low-to-mid 60s), coupled with surface
dew point temperatures in the mid-50s to low-60s, have kept
instability modest across New England. However, recent satellite
imagery suggests thinning and/or breaks in the cloud cover
developing across eastern New York and spreading east through the
early afternoon. These breaks should allow for a modest increase in
instability and the development of isolated to scattered
Given the modest instability, thunderstorms are expected to remain
fairly low-topped, limiting the overall large-hail potential despite
mid-level-lapse rates steepening to between 7-8 C/km. However,
deep-layer shear values on the order of 50-60 kt will support
supercell-like structures, which would tend to favor development of
hail at least up to an inch in diameter. Additionally, despite weak
low-level lapse-rates, the overall strength of the mid-level flow
may support isolated thunderstorm wind damage.
Current thinking is that the limited instability and low-topped
nature to the convection will result the majority of hail to remain
below an inch in diameter, and that any wind damage potential would
remain fairly isolated, precluding the need for a watch. However, if
instability is greater than currently expected or thunderstorm
organization greater than expected, a watch could eventually be
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 41597463 42887460 44137252 44997038 44976934 44476875
43326943 42857023 42437019 42186998 41406942 40986998
40717135 40507253 40437325 41597463