Westchester's own hazard-mitigation planning exists because weather here is a municipal problem rather than an aesthetic one (Westchester County Planning). Your wedding gets the same weather.
So price both weddings before you sign either.
The indoor alternate has to prove three things
Ask for the alternate by name and get these in writing, because a venue that answers all three quickly has thought about it and a venue that improvises has not.
Its seated capacity with a dance floor in it. Not its standing capacity, not its capacity without a band. If the number is smaller than your guest list, you do not have a rain plan, you have a hope.
Its price. If the indoor alternate costs the same as the outdoor space you fell in love with, ask what you were paying the premium for. Some venues will not move on this and their reasoning is legitimate — they lost the same Saturday either way. But you should know the answer before you are told it in April.
The call time. Who decides, on what forecast threshold, and how many hours before the ceremony. A venue that will not commit to a decision window is a venue that will make the decision at 3 p.m. while your guests are dressing.
Then go and stand in that alternate room, at the hour of your reception, in bad light. If it is a room you would not have booked on purpose, it is your real venue every time there is a 30 percent chance of showers, and you should be choosing between venues on that basis.
What a real tent quote contains
North county and most estate weddings default to canvas. A tent is not a line item, and a quote with one number on it is not a quote. Ask for these itemized.
The structure, at the size that fits your guest list with the sidewalls down. That is the configuration you will be using if you use it at all, and it is smaller inside than the same tent open.
Sidewalls, clear or solid, and how many of each. This decides whether the view you paid for survives the rain.
Flooring, and whether it is a subfloor over uneven ground or a mat on grass. On a wet lawn the difference is a fall risk and a dress.
Heating or cooling, with fuel. An October evening on a Hudson terrace is cold and the heaters run on propane somebody has to deliver.
Lighting, and power — usually a generator, plus fuel, plus a location far enough from the ceremony that nobody hears it.
The permit. Tents above a threshold size require a permit from the town, and the venue may or may not be the party that pulls it. Establish who does. A permit is also an inspection, and an inspection has a date.
The delivery and strike window. Frequently a day either side, which can commit the site and trigger a second day's site fee. This is the line that surprises people.
The two-tent problem
At a raw-space wedding you will often need more than one. The reception tent is the obvious one. The second is the catering tent, because the property has no commercial kitchen, and it has its own power draw, its own footprint and its own place in the site plan. A third small one for the bar or a guest arrival area is common.
Get the site plan drawn before you get excited about the field. Where the tents go determines where the trucks drive, and where the trucks drive determines what the lawn looks like by 5 p.m.
What rain costs at each venue type
Hotels. Nothing. The rain plan is the building, and this is the strongest argument in the category. More on hotels.
Halls. Nothing, mostly, unless you had planned an outdoor ceremony on a patio. Ask what the indoor ceremony setup does to your timeline, because it usually means a room flip and the flip has a labor cost. More on halls.
Clubs. Variable, and the constraint is often the grounds rather than the room — a wet course is a course you cannot photograph on. More on clubs.
Estates. The tent is frequently the venue, not the backup, and the drawing room seats a fraction of your list. More on estates.
Barns and farms. The tent, plus parking on grass that has just taken two inches of rain, plus the shuttle you now need. More on north county.
Put it in the comparison
When you set two proposals side by side, compare them wet. Take the outdoor venue's per-head, add the tent quote at your guest count divided by that count, add the extra rentals the tent requires, and compare that number against the hall or hotel that needed none of it. Landed per-head is the only comparison that works, and here is how to build one.
A venue whose outdoor space is genuinely worth the premium survives that comparison. Several in this county do. The ones that do not are the ones selling you a lawn and a shrug.
Where to check before you sign
Westchester sits in the National Weather Service New York office forecast area, which publishes climate normals by month — worth ten minutes before you commit to an outdoor ceremony date. For the tent itself, New York State requires permitting for temporary structures above a certain size; the rules sit with your venue's local building department, and the NYS Division of Building Standards and Codes is the authority your tent vendor will be working to.