Monday, May 9, 2011

May Deluge

Early spring is back and we're seeing some healthy rainfall totals across the state.  Sites with a half inch or more can be found through much of northern Utah including .77" at Mendon, .73" in Roy, 1.04" in Cottonwood Heights, and .56" in Pleasant Grove.  These are storm totals as of 3 or 4 am this morning.

Storm total precipitation through 4 am MST 9 May
Source: NWS
April powder brings May powder in the mountains.  As of 8 am, the Alta-Collins observing site recorded 6" of snow, although that's with .83" of water for a density of 14%.  That's really more like Cascade Concrete than the Greatest Snow on Earth, but it is May after all.

Much has been made of the potential of flooding with this rain, but the bigger concerns may be a few days away.  The Blacksmith Fork is presently above flood stage, but that the outlook shows even higher flows beginning on the 13th.  

Ditto for Little Cottonwood Creek, although flows are presently projected to be below flood stage.

The reason for this is that we are going to see a big warmup once this trough moves through the state with a persistent high-amplitude ridge parking over Utah.  700 mb temperatures rise to about +7C by Friday morning, which puts us solidly into the mid 70s.  Keep in mind these are runoff outlooks with some uncertainty, but the bottom line is that it's going to be a long few weeks for folks living along these rivers and streams.  

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