ITSY BITSY SHOWERS

There were a bunch of clouds floating around the country yesterday, resulting in cooler than normal temperatures and in some cases rain. My area, happened to be in one of the better spots for weather, with some breaks for sunshine. That allowed enough heating locally for a pleasant, mild afternoon with highs in the low 70s. All things considered, another respectable day. That was not the case in western Iowa, where showers and clouds combined to keep readings only in the upper 50s. As they say, location, location, location.

In the midst of all the cloud cover, a developing cut-off low is forming over Minnesota that is displaced from the westerlies. The cold core low will spin slowly southeast directly over my area Thursday. In doing so, spokes of vorticity will rotate around the circulation center through Thursday. These, along with cold air aloft, will produce the forcing necessary for widely scattered showers through that period. Eventually, the energy will merge with another system diving out of Canada to forge a formidable trough over the northeast, something we've seen a lot of the past couple of months. In essence, this large scale bump in the weather road will control our sensible weather through Sunday.

The initial impacts will be the addition of some wet periods the next 2 days. A low pressure wave contributed to the development of showers overnight as it slipped southeast ahead of the upper air low entering NC, Iowa. What's left of these light to occasionally moderate rains, will be lifting out of the northeast half of my area Wednesday morning as that forcing departs. However, additional light instability showers are possible later in the day and evening with the arrival of the upper air low itself and some weak vorticity. These should wane Wednesday night but will likely pop up again Thursday afternoon with the cold core directly overhead, contributing to instability during peak heating. This type of set-up usually delivers the rains on a hit-and-miss basis. With water vapor of 8–9 tenths of an inch and some minor CAPE (instability) a few thunderstorms are even possible. So are some downpours, but they should be spotty and brief. The short range ensemble forecasts (SREF) shows rain totals through Thursday evening on the order of 2 to 4 tenths of an inch from west to east.

The EURO indicates totals such as this.

The GFS has this.

The 3k NAM indicates this.

Temperatures Wednesday and Thursday will be highly dependent on clouds and one's proximity to any showers. It does appear likely that most places are at least 5 degrees cooler Wednesday, maybe closer to 10 in the north. The HRRR pops just enough sun in the SW to get mid to upper 60s, but elsewhere north of I-80 a heavy overcast could limit highs to the upper 50s to low 60s, similar to what western Iowa saw Tuesday.

Thursday should be a bit better but still well below normal with highs in the mid to upper 60s.

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DELAYED BUT NOT DENIED...

As I mentioned at the top of the post, our energy consolidates with another surge dropping south out of Canada to sharpen the trough over the east Friday and Saturday. It looks like this at 500mb going into Saturday. That's a healthy looking trough for the last day of May.

Looking at temperature departures Saturday evening, you can see the back edge of the cool air within the eastern trough reaches back into eastern Iowa.

There are two effects from that. First, that keeps us on the baroclinic boundary of warm air to the west and cool air to the east. Vorticity likes to ride that edge, and it's possible that a shower or thunderstorm could impact the region Saturday afternoon. Additionally, the northwest flow will keep our temperatures through the weekend in the 70s, maybe 80 in the SW Sunday. A lot of forecasts are showing highs in the 80s Friday through Monday and beyond. I do expect much warmer readings next week but as I mentioned yesterday, I think the warmth is just delayed, not denied.

The latest EURO and GFS are catching onto that trend, and you can see the EURO meteogram holds off on 80s until next Monday when it shows 81.

24 hours ago the EURO was at 88 Monday and I said in my previous post, that was probably too fast and unlikely in the synoptic pattern shown. So far so good.

The GFS is all in though on a summery pattern developing long term with 11 consecutive days in the 80s (1 in the 90s) June 2nd through the 12th. Maybe the eastern trough that's been in play for the past 2 months will finally break down.

With the addition of moisture and warmer temperatures, that brings to mind the kind of conditions that can produce thunderstorms. At this distance, it's impossible to see the specific mesoscale details that would create them and when. However, the Supercell Composite Parameter of both the CFSv2 and GEFS indicates a much higher potential for severe weather in the week 2 period, June 3rd-10th. That makes sense, especially with my local area at the peak of the severe weather season at that time. Something to watch.

I guess that's enough for one night. I've got a bunch of grass seed planted, and I'm hoping for some of those itsy bitsy showers to eliminate the watering I'm going to end up doing if they miss me. Here's to good luck and a good day for all of you. Roll weather...TS