Ups and downs
We weather geeks call it a "high amplitude pattern."
It's what the jet stream looks like when it makes big loops and waves across the USA. The resulting weather at your door changes slowly or not at all depending on how progressive or blocked the pattern is.
Monday's cool and showery weather was courtesy of the lead trough in the pattern. The prolonged sunshine and gradual warming trend ahead is brought to you by the ridge of high pressure building in from the west.
We may have a bit of forecaster "group think" going on in the Twin Cities again this week. Some of our computer models (and local forecasts) want to stop our warming trend with highs only reaching the upper 70's this weekend.
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The computer model output statistics (MOS) are notorious for underestimating the magnitude these high amplitude warm and cool trends. Many forecasters are hesitant to forecast a big round number like our first 80 degree reading for fear of being wrong and suffering the wrath of those who would say; "you said it was going to hit 80 this weekend." This is especially true for big holiday weekends and after a chilly spring like we've had this year. So you'll see a lot of 77 to 79 degree forecast highs this week for the upcoming Memorial Day weekend. History suggests those forecast numbers will move closer to 80 as the week goes on.
If you forecast 79 and hit 80 no one cares right? But if you forecast 80 and only hit 78 then you're going to get nasty email and harassed at the picnic. I guess the idea is under promise and over deliver. I've never bought into that psychology as a forecaster. If the pattern looks right, put out the number that best fits I say.
It is possible we may not get above 79 this weekend, but my best estimate is that we will manage our first 80 of the season somewhere in the metro between Saturday and Monday.
At any rate it's going to be a great holiday weekend. Saturday looks spectacularly warm and dry. A little passing thunder may roll through Saturday night into Monday, bringing a few hours of rain here and there but the majority of the weekend should be thunder free.
Enjoy the warming trend this week, and hopefully our first 80 this weekend.
PH