11/30/2016 – Winter Threat Assessment Blog – Discussing a Continued Active Pattern
Synopsis: I wanted to piggyback on where I started with the last post on Monday, concerning the cold air intrusion pushing from west to east across the Country from a cross-polar flow as we usher in the first 2 weeks of December. The question that continues to surface is: how far east does this cold air go? Depending on how far east the cold air moves helps improve confidence with the dates we target for wintry systems. One caveat that I wanted to reiterate early on in the blog is our lack of confidence this colder pattern sticks around especially beyond the 15th of December…there are still risks of a warmer pattern following this cold as you can see the GEFS hint at near the end of the loop below. Let’s dig in!
This is a classic La Nina background state response, where high pressure pushes poleward near the Bering Sea and the response is forcing that colder, cross-polar flow into the western half of the Country, modifying as it comes east.
Next Targeted System (December ~9th): As we mentioned in our blog update Monday, we first saw this system pop up via the BSR (Bering Sea Rule) 2-3 weeks ago and has been on our radar ever since. If we apply the 400 mile NW bias of the BSR to this system during our date range, we have a Midwest to Ohio Valley winter storm.
The key to nailing this system is to understand that your forecast doesn’t change with every model run that initiates…this far out the models are going to throw out there some crazy scenarios that track this thing 500 miles apart between runs. Instead, if we target a “pattern” we allow ourselves the flexibility of letting things sort themselves out. The positive trend here also is the source of air is much colder than what we’ve seen here closer to the Midwest yet this season…time will tell.
Here’s an animated loop of the latest European Operational run showing the progression of this system from wets to east, tracking through the Plains eastward…really pulls down that cold air with this system.
Here’s the GFS solution…a similar scenario as the Euro just differing on the timing and depth of the cold air available.
Winter Threat Assessment:
Targeted System (December 15th-18th): I wanted to briefly touch on a system that is way out but is starting to show up in East Asia, via the BSR as well as the CFS. At this point we need more data to narrow down a more specific target location as to where we are thinking a winter system is possible, but we wanted you to be aware of the possibility as far out as possible.
Here’s what the BSR has during this timeframe
This is the signal in East Asia we are keying in on…if we apply the 6-10 days to East Asia Rule (EAR) we have this system through our timeframe.
The CFS is starting to pick up on this system as well during this period…again, don’t take the date or the location of this system verbatim, the biggest takeaway is that we are targeting the potential for wintry weather during this timeframe and multiple pieces of data are beginning to support it.
Conclusion: We continue to see a very active December pattern especially through the Plains, Midwest and Ohio Valley…the thing we are concerned with the most is how much cold air is available to allow these storms to produce snow vs rain as they head east. Stay tuned for more information as we gain more model support for our dates we have targeted!
Confidence and Risk:
- We have increasing confidence the first 2 weeks of December start trending cool to colder.
- We have below normal confidence the cold sticks around for all of December…There are warmer risks from the 15th and beyond, the Pacific pattern/tropical forcing is key to the overall cold for the remainder of December
- Confidence is increasing in our system next week having wintry potential through the Midwest/Ohio Valley.
- Right now we have low confidence in our targeted system Dec 15-18th but we are starting to see multiple sources suggest a system to move through during this timeframe.
Interested in getting the details any of these systems within 7 days, including timing, intensity, precipitation-type etc? Send us an email to “Info@BAMwx.com” expressing your interest and we will get you taken care of!
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