Northwest flow is moving out and will be replaced by an elaborate southwest flow setup featuring the classic trough in the west. The overall pattern has me thinking heat and severe weather. I foresee several days with temperatures in the upper 80s/90s from Saturday through Wednesday. After Wednesday we may trade heat for wet weather. The long term trend seems to favor stormy and active; I'm betting this is the peak of the 2017 Wisconsin severe weather season here before the end of June.
- Southwest sub tropical flow phases with the polar jet across the northern Great Lakes and southern Canada this weekend
Today - Tomorrow - A week upper level disturbance, weak low pressure will kick off scattered showers or storms. Best chances seem to be across northeast or maybe central Wisconsin with peak heating. After sunset I expect storms to weaken. I may chase these storms if I like the opportunity. Could have a strong t-storm in there with hail, but want to downplay for sake of what appears to be coming up the road. Friday will be a tweener day between today's precipitation chances and this weekends heat & storm chances. Brief northwesterly flow aloft should provide for a nice day. Cannot rule out a shower with possible surface boundary hanging around.
Saturday - Sunday - Southwest flow takes over and heat arrives. This is a July-like pattern with disturbances riding along the northern side of the ridge. A respectable elevated mixed layer develops from the plains into Wisconsin and no trigger to remove it for most. The first upper level jet streak pushes through north of Wisconsin Saturday through Sunday and phases with the polar jet. Rain may graze the northern counties Saturday morning. I'm really interested in severe weather chances even though coverage should be minimal. You might say this is the perfect situation for storm chasing.
Saturday has that May 16 feeling of "under the radar" despite everything coming together across northwest Wisconsin. I'm not trying to make a direct connection, there are many differences. Storm development will face an up hill battle. With lack of upper level support, the trigger for storms will need to be a frontal boundary. A weak cold front will approach late in the day and I believe it will be enough to overcome the capping inversion. If everything comes together, a supercell or two could move into northwest Wisconsin late in the day (perhaps around or after sunset). These storms would be capable of all modes of severe weather including tornadoes, but because coverage will not be widespread you may not hear anything about it. Whether or not I chase this depends both on how much activity is expected before sunset, as well as what is going to happen on Sunday.
Sunday is a different animal. The cold front from Saturday night will settle across Minnesota/Wisconsin. The right entrance region of the upper level jet or an embedded shortwave, in concert with previously mentioned stationary front will kick off powerful storms. Latest models indicate the region along a line from Mankato, MN over to Stevens Point are under the gun the most. It's too early to be exact, but I'm guessing a powerful complex(my bet) or dominant tornado-producing supercell will develop early in the afternoon across Minnesota sliding east along the stationary front. How this evolves as it slides east under strong westerlies aloft will be interesting. Someone could get railroaded pretty hard. Railroaded? When a tornadic supercell or complex rides a surface boundary for many, many miles. Do not overlook Sunday, especially southern Minnesota and central Wisconsin. Another situation that may not get the attention it deserves. It's a must-chase day in my opinion.
- Sunday afternoon a strong supercell or complex could railroad southern Minnesota and/or central Wisconsin.
It should go without saying that things can and probably will change. I'll counter that by noting that forecast models have performed well recently.
The main upper level low and associated trough is expected to move into the northern Plains, effectively cutting itself off. Throughout the week, in addition to heat through Wednesday; there will be thunderstorm chances but I don't feel comfortable getting detailed about that yet. I think Monday will be capped with no trigger. It will be southwesterly flow through Wednesday. I find the pattern that comes for the following weekend to be very interesting looking at mid range GFS which is somewhat at odds with other models. Strong westerlies and a possibility of a potent shortwave being driven into the great lakes. On the average I expect unsettled and continued stormy weather, but I wonder if there is more unique and widespread t-storm event lurking in there?
- 7 Day forecast for Wisconsin Rapids
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