Weather is a battlefield. Battling a forecast, snowfall totals, or a battle of air masses. This weekend's storm shows how high pressure and low pressure battle it out.
On our surface maps and futurecasts, there is a distinct end to the precipitation. It's snow vs no snow, and cuts the Valley in half. But why?
Strong high pressure is developing to our northwest. By the time the low pressure starts moving east, high pressure is situated near Wisconsin. Being to the east of a strong high pressure means that the Valley receives strong northerly winds. Northerly winds are usually cold (hence highs in the upper 20's Friday and Saturday) and dry. That air eventually will hit the warmer, moist air being drawn up from the Gulf of Mexico with the low pressure system.
The distinct line we see on our futurecasts and surface map is the battle line between strong high and low pressure. If you're seeing cloud cover and no precipitation, high pressure has won the battle. If you're seeing snowfall, low pressure has won.
This storm will cut the Valley in two on Saturday, leaving the northern Valley with a chance of snow and a dusting possible. The southern Valley will likely see snow and a few inches of accumulation are possible. The heaviest precipitation will stay to the south as low pressure takes a more southern route than previously indicated by computer models. The low pressure system will quickly move off the eastern seaboard and high pressure will dominate Sunday with sunny skies and cold temperatures.