Re: Rain report - Tuesday & post-mortem

Posted by Bret B on February 3, 2015, 10:11 am, in reply to "Re: Rain report - Monday"
187.148.141.155

We got 2.35" / 60mm since yesterday morning (mostly from the heavy thunderstorm yesterday afternoon.) 4.15" / 105mm storm total so far (3 days.) All the forecast tools predict very little rain today for us, clearing gradually by this afternoon, then nothing else brewing for at least the next few days. However, a substantial plume of moisture might remain for a few more days, hopefully staying over the coast to our south. If the plume wanders back up here, our forecast could change. What was causing this unusual February rain? There was a stubborn upper-level low pressure camped out between central Baja California and the mainland Mexican coast the last few days. In conjunction with a southern arm of the jet stream, this low pumped and guided a heavy plume of moist mid-to-upper level air from the inter-tropical convergence zone (down around 5° north latitude) over our part of the coast. Then we had a surface low pressure trough just off shore from us to give the moisture a "trigger" to precipitate out as rain. Here is an excerpt from the NHC's Eastern Pacific Tropical Weather Discussion ( http://www.nhc.noaa.gov/text/refresh/MIATWDEP+shtml/ ): "SW FLOW ALOFT E OF AN UPPER LEVEL LOW IS PUMPING MOISTURE INTO THE CENTRAL MEXICAN COAST...WITH SHOWERS MAINLY ALONG A TROUGH FROM 20N105W TO 13N110W. THE UPPER LOW WILL WEAKEN TODAY AND MOVE NE...BUT A SUBSTANTIAL MOISTURE PLUME IS EXPECTED TO REMAIN IN PLACE ACROSS THE REGION." And here is an excerpt from their latest surface-level weather map. It's pretty cluttered. Hopefully you can see the trough (dashed line) aiming right at us. I added the upper-level low to our north with its counterclockwise circulation helping to pump the "moisture plume" along the trough right to us: And what's behind these weather features? We can't blame El Nino; we are in "ENSO-neutral" conditions right now. http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf Beyond that, I don't really know.

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