Turning Down the Heat
Posted April 2, 2007
Confidence continues to grow regarding a significant pattern change that will replace the warm high pressure ridge that has frequently dominated across the southeastern U.S. for the past few weeks with a deep, slow moving trough later this week and through the extended Easter weekend. The image above is a temperature outlook from the Climate Prediction Center for the period 7-11 April, and indicates a very high probability of below normal temperatures for about the eastern half of the country when averaged over that time frame.
While it's impossible to be certain yet about the exact numbers involved, it appears we may end up with high tempertaures that run anywhere between ten and twenty degrees below normal through the period (mainly in the 50s) and more importantly, perhaps, lows may dip to the mid 30s (cold enough for frost if winds are light and skies are clear at times) and possibly even into the 20s on one or two mornings during the Friday through Tuesday time frame. This could be hazardous to some vegetation, and, as one example, there is significant concern about the peach crop in western parts of North and South Carolina, and about strawberries farther east, among others.
At this point, it appears that the cold air will be mostly dry for us, with rain chances and amounts remaining on the low side. It does look as if some low level moisture flowing upslope in the northern and western mountains of our state could produce a few episodes of light snow shower activity there, perhaps as soon as late Wednesday night. In our area, it appears the initial cold front marking the first surge of colder air will push through on Wednesday, perhaps preceded by a few widely scattered showers or thunderstorms. The Appalachians will likely delay or blunt the progress of the low level cold air a bit, so that most of us reach the upper 70s or low 80s by midday on Wednesday, but we could see temperatures falling rapidly later in the afternoon and evening, and may struggle to reach 60 on Thursday. After that, reinforcing surges of cooler air will likely cause temperatures to ratchet downward a time or two as we head into and through the weekend. By that time of year, the normal high at the Raleigh-Durham airport is near 70 degrees, with a standard deviation of about +/- 10 degrees, while the normal low is in the mid 40s, with a standard deviation of +/- 9 degrees.
All of this comes after quite a warm March at the Raleigh-Durham airport. A climate summary for the month that was just released by the National Weather Service shows that we had an average maximum temperature of 69.5 (7 degrees above normal) and an average low of 42.2 degrees (3.3 degrees above normal), with observed temperatures ranging from a low of 26 on the 5th and 19th to a high of 87 on 27th. This made it the third warmest March at RDU since 1944, and we managed 4 new record high temperatures. There was also a daily record rainfall during the month, when 2.14 inches fell on the 16th. For the month as a whole 3.52 inches of rain was recorded, just over a half inch below normal.