In a surprisingly good mood? It might be this week’s sunshine.

If you woke up in an inordinately positive mood these last few days, the reasons likely transcend the fates of the local sports teams or any discipline you may have exercised during the weekend.

The forecast has the sun shining through Thursday with highs in the 80s Tuesday and Wednesday, and near 80 Thursday — with comfortable nights nearly perfect for the Phillies-Marlins wild-card series in South Philly. (As for Friday, we’ll leave that subject for another day.)

And this doesn’t happen very often in a place that is so close to a major ocean and a substantial bay with hundreds of rivers and tributaries emptying into them: The weather service has an absolute 0% chance of rain Tuesday and Wednesday, and not far from zero on Thursday.

Clear skies are expected until Friday morning, which bodes well for the regional mood.

Various research has concluded that sunshine can be a significant mood enhancer, and the run of sunny days is especially fortuitous given that the hours of daylight are shrinking at their fastest rate of the year, not to mention the September gloom we’ve just been through.

» READ MORE: The days are losing light quickly, but the rate will slow

Here are five reasons to to be grateful.

September featured the longest heat wave of the year, seven days starting on Sept. 3. Then the rains came, and nature decided to install a dropped ceiling. The last eight days of the month were 90% cloud-covered, according to the weather service. Absence really can make the heart grow fonder.

Temperatures this week will be several degrees above normal, with a high in the low 80s on Tuesday, though that’s well below the Oct. 3 record of 90. Wednesday’s forecast high, 84 degrees, would be normal for the middle of June. Again, however, the daily record appears safe. That was set in 1919, when the Phillies weren’t in the postseason. Nor were they in 1941, which has the standing record for Wednesday, 88, and Thursday, 96. The high in New York was 94 degrees on what was the last day of the 1941 World Series, won by the Yankees over the Brooklyn Dodgers. This year’s could end Nov. 4.

Locally, The Inquirer’s coverage noted that the heat “revived the ‘summer’ vacation trade, forcing thousands of Philadelphia motorists to seek relief at seashore and mountain retreats.” Poor things!

On Oct. 4 of that year, on the last of three days of rain from the remnants of a tropical storm known as the “Saxby Gale,” Philadelphia experienced its all-time worst floods — even worse than Ida’s in 2021. The Schuylkill at Philly reached a record crest of 17 feet that withstood Ida’s challenge. Confirmed rain data are wanting — the weather service’s Philly records date to 1872 — but the rain totals must have been prodigious, especially upstream. According to the weather service, Saxby’s floods carried away the Penrose Ferry Bridge and two bridges at Manayunk. And this was long before runoff-generating highways, malls, office parks, and mega-houses. (It did not affect the Phillies. They didn’t start playing until 1883.)

No worries this week. In fact, the Atlantic hurricane traffic has slowed considerably, and that may be related to all the warm water in the tropical Pacific — El Niño — which can generate winds that tear apart tropical storms in the Atlantic.

» READ MORE: This time in 1869, Philly was under water

The sun is setting earlier, but it’s still not getting dark until after 7, and these should be fabulous days for admiring those first flecks of fall-foliage color, hors d’oeuvres for what is shaping up to be an excellent show. “I do expect a very colorful season,” said Ryan Reed, program specialist with the Pennsylvania Department of Conservation and Natural Resources, who assembles the agency’s weekly foliage reports. The warm-up may slow progress, he said, but cooler times are coming next week. He said we should expect peak around here between about the 25th and Halloween.

» READ MORE: The best places to see fall foliage in the Philly region

Numerous studies have documented that sunshine is an ultimate mood elixir. One 1990s study by a Temple University professor at an Atlantic City casino hotel found that sunny-day tipping increased by as much as 60% compared with rainy days. The sun evidently can even have a positive effect on the stock market when the sun shines on New York. But that won’t necessarily lead to riches for weather-savvy investors. “The effects are not large enough to be exploited,” wrote the researchers at Pomona College in California. “The weather does not leave $100 bills on the sidewalk.”

Just why it is that the sun has such positive effects has been the subject of extensive research through the years. It might have to do with the benefits of Vitamin D, obtained in part from sunlight, or how sunshine produces mood-enhancing serotonin.

Then again, as they said in a commercial for an extinct beer some years back, “Why ask why?”