Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 1:05 PM GMT on October 19, 2012
Good morning! It is almost the end of October and days are rapidly becoming shorter. Global wavelengths in the northern hemisphere are beginning to shortern in correspondance with a strengthening polar jet that continues to drop more south with each passing trough. These are sure signs that winter is fast approaching and actual snow chances are a little more than two to three weeks away for parts of the Northeast. The upcoming week looks relatively benign weatherwise, with the biggest story in the east being some abnormally warm temperatures. Highs will shoot into the 70s as far north as southern new England for several days with daily means nearly +10F.. This will likely solidify October as another abnormal month for mean temperatures continuing the two year trend. Below, this blog will take a look at the longer range forecast highlighting the possible first winter blast.
The Madden-Julian Oscillation is a measure of the position of convection and monsoonal patterns across the Indian Ocean. Several ensembles are operation models forecast the position of the convection, which then helps to give an idea of a general phase. This phase indicates the position of rossby waves across the Northern hemisphere, and therefore we can attempt to predict where troughs and ridges will be located. The current GEFS mean indicates a general shift through phase 8 into 1 through the end of October. The analogs for mean temperature composites for phases 8 and 1 are located below.
This would signal cooler air funneling south from Canada into the inner mountain west and northern Plains. The trough axis will likely center west of the central Plains. Therefore any cold-air intrusion will likely remain west of the Appalachians. It is expected through the end of October that warmer than normal temperatures will prevail across the Northeast.
The ensemble forecast for the AO and NAO teleconnections are listed below. During the transition seasons, the NAO and AO have less impact on the weather patterns across the Northeast than winter due to the larger wavelengths currently present. Although this correlation is still relatively misunderstood. The present NAO, while negative on CPC composites, is generally east-based and therefore the impacts on the Northeast are meager at best. A west-based positioning to the pressure differences is correlated to the significant troughing and storminess that is very common in winter forecast discussions for east coast snowfall.
As we continue edge closer to the months of November and December, these indices will have a larger impact on the short and long term weather.
Long range models are beginning to hint at another pattern swing by early November.
GFS ensembles are highlighting the development of a more west-based negative NAO as heights begin to increase towards Iceland and Greenland. Wavelengths are showing favorable trends for a winter storm possibility around the beginning of the second week of November. Composites for MJO phases begin to modify after October with phases 6,7,8,1 becoming the most favorable for east coast storminess and troughing. This allows convection to focus along the 180 degree longitude with troughing near Japan, the Aleutian Islands, and the east coast.
The OP ECMWF brings about this slight pattern change a bit later with warmer conditions prevailing through at least Halloween. But the most recent ECMWF weeklies indicate that cooler weather will reappear by November.
The GGEM ensembles are a bit constrasting at this point in the longe range, but still note cooler weather slowly spreading east over time from the west.
I am expecting that October will finish out above normal in all climatological reporting stations at or around a mean of (+)1.5F for the month. As the -NAO becomes more situated favorably, colder air over the western plains will begin to slowly spew east in a step-down pattern. Each cold front will allow the colder air to reach further and further east with each subsequent passing. This regime will allow for the development of several Great Lakes cutters. By the first week in November, near normal temperatures will begin to filter back into Northeast and by the second week cooler weather is possible. Given current wavelengths and equitorial convective patterns, it is likely the development of a storm system in the eastern half of the country will bring some areas this first bought of wintry precipitation.
I am relatively confident that there will be no snowfall through the end of the October across the Northeast. Precipitation means will range near normal also for this time period. My winter outlook will hopefully be posted by Halloween. Stay tuned!
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"Lower Susquehanna Valley Doppler"
(Courtesy of WGAL)
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