RodneyS

Thanks for this analysis, Tom. Regarding February in DC in recent years, your memory is spot-on. If you compare DC temperature averages during 1872-1983 and 1984-2024, the average monthly increase from the earlier period to the latter period is 2.7 degrees. But as I think you suspected, February has experienced the largest increase of any month, at 3.6 degrees. December is second largest at 3.5 degrees. So, in keeping with the idea that the winter is being pushed back a couple of months, January must be third largest, right? Wrong! January has the second smallest increase, at only 2.2 degrees. Why? Because while a number of January days have had large daily increases, including the largest of the year on January 13th (7.4 degrees), a number of other January days have experienced temperature decreases, including the largest of the year on January 21st and 22nd (-4.6 degrees on each day). So anyone attempting to calculate recent daily January Temperature Normals in DC is in for a head-spinning experience. Regarding "Winter conditions more common in Mar/Apr, Summer conditions in Sept/Oct" -- the numbers do not support that in DC. Between 1872-1983 and 1984-2024, March has increased 3.1 degrees (3rd largest), and April has increased 3.0 degrees (tied for 4th largest), while September has increased only 2.4 degrees (4th smallest), and October has increased only 2.5 degrees (5th smallest). So, the picture is quite muddled, but January is in a class all its own. FYI, here are each of the average monthly temperature increases in DC from 1872-1983 to 1984-2024 in ascending order: May 1.7, January 2.2, June and September 2.4, October 2.5, November 2.7, July 2.9, April and August 3.0, March 3.1, December 3.5, February 3.6.

Thanks, Tom. I have looked at other January dates, but I thought that the 13th and 21st were the best to illustrate this phenomenon. I remember in the 1980s reading about the "January thaw" that tended to occur in the East around January 21st, which is now the coldest day of the year in DC! However, my analysis is quite simplistic, and so expanding upon it may shed additional light as to what is going on. It's great that some of you younger guys are now taking this seriously. The way science usually progresses is for the older generation, which is in a position of authority, to dismiss any new idea that challenges the conventional wisdom as being unworthy of investigation. But if something is really there, eventually the younger generation will take over that position of authority and make the new idea part of mainstream science.

Hmm, that may be something to look at -- I think the more creative ideas we have here, the better off we are.

The mystery is why this January 13th/21st thaw-freeze scenario began happening about 41 years ago in DC. Between 1872-1983, it was just the opposite, with the temperature rising on average by about 3.5 degrees between these two dates. Suddenly, around 1984, the temperature began falling on average by more than 8 degrees between these two dates, and it's still happening. Because the recent period has coincided with warmer temperatures worldwide, I would guess this phenomenon is somehow related to those warmer temperatures. However, why is it that January 21st in DC has defied the warming trend, by now being more than four degrees colder than it used to be? What is the forcing mechanism that brings about this counter-intuitive result?

Thanks. That helps a few competitors, including@MillvilleWxand @midatlanticweatherinch up the leaderboard.

This year on January 13th DCA recorded a minimum of 28 and a maximum of 51 degrees, and on January 21st DCA recorded a minimum of 16 and a maximum of 24 degrees. Those temperatures continue the strong trend toward a lower average temperature on January 21st than on January 13th, and bring both the January 13th and 21st DCA average temperatures for the 12 years that I have now been tracking them (2014-2025) very close to the prior DCA 30-year averages (1984-2013) for those two calendar days. That, in turn, means that the differences at DCA in the January 13th and January 21st average temperatures for 2014-2025 and 1984-2013 are about the same during each period. Specifically, the average temperature at DCA during 2014-2025 for January 21st was 8.8 degrees lower than the average temperature for January 13th, whereas during 1984-2013 that lower difference was 8.2 degrees. That provides even stronger evidence that what I found in January 2013 was not merely an aberration from the first 112 years of daily temperature recordkeeping in DC (1872-1983) -- in which the average temperature was 3.5 degrees higher on January 21st than on January 13th -- but rather a fundamentally new, if currently unexplained, reality: Period Jan 13 Jan 21 Jan 21 minus Jan 13 1872-1983 33.3 36.8 +3.5 1984-2013 40.3 32.1 -8.2 2014-2025 41.3 32.5 -8.8 Note that@Rhino16and I have done some additional research that indicates that a similar January 13th to 21st temperature shift has occured in other Eastern locations in recent years -- see my post of February 20, 2020 and his post of February 28, 2024 above. Does anyone here have a hypothesis as to what is causing this shift or know of someone who is researching this issue?

A little more snow yesterday at BWI, DCA, and IAD, but none at RIC -- @psuhoffman is still on top, but now with negative departures at all four airports. So @87stormsis in good position to take the lead with just a tad more snow at BWI, DCA, or IAD, and plenty of contenders are lurking with positive departures at each of those airports.

Another 0.1 inch at DCA and 0.3 inches at IAD Thursday evening. No change to the top of the leaderboard, but minor changes further down, as we prepare for perhaps 1-3 inches more on Sunday.

Just as BWI was earlier upgraded to 1.8 inches for this storm and RIC was finalized at 3.0, IAD has now been upgraded to 2.6 inches, and so the 2024-25 seasonal total there is now 8.9. See below revised table, which does not change the leaderboard much:

Thanks. Perhaps the snow measuring crew at RIC is inexperienced, and is not following the guidelines set forth here, although snow measurement is as much of an art as it is a science: https://www.weather.gov/gsp/snow

Thanks. It looks a little odd for RIC to have received 3 inches of snow with only 0.20 inches of precipitation. That's a ratio of 15 to 1, whereas the previous night's listing was 1 inch of snow with 0.09 inches of precipitation -- a ratio of 11 to 1. Not that ratios can't vary that much during a storm, but the initial report today of only 2 inches of snow at RIC would translate into a ratio of 10 to 1. In any event, if the 3 inches holds, it won't change the top of the leaderboard much, with @psuhoffmanstill holding a clear lead.

Thanks -- here is a further update to reflect that change:

Thanks, I found that same storm total at https://forecast.weather.gov/product.php?site=AKQ&issuedby=AKQ&product=PNS&format=CI&version=1&glossary=1&highlight=on

I think I have found the amount for RIC, which is 3.0 inches. So, pending any further updates, it appears that @psuhoffmanhas taken the lead:

I have the following reported snowfall for the Friday-Saturday overnight storm: BWI: 0.5, DCA 0.7, IAD 1.8. Does anyone have the amount for RIC? Perhaps @RIC Airport?