Technical Discussion

Technical Discussion

Synopsis:

A strong system of low pressure  (currently affecting the eastern third of the nation) can be expected to make its way towards New England on Thursday. In its wake it will leave a measurable amount of freezing rain in the central and northern sectors of Pennsylvania. A shortwave system of high pressure will move into the area and provide the possibility of spotty sunshine for the Commonwealth later Thursday into Friday. However this will be short lived. Yet another low pressure system will track north along the Atlantic Seaboard by Saturday morning. It will quickly move out of the area by Saturday evening.

Short Term (Through Wednesday Afternoon):

Pennsylvania will see varied types of precipitation from the disturbance before it makes its way out of the area Wednesday afternoon. The difficulty in predicting the type of precipitation that a sector would receive was in predicting the position of the freezing line. To accurately predicting the freezing line's position, a multitude of tools were utilized, including: Skew-T (GFS and WRF 12z), the Oz GFS and WRF runs, SREF plumes, and HRRR RUC. Every tool seemed to hold a different view in the position of the freezing line, but when poised against the current conditions, it became simpler. The frozen precipitation (freezing rain, ice pellets, sleet, and snow) is forecasted to occur in the northern half of the state. The southern half will experience mostly rain with some mixing possible. The freezing line appears to be steady over the mid-line of the state, but warm air advection prior to the passing of the front will bring temperatures above freezing briefly tomorrow morning. Rain can be expected in that period. After passing, light snow can then be expected for a brief period of time. A pocket of dry air (shown by IR satellite) will then move into the area associated with a shortwave of high pressure.

Long Term (Through Sunday)

A shortwave high pressure system will build into the Commonwealth on Thursday. It will provide the area with spotty sunshine as westerly winds continue to advect cold air. Thursday night could possibly see mostly clear conditions, giving way to frigid morning temperatures. Friday afternoon will see a shift in surface winds from the west to the south west, initiating the arrival of yet another low pressure system. Extended GFS models place the system moving into the area around Saturday morning, and exiting late Saturday night. For now it appears that precipitation will be light to moderate, but mostly concentrated in the eastern sector of Pennsylvania. The snow will not completely leave the state however. Lake effect snow showers can be expected during the day Sunday associated with cold air advection from the northwest.

Forecaster: Tom Bedard