Dew as rain predictor

[midlf]

The spouse heard somewhere that dew in the morning means no rain in the forecast and dry in the morning indicates rain. Our location is SE Wisc. Anyone ever heard this before? She has been keeping track the last few weeks and so far it's somewhat reliable.

 

[deereguy]

I heard the same thing from a golf course sup. They used the theory to know whether to turn on the irrigation or not that day.

It seems to be a very predictable method.

 

[jbrumberg]

midlf:

I pasted the definition of dew that I got from Googling. I am a certified weather geek, but not a meteorologist. I am/was a certified weather watcher. There is an element of truth to the "rule". The key to dew formation is the radiational cooling effect which is most prominant during cloudless cold nights which is typical of a good strong high pressure weather system that usually means good weather . I have been scrutinizing the weather for over thirty years and I think the "Dry Rule" holds an element of truth for the reasons I mentionned. I do not support the "Dry Rule" just for the reasoning that the same conditons paired with wind and/or a very low dew point high pressure system will inhibit dew formation.

dew, thin film of water that has condensed on the surface of objects near the ground. Dew forms when radiational cooling of these objects during the nighttime hours also cools the shallow layer of overlying air in contact with them, causing the condensation of some water vapor.

Jay

 

[Amontilado]

Midl,

Never heard of that rule, but as with any "rule of thumb", it's in how it is applied. Dew forms with a very calm boundary (near ground) layer, even more calm than when fog forms. Down here on the "Guff"(Gulf) coast, we can have dew in the morning, but when the Gulf breeze comes onshore during the late spring into early fall, it may or may not touch off thunderstorms in one little piece of the world. It's just a part of the big equation.

Steve

 

[jbrumberg]

Midl,

Never heard of that rule, but as with any "rule of thumb", it's in how it is applied. Dew forms with a very calm boundary (near ground) layer, even more calm than when fog forms. Down here on the "Guff"(Gulf) coast, we can have dew in the morning, but when the Gulf breeze comes onshore during the late spring into early fall, it may or may not touch off thunderstorms in one little piece of the world. It's just a part of the big equation.

Steve

Amontilado AKA Steve:

I agree. Convective uplifting = thunderstorms and/or showers which are just thunderstorms that did not quite "make it". There are too many variables to make weather "Rules". "The Red Sky In Morning... Sailors Take Warning Rule" kind of applies better to the British Isles than the eastern US. Sun dogs and rings around the sun/moon, jet contrails becoming cirrus clouds are pretty accurate indicators of rains usually within 24 hours. I never could understand the old sailor Rule- "When the Sea Hawg Jumps... Man the Pumps" Jay

 

[Marine1]

If I have dew in the morning there will always be rain in my bathroom by noon.

Seriously though, the one about the moon's halo means rain in 24-48 hours seems to be fairly reliable in my neck of the woods.

Is there always dew in the desert because they don't get much rain there. I know it gets cold overnight so maybe. I don't know.

I'm just waiting for Global Room Temperature.

 

[rogdan]

I've heard this all my life and just believed it as passed down knowledge through generations of my family. I have never put it to the test though but we had no dew this morning and the forecast is for rain today (we need it).

 

[scott_vt]

The spouse heard somewhere that dew in the morning means no rain in the forecast and dry in the morning indicates rain. Our location is SE Wisc. Anyone ever heard this before? She has been keeping track the last few weeks and so far it's somewhat reliable.

Mornin Steve,
Gee thats possible, but I have heavy dew this morning and we are supposed to get thunder showers later on today !

Cant make heads or tails out of that !

 

[jbrumberg]

scott vt:

I had the same conditions this morning and had some T storm activity this afternoon as you. It's the high humidity and convective lifting dynamic. Your VT hills contribute to this as well. The sunlight "stirred things up" today. I love watching those cumulus clouds build up in the afternoon ! I really can not help myself when it comes to weather and unfortunately a few other things. Jay

PS: Any idea what a "sea hawg" is?

 

[rogdan]

I've heard this all my life and just believed it as passed down knowledge through generations of my family. I have never put it to the test though but we had no dew this morning and the forecast is for rain today (we need it).

The theory didn't hold water, no rain yesterday.

 

[scott_vt]

scott vt:

PS: Any idea what a "sea hawg" is?

Afternoon Jay,
Ahhyup, we see a hawg and eat it !

Honestly Jay, I dont have a clue !

 

[Amontilado]

Seriously though, the one about the moon's halo means rain in 24-48 hours seems to be fairly reliable in my neck of the woods.

This one tend to be one of the better rules of thumb, but again, I've seen cirrus coming off of a system upstream for days, and end up with little to no rain in the area/county(sigh). I'm surprised I still have hair after some of the curve balls Mother Nature has thrown at me.


Steve

 

[goaliedad]

I just talked to the meteroligist ( spelling ain't my strong point ok!) for the radio station I work for- he said that dew in the morning means a dry START to the day- it may or may not rain later in the day. Now that everything is clear as mud.....

 

[Arkie1940]

In this part of the country, we have been having dew point temperatures consistently in the low 70s. The temperature at night will generally drop to about the dew point so there is dew on the grass in the morning. It also means that the air has a lot of moisture which is one of the conditions conducive to thunder storms.

 

[jbrumberg]

In this part of the country, we have been having dew point temperatures consistently in the low 70s. The temperature at night will generally drop to about the dew point so there is dew on the grass in the morning. It also means that the air has a lot of moisture which is one of the conditions conducive to thunder storms.

Arkie1940:

I agree you have "fine tuned" what I have stated earlier. I really did not get into relative humidities and dew points as clearly as you have. I can assure you that your observations have proved themselves to be quite accurate in NE this week . As to predictability, I rely more on direct observation than any of the "established" weather service providers (which I check twice daily). It is flattering that the school I work for asks me first when planning any outdoor activities. The students have been tracking my "successes" for the past 2 years; they consider me quite accurate . Jay

 

[Toiyabe]

Is there always dew in the desert because they don't get much rain there. I know it gets cold overnight so maybe. I don't know.

Dew? What's dew? We occasionally get frost or even the dreaded pogonip (freezing fog of death), but I can't recollect ever seeing dew in this neck of the woods. Maybe in trace amounts.