Character of Surface High Pressure An arctic high pressure is key for heavy snow to fall in Philadelphia. An arctic high pressure, if positioned correctly, and with enough strength, will aide in keeping the storm mostly snow or all snow. In addition, an arctic high pressure with good position and strength will also slow down the movement of the coastal low allowing for precipitation to fall for a longer period of time. For heavy snow events to occur in PHL, the best position for a high pressure is to the west of Maine and to the north of the PA/NY border. The high can also be located in the Northern Plains/Midwest. As far as strength goes, pressures above 1020mb are adequate enough to provide decent low level cold air.

For current surface data, click here