575 FXUS61 KBGM 281839 AFDBGM Area Forecast Discussion National Weather Service Binghamton NY 239 PM EDT Sat Sep 28 2019 .SYNOPSIS... A cold front will pass through this evening with scattered showers and isolated thunderstorms expected ahead of it. Canadian high pressure builds in Sunday and Monday with partly cloudy skies and seasonable temperatures. The pattern turns more active Tuesday through Thursday as a cold front gradually moves southward across the area. Warmer and more humid conditions will return ahead of the front along with a chances for showers and storms. && .NEAR TERM /THROUGH SUNDAY NIGHT/... A cold front continues to progress eastward and was on the western doorstep of Lake Ontario and Erie early this afternoon. Farther downstream, a pre-frontal trough was sharpening across the Finger Lakes into western portions of the Southern Tier of NY. Convergence along this trough is expected to focus convective development late this afternoon as the boundary layer further destabilizes and the capping inversion erodes. The potential for thunderstorm development is much lower to the west of this surface trough. The latest CAMs are less bullish with the late day convection. Given modest instability/shear profiles, the residual cap, and deeper lift along the synoptic front lagging to our west, thunderstorms should be very limited in coverage/intensity and mainly confined to the I-88 corridor southward and the I-81 corridor eastward late this afternoon and evening. Accordingly, PoPs trended lower with the early afternoon forecast update. A wind shift from W to N-NW is expected behind the cold front this evening. A trajectory off Lake Ontario, cold-air advection and moisture trapped under the subsidence inversion should lead to the development of low clouds over much of the region (except maybe the Wyoming Valley in our far southeastern zones) late this evening and overnight. Patchy light rain or drizzle is also possible especially across the upslope areas (north-facing slopes) in CNY. Despite a wet ground where it rains later today, low clouds should prevent limit fog development assuming there aren't many breaks in the stratus deck. Canadian high pressure will continue to build south/eastward into our region on Sunday. Stratus deck should gradually dissipate from south to north during the late morning and early afternoon as the boundary layer deepens with heating and drier air associated with the subsidence inversion mixes down. Accordingly, forecast highs in the mid to upper 60s in CNY where clouds are expected to hold on the longest while highs in the lower to mid 70s are expected in NEPA where sunshine breaks out earlier in the day. The center of the high will pass north of our region Sunday night. Good radiational cooling conditions should setup over the area as the ridge axis shifts over the region and the pressure gradient weakens. Although there is some uncertainty regarding the extent of radiational fog development owing to a very dry airmass (upper 30s to mid 40s dewpoints) in place, river valley fog is a good bet this time of year. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... 215 pm update... Main challenges in the short term remain centered on the timing of the next batch of showers and storms Monday night into Tuesday...and the near record warmth on Tuesday. Dry and quiet weather conditions expected early Monday, and likely through most of the daytime hours...as high pressure to the north noses south into central NY and ne PA. Weak ridging aloft will also contribute to the large scale suppression and allow for mostly dry weather. An embedded surface warm front across the Ohio Valley/srn Great Lakes will lift to the e/ne later in the day Monday...but be situated within the the nrn periphery of the broad upper ridge. The latest GFS and ECMWF keep the impacts from this front fairly benign through Monday evening, but the CMC and NAM trigger convection during the afternoon and through the evening. At this point will continue to lean toward a drier forecast through most of Monday evening...with the ridge winning out...and then start to bring in high chance pops across the northern counties late Monday night and Tuesday morning. The atmosphere will become quite unstable on Tuesday with a strong push of warm/moist air from the SW arriving late morning and afternoon. This positively buoyant air mass will not have much of forcing mechanism to focus around, with most of the stronger dynamics remaining well to the north. The most favorable area for developing convection still remains across the north through the day Tuesday. The well above average temperatures on Tuesday will also be of note. Forecast temperatures are currently 2-4 deg below record highs for Oct 1. It wouldn't be out of the question to break a few records on Tuesday. Highs will be topping out in the upper 70s and lower 80s. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... 410 AM Update... Yet another transition occurs in the long term; this time from quite warm initially to the coolest air mass so far this season late in the week. A surface low will track down the Saint Lawrence Seaway Tuesday night into Wednesday, and models agree that will trail a cold front into the region with showers and a chance of thunder. However, the front will become nearly parallel to the flow aloft, and thus may have trouble getting entirely south of the area. Regardless, another wave of low pressure is likely to pass along the stalled frontal zone Thursday or even early Friday depending on the model. While models are differing in the details for frontal zone placement and timing of waves/showers and perhaps thunder, the end result turns out the same. That is, a troughy northwest flow and much cooler air spilling into the region by the end of the week. By Friday-Saturday, we are currently projecting highs of only mid 50s-lower 60s with mainly dry conditions. First frosts are potentially in sight; if not some spots Thursday night then larger chunks of the area as we head into next weekend. This kind of timing for first frost is not at all unusual; even a bit late for some parts of the region. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Predominately VFR conditions thru sunset. However,brief/ localized restrictions possible with heavier showers and storms that develop late this afternoon and evening. The greater risk for storms will be at BGM (20-23Z) and AVP (23-02Z). However, opted to only include TSRA in 18Z TAFs at AVP as the anticipated storm coverage keeps trending lower. W-SW winds 6-12 kt with gusts to 18 kt this afternoon will become NW behind a cold front this evening. Stratus deck expected to form behind the front between 23Z and 03Z, resulting in MVFR CIGs. Some guidance indicates CIGs lowering to IFR with patchy DZ, particularly at BGM and ELM overnight. High uncertainty with ending time to the low clouds late tonight into Sunday morning. However, generally expect terminals across the Southern Tier of NY to hold on to the stratus deck and MVFR CIGs the longest Sunday morning. Improving to VFR everywhere by the afternoon. A light N wind under 10 kt is expected. Outlook... Sunday night through Monday...River valley fog could lead to IFR conditions early Monday morning at KELM. Otherwise VFR is expected. Monday night through Thursday...Brief restrictions possible in scattered showers; mainly the NY terminals. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...None. NY...None. && $$ SYNOPSIS...JRK/MJM NEAR TERM...JRK SHORT TERM...BJT LONG TERM...MDP AVIATION...JRK