Technical Discussion 2/16/11

Synopsis:

A high pressure system off the Carolina coast will continue to be the prominent weather maker through Friday. This high combined with a low pressure system in southern Canada creates a strong southwesterly flow keeping temperatures above normal. A low pressure system in the Pacific Northwest will travel across the country and deepen before it reaches PA on Friday. A cold front associated with this low is expected to pass through the commonwealth Friday afternoon/evening. This will bring a slight chance of showers and temperatures closer to normal with gusty winds.

Short Term (through Friday):

WAA will take its toll as temperatures remain above normal for today through Friday as high pressure and southwesterly flow dominate over the region. Skies will remain mostly cloudy to overcast throughout the night as a shortwave comes through. Skies should become partly sunny by afternoon as suggested by the 12z ETA. These clearer skies along with WAA will make temperatures a few degrees warmer than today. Both NAM MOS and GFS MOS are in agreement for highs in the low 50's tomorrow. The next band of clouds comes in with the cold front on Friday. Both 12z ETA and 18z WRF show the potential for the rain band to break up before it reaches State College. Even the chance of rain for the western third of the state is very small. The cold front passes very quickly through the state taking most of the clouds with it, but leaving colder temperatures behind. The newest model run of the WRF-NMM (18z) has the front moving slower than previous model runs with a bit more rain potential. This rain however still looks like it will disband over the laurel highlands. Sustained winds behind the cold front will be between 10 and 15 knots on Friday.

Longer Term (through Sunday):

Friday night winds will pick up especially for the central third of PA due to the LLJ. Most effects from this will be seen on Saturday. Winds will be out of the west at 15-20 knots and continue through Saturday morning. As the day progresses, strong upper level winds will mix to the surface causing 20-25 knot winds for the eastern half of the state according to the 18z WRF- NMM. Winds will subside overnight Saturday becoming calm by sunrise on Sunday. As the low moves up the coast, high pressure will build in for Saturday to Sunday afternoon.