Observed Mesoscale Hydroclimate Variability of North America’s Allegheny Mountains at 40.2° N

Spatial hydroclimatic variability of Eastern North America&rsquo:s Allegheny Mountain System (AMS) is commonly oversimplified to elevation differences and the rain-shadow effect. Descriptive and higher order statistical properties of hourly meteorological observations (1948&ndash:2017) from seven airports were analyzed to better understand AMS climatic complexity. Airports were located along a longitudinal transect (40.2 &deg:N) and observation infrastructure was positioned to minimize climatic gradients associated with insolation, slope, and aspect. Results indicated average ambient temperature was well correlated with airport elevation (R2 = 0.97). However, elevation was relatively poorly correlated to dew point temperature (R2 = 0.80) and vapor pressure deficit (R2 = 0.61) heterogeneity. Skewness and kurtosis of ambient and dew point temperatures were negative at all airports indicating hourly values below the median were more common and extreme values were less common than a normal distribution implies. Westerly winds accounted for 54.5% of observations indicating prevailing winds misrepresented nearly half of AMS weather phenomena. The sum of maximum hourly precipitation rates was maximized in Philadelphia, PA implying a convective precipitation maximum near the border of Piedmont and Coastal Plain provinces. Results further indicate the AMS represents a barrier to omnidirectional moisture advection suggesting physiographic provinces are characterized by distinct evapotranspiration and precipitation regimes. The current work draws attention to observed mesoscale hydroclimatic heterogeneity of the AMS region and identifies mechanisms influencing local to regional water quantity and quality issues that are relevant to many locations globally.