Monday Night Technical Discussion

Synopsis

 

A mean southerly flow will dominate tonight, allowing temperatures to warm up near the surface ahead of the cold front Tuesday morning. Rain and snow showers ahead of a cold front will affect the state Tuesday. The cold front will cause temperatures to plummet and set up conditions favorable for significant lake effect snow for northwestern Pennsylvania. A stronger system could bring some wintry precipitation later in the week as a storm moves across the nation and strengthens along the southeast coast Friday night.  

 

Short Term (Monday Night thru Tuesday Night)

 

The state will experience warm conditions, as southerly flow ahead of the cold front will produce a warm surface layer Tuesday Morning. Areas of central Pennsylvania will see warming aloft but cold air damming will cause surface temperatures to remain cold for several hours. The cold front should enter the state close to 09Z and make its way east, as mixed precipitation at the leading edge of the front will fall statewide.  The 18Z GFS and NAM agree with precipitation beginning to fall for western PA around 09Z. The 18Z GFS has the precipitation associated with the cold front exiting eastern portions of the state by 01Z, but the 18Z NAM has the precipitation lingering in the east until 04Z. The precipitation will begin to fall as rain in the west and quickly mix and transition to snow within the first two hours of precipitation. This mix should spread across the state through the morning before changing to rain during the afternoon, especially across southern Pennsylvania. Portions of central and northern Pennsylvania could see light snow and ice accumulations before the changeover Tuesday afternoon. Later Tuesday evening, the cold front will wrap in much colder air changing any remaining rain showers to snow showers. As the snow showers exit the state to the east, a westerly flow and cold air advection will begin to produce lake effect snow showers for northwestern counties late Tuesday night.

 

Long Term (Wednesday thru the weekend)

 

Westerly flow will slowly change to northwesterly flow, creating a large fetch over Lake Erie. The large fetch and cold air advection will help produce significant lake effect snow throughout the day Wednesday and Thursday morning for northwestern PA. Extreme northwestern counties could see as much as 3" of additional snow, with light accumulations possible as far southeast as Centre County. A strong mean northerly flow will persist through Thursday keeping temperatures cold, but warm air associated with a weak system approaching from the south will move in with a chance for a few rain or snow showers across the state Friday night according to the 18Z GFS. As the showers associated with the weak system dissipate early Saturday morning, the 18Z GFS indicates a Miller Type B storm situation may form and produce a coastal low that could bring mixed precipitation across the sate Saturday.

~Aaron Herbert