currently in your area
Posted by cypresstx on 9/9/2018, 11:57 am
makes for stressful prep I would imagine - keeping you all in our good thoughts

https://twitter.com/iembot_akq





Mesoscale Precipitation Discussion 0813
NWS Weather Prediction Center College Park MD
1138 AM EDT Sun Sep 09 2018

Areas affected...Virginia Tidewater, Lower Eastern Shore

Concerning...Heavy rainfall...Flash flooding likely

Valid 091536Z - 092130Z

Summary...Thunderstorms and heavy rain showers are likely to
persist around the Lower Chesapeake Bay region through much of the
day, including the Virginia Tidewater and Lower Eastern Shore.
These showers and storms may be nearly stationary at times, and
may produce localized extreme rain rates. Although flash flooding
may not be widespread, localized flash flooding is expected where
stalling storms occur.

Discussion...Surface observations revealed a surface wave or weak
low in the vicinity of Wakefield VA, with a complete circulation
evident in the wind field. This was forming along an existing
quasi-stationary front. From the mouth of the Chesapeake east into
the Atlantic, strong, confluent, low-level easterly flow was
developing along and north of the surface front, which was leading
to a highly focused area of low-level moisture flux and
convergence that was maximized in the Tidewater region near and
northeast of the surface low. The inflow region was also
characterized by precipitable water values over 2 inches, and
increasing instability with MLCAPE approaching 2000 j/kg. The RAP
forecasts show the surface wave/low slowly drifting north through
the day, which should lead to a relatively steady-state mesoscale
setup with abundant unstable, moist inflow arriving into a region
with significant low-level convergence. This favors continued
convective activity into the afternoon hours.

The convergence does not seem to be manifesting as a single,
dominant band, but instead is being modified by the shape of the
coastline and maximized in very localized areas. There is some
evidence of this in the highly variable storm motions on the KAKQ
radar at the moment, some quite different from the background mean
flow vectors or even Corfidi/Bunkers storm motion vectors. The
convection generally seemed to be either anchored on low-level
convergence maxima or showing different storm motion along a
low-level boundary. This should generally continue into the
afternoon hours, with convection anchored at times at points along
the complex coastline, perhaps initially in the Tidewater Region,
and eventually migrating north with the surface low toward the
Northern Neck, Middle Peninsula, and Lower Eastern Shore on the
southern portion of the Delmarva Peninsula.

MRMS and KAKQ dual pol radar estimates have shown rain rates
occasionally getting as high as 3 in/hr with nearly stationary
storms, although some of them have been just over adjacent marine
areas. The 12Z HREF neighborhood probability of 3+ inch per hour
rain rates generally exceeds 30 percent on most of the daytime
hours in some part of the region. And the HREF localized
probability matched mean, and recent runs of the operational HRRR,
show localized extreme rainfall totals approaching 10 inches by
00Z. Whether totals this high could occur is not certain, the
convection at the moment is rather limited in size, and the models
may be unable to resolve the very small nature of the convective
cells. Nevertheless, there is a strong model signal for locally
extreme rainfall rates (3+ in/hr) and that has been supported by
radar estimates in real time. These would be more than sufficient
to create flash flooding. Whether significant totals can
materialize in one or two areas remains to be seen, but is at
least a possibility.

Lamers

ATTN...WFO...AKQ...LWX...

ATTN...RFC...MARFC...SERFC...

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Comments from and concerning SE Virginia - AquaRN, 9/8/2018, 4:18 pm
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