Joe’s Weather Blog: Severe weather risk and maybe some snow too (WED-4/11)

April in the Plains…my goodness. There are a few high confidence items regarding the forecast which I’ll talk about in the blog today. There are a couple of lower confidence things and there is more cold weather. It’s been a wild last month or so…and Friday>Sunday will sort of be a mini version of what we’ve dealt with for awhile.



Forecast:

Today: Partly cloudy and warm. Windy with gusts to 30+ MPH. Highs into the 70s

Tonight: Mild and breezy with lows in the 50s

Thursday: Variable clouds and warm with highs approaching 80°

Friday: Clouds with thunderstorm chances later in the afternoon/evening. Highs into the 70s. Windy too with gusts to 30 MPH



Discussion:

The cold April weather is going to leave us, for a few days…believe it or not we have 3 straight days of above average temperatures coming into the area starting today. We deserve it because the 1st 10 days of April are the coldest (not even close) since weather records started back in the 1880s

That’s #1 by almost 3°…that’s pretty impressive.

In case you’ve lost reference…today’s average high is close to 64° with an average low of around 42°. We did make a late afternoon surge into the lower 60s yesterday but with the low yesterday of 26° it was still overall 9° below average.

So one of the items that I have high confidence about is the fact that the next 3 days are going to be nicely above average. 70s to near 80°…into Friday.

Persistent and strong south and south-south-west winds will help that cause. This persistent flow will eventually tap into some Gulf moisture that will start flying northwards tomorrow night. This moisture should be about 4-5,000 feet deep and will take the form of low clouds tomorrow night into Friday. Dew points at the surface will be jumping well into the 50s…maybe 60s on Friday and you’ll start to “feel” the humidity increasing

A strong April cold front will be cutting through the Plains region later Friday and sweeping into KC late Friday afternoon into Friday night. Behind the front it’s going to be cold and blustery for the weekend. Saturday may only be in the 40s and Sunday may struggle to 40°…impressive for mid April in KC. I’m watching Sunday for the potential of a record cold high temperature (41° set in 1921) and also the potential for some snow again. The record snow is .6″ set in 1921. There is also a chance of a record low temperature (28° set in 1921 as well). It might not be until before 12AM later Sunday night though that that happens…but we actually have a chance at a 3 record trifecta on Sunday making Sunday the coldest overall April 16th day in KC weather history.

The set up on Friday is interesting and rather common now that we have warmer air clashing with colder weather. Remember about 7 days ago (may more?) when I mentioned that regardless of the models, this was a favorable set-up for a powerful Plains storm system. The clashing air masses creating a strong surface low…with blizzard conditions…severe weather…big winds…blowing dust…etc. Well the players are now on the court and things are going to get going in a couple of more days.

As far as the severe weather risk goes on Friday…this area is in play.

 

Slight>enhanced risks of severe storms are up and down the State Line region…

Since this will be our first severe weather risk day…you may not be familiar with the categories that are associated with severe weather communication. I wish we could use better wording to convey this but that’s for the government to figure out. There are 5 levels of “risk”. ranging from “Marginal”>”High”. High risks are few and far between each year…there are even some years where “high” risks are not even issued.

The ones that you should pay the most attention to (in my opinion) are Slight (I really hate that word in these situations)…”enhanced”…”moderate”…and obviously “high”. There has been, in the last few years, a slow push towards a number system…1-5.

So on Friday we are in the slight to enhanced region (our viewing area).

The ingredients in play are … 1) low level moisture. We’ll measure this by looking at the surface dew points. Dew points are a way for us to measure moisture. The higher the dew point…the higher the “muggy” feel to the air. It’s tough to get a lot of severe weather (typically) when the dew points are below 55°. We typically like to see dew points in the 60s and we should be there. 2) a trigger…in this case it will be a rather strong cold front knifing into the warm and moist air that is flowing northwards.

Here is the forecast surface map for Friday evening at 7PM…

That cold front is the bigger trigger for us. Also note the dry line with the leading edge of a drier push of air cutting through far SE KS.

Above what’s happening at the surface will be strong winds…and the winds will be increasing with height. This would be ingredient #3…shear. There are several shear parameters that can enhance severe storms…one is directional shear. This is when the winds “veer” or turn clockwise as you go higher into the atmosphere. Ideally…let’s say the winds are blowing from the SE>NW at the surface…then the switch from the south blowing towards the north a few thousand feet up. Then as you go higher up…they blow from the SW to the NE…then perhaps even from the WSW to to the ENE.. This creates directional shear. Another shear parameter that we look for is “speed” shear. This occurs when the winds at the surface, for example, may be close to 20 MPH…but as you go upwards…the wind increase to 40…50…60…70…80 MPH.  We’re going to have the “speed” shear in abundance. Direction shear isn’t as favorable but still there is some to work with.

The reason why “shear” is important is that “directional” shear helps in the formation of rotating updrafts within a storm while “speed” shear keeps the updrafts and downdrafts of the storm separated better. This keeps the storm moving quickly. It’s also indicative of storms that can produce larger hail and stronger wind gusts…since the wind speeds in the atmosphere are stronger…the rain from the storms can help drag those stronger winds to the surface and that’s how you get stronger wind gusts from the storms.

At this point to me…it seems the storms would be more of a hail>wind threat than a tornado threat for the KC region and eastwards. Areas farther towards SW MO and perhaps even closer to the Lakes area into SE MO may have more of a tornadic threat. One thing to watch as well…the “cap”. This is a layer of warmer air (in this case about 6-8,000 feet up that restricts air from rising higher in the atmosphere. There are signs that it will be an issue through 5PM then be erased after that allowing convection to get going for the evening. Data this morning indicates 50-70 MPH winds between 5000-10,000 feet up so it wouldn’t take a lot to get those stronger winds to come down. Storms will be flying towards the NNE at close to 50 MPH as well, if not faster. Another thing that I’ll be watching is that sometimes in these “early” season set-ups…IF there is enough “speed” shear…you can get tornado formation. This process can occur rather rapidly in the right scenario. Soit’s worth monitoring, especially on the MO side east of KC.

So there is a lot going on in the atmosphere later Friday…tomorrow I’m thinking of taking a deeper dive into the severe weather categories for you…many may be familiar with the “names” that Ii talked about…but there is more to consider.

Our feature photo is from Todd Bryan who was flying into Chicago today. Neat shot!

Joe

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