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HMT discussion for Sunday 25-March-07

Our main storm is still on track with timing as we have been discussing and the latest model precipitation totals generally in the 1.25-1.5 inch range (somewhat more on the 00z GFS), but forecasters going more in the 1.5 to 1.8 inch range. The tropical plume we have been watching is currently into northern California and will sink over the HMT area by late today and tonight. Max PW from SSMI around an inch and this agrees with the model analyses. The operational models don't predict much of anything today and forecasters in the area have extremely low pops today gradually upping to scattered overnight. The moisture looks pretty high-based right now on the Oakland sounding so apparently will take a while to moisten things up. Your timing is pretty safe for not missing anything in terms of the collection for rainwater, not sure how much will happen overnight but some showers are possible as this plume moves over the area and gradual moistening occurs. The GFS 12z run does get more precip going tomorrow morning in the 6-h up to 18z, somewhat more to the north, and our local models also gradually shift a band of precip southward. But for the most part agreement remains excellent on the main period from 18z/Monday through 03z or so Tue (Monday night), when trough passage occurs through 06z. Thereafter some variation on the amount of cold advection precip with lowering snow levels (4000 feet or so?, maybe lower), with the end to precip by 00z-03z/Wed. Our local WRFNMM downscaled to 3 km has 1-1.5 inches of precip by 12z/Tue, then shows a nice burst of convection Tuesday afternoon in the cold air especially over the higher terrain with up to another half an inch before things end by 03z. This seems reasonable with good orographic flow and the cold air.

So all in all should be a good dynamic event, apparently relatively null for anything significant with this moisture plume until it wraps into and just ahead of the main system tomorrow.

ed szoke NOAA/GSD


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