Technical Discussion 2/15/11

Synopsis:

A ridge of high pressure, currently stationed over the eastern third of the country, will be the largest influence over weather in the Commonwealth for the next few days. Steadily rising temperatures, mostly sunny skies, and calm southerly winds will be the main story until later in the week when a cold front makes its way through the eastern half of the country. Prior to its arrival, clouds will begin to build into the area on Thursday with the possibility of rain showers on Friday. The front will pass later Friday night, bringing with it cooler air and blustery winds.

Short Term (Through Wednesday Evening):

As a center of high pressure moves to the south and east of Pennsylvania, a shift in the surface-level winds can be expected from the southeast to the southwest. This will allow for warm air advection to raise temperatures to the low to mid 40s during the day on Wednesday. This is above the average high of 38 degrees for State College. Across the state, NAM MOS temperatures tended to run higher than GFS MOS for the next 24 hours. This can be attributed to an increased wind speed. We tended to go with the NAM MOS as wind speeds tomorrow can be expected in between 2-10mph. This slight adjustment will raise the temperatures a few degrees. Mostly sunny skies will also be prevalent. A small disturbance, currently in the western reaches of the state, will bring some clouds into the area then move out quickly. It is not expected to be a significant weather maker.

Long Term (Through Sunday):

The current low amplitude pattern will maintain throughout the forecasting period. A weak cold front will push through the state on Friday afternoon into late Friday evening. While passing, the low will remain centered in the northern provinces of Canada with the vortmax occurring in central Quebec. GFS models have the storm taking a slower and more southerly path than WRF models. However GFS predictions did not line up with current conditions across the state and were instead slightly delayed. The WRF, on the other hand, updated adequately so we have decided to trust the path it has projected for the cold front. The air associated with this front will be relatively dry (note GFS and WRF agreement), agreeing with our prediction that the cold front will be weak. However winds in excess of 25mph from the WNW will occur in its wake. However because of the relative weakness of the system, temperatures will not be drastically affected. 

Forecaster Tom Bedard