Blizzard to impact eastern United States...
Thoughts on December 26-27 Possible Snowstorm...
Despite a moderate to strong La Nina, an anomalous negative NAO and record breaking negative AO have made for unusual blocking in the northern Atlantic. This has allowed for a steady trough over the east coast with the core of the coldest standard deviation over the Southeast where some areas are running near 12F below normal. Across the northern Middle Atlantic most temperature means are around -5F below normal. This cold and suppressed pattern has prevented synoptic storms from entering the area north of the Mason-Dixon line. The only snows in Pennsylvania have been from lake effect with impressive totals near 3ft across the northwestern portion of the state. South across Maryland and Delaware a clipper paved a path of light snow over the region with steady light accumulations. Currently we have a semi-similar upper level pattern as portions of last winter during the multi-blizzard period. Again this is all thanks to the anomalous blocking in Greenland and the Davis Straights. A split flow could result in the phasing of the subtropical and polar jets off the coast of the Southeast and drive up along the western periphery of the trough. Model guidance certainly highlights an impressive upper level ridge over the western United States. A piece of energy will be ejected out of the southwestern United States and gather strength near the mouth of the Mississippi River. 500mb maps indicate a closed low forming in southern Louisiana. This energy will rotate through the Gulf Coast and will track dependent on the exact phasing of the separate jets and the alignment and timing of the negatively titled trough. A strong area of confluence associated with a Polar Vortex in Canada will slow the progression of the 500mb synoptic pattern and maintain a slow progression of this enhanced vortex. As the area of confluence lifts northward and the ridge in the west becomes more amplified, a surface low will try to develop in the southeast and move northeast. If we can get the ridge axis far enough west and slow the progression of the pattern enough, we may be able to get a strong area of cyclongenesis to occur south of Cape Hatteris. Often significant eastern cyclones occur during phases of the NAO transitioning from negative positive. Therefore signaling a pattern change. This would be our pattern changing storm and fits nicely as the NAO transition is supported by ensemble and operational model guidance. While climatology in high end moderate La Ninas completely signals against Miller A storm systems, the record breaking high heights/blocking over the north Atlantic may outweight climatology for a rare event. Given the incredibly amplified ridge in the western United States, the players are certaintly there. It all comes down to timing. If we can get the phasing to occur as the trough becomes negatively tilted then this will turn up the coast and stay about 100mi offshore. But if we do not get this pieces of the puzzle together, then this will travel offshore.
Model guidance has been polar opposite recently with the ECMWF harping on several runs of a near historical east coast snowstorm. The GFS and other models have been indicating a weaker low with a less amplified flow therefore paving a storm for the fish. But the models each have a few biases. The ECMWF tends to overamplify storms and hold back energy in the southwest. If this were bias were to be occuring, then that would be the reason we are seeing the very strong low pressure. The GFS on the other hand tends to be east with coastal cyclones along with underestimating the strength of the southern and northern streams. While the ECWMF has remained relatively steadfast with a slow moving low undergoing bombogenesis near the Delmarva, the GFS has been quite inconsistent. In fact the 12z run took significant strides with a much more amplified pattern and deeper initial shortwave. Given the 500mb pattern, it would not take much for the 12z GFS to be a huge hit. Also encouraging are trends on the 12z ECMWF and GFS ensembles which both have moved about 100mi to the west. The 18z NAM is also significantly trending more favorably towards the ECMWF with quicker phasing and a stronger surface low developing in the Gulf of Mexico. At this point, a forecast is impossible. Yes, the ECMWF is probably overdone, but you cannot ignore the trend of its consistency. Keep in mind last week or so when the ECMWF persistently indicated that very impressive low over the Midwest, while other guidance danced around.
Given the high impact this potential nor'easter would have given the calendar days, I thought it was relative to post a new blog to discuss the threat. Also the recent boring weather pattern has been quite dull forecasting-wise, so this is a decent change. If I see the 12z ECMWF tomorrow maintaining the strong coastal low, I will then signal the whistle. For now feel free to discuss the threat in the blog above. If the storm becomes an imminent threat, I will update the sections below as usual.
This is my current rain/snow line...
Selected City Accumulations for the Northeast...
New York City, NY-
"Subject to Change"
After the storm...
Please post storm reports in this blog from across the Northeast during the winter storm and please post location of observation in each report...
This blog is in progress. Check back soon...
Please take an opportunity to vote in the new poll!
"Here northeast of Harrisburg 2010-2011 winter statistics"
Current Snow Cover- 0.00in
Monthly Total (November)- Trace
Monthly Total (December)- 0.6in
Seasonal Total- 0.6in
Winter Weather Advisories- 1
Winter Storm Warnings- 0
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 1
Winter Storm Watches- 1
Lowest High Temperature- 24.1F
Lowest Low Temperature- 12.8F
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Snow Storms Stats)
First accumulating snow - December 10 - 0.50in
Lower Susquehanna Valley Doppler...
(Courtesy of WGAL)