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Rain, Thunderstorms, Up and Down Temperatures

Updated: Dec 4, 2020

Forecast: Simple Overview:

Discussion: Mostly Cloudy skies are expected tonight with a small chance of light rain showers and possibly even a few snowflakes mixing in. No travel impacts are expected with temperatures staying just above freezing. Even if you do see a snowflake, nothing will stick. Tuesday looks dry before more rain is likely Tuesday night. Winds will increase Wednesday, but the daylight hours look dry once again. A strong Low-Pressure system will develop and track towards the Great Lakes by Friday. Rain is possible for a portion of Wednesday night and Thursday along a warm front. Although highs are in the 50s Thursday we will actually warm into the 60s Thursday night.

Forecast: What Will Happen through the remainder of the week?

Mostly Cloudy skies are expected tonight as a shortwave trough brings a chance of some light precipitation to the area. Light rain/drizzle and possibly a few snowflakes will be possible, but not everyone will see them and precipitation will be light. No travel impacts are anticipated with lows forecast to remain around 34 degrees. Tuesday looks dry with highs in the lower-50s ahead of our next system that will bring widespread light rain into the region Tuesday night. Temperatures will hold steady around 50 during the night as we will be under the influence of a short lived overnight warm sector. We’re not done, though, as this week is in the midst of an active weather pattern. A more potent Low Pressure system will develop in the Rockies Wednesday and eventually track through the UP and Lake Superior on Friday. This will send showers along a warm front our way Wednesday night into Thursday and then more Showers and Thunderstorms Friday along a strong cold front. Highs Thursday will range from the 50s north to 60s/near 70 south of I-96. Both the ECMWF and GFS don’t bring the warm front up to Mount Pleasant until around/after 8pm on Thursday. Given the nature of warm fronts, I agree that it will not reach us until late in the day, so most of the day in central MI will be spent in the 50s before climbing into the 60s after sunset and overnight. I expect enough WWA on a gusty southwest wind over 20 MPH to boost temperatures into the mid and upper-60s without daylight, so any sunshine Friday morning with that continued wind would push us over 70. The biggest uncertainty with Friday at this time is what is the exact timing of the front because that will impact how much sunshine we see, exactly how warm we get, and how strong thunderstorms could become. Right now, it looks like a mid-afternoon frontal passage, so will include thunderstorms in the forecast and place highs in the lower-70s.

4-Day Forecast:

Descriptive Forecast in Text Format:

Tonight...Mostly Cloudy with a 30% chance of rain showers, possibly mixed with snow showers. Low: 34. N winds around 5 MPH.

Tuesday...Partly Sunny. High: 52. NE winds 5 to 10 MPH becoming E 5 to 15 MPH in the afternoon.

Tuesday Night...Light Rain Likely. Low: 45. E winds 5 to 10 MPH becoming SW 10 to 15 MPH overnight. Gusts up to 20 MPH. Chance of rain 70%.

Wednesday...Partly Sunny. High: 56. WSW winds 10 to 20 MPH with gusts to around 30 MPH.

Wednesday Night...Mostly Cloudy. A 50% chance of rain showers overnight. Low: 43. NW winds 5 to 10 MPH becoming NE overnight.

Thursday...Rain showers likely and a slight chance of Thunderstorms until midday, then a chance of rain showers in the afternoon. High: 55. SE winds 5 to 15 MPH. Chance of rain 60%.

Thursday Night...Partly Cloudy. Low: 54. SW winds 10 to 20 MPH with gusts to around 25 MPH.

Friday...Showers and Thunderstorms likely. High: 72. Chance of rain 60%. SW winds 15 to 20 MPH becoming NW 10 to 20 MPH in the afternoon. Gusts up to 25 MPH.

Detailed Forecast: WHY is it going to happen?

Many areas will stay dry tonight with limited moisture and PWAT values only around 0.5”. Dewpoints are in the upper-20s and lower-30s this afternoon, which is another signal for dry air. Still, with a short-wave trough advancing eastward through mid-MI tonight, I believe low-end POPs are still needed for tonight’s forecast. HRRR does suggest some light precipitation around tonight. Temperatures will drop to the lower-40s and upper-30s around when precipitation may be in the area. In this case any light precipitation that can begin will eventually fight through the dry air to allow for at least some isolated light precipitation tonight. Most of this would be light rain/drizzle, but the air aloft is below freezing above 925mb, so any evaporational cooling that may occur from the virga fighting the dry air could drop localized areas cool enough to mix in a few snowflakes. Low temperatures are forecast to remain just above freezing through the night, so no travel impacts are expected and any rain/snow mixture that might form would be light and not everyone will see it. High Pressure should be enough to keep precipitation chances out of our Tuesday forecast, but a considerable amount of cloud cover will persist. We’ll call it Partly Sunny to Mostly Cloudy thanks to plentiful high clouds ahead of the next system quickly approaching. Highs will reach the lower-50s. Another shortwave and associated quick-moving weak area of Low Pressure around 1010mb will bring a warm front late Tuesday evening followed by a cold front Wednesday morning. The vorticity max will stay in northern WI and the UP of Michigan, but we still expect rain to overspread the area Tuesday night and early Wednesday as we tap briefly into Gulf Moisture during the nighttime hours. The rain will not be heavy with little to no CAPE to work with, so no thunder is expected. This will be a light rain at night event with totals generally between 0.1 and 0.25”. Lows will stay in the 40s during the rain. In fact, some areas may rise above 50 during the night during the brief period in the warm sector. The daylight hours of Wednesday look to be rather quiet, albeit it a bit breezy as a result of a more potent Low developing in the Rockies ahead of a stronger trough digging into the Pacific north west. The return flow downstream of this trough will be a ridge of decent magnitude in the eastern US. Both the ECMWF and GFS agree on a 588 dm ridge developing in the vicinity of the Mid-Atlantic states Wednesday and lasting into Thursday. This will be an opportunity to draw both Gulf moisture and warm temperatures from the south into the Great Lakes for a couple of days. Wednesday night, the warm front will lift north towards us, setting up roughly west to east along I-80 from IA to OH. This warm front will gradually lift north though Lower MI during the day Thursday and will likely setup a strong temperature gradient form north to south across the state, with 60s south of I-96 by afternoon and 40s and 50s north. Rain is most likely to occur north of this front after the air flowing from the south crosses it and lifts. Instability looks limited, with both the ECMWF and GFS operational runs showing little to no instability. The ECMWF has a narrow corridor along/just north of the front of 250 j/kg CAPE at best, so will leave thunderstorm chances at slight chance (20%) category along the warm front. Thursday evening and overnight will feature the warm sector with strong WWA on south winds sustained at 15 to 20 MPH, which will result in temperatures holding steady if not climbing thought the 60s during the night. Depending on how much sunshine we see Friday morning, temperatures should reach the upper-60s to perhaps as warm as the mid-70s for portions of central and southern lower MI before the strong cold front moves through Friday afternoon. The confidence on this timing of the cold front is actually medium to high, as models agree within just a couple of hours even at day 4. Instability should be higher ahead of the cold front Friday morning and especially afternoon. Combine that with temperatures near 70 and dewpoints potentially near 60, thunderstorms will be possible and will be included in the forecast. As far as strong/severe storms, this is a trend we will need to monitor throughout the week and a threat that, at this time, based on current cold front forecast timing, would be highest east of US-127. Temperatures will drop significantly behind this front Friday night and highs this weekend will only be in the 40s. It looks like this active weather pattern will continue through at least the end of this month as the Polar Jet Stream continues to separate the warmer air southeast and the colder air northwest. This is somewhat reflective of a La Nina type weather pattern, which would make sense, since we are in a La Nina currently. This type of an active, wet, weather pattern could be foreshadowing what portions of the upcoming winter may look like. If the pattern does stay this active, it’s only a matter of time before the Jet shifts just enough to allow snow into our forecast. As we see this week, though, the Jet is far enough to our west still to allow 60s and potentially 70s briefly into our forecast.

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