Wednesday, November 29, 2017

It gets cold, then what??

Most of my friends and followers for my weather stuff likely follow other weather resources ( Yes, I consider that cheating :))  Haha, I should make a list of good people to follow (Kevin Myatt, Blue Ridge Weather, Wxrisk) and those to avoid (DooleyCaster)

So, this means that most knew the pattern change to cold was coming.  However, what it means in your backyard is much different.  Here are a few thoughts.

1. It will be cold by December 7th. Well below normal for a few days here and there and seasonable cold many other days.  Normal to above will be limited, but still happen.
2. The pattern looks more cold than not through December 20th, then make sink back colder after a lull or small break. Most data supports cold through the end of December and maybe even into the first 2 weeks of January. (The further out we get, the more risk is involved with that statement)
3. Most people care mostly about snow chances. Now, I do love a cold brisk day.. but reality is cold without snow kinda sucks. So, what do we know about snow changes.
A. No specific threats to really track. The models have flashed a couple of things starting December 7th, but nothing at all to "track".
B. It's not out of the relm that we don't see a decent snow, even though it will be cold.
C. With that, It's been snowless in December since 2010, and I think odds are greater than 50% that we break that streak.

Types of storms that impact our area (Central and Southwest VA, including Lynchburg, Danville, Roanoke and Blacksburg) that bring ice/snow to the region. 

1. Nor Easter, Coastal lows(Also called Miller A )- These are the classic big storms. They originate in the Gulf and head up the coast. These have the most potential for big events.

Risk of mix- high, especially east of the blue ridge.
These storms often deepen quickly, which creates for stronger winds.

2. West of the Mountains (Miller B)
These storms form in the south/west and end up west of the mountains. At some point, the jump to the coast, 99%of the time too far north to impact our area.

These often start as snow, change to ice and eventually rain. Snow amounts can be small to at times significant (each set up is different, and is dependent on the strength and depth of the cold air in place

3. Clipper systems (Alberta, not Los Angelos)
These systems originate over the Alberta Region of Canada and head south east. Most often, the pass to our north, but in times of strong blocking, will dip over our region. These systems are usually in the 1-3/2-4 inch amounts with the occasional amounts hitting the 3-6 inch range.

4. Overrunning-
No realy defined low pressure, but cold air in place and the flow aloft turns to the south and southwest pushing warm air our direction). These systems vary from ice events to decent snow events. Bigger overunning events can be in the 6-12 inch area, but more often are a few inches that changes to ice ( Think this way, if there is cold air in place and warm air pushes in, it would eventually change to ice/rain unless more cold pushes in

5. Souther slider- A coastal low like a nor easter that heads out to sea near the NC coast rather than up the coas.t

Less likely to mix, can be a big or biggest event

Now, these are labels we put on storms and not every storm falls into a box like I've described.  Once  we have a few storms to track, this is a handy glossery to use when I start talking about storm tracks.

Sunday, November 19, 2017

A winter outlook so to speak..

In the past I have done a more in depth write up and conveyed more "personal"ideas about what may happen in the upcoming winter. In General, long range at some levels is more of a "good guess" area rather than skill. Often I read many outlooks then do some local research and put out a forecast. This year,  I have some ideas

This year we have two schools of thought.

1. Normal "La nina" winters which would favor milder tems and less snow/dry. 

2. Other impacted "La Nina "winters which would feature more snow/maybe more snow. 
- Other impacts are the QBO, Hurricane season and global SST's. 

Analog years are harder in the context of weather or not you are a "believer" in some type of climate change, the globe is very warm and this does impact our sensible weather.  You could go above normal temps in an season at this point and be correct maybe 80% of the time. 

For our area (Lynchburg, Roanoke, Danville, Blacksburg) I'm to hedge colder, with below normal snow, but due to ice/mix and dryness. 

Temps- All Areas Normal to -1. I do think we see a couple of significant artic outbreaks. Let's be honest, if our lows are in the single digits with wind chills, kids are getting snow/Cold  days  from school. 

Danville 2-12 inches
Lynchburg 5 to 15 inches
Roanoke 7 to 17 inches
Blacksburg 11-21 inches. 

Upslope regions will be above normal (those places that just snow when it's cold)

Why the weird snowfall range?
La Nina winters tend to lack  the sub tropical Jet.  With that you tend to have system that are a smidge to north for our region. Storm track may feature systems going into eastern Kentucky then jump to the coast north of our region. Those are classic snow to mix or just mix events here. The risk for increase blocking could push those to our south under the block and increase our snowfall.

Snowfall is a guess at best, so take that for a grain of salt. I'd expect a little drier than normal winter. IF we over achieve on blocking (Blocking up north pushes cold air south) during an active storm pattern, we could easily over achieve on snowfall.

Be ready for frequent twitter, facebook and blog updates when pattern changes arive. We should remain seasonable chilly for the rest of the month. Good bet that we remain snow/ice free through mid December.