Watched most of the evening data roll in..
We have a very dynamic system heading our way. My biggest fear all along has been the "north" trend that the models often show. Consider the Dec 18-19 09 event that the models had dumping 2 inches of liquid here in Lynchburg-- all snow, 20 inches. Ended up with 14.5 here at the house-- about 75% of the total possible. The models in the last second jogged something called the 700mb a little to close. If you've heard the term dry slot-- it basically is a place in the development of a low that a wedge of dry air works up. We never got into the dry slot, but sat close enough to turn hours of HEAVY snow into hours of LIGHT snow.
My point-- some data is pulling the 500mb low just a little too close. This is the catalyst, the gasoline that makes our system go. There is a physical connection between the exact tract of this feature and the snow bands that will develop. The more north this 500mb low travels, the shorter time we spent in these bands. The less time, the less snow that falls.
My original call was 4-8. Since I jumped on that number early, I am completely OK with being graded on that amount. If I had waited, I'd likely thrown out 3-7 for the regions marked 4-8-- based on the data today.
SOME data shows 2-3 inches, with a shot at 5-6 depending where the banding sets up.
My point-- grade me on the 4-8. meaning if the official totals from LYH and ROA are 4, its a win. I'd lean towards 3-7 being the range at this point, the 7 being in the places where the best bands set up.
If you are wondering why I can't say exactly where-- these are like a thunderstorm. One can pinpoint a region where these set up, but not an exact location. Random example-- Roanoke gets 3, Bedford 5, Forest 4, Evington 5, Concord 7, Spout Sprints 3.
Best snows fall between 1 and 5 PM..
Grade me on the 4-8, now expect 3-7.
Tuesday, January 25, 2011
Because you're mine, I walk the line-- Mid day update.
Noon data is about done-- except the ECMWF
Some of the data infers that the snow is all but done at 7PM and our best snows fall between 1 and 5 PM-- a little quicker compared to before.
There's quite a bit that could go wrong, but so much about this event looks great.
What can go wrong--
1. Temps are borderline-- will start as a mix or rain and change over. Any delay kills the forecast 4-8 inches.
2. The pieces in motion are not set in stone, any deviation can change a forecast. One concern is the upper air support nudges just a little too far north and spares our region the best snows.
3. The overall storm will be moving fast. I've made some assumptions that it snows hard for 4 hours give or take. If the development is SLIGHTLY delayed, we have issues.
4. Some of the model data races the precip out of the MNTS area pretty quickly leaving the Mt. Empire and NRV on the lower side of accumulations.
The good--
1. The models all have about the general same idea-- the fine details is what makes this a 2-3 inch event or 6-8 inch event.
2. The model ideas are slowly clustering towards a general track.
3. Dynamics-- strong upper air low. History tells me this blows up early and not later. Thundersnow is likely some places, especially to our North.
My early AM map stands-- any changes would likely be to adjust the NRV if needed and "MAYBE" a little better detailed for the southside areas. Trace to 4 inches is broad. (But, I don't think I have any readers down there anyways.)
Some of the data infers that the snow is all but done at 7PM and our best snows fall between 1 and 5 PM-- a little quicker compared to before.
There's quite a bit that could go wrong, but so much about this event looks great.
What can go wrong--
1. Temps are borderline-- will start as a mix or rain and change over. Any delay kills the forecast 4-8 inches.
2. The pieces in motion are not set in stone, any deviation can change a forecast. One concern is the upper air support nudges just a little too far north and spares our region the best snows.
3. The overall storm will be moving fast. I've made some assumptions that it snows hard for 4 hours give or take. If the development is SLIGHTLY delayed, we have issues.
4. Some of the model data races the precip out of the MNTS area pretty quickly leaving the Mt. Empire and NRV on the lower side of accumulations.
The good--
1. The models all have about the general same idea-- the fine details is what makes this a 2-3 inch event or 6-8 inch event.
2. The model ideas are slowly clustering towards a general track.
3. Dynamics-- strong upper air low. History tells me this blows up early and not later. Thundersnow is likely some places, especially to our North.
My early AM map stands-- any changes would likely be to adjust the NRV if needed and "MAYBE" a little better detailed for the southside areas. Trace to 4 inches is broad. (But, I don't think I have any readers down there anyways.)
No Basic Changes--yet?? Winter Storm Watches issues for the Blue Ridge West.
Most of you know I'm a guy who always loved weather-- even took a couple years online classes in the early 00's and do this "tracking and forecasting" all winter. I'm usually tempered with calls and yesterday and I pushed the BIG BUTTON a little early. I was hoping the model data would increase my confidence but reality is it dropped somewhat.
The basis of this was model support was growing for that solution with some adjustments made on climatology and past behavior of systems like this. Last nights model runs where ALL over the place-- most give a minimal of 2-3 inches and some get closer to the 8.
In a set up like this, the exact track of the upper air support ( the tv guys often show a little swirl in the clouds away from the surface low) will make all the difference. Also, often its possible SOME areas verify in the 4-8 ranges while others fall short. During the March 09 storm-- Most of the Lynchburg region had 8-12 inches while 15 miles away in Big Island had only 3 inches.
The basis of this was model support was growing for that solution with some adjustments made on climatology and past behavior of systems like this. Last nights model runs where ALL over the place-- most give a minimal of 2-3 inches and some get closer to the 8.
In a set up like this, the exact track of the upper air support ( the tv guys often show a little swirl in the clouds away from the surface low) will make all the difference. Also, often its possible SOME areas verify in the 4-8 ranges while others fall short. During the March 09 storm-- Most of the Lynchburg region had 8-12 inches while 15 miles away in Big Island had only 3 inches.
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| No major changes today-- Final call after tonights model data. |
Monday, January 24, 2011
Nothing but a chilly rain and suddenly BOOM, its heavy snow
The model data is trending exactly where I had hoped. First half of the storm will be to warm for snow. I had held out some hope that we might cold enough, but not it's in the cards. The storm has trended SLOWER as first thought were this could be a Monday event and now its a Wednesday event so our cold air support is gone. We are totally dependent on the storm to make its own cold air.
Surface low from the Gulf of Mexico across east NC to near the Delmarva. It is a little disjointed from the upper air low but does drop between .25 and a half inch of rain. As the upper air support approaches we flip to snow. Its taking an ideal track as modeled. It doesn't have to do that--so there is some open chances this changes. We have plenty of wiggle room from the south--as some of the data first plaster Winston Salem and move it Northeast at us.
Between a half inch and literally an inch of liquid can fall in the snow band-- considering its wet snow, 4-8 inches. Attached is a graphic from the model output-- it can be hard to read. First column I've marked is surface temps. Second is temp at 5k feet and third is liquid that falls.
The air is chilly and raw. As the upper air low approaches from the west, the air cools, which had been running from about 35-40 degrees from 5k feet down rapidly cools. The light drizzle suddenly has huge rain drops mixing and rather quickly the rain becomes heavy. The TV breaks in and announces 8+ inches has fallen in places in North Carolina and heavy snow is now falling in Blacksburg, Roanoke and Martinsville. Perhaps a quick rumble of thunder and suddenly a flake of snow appears. Quickly, more and more snow mixes in and suddenly it all snow. Surface temps drop to 32 and flakes the size of pancakes are falling. Heavy snow lasts for 2-6 hours. While flapjacks no longer fall from the sky, such large flakes, the size of silver dollars are not often witnessed around this parts. With the wet nature of the snow, everything is plastered. Trees branches that stand tall in the sun now scrap the ground under the heavy weight of the snow. As quickly as it started, the snow has tapered to just flurries.
This upper air energy is similar to the March 1-2 09 event. That event was much colder and we had snow on the front side. The upward motion in the clouds was so great that before the second band of snow came in--we had 20 minutes of graupel where the fast upward movement precluded the snow growth.
Pic from that event-- this is in the two hours were 5 inches fell.
Surface low from the Gulf of Mexico across east NC to near the Delmarva. It is a little disjointed from the upper air low but does drop between .25 and a half inch of rain. As the upper air support approaches we flip to snow. Its taking an ideal track as modeled. It doesn't have to do that--so there is some open chances this changes. We have plenty of wiggle room from the south--as some of the data first plaster Winston Salem and move it Northeast at us.
Between a half inch and literally an inch of liquid can fall in the snow band-- considering its wet snow, 4-8 inches. Attached is a graphic from the model output-- it can be hard to read. First column I've marked is surface temps. Second is temp at 5k feet and third is liquid that falls.
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| Surface temps are JUST above freezing, mid levels are JUST below freezing. I'd estimate that from the 1.07 liquid that falls in these 12 hours, .80 is snow. Because its a wet snow, let assume it falls as 8-1 ratio and that makes 6.4 inches. |
The air is chilly and raw. As the upper air low approaches from the west, the air cools, which had been running from about 35-40 degrees from 5k feet down rapidly cools. The light drizzle suddenly has huge rain drops mixing and rather quickly the rain becomes heavy. The TV breaks in and announces 8+ inches has fallen in places in North Carolina and heavy snow is now falling in Blacksburg, Roanoke and Martinsville. Perhaps a quick rumble of thunder and suddenly a flake of snow appears. Quickly, more and more snow mixes in and suddenly it all snow. Surface temps drop to 32 and flakes the size of pancakes are falling. Heavy snow lasts for 2-6 hours. While flapjacks no longer fall from the sky, such large flakes, the size of silver dollars are not often witnessed around this parts. With the wet nature of the snow, everything is plastered. Trees branches that stand tall in the sun now scrap the ground under the heavy weight of the snow. As quickly as it started, the snow has tapered to just flurries.
This upper air energy is similar to the March 1-2 09 event. That event was much colder and we had snow on the front side. The upward motion in the clouds was so great that before the second band of snow came in--we had 20 minutes of graupel where the fast upward movement precluded the snow growth.
Pic from that event-- this is in the two hours were 5 inches fell.
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| 12:30 AM March 2, 2009. |
Will do a full update after tonights model data-- as of now, our odds for 4-8 inches sits at about 60%
Like a winning three point shot at the buzzard---
As we get closer to the event-- it is slowly coming into focus. Challenging event to say the least and really, we won't truly get a true read until about 24 hours out. Sometimes I break down model data by model, from this blog forward, I'll just describe how I think it unfolds. Model data has about settled on a storm track-- its just the amount of moisture and the exact temps we have to deal with.
Our HP leaves and since the storm is now a WEDNESDAY event-- the cold air is our biggest obstacle. We cool enough for snow only due to a truly dynamic system. Storm forms in the Gulf of Mexico and heads towards the South Carolina Coast. Rain breaks out over most of the region including the Mountains. Mountains change to snow a little quicker simply due to the elevation. As the 500 MB low moves into a favorable position, rain rapidly changes to snow from the mountains east. Thermal profiles drop to right near freezing from about 5k feet down making this a TOUGH event. A couple degrees too warm and it snows, but hardly accumulates. This type of event has the potential to have 3-4 hours of VERY heavy snow.
What can go wrong?? While I'm convinced the storm will bring needed rain, if the 500 MB track is wrong, we will not get as long of a period as snow. I've listed 2 inches as the low side-- which seems reasonable as of this time. Also, intense bands could set up-- where place A sits under a band for 3 hours and gets a nice event while region B sits on the outside and gets minimal accumulations.
Any significant changes in the track, strength and speed of the 500 mb low will change our forecast. I've slightly adjusted it north compared to model data as is now.
Only changes made to the outlook map is moving Roanoke to the 2-8 zone. Elevation will be a factor-- so just outside Roanoke city will do better.
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| Early Morning 1/24/2011 for the 1/26 event. Click to enlarge. |
Sunday, January 23, 2011
Quick Mid Day Model Update
4 Models--
2- mostly snow LYH to ROA and west. Danville- rainy mess. (GFS and NAM)
1- WAYYY to warm and most of the region is rain.( GGEM)
1- Slightly warm-- Mostly snow, NRV and Mounts, Rain to snow a little quicker in ROA, A COLD rain in LYH that ends as a little snow. Everywhere else-- RAIN.
The greatest concern all along has been it being to warm if snow is your desire. The 12Z NAM was about as perfect as you could get track and strength wise. Implied 6+ inches of heavy wet snow with a little more after the model quit running (84 hours out)
After reading these models for 10+ years-- they TEND to be a little too cold aloft and a little to warm at the surface in winter precipitation events. I can't rule out some freezing rain as the event unfolds either.
2- mostly snow LYH to ROA and west. Danville- rainy mess. (GFS and NAM)
1- WAYYY to warm and most of the region is rain.( GGEM)
1- Slightly warm-- Mostly snow, NRV and Mounts, Rain to snow a little quicker in ROA, A COLD rain in LYH that ends as a little snow. Everywhere else-- RAIN.
The greatest concern all along has been it being to warm if snow is your desire. The 12Z NAM was about as perfect as you could get track and strength wise. Implied 6+ inches of heavy wet snow with a little more after the model quit running (84 hours out)
After reading these models for 10+ years-- they TEND to be a little too cold aloft and a little to warm at the surface in winter precipitation events. I can't rule out some freezing rain as the event unfolds either.
Clear as Mud?? Early outlook map included- hand made!
Slowly, we are coming to viable solution--My confidence is a little lower, especially compared to last winter where we knew early and often a big event was coming.
Rather than breaking down model data, I'll place chances on each event happening. Model data has slowed this event down, which is actually good because another piece of high pressure TRIES to build in.
20% Storm chuggs WAY inland and its mostly rain, WELL into the mountains get snow.
20% Storm is a little to far east and we get some snow, not much
60% Something close to my map happens.
Description- Low develop as foretasted in the New Orleans area and slides to a position just east Charleston, SC and moves NE from there. Places along and west the Blue Ridge are mainly snow and 6-15 inches fall, middle regions including Lynchburg start as a mix or rain and change to snow. 2-8 inches, depending on the time of the change over and exact track of the 500 mb low. South and East regions start as rain and will mix or change to snow eventually. A couple inches can't be ruled out, but without significant cold air it may just snow a couple hours and not accumulate.
**Track of the 500 MB low is huge** When you get under or near the track of this, a couple to several hours of heavy snow take place. This event is moving pretty quickly, but this is a wild card.
I spent some time looking for a decent map to start showing my ideas better. Because I need a white background, a google map is the best I can do. Please click to get a good look.
Rather than breaking down model data, I'll place chances on each event happening. Model data has slowed this event down, which is actually good because another piece of high pressure TRIES to build in.
20% Storm chuggs WAY inland and its mostly rain, WELL into the mountains get snow.
20% Storm is a little to far east and we get some snow, not much
60% Something close to my map happens.
Description- Low develop as foretasted in the New Orleans area and slides to a position just east Charleston, SC and moves NE from there. Places along and west the Blue Ridge are mainly snow and 6-15 inches fall, middle regions including Lynchburg start as a mix or rain and change to snow. 2-8 inches, depending on the time of the change over and exact track of the 500 mb low. South and East regions start as rain and will mix or change to snow eventually. A couple inches can't be ruled out, but without significant cold air it may just snow a couple hours and not accumulate.
**Track of the 500 MB low is huge** When you get under or near the track of this, a couple to several hours of heavy snow take place. This event is moving pretty quickly, but this is a wild card.
I spent some time looking for a decent map to start showing my ideas better. Because I need a white background, a google map is the best I can do. Please click to get a good look.
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| Better than handspun shakes from Chick-fil-A. |
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