Central PA Winter 25/26 Discussion and Obs

[Blizzard of 93]

12z Euro coming in slightly better for snow & precip in the LSV over its previous run.

Maps coming soon.

[Blizzard of 93]

4 minutes ago, Blizzard of 93 said:

12z Euro coming in slightly better for snow & precip in the LSV over its previous run.

Maps coming soon.

 

[Blizzard of 93]

12z Euro precip improved for the LSV at 12z vs. 6z.

[Voyager]

Exceeded the forecast high for today. Currently 46 here (41), but we seem to have exceeded the wind, as well.

[Blizzard of 93]

51 on my home Marysville station.

Felt great to go out without a coat!

[CarlislePaWx]

Here in Carlisle just after 1:00pm, the skies are mostly sunny and the temperature has risen to a balmy 48.7 degrees.  The last time the temperature was at or above this was on January 13th with a high temp of 50.2 degrees.  So, we managed to stay below 50 degrees for an entire month.  My snowpack continues to fight off the warmth and is still at 3" solidly everywhere.  This is just about a 50% decrease from the Jan 25th storm.  That 1" of sleet I had at the end of the storm has helped to put on the retention fight.

[Mount Joy Snowman]

56 minutes ago, Itstrainingtime said:

It's actually 2/10s of a mile south of me.

Haha I was actually going to chime in to say the same, that you are probably juuuust outside of the blue dot. 

[Blizzard of 93]

5 minutes ago, Mount Joy Snowman said:

Haha I was actually going to chime in to say the same, that you are probably juuuust outside of the blue dot. 

Lol, .49 for ITT!

[Itstrainingtime]

33 minutes ago, Blizzard of 93 said:

51 on my home Marysville station.

Felt great to go out without a coat!

Today your first day this week without one?

[Blizzard of 93]

I do like seeing the healthy looking established precip shield already covering most of Missouri & extending the whole way down to the Texas Gulf coast.
The ingredients are there for us to over perform if we get the rates in southern PA tomorrow evening.

[Itstrainingtime]

23 minutes ago, Blizzard of 93 said:

I do like seeing the healthy looking established precip shield already covering most of Missouri & extending the whole way down to the Texas Gulf coast.
The ingredients are there for us to over perform if we get the rates in southern PA tomorrow evening.

My apologies! I intended to like your post and just realized that I did not. Sorry about that!!!

[canderson]

Car reads 51 at LL Bean in Mechanicsburg. It’s like Christmas Eve out today with traffic. 

[Itstrainingtime]

15 minutes ago, canderson said:

Car reads 51 at Lal Bean in Mechanicsburg. It’s like Christmas Eve out today. 

52.2 here. Feels like 65. As much as I love cold weather, today is a stellar day.

[canderson]

Just now, Itstrainingtime said:

52.2 here. Feels like 65. As much as I love cold weather, today is a stellar day.

Short sleeve weather - next week looks even warmer possibly 

[Ruin]

up to 50 forecast 41? yeah how can it be this inaccurate lol 

 

 

 

[Ruin]

[canderson]

CTP now has Harrisburg with snow accumulation Sunday evening - less than .5” current forecast. 

[Mount Joy Snowman]

At 18z the HRRR still isn't on board and the NAMs now keep things mostly all rain.  Guess we'll find out tomorrow ha.

[pawatch]

3 hours ago, Blizzard of 93 said:

Lol, .49 for ITT!

52 degrees here today. Was outside with just long sleeve shirt.
Snow is melting but looks to be soaking into the ground ,don’t see any runoff.

[Blizzard of 93]

1 hour ago, Mount Joy Snowman said:

At 18z the HRRR still isn't on board and the NAMs now keep things mostly all rain.  Guess we'll find out tomorrow ha.

18z just cut back as well. About .20 less precip for the LSV, so snow amounts are now less than 2 inches for most of us this run.

[Blizzard of 93]

I am so ready to be done tracking this system!

2 weeks ago, many of us started watching this weekend period. It went from potential major storm to no storm to late yesterday looking like a potential recovery to an Advisory event to now who the bleep knows!

 

[Blizzard of 93]

Under 48 hours, nine times out of 10, once a trend starts, it usually either builds momentum or levels out. These continual all over the place rug pulls are brutal with this potential event.

[Blizzard of 93]

I mean, just look at thIs from @Newman in the Philly thread.

Just a tiny difference between 12z and 18z RRFS. Something must've gotten into the NOAA mesoscale products at 12z LOL

[MAG5035]

17 hours ago, Itstrainingtime said:

Please understand, I wasn't being critical of you in any way. I don't do that. It was just ironic that the GFS jumped on to something it largely wanted no part of even when the Euro did.

No worries, I didn’t at all take it as any kind of criticism. I did think it was funny that I pretty much gave this storm 2-3 days up to the 48-60hr range for it to come back north and then of course it does right after I made my “it’s probably not happening” post. 

So now a period of steadier precip happening with this looks fairly likely, certainly from the turnpike south but perhaps as expansive as from I-80 south. Big issue now that’s happening with guidance overall is suggesting the lower column might not be cold enough. GFS has obviously been the coldest solution in that regard, but high res NAM, HRRR, Euro to a degree present that this might start as rain and possibly remain so for a majority of the event. While surface temps probably won’t be as warm as today (likely more high 30s to low 40s), there’s depth to the low level warmth in the column all the way up to about 850mb. 925mb (3000 ft) temps are progged as much as +5-6ºC prior to precip onset on most guidance. That makes a rain start pretty likely. Colder sub 0ºC air at that level eventually tries to advect in from the NE as the storm deepens as it gets off the coast. GFS does it the fastest, hence its snowier solution. Euro draws it in late, which leads to measurable snows more in eastern PA. High res guidance like the 3k NAM isn’t drawing it down in time. 

[Ruin]

3 hours ago, canderson said:

CTP now has Harrisburg with snow accumulation Sunday evening - less than .5” current forecast. 

little to no accumulation is what they love the best fav phrase lol

[Ruin]

1 hour ago, Blizzard of 93 said:

I am so ready to be done tracking this system!

2 weeks ago, many of us started watching this weekend period. It went from potential major storm to no storm to late yesterday looking like a potential recovery to an Advisory event to now who the bleep knows!

 

notice how every system is a big one then as the event gets closer it just gets weaker 90% of the time 

[Itstrainingtime]

37 minutes ago, Ruin said:

notice how every system is a big one then as the event gets closer it just gets weaker 90% of the time 

Not overly surprising in a progressive flow.

[canderson]

50 my the high at the house today. The snow on the west-facing garden is about 80% gone. And really no signs or hope of a winter storm in the next week and a half. Time is starting to tick quickly. 

[Ruin]

2 hours ago, canderson said:

50 my the high at the house today. The snow on the west-facing garden is about 80% gone. And really no signs or hope of a winter storm in the next week and a half. Time is starting to tick quickly. 

yep I lost 3 plus inches in my front yard today 

[Jns2183]

Subject: 90 Years of Harrisburg (MDT) Hourly Weather — Full Deep Dive (1935–2025)

Alright everyone, stuck at home in bed I went down the rabbit hole so you don’t have to.

I pulled the entire hourly MDT dataset from 1935 through March 30, 2025 — roughly 701,600 hourly observations spanning just over 90 years. This wasn’t a daily summary skim. This was raw hourly temperature, dewpoint, precipitation, visibility, and related fields.

Before I even looked at stats, I did cleanup and QC because raw long-term station data is messy:


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Data Cleaning & Methodology

1. File scope

Period: Feb 1935 – Mar 2025

~701,594 hourly bins

Observations normalized to hourly resolution (multiple obs per hour consolidated)


2. QC steps

Removed physically impossible dewpoints (e.g., below −80°F artifacts)

Filtered obvious temperature spike errors (one 60°F+ 6-hour swing in 2013 was clearly a glitch)

Precipitation analysis restricted to hours where precip reporting was valid (so “missing” ≠ “dry”)

For daily metrics (high/low, freeze dates, heat streaks), only days with sufficient hourly coverage were used

Snow depth largely unavailable in this dataset (only ~200 total depth entries), so snow retention metrics were excluded


This gives us a dataset that is physically realistic and trend-consistent.


---

The Results

Absolute Extremes

Coldest hour: −22°F (Jan 21, 1994 at 12:00)

Hottest hour: 105°F (July 23, 1991 at 20:00)


That’s a 127°F total observed range at MDT.


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The “Weather Whiplash” Award

Largest temperature swings (QC’d):

Largest 6-hour warm-up: +39.96°F (March 31, 1943)

Largest 6-hour cool-down: −43.02°F (March 1, 1937)


Classic Mid-Atlantic frontal violence.


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Longest Deep Freeze

Continuous ≤32°F streak:

398 consecutive hours

Jan 19 – Feb 4, 1961

~16.6 straight days below freezing


Runner-up: Dec 25, 2017 – Jan 9, 2018 (363 hours)

So yes — modern winters can still lock in.


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Freeze–Thaw Chaos Index

I counted crossings of 32°F in winter (Nov–Mar).

Most chaotic winter: 1941 (188 crossings)

Modern median winter: ~60 crossings


That’s a real structural shift in winter volatility.


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Heat Wave Persistence (Daily-Based)

Consecutive days with highs ≥90°F:

Longest streak: 16 days (July 26 – Aug 10, 1983)

Next longest: 15 days (July 1955)


Hourly streaks don’t tell the real story because nights cool. Days do.


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The “Swamp Index”

Defined as: Temp ≥90°F AND Dewpoint ≥70°F

Total oppressive hours in record: 2,348

Top oppressive years:

1952 (92 hours)

1959 (87)

1949 (84)

1991 (83)


Mid-century humidity was not subtle.


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Fog / Visibility Shift

Hours with visibility ≤1 mile:

Total: 22,368 hours

≤0.25 mile (“pea soup”): 4,860 hours


By decade:

1940s–50s: ~5–6% of hours ≤1 mile

2000s–2020s: ~1.5–1.7%


That is a massive drop. Possible contributors:

Instrument changes

Air pollution regulation

Land use changes

Reporting practices


But the decline is statistically obvious.


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“Perfect Weather” Hours

Defined as:

65–75°F

Dewpoint 45–55°F

No precip

Visibility ≥10 miles


Total perfect hours: 4,484

Best months by frequency:

1. September


2. June


3. May



July is loud. September is elite.


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Precipitation Extremes

Largest 1-hour precip: 4.27" (July 23, 2017)

Wettest 24-hour day (reliable coverage): 16.29" (Oct 11, 2013)

Wettest 72-hour total: 22.66" ending Sept 8, 2011


Those 72-hour numbers are hydrologically serious.


---

Dry Spells

Longest continuous dry streak (with reporting active):

286 hours

Oct 20 – Nov 1, 2024

~11.9 days


Longest continuous rain streak:

33 hours (Oct 16–17, 2009)



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“Most Normal” vs “Most Weird” Year

I computed daily mean deviations from long-term day-of-year climatology.

Lowest RMSE (most “boring” year):

2019


Highest RMSE (most structurally weird year):

1967


1967 wasn’t just warm or cold — it was off-pattern.


---

Structural Climate Signals (The Interesting Part)

Comparing 1936–1959 vs 2000–2024:

Diurnal Temperature Range

Early period: 17.94°F average daily range

Modern period: 16.36°F

Change: −1.58°F


Days and nights are less swingy now.

Night vs Day Warming

Mean daily minimum change: +2.64°F

Mean daily maximum change: +1.07°F


Nights warming more than days is a classic humidification / greenhouse signature.

Dewpoint Drift

+0.79°F increase in daily mean dewpoint


Combine:

Warmer nights

Slightly higher dewpoints

Reduced diurnal range


That suggests a shift toward a more moisture-retentive boundary layer and fewer extreme radiational cooling setups.


---

Growing Season Length

Using freeze date methodology:

Earliest first fall freeze: Oct 16, 1939

Latest first fall freeze: Nov 13, 2024

Longest growing season: 233 days (2024)

Shortest: 158 days (1983)

Typical: ~203 days


The envelope is expanding.


---

Big Takeaways

1. The 1940s–1960s were much foggier and had more freeze–thaw volatility.


2. The 1980s still dominate heat wave duration.


3. Extreme precipitation events are clustered in the 2000s–2010s.


4. Nights have warmed faster than days.


5. Diurnal range compression is measurable.


6. Dewpoints are nudging upward.


7. Growing season envelope has widened.



This isn’t just “it’s warmer now.”
It’s structural atmospheric behavior shifting.




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