San Marino | Vatican City
The cradle of the Renaissance was also the location where weather observing as we know it evolved, thanks to the efforts of Torricelli, Galileo and other Italian scientists and inventors. There is plenty to observe weatherwise across this varied country. Jutting into the sea, Italy is a sitting duck for Mediterranean depressions. These centres of low pressure spin up over the water, especially in the Gulf of Genoa. As they drift inland, they bring pulses of rain and thunder that vary in character depending on the time of year and the part of the country. The Alps and the Apennines produce more wintry regimes at elevation; they also help create a wide array of micro-climates at lower levels by blocking the regular passage of Atlantic fronts, which allows moist air from the south to get into the mix. The Po Valley – running across northern Italy from Turin to Venice – has one of the nation's sharpest and most distinctive climates. Summers are warm, with oppressively muggy periods that build toward thunderous downpours.
After a brief, golden respite in September, autumn becomes progressively damper and chillier. From December through February, dense fog and cold, clammy air plague the valley. Visibility can fall below 1km/0.6 miles for days on end. The eastern Po Valley is also prone to cold bora winds that plunge south from eastern Europe. Rain and snow across the valley during this mid-winter gloom is frequent, but usually not too heavy. The Gulf of Genoa may get drenched by passing depressions, but it's shielded from the worst cold. As elsewhere in Italy, spring is a variable, showery season. The western Po Valley gets some of its stormiest weather in March and April in between rounds of sunshine. The arc of the Alps running above the Po is predictably cooler and moister on average, although it can be clear and sunny here while the valley is encased in cloud and fog. At heights of around 1500m/4900ft, snowfalls may total around 50cm/20in per month in mid-winter. The Valle D'Aosta is a drier pocket where winter nights can be bitterly cold. Autumn can bring torrential rain and serious flooding to the Alps foothills as well as other parts of the Italian peninsula.
From Liguria southward lies a more classical Mediterranean regime. Florence and Pisa are markedly milder and sunnier than Milan in winter, with fog a rarity. Rome and Naples are milder still, enough so that a thunderstorm or two will strike even in January (autumn and winter is the most thundery time across southern Italy, although it's drier and milder than in the north). Summers are only a little muggier across the Tyrhennian Coast than in the Po Valley, but the Adriatic coast south of Bari – especially around the Gulf of Taranto – is among Italy's hotter regions, as are the Ionian coasts of extreme southern Italy and Sicily. Winters across the far south are mild but frequently damp and thundery. The highest terrain, including Mt Etna, can experience surprisingly heavy snows on occasion. As for the two independent states within Italy's borders, neither San Marino nor Vatican City are sizeable enough to get weather that differs from the surrounding areas.