Tuesday, January 6, 2009


UPDATE: Tue Jan 6 - 1:45 PM. Carroll and Frederick counties have dismissed 2 hours early, and that was expected, along with a host of Virginia and West Virginia counties. It remains unclear if any central MD districts will cancel afternoon or evening activities as temperatures appear to be holding steady. Our local NWS office states that computer guidance is pointing to a warming trend into the evening. They doubt the current regime of surface cold air will remain in place as the high pressure system moves off the New England coast and allow our winds to veer from northeast to southeast. Observers from this website reported a cold rain is being endured across the area, and the hope is temperatures do not drift any lower to yield a much more tricky evening commute.

Data from the interactive MD Roadway Weather feature in the left sidebar indicates the road surface temperature of main highways in central MD remain between 35 and 40 degrees F. This morning's vertical sounding from Dulles airport continued to indicate the most likely frozen precip would be only sleet, as the temperature and dewpoint remain too far apart at the surface (33 T versus 31 DP) for there to develop a significant icing event. In addition, both the temperature and dewpoint at roughly 5000 feet are 35 F or higher, showing there was never any chance for snow of this in case you were holding onto hope. At present it appears unlikely the atmosphere or surface will cool further overnight to produce ice-related school delays on Wednesday.

SPECIAL THANKS. My heartfelt appreciation is publicly extended to the Websense filtering team of Baltimore County Public Schools for allowing this site to be recategorized as "News." Many colleagues have already conveyed their thanks in being able to make use of information here when it is relevant to their instruction. In honor of the hard-working grounds crews, I will do my best the remainder of this winter to keep that space heater running outdoors so we have no more wintery precip to contend with. (After all, my devious heater plan did seem to work today, huh?)

SUMMARY: Tue Jan 6 - 7:45 AM. A Winter Weather Advisory continues until 9AM Wednesday 1-7 for most of central Maryland except for Anne Arundel, Baltimore City and southern Baltimore County. Overnight changes in NWS forecasts throughout the Mid-Atlantic included upgrading areas of central Pennsylvania to an Ice Storm Warning, and expanding the coverage of a Winter Storm Warning in western Maryland and southwestern Virginia. We all awoke to temperatures above freezing, as was suspected by many on this website and in other weather observing communities. Despite daytime warming and a strong influx of warm moist air aloft from the southwest, surface winds have shifted to the north and will be from the northeast for remainder of the day. With a seasonally cool High pressure center moving across Pennsylvania today, those northeast winds will continue to funnel cold dry air across central-western Maryland and the Blue Ridge. The evaporative cooling process caused by rain falling through that layer of dry air just above the boundary layer will allow temperatures to remain steady or slowly decrease throughout the day.

NOWCASTING THE STORM. For those of you who like to follow up-to-the-minute developments, some links to help include Accuweather's regional radar loop, this animation of surface conditions, and of course a current listing of delays and cancellations. The Baltimore ABC2 Weather page also presents a number of useful features. If you really want a heavy-duty scientific analysis of local atmospheric dynamics, try the Storm Prediction Center's vertical soundings page, with Dulles airport's readings as the nearest observation site.

QUESTIONS YOU MAY HAVE. I'll be adding brief, curriculum-relevant answers to these questions as time permits, if you wish to present them to your students or colleagues. For now, I offer my basic thinking on the event:

1. "Are we getting out early?" BCPS: Probably not, ground is too warm for icing.
2. "When will it turn to freezing rain?" Depends on where you are, not likely until after 12.
3. "What about Wednesday?" Delays are most likely east, and closings to the west.
4. "Are we getting out early?" Uh, let me think about that one more, now get to work.
5. "When will travel be the most difficult?" As Justin Berk of ABC2 news is pointing out, the evening commute after 4PM is the target time for most ice problems today.

Those of you with access to the comment feature are welcome to add more, and I will try to answer if time permits. I do have a busy day today with a late morning meeting, getting my graduate coursework done (so my wife does not hire a babysitter to watch ME!), and keeping a 3-year old entertained..ah..educated with more than just letting her watch Sesame Street on continous play. To those who are wondering why I'm not in school this year, I asked for an academic leave to complete my MD Advanced Professional Certificate, which yes I am on track to complete by June 15. In fact, delays and closings this year would actually hamper my academic schedule more than help it, so I've been running a space heater outdoors for some time now to heat the atmosphere and hence prevent any frozen precipitation, sorry.

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