Sunday, January 25, 2009

- Hit single from Tears for Fears 1993 album Elemental

PROJECTION: SAT JAN 24 - 8:45 PM. Next week's winter weather event is looking more certain as a widespread Mid-Atlantic snowfall followed by a period of freezing rain and some rain. Wednesday and Thursday remain at risk for disruption to school and commuter schedules. Little or no risk of disruption is likely for Monday, Tuesday or Friday. The map above shows the current GFS projection for 1PM Tuesday 1/27. SUNDAY 1/25 update: Our winter storm potential outlined since last Wednesday remains on track. The links you can follow today to monitor forecasts include the Baltimore/DC NWS discussion, the HPC's surface low track, current 5-day QPF map, US Hazards Assessment, short range analysis, heavy snow/ice discussion, of course the NAO index, and if you're really ambitious, the Numerical Model suite. I am away from the computer until at 3PM, so keep an eye on things for me!

PRELIMINARY TIMELINE: (some of you get thrilling little goosebumps when this section appears, don't you?) This section is refined until 24 hours before the event, followed by the "storm grade" section of predicted accumulations for observable locations. I advance to this level when a high probability exists of measurable wintry precipitation. The geographical range of this projection is from Martinsburg, WV south to Washington, DC north to Elkton, MD

TUE 1/27: (Sun AM comment) As evidenced by this HPC-manipulated map called the QPF 5-day, you can plainly see the anticipated liquid equivalents are getting more juicy with time. Clouds increase throughout the day, with light snow arriving in western MD counties by 1PM and Baltimore-Washington metro by 4PM. View the current GFS map for 1pm Tuesday. Actual time of onset will be tough to pin down, as evaporative cooling is likely to produce the reviled "virga" effect, and could delay arrival of accumulating snow until the evening rush hour. This onset timing will be closely monitored for signs of acceleration that would unexpectedly impact schools Tuesday causing early dismissals. At present that does not look likely, but there are signs this troubling development may have some credence.

WED 1/28: Light snow overnight Tuesday (shown on the GFS map for 1AM Wed) will continue into the early-morning hours Wednesday, but begin mixing with freezing rain around mid-day, and taper off as a period of light rain/freezing rain toward evening. This transition occurs as the first wave of weak low pressure crosses southern Maryland. Placement of a high pressure center in the Northeast in conjunction with how close the primary surface low tracks toward MD-VA will determine how long frozen precip holds. If the primary storm strengthens on it's approach, yet remains south of DC, it may be able to draw in colder air, and areas north of DC would then receive mainly snow and not see much of a changeover. (shown on the GFS map for 1PM Wed)

THU 1/29: The departing storm will usher in a cold front to sweep the region by Thursday morning, as leftover precip turning to rain before ending, and returning colder temperatures late day and the possibility of icy spots for commuters overnight into Friday.

ANALYSIS AND COMMENTARY: I hope that "breaks it down" for those of you starting to plan ahead for dealing with this next winter weather event. Part of the rationale behind my forecast goes back to the ideas discussed all week. Pieces of energy ejecting out of the southwest more quickly, becoming embedded in a rapid upper level flow at the same time a dominant high pressure is pressing southeast, as evidenced by the NAO index among other climate indicators. I believe the cold air will become entrenched first, followed by moisture arrival, and expect many forecasters to revise northward their area of expected impact to include central Maryland and southern Pennsylvania. Since it's a fairly complex setup, I thought today's title song (available from youtube) best fits the situation, and the lyrics are a perfect way to conclude :

"Break it down again - so those are my dreams - and these are my eyes - Stand tall like a man - Head a strong like a horse - When it's all mixed up - Better break it down - In the world of secrets - In the world of sound - It's in the way you're always hiding from the light - See for yourself you have been sitting on a time bomb - No revolution maybe someone somewhere else - Could show you something new about you and your inner song - And all the love and all the love in the world - Won't stop the rain from falling." (Note: I hope the last line was not an unintentional omen, as I know some of our alert readers are going to latch on to that and say, "see--- it's already foretold in the song." ;-)


UPDATE: SAT JAN 24 - 4:45 PM. This map was sent by an alert reader, and it is an indication of what some computer models are seeing for the Mid-Atlantic for the middle of next week. While I'd like to get excited about this map, my inner adult reminds me it is not desirable to be in the bullseye 5 days out if you are counting on snow. For now, I agree on the moisture amount, ranging near 1.00 liquid equivalent, but as the Sterling VA NWS is already hinting, this event may end as mixed precip overall (as in sleet/freezing rain) then purely snow. That's a position I adopted from the beginning. I still assert that while much of the Mid-Atlantic sees snow, amounts should be light and short-lived, with warmer air intruding into a cold air damming setup by Wednesday leading to a possible icy travel situation Tuesday night to Thursday morning. Additional graphics and supporting links will be added as time permits.

No comments: