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COMMENTARY

A brief respite from the heat, but higher temps should return

Don Paul

First a quick sidebar look ahead to the Game of Games forecast in this young season with you-know-who next Sunday. We won’t match the 85 degree high in the Bills-Bengals game, but shivers will be in rare supply unless someone spills a cold drink on your pants. As of this writing, it appears a weak cool front will sink to our south Saturday night, possibly accompanied by a few brief showers. The front should be far enough past us by Sunday morning to allow abundant sunshine, low humidity and slightly above average (upper 60s is average) temperatures to prevail.

The timing of this front would allow game time temps to be in the comfortable low 70s, as opposed to the low 80s likely on Saturday ahead of the cool front. Light northeast winds would not be a real factor in the game, unlike this past game’s brisk southwest wind. The one possible caveat would be a slowing of this front, which would cause overcast skies and a few showers to linger into Sunday, at least in the AM.

As for the overall warm pattern, our coolest days this week will be Tuesday and Thursday, with readings in the mid-upper 60s. We’re back to the 70s on Wednesday and again Friday, with a summery Saturday to follow. The two cooler days are associated with the passage of cold fronts. However, the air masses behind each front is Pacific in origin, rather than from the far northwest reaches of Canada. In such a pattern, the coldest temperatures tend to be confined to the northwest quarter of the U.S., particularly in the northern Rockies.

What we have seen this month is a prevalence of warm high pressure stacking up over the eastern U.S. and cooler low pressure troughing over the Pacific northwest. Posted by SUNY Albany’s Dr. Alicia Bentley, this is what the American GFS ensemble is showing for next Saturday, which doesn’t look all that different from what we had in place this past weekend.

If you eyeball this pattern, you may sense it is something of a high amplitude pattern with a big ridge and a big trough. This kind of high amplitude can tend to be “blocky,” slowing progression of weather systems. As I’ve written many times, the more frequent blocking episodes in the northern hemisphere has a strong link to arctic warming and the weakening of upper-level winds. Other factors can include sea surface temperatures that are anomalously warm near the Pacific coast and off the middle and southeast Atlantic coast, along with some other oscillations, but it is the arctic warming that has been the most consistent forcing mechanism in stalled systems. The latter includes the disastrous stalling of Dorian over the northwest Bahamas, Harvey in 2017 near Houston, Florence over the Carolinas last year, and what had been tropical storm Imelda over southeast Texas, producing more than 40 inches of rain in a couple of days not far from Houston just a few days ago.

The next somewhat esoteric chart was posted Monday by Greg Carbin, chief of the Forecast Operations Branch of the National Weather Service. It shows the geographic coverage from 25 of the wettest U.S. tropical cyclones that have occurred since 2005. The majority produced such enormous rainfall totals because of their slowed or stalled forward motion which has, again, become more prevalent in this era of warming.

The mean global warming has had less of an impact in Western New York than in quite a number of regions in the northern hemisphere, but that is not to say the impact hasn’t been significant. For example, in the autumn months the trend since 1970 has been clear. It’s not linear, and not every autumn has been milder than average, but the majority of autumns have been warmer. Official climate data is supplied by Climate Central:

The current warm ridging in the east and cool troughing in the Pacific northwest extends into the start of October.

Even as we extend into the second week of the month, there is still no pathway evident into the east for any truly cold air from northern Canada. The Pacific west-to-east flow continues in the ensembles.

This kind of a pattern does not preclude any cool days. Further out in time, the ensemble tends to flatten out from the high amplitude. That is because the 21 individual member model runs of the GFS ensemble spread farther apart from one another in a “spaghetti chart.” That spread-out spaghetti tends to smooth the ensemble mean 16 days out.

The spaghetti earlier in an ensemble is more tightly organized, implying greater certainty.

Confidence in the mean Pacific flow wanes in the Climate Prediction Center/CPC experimental weeks 3-4 outlook. One would naturally expect higher probabilities for cooler temperatures by mid-October due to seasonal climatology. The white “EC” designation for our region suggests high uncertainty – equal chances – for temps to run above or below average. Prior to this time period, CPC is firmly in the camp of higher probabilities for above-average temps in the east. Something of a change is brewing in their minds as of mid-October.

That may be, but the long-range ensemble mean of the European, which has 51 model run ensemble members (compared to the American GFS 21 members) still points to higher probabilities for above-average temperatures to prevail in the east well into late next month. My bottom line: I do not yet see a lasting transition to a colder pattern in the next few weeks.

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