I just looked at the weather.com information for Fitchburg, MA.
The report shows the current temperature (actually, the 7:52 PM
temperature) as 81 degrees. Looking at the hourly forecast, the 9 PM
temperature is predicted to be 71 degrees, 68 at 10 PM, and so on.

I've checked the weather reports for a few local towns several times
today, and the situation was always the same: The current temperature
has been much higher than the series of temperature predictions in the
hourly forecast. And today isn't unique -- I've seen that happen many
times with errors in both directions.

My question is: How can this happen?

I can understand how distant forecasts can be off, but shouldn't the
current temperature be a strong factor in short-term temperature prediction?

Thanks for any insight.
B.J.
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B.J. Herbison wrote:

I just looked at the weather.com information for Fitchburg, MA.
The report shows the current temperature (actually, the 7:52 PM
temperature) as 81 degrees. Looking at the hourly forecast, the 9 PM
temperature is predicted to be 71 degrees, 68 at 10 PM, and so on.

I've checked the weather reports for a few local towns several times
today, and the situation was always the same: The current temperature
has been much higher than the series of temperature predictions in the
hourly forecast. And today isn't unique -- I've seen that happen many
times with errors in both directions.

My question is: How can this happen?

I can understand how distant forecasts can be off, but shouldn't the
current temperature be a strong factor in short-term temperature prediction?

You should probably ask them - but I don't know if you'd get a response.

I thought automated forecasts of that sort adjusted to some extent to current
conditions - at least for the short term. Maybe they don't. Programming
something like that would not be difficult - some weather providers actually
have their forecasts updated automatically based on trends of radar &
satellite images - though I think we are still a long way from that being
as good as a human for that.


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I checked the forecast for today for my zip code (18344), and after a few
clicks & pop-up ads, I got the following :


Thursday, May 13 Temp °F Feels Like Dew Point Precip. Humid. Wind

11 AM Partly Cloudy 76° 78° 60° 20% 59% From the South at 5 mph
12 PM Partly Cloudy 78° 80° 60° 20% 54% From the South at 6 mph
1 PM Isolated T-Storms 79° 80° 60° 30% 52% From the South at 7 mph
2 PM Isolated T-Storms 79° 80° 60° 30% 52% From the South at 8 mph
3 PM Isolated T-Storms 79° 80° 60° 30% 51% From the South at 8 mph
4 PM Isolated T-Storms 78° 79° 59° 30% 51% From the South at 8 mph
5 PM Isolated T-Storms 77° 79° 58° 30% 52% From the South at 8 mph
6 PM Isolated T-Storms 76° 78° 58° 30% 54% From the South at 7 mph
7 PM Isolated T-Storms 74° 74° 58° 30% 57% From the South Southeast at 6 mph
8 PM Isolated T-Storms 72° 72° 58° 30% 61% From the South Southeast at 6 mph
9 PM Isolated T-Storms 69° 69° 58° 30% 66% From the Southeast at 6 mph
10 PM Partly Cloudy 67° 67° 58° 20% 72% From the Southeast at 6 mph
11 PM Partly Cloudy 65° 65° 57° 20% 77% From the Southeast at 6 mph

Friday, May 14
12 AM Partly Cloudy 63° 63° 57° 20% 81% From the East Southeast at 6 mph
1 AM Partly Cloudy 61° 61° 57° 20% 85% From the East Southeast at 4 mph
2 AM Partly Cloudy 60° 60° 56° 20% 87% From the East Southeast at 4 mph
3 AM Partly Cloudy 59° 59° 56° 20% 88% From the Southeast at 4 mph
4 AM Mostly Cloudy 59° 59° 55° 20% 88% From the Southeast at 4 mph
5 AM Mostly Cloudy 58° 58° 54° 20% 88% From the Southeast at 4 mph


The temperatures are good - 77 at MPO (which I don't think is in zip 18344,
actually) and my location. That was updated at 10:30 AM though.

Their day/night forecast is for a high/low of 80/57 and precip probabilities
of 30/30 %.

The thing I find most peculiar is the precipitation probabilities. If
they are hourly probabilities, this would imply a very large likelihood
of precip during both day and nighttime periods. If the probabilities
are considered independent, the likelihood of precip from 11 AM to 8 PM
is 1 - (.2^2 * .7^7) = .947 = 94.7 %. They are not close to being independent
events though - if thunderstorms do form, it is likely precip will occur
a few hours of the day. Yet if the probability each hour is 30 %, the
daily probability should be much greater - because the storms won't persist
all day.

So the correct interpretation of the forecasts shown above is that there's
a 30 % chance of precip today, and if it does occur, it'll persist all day
(i.e., occur each of those hours the probability is 30 %). That is obviously
not what they mean, but if the daily probability is 30 %, those for each
hour should be much lower.

Note that the nighttime probabilities are almost the same as the daytime
ones - 20 % every hour between 10 PM & 5 AM. I can't believe precip is
nearly as likely those times as it is between 2 & 7 PM.

I am thinking the probability is about 70 % for the daytime period now
and 20 % for the nighttime - hourly probability would be about 5 % ending
at 12 PM, peaking at about 25-30 % ending at 5 PM, then decreasing to about
10 % ending at 10 PM and to near 0 % ending at 5 AM. Saying that is one
thing, programming a computer to think like that another.

Maybe I am overestimating a bit, though storms are common over the elevated
locations during warm & humid days. We had some hail as large as 3/8 inch
diameter yesterday.


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Joseph Bartlo wrote:
I checked the forecast for today for my zip code (18344), and after a few
clicks & pop-up ads, I got the following :


Thursday, May 13 Temp °F Feels Like Dew Point Precip. Humid. Wind

11 AM Partly Cloudy 76° 78° 60° 20% 59% From the South at 5 mph
12 PM Partly Cloudy 78° 80° 60° 20% 54% From the South at 6 mph
1 PM Isolated T-Storms 79° 80° 60° 30% 52% From the South at 7 mph
2 PM Isolated T-Storms 79° 80° 60° 30% 52% From the South at 8 mph
3 PM Isolated T-Storms 79° 80° 60° 30% 51% From the South at 8 mph
4 PM Isolated T-Storms 78° 79° 59° 30% 51% From the South at 8 mph
5 PM Isolated T-Storms 77° 79° 58° 30% 52% From the South at 8 mph
6 PM Isolated T-Storms 76° 78° 58° 30% 54% From the South at 7 mph
7 PM Isolated T-Storms 74° 74° 58° 30% 57% From the South Southeast at 6 mph
8 PM Isolated T-Storms 72° 72° 58° 30% 61% From the South Southeast at 6 mph
9 PM Isolated T-Storms 69° 69° 58° 30% 66% From the Southeast at 6 mph
10 PM Partly Cloudy 67° 67° 58° 20% 72% From the Southeast at 6 mph
11 PM Partly Cloudy 65° 65° 57° 20% 77% From the Southeast at 6 mph

Friday, May 14
12 AM Partly Cloudy 63° 63° 57° 20% 81% From the East Southeast at 6 mph
1 AM Partly Cloudy 61° 61° 57° 20% 85% From the East Southeast at 4 mph
2 AM Partly Cloudy 60° 60° 56° 20% 87% From the East Southeast at 4 mph
3 AM Partly Cloudy 59° 59° 56° 20% 88% From the Southeast at 4 mph
4 AM Mostly Cloudy 59° 59° 55° 20% 88% From the Southeast at 4 mph
5 AM Mostly Cloudy 58° 58° 54° 20% 88% From the Southeast at 4 mph


The temperatures are good - 77 at MPO (which I don't think is in zip 18344,
actually) and my location. That was updated at 10:30 AM though.

Their day/night forecast is for a high/low of 80/57 and precip probabilities
of 30/30 %.

The thing I find most peculiar is the precipitation probabilities. If
they are hourly probabilities, this would imply a very large likelihood
of precip during both day and nighttime periods. If the probabilities
are considered independent, the likelihood of precip from 11 AM to 8 PM
is 1 - (.2^2 * .7^7) = .947 = 94.7 %. They are not close to being independent
events though - if thunderstorms do form, it is likely precip will occur
a few hours of the day. Yet if the probability each hour is 30 %, the
daily probability should be much greater - because the storms won't persist
all day.

So the correct interpretation of the forecasts shown above is that there's
a 30 % chance of precip today, and if it does occur, it'll persist all day
(i.e., occur each of those hours the probability is 30 %). That is obviously
not what they mean, but if the daily probability is 30 %, those for each
hour should be much lower.

Note that the nighttime probabilities are almost the same as the daytime
ones - 20 % every hour between 10 PM & 5 AM. I can't believe precip is
nearly as likely those times as it is between 2 & 7 PM.

I am thinking the probability is about 70 % for the daytime period now
and 20 % for the nighttime - hourly probability would be about 5 % ending
at 12 PM, peaking at about 25-30 % ending at 5 PM, then decreasing to about
10 % ending at 10 PM and to near 0 % ending at 5 AM. Saying that is one
thing, programming a computer to think like that another.

Maybe I am overestimating a bit, though storms are common over the elevated
locations during warm & humid days. We had some hail as large as 3/8 inch
diameter yesterday.



Joseph, this is off topic, but it should still make it through the spam
block.
I found your assessment of the song "American Pie" by Don McLean very
interesting and illuminating.


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http://www.rbwaters.com wrote:

Joseph, this is off topic, but it should still make it through the spam
block.
I found your assessment of the song "American Pie" by Don McLean very
interesting and illuminating.

Thank you. Yes - it is off-topic and you could simply e-mail me.

Maybe you are trying to tell me I should write about pop music instead of
weather ? Yes, I overpredicted the thunderstorm potential, but American
Pie almost certainly includes nothing about Kennedy also. So one incorrect
comment about weather is no worse IMO than one incorrect comment about that.
My post about the previous day's weather was basically correct.

Regardless, my primary purpose for that post is to note how the hourly
precipitation probabilities in TWC forecasts are misleading. If you look
at them, you'll see that the highest probability for any hour of the daytime
period corresponds with the total daytime probability on their daily forecasts.
That is fundamentally incorrect from a statistical view. Even during a day
when showers are likely, the probability for any particular hour is quite low.
It doesn't rain all day. My post about the Gettysburg trip is a good example
of this. As I mentioned, TWC forecast maps would lead you to believe we'd
have basically a showery day - but it was a beautiful day, perhaps with a
brief period of late day or evening showers. That was long after we left,
so I don't know what they saw. I.e., the probability of rain while we were
touring the battlefield, etc. most of the day was very low - maybe 10 % for
any hour - but I bet TWC forecast had something like 60 % for each of those
hours.


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TWC hourly forecast today for Mount Pocono :

Friday, May 14 Temp °F Feels Like Dew Point Precip. Humid. Wind

12 PM Mostly Cloudy 65° 65° 59° 20% 69% From the South at 8 mph
1 PM Mostly Cloudy 67° 67° 60° 20% 66% From the South at 8 mph
2 PM Mostly Cloudy 70° 70° 60° 20% 64% From the South at 9 mph
3 PM Partly Cloudy 72° 72° 61° 20% 61% From the South at 9 mph
4 PM Partly Cloudy 74° 74° 59° 30% 59% From the South at 11 mph
5 PM Partly Cloudy 75° 75° 59° 30% 59% From the South Southwest at 11 mph
6 PM Partly Cloudy 74° 74° 59° 30% 60% From the South Southwest at 10 mph
7 PM Showers 72° 72° 59° 40% 63% From the South Southwest at 8 mph


The daily forecast :

High/Low (°F) Precip. %

May 14 Partly Cloudy 76°/60° 20 %


Now some of the hourly probabilities are greater than the daytime ones,
which is impossible

Someone in charge probably graduated with a D- in probability & statistics.

I would direct these concerns to them, but I've never seen an indication
they consider them. We were discussing this here.


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On 14 May 2004 10:17:58 -0400, Joseph Bartlo
wrote:


Regardless, my primary purpose for that post is to note how the hourly
precipitation probabilities in TWC forecasts are misleading. If you look
at them, you'll see that the highest probability for any hour of the daytime
period corresponds with the total daytime probability on their daily forecasts.
That is fundamentally incorrect from a statistical view. Even during a day
when showers are likely, the probability for any particular hour is quite low.
It doesn't rain all day. My post about the Gettysburg trip is a good example
of this. As I mentioned, TWC forecast maps would lead you to believe we'd
have basically a showery day - but it was a beautiful day, perhaps with a
brief period of late day or evening showers. That was long after we left,
so I don't know what they saw. I.e., the probability of rain while we were
touring the battlefield, etc. most of the day was very low - maybe 10 % for
any hour - but I bet TWC forecast had something like 60 % for each of those
hours.

You should write TWC about this and see what they say (they'd probably
email you with an ad). Heck, you may even win a date with one of
their single female OCM's, but finding a non pregnant one is pretty
difficult these days.


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The Artist Formerly Known As Your Highness wrote:

You should write TWC about this and see what they say (they'd probably
email you with an ad). Heck, you may even win a date with one of
their single female OCM's, but finding a non pregnant one is pretty
difficult these days.

My response may have me banished from this group, so see ne.weather if you want
my response. I don't think there's anything wrong if I don't cross-post it.


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On 5/14/04 11:28 AM, in article ,
"The Artist Formerly Known As Your Highness"
wrote:

On 14 May 2004 10:17:58 -0400, Joseph Bartlo
wrote:


Regardless, my primary purpose for that post is to note how the hourly
precipitation probabilities in TWC forecasts are misleading.

You should write TWC about this and see what they say
[other comments deleted]

I won't comment about the rest of the Artist's post, but I actually would be
curious to see what TWC would say about this.

But Joseph, I wonder when you question the accuracy of hourly forecasts.
I'd expect them to be better about things like precip prob at a well-known
location like Gettysburg. But if you're talking about the hourly forecasts
given for a specific zipcode, I wouldn't expect much in the way of accuracy.
Especially for a place like the Poconos, where I'm sure there's a large
variability throughout the area.

I live in Acton MA, but as far as I know, the TWC forecasts are all based on
Bedford, which is about 10 miles closer to the coast. I don't know about
other weather stats, but I know that snow amounts can vary tremendously
between those locations.

To me, these forecasts are like extra decimal digits beyond the limits of
significance in a physics problem answer, when you really don't have enough
data to make a prediction beyond regional daily conditions. In that way, I
think that publishing hourly predictions is misleading. Perhaps TWC should
limit itself to what it can reasonably predict.

- Steve Stein


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TerriTickle wrote:

Joseph Bartlo wrote:


Well, on the trip to Gettysburg last weekend, my mother asked me if I wanted
to see an Amish community on the way back. I replied that I could probably
find plenty of ignorant people in Mount Pocono Same thing for single
women who were given jobs they don't deserve.



Hey now, some single women have very respectable jobs, you know. Take a
look at me : I have a highly respectable career distributing short
duration filmed entertainment.

There are lots of Amish people in Pennsylvania.
And lots of single women.
My question is, though, are there lots of Amish Single Women?
I'll bet there are, and in Pennsylvania no less.


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Oh, and your gigs roll over.
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In this message m I
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Robert "I'm So Queer I Can't Even Pee Straight" Buchanan gets smacked HARD!