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Tuesday, November 2, 2010

Winter Outlook 2010-2011

I'm running a day later than I had promised--but the crisp cool day today inspired me to put my thoughts and forecast on paper. I've had my general ideas for several weeks, was just waiting for a little more data to trickle in to double check things.


Winter 10-11

Quite the shift from last winter where we had 200% normal of snow

Season Temp. Forecast +2 above normal

Seasonal Snowfall 5-10 inches. (Same forecast for Roanoke, 2-5 inches for the Danville region) 10-18 inches for the NRV, The favored high elevations of the region get more due to upslope snows. (AKA, places were I doubt anyone will read this blog)
Higher risk for ice storms. 

Monthly breakdown temp bread down

December-

-2 below normal

January

Starts cooler but ends warm

+2

February

+4
Still has some colder outbreaks, just warmer overall.

As the long wave pattern adjusts to spring, March will feature rapid swings (Normal to some extent in March) with a higher then normal risk of wintry weather.

Technical talk--

This may bore you if you don't enjoy weather. (I need to post a glossary of terms for those who may care--but if you google these terms you can find them)


I derive my outlook by many means-- First and foremost I read as many detailed outlooks from REAL meteorologists as possible. From there, I study the global patterns based from the El Nino/La Nina regions and other terms such as GLAAM, Mountain Tourque, PDO,QBO, MJO, AO  the past season's hurricane pattern and even snow cover in Eurasia this time a year. From this information I can get a set of years that had similar pre season patterns and check the climo records for those seasons. Its not an exact science, nor do I claim to be my one and only source. With more qualified people creating these "usable comparable years" I see little sense in recreating the wheel as a less qualified forecaster.


Last year, the west based moderate el Nino made it somewhat of an easy call and I'd rate my call an A--- didn't foresee the big snow in December and missed the extreme cold in early January--but other then that it was excellent. The big factors all lined up and I went big and scored big.

This winter's outlook has half the confidence as last years--

Why?

In favor of warmth--
Strong La Nina, The Indian Dipole, Positive QBO

In favor of colder--
Long term pattern of the NAO being negative
Snowcover in Eurasia being above normal.
Some research shows that re curving hurricanes from the east coast may be an harbinger of the -NAO being negative in the winter.


We don't have many close analogs because the El Nino went rapid to La Nina and is currently strong. This COULD disrupt the forecast because the norm is a colder December transitioning to warmer as the winter progresses. (If the La Nina has peaked sooner--does the December climo norms not matter is the thought here)

Piecing this together--

Strong La Nina's don't usually bring big snows to our region. Hence, I'm starting cold and moving warmer and expecting below normal snow. However, the snowcover in Eurasia, Re-curving hurricanes and longer term trend of the NAO I expect us to end up in the battle zone between colder air that spends much of the winter bottled up well to our north.

Monthly break down--

December-- Cold pattern develops late November and is strongest until middle of the month. The pattern begins to adjust to a warmer and by early Jan we are in a warmer pattern.


January--

Early month cold gives way big and its a good month- Late month holds chances for a few severe cold outbreaks, but warm wins the month.

February-
Warm pattern holds on with still the occasional risk of a couple cold days with trailing storms as cold fronts clear (See Feb 89 as example)


Storm pattern---

Last season the mean storm track for our region was to our south and east, hence most events were mostly snow and a ton of it. This season, I expect the mean storm track to go to our west placing us in the warm sector. However, the Appalachian Mountains play a role here where the cold air gets trapped against the mountains and we end up with an ice event. Strong La Nina = south east ridge= Warmer temps on the east coast, especially south of 40 latitude. Cold air damming plays BIG role in our ice storms.

These events can be subtle--For example.

Monday is a great day- High 61, low 32
Tuesday feels a little cooler--52 high but the relative humidity drops and the dew point is 8.
Clouds come in Tuesday night and sleet develops. Temp falls down to 25 with the sleet. By the next morning it is 29 with freezing rain. On the other side of the blue ridge towards Tazwell its 44, Charleston WV is 48 and to our east Richmond is 36 and south Danville is 38. Freezing rain lingers all day. The next day the temp is back into the upper 40's. 2 days later temps are back in the 60's.

These type storms come out of the SW--- and can head up into Ohio then reform well to our northeast. That low level cold air being trapped along the Appalachian mountain (There are three types of this "cold air damming" that causes aides in these ice and snow storms) places us in a unique spot for these ice events. If we tap into the colder air that build up over the Arctic (And didn't build up last year because of the pattern) we could see a nasty ice event or two.

For the record, LYH has one of the highest "per hour" freezing rains in the nation--close to 50 hours a year of freezign rain. I use to have a map of the hours. This is a unique climate trait to our region due to the proximity of the Blue Ridge which creates the inability to remove cold air at the bottom 2k or often less feet of the atmosphere.

Much different than last winter--warmer, less snow and more ice. More rapid shifts and in some sense laster winter was cold with shorter bursts of warmth. This year will on some levels be the opposite. Warm, with short bursts of cold.

My biggest concern is 1-2 nasty ice events, not the nuisance ice events I described-- Also, La Nina's breed drought as the pacific jet dominates and everything is progressive with little interaction from the subtropical jet. This is something to monitor as we head into the spring growing season.
Will update as needed.

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4 comments:

  1. Looks good, Keith! We're going to air ours on Thursday. We only have 60 seconds to do it. :(

    I agree about the ice threat this year. My only difference is that I'm going with the core of the cold in January.

    We'll see how it goes! -ss

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  2. Thanks, Sean.

    I was torn on the "cold" period. With some signs of the MJO making into phases 1-2 Late November Early December--I went cold early. Could bust either way as some history had the Christmas week into mid Jan as the cold season and 75-76 was cold all of January. I'm hoping you guys do a write up on line as well--always enjoy your blogs.

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  4. Along the same lines ... a brief look at Roanoke's La Nina winters historically.

    http://www.roanoke.com/weather/wb/263156

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