CHILLIN' IN LATE MAY...

Our weather pattern is in the process of re-aligning itself, and the screaming message this week is that temperatures will be on the cooler side of the ledger to close out May. The first of two NW flow disturbances came through Monday with clouds and scattered showers and storms. A second, is slated for Tuesday with some additional showers and a reinforcing push of cool air. The energy carves out a healthy trough, opening the door for the cool air through late week.

The resulting negative temperature departures are impressive over the upper Midwest, Great Lakes, and Ohio Valley Tuesday afternoon.

Considering how strong the sun is (the days start getting shorter in just 3 weeks), holding highs in the 60s is a challenge. That's exactly what the GFS shows the next few days in Cedar Rapids. No need for the air conditioner, that's for sure.

If you think the days are cool, just take a look at the nights. Wednesday morning lows should be well into the 40s!

If there is a positive about the upcoming pattern, it's the fact precipitation is expected to become lighter and less frequent longer range. The 8-14 day precipitation outlook from the Weather Prediction Center shows rainfall near to even a bit below normal with less in the way of available moisture.

As mentioned above, showers and a few storms are again possible Tuesday, especially in the afternoon during peak diurnal heating and maximum instability. Much like Monday's rains, these will be rather hit-and-miss and generally light, with more of a focus on the NE half of the region. However, where a thunderstorm can pop up, some brief heavy downpours are possible. Highs will be in the mid to upper 60s, but may fall into the low 60s for a time in rain cooled air. This is what models suggest for rain Tuesday.

The EURO

The GFS

The 3K NAM

Here you can see the scattered nature of Tuesday's rains by way of this 4:00pm simulated radar derived from the 3k NAM.

Below are the Doppler estimates of the rain that fell Monday. Notice how it was banded in nature, with a couple of organized thunderstorms tracking SE through eastern Iowa. While the bands were quite narrow, with much lighter amounts outside of them, places within the swaths picked up more than an inch of rain within a short period of time. A similar set-up is possible Tuesday.

After Tuesday, high pressure should be strong enough to keep any rain from penetrating the region until Friday evening at the earliest. Skies Wednesday and Thursday look to be mostly sunny, with some passing fair weather cumulus. Highs will be in the range of 68 to 73, about 10 degrees below normal.

Friday, a new disturbance approaches from the west. It will be bucking a strong high pressure over the eastern Great Lakes and some lingering dry air. My feeling is that it will take most of the day for the atmosphere to saturate and allow precipitation. While clouds will increase later in the day, it seems most areas will stay dry. Friday night, the trough passes which should set off some showers and a few thunderstorms, with the best forcing across the south. Rain amounts should be confined to the light to moderate category. Highs Friday will inch into the low to mid 70s.

THE COMING WEEKEND

Upper level heights slowly begin to build this weekend, along with a gradual return of moisture. Temperatures should warm to more seasonal levels, reaching near 80 by Sunday. This creates some CAPE and instability and a few showers or storms are possible Sunday, but I don't see much in the way of organized forcing. It's possible, coverage is somewhat limited. We will know more in coming days.

Rains chances improve some later Sunday night and Monday as our next cool front approaches. For now, it's back to the grind after a holiday weekend. Hope you all had a great Memorial Day. Roll weather...TS