Before getting to the actual forecast, so many people have been asking that I need to explain why the forecast for this week has changed so much from what we expected last week.
We knew all last week that a storm system was going to cross the state on Sunday, and it initially appeared that its upper level system was going to be what we meteorologists call progressive. That means that we thought it would pass on through and progress to the east coast.
Well, late in the week we started seeing a change in the long-range computer models: that upper level system was going to deepen further and turn into what we call a cut-off low. What that means is that the jet stream dip was instead going to develop into a deep low pressure area aloft that is cut off from the steering winds aloft. Translation: it would slow down and meander.
Is this rare? Not at all. In fact, this is the time of year that cut-off lows are most common. But the problem for us is that the computer models are typically dreadful in their handling of these systems far in advance, and that was the case this time with the slow-moving low.
Again, cut-off lows are slow movers…consider that the cut-off low, which is over Illinois today will have only drifted southeast toward Kentucky/Tennessee by Wednesday.
So we’ll keep the rain around today and part of Tuesday, get a couple of dry days Wednesday and Thursday, then maybe get a few showers on Friday as the cut-off low weakens and finally drifts to the northeast. Here are the specifics:
Rain today
Numerous showers with some heavy downpours and possible thunder will be around today, with highs in the mid 60s (19 degrees Celsius). All of us will get at least one to two inches, with up to three inches possible in spots, so the Flood Watch remains in effect until 8:00 p.m.
Today’s daily rainfall record of 1.50″ set in 2000 is in jeopardy.
Adding insult to injury is the east wind at 10 to 20 mph (with higher gusts), which will keep the Lakeshore Flood Warning going for the Michigan shorelines of Lakes Erie, St. Clair and Huron.
The east wind combined with the heavy rain has also prompted the National Weather Service to issue a Flood Warning for the Michigan side of the St. Clair River.
Today’s sunrise was at 6:09 a.m., and today’s sunset is at 8:51 p.m.
Tuesday
Rain continues Monday night, then diminishes in coverage from north to south during the day on Tuesday. Lows Monday night in the mid 50s (13 degrees Celsius), and breezy highs Tuesday in the mid 60s (19 degrees Celsius).
Wednesday and Thursday
Wednesday and Thursday appear dry right now, with at least partial sunshine. Highs Wednesday in the low to mid 60s (17 to 18 degrees Celsius), then moderating into the upper 60s (20 to 21 degrees Celsius) on Thursday.
As mentioned above, there’s at least a chance for a few showers on Friday, with highs in the low to mid 70s (23 degrees Celsius).
Memorial Day Weekend
Although confidence is lower than usual due to that pesky cut-off low, it appears right now that we’ll finally get some of the summery weather we promised last week…just in time for the holiday weekend. At this point, I’ll go with partly cloudy skies on Saturday and Sunday, with highs in the upper 70s (26 degrees Celsius) Saturday and near 80 degrees (27 degrees Celsius) on Sunday.
Memorial Day itself looks warm, but the timing of an approaching front will dictate whether or not we get any showers. Highs in the low 80s (28 degrees Celsius).
Again, I wouldn’t carve in stone any holiday weekend outdoor plans just yet. Right now, the weather LOOKS promising, but I’d love to see another day or two of computer model runs and make sure that cut-off low doesn’t have any more surprises.
We’ll have updates through the week here on ClickOnDetroit.com, on Local 4 and, of course, on the free Local4Casters Weather App!