Our region's extreme run

[RodneyS]

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.

[PrinceFrederickWx]

4 hours ago, RodneyS said:

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.

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

[RodneyS]

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.

[PrinceFrederickWx]

1 hour ago, RodneyS said:

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.

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

[RodneyS]

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.

[PrinceFrederickWx]

@donsutherland1

@RodneyS

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

[RodneyS]

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. 

[donsutherland1]

4 hours ago, PrinceFrederickWx said:

@donsutherland1

@RodneyS

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

That's correct.

[PrinceFrederickWx]

3 hours ago, RodneyS said:

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. 

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.

[RodneyS]

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. 

[Fozz]

I did a Python analysis on Baltimore's precip totals, just cause I felt like it, and it turns out that 2018 single-handedly wrecked the normal distribution. Precip totals are now skewed to the right. Sometimes one extreme outlier is all it takes.

Baltimore's final total of 71.82" is over 4 standard deviations above the long-term pre-2018 average.

[RodneyS]

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. 

[PrinceFrederickWx]

2 hours ago, Fozz said:

I did a Python analysis on Baltimore's precip totals, just cause I felt like it, and it turns out that 2018 single-handedly wrecked the normal distribution. Precip totals are now skewed to the right. Sometimes one extreme outlier is all it takes.

Baltimore's final total of 71.82" is over 4 standard deviations above the long-term pre-2018 average.

Doesn’t NWS remove or smooth over extreme outliers when calculating averages though? I thought I remember reading they did something to Dec 09 and Feb 03 when calculating 1981-2010 snow averages, for example.

[Fozz]

4 hours ago, PrinceFrederickWx said:

Doesn’t NWS remove or smooth over extreme outliers when calculating averages though? I thought I remember reading they did something to Dec 09 and Feb 03 when calculating 1981-2010 snow averages, for example.

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.

[RodneyS]

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. 

[Fozz]

22 minutes ago, RodneyS said:

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. 

I agree, which is why I ran the numbers using the entire period from 1871 to 2017. I'm not all that comfortable with a sample size of only 30 if I can do better.

[cae]

On ‎1‎/‎1‎/‎2019 at 6:20 AM, Fozz said:

I did a Python analysis on Baltimore's precip totals, just cause I felt like it, and it turns out that 2018 single-handedly wrecked the normal distribution. Precip totals are now skewed to the right. Sometimes one extreme outlier is all it takes.

Baltimore's final total of 71.82" is over 4 standard deviations above the long-term pre-2018 average.

From what I can tell, nobody knows the appropriate probability distribution for precipitation data.  It appears to vary by region.  The normal distribution isn't widely used because it allows for negative precipitation values and underestimates the probability of large totals.  The gamma distribution is widely used, but it too can underestimate the probability of extreme events. 

[Fozz]

17 minutes ago, cae said:

From what I can tell, nobody knows the appropriate probability distribution for precipitation data.  It appears to vary by region.  The normal distribution isn't widely used because it allows for negative precipitation values and underestimates the probability of large totals.  The gamma distribution is widely used, but it too can underestimate the probability of extreme events. 

I did a Shapiro-Wilk test on the precip data through 2017, and it confirmed a normal distribution (or close enough to it). But with 2018 included, that was no longer the case.

[RodneyS]

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.

[MN Transplant]

13 minutes ago, RodneyS said:

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.

I’m surprised we haven’t had more days like this.  Nice catch.

[RodneyS]

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.

[RodneyS]

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. 

[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.

[WxUSAF]

BWI set a record low max today of 21.

[RodneyS]

Today's high temperature of 74 at DCA was 50 degrees warmer than the high of 24 recorded there just four days ago.  As best as I can tell, that 4-day warm-up of 50 degrees in the DC maximum was second only to the 52-degree 4-day warm-up in maximum temperatures that occurred from February 16, 1930 (24) to February 20, 1930 (76).

[PrinceFrederickWx]

Not sure if @RodneyS had noticed this, but for DCA, the 10.3" recorded from 1/12-14 this year would make #7 on the list of top 3-day snowfalls, per their criteria (i.e. snowfall must have occurred on all three days). This would be on the second chart, not the first one that lists top snowfalls overall.

https://www.weather.gov/lwx/winter_storm-pr#TopDaySnowfall

[RodneyS]

5 hours ago, PrinceFrederickWx said:

Not sure if @RodneyS had noticed this, but for DCA, the 10.3" recorded from 1/12-14 this year would make #7 on the list of top 3-day snowfalls, per their criteria (i.e. snowfall must have occurred on all three days). This would be on the second chart, not the first one that lists top snowfalls overall.

https://www.weather.gov/lwx/winter_storm-pr#TopDaySnowfall

I had not noticed that, but had noticed that overall that snowstorm tied for 23rd on the all-time DC list (with February 22-23, 1987).  Also, the 10.6 inches received at Dulles in that storm was 16th all-time there, displacing the 10.3 inches that fell at Dulles during the infamous (poorly-forecast) 10.3-inch snowstorm of January 25, 2000. 

[RodneyS]

April 2019 averaged 62.4 degrees at DCA, second all-time in DC to the 63.8 recorded in April 2017.  However, precipitation was only 2.24 inches -- the first below normal month at DCA since October 2018.

[Subtropics]

On 5/1/2019 at 12:28 PM, RodneyS said:

April 2019 averaged 62.4 degrees at DCA, second all-time in DC to the 63.8 recorded in April 2017.  However, precipitation was only 2.24 inches -- the first below normal month at DCA since October 2018.

Two historically warm years out of 3, with last year being historically chilly if I remember correctly? Doesn't seem like DC has "average" months all that often in the spring.

[RodneyS]

16 hours ago, Subtropics said:

Two historically warm years out of 3, with last year being historically chilly if I remember correctly? Doesn't seem like DC has "average" months all that often in the spring.

You're right that last April was relatively cool at DCA -- 54.9 degree average, which was 1.9 degrees below the 1981-2010 normal, and 7.5 degrees cooler than this year.