Central PA Winter 25/26 Discussion and Obs

[Mount Joy Snowman]

7 minutes ago, AccuChris said:

12z ICON went all in on the weekend system the GFS has been showing on and off


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Das ist sehr gut!

[pasnownut]

42 minutes ago, AccuChris said:

12z ICON went all in on the weekend system the GFS has been showing on and off


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Just saw it.  If we could get this to deliver as depicted, just give me a few days to enjoy and I'll stop wishing for snow.....

 

Till the next one comes.  36 hr event verbatim. 

[pasnownut]

GFS still has decent event for same time frame.  While I know we are skeptics of much modeling of late, one thing that GFS has done a decent job of in recent years, is seeing an event at 7 days.  While obviously not a lock, it often has the right general idea, and since I like what it's showing in the last few runs.  I'm huggin. 

[Mount Joy Snowman]

Ukie on board with the Miller B type scenario for Sunday.  We may have another week of tracking ahead fellas.  Buckle up.

[pasnownut]

5 minutes ago, Mount Joy Snowman said:

Ukie on board with the Miller B type scenario for Sunday.  We may have another week of tracking ahead fellas.  Buckle up.

Yep.  Just checked pivotal and it has a B w/ nice transfer.  Little scary thermally, but I'd sign.  

 

so, Ukie/GFS/Icon have us snowing Sunday.  Let see how this goes, but yeah definitely something to watch.  

[pasnownut]

also not sure how much time we have left, cause tellies look less than stellar beyond, so yall might wanna get pom poms out for this one.  

 

[CarlislePaWx]

32 minutes ago, pasnownut said:

also not sure how much time we have left, cause tellies look less than stellar beyond, so yall might wanna get pom poms out for this one.  

 

Last night's GFS had all of us well into the sixties at the end of its run on March 4th.  However, temps were all over the place through the run (0 Z).

[AccuChris]

12 Euro Op still not buying next weekends storm but the 12z AI GFS was on board and the 12z Euro AI was not a full hit for us but was very close and much more amped then its Operational suite


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[anotherman]

12 Euro Op still not buying next weekends storm but the 12z AI GFS was on board and the 12z Euro AI was not a full hit for us but was very close and much more amped then its Operational suite


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Not that is matters as much but the ICON and UKIE were massive hits.

[Superstorm]

Ukie on board with the Miller B type scenario for Sunday.  We may have another week of tracking ahead fellas.  Buckle up.

Sure hope so


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[canderson]

A friend of mine in who knows the river well is worried about an ice jam in HBG. 

[MAG5035]

In what has been a pretty good indicator of warmer times ahead for us the last few winters, Mammoth Mountain point and click has 59-93” in the grids from now through Thursday lol. 

I do like the weekend timeframe if we can line something up at the proper time. There looks to be 2-3 different waves this week… Wed, Fri, and then the Sunday system that has occasionally shown up as a snowstorm. The first two waves favor rain with some potential for mix NE. 

[Itstrainingtime]

12 minutes ago, MAG5035 said:

In what has been a pretty good indicator of warmer times ahead for us the last few winters, Mammoth Mountain point and click has 59-93” in the grids from now through Thursday lol. 

I do like the weekend timeframe if we can line something up at the proper time. There looks to be 2-3 different waves this week… Wed, Fri, and then the Sunday system that has occasionally shown up as a snowstorm. The first two waves favor rain with some potential for mix NE. 

I've been following Mammoth's weather almost daily since my visit a few years ago. They desperately needed this storm, it hasn't snowed of much significance since right around New Year's. That's the thing about out there though - all it takes is a good week or so and they can pile it quickly. Despite the weeks without snow, this storm will put them over 200" for the season. Far short of normal but it's a start. They need to build up the water table now, otherwise fire season later this year might be grim. 

[Superstorm]

Euro AI is a beat down


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[Blizzard of 93]

39 minutes ago, Superstorm said:

Euro AI is a beat down


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Yes, indeed, hopefully we reel this one in for Sunday.

[Yardstickgozinya]

12 minutes ago, Blizzard of 93 said:

Yes, indeed, hopefully we reel this one in for Sunday.

It moves like a tortoise.I like it. If it does the old loopy loop or retrogrades on the next panel, I'll take. 

[AccuChris]

18z Euro AI 10:1 snowmap just for fun


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[Yardstickgozinya]

7 hours ago, pasnownut said:

also not sure how much time we have left, cause tellies look less than stellar beyond, so yall might wanna get pom poms out for this one.  

 

  I'm not disagreeing with you. Maybe my constant search for cold and snow has given me cold bias algorithms. Is there still two trains of thought on this or has there been some type of agreement.  From what I'm gathering the Europeans don't  seem to agree with this but everything i've read, is a few hours to a day old so maybe a lot has changed.

[Blizzard of 93]

18z EPS & 18z AI EPS look great as well for the Sunday chance. Lots of maps are posted in the Mid Atlantic thread for your viewing pleasure.

[Yardstickgozinya]

7 hours ago, pasnownut said:

also not sure how much time we have left, cause tellies look less than stellar beyond, so yall might wanna get pom poms out for this one.  

 

My understanding has been that the p v was to split and send down at least two cold lobes into  central then the eastern US late this month, but the MJO would be somewhat muting, and delaying its effects here on the east coast. Was it a pile of rubbish i've been reading, or still being worked out? 

[Jns2183]

I essentially turned Harrisburg daily weather record over the past 125'years into an audio signal. Frequency depends on waves and times. Basically synoptic patterns and longer. I then fingerprinted bigger events and other thresholds for storms and tried to deduce a pattern the leading up to them.

In the context of your Harrisburg weather data, Power Spectral Density (PSD) is the "volume control" for the different heartbeats of the atmosphere.
While a standard average tells you how much it rained, the PSD tells you how rhythmic that rain was.
1. The Plain English Definition
If you think of the weather as a piece of music, the PSD is the Graphic Equalizer (the bars that jump up and down on a stereo).
* The Bass (Low Frequency): These are the long, slow movements like the MJO or the seasonal cycle (30–90 days).
* The Mid-Range (Synoptic): These are the steady beats of the storm track (5–10 days).
* The Treble (High Frequency): These are the fast, "noisy" events like daily afternoon thunderstorms.
The PSD measures the strength (Power) of each of these "musical" notes in your data.
2. The Mathematical Core
The PSD describes how the variance (the "wiggle" in your rain data) is distributed across different frequencies. For a signal x(t), the PSD (S_{xx}(f)) is technically the Fourier Transform of the autocorrelation function:
In your CSV files:
* Frequency (f): How many cycles occur per day.
* PSD Value (P): The amount of "energy" at that frequency.
If you see a massive spike in the PSD at a frequency of 0.16, it means the atmosphere is "vibrating" with a 6-day period, and that specific rhythm is responsible for a huge chunk of the rain you received.
3. Why is it called "Density"?
It is a "density" because it tells you how much power is packed into a frequency band rather than a single point.
If you want to know the total "energy" of the weather for a whole month, you integrate (find the area under the curve) of the PSD across all frequencies:

This is exactly how we calculated your Welch Band Power Ratios. We took the "Power" in the 6–12 day band and compared its "Area" to the "Total Area" of the whole graph.
4. Physical Meaning in Harrisburg
When you look at your TotPHigh.csv (Wet Years) vs TotPLow.csv (Dry Years), the PSD values tell a physical story:
* Higher PSD in the 10–15 day range: This means the atmosphere has "locked in" to a rhythmic, clumping pattern. It’s not just raining more; it’s raining with intent and timing.
* Flattened PSD: This means the weather is chaotic or "white noise." Rain is falling randomly without any dominant wave driving it.
How to read your specific plots:
* Y-Axis (PSD Mean): Higher values mean a "louder," more dominant rhythm.
* X-Axis (Frequency): Moving left to right goes from slow, massive waves (months) to fast, quick storms (days).



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[Voyager]

1 hour ago, Blizzard of 93 said:

Yes, indeed, hopefully we reel this one in for Sunday.

What is it with Sundays? Ruins the weekend. I want a blockbuster weekday storm so I can have a day or two off from work. 

[Jns2183]

Based on your datasets for Harrisburg/Camp Hill, I have synthesized a comprehensive spectral report. This analysis goes beyond simple rain totals to explain the mathematical rhythm of our local weather.
1. Executive Summary: The Harrisburg "Rhythm"
From 1900 to present, the Harrisburg climate operates on a distinct frequency. While the average annual precipitation is ~39.8 inches, the way that water falls is dictated by three competing atmospheric "clocks."
| Metric | Historical Average (1900–Present) |
|---|---|
| Total Annual Precip | 39.77 inches |
| Wet Day Rate | 0.34 (Rain/Snow every ~2.9 days) |
| Dominant Cycle | 6–12 Days (The Synoptic "Storm Track") |
| Synoptic Band Power Ratio | 0.167 (16.7% of all spectral energy) |
2. The "Wet Year" vs. "Dry Year" Fingerprint
Your Tercile Summary reveals exactly what happens to the atmosphere when we move from a drought year to a record-breaking wet year.
The Shift in Power
When Harrisburg moves from a Low Tercile (Dry) to a High Tercile (Wet) year:
* Synoptic Power (6–12 days) increases from 0.198 to 0.215.
* Quasi-biweekly Power (10–15 days) increases from 0.062 to 0.082.
> The Insight: Wet years in Central PA aren't just "luckier." The atmosphere becomes more mathematically organized. In wet years, the 10–15 day "Rossby Wave" becomes significantly stronger, meaning storms start "clumping" together in predictable pulses rather than falling randomly.
>
3. Anatomy of a "Big Event" (\ge 1.0 inch)
Using the BigEvent Spectral Fingerprint data, we can see how the atmosphere changes immediately after a major storm hits Camp Hill.
* Self-Excitation (The Hawkes Effect): After a 1-inch event, the power in the 6–12 day band increases (Median Delta: +0.0063).
* The Diagnostic: The "Frac Post > Pre" is 52.5%. This means that after a heavy rain, the atmosphere is more likely to stay in a "stormy rhythm" than it was before the rain started.
* The Fade: Interestingly, the 15–35 day band actually decreases in power slightly after a big event. This suggests that big storms "reset" the long-term moisture buildup but "prime" the short-term storm track.
4. Top Drivers & Correlations
Which atmospheric rhythms actually predict a wet year? Your TopCorrelations file gives us the answer:
* The "Clumping" Predictor (r = 0.17): There is a positive correlation between Total Precipitation and the 10–15 day band. If you see storms starting to repeat on a ~2-week loop, a high-precip year is likely.
* The "Stagnation" Warning (r = -0.20): There is a negative correlation between the 60–90 day band and total precipitation.
* Interpretation: When the atmosphere moves very slowly (long, 3-month cycles), Harrisburg tends to be drier. Fast, rhythmic cycles (Synoptic) are what bring our water.
Report Conclusion
The weather in Camp Hill is a system of Wave Interference.
* High-Precip years are characterized by a strong 6–12 day pulse.
* Big Events act as "triggers" that reinforce this 6–12 day pulse (Hawkes self-excitation).
* Droughts are associated with a breakdown of these short cycles and a shift toward very slow, 60–90 day atmospheric stagnation.

This visualization compares the Power Spectrum Density (PSD) of precipitation in Harrisburg during its wettest years (High Tercile, Blue) vs. its driest years (Low Tercile, Brown).
Spectral Report: Dry vs. Wet Year Dynamics
The plot reveals where the "energy" of our weather comes from. When the blue line is higher than the brown line, it means that specific frequency is more active during wet years.
1. The "Wave Interference" Peak (10–30 Days)
The most striking difference occurs in the Quasi-biweekly band (orange shaded area).
* Wet Years: Mean Power = 0.643
* Dry Years: Mean Power = 0.592
* Interpretation: In Harrisburg's wettest years, the "clumping" of storms every 2 weeks is a dominant physical force. Notice the sharp blue spike near the 12–14 day mark. This is the mathematical fingerprint of "Wave Interference"—large-scale atmospheric waves (like Rossby waves) stalling and forcing multiple storms through the Susquehanna Valley in quick succession.
2. The Synoptic "Storm Clock" (2–10 Days)
In the Synoptic band (gray shaded area), the power levels are more similar, though wet years still maintain a slight edge (0.431 vs 0.420).
* Interpretation: This suggests that the "base rate" of cold fronts and low-pressure systems is relatively consistent in Central PA. A dry year isn't necessarily missing its weekly front; rather, those fronts lack the secondary pulse of the slower 10–30 day waves that would make them "clump" and produce heavy totals.
3. Intraseasonal "Priming" (30–100 Days)
In the Intraseasonal band (green shaded area), we see how long-term moisture "regimes" like the MJO influence our totals.
* During wet years, the power is distributed more evenly across these slow frequencies.
* During dry years, you often see a single, large "stagnation" peak (the brown spike near the 80–100 day mark), which suggests a weather pattern that gets "stuck" in a dry phase for months at a time.
Summary of the Diagnostic
To predict a high-precipitation year in Camp Hill, one should look not just at individual storm intensity, but at the Power Spectrum Ratio. If the 10–15 day frequency begins to show higher energy (a "sharper heartbeat"), it indicates the atmosphere is moving into a self-exciting, "clumped" regime that traditionally leads to record-breaking annual totals.

This comparison of \ge 1-inch vs. \ge 2-inch events reveals a "threshold effect" in the Harrisburg/Camp Hill atmosphere. When a storm crosses the 2-inch mark, it doesn't just bring more water; it significantly alters the atmospheric rhythm for the following month.
1. The "Spectral Shock" (Intensity Response)
Looking at the LogP (Intensity) series, the difference between a 1-inch and a 2-inch storm is massive:
* 6–12 Day Band: The intensity of the 1-week rhythm increases nearly 10 times more after a 2-inch storm than it does after a 1-inch storm.
* 15–35 Day Band: For 1-inch storms, the 2-to-4 week cycle barely responds. However, after a 2-inch storm, the intensity delta jumps to 0.0047.
> The Insight: A 2-inch rain event acts as a "resonance trigger." It effectively kicks the atmosphere into a higher-energy gear, making follow-up heavy rain events significantly more likely over the next 15–35 days.
>
2. The "Rhythm Shift" (Frequency Response)
The Wet/Dry (Rhythm) series shows that even the simple binary pattern of "will it rain today?" changes:
* After a 2-inch event, there is a +0.0105 median jump in synoptic power (6–12 days).
* More importantly, 54.9% of 2-inch events are followed by an increase in storm-track frequency.
3. Why 2 Inches Matters for "Wave Interference"
This data supports the theory that extreme precipitation in Central PA is not an isolated incident but a part of a Hawkes-like self-excitation process:
* The Trigger: A massive 2-inch event (often associated with a stalled front or tropical moisture) occurs.
* The Echo: This event "shocks" the 15–35 day Rossby wave, increasing the spectral power in that band.
* The Interference: Because the 15–35 day "background" wave is now energized, it interferes with the standard 6–12 day storm track, causing storms to "clump" together.
Final Report Summary
| Event Type | Effect on 1-Week Rhythm | Effect on 2–4 Week Rhythm |
|---|---|---|
| \ge 1.0" Rain | Moderate increase in frequency. | Negligible effect. |
| \ge 2.0" Rain | Significant "locking" of the storm track. | Strong activation of long-term wave interference. |
In short: Big storms create their own weather. In Harrisburg, a 2-inch rainfall is a mathematical signal that the "rhythm" has shifted, and the next few weeks are likely to remain active and organized.




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[Jns2183]

Primer

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