thunderstorms

[andorsky]

Any tips on how to judge direction and speed of a thunderstorm visually?

[OtterGreen]

first off is " red sky at night, sailors delight, red sky at morning sailor take warning" but if you already know a storm is coming, for my area anyway it is usually the following:
Storms here on the Barnegat Bay in the summer approach predominately from the West. First off check the clouds and stability of the atomoshphere. Nimbostratus are the ones to really take warning of. Alot of vertical development means a heft storm is coming, the higher the anvil of the cloud the more intense of a storm. Watch for changes in wind humidity and tempurature also if you have a barometer watch to see if it is dropping. Watch for wildlife such as birds. if there are usually alot in your general area and now there are none, or you see them flying away take notice. It has been said that when birds fly low its because they can sense the barometric pressure change which causes pain or discomfort. Going one step further, if you have a smartphone, download a reliable weather forecase and radar, if not buy a handheld VHF and keep it on a WX channel. I know you said visually but this day in age there are alot more ways than just visually and safety is always the top factor. Remember also to look for boats on the water. Are they going about their boating? or are they battoning down the hatches and headed for the dock? One storm here a few years back a storm literally came up within 20-30 mins and packed a punch of 75 mph winds. The Coast Guard Ribbed boats came to the anchorage over there PA speaker and said to seek shelter asap, as we were moving to another cove that was better sheltered and less crowded it hit. it was only me and my brother and we did the best we could but were pushed up on the salt marsh which was actually better than being at anchor as boats were being dragged. we have a water ballast and centerboard on a 23 footer and when we were pushed up i threw the anchor on shore and started draining the water. when it was all said and done 4 waterspouts were recorded in the area with the 75 mph winds. when in doubt dont go out! or stay close to the dock ! happy sailing

[Barquito]

I think, in general, it is difficult to visualize a storm from the water. You may know, for example, the storm is within a certain distance if the town that is 5 miles away onshore just dissapeared behind a wall of water. You can count time from lightning, AM radio trick, etc. However, I can't think of anyway that you could tell which direction the strom is tracking.

I would be interested in knowing what to look for to determine if there will be an intense leading-edge wind gust.

[Zanshin]

No, there is no method to visually determine which direction a thunderstorm is growing. When a Cu (cumulus) overdevelops in to Cb (cumulonimbus) it is usually due to thermal action; this can be triggered from orographic features over land but is more difficult to predict over water. I like to use the analogy of water droplets on the ceiling of a steam sauna, the water collects gradually all over the surface and once you stick a finger in somewhere to act as a trigger all the water flows to that point. A thermal is the reverse, latent energy on the ground gets sucked up into the cloud. The general direction of the cloud is with the ambient wind at the surface and middle layers, but if the wind is from the north and the main thermal upwards movement is also in the north it might overcome the wind and make the cloud grow towards the north as opposed to the south. Often the base of the cloud is concave where the air is rising and that is where the cloud is most likely to grow.
Once the cloud stops growing and downdrafts begin dumping water (or hail) it will tend to drift in the direction of the upper level winds. Surface winds can't be used, since the winds from the Cb are so powerful that they will overpower any wind, if the temperature goes down then the wind is coming from the downdrafts in a Cb cell and unfortunately say nothing about which direction the storm itself is going.
This applies to thunderstorms generated from normal thermal activity, frontal thunderstorms are driven by larger-scale phenomena and will travel in the direction of the front.

[noelex77]

Originally Posted by andorsky

Any tips on how to judge direction and speed of a thunderstorm visually?

Yes.
They are always heading for me!!!

This was yesterday

[AdamLein]

You have a couple of options; both are good "rules of thumb" that don't require a lot of technical knowledge about air masses and fronts and what-not; they're also not foolproof, so use them with care:

1) Visually find your VHF radio. Turn it on and set it to a weather station, and wait for a meteorologist to tell you.

2) Visually inspect a meteorology website.

[dnf777]

I'll second a VHF radio with NOAA freqs.
I've been a pilot and weather observer for many years, and will tell you its often impossible to predict the severity of a storm by how it looks as it approaches. Often in the thick of it before realizing how severe it is.

Knowing local and seasonal weather patterns is always a help, but a radio or smart phone with radar is tough to beat.

[T37SOLARE]

1) Visually find your VHF radio. Turn it on and set it to a weather station, and wait for a meteorologist to tell you.

2) Visually inspect a meteorology website.

3) Get a smart phone and watch the weather on the NOAA radar on your web browser. (or even better yet tether your phone to your laptop and get the bigger picture)

[Ulladh]

Thunderstorms tend to follow general patterns, get to know your local weather patterns. In my area Delaware River and Bay the thunder storms are usually from the WSW, late afternoon and evening.

9 times out of 10 the storm will come from the same direction and you may even feel the change in pressure on your skin as the system approaches.
As the storm gets closer, maybe to close, you may feel an increase in static electric on bare arm hairs.

Reduce sail, and start the motor if close to a shipping lanes or land, and wait for the storm to pass.

[Ulladh]

Thunderstorms tend to follow general patterns, get to know your local weather patterns. In my area, Delaware River and Bay, the thunder storms are usually from the WSW, late afternoon and evening.

9 times out of 10 the storm will come from the same direction and you may even feel the change in pressure on your skin as the system approaches.
As the storm gets closer, maybe to close, you may feel an increase in static electric on bare arm hairs.

Reduce sail, and start the motor if close to a shipping lanes or land, and wait for the storm to pass.