Thursday, July 19, 2012

Historical Ebbs of Heat

Yesterday marked our 25th 90 degree day of the year.  We're not on a record pace though; 2010 through yesterday was at 29 days en route for the gold standard of 55.  We have had 19 days in the last 21 (going back to late June) where the high crossed the 90 degree barrier...if today features a 90 degree high, make it 20 in 22.  The last time we came close to anything similar was the 24 in 25 day stretch back in 1995.

What has made this year a bit more nasty in terms of heat is that we've also dealt with a high frequency of 95+ days.  We've already had 11 such days -- the record for an entire year is 19 (2002) and second place is 18 (1988).   While we are off the record of most 95+ days to this point (1988 was at 15 such days through yesterday), the record year only had seven such days through this point, buoyed by a rather strong August.  If we have another strong surge of heat going into August and continue to remain dry, we could make a run on this record since we're just eight away and still have a good six or seven weeks to work with. I do think the 55 90 degree day mark is safe but we could end up back over 40 90 degree days before the year is out as we're just 15 away through yesterday.

We're in the midst of one of the more remarkable three year stretches of heat on record in Philadelphia.  The only other time on record in Philadelphia where the high crossed the 100 degree barrier twice in three consecutive year was between 1953 and 1955.  Even though the 50's had similar heat in intensity, the frequency of 90 degree days has increased a bit between the 1950's and 2010's.  1953 had 38 90 degree days, 1954 had 28, and 1955 had 33.  The 1988-1995 period of time could rival this current stretch regarding the number of 90 degree days as 1988, 1991, 1993, and 1995 all surpassed 40 90 degree days...with 1994 hitting 36.