An NSSL/SPC Spring Program daily map discussion

31 May 2004 - An SPC forecaster sits hunched over a keyboard in the Science Support Area of the Storm Prediction Center (SPC). He is preparing for today's Spring Program map discussion. It is shortly after 1:00 p.m. and many of the attendees are just getting to their lunch. The room is surrounded by workstations and displays and holds about eight people fairly comfortably. Today, however, all the chairs are full, leaving ten more people standing.

It is Monday. The map discussion begins with a briefing on the initial experimental forecast from the previous Friday. This "control" forecast was based on routinely-available observations and model guidance. It contains probability contours for the occurrence of severe convection. In this case the 15% contour covers a broad swath from northwestern IA into southwestern ND (upper right figure). Steve Weiss, SPC Science and Operations Officer and the PI for the SPC, points out that this forecast captured the dense cluster of reports in southeastern SD, but also contained a lot of "dead area" without any reports. "We gave it a 5 out of 10," Steve notes.

The discussion moves on to the second experimental forecast. This one was made after the forecast team had examined the hi-res WRF output, and it shows a remarkable improvement, including the addition of a 25% probability contour focusing on the region where most of the severe weather was reported and a reduction of the 15% area that eliminated much of the inactive region (lower right figure). "We gave this one an 8," Steve says, "one of the biggest improvements we've seen so far." From here the discussion moves on to comparison of the model forecasts and observations, including satellite and radar images. One look at this data and it is clear to see why there was such a big improvement in the second forecast. Two of the WRF models developed intense convective cells over SE SD in nearly perfect correspondence with the radar loop. "If the models could just do this for us every day, we'd be in great shape," Steve quips.

The map discussion moves on to the current weather and areas targeted for severe weather today. "The RUC seems to do well with initiation, but not evolution," says a visiting forecaster. "Each model has its own issues," says another.