Sunday, February 25, 2007

"BUT WHEN WILL IT BE...AND HOW WILL I KNOW?"
-Michael W. Smith, in Somebody Love Me from the album Change Your World


The next line is in that song is..."I don't want to wait here forever." While Loudon County, VA has already pulled the plug, those of you in Maryland know you'll have to wait until morning until you know. When will it be? 5:37.58 AM ? No in actuality I imagine most Maryland and Pennsylvania schools are going to make the decision fairly quickly and will be ready to announce first thing starting at 5:00 AM. For those counties and municipalities which did not receive the heavy duty snow (4+ inches) it's all going to come down to a few scientific factors: (1) How much re-freezing occurred overnight? (2) Are secondary roads just wet or icy? (3) Will daytime warming assist in the melting such that a 1- or 2-hour delay seems the most reasonable path to take? To augment your own personal decision making, are three graphics to round out the evening, or to greet you in the morning, whichever time you are reading this. Let's start with the best interactive roadway weather map I think exists anywhere...operated of course by the State of Maryland. If you have not seen or used this system, definitely bookmark it.. this is known as C.H.A.R.T.

Maryland Roadway Weather 2-25-07


Overall this map is indicating most major roads in Maryland are at or above 32*F as of this 9:45 PM update. You can roll over the little dots and see roadway conditions. However, most counties in this image have their snow emergency plans still in place, except for Baltimore City, Prince Georges and Kent. That takes us to the next graphic, current regional surface temperatures.

Surface Temperatures 2-25-07

While some of you are no doubt disturbed by the slot of warm air to your west, keep in mind it has been there for many hours now and has not really advanced much. Also refusing to budge is the wedge of cold air that's deep into Virginia. This is due in part to the recent snowpack that's been established over the past 12-16 hours, and the fact that a large region has essentially similar temperatures. If my facts are straight, that is called a "Baroclinic zone" in that the air mass takes on the characteristics of the area over which it occupies, thus influencing the weather underneath. If I'm off base with my concepts, I encourage the professional meteorologists who frequent this site to please help set the record straight on this. Which leads to our third map of the night: 3-hour pressure changes.

3 Hour Pressure Change 2-25-07

This connects the other 2 maps together. The dark purple shading off the DelMarVa coast is the developing secondary Low, as indicated by 3-hour decreases in surface millibar pressure. This low is forming, but will take a while yet, and by morning the precip should have cleared Philly and NYC with the fringes scraping Southern New England. Point of the map is if that weak Low forms in conjuction with the High to the north and a cold wedge in place, it will help to reinforce the cold over the region even with very nominal counter-clockwise air flow...because it is in tandem with air flow south out of the High. (Many thanks to Mr. TQ for providing the link for this during the afternoon on Sunday.)

WHAT ABOUT SCHOOL ON MONDAY?

Given what observations you've made about the maps I provided, here's a call that hopefully seems reasonable to you:

CLOSED: Frederick, Carroll, Montgomery

2-HR LATE: Anne Arunde, Howard, Harford, Cecil, SE York County PA

1-HR LATE: Baltimore City and County

3-HRS EARLY: Howard County. (Ha just wanted to see if you were attentive)

MY GUIDELINES FOR ACCURATE PREDICTION OF CLOSED THIS TIME: Condition of secondary roads, extent of icing overnight from dropping temps, expected daytime temps. This is assuming most schools will be able to clear their parking lots, sidewalks by 6:00 AM.

That is all for now, see you in the morning for the morning reports.

12 comments:

tirsch said...

My husband came in from shoveling around 8:30 and said it was ridiculously slippery. And we're in Dundalk. So we'll see :) Let's hope for another day off!!

crazedsnowboarder said...

I just got back inside from clearing the driveway and it is VERY icy on the driveway. My road hasn't been plowed and it’s almost as hard as the ice that we had from the Valentines Day storm. I seriously doubt that they would try to send us to school tomorrow b/c of road conditions and still freezing-rain is coming down hard with periods of sleet and snow.

tirsch said...

Crazed...where are you at?

crazedsnowboarder said...

I'm in White Hall about 5 minutes north of Hereford High. Hereford high when I drove by at 7 just had one truck in there working and he had just started no one was clearing sidewalks.

Mr. Foot said...

Another manic Monday. It would appear 2 hours is in the cards. Howard and Anne Arundel have gone that way. If Harford does, so will everyone else.

33 in Dundalk but looks very glazed outside.

terpguy said...

BCPS- 2 hours late

Harford???????

The waiting game begis...

terpguy said...

...begiNs

Anonymous said...

Check out HoCo... made decision at 5 AM!

Gonna need the 2 hours to get out of the snow plows handiwork! GRRR!

Mrs. Burke said...

Come on Harford ... I am exhausted!

TQ said...

I think the warm slot observed over western WV...southern OH...and eastern KY was a consequence of being on the west side of the occluded front as indicated by the surface analysis at this URL.

http://weather.unisys.com/archive/sfc_map/0702/07022600.gif

Some of the warmer temps in eastern WV could be a consequence of elevation. Remeber...there was strong warm air advection (WAA) occurring which changed the precipitation from SN to IP then FZRA.

East of the mountains was a wedge of cold air reinforced by northerly wind and diabatic cooling as precipitation fell into the air mass.

A 'baroclinic zone' is a narrow region of strong thermal contrast or gradient...observed across frontal boundaries (surface and aloft) or along the SE US coast where the warm water of the Gulf Stream is in close proximity to the colder land.

Baroclinic zones induce vertical motion and ageostrophic circulations as the atmosphere tries to neutralize the gradient.

TQ said...

The three-hour pressure change chart shows the isallobaric field at the surface. If you draw a line from the center of the pressure rises to the center of the pressure falls..and then extrapolate a little bit downstream...you can make a short-term forecast of where the LOW is going.

http://amsglossary.allenpress.com/glossary/search?p=1&query=isallobaric

Linda said...

Saying that a clipper may come in tuesday or wednesday! Record for March 7th is 4 inches! We will see. How is everybody? Sad to see winter over.