CHRISTMAS IN JULY...

There's some active weather coming our way for the late week period that includes thunderstorms and potentially bands of heavy rain. Next week, around the 17th, models are consistently pointing towards a stretch of cool mid-July weather with several days in the 70s, at what typically would be the hottest time of the year. That's what I call Christmas in July! Before some thoughts on that, here's what going on with the storm threat in the short term.

Following a warm and generally dry day Wednesday (just a couple stray storms in the south), the pattern begins to turn more active Thursday and Friday with the addition of multiple lobes of storm producing energy. The first round of positive vorticity and its forcing is slated to arrive on Thursday morning in the form of a decaying thunderstorm cluster. How far it can penetrate into my counties northwest of the Quad Cities is questionable before it dissipates. My counties well west of the Mississippi have the best shot at seeing anything from this activity. It's far from certain if it can hold together.

An additional challenge will be outflow boundaries (mini cool fronts) from the decaying storms. With afternoon heating, these cool pockets could initiate new storms when the convective temperature is reached. Generally, these pulse single cell storms are fairly scattered and coverage should be less than 40%. Due to very high levels of water vapor, heavy downpours and gusty winds are possible where any updrafts develop. A common theme of our weather lately. In summation, some storms will likely occur Thursday, particularly over the north and west. Otherwise, temperatures will be a challenge, ranging from the low 80s north to near 90 in the south. It will also be more humid.

Thursday afternoon's storms should dissipate after sunset, leading to a quiet period until the late night hours. At that point, warm advection and an intensifying low level jet could fire additional storms, especially over the north. Any of these would also have the ability to dump locally heavy rain.

By Friday morning, vast amounts of tropical moisture are flowing into the region, leading to very muggy conditions. Water vapor ahead of the primary energy is shown to be as high as 2.20 inches which is in the 90th percentile of NWS soundings in Davenport. With a boundary laid out across the region, there is certainly strong evidence for a swath of heavy rain and potentially strong storms. Models are still struggling to reach a consensus on when storms will develop and the amount of instability they will have to work with. The mesoscale details will not become clear until Friday, after the details of Thursdays storms are known.

It is looking like the baroclinic boundary holds nearly stationary into Friday evening. With minimal movement of the instability axis, (multiple thunderstorms) could roam over parts of the area, producing training and excessive rains and a flash flood threat. The situation needs to be closely monitored going forward. The 3k NAM has very high instability in place Friday afternoon with big CAPE over 4,000j/kg.

The instability is not surprising with approaching water vapor levels of 2.37 inches.

And highs of 87-91 fueling the energy.

It's a well known fact models struggle with rainfall forecasts when the element of convection is at play. Thus, what I'm showing is not to be confused as fact. It is just one model's interpretation of what the parameters it sees the next 48 hours could produce as far as rain. I highly doubt 7 inches of rain will fall in Dubuque, and I'm not calling for it anywhere. However, that is a disturbing trend, even if amounts are cut in half. There is some reason to be concerned about excessive rains, and I could certainly see amounts of 3–4 inches plus in some local band with water vapor as extreme as is shown. This is not intended to be hype, just a cautionary statement regarding early potential. Other models are not as high, but they are also not convective allowing and thus would tend to be lower as a rule.

At least at the moment, the WPC shows slight risk assessments of excessive rain Thursday night and Friday night.

Hopefully, a cold pool develops Friday night from the storms to force the boundary far enough south to take the threat of heavy rain out of the southeast Saturday morning. That trend is evident, but any slowing of the system could keep things wet into the day Saturday, especially in the south. By Sunday, cooler and drier air should bring a chance to dry out in those locations that get into the heavier rains.

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CHRISTMAS IN JULY...

As I mentioned at the top, models are suggesting a healthy dump of cool air by July standards near the 17th. The EURO shows 4 days in the 70s from then on to the 24th, which is tough to do in mid-July.

One of the factors that helps with confidence regarding the trend is the MJO (Madden Julien Oscillation). It is shown moving through phases 6, 7, and 8 starting the 18th going into August 8th.

As you can see in the phase correlation products below, all of those phases in June, July, and August analog to below normal temperatures in the Midwest. Phase 6 and 8 on the significant percentile analogs show especially strong chances.

How about these departures, the morning of July 18th. Wrap it up, that's Christmas in July.

That's where things stand for the time being. We'll see how details evolve tomorrow on all of this. Roll weather...TS