Thursday, January 17, 2008

7:35 update: Saturday could be "all or nothing"

The 18z runs of the NAM and GFS look similar -- both gives us a moderate to heavy snow on Saturday.

Here is the NAM at dawn. Precip just moving in.
Then just after lunch. A nice snow.

Total accumulation for this model run is about ...

Now, here is the GFS at dawn. Looks pretty similar, huh?
And early afternoon. The field of precip looks different, but the amount is about the same.

Both atmospheric profiles show all snow, perhaps starting as rain for an hour or so.

Total snowfall for the NAM would be 5-8 and for the GFS would be 3-6.

I'd take either of those, wouldn't you?

The Euro, though, gives us just a dusting. The UK model nothing.

So, very much up in the air, but two of the most reliable models say we get a significant event starting Saturday.

Here's my first percentage breakdown on the storm:

No precip: 30 percent
All rain: Less than 1 percent
Marginal event (1 inch or less of snow): 5 percent
Minor event (1-2 inches): 10 percent
Moderate event (2-4 inches): 15 percent
Major event (4-6 inches): 25 percent
BIG DOG event (6 inches or more): 15 percent


Now, this might look odd, but there is rhyme to the reason. The gradient for this storm is going to be sharp. So, you'll have a broad area with major snows a broad area with nothing and then a small area with totals in between. So, it's kind of an all-or-nothing setup which means we have a 40 percent change of a major or big dog event and a similarly high percentage of nothing at all.

I would call this a particularly low confidence forecast, given the major model disagreement this close to the event.

6 comments:

School ?? said...

Skip what about delays tomorrow? What do you think the Shelby zone will be on?

Skip Foster said...

Just don't know about that -- no insight, sorry. We'll have to wait and hear from the schools. You can check our web site for the latest -- probably no decision until early AM.

Anonymous said...

For the record, I thoroughly enjoy your forecasts Skip! You can't find weather predictions as honest as yours. Most "professional" meteorologists are too conservative and not bold enough to give the predictions that you give for fear of seeming foolish. Their forecasts are sugar-coated. I say all of that to say this, thanks for being bold enough to "give it to us straight."

Anonymous said...

Skip what do you think area roads in Shelby will be like tomorrow?

Skip Foster said...

Thanks for the kudos although there is a fine line between bold and stupid and I'm liable to cross it at any time.

On the roads -- my general experience is that they're often not as bad as people think they'll be. The low tonight is 28, but it's still 35 now and I'm not sure for how long the temps will be below freezing.

With a high of 48, whatever freezes will melt again quickly.

Whatever you do, take it slow.

Anonymous said...

do you think the roads will be slick for morning commute in shelby?