Wednesday, January 14, 2009


DATA REPORT: WED JAN 14 - 1:45 PM. Unless my map reading skills are off-base, the 3 hour pressure falls indicator shows the surface low may be shifting location to central Kentucky from southern Indiana and Ohio. According to the 1PM US surface analysis, there is a mini-High right over the Chesapeake Bay, and what I am suspecting is be a minor "surface reflection" Low over West Virginia. (Note: Am waiting for the 00Z upper air charts to release my shortwave analysis). Until then I see what's going on here, does anyone want to read my mind and post my hypothesis? I've seen this setup before. Be sure to use proper scientific terms in your response.

UPDATE: WED JAN 14 - 8:45 AM. I'm taking a closer look at the Wed night-Thu morning clipper as there is some potential for the surprise fluff factor similar to Dec 5, 2007 and Jan 4, 2003. For school administrators (especially elementary) I'm sure the Dec 07 surprise mayhem is still fresh in your memory. Look back over that post to see the original call and what happened. Now you should glance over the Balt/DC NW graphical page to see a visual representation of my summary below.

CLIPPER TIMING & IMPACT: Central MD, Northern WV, Southern PA.
1. Projected liquid equivalent from 7PM Wed to 7AM Thu: .04 "
2. Duration of light snow: Arrives 10 PM - best accumulation from 10PM-4AM - tapering to snow showers from 4AM - 7AM. Flurries after 7AM.
3. Surface temps: Low to mid 20's through the region and during event.
4. Upper level temps (just 850 mb): 14 to 19 F depending on your latitude
5. Liquid to snow ratio: (rough estimate until I confirm data) 20:1
CURRENT POTENTIAL SNOWFALL: .04 " x 20 = .8 to 1 inch (by 7AM Thursday)

I know it seems like I'm splitting hairs here, but I did not examine the Dec 5, 2007 situation closely enough before issuing my call that morning. I recall my prediction for 1.56 inches was the UPPER end of area forecasters, and you all remember the stunning 3-4 INCHES that resulted. Granted this storm has less moisture available, but my canary is tweeting in the coalmine.. the NAO has topped at a +1 deviation and is edging ever so slightly down. It is coincidental this trend is mimicked by the HPC track?

RECORD OF DATA ANALYSIS. For the analytical aficionadoes out there, I'm tracking the 00Z and 12Z posted upper level shortwaves at 500, 700 and 850 to see what indications we have from them. While moisture content IS limited (less than 1/10th of 1 inch liquid equivalent), with such a cold air mass, even .05" x a possible 30:1 ratio along the PA border brings 1.5 inches, and enough to prompt surprise school delays Thursday morning in northern MD and south central PA. Also note that HPC storm track shown to the right has DEFINITELY shifted approximately 40 miles to the south as it crosses MD. I also observe 700 mb relative humidity in northern MD is in the 50 to 70% range.. moist enough at that level to permit whatever snow forming to make it all the way down.

Throughout the day, I will post data as time permits. For science teachers, this will be an excellent case study in how slight nuances in the upper air flow can create big changes on the surface, especially when the outcome ends up totally different than what you expected.
In fact, just having student investigate how flucuations in the NAO index affect storm tracks is higher-order enough to qualify for an exit ticket. For school watchers, scroll to the previous post for section #4 and the text in red.

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