Friday, January 20, 2017

Light Showers Parts Of Metro This Morning

There have been light showers here in the north part of the City this early morning and they are continuing, with coverage perhaps increasing a bit. Yesterday we had some sprinkles around and there was a Trace here at house.

Took a quick look at 06 UTC model forecasts for today and tomorrow's event. The WRF-GFS forecast of total precipitation though midnight tomorrow night is shown above. Most significant accumulations are forecast for the Sky Islands. The forecast amount for airport is now 0.4" but with significant gradients north and northeast of airport, where amounts increase. Snow amounts forecast on the Sky Islands are substantial and reach 1 to 2 feet.

The model also forecasts very strong winds tonight into tomorrow morning. The 10-m wind forecast below is valid at 02:00 am on the 21st. The very strong winds are downslope at many locations within the 1.8 km grid, and the impacts on precipitation amounts are clearly evident in the blue shades over southeast Arizona (above).

The GEFS plumes for QPF at the airport (bottom from 06 UTC) are considerably higher than the forecast from WRF-GFS. However, based on previous posts and comments it is not clear exactly how amounts are interpolated from nearby grid points to the airport location. The nearest four grid points are at higher elevations, so the lower amounts for downslope areas in WRF are not surprising. The numerical forecasts of QPF continue to be somewhat inconsistent, reflecting the difficulties inherent in forecasting this most important parameter.

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