A Reflection On Wednesday Night’s Rain Event

Hello everyone!

This past week brought us our first potent Autumn storm of the season and while the weather is quiet this weekend, I’d like to take a look back on the forecast to see what went well, what didn’t, and why.

Preliminary Rainfall Totals From NWS Gray

Looking at the NWS Gray preliminary rainfall map, the forecast panned out pretty well for most areas with the dark green areas representing the 1-2″ forecast for most areas with the south sides of the mountains seeing mainly the forecast 2-3″ amounts (yellow/orange colors). The only real bust in the forecast would be the higher amounts along the coastal plain where over 2″ was reported in many areas surpassing the upper limit of the forecast. The main reason for that was unusually high precipitable water values (geek speak for humidity) that led to an atmosphere ripe for heavy rain. That was well forecast in advance of the storm but my reasoning for keeping totals a little lower was that the storm would move out quickly thus keeping rainfall totals low.

Rainfall moved into the Portland area around 6PM which was right on forecast, rain and some isolated mixed precipitation arrived in the mountains earlier, a little ahead of forecast. The rain did not give up as easily as I thought in the morning however with rain being reported in Portland through 11AM. A continuous feed of heavy rain also developed in the morning shifting gradually east along the coast and the 2″+ areas on the map show where this band moved. The slow moving nature of this band is the main reason coastal areas overperformed this time around.

Winds were nearly exactly on forecast with the peak gust at Portland being 48mph with lesser values inland.

A quiet and warm ‘Indian Summer’ type week is ahead with temps in the 50’s and 60’s under mainly sunny skies.

-Jack

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