St. Cloud, MN Weather Forecast

Early Wednesday Storms Meant PM Storms Mostly to Our East

Why do I often say that it is difficult to forecast afternoon and evening thunderstorms until I can see where the storms from the previous night end up? The warmest and stickiest air ends up on the southern and eastern flank of the old clouds and the atmosphere creates a mini-front (outflow boundary) with a wind shift and a difference between the ripest air and the air that was cooled by the rainfall from the previous night.

That is what happened yesterday afternoon. The strongest afternoon and evening thunderstorms developed on the edge of the leftover clouds in eastern Iowa and Missouri (see College of DuPage North America clean infrared satellite loop). Some of those storms moved through south central, southeastern, and east central Minnesota on their way into Wisconsin (set number of frames to 200 on the College of DuPage north central US radar loop). Those storms produced wind damage from wind gusts of 60-80 MPH.

The main cold front did push west-to-east into Minnesota by late afternoon (see NWS WPC 24-hour loop of Continental US surface maps), but the couple of lines of thunderstorms were dwarfed by the storms to the east and southeast. A couple of the storms did produce hail of 1 3/4 to 2 1/2 inches diameter (baseball-sized) near Wadena and Villard.

The rainfall totals were again light (0.10 inch in Rochester, Trace at Minneapolis-St. Paul International Airport and St. Cloud) except in northern Minnesota (Duluth 0.53 inch). We've had a number of days with some rain from thunderstorms (6 of the past 8 days in St. Cloud, including the early morning 0.13 inch from yesterday). In St. Cloud, the June total is up to 0.97 inch, but that's still a quarter inch behind the average. So, this rain isn't helping make up the six and a half inch precipitation shortfall since last August.

Thunderstorms Don't Help the Water Budget as Easily as Cool Rain

That's the trouble with using thunderstorms to catch up on rainfall. First, the thunderstorms only produce spotty heavy rainfall. Some parts of central and western Minnesota have picked up more than 2 inches of rain during the past week (see yellow areas when you set NWS Water Prediction Services Minnesota map to yesterday's date and last 7 days period), but there are areas with under half an inch (dark blue). And, the rain falls typically in very warm air, so the evaporation rate is higher. So, the rain doesn't linger on the ground as long as during the colder season. In Minnesota, unfortunately, most of our precipitation happens during the warm season (see steepest climb of light green line, average precipitation, on the St. Cloud annual precipitation map).

Cooler Pattern With Scattered Showers (Not Significant Rain Potential)

We are now in a new pattern of flow, which will continue well into next week. A series of low pressure systems from the northeastern Pacific will reinforce the current low as it moves into western Ontario. We are now in considerably drier air (dew points in the more comfortable lower 50's, see UCAR hourly dew point map, versus yesterday afternoon's upper 60's, see NWS: last 72 hours of St. Cloud observations). So, the air has lost about half of the moisture from yesterday. There will be frequent chances for scattered rain showers and perhaps a thunderstorm, mainly because the nearby upper-air low will have a cold pocket of air aloft. That should allow highs in the 70's or perhaps merely near 70 to produce the necessary 80-degree temperature gap between the ground and about 3 miles up each midday and afternoon. That will allow scattered showers and perhaps even a thunderstorm, but these will be brief and most of us won't get much (see Days 2-7 potential rainfall on the NWS WPC quantitative precipitation forecast).

50-50 Chance for Showers This PM

That rain chance will be 50-50 today as the upper-air low pushing into Manitoba from North Dakota (see College of DuPage North America water vapor loop) moves to Ontario. There are already some clouds to our southwest (see College of DuPage North America clean infrared satellite loop) and more will develop by midday today (current radar echoes will broaden by midday). Highs will be knocked back into the middle 70's.

Only Widely Scattered Showers Through Weekend

After today, I still have more afternoon clouds and a few scattered showers, but the chance will be no better than one in 5. Highs will again climb well into the 70's tomorrow, but a reinforcing cool shot will limit highs to no better than the lower 70's during the weekend through Monday. Overnight, it looks like there will be enough breeze to keep lows in the lower 50's, but an upper 40's low can't be ruled out. There would be a fog threat if the winds calm down, but I can't see a reliably calm night through the weekend.  

The May-like temperatures will continue until at least Tuesday. The latest forecasts have a potential storm system moving through sometime on Wednesday. That would be our next chance for significant rainfall. 

We will hold on to the cooler temperatures through at least Tuesday. There is an uncertain chance for showers on Monday, but the computer forecasts disagree about the track and timing of that system.