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Excellent afternoon AFD from LWX for tonight into tomorrow .DISCUSSION... KEY MESSAGE 1...Slight Risk of severe thunderstorms today and Friday. Clouds have readily thinned in the wake of morning shower and thunderstorm activity. This is allowing for temperatures to rise quickly through the 80s to near 90. This heating will play an important role in the potential for severe weather through the evening hours. As of 2:30 PM, a few discrete (transient supercell) thunderstorms had developed over the Shenandoah Valley, and had a history of producing large hail and wind damage. These storms are developing in an area that has been clear since daybreak, and in an area of enhanced low-level convergence due to residual outflow from morning convection to the north, a washed out front, and terrain circulations. Anticipate this activity to continue into the late afternoon hours with a risk of localized damaging wind gusts and large hail. Meanwhile, upstream over the lower Great Lakes and Ohio Valley, a large reservoir of MLCAPE 3000-4000+ J/kg exists. The north end of this CAPE pool lies along the southern edge of the westerlies, with a 100+ kt 300 hPa jet streak and mid-level shortwave impulse located just to the north. This setup is favorable for the development of a Mesoscale Convective Complex (MCS), which is an organized line of thunderstorms that persists for several hours. Locally, mid-level lapse rates of 6.5-7 C/km (per latest mesoanalysis and the KIAD 12Z RAOB) atop a very moist boundary layer with surface dew points well into the 70s F will lead to increasing CAPE despite the late start at surface heating. The question then becomes just how organized upstream storms become, and how stable the boundary layer is heading further into the evening. A more organized and potent line of storms a bit earlier in the evening would result in a notably higher risk for more numerous damaging wind gusts, especially focused along the residual baroclinic zone/theta-e gradient which should lie near the Potomac River/US-50/I-66 this evening. A somewhat slower and/or more disorganized line would result in a lower risk for severe surface gusts, though some isolated damaging winds would still be possible given high CAPE/DCAPE and the shallow nature of the stable layer near the surface. Areas of western Maryland and perhaps into the eastern West Virginia panhandle are most likely to see the storms prior to the onset of appreciable nocturnal boundary layer stability. The area remains in a Slight Risk (level 2 out of 5) for severe weather from SPC as of the midday outlook update, driven mostly by the threat of damaging wind gusts. There is a threat for large hail in stronger cores, though mid-level lapse rates will gradually become less steep tonight. A linear storm mode would tend to be less favorable for large hail production (as opposed to discrete/individual cells), as well. A few discrete cells are possible this evening in weak low-level WAA, however, independent of any linear system that may affect the region. These storms would be most likely to develop over northern and central Virginia into central Maryland along a weak surface trough and the aforementioned moisture/instability gradient. Additional showers and thunderstorms, possibly strong to severe, are anticipated again on Friday. Timing is a bit uncertain given the subtle waves aloft, but increasing low-level convergence paired with another upper impulse may very well result in another round or two of storms with a damaging wind risk. The latest guidance has nudged the threat a bit further north, encompassing areas as far north as I-70 or the Mason-Dixon line (as opposed to I-66/US-50). This will depend on any residual early day clouds or convection, of course.

Just went out to my truck to get something and its just 101.1 outside here. Did you get any rainfall from the cell yesterday late in the day? Its been bone dry here for the last week and a half.

I see Mt. Holly and State College both issuing Heat Advisories for temps in the 80s now. (Maybe residual from a blown forecast or something. But still...)

probably just misses east but given the strength, way too close to totally write off now for some of those islands. Big Island probably fine outside of dangerous waves but those far northwestern islands...I'd be a little sweaty if I were them.

Ring of Fire week of mid 90s in September produces not a single drop of rain here. Not one.

As I said yesterday, despite the “pause” in Nino 3.4 in August, it has become significantly more east-based regardless.

Looks like a very near miss to me. I had flights and hotels pulled up yesterday though.

Such a storm today would be unreal with regard to damage

Similarities to 2025. That's what I thought you meant when responding to my post. Edit: nevermind, I see the PNA was negative 3/4 months last year. We are also following 2024 close with the 90N Summer +AO and that had this DJF PNA 1.70 2025 1.05 1.41 80-90N ridging in the Winter sometimes will pop a low south of it, over the Aleutian islands. That's what I mean by +PNA coming from the arctic

That's what the model predicted. I'm not talking about the Great Lakes.

Nino 1+2 is very warm, but Adam’s post: -is ignoring the effect of GW on skewing Nino 1+2 upward in 2026 vs 1997. The highest relative weekly in 1997 was +4.1 (set twice). Relative values for Nino 1+2 are currently 0.5 or more cooler than the non-relatives. NOAA and other orgs have recently been using relative values as official because of the skewing caused by GW. -He’s looking at yesterday’s daily rather than at a weekly average, which is what the historical data is based on. -These OISST charts have recently been warmer than the released NOAA weeklies as has been noted in many posts since July. -Let’s see what this Monday shows for relative Nino 1+2 averaged over this week. I doubt it will reach +4.1, but we’ll see. I’m guessing high 3s.

It's likely the hail core interfering with the radar beam. Note how the broad rotation is behind the best VIL.

There were 2 tornadoes within the derecho

I thought that was a tornado outbreak. That's how my mind remembers that event anyway. Didn't we have another one around Memorial Day weekend in the same year?

almost that time of year. GEFS is hinting at a pattern favorable for early season snow cover advance, but time will tell on that.

The HRRR shows nothing for Augusta/Rockingham thru 4 pm. It is wrong as convection is firing Staunton to Harrisonburg. The NAM 3k is on the money. Sorry to lose it.

By all accounts the 1821 hurricane that hit NYC on this date was even worse. A Cat 4 right into NJ and a Cat 3 up to NYC and a direct hit! Our own Labor Day hurricane before Labor Day even existed!

We need at least 2 weeks of uninterrupted sunshine. I'm going to enjoy hearing people who whined about this summer being hot are shocked when next summer is 3-5 degrees hotter. This wasnt a hot summer, mostly just humid and wet. We better hit 90 for my birthday on September 15th!

Like yeah…the PDO might alter pacific storm tracks, but it’s on the scale of 0s to 10s of miles, not 100s to 1000s. Same way that Canadian snow cover might force baroclinicity southward, so an individual snowstorm might track over the turnpike rather than I-80. But it’s not going to stop a cutter from going to the Ohio valley. It’s a bit ridiculous that the PDO is being discussed so much in this thread when you actually have a record breaking Nino that *will* actually alter the long wave pattern by *thousands* of miles.

This is MUCH better than yesterday was.

Can't have nice crisp Fall weather with soggy miserable foggy weather either. Endless sunshine is needed.

0.42” from the storms this morning but skies are clear now. 82 degrees here.

I saw the line coming in before I went to bed last night, but how bad were the winds? My Ambient is showing 13mph gust around 3am. Very surprised to see the backyard littered with leaves this morning.

Martz isn't an expert on glaciers, geology or Nepal. Pictures of the area in question from the blog I linked above show evidence of melting: 1) The glacier has shrunk quite a bit since 2017 and 2) the glacier isn't the pristine white of unmelted snow. The storymap that I also linked contains the following paragraph about local temperatures: Temperature data from nearby climate stations installed by University of Potsdam show the region has been very warm in the past weeks and months. In addition to the high temperatures across the network, station NPA6 (located approximately 20km from the source area, at 85.28567°N, 28.23455°E) shows rapid temperature increases in the morning in the three days prior to the event, which aligns with the timing of failure (8.37AM Nepal time). These quick temperature swings are a key driver for frost cracking and glacial instability. Bodo Bookhagen (Professor at Uni-Potsdam, Germany) notes that these rapid temperature swings are not evident in the other network sites, indicating this was likely a local event. Let me be clear though, its too early to say whether this event was climate related. That's an expert call.

The PDO index has none/negligible effect on the long wave pattern. There isn’t a really a reason to RONI it except for record keeping purposes. It’s a fully extratropical index.