Thursday, January 17, 2008


With precip not starting as early as I expected, it's obvious why all area Baltimore and DC Metro schools are heading in on time. I'm sure they're grumbling out in Frederick and Carroll Counties, being under a Winter Storm Warning and yet in school. Once snow and sleet begin this morning, roads will become slick since whatever falls is going to freeze on contact. I envision widespread early dismissals being announced in the mid-morning, making for a very headache filled day. In fact, it seems as though this might even turn out similar to the Dec 5 "Little Storm That Could" which brought many area schools an early dismissal followed by delays the next day.

Wednesday, January 16, 2008


WED 1/16 - 10:00 PM UPDATE: I am now expecting an earlier start time, based on rising dewpoints and faster than anticipated movement of the southern system. I believe you'll see snow and sleet mixed outside your window at 5 AM in the Baltimore/DC area. If I'm right and you see precip before daybreak, this will be the field goal that nets you that day off you've been hoping for so long (if you're in Baltimore County or City, Harford, Carroll, Frederick and yes even lil' ole' stodgy Howard County too, believe it or not.) The map below is the 10:30 PM Radar, and you can see precipitation is already intruding southwest Virginia. Even though much of that may not be reaching the ground, the speed of arrival tells me that it should overspread the area between 4:00 and 5:00 AM. Late-breaking addition...NWS Sterling, VA has upped the amounts on your Winter Weather Advisory, and upgraded large swaths of Virginia to Winter Storm Warnings. If that all comes to pass, the school forecast is, as George Tenet might say, a SLAM DUNK.

Thursday Surprise 3

Now compare how hugely different this map has become from just one hour previously. Didn't your grandfather always used to say "the biggest storms always came from the south." Here's a another weather rule that never fails: If it's snowing in Atlanta, it'll be snowing in Baltimore.

Thursday Surprise 2

WED 1/16 - 7:00 PM UPDATE: This projection from the GFS model indicates snow and/or frozen precip may still be falling even at 1 PM Thursday across most of central and western Maryland.

Thursday Surprise 1

WED 1/16 - 6:00 PM: I figured you'd be back here before long. Perhaps you were wondering if I would ever be back, but since the weather has provided us a new topic, as Captain Kirk might say: "Well, now you have something new to talk about." As many of you already know, the Baltimore/DC NWS issued a Winter Weather Advisory for the most of Maryland west of the Chesapeake Bay, including the DC and Baltimore Metro areas. I've been watching their discussions, the observations, satellite, and of course our old friend, the computer models, for several days now in anticipation this storm was going to deliver some sort of winter precipitation on Thursday. Those in this region whom follow winter weather are beginning to suspect that this system is not turning out as expected, and I anticipate a diversity of surprise closings and delays throughout the DC-Baltimore Metro areas are on tap Thursday morning. Low level cold air appears entrenched into the deep South, as evidenced by the extent of NWS winter weather advisories from here to Georgia.

This fast-moving system will display unique impacts across the Mid-Atlantic area (specifically in Maryland west of I-95, south central Pennsylvania, Northern Virginia, the West Virginia Panhandle, and of course the Shenandoah region):

1. Persisent high pressure "centers" in the Mid-Atlantic will allow temperatures overnight to drop below freezing. By daybreak, whatever precip that begins to fall will freeze on contact, allowing slippery travel conditions to develop quickly, and catch unsuspecting motorists/walkers off guard.
2. A rapid onset of precipitation from southwest to northeast in the pre-dawn hours.
3. The timing of snow and sleet is such that it will disrupt and delay traffic in the critical hours from 5 to 9 AM, and a changeover to "liquid precip" may not occur until afternoon.
4. Changing and unresolved precipitation timing concerns that may disrupt school schedules.
5. A fast moving system that WOULD become a major snowstorm were it not for lack of access to an Arctic high in Southeast Canada. (actually there is one there, but the timing and orientation are not right this round)

The biggest concern which prompted NWS to hoist advisories for the Maryland region is that computer models do not see to be handling the presence of low level cold air across the region. Secondly, the eventual intrusion of warm air aloft may be delayed such that frozen precip is now more likely over a wider area than originally thought, and for a longer period of time. Accuweather, on the other hand has been downplaying the potential for ice or mixed precip. As I remind my students in situations like this, the amounts sometimes does not matter if we have a mixture of frozen precip, because even one tenth of an inch of ice as you all know can wreak far greater havoc than just one inch of snow. The movement of this storm can be seen in a computer model animation from a site I've recently discovered:

For those who have wanted to know what's been going on: The lack of activity on this site is due mainly to the challenge of managing young children, on going winter illness and teaching high school. Those of you with children, or who teach children, or even just know how to spell children understand how rewardingly drained one feels at the end of the day sometimes. Hence there has been little energy left over to post on our recent weather events. I am grateful for the ongoing support of the many loyal readers out there, and feel bad I could not deliver more frequent updates the past month. Especially for my Pennsylvania, New Jersey and New England colleagues who must think we're no longer on speaking terms, as I stopped forecasting altogether even for Boston's recent snows, sorry guys! I will make it up to you. There are big things in the offing for next week and I have a special post in preparation for the announcement that "something is brewing out there...and it's not just the coffee."

Overnight and tomorrow morning: Please post your observations and location in the comments if you are able and willing.