Raise your hands if you remember the derecho of of May 31 1998.
The early morning hours of Sunday, May 31, 1998, brought one of the most memorable storm events to Michigan. A derecho — a long-lived line of intense, fast-moving thunderstorms producing widespread destructive winds — tore through much of the Great Lakes region. The storm complex started in South Dakota around 7 PM CDT May 30, and by 11 AM EDT May 31 it reached upstate New York. The storm crossed the Lower Peninsula of Michigan between 4:45 AM and 8 AM, killing 4 people and injuring 146.
Straight-line” winds from the storm were commonly in the range of 60 to 90 mph, though winds were estimated as high as 130 mph in a few locations in southern Wisconsin and western Lower Michigan. Several tornadoes developed within this storm complex, including a violent tornado in Spencer, South Dakota. In Michigan, 5 tornadoes were officially discovered embedded in the larger pattern of downburst winds.
Most of the tornadoes occurred in northern Lower Michigan on the north end of the storm line. These tornadoes were rather short-lived and developed along the chaotic interface between the thunderstorm outflow “gust front” and the warm & unstable pre-storm air mass. More common, and just as intense, was the west-to-east moving wall of wind that traversed Lower Michigan at an average speed of 70 mph.
Area of Lower Michigan affected by the worst damage from the May 30-31, 1998 derecho. Red numbers are maximum measured wind gusts in mph. Orange numbers are estimated maximum gusts in mph, based on a damage survey by Grand Rapids NWS Forecast Office meteorologists.
The images below are recently re-analyzed depictions of archived radar data from the National Weather Service in Grand Rapids, Michigan, collected the morning of May 31, 1998. On the left half of the images are radar reflectivity, which shows rain intensity. On the right half is radial velocity, which shows the component of wind speed moving toward or away from the radar. In the radial velocity image, green to blue colors are winds moving toward the radar, and red to orange colors are winds moving away from the radar. Dark purple colors in the velocity image are data that could not be accurately gathered due to range-folding.
Above: Radar image from 5:06 AM EDT May 31, 1998. The leading edge of the destructive thunderstorm winds are indicated by the dashed white line labeled “Gust Front.” The farther the radar beam travels from the origin site in Grand Rapids, the higher above ground the radar beam scans. An intense rear-inflow jet behind the storm line between 3000 and 8000 feet above the ground had winds sampled between 90 and 115 mph. These winds behind the storm line stayed above ground, but closer to the front edge of the storm line, some of that wind momentum was channeled down toward the ground. A close-up of the circled “downburst cluster” area is shown in the image below.
Above: Radar image from 5:06 AM EDT May 31, 1998. Winds sampled over Grand Haven area were in the range of 70 to 115 mph at 2000 to 3000 feet above the ground. These pockets of strong winds were indeed reaching the ground. Winds estimated as strong as 130 mph in Spring Lake, just east of Grand Haven, destroyed buildings.
Above: Radar image from 5:21 AM EDT May 31, 1998. The leading edge of the destructive thunderstorm winds are indicated by the dashed white line labeled “Gust Front.” A close-up of the storm as it was west of Grand Rapids is shown in the image below.
Above: Radar image from 5:21 AM EDT May 31, 1998. Particularly hard-hit by this storm was the city of Walker. The radar velocity data shows winds between 100 and 115 mph just 750 feet above the ground. The scattered pockets of stronger winds embedded within the line shows how some communities were hit by 90-110 mph winds while others were hit by “only” 60-70 mph winds.
Above: Radar image from 6:02 AM EDT May 31, 1998. The leading edge of the destructive thunderstorm winds are indicated by the dashed white line labeled “Gust Front.” 60-90 mph winds were occurring at this point in the storm’s life. There is a wavy pattern of embedded “bowing segments” within the larger storm line.
Mainly dry weather is expected from today through Friday across Southwest Lower Michigan. An isolated shower is possible this afternoon, but most areas will remain dry. High pressure will be in control of our weather tonight into Thursday night and will be responsible for the dry conditions.
Friday a warm front will be developing to our southwest with better chances for showers and storms as we head into Saturday. After below normal temperatures today, with highs in the 60s, we will return to the 70s for Thursday and Friday.
HRRR and Futurecast models runs are for 18 hours beginning at 7am – a second model run begins at 3pm
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Fairly minimal concerns through the short term period with dry weather expected. The change in the models from last night is to keep the warm front in the Thursday night and Friday time frame further to the southwest. Therefore, less in the way of precipitation is expected during this time frame.
Isolated showers will continue in the forecast today as the upper low circulation remains entrenched across the Great Lakes. High resolution convection allowing models like the 3km NAM show a few showers after 20z this afternoon.
A dry period is expected from tonight through at least Thursday night with ridging in place across the Southern Great Lakes. Deep layer RH values are fairly low during this time frame, generally 50 percent or less below 700mb`s. So, high confidence in dry weather with limited cloud cover.
Tonight we may dip into the upper 30s in a few of the colder spots along the U.S. 10 corridor. Friday, a developing warm front will begin to take shape in the plains. Feel Friday will end up being dry for most area across the area. For continuity with neighboring offices, have a small chance for showers (20 percent) in the far south, closest to the warm front. .
The weekend is shaping up to be stormy. Models have been advertising a warm front to push into the cwa from the west Saturday afternoon, followed by a sfc low Saturday night and Sunday. The sfc low has pretty good upper support with several short waves rotating around a deeper trough. Highest pops will be Saturday night.
Shear values approach 45 knots Saturday night suggesting that a few of the storms could be strong. Conditions will improve somewhat Monday as the sfc low moves east, but the upper trough will linger and both the ecmwf and gfs show a strong short wave rotating through Lower Michigan. Showers will remain in the forecast Monday and Tuesday.