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September Discobs 2022


George BM
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36 minutes ago, leesburg 04 said:

Seriously though are we done or does something magically appear later?

CAMs putting all their money into a 3 - 6 hours period of rain after beginning around midnight - 2:00 am Tuesday. Been watering my lawn all day so maybe I'll tick off the rain gods.

EDIT: 18z NAM is ugly. Less than 0.3" rain south and east of I-81. If this were winter people would be screaming.

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Mesoscale Precipitation Discussion 0952
NWS Weather Prediction Center College Park MD
450 PM EDT Mon Sep 05 2022

Areas affected...Portions of the Central Appalachians...Northern
Mid-Atlantic...Central/Southern NY

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

Valid 052050Z - 060250Z

SUMMARY...Persistent areas of heavy rain with locally focused
areas of showers and thunderstorms producing enhanced rainfall
rates are expected to drive an increasing threat of flash flooding
heading through the evening hours.

DISCUSSION...The latest GOES-16 IR/WV suite shows a deep layer
southwest fetch of moisture and energy aloft traversing a large
area of the eastern U.S. with an emphasis on the Appalachians,
northern Mid-Atlantic and southern New England this afternoon.
Already areas of heavy rain with locally embedded pockets of
stronger convection are impacting areas from central WV northeast
through central to northeast PA, and across areas of central and
southern NY.

The airmass out across the eastern slopes of the Appalachians and
the Piedmont areas of the central/northern Mid-Atlantic has been
gradually destabilizing over the last several hours with the
persistence of at least filtered solar insolation. MLCAPE values
have increased locally to 500 to 1000 j/kg. Meanwhile, PWs across
the region are high with values of 1.8 to 2.0 inches which are
locally over 2 standard deviations above normal for this time of
the year.

Over the next several hours, this moisture and energy transport up
from the south and southwest will be interacting with some of the
more orographically favored terrain along and adjacent to the Blue
Ridge from eastern WV through south-central and southeast PA for
concerns of locally focused and slow-moving showers and
thunderstorms. Radar imagery over the last couple of hours has
been showing the development and expansion of convective activity
as confluent low-level flow and the improving thermodynamic
environment focuses across these areas.

Meanwhile, areas farther north across north-central to northeast
PA and adjacent areas south-central and southeast NY will also be
a focus area for locally very heavy rainfall, and especially with
a front stalled out across this region. Stronger frontogenetical
forcing and isentropic ascent more broadly over the region coupled
with pockets of elevated instability are expected to maintain a
broad shield of moderate to locally heavy rain, but with localized
swaths of slow-moving convection capable of enhanced rainfall
rates.

Warm rain processes will be in place this evening given the deeper
layer transport of tropical moisture into the region and with much
of the forcing noted in the lower/mid-levels of the column. This
will yield some efficiently high rainfall rates that will
occasionally reach 2 to 3+ inches/hour. Additional rainfall
amounts at least locally going through 03Z this evening may reach
3 to 5 inches, with some of the heavier signals for this showing
up over areas of south-central NY. Observational trends suggest
areas of south-central to northeast PA will need to be closely
monitored for similar rainfall amounts.

Given the enhanced to locally extreme rainfall rate potential, and
the storm totals through mid-evening, the threat for flash
flooding will be increasing over the next several hours.

Orrison

ATTN...WFO...ALY...BGM...BUF...CTP...LWX...OKX...PBZ...PHI...
RLX...

ATTN...RFC...MARFC...NERFC...OHRFC...NWC...

mcd0952.gif

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23 minutes ago, Eskimo Joe said:

^We're on the wrong side of the front. All the efficient rain making processes are up in PA.

For now. As the W Atlantic ridge continues to weaken, the front will progress southward. Remains to be seen if the combo of upper jet, mid level vorticity advection, and PWAT coincide further south tomorrow. The way things look on latest guidance, I may have to be happy with a half inch here.

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15 minutes ago, CAPE said:

For now. As the W Atlantic ridge continues to weaken, the front will progress southward. Remains to be seen if the combo of upper jet, mid level vorticity advection, and PWAT coincide further south tomorrow. The way things look on latest guidance, I may have to be happy with a half inch here.

Always seems like in mid-Septemberish we get a week or cooler cloudy wet weather.  I time it every year to plant my grass seed.  I've always assumed it's that the front path has finally sunk down to our latitude.  

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Rained a little yesterday and a little today. What’s been kinda surprising to me is how quickly the trails have dried this summer after each rain event. I think fall and winter were somewhat dry which may be part of the reason. I know there have been areas with localized flooding esp closer to dc, but overall it feels like we’ve had just the right amount of rain here. Took a trip to Michaux a couple weeks ago and it was the same story.

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...FLOOD WATCH IN EFFECT FROM 4 AM EDT TUESDAY THROUGH TUESDAY
AFTERNOON...

* WHAT...Flash flooding caused by excessive rainfall is possible.

* WHERE...Portions of DC, Maryland and northern Virginia, including
  the following areas: in DC, District of Columbia. In Maryland,
  Anne Arundel, Carroll, Cecil, Central and Southeast Howard,
  Central and Southeast Montgomery, Frederick MD, Northern
  Baltimore, Northwest Harford, Northwest Howard, Northwest
  Montgomery, Prince Georges, Southeast Harford and Southern
  Baltimore. In northern Virginia, Arlington/Falls
  Church/Alexandria, Eastern Loudoun, Fairfax and Western Loudoun.

* WHEN...From 4 AM EDT Tuesday through Tuesday afternoon.

* IMPACTS...Excessive runoff may result in flooding of rivers,
  creeks, streams, and other low-lying and flood-prone locations.

* ADDITIONAL DETAILS...
  - An area of low pressure is expected to develop along a slow
    moving boundary draped across the region Tuesday morning
    through early Tuesday afternoon. Heavy showers and a few
    thunderstorms are expected to drop 2 to 3 inches across much
    of the watch area, with isolated higher amounts up to 5
    inches possible in the heaviest cells.
  - http://www.weather.gov/safety/flood
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