Cloudy, drizzly and unsettled through weeks end

The combination of a weak coastal system, meandering off the Mid Atlantic coast, and multiple mid level disturbances moving through the Northeast US will result in generally unpleasant weather from Wednesday through the end of the week. The coastal system is weak but brings moisture and an onshore flow, as the decaying mid level vorticity slowly retrogrades towards the coast on Wednesday. Low clouds and drizzle are possible, despite the lack of any steady rain, especially near the coasts.

Mid level disturbances shifting northeast from the Mississippi and Ohio Valleys through the Great Lakes and Northeast will bring more unsettled weather through the end of the week — signaling the beginnings of a more active pattern. The weekend is expected to feature improving conditions once the frontal system eventually moves off the coast.

High resolution models showing increasing Precipitable Water values by later Wednesday evening.

High resolution models showing increasing Precipitable Water values by later Wednesday evening.

The pattern change, however, will continue and become more obvious through the last week of October. Driven in part by the re-curving Typhoon Wipha in the Pacific, a large mid level ridge will spike on the West Coast of the US into British Columbia. The more amplified pattern will drive a mid level trough, and below normal height anomalies, into much of the Eastern US. Medium range forecast guidance has been consistent in indicating the potential for below normal temperatures through the last week of October — with the European and GFS model ensembles showing weak blocking developing in tandem with the ridge spike on the west coast as well.

The global pattern change continues on the heels of a -EPO, which will certainly be an increasingly large player in the developing pattern over the next 1 to 2 months. Yesterday, we detailed how the effects of a -EPO can often lead to below normal temperatures throughout much of the Continental US. This teleconnection’s effect on the pattern becomes much more amplified by the winter months.

GFS ensemble mean height anomalies (left) and spaghetti plots (right) showing below normal heights over the Eastern US next week.

GFS ensemble mean height anomalies (left) and spaghetti plots (right) showing below normal heights over the Eastern US next week.

With above normal height anomalies and a ridge axis over British Columbia, as well as ridging building over Greenland, below normal height anomalies are forced southward from Canada into the Central and Eastern United States. In fact, such a pattern usually brings below normal temperatures and snow chances during winter. It remains to be seen how much of the modeled pattern will eventually come to fruition, but below normal or cooler temperatures appear to be a near certainty by around Halloween time.

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