Area Forecast Discussion
Issued by NWS Binghamton, NY

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560 FXUS61 KBGM 221103 AFDBGM Area Forecast Discussion National Weather Service Binghamton NY 703 AM EDT Sat Jul 22 2017 .SYNOPSIS... A chance of thunderstorms will visit mainly Northeast Pennsylvania late today into tonight. Some showers and isolated thunder could edge into Central New York. After quiet conditions late tonight to midday Sunday, there will be a more areawide likelihood of showers and thunder late Sunday through Monday. Dry high pressure is expected Tuesday and Wednesday. && .NEAR TERM /THROUGH SUNDAY/... 7 AM Update... High clouds blowing off of convection well upstream is fairly thick, which will limit diurnal heating for most of the area. This supports the continued trend in the models shunting instability and thunder chances to the far southern zones for late afternoon-evening. More details below. Previous discussion... There is a limited risk for thunderstorms with locally heavy rainfall and gusty winds late today through this evening, but the focus will be mainly south of our area, in Central to Southern Pennsylvania. Then Sunday afternoon, while shower and thunder chances will begin to increase areawide, most of it will hold off until Sunday night. Models have continued their recent shift in placing instability further south compared to prior thinking. This is a welcome development, in that while not completely removing the threat, this trend significantly diminishes it in size and scope. Mesoscale convective complexes have erupted in the Midwest, around Chicago to Indianapolis. The frontal boundary ahead of it will sink further south than previous expectations. The upstream convection and associated shortwave aloft will roughly follow along 500mb height lines, almost due east yet slightly south. Deep layer shear will definitely be present especially the 3-6 km layer which along with dry air in the lowest levels will promote gusty winds in the storms that carry across, but the stalled out stationary or warm front ahead of the wave of low pressure will be positioned from northwest to east-central Pennsylvania. So for our area, Northeast Pennsylvania and specifically the Wyoming Valley/Scranton /Wilkes- Barre/Poconos areas will have this risk for thunderstorms with strong gusty winds roughly between 5PM-11PM. The air mass just to our south will be very moisture-rich, with precipitable values around 2 inches. Though the surface front will be quite far south, late today at 850mb a low level jet will attempt to force moisture over that surface front. Convection will tend to move very fast yet could also contain brief heavy rainfall rates in Northeast PA and especially Wyoming Valley area. Showers and isolated thunder, harnessing some instability aloft, may encroach into the Southern Finger Lakes-Southern Tier-Catskills late today and especially this evening. However, the risk for excessive rainfall now appears minimal compared to further south. Late tonight through midday Sunday, a fairly quiet period is foreseen between waves. However, frontal boundary will begin to drift northward with time Sunday afternoon. Models significantly differ on how long it takes instability and moisture to materialize in the form of convection. The GFS model actually poses the most problematic solution in terms of severe weather potential, due to quicker northward push of warm sector ahead of the next low pressure wave, and a sheared wind profile that is common with shallow warm fronts. However, most other model guidance has trended less significant with the threat Sunday especially during the day. Regardless, the better chance for showers and thunder appear to be as we head into Sunday night. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... Unsettled and potentially stormy this period as a fairly sharp upper level trough and associated surface low move through the area. To begin the period Sunday evening, progressive upper trough will be diving S/E toward the area with most models indicating surface low positioned over the Finger Lakes. This would place western parts of the CWA in the warm sector where showers and storms will likely be ongoing. The notable exception is the NAM which is much slower and weaker with this system and keeps more stable air over the area due to stronger ridging from the east. So there is uncertainty with this forecast but we generally leaned toward a non NAM compromise. If this solution (non-NAM) is what verifies concern is that there could be a fair amount of instability in the warm sector over the western southern tier into the Finger Lakes with ML CAPES possibly exceeding 1000 j/kg. Deep layer shear also looks to be in the 30-40 knot range with forced deep layer ascent due to good jet dynamics. Finally, there also looks to be good low level turning of the winds. These factors all indicate the potential for severe weather and also the possibility of Flash Flooding as there will be a deep moist layer with PWATs near 2 inches. Again, a lot of uncertainty at this point as it`s possible the best severe weather threat may be just west of our forecast area more through western NY/PA. However we`ll continue to mention threat in HWO. As the system moves across the area Monday night, best chance for heavy showers/storms and severe weather would be in the evening with the warm sector getting shunted off to the east overnight. Monday...the initial slug of moisture will have moved off to the east however a surface trough looks to hang back across the area with lift also being supported by the upper trough axis which will swing through during the day. This will keep showery weather over the area with additional thunderstorms also possible...especially in the afternoon. Temperatures will be cooler with highs mainly in the 70s. Monday night...system will be moving away but one final shortwave will move through which will keep the chance of some showers going, especially in the east. However do expect that showers will become lighter and more scattered to isolated with time. Also, cooler air moving in behind the system will result in lows dipping into the mid to upper 50s so a more comfortable night compared to many recently. && .LONG TERM /TUESDAY THROUGH FRIDAY/... The area looks to see another respite from active weather Tuesday through Wednesday as high pressure moves in. For Tuesday there could still be a couple isolated lingering showers mainly east of I-81 but otherwise expect these days to be dry under a mix of sun and clouds. Temperatures will be on the cooler side with highs in the 70s along with comfortable humidity levels. Beyond this time, the next front looks to move south through the area Wednesday night into Thursday bringing another round of showers and thunderstorms. Seasonably cool conditions look to then follow for the end of next week with the chance of lingering scattered showers as models indicate the area will be in cyclonic flow aloft under the influence of a large upper trough over Quebec. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Generally VFR conditions are expected today, thanks to high thin clouds at 15-20 kft preventing fog formation overnight except for MVFR VIS at KITH. After 22Z, some showers and thunderstorms will skim a part of the area. There is uncertainty as to where, but KAVP stands the best chance of at least showers if not thunder during the 00Z-06Z Sunday period. SHRA included in KAVP TAF; if confidence in TSRA increases, CB will be added. Thunder and restrictions are not impossible further north, such as KELM-KBGM, but it will have a much tougher time reaching there thus it is not in TAF at this time. Winds will be generally variable less than 5 knots through the period. Outlook... Sunday through Monday night...Periodic restrictions in showers- thunderstorms, especially late Sunday into Monday. Tuesday through Wednesday...VFR. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...None. NY...None. && $$ SYNOPSIS...MDP NEAR TERM...MDP SHORT TERM...PCF LONG TERM...PCF AVIATION...MDP

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