Wednesday, December 30, 2015

December 2015 Mostly Dry - What Will January 2016 Bring?

The last two possible precipitation events of December fizzled away into non-events, after promising long-term global-model forecasts. The month ended up here at house having only measurable rain falling from the 12th to the 14th, with dry and cold conditions for entire rest of the month. Precipitation did total 0.60 inch. The year ended up at 11.15 inches - 3 months (Jan., Sep., and Oct.) had over 2.00 inches of rain, with January 2015 being the wettest month at 2.48 inches. Six months had  less than 0.50 inches, with February being the driest at 0.04 inch. Will summarize morning cold after month ends - but so far there have been 13 days with lows in the 20s F here near the Rillito wash.

The NWS GFS model is forecasting the current, strong westerly jet-stream over the central and west Pacific to extend eastward and intrude into the Southwest during the first week of January 2016. Above graphic shows 250 mb winds analyzed at 00 UTC last evening, while below shows the GFS 250 mb forecast valid at 00 UTC on January 4th. The forecasts indicate that the main branch of the westerlies will be affecting lower latitudes and bringing moist conditions to the Southwest. The model forecasts no precipitation for Arizona through the 4th, but then during the next 5 days (bottom forecast shows total precipitation from the 4th through the 9th) a very wet period is forecast for the Southwest. If the forecasts are accurate, January 2016 would start the year off on a wet note, just as happened last January.

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