Thursday, January 29, 2009

-Altrus, fictional author in the Myst game series for PC

EVENING UPDATE: FRI JAN 30 - 10:30 PM. This report is continuing in the vein of today's headline, as the story of our as-yet-to-develop storm has taken another twist. By now you know most of the major computer modeling programs run by government agencies took a hard right turn today and shifted the future storm's track EAST by 200 miles or more. This occured over 3 "runs" or periods of the models, I believe at 2 AM, 8AM and again at 2PM Eastern time. It spooked the Baltimore/DC Weather Service (and HPC forecasters in Camp Springs) so much they launched an "outlook" as referenced below. When the European model joined the team, it was meteorological pandemonium as everyone in the weather business was running for cover, trying to update their forecasts, re-explain the change, and still save face. It is a tough business, so cut them some slack!

"So What Happened?" That's what everyone following this storm potential is trying to figure out. What caused just about ALL the computer models to shift so far east on the storm track so quickly? Among the reasons include data being initialized this morning may have indicated the Atlantic high was going to be weaker than expected (this was pointed out by a meteorologist on Eastern US Wx). This would allow for the trough over the Eastern US to shift east in order to fill the pressure gap, and with it, also shift the storm track. As soon as I read the HPC discussions today around 1PM while at my seminar, I knew exactly what was happening. I thought "The NAO must be starting it's downward slide, and the models are detecting this, and adjusting accordingly."

An eastward track also means the storm would be able to incorporate coold surface air more readily, creating a situation called "dynamic cooling" in which given ambient cold air, not necessarily a well-placed surface high, can create an environment that allows the storm to generate it's own cold air by the circulation physics. Weird stuff, huh? It just about burns out my brain analyzing it. Okay, that's enough preview for the moment, more in a few minutes.

HAPPY FRIDAY UPDATE: JAN 30 - 4:15 PM. National and local NWS offices processing significant changes to the forecast for next week's storm. The trend indicates a potentially heavy accumulation of snow for portions of the Mid-Atlantic, provided the storm track does not shift farther east. It would be wise for all those concerned to closely examine next week's plans to determine priorities needing completion before this storm arrives. I mentioned earlier this week that if concern was building over this event, the Sterling, VA NWS office would post a Hazardous Weather Outlook. Right on schedule, they did.

Continue monitoring your NWS weather outlet for the latest information, and a full discussion will be posted later this evening, but not before 8PM tonight. You are welcome to post questions and will do my best to respond as time permits.

REVISED SYNOPSIS: The atmospheric pattern over North America is aligning to produce what could be an historic winter weather event for the Eastern United States starting on Groundhog Day, Monday 2/2, continuing into Wednesday 2/4. While many details remain uncertain, such as amount and type of precipitation, it is becoming clear that comparisons to the March 1993 event are not unrealistic. There is an equal probability of this system producing both heavy snow AND heavy rain for the Mid-Atlantic as it traverses the region. This will include strong, gusty winds of 30 mph or greater, and localized thunderstorms along the Del-Mar-Va peninsula. There is an increasing threat of significant heavy snow along the I-95 corridor. It is also possible the storm track may trend even farther east, and shift the axis of snow to the Del-Mar-Va instead of the western coastal plain.

WEATHER SYNOPSIS: The factors being closely watched that will lead to development of this storm include:
(1) The rebuilding of a ridge over western North America.
(2) The expectation of a neutral to negative trend in the North Atlantic Oscillation.
(3) Presence of ambient cold air across the Northern U.S. and Great Lakes.
(4) Arrival of upper-level shortwaves in the 5000 ft flow from Alaska to the Mississippi Valley.

It is believed that these 4 factors are aligning to compress the atmospheric over central North America in a way that leads to "amplification" of the upper level flow, producing a deep trough over the Eastern US. The deep nature of this trough then allows disturbances to travel more quickly and produce more instability. One or more short-waves in the flow will reach copious moisture in the Gulf of Mexico on Monday, and ignite a surface low. Once this low has formed, it will rapidly intensify along the trough due in part to the sharp contrast between cold dry air and warm moist air in the Southeast US. The latest computer guidance suggests a track that can bring significant wintry precipitation and strong winds to much of the Eastern US not unlike the March 1993 Superstorm. Regardless of how the storm plays out, much colder air and gusty northwest winds will replace it from Wednesday to Friday.

As a closing comment: Two pieces of insight from my family that will serve us well in the upcoming storm. My stepfather is fond of saying: "The amount of snow that will fall is inversely porportional to the amount of hype prior to the storm." My father enjoys pointing out that "asking Mr. Foot for a weather update is like going to a fire hyrdant for a sip of water."

I thought those pearls would give you a chuckle on this Friday.

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