Comparing NUCAPS temperature values to forecast fields
Gridded NUCAPS estimates of 850-mb Temperature, 1851 UTC on 30 November 2020 (Click to enlarge)
Late November is a time when cold outbreaks can pass over relatively warm Great Lakes waters (click here for recent observations) and produce lake-effect snow. Gridded NUCAPS observations derived from NOAA-20 CrIS and ATMS data, above, shows a large area with temperatures colder than -12ºC over northwest Ontario and northern Minnesota, just upwind of the Great Lakes; Lake Superior’s surface temperature at the time was around 5ºC — a temperature difference that support lake-effect precipitation. How well do the NUCAPS observations compare to model predictions of the environment?
Forecasts from the 1200 UTC run of the NAM, below, valid at 1800 UTC, and from the 1500 UTC run of the Rapid Refresh, valid at 1900 UTC, show -12ºC in bright magenta. (Model analyses taken from this website) NUCAPS analyses suggest the cold air is moving south faster than anticipated by the model.
6-h forecast of 850-mb Temperature, valid 1800 UTC on 29 November 2020 (Click to enlarge)
4-hour forecast of 850-mb temperature from the Rapid Refresh, valid 1900 UTC on 29 November 2020 (Click to enlarge)
This site can be used to view gridded NUCAPS fields outside of AWIPS. The 850-mb analysis from the pass is shown below. It’s important to recall that Gridded NUCAPS fields include data from all retrieved profiles — including profiles for which the infrared retrieval failed (usually in locations with thick clouds, and those from which the infrared and microwave retrievals both failed (usually in locations with rain). This mapping for the temperature gridding below shows where infrared retrievals failed (yellow) and where infrared and microwave retrievals both failed (red).
850-mb Temperature fields, 1849 UTC on 29 November 2020 (Click to enlarge)
The ‘yellow’ points north and west of the Great Lakes were associated with clouds that are apparent in this VIIRS True Color image, taken from the UW-Madison Direct Broadcast ftp site (Link). The clouds were associated with a departing low pressure system (link).
NOAA-20 VIIRS True-Color imagery, 1850 UTC on 29 November 2020 (Click to enlarge)