01-11-18: An Unusual January Storm - NE/KS/IA

Discussion in 'Winter weather' started by Royce Sheibal, Jan 10, 2018.

  1. Royce Sheibal

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    Since we haven't had a winter forecast discussion in a while, here we go.

    GFS, NAM, EURO have all been in agreement all week for a pretty major winter storm hitting the plains Thursday. An unusually strong stacked low coming out of SO CAL will induce a classic Colorado low that will merge with a nasty Canadian front and potentially bring some odd thunderstorm / snow mixes in KS / NE / IA.

    Why is this so freaky? Because this looks more like a late winter or late fall storm. Td's may be near 50 in Omaha before the front passes, thunder is possible, and some crazy frontogenetic forcing may bring some snow bursts of 3" per hour. None of this is normal for mid-January. I've been in the Omaha area for 33 years and counting, and I can't remember ever a threat of thunder in January, and 50 TD's outside of an el-nino year seem impossible. Is the RRR+La Nina making a hybrid La Nina with strange, but not unexpected results?

    As for the models: GFS has been solid all winter here, with NAM being terrible and EURO being serviceable. I tend to lean toward GFS in this situation, and it had been solid with the main convective band over OMA to LNK for a couple days, until this morning it finally shifted SE to agree with EURO and NAM, which had both shifted SE overnight. Ongoing rain + storms will likely complicate the forecast, but a full freeze over by 3am across much of the area will cause major road issues. 4-6 inches across the board seems likely with the front pushing through earlier than previously forecast. 6-9+ inches in the frontogensis zone seems like a good bet, with models still putting down 12+ inches in a few spots. With the colder temps we're also seeing 15:1-17:1 ratios, so light fluffy blowing snow will be an issue.

    What we still don't know is how the low is going to interact with the frontal positioning. Looking at HRRR it would seem that a meso-low might form ahead of the main low (related to convection) and that could possibly focus heaviest precip over the OMA area as it meets the front. 850 temps are quite cold with no warm layer forecast, so sleet / freezing rain doesn't seem to be a huge issue, but there is enough instability that graupel / small hail might occur. I'm also not confident in frontal positioning, as that front in SD is really booking, and the low is moving slowly, so if we get really lucky the front will undercut the precip before it gets here and we'll have minimal snowfall. Either way, the rain freeze-up will make travel from LNK to DES to KC near impossible for both rush-hours.
     
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