We could be in store for a WILD ride...

What a RAPID shift yesterday--

Winter Storm watches in effect EVERYWHERE west of the Blue Ridge. My hunch is if the model data holds serve, they expand it region wide. 

There are off hour runs of the GFS and NAM, both are still the crazy snow changover- but timed a bit different. GFS is over to snow much faster-- but the event is faster. NAM waits a while, but last longer. In the end, results are about the same. 

If you want a "first guess"

Areas west of the Blue Ridge-- 5-10, high elevations may see 12. 

East of the Blue Ridge- 3-6, local spots up to 8. 

Going to be some issues-- change over will happen quickly in the NRV and Highlands- and then slide east. If you are out when it changes, roads will get bad QUICKLY. If nothing changes on the model data, it will be ROUGH travelling. Further, While the NAM radar looks impressive, these band have a life of their own, You may see and inch or two and your brother 40 miles away sees 8. 

Here are two simulated radar shots from the NAM, (slower with the system model)

Yellow is what you often see under thunderstorms-- and once you get under the yellow, it's likely snow. 

First shot is at 7 PM tomorrow and second is 10 PM. Mega band just ROLLS our region. 

Per this model- 7 PM-- just getting crushed NRV ROA up and down 81. 

And three hours later it rolls through the rest of the area. Snow rates 1-3 inches in that band for 3-5 hours. 

From Bat Signal engaged

**Euro is on board, not as spectacular as the other models. However, LYH went from about  quarter inch of liquid to almost an inch. Getting the 6-8 inches was a tall order. I'd be thrilled with a 1-2 inch snowfall Thursday**

To Bat out of hell ..

If the Euro jumps on board, you will hear BIG time honking Wednesday AM about snow Thursday.

Will update this when ECMWF comes out.


The Set Up....

Lost in the inches of rain has been a slow, meandering upper air low coming out the southwest. Traditional thought is outside of 3 days, hard to get 2 separate systems back to back that close.

So, a few model runs here and there have been showing the second just sneaking in a bring a rain to snow even and they've been dismissed. As we've moved closer, the southern ULL has held together and is modeled stronger. The temps are initially too warm, but the ULL cools the atmosphere and shows the system going from HEAVY rain to HEAVY snow. Often, if model data shows a cold front pushing in and a switch from rain to snow, they struggle. However, getting a vortmax in the right spot is a GREAT way to get that rapid shift.

Until-- the model data mid and late afternoon shifted more towards a possible snow event and so far ALL the models have come on board with rain developing Thursday and then changing to snow-- and then DUMPING snow for 3-5 hours. In that 3-5 hours a GOOD snowfall could happen in the lines of maybe 3-10 inches. These are tricky events, and with the type of banding some places may only get 1-2 inches and other 8-9.

The cool thing is because of the ULL, MUCH of VA, down to even the coast CAN cash in on some snow.

The pictures..

Here is the 500 mb low-- these are often shown by mets on TV-- these are the upper air energy that help form and enhance storms.

500 MB low, goes negative. (tilts NW to SE, common in stronger storms)--heads off the NC coast, perfect for VA snows.

NAM snow map-- NOT a forecast, but snows potential. Purple is 7-8, RED is 10+

Can you get a January thaw

When it was NEVER frozen??

Next week is going to be NICE-- VERY nice.

This weekend will be seasonable and very nice. Next week will heat up to have some days well into the 60's.

However, a term we used quite a bit last year called a "sudden stratospheric warming" is about under way. What this does is breaks down the polar vortex and pushes the cold away from the north pole. This will be underway over the weekend. Lag time before impact is 10-14 days. So, pattern change begins Jan 15th or so but should take another 5 days or so to adjust to our region.

What to expect??

Hard to say looking 2 weeks out, however if we want decent snow if this pattern comes to fruition this may be our best shot at a wintry couple weeks. The cold air seems to start in the plans and mid west and then build east. Tough call, because the last cold snap was more west based and built east. This seems to have a better set up with what is called "cross polar flow" meaning the air is coming from the coldest regions rather then last time where it wasn't SUPER cold.

Can this fail??

Well, the SSW is a lock. The only issue we can see with these is the cold goes to the wrong side of the globe. It happened last year. However, the arctic oscillation hit -3 in December and it seems to be heading that way again. (stats show that is likely). That should being some cold air to our side of the globe. Next issue is getting the fully into the east coast region-- which should happen, but not till after January 20th.

I will update late this weekend.

SNOW!!!

Model data- Worst type of storm with no real hedge.

Looking at the 0z NAM-- it's literally an 4-5 hour event if that. Flurries or drizzle for an hour, bangs to decent snow for 2 hours and ends as drizzle/flurries. Maybe an inch or two anywhere east of the  Mountains NORTH of the Staunton River.

SO, 1-3 mountains, Coating to 2 inches east of Mountains. Get up early-- snow ends fast and melts by early afternoon. :)

Danville, South Boston, barring a miracle this won't be your event.

**Heading to my Dad's in Parkesburg, WV-- stopped for the night in Lewisburg for the snow and a swim at the hotel. We already got a little sledding in. Hoping to get 4 inches out of this event up here**

The little event that won't--

If you've read my tendencies, you'd note that I usually blog when I feel strongly about the event. So, a blog this AM on the cusp of our first possible accumulating snow isn't a good sign.

Strike 1- Marginal temps. No model gets the last 2-4k feet below freezing.

Strike 2. Strung out low pressure. That's not a good sign for heaving precipitation. With temps near or above freezing we'd need heavy stuff to cool the atmosphere and or accumulate.

Strike 3- total QPF is forecast between .15 and .25-- that's much much either way and we know it will mix.

The NWS forecast is under and inch of snow in Roanoke and maybe a little ice in Lynchburg. These seem about right. Places like Blacksburg and Radford could see 2-3 inches and Hot Springs and Lewisburg could see 2-4 or so. Will update if any major changes, but I'm not expecting any. If anywhere east of the Blue Ridge sees an inch, consider that a blessing from the snow gods.

Ice event and the next 10 days.

Tricky forecast for Lynchburg, VA- Roanoke, a little easier but still tricky. Few degrees either way make a BIG difference.

The Good:
We need the rain and will get quite a bit. Between an inch and a inch and a half most regions.
Ice impact-- While we could see some ice build up on the trees in places that get freezing rain, but the rain will come down heavy so it won't have a chance to freeze as much + temps won't be that cold.

The Bad:
If I were king of the world, I'd of expanded advisories a county south and east of Lynchburg to include Campbell and Appomattox. It may not materialize, but considering the holiday, people heading to work-- if there is marginal temps a bridge or overpass is icy-- bad situation.

The Data:
Interesting trends as far as temps-- we spiked early and between the cloud cover later in the day and a little colder air dipping in from the north, we went from 53 to 43 in a couple hours. Temps will hover in the upper 30's until the rain starts. There is some dry air, especially between 6 and 10k feet. This will cool the atmosphere from the mid levels down mix the rain with sleet for a time between lets say 5 am and 10 am tomorrow. The surface temp will slowly drop as well and will stop in Lynchburg somewhere between 31 and 34) Obviously, getting below 32 is a big deal. Elevations above 1500 feet or so will get much more freezing rain. Just outside Roanoke in the elevations above 1200 feet should see a decent amount of ice accrual as well.

The issue with the sleet is this-- ideally, you want air colder than -3 or -4 C for 4-5 thousand feet for sleet. This is more like -2 or -3 for 3 thousand feet as modeled. So, this is marginal for sleet. However, some sleet will fall. I can see the ground getting coated for a period tomorrow between 7-9 am .

Biggest thing-- be careful in the am. Check the weather, warn your friend to check. A few degrees-- better safe than sorry.

The Future:
Saturday has a possible event on tap. AS of now, looks like a risk of a moderate snow event of maybe 2-4 inches. Still need to shift over the data. Part of the deal will be what happens with our first storm and where that ends up.

Jan 2-3 has another "potential event". If you track some of my blogs, I talk about the the "PNA" or ridging in the west. Seems like we MAY have some cold air and SOME chance of of a decent storm. I like the potential for 7 days out.

Bat signal engaged

Well, this may be one of my more terrible storms as far as the waffle. I felt good as far as where were we 48 hours ago, but the rapid and consistent move of all the models made it seem like that was the movement it was heading. I was expecting MAYBE a little sleet in Lynchburg to start, and Roanoke maybe a little sleet and freezing rain. Nothing that was a big deal and over early.

The model data started to shift back this AM and now all agree the other way. Taken literally-- 2-3 inches of sleet in Lynchburg and even more snow/sleet in Roanoke. The weather happens, the models try and guess.

The facts:

The storm arrives after midnight. When there is low level cold air, it's common that some places start as what seems as rain and as the intensity picks up it goes from that to even sleet or snow. There was an ice event in December of 2005 that started as freezing rain, went to snow-- back to sleet and then a pretty good ice event. This may end up somewhat like that.

Heaviest of the precipitation will be from dawn on Boxing day till mid afternoon.

The speculation:

If the colder trends are legit- we will have Winter Storm warning west of the Blue Ridge and advisories east, north of the Staunton river. Since .5 is a warning, these cold be expanded.


The issues:

We need the cold air to get here. If the cold air is a little later or storm quicker, we will get more rain and less ice. This is a very plausible option at this time.


I love these "computer generated snow maps- they are usually full of crap. this one is, as it's accumulating snow when it should be sleet. This one has from the GFS has 4 inches in Lynchburg near Campbell county and 0 down near Brookneal in Campbeel County. My guess is this map isn't seeing the warm air above 5000k feet and this is more sleet. As a result, it's more like 25% of what falls here like an inch in LYH. Possible, not a forecast. Yet.