high risk

Agreed, and it's usually really good on this, but it can sometimes stay too cool if a bit of sun can break through on the cool side of the front. Regardless, it really looks like those of us on the east side of the river will get our max temp today at 11:59pm. Tomorrow could get sneaky warm ahead of the weak front sagging southward. The exact timing of the front is in question, which greatly affects the potential to get warm, but southern MD probably has the best chance of getting to the 70s.

If we do get some warmup east of the Potomac, it will likely be very late in the afternoon. There is a good amount of model agreement that Saturday’s max temp will occur at 11:59pm.

There are lightning strikes to our west, and there is good agreement in guidance for convection this evening into the overnight for at least the northern half of the region. Forecast soundings suggest enough instability for a continued threat of thunder.

Way too stable for severe east of the mountains, but there will be some elevated instability, so I expect some thunder during the evening / overnight, especially for areas north of 66 (VA) and 50 (MD).

Yes, completely elevated, but the forecast soundings do indicate some instability for parcels originating well above the surface.

Pretty good chance that at least the northern half of the area gets thunder later this evening.

Nice to see the thread ready to go for the upcoming season!

Moderate snow in downtown Silver Spring

yeah, clearly a rain sounding.

While a messy Tuesday morning rush hour has been in the cards for a while now, I'm becoming increasingly intrigued by the Monday afternoon snow event. My question is what the road temps will be like Monday after a couple of warmer days but a cold night. The NAMs and HiResW FV3 suggest that temps will only barely go above freezing tomorrow before arriving snow cools it back a few degrees. It's still tough to imagine messy roads during the daytime, but maybe if it comes down hard enough? Ultimately, it's *probably* just going to whiten grassy surfaces until you get further west and northwest, but the Monday afternoon through Tuesday morning period will be a nice reminder of winter before the big warmup.

Those of us north of DC got HRRR'ed for Monday afternoon. Notable shift north for the NAMs as well.....

The primary question to be resolved regards the impacts for the Tuesday morning rush hour. Monday afternoon definitely has potential for a coating of snow, and surfaces will be cold after temps fall into the 20s tonight, but I would think that daylight would mitigate road issues Monday afternoon. Models agree, however, on a batch of light-ish precip arriving later Monday night, favoring some sort of snow to sleet to freezing rain sort of progression before going to plain rain. The timing is favorable for road impacts, but guidance now suggests that it won't be as cold Monday night as initially forecasted. Would still expect at least some impacts on roads, north and northwest of the cities at a minimum.

Beware that there are hints in the guidance, mainly in the ECMWF and its AI version, of some back door cold front action during that period.

Looking over recent guidance, while the chances of a significant snow here appear to be waning, even if the Monday snow stays to our south (not entirely certain), there is some growing consensus that a modest slug of moisture will approach from the southwest late Monday night. While temperatures will be warming during Tuesday, it appears likely at this time that it will be well below freezing for the Tuesday morning rush hour, so a fairly high-impact event (even if amounts of snow or freezing rain are modest) is still on the table.

Verbatim, the GFS would be a messy Tuesday morning. Even as temps slowly rise, we will have had a long preceding period of temperatures below freezing.

Great post, but you really need to check what MDL stands for.

I never buy the NAM for any reason. NAMNest thermals and sometimes the QPF, but otherwise, the 12km parent I ignore almost exclusively. The other problem is that the "total snowfall" maps are NOT predictions of what the NAM thinks will be on the ground. When the model's hydrometeors are not liquid (i.e. snow or sleet) as they reach the surface, the amount of liquid goes into a water equivalent bucket. That is what these sites grab and then apply either a 10:1 or Kuchera ratio. What the model thinks will be on the ground is the snow depth product. Unfortunately, that tends to run low in events like these we we've had a warm couple of days prior to the onset.

Certainly looks like the GFS has lost the idea of heavy snow during the midday hours Sunday.

I love the usage of the snow depth field, but two flaws of that product are that it tends to be too low when 1) it gets warm before an event 2) rates are legit

That's not true. The 06Z para GFS did have a low, but it was notably offshore and quickly trucked out to sea. The same is true for the 12Z cycle - it looks nothing like the ops GFS. And apologies for not being able to share graphics.

No. Still FV3-based.

Huge upgrade to the “regular” GFS coming later this year.

Very concerned that if much of the snow falls during the daylight hours Sunday, it will really struggle to accumulate in very marginal low-level temperatures. Rates will be critical to our chances of a measurable snowfall.

Most of the 12Z mesoscale guidance today showed that the organized snow would have a really tough time making it into the DC Metro area, and that seems to be playing out.

Maybe? I haven't looked at the mechanics of why this band is way out ahead of the actual arctic boundary. Another possibility is a few scattered bursts of snow right on the late night front....