REX BLOCK, LOVE IT OR HATE IT

A Rex block is simply a term named after the meteorologist who first identified the pattern, Daniel Rex. It is defined by a strong high pressure area with a region of low pressure "underneath" or south of the high pressure. The jet stream often resembles a backwards letter S in this type of atmospheric structure. It's called a block because it causes the air to swing in near stationary loops near the same longitude. The overall wind flow makes little eastward progression due to the north-south alignment of the jet steam, resulting in a stagnant weather pattern that can last a week or two.

Once the block is established, what you see is generally what you are going to get for an extended period of time. If you are in the "wrong spot", the weather is likely to be cool and stormy, with multiple days of rain or snow. In the coming case, the Midwest will be under the influence of high pressure. That causes subsidence (sinking air) which compresses the air and heats it up. Additionally, it puts us in an area that features minimal moisture and forcing that simply adds up to a lengthy period of warm, dry weather. For this time of the year, we are decidedly in the "right spot" for summery weather.

Another feature which should enhance the pattern is the MJO (Madden Julien Oscillation). It's kind of a jumbled mess, but if you focus on the most concentrated squiggles of yellow, the majority of the EURO's ensemble members are shown in phase 2 now through the first week of October. (Phase 2) is known to be prime time for Atlantic tropical cyclone formation and intensification. A slow-moving MJO in this phase creates especially favorable conditions by reducing vertical wind shear over the Caribbean and the Atlantic's Main Development Region.

Sure enough, the tropics are heating up, with two tropical cyclones shown in the Atlantic by next Monday. One stays out to sea, the other spins into or remains just off the coast of the Carolina's. The ensembles of the EURO show the range in locations of possible tropical systems Monday evening. As these eventually track NE through the western Atlantic, they will further enhance the strength of the Rex Block, making it harder to break the pattern down until the MJO gets out of this favorable phase.

I mentioned earlier how we are setting up for a prolonged period of dry weather, and MJO phase 2 precipitation analogs do show a high probability of below normal precipitation across the nations' midsection.

Look how nicely the analog matches the actual rain departures shown on the EURO below. Basically, teleconnections are telling me the next 7–10 days make for an unusually high confidence forecast with regard to warmth and dryness.

These are the actual rainfall departures shown on the EURO for the 10-day period ending October 6th.

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HIGH AND MIGHTY...

Regarding temperatures, here's what the EURO indicates in the Quad Cities for the next 15 days. This should impress you, a 13-day stretch of highs in the 80s, with several days close to 90. I don't have the records for such things, but if we managed to accomplish this feat, I maintain it could very well set a record for consecutive days with highs in the 80s so late in the season

Ever curious, I asked Chat GPT for a deep dive on warm streaks in late September and October and came up with this. It's artificial intelligence but seems accurate to me.

🌡️ Quad Cities (Moline) Climate Records

• Longest “Indian Summer” streaks (80s into October):

  • Sept 26 – Oct 2, 1971 → 7 days in the 80s.

  • Sept 24 – 30, 1994 → 7 days.

  • Sept 25 – Oct 1, 2007 → 7 days (several upper 80s to near 90).

  • Sept 27 – Oct 3, 2011 → 7 days.

    
    

📊 What This Means

• The record-longest consecutive streak of 80°F+ highs after Sept 20 in the Quad Cities is 7 days, and it’s happened a handful of times in the past 50–60 years.

• Going much beyond 7 straight days into October hasn’t been documented in the modern record.

• By October, you may get isolated 80°F days, but never 1–2 weeks straight.

To be short and sweet, the remainder of this weekend is going to be exceptional. Look for sunshine, low humidity, warm days, light winds, and low humidity. This ain't your average late September weekend. Enjoy and as always, roll weather...TS