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Old 19-04-2007, 10:31   #1
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Weather predcition question

As I try to learn more about weather prediction I have become confused about seemingly conflicting information coming from what I assume is the same source. As an example from this morning (Thur 4/19):
For the waters off the southern Florida coast. The NOAA NWS Marine Text Forecast for Friday AM clearly states that the wind will start coming out of the east by Fri AM and will continue that way through the weekend. On the other hand the NWS/NCEP Ocean Prediction Center radiofax charts for Friday clearly show the wind coming predominantly from the north. I guess my question is whether these 2 forecasts are being done by 2 different people looking at the same data? If so is one source usually more correct than the other?
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Old 19-04-2007, 11:12   #2
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Make sure you have the same time (UTC vs. Local) and the same level for winds--500 milibar vs. surface.
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Old 19-04-2007, 12:00   #3
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Wallm, Welcome to the wonderful world of NWS and NOAA. Granted they are better than nothing but not much. You will seldom if ever get a text forecast and a Wefax that match and your guess is as good as any as to which one is correct. We came down the East coast just off shore one year and kept track of forecasts and actual conditions and found the forecasts wrong 85% of the time. They can't seem to get it right even 24 hours in advance. many times the forecast has changed hour by hour and many times not for the better. I understand weather is not an exact science but I also understand that with the tools and money the NWS has that they could at least come close. I have email them several times about the differences between charts and text and they assured me they would look into it. And I have a bridge for sale. You just have to take the info and try to make an educated decision based on experience and actual conditions.
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Old 19-04-2007, 13:07   #4
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Quote:
Originally Posted by wallm
... The NOAA NWS Marine Text Forecast for Friday AM clearly states that the wind will start coming out of the east by Fri AM and will continue that way through the weekend. On the other hand the NWS/NCEP Ocean Prediction Center radiofax charts for Friday clearly show the wind coming predominantly from the north ...
Post the two URLs, and we might determine if one (text) represents a forecast, and the other (chart) current observed conditions.

A friend charted NWS forecasts against actual observed conditions over a winter. He noticed a forecast “error pattern”, that turned out to represent an individual forecaster (person). As with Doctors & Electricians (et al), some are better than others.
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Old 19-04-2007, 13:48   #5
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It can also be to do with far smaller "localised" patterns that may go against the bigger pattern. Especially in very light airs. Land and water can have a very big influence on the greater pattern due to heat creating an air flow on/off shore that then may bend a greater air flow, or land forms like hills and peninsula's may bend/speed/slow air flows. It is quite complex and a lot more complex than just the overall pattern. Probably no other country would be more complex than NZ. We can have so many different wind speeds and directions all coming out of the one air mass, that prediction is extremely difficult here.
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Old 19-04-2007, 14:56   #6
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The radiofax site I looked at was Radiofax Charts - Boston. I then have been looking at the 24 and 48 hr predictions which seem to show the wind roses off southern Florida coming out of the NNE for the next couple of days. The text site I looked at was U.S. Coastal Waters Forecasts by Zone - South - Miami, FL. When in that site I clicked on the link for Deerfield to Ocean Reef, from 20 nm offshore to the Bahamas. I should note that the text has changed a bit in the last 6 hrs but it basically says winds out of the east for Fri. My question is whether this is 2 different forecasters looking at the same data (which indicate a low coming thru) and making somewhat different interpretations about when and where the low will come through versus the same forecaster whose intepretation is ending up differently on the radiofax map vs the text.
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Old 19-04-2007, 15:37   #7
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It could be that near shore winds are influenced by the large land massess and act accordingly as heatign occurs and thermals form over land during the dak. Even for large lakes like i sail there are differnet winds directions at play all the time and different forcasts for near shore and open water.

Could be some local influences are predicted in the south Florida forcast that are not identified in the larger east coast forcast.
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