Forecast Model Comparison

>> Thursday, December 09, 2010

Model Comparison: Some details are beginning to surface. One of those is a strengthening trend with the upper-level energy as the tilt of that energy pivots... the more the tilt is to the RIGHT, the better the chances of the cold air cooperating with the precipitation. I have drawn a "black line" to mark the tilt and it bisects the center at "X" or "N" of the upper-level energy responsible for producing precipitation and bringing in the cold air. The maps show corresponding upper-level energy and precip (same timeframe).

Also, as Matt has pointed out many times, when a cold snap presents itself... it's important show the increase in US snow-cover. That increase is obvious since November 19th.

Reason for posting the map bbove is to emphasize next week's cold snap. The arctic air in the forecast for next week will travel over a vast amount of snow cover. A considerable area of 4-8" currently exists in the upper midwest and 4-8" also exists in Western NC. Most of that snow has been produced by this latest cold snap. More snow will also fall from the low pressure system headed toward the Great Lakes on Saturday. Numbers will come crashing down. December standards (averages) won't be touched and records may fall next week.


Weekend Storm... A Lot of Bark, But How Much Bite?

Saturday: Cloudy with rain possible very late, but most of it holding off until Sunday morning. Highs 52-56 around Charlotte & 51-54 northern Foothills.

Sunday: This one is complex! The storm system creating all the buzz will move toward the Great Lakes Saturday evening and produce a strong cold front advancing through the TN Valley Sunday morning. Rain will move in Sunday morning as snow mixes in along the ridgetops of the NC Mountains and some sections of the NC Foothills. Again, rain will move in first. That is the main focus of the weekend forecast, yet will probably be OVERLOOKED from now until Sunday.

Now that all the seemingly boring "rain talk" is out of the way, the focus shifts to cold and the possibility of… well ______ . ***Snow will fall in Western North Carolina (mainly above 3000') and will accumulate… with a rough estimate on accumulations at 2-5″. Even though I'm not real familiar with the foothills area, I do think Hickory gets snow in this situation, as does the Burke County area near Morganton. Not only accumulating snow, but high winds driving wind chills at or below zero!*** I also feel good about snow in North Georgia due to a somewhat limited dry-downsloping effect from lesser elevations of southeast TN. I have to tell you that I'm usually optimistic about snow chances when they present themselves, but As of yet, I haven’t forecasted accumulating snow for the Upstate of SC. In this situation I’m glad I haven’t. Here’s why:

2 things:

(1) As many people know, the NC Mountains have a major impact on the Charlotte area (in a westerly or northwesterly wind situation). Forecasters can’t ever discount this area’s topography and it’s impact on storm systems. For snow in the Charlotte area, if you don’t have the storm system to your south (or along the coast) and you want snow, well it’s a stretch. This time we don’t… this system will be centered north of us as it tracks into New England. In this situation, a downsloping wind may completely knock out most of the precipitation unless the cold front and temperature gradient produces enhanced precipitation along the front.

(2) All models indicate a nice, uniform line of rain along this front. Word of caution: forecast models always lay out an eye-pleasing, uniform line of rain along the front… yet when the actual storm gets here it’s usually broken and ragged. That’s just the fact of the matter. A ragged line of precipitation makes a lot of sense when you consider that most of the storm energy will pivot north of us.

With all those things said, I suppose Charlotte to Greensboro will have a chance at a narrow band or quick burst of snow along the tail end of the system. That is, unless this thing shows a CONTINUING strenthening trend on forecast models, tilts further negative and allows for cold air intrusion quicker. Still, my gut says forecast models are optimistic on the moisture along the front.

I will have a model comparison of upper-level energy up shortly...


Greenland Block = Brutal Cold on Monday

>> Tuesday, December 07, 2010

Lows This Morning: Talk about a BITTERLY COLD shot of air for Early December! Just as Matt forecasted and blogged about, towns hit rock bottom this morning as arctic air settled into the Charlotte area and the Triad. Somebody call that dude named Gore because temperatures were nearly 20-degrees below normal today! Here's a rundown of how cold temperatures were this morning:

Charlotte: 16

Hickory: 16

Asheville: 16

Winston-Salem: 19

Greensboro: 20

Starting Colder Wednesday Morning: As I write this (7:45ET), winds are calming a bit around the Charlotte area. Winds dying down overnight combined with a clear sky sets up the perfect situation for more cold temperatures. I expect lows to range from 12 to 16 in most areas tomorrow morning as more dry air downslopes off of Mountains in Western North Carolina. With more sunshine and less wind tomorrow, highs may actually reach the upper 30s, but then again maybe not! Middle-upper 30s under a good bit of sunshine is a good bet in many towns.

Strong Weekend Storm, Then Stronger Shot of Arctic Air: Over the past few days, the focus has not only been on the present cold snap, but also a strong storm system poised to move in this weekend. For a time last week, some analysis had shown the upper-level energy diving into the southeast and spawning a coastal area of low pressure (out east of Chaleston). That's when the rumors of snow began, but those hopes ended fairly quickly in all areas outside of the high terrain in Western North Carolina once the GFS and European locked into agreement on more of a TN Valley to Ohio Valley storm track in the direction of the Great Lakes.

The first map below was pulled from today's 12Z run of the GFS forecast model. As stated on the image, this shows a projection of conditions for Sunday evening at 7PM. Beofre I get started on the cold, I do want to point out that there is a possibility of some severe storms Sunday morning given the position of the low and wind shear produced by the strength of the low. On the the cold air though... at 7PM on Sunday, a line of showers/possible thunderstorms will have already pushed through the Charlotte area with very cold air behind the rain. The 0C/freezing line at 5,000ft is projected to be east of Charlotte at that point as northwest winds kick up.

The second map projects conditions 12-hours later (7AM Monday). At that point, it won't be all that fun to be outside! Very cold northwest winds will likely be howling. More arctic air will settle in Monday and it will be VERY INTERESTING to note highs on Monday... may not warm much past of the lower 30s! The ridgetops northwest of Asheville are going to have to deal with more accumulating snow, although tough to tell on accumulations at this point. Also, I have a sneaky feeling that parts of the Western North Carolina Mountains will go under a Blizzard Warning for winds higher than 35mph along with that snow. It will be interesting to watch conditons play out up there as well!

The last map I have posted shows a comparison of the GFS and European forecast models at the same time - next Tuesday at 7AM. Both models are in good agreement of the overall setup. Both show a very sharp trough and brutally cold air for early December! Both also show a persistent Greenland block - strong ridge of high pressure nosing into eastern Canada. This is helping keep fresh supplies of arctic air moving south. Also, as I mentioned earlier, a relatively weak ridge near the west coast looks as if it will remain in place for early next week. If that ridge along the west coast were more amplified, it might be scary how cold things would be around here!

I will try to post a snow-cover somparison tomorrow... hope everyone is able to stay warm!


Frigid stuff....

>> Monday, December 06, 2010

Cold is the weather word this week. Many Piedmont locations will see highs shy of 40 for the next few days, and many lows will dip down into the teens. This is pure arctic air.

No storm system until we get to next weekend. Models still look all over the place with the exact track of that one, so tough to have any confidence at this point.

I will be out of town this week, but my buddy Andy Wood, a meteorologist at Fox Carolina in Greenville-Spartanburg, is kind enough to provide some information here on the blog this week. Andy is a bright meteorologist, and if you have never read his stuff, I think you will enjoy what he has to say.

Everyone have a great week. Throw another log on the fire and stay warm!


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