Synopsis:
An area of low pressure will slowly intensify as it travels up along the eastern coast, spreading wintry precipitation across Pennsylvania. The system is forecast to be just off Jersey Shore by Tuesday afternoon and continue moving northeastward. A trailing area of low pressure will pass over our region on Wednesday, giving us another chance of some light snow. Skies will finally clear out Wednesday evening and Thursday should be a decent day. Some high clouds will start to build Thursday evening as a vigorous low pressure approaches from the west. Some snow might break out by Friday daybreak and continue throughout the day.
Short-term (Tuesday – Wednesday evening)
The precipitation shield associated with an area of low pressure moving up the eastern seaboard will spread all kinds of wintry precipitation from snow, sleet, to freezing rain across the state Tuesday morning. The 540mb thickness line and the 850mb line will both be well to the north of the NY-PA border, indicative of warmer air infiltrating into mid troposphere. However, the temperature at the surface might be just cold enough for the occurrence of freezing rain, especially towards the eastern half of the state. The precipitation type could stay mainly snow around Central Pennsylvania as the precipitation will likely end early before warmer air flow into mid troposphere. The bulk of precipitation should be gone by Tuesday night. However, the chance of precipitation will linger into Wednesday as a weak low pressure trailing behind Tuesday's storm moves across the region. Clouds should gradually break up Wednesday night.
Mid-term (Thursday – Thursday evening)
Thursday could be the calm before the storm. Partly cloudy skies will prevail throughout the day on Thursday with drier air at 850mb and 700mb. However, some high clouds may start to move in towards the evening hours ahead of a low pressure system approaching from the Midwest. Clouds will gradually build throughout the night with some possible snow showers breaking out across the Commonwealth, especially in the western part of the state.
Long-term (Friday – Saturday)
This is where the forecast diverges with this upcoming storm on Friday. Most of the shorter range models such as the ETA, WRF, and RSM are all indicating a stronger northern stream system swinging across the Midwest Thursday night. As it is doing so, the 500mb trough associated with low pressure system will become increasingly negatively tilted and could potentially close-off as it approaches the east coast of the United States. All of the shorter range models are indicating a storm of varying intensity over the Delmarva Peninsula by Friday morning, with the WRF model being on the stronger side. However, these models all suggest a secondary development somewhere near the Delmarva Peninsula, but the exact location remains quiet uncertain. For now, it looks like the heavier precipitation will fall in eastern half of the state as the secondary low rapidly intensifies offshore. The 00z GFS model is on the weaker side of the system with lighter precipitation falling across the state on Friday. The snow should end on Saturday if the system does not stall offshore.
David Wang
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