The Forecasting Process, page 13 of 20

Rapid City, South Dakota: The big Picture

I place the windshift around 00Z, at the time of the first map. The pressure trough is right on top of RAP; as it moves east, RAP will be on the backside of the trough, with a pressure gradient that implies northerly or northwesterly geostrophic winds. So the cold air ought to arrive before the beginning of the forecast period, 06Z.

While I'm on the big picture, I take a look at the precip forecast. It's not good news. A major swath of precipitation is forecast to develop between 00Z and 12Z (map 1 and map 2) right over RAP, with nearly an inch forecasted to have fallen by 12Z. More rain is forecasted after 12Z, but it's a bit difficult to get an exact number because there's such a rapid variation of precipitation across western South Dakota. The bottom line is, it looks like the model is forecasting category 4 or category 5.

Developing precipitation is never good news. If something is not supposed to form until after you make your forecast, you have no way to determine whether the model is right so far.

Questions or Comments

Scientific: E-mail John Nielsen-Gammon < n-g@tamu.edu >
Technical: E-mail John Fulton < jdfult@nimbus.met.tamu.edu >