Record Setting August 13

For a record low maximum temperature. In fact it tied the old record for low maximum for this day. Here is the report from the National Weather Service in Raleigh...

... Record low Max temperature tied at Raleigh-Durham international
Airport today...

As 500 PM EDT... a record low Max temperature of 74 degrees was set
at the Raleigh-Durham international Airport today. This ties the
previous record for August 13th for the coolest high temperature...
last set in 1996.

The normal high temperature for the Raleigh-Durham international
Airport for August 13th is 88 degrees

...

As far as the rainfall, my hunch on more rainfall further northwest was true but amounts were relatively light except in isolated spots that got under some slow moving showers or locations down south such as Fayetteville.

On August 13, 2007, RDU hit a temperature of 98. This was during the stretch of very warm temperatures that we had that included two 104 readings as well as a 105 on August 21. One of the meteorological fields I look at to get a feel for the general atmospheric flow is a 500mb height chart. The lines on the chart show the general wind flow as at this height winds blow parallel to the contours. These contours represent lines of equal 500 mb pressure level height. The barbs are showing the wind direction and speed and the color fill is where the strongest winds are located.

Below is last August 13, 2007 8am 500 mb chart.. Notice how the majority of the lines are to the north across the northern US and southern Canada. This means the majority of the country was under a ridge with very warm temperatures. The ridge is indicated by the large closed contour labeled 5940. This is a large anticyclone meaning high pressure and sinking air.



And here is this morning at 8am. Wow what a difference as the ridge is placed over the SW part of the country and is weaker than last year and there is a deep trough for August standards across the eastern US. This has allowed the cooler air to filter towards our region and because we had little sun today and rain most of the day temperatures were held down. This trough was also responsible for the cool Tuesday morning when we hit 56, and for the development of the low pressure that caused a gloomy, cool fall like day here in NC.




Oh and if your out driving tomorrow morning around sunrise, please be careful of dense fog. There are very light winds, moisture left over from today's rain and dry air on top of the moisture that has allowed for the development of fog. Visibilities have decreased to as little as 3 miles at RDU and 2.5 miles at Chapel Hill. We could also see the mercury drop to 58 or 59 in the morning coming short of the record low for August 14 of 55 set back in 1964.

UPDATE 12:05 AM AUG 14:
RDU does not seem to be sending out its observation for midnight but at Chapel Hill visibilities are down to a half a mile. The fog is getting denser out there and I would not be surprised if Dense Fog Advisories are hoisted for the early morning commute.