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Messages - EricPeterson

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1
Yes, that's quite possible.  We know that the numbers of strong (F3 and up) tornadoes are decreasing.  Whether that translates to less severe thunderstorms in non-tornado country is still TBD.  I'm not sure how to get a decent metric for thunderstorm severity.  Also it could be that the extreme short duration rainfalls are not severe but just stalled or regenerating.  Don't know why that would be decreasing.

2
After a sabbatical I am back analyzing the weather.   This analysis is about short duration rainfalls that cause flash floods.  It's a very simple analysis looks at the maximum rainfall for a one hour duration through six hours duration.  The trend is the slope of the linear fit for the highest rainfall of the year.  I also do the trend for each month, although the monthly trend is interesting for reasons other than flooding.  The flash flood is really based on the maximum rain for the year.  I try to get 70 years of data, but you will see on some individual stations there can be a lot of missing or junk data even with a reasonable threshold for file size.

There's a consistent pattern which shows up with a few exceptions at individual stations.  The pattern is that the longer the duration, the more likely that there's a less negative (or positive) trend in max rainfall.  It's most noticeable in October.  It's possible that warmer oceans are lingering into that month causing higher extreme rainfalls or perhaps late season hurricane remnants since the upward trends seem to be clustered in the eastern US.

I simply follow the data, but  I ask myself why would extreme hourly rainfall be trending down in light of global warming which increases atmospheric moisture in general?  My guess, so far, is that the dynamics have changed, perhaps with less severe cold fronts there are less extreme rainfalls.

Results, code and compressed (processed) data: https://followthedata.dev/wx/rfhourly/

3
Weather / Re: Chilly morning
« on: January 24, 2021, 1458 UTC »
16 here in the valley.  I've collected up some of the virtual snowstorms for this year here: https://virtualsnowclub.com

4
Weather / Re: Rain to snow possible in the northeast Christmas Eve/Day
« on: December 19, 2020, 1514 UTC »
Today's euro says zip and has been pretty consistent.

5
Weather / Re: Big Snow possible Wed/Thu in the Northeast
« on: December 12, 2020, 1702 UTC »
Snow is good for getting nice even moisture into the ground.  I can also get lots of steps into the fitbit shoveling about 400 feet of driveway.  Sunny and 57 here right now, should make low 60's.

6
Weather / Re: bye bye warm weather
« on: December 09, 2020, 1336 UTC »
22 in the valley, coolest so far for the season.  Getting any of that snow up there Chris?

7
Weather / Re: Rainfall trends DC and C-Ville
« on: December 06, 2020, 2328 UTC »
Well there's not much change regardless of how you look at it.  One thing I think is noteworthy though, the decrease in weeks with zero or almost no precip on the seven day plots.  I suspect that would hold for much of the midwest through the east but I'd have to look at a lot more stations to show that effect is real.

8
Weather / Rainfall trends DC and C-Ville
« on: December 06, 2020, 1700 UTC »
I added up days of rainfall for DCA and Charlottesville.  There is an increase in days of measureable rain (a hundredth or more) but a slight decrease in "real" rain (a tenth or more).  That decrease is probably negligible.  That plot is here:

Because of that slight divergence, I got interested in the trend in each bin of rainfall from very light to very heavy.  Unfortunately the daily rainfall totals don't indicate the timing so there's no way to know if 0.2 one day and 0.8 the next day is really one rainfall of 1.0 falling before and after midnight.  So I double counted the days and trended that.  Double counting creates a few trend artifacts.   Finally I did the seven day totals (not double counted).  The seven day plots show an increase in seven day rain amounts of about 2 inches.  For our area that's a relatively wet week.  More plots and links to the code here: https://virtualcoinclub.com/wx/rftrends/  The README has instructions to download the data for any location although you have to search a bit to find longer complete records.

9
Weather / Re: bye bye warm weather
« on: December 03, 2020, 1548 UTC »
24 here in the  Shenandoah Valley this morning.  Second coldest of the year so far (23 about two weeks ago).  I finally bit the bullet and cleaned the wood stove last Saturday and have been running it since.  There's nothing like the cheap comfort of radiant heat from a wood stove.

10
Weather / Atlantic hurricane rapid intensification trends
« on: November 24, 2020, 1817 UTC »
Continuing my exploration of the HURDAT2 dataset, I've calculated trends for the rapid intensification of hurricanes in the Atlantic basin. The claim is that warmer waters from global warming are leading to more episodes of RI.  I believe that claim is true for some categories of RI although there is a lot of natural variation.  However the vanilla claim of RI, which is defined as strengthening of 30 knots or more in 24 hours, is very common, about 60% of all hurricanes have at least one 24 hour period with >= 30 knots of strengthening.  That 60% number is flat over the past 30 years:


However if you consider all tropical storms, not just hurricanes, there's a pronounced drop in RI:


I believe that is due to the detection and naming of more tropical storms.  There's an insinuation in some news stories that the glut of named storms this year is also due to global warming.  But they have to pick one thing to blame on global warming: more rapid intensification or more named storms, and then show the evidence.  I believe that Wilma (2005) and Felix (2007) are potential evidence of extreme RI that might be increasing although it is very sporadic.
Finally I also calculated and plotted rapid weakening. 

Not surprisingly a number of the strongest storms weakened rapidly.  I explicitly excluded weakening over land since that is obvious and not what I am looking for.  I assume the trend in rapid weakening should be flat.  Storms that head into high latitudes can weaken rapidly but there should be no trend in high latitude movement over time.  Instead I see a slight uptick in rapid weakening over time.  The descriptions of those storms sometimes include the phase "unexpected collapse".
Graphs and link to code at https://virtualcoinclub.com/wx/ri/  The page includes a table generated from the data of all the rapidly intensifying storms since 1950.

11
Weather / Re: Atlantic hurricanes are slowing down at landfall
« on: November 23, 2020, 0301 UTC »
Actually the results aren't quite the same.  Storm motions in storms like Dorian are now calculated more precisely.  Dorian was special because it only hit one Bahamas island according to the lat/lons.  I calculate the motion in 6 hour intervals before and after and find the slowest 6 hour segment (1.5 mph).  The bottom line is there is also an increase in the percentage of the slowest-of-the-slow storms.

12
Weather / Re: Atlantic hurricanes are slowing down at landfall
« on: November 23, 2020, 0256 UTC »
I rewrote the code.  Same results but much cleaner Python.  The per-storm logic is all in one location, about a page of code.  The year summary logic is about a half page of code.  The biggest difference is instead of separate copy/paste versions for each analysis, the code is consolidated.  Another feature is to automatically generate the HTML table of slow moving storms.  Yeah, that's 20 year old generation and done better in table generation code available on the server side or in javascript.  But nothing's quite as good as roll-your-own if you have the time since data is being pulled from various dictionaries (e.g. storm metadata).

Now I need to re-implement the rest of the plots like rapid intensification, slower weakening after landfall, etc.  I'll add a rapid weakening plot (obviously not including storms over land) to see if that's change.  Rapid intensification was flat in the old code, should be the same with the new code.

13
Weather / Re: bye bye warm weather
« on: November 19, 2020, 1913 UTC »
Got down to 23 here and the last ice in the barrels in the shade just melted.  It's 63 now and I opened some windows.  Winter is over, spring is here.

14
Weather / Re: bye bye warm weather
« on: November 18, 2020, 0212 UTC »
It's here now.  Winds still gusting to 25-30 and actually keeping it a little warmer (mixing), 38 now.  I picked some green cherry tomatoes, they are not going to be very good even if they ripen.

15
Weather / Re: bye bye warm weather
« on: November 15, 2020, 1437 UTC »
We have some transition days here on the east coast.  Some 60's today with showers.  Probably 50's tomorrow and 40's by Wed.  I think La Nina winters bring these cold shots with moderation and mostly dry weather for us (not much southern stream moisture).  For you La Nina should bring the same variation but a better chance of storms.

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