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Tuesday, 09 August 2016 08:06

Possibility for Flash Flooding Tuesday Afternoon - Thursday Featured

Dr. Curtis James

Rain and floods are in the forecast this week.

The figure above indicates the forecasted high in orange (with error bar denoting the range of ensemble forecast members), average high for this time of year in orange (dashed line), forecasted low in blue (with error bar), average low this time of year in blue (dashed line), and forecasted wind speed in purple. Note that the wind speed forecast is sustained wind (not gusts), and it is based on only one model (not an ensemble).

Weather Discussion:

An interesting weather situation is setting up this week, which could potentially lead to flash flooding in portions of northern Arizona. Last week, Hurricane Earl hit Belize and Guatemala and weakened as it moved westward across southern Mexico. This week, Tropical Storm Javier has formed along Mexico’s west coast, developing from the remnants of Earl. Javier is now moving up the Baja of California and dissipating. Along the east side of Javier, a surge of moist and unstable air is forecast to flow up into Arizona. Beginning Tuesday afternoon, dew point temperatures will rise dramatically (into the 60s Fahrenheit). The low-level winds across the mountains of Northern Arizona will be from the south or southwest at speeds between 10 and 20 mph, which could help produce lifting to trigger thunderstorms.

Meanwhile, an upper-air trough will approach from the west and direct a southwesterly upper-level subtropical jet stream in the upper atmosphere over Arizona. The trough will also provide lifting in the upper atmosphere, cooler air aloft, and shearing. The result will be widespread showers and thunderstorms developing Tuesday afternoon - Thursday, which storms will tend to move toward the northeast at speeds of 20-30 mph. The greatest potential impact of this event could be flash flooding, where multiple thunderstorms develop in succession and move across the same areas. This phenomenon is what is termed “echo training” and is often the result of flash flooding, especially in mountainous areas. It will be interesting to see how this pattern develops.

Friday – Sunday, expect thunderstorm probabilities to diminish once again after the passage of the upper trough from the west, bringing drier air back across the state.

C. James

 
Last modified on Tuesday, 09 August 2016 17:05
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