Updated to include anomaly forecasts…
The NAM, GFS, ECMWF and Canadian are all forecasting some unheard of 850-hPa temperatures across the Carolinas through the weekend. The figure below provided by Jason Cordeira from the University of Albany is a histogram of 850-hPa temperatures at Greensboro, NC (KGSO) from January 1948 through May 2008. All of the available 850-hPa temperatures, 00 UTC, 12 UTC, and specials were collected. The number of occurrences of 1.0-1.9 C was calculated and given the bin of 1C, 2.0-2.9C was given the bin of 2C, etc.
The histogram shows a dramatic decline in the frequency of 850-hPa temperatures greater than 20 degrees C. In this analysis there were only 46 observations of 23 degrees C or greater, 14 observations of 24 degrees C or greater, and 2 observations of 25.0 exactly.
The two observations of 25.0Coccurred during record breaking heat, one occurrence was 25.0C degrees C at 15Z on 26 June 1952 and the other (also 25.0C) was at 00Z 19 August 1988. The high temperature on 26 June 1952 was 102 at RDU and 101 at GSO while on 18 August 1988, RDU had a high of 105 (tied the all-time high) and GSO had a high of 103 (one degree below the all-time high). The 00Z sounding from KGSO at 00Z on 19 August is shown below (the sounding for 26 June 1952 were not available).
Guidance from the 12 UTC 28 June NAM and GFS suggest that 850-hPa temperatures will be the hotter than the database that stretches back to 1948. In the table below, the 850-hPa temperatures for Greensboro NC are shown. Both the NAM and GFS predict 850-hPa temperatures of greater than 26 on Friday and Saturday evening, with the GFS holding onto 26+ temperatures on Sunday evening. Not included in the chart is the ECMWF because of contractual issues, but the ECMWF predicts an 850-hPa temperature of 29.3 degrees at 00Z Saturday!
I grabbed the anomally charts from the WFO CTP/PSU web page for the NAM, GFS, SREF, and GEFS for 00Z Saturday, 30 June. across the Southeast. As you might expect, 850-hPa temperatures are 3-4 standard deviations above normal across much of NC with areas of 5 SD across SC.
The forecast for the next few days for central NC (Raleigh) is shown below and includes record breaking temperatures for much of the area. We’ll see how things bake out.