Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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394 FXUS61 KBUF 241329 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 929 AM EDT Tue Sep 24 2024 .SYNOPSIS... Low pressure will cross the Great Lakes this afternoon through tonight, spreading another round of rain across the region. A trailing front will move slowly across the area Wednesday through Wednesday night and support some additional rainfall, especially in southern and eastern portions of the area. A few showers may linger Thursday, especially east of Lake Ontario. High pressure will then build into the Great Lakes region, supporting a return to mainly dry weather Friday through next weekend. && .NEAR TERM /THROUGH WEDNESDAY/... A deep and complex longwave trough will carve out over the Great Lakes and Ohio Valley today through Wednesday as northern and southern stream shortwaves partially phase. The southern stream shortwave will move northeast across the Ohio Valley and Central Great Lakes this afternoon through tonight before reaching southern Quebec by late Wednesday. A weak surface low will track from near the southern tip of Lake Michigan today to Georgian Bay Wednesday morning. Large scale forcing for ascent will increase ahead of the trough later today through tonight as DPVA spreads into the eastern Great Lakes, topped by mid/upper level diffluent flow ahead of the digging trough. Deep moisture will be transported northward by a 40+ knot southerly low level jet. The quality of moisture and forcing will support fairly widespread showers moving into Western NY by early to mid afternoon, then spreading to the Genesee Valley and western Finger Lakes late afternoon and this evening, before reaching the eastern Lake Ontario region overnight. Terrain influences will play an important role in coverage of rain and also rainfall amounts. Persistent south/southeast downslope flow will result in shadows of lower rainfall amounts and diminished rain coverage to the north of terrain and on the lake plains. The highest rainfall totals will track from southern Ontario over and north of Lake Ontario to the Saint Lawrence Valley late today through early Wednesday, away from the diminishing influence of downsloping. Late tonight through Wednesday morning the best forcing and deepest moisture will continue to move northeast into southern Quebec, with rain tapering off across Western NY overnight, and by mid to late morning east of Lake Ontario. Southerly downslope winds will continue, so the lake plains may see a period of completely dry weather supported by the mid level dry slot and drying influence of downslope flow. The frontal zone will remain draped from the Ohio Valley to Central NY, and model guidance continues to suggest a baroclinic wave will ripple along the boundary starting Wednesday afternoon. Differential temperature advection across the depth of the boundary in response to the wave of low pressure will likely allow for showers to expand in coverage again from south to north Wednesday afternoon. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... An anomalously strong ridge will be across the Plains while a trough resides across the Northeast Wednesday night. The trough will move east while the ridge into the Great Lakes region through Friday. During this time, a closed upper level low will remain centered near the Ozarks while Potential Tropical Storm Nine moves into the southeast U.S. A mid-level trough axis and cold front near Michigan Wednesday evening will move east across the forecast area overnight. A 35 kt low level jet will be across western and north central NY with the nose of the jet near north central/central NY. Theta-e advection within a moist environment will result in medium to high chances for showers and a few thunderstorms especially east of the Genesee Valley. Rainfall amounts will average 0.1-0.30 inches east of the Finger Lakes region and less than 0.1 inches west of the Finger Lakes region. Mild overnight with lows in the upper 50s to low 60s. Dry air filters into the region Thursday as the mid-level trough axis moves east of the forecast area. The strong ridge will move into the Great Lakes region while the potential tropical storm moves into the southeast U.S. through Thursday night. A strong southeasterly jet will transport moisture into the Mid-Atlantic region and central Appalachians, however the strong ridge will suppress moisture south of the forecast area. By Friday, the remnants of any tropical storm will move northward while high pressure extends into the forecast area from Quebec. Dry weather will continue across the forecast area. Temperatures will be slightly above normal with highs in the low to mid 70s Thursday and Friday and lows in the 50s Thursday night. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... The evolution of the upper low over the Mississippi Valley will be the large scale feature to watch during this period. Ensemble systems show a ridge across the Great Lakes region which should keep the forecast mostly dry, however there are some signals from the ensemble systems that draw the upper low further north and/or open the low into a trough across the forecast area. This could result in increasing moisture and therefore there are low chances of showers across the forecast area through the weekend and into Monday. Temperatures remain above normal through the period. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... CIGS have improved a mix of VFR and MVFR across the lower elevations of Western NY thanks to increasing southeast downslope flow. IFR remains solidly entrenched across the higher terrain of the Southern Tier, with VFR east of Lake Ontario. Expect this same pattern of CIGS to hold through midday or early afternoon. Surface low pressure and a strong upper level system will move from near Lake Michigan this morning northeast across the central and eastern Great Lakes later today through tonight. A broad area of ascent ahead of this system will bring another round of widespread rain showers, entering Western NY midday to mid afternoon, then spreading east across the rest of the area later this afternoon through tonight. Pockets of moderate rain may bring a few periods of lower VSBY. Expect widespread MVFR/IFR CIGS across Western NY this afternoon, spreading east across the remainder of the area tonight. IFR will be favored across higher elevations. S/SE downslope flow will try to hold the CIGS higher across the lake plains including most of the terminals. MVFR CIGS are still likely, but the downslope flow may help to keep IFR at bay this afternoon through tonight. Outlook... Wednesday...MVFR/IFR with showers likely. A few widely scattered thunderstorms possible. Thursday...MVFR east of Lake Ontario with a chance of showers. Becoming mainly VFR elsewhere. Friday through Saturday...Mainly VFR. Local IFR in valley fog across the Southern Tier each overnight and morning. && .MARINE... A moderate pressure gradient will remain in place over the eastern Great Lakes through Wednesday between persistent high pressure over the Canadian Maritimes and low pressure moving through the central Great Lakes. This will maintain moderate southeasterly flow today through Wednesday, with the strongest winds on the east half of Lake Ontario tonight through the first half of Wednesday. The southeast wind direction will continue to push the greater wave action into Canadian waters, but the offshore winds will become strong enough to require a Small Craft advisory for the eastern end of Lake Ontario and Lake Erie. Winds will gradually become southwest and then west Wednesday night through Thursday as a trough crosses the eastern Great Lakes from west to east, with wind speeds decreasing with the passage of the trough. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory from 7 PM this evening to 8 AM EDT Wednesday for LEZ040-041. Small Craft Advisory from 10 PM this evening to 2 AM EDT Thursday for LOZ045. && $$ SYNOPSIS...Hitchcock NEAR TERM...Apffel/Hitchcock SHORT TERM...HSK LONG TERM...HSK AVIATION...Hitchcock MARINE...Hitchcock