Joe’s Weather Blog: It may feel 35° cooler this weekend! (THU-9/22)

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Good morning…great weather to start the new season today as fall arrives at 9:21 this morning. On the other hand the heat and the humidity will continue through the region for another 2 days. It may be a good idea to get some fertilizer down and maybe some grass seed (read more about that in the discussion). Some potentially significant rains are coming towards the area later into the weekend. Sunday’s weather will be a MAJOR change to what we’ve been dealing with this week.

Forecast:

Today>Friday: Hot and humid with highs near 90°. Heat index 90-95°. We may see an increase in the dew points on Friday sending the heat index values a bit higher.

Saturday: Gradual increasing clouds with highs well into the 80s.

Saturday night: Showers and storms will be increasing in coverage from the west to the east. Areas farther east of KC may not get rain till Sunday. Meanwhile this will be the change in the weather that I’ve talked about. Lows in the 60s

Sunday: Rainy and cool for a good part of the day. Cooler air coming through + a fair amount of rain means the potential of falling temperatures. There may be some sort of early AM high but I still feel that we’ll be 60-65° in the afternoon assuming we have rain out there.

Discussion:

Odds are by the time you read this blog…fall will be here. It still feels like summer but give it a few days…trust me. I was very aggressive with this temperature switch last night…my guess is the most aggressive forecasting highs only in the 60s for a few days. Let’s see how that plays out and whether I’m right or wrong.

Our average high is dropping into the mid 70s over the next few days. This air mass will be rain cooled on Sunday and potentially at least part of Monday as well. we should start warming back up towards the middle of next week…and may be setting up for some very nice weather heading into the last few days of the month!

Meanwhile today, as mentioned, is the 1st day of fall. Technically days and nights are the same but that is not true in all places today…including KC. Today is actually an equinox. Here is more information from Earth and Sky.

What is an equinox? The earliest humans spent more time outside than we do. They used the sky as both a clock and a calendar. They could easily see that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shift in a regular way throughout the year.

Our ancestors built the first observatories to track the sun’s progress. One example is at Machu Picchu in Peru, where the Intihuatana stone, shown above, has been shown to be a precise indicator of the date of the two equinoxes and other significant celestial periods. The word Intihuatana, by the way, literally means for tying the sun.

Today, we know each equinox and solstice is an astronomical event, caused by Earth’s tilt on its axis and ceaseless orbit around the sun.

Because Earth doesn’t orbit upright, but is instead tilted on its axis by 23-and-a-half degrees, Earth’s Northern and Southern Hemispheres trade places throughout the year in receiving the sun’s light and warmth most directly.

We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun.

Earth’s two hemispheres are receiving the sun’s rays about equally around equinox-time. The sun is overhead at noon as seen from the equator. Night and day are approximately equal in length.

The name equinox comes from the Latin aequus (equal) and nox (night).

Now as far as why isn’t a perfect 12 hours of daylight and nighttime…well there 2 reasons for that..again from Earth and Sky.

The sun is a disk, not a point. Watch any sunset, and you know the sun appears in Earth’s sky as a disk.

It’s not pointlike, as stars are, and yet – by definition – most almanacs define sunrise as when the top of the sun first touches the eastern horizon. They define sunset as when the sun’s upper limb finally touches the western horizon.

This in itself provides an extra 2.5 to 3 minutes of daylight at mid-temperate latitudes.

Atmospheric refraction raises the sun about 1/2 degree upward at sunrise and sunset. This advances the sunrise yet retards the sunset, adding several minutes of daylight at each end of the day. Image credit: Wikipedia

Atmospheric refraction actually raises the sun about 1/2 degree upward at sunrise and sunset. This advances the sunrise yet retards the sunset, adding several minutes of daylight at each end of the day. Image via Wikipedia.

Atmospheric refraction. The Earth’s atmosphere acts like a lens or prism, uplifting the sun about 0.5o from its true geometrical position whenever the sun nears the horizon. Coincidentally, the sun’s angular diameter spans about 0.5o, as well.

Therefore, atmospheric refraction advances the sunrise and delays the sunset, adding nearly another 6 minutes of daylight at mid-temperate latitudes.

Astronomical almanacs usually don’t give sunrise or sunset times to the second. That’s because atmospheric refraction varies somewhat, depending on air temperature, humidity and barometric pressure. Lower temperature, higher humidity and higher barometric pressure all increase atmospheric refraction.

On the day of the equinox, the center of the sun would set about 12 hours after rising – given a level horizon, as at sea, and no atmospheric refraction.

Contemplating the sunset on the Philippine island of Leyte.  Photo by Abie Oquias Baybay.

Contemplating the sunset on the Philippine island of Leyte. Photo by Abie Oquias Baybay.

Bottom line: There are two reasons why we have more than 12 hours of daylight on the day of equinox. First, the sun is a disk, not a point of light. Second, the Earth’s atmosphere refracts (bends) sunlight. These factors add up to provide an additional 8 or so minutes of daylight on the day of the equinox at mid-temperate latitudes.”

So with all that taken care of…let’s get into the meteorology part of things.

There is actually a subtle difference this morning compared to other mornings this week. At this point the dew points are a bit lower than they have been. I remember the EURO model in particular showing this last weekend. Here is the 8AM surface map showing this…notice the dew points in green…they are closer to 65°. It allowed our morning low to drop to 70° this morning…still almost 15° above average.

We’ll see if we can keep the thickest (70-75°) dew points at bay for a day or so…hopefully keeping the heat index in check a bit today.

There are also clouds this morning north of the I-70 corridor. These clouds should knock a few degrees off the highs for areas that are under the blanket of gray for awhile

Meanwhile there are still some wavering in the model data regarding the evolution of SUN>MON.

Here is what I continue to think.

A) It will be cooler on Sunday. Unless there is a slow down in the front…I expect it to feel 35° or so cooler. This is based on the heat index this week being around 100° and the potential of late morning or afternoon temperatures to be in the mid 60s on Sunday (it could be cooler!). That’s 35° difference!

B) The rain situation: We may have some showers,, especially farther west on the KS side later Saturday afternoon. From KC westwards though the chances increase into the evening and overnight…although it may not be till Sunday morning when we get into the waves of rain moving from the SSW to the NNE.

C) How much? This is a bit tough to say because IF we’re fighting the rain through mid day on Monday…1-3″ is possible. IF we’re just dealing with a more progressive front and system…then perhaps 1/2-1 1/2″ is the scenario. I’m not sure IF the EURO which is the slowest in taking the rain out of here is right…but it does have solid 1-2″ totals in the region. The GFS is also rather bullish as well. A slow moving cold front combined with winds above that front blowing from the south to the north spell a decent amount of “overrunning” rain.

D) Sunday impacts for the game. Well again slower timing means that there would be more impacts during the late afternoon game. Faster solutions mean that maybe we can dry things out during the game itself. My suggestion is to be prepared for wet tailgating and at least wet conditions for the 1st half. From a temperature standpoint I don’t see how we’re not closer to 65° later in the afternoon. Rain in the AM will drop temperatures…leftover rain in the PM will keep temperatures from rising…cool air flowing into the area will exacerbate that. We may have some sort of daybreak high around 70° but it will be falling into the 60s as the day evolves and shouldn’t really recover. Heck the GFS drops temperatures into the 50s (wouldn’t shock me)

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7AM temperatures on Sunday via GFS (above)

 

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1PM temperatures on Sunday via GFS (above)

 

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7PM temperatures on Sunday via GFS (above)

Can you see why I’m sniffing out out the chill coming…and why I’m being so aggressive with my cool temperature forecast for Sunday into Monday (only in the 60s)? Again in the end we’ll see if I’m an island of “right” or an island of “wrong”. Right now I like my chances.

I really like where we’re going temperature wise to finish the month…some very pleasant weather is on the docket for the region in the big picture I feel. Nothing too hot and overall more seasonable conditions during the day and also at night. Odds are this will be the last few really hot days till next summer.

Our feature photo is from Sherry Creek Odell from rural Clay County!

Joe

 

 

 

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4 comments

  • Patrick Trudel (@sedsinkc)

    Joe, I sense climatology would help to verify those cool readings on Sunday can actually happen. Not at all unusual from a climatology standpoint to get a late September cold front with overrunning post-frontal rain cool a surface air mass to the upper 50s or 60s during the bulk of the daylight hours here. One thing for sure, starting Sunday will be a refreshing change from the miserable heat and humidity featured this week.

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