Jns2183

Here Sent from my SM-S731U using Tapatalk

In Arkansas it was best model for snow. The GFS, euro were close. Sent from my SM-S731U using Tapatalk

It's driving me nuts. Something is there but after how I saw it do so far, a pixel analysis correlation of .18 vs every model being 2.5x-3.5x higher because of how bad it screwed up the changeover line Sent from my SM-S731U using Tapatalk

The HRRR Consistency: The HRRR was the most balanced. It had the lowest error across both categories, making it the most reliable tool for this specific event. It handled the "Rain-Snow line" better than any other model. Sent from my SM-S731U using Tapatalk

Same as before I mean it also never backed down in Oklahoma and Arkansas as was and this was the result The NAM Split: The NAM is the most interesting case. For liquid rain, it has a staggering 0.96 correlation, meaning it mapped the storm's shape almost perfectly. However, for snow, its correlation plummeted to 0.18. This proves the NAM understood where the moisture was, but failed completely at the "transition physics"—it thought the air was too warm, keeping it as rain when it should have been snow. Every other model had snow correlation between .5 to .7 Sent from my SM-S731U using Tapatalk

I've also never seen a sleet changeover blow through at 60mph like it wants Sent from my SM-S731U using Tapatalk

Look way above at the snow ratio table image. What made me confused as hell was NAM being less than half that of the SREF. The nam is one of the members of the SREF and its core engine accounts for half the ensemble members just with physics tweaked a bit. Usually SREF and nam are pretty close. This tell me the cam ensemble members are mostly much much higher than nam. It's weird Sent from my SM-S731U using Tapatalk

The 18z NAM had the sleet line coming from Westminster Maryland to Harrisburg in 1 hour, which is absolutely flying Sent from my SM-S731U using Tapatalk

For closer Sent from my SM-S731U using Tapatalk

I made a leading indicator watchlist for tonight starting at 1am This Final Accumulation Decision Matrix is designed to give you a definitive forecast range for Harrisburg based on which leading indicator stations verify tomorrow morning. Key Decision Thresholds for Tomorrow * The 5:00 AM "Lynchburg Check": If KLYH (Lynchburg) is still reporting pure snow at 5:00 AM, the NAM's 11:00 AM sleet arrival for Harrisburg is effectively impossible. You can immediately shift your planning toward the 15"+ range. * The "Sleet Ratio" Penalty: For every hour the "warm nose" arrives earlier than 6:00 PM, you lose approximately 0.6 to 0.8 inches of potential snow accumulation as the ratio drops from 13:1 to 6:1. * The QPF Floor: Regardless of the timing, all high-resolution models agree on a liquid equivalent (QPF) of 1.0" to 1.3" for Harrisburg. This guarantees that even a "sleet-heavy" outcome will likely result in at least 9–10 inches of dense, frozen mass. Final Forecast Recommendation Stick with the 11"–16" range as your baseline, but keep a close eye on Fredericksburg (KEZF). That station is your "Early Warning System"—if they are still snow at 8:00 AM, the HRRR's 18-inch solution is no longer just a possibility; it becomes the most likely outcome. Sent from my SM-S731U using Tapatalk

Thank you The last stats I provided basically was for each model qpf I used all ratios within that type to create a 94'row sensitivity matrix. Basically trying to create an "ensemble" at the expensive of assuming qpf and ratios are independent. Key Vulnerabilities Identified CAM Extreme Variance: The CAM group shows the widest volatility, with a 12.8-inch spread. This is driven by the 3kmNAM and RRFS predicting heavy/wet ratios (6.2–6.5), while the HRRR and FV3 predict high ratios (13.4–14.5). If the FV3's QPF (1.31") meets the HRRR's SLR (14.5), Harrisburg would see 19.00". Regional High-End Potential: The Regional models (NAM, RDPS, RAP) produced the highest theoretical mean of 12.44" and a maximum potential of 20.00" (NAM QPF × RAP SLR). This confirms that if the regional models resolve the moisture axis better than the globals, totals will likely exceed the current consensus. Global Stability: The Global models are the most "stable," with a relatively narrow 5.9-inch spread. Their consensus (9.5" to 15.4") acts as a high-confidence "floor" for the event. Ensemble Mean Consensus: The Ensemble Means (SREF, GEFS, etc.) show a heavy lean toward the 13.5" mark, suggesting that the statistical "most likely" outcome is currently hovering just above a foot. Sent from my SM-S731U using Tapatalk

Model Type Combinations Min Snow (in) Max Snow (in) Mean Snow (in) CAM (Convective) 36 6.20" 19.00" 11.45" Regional 9 7.11" 20.00" 12.44" Global 25 9.51" 15.44" 12.23" Ensemble Mean 24 8.46" 18.09" 13.56" Sent from my SM-S731U using Tapatalk

The statistical distribution of the 18 model forecasts for Harrisburg reveals a tightly clustered consensus with a specific high-end skew, indicating that while a significant winter storm is certain, the exact "boom" potential remains tied to moisture efficiency. The ensemble mean of 12.72 inches serves as the mathematical anchor, but the standard deviation of 3.11 inches highlights a notable disagreement between model families. Specifically, regional models like the NAM and SREF are pulling the distribution toward the 90th percentile of 16.38 inches, whereas global models like the GDPS and ICON remain more conservative near the 11th-inch mark. This spread suggests that the primary forecast challenge is not the track of the storm, but the Snow-to-Liquid Ratio (SLR); models predicting lower totals generally expect a warmer, denser "heart-attack" snow, while the high-end outliers assume a colder, fluffier accumulation. The implications of this distribution, particularly when viewed through the lens of the Z-score mapping, suggest that the "most likely" outcome is not a single number but a high-confidence corridor. The data shows that 68% of all model guidance (the +/- 1.0 standard deviation range) falls between 9.61 and 15.82 inches, creating a very stable target for infrastructure planning. The fact that the Mean Absolute Deviation (MAE) is a relatively low 2.36 inches indicates that the models are in better agreement than typical for a complex transition-zone event. However, the 100-mile Northwest bias observed in Arkansas—where models like the NAM missed the core entirely—suggests that the statistical "tail" of the distribution should not be ignored. If the storm over-performs its moisture transport as it did upstream, the 17.38-inch mark (+1.5 sigma) is a scientifically plausible outcome rather than just an outlier. Based on this statistical synthesis, the final forecast range for Harrisburg is set at 11 to 16 inches, with a localized "boom" potential of 18 inches if the higher SLRs verify. This range captures the bulk of the probability density, spanning from the 25th percentile (11.35") to just below the 90th percentile (16.38"). The lower bound is protected by the consistent 1.00"+ QPF (liquid equivalent) seen across almost all guidance, which provides a high floor for accumulation. Conversely, the upper bound is capped by the warm-nose intrusion observed in the regional NAM runs, which currently prevents the consensus from shifting entirely into the 20-inch category. Sent from my SM-S731U using Tapatalk

That's the 3k nam, reg nam, observed The NAM suite’s performance during the Arkansas snowfall event was a case study in systematic failure, characterized by a severe northwest displacement and a critical underestimation of moisture transport. Both the NAM 3km and Parent models shifted the entire storm track 95–110 miles too far northwest, which effectively "erased" the heavy 7.8-inch snow core from Central Arkansas by placing it in a modeled dry slot. While the models were predicting 0.0" for Little Rock and Conway, the actual atmosphere was tapping into a rich Gulf moisture plume that the NAM fundamentally failed to resolve, leading to a massive +7.8-inch error at the storm's most intense point. The root of this "NAM Gap" was a flawed thermal profile that modeled the 850mb "warm nose" much too aggressively and far north of its verified position. By over-amplifying the ridge ahead of the storm, the NAM physics engine incorrectly predicted that dry air would "eat" the incoming precipitation shield, when in reality, the column stayed cold and saturated enough for high-impact snowfall. For those tracking the storm's progression into the Ohio Valley and Northeast, the takeaway is clear: the NAM’s known dry bias and tendency to over-pump warm air can lead to a 100% miss in the transition zone, making a weighted consensus of the HRRR, Euro, and NBM a far more robust strategy for defining the true snow line. Sent from my SM-S731U using Tapatalk

Lessons from Arkansas below. Later I'll do an update for round two and look at Kentucky/Missouri, Ohio Trust the NBM for the most likely total. * Use the HRRR to define exactly where the heavy bands will set up (the "where"). * Keep the Euro in the mix to ensure you aren't being "fooled" by a high-res model (like the NAM) that might be missing a major moisture plume. Sent from my SM-S731U using Tapatalk

Let's see how the NAM handled snow in Arkansas so far First image is snowfall output from NAM 2nd is observed at official stations Take a big look at Little Rock Out of all the models euro preformed best there Almost all pushed mix to far north Different system when it gets up here but at least we have some data Sent from my SM-S731U using Tapatalk

Even better video https://x.com/i/status/2014698738137117002 Sent from my SM-S731U using Tapatalk

Verizon network is once again down Sent from my SM-S731U using Tapatalk

7"/hr https://x.com/i/status/2014722834476466189 Sent from my SM-S731U using Tapatalk

Here Sent from my SM-X210 using Tapatalk

That high being a bully is our friend Sent from my SM-X210 using Tapatalk

This is the sounding for Norman Ok, off the 18z NAM for 21z, a mere 3 hours after initiation. Next image is temperature from weather ballon launched at 21z. Sent from my SM-S731U using Tapatalk

It also seems like it may start much earlier Sent from my SM-S731U using Tapatalk

Here Sent from my SM-S731U using Tapatalk

The HRRR looked amazing Sent from my SM-S731U using Tapatalk