After a colder and snowier than average start to meteorological winter over the last 20 days, astronomical winter is off to a spring-like start with temperatures in the 50s today and the 60s on Sunday, approaching 70 degrees near NYC. After some showers overnight and into Monday, a significant temperature swing is expected with high temperatures only in the 30s on Tuesday and the mid-upper 20s on Wednesday (Image credit: PSU e-Wall).
Today – Monday: Record Warmth, Some Rain
Synopsis: As shown to the left with the latest WPC surface analysis, an elongated frontal boundary currently stretches from Texas up the Ohio Valley and into the northern Northeast region, with a strong temperature gradient along the frontal boundary separating an unseasonably warm and moist air mass to the south from a frigid polar air mass to the north. There is no well defined low pressure center along the frontal boundary at this time, with an elongated area of heavy precipitation spreading northeast along the frontal boundary associated with a surge of subtropical moisture extending from the Gulf of Mexico with precipitable water values near 1.5 inch.
A strong shortwave currently over southern New Mexico will quickly track to the northeast with a strong southwesterly flow in the mid-upper levels, aiding in the development of a surface low pressure near Texas which will continue to deepen while rapidly tracking northeast through the Ohio Valley tonight and the Northeast US by Sunday. The frontal boundary will remain nearly stationary over the central-northern Northeast, where periods of rain will continue to train with over 1-2 inches of precipitation expected, with record warmth to its south and a significant ice storm to its north. As the frontal boundary pushes east on Sunday night into Monday, another wave of low pressure will develop along the boundary, leading to heavy rainfall over the coastal Mid Atlantic and parts of Long Island/coastal New England before completely pushing offshore.
Temperatures: As the deepening low pressure quickly tracks through the Ohio Valley and Northeast tonight into Sunday, warm and moist air will be advected into the Mid Atlantic and southern Northeast, with unseasonably warm temperatures near 14-16C at 850mb. Along with a lack of rain, this will result in record high temperatures along the I-95 corridor into NYC. The warmest temperatures are expected south of central NJ where some periods of sunshine are possible, with highs in the low-mid 70s. In the NYC area, upper 60s are likely to extend into NYC and northeast NJ, while the rest of the area peaks in the low 60s. Temperatures will slowly fall into the mid 50s-low 60s overnight, peaking in the mid-upper 50s for highs on Monday.
Precipitation Amounts / Types: With subtropical moisture being pulled along the frontal boundary, significant precipitation totals of nearly 1-2 inches are expected along and north of the frontal boundary, with the axis of heaviest precipitation over Ohio/Indiana into central-northern NY state and northern New England. Over the NYC area, little rain is expected through Sunday night, when the frontal boundary will push through with scattered showers likely amounting up to 1/4 inch. A wave of low pressure will develop along the front on Monday, resulting in an area of heavy rain in the Mid Atlantic coast as PWATs likely exceed 1.5 inch; there is some uncertainty regarding how far inland this spreads, although at this time moderate rain is likely over Long Island with 1/2 to 1 inch of rain possible, locally higher further east, and 1/4 to 1/2 inch near and north/west of NYC. This will continue to be monitored over the next day, however, for the possibility that the wave of low pressure develops further west with increased rain totals over the area.
Most of the region will observe rain, but with frozen precipitation expected in the northern Northeast. A strong surface high pressure will extend into Quebec, keeping low level cold air firmly entrenched over northern New England and setting up for an even stronger temperature gradient on Sunday, with a significant ice storm expected over far northern NY state into the Maine/NH border, where over 1/2 inch of freezing rain is anticipated as temperatures remain above freezing aloft. With the second wave of low pressure on Monday, cold air is expected to be too slow to catch up with the precipitation to result in frozen precipitation affecting the NYC area.
Tuesday – Beyond: Significant Temperature Swings Return
Shortly after Sunday’s record warmth with temperatures approaching 70 degrees, winter will make a quick and significant return as some of the frigid Canadian air mass surges into the region behind the departing frontal boundary, with temperatures crashing back to below average. These temperature swings have been common since late November with the progressive pattern in place, and the frigid cold air that has been present over Canada for the majority of this month which provided parts of the region with well below average temperatures in the last week, with additional temperature swings expected to continue through the rest of the week and beyond.
More winter-like conditions will return for Tuesday with partly cloudy skies, highs in the low-mid 30s, a breezy northwesterly wind at 10-20 mph, and the possibility of isolated snow showers. Temperatures overnight are expected to crash into the low 20s near NYC and the coast and the mid-upper 10s for most other locations, with low 10s possible towards interior NW NJ/SE NY and Connecticut. Mostly sunny skies are expected for Wednesday with highs struggling to exceed the upper 20s across the area.
As the early week trough departs and another one enters the north central US, rising heights are expected aloft over the region with temperatures rebounding into the upper 30s-low 40s on Thursday. A few showers are possible overnight with a frontal passage, followed by another surge of frigid cold air into the region with high temperatures again likely to struggle reaching the low 30s by the weekend with lows in the 10s/20s. Generally dry conditions are expected to continue through the rest of the month, with no indication of significant storminess likely until at least the very end of the month or the first week of January.
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Friday, December 20 Observations:
The moderating temperature trend continued through Friday as a stationary frontal boundary set up over the northern Northeast with rain falling well to the north of the area. A continued southwesterly flow continued the warming trend, with partly to mostly cloudy skies and highs reaching the upper 40s to low 50s across the area.
The highest temperature was 54 degrees in LaGuardia airport, and the coolest high temperature was 46 degrees in Bridgeport and New Haven, CT.