Joe’s Weather Blog: Upper level storm moves over our region (TUE-5/23)

I may try to keep this blog shorter than my usual 1000 words for a change…because everything that I’ve written about over the past couple of days seems to playing out the way I thought it would. We’re starting this morning with some light, fast moving showers as I type this…but conditions will improve as the morning moves along. Meanwhile an upper level storm (sort of unusual for late May) will be moving overhead into Wednesday…then the weekend forecast still has some questions.


Forecast:

Today: Variable clouds with additional showers possible later this afternoon. Highs struggling in the 60s

Tonight: Mostly cloudy and cool with lows in the 40s to near 50°

Wednesday: Mostly cloudy with a few isolated showers possible in the afternoon. Highs near 65° with enough sunshine.

Thursday: Nicer and more seasonable with highs into the mid 70s


Discussion:

Today the main feature in our weather, and this will be a factor into Wednesday as well is an upper level wave dropping southwards. This is in response to a broader upper level storm spinning in Canada. Imagine a bicycle wheel…and the spokes on the wheel are little waves that spin around the center of the wheel.

Take a look at the water vapor images this morning…and notice a couple of things…one the broader upper level storm in Canada (the main wheel if you will) and two the little circulation dropping southwards from MN (a spoke of the wheel)…there is another one in NW WI and NE MN this morning as wheel

The little circulation will continue to drop southwards today and and pass through MO Wednesday and drop towards the TN Valley Thursday before lifting towards the northeast (may spell a rain-out or a very delayed start in NY for the game Thursday afternoon)

These circulations represent pockets of colder air…in the middle part of the atmosphere that eventually work down towards the lower part of the atmosphere. For example…if we go up to about 10,000 feet…and look at the expected temperatures of the air at around that level (we refer to it as the 700 mb level) you can make out that colder air. The temperatures in the map below are in °C.

So that -5°C line (or isotherm) is on top of us…that’s about 23°F at that level.

Can you make out in the map above the colder air…and then towards the SE US and the western 1/4 of the country the warmer air?

So that pocket of colder air will be over us later today>Wednesday. This though is late May…and when the sun is out…despite the colder air above us, because of the higher sun angle…it tries to really warm up. This leads a “big” temperature spread from the ground upwards…some 40° or so from the surface…mid 60s to the level shownn above…low>mid 20s.

Time for Weather 101…

Any change in temperatures from one level to another level (regardless how far those levels in the air are separated) is calculated and called the “lapse rate”. These can be measured and we then can determine IF the change is big enough to cause more unstable air. The faster the change in temperatures between levels…the “steeper” the lapse rate…the more unstable the air is. Unstable air rises (lifts) and so as a result the “lifting” air then cools…condenses…clouds form…and IF there is enough “lift” the clouds grow more and more vertically and eventually create rain and potentially storms.

The thing is…as you go higher in the air in these situations…remember how cold it gets. So we check to see IF the clouds developing upwards go above the part of the atmosphere where the temperatures drop below 32°F. Now IF there is rain in the clouds and the rain is lifted above that level…you can get small hail to form. This afternoon that level will be around 6500′. Decent vertical cloud development…like in convective situations like this afternoon have no problem getting to at least that level.

So what does this all mean? Basically it means that sometimes the showers that develop may actually produce some small pea-sized hail. So don’t be shocked if that happens late this afternoon. What then happens as well is that the showers/rain cool down the lower part of the atmosphere to the surface…this then kills the lapse rates around the rain and the rains fall apart. It’s all fascinating to watch “bubble up” on radar. So pay attention to it this afternoon. The rains will be rather haphazard…perhaps developing 1st towards the IA border…where the sunshine and heating occur quicker today…

All this is predicated on sunshine though and 65-70° surface temperatures…and looking at the latest satellite image this morning…it does appear as if the sun will be coming out before lunch in the area.

No blog tomorrow…I’ve done a ton of blogging the last 10 days or so!

Our feature photo comes from Suzanne Luna of the storms that affected parts of the region yesterday afternoon…this one near Lenexa.

Joe

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