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NWS Area Forecast Discussion question


chescowx
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This might be best directed to Mitch but a question...and probably means I have way too much time on my hands this week!!

But in reading today's AFD it mentions a period of "seasonably cool" weather through the beginning of next week. In the next section is again says "seasonable" but then shows forecast highs and lows will be 5 to 10 below average. To a non-professional like me this sounds like "unseasonably cool"...is there a threshold or standard deviation of what seasonably cool is vs. unseasonably cool - unseasonably 10 or more?? Is this different by season (summer vs. winter etc.)??

Thanks for any answers and clarification!
Paul

 

 

 

 

 

 

 

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Sorry Tom - should have included the actual AFD in question - see bolded for what I am talking about - thanks!

The main concerns for the long-term forecast are a prolonged
period of mostly dry and seasonably cool weather through early
next week followed by large uncertainty regarding the evolution
of two tropical systems.

The forecast for Friday through Monday is fairly
straightforward. A large-scale trough will progress through the
Great Lakes and the Northeast through the period, with smaller-
scale vorticity maxima progressing around the larger-scale
trough. One of these perturbations should be advancing through
New England at 12Z Friday, and cold air advection on the
upstream side of the shortwave trough should reinforce the
cooling trend already commencing in the region. Forecast highs
should be around five degrees or so below seasonal averages, and
forecast lows Friday night may be 5-10 degrees below average
.
Latest MEX/ECE numbers are well below 50 in the Poconos, and it
is not out of the question Philly may dip below 60. Similarly
cool conditions are expected on Saturday.
 

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I don't have a scientific answer, but 5 degrees above/below average would seem to me to fall within the colloquial definition of "seasonably warm" or "seasonably cool."  Looking at it another way, today's normal high for PHL is, I believe, 84 degrees -- 89-90 on August 25 wouldn't strike me as unseasonably warm and 78-79 wouldn't strike me as unseasonably cool.

I think most people are mentally skewed to accept warmth as "seasonable" in the summer (most likely wouldn't consider 94 to be unseasonably warm for August 25, even though it is a +10 departure) and cold as "seasonable" in the winter (most also likely wouldn't consider 30 to be unseasonably cold in January, even though it is around a  -10 departure for PHL).

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On 8/24/2017 at 0:38 PM, chescopawxman said:

This might be best directed to Mitch but a question...and probably means I have way too much time on my hands this week!!

But in reading today's AFD it mentions a period of "seasonably cool" weather through the beginning of next week. In the next section is again says "seasonable" but then shows forecast highs and lows will be 5 to 10 below average. To a non-professional like me this sounds like "unseasonably cool"...is there a threshold or standard deviation of what seasonably cool is vs. unseasonably cool - unseasonably 10 or more?? Is this different by season (summer vs. winter etc.)??

Thanks for any answers and clarification!
Paul

 

 

 

 

 

 

Paul,

Which AFD (as in what time was it issued) are you referring to?

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21 hours ago, chescopawxman said:

Sorry Tom - should have included the actual AFD in question - see bolded for what I am talking about - thanks!

The main concerns for the long-term forecast are a prolonged
period of mostly dry and seasonably cool weather through early
next week followed by large uncertainty regarding the evolution
of two tropical systems.

The forecast for Friday through Monday is fairly
straightforward. A large-scale trough will progress through the
Great Lakes and the Northeast through the period, with smaller-
scale vorticity maxima progressing around the larger-scale
trough. One of these perturbations should be advancing through
New England at 12Z Friday, and cold air advection on the
upstream side of the shortwave trough should reinforce the
cooling trend already commencing in the region. Forecast highs
should be around five degrees or so below seasonal averages, and
forecast lows Friday night may be 5-10 degrees below average
.
Latest MEX/ECE numbers are well below 50 in the Poconos, and it
is not out of the question Philly may dip below 60. Similarly
cool conditions are expected on Saturday.
 

Sorry Paul, for some reason I thought you started the thread on Friday and couldn't find the afd that day.

Anyway the long term period goes from Friday through Wednesday, so that first sentence (mostly) is covering expected temps on five days, not just Friday night.  As to one person's threshold as to when it

becomes unseasonably warm or cold, probably the most objective way would be to use 1 std from typical temps for that time of year.  I remember Mark DeLisi used to use 2 std(s) to corroborate events which were unusually cold or warm.

 

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5 hours ago, Rainshadow said:

Sorry Paul, for some reason I thought you started the thread on Friday and couldn't find the afd that day.

Anyway the long term period goes from Friday through Wednesday, so that first sentence (mostly) is covering expected temps on five days, not just Friday night.  As to one person's threshold as to when it

becomes unseasonably warm or cold, probably the most objective way would be to use 1 std from typical temps for that time of year.  I remember Mark DeLisi used to use 2 std(s) to corroborate events which were unusually cold or warm.

 

Got it - makes sense - thanks Tony!!

 

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