May 2021 archive

Updated 05.07.21 @ 8a

Many find themselves waking up to the upper 30s this morning.

While certainly chilly by May standards, we’ll be even colder tomorrow morning. This will come behind a passing upper level disturbance that will likely kick up another round of scattered thunder (some storms may contain small hail) this afternoon and early evening. Lows Saturday morning may rival records in spots. The record low in Indianapolis tomorrow morning is 31° set in 1976 and 1947.

We still anticipate a Mother’s Day soaker (rain may begin around sunset Saturday after what should otherwise be a very nice day), including embedded thunder. Rainfall totals with this system will check-in between 1.5″ and 2″ for most, including locally heavier totals above 2″. The axis of heaviest rain is forecast from Indy and points north with the latest American model guidance and central and southern portions of the state from the European guidance. Expect the consensus of modeling to improve on precisely where the heaviest totals setup over the next 24 hours.

The primary purpose of this morning’s post is to look at the chilly start to May and where we think things are headed for the 2nd half of the month.

The “revved up” MJO (into the traditionally cold May phases) initially is what tipped us off to the cold open to the month. For those that have been paying attention to the modeling, you could see how the data had to continue correcting colder and colder up until “real term.” Officially, we’re running 1.6° below normal so far, but with the cool in the week ahead, that will grow much more impressive in the days to come.

This should come as no surprise with us set to move strongly into Phases 2-3 over the course of the upcoming 7-10 days. Note greatest temperature departures from normal occur across the Ohio Valley in these phases in May.

What’s more interesting is what transpires after this period (mid and late May). The MJO is expected to head into the “null phase” for a time.

One could extrapolate the data and build a case we’re headed for phases 7-8 to close the month. If so, things would moderate (against the norms) by Phase 8.

This is something we’ll watch. If we do, indeed, get into Phase 8 prior to Memorial Day, we’d expect the heat to build to close the month. The transition will likely be less significant though. The thinking here is still relatively cooler than normal mid-month before moderating closer to and/ or slightly above normal prior to Memorial Day.

From a precipitation perspective, the pattern continues to look quite active for the foreseeable future.