The most sustained warm-up and first widespread rain event in over a month will begin starting today, as a weak low pressure tracks through the area with occasional showers, starting out as light freezing rain/drizzle inland of NYC. Following the passage of this system, a temporary warm up will occur through the remainder of the week, peaking on Friday with highs in the 50s and rain/thunder possible. This will not mark the end of winter, however, as strong indications signal yet another cold outbreak and more snow in the longer range.
Today’s Outlook: Light Rain, Morning Freezing Rain
Posted above from left to right are the latest surface analysis and radar composite from WPC, and the 3-hour forecast of the GFS 500 millibar heights and vorticity from NCEP MAG; both are valid at 9z (4am). Yesterday’s storm system, associated with a compact low pressure but strong mid level shortwave aiding in heavy snow over eastern New England over 8-12 inches, has moved out into Atlantic Canada, while the focus shifts to the next shortwave trough over eastern Illinois, with a broad area of low pressure extending southeastward into Ohio and Kentucky. As of this morning, this area of precipitation has entered central PA into West Virginia, and continues to progress northeastward. While temperatures aloft at the 850 millibar pressure layer are above freezing, surface temperatures remain below freezing across parts of the region, leading to the development of freezing rain and drizzle. The highest risk for up to a tenth of an inch of ice is over central-NE PA into northwest NJ and interior SE NY, where temperatures are still in the 10s.
Wind direction today will remain out of the south/SSE, which will help to gradually warm temperatures and result in a changeover to rain after at least 10am-12pm, while the rest of the area outside of NW NJ/SE NY generally observes light rain, perhaps starting out with a brief period of light freezing rain as temperatures reach and climb above freezing. High temperatures are expected to climb into the mid-upper 30s inland and the upper 30s-low 40s for the rest of the area, with showers mostly ending by the mid-late afternoon hours and drying out by the evening as a breezy westerly wind briefly develops up to 10-15 mph.
Thursday – Friday: Brief Warmth Spike, Rain/Possible Thunder
6z GFS hour 42, at 0z Friday (7pm Thurs), depicting the rapidly deepening low pressure over Wisconsin with blizzard conditions to its west and a strong cold front to its south. This front will reach the area on Friday, resulting in a brief spike of warmth and a line of rain/possible thunder (image credit: PSU e-Wall).
The main highlight over the eastern half of the US on Thursday and Friday will be a significant low pressure system, associated with the shortwave trough currently over the NW US, which organizes over Kanasas tonight before tracking northeast and rapidly deepening to reach a minimum pressure near 976mb near Wisconsin tomorrow night, leading to heavy snow and blizzard conditions in the Midwest. Additionally, the system will pull in moist, warm air from the southern US, leading to severe thunderstorms developing near the Plains and Ohio Valley tomorrow evening along the cold front, which then progresses east into the region on Friday.
The warm front will slowly approach during Thursday afternoon and evening, with high temperatures in the low to mid 40s along with isolated rain showers. Warm air advection will continue overnight with a strengthening S-SW flow aloft, aiding in the development of more widespread rain northeast of the area, but with cold surface temperatures leading to freezing rain in the high elevations of New England, northeast of the NYC area. Most of the rain will remain to the north and east, with occasional light rain showers expected overnight as temperatures slightly fall into the mid 30s inland and the upper 30s-low 40s elsewhere, holding steady as the warm front slowly approaches NYC during the overnight hours.
During Friday, weakening forcing is expected as the low pressure becomes vertically stacked over south central Canada and the vorticity maximum lifts to the north, although a strong mid level temperature gradient will persist just behind the front, and along with a strengthening low level jet and some instability ahead of the front will result in a narrow line of moderate to locally heavy rain moving through on Friday, perhaps accompanied by thunder and strong wind gusts. The exact impacts and high temperatures depend on the timing of the front; the GFS and NAM are currently the most progressive with less rain and lower temperatures, while the remainder of the models are slower with the timing; given typical model biases I am siding closer to the slower timing of the front at this time, which would support the line moving through around 12pm-2pm; this would allow temperatures in the late morning to briefly spike into the low-mid 50s near the immediate NYC area and further east, while interior NW NJ/SE NY likely struggle to warm up beyond the mid 40s. The greatest risk of strong thunderstorms exists south of the area, towards southern NJ and further southwest where more instability is expected with highs in the 60s, although the possibility of thunder and strong wind gusts over 40 mph exists for the area as well. Drying conditions are expected by the evening hours with clearing skies overnight and temperatures falling into the upper 20s-low 30s for lows overnight.