Nov 4, 2013: Cold Tonight, Warmer Mid-Week

Forecast Highlights:

temp11A trough entering the region brought a much colder air mass into the region today and yesterday, with temperatures struggling to warm above the 40s for highs. A strong high pressure will remain overhead tonight, with light winds and cold temperatures in the typical radiational cooling locations. A quick warm up will follow with highs in the mid-upper 60s by Thursday, but with the dry pattern continuing as the storm on Thursday is weaker than originally anticipated, with drier conditions continuing into next week along with cooler temperatures (image credit: PSU e-Wall).




Tonight – Thursday: Cold Tonight, Then Quick Warming

A transient yet strong cold air mass moved through the region last night and today, with 850 millibar temperatures falling to near -6 to -8C, but have since moderated and are rising above freezing. Cold morning temperatures were observed across the area, as a breezy north wind resulted in a typical cold interior/mild coast setup with Sussex, NJ and Montgomery, NY falling to 19 degrees. Central Park, meanwhile, fell only to 35 degrees, and Westhampton Beach in Long Island struggled to fall below the mid 30s as well. This night, however, the strong high pressure will be positioned overhead, which will result in light winds allowing for strong radiational cooling early in the overnight hours, such as Long Island where Westhampton Beach fell from 44 to 28 degrees in just 2 hours (4-6 pm) and is currently at 25 degrees. Increasing cloud cover, however, will limit the temperature drop, which is expected to stabilize after midnight and slightly warm up for some locations towards the morning. Partly cloudy skies are expected on Tuesday with high temperatures slightly warming into the low to mid 50s.

Strong mid-upper level ridging is building over the southeastern US ahead of a shortwave trough swinging through the central US towards the region, advecting a warmer air mass into the region for Wednesday and Thursday with 850mb temperatures reaching 10C. The warm front is expected to move through on Wednesday, with widespread mostly cloudy to cloudy skies and areas of fog; despite this, temperatures are still expected to warm up into the low to mid 60s with the warm air advection. Temperatures overnight will only cool down into the low to mid 50s for most, which is much warmer than average for a November night.

The aforementioned central US trough will reach the region on Thursday as a developing surface low pressure tracks northeast into Canada, bringing a cold front into the region. Earlier forecast discussions expected a widespread rain event with the potential for 1/2 inch as a sharp frontal passage was likely with the trough becoming negatively tilted. Over the last 2 days, however, the model guidance trended towards a much flatter trough that quickly moves through, which results in a weaker cold front and low level jet, decreasing the rain and wind potential. Given the latest indications, showers are expected to affect the area on Thursday late afternoon through the early overnight hours, with minimal rain amounts at most, generally up to or locally over 1/4 inch, continuing the dry trend that has been present this fall and offering little relief to the current drought conditions. Mild temperatures are expected on Thursday, reaching the 60-65 degree range west of NYC and the mid to locally upper 60s from NYC and further east.


Friday – Next Week: Dry Again; Cooler Weekend, Warmer Next Week

A trough will move in behind the weak cold front, with high temperatures falling into the upper 40s-low 50s inland and low-mid 50s elsewhere for Friday and Saturday, and overnight lows falling into the mid 20s to low 30s away from NYC and the coast. Behind the trough, another shortwave trough is expected to move in for Sunday associated with a relatively weak surface low pressure well to the north; this will lead to a brief warm up on Sunday into the 55-60 degree range, but with scattered rain/snow showers again staying well to the north.

As this trough moves out, with a digging trough off the western US coast, a zonal flow aloft is expected to develop over the US. In this case, however, this zonal flow will not immediately translate to widespread warmth, as a strong upper level low in Canada will dive south into southern Canada before flattening and shifting east, leaving a cold air mass over the northern US into the middle of next week, keeping the central US region warmer than average and the northeast US region with near to below average temperatures. How cold temperatures end up depends on how far south the cold air mass slides; at this time, the GFS is leaning towards the colder end of the model guidance, with 850mb temperatures near -5C and highs in the 40s, while the ECM is further north, with 850mb temperatures briefly touching 0 to -2C. While the exact temperatures are uncertain at this time, a cool down is expected for Monday and Tuesday with high temperatures at least back into the upper 40s-mid 50s range, ending up several degrees colder should the cold air mass extend further south. Another warm up is likely towards the second half of next week, with the possibility of a frontal passage and perhaps rain by the late week, which will also determine the duration of the next warm up, whether brief or extending into a prolonged warmer pattern.

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