August Discobs 2025

[yoda]

https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=0925&yr=2025

 

Mesoscale Precipitation Discussion 0925
NWS Weather Prediction Center College Park MD
1025 AM EDT Wed Aug 13 2025

Areas affected...Portions of the Central Appalachians and
Mid-Atlantic

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

Valid 131425Z - 132025Z

SUMMARY...Clusters of heavy showers and thunderstorms with locally
extreme rainfall rates will tend to expand in coverage over the
next several hours. Scattered areas of flash flooding will
gradually become likely, and especially later this afternoon
closer to the I-95 corridor of the Mid-Atlantic where an urban
flash flood threat is expected to evolve.

DISCUSSION...The latest satellite and radar imagery shows a band
of heavy showers and thunderstorms moving into northern WV, and
the latest trends show cooling cloud tops associated with this
activity.

This convection is associated with the southwest flank of
mid-level vort energy going into the central Appalachians which is
embedded within a very moist and moderately unstable environment.
MLCAPE values across northern WV and western MD, and areas east of
the Blue Ridge over the Mid-Atlantic, are locally on the order of
1000+ J/kg. However, the PWs are quite high and locally over 2
standard deviations above normal.

In fact, the 12Z RAOB soundings from KPIT and KIAD showed PWs of
1.86 and 2.22 inches respectively with tall skinny CAPE profiles
and elevated WBZ/freezing levels. This is strongly suggestive of a
very efficient and tropical environment that will promote highly
efficient processes for locally extreme rainfall rates that may
reach well into the 2 to 3+ inch/hour range.

Convection should tend to generally build in coverage over the
next several hours as this vort energy advances off to the east
across the central Appalachians and northern Mid-Atlantic region.
This will support heavy showers and thunderstorms advancing east
through central and northern WV, western MD and southwest PA in
the near-term.

However, as instability and convergent low-level flow becomes
better established this afternoon east of the Blue Ridge and into
the Chesapeake Bay region, there will likely be the development
and expansion of very heavy showers and thunderstorms across much
of northern VA, central to northeast MD and southern PA, including
areas along the I-95 corridor from Washington D.C. to Philadelphia.

The latest hires model guidance may be underplaying the rainfall
potential given the level of moisture that is in place, and there
will the influence of diurnal heating and orographics that will
also support an uptick in coverage of showers and thunderstorms.

Slow cell-motions and localized cell-training concerns coupled
with locally extreme rainfall rates may support some localized
rainfall totals of 3 to 5 inches. Areas of scattered flash
flooding will become likely in time, and this will include an
increasing urban flash flood threat near the I-95 corridor by
later this afternoon.

Orrison

ATTN...WFO...AKQ...BGM...CTP...LWX...PBZ...PHI...RLX...RNK...

ATTN...RFC...RHA...TIR...NWC...

[JenkinsJinkies]

How much do you want to bet this dies as soon as it hits the 95 corridor?

[George BM]

1 hour ago, yoda said:

https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=0925&yr=2025

 

Mesoscale Precipitation Discussion 0925
NWS Weather Prediction Center College Park MD
1025 AM EDT Wed Aug 13 2025

Areas affected...Portions of the Central Appalachians and
Mid-Atlantic

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

Valid 131425Z - 132025Z

SUMMARY...Clusters of heavy showers and thunderstorms with locally
extreme rainfall rates will tend to expand in coverage over the
next several hours. Scattered areas of flash flooding will
gradually become likely, and especially later this afternoon
closer to the I-95 corridor of the Mid-Atlantic where an urban
flash flood threat is expected to evolve.

DISCUSSION...The latest satellite and radar imagery shows a band
of heavy showers and thunderstorms moving into northern WV, and
the latest trends show cooling cloud tops associated with this
activity.

This convection is associated with the southwest flank of
mid-level vort energy going into the central Appalachians which is
embedded within a very moist and moderately unstable environment.
MLCAPE values across northern WV and western MD, and areas east of
the Blue Ridge over the Mid-Atlantic, are locally on the order of
1000+ J/kg. However, the PWs are quite high and locally over 2
standard deviations above normal.

In fact, the 12Z RAOB soundings from KPIT and KIAD showed PWs of
1.86 and 2.22 inches respectively with tall skinny CAPE profiles
and elevated WBZ/freezing levels. This is strongly suggestive of a
very efficient and tropical environment that will promote highly
efficient processes for locally extreme rainfall rates that may
reach well into the 2 to 3+ inch/hour range.

Convection should tend to generally build in coverage over the
next several hours as this vort energy advances off to the east
across the central Appalachians and northern Mid-Atlantic region.
This will support heavy showers and thunderstorms advancing east
through central and northern WV, western MD and southwest PA in
the near-term.

However, as instability and convergent low-level flow becomes
better established this afternoon east of the Blue Ridge and into
the Chesapeake Bay region, there will likely be the development
and expansion of very heavy showers and thunderstorms across much
of northern VA, central to northeast MD and southern PA, including
areas along the I-95 corridor from Washington D.C. to Philadelphia.

The latest hires model guidance may be underplaying the rainfall
potential given the level of moisture that is in place, and there
will the influence of diurnal heating and orographics that will
also support an uptick in coverage of showers and thunderstorms.

Slow cell-motions and localized cell-training concerns coupled
with locally extreme rainfall rates may support some localized
rainfall totals of 3 to 5 inches. Areas of scattered flash
flooding will become likely in time, and this will include an
increasing urban flash flood threat near the I-95 corridor by
later this afternoon.

Orrison

ATTN...WFO...AKQ...BGM...CTP...LWX...PBZ...PHI...RLX...RNK...

ATTN...RFC...RHA...TIR...NWC...

Flood Watch
National Weather Service Baltimore MD/Washington DC
1157 AM EDT Wed Aug 13 2025

DCZ001-MDZ006-008-011-013-014-504-506>508-VAZ053-054-140000-
/O.NEW.KLWX.FA.A.0032.250813T1800Z-250814T0100Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
District of Columbia-Northern Baltimore-Cecil-Southern Baltimore-
Prince Georges-Anne Arundel-Central and Southeast Montgomery-
Central and Southeast Howard-Northwest Harford-Southeast Harford-
Fairfax-Arlington/Falls Church/Alexandria-
1157 AM EDT Wed Aug 13 2025

...FLOOD WATCH IN EFFECT UNTIL 9 PM EDT THIS EVENING...

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

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

* WHEN...Until 9 PM EDT this evening.

* IMPACTS...Excessive runoff may result in flooding of rivers,
  creeks, streams, and other low-lying and flood-prone locations.
  Flooding may occur in poor drainage and urban areas.

* ADDITIONAL DETAILS...
  - Thunderstorms are likely this afternoon into this evening
    with heavy rainfall within a short period of time. Localized
    rainfall amounts around 1 to 2 inches within an hour are
    likely. Multiple rounds of storms are possible with total
    rainfall amounts around 2 to 4 inches. This may cause creeks
    and small streams to rise out of their banks with flash
    flooding possible.
  - Please visit www.weather.gov/safety/flood for flood safety
    and preparedness information

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

$$

AVS

[Interstate]

The Latest HRRR says what rain.

[flsch22]

another ridiculous flood watch posted by LWX this summer.  Expecting <.25 in

[high risk]

models are not particularly impressive for this afternoon, but none seem to have a good handle on the evolving area of widespread, heavy convection to our west.    Radar is quite impressive.

[87storms]

Gorgeous humidity today. Looks like a swath of rain to the west, but will it get here? That’s a tall order based off the current steppe conditions.

[Weather Will]

Hope that rain makes it.  Has not rained in weeks in my backyard....

[Mrs.J]

29 minutes ago, 87storms said:

Gorgeous humidity today. Looks like a swath of rain to the west, but will it get here? That’s a tall order based off the current steppe conditions.

I brought the Catio inside. So you can curse me for jinxing our chances here in Frederick Co. 

[frd]

28 minutes ago, Weather Will said:

Hope that rain makes it.  Has not rained in weeks in my backyard....

Soil moisture is diving down rapidly. 

Needing rain is an understatement.

 

[WVclimo]

Getting some loud thunder already from a small cell to my north that developed ahead of the main batch moving this way from western Md.  Looks like a pretty interesting afternoon possible here.

[Weather Will]

It is raining!!!!!  

[Eskimo Joe]

Sneaky severe day today:

• Surface CAPE 3,000 + across most of the area
• LI -6 or better east of US 15
• High PWATs w/ some mid level drying to aid propagation of isolated wet microbursts.
• Surface lapse rates are decent

Might see a few decent cells fire along some boundary. 

[frd]

 

This will be missed.

 

 

 

[dailylurker]

It looks like the NAM 3k from this morning. It had most of the heavy stuff slipping south of DC. It looks like it might be onto something. 

[WxUSAF]

3 minutes ago, dailylurker said:

It looks like the NAM 3k from this morning. It had most of the heavy stuff slipping south of DC. It looks like it might be onto something. 

Yup. Looks like a MD split unless something changes in a hurry.

[87storms]

2 hours ago, Mrs.J said:

I brought the Catio inside. So you can curse me for jinxing our chances here in Frederick Co. 

You might have been onto something...looks like the humidity is simply no match for the FDK rain shadow.

[EastCoast NPZ]

Simply amazing watching the rain literally move around to avoid my area.  

[87storms]

35 minutes ago, WxUSAF said:

Yup. Looks like a MD split unless something changes in a hurry.

Probably not the 270 split, though...that's a powerhouse microclimate.

[MDphotog]

5 hours ago, JenkinsJinkies said:

How much do you want to bet this dies as soon as it hits the 95 corridor?

Uh, you have any lottery numbers you like for us Hagerstown/Frederick peeps? 

[Interstate]

The HRRR did a pretty good job with that blob earlier in western MD

[scope1]

Been sitting in the sweet spot constant thunder lightning and rain. Flash flood warning for my house. 

[frd]

Will be interesting to see storm development in the next few hours on the upper Eastern Shore, maybe some interactions from earlier storm outflows. 

Storms are developing East of Baltimore and West of the Aberdeen Proving Ground. 

[WxUSAF]

Swing and a miss

[JenkinsJinkies]

CWG says there’s storm chances every day next week. How likely is it that they all go down the tubes?