Thursday, December 03, 2015

Bouncing Temperatures

We continue to have very large temperature gradients across parts of Tucson, as nighttime cooling is much greater in some locations than others. I was curious how the high-resolution, grid point forecasts issued by the NWS are doing - so I followed the forecasts and observations for a number of sites. Data shown below are for the low temperatures forecast for last two mornings, with the actual observed lows in parentheses.

TUS                   32 (34)             37 (37)
Here                   32 (23)             36 (25)
Sasabe                25 (21)             30 (23)
Empire               28 (23)             31 (40)
Mt Hopkins        32 (45)             38 (49)
Rincon                31 (37)             31 (43)

The bottom four stations are from the RAWS network.

Generally the forecasts are close at the airport, but all over the place for other sites depending on both exposure and character of the nighttime winds. Locations in and near washes, as here, tend to be colder than forecast, while the high elevation sites have been much warmer than forecast. At Empire the winds picked up after midnight, resulting in a forecast that was too cold this morning - exact opposite wrt yesterday morning. I would certainly like to access a technical document explaining how the software used at the NWS generates the grid point forecasts.

Jack Diebolt, in Kansas City, sent the following graphics and discussion from NWS Tucson regarding the topsy-turvy temperatures around 6:00 am MST this morning.

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