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Seems like models are leaning towards a type of overrunning event.

Just gunna' post this! Certainly, best case.

?

Rgem would be a fun little start

Nam and rgem come in colder at 00z

Ran the 00z ICON from my basement.

Surprised I haven't seen much if any mention of this lurking around the forums. As everyone knows NoVa and specifically Ashburn, VA is *the* hub of the AI data center boom going on right now. And as everyone also knows, data centers use a ton of water and electricity - most of which ultimately ends up in the atmosphere as waste heat and water vapor. Thinking about this from an urban heat island perspective, you could chalk it up as typical development in an area that's been sprawling for decades, except you'd be way off on scale. These things are unprecedented in terms of energy and water throughput density, they compare absolutely none to any other type of development we've seen before ever and I highly suspect if people looked closely we'd already see some unique effects on regional climate that will continue to grow as more of these things come online in a very concentrated area. How do data centers compare to other sources of UHI? Scale - around 6 GW of capacity used for existing data centers in Loudon county alone, future plans might require upwards of 20. Roughly 2 billion gallons water consumption. Total VA build out, most of which is in NoVA would consume 66 to 100 TWH per year, which is comparable to the state of Tennessee. This isn't normal sprawl. It is the energy usage of entire states, concentrated into waste heat and moisture in a few square miles. It dwarfs the energy consumption of DC proper. The water usage otoh is about 5% of what DC consumes - not off the scale - but consider how it's used. Interaction w/ Environment - New build data centers tend to be built using closed-loop cooling systems, featuring roof-top cooling towers that use airflow + evaporation to chill an internally circulated coolant. I can't find an actual source, but chat GPT suggests that roughly 80% of the waste heat handled by these systems is offset by latent cooling, with about 20% remaining in sensible heat to the atmosphere. All of that water is for the most part being output to the atmosphere rather than being flushed to the bay like most urban water supply - so that 5% figure is actually quite significant. And since these cooling towers are quite low/not that hot, unlike the direct cooling towers on power plants, the moisture output is all going into the PBL rather than the free atmosphere. Long story short, gigawatts and gigawatts of energy is being used to humidify the lower atmosphere in NoVA. It's important to note that this waste heat and humidity is being output in a suburban area, so it will express itself in unfamiliar ways compared to traditional urban UHI. From most studies I've seen, daytime urban UHI is primarily SW albedo + transpiration effects, whereas nightime UHI is attributed to radiative inefficiency (urban canyon + higher heat capacity of surfaces) and waste heat from buildings and vehicles. The night-time effects notoriously combine in various ways, and so for waste heat in a suburban areas you may not see the dramatic increase in over-night minimums that are usually the hallmark of UHI, since there aren't the same kinds of surfaces to trap spatially and temporally varying fluxes of waste heat and dispense them out evenly over the AM hours, and the fluxes from data centers are not as uniform in the first place as cars and buildings that ring every block of a city. Questions Do observations so far indicate anything odd around NoVA? Temperature wise, but also dewpoints How widespread would any effects be? Would it be hyper-local within NoVA or would we get significant downstream transport? If the waste heat and moisture output of data centers is significant, will it express itself in changes to regional convective season climo? This seems reasonable since PBL moisture distribution is a huge factor I plan to dive through the data at some point and post updates, but right now I thought I'd get some input to make sure it's not crazy Here are some articles on NoVA data centers and their electricity/water usage: https://www.businessinsider.com/virginia-data-center-construction-boom-amazon-2025-10 https://www.visualcapitalist.com/map-network-powering-us-data-centers/ https://www.itbrew.com/stories/2024/08/26/northern-virginia-s-data-center-alley-is-thirstier-than-ever

Best disco for those of us on the southern edge. Shallow warm layers in these setups tend to produce little liquid. Takes a little more umph/depth in temp rise right along the transition to produce more robust liquid, especially with a fresh snow pack preceding. I've rarely seen more than light drizzle in setups like these, better chances of a full light or heavier rain switch with temps above 34 and at least a +freezing 850 nose to help. Not saying it cant but this setup is half my winters lately. Now where and how long does it last? Starting to call my area Kitchen Sink Canyon lol

Looks like amounts really dropped off south of I-89. Judging from webcams, probably 1-2 windblown inches at MRG/Sugarbush

9" measured on elevated surfaces within 24 hours is a solid snowfall (1-1.5" before the flip). Closing in on a half inch per hour average over an entire calendar day. That's a good shot of snow for the northern Greens as the trough moves through.

I completely agree. It was recently made operational (Feb. 2025) and its primary purpose (imo at the current moment) is to provide an efficient (few resources and fast to simulate), medium/long range ensemble... I consider it a less accurate version of the CFS, honestly. They're years, if not decades, away from making the AIFS comparable to any traditional NWP modeling system. I'm not even fully sold on that being a possibility either... I'll take it seriously when the AIFS outperforms the IFS at the surface and not 500-50mb Vendors will provide any modeling system to stand out, unfortunately... At this range, I'd primarily consider the ECMWF, GFS, CMC, ICON, and UKMET (with more emphasis on their ensembles). Maybe look at trends of the AIFS for S&Gs.

Tuesday morning could be interesting for the escarpment and immediate lee.

8 new 9 24 hrs nice recovery on the slopes

IMO the low placement favors Wisconsin shore more than Illinois. Between mke and Sheboygan in WI look money with those SE winds

From what I see on most guidance, it’ll increase QPF but will also reduce the ratios due to the warmer lake waters, so it’s almost a net zero. Not sure what will actually happen

What are the thoughts on lake enhancement? MKE is mentioning it will increase totals but LOT seems to disagree.

Probably backing down more towards reality. Still high-end event nonetheless.

I’m in Maine but I heard I-89 has had quite a few accidents on the high ground between Randolph and Berlin.

Has to do with placement/handling of heavier and more convective precip, not actual drying per-se.

Yea, I text him ...work been nuts. In Asia alot

Watch it be right. Lol. I hope this precip shield fills in south like hrrr shows later. Right now main waa band setting up pretty north in Iowa. Always nail biting watching these evolve.

I don't think it will be high end around our area (probably no widespread 12"+ totals that is, unless ratios surprise, which seems doubtful at this time). The metro region as a whole will likely see a general 6-10" overall (locally higher), though. Highest totals will likely be western areas, with the overall setup peaking west and slowly dampening out as it heads east.

I want frozen ground, But we don't always get what we want.

You may do it, sure enough. Thinking I might bottom out around 24-25.