The CPC has issued their outlook, as of yesterday, for the 6-10 day, 8-14 day and 3-4 week outlooks. This is the 6-10 day outlook, but I assure you, the other two vary only slightly.

The jet flow is going to be bifurcated throughout the next couple weeks, with a strong jet running along the northern Gulf Coast. The Polar jet will be wavering along the Canadian border, often dipping into the US as a trough, ensuring some active weather, however the jet streak to the south will be an effective barrier to moisture rising into the continental US. We aren’t anticipating many soakers around the Great Lakes. This will do wonders for the drought in the southeast, though.

Even with successive waves from the northern jet, it’s really just seasonal thermal forcing that is going to break down the feature to the south and start allowing warmth and moisture back to the north. This isn’t expected to happen until around the 11th, though, which is why we have such a lengthy stretch of below normal temperatures East of the Rockies. It’s still nearly two weeks out, but the action of the northern jet by the 11th tells me that it won’t suddenly get hot in the northern tier, with ongoing showers and storms remaining likely, which will keep temperatures a little cooler if the showers are too widespread

If you are a fan of warm weather, this forecast is a bummer. If you are a storm chaser, this is also a bummer, as this should put a damper on what is historically one of the most active storm periods on the calendar. If you live on the West Coast, you can ignore everything above and enjoy the beach.

Just after sunrise on April 27th, the SPC elevated the thunderstorm forecast for southeastern Missouri to a moderate risk. A deep upper level trough was generating a strong area of low pressure in the Plains that was feasting on the chaos of colliding air masses. Cold and Canadian with tropical and maritime. The helicity in the atmosphere meant tornadoes were likely.

There were indeed several tornadoes from Missouri to Indiana, with a great deal of damage wrought by straight line winds. The tornadoes were embedded within a line, and at some point, it becomes a bit academic as to whether damage is caused by winds or tornadoes.

The changes to the SPC and the deeper set of information within the convective outlook are new features to the thunderstorm season. I wanted to take this specific example to look at what the SPC released, and see what factors best correlate to the outlook that is provided. First, here is the outlook, issued in the early hours on Monday.

As a bit of background, the change that was recently made to the storm hazard maps added a storm intensity rubric to go along with the probability guidelines that had been a part of those maps before. Take a look at the wind and hail maps to get the idea.

So, you can see there was a high probability of strong wind, and a lower probability of hail, but the hail in the forecast was expected to be larger. We can also see that neither the high probability of severe wind, or the expectation of large hail defined the moderate outlook boundaries. That’s not particularly surprising. That the significant hail in central Texas didn’t lead to a higher outlook than a marginal risk in central Texas surprised me, though.

Moderate and high risk events generally need a threat of tornadoes, so let’s look at the tornado outlook issued at the same time as the full outlook.

The threat for strong tornadoes is only designated on the charts as 1, 2 or 3, and the probability of a tornado within 25 miles of a spot is more well defined. Perhaps it is no surprise, then, that the moderate hugs the 15% chance of a tornado risk. I’m sure it didn’t hurt the case that the forecast was a level 2 on the intensity scale, either.

For what it’s worth, here is the break down of severe reports.