In this part of the world, weather typically moves from west to east. This is why what's happening in Chicago on one day can often arrive here a day or two later.
Of course, it's not quite that simple. But, because of the way the Earth spins and since it is cold to the north and warm to the south, air generally flows from west to east here.
Sometimes this rule doesn't stick, though, and a current weather pattern gets stuck instead. We call these blocking patterns: the movement of weather system slows or even stops. These blocks are most common in the spring, and although we haven't seen a pattern like this is a few years, it's not really that unusual.
The initiation of the block often occurs as a storm develops. The system brings a slug of rain (or snow in winter) and then the storm just sits and spins over the region. The storm kind of just falls apart on top of us. This causes clouds and showers to remain in the forecast for many days.
As this pattern begins, today we'll see a mix of clouds and sunshine along with temperatures that stay seasonable featuring highs in the low to mid-60s. Then, the storm comes Friday, with the bulk of the rain expected to fall from the middle part of the day through much of the night.
I am expecting 1 to 2 inches of rainfall on Friday, which is not enough for a major flooding issue but will make for a really slow homebound commute. The morning commute that day should be dry before the rain arrives in the early afternoon.
Let's call the weekend a 5 out of 10. It won't be a washout — that would be a 1 — and it won't be sunny with light winds and highs in the 70s — a 10. We will have temperatures in the 60s, some sun, some showers and a lot of clouds during the majority of the weekend.
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Wednesday: A blend of clouds and sunshine, seasonably mild. There could be a quick sprinkle. Highs in the low to mid-60s.
Wednesday Night: Seasonably cool with clear skies. Lows 37-44.
Thursday: Sunshine with building afternoon clouds. Highs 62-66.
Friday: Rain overspreads the region and becoming breezy. Highs 50-55.
Saturday: Some showers, also some sunny break possible. Highs 60-65.
Sunday: More of the same with scattered showers, some sun and clouds mixed together. Highs in the lower 60s.