July 25th Central Minnesota Weather Discussion
July 25th Central Minnesota Weather Discussion
By Aidan Cera
For the first time in a long, long time, I have quite a bit to talk about today with regards to both the excessive heat across central Minnesota and the continuing severe storm risk through much of this week.
The Heat
Fig 1. NWS Twin Cities Maximum Temperature Forecast Through Monday 07/31 For Central/Eastern Minnesota and Western Wisconsin.
Yesterday was quite toasty for central Minnesota with highs reaching into the mid to upper 80s for a decent chunk of the area, at least before the scattered thunderstorms blew up and multiple outflow boundaries and cold pools were spread across the area. Today will be even warmer without any afternoon thunderstorm activity expected. Given the abundant sunshine, highs today should climb into the low to mid 90Fs with dew points in the mid to upper 60Fs. These high temperatures and dew points will yield heat indices near 100F or so. Given these conditions, it is highly recommended that any outdoor activities should be limited and those who are required to stay outside for long periods of time should drink PLENTY of water (at least 24-36 ounces per hour) to stay hydrated and avoid heat exhaustion or heat stroke.
Tonight lows are expected to dip into the lower to mid 60Fs across most of central Minnesota. Rain chances could lead to lower temperatures in our southern and northern counties otherwise a mild night lies ahead.
For Wednesday, the heat will intensify even more so, with highs generally in the mid to upper 90Fs across most of central Minnesota, with a few exceptions in the lower 90Fs closer to Brainerd, MN. Lows Wednesday Night may not get much lower than 70F for a majority of the area with a very light breeze only around 5 mph.
Thursday will not be any better and will likely be the hottest day for most just before the cold front passes through. Highs are expected to range from the lower 90Fs (closer to Brainerd) to potentially near 100F (closer to Monticello and the Twin Cities). Winds could be slightly stronger out of the SSW at 5 to 10 mph but these winds will not result in much relief from the heat. The moral of the story is that the next 3 days are looking very hot and humid, and highs in the 90Fs with dew points as high as near 70F expected.
Fig 2. NWS Twin Cities Information Regarding Excessive Heat, The Dangers It Poses, and What You Can Do To Prevent Negative Health Effects From It.
The heat finally looks to abate slightly going into Friday after the passage of a cold front Thursday Night. Winds are also expected to increase out of NW behind the cold front, which should bring in some cooler air behind it. Storm chances also diminish after the front passes through, leading to a much more pleasant weekend ahead with plenty of sunshine and cooler temperatures.
The Storms
Fig 3. Storm Reports From 07/24 Storms Issued Tuesday 07/25 By NWS Twin Cities.
Yesterday central Minnesota and eastern Minnesota saw pop up thunderstorm activity during the late morning and afternoon hours with some storms producing severe weather. Most reports came in from eastern Minnesota and western Wisconsin but central Minnesota was treated to some rather adverse weather as well. Lightning struck downtown St Cloud leading to power outages for many areas near St Cloud State University Campus despite no rain falling in the city.
Thankfully, no storms are expected to pop up today so I don't think we have to worry about loosing power again in the St Cloud metro, but storm chances return overnight tonight for parts of central Minnesota as a potent Mesoscale Convective System approaches from the west northwest.
Fig 4. NWS and SPC Graphic For Severe T-storm Chances Across Minnesota This Evening Into Tonight. Issued 07/25 At Around 9:00 AM CST.
There is a slight risk of severe weather according to the Storm Prediction Center (SPC) for central Minnesota's southern counties including portions Kandiyohi, Meeker, Pope, McLeod, Sibley counties and all of Renville county. A marginal risk of severe weather follows the I-94 corridor through much of Stearns, Meeker, Wright, and down to Carver and McLeod counties. The primary threats from any severe thunderstorms will once again be large hail and damaging winds. There is no tornado threat predicted by the SPC at this time.
Looking at water vapor imagery, there appears to be a shortwave trough advecting rapidly eastward across Montana and Alberta this morning. This shortwave seems to be the focus for broad scale ascent as indicated by higher level and mid level cloud coverage across the Dakotas. This region of ascent will be the main focus for today as it tracks further east and taps into higher heat and humidity values across eastern North and South Dakota. Rapid supercell development seems quite likely given the expected perimeters with decent shear vectors and steeper (although conditional) lapse rates. In basic terms, strong thunderstorms are expected to develop across eastern North and South Dakota this afternoon due to forced rising air ahead of the trough with ample moisture in the air to feed the developing thunderstorms.
Thunderstorm development should take place later this afternoon into the evening hours across the Dakotas, with storm profiles being highly elevated in nature initially due to rather dry air at the surface. As storms work their way into western, central and southern Minnesota, however, cloud bases should lower aiding in cold pool progression associated from previously elevated convection. As a result, damaging winds will likely be the main threat as these storms pass through portions of central Minnesota later tonight. Track of the storms is going to be highly dependent on where the storms fire and how quickly the converge together into a multicellular mode, so this will be an evolving situation and finer details won't be known until later.
As of right now, I do not expect these storms to impact areas along or especially north of I-94, as most mesoscale models show these areas being mostly dry. Our more northern counties may see some more synoptically forced shower activity but I don't expect that to be any further south than Morrison and Todd counties. It looks like our most drought stricken parts of central Minnesota will miss out yet again tonight sadly. Areas closer to Granite Falls and Willmar could see significant rainfall overnight from this system however. The NWS Twin Cities is explicitly forecasting 1-2 inches of rain for this area given the high PWAT values in this area due to high humidity (more water in the air for the storms to squeeze out). This will be the theme for much of the week with any storms that do fire thanks to the higher humidity values expected.
Fig 6. GFS 250mb Wind Speed/Streamlines (kt) & MSLP Extrema (mb) For Tuesday Through Saturday. Imagery courtesy of tropicaltidbits.com.
Heading into Wednesday and early Thursday things look dry across central Minnesota with storm chances returning Thursday afternoon and evening. We are in a weather pattern dominated by both a strong ridge of high pressure in the southwestern CONUS and shortwave trough propagating around the periphery of the ridge, leading to frequent storm chances for those on the ridges periphery. Thursday and Friday is the time period I will be fairly concerned with given the high dew points and temperatures expected this day and the passage of the cold front. High dew points will mean high PWAT values once again, and the NWS Twin Cities is already putting out high precipitation totals for Thursday Night. Friday may be a day to watch as well, however, there is considerable model disagreement on how things may play out, so not going to go into much detail at this time. The important thing to remember is that we are in a weather pattern where things can change rather quickly, so it will be important to keep an eye on the weather as the days progress for any updates with regards to storms that may take place.
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