Monday, February 26, 2007

13 comments:
"THAT'S ALL FOLKS!"
-Porky Pig from the oldtime Saturday morning cartoons

Put it this way, wasn't it nice that your underperformer of a winter at least ended on a snowy note? While I did promise those of you in the Mid-Atlantic a "Very Fabulous February" ...you could say it did work out that way for students and teachers hoping to get some time off. However, it is time to break the sad climatological and meteorological truth... looking at long range patterns (going out beyond 144 hours from now) indicate there is little in the way of a similar snow event. There is the rare occurrance of a March 13, 1993 or March 20, 1958...but the atmosphere's teleconnective signals do not point toward anything of that magnitude the remainder of this winter. To clarify from a geographical standpoint...south of I-80, I believe significant snow for the season has ended, except for the Laurel Highlands of western and central Pennsylvania. There remains the possibility of an inch here or there, but another event such as this one looks highly unlikely given reduced availability of Arctic air moving forward in time. So as you bask in the glow of have one more day to see snow out your window, here are two photos submitted by readers in the Baltimore Metro area:

The Final Snow of the Season

Courtesy of Julee in the Hereford Zone of northern Baltimore County, Maryland

See You Next Year!

Courtesy of Mr. S from Anne Arundel County, Maryland

Forecasting and analysis of the weather pattern will continue into mid-March, and then the focus of this website shifts to the mundane and non-controversial topics of climate change and pandemic influenza in the ramp up to tropical cyclone season. I can give you a tidbit of that by saying that El Nino is now trending to neutral and we may see La Nina by mid summer, I have a sneaking feeling this will be a bad year for hurricanes and could resemble 2004 or 2005 in terms of frequency and severity of storms. But much research on that awaits me, so if you want more information on that topic, please read over Dr. William Gray's preliminary forecast for the 2007 season.

Sunday, February 25, 2007

12 comments:
"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.

79 comments:
"SUPPOSE YOU'RE WRONG THIS TIME?"
-Comment made by Kenneth Welsh, playing the Vice President in Day After Tomorrow to paleoclimatologist Jack Hall, played by Dennis Quaid when he suggests the climate is changing.

2:30 PM Update - SUNDAY 2/25

If you reside in the Mid-Atlantic area near the DC-Baltimore-Philly Metro areas, obviously what you see out your window would indicate a few changes to the forecast are in order.
And you would be correct. First, the current radar:

Surprise Snow on 2-25..at least it's not ice


The unexpectedly heavier snow is occuring due to a couple factors. The wedge of cold air was more entrenched across the coastal plain than computer models had indicated. Despite overnight temperatures not falling to far, the orientation of the airmass was more widespread in a north to south arrangement (along the East Coast) than in the East-West setup in the Valentine's Day Storm. As a professional meteorologist dutifully noted in the chat feature last night... we were concerned about the marginal aspect of surface temperatures. He made a point that has rung loud and clear today. Upward motion. The strong onshore flow into the Northeast and Mid-Atlantic caused by the tandem combination of the decaying Midwest low and the High pressure ridge setup from Canada down to the south east provided ample moisture. For simplicity sake, let me explain it this way by saying Atlantic moisture is riding in along the coastal plain, striking the pervasive dome of "cool" air, (not really cold) forcing it upward quickly.


The moisture then falls through the cool air at upper levels, crystallizing into snow. As it falls, the snow slowly evaporates, creating what I discussed yesterday...evaporative cooling. This in turn chills the atmosphere and brings the air temperature near the surface "down with the snow." It is a perfect example of micro- to mesoscale atmospheric dynamics. Proof is in thermometer at your house..dropping all day when climatology this time of year suggests sun angle among other things should send that temperature up. The result? A chilled air mass which can produce a hefty amount of snow in a short time even during maximum daytime heating, overcoming subpar temperatures at the surface.


HOW LONG WILL THE SNOW LAST ?
WILL A SECONDARY LOW FORM ALONG THE COAST ?


Surface Observations 130 PM 2-25


Review with me the current surface observations from Penn State's e-Wall. Notiee position of that teensy high around the Delaware Bay? I think that's inhibiting development of the secondary. You cannot have a surface Low forming in the same place as a Surface High. That's the Theory of Reciprocity, right Physics teachers? There can be an upper level low contaminating a surface High, or a weak Low next to a weak High, but not both in the same place at the same time. Momentum from the eastward pivoting dry line behind the cold/occluded front associated with the maturing Midwest low is simply flushing all the moisture to the coast. There it meets enhancement from Atlantic moisture being sent onshore by the double-barrel nature of air flow around both pressure systems. (Counterclockwise for the Low, clockwise for the High). So where is the Secondary Low to form? If it does, it will probably be weak, and have little or no effect on the final outcome of the precip in the Mid-Atlantic right now. Perhaps it will form under the High somewhere in North Carolina, but certainly not along the DelMarVa coast, at least not until pressure falls can indicate the High has decayed enough to allow for a pressure difference.


THE SNOW? WELL, THE BAD NEWS IS IT WON'T LAST LONG. Once that sharp back edge works it's way to the coast, that's probably it for those of you in northern/central Maryland. Redevelopment of a secondary isn't going to happen quickly enough to wrap a lot of energy back around and keep the snow going....there's too great of a north-northeastward motion for that I think. Energy for an explosive coastal low has basically been sapped out. What about the freezing rain that was originally predicted? That may still happen, but I am thinking not anywhere to the extent that was first believed, which is a good thing. There are still many nuances yet to uncover in this drama, and I may have to come back and re-unexplain myself if it changes again. Just remember the headline up top.


BUT THE REAL ANSWER YOU WANT TO KNOW: SCHOOL ON MONDAY?
If snow ends this afternoon, and air behind it is not cold or below 32, and DC-Baltimore metro areas get cut off from the High pressure source region, I could see this snow starting to melt right away. Crews would have many hours to clean up, overnight temps are not projected to sink into the 20's regionwide, all of which makes me lean towards a delay rather than closed for many schools in affected counties of Maryland.

I'll take a look at things again later this afternoon after I get some snow cleared off the sidewalks. Enjoy it now while it lasts. This time of year it'll start falling off the trees quickly and become clumpy and wet before long. If you have a digital camera, snap some nice pictures from your area and I'll be introducing a photo sharing feature on here using flickr.com (that is.. if school closes tomorrow!) Meanwhile, our weather spotters across the land of education... I guess it's time we start the traditional scientifically based speculation on school tomorrow. What are your thoughts on it?

"BABY, BABY...
LOOKS LIKE IT'S GONNA HAPPEN."
-artist and title unknown, maybe the Stray Cats?

The Sickest radar you've ever seen


Ready or not, here it comes. With a projected liquid equivalent of anywhere from .5 to 1.25 inches, this will be a juicy event for Maryland, Virginia, the Del-Mar-Va, Pennsylvania and New Jersey. Be sure to check your local NWS sites for changes in the advisories. I have no major changes to my forecast except to say that temperatures today will determine extent of frozen vs. liquid precip. If northern Maryland receives the widespread icing indicated by NWS, (up to 1/2 inch freezing rain) then school Monday is in jeopardy for those areas (Frederick, Carroll, Baltimore, Harford, Cecil counties). More information later. Please post your observations in the comments or the storm chat center. I will not be able to participate in either until this afternoon, so will talk to you all then.


Special note of thanks to Mr. B in Greencastle, PA for providing this link to the neatest looking radar program I've ever seen, the image above of which is a capture from this morning. Bookmark that one for sure and I'll be adding it in the links soon.