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The January 5/6 Thing


stormtracker
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2 minutes ago, pazzo83 said:

doesn't seem like it's picking up any CAD signal.  We know how strong that can be in these parts.

Actually, it kinda-sorta is in a way.  Looking at that 2-m temperature plot @snowfan showed above, you can see the signature.  So I'd guess that "rain" in the corresponding plot would actually be sleet/freezing rain (the ICON plots for some reason don't show a different color for freezing precip, it's all greens).  But yeah, why parse and stress the thermals of that model right now?

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Just now, J.Mike said:

Where is Ji’s “the most important run of my life” post?

Mappy moved it to banter. Lol

In all seriousness, the track appears to be pretty much set within tight goalposts at this point.  Now it is thermals and soundings that are most important to those south of the mason-dixon line.  Stinks to be worried about thermals (especially down here) in our epic cold pattern, but it what it is.  Rooting for a Ukie/Euro blend here.

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One of my favorite products in assessing the potential for extreme events is the ECMWF's Extreme Forecast Index (EFI). The link for the page is here: https://satable.ncep.noaa.gov/efi/. To read up on it more from the ECMWF, you can visit here: https://confluence.ecmwf.int/display/FUG/Section+8.1.9+Extreme+Forecast+Index+-+EFI%2C+and+Shift+of+Tails+-+SOT. If you haven't seen it before, in quoting the ECMWF page, the EFI "compares the medium range ensemble forecast probability distribution of an event to the M-climate distribution for the chosen location, time of year and forecast lead time.  The underlying assumption is that, if a forecast is anomalous or extreme with respect to the M-climate (re-forecast database over the past 20 years), the real weather is also likely to be anomalous or extreme compared to the real climate.   Simple probabilities derived from the ensemble (e.g. the probability that forecast temperature >32°C) do not highlight the differences in the distributions of forecast.  However, EFI will do so because it accounts for the distribution of all the ensemble members.  EFI takes values between +1 and -1.

Experience suggests: EFI values between 0.5 to 0.8 (irrespective of sign) can be generally regarded as signifying that ““unusual”” weather is likely,

EFI values above 0.8 (irrespective of sign) as usually signifying that ““very unusual”” or extreme weather is likely. "

In this case using the new 12Z ECMWF EFI, maybe it is because it's been so long, but we do have some >0.8 values in northern VA that I can't recall seeing before (granted this product is still fairly new). Note as well is the Shift of Tails area. The Shift of Tails according to ECMWF "...compares the tails of both distributions of M-climate and ensemble based on the 90th and 99th (upper tail) percentiles...The SOT index complements EFI by providing information about how extreme an event could potentially be.  Specifically, it compares the tails of the ensemble and M-climate distributions." Usually, my eyebrows rise some when we have a ~0.7 and >1 SoT look. We have a >0.8 and even a 5 SoT in Northern VA. This tool can be used to show the event that the ECMWF ENS distribution suggests a very unusual snow event is likely based off the 20-year running climo, but some of the members are on the more extreme side given the higher SoT. 

ECMWF EFI.png

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Just now, stormtracker said:

I mean...there really are no huge differences right now.   DC metro got a hair warmer so, as we know our climo, we flirt.  But all in all...nothing panic inducing imo

Tried to get a lil coastal going also.

It's not a bad run, no one panic. It's a little more amped at h5 and low is a hair stronger, which draws in a bit more ML warmth with that angle of approach. Reality is, the 2m temp 32 line is actually a bit more S. 

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