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December 2020 Discussion


40/70 Benchmark
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3 minutes ago, CoastalWx said:

Sell.

 

9 minutes ago, wdrag said:

12/27 620AM Topic Update.  Evolution of this topic continues as 12/29 is gone (except a few I-84 snow showers) . This includes dropping graphics for 12/29 as 12/21ish modeling completely missed this non-event for our area.  New graphics will be added Monday morning as modeling consensus grows for 12/31-1/2. 

This system for 12/31 and especially Jan 1-2 is trending toward broad high impacts, ranging from at least a period of advisory or warning ice and possibly advisory snow for the I84 corridor (high terrain above 1000 feet especially), to a multiple slow response river flood response (minor to moderate flood stages in our NYC forum), depending on new qpf (not including any remaining snowmelt) and how much of that qpf is ice and remains ice through Jan 2. In my mind this is complex. 

Scenario is a weak northern stream short wave passage on the 31st dragging a cold front through the NYC forum accompanied by rain, (possibly a little snow or ice I84 high terrain). It's possible NY eve celebrations will be precip free for a few hours? Meanwhile the southern stream short wave may split into two pieces, leaving something behind for the 3rd, but of little or no impact here. It's the preceding newd lift out of the Gulf States short wave that is going to be a potential high impact player here on the first and second of January. How this plays out is uncertain but clearly the 00z/27 GFS and EC op have trended colder while the run to run inconsistency of the UK and ICON continues. In essence though...it appears to me that a warm front to our south will provide the necessary lift with a southerly jet of 50kt (PWAT 1") impinging on it,  to dump heavy qpf on a large part of the NYC forum, on the order of 1-3". I am tending to lean widespread heavier than 1.5". That front may eventually lift north of LI/I80 but I think there is a chance of an occlusion and waves of low pressure moving out to the s of LI. That leaves potential for heavy icing parts of I84. So, tbd, if this read is generally reasonable but worthy of comment-updates. Wind:  50+MPH gusts...still possible for LI/NJ but less likely.  Have left the Topic TAGS as is, but updated the topic headline.  Basically done w this for 24 hours. Thank you for your updates-impressions of the modeling. 

I know this differs from the GFS parallel (not necessarily a desired model upgrade yet, in my mind,  especially if it misses this qpf event down here-remains to be seen but I'm concerned about consistently better GFS V16 performance vs the operational V 15). Ice, snow and wind support for my expectations above are derived from 00z/27 GEFS probs and operational model trends. 

 

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