Onshore Flow and Offshore Flow: Which Makes For A Nice, Hot Day?April 20th, 2009 by Matthew Leach
This question gets brought up from time to time: what is onshore/offshore flow and what affect does it have on our temperatures? The answer is actually really simple and today was a good example of why it didn’t get warmer than the low 70s today when models were indicating we could have.
ONSHORE FLOW: This is where we get our “sea breeze” in the summer time that keeps the temperatures here from getting TOO hot. These winds originate off the ocean and blow west to east onshore, hence “onshore flow”, which in turn keep us cooler and can also make us a little cloudier than we want to be as winds off the ocean usually bring low clouds with them.
OFFSHORE FLOW: This is exactly the opposite. These winds originate on land and usually blow from east to west towards the ocean bringing in warmer air from Eastern Washington with it. These are the setups that bring us our summer heatwaves.
And of course in the winter the situation is different. An onshore component is typically a bad one if you want snow as the moderate ocean air colliding with the little cold air we have in the interior can usually scour out any chances for a nice dumping of snow, however without a little onshore flow it gets hard to produce moisture for the snow in the first place. Conversely, offshore flow filters in bitterly cold air from Eastern Washington, but this is typically a dry cold and we don’t usually see major snow events with those setups.
So now can you guess what flow we are under today? If you guessed “onshore flow” you win! The cool sea breeze from the west has been lightly blowing all day, but the downside to this is the low clouds it will likely bring tomorrow morning. The areas that will not be so lucky are the northern portions of the state while the southern areas will get another nice sunny and warm day to enjoy. I’m thinking we’ll be right in between the low clouds but partial sunshine in the afternoon. Highs will be a little cooler than today in the mid to upper 60s. But hey, despite the onshore flow it’ll be a nice day.
Onshore flow REALLY kicks in for Wednesday as low clouds make a move and cool temperatures down dramatically. Highs will have a hard time reaching 60 degrees believe it or not!
The cool temperatures continue for the rest of the forecast, but interestingly enough it doesn’t look incredibly cloudy or wet, just partly sunny with occasional bouts with rain.
Have a good evening!
7 DAY FORECAST