Tuesday, January 25, 2011

A Ridge to Remember?

Forecast model are indicating the first long-lived cloud-free ridge of high pressure during the PCAPS field campaign will begin building into Northern Utah on Wednesday and strengthen through Friday before flattening and weakening thereafter. Dozens of PCAPS volunteers are preparing for major observational operations into the weekend. Winds will be light above the inversion and skies will be mostly clear outside of patchy fog (the amount of fog remains an unknown). Several nights of radiational cooling will likely be experienced, which will allow for strengthening of the inversion from below. This will be in stark contrast to recent PCAPS IOPs, where most of the inversion strength was due to warming aloft versus radiational cooling at the surface. The lack of surface radiational cooling effects during most PCAPS IOPs to date is largely due to the record amount of cloud cover experienced over the region the last 6 weeks. Numerical forecast models are hinting at a pronounced inversion but these models may be underforecasting the amount of surface cooling, particularly with an unexpected fresh coat of snow on the ground. The NAM forecast for Friday morning has temperatures in the SL Valley near -3 degrees Celsius while warming to over 2 degrees C at mountaintop level (see image). In addition to the surface cooling, decent warming aloft will also will also occur, with mountaintop temperatures warming from -8 degrees Celsius Tuesday night to around 2 degrees Celsius on Friday. Large-scale operations looking at multiple aspects of the cold air pool evolution are planned Wednesday-Saturday. Let's hope that the clouds stay away and the nighttime cooling happens as planned.

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