Thursday, August 28, 2014

End Of August Dry-Out

Only isolated mountain storms yesterday afternoon in southeast Arizona - see plot of CG flashes through 1 am this morning - August 28th. Six high elevation ALERT stations in Cataliinas, Redington Pass, and the Rincons recorded light rainfall yesterday. We will experience a substantial dry-out for next few days as westerly winds dominate and bring in dry, Pacific air. The dry air reaches down to 700 mb this morning and will continue mixing downward, resulting in dry and stable conditions for the Holiday weekend. The early WRF-NAM forecast for total accumulated rainfall through 11 pm next Saturday night is shown below (on the 5.4 km grid). The Southwest holds very dry, except for some showers over Colorado Rockies early in period.

As I mentioned back on the 22nd, the longer-range forecast models were keeping westerly troughiness over the Southwest and it looked like our summer rainy season (aka monsoon) was ending, barring a tropical interlude. The tropical interlude is over and the models continue to keep westerlies dominating the middle and upper-levels. The GFS becomes a bit ambiguous out at 7-days, but basically we'll be watching for transition events with strong westerly short-waves, or more tropical systems heading north. Above and below are the 84-h and 168-h GFS ensemble means for 500 mb.

No comments:

Post a Comment