FL1 FORECAST: Sunny Tuesday gives way to showers and a humid Thursday

Sunshine will send temperatures back into the 70s across the Finger Lakes and Central New York on Tuesday before clouds thicken and the region enters a more unsettled stretch lasting through Thursday night.

Sunshine and a warmer Tuesday

The day will begin cool and generally clear, with areas of valley fog possible across the Southern Tier and nearby valleys. Any fog should fade during the morning as high pressure shifts east and sunshine takes hold.

Most of the region will be mostly sunny through the afternoon, though clouds will begin to increase from west to east later in the day. Rochester is expected to reach the mid-70s under partly sunny skies, while Geneva, Ithaca and Syracuse should climb into the lower to mid-70s. Highs near Elmira will be around 72.

South to southeast winds will strengthen as the high moves away. Sustained winds of roughly 8 to 15 mph are expected across parts of the Finger Lakes, with gusts of 20 to 25 mph possible by late afternoon and evening. The breeze will be lighter in some sheltered valleys.

The increasing clouds will be tied to a weakening warm front pressing into the region. Dry air near the ground should keep most places rain-free during the daytime, making Tuesday the most reliably dry part of the forecast before the pattern becomes more changeable.

Showers develop Tuesday night

Scattered light showers will become possible Tuesday night as the weakening boundary crosses western New York and runs into a strong ridge over Central New York. Rain could reach the Rochester and Geneva areas during the evening, while chances farther east increase mainly after midnight.

The showers are not expected to produce much rain Tuesday night. Forecast totals in areas that receive rain generally remain below one-quarter of an inch, and many locations may see less than one-tenth of an inch. An isolated thunderstorm cannot be ruled out in western sections, but instability will be limited.

Clouds and a south wind will make Tuesday night noticeably milder than the start of the day. Lows are expected to range from the mid-50s in the Southern Tier and around Ithaca to the lower 60s near Syracuse and Geneva and the mid-60s in Rochester.

Wednesday stays warm with spotty rain

Wednesday will remain warm as the weakening front settles into the region. Most of the day will not be a washout, but scattered showers could occur at almost any point, especially across the western and northern Finger Lakes.

Cloud cover is expected to be more persistent closer to Lake Ontario and the New York State Thruway, while areas farther south may see longer breaks of sun. Forecast highs range from the mid-70s near Rochester and Geneva to the upper 70s around Syracuse and Ithaca and near 80 in the Elmira area.

Humidity will rise during the afternoon. A few thunderstorms could develop late in the day near the Southern Tier, where instability may be somewhat greater, but the exact placement of the front remains uncertain. If the boundary settles farther south into Pennsylvania, storm coverage in New York would be lower.

Rain chances will continue Wednesday night as the front stalls nearby. Skies will be mostly cloudy, with lows generally in the lower 60s. The location of the boundary heading into Thursday will help determine where the steadiest rain develops and how much instability can build during the day.

Humid Thursday brings heavier downpour potential

A weak area of low pressure moving along the front will bring a broader chance for showers Thursday. The day is expected to be mostly cloudy, warm and very humid, with highs in the mid-70s to near 80 and dew points approaching 70.

Atmospheric moisture will be unusually high for mid-September. That will allow showers and thunderstorms to produce efficient rainfall, including localized heavy downpours. The risk of excessive rainfall is considered low, but a slow-moving or repeatedly developing shower could leave substantially more rain in one place than another.

The highest rain probabilities are currently centered from the central Finger Lakes into Central New York and the Southern Tier. Chances Thursday are near 80% around Ithaca, about 70% near Syracuse, Geneva and Elmira, and closer to 50% in Rochester. Those figures may change as the position of the front becomes clearer.

There is still uncertainty about how much instability will develop under the cloud cover. If enough warmth reaches the surface, a few organized thunderstorms could produce gusty winds and higher rainfall rates. If clouds remain thicker, the main weather would be periods of rain with less thunder.

Showers and a few thunderstorms may continue into Thursday evening before the system shifts south and drier air begins moving in from Canada. Rain should taper from north to south overnight, though clouds could linger into early Friday.

Sunshine and lower humidity return Friday

High pressure building south from Canada is expected to bring a dry Friday with increasing sunshine and a noticeable drop in humidity. Confidence in the return to fair weather has increased, although some morning clouds may take time to clear.

Afternoon temperatures will be seasonable, ranging from near 69 in Rochester to the lower 70s across much of the Finger Lakes, Central New York and the Southern Tier. A northerly breeze will reinforce the cooler and drier feel.

Friday night will turn cool as winds ease. Lows should fall into the upper 40s and lower 50s across much of the region, with colder readings possible in normally cooler locations north and east of the Finger Lakes.

Weekend starts dry before rain chances return

Most of Saturday is expected to remain dry, with a mix of sun and clouds and highs in the lower 70s. A warm front approaching late in the day could bring a few showers to northern sections, but rain chances remain low enough that many locations may stay dry through the afternoon.

The pattern becomes more active again Saturday night and Sunday as low pressure moves from the Plains toward the Great Lakes. Showers will become more likely, and a few thunderstorms may develop as deeper moisture returns. In western New York, the chance of receiving at least one-half inch of rain during the weekend system is currently around 50% to 60%.

Clouds and showers may linger into Monday as waves of low pressure move along a stalled front. The exact location of that boundary remains uncertain, but current trends favor seasonably cool weather with highs slipping from the lower to mid-70s Sunday into the 60s early next week.