September 2001 Climate Summary

 

September 2001 brought a balanced mix of sun and rain to a dry Pennsylvania.  The average max temp in most spots was a comfortable 70 and the average min was 50.  There was measurable precipitation for 11 days, 2 of which had an inch or more.

  

Above average temperatures graced the entire region for the first 12 days of August.  A high pressure system off the coast brought southwesterly flow giving PA much of PA consistent highs in the 80’s.  The first two weeks of September stayed dry thanks to this high.  Night-time lows dipped into the upper 40’s to low 50’s for the first week as the high pressure system provided northern flow, but once the high moved off the coast and the southwesterly flow ensued, the lows lingered around the 60 degree mark.

 

The first precipitation arrived on the 14th thanks to a very strong cold front associated with a northern low pressure center.  Some regions received upwards of an inch thanks to the frontal passage.  The following high pressure system’s northerly flow and the post-frontal cool air brought the high temperatures back to average or below.  Strong high pressure moved slowly over the PA region for the next week providing clear skies.  Again as the high moved off the coast, temperatures began to warm and get back into the upper 70’s. 

 

An approaching low pressure system provided the next batch of precipitation.  As the low turned north and centered itself over the Great Lakes, the warm front and the cold front tag-teamed the state with precipitation.  On Thursday the 20^th and Friday the 21^st, first the warm front moved through just sprinkling the region with about a tenth of an inch.  The cold front followed by dropping about half an inch of rain in most spots.  There was no break in the cloud cover this time though.  Another low pressure system advanced in following this one and on the 24^th- 25^th dropped over 2 inches of rain in some spots.  A negatively tilted 500 mb trough provided the region of lift directly over PA.  Williamsport was actually the highest reporting rainfall site from this low pressure system for the 25^th.

 

This low again shifted back to the Northwest over the Great Lakes and managed to keep bringing drizzle throughout most of PA up until about Saturday the 29^th.  The high temperature didn’t make it above 60 from the 25^th to the 29^th.   Finally on the last day of the month, the high pressure managed to build back into the region and clear out the skies and bring the temperature above 60. 

 

-Daniel Heim

 

 

September  2001 Extremes for Pennsylvania