[CALV-AUXCOMM] Tropical Storm Ida/Impact to Maryland

[Shawn Donley]

Calvert AUXCOMM members. 

Latest from the NWS below. Highlighting is  mine. Also see that attachment (if it makes it...size limit of Reflector might be exceeded).


.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
All eyes will turn to the remnants of Ida tomorrow, as a
potentially significant weather event unfolds across our area.
While there still is a small amount of spread, 12z guidance has
started to come into better agreement with respect to the track
of Ida and the resultant rainfall https://forecast.weather.gov/glossary.php?word=rainfall distribution across the area.

The character of the event can be split up into two separate
regimes across our forecast area. The first regime will be to
the west of the Blue Ridge https://forecast.weather.gov/glossary.php?word=Ridge, where steady precipitation will
persist nearly continuously from tonight through tomorrow
afternoon. Dynamically speaking, this is where the remnants of
Ida will interact with the mid-latitude https://forecast.weather.gov/glossary.php?word=latitude trough https://forecast.weather.gov/glossary.php?word=trough off to our north
and west, undergoing extratropical https://forecast.weather.gov/glossary.php?word=extratropical transition as it tracks
across our forecast area. As the remnant wind field and copious
amounts of moisture https://forecast.weather.gov/glossary.php?word=moisture associated with Ida encounter the
baroclinic zone associated with the trough https://forecast.weather.gov/glossary.php?word=trough to our west, strong
warm advection https://forecast.weather.gov/glossary.php?word=advection/frontogenesis https://forecast.weather.gov/glossary.php?word=frontogenesis will ensue aloft, leading to a long
lived period of heavy rainfall https://forecast.weather.gov/glossary.php?word=rainfall within the right entrance region
of the upper level jet https://forecast.weather.gov/glossary.php?word=jet situated to our north. This prolonged
period of steady, heavy rain will primarily be located across
the WV https://forecast.weather.gov/glossary.php?word=WV Panhandle and western MD, where widespread rainfall https://forecast.weather.gov/glossary.php?word=rainfall
totals of 3-6" are expected, with localized totals exceeding 8"
also possible. Some of these totals may also extend across far
northern MD further to the east as the zone of interaction
between Ida and the upper jet https://forecast.weather.gov/glossary.php?word=jet spreads eastward across PA. This
will lead to a high end threat for flash https://forecast.weather.gov/glossary.php?word=flash flooding across these
areas tomorrow, and then a threat for river flooding in the days
following (see hydrology https://forecast.weather.gov/glossary.php?word=hydrology section for details).

Locations to the east of the Blue Ridge https://forecast.weather.gov/glossary.php?word=Ridge will be further
displaced from the upper trough https://forecast.weather.gov/glossary.php?word=trough and resultant jet https://forecast.weather.gov/glossary.php?word=jet dynamics https://forecast.weather.gov/glossary.php?word=dynamics. As a
result, many locations there may start off the day dry. Not
only will locations be dry, but a few breaks of filtered
sunshine may develop by later in the morning into the early
afternoon hours. This will lead destabilization, with MLCAPE https://forecast.weather.gov/glossary.php?word=MLCAPE
values increasing into the 1000-1500 J/kg https://forecast.weather.gov/glossary.php?word=J/kg range. Also of note
from a thermodynamic perspective is the steepening of low-level
lapse rates near the surface in many of the CAMs, which when combined
with 3CAPE values of 100-150 J/kg https://forecast.weather.gov/glossary.php?word=J/kg should promote low-level
stretching of vertical vorticity https://forecast.weather.gov/glossary.php?word=vorticity in any stronger storms.
Kinematically speaking, the wind field associated with the
remnants of Ida is very impressive, with 40-50 knots of flow https://forecast.weather.gov/glossary.php?word=flow
extending from 925 hPa https://forecast.weather.gov/glossary.php?word=hPa all the way up through the mid-levels of
the atmosphere https://forecast.weather.gov/glossary.php?word=atmosphere. Hodographs have impressive clockwise curvature
through up 6 km, making ample streamwise vorticity https://forecast.weather.gov/glossary.php?word=vorticity available to
any right moving storms. CAMs show multiple arcs of storms
developing to the east of the Blue Ridge https://forecast.weather.gov/glossary.php?word=Ridge tomorrow afternoon.
Given the environment in place, any storm that forms tomorrow,
whether discrete or embedded within a larger linear structure
should be capable of exhibiting supercellular characteristics.
Multiple tornadoes and instances of damaging straight line winds
appear possible across the area in association with these
storms. As a result, the Storm Prediction Center has upgraded a
large portion of the area to the east of the Blue Ridge https://forecast.weather.gov/glossary.php?word=Ridge to an
Enhanced Risk for severe thunderstorms.

While rainfall https://forecast.weather.gov/glossary.php?word=rainfall won`t be steady to the east of the Blue Ridge https://forecast.weather.gov/glossary.php?word=Ridge,
individual thunderstorms will be capable of producing very high
instantaneous rainfall https://forecast.weather.gov/glossary.php?word=rainfall rates, given the potential for very
strong updrafts and the high precipitable water environment in
place. As a result, flash https://forecast.weather.gov/glossary.php?word=flash flooding is also possible in these
areas as well, but on a more localized basis compared to west of
the Blue Ridge https://forecast.weather.gov/glossary.php?word=Ridge.

Ida`s remnants will progress off to the east overnight Wednesday
night, bringing precipitation to an end areawide by daybreak
Thursday. High pressure will build in behind Ida during the day
Thursday, bringing a return to quieter weather conditions.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 210831_NWS_Ida_MEMA_200pm(1).pdf
Type: application/pdf
Size: 1493521 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/calv-ares/attachments/20210831/3e24cbc9/attachment-0001.pdf>