Thursday, November 12, 2009

The November 2009 East Coast "Smackdown"



Maryland Core Learning Goal 2 - Earth/Space Science
Indicator 2.3.1 The student will describe how energy and matter transfer affect Earth systems. Assessment limits: Atmospheric circulation; pressure gradients.
Indicator 2.3.2 The student will explain how global conditions are affected when natural and human-induced change alter the transfer of energy and matter. Assessment Limits: Ocean-atmosphere-land interactions; cloud cover; climate distribution of temperature and precipitation.

FRIDAY, 11/13/09. The severity, extent and duration of this storm qualifies it as a smackdown event for the coastal Mid-Atlantic and Southeast. This storm developed from remnants of Tropical Storm Ida interacting with a strong upper level Low. Energy in the sub-tropical and sub-polar jet streams "phased together" producing a significant surface low pressure system. The combined influence of this low with a strong and stationary high pressure cell in southern Canada created a long duration pressure gradient across the much of the East Coast. For two days early this month, the GFS computer model projected an extremely powerful storm traveling up the Eastern seaboard. Detailed cautionary statements about the impacts of this storm were also conveyed by Accuweather days in advance.

Frank Roylance at the Baltimore Sun has an excellent overview of the storm's effects on coastal Maryland and the upper Chesapeake Bay region. The Norkfolk-Hampton Roads area newspaper Virginian-Pilot has detailed updates on how that region is coping with a storm which for them, has more resembled the fury of Hurricane Isabel in 2003, than a standard "nor'easter." The NWS Wakefield, VA Office assembled a brief .pdf report on the event,  well worth the time to read for background and data on the storm. If all this is not enough for you, Accuweather is ascertaining the potential for Ida's remnants to loop in the Atlantic and COME BACK to threaten the East Coast next week. As Dave Barry might say, "I am not making this up."

REPRESENTATIVE DATA:
- Wind: Sustained winds of 40 to 60 mph have been observed from coastal North Carolina to New Jersey, with frequent gusts to hurricane force. While not a tropical system, this is well within the NWS criteria for gale force (39-55 mph) and storm force (55 mph+). Last night, winds in Norfolk, VA gusted near 64 knots, equivalent to 74 mph- or Category 1.
- Rainfall: Amounts exceeding 9 inches in southeastern Virginia. A daily total of 5.11" at Richmond for 11/12 now exceeds the amount of 4.32" received in Hurricane Isabel.
- Waves: The Ocean Prediction Center reports that wave heights along the coastal Mid-Atlantic and southern New England may range from 9 to 15 feet until Sunday afternoon. Wave heights at the center of circulation are 25 to 30 feet.
- Impacts: Hundreds of schools were closed Thursday and Friday, with power outages nearing 200,000 observed on Friday 11/13 across eastern Virginia and the DelMarVa. Damage estimates reported to the Virginian-Pilot for just the Norfolk-Hampton Roads area are in the hundreds of millions of dollars.

REVISITING ORIGINAL FORECAST SEQUENCE
Note: This weekend, observed climate data for the dates already passed will be added to determine accuracy of the projections made below. Text of original forecast:
"If my pattern ideas continue to play out, it could unfold in this manner..."
11/01-09: A mild to cool period then brief warmup;
Actual Temperatures at BWI in this period were below normal then above normal
11/10-15: Possible outbreak of Arctic air on or before 11/15;
Actual No significant outbreak of "Arctic" air was observed. It is important to note however the placement of a large and persistent high pressure system in northern New York is identical to previous Arctic air masses which produced major snow events.
In same week, a "smackdown" storm with snow at the onset;
Actual While the hypothesis states this qualifies as a "smackdown" storm in terms of wind, rain and impacts, the only snow observed was at 3,500 feet in the Blue Ridge and Shenandoah mountains of Virginia and West Virginia. This data point failed to materialize.
11/15-25: "yo-yo" period of below then above-normal temps;
11/25-12/5: Seasonal temps leading to kickoff event by 12/5.

WORKING HYPOTHESIS: As well-stated by other readers of this site ( Eric, 11/12/09) the final pattern change to winter weather in the Mid-Atlantic will occur once upper-level dynamics across sub-polar regions of Alaska and Canada migrate toward the northern Gulf of Alaska. This would allow any reservoir of cold air to begin a southward push. Prior to that time, it is clear from water vapor imagery that the El Nino-enhanced subtropical jet, re-energized by the downstream ventilation of this week's storm, will dominate the interim pattern.

FORECAST SUMMARY: November 15 to 25 will feature a period of seasonal to possibly above normal temperatures, with brief and intermittent cool weather produced by an occoasional cold front. This interim period will begin to transition on or about 11/25 toward a noticeable pattern change to much colder weather. The original time frame for significant winter weather in the Mid-Atlantic (defined by NWS as 4" or more of snow in 12 hours) is still projected to occur between 11/30 and 12/5.

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