The study, conducted by Stefanos P. Stefanidis of the Forest Research Institute of the Hellenic Agricultural Organization DIMITRA and Nikolaos D. Proutsos of the Institute of Mediterranean Forest Ecosystems, mined a remarkable archive: 20,817 scheduled observation intervals recorded at the Pertouli station between 2001 and 2020, with 2006 treated as a complete data gap. Rainfall and fresh snowfall were accumulated over intervals ending at 08:00, 14:00 and 20:00 local time, while 2-meter air temperature and relative humidity were read at each endpoint. This is precisely the kind of ground-truth data that Mediterranean mountains have long lacked, even though the phase of precipitation there determines whether water arrives as immediate liquid input to streams and soils, or as temporary snow storage that shapes the timing of spring runoff.

The headline number is a 50% snow-occurrence temperature of 0.34 °C, with a 95% confidence interval running from 0.10 to 0.60 °C. In other words, at Pertouli, precipitation is equally likely to fall as rain or snow when the air is just a third of a degree above freezing — slightly warmer than the 0 °C assumption embedded in many hydrological models. More revealing is the width of the transition itself: the zone in which the probability of snow slides from 90% down to 10% stretches from −1.10 °C to 1.78 °C. That nearly three-degree window is where forecasting becomes genuinely difficult, and where the study’s most striking diagnostic results emerge.

To test that difficulty quantitatively, the researchers set aside intervals in which rain and fresh snow occurred simultaneously — 112 of them — and refused to use them when fitting the occurrence models. Instead, these mixed-phase events were held out as an independent diagnostic of the transition zone. The result was emphatic: 97 of the 112 co-occurring intervals, or 86.6%, fell inside the transition zone defined by held-out years, compared with only 15.1% of single-phase intervals. The odds ratio of 36.3, with a confidence interval from 25.4 to 59.1, means that mixed precipitation was more than thirty-six times as likely to occur within the transition band as outside it — a powerful confirmation that the fitted probability function captures where the atmosphere genuinely straddles both phases.

Methodologically, the study is notable for its validation discipline. Logistic occurrence models and nominal precipitation-amount models were evaluated with leave-one-year-out cross-validation, in which each calendar year was excluded in turn and the model was tested against it, or with year-block bootstrap resampling. This approach respects the strong temporal structure of climate data, avoiding the optimistic bias that arises when models are validated on randomly shuffled observations from the same seasons they were trained on. The researchers also confronted a stubborn practical problem: converting fresh snow depth to snow-water equivalent requires an assumed density ratio, and the archive’s convention of 10:1 (ten centimeters of snow to one centimeter of water) is itself a modeling choice. Under that baseline, the amount-weighted 50% threshold came out at 0.17 °C; across fixed ratios from 5:1 to 20:1, it ranged from 0.55 down to −0.22 °C. Crucially, occurrence-based estimates were unchanged by these assumptions, which is why the authors treat the occurrence threshold as the more robust quantity.

Perhaps the most practically useful finding is the performance of the simplest possible rule. A fixed 1 °C air-temperature threshold — the kind of rule a field technician or a coarse model might apply — achieved a record-wide balanced accuracy of 0.951 across the entire twenty-year dataset, a figure that rivals far more elaborate schemes. But that headline skill conceals a weakness: accuracy deteriorated sharply inside the transition zone, where the atmosphere itself refuses to commit to a single phase. Outside that band, the 1 °C rule is nearly perfect; inside it, even the best near-surface meteorology struggles.

That struggle motivated the study’s second question: can humidity information rescue the ambiguous cases? On a response-qualified subset of relative humidity data, adding RH improved logistic temperature classification within the transition zone by 0.081 in balanced accuracy, with a confidence interval of 0.038 to 0.119 — a real but modest gain. The researchers also tested wet-bulb temperature estimated with the Stull formulation, a physically motivated alternative that combines temperature and humidity into a single variable often favored in snow-modeling literature. Neither humidity-enhanced approach outperformed the plain 1 °C temperature benchmark across the full record. The finding aligns with recent machine-learning work suggesting there is a fundamental limit to how accurately precipitation phase can be partitioned using near-surface meteorology alone, because the phase of a falling hydrometeor reflects conditions aloft as much as conditions at the gauge.

The hydrological stakes are quantified directly: about 25.1% of nominal November-to-April precipitation at Pertouli fell inside the observed transition zone under the 10:1 baseline. One quarter of the cold-season water budget, in other words, arrives in conditions where a one-degree shift in temperature — or a slightly different snow-density assumption — could flip it from snowpack to streamflow. For a Mediterranean mountain forest, where snow acts as a delayed reservoir feeding soils and streams well into spring, that fraction represents a substantial exposure to phase uncertainty. As regional warming pushes more winter precipitation events toward the warm edge of the transition zone, the practical difference between a 0.34 °C threshold and a 0 °C assumption becomes a matter of water-supply planning, not academic refinement.

The authors frame their results as a locally validated probability function and a quantified hydrological exposure for snow and forest-hydrology models, and the deliverables are concrete: a fitted logistic curve with confidence bounds, a documented sensitivity of amount-based thresholds to snow-density conventions, and a benchmark against which humidity-based schemes can be judged. The underlying meteorological data from the Pertouli station, operated by the Aristotle University Forest Administration and Management Fund, are freely available, allowing other researchers to replicate the analysis or extend it to neighboring sites. In a region where direct phase observations remain scarce and snow hydrology is chronically under-constrained, a single well-observed mountain station has now produced both a precise threshold and an honest measure of the uncertainty that surrounds it — a combination that modelers of Mediterranean water resources will find hard to ignore.

Subject of Research: Rain–snow partitioning thresholds and transition-zone uncertainty at a Mediterranean mountain forest station

Article Title: Observed rain–snow partitioning at a Mediterranean mountain forest station: temperature thresholds, humidity sensitivity, and transition-zone uncertainty

Article References: Stefanidis, S. P., & Proutsos, N. D. (2026). Observed rain–snow partitioning at a Mediterranean mountain forest station: temperature thresholds, humidity sensitivity, and transition-zone uncertainty. Theoretical and Applied Climatology, 157(11), Article 711. https://doi.org/10.1007/s00704-026-06658-1

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06658-1

Keywords: rain-snow partitioning, precipitation phase, temperature threshold, Mediterranean mountains, snow hydrology, Pertouli, Greece, logistic model, transition zone, relative humidity, wet-bulb temperature, forest hydrology

BPH is not cancer, but it is hardly a minor inconvenience. The noncancerous overgrowth of prostate cells becomes increasingly common as men age, and as the gland swells it can compress the urethra, the narrow tube that carries urine out of the body. The consequences are familiar to millions of older men: frequent urination, repeated nighttime trips to the bathroom, a weak urinary stream, and the frustrating sensation that the bladder never fully empties. Despite how widespread the condition is, the biological events that set it in motion — and in particular the question of why it arises almost exclusively in one region of the prostate — have remained stubbornly unresolved. Senior author Vasan Yegnasubramanian, a professor of oncology, pathology, and radiation oncology and molecular radiation sciences at the Johns Hopkins Kimmel Cancer Center and director of inHealth Precision Medicine at Johns Hopkins Medicine, noted that although BPH affects millions of men worldwide, scientists still do not fully understand why it develops primarily in the transition zone while other regions of the gland remain relatively unaffected.

That regional puzzle is rooted in the prostate’s internal architecture. The gland is not a uniform organ but is divided into several anatomically and biologically distinct compartments, most notably the peripheral zone, the central zone, and the transition zone. These regions differ in their cellular makeup and in their vulnerability to disease, and the split is dramatic: BPH arises almost exclusively in the transition zone, the area surrounding the urethra, while the majority of prostate cancers emerge in the peripheral zone. Understanding why the same organ hosts two such different disease patterns has long been a goal of prostate biology, and it suggests that the answer lies in fundamental differences in the cells that populate each zone.

To pursue that question at single-cell resolution, the research team, led by Yegnasubramanian together with Rulin Wang, a research associate and the study’s first author, and Angelo De Marzo, professor of pathology at the Johns Hopkins University School of Medicine and associate director of cancer research pathology at the Kimmel Cancer Center, turned to single-cell RNA sequencing. This technology allows investigators to determine which genes are switched on or off in individual cells, rather than averaging signals across a bulk sample in which rare cell types can vanish into the noise. The team studied noncancerous prostate tissue collected from 10 men undergoing surgery for localized prostate cancer, obtaining samples from all three major zones of the gland and profiling gene expression in nearly 130,000 individual cells.

The first task was cartographic: identifying the major cell types present throughout the prostate and confirming how they were distributed across zones. With that atlas in hand, the researchers zoomed in on basal epithelial cells, a population that helps form the lining of the prostate and is thought to include progenitor-like cells capable of contributing to tissue maintenance and repair. Rather than finding a single homogeneous basal population, the analysis revealed that these cells split into four distinct molecular subtypes — a level of diversity that conventional histology had not exposed.

One of those four subtypes immediately stood out. Its cells expressed high levels of a gene called WIF1, along with several other genes, and their distribution across the gland was anything but random. Additional laboratory tests confirmed that these WIF1-positive basal cells were abundant in the transition zone but nearly absent from the peripheral and central zones. In other words, the researchers had found a cell population whose geographic footprint within the prostate matched, almost exactly, the territory where BPH takes hold.

The molecular profile of these cells offered further clues about what they might be doing. According to Wang, the analysis revealed that the cells possess molecular features associated with tissue remodeling that could contribute to prostate enlargement, as well as an ability to communicate with neighboring cells, suggesting they may help establish the unique biological environment of the transition zone. Tissue remodeling — the orchestrated breakdown and rebuilding of structural components — is a normal part of organ maintenance, but when it runs unchecked it can drive the kind of nodular overgrowth seen in BPH. A cell type equipped with remodeling programs and embedded in the exact region where that overgrowth occurs is a compelling candidate for a local driver of the disease process.

Perhaps most tellingly, the team found that WIF1-positive basal cells are expanded in BPH tissues. That expansion raises the possibility, the researchers say, that these cells contribute to the regional processes that make the transition zone particularly susceptible to BPH. The gene whose name the cells carry, WIF1, encodes a Wnt inhibitory factor, a secreted molecule that modulates Wnt signaling — a pathway with well-established roles in development, stem cell behavior, and tissue growth. The presence of a Wnt-pathway regulator in a remodeling-competent basal population enriched at the BPH epicenter suggests a plausible mechanism by which local signaling environments could shape where and how the gland enlarges, though the study’s authors frame this as a foundation for future work rather than a settled causal story.

The significance of the finding lies less in any single gene than in the strategy it validates. Bulk analyses of prostate tissue have long averaged together the signals of many cell types, obscuring the rare, regionally restricted populations that may hold the key to zonal disease patterns. By dissecting the gland zone by zone at single-cell resolution, the Hopkins team showed that the transition zone carries its own distinctive cellular identity, embodied in a basal cell subtype found almost nowhere else in the organ. That identity, the researchers suggest, may be what renders the transition zone uniquely prone to the proliferative and remodeling processes of BPH — and, by extension, may help explain why the peripheral zone instead becomes the favored soil for prostate cancer.

By uncovering this distinct cell population associated with the region where BPH begins, the research provides new insight into the cellular mechanisms underlying prostate growth and remodeling, and it offers a foundation for future studies aimed at understanding how the condition develops. The long-term hope, the researchers say, is that a clearer picture of the transition zone’s biology will ultimately support more precise ways to prevent, diagnose, and treat BPH — potentially allowing therapies that target the specific cell programs driving enlargement rather than broadly suppressing prostate growth. The study also involved contributions from Qizhi Zheng, Mindy Graham, Ajay Vaghasia, Jianyong Liu, Jordan Gregg, Tracy Jones, Anuj Gupta, Nicole Castagna, Yan Zhang, Kornel Schuebel, Jennifer Meyers, Alyza Skaist, Dixie Hoyle, Jasmine Kung, Jessica Hicks, Alok Mishra, Yuhan Yang, and William Nelson. The work was supported by the National Institutes of Health and the National Cancer Institute, the Prostate Cancer Foundation, and several philanthropic and institutional funds, including the Patrick G. Walsh Fund and the Maryland Cigarette Restitution Fund.

Subject of Research: Identification of a WIF1-positive basal epithelial cell type in the prostate transition zone associated with benign prostatic hyperplasia

Article Title: Newly identified prostate cell type may help explain why enlarged prostate develops in one region of gland

Article References: Newly identified prostate cell type may help explain why enlarged prostate develops in one region of gland. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: benign prostatic hyperplasia, prostate, transition zone, basal epithelial cells, WIF1, single-cell RNA sequencing, Johns Hopkins, tissue remodeling, prostate zones, urology, aging, cell biology