National Weather Service Buffalo NY
1050pm EDT Fri September 6 2024
Synopsis
A strong cold front will move slowly across the area, with periods of rain and a few thunderstorms overnight across Western NY, and late tonight through a portion of Saturday for areas east of Lake Ontario. A much cooler airmass will pour into the eastern Great Lakes behind the cold front, with chilly temperatures and some lake effect rain east of Lake Erie and Lake Ontario at times later Saturday through Monday. The cool down will not last long, with summer-like temperatures and an extended period of dry weather starting Tuesday.
Near Term - Through Saturday
A sharp mid level trough will dig across the eastern Great Lakes and western Quebec by Saturday evening, with the trough axis taking on a negative tilt with time. A mid level closed low will evolve in the base of the trough near Georgian Bay tonight, then move to the southwest corner of Quebec by Saturday evening while strengthening with time. This system will drive a strong cold front through the region overnight and through the first half of Saturday.
The front, which is slowly making its way through WNY this evening, will become increasingly anabatic in nature as one or two weak baroclinic waves run northward along the boundary. The wavy nature of the front will slow its eastward progression to a crawill at times, and also enhance convergence and frontogenesis along the boundary in response to low level flow adjustments associated with the baroclinic wave. The increase in moisture and forcing along the front will cause the fairly widespread area of rain (both ahead and behind the surface front) to slowly progress east-northeast through the forecast area. The best chance of thunder will be across the Gensee Valley early tonight before decreasing with time and eastern extent tonight through Saturday, although there may still be a minor amount of embedded thunder present. The threat for any additional severe weather remains very limited.
The most widespread rain in WNY will be through the first half of tonight, through early Saturday morning for the Genesee Valley and western Finger Lakes, and late tonight through early afternoon Saturday east of Lake Ontario. Additional rainfall amounts will average 0.50" to 1.0" in most areas, but some locations will likely exceed 1.0" especially where the baroclinic wave stalls the boundary.
Much cooler air aloft will pour into the eastern Great Lakes in the wake of the departing cold front late tonight and Saturday. A brief mid level dry slot and subsidence behind the cold front will give way to increasing wrap around moisture and growing convective cloud depths over the lakes in the afternoon as the cold air deepens. This will allow for increasing lake response on WNW flow. Off Lake Erie, expect lake effect showers to increase across the Western Southern Tier during the afternoon. Off Lake Ontario, lake effect showers will increase along, or just offshore of the south shore of the lake in the afternoon, reaching Oswego County by late afternoon or early evening. Outside of these areas, a few scattered showers will develop Saturday afternoon in response to wrap around moisture and steepening lapse rates. There may also be a few meandering bands of lake effect showers from Lake Huron.
The other big story will be the much cooler temperatures. Highs may briefly touch 60 east of Lake Ontario and on the lake plains of Western NY, but otherwise ongoing cold advection will keep temperatures in the 50s for most of the day.
Short Term - Saturday Night Through Monday Night
Main focus during the short term period will be the potential for lake effect rain east of the Lakes as a batch of anomalously cold air pours in across the lower Great Lakes. Goes without saying, but this will also mean below normal temperatures, although temps will moderate some by Monday. The details... Core of the coldest air aloft (H85 temps 0C to +1C) will move across western and northcentral NY Saturday night and Sunday morning. This will also correlate to the best potential for lake effect rain off the Lakes with this degree of over lake instability plenty to trigger a lake response. However, the lack of available synoptic moisture will limit any significant organized lake effect rainfall. That said, does look like there will be the chance for a period of at least moderate lake effect rain off Lake Ontario during this time as some added synoptic moisture/lift tied to the upper level low passing by to our north briefly moves overhead. This will likely set up a stripe of Quantitative Precipitation Forecast stretching from northeast Monroe to southwest Oswego County under a predominantly WNW boundary layer flow, with up to a half inch of rainfall possible. Otherwise, expect lighter lake effect showers east of Lake Erie to taper off overnight as some drier air/subsidence starts to build in from the southwest. Much cooler night on tap as lows fall back into the low and mid 40s, with upper 30s possible across the Tug Hill/western Dacks.
Upper level low will pull away Sunday, stripping away any added synoptic moisture/added lift this feature provided. Main boundary layer flow will also back a bit to westerly, which allow the lake band to shift north across northern Oswego/southern Lewis County all while weakening as drier air continues to build in and temps off the deck begin to warm some. This should leave a good portion of the area mainly dry, especially by Sunday afternoon. The exception will be east of Lake Ontario where some scattered light lake effect showers may linger through the remainder of the day. It will be a blustery, fall-like day with winds gusting upwards of 25 to 35 mph area wide with highs ranging from the mid 50s across the Tug Hill/western Dacks to the low and mid 60s across the lower elevations.
Airmass will be slowly modifying through the night Sunday night as somewhat warmer air gradually pushes northeast across the area with H85 temps averaging from around +5C over eastern Lake Ontario to +7C over eastern Lake Erie. With lake surface temps in the +21C/+22C range, may see some scattered lake effect showers redevelop overnight on a W to WSW boundary layer flow as some synoptic moisture works in aloft in advance of the next, and what should be the last shortwave dropping southeast toward our region. Not quite as chilly as the previous night with lows mid/upper 40s higher terrain and low to mid 50s lower elevations.
Models remain consistent with this aforementioned shortwave crossing the area Monday, thus introduced SChc/Chc Probability of Precipitation across much of the region along with a rumble of thunder or two possible Monday afternoon. H85 temps still be marginally cold enough to possibly contribute some lake enhancement E/ENE of the Lakes as well. Otherwise, the main trough will pull out Monday night, thus aside from a linger shower or two early, drier air and subsidence associated with high pressure will rapidly build in through Monday night. Airmass will continue to slowly modify with highs Monday mainly in the upper 60s to low 70s and lows Monday night mainly low to mid 50s, with upper 40s interior higher terrain.
Long Term - Tuesday Through Friday
A large area of high pressure and stout ridge will build into the region for the entire period and beyond. This will provide for fair dry weather from Tuesday onward, with warming temperatures through the new work week. The large ridge over much of the country during the period will become more amplified over the eastern half of the CONUS later in the week. This will result in continued fair dry weather beyond the period.
Above normal temperatures will start out the period with some continued warming through the end of the week. This will result in afternoon highs around ten degrees above normal for most of the forecast area by the middle and late portion of the week. These temperatures are expected to remain in place through the following weekend as well.
Marine
A strong cold front will slowly cross the lower Great Lakes tonight through early Saturday with periods of rain and a few embedded thunderstorms. Behind the front much cooler air will pour into the region, with a moderate pressure gradient and very unstable boundary layer thermal profiles supporting an extended period of blustery conditions on the lakes.
Small Craft Advisories start on Lake Ontario late tonight as west to northwest winds quickly become elevated behind the cold front, though the higher wave action will lag behind into Saturday morning. While choppy conditions are also expected on Lake Erie overnight, SCA (Small Craft Advisory) level winds and waves will likely hold off until later Saturday afternoon.
Winds and waves will then continue to be elevated all the way through Monday, with the stronger winds and higher waves on Lake Ontario. Sustained winds will occasionally reach or exceed 25 knots on Lake Ontario over the weekend. Winds and waves will first make a subtle southwesterly shift Sunday night before finally starting to subside Monday night and Tuesday as the pressure gradient relaxes.
The risk of waterspouts will increase Saturday as cooler air aloft arrives, and continue through Monday. Waterspouts are most likely in and near bands of convective lake effect clouds and showers where low level convergence/vorticity is found.
NOAA Buffalo NY Office: Watches - Warnings - Advisories
NY...None.
Marine
Small Craft Advisory from 2am Saturday to 2am EDT Monday for LOZ042>044. Small Craft Advisory from 2am Saturday to 8pm EDT Monday for LOZ045.
