2025 Severe Weather General Discussion

[yoda]

MRGL risk up, SLGT out into western MD for Monday 

[high risk]

16 hours ago, yoda said:

MRGL risk up, SLGT out into western MD for Monday 

         Simulated radars look really interesting, but the soundings suggest that the convection will be elevated due to early evening cooling and therefore have limited SVR potential.     That said, the dynamics are really strong, so this is certainly worth a look.

[yoda]

9 hours ago, high risk said:

         Simulated radars look really interesting, but the soundings suggest that the convection will be elevated due to early evening cooling and therefore have limited SVR potential.     That said, the dynamics are really strong, so this is certainly worth a look.

Excellent writeup from LWX this morning in their AFD regarding the threat 

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The weather pattern becomes active for the start of the work week,
with several systems bringing the chance for severe thunderstorms,
strong winds, and mountain snow.

Brief mid-level ridging over the area Monday fades as a strong upper
trough over the Great Lakes tracks toward the Mid-Atlantic Monday
night into Tuesday. The parent surface low deepens as it moves over
the Upper Great Lakes into Ontario. A leading shortwave trough and
its associated cold front cross the OH Valley Monday afternoon, then
the Mid-Atlantic Monday night where the front flattens out. The main
upper trough digs into the Mid-Atlantic Tuesday into Wednesday,
bringing with it a series of reinforcing cold fronts.

Dry and mostly cloudy conditions to begin Monday, as highs reach the
upper 60s to 70s. Some spots in Central VA could reach around 80F.
The subtle mid-level ridging Monday afternoon could help break some
of the clouds, allowing temps to get a little higher than forecast
north of I-66. Uncertainty is still rather high on how warm we get,
and also how quickly/how far north 50s dew points advect in from the
south/west. The current forecast has highs around 70F and dew
points in the low/mid 50s by late afternoon for most of the area.
How much instability develops is going to be the biggest factor in
whether severe thunderstorms can persist east of the Allegheny Front.

Thunderstorms that develop along the cold front in the OH Valley
reach the Alleghenies late Monday afternoon to Monday evening.
Models continue to indicate a favorable environment to support
severe thunderstorms Monday evening (instability aside). An EML
advecting in aloft brings steep lapse rates around 7-8 C/km. With
500mb temps approaching -15C there is going to be a threat for large
hail with any severe thunderstorm that develops. The EML is going to
cap convection for most of the day, though models continue to insist
it is overcome by mid-level height falls atop the advancing surface
front. Strengthening winds aloft result in deep-layer shear in
excess of 65 knots, with curved low-level hodographs also adding to
increasing helicity values.

Fast moving severe thunderstorms will be capable of producing
damaging wind gusts and large hail. SPC has expanded the Slight Risk
(level 2 of 5) across all of the Potomac Highlands and Northern
Shenandoah Valley, with a Marginal Risk (level 1 of 5) for the
remainder of the area. As storms move east of the Blue Ridge they
likely become elevated as the boundary layer stabilizes in the
evening and/or due to a linger cap. Depending on how much
instability lingers, could see a severe storm or two approach the I-
95 corridor later in the evening. Showers and thunderstorms decrease
in coverage overnight, though some showers could linger overnight.
Mild temps in the 50s Monday night.

[yoda]

Oh ok then

ay 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1243 AM CDT Sun Apr 13 2025

   Valid 141200Z - 151200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN THE UPPER OH
   VALLEY AND CENTRAL APPALACHIANS...

   ...SUMMARY...
   A couple tornadoes along with scattered damaging winds and large
   hail are possible from mid-afternoon to mid-evening across parts of
   the Upper Ohio Valley and central Appalachians.

   ...Synopsis...
   A shortwave trough will further amplify over the Upper Great Lakes
   towards the ON/QC border, supporting gradual deepening of a surface
   cyclone from 995 to 990 mb. In its wake, a separate shortwave
   impulse and intense mid-level jetlet will dive southeast across the
   northern Great Plains towards the Lower OH Valley. A surface cold
   front will arc south across the Lower Great Lakes and then
   southwestward through the Mid-South by late afternoon Monday. 

   ...OH Valley to the Mid-Atlantic States...
   While guidance has largely been consistent with synoptic-scale
   pattern over the past several days, large spread exists in the
   degree of boundary-layer heating on Monday afternoon ahead of the
   surface cold front. For example, the 00Z NSSL-ARW and HRW-FV3 are
   10-15 F colder with warm-moist sector surface temps compared to the
   00Z HRRR and HRW-ARW. These latter models simulate multiple
   long-track supercells. This heating discrepancy, along with low
   confidence in the aggressive low-level moistening indicated by most
   guidance beneath an expansive EML, mitigates a categorical upgrade
   this cycle. But all three hazards have been highlighted with level
   2-SLGT risk probabilities. 

   Overall expectation is for a ribbon of mid to upper 50s surface dew
   points to advect as far northeast as the Upper OH Valley. If robust
   boundary-layer heating indeed occurs, this would support MLCAPE near
   1000 J/kg. The initial presence of the EML may delay storm
   development along the front until mid afternoon. But guidance
   consensus suggests at least scattered thunderstorms should form in
   the Central to Upper OH Valley vicinity as mid-level height falls
   increase atop the modestly convergent surface front. The approach of
   an intense mid-level jet will support fast-moving convection, along
   with effective bulk shear above 60 kts. Despite veered surface
   winds, low-level hodograph curvature should be moderately enlarged.
    
   A few supercells seem plausible in this setup, a couple of which may
   become long-tracked. These appear most probable across the southeast
   OH to northern WV vicinity, where tornado potential should be
   maximized during the early evening. Otherwise, a mix of large hail
   and damaging wind swaths are expected. East of the higher terrain in
   MD/northern VA, remnant steep low-level lapse rates may support
   isolated damaging gusts and marginal hail, before convection
   wanes/becomes increasingly elevated Monday night.

   ..Grams.. 04/13/2025

[yoda]

SLGT risk gets into the i81 corridor in VA, all of E WV and right next to C MD now.  15% hail and wind, as well as 2% tor

[Kmlwx]

Wow yeah the 6z HRRR looked ferocious on sim reflectivity. We'll see...

[yoda]

2 minutes ago, Kmlwx said:

Wow yeah the 6z HRRR looked ferocious on sim reflectivity. We'll see...

I think as LWX mentioned in their AFD and as you have mentioned multiple times in your posts regarding this potential threat, how much sun can we get and the dewpoints WRT moisture return 

[Kmlwx]

4 minutes ago, yoda said:

I think as LWX mentioned in their AFD and as you have mentioned multiple times in your posts regarding this potential threat, how much sun can we get and the dewpoints WRT moisture return 

I think the most excitement would come from us getting to the warmer/more moist side of guidance AND perhaps the storms arriving a bit earlier than currently forecast. This would offset both the waning daytime heating and overall potential for lacking instability. Even elevated convection can be fun, though.

This will be an interesting test of the @Eskimo Joe theory that having good MLLR/remnant EML impacts can offset other less favorable factors. Of course, it's not an ace to just have the EML...but we haven't had one in ages. 

[yoda]

1 hour ago, Kmlwx said:

Wow yeah the 6z HRRR looked ferocious on sim reflectivity. We'll see...

*takes a peek at the 12z HRRR UDH swaths and sim reflectivity*

Oh...

[yoda]

12z NAM has what looks to be a complex I'm guessing on sim radar that moves through between 03z and 06z... but sub severe as @high risk has mentioned above

12z NAM Nest is more MD centric on sim radar... has a light UHD swath in C MD just north of DC between 03z and 05z

[high risk]

2 hours ago, Kmlwx said:

I think the most excitement would come from us getting to the warmer/more moist side of guidance AND perhaps the storms arriving a bit earlier than currently forecast. This would offset both the waning daytime heating and overall potential for lacking instability. Even elevated convection can be fun, though.

This will be an interesting test of the @Eskimo Joe theory that having good MLLR/remnant EML impacts can offset other less favorable factors. Of course, it's not an ace to just have the EML...but we haven't had one in ages. 

       The EML will definitely be there, but the impact of an EML can be significantly lessened if you're dealing with a stable surface layer.   You're all spot on that every hour earlier that convection arrives makes a huge difference here.

       Let's look at the HRRR temperatures, since it's the warmest model.   Here is peak heating time:

 

          That's plenty warm for the Shenandoah Valley and across most of northern VA, but it's much cooler across central MD, and other guidance seems to be in agreement.   Not sure that earlier arrival will help as much for areas east of the Potomac as we think.    The HRRR brings convection racing west to east generally north of I-66, and the reflectivity looks super cool, but the forecast soundings in advance are not awesome:

 

  

      Thunder?   With those lapse rates generating a good amount of elevated CAPE, you betcha.     Shear is super.    But that very stable surface layer  is going to make it incredibly difficult to get wind down to the ground.    And despite the good lapse rates to promote hail, the freezing level is quite high, so the stones would likely melt before reaching the surface.     But perhaps the overall speed of the MCS (or whatever you want to call it) will drive some better gusts than this sounding might imply.    As mentioned earlier, the dynamics (500 height falls are nice!) are super.   As the outlook implies, the highest threat is definitely further west and northwest with lowering threats the farther east one goes.

[Kmlwx]

Great writeup as always!

One thing I'm noticing is the past few HRRR runs (the ones that go out far enough) have been shifting south with the elevated activity. I'm interested to see if that continues. 

[Eskimo Joe]

I'm not sold on tomorrow. We don't have any real surface instability.

[Kmlwx]

10 minutes ago, Eskimo Joe said:

I'm not sold on tomorrow. We don't have any real surface instability.

Me either - I mean I do think we will see some sort of elevated thunderstorm activity moving through (probably after dark) but severe risk remains to be seen. Waste of an EML if it plays out like that. 

[yoda]

SLGT risk for just about everyone per new Day 1 from SPC... 2/15/15

[yoda]

Morning AFD from LWX 

NEAR TERM /THROUGH TONIGHT/...
A strong upper trough over the Upper Plains/Great Lakes swings
through the Midwest/OH Valley today into tonight. Ahead of this
system, a leading shortwave trough and its associated surface cold
front are expected to move across the OH Valley to Mid-Atlantic
through tonight. At least scattered thunderstorms that develop along
the front move across the Alleghenies late this afternoon, then into
the I-81 corridor toward I-95 this evening. Multiple clusters of
strong to severe thunderstorms are possible as the front moves
through this evening.

Abundant mid level clouds are present this morning, with
temperatures generally in the 40s. Conditions are expected to remain
dry for most of the day, with showers/storms approaching the
Alleghenies probably around 5-6PM.

A warm front is forecast to move north through the area today,
bringing with it warmer temperatures and increasing low-level
moisture. However, even now there remains some uncertainty in how
far north the front makes it. While most of 00Z guidance shows the
front making it to the MD/PA border, there are still a few models
that keep the front around the Potomac River or near I-66. This
leaves uncertainty in the amount of instability that develops across
the northern portions of the CWA. To the south of the front,
temperatures are expected to warm quickly to the 70s this afternoon
with low 80s in parts of Central VA. Dew points reach the low to mid
50s by late afternoon.

Generally expecting favorable conditions for some clusters of strong
to severe thunderstorms to move across the area this evening. The
entire area will be overspread with 60-65 kt of deep layer shear and
steep mid-level lapse rates (due to a passing EML). Model soundings
indicate MLCAPE values of 600-1200 J/kg reaching the I-81 corridor,
and 500-800 J/kg east of the Blue Ridge to I-95. Due to backed low-
level flow and increasing winds aloft, 0-3km SRH values approach 200-
300 m2/s2 across most of the area this evening. This could provide a
small window for a tornado or two to develop, though the greatest
chance for that will be west of the Blue Ridge. Otherwise,
supercells and line segments will be capable of producing damaging
wind gusts and large hail.

As the front moves through the area, it is forecast to flatten and
slow down tonight. This could keep showers in the forecast
along/south of I-66 and along/east of I-95. Mild conditions tonight
as lows settle in the 50s to low 60s.

 

[Warm Nose]

SPC pretty consistent we'll get some severe weather

 

SPC AC 141249

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0749 AM CDT Mon Apr 14 2025

   Valid 141300Z - 151200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   INTO EARLY TONIGHT FROM EASTERN KENTUCKY ACROSS WEST VIRGINIA INTO
   CENTRAL VIRGINIA...

   ...SUMMARY...
   Scattered strong to severe storms are expected this afternoon
   through early tonight from the Upper Ohio Valley eastward to the
   Mid-Atlantic. Large hail, severe wind gusts, and a couple of
   tornadoes will be possible.

   ...Upper OH Valley this afternoon into VA early tonight...
   An initial shortwave trough and surface cyclone will occlude by
   tonight between Lake Superior and James Bay, as an upstream
   shortwave trough digs southeastward from the northern Plains toward
   the OH Valley.  An associated surface cold front will move
   southeastward across the OH Valley today, while a corridor of
   moisture return occurs ahead of the front from the Mid-South to WV. 
   Surface heating in cloud breaks will drive temperatures into the 70s
   by early-mid afternoon, coincident with northeastward advection of
   55-60 F boundary-layer dewpoints beneath the northeastward extent of
   an elevated mixed layer.  Though the upstream moisture source is
   rather modest by mid April standards, recent green up and unusually
   moist ground across the OH Valley will augment evapotranspiration. 
   These processes will result in MLCAPE of 1000-1500 J/kg with minimal
   convective inhibition as low-level ascent focuses along the front.

   Thunderstorm development is expected by mid afternoon in a broken
   band along the cold front from northern KY into southern OH, and
   storms subsequently expand in coverage while spreading
   east-southeastward across WV into VA through early tonight.  The
   moderate buoyancy and long hodographs will support supercells
   capable of producing large hail of 1-2 inches in diameter, and
   damaging winds of 60-75 mph are also expected, especially with any
   upscale growth into bowing segments.  Low-level shear/hodograph
   curvature will be sufficient for some tornado threat, though this
   will be modulated by the degree of low-level moistening. 
   Clusters/line segments will persist east of the Appalachians into VA
   through early tonight, though the severe threat will diminish with
   eastward extent and after 03z. 

   ...SD to IA this afternoon/evening...
   Despite limited low-level moisture, surface heating beneath cooling
   midlevel temperatures will support weak surface-based buoyancy and
   the potential for low-topped thunderstorms from SD into IA (in
   advance of the digging shortwave trough now over western ND/eastern
   MT).  Relatively cold temperature profiles will favor some threat
   for small hail, while steep low-level lapse rates and 30+ kt flow
   through the mixed layer favor gusty outflow winds of 40-50 mph.

   ..Thompson/Dean.. 04/14/2025

[Kmlwx]

I saw some breaks in the clouds on the way into work this morning. 

[yoda]

14 minutes ago, Kmlwx said:

I saw some breaks in the clouds on the way into work this morning. 

Lots of blue sky here

[Kmlwx]

HRRR is focusing the most intense activity south of the Potomac. NAM nest looks better for MBY...and all that to say it's still probably elevated stuff. 

[Kmlwx]

HREF also focuses most UH tracks south of the Potomac. I think this is reasonable given those areas are much more likely to be south of the boundary and perhaps more susceptible to surface-based convection. Not ruling out storms for MBY - but I'm less enthused up this way (for now). 

[Eskimo Joe]

13z HRRR insists on tornadoes for West Virginia and Virginia. I could see SPC bumping the torn risk up to ENH for West Virginia, and/or extending the 5% east to the I-81 corridor.

[yoda]

11 minutes ago, Eskimo Joe said:

13z HRRR insists on tornadoes for West Virginia and Virginia. I could see SPC bumping the torn risk up to ENH for West Virginia, and/or extending the 5% east to the I-81 corridor.

The 5% tor on 1300z is just about there already tbh... it'd only need like a 50 mile shift east.  Unless you are talking more about into the Panhandle of WV...

[Eskimo Joe]

45 minutes ago, yoda said:

The 5% tor on 1300z is just about there already tbh... it'd only need like a 50 mile shift east.  Unless you are talking more about into the Panhandle of WV...

Yea that too.

[yoda]

ENH up for wind.  30 from WV into and just east of the i81 corridor 

[Eskimo Joe]

4 minutes ago, yoda said:

ENH up for wind.  30 from WV into and just east of the i81 corridor 

Called it, well the ENH upgrade at least.

[Kmlwx]

HRRR continues to prefer well south...it might still be trending south with the activity too...

If I was just going off of the HRRR, I'd probably stop even saying the Potomac as the dividing line...more like somewhere between I-66 and I-64. 

 

[dailylurker]

12 minutes ago, Kmlwx said:

HRRR continues to prefer well south...it might still be trending south with the activity too...

If I was just going off of the HRRR, I'd probably stop even saying the Potomac as the dividing line...more like somewhere between I-66 and I-64. 

 

So we stay dry around DC?

[Kmlwx]

Just now, dailylurker said:

So we stay dry around DC?

Perhaps not dry - but I wouldn't bank on severe if you're going by the HRRR up here. HRRR could be wrong, of course. 

[Kmlwx]

Looks like 17z will have a Warn-on-Forecast domain run centered over West Virginia.