Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 6:31 PM GMT on November 14, 2010
A relatively quiet weather week is in store for much of the northern Middle Atlantic. Midweek will allow for some needed rainfall across Pennsylvania, Maryland, and Delaware as low pressure treks up through Ohio. This will put all of the northern Middle Atlantic in the warm sector with moderate rainfall. QPF estimates are slightly above 0.50in for all areas. This low will bring down the first of several cold fronts enhancing a trough over the eastern seaboard by the 19th/20th of November.
GFS ensembles remain relatively consistent for the 18th-21st time frame for below normal temperatures. Looking at surface normal highs for this time of year for KMDT ranges around 51-54F. GFS prognostics indicate highs in the mid to upper 40s for this time frame. This puts surface highs about 3-5F below normal during this period, so nothing too unusual. As far as precipitation chances, guidance has showed a weak 850hPa wave moving just south of Pennsylvania in the form of an Alberta Clipper. At this time, it appears it will remain very weak with little moisture aloft in the 700mb layer. But it does bare watching for the potential for a few rain/snow showers over much of the Middle Atlantic. Accuracy and consistently dramatically declines after the 21st of November. Teleconnections begin to show an unsual signal with a starckly negative NAO and negative PNA.
Analogs show a negative PNA and negative NAO correlate to well below normal temperatures for the central northern United States through the northern Great Lakes and through New England. Throw in the ENSO status of a moderate La Nina and the analog reanalysis shows a southeast ridge with again very cold air in the extreme northern parts of the United States. This puts a battleground regions towards the Ohio Valley and Middle Atlantic. The blocking in the north Atlantic is quite impressive, but is a bit off-centered for an ideal position. It will be slightly east-based and this has been highly supported by the operational GFS for the last 5-7 days or so. The NAO though is not as strong a correlation for the eastern United States weathern patterns in November. The Pacific is more important. And while the EPO will go sharply negative drawing very cold air into North America, the negative PNA will counter-act keeping some of this in Canada. At this point the chaos pattern is highly volatile and long range operational models remain uncertain. It does appear after the first trough, that a storm system will work up through the Great Lakes ahead of the first of the -2SD troughs around the 22nd-24th of November. This will put the eastern seaboard in the warm sector allowing for the period to average above normal in the temperature department and likely accompanied by some amount of rainfall during the frontal passage. After this front, the colder air bottled up in Canada and the northern Great Lakes will likely become a bit more permeable and surge southward even reaching the Middle Atlantic. The period around Thanksgiving is likely to be relatively cold across the entire northern half of the United States.
In fact the long term GFS around the 28th of November shows an impressive sub 510dm 1000-500mb thickness with a core of cold air centered over Pennsylvania. Keep in mind with the latest resolution upgrages, the long term GFS cold bias has been eliminated this year. After this cold air anomaly, the PNA should begin to rise along with the NAO slightly as the cold air shoots back up into Canada. While it is not encouraging to see a large southeast ridge despite an impressive upstream blocking orientation, at least snow cover will continue to build in Canada helping in the long run.
Snow cover for the most part is above normal in the northern hempisphere with below normal areas focused on western Canada. This will likely fill in towards that region as a core of cold air enters the region towards the 22nd-24th of November. Now that I mapped out much of the rest of November, what does this all mean? Well many of these signals actually could be noted following the Indian Ocean MJO signals. After a large MJO phase 4/5 pulse in the middle to end of October associated with the eastern US cold spell, the MJO has relaxed a bit with little forcing other than a quick pulse to phase 8 as illustrated by the HIRES GFS.
Phase 8 for November typically results as noted above in above normal temperatures. This can be correlated to the current weather pattern.
Many signals are still highlighting a blocky pattern as we enter December and I still like my forecast for a colder than normal December. As for snow chances, I do not see any immediate threats, although next Friday's clipper bares watching. In any case we first need to get the cold air before thinking about snow. I do think most all areas will see at least a trace of snow by the month's end. Next weekend I will be back to posting a normal weekly weather blog with all of the typical maps and seven day forecast. For this blog I just wanted to highlight the upcoming chaotic and changing weather pattern. November will likely be the first below normal temperature month in nearly six months across Pennsylvania, Maryland, and Delaware. Keep in mind this past week's warm highs temperatures were balanced with well below normal lows due to the dry air mass.
"Here northeast of Harrisburg 2010-2011 winter statistics"
Current Snow Cover- 0in
Monthly Total (November)- 0in
Seasonal Total- 0in
Winter Weather Advisories- 0
Winter Storm Warnings- 0
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 0
Winter Storm Watches- 0
Lowest High Temperature- 49.7F
Lowest Low Temperature- 24.9F
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Snow Storms Stats)
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