RodneyS

On 1/7/2018 at 10:29 AM, RodneyS said:

Dulles fell below zero this morning for the first time since February 24, 2015.  This morning's reading of -1 broke the record for January 7th of +1 that was set in 2014.

This morning, Dulles fell below zero for the first time since January 7, 2018.  However, this morning's reading of -2 fell short of the January 31st record of -7 set in 1965.

On 1/1/2019 at 8:08 AM, RodneyS said:

The final 2018 figures are 66.74 inches at IAD and 66.28 inches at DCA.  The IAD total broke the 2003 record by 1.07 inches and the DCA total broke the 1889 record by 4.95 inches. 

DCA just recorded its first 1-inch or more precipitation day of 2019, after a record-breaking 24 such days last year.  More remarkably, the amount of precipitation there since July 1, 2018 is now more than 44 inches.  The previous record for any July-March period was only 43.81 inches, set during July 1934-March 1935.  So, we have exceeded that total with more than two months still to go. 

On 1/22/2013 at 8:31 AM, RodneyS said:

If the 1981-2010 temperature normals for Reagan National Airport are taken at face value, DCA temperatures on average bottom out during January 12th-17th (at a mean of 35.7 degrees), then rise gradually (to 35.9 degrees on January 21st, 37.2 degrees on February 5th, and peak between July 12th-21st at 80.0 degrees). However, January daily temperatures during this period -- and even more so during the most recent 30 years, 1984-2013 -- appear inconsistent with those normals. During the past 30 years, the first 14 days of January at DCA have each averaged above the 1981-2010 normals, whereas January 19th-23rd have each averaged below those normals. This may be illustrated by comparing January 13th to January 21st average temperatures during the past 30 years at DCA, as well as looking at the historical DC temperature record for those two days and the coldest average day of the year.

For the first 112 years of official DC daily temperature history -- 1872-1983 -- January 13th was the coldest January day, at 33.3 degrees on average; and January 21st was the second warmest January day, at 36.8 degrees on average. The January temperature peaked on the 22nd at 37.2 degrees on average during 1872-1983, with the annual mean temperature bottoming out on February 5th at 32.6 degrees on average.

However, during 1981-2010, the mean temperature at DCA on January 13th was 38.7 degree on average, decreased sharply to an annual minimum of 32.2 degrees on average on the 21st, and rose about halfway back to 35.3 degrees on average on February 5th. Further, the disparity with 1872-1983 has widened during 1984-2013, with January 13th the warmest January day of this most recent 30-year period at 40.3 degrees on average, January 21st the coldest day of the year at 32.1 degrees on average, and February 5th the coldest February day (29 years through 2012) at 35.9 degrees on average.

To recap, January 13th has gone from being the coldest January day at 33.3 degrees on average during 1872-1983 to the warmest January day at 40.3 degrees on average during 1984-2013 -- an increase of 7.0 degrees. January 21st has been the mirror image of January 13th -- going from the second warmest January day at 36.8 degrees on average during 1872-1983 to the coldest day of the year at 32.1 degrees on average during 1984-2013 -- a decrease of 4.7 degrees. Finally, February 5th has gone from being the coldest day of the year at 32.6 degrees on average during 1872-1983 to merely the coldest February day at 35.9 degrees on average during 1984-2012 -- an increase of 3.3 degrees.

The increase in temperature on February 5th between these two periods has been pretty clearly within the range of what would be expected in an era of warming temperatures, as February temperatures 1984-2012 have been 2.9 degrees warmer on average than during 1872-1983. But what about the January temperature record, and in particular, the contrast between January 13th and 21st during these two periods? Is that merely an aberration, or is a more fundamental change taking place that is not reflected in the current temperature normals?

Time for an update.  The 1984-2013 trend that I observed six years ago regarding January DCA temperatures peaking on or about the 13^th and bottoming on or about the 21st has continued.  If that trend during the period 1984-2013 were only a temporary aberration, since that time January 13^th would be as likely to be colder than January 21^st as it would be to be warmer.  However, during 2014-19, January 13^th DCA temperatures averaged 39.1 degrees, whereas January 21^st DCA temperatures averaged only 34.4 degrees.  That brings the average DCA temperature during 1984-2019 to 40.1 degrees on January 13^th vs. only 32.6 degrees on January 21^st.   A statistical test (two-tailed T-test) indicates that it is highly improbable that this 7.5-degree difference for that 36-year period is a random variation, with the odds of that being only about 1 in 2200.

Moreover, in the not-too-distant future, NOAA's National Climatic Data Center (NCDC, now part of the National Centers for Environmental Information in Asheville, NC) will begin to calculate its new daily 30-year temperature normals for the period 1991-2020. That period is now only one year shy of completion for January 13^th and January 21^st, and the average DCA temperature during 1991-2019 is 41.3 degrees on the former day and 32.6 degrees on the latter day.   A two-tailed T-test of this 8.7-degree difference for that 29-year period shows that difference is even more unlikely to be a random variation, with the odds of that being only about 1 in 8500.

So, how will the NCDC handle the fact that January temperatures at DCA now seem to peak around January 13^th and bottom around January 21^st? Does anyone here know someone at NCDC that works on temperature normals or know someone else (including yourself) that is knowledgeable in this area?

On 1/14/2018 at 10:17 AM, RodneyS said:

According to my records, yesterday's 41-degree temperature spread at DCA (62 maximum, 21 minimum) was the greatest since December 22, 1998 (67/24).

And the January 20, 2019 38-degree temperature spread at DCA (56 maximum, 18 minimum) was the greatest since the January 14, 2018 41-degree spread.

This morning both DCA and IAD recorded their daily high temperatures.  However, DCA's high was 56 degrees vs only 40 at IAD.  As best as I can tell, that 16-degree high temperature difference at the two airports was the second greatest ever, behind only December 9, 1975, when DCA recorded a high of 53 and IAD recorded a high of 36.

Thanks for your voluminous stats work, Roger.  By the way, the National Weather Service is currently showing 13.0 inches of snow for Richmond so far this season; see https://w2.weather.gov/climate/index.php?wfo=akq

DCA _ NYC _ BOS __ ORD _ ATL _ IAH ____ DEN _ PHX _ SEA

3.2      3.5     2.8       4.9     3.4     2.2          1.9     -1.5     0.4 

7 hours ago, Fozz said:

I'm not sure of their exact methods. I guess it would make sense to do that with their 30 year averages since the sample size isn't so big. I know they reduced the totals of Dec 2009 and Feb 2010 a few months after that winter, probably because of measurement issues or some other reason I can't clearly recall.

I can state with a high degree of confidence that the NWS does not smooth outliers in its 1981-2010 monthly and annual precipitation "normals" but rather uses the 1981-2010 averages, albeit with an unconventional rounding methodology.  I state this because I have computed the 1981-2010 averages for each month at DCA, and they either match the DCA normals exactly for each month or they are rounded up by 0.01 inches. For example, if you average the January 1981-2010 precipitation totals at DCA, you get 2.803 inches.  For some reason, NWS rounds this to 2.81, whereas using a conventional rounding methodology would result in 2.80.  The annual 1981-2010 precipitation normal at DCA is shown as 39.74 inches, whereas  I calculate 39.71 inches. However, there is no smoothing.  So, for example, the August 1981-2010 normal at DCA is only 2.93 inches, which is rounded up from the 1981-2010 2.924 inch average.  However, the historical August 1871-2018 DC precipitation average is 4.07 inches, and that is not taken into account. So, the 1981-2010 DCA August normal makes it appear that August is now a relatively dry month at DCA.  But is it really, or was the 1981-2010 August average there an aberration?  I would guess the latter, because beginning in 2011, August precipitation at DCA has averaged 3.77 inches -- closer to the long-term average than to the 1981-2010 average.  

In other words, you have to be careful with monthly precipitation normals because they may have little predictive value.   Regarding annual precipitation normals, 30-year annual precipitation averages have ranged between 38.62 inches during 1961-1990 to 43.01 inches during 1871-2010, with an 1871-2018 average of 40.92 inches.  So, again, using a 30-year annual precipitation "normal" can be misleading, as the most recent 30-years may be too short a period to conclude that anything other than a random variation is occurring. 

Congratulations to Roger, wxallannj, and especially overall winner Scotty for their impressive performances. 

13 hours ago, RodneyS said:

I've been away for a few days, but I just discovered that IAD broke the annual precipitation record on Friday, with 1.08 inches.  It has now added 0.52 inches today, and so the current total is 66.73 inches, which exceeds the previous record by 1.06 inches. Both IAD and DCA figure to get a little more rain before midnight, and so I'll post the final 2018 totals tomorrow morning. 

The final 2018 figures are 66.74 inches at IAD and 66.28 inches at DCA.  The IAD total broke the 2003 record by 1.07 inches and the DCA total broke the 1889 record by 4.95 inches. 

On 12/22/2018 at 5:09 PM, PrinceFrederickWx said:

IAD’s in the red zone but misses the game-winning field goal lol

There’s a chance of rain tomorrow night, but probably the last significant chance to win would be the Thursday/Friday system.

I've been away for a few days, but I just discovered that IAD broke the annual precipitation record on Friday, with 1.08 inches.  It has now added 0.52 inches today, and so the current total is 66.73 inches, which exceeds the previous record by 1.06 inches. Both IAD and DCA figure to get a little more rain before midnight, and so I'll post the final 2018 totals tomorrow morning. 

58 minutes ago, PrinceFrederickWx said:

@donsutherland1

@RodneyS

We still need another 0.58” at IAD to break the record right?

That's correct.  And nothing all that promising on the immediate horizon -- AccuWeather is now projecting only 0.2 inches at Dulles through year end. 

12 hours ago, PrinceFrederickWx said:

Nice- we have a legit shot at this now with the late week storm coming too.

Again, for what little it may be worth, AccuWeather is currently projecting 1.53 inches of precipitation through year's end at Dulles, which would exceed the annual record there by 0.21 inches.

On 12/15/2018 at 12:49 PM, PrinceFrederickWx said:

Where are we on IAD? They have 1.33” for this system so far by my count.

Timely question, as the IAD record is 65.67 inches, set in 2003.  The total through today for 2018 is 64.36 inches.  So, IAD is closing in on the record, but still needs 1.32 inches to break it.

On 12/8/2018 at 8:55 PM, RodneyS said:

That's right -- not a done deal yet, especially with the big southern snowstorm staying to the south of DC.  For what it's worth, AccuWeather is currently projecting 1.23 inches at DCA through month's end.  However, only 0.28 inches is projected there through December 19th, and long-range precipitation forecasts are not exactly sure things.  

AccuWeather's shorter term forecast was too low, and DCA broke the all-time DC record between 5:52-6:52 this morning.  We now (as of 7:52 AM) are up to 61.40 inches of precipitation for the year vs the previous record of 61.33 inches set in 1889.

On 12/6/2018 at 12:11 PM, PrinceFrederickWx said:

I think DCA needs another 0.56" to break the record now, right? Looks like they had 0.32" Dec 1-2. I'm getting slightly concerned that we're gonna find a way to fail at this now lol

@RodneyS

That's right -- not a done deal yet, especially with the big southern snowstorm staying to the south of DC.  For what it's worth, AccuWeather is currently projecting 1.23 inches at DCA through month's end.  However, only 0.28 inches is projected there through December 19th, and long-range precipitation forecasts are not exactly sure things.  

On 11/26/2018 at 1:18 PM, RodneyS said:

Not sure whether we're done for the day, but DCA already has recorded 0.44 inches of precipitation, bringing the November total to a DC record 7.55 inches.  So, one record down, one to go -- DCA needs just 0.9 inches between now and the end of the year to break the annual record.  Every December except nine in DC weather history has seen at least that much. 

November 2018 precipitation at DCA appears to be finalized at 7.57 inches, leaving the annual total of 60.46 inches there just 0.87 inches shy of the 1877 DC annual record.  As 138 of 147 previous Decembers in the official precipitation history of DC have exceeded 0.87 inches, the odds of breaking the record are about 94%.  Also, the second half of 2018 (July-December) DCA precipitation total of 35.28 inches has already broken the second half record of 33.55 inches set in 1878.

Additionally, November 2018 average temperature at DCA appears finalized at 46.5 degrees, which is 3.1 degrees below the 1981-2010 normal, and the lowest average November temperature there since 1997. 

DCA _ NYC _ BOS __ ORD _ ATL _ IAH ___ DEN _ PHX _ SEA

0.0      0.0     -0.6      0.7     -0.5    0.2         0.7     1.0     0.3

On 11/24/2018 at 8:35 PM, donsutherland1 said:

I believe there's a pretty good chance that both the November and annual precipitation records will be broken.

Not sure whether we're done for the day, but DCA already has recorded 0.44 inches of precipitation, bringing the November total to a DC record 7.55 inches.  So, one record down, one to go -- DCA needs just 0.9 inches between now and the end of the year to break the annual record.  Every December except nine in DC weather history has seen at least that much. 

On 11/16/2018 at 10:00 AM, donsutherland1 said:

4th with 58.58" precipitation. That record is within reach. The record is 61.33", which was established in 1889.

With today's 1.42 inches at DCA, the yearly total now stands at an even 60 inches -- still 4th all-time in DC, but now a strong likelihood to break the record.  Even assuming no more precipitation in November, DCA would need only 1.34 inches in December to do so.  In the previous 147 Decembers in official DC precipitation history, only 17 times has precipitation been less than that.  Moreover, should DCA record only 0.08 inches more this month, that would break the all-time DC November record of 7.18 inches, set in 1877.

BWI: 20.3"

DCA: 13.9"

IAD: 23.6"

RIC: 13.3"

Tiebreaker (SBY): 10.5"

On 11/16/2018 at 10:00 AM, donsutherland1 said:

4th with 58.58" precipitation. That record is within reach. The record is 61.33", which was established in 1889.

Not only within reach, but based on historical DC precipitation averages for November 18-December 31, we would receive another 4.28 inches through year's end, bringing the total to 62.86 inches.  Further, AccuWeather currently is projecting an additional 4.39 inches in DC through year's end. Cautionary note: While, as Don says, 1889 was the all-time wettest in DC history, oddly enough December 1889 was the driest DC December ever, at only 0.19 inches.  

DCA _ NYC _ BOS ___ ORD _ ATL _ IAH ___ DEN _ PHX _ SEA

3.5     2.9      2.4         0.0      0.0     0.0       -1.5     3.7     1.9

DCA _ NYC _ BOS ___ ORD _ DTW _ BUF ___DEN _ SEA _ BTV

12.5"  25.0"  37.5"      41.0"   43.5"   89.0"     52.5"  4.5"   73.0" 

On 9/22/2018 at 2:51 PM, RodneyS said:

We are now up to 7.54 inches of precipitation at DCA in September 2018. That means that the previous April-September DC record of 39.91 inches established in 1889 has fallen.  The April-September 2018 total at DCA now stands at 39.99 inches, and the May-September 2018 total there is now 36.40 inches. 

September 2018 precipitation at DCA was 9.73 inches, good enough for 5th on the all-time DC list.  January-September 2018 precipitation at DCA was 49.83 inches, third on the all-time list, behind only 1886 (50.65) and 1889 (50.63).