Category: Ensemble Discussion

Updated: 04.29.21 @ 7:42a

Before we dig into some of the wetter trends being shown on the majority of forecast models, let’s review the basis of the medium to longer range forecast through the 1st half of May.

We’ll start with the MJO (Madden-Julian Oscillation). This is forecast to be quite amplified into May, swinging through Phases 1, 2, and 3. These are cooler than normal phases this time of year. Phases 2 and especially 3 are wet.

The 2 primary teleconnections we lean on this time of year include the EPO (East Pacific Oscillation) and PNA (Pacific North American pattern). While we still keep close tabs on the NAO, the influence it has begins to wane compared to late winter into mid spring. In any event, the EPO is largely forecast positive (a warm signal) while the PNA is forecast negative (also a warm signal).

Let’s dig into the data. As it’s Thursday, we’ll start by taking a look at the new JMA Weeklies. Wetter than normal with seasonal temperatures sum up the upcoming 3-4 weeks.

The CFSv2 Weeklies show a wet, cool (compared to normal) theme for our neck of the woods. Warmth is constant across the Southeast.

The GEFS and EPS are in relatively good agreement as we look at the upcoming couple of weeks. Both show a wetter than normal pattern from TX into the Northeast, including the Ohio Valley and Great Lakes.

The GEFS is trending significantly cooler in the Week 2 timeframe and given where the MJO is heading, it wouldn’t surprise us if other models cool from where they currently are during this time period.

While the EPS is trending cooler Week 2, it’s not nearly to the magnitude of what the GEFS shows above.

Given the pattern drivers discussed to start, we should enter a rather active weather pattern into the 1st couple weeks of May. While these are likely to be fast moving storm systems (usually not depositing excessive rainfall amounts), the frequency of the systems will likely add up over time (above normal rainfall). The wetter trends depicted on the modeling are hard to ignore. I would also keep close tabs on that Week 2 timeframe for the potential of cooler trends to show up and feel the GEFS is doing the best job from this distance.