Weather Forecast Models

[tpbrady]

While at anchor in a small nook in Gambier Bay waiting out winds in Stephens passage, I started comparing the weather forecast models prediction for tomorrow. The range of winds at 8 am at a point I need to go around before I can head north, is from 5 (GFS) to 21 (HRRR), with other models clustered between 12 and 15. When I look at the forecast winds at locations where I have current observation sites, all the models understated the winds by 3-5 knots in the south and overestimated the winds in the north by the same.

All the models converged toward the observation in their forecast. Based on this, it appears the NWS forecast is more or less based on the scoring system used in ice skating, throw out the low and high score and average the rest.

Anyone have any insight into how the NWS marine forecasts are developed?

Tom

PS. Thanks for having Starlink, otherwise, I could not see the current observations and with the Cape Fanshaw weather radio down, I would be in the same condition as last year. The only way to get weather was to pull the anchor and go out and look.

[O C Diver]

Originally Posted by tpbrady

Anyone have any insight into how the NWS marine forecasts are developed?

Ouija Board.

Ted

[Don L]

The only time it seems the forecast is right is when it predicts bad weather. After that adding 5 to the wind forecast normally seems to work.

I crossed from the Bahamas back to Florida in April and all 4 predictions plus Chris Parker were wrong and it SUCKED!

[sledge]

Tom,
I know you're on the opposite coast but yes its a struggle to pick the best model. I can tell you in the SE US coast in the past year, we seem to have the closest match by using the GFS model, but no guarantees its still kind of a crap shoot....

[Bacchus]

My rule of thumb and recommendation to other boaters is to look at and consider the various models but NEVER try to puck one and rely on it.
Don't take a chance on a single or multi midels... consider that any are possible so consider worst case NOT best case.
I've taught the USPS Wx course for 25 yrs.
I encourage boaters to ask themselves if they are comfortable living when CONSIDERING ALL the possibilities?

[OldDan1943]

Models are just that, best guess.
I have yet to to meet a ‘weather man’ willing to hang his hat on a prediction made more than 1 day and then it is too late to move your boat any meaningful distance.

[mvweebles]

I don't know the OPs area, but sounds like a very small area where local conditions could greatly influence variations to the macro forecast. There is still a place for local knowledge.

I realize it's fashionable to reference various models and highlight when they're wrong. But more often than not these days, folks are actually referencing an app that has an algorithm that autonomously interprets the weather data from a source such as GFS.

I realize NOAA surface charts and synoptic charts can be a bit boring and perhaps intimidating. But they have a ton of information and give an accurate view of the weather forecast - its a relatively macro view that covers a lot of large expanse. Asking for micro-interpolation by an algorithm is a nice idea, but please don't complain when it changes.

What I really like about the NOAA surface charts is that each one is digitally signed by an experienced meteorologist.

Sure forecasts change. But they change for a reason. If you're not tracking pressure systems, you are at risk of being informed too late that a forecast has changed.

Peter

[LovetoBoat]

So two things that have worked for me.
1) I have the buoys from Florida to Nova Scotia on my PC and I watch them as I approach the areas - wind speed and direction - wave heights and direction for the last 6 hours to see if they are growing or shrinking.
2) I then look at the forecast and ask if the forecast is off by 10 knots in the wrong direction would I want to be out there?

If the answer is no - I stay where I am and wait...
Stay Safe.

[fryedaze]

Originally Posted by O C Diver

Ouija Board.



Ted

I have been burnt so many times by the weather magicians. I just did the Albemarle sound with a 15 mph north predicted wind. It was 20-24. My 14 ton 42' boat was half out of the water several times until I powered up and got the nose and speed up. We should dock these guys pay.

[Hippocampus]

Once again agree with peter. Synoptics are definitely worth looking at and would take one step further and look at the 500mb if doing anything near or off shore of any significance. Have always liked Chris if dealing with US east coast and eastern Caribbean but commanders for elsewhere. Totally agree with looking at all the models. Plan for the worst outlook among the models. Overall my impression is the European model is the most reliable in general.
Did the Lee Chesneau course and afterwards realized how little I know but still think it’s your boat and your life so it’s worthwhile to independently review as many sources as you can. To judge a particular source at a particular time having a baseline of knowledge even if like me it’s limited is worthwhile. You then can sense those times when predictions will be less reliable. It’s rarely a mistake to stay put if you’re nervous and remember schedules kill. Still use a recording barometer (meteoman) and still don’t trust GRIB files. They’re ok if looking at a large enough field of view but as a boater all weather is local so they can be very misleading. For US coastal find NWS surprisingly good.
Don’t understand why people pay for GRIB files when they’re available or free. And don’t understand why people only look at them.

[Retriever]

I’ve found the “gust” predictions far more accurate. If I’m happy with the gust forecast on the worst model, I’ll probably go.

I have much more faith in the models when they are in agreement about timing and trends.

I’m writing this on passage between Hokkaido, Japan and Attu at the end of the Aleutians. This is one of the few passages I’ve been on where the GFS gust model has often predicted stronger wind than the ECMWF model.

In both cases the “gust” forecast has, so far, overestimated wind speed and the “wind” model has underestimated wind speed. They’ve been spot on with the wind and sea trends, but not very good with current velocity or direction predictions. It will be interesting to see how they do with local effects once we get up to the Aleutians.

[tpbrady]

Sam,

Have a good trip to Attu. I’ve been there once and Shemya numerous times. I look forward to seeing details of your trip.

I happen to be rereading 1000 Mile War, a history of WWII in the Aleutians. If you haven’t read it, get it for Kindle because it will put context to places you are going to see and hear their impressions of weather. The only inhabited islands I am aware of are Shemya (USAF, don’t go there), Atka, and Adak. There might be a few people at Nikolski.

Tom

[HeadedToTexas]

Originally Posted by O C Diver

Ouija Board.

Ted

That’s my read as well.

[sledge]

For the East and the gulf states at least, NASA and science continues to attempt to improve prediction tools. I found this news item interesting, a new set of satellites launched for this problem and are apparently operational just in time for the 2023 Hurricane season...
Includes an incredibly long acronym so it must be good, Ha!

TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats)

https://www.nasa.gov/press-release/n...-constellation

[OldDan1943]

Ah yes, we look at the weather prediction models and then finally, look out the window. HAHA

I will say, seldom does a major weather event sneak up on us.

[Bacchus]

Frequently, ( not always) the difference between models is either timing or location to location variation. Models cover a fairly wide ( it varies) area and different areas within the larger may see local conditions different that other areas. All that leads individuals to think fcsts are never correct... when they are correct God a different nearby area or at a different time than anticipated.
Local terrain/conditions can have a significant affect in coastal & inland areas... not so much off shore.

[DDW]

Often there is a forecast discussion page associated with the forecast, though it may be hard to find. In it is a narrative description of how the particular forecaster arrived at what he/she wrote. We have this for NOAA aviation forecasts for example. It can be quite illuminating. They may say they looked at this and that, discounted the other, but feel that what they wrote is most likely because.... One thing about weather is you need to embrace uncertainty. If I look at 5 models and they all say the same thing, then I'm pretty confident in what I will find. If they all say something different, they you need to be ready for anything.

I'm in somewhat the same position, departing south from Craig intending to go around Cape Chacon and run the Dixon west to east in the next few days. Several models seem pretty consistent for that period, but 5 or 6' waves don't sound appealing.

[murofrelwart]

Originally Posted by DDW

Often there is a forecast discussion page associated with the forecast, though it may be hard to find. In it is a narrative description of how the particular forecaster arrived at what he/she wrote. We have this for NOAA aviation forecasts for example. It can be quite illuminating. They may say they looked at this and that, discounted the other, but feel that what they wrote is most likely because.... One thing about weather is you need to embrace uncertainty. If I look at 5 models and they all say the same thing, then I'm pretty confident in what I will find. If they all say something different, they you need to be ready for anything.

I'm in somewhat the same position, departing south from Craig intending to go around Cape Chacon and run the Dixon west to east in the next few days. Several models seem pretty consistent for that period, but 5 or 6' waves don't sound appealing.

Link to forecast discussion for SE Alaska. Today's discussion doesn't go into as much depth of discussion of the various models as I've seen in the past.



https://www.weather.gov/aawu/afd

[Mike H]

You have to remember your location. Having previously lived in Alaska with the numerous mountains, valleys, and terrain that wanders this way and that, weather can change rapidly simply by a small shift in wind direction. I was once in Dutch Harbor/Unalaska waiting to give a presentation on wind energy to the City Council. Sitting in my hotel room, I could see the ripples on Margaret's Bay traveling one way. A few seconds later, the ripples are going the complete opposite direction. The overall wind did not shift that much, but a few degrees difference can mean going left or right along a valley sitting cross to the wind. Hard to put up a wind turbine there.

After moving to Maine, it was pure pleasure actually being able to plan a few days in advance.

[Jc180]

Have spent considerable time over the past number of years looking at the weather model forecasts for the SE US, Florida, and the Bahamas. The two prominent models are the ECMWF (European model) and GFS (model used by US NWS). Agree with others who have said best when the models agree. Also agree with others who have said actual wind speed and direction best described in gust forecast. Obviously have no idea about the actual algorithms in each model, but have observed that the ECMWF more accurate more often. Like the Windy App. You can easily select the forecast for each model, compare, and then develop cruising strategy.