Fri 11:30 PM – The two versions of the WRF model just available show showers as early as 1PM Sunday and more sun than the GFS or NAM. High temp 86-88 on Sunday.
The WRF model forecasts have been really impressive lately. The downside is the model comes out late, only forecasts out to 48 hours and is only run twice daily. But accuracy is worth the wait.
Fri 10:45 PM – Tonight’s NAM has more sun, less cloudiness on Saturday afternoon, more clouds on Sunday.
Saturday will begin with the incredibly nice weather we had today (Friday).
As the crisp, unseasonable airmass over us moves off to the east, weak low pressure from the Midwest will pass to our north on Sunday. A southwesterly flow of increasingly humid and unstable air will move in for Sunday.
Saturday will start sunny and delightful. High temperature 82-84. During the afternoon a very weak “pseudo warm front” will approach. An increase in cloudiness expected with mostly cloudy skies by late afternoon.
Sunday will be mostly cloudy (some bright spots possible), warm and increasingly humid. As the warm front slowly moves to our north Sunday, light showers are possible in the morning, mostly far north and west, although a sprinkle or quick shower can’t be ruled out here. With increasing heat and humidity and an upper air disturbance moving through, expect showers and thunderstorms to break out in the afternoon.
The FV3-GFS I spoke of earlier this week has fully replaced the older GFS. The “FV3-GFS” after this past Wednesday IS the “GFS” now.
The GFS has the chance of light showers as early as 1 PM. Most of the shower and thunderstorm activity is expected during the late afternoon and evening hours according to both the NAM and GFS.
I’ll update over the weekend to give a more specific timing and indicate whether some areas will have any severe weather.
What’s with this cool weather? Remember, we’re just coming off the 10 year sunspot cycle minimum. Back in the summer of 2009, we had fewer days in the 90s and many similar very cool spells. I’ve talked about this in the past.
Fri Morning Update: The latest models have shifted the showers to late Saturday and most of Sunday into Sunday night. So Saturday is looking like a better day, especially from PHL and northward. I’ll do an updated weekend forecast Friday evening.
The weather for this weekend is again looking unsettled. There are huge differences between the NAM and GFS models for Saturday with the NAM being much wetter than the GFS.
Basically, there are timing differences with the disturbances that are expected to move along a frontal boundary. The position of the front is also in question.
Perhaps there’s insight in the fact that the new GFS model under development (referred to as the GFS FV3- “Finite Volume Cubed Sphere” ) has a similar forecast for Saturday as the NAM. By the way, I’ve been looking at the GFS FV3 more and more.
That would mean that Saturday would be the wettest and Sunday would be dry. Too soon to be sure.
People are asking me, what’s with this prolonged winter weather and cold?
One thing not talked about recently is the solar cycle. We are about to enter a solar minimum. The solar cycle is a regular, periodic change in sunspot number and the mimimum correlates with reduced total solar irradiance.
The solar cycle repeats ever 10-11 years.
The SORCE PROJECT has been measuring the total solar irradiance since 2003.
The previous solar minimum was in 2009. The minimum has been shown to have a total solar irradiance that is reduced by about 0.5 -1 watt/m2. Over the surface of the entire earth, that reduction adds up.
Maybe you’ll recall that the summers of 2009 and 2010 were usually cool? I think the coming summers of 2018 and 2019 might be similarly cool. (We’ll find out!)
So if it’s a cool summer, remember, it may be the sunspot cycle.
BTW, Here’s a link from my old blog in 2009 talking about the solar cycle.
Clarification 4-14-18: When I say cooler weather, it doesn’t mean we won’t have heat waves. But it means that there will be fewer days in the 90s and average temperatures for the months of June July and August may be just below average.