Sunshine and lower humidity will give the Finger Lakes and Central New York a dry, pleasant Tuesday before warmth, moisture and repeated chances for thunderstorms return during the second half of the week.
National Weather Service forecasters in Buffalo and Binghamton expect high pressure to control the region through Tuesday night. The pattern begins to change Wednesday, with Thursday and Friday carrying the most widespread chances for thunderstorms, locally heavy rain and a few stronger storms.
Fog gives way to sunshine Tuesday
Areas of fog will be the main early concern Tuesday, especially in river valleys and places that received recent rain. The combination of clear skies, light winds and lingering ground moisture may briefly reduce visibility around daybreak, but the fog is expected to lift by midmorning.
Once it clears, most of the region should see sunny skies and light winds. Highs will generally reach the lower to mid-80s, including about 82 degrees around Rochester and Geneva and the mid-80s near Syracuse, Elmira and parts of the Southern Tier.
Humidity will remain relatively low for early August. Binghamton forecasters expect dew points mainly in the 50s, keeping the afternoon more comfortable than the increasingly humid weather projected later in the week.
Tuesday night should remain quiet under mostly clear skies. Temperatures will fall into the 50s and lower 60s, with the coolest readings in some valleys and higher terrain. Fog may redevelop late Tuesday night into early Wednesday where winds become light and skies stay clear.
Warmth builds Wednesday
Wednesday begins with high pressure shifting toward the Atlantic coast, allowing southerly flow to bring warmer air and more moisture north across New York. Most communities should still get substantial dry time, and current point forecasts keep much of the Finger Lakes and Central New York rain-free through the daytime hours.
Temperatures will respond quickly. Highs are forecast to reach the upper 80s across much of the region, including around 88 degrees near Rochester and Geneva and close to 90 around Syracuse. The Southern Tier should generally reach the mid to upper 80s.
The timing of the first showers remains uncertain. Buffalo forecasters expect an unsettled pattern to begin Wednesday as weak disturbances move through the broader flow, while Binghamton notes that dry air and a possible cap could limit storm development during the day. A few showers or thunderstorms become more plausible Wednesday afternoon or Wednesday night, but a widespread round is not certain.
Wednesday night will also turn noticeably milder, with lows mainly in the upper 60s to around 70. That rise in overnight temperatures will mark the return of a more humid air mass that remains in place through the end of the week.
Thursday brings the highest storm chances
Thursday currently stands out as the first broadly active day. A weak disturbance approaching from the west will move through air containing much more moisture and enough instability for numerous showers and thunderstorms to develop.
Forecast rain chances exceed 70 percent in many point forecasts and top 80 percent in parts of the Finger Lakes and Southern Tier. The exact start time and placement of individual storms will depend on the smaller disturbances crossing the region, so rain is unlikely to begin or end everywhere at once.
The atmosphere will be capable of holding unusually high moisture, with precipitable water values approaching 2 inches in the Binghamton forecast area and reaching roughly 1.5 to 1.7 inches farther west. That may allow thunderstorms to produce locally heavy downpours, especially where more than one storm crosses the same location.
Recent rainfall adds to that concern in the Southern Tier and toward the Catskills. Binghamton forecasters said seven-day rainfall totals have run 200 percent to 400 percent of normal in parts of that broader area, leaving less room for additional water despite the dry break Tuesday and much of Wednesday. Isolated flash flooding is possible Thursday, but the current forecast does not indicate that flooding will be widespread.
A few stronger thunderstorms also cannot be ruled out. Forecast wind shear is modest, which may limit organized severe storms, but the combination of instability and abundant moisture could support wet microbursts with gusty winds and some small hail. The strength and coverage of storms will depend heavily on how much daytime heating occurs before they form.
Highs Thursday should again reach the upper 80s in many lower elevations, although clouds and earlier rain could hold some places below forecast levels. Increasing humidity may push heat index values into the 90s in valleys before storms arrive.
Showers and storms continue Friday
The active pattern is expected to continue Friday as a broad upper-level trough advances east and another disturbance passes through. Current forecasts carry likely or higher chances for showers and thunderstorms from Rochester and the Finger Lakes through Syracuse, Ithaca, Elmira and nearby communities.
Friday's hazards look similar to Thursday's: locally heavy rainfall, isolated flooding where storms repeat, gusty winds and perhaps small hail. Slow-moving showers may become more of a concern from Friday into Saturday because the steering flow is expected to weaken, though confidence in the placement of the heaviest rain remains limited.
Temperatures will stay warm, with highs mainly in the mid to upper 80s before any rain-cooled periods. Lows Friday night should settle into the mid to upper 60s, and the muggy feel will continue.
Weekend remains unsettled
Showers and thunderstorms remain possible Saturday, but the heavy-rain threat may begin to ease as somewhat drier air moves into the region. Rain chances currently range from about 35 percent around Rochester to around 50 percent in parts of the Finger Lakes and more than 60 percent toward Elmira and the Southern Tier.
That does not make Saturday a washout. Storms are expected to be scattered, and some areas may have extended dry periods between showers. Highs should reach the mid-80s, with humidity staying elevated.
Another weak front may cross the region Sunday, bringing an additional chance for afternoon or evening showers and thunderstorms. Timing remains uncertain several days in advance, but current forecasts favor more dry time than Thursday or Friday, with highs climbing back into the upper 80s in many lower elevations.
Check the latest forecast at the FingerLakes1.com Weather Center.
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