GEOS5ftw

The low CCs on the LWX radar have really collapsed in the last few frames, so the melting layer seems to be dropping to the surface. However - ground truth in Wheaton has been mostly drizzle/light rain all day besides a few bursts of mangled flakes in heavier bands around 10am and 11:30am.

The high CC we are seeing everywhere is actually snow above the melting layer (which is very shallow today - anxiously awaiting the 12Z IAD sounding to verify). The lower CC near the radar (where the beam is lowest) is the melting layer which is in the lowest 1500 ft if I'm interpreting Radarscope's beam altitude correctly. We should see that zone of low CC collapse to the radar site as the snow reaches the ground. During the January storm, someone posted time series of quasi-vertical profiles from LWX and other radars. These are an awesome tool to see subtle vertical shifts in melting layer/ptype over time (you give up horizontal resolution for vertical resolution). I can't seem to find a site for these so maybe they were manually generated? Would love to monitor them in real time for this storm.

Serious question, but probably belongs here: I am supposed to fly IAD to IAH Sunday afternoon (yes this is for AMS). Do I try to get out ahead of the storm (and miss probably the biggest snow in 10 years IMBY), roll the dice with my current flight, or book something for Monday and assume it will get out (I really need to get in Tuesday at the absolute latest). When do we think timing and impacts will be nailed down enough to make this decision?

I’m not 100% sure, but I believe they use the same initial conditions. The AIFS is essentially predicting the next time step based on relationships between time steps learned from the ERA5 reanalysis, and then repeating this process out to 360 hours.

This reminds me a bit of the evolution of the early January 2022 storm. Which the GFS also caught onto a few cycles before EC. Not sure it matters (probably not), but something to consider.

I mentioned this yesterday...it looks like the 00Z ML suite also shifted significantly S/E with the low pressure compared to 12Z yesterday. Which tells me (from this extremely small sample size) most of the trend is a result of changes in the initial state, not biases in the ECMWF model physics.

Those 1994 ice storms were what got me into weather which eventually became my career! I do remember 93 but it was 94 that I got into watching TWC all the time. Two distinct memories from that year (all these are from near IAD) - the MLK day ice storm which started out as snow in the morning, then progressed to sleet and freezing rain during the day. Just when the temp hit 32 the arctic front came through and froze everything solid...the water that had ponded in my backyard literally become a skating rink (I had taken ice skating lessons a couple years earlier, and jammed my feet, which had grown a good deal in those 2 years, into my skates just so I could say I skated in my yard!). This week had a few sub-zero low and single digit highs, and there was a clipper that came through later in the week that dropped 1-2 inches of some of the lightest, fluffiest snow I have ever seen. Mid-February there was a huge sleet storm - I want to say that the piles of sleet that bounced off the roof created 2 foot "drifts" around the house but the accumulation elsewhere was more like 4-6 inches. Then we had 2 inland runner storms, one in early january and another in early march, which were 3-6 inch type deals with wet snow, although I remember hearing that north and west did much better in these.

FWIW, I took a look at the AI models that ECMWF is running here: https://charts.ecmwf.int/?facets={"Product type"%3A["Experimental%3A Machine learning models"]} With the caveat that they only produce the 850T/500 height/mslp fields, to my eye they all look pretty similar to the Euro op at 12z, if not more NW/warmer. I'm going to try to follow them this winter to see if they are less susceptible to trends than the physics-based suite.

Spire is running a similar model to the GFS ( I think) but with additional soundings from their GNSS-RO satellites. I haven’t seen accuracy scores so it will be interesting to see how it performs this winter. The AI models (pangu, fourcastnet, etc) are all trained on reanalysis. From my perspective of both seeing a small bit of their output and published verification scores, they can do a bit better than deterministic and similar to ensembles in the 5-10 day range. The real advantage is how fast they run. But they only produce a limited number of output fields and precipitation is a known deficiency. .

There's a million moving pieces that have to come together for it to work next weekend but the GFS and para are seeing the effects of the block now. Ensembles should have some good hits I would think.

Can confirm, some big aggregates mixed with rain in Wheaton.

39.04, 77.02

A few icy flakes mixing in with the heavy sleet. About 0.3" sleet accumulation so far.

I don't think the high res windows have been mentioned but they are coming into range. I took a look to see if the ptype is correlated to banding structure at all, and there's some evidence for this. In general, ARW and NSSL are warmest aloft (similar to NAM), probably sleet/snow mix or sleet by 12Z for the I66-I70 zone, whereas NMMB and HRRR are colder aloft and mostly snow north of EZF. Interestingly the ARW/NSSL are colder at the sfc than the NMMB and NAM. Not sure how this aligns with typical biases. HREF output should be really useful starting at 0Z tonight.

I'd wait for the 3km which should be in range for most of the storm now. A lot of these subtle mid level temperature changes are related to banding which the 12km NAM does not resolve as well as 3km. Could very well be that heavier precip=snow and lighter precip=sleet in the transition zone.