Area Forecast Discussion

WHAT HAS CHANGED

Severe weather risk lowered today for much of western and north central New York and across western New York Friday.

KEY MESSAGES

1) Above normal temperatures and high humidity today and Friday. Warmest heat index values reaching the mid 90s and allowing for an increased risk in heat related illnesses.

2) Scattered showers and thunderstorms are expected through Friday evening.

DISCUSSION

KEY MESSAGE 1...Above normal temperatures and high humidity today and Friday. Warmest heat index values reaching the mid 90s and allowing for an increased risk in heat related illnesses.

A mid level ridge will amplify over the lower Great Lakes and Northeast through Friday. This will increase heat and humidity across the region. 850 mb temperatures will climb to near +18/+19C and the combination of heat and humidity will support heat index values in the lower to mid 90s. Heat Advisories remain in place today for portions of the Finger Lakes and the counties lining the south shore of Lake Ontario, where confidence remains the highest of heat indices reaching the mid 90s.

Similar conditions will be possible Friday, with heat headlines once again a possibility for some areas. Confidence is a bit lower as a faster arrival of a cold front may keep areas cooler.

Cooler and more comfortable weather are expected across the region behind a cold front this weekend.

KEY MESSAGE 2...Scattered showers and thunderstorms are expected through Friday evening.

A very moist airmass will remain in place today. Scattered convection expected during the morning, with heavy downpours as the primary impact. Impressive instability developing by afternoon will lead to additional convection, mainly on lake breeze or convergence boundaries inland from the lakes. However, amplifying ridging aloft building in from the west maintaining relatively weak shear profiles this afternoon, limiting severe potential.

A trough will deepen across the Great Lakes region Friday. A very warm, moist airmass will be in place ahead of an approaching cold front. The combination of an increasing wind fields and a unstable airmass will support the potential for strong/severe thunderstorms with the primary risks being damaging winds and large hail. Latest models have sped up timing of the arrival of the cold front shifting the axis of greatest instability and severe weather potential to the east. The faster arrival of the front will greatly limit the severe threat across western New York, with the higher risk of severe weather east of the Genesee Valley during the afternoon and evening. Potential exists for locally heavy rainfall, as PWAT values are expected to exceed 1.5", which is above the 90th percentile for this time of year. Drier air is expected to move into the region for the start of the weekend.

AVIATION /06Z THURSDAY THROUGH MONDAY/

A very moist airmass will linger through the TAF period, with opportunities for showers and thunderstorms as well as lower ceiling heights and or fog formation within the very moist boundary layer. Fog formation is possible through 12Z. There is low confidence that IFR or lower conditions develop at KBUF and KART within a light southwest flow over the cool lake waters.

Scattered showers and thunderstorms early this morning, will increase in coverage through peak heating today. Given the very moist atmosphere any shower or thunderstorm may contain heavy downpours, lowering visibility for a brief time to IFR or lower.

Outlook...

Tonight through Friday...Mainly VFR with a chance of showers and thunderstorms. Localized lower flight CATs within any heavier showers or storms. Also, lower CIGS possible tonight across the higher terrain.

Saturday...Mainly VFR.

Sunday...VFR/MVFR with a chance of showers and thunderstorms.

Monday...Mainly VFR, though there is a slight chance for a few showers.

MARINE

Southwest to west flow will remain through tonight. Wind speeds likely remaining 15 knots or less with only the expectation of a light chop with waves 2 feet or less.

The passage of several waves of low pressure will generate a few thunderstorms with localized strong winds over the lakes at times through Friday.

The passage of a cold front Friday could bring a brief uptick to winds, but headlines are not anticipated. Drier air behind the cold front will end the thunderstorm threat.

BUF WATCHES / WARNINGS / ADVISORIES

NY...Heat Advisory from noon today to 8 PM EDT this evening for NYZ001>005-013-014. MARINE...None.