Weather chart quiz

[Scott Dennstaedt, PhD]

On the short range prog chart below, what does the dark green color depicted over northwestern Georgia imply?

A - A forecast for the likelihood of moderate to heavy non-convective rain over a six hour period ending at the valid time on the chart
B - A forecast for a 55% or greater likelihood of non-convective rain reaching the surface at the valid time on the chart
C - A forecast for non-convective heavy rain over a 12 hour period beginning at the valid time on the chart
D - None of the above

[Ulysse]

Thank you for giving the chance of reviewing the interpretation of these charts. 

I'll try (after googling): This is a 36h forecast because generated at 1900z sunday and valid at 0000z tuesday. Dark green represents a >60% chance of rain at the valid time.

But is >0.01" of rain considered heavy ? I couldn't find a definition of "heavy" rain.

B is the correct answer?

 

Edited February 21, 2022 by Ulysse

[Danb]

In regard to the chart, where are the appropriate definitions of the information provided by the chart. Tremendous amount of info on the chart, it’d be great to be able to interpret it properly 

[Unit74]

Looks like to me Alabama refused to authorize any measurable precip and deferred to Ga.  My untrained observation is that a division on this boundary is arbitrary and lacks any scientific foundation.  

My answer is none of the above for this reason.

Edited February 21, 2022 by Unit74

[Scott Dennstaedt, PhD]

1 hour ago, Unit74 said:

My untrained observation is that a division on this boundary is arbitrary and lacks any scientific foundation.  

Yes, that is correct.  But there is a reason for this.  I discuss that in one of my YouTube videos that discusses these progs charts. You can view it here. I apologize for the audio...my other microphone I normally use was TU when I made this video.

Having said that, this is just an administrative aspect of how this chart is created, but does not drive the answer to the original question on how this area in northwestern GA should be interpreted.  

[Scott Dennstaedt, PhD]

1 hour ago, Danb said:

In regard to the chart, where are the appropriate definitions of the information provided by the chart. Tremendous amount of info on the chart, it’d be great to be able to interpret it properly. 

Ah yes...and the reason for the question.  You fell into my trap Dan.  

[Scott Dennstaedt, PhD]

On 2/20/2022 at 10:31 PM, Ulysse said:

Thank you for giving the chance of reviewing the interpretation of these charts. 

I'll try (after googling): This is a 36h forecast because generated at 1900z Sunday and valid at 0000z Tuesday. Dark green represents a >60% chance of rain at the valid time.

But is >0.01" of rain considered heavy ? I couldn't find a definition of "heavy" rain.

B is the correct answer?

 

Yes, B is the correct answer.  This area is a forecast for a 55% or greater likelihood of non-convective rain reaching the surface at the valid time on the chart. As I discuss in my Pilots Guide on page 115, this is non-convective rain expected at the surface at the valid time on the chart.  This defines precipitation coverage. The colors represent a likelihood forecast not a calibrated probability, however. Dark colors represent a 55% or greater likelihood this will occur at the valid time on the chart.  For those interested, please read my recent blog post that will provide more details.