National Weather Service Buffalo NY
206am EDT Thu August 15 2024
Synopsis
High pressure draped across the central and eastern Great Lakes will bring fair dry weather to much of the area through Thursday...with just a couple isolated showers and storms possible across the North Country at times. The high will then exit to our east Thursday night, opening the door for a large, slow moving storm system to affect our region from Friday afternoon through the weekend. The most unsettled conditions will be Saturday and Sunday when we can expect occasional showers and scattered thunderstorms.
Near Term - Through Today
Over the last couple hours a few isolated showers and storms have popped up over the Upper Saint Lawrence Valley...on the western fringes of the Upper Low over the Canadian Maritimes and in the vicinity of a lingering weak surface trough extending southwestward across the Saint Lawrence Valley. A few of these may make it into Jefferson and Lewis counties over the next couple of hours...for which some slight chance Probability of Precipitation remain in place. Otherwise high pressure draped across the central and eastern Great Lakes will provide fair dry weather to the rest of the region...with a little valley fog possible across the Southern Tier overnight. Lows will range from the lower to mid 50s across the interior of the Southern Tier and far interior of the North Country to the upper 50s to lower 60s elsewhere.
On Thursday the surface high will remain nearly stationary across the central and eastern Great Lakes...and will provide continued fair dry weather to western New York. Further east...the eastern Lake Ontario region will remain on the western fringes of the upper low over the Canadian Maritimes...and with daytime heating and another disturbance rotating around the backside of this low...there will be the chance for a few more isolated to widely scattered showers and thunderstorms...with the best chances of these across Lewis county. Otherwise it will be a little warmer than on Wednesday...with highs ranging from the upper 70s across the higher terrain and along the southern/eastern shores of Lake Ontario to the lower to mid 80s elsewhere.
Thursday night the axis of the surface high will drift east into central and eastern New York...while weak ridging builds in aloft. Coupled with nocturnal stabilization...this will bring an end any lingering convection across our far eastern zones...with a dry and quiet night otherwise expected. Later on in the night some high clouds should begin to arrive across far western New York...with some patchy valley fog again becoming possible across the Southern Tier. Overall...low temps will be a touch milder than those of the previous night...ranging from the mid 50s across the interior of the Southern Tier and North Country to the upper 50s to mid 60s elsewhere.
Short Term - Tonight Through Sunday
The longwave pattern across the CONUS will evolve to bring the forecast area a much more unsettled stretch of weather moving towards the end of the week. This will come in the form of a deep longwave trough digging south from Canada to the Ohio Valley across the Great Lakes, flanked by ridges of high pressure across the Rockies/central Plains and across the Canadian Maritimes. A cyclonically curved jet streak rounding the base of this trough will allow for a steady transport of GOMEX based moisture into the eastern Great Lakes region, causing PWATs (Precipitable Waters) to sharply increase from west to east Friday and remaining elevated through Sunday, generally hovering in the 1.5-1.9" range. As these features slowly shift eastward through the weekend, the trough will become nearly vertically stacked while partially closing off in the 850-700mb layer, as TC Ernesto slowly climbs north across the western Atlantic. This will serve to slow the progression of the trough, with the mid-level axis likely remaining upstream through the period.
In terms of sensible weather, our stretch of mostly dry weather will come to an end Friday and Friday night as a warm front and deep synoptic moisture lifts into the eastern Great Lakes. While the day should start off dry with just increasing mid/high cloud cover, shower and thunderstorm chances will ramp up from west to east by the afternoon. Convection could be as far east as the Genesee Valley by early Friday evening, with showers and a few thunderstorms 'likely' ongoing in the western Southern Tier. Mid-range guidance only indicating about 400-600J/kg of CAPE and < 30kts of bulk shear in this area during peak heating, so while severe risk looks limited, there's a small chance in a few isolated strong wind gusts Friday afternoon especially if any deeper convection that forms upstream in the Ohio Valley (where CAPE values will be much higher) manages to move into our region.
A period of widespread rain with embedded thunderstorms, some of which could be heavy given the high PWATs, is expected Friday night west of the Genesee Valley. With a lack of daytime instability this activity should diminish some in coverage and/or intensity as it moves towards the Finger Lakes and eastern Lake Ontario region overnight. While there will likely be a brief break in the precipitation back across WNY late in the night as a small dry slot works into the region, the next slug of deep moisture will arrive back across the western zones by Saturday morning. Thereafter, with the trough and associated surface low slowly moving into the eastern Great Lakes, expect very unsettled weather with occasional showers and thunderstorms punctuating nearly the entire period. Coverage is expected to be fairly widespread during peak heating in the afternoon hours both days, though with large scale support present convection could persist well into (or even through) Saturday night. WPC has maintained a Marginal Risk for excessive rainfall across the entire forecast area for both Saturday and Sunday.
In regards to temperatures this period. Friday and Friday night will be warm and humid, with highs in the upper 70s/mid 80s and mid 60s/low 70s respectively. Thereafter, a general day-to-day cooling trend is expected through the weekend.
Long Term - Sunday Night Through Wednesday
A stacked low pressure system will be directly over the eastern Great Lakes moving into Sunday night. This will likely displace the greater forcing for ascent just east of the region as diurnal instability falls off by Sunday evening. While this should reduce the overall coverage and intensity of convection overnight, given the proximity of the low, scattered showers and thunderstorms will continue to be possible.
The mid-level trough axis should then slowly cross the region Monday quickly followed by a period of strong cold advection, with the latest suite of guidance trending a bit faster with this pattern overall. While a few showers or thunderstorms are not yet out of the question through Tuesday, have trended Probability of Precipitation downward this period as the airmass with the front looks very dry. Should this trend continue to hold, could see Monday and especially Monday night into Tuesday being even drier than NBM/continuity. Surface high pressure should then guarantee a period of areawide dry weather Tuesday night, though with the cooler airmass advecting overhead, precipitation chances increase some again for Wednesday.
Much cooler and less humid air will arrive with the front Monday and last through Wednesday. High temperatures will range from the upper 60s across the hilltops to the mid 70s across the lower terrain, while overnight lows will fall back in the 50s to near 60 each night.
Marine
High pressure draped across the central and eastern Great Lakes will maintain quiet conditions on Lake Erie and Lake Ontario right through Thursday...with the weak pressure gradient supporting the development of lake breeze circulations during Thursday afternoon.
A modest southeasterly to southerly flow will then develop later Thursday night and Friday as a warm front approaches the region... but speeds should remain less than 15 knots. Following the warm frontal passage...a general south to southwesterly flow should then ensue for the weekend...though winds should again generally remain below 15 knots.
Of greater concern to marine interests will be the potential for scattered thunderstorms with locally higher winds and waves...with this beginning Friday afternoon across Lake Erie and western Lake Ontario...then spreading east across the remainder of the region over the weekend.
NOAA Buffalo NY Office: Watches - Warnings - Advisories
NY...None.
Marine
None.
