Big Heat Week into July 4th Weekend

[winter_warlock]

10 hours ago, stormtracker said:

I think the Heat Advisory is just for Wed

Extreme heat watch here ( north central md) for Thursday and Friday I beleive

[mdhokie]

6 hours ago, Eskimo Joe said:

Interesting low level humidity increase in the mountains. Some dewpoints in the mid 70s already. Hancock mesonet site has a heat index of 99° already. 

Last year it was super humid out here. We also had monsoon type rains that would blow out gravel driveways.

Looks like the humidity is gonna happen again this year. First couple summers didn't have this many days of high humidity during the day. I've had to invest in dehumidifiers! 

[katabatic]

1 hour ago, mdhokie said:

Last year it was super humid out here. We also had monsoon type rains that would blow out gravel driveways.

Looks like the humidity is gonna happen again this year. First couple summers didn't have this many days of high humidity during the day. I've had to invest in dehumidifiers! 

It was groooosssss today. 86-87/73-74 all afternoon. Very high DPs for this area. Also, looking solid Thursday for our first 90+ here. 

[nw baltimore wx]

2 minutes ago, katabatic said:

It was groooosssss today. 86-87/73-74 all afternoon. Very high DPs for this area. Also, looking solid Thursday for our first 90+ here. 

I was in Davis recently and I looked up Davis’s all time record high and it said 89. Is that accurate? If so, that’s crazy.

[SnowenOutThere]

On 6/29/2026 at 8:32 PM, CAPE said:

@SnowenOutThere

Metrology is important(essential) to meteorology. Not sure that it is taught in a meteorology program(probably not), but imo it probably should be. If not, you can get a more profound understanding of some of the questions you seek by learning a bit more about it. Just a suggestion.

My original post was more concerned with the microclimatology that takes place near the ground during strong surface heating or radiative cooling. Agree that the function and possible inaccuracy of thermometers is important in this discussion, but the variation near the ground is amazing regardless. Below is a page right out of my textbook from last semester! Look at the frequency of super adiabatic lapse rates or inversion near the ground! Only around 10% of the time in the lowest 15 meters of the atmosphere are the lapse rates "normal" in our human range. The difference in air temperature between the street and the rooftop of a several story building could be several degrees C. Therefore, I think its fair to question how representative our 2m standard is. 

Additionally, this problem is exacerbated at nighttime when temperature inversions develop without strong eddy diffusion to disrupt the inversion sublayer. The graph below shows how much temperature variations exists right beneath our noses! Within the lowest 1m of the atmosphere we can see a temperature variation of 3 degrees Celsius. Then the difference 1m to 10m is another 4 degrees Celsius under calm conditions. 

These discrepancies matter! The lowest segment of the boundary layer that humans inhabit are defined by rapid changes with height. Take CO2 PPM as an example of the practical effect of this microclimate, a sensor at 2m is a great data point, but does it really represent the CO2 available to crops growing on fields? 

It is important to remember that our standards are just that: standards. They are abstractions that always leave some part of reality behind. When making decisions about heat, frost, drought, or other atmospheric events the local microclimate must be kept in mind. As a closing example, take a pool deck in the summer. Say the standard 2m temperature is a heat advisory on its own. The pool deck may instead reach extreme heat criteria as the latent heat flux of the pool water increases humidity and hot concrete deck makes the effective temperature to children, who are only a meter tall, significantly hotter than anticipated. The point of this and my previous post wasn't to say that the 2m standardized station isn't useful, nor was it to imply that the science behind our tools is not important. It was to instead clarify that these microclimates near the ground are extremely important in their own right and must be considered for effective decision making. 

[vortex95]

6 hours ago, SolidIcewx said:

Its been a little over a week since solstice I wouldn’t think that would have an impact currently. August perhaps.

No discernible impact from slightly less sun angle  July is the warmest month climatologically even though the days are getting shorter.  This has to do w/ the Earth's heat balance, and the lag that exists in the atmosphere and ocean.  1 month lag for the atmosphere and 3 months lag for the oceans as to max avg temps.

 

[wxmeddler]

45 minutes ago, SnowenOutThere said:

My original post was more concerned with the microclimatology that takes place near the ground during strong surface heating or radiative cooling. 
<snip>

In North Dakota we regularly saw -12 to -18F inversions between 0.5 and 9m. Between +2 and +6F during the daytime depending on soil dryness and vegetation. AASC Standard is between 1.5m and 2m. WMO is 2m. I prefer the 1.5m personally, but MD Mesonet follows the 2m.

[CAPE]

11 hours ago, SnowenOutThere said:

My original post was more concerned with the microclimatology that takes place near the ground during strong surface heating or radiative cooling. Agree that the function and possible inaccuracy of thermometers is important in this discussion, but the variation near the ground is amazing regardless. Below is a page right out of my textbook from last semester! Look at the frequency of super adiabatic lapse rates or inversion near the ground! Only around 10% of the time in the lowest 15 meters of the atmosphere are the lapse rates "normal" in our human range. The difference in air temperature between the street and the rooftop of a several story building could be several degrees C. Therefore, I think its fair to question how representative our 2m standard is. 

Additionally, this problem is exacerbated at nighttime when temperature inversions develop without strong eddy diffusion to disrupt the inversion sublayer. The graph below shows how much temperature variations exists right beneath our noses! Within the lowest 1m of the atmosphere we can see a temperature variation of 3 degrees Celsius. Then the difference 1m to 10m is another 4 degrees Celsius under calm conditions. 

These discrepancies matter! The lowest segment of the boundary layer that humans inhabit are defined by rapid changes with height. Take CO2 PPM as an example of the practical effect of this microclimate, a sensor at 2m is a great data point, but does it really represent the CO2 available to crops growing on fields? 

It is important to remember that our standards are just that: standards. They are abstractions that always leave some part of reality behind. When making decisions about heat, frost, drought, or other atmospheric events the local microclimate must be kept in mind. As a closing example, take a pool deck in the summer. Say the standard 2m temperature is a heat advisory on its own. The pool deck may instead reach extreme heat criteria as the latent heat flux of the pool water increases humidity and hot concrete deck makes the effective temperature to children, who are only a meter tall, significantly hotter than anticipated. The point of this and my previous post wasn't to say that the 2m standardized station isn't useful, nor was it to imply that the science behind our tools is not important. It was to instead clarify that these microclimates near the ground are extremely important in their own right and must be considered for effective decision making. 

That's good stuff but way overcomplicates it. The simple fact is that the sun doesn't really heat the air- it heats the ground which then transfers the heat to the air by radiation, and it was probably determined that 2 meters was a height where there is significantly less direct influence from retention of heat/ radiation of heat from ground. And again, that height is approximately human head level.

[Eskimo Joe]

According to my records, my Cooperative Observation site (RSTM2) has never recorded a 100° air temperature. Wonder if we may it this time? I'm leaning towards a no.

[Eskimo Joe]

DCA and BWI almost 80 degrees at 7am.

[BlizzardNole]

2 hours ago, CAPE said:

That's good stuff but way overcomplicates it. The simple fact it that the sun doesn't really heat the air- it heats the ground which then transfers the heat to the air by radiation, and it was probably determined that 2 meters was a height where there is significantly less direct influence from retention of heat/ radiation of heat from ground. And again, that height is approximately human head level.

6-foot-8 is head level?  That is some tall people!  

[CAPE]

12 minutes ago, BlizzardNole said:

6-foot-8 is head level?  That is some tall people!  

Approximately lol. I think it has more to do with getting the measurement point reasonably high enough so that heat from near the surface has less influence. My station is probably 4 1/2 feet. Having it in shade is a bigger deal. A radiation shield and proper ventilation can minimize errors when in direct sun.

[nj2va]

16 hours ago, RIC_WX said:

Most of the PWS I see around Garrett reporting 85-88 with dewpoints around 70.  90* degree days are pretty rare up there and assuming the next 3 days will be warmer...

My all time high since we’ve had our house in Deep Creek is 89 (hitting 10 years this fall)..would love to avoid hitting 90. 

One thing I’ve noticed as @mdhokie pointed out, is how much the humidity has increased.  I definitely don’t remember that the first 6-7 years we had the house.

[yoda]

55 minutes ago, Eskimo Joe said:

DCA and BWI almost 80 degrees at 7am.

Looks like 82/70 at 9am for DC 

[RIC_WX]

34 minutes ago, nj2va said:

My all time high since we’ve had our house in Deep Creek is 89 (hitting 10 years this fall)..would love to avoid hitting 90. 

One thing I’ve noticed as @mdhokie pointed out, is how much the humidity has increased.  I definitely don’t remember that the first 6-7 years we had the house.

5 years for us now, time flies.  My PWS hit 90 twice yesterday, but it gets direct afternoon sun so I would suppose 87-88 is probably closer to reality.  My POV on the humidity is there are no drought conditions from the spine of the Alleghanies westward, the combination of higher soil mositure and compressional downsloping east of the mountains helps to explain why the mountains seem to feel "as humid" right now as lower elevation areas further east.

Summer is still short, this will be our first weekend all season we can sit outside in the evenings without hoodies on.

[nj2va]

3 minutes ago, RIC_WX said:

5 years for us now, time flies.  My PWS hit 90 twice yesterday, but it gets direct afternoon sun so I would suppose 87-88 is probably closer to reality.  My POV on the humidity is there are no drought conditions from the spine of the Alleghanies westward, the combination of higher soil mositure and compressional downsloping east of the mountains helps to explain why the mountains seem to feel "as humid" right now as lower elevation areas further east.

Summer is still short, this will be our first weekend all season we can sit outside in the evenings without hoodies on.

September is my favorite month there (outside of winter storms ofc).  Days in the 60s and cool nights…lake is still warm and way less crowded with schools back in session.  And thanks for the humidity POV…seems right!

[Eskimo Joe]

The Washington County mesonet sites already pushing HI of 100° before 11am is impressive. Those are all calibrated sensors too!

[chris21]

11 hours ago, nw baltimore wx said:

I was in Davis recently and I looked up Davis’s all time record high and it said 89. Is that accurate? If so, that’s crazy.

Down here in the Roan Highlands of NC at 3800 feet, the highest temp I’ve recorded in my two years of living here is 82. Unfortunately looks like we will break that this week. Beech Mountain, NC highest temp ever recorded is 83.

[Eskimo Joe]

Looks like LWX upgrading western MD and the WV panhandle. Makes sense. We definitely appear to be outpacing guidance for at least today.

[TSSN+]

90 feels like 98 at 10:45 here. On our way 

[astarck]

DCA well off the pace. Change in wind direction equal a big jump later?

[TSSN+]

1 minute ago, astarck said:

DCA well off the pace. Change in wind direction equal a big jump later?

Heat be wester. lol Martinsburg at 89 while dca at 84 

[TSSN+]

Hagerstown be cookin. 

[Eskimo Joe]

Wouldn't it be hilarious if DCA got river winded through this entire event and failed to reach 90 degrees?

[TSSN+]

2 minutes ago, Eskimo Joe said:

Wouldn't it be hilarious if DCA got river winded through this entire event and failed to reach 90 degrees?

Reach 90? That’s silly they will get past 90 reaching 100 is questionable at least today at this point. 

[Mrs.J]

This early humidity and heat is no joke. Just got a call from my youngest who is helping at a Pony Camp in Bluemont. She just passed out. She is ok but it was a wake up call that she needs to get some issues she has been having figured out. It was definitely the heat that cause it. 

[George BM]

90/75 w/a 100F HI currently at IAD.

[Eskimo Joe]

4 minutes ago, George BM said:

90/75 w/a 100F HI currently at IAD.

I believe that Leesburg (KJYO), but that matches the Poolesville mesonet site well.

[weatherCCB]

90/74

[dailylurker]

29 minutes ago, Eskimo Joe said:

Wouldn't it be hilarious if DCA got river winded through this entire event and failed to reach 90 degrees?

New around here? Lol It’s heat. Of course DC will reach 100 today, and probably will for the next 5 days