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

Tue Aug 31 18:47:34 EDT 2021

Thank you Shaw. Dale

On Tue, Aug 31, 2021, 18:17 Shawn Donley <n3ae at comcast.net> wrote:

> 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.______________________________________________________________
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