May 22, 2013
Long Duration, Heavy Precipitation Over Northern California...
Preliminary Update...
Used An Even Blend Of The 00z/26 Ecmwf And Ecens Mean To Update The Preliminary Fronts And Pressures For Days 3 Through 7.
This Is The First Cycle In A While Where There Was Enough Agreement Among The Various Models At The Medium Range To Confidently Blend A Significant Chunk Of A Deterministic Solution Into The Manual Progs. The Ecmwf Fit Both The Ecens And Gefs Means The Best, So Elected To Rely On Its Mass Fields For Half Of The Blend.
The Highest Impact Event Will Be The Long Duration Onslaught Of
Precipitation Into The Far West, With Northern California And The
Northern And Central Sierra Nevada Range At The Center Of The
Threat. The Culprit Is A Strong, Mean Trough Just Off The Pacific
Coast, With Unrelenting South-Southwesterly Flow Intersecting The
High Terrain Of Northern California.
The Effects Of This Pattern Will Extend All The Way Inland To The Continental Divide, With Each Successive Major Mountain Range Netting A Commensurately Smaller Precipitation Total. Snow In The Feet Is Anticipated Over The Highest Terrain.
Elsewhere, A Major Warming Trend Is Expected, With The Polar Jet
Retreating North Of The Canadian Border By The End Of The Period.
A Shear Axis Over The Central States Should Be Able To Tap Enough
Moisture From The Gulf Of Mexico To Produce Scattered Showers,
With The Highest Rainfall Amounts Closest To The Moisture Source-
i.e., South Texas.
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