Wednesday, January 19, 2005

PREPARE TO GO NOWHERE FAST

SEVERE WINTER STORM TO CRIPPLE PARTS OF THE MID-ATLANTIC
AND EAST COAST THIS WEEKEND...BLIZZARD CONDITIONS POSSIBLE

FIRST, a check of where we stand with public knowledge of the storm:

- a Marty Bass alert has been issued. A Baltimore area TV forecaster, Marty is getting ramped up from what I hear, starting to drop hints about the storm.

- Carl Parker on the Weather Channel has been particularly adamant this evening about doing a "up play-down play" on this by saying things like: "There's the potential for a huge snowstorm to develop this weekend for the Mid-Atlantic." And they keep saying this about every four mintues. You know that when Paul Kocin gets on there, it's a serious situation. If you don't know who these people are, it's okay, you're probably a normal person.

- As of Wednesday afternoon, only the Baltimore/Washington and New York City NWS offices issued Special Weather Statement Wednesday afternoon. All other NWS offices held back until Thursday morning. State College, Philadelphia and Pittsburgh now have come out with their Winter Storm statements. Read their forecast discussions: (scroll down a page to get the weekend analysis), very interesting to see how they all still carefully avoid even talking about the liquid-to-snow rates. PIttsburgh, State College, Philadelphia, New York, Baltimore.

- Accuweather is calling it what it is... a major winter storm, and has a series of graphics on their site which would indicate the I-95 corridor is going to the under the gun either way. And it appears they believe a secondary low will develop off the SC coast and more northeast, delivering a wrap-around punch of snow over the big cities of the northeast.

- Mainstream media outlets, such as MSNBC, local TV station websites, etc. have not begun advertising the storm, but I think that will start to change in a big way Thursday. By Friday everyone will be in major hype mode, and the NWS will roll out Winter Storm Watches for most of the Mid-Atlantic.

SECOND, what will be the evolution of this as a significant snowfall event?

- Liquid to snow ratios will be generally 15:1 and 20:1 in higher elevations, due to the Arctic air being delivered by the clipper which just passed and the next one on Thursday. I think highs throughout the Northeast will in the lower 20's.

- The current QPF (Quantitaitive Precipitation Forecast) as put out by the Climate Prediction Center (CPC) is calling for a general 1.0 to 2.0 avaiable liquid because it appear likely Gulf moisture will be drawn into the first system diving southeast from the upper Midwest on Friday-Saturday, and then Atlantic moisture will wrap-around the second system on Sunday.

- A ridge off the Southeast coast is going to slow forward motion of the east-moving low, so the Mid-Atlantic will get a longer duration event on Saturday into the evening before energy transfer begins and the second low cranks up as it moves north from the VA/NC border.

- Colder air means more snow. While a forecast is more complicated than some simple calculations, I do base my snowfall amounts on the tried-and-true formula that gave us 23.5 inches in the Feb 2003 Storm. It is the snow ratio as determined by the air temperature, X available moisture. A rule of thumb in snow is that 1" of rain is 10" of snow at 32 degrees F. But the colder the air, the more snow you can squeeze out of the same parcel of air.

Let's say the average available moisture in this storm for the Mid-Atlantic (including all of PA south of I-80, all of Maryland from DC north, all of DelMarVa from Dover north) is 1.25 inches of liquid. Now take your location... if you are near the coast, temps are warmer, around 25 F, so you'll have a 15:1 ratio. In the mountains of PA and MD, where temps will not crack 20 F, it'll be 20:1 and possibly 25:1 at ski resorts like Seven Springs, Blue Knob, all of the Poconos, Whitetail, Liberty, Roundtop and so on).

Do the math...multiply 1.25 by the ratio of your area, to get your projected snowfall:

Northern Virginia/Northern West Virginia/Southwest PA: 1.25 x 25 = 31 inches. Not impossible, given forecast highs of 18 F around Pittsburgh, and liquid equivs topping 1.5 inches. Probably more like 18-24"

Central PA south of I-80: (Cold, highs in 20's, but slightly less moisture)
.75 x snow ratio of 20 = 12-15 inches anywhere from Altoona east to the Blue Route/Northeast extension, including State College, Harrisburg, Lancaster, Selinsgrove, Chester County, Bucks County, Allentown.

Southern PA to Northern/Central MD, the I-76, I-83, I-70 corridor: (Saturday Highs in mid 20's, but more moisture) 1.25 x snow ratio of 15 = 18.75, so I'm calling for a general 12-18 inches, with some localized amounts in the lower Susquehanna Valley near 2 feet. That would include York-Franklin Counties.

All important I-95 corridor from DC to NYC: (Saturday highs in upper teen's NY, lower 20's south, moisture will be over two storms, Saturday system, then Sunday system) 1.25 x a snow ratio of 10 south, 15 north means a general range of 12-18 inches from metro DC north to metro Philly on the ground by 8pm Sunday.

Northeast/New England from NYC to Boston: (Sunday highs in teens to low 20's) This is more tricky, because these areas will be affected by the second and third systems coming north from the VA/NC border, bringing hefty moisture. CPC has a liquid equiv of 2-3 inches just off shore NYC on Sunday, which would pretty much be a rerun of "The Day After Tomorrow" That's 2.0 x a snow ratio of at least 15 = 30 inches! Seems crazy but then again who would have forecasted 30.7 for Philly in the 96 Blizzard?

THIRD, how would this kind of snowfall affect schools?

The historical pattern in Maryland seems to be that it takes one full workday for maintenance crews to clear 5" of snow. It is a tremendous amount of work, and they go sometimes two full shifts to get it done. That means for every 5", you are going to miss one day of school.

So the early no brainer call is: NO SCHOOL MONDAY for the vast majority of students living throughout the Mid-Atlantic, (except for Garrett County, MD, which got 50 inches in Feb 2003 and never lost a day of school)If 10" then a delay on Tuesday. If 15" school is closed Monday and Tuesday, 20" is closed until Thursday, and so on.

AND FINALLY, answers to your comment questions:

1. Dad, flight should be fine, but will be delays as PHL is going to have tough time keeping runways clear. Height of storm is Saturday night-Sunday AM.

2. MA...when the hype starts on Friday, you'll start having more believers. They'll really believe you when they are shoveling 15 inches.

3. York County...20 to 30 inches is not out of the question if the air is colder than we anticipate and the liquid equivs go up above 1.25. Blizzard-like conditions are possible on Saturday night-Sunday, but only in brief bursts when winds gust to near 35 mph.

4. Glenville, PA... yes, drifting is going to be a bigger problem, as this is wind-driven powder that will fluff all over the place. I would imagine drifts of 3-5 feet would not be unusual.

IN CLOSING for the evening, if I am wrong on this, or the snowfall totals do not materialize the way I thought they would, I will keep in tradition with my students and wear a bag. Except this time, I'll do a picture of me wearing the bag on this site, just for fun.

Please note that any previous information posted below is still considered valid. The current post does not supersede a previous post unless I specifically state I have changed the forecast.

No comments: