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End in sight for consistent 100º days

AUSTIN (KXAN) — First things first, this week is going to be hot again. We’re forecasting triple digit heat every single day and it gets hotter toward the end of the week.

Highs this week
Highs this week

Now that’s out of the way, let’s look farther ahead.

An end to daily highs of 100º?

We’re starting to see some signs that a turning point away from consistent 100º days may be in sight after September 10.

Both the American (GFS) and European (ECMWF) computer models suggest the unrelenting triple digit heat may actually relent after this upcoming weekend (September 9-10).

GFS forecast highs for Austin (Courtesy: Weatherbell)
GFS forecast highs for Austin (Courtesy: Weatherbell)

The GFS begins a stretch of 90s on September 11 (see above).

ECMWF forecast highs for Austin (Courtesy: Weatherbell)
ECMWF forecast highs for Austin (Courtesy: Weatherbell)

The ECMWF begins the 90s a day earlier on September 10 (see above).

Why would temperatures drop?

Persistent high pressure over Texas or the southwestern United States much of the summer has allowed temperatures to soar.

As our ground has dried out, that’s made it even easier to heat the air. Drier air takes less energy to warm than more humid air. The drier the ground, generally the hotter it can get.

High pressure this week will remain strong and over the southwestern U.S. The heat will get worse before it gets better. Hint: The bigger and darker the red, the stronger the high.

Strong high pressure parked over the southwest and Texas late this week
Strong high pressure parked over the southwest and Texas late this week

But, look what happens as we head through early next week. The high weakens and shifts a lot farther southwest.

High pressure appears much weaker and farther south early next week
High pressure appears much weaker and farther south early next week (Tuesday September 12)

As high pressure causes sinking air and hotter temperatures, a weaker high more to our southwest would take away some of the sinking air and ease up on the temperatures. This would result in both more clouds, higher rain chances and lower temperatures.

Climatology is on our side

We’ve got a lot going for us in the month of September that spells some relief from this heat, not the least of which is that typically temperatures drop quite a bit through the month.

Average high on September 1 in Austin: 95º

Average high on September 30 in Austin: 88º

There are also several days later this month where the record high isn’t even in the triple digits. September 15, 17, 24 and 30 all have record highs in the 90s.

Now, just because a record high is in the 90s doesn’t mean we can’t top it with a new record in the triple digits, but that becomes less likely as we head through the month.

Even 2011, the hottest summer on record and the year with the most triple digits ever (90) had more 90s than 100s in September that year.

The outlook is still hot

The 8-14 day temperature outlook for the Climate Prediction Center still points toward hotter-than-normal temperatures throughout Central Texas around mid-September. Just because we expect to see fewer 100º days after this week, doesn’t mean we won’t be hotter than normal.

8-14 day temperature outlook (CPC)
8-14 day temperature outlook (CPC)

Normal highs by next week are in the low 90s, and we still should be hotter than that.

Some 100º are still possible later this month

Ending consistent triple digits doesn’t mean 100º days go away completely. I still expect some less frequent triple digit days later this month, unless we can get a widespread soaking rain to moisten up the soil and mitigate some of the warming.

Latest triple digits ever?

We’ve hit 100º in October in two years, 1923 and 1938. Both of those years had triple digits last as late as October 2. No year has ever had triple digits later than that!

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