Retired senior lecturer in the Department of Meteorology at Penn State, where he was lead faculty for PSU's online certificate in forecasting.
By: Lee Grenci , 3:18 PM GMT on February 02, 2013
One of the graduates from the Penn State online certificate program posted the METARS from Scranton, PA, at The Milli Bar (for PSU certificate students) on January 28, kicking off an interesting discussion about the sporadic jumps in temperature at the Avoca Airport (KAVP).
In a nutshell, the airport's temperature at 15Z (10 A.M. local time) was 44 degrees (see the image of 15Z station models below; larger image). Meanwhile, temperatures at nearby airports were in the 20s or low 30s. The catalyst for the graduate's question was a television meteorologist who attributed the anomaly to a temperature inversion and the fact that the Scranton airport was one of the highest in the region (highest elevation). A bit of "sleuthing" quickly revealed that the explanation was faulty, proving that you can't always believe what you hear on television or what you read on the Internet.
The 15Z station models on January 28, 2013. The temperature observation at the Scranton Airport (KAVP), 44 degrees Fahrenheit, was an outlier compared to nearby temperatures. Larger image. Courtesy of Penn State.
To refresh your memory about the prevailing weather pattern, a warm front extending eastward from a low-pressure system centered over Lake Michigan was approaching Pennsylvania (15Z surface analysis). Ahead of the warm front, warm advection above the earth's surface produced stratiform precipitation over the region (check out the 15Z mosaic of composite reflectivity). By warm advection I mean that winds were blowing from areas of warmer air toward colder regions. You can get a better sense for the warm advection by studying the 12Z NAM model analysis of 850-mb isotherms (in degrees Celsius) and 850-mb streamlines below (larger image). I circled the region where relatively large warm advection was occurring at 850 mb (roughly 1500 meters above the earth's surface).
The 12Z NAM model analysis of 850-mb isotherms, in degrees Celsius, on January 28, 2013. Dashed contours indicate isotherms whose values are less than 0 degrees Celsius. Larger image. Courtesy of Penn State.
So, with warm air arriving aloft and cold air hanging tough near the ground, a strong temperature inversion formed in the lower troposphere, as the 15Z Rapid Refresh model analysis of the temperature and dew-point soundings at Scranton showed. So the television meteorologist was correct in asserting that there was a strong, very stable temperature inversion over Scranton (and much of the rest of the region ahead of the warm front). But the truth of what he was selling on television ended there.
First, Scranton's airport is not one of the highest valleys as he suggested. The elevation of KAVP is 962 feet. In contrast, the elevation at the airport at nearby Mount Pocono (KMPO), is 1915 feet, almost 1000 feet higher than KAVP. Moreover, temperatures at KMPO on the morning of January 28 did not get out of the 20's (for proof, check out KMPO's meteogram). So Mount Pocono, which is nearly 1000 feet higher than Avoca, was below the inversion. So it didn't make any sense to me that morning temperatures in the 40s at Avoca meant that KAVP was in the inversion (as advertised on TV).
Clearly, the television meteorologist's claim that KAVP was so warm because it's high elevation put it squarely in the temperature inversion was, for lack of a better word, hogwash. So he made his assertion without looking at a skew-T and without looking closely at surrounding observations.
I suspected that this was a case of instrument error. One of the certificate graduates sent an e-mail to the person who maintains the ASOS station at Avoca, who then sent a notice to the technicians at WFO BGM (the ticket number was 130130-137). It was promptly fixed.
Site Trouble Ticket Update
Site Identifier:aKAVP Office:aWFO BGM (Binghamton, New York) << Back
Location: a Wilkes-Barre/Scranton, PA AOMC/RMM ID: a AVP
Class: C2T Towered SvcLvl: C
Agency: NWS Region: Eastern
AFOS PIL / WMO Header: PHLMTRAVP LongLineComms: ADAS
ALDARS Site: No
Comments: ZNY (New York) ADAS/External
Number: 130130-137 Opened: 01/30/2013 18:42 GMT
Updated Trouble Ticket Information
Updated Problem Category(required when closing): Temp
Updated Problem Description(required): Closed ticket. Tech (DE) WFO BGM (Binghamton, New York) replaced temp sensor aspirator housing. sensor ops checked good.
Actual Return to Service: 01/30/2013 18:10 GMT
When I was teaching, I always tried to instill in students a scientific curiosity that motivated them to question things that they heard on television or read on the Internet. Being skeptical, within reason, is an attribute of any good scientist. And looking at real data to confirm or disprove what they hear or read is another quality I always tried to nurture in students. So I was impressed by how certificate graduates questioned and then discovered the truth about Scranton's temperature observation, even though a professional meteorologist had already offered an explanation.
And, yes, I also make mistakes sometimes, and my students are usually happy to point them out to me. :-)
Comments will take a few seconds to appear.