high risk
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Everything posted by high risk
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I lost track trying to count the number of incorrect details in this post.
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While it's a bit unclear how much precip will linger immediately behind the front (for a brief period of sleet or snow early Christmas morning in the DC metro area), there may be more hope for a period of snow showers during Christmas Day as the upper trough axis swings through, and low-level lapse rates steepen. There is a very weak signal in the NAM nest, but there is a smack-you-in-the-face-with-a-small-snowball signal in the 18z HRRR.
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I'm not sure about the EPS, but the GEFS members are run at 25 km resolution, while the ops GFS is 13 km. So yes, that could be making a difference.
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Definitely much more dispersive than the previous version of the GEFS.
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The previous version of the GEFS was extremely underdispersive, but the new GEFSv12 has way more spread. That was one of the strengths of GEFSv12 noted in the summary presentations on the evaluation web page: https://www.emc.ncep.noaa.gov/users/meg/gefsv12/ (It also helps that 10 additional members were added.) If most members agree something at day 5, that's a much bigger deal in the new version.
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The parallel GFS had statistically significant synoptic range improvement over the ops GFS in the medium range over the full course of the retrospective runs. But that certainly doesn't preclude it doing worse on any single event. I wish we were able to run it more than once per day right now.....
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Honestly, those details haven't been sorted out yet. It's not an output in the RAP/HRRR (which have actual snow accumulation as an output), although their SLR methodology is documented. The plan is to carry over the RAP/HRRR products into the RRFS (replacing all of the regional models in 2023) and build it into the 2024 GFS/GEFS upgrade.
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They do run tend to a bit low (especially when the ground is relatively "warm", but they're so much better than 10:1 maps in any event in marginal thermodynamic environment. I honestly don't blame WB or TT. The problem is that NCEP doesn't generate true snow accumulation output for any models except RAP and HRRR, so it's up to the user to assign and apply an SLR. This is going to be addressed going forward.
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In these events with very marginal temperatures, the Tropical Tidbits accumulated positive snow depth change are the best maps to examine. They show what the model believes can actually accumulate on the ground.
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Speak for yourself. It basically hits a wall at the Potomac.
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00z NAM continues to show a deformation band of snow across the area Saturday.
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You left out the next panel in which it basically wipes out that line as it moves into the metro area..... That said, the HRRR has the same feature, and it keeps it going further east, but the HRRR is warmer in the low levels and keeps it as rain for the metro area.
