Inside weather baseball: Tracking the rain-snow line
Location of 32-degree isotherm critical in determining snowfall totals
Go Deeper.
Create an account or log in to save stories.
Like this?
Thanks for liking this story! We have added it to a list of your favorite stories.
Here’s a little meteorological inside baseball.
There are several critical numbers that meteorologists use to indicate certain weather thresholds. This is a little geeky, but here are a few numbers that mean something special to meteorologists.
The 20C isotherm at 850 millibars about 5,000 feet above the ground. (A common indicator of temperatures at ground-level may reach 90 degrees in summer.)
The “540 line” is a common rain-snow indicator. (As in 540 decameters of atmospheric thickness value between the ground and about 18,000 feet above the ground.)
0 is a common threshold for the Lifted Index for thunderstorm instability. (Subzero values indicate an unstable atmosphere capable of producing thunderstorms if lift is present.)
There are many more numbers that mean something special to meteorologists. But when it comes to pinpointing the rain-snow line, the 32-degree isotherm (0C) is critical to pinpointing the rain-snow line in storms.
There can be a variety of liquid and frozen precipitation types depending on how the 0C line sets up in the lowest mile of the atmosphere.
Turn Up Your Support
MPR News helps you turn down the noise and build shared understanding. Turn up your support for this public resource and keep trusted journalism accessible to all.
Thursday rain-snow line?
Our inbound storm system Thursday and Friday presents some interesting early forecast challenges.
There’s growing consensus that a storm will arrive. (high confidence)
There’s growing consensus that significant rain or snow will fall. (medium confidence)
There’s a high degree of model spread on where the rain-snow line will set up. (low confidence)
Take a look at some of the forecast model output from Monday.
American model
NOAA’s GFS model has been painting the 32-degree (0C) isotherm near the Twin Cities late Thursday. That scenario would mean heavy snow north and west of the Twin Cities, with rain from the metro south trending toward snow by Friday morning. This would place a band of heavier snow across the Twin Cities early Friday morning.
Canadian model: Northern outlier
The Canadian model is a little further north. That scenario would shove rain and the heaviest snowfall zone farther north.
European model: Southern outlier
The often trusty Euro is taking the southern route with this system. Under this scenario, the heaviest snow bands would layout across southern Minnesota generally south of the Twin Cities.
Let’s see if we get greater model consensus Tuesday.
Stay tuned.
