January is the quiet heart of winter and the thinnest stretch of the river-cruise calendar. Afternoons top out near 44 degrees, nights drop to about 35, and rain is frequent rather than heavy at roughly 58mm, so pack a warm layer and a compact umbrella. The upside is short queues at the Louvre and the Orsay and a city that belongs to Parisians again. Jour de l'an on the 1st closes many shops and museums, so check hours if you sail over New Year, and lean on the covered galleries and cafes when the wind picks up along the Seine.
Still firmly winter, February stays cold and grey, with highs around 47 and lows near 35 and about 54mm of rain across the month. Sailings are few, but the trade is real: the big museums are at their calmest and a warm brasserie lunch feels earned. No public holiday falls this month, so opening hours are normal. Dress for damp cold, plan the day around indoor sights with a riverside walk between them, and treat any bright spell as a bonus rather than the plan.
March is the shoulder that opens the season, and the light starts to return even as the chill lingers. Expect highs near 52, nights around 38, and roughly 54mm of rain, so layers and a fold-away umbrella still earn their place. Gardens begin to green and terraces reappear on the first mild days. Lundi de Paques can land late in the month and shorten some hours, so check the calendar if you sail near Easter, and otherwise enjoy a city waking up before the crowds arrive.
April is proper spring and one of the loveliest times to be ashore, with the chestnuts in blossom and cafe terraces filling up. Highs run about 58, nights near 42, and rain eases only a little to around 51mm, so showers still pass through; carry a light layer and keep plans flexible. There is no public holiday in the window this month, which keeps hours predictable. It is a fine time for the gardens, the riverbanks, and a long walk between sights before the summer rush builds.
May is warm, green, and busy, arguably the sweet spot of the Paris season. Afternoons reach about 66, nights sit near 49, and rainfall is around 60mm in passing spring showers, so an umbrella still travels with you. The month is thick with public holidays, Fete du Travail on the 1st, Victoire 1945 on the 8th, plus Ascension and Lundi de Pentecote, and any of them can close shops and draw crowds to the parks. Plan ticketed sights around the dates, start early, and the long light evenings are yours for the riverside.
June brings long days and reliable warmth, with highs near 71, nights around 55, and roughly 63mm of rain in occasional afternoon showers. The city stays out late, terraces are full, and the Fete de la Musique fills the streets with free concerts around the solstice. No public holiday interrupts the month, so hours are steady. It is a strong time for a full day ashore: use the light to stretch the day, keep a thin rain layer handy, and take the evening slowly along the Seine.
July is high summer, warm and mostly bright, with highs about 76, nights near 58, and around 51mm of rain that tends to come in short storms. It is peak season, so expect queues at the marquee sights and book timed tickets ahead. Fete nationale on the 14th, Bastille Day, is the spectacle of the year: a morning military parade on the Champs-Elysees and fireworks over the Eiffel Tower at night, with many businesses closed and the centre busy. If you sail around it, plan for crowds and lean into the celebration.
August is warm and a touch drier than July feels, with highs near 75, nights around 58, and roughly 51mm of rain. It is the month Parisians leave on holiday, so some family-run bistros and shops shut for a few weeks even as the monuments stay open and busy with visitors. Assomption on the 15th closes many businesses. Expect a slightly emptier, more relaxed city in the residential quarters and a crowded core; time the big sights early and keep the afternoon loose.
September may be the best all-round month to be ashore: still warm at about 70 by day and 54 at night, with rainfall easing to around 44mm, the driest stretch of the year here. Summer crowds thin as the school term begins, terraces stay lively, and the light turns golden. No public holiday falls this month, so hours are normal. It is an easy month to fill with a long walk between sights, a garden hour, and a late lunch, with less need to plan around weather or queues.
October is autumn proper, cooler and wetter, with highs near 60, nights around 47, and the year's heaviest rainfall at roughly 73mm. Bring a real jacket and an umbrella, and build the day around a mix of indoor sights and covered walks. The upside is thinning crowds, turning leaves in the gardens, and a softer light for photographs. No public holiday interrupts the month. Aim outdoor time at the drier spells and keep a museum or a long cafe lunch in reserve for when the rain sets in.
November is late autumn sliding toward winter, with highs about 51, nights near 40, and around 56mm of rain under often grey skies. Sailings taper off, but the city is calm and the museums uncrowded. Two public holidays land this month, Toussaint on the 1st and Armistice 1918 on the 11th, and both can shorten hours and bring commemorations. Dress warm, plan around indoor sights and the covered passages, and treat a bright afternoon on the riverbank as a small gift.
December is cold and festive, with highs near 45, nights around 36, and roughly 64mm of rain, and the occasional cold snap. River sailings are limited, but the ones that run meet a city dressed for Christmas: markets, lights along the grand avenues, and warm dining rooms. Noel on the 25th closes most shops, museums, and many restaurants, so check hours closely if you sail over the holiday. Wrap up, keep the day short and indoor-leaning, and let the lights and a hot chocolate carry the evening.