The weekend was hot, but not overly humid as temperatures warmed into the mid and upper 80s both days. Following a cold front Friday afternoon there was a nice drop in the dew point temperature, with numbers falling through the 50s. This helped keep the humidity at bay through the weekend. For anyone who may be enjoying any Fourth of July festivities Sunday evening, the weather looks perfect. It'll be a warm evening with a breeze from the south. Temperatures will remain in the 80s through sundown, slowly falling back once the sun sets. Skies remain clear making for perfect viewing of any fireworks displays that may be taking place.
All eyes, however, will be paying close attention to the forecast for the actual holiday - Monday - as showers and thunderstorms are likely to impact parts of the region not only during the afternoon, but possibly at night. As we enter into the first full week of July, we are also entering into a very typical summer-like pattern, known as the 'ring of fire' pattern. Under this pattern, thunderstorms and storm clusters form on the outer edge of a strong, and usually rain free, heat dome. These storms follow the winds within the jet stream, feeding off of the heat and instability. It's an often difficult type of pattern to forecast for as the exact path and timing of those storms depends on quite a few factors; a couple of those being any overnight or early morning storm activity, storm activity upstream and impacts that may have on further development downstream. For Monday, it does look like we have an opportunity for a couple storm systems to move through the region; the first during the afternoon and the second later in the evening/night.
Skies should begin relatively quiet Monday morning ahead of increasing cloud cover from the west. Temperatures will fall into the mid 60s during the early morning, rising into the mid 80s by the afternoon. An upper level disturbance currently over the Rockies is forecast to move through the Plains and right across northern Illinois and southern Wisconsin either late morning or early afternoon. It looks like our window for this first wave is roughly Noon to 5-7pm. There will likely be a dry period following the first round of rain during the evening, perhaps a couple hour window, before the second round moves through.
That second round of thunderstorms is expected to develop to our north/northwest sometime during the evening, shifting to the southeast towards southern Wisconsin and northern Illinois. These thunderstorms will be developing on the nose of an increasing low level jet (strong winds in the lowest levels of the atmosphere), as well as with increasing moisture and instability. The big question mark at this point is when do the storms develop and what is the exact track. As it stands Sunday evening, the storms could move right over southern Wisconsin and northern/northeast Illinois as early as 9pm/10pm, or hold off until after 11pm. It's also possible that the storms form more to the northeast, passing through southeast Wisconsin and northeast Illinois, bypassing most of the area. Again, this second round depends on what happens earlier in the day. Wherever these storms develop, there is a risk for a few strong/severe storms late Monday evening. Strong winds and heavy rainfall would be the biggest concerns.
If you are planning on heading out for any of the fireworks displays, please make sure you keep a watchful eye on the forecast for the evening. We'll continue to provide updates on our storm chances throughout the day.
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