textproduct: Binghamton

WHAT HAS CHANGED

The potential for severe thunderstorms and excessive rainfall remains for today through tonight.

KEY MESSAGES

1) Corridor of severe thunderstorm risk straddles the area through early Thursday morning, with uncertainty on timing details, yet presses southward with time into the day on Thursday.

2) A risk for locally heavy rainfall exists, with isolated flash flood possible. Primary focus of concern is late today through tonight 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... A frontal zone over the region will become even more pronounced today. 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 2.50 inches with a stronger wave by this 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 yesterday, 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 they 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. Latest guidance continues a sharp CAPE gradient along the I81 corridor in NY and Northern PA. This gradient may once again be the focus of the edge of strong/severe storms such as was the case Tuesday evening.

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 through Thursday morning of 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 /06Z WEDNESDAY THROUGH SUNDAY/

Widespread stratus deck and fog have developed across much of the area. IFR and lower restrictions should prevail at BGM/ELM/ITH through the night with AVP/RME seeing periodic IFR ceilings move into the area. SYR should stay out of IFR restrictions but some MVFR ceilings may work their way into the terminal tonight.

These restrictions should linger into the mid to late morning hours as rain shower work their way into the area from the west. These showers will originate from storms developing over Michigan tonight and model guidance remains uncertain as to if they will hold together.

Another round of thunderstorms is forecast to move into the area late this afternoon into the overnight hours. Once again, guidance remains uncertain as to the timing and path of the storms as several parameters for strong to severe storms are present but location and timing of these parameters coming together remains somewhat uncertain. Current thinking is some discrete storms will form across CNY in the mid to late afternoon hours before a squall line dives through the area from the north. PROB30 lines were used for these storms given the uncertainty. If storms move over a terminal, IFR and lower restrictions will be possible given the high moisture expected in the atmosphere.

Outlook...

Wednesday night through Thursday... Restrictions with widespread showers and thunderstorms Wednesday night. Then additional thunderstorms close to KAVP,KELM and KBGM Thursday afternoon.

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.