My 2020-2021 Winter Outlook

[OHweather]

Hey all, I just wanted to pass along my winter outlook and technical write-up. I'll post the monthly maps and brief discos with each month here. The entire write-up is quite long, so I will link to the rest of it if interested (it takes too long for me to upload all of the images to do it again on each forum)

December:

A +PNA to end November and start December leads to a very mild / warm start to the month across the CONUS (slightly cooler over the Southeast / East Coast)…however, an active STJ and a wavier pattern than the ensemble means will show at this distance may allow for enough polar influence for an opportunity or two at a winter storm across the central or eastern U.S. Given the +PNA and active STJ, this may occur in areas such as the Ohio / Tennessee Valley, Appalachians, Southeast or Mid-Atlantic, farther south than what you may expect in a La Nina and more typical of an El Nino. A +PNA, split flow, and active STJ are features that are frequently seen in an El Nino!

This window is brief, the first week or so of the month and with a questionable amount of polar air to work with, so it may not work, but there should be a bit to track on the models as this comes into range. Thereafter, the SPV moving away from Alaska, persistent +EAMT, and convection getting into the 120-150E area (and likely persisting a bit more as the GEFS has due to the lower frequency forcing in that region this fall) likely allows for a window of -EPO, and a pattern more typical of a December La Nina. I think there’s still enough momentum in the Pacific jet that this dumps into the Midwest and Northeast as opposed to the Rockies and Plains as typically occurs with EPO shots.

This trends towards cold edging towards the Northwest / northern Rockies into late December, with a Southeast Ridge cropping back up due to forcing becoming more focused on the Indian Ocean, and due to Indonesian convection beginning to teleconnect to a Southeast Ridge in later December.

With the start of end of December quite possibly warm for a large portion of the country, the month as a whole will be mild across the CONUS.

While I think the NAO likely ends up positive for the month, if we take advantage of the potential to develop a -NAO in early or mid-December, it would up the ante for snow in the Northeast and Mid Atlantic in that window, and may slow the warm-up later in the month. Even without a -NAO, I think there are opportunities for some snow in December in the central and eastern U.S. (even the southwest may have a window with the STJ, the NW and Rockies will be active and trend colder later in the month as well).

January:

January may start cold in the Northwest U.S. and warm across the southern and eastern U.S. However, I think the MJO has another opportunity to propagate east during the first half of the month. I believe the PV will be weaker and more receptive to the MJO producing a blocking response than it is in early December. This may cause another period of -EPO, -NAO, and a somewhat active sub-tropical jet for a couple of weeks starting the first or second week of January. This will bring another window of winter farther southeast towards the Ohio Valley, Mid-Atlantic, and perhaps even the Southeast.

I think we start trending towards a Southeast ridge later in January as the MJO fades and Indian Ocean forcing crops back up. How much blocking develops in the first half of January will of course influence how quickly this warm-up occurs.

February:

This is generally the warmest month in the analogs, with an amped central Pacific ridge dumping cold into Alaska, western Canada, and the northwest / north-central CONUS. If we have persistent Indian Ocean forcing and a strengthening PV to open the month, that will probably be the case again this year. If there’s cold available in Canada, the +NAO may lead to confluence east of New England that leads to high pressure over eastern Canada that can cause cold air to seep down into New England and perhaps the Great Lakes in February, causing some wintry threats in these areas…however, the pattern I envision for February is not snow-friendly in the Ohio Valley, and especially the Southeast and Mid-Atlantic.  

March:

Cold air likely remains available in Canada, so if the MJO becomes active again in late-February or March it may shake-up the pattern enough to bring it south and bring one last shot of winter in March. If this does not occur early enough, the Southeast Ridge dominates much of March and keeps the cold over the Northwest, Plains, and Midwest / northern Great Lakes / northern New England.

Seasonal Snowfall:

Teleconnection Guesses:

AO: Generally positive, but may go neutral or negative briefly in early-mid December, and perhaps a bit more legitimately in January

NAO: Generally positive, may briefly go negative in early-mid December, with greater potential for a couple-few weeks of a variable / negative at times NAO in January

PNA: Generally negative aside from early December, and perhaps another brief spike later in the season

EPO: Generally somewhat positive, but will dip at times. Mid December and perhaps mid-late January may offer windows.

Here is the link to the full technical write-up: https://jimsullivanweather.com/2020/11/21/jim-sullivans-2020-21-winter-outlook-write-up/ 

[raindancewx]

Are you the Jim Sullivan here? My main issue with 1988 has always been the high solar activity and to a lesser extent the super active monsoon in the SW US. For 1999, you had a very cold Summer in the Southwest and also very high solar activity. July-June years in the desert southwest when filtered by ENSO tend to see ~constant rates of incoming precipitation/outgoing precipitation (evaporation and sublimation), so in the years with well below-average evaporation in the Summer in La Ninas, we tend to suffer for it with hot or very dry winters, which is what happened in 1999, but also 2005, and 2017 to some extent. The hottest driest Summers in La Nina tend to have the opposite effect, with more moisture and/or cold necessary to offset the extra evaporation in Summer. Those years include 2007, 2011, 2016 - all very hot and/or dry Summers that were either cold and wet (2007), mild and wet (2011), or warm but very wet (2016). These patterns extend back to older years I find - with 1933 fitting the first pattern, and 1954 fitting the second as examples. Tends to work with cold-Neutral years too (2012 fits the second pattern, 2013 the first). I guess my point is I like that you have some wetter years in there for the SW winter, but I think it may be somewhat colder than people expect too. The +NAO La Nina November pattern (like 2011 say) is generally cold at least in December in the SW.

 

[OHweather]

20 hours ago, raindancewx said:

Are you the Jim Sullivan here? My main issue with 1988 has always been the high solar activity and to a lesser extent the super active monsoon in the SW US. For 1999, you had a very cold Summer in the Southwest and also very high solar activity. July-June years in the desert southwest when filtered by ENSO tend to see ~constant rates of incoming precipitation/outgoing precipitation (evaporation and sublimation), so in the years with well below-average evaporation in the Summer in La Ninas, we tend to suffer for it with hot or very dry winters, which is what happened in 1999, but also 2005, and 2017 to some extent. The hottest driest Summers in La Nina tend to have the opposite effect, with more moisture and/or cold necessary to offset the extra evaporation in Summer. Those years include 2007, 2011, 2016 - all very hot and/or dry Summers that were either cold and wet (2007), mild and wet (2011), or warm but very wet (2016). These patterns extend back to older years I find - with 1933 fitting the first pattern, and 1954 fitting the second as examples. Tends to work with cold-Neutral years too (2012 fits the second pattern, 2013 the first). I guess my point is I like that you have some wetter years in there for the SW winter, but I think it may be somewhat colder than people expect too. The +NAO La Nina November pattern (like 2011 say) is generally cold at least in December in the SW.

 

Yes, that is me.

Thank you for that insight about how La Nina summers in the SW tend to correlate (oppositely) to winter precip...and this winter, early on, does look to keep that up with a hot/dry summer and a fairly wet start to winter. I'm curious to see if that keeps up through the season, and I'm curious what could drive that (perhaps the PMM?). When going through years and selecting analogs for this winter, it was certainly not easy to find years that are matches everywhere. I wasn't thrilled that 88-89 and 99-00, which both have some things to like, had much higher solar than this year. The reason I was OK with including them with a higher weight was because it seems, from the research I've read, that solar's greatest influence on the winter is via the stratospheric PV. Given we have a strong PV early on, which is more common in high solar years, I was OK with those analogs, although to some extent it was out of necessity. What to do with Desert SW temps and precip was a debate when I put together my personal outlook over the last couple of weeks, as I do think you guys remain somewhat active through at least December and perhaps into January. If it turns quieter mid-late winter you may still finish on the somewhat dry side unless it's exceptionally wet over the next few weeks. Either way it'll be better than some of the very dry La Nina winters. 

[raindancewx]

This is what I have if you're curious for a SW perspective on national trends. It's pretty amateurish compared to yours but I do have the advantage of knowing what tends to precede the better winters here.

https://t.co/HJU1iBGTa4?amp=1

What I had for New Mexico is pretty similar to what you just said - relatively normal winter for precipitation, and then a very hot/dry Spring, probably starting late winter. The best indicators for La Nina here seem to be the ACE index for mid-winter highs (12/16-1/15 is very well correlated here to ACE) and actually September rainfall is correlated somewhat well to Oct-May precipitation believe it or not. September 2017 had 2.20 inches, and super high ACE and then there was a literal 96 day period without precipitation starting in October, with perpetual near record warmth. The current Fall is mostly warm but with strong recurring cold shots. Albuquerque only finished with 0.62" this September, which is low for a La Nina, and favors pretty normal total Oct-May precipitation (we get about 4.0" from Oct-May in a normal year).

I've also found that since 2007, the cold-ENSO years with <=4.3 million square kilometers sea ice extent in September have all been cold or at least near normal in the Rockies or West, somewhere, while the years higher than that have been warm in the West, and cold in the Plains or Eastern 1/3 of the US.

 

[Roger Smith]

That looks generally similar to winter 1975-76. I recall that one producing about two weeks of intense cold in the Great Lakes region (mid to late Jan) and record warmth by end of February. There was quite a long stretch of heavy mixed precip at the start of March (in southern/central ON at least, probably also in the Midwest U.S.). 

My thoughts for the winter are fairly similar by the way. I think it will be more about week to week variability than long-term trends, with the warming more pronounced towards end of February. Some part of January could be a brief east coast wintry spell but I can't see it dominating south of the lower Great Lakes.

Great Lakes water temps must be well above average given the very warm November, similar to 1975. Then there was a spell of extremely heavy lake effect snow in Dec 1975 and Jan 1976, London ON had a state of emergency from huge snowdrifts created during this period. 

Good luck with this. 

[OHweather]

On 11/23/2020 at 5:59 PM, raindancewx said:

This is what I have if you're curious for a SW perspective on national trends. It's pretty amateurish compared to yours but I do have the advantage of knowing what tends to precede the better winters here.

https://t.co/HJU1iBGTa4?amp=1

What I had for New Mexico is pretty similar to what you just said - relatively normal winter for precipitation, and then a very hot/dry Spring, probably starting late winter. The best indicators for La Nina here seem to be the ACE index for mid-winter highs (12/16-1/15 is very well correlated here to ACE) and actually September rainfall is correlated somewhat well to Oct-May precipitation believe it or not. September 2017 had 2.20 inches, and super high ACE and then there was a literal 96 day period without precipitation starting in October, with perpetual near record warmth. The current Fall is mostly warm but with strong recurring cold shots. Albuquerque only finished with 0.62" this September, which is low for a La Nina, and favors pretty normal total Oct-May precipitation (we get about 4.0" from Oct-May in a normal year).

I've also found that since 2007, the cold-ENSO years with <=4.3 million square kilometers sea ice extent in September have all been cold or at least near normal in the Rockies or West, somewhere, while the years higher than that have been warm in the West, and cold in the Plains or Eastern 1/3 of the US.

 

Thanks for linking me to your outlook. I remember reading your outlooks the last two winters, and you were right to be more bearish with snow along the East Coast than a lot of others (including myself) were. All of the connections you find are interesting and work in multiple different examples; I'd suspect a lot of it is interconnected to the larger pattern that drives a given season, and it's interesting how that can manifest itself on a regional scale like that. I am certainly curious to see how this winter plays out; it is definitely off to a more active start in the Southwest than a lot of La Ninas are...based on your research and outlook, that may be a sign of things to come. 

On 11/23/2020 at 6:17 PM, Roger Smith said:

That looks generally similar to winter 1975-76. I recall that one producing about two weeks of intense cold in the Great Lakes region (mid to late Jan) and record warmth by end of February. There was quite a long stretch of heavy mixed precip at the start of March (in southern/central ON at least, probably also in the Midwest U.S.). 

My thoughts for the winter are fairly similar by the way. I think it will be more about week to week variability than long-term trends, with the warming more pronounced towards end of February. Some part of January could be a brief east coast wintry spell but I can't see it dominating south of the lower Great Lakes.

Great Lakes water temps must be well above average given the very warm November, similar to 1975. Then there was a spell of extremely heavy lake effect snow in Dec 1975 and Jan 1976, London ON had a state of emergency from huge snowdrifts created during this period. 

Good luck with this. 

Thanks! 

[raindancewx]

Update -