TO STORM OR NOT TO STORM
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EARLY SEASON STORMS?
There's not many times (if any) that I can recall addressing a severe thunderstorm threat February 8th. Most likely it won't amount to much, but there is a "conditional" risk of severe storms, and if nothing else, I'm talking about it. That in itself is rather remarkable. And why not, these days seasons and the old ways don't seem to matter anymore to mother nature anymore!
So when I say conditional risk, what does that mean? Well, in this case it means the chance of storms is not high, but if a few are able to develop or move into the area, they could be strong to severe. The main threats with any storms will be strong gusty winds, perhaps some hail, but there's even a slight chance of a brief tornado. With limited heating and instability (but respectable shear), storms of this caliber would fall into the classification of low topped supercells. While confidence is fairly low in convective initiation, there appears to be enough signals in various model guidance to support a small marginal severe risk. In the end, much will depend on the amount of daytime heating that can be generated. The window will be small and confined to late Thursday afternoon or early evening. SPC shows the limited scope of the marginal risk area.
The thunderstorm potential is being driven by a cold front that passes the region from west to east, generally between 3:00 and 7:00pm. Moisture is definitely not high, with dew points at best nearing 50. However, considering the dynamics and time of year, this may be just enough to pop some robust updrafts. The HRRR does show decent instability, with CAPE values over 1,200 j/kg. in spots.
The HRRR also shows a supercell index of 6 to 7 near and SE of the Quad Cities. That's implies a healthy chance of surface based thunderstorms that would rotate.
Additionally, the significant tornado index from Galesburg to Galva is progged to reach 3 to 4 around 4:00pm. That's not bad for February 8th.
The K index which measures thunderstorm potential maxes out at 30-34 around 5:00pm. Again, that indicates a pretty good chance of scattered storms by evening.
Of course, all the parameters I've showed you are on paper and highly dependent on a certain level of instability being met. If clouds are a detriment or moisture is insufficient, this all goes out the window. That is why this is a "contingent risk, a low confidence set up". We should know much more on the heating and instability potential by late morning after fast moving morning showers streak off to the northeast.
As for temperatures, there is big "bust" potential. Some solutions show record highs in the 60s. Other's are substantially lower due to clouds and spotty showers that limit heating. I could see this going either way. At this distance, it's very difficult for models to pick up on mesoscale details such as breaks for sunshine. Right now, I'm thinking upper 50s to low 60s looks pretty solid, perhaps mid 60s in the far south. Here's what the HRRR shows, which is what all those parameters above are based on.
Regarding any records, these are current records that may be challenged Thursday afternoon.
Records February 8th:
Cedar Rapids 57, 1925
Dubuque 55, 1925
Moline 63, 1990
Burlington 66, 1990
All guidance is consistent on showers and storms ending by early Thursday evening. Due to the fast movement of individual cells, rain totals should generally be on the light side (under 2/10ths) of an inch. Take a look.
Temperatures will cool significantly following the cold front over the weekend. However, readings will still be near to slightly above normal in the upper 30s to low 40s Saturday and Sunday. Dry conditions will prevail.
Before I wrap this up, I did want to touch on my previous post where I showed the GFS driving an Arctic front into the Midwest February 18th. It showed a massive 1054mb high building in from Canada.
Temperature the morning of the 18th were near zero with wind chills 15-20 below.
The latest run of the GFS is night and day, a totally different look. It has no evidence of the extensive high and has eliminated the Arctic onslaught. Take a look and compare the before (above) to the current (below). I was not expecting to see this!
Temperatures for the same time period are 35 degrees warmer. You should not (and do not want) to see such extremes from one run to the next. Good grief!
If that's not enough, the latest EURO just came in with a low of 5 in Dubuque the morning of February 20th. That's 21 degrees colder than the previous run of 26. Ugh, what a change and what a mess.
This inability for models to hold trends is a frustration I've been dealing with lately. It signals the atmosphere is noisy and in a rather complex state handling energy transfers in the split flow that exists. The cold is there, models just can't figure out when (or if) it will break loose. Frankly, I'm totally fine without the Arctic air, but if it's not cold, it won't snow. I'm not thrilled about that. We'll see where things are tomorrow after this thunderstorm threat passes. Have a fine day and roll weather...TS Additionally with my recent health issues, I very much need to reach my fund-raising goals. To keep things as they are, I'm in humble need of your donation to the site more than ever. If you use it and find value in it, please consider a contribution. Thanks to you who have already helped the cause!