Verification (with Low Population)

The target area yesterday was very small, hugging the U.S.-Mexico border from the Big Bend region of Texas northward and westward to New Mexico. This area is sparsely populated, which becomes an issue when trying to verify forecasts of severe weather. The United States is far from the only country to have this problem - one participant gave a talk this week that mentioned how the area with the most severe weather in South America is also sparsely populated. When we're forecasting for an underpopulated area in the experiment we have to examine metrics other than Local Storm Reports (LSRs), particularly because the verification of yesterday's forecasts is the first activity each morning.

High-Resolution Verification Challenges

Afternoons at the Spring Forecasting Experiment involve some forecasting activities, but much of the time is spent doing evaluations. These differ between the two desks and from year to year, as we subjectively verify cutting-edge diagnostics and model updates. Specifics on this years' verifications will be the feature of a future blog post. Inevitably, during the evaluations aspects of both the products we're evaluating and the evaluations themselves are discussed, and even the facilitators don't always have easy answers to the questions participants raise. But that's part of the informal atmosphere (pun somewhat intended) that leads to better understanding between forecasters and researchers, and allows for the communities to brainstorm improvements. Today, such a question came up on the total severe desk: how do we verify high-resolution forecasts when we don't have high enough resolution in our observations?

MPAS forecasts for 16 May 2016

Yesterday's forecasts were incredibly consistent between CAMs in developing a supercell or two in the vicinity of southern Colorado and the Oklahoma/Texas panhandles, before growing those storms upscale into an MCS that would then sweep across Oklahoma overnight. Due to the consistency of these CAMs, our full period outlooks showed high probabilities, with high certainty, over a relatively small area:

Question of the week: Will we get recovery?

Last week, the overarching question plaguing the SFE daily was a fairly simple one: Will we get recovery? Due to low moisture across the Gulf of Mexico from a front that swept through during the weekend of May 7-8, instability was hard to come by last week. Since the necessary requirements for severe convection are lift, shear, and instability, this question is extremely relevant to our daily activities. On the other hand, it gave our participants the chance to deal with a forecast scenario that is fairly common, if unusual for May: how do we forecast when we have high shear, but relatively low instability? Last week, CAPE values were typically around 1500J/kg or less - sufficient for severe storms, but low enough that the questions of whether that CAPE would be realized and whether significant severe weather would occur.