Thursday, March 31, 2016

Real Rain Event On Horizon?

Today, the final short wave associated with the large 500 mb cyclone that moved into the Great Basin this week will be crossing along the Borderlands of Arizona/Mexico. The WRF forecasts from Atmo indicate a slight chance of sprinkles and showers later today, but mainly off to our east and south. We will then have to look ahead toward the end of the first week in April, as we still hope for a rainy period before the hot and dry weeks set in before the summer thunderstorm season.

The operational forecasts from the GFS model are shown here way out at 5:00 pm MST on April 7 - a week from today. The 500 mb forecast (above) indicates a system moving into the Southwest from low-latitudes, bringing with it a very nice plume of subtropical moisture. Wouldn't this be a great change? The model's forecast of accumulated precipitation through the same period (below) indicates a widespread and significant event for most of the Southwest. This would be the first such event since the first week in January. Although, in the model forecast world there have been several false alarms during past months, all out at seven days and longer.

A look at this morning's QPF plumes (above) shows the ensemble members (at least a majority of them) forecasting decent rainfall at TUS. However, there's another caution here - note that the operational version of the model (blue) is one of the wettest members. This happened back in late January also, and as that event approached, the operational model reverted to its usual dry mode, as the event slowly fizzled. 

The evening runs of the WRF-GFS at Atmo usually extend out to long time periods also, and here are the forecasts valid at 5:00 pm on April 7th. Above is forecast of composite radar echoes and below is forecast of accumulated precipitation within the model through that time. It is the operational member  of the GEFS that is driving these high resolution forecasts, so we'd expect something like these outcomes. 

Hopefully, this future event won't fade away during subsequent forecasts early next week.

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