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George BM

August Discobs 2020

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9 minutes ago, snowfan said:

GFS = Enjoy rain chances for the next week. Ugh. 

Yeah it’s a bit damp. Ggem much less as it gives a better push to the fall-like HP next week.

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26 minutes ago, southmdwatcher said:

GFS 12Z----How about plentiful rains for the next two weeks. We do not need that to verify

Exactly, Winds either from the South, SE  or the East for days on end. Like to see the EPS later. 

 

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Flash Flood Watch posted for tomorrow for most in the region except NW VA/E WV and W MD from Hagerstown westward... 1-2 inches with potential for 4 inches in isolated areas...

Flood Watch
National Weather Service Baltimore MD/Washington DC
319 PM EDT Tue Aug 11 2020

DCZ001-MDZ004>006-011-013-014-016>018-503>508-VAZ025-026-029-
036>040-050>057-501-502-505>508-120400-
/O.NEW.KLWX.FF.A.0020.200812T1600Z-200813T0300Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
District of Columbia-Frederick MD-Carroll-Northern Baltimore-
Southern Baltimore-Prince Georges-Anne Arundel-Charles-St. Marys-
Calvert-Northwest Montgomery-Central and Southeast Montgomery-
Northwest Howard-Central and Southeast Howard-Northwest Harford-
Southeast Harford-Augusta-Rockingham-Page-Nelson-Albemarle-Greene-
Madison-Rappahannock-Orange-Culpeper-
Prince William/Manassas/Manassas Park-Fairfax-
Arlington/Falls Church/Alexandria-Stafford-Spotsylvania-
King George-Northern Fauquier-Southern Fauquier-Western Loudoun-
Eastern Loudoun-Northern Virginia Blue Ridge-
Central Virginia Blue Ridge-
Including the cities of Washington, Frederick, Ballenger Creek,
Eldersburg, Westminster, Reisterstown, Cockeysville, Baltimore,
Bowie, Suitland-Silver Hill, Clinton, College Park, Greenbelt,
Laurel, Camp Springs, Glen Burnie, Annapolis, Severn, South Gate,
Severna Park, Arnold, Odenton, St. Charles, Waldorf,
Lexington Park, California, Chesapeake Beach, Huntingtown,
Dunkirk, North Beach, Lusby, Prince Frederick, Germantown,
Damascus, Bethesda, Rockville, Gaithersburg, Silver Spring,
Lisbon, Columbia, Ellicott City, Jarrettsville, Aberdeen,
Staunton, Waynesboro, Stuarts Draft, Harrisonburg, Luray,
Shenandoah, Stanley, Lovingston, Charlottesville, Stanardsville,
Madison, Orange, Gordonsville, Culpeper, Dale City, Manassas,
Woodbridge, Lake Ridge, Montclair, Reston, Herndon, Annandale,
Centreville, Chantilly, McLean, Franconia, Arlington, Alexandria,
Falls Church, Falmouth, Fredericksburg, Dahlgren, Warrenton,
Turnbull, Purcellville, Leesburg, Ashburn, Sterling, Big Meadows,
and Wintergreen
319 PM EDT Tue Aug 11 2020

...FLASH FLOOD WATCH IN EFFECT FROM WEDNESDAY AFTERNOON THROUGH
WEDNESDAY EVENING...

The National Weather Service in Sterling Virginia has issued a

* Flash Flood Watch for portions of Maryland, The District of
  Columbia, and Virginia, including the following areas, in
  Maryland, Anne Arundel, Calvert, Carroll, Central and
  Southeast Howard, Central and Southeast Montgomery, Charles,
  Frederick, Northern Baltimore, Northwest Harford, Northwest
  Howard, Northwest Montgomery, Prince Georges, Southeast
  Harford, Southern Baltimore, and St. Marys. The District of
  Columbia. In Virginia, Albemarle, Arlington/Falls
  Church/Alexandria, Augusta, Central Virginia Blue Ridge,
  Culpeper, Eastern Loudoun, Fairfax, Greene, King George,
  Madison, Nelson, Northern Fauquier, Northern Virginia Blue
  Ridge, Orange, Page, Prince William, Rappahannock, Rockingham,
  Southern Fauquier, Spotsylvania, Stafford, and Western
  Loudoun.

* From Wednesday afternoon through Wednesday evening

* A cold front will move into the area Wednesday and then stall
  out. Numerous slow moving showers and thunderstorms will pose a
  risk of flash flooding. Thunderstorms could produce one to two
  inches of rain with isolated amounts up to four inches possible.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Flash Flood Watch means that conditions may develop that lead
to flash flooding. Flash flooding is a very dangerous situation.

You should monitor later forecasts and be prepared to take action
should Flash Flood Warnings be issued.

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Nice cell over Whitemarsh Middle River area.  Been tracking it on private cameras near Route 40 and Allender Rd.

It just keeps training.  If this picks up there's gonna be some swimming tonight. ;)

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Going to ocmd Saturday for the airshow. It does look much drier than the wed thru fri period so it should be mostly dry.

Looking for some weenie training cells tomorrow :weenie:

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2 minutes ago, George BM said:

Thunder woke me up in Herndon.

Woke me up here in West Springfield as I was falling asleep 

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4 minutes ago, DanTheMan said:

Several car alarms in my complex just went off with a close strike and BOOMING thunder

Looks like the line is slowly forming and moving slowly east too... could be one of those long term storms that last a while

  • Like 1

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Yup already 

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Flood Warning
National Weather Service Baltimore MD/Washington DC
355 AM EDT Wed Aug 12 2020

VAC059-153-683-685-121400-
/O.NEW.KLWX.FA.W.0110.200812T0755Z-200812T1400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Fairfax VA-City of Manassas Park VA-Prince William VA-
City of Manassas VA-
355 AM EDT Wed Aug 12 2020

The National Weather Service in Sterling Virginia has issued a

* Flood Warning for...
  West central Fairfax County in northern Virginia...
  The City of Manassas Park in northern Virginia...
  Central Prince William County in northern Virginia...
  The City of Manassas in northern Virginia...

* Until 1000 AM EDT Wednesday.

* At 354 AM EDT, Doppler radar indicated thunderstorms producing
  heavy rain which will cause flooding. Up to two inches of rain
  have already fallen. Additional rainfall amounts of up to an inch
  are possible.

* Some locations that will experience flooding include...
  Bull Run, Manassas, Sudley and Manassas Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don`t drown when encountering flooded roads. Most flood
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the
dangers of flooding.

Excessive runoff from heavy rainfall will cause flooding of small
creeks and streams, urban areas, highways, streets and underpasses as
well as other drainage areas and low lying spots.

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BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Baltimore MD/Washington DC
407 AM EDT Wed Aug 12 2020

The National Weather Service in Sterling Virginia has issued a

* Flash Flood Warning for...
  West central Fairfax County in northern Virginia...
  The City of Manassas Park in northern Virginia...
  Central Prince William County in northern Virginia...
  The City of Manassas in northern Virginia...

* Until 800 AM EDT.

* At 406 AM EDT, Doppler radar indicated thunderstorms producing
  heavy rain across the area. Up to three inches of rain have already
  fallen. Rain of one to two inches is expected in the next hour.
  Flash flooding is ongoing or expected to begin shortly.

  HAZARD...Life threatening flash flooding. Heavy rain producing
           flash flooding.

  SOURCE...Radar indicated.

  IMPACT...Life threatening flash flooding of creeks and streams,
           urban areas, highways, streets and underpasses.

* Some locations that may experience flooding include...
  Centreville...                    Linton Hall...
  Bull Run...                       Manassas...
  Sudley...                         Manassas Park...
  • Like 1

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Manassas is getting clobbered, radar estimated 3 inches just south of me, .3ish so far in Centreville with plenty to come. Very tropical morning.

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Good read on the setup for today from Mount Holly. There will probably be plenty of areas that don't see heavy rain, or much of anything. Locations that get under a storm will get dumped on.

Quote

The front is expected to stall over our region today. As mentioned by the previous shift, we will have precipitable water values well above normal along and southeast of the front. As we have seen the last few days, we will likely have CAPE values getting near or above 1000 J/kg ahead of the front with little (if any) CIN. Synoptic scale lift is still quite limited (though we will be on the fringe of the right entrance region of the upper level jet by late today into this evening). However, weak mesoscale lift both along the front and along any sea and bay breezes should be more than enough for convective initiation.

What is most unusual about today is the wind profiles over the region. Model soundings show wind speeds 6 kt or less through a deep layer (from the surface through approximately 450 mb). Consequently storm motions are going to be very slow (likely 5 mph or less!). Additionally, this means that bulk shear values in some areas are near zero. Bottom line is that with the weak lift and almost negligible shear, I`m not sure how widespread the coverage of showers and storms will be. However, for anything that does develop, heavy rain leading to flash flooding will be a concern.

 

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9 minutes ago, CAPE said:

Good read on the setup for today from Mount Holly. There will probably be plenty of areas that don't see heavy rain, or much of anything. Locations that get under a storm will get dumped on.

 

LWX seems the total opposite in their morning AFD if I am reading what you posted right 

Quote
NEAR TERM /UNTIL 6 PM THIS EVENING/...
Weak upper level disturbance moving over the region presently
has caused a late-night outbreak of thunderstorms. Heavy rain is
common given the high PW`s and slow motion. Think flash flooding
with this initial burst of storms today will be isolated, but
have considered extending watch to start presently. Will monitor
radar trends.

Should see a lull with some sun later this morning as the upper
disturbance moves away. Then another, more potent disturbance
will move in along with the surface front, spelling a more
significant round of heavy thunderstorms. Certainly will have
some isolated severe risk, but with slow motions, high PW`s and
wet antecedent conditions in many areas, a significant flash
flood threat exists. Highs will reach the low 90s before the
storms re-erupt, possibly for the last time for several days.

&&

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1 minute ago, yoda said:

LWX seems the total opposite in their morning AFD if I am reading what you posted right 

Not really. LWX doesn't mention how widespread the coverage will, or wont be, while Mount Holly went into more detail on the mechanisms that will be in place for storm initiation, as well as uncertainty on the coverage due to weak lift/ shear. Bottom line is there will be some slow moving cells that will drop a lot of rain in a short amount of time, thus the FFW.

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WPC has the region in a moderate risk for excessive rainfall.

 

Quote

.THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER THE HEART OF THE MID ATLANTIC URBAN CORRIDOR... ...Eastern U.S...

There is a marked potential for scattered intense rainfall today, which first appears as a local maximum in the hi-res model consensus, but when one zooms in it comes more fully into focus. It is difficult to outline a Moderate Risk area for flash flooding associated with loosely organized summertime convection within weak low level inflow winds. Today, however, we have the heaviest model signal located across an area that is both urban and already saturated, and the environmental signal for heavy local rainfall rates is pretty exceptional. The 00Z KIAD sounding at Dulles Airport was particularly telling, with steep lapse rates and little inhibition, coupled with nearly a 2.00 inch precipitable water value. An upper trough is merely brushing across the top of this region, and into northern New England, and while this will provide only minimal lift, it will drop a cold front into position across southern Pennsylvania to near NYC by midday, helping to focus the pool of moisture and instability over the Mid-Atlantic states. Models forecast a swath of MUCAPE 2000 J/kg or more in the Moderate Risk area. Consumption of this instability pool may be chaotic, owing to storm initiation along sea breezes, mountain ridges, and outflows. But the net effect is usually for fairly broad scale overturning, resulting in scattered very heavy rain. In recent events the HREF has been good at placing the general axis of heaviest rainfall, and today that axis is essentially right along I-95 from Philadelphia to Washington D.C., and also cutting across the wet soil footprint left behind by a soggy 2-week period. We expect to see 2.0 inch PW in the pre convective environment, and note that the NAM Nest produces spotty 3-inch per hour rain rates today. That model frequently produces 2.0 to 2.50 inch rain rates, but rates of 3 are fairly rare in the model. This seems entirely plausible given the moisture, instability, and mean 0-6 km winds of only zero to five knots. Although there is not enough shear for well organized storms or training, the individual cells should be very robust and efficient, as well as nearly stationary.

 

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Yikes

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
556 AM EDT WED AUG 12 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0554 AM     FLASH FLOOD      1 WNW MANASSAS PARK     38.78N  77.47W
08/12/2020                   CITY OF MANASSAS   VA   911 CALL CENTER

            ROAD CLOSED DUE TO A SINKHOLE AT THE INTERSECTION OF
            MOSEBY CT. AND MOSEBY DR.

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6 minutes ago, CAPE said:

WPC has the region in a moderate risk for excessive rainfall.

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Wed Aug 12 2020
 
Day 1
Valid 01Z Wed Aug 12 2020 - 12Z Wed Aug 12 2020 

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER THE HEART 
OF THE MID ATLANTIC URBAN CORRIDOR...

...Eastern U.S...
There is a marked potential for scattered intense rainfall today, 
which first appears as a local maximum in the hi-res model 
consensus, but when one zooms in it comes more fully into focus. 
It is difficult to outline a Moderate Risk area for flash flooding 
associated with loosely organized summertime convection within 
weak low level inflow winds. Today, however, we have the heaviest 
model signal located across an area that is both urban and already 
saturated, and the environmental signal for heavy local rainfall 
rates is pretty exceptional. The 00Z KIAD sounding at Dulles 
Airport was particularly telling, with steep lapse rates and 
little inhibition, coupled with nearly a 2.00 inch precipitable 
water value. An upper trough is merely brushing across the top of 
this region, and into northern New England, and while this will 
provide only minimal lift, it will drop a cold front into position 
across southern Pennsylvania to near NYC by midday, helping to 
focus the pool of moisture and instability over the Mid-Atlantic 
states. Models forecast a swath of MUCAPE 2000 J/kg or more in the 
Moderate Risk area. Consumption of this instability pool may be 
chaotic, owing to storm initiation along sea breezes, mountain 
ridges, and outflows. But the net effect is usually for fairly 
broad scale overturning, resulting in scattered very heavy rain. 
In recent events the HREF has been good at placing the general 
axis of heaviest rainfall, and today that axis is essentially 
right along I-95 from Philadelphia to Washington D.C., and also 
cutting across the wet soil footprint left behind by a soggy 
2-week period. We expect to see 2.0 inch PW in the pre convective 
environment, and note that the NAM Nest produces spotty 3-inch per 
hour rain rates today. That model frequently produces 2.0 to 2.50 
inch rain rates, but rates of 3 are fairly rare in the model. This 
seems entirely plausible given the moisture, instability, and mean 
0-6 km winds of only zero to five knots. Although there is not 
enough shear for well organized storms or training, the individual 
cells should be very robust and efficient, as well as nearly 
stationary.

The flash flood threat may only last for about 4 hours, give or 
take, along the urban corridor, beginning around 17Z, but within 
that short period there may be some significant flash flooding.

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i guess i haven't been following closely enough to understand all the flood watches and excessive rainfall forecast. haven't seen shit for rain up here

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10 minutes ago, mappy said:

i guess i haven't been following closely enough to understand all the flood watches and excessive rainfall forecast. haven't seen shit for rain up here

It's because the set up is favorable for isolated to scattered convection, with high pwats and little in the way of steering flow. Hard to pinpoint exactly where this will occur, thus the broad brush flood watch. So yeah not everyone will see the heavy rain, but for places that do, it may be excessive, and given the recent bouts of heavy rain it wont take too much to cause flash flooding in the more saturated areas.

  • Thanks 1

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Looks like the trend on the latest guidance is for the High over SE Canada to nudge far enough south to give us a mostly dry weekend. It wont be "perfect", but more comfortable with temps in the low to mid 80s and somewhat lower dew points

 

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15 minutes ago, CAPE said:

It's because the set up is favorable for isolated to scattered convection, with high pwats and little in the way of steering flow. Hard to pinpoint exactly where this will occur, thus the broad brush flood watch. So yeah not everyone will see the heavy rain, but for places that do, it may be excessive, and given the recent bouts of heavy rain it wont take too much to cause flash flooding in the more saturated areas.

thanks! i should probably pay attention more :lol: 

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54 minutes ago, mappy said:

i guess i haven't been following closely enough to understand all the flood watches and excessive rainfall forecast. haven't seen shit for rain up here

Same here....probably the only place in Va that can say that... massive rain totals just minutes away in all directions ...1.72 inches

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