Nov 6, 2013: Showers Tomorrow, Then Colder

Forecast Highlights:

gfs_namer_120_850_temp_mslp_precipA warm air mass continues to spread into the region, with temperatures today and tomorrow returning into the low to mid 60s range for most along with mild overnight lows as a cold front approaches. Scattered showers with up to 1/4 inch are expected on Thursday, followed by a minor cool down into the weekend, peaking early next week with widespread cold temperatures. A warm up is likely late into next week and weekend with the potential for rain to return.




Today – Thursday: Mild, Some Showers

The current pattern setup consists of a strong ridge over the southeastern US, and a progressive trough in the central US shifting east towards the region ahead of another incoming shortwave trough in the northwest US. The surface low pressure will intensify as it tracks through the Great Lakes and Canada, bringing a cold front through the Ohio Valley today and the Northeast US region tomorrow. This will advect a warm air mass into the region with 850mb temperatures reaching 10C; partly to mostly cloudy skies are expected today with highs peaking in the upper 50s to mid 60s. Temperatures will struggle falling below the low to mid 50s tonight as the cold front approaches.

The last forecast update on Monday noted that the trough is much flatter than originally anticipated, which will lead to a minor rain event and typical moderate winds around 5-15 mph. Last night continued the trend towards a flatter trough, which will result in a the front moving through faster than previously expected, keeping most of the showers during the daytime on Thursday, clearing by the mid to late afternoon with less than 1/4 inch expected. This will also limit high temperatures, which are expected to peak in the upper 50s inland and low to mid 60s elsewhere. Colder temperatures will return overnight, falling into the 30s away from NYC and the coast.


Friday – Sunday: Chilly, Dry Conditions Return

As the trough exits, a progressive flow aloft will continue over the region, flattening out to a near zonal flow aside from a shortwave trough quickly moving through New England on Saturday and Sunday. A colder air mass will briefly return for Friday and Saturday with 850mb temperatures near -6C, with high temperatures reaching the upper 40s-low 50s inland and low-mid 50s elsewhere, and overnight lows falling into the mid-upper 20s inland, low 30s for the north/west suburbs, southern CT and Long Island, and mid-upper 30s in NYC and the coast. As the aforementioned shortwave trough quickly moves through the region, temperatures will briefly warm up into the mid to upper 50s on Sunday with partly cloudy skies as scattered showers stay well to the north.


Next Week: Much Colder Temps Possible; Rain Next Weekend?

A more complex pattern sets up over North America in the coming days with several anomalous features, starting with a very intense 955 millibar low pressure currently passing to the west of Alaska. As ridging east of this system pushes east into northwestern Canada, an arctic air mass will begin to dig south through western Canada. By Sunday, another strong low pressure is expected to pass over western Alaska, which will push ridging further east into central Canada while an extremely anomalous block develops over the north central Pacific, with 500 millibar heights rising to nearly 594-597 decameters as far north as the Aleutian Islands. The western Canadian ridging is then likely to expand east to the north of the displaced arctic air mass, which along with a weak NW flow over the region and a minor ridging signal in the western US, will allow the arctic air to surge southeast towards southeastern Canada and the northern US with 850mb temperatures of at least -10C to -15C.

The main uncertainty at this time is the timing of the air mass and how far south it expands, although at the very least temperatures are expected to cool down into the upper 40s-low 50s for highs and the mid 20s-low 30s for lows away from NYC and the coast. Should the cold air mass with 850mb temperatures near -10C extend south into the area, which at this time is supported by the majority of the model guidance, high temperatures on Tuesday and Wednesday would struggle to reach the low-mid 40s with widespread lows in the 20s across the area, falling into the 10s for interior areas. This is an uncertainty at this time, and will be monitored over the next few days.

Towards late next week and weekend, troughing is likely to return into the northeast Pacific, with a warming trend likely over the region. The main uncertainty at this time is regarding any potential storminess, as the long range model guidance shows varying solutions ranging from any storm staying well to the northwest with ridging building overhead, to cold temperatures sticking into the weekend suppressing any storm to the south. At this time, it appears the next chance for rain may be in the November 14-18 time frame, although this is subject to some changes.

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