Friday, February 01, 2013

High Clouds In The WRF-GFS Forecast

The Outgoing Long wave Radiation (OLR, in watts per square meter) product can be used to evaluate the model's forecast of cloudiness. The model keeps skies mostly clear today until late afternoon and evening, and then brings a large patch of high clouds in from the Pacific during the night (below is OLR forecast valid at 6 am tomorrow morning) with gray-scale indicating watts per square meter. Low OLR indicates increased cloudiness, while high values indicate clear skies. So the model is forecasting significant high-cloudiness during the night tonight. If this verifies, it will keep low temperatures mild (the early WRF-GFS forecasts lows next two mornings at TUS to be in the 50s, i.e., considerably milder than this morning).

During the day tomorrow the clouds move away and the forecast for OLR at 3pm (above) indicates mostly clear skies again. But, by midnight tomorrow night (below) the model has forecast an even larger area of cirrus across southern Arizona. Timing and duration are everything with these patches of cloudiness wrt both high and low temperatures.

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