textproduct: Binghamton

WHAT HAS CHANGED

Storm potential has decreased for the rest of today, though it is still at least somewhat present from Twin Tiers southward. However, concern has further increased for late Wednesday afternoon through evening for both severe and excessive rainfall potential.

KEY MESSAGES

1) Corridor of severe thunderstorm risk straddles the area today and Wednesday, with uncertainty on timing details, yet presses southward with time into Thursday.

2) A risk for locally heavy rainfall exists, with isolated flash flood possible. Primary focus of concern is late Wednesday through Wednesday night for Central NY into the Twin Tiers.

3) A seasonably cooler and mainly dry pattern is anticipated for the extended Labor Day Holiday Weekend.

DISCUSSION

KEY MESSAGE 1... There remains a severe thunderstorm risk this afternoon- evening, and even with a potential wave of convection Wednesday morning. However, the bigger timeframe of concern has shifted to primarily late Wednesday afternoon into evening.

A wave of non-severe thunderstorms passed through the region this morning with locally heavy rainfall, extending from the greater Ithaca and Binghamton NY areas into Susquehanna-Wayne Counties PA. Despite the shallow warm frontal regime that has set up straddling our region, we are between waves aloft and have a lack of a trigger. We will continue to monitor for a diurnal-heating forced convective cells that could still manage to pop up in Northeast PA but overall the severe thunderstorm risk has somewhat scaled back as shear values have decreased. Whatever we do still get from heating will wane quickly this evening for a fairly quiet night with patchy fog.

The frontal zone will become even more pronounced Wednesday. Upper flow will steadily increase through the day, with a couple waves passing through to interact with the temperature gradient zone. Precipitable water values, after stepping back a bit overnight, will ramp back up a bit with a lead shortwave in the morning and then top off approaching 2 inches with a stronger wave by Wednesday evening. Undercutting these waves aloft, will be the light southeast flow encroaching at the surface, advancing around high pressure over New England to push in some marine layer. So there will indeed be a gradient of conditions for the area, with highs ranging form only upper 60s-lower 70s Poconos-Catskills to lower-mid 80s in Finger Lakes.

With the lead shortwave, there is considerable uncertainty for whether it will generate and sustain a line of convection/for how long. Some convection allowing models (CAMS) allow it to bring a decaying line of convection into the region during the morning. It will be driven by aloft-processes instead of being surface-based, so the severe risk may be limited. However, on the mesoscale we will have to see if it generates renewed convection with boundaries on the way out, which could lead to isolated strong to severe.

Wednesday afternoon, convective available potential energy (CAPE) climbs in a warm and very humid environment. As with today, there may be a lack of triggers between waves. However, this time a stronger wave in projected to enter the area late afternoon through evening which will harness whatever CAPE builds up before then. Convective parameters especially more comfortably on the warm side of the frontal zone appear quite concerning late Wednesday. Surface-rooted storms that fire with the wave will then ride up the shallow warm front, with time becoming more elevated. However, shallow warm fronts can be quite problematic with the shear that the generate in the low levels. There will be an overlapping zone of elevated helicity, which is why isolated tornadoes cannot be ruled out in addition the downburst potential from storm cores. Mitigating factors are limited midlevel temperature lapse rates as thermal profiles approach moist-adiabatic, and the trend towards a later arrival of the wave which is less able to harness diurnal heating.

Though the parade-route of passing shortwaves gradually presses south into Thursday, it is still close enough to pose a threat for stronger thunderstorms at least in Northeast PA, and elevated showers-embedded thunder farther north across the rest of the region.

KEY MESSAGE 2...

With a stalled front and high precipitable water values Wednesday into Thursday morning of around 2 inches, potential for locally heavy rain and at least isolated flash flooding is a concern. Though there will be a gradient of severe weather parameters that lessens east of I-81, the parameters for excessive rainfall will exist well north and east of the frontal zone in addition to along it. Warm cloud depths will be quite high, above 12kft agl, and a very moist low level jet will keep feeding in moisture. The High-Resolution Ensemble Forecast (HREF) model suite probability matched mean continues to depict stripes of 2-3 inches. Even though exact locations could change, there in increasing confidence in the scenario leading to excessive rainfall amounts somewhere within our general area. Conjunction of parameters puts more of the focus on Central NY to Northern Tier of PA versus points farther south. Timing of waves, and frontal zone location at those times, will be key for who ends up with flash flooding, with potential for isolated amounts above 3 inches.

KEY MESSAGE 3...

After the busier pattern through Thursday, the extended Labor Day Weekend actually looks pretty benign. Friday into early next week, the large ridge in the central US retrogrades west with the trough in the northeast nudging into the mid Atlantic. This will help the flow become more northerly with seasonably cooler and drier air advecting in. Depending on how cool the 850mb temperatures are, there could be some lake effect rain showers to deal with at times but for the most part the weekend into early next week is looking mostly dry. We will be back to fresh nights with lows of upper 40s-mid 50s, and highs of mainly 70s.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

A mix of VFR and MVFR conditions this afternoon and early evening within the vicinity of a warm front. TSRA potential exists given high moisture levels and increasing heating as ceilings become a bit more broken to scattered. Model guidance is devoid of much storm development due to lack of a broad scale trigger, except in the vicinity of KAVP where confidence is highest late PM and evening. Isolated TSRA possible elsewhere, but confidence too low. Flight restrictions tank to IFR tonight within deep shallow moisture. Alternate mins are possible along with a non-zero chance for airport minimums. Recovery after 12Z Wednesday will be slow but expect MVFR-IFR threshold by end of period. Rounds of low confidence convective activity are being hinted at within model guidance for Wednesday, so wouldn't be surprised to see later updates carry TSRA between 12Z-18Z, but confidence is a long shot right now.

Outlook...

Wednesday night through Thursday...Occasional SHRA/TSRA with associated restrictions.

Friday through Sunday...Low operational impact. Chance of early AM fog each day. Chance of showers Saturday.

BGM WATCHES/WARNINGS/ADVISORIES

PA...None. NY...None.