Record setting POSITIVE Arctic Oscillation could be harbinger of coming winter--

I know my readers don't always get the technical weather talk and I strive to break it down where it's easy to understand. Back in the past 2 winters-- the Arctic Oscillation has been VERY negative in our very cold times, RECORD negative in 09-10 when we had those major snowfalls. This scale tells us in simple terms whether the cold air will be bottle up towards the north pole or be shoved away from the pole. Currently we have a NEAR RECORD POSITIVE Arctic Oscillation. (It hit OVER a +5, 2 highest reading EVER)

This doesn't mean we won't get any cold - but future events can be hedged by looking at past events. We can get cold here-- one of the years the DAY we set the record "Christmas Eve 99"-- there was a surprise snowfall in the Lynchburg area of close to 3 inches. (One of my favorite surprise events ever- I was tracking the clipper and it was expected to be dry east of the Mts-- the snow started just as a dropped off some gifts for a VERY special family-- was a special day) We can get cold air-- but long lasting cold air is harder to get. Ice events are more likely as there is nothing to FORCE the storm to our South and East.

Years with the record AO+  that took place in December,
Winter 51-52,  71-72, 75-76, 79-80,  83-84, 91-92. 92-93, 99-00, 06-07

Big snow winter-- 79-80

Average- 99-00, 71-72

The rest were BELOW-- some worse than others with 75-76,  83-84, 06-07 being among the 10 LEAST snow winters ever.

The two that are second yea La Nina's-- like this is would be 75-76 (Yikes) and 99-00.

99-00 had a really aggressive winter pattern with 4-5 events in a two week stretch and that was IT. The last even LOOKED to be a big snow event but as it trended closer became a snow to sleet to ice to sleet with 2-3 inches near LYH of ice/slush and more like 5-7 out in Roanoke. The BIG event was a surprise event on Jan 25-- that shocked us all. The synoptic pattern was unique in that there was a negative tilt troff sitting just of the SC/GA coast and a shortwave dug in like crazy and blew up. There was a ton of dry air aloft and so it was literally 10 minutes from 8 inches of snow in LYH to NONE in Bedford. My point-- that was a rare event and atypical for a La Nina winter.

With that, I'd strongly hedge that we pull back our winter expectations. Mts will still get plenty of upslope snows, I'd be shocked if anyone east of the mountains (Roanoke included) breaks 10 inches on the year. I'd increase the risk of an more significant ice storm with low level cold lurking and a bad storm track.

In the near term-- we do have a few shots of cold air incoming, but they won't last long.  I don't see much to think we get into a pattern that looks anything like winter in our region. A cold front passes Wednesday and SOME data has hinted a shot of snow as it passes, especially to our north. Those events are RARE and I don't expect it to pan out.

Safe travels today-- big ticket weather event late weekend.

Everyone is likely about on the road now. The weather has been warm a few days, a couple cold and back to warm. This will continue. We've had the exact opposite of the pattern we'd need to get sustained cold. (Not that it's a bad thing in November, but often the November pattern does tip the hand of winter)

Keep an eye on the forecast for Sunday. Pretty intense storm passes to our west will place much of east coast in the warm and unstable sector. (AKA- late fall severe weather likely)

Good link to an article written by Wes Junker- He's likely the best forecaster I know- and it ain't that close from him to second. The article discusses what goes wrong and forecasting and why. Worth the read, even if you don't get all the science part.

http://www.washingtonpost.com/blogs/capital-weather-gang/post/why-are-snowstorm-forecasts-sometimes-so-wrong-part-one/2011/11/23/gIQA4ZfaoN_blog.html#pagebreak


Happy thanksgiving to all! If a pattern change comes- I suspect Dec 15-20 will be the NEAREST time we experience it.

Winter Outlook--2011-2012

I waited until November to get in some data and the data does really help me at all. My sneak peak talked about the QBO-- and I wanted to see the October number and had that drop continued, I'd feel much more confident with a colder and possibly more snowy compared to the normal numbers. With that, my confidence is a lower than normal because the QBO dropped slightly, not a deeper drop.

I really should make a glossary that explains all these QBO, NAO stuff-- if your curious feel free to shoot me an email.

Winter 2011-2012

Slightly colder than normal winter wide--
Snowfall- slightly below LYH to DAN , NORMAL ROA Valley, Slightly above NRV up to the Highlands.

Maybe a decent event of 6-10 inches region wide, the rest will be more in the 1-3 inch range, often mixed with sleet, rain and freezing rain. These events will do much better to our west, hence my logic of normal to even above in the NRV and Highlands.

Snow guesses-

LYH  15.5
ROA 19
DAN 7
NRV   28

Give me a range of 2.5 inches either way on the snowfall. However, despite my snowfall totals being pretty good the past 2 years, it's some educate guesses and some luck.

Temps- compared to average

Dec  -1.5
Jan -1.5
Feb +1

So,that's slightly below normal

Factors- weak to moderate second year La Nina, -qbo (still hedging it drops) longer term pattern of blocking  up north (-NAO and -AO) -PDO (Usually favors warmth, but in second year nina's tend to trend cooler)
AMO- favors blocking as well.

Storm track-this fall has seen quite a bit of coastal storms both via Hurricane tracks and general areas of low pressure. I'm hedging less snow because of a moderate SE ridge-- won't kill the warmth but will allow storms to take a generalized pattern of INTO TN, KY WV region and reform to our north along the coast. That places us in the slope storms of 1-3 inches. I do expect QUITE a few of these storms and once or twice when the -NAO and AO are extremely negative we get 1-2 decent events.

There are some early signs that our December cold pattern is in the genesis stage and the pattern may begin to shift NOV 20th give or take and the cold may be evident by late month. Considering tomorrow is Nov 5th-- we've had WAYY to many snows on December 5th in the past 10 years.

Cold rain with some flakes

Historic event on tap-- but nothing here but a fierce cold rain with occasional snow mixed in. I can see a couple time periods where it cools enough to be ALL snow with huge flakes falling. If this was Nov 28th- I'd be calling for a foot. (Blacksburg, Roanoke and Lynchburg included in this)

Places north of 64 (Stuanton) NE will have a HUGE event-- tons of snow and tree damage. I can see places getting 16 inches with only max accumulations of 8-10 with melting on the bottom. This will extend NE along 81 and curve into New England. This is literally, one of the biggest Octoboer snowstorms on record in the makings.

If there was an actual "snow meter" I'd have to raise it to 6.5

Two models, the GFS and ECMWF have had subtle shifts in the past 2 days-- one shifted east, one shifted west, both had a weaker storm. It seems like SLOWLY they are coming to an agreement.

It not locked in-- but late Friday evening rain should develop and once it becomes heavy it will mix with or change to snow. High elevations are at the best chances to see SOME accumulations but I'd not be shocked it even close to Lynchburg sees a coating. These storms are tough as it involves upper air energy diving our way and spawning a storm that forms JUST far enough south to throw back moisture into our region. While it's cold enough aloft- 3k feet down as modeled is just above freezing.

This could be a pretty damaging storm to trees up towards Wintergreen, Afton Mt and other places NE along the Blue Ridge Parkway.

If your nose has been twitching-- Could it be "snow" has been mentioned MAYBE in our region??

October snows are rare-- but no unheard of. Oct 1979 had a rather large event that dumped 2.5 inches in Lynchburg as heavy rain changed to heavy snow. Parts of the Blue Ridge- Skyline drive had upwards of a foot or more in that event- Drastic change as the temps near midnight were 53 degrees and 9 hours later we had heavy snow falling-- in OCTOBER.


We currently have a strong short wave ( upper air energy) diving in from the MN region and it spans a storm that spins up and on some modeled data shows rain changing to snow for our area. (Not ALL areas-- seems to be mainly rain S and E of Lynchburg). Time frame on this event is Friday night into Saturday AM.

Here are a couple snow maps-- the first is made by the GFS and shows a strip of snow along and east of the Blue Ridge-- 1-2 inches.
Next, the ECMWF has the storm more amplified and the snow is MAINLY to our north, but-- its a ton of it!

Wild stuff!

I'd guess that there is some type of "abnormal" even happening, but I'm not convinced we see here. Hot Springs has a good shot, up into the Mts of WV, PA and NE from there- if anything changes, I will certainly update.

Winter Sneak Peak

I'm not ready to fully commit to a winter outlook-- so, let's consider this my preseason outlook. I'll lock and load it in by Nov 10th or so as there is a little more data that I'd like to see before a final outlook.

This will be the 3rd winter I've made a public outlook-

09-10 was pretty cold- called for 30-45 inches of snow region wide, colder then normal and targeted the end of Jan/ Feb as the BIGGEST snow threats. 

LINK to the forecast

https://www.facebook.com/note.php?note_id=174886414694

Good outlook, A grade IMHO

10-11

Went cold December-cold breaks in January, 5-10 inches of snow for the winter.

Good call, not cold enough but it's foolish to go -9 or whatever the mean December and broke the cold to early. Part of the cold hanging on longer was a spike in the PNA (PNA= ridging or trough on west coast--ridging on west coast translates to trough on the east coast-- troughs are characterized by colder and stormier in general terms.)

Good outlook, I'd put in in the B+ range. 

http://lynchburgweather.blogspot.com/2010/11/winter-outlook-2010-2011.html

Winter 2011-2012

We are in a second year La Nina that is in the weak to moderate range. 

La Nina's in general feature colder then normal Decembers that warm once we move into January and usually have  mild February in our region. This happens because the mean trough shifts west and get riding along the SE coast. 

Why I'm not 100% locked in yet--

1. Something called the QBO or

 Quasi-Biennial zonal wind Oscillation

  -- we have a tendency to see more high latitude blocking. High latitude blocking. This blocking helps keeps cold air on our region. The QBO has dropped to just below positive and I'd like to see a stronger drop when the October data comes out. Further, we have a a split QBO where the 30 MB is negative but the 50 MB is positive. 

When the QBO runs negative (based on wind direction WAYYY up in the sky which was discoved in 1883 when Volcano Krakatau erupted and the ash circled the globe in 15 days on strong westerlies at this level and further research developed from there)

2. Recent tendencies of Artic Oscillation and North Atlantic Oscillation to run negative.- This links the first point-- this is the high latitude blocking I was talking about. 

3. Solar flares-- reading some research on this and they've some what established a lag time between low solar flares and impact on global weather patterns. I'm still chewing on this one in my hierarchy  of impact- this impacts the amount of blocking as well. 

This summary- our entire winter depends on how much high latitude blocking we get. If we lack the blocking-- it's going to be a warm winter. Conversely, if the blocking is stronger, more dominant we could be colder/more stormy as the mean storm track slides east putting us in the colder, stormier pattern. 

Early Thoughts--

I like the idea of a colder pattern developing late November and lasting 3 weeks into December. Pattern relaxes into mid January and the block emerges again Mid month to early February. Pattern relaxes again with another "possible" block 2nd week of March to the end of the month. 

So, starting Dec 1-- Cold 3 weeks, warmer 3-4 weeks, cold 3 weeks-- warmer/relaxed 3-4 weeks, colder march 10th or so but that's all relative to seasonal averages when you get into March. 

Snowfall-- this is what people care about most, yet has the highest element of luck as you can't really time short waves. 

La Nina's tend to low on sub tropical jet - think of those big snows in 09-10 where the tv guys showed this STRONG wave that came from the equator. So, we are dependent on the northern (polar jet) to provide storms. Unless we get strong blocking, we won't get a HUGE storm. 

Can we get a huge storm-- Yes! The polar jet gets forces south and becomes a part of the subtropical get provided the short wave (spin the weather men like to show on sat. shots)  If we DON'T get that via timing or other issues the "colder events" will be light on the precipitation, like .25 of an inch to maybe .75. Issues with the strorm track will always have mixing as a risk. I'm leaning we can see a 4-8 region wide snowfall-- good event, not historic or memorable and a bunch of 1-4 inch mix messes. (More in those events in the Mts to our west) Good risk of an I 81 special where the heaviest snows(BIG EVENT) run up 81 and tails of quickly east of there due to mixing/rain. 

The cold snaps will have a bit to them and the warm breaks will seem GREAT comparatively speaking. - Snowfall total ideas-- I like a pronounced gradient from NW to SE where I can see Harrisonburg and Staunton being a good bit about normal, Blacksburg and Roanoke very close to normal, Lynchburg slightly below normal and Danville to Richmond below normal. This is caused by a storm track that approaches from the west/Soutwest and the low ends up in eastern TN or SW West Virginia and jumps to the coast east of Virgina Beach or even the Delmarva/ NJ. The snow is usually slower to slide east and the mountains due to dry air and the Mt regions have snow for HOURS before even Lynchburg does. Once the moisture gets in the air is warming aloft and while Blacksburg/Staunton have already had 4-5 inches, Lynchburg gets a quick inch and it changes to sleet/freezing rain. Danville gets some sleet and freezing rain that changes to rain. 

Expect a final call with more exact data, comparable years by November 10th.