Thursday, December 10, 2009

UPDATE ON STORM POTENTIAL AND SITE CHANGES WED 6:00 AM

SUNDAY 12-13-09 AM COMMENT: There was no post or tracking of this morning's winter weather tease because lack of ample cold air and boundary layer temps made it seem not worthy to investigate further. Thanks to those who posted updates in the comments. The bigger area of focus will be behavior of the Arctic front on Tuesday night as well as continued monitoring of atmospheric signals for winter storm potential. The pattern remains favorable for one or more significant storms through 12/26. Several other researchers have identified some interesting disturbing signals for second half of the month. For details on storm ideas, I refer you to Meteorologist Allan Huffman of the DC Weather Examiner.

A summary of his and others' findings will be posted by this evening. Upper air patterns suggest a period of cold similar to Dec 1977 or Dec 1989 is possible in the near future. Yeah, that made you sit up straight, didn't it? Those of you who know or remember those time periods realize how significant that kind of cold would mean now. This is not hype-casting, just a heads up that a lackluster winter pattern at the surface belies the true action far above our heads.

ABOUT FEEDBLITZ POST TIMES: For those concerned about the odd and early arrival time of posts from feedblitz, please know that each night, the program automatically scans for updates. Any new articles found are forwarded to you. The time you receive the update is not the actual time I published it. Being up at 1:30 AM writing is not something I do, unless it is an extreme emergency. Thank you for bringing those concerns forward, and yes, I do sleep daily.

"All that we see...
is but a dream within a dream."
- Edgar Allen Poe

6:00 AM Friday, 12-11-09  [revised from 12-10] Synopsis of forecast ideas to Thursday 12-17:
1. Surface and upper level patterns across North America indicate atmospheric conditions remain favorable for development of East coast winter storms over the next 10 days
2. Strength and placement of the current high pressure ridge over the Eastern U.S. this weekend should reduce potential for significant snow in the Saturday-Sunday period.
3. As the high moves east, return flow will provide a brief warmup in advance of an Arctic cold front Tuesday. The Tuesday-Thursday period needs close monitoring for short-waves, clippers or coastal development associated with the front. Similar shortwave events produced "surprise snow" across the Mid-Atlantic, including 12-5-07 and 1-27-09.

STUDENT CLIMATE RESEARCH: Our student data teams report the following values according to the "three spheres" of analysis, listed east to west across the continent:

ATMOSPHERE
NAO:  Moderately negative at -1.0 ; gradual trend to -2.0 by 12/16.
AO: Moderately negative at -1.2 ; trending to -4.0 by 12/16.
PNA: Weakly negative at -0.5 ; trending  to +1.0 by 12/16
EPO: (East Pacific Oscillation): Moderately positive at ~1.0

CRYOSPHERE
US Snow Cover: Sharp increase this week to approximately 60%.
Canadian Snow Cover: Gradual recovery to approximately 95%.
Arctic Sea Ice: November 2009 average of 10.25 million sq. km., 1.05 mil. sq. km. below the 30-year average

HYDROSPHERE
SSTA's (Sea Surface Temperature Anomalies): Global  analysis shows a large pool of +1.5 to +3.5 C anomalies in the Northwest Atlantic ; The Gulf of Mexico appears to remain slightly cooler than normal, with anomalies ranging from -0.5 to -1.5.
PDO: Declined from +0.40 in October to -0.27 in November.
ENSO Status: SST anomalies remain 1.0 to 2.0 C above normal. The 3-month average for region 3.4 is now +1.2 C. Source: 12-7-09 CPC Weekly El Nino Report

OBJECTIVE: Student researchers will investigate how atmospheric indicators can signal a trigger event resulting in development of a significant winter storm along the U.S. East Coast. 

ORGANIZING QUESTION: Can a simultaneous change in 3 climate indices point to this trigger event? Would a sharp increase in the PNA Index in conjunction with a strongly negative AO and negative but slowly rising NAO lead to favorable conditions for snow along the U.S. East coast?  Then we will know if this storm potential is real, or remains a dream within a dream. Additional background of key indicators:  

1. Placement of the High: A strong, surface high pressure in "upstate" New York, southeast Canada or even over the Great Lakes are the most preferred locations. A high that ends up near Maine sliding east sharply reduces probability the Mid-Atlantic area receives significant snow from a coastal storm. It's a simple rule to follow this and future winters: Predict the high and you predict the storm.

2. Snowcover: The previous two storms have sharply increased snowcover across the U.S. and Canada. This provides an additional cooling effect on all air masses inside or moving through the country, and in turn stabilizes Highs as they travel in the flow.

3. North Atlantic Oscillation: Movement of large air masses across the polar region, influenced by similar movements in air masses from the Atlantic and Greenland has a direct impact on extent and duration of cold in the Eastern U.S. A key indication to watch is if the NAO is shown negative prior to a storm, then has a slight rising trend. This signal tells us surface cold air can be delivered prior to precipitation onset, as the rising index points to a slow "backing off" of air masses that might push the storm out to sea.

Case study: The February 2003 President's Weekend Storm. The NAO went negative before the storm, then rose slightly as the storm tracked east while it gathered moisture from the East Pacific and Gulf. That moisture then overran a massive and cold surface high pressing in from southeast Canada. The NAO was an extremely key factor overlooked by many forecasters at the time trying to nail all the details of the storm. A certain group of 10th grade science students at Dundalk High School in Baltimore County, MD did not overlook it. There are witnesses on this site who can attest that four days before the storm, those DHS students predicted a crippling snowfall of 18-24" when everyone else said light snow for late that weekend.

4. ENSO and the Sub-Tropical Jet Stream (STJ): Obviously you can tell the STJ is wide awake, because almost every coastal storm to impact the Mid-Atlantic since August has been laden with heavy soaking rain and a lot of it. In addition, the 3-month ONI (El Nino Oceanic Index) has made a steaming hot jump from 0.9 C+ to 1.2 C+ and is likely to go further. This is a huge increase of average sea surface temperatures over a three month period, and the concern is that too much tropical moisture could easily overwhelm the pattern with more soaking rain.

5. Other big signals: Long time readers and weather experts know there is a plethora of additional indicators, including the placement of the polar vortex, the PDO (negative),  the MJO phase, whether the QBO is in an eastward or westward progression, and so on. If time permits, we can revisit those higher-level concepts this weekend.

SO WHAT SHOULD WE WATCH? One classic "contra-indication" to look for will be how day-to-day computer models react to changes in their own NAO forecasts. The CPC (Climate Prediction Center) in their own 6-10 day outlook and discussion notes that while models are showing a wide range of coastal solutions for next week, those same models also point to a moderately negative NAO and an active subtropical jet. Look closely at their discussion for the period Tuesday 12/15 to Saturday 12/19. Do you see what I see?

A hearty round of thanks to all the enthusiastic commentors and for your robust discussion. I think many can agree we enjoy the company of your participation as much as we do following the storms!

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