Weather! It’s not the heat-oh wait, yes it is…
The heat is already here, and it’s only going to get warmer this week. Stay cool, everyone!
As our beloved Scott Pharr mentioned this morning, “I hope everyone really enjoys hot weather. Because you don’t have a choice.”
Before I tackle the impending heat, we’ve got some action in the tropics. Tropical Storm Bret was named by the National Hurricane Center last night.
Bret, thankfully, isn’t forecast to impact the US mainland, aside from kicking up some heavy surf along the coast. The forecast track has shifted north over the last six hours as well, meaning that Bermuda is now out of the cone of uncertainty. If you have plans to head Bermuda-ward in the next week, you need to continue to monitor the progress of Bret, but know that the current trend takes the storm mostly away from the island.
By the end of this week, I think many Richmonders will be wishing for a tropical storm to blow through. The oven has already kicked into high gear today, and it will only continue to ramp up this week. Temperatures Monday are into the upper 80s this afternoon, and should top out in the low 90s under partly cloudy skies. Overnight lows tonight will only make it down to 70.
By Tuesday, the core of an intense ridge of high pressure will continue sliding east, sending temperatures into the mid 90s. A weak frontal system passing through the area may bring us some scattered showers and thunderstorms – possibly severe – during the afternoon and evening hours, but there’s nothing particularly organized or widespread about these. It will, as usual, be a summer thunderstorm crap shoot. Temperatures overnight will again drop into the low 70s.
By Thursday, the heat will be in full force, and we’ll have several consecutive days of temperatures approaching 100. This plot shows the NWS forecast (green) for the next several days vs. model forecasts over the next week. Enjoy. It’s going to be a very hot week.
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Weather Dan
Dan Goff is now a two-time former Richmonder, having departed the River City yet again in favor of southwest Virginia, where he is working on degrees in geography and meteorology at Virginia Tech. Have a question about the weather or weather-related phenomena?
Notice: Comments that are not conducive to an interesting and thoughtful conversation may be removed at the editor’s discretion.
Seem’s like there’s always less humidity and less chance of T-storms when it gets this hot – meaning upper 90’s and low 100’s. Does it just get too hot for rain at these times? Does the intense heat itself drive the moisture out of the air?
It’s certainly not too hot for rain; summertime pop-up thunderstorms have been a part of summer for as long as I can remember.
There isn’t always less humidity at these temperatures either, though it may seem that way if you’re looking at the relative humidity values.
There’s an important distinction to be made here: that of absolute humidity versus relative humidity.
The relative humidity is a number you’ve all probably seen, usually in percentage form, and refers to the ratio of water vapor — the gaseous form of good old H2O — in the air compared to the total amount of water vapor that can exist in the air at a given temperature. At warmer temperatures, more water vapor can exist. When the relative humidity value reached 100%, no more water can evaporate and any excess will condense out in the form of precipitation or surface condensation.
This RH value can be misleading, though. There is more moisture in the air at 50% humidity and a temperature of 90 degrees, than there is at 100% humidity and a temperature of only 40 degrees.
So while it may seem like there’s not as much humidity during these hot summer days, there’s still plenty of moisture for rain and thunderstorms. The key figure to look at is the dewpoint: it’s the temperature at which, given the current level of moisture in the air, the air would be completely saturated. Dewpoint values above 60F get into the “sticky” range; by the time you approach 75F, conditions are downright tropical.
To answer your question, these really hot summer days don’t see a lot of thunderstorms because of pressure. To get really hot summer days, you have to have a lot of sunlight heating the surface, and by extension, very little or no cloudcover.
When a ridge of high pressure moves into the region like the one that we’re about to deal with, this pressure suppresses rising air. Without rising air, you have no updrafts, and you have no clouds and no thunderstorms. The heat doesn’t drive moisture out of the air, but it does increase the atmosphere’s capacity for moisture, if there is any to evaporate. We’ve been relatively dry here so there’s not as much water to evaporate from soil and plants, but in the midwest and northern plains, where there’s been significant flooding, soil moisture content is quite high and hot days will zap quite a bit of it.
Thanks for the explanation! I actually had no idea about the two measures of humidity…or the affects of a high pressure ridge. Makes much more sense now!