Feb. 22 Technical Discussion

Technical Discussion

Synopsis:

A weak storm system will bring some light snow Monday night with heavier amounts to the southern portion of Pennsylvania. The snow should gradually taper off to isolated snow showers early Tuesday morning with some breaks in clouds later in the afternoon. Expect mostly sunny skies on Wednesday with seasonal temperatures across the State. More clouds will move in during the day on Thursday with some possible rain/snow showers for Thursday night. Showers will continue into Friday but the weekend looks to be relatively calm.

Short-term (Tuesday-Wednesday night)

An upper level situated over the Midwest and its associated surface low will bring periods of snow across the Commonwealth Monday night. Since this is mainly an overrunning snow event, only expecting 2-4 inches of snow across the majority of the state, with some heavier amounts of 4-7 inches for the southern portions. However, all lingering snow showers should end early Tuesday morning as a high pressure over eastern Canada strengthens and shears the storm system apart. Clouds will gradually decrease throughout the day on Tuesday as upper and lower-level air dry up. This will give way to starlit skies Tuesday night but the temperature will also be very cold. The temperature shall rebound nicely on Wednesday as the aforementioned high pressure ridge slides offshore and allows warmer air to advect into the region. A 500-mb shortwave moving into Central Canada will swing some upper-level moisture over Pennsylvania Wednesday night, thus expect a few passing clouds.

Mid-term (Thursday – Friday night)

Clouds will continue to thicken during the day on Thursday ahead of a developing storm system over the lower-Midwest. Some moisture riding along the warm front ahead of the system will bring us some showers later Thursday night and into Friday. However, the models diverge on the scenario where the system's warm front will set up. The longer range models, the GFS and CMC, are the outliers at this point as they suppress the warm front just enough to keep the colder air over our region Thursday night and into Friday. This will result a colder solution for Friday with a higher chance for frozen precipitation. The other shorter range models, the WRF and ETA, set up the warm front much farther north into Ontario, allowing for warmer air to infiltrate the region starting Thursday night. If this solution verifies, expect many rain Thursday night and Friday, but still can't rule out the probability for some mixed precipitation in the northwest corner of the state.

Long-term (Saturday – Saturday night)

Any lingering precipitation should end toward the daybreak hours on Saturday. However, some clouds will linger as pieces of upper-level energy over upstate New York will scrape the region. Expect some high clouds throughout the day on Saturday, especially for the northern portion of the state. Clouds will be on the increase once again Saturday night, as a 500-mb vort max swinging down from Canada will initiate the development of a surface low over Ohio Valley. Though, it is still too early to predict the progression of the storm as of now.

 

David Wang