Over six inches of rain in August, two inches above normal in the Twin Cities and in southeastern Minnesota where over 9 inches has fallen a two month's worth of rain in just one month. The trails have been tacky, downright damp at times as tropical-like rains poured over the metro. There were five days this August with over one inch of rainfall.
Drier days have returned with some of the nicest weather this summer through Thursday. Dewpoints remain in the 50s resulting in low humidity and comfortable riding conditions. In addition, a stronger southwesterly wind will further dry out the singletrack. This reprieve is short-lived, however, as yet another heavy rain event returns this weekend.
A return of rich moisture and a stalling front spell out soggy weather starting Saturday night lasting through Tuesday of next week. Forecast models hint at widespread rainfall amounts of 2-4 inches through Tuesday.
Take Home Message: get your dirt riding in now while the humidity is low and the sky is dry. Labor Day weekend will likely be a wet one.
Mid level steering currents (black lines) indicate a west to east flow over Minnesota. Embedded within this westerly flow aloft will be cold pockets of air/mini low pressures (yellow & red blobs) capable of producing rain over the area from time to time. Subtle ridging (black lines bulging north) allows warm and slightly humid air to remain across the Midwest. This pattern stands to continue into Labor Day making for a dicey forecast over the holiday weekend.
September is known for being a changeable month as cold front this time of year can mean business. Looking ahead, however, summer warmth holds on strong through the first full week of September. No signs of a serious cold front anytime soon.
Evaporation rates increase early this week with the return of a warm, south wind. Tacky trail conditions quickly turn wet as thunder and lightning erupt along a cold front Tuesday night. Once again these thunderstorms can be heavy rain producers. Trails will get a chance to dry out the remainder of the week before rain creeps back in the forecast over the weekend.
Forecasting Water Flow
Last week the National Ocean and Atmospheric Administration (NOAA) announced the new National Weather Model that "will improve resiliency to water extremes in American communities." Previously NOAA was only able to forecast for 4,000 water locations every few hours. Now "the National Water Model uses data from more than 8,000 U.S. Geological Survey gauges to simulate conditions for 2.7 million locations in the contiguous United States."
From farming to recreational activities like mountain biking, this model will be able to give more accurate and frequent water information. Thomas Graziano, Ph.D., director of NOAA’s new Office of Water Prediction at the National Weather Service explains:
“Over the past 50 years, our capabilities have been limited to forecasting river flow at a relatively limited number of locations. This model expands our forecast locations 700 times and generates several additional water variables, such as soil moisture, runoff, stream velocity, and other parameters to produce a more comprehensive picture of water behavior across the country.”
Summer Thunderstorms. While thunderstorms dampened the singletrack Tuesday even heavier, more widespread rain arrives late Thursday into Friday. This late-week rain is associated with a sharp cold front that will bring a drastically different airmass into the Twin Cities.
Cooler by the Weekend. By the weekend a stiff northwest flow will funnel cool and very dry air into Minnesota. High temperatures in the 60s are certainly possible north of St. Cloud. Dewpoints are even expected to bottom out in the 40s making for a real fall feel to the air.
Observed Rainfall & Departure from Normal Past 7 Days
Abundant Rainfall. The Twin Cities received nearly 3 inches of rain the past 7 days. Locations just south and west of the metro saw even more. Rainfall for the month is now running between 2"-5" above normal for August.
The transition from a warm El Nino to a cooler La Nina has been made in the eastern Pacific Ocean. Even a La Nina Alert has been issued. This anomaly generally favors drier than normal conditions across Minnesota into the autumn season. The Dakotas have been experiencing a worsening of drought conditions. Luckily, due to recent heavy rains, drought is very minimal in Minnesota. We may still see rapid drying September-October but for now the large scale weather patterns will keep drought at bay.
The long range upper pattern features a persistent trough of low pressure over the Pacific Northwest. This will make for an active northern branch of the jet stream routinely sending storms across the Northern Plains and Midwest. Above normal precipitation is favored from the Northern Rockies to the Great Lakes through mid-August.
Above normal temperatures can be expected as an upper level high pressure remains anchored across the central and eastern U.S. Enhanced above normal probabilities are relatively low across northwestern Minnesota yet high in the Twin Cities and southeastern Minnesota.
The Cuyuna Lakes Mountain Bike Trails had over 11 inches of rain in July; the wettest July ever on record for the area! St. Cloud's Jail Trail had the 9th wettest July with a daily record rain on the 11th of the month. As it turns out the Twin Cities had above average rainfall but no records..
Summer stickies linger through midweek before cooler, drier air takes over this weekend. The precipitable water forecast model (below) says it all. A frontal boundary wavers back and forth over the Midwest this week before finally pushing south on Friday. The drier air (brown) is very noticeable over the area by Saturday.
While the heaviest rain stayed north of the Twin Cities Tuesday morning an even greater chance of rain (and severe thunderstorms) exists Thursday. The Storm Prediction Center has already highlighted the area for severe thunderstorms.
Severe THREAT thursday
Summer brings warm afternoons perfect for biking, but the summer heat and humidity can also spark thunderstorms and severe weather. Be prepared for any type of adverse weather headed your way with Aeris Pulse.
NWS Twin Cities Weather Story