Difference Between Partly Sunny and Mostly Cloudy


I’m actually kind of glad this week wasn’t TOO weather crazy because it’s been a busy one with finals, college applications, you name it. But now that I (and every other student out there on the peninsula) have a 3 day weekend ahead of me, I’d like a LITTLE bit of snow to forecast before school starts up again. Unfortunately for me (and fortunately for others) snow is not in the forecast for the next little while…

Now, before I go into the forecast for the next 7 days, I’d like to answer a question that I’ve been asked several times ever since I began forecasting at CK two years ago: “What makes a day ‘mostly cloudy’ and another day ‘partly sunny’? Aren’t we getting partial sunshine either way?”

Well, yes, but there is a big difference between partly sunny and mostly cloudy, at least in my book (which is not nearly as big or knowledgeable as say…Cliff Mass’s :)). A partly sunny day means clearing out most of the morning low clouds by noon and having an even amount of clouds and sun in the sky…you know, not too much of either. That means it’s “partly sunny”.

Mostly cloudy is defined as being, well, mostly cloudy throughout the day. There may be sunbreaks in the clouds, but they are usually brief (5-10 minutes for each break) and shallow, breaking through only a fraction of the cloud cover. Also, if it has been cloudy all day until 3 pm or so when the sun FINALLY wants to break through, I consider that “too late” as most of the day has been cloudy thus being dubbed mostly cloudy.

For most areas, yesterday would be a good example of partly sunny while today would be a good example of mostly cloudy. And believe me, people can be VERY analytical about a forecast that calls for mostly cloudy skies and it ends up being partly sunny. For some, it matters just that much.

Now on to the 7 day forecast! Tonight will be PARTLY clear with lows dipping down into the 30s. After some morning low clouds/fog, tomorrow AM will be PARTLY sunny, but increasing mid and high level clouds will make the sky MOSTLY cloudy during the day. Highs will be mild, however, in the mid to upper 40s.

Saturday and Sunday both look pretty “blah” as sunbreaks, clouds, and showers will rule the weather. Oh, and it’ll be a bit chilly. Highs will be in the lower to mid 40s.

MOSTLY cloudy skies look likely for Monday with just a few light rain showers, but great improvement is in store for the rest of the week as the jet stream does the splits and sends moisture to our north (Vancouver) and to our south (California). That means PARTIAL sunshine for us Kitsapers.

At this time, it looks like an inversion will not be a huge problem next week. Heaven forbid we enter that pattern again. I may have to check in “the clinic” if we do. What a miserable pattern low clouds, fog, and drizzle is! Stay tuned.

One thing is for sure, even if we turn PARTLY sunny, highs would likely be quite mild in the low to mid 50s…maybe even warmer…

Tomorrow I’ll talk in more detail about the long range trends and what is in February’s future…

Have a good Friday!

Matthew Leach

Kitsap Weather