textproduct: Binghamton

WHAT HAS CHANGED

Increased the threat for strong to severe storms across the region this afternoon and tonight, along with the potential for heavy rain and flash flooding.

KEY MESSAGES

1) Enhanced Risk for severe weather today and tonight as a line of thunderstorms move through with the potential for damaging winds, hail and a few tornadoes.

2) Slight risk for excessive rainfall that could potentially lead to flash flooding across portions of central NY and northeast PA tonight.

3) Quiet weather with lower humidity and seasonal temperatures Friday through the Labor Day weekend.

DISCUSSION

KEY MESSAGE 1...

One of the two main concerns the rest of today and tonight will be the threat for damaging winds, hail and a few tornadoes from severe thunderstorms expected to roll through the region later today and this evening.

Large ridge of high pressure continues to dominate the TN Valley region this afternoon as a series of short waves track eastward along the northern periphery of the ridge through the Great Lakes. The forcing from these waves will combine with an abundance of moisture and instability throughout a deep layer which will contribute to strong/deep convective development later today.

Strong storms moved through earlier this morning and left behind residual moisture and a boundary layer well-turned over. However, the atmosphere appears to have recovered and the stage is set for another round of strong, and likely, severe storms into central NY and northeast PA after 5 PM. Current satellite and radar imagery has indicated in the past hour an area of rapidly developing storms in southern Ontario. Latest high resolution guidance (i.e. HRRR) is indicating that the trailing short wave in MI will catch up with this convection and eventually tap into a very unstable and highly sheared environment to the east (western NY) and initiate convection that will move rapidly eastward this evening.

The convective mode appears to be mostly discrete initially and then transition to either a dominant singular line or smaller line segments later this evening and overnight. Surface analysis does indicate a warm front hanging around across NY, which would aid in localized enhanced shear for maturing storms. The tornado and hail threats appear to be early in the event, associated with storms along this boundary. As the storms grow upscale and become more linear the threat of damaging winds increase. Cannot rule out quick spinup tornadoes embedded in the lines as well given the extreme amount of low level shear.

Environmental parameters for severe storms are mostly favorable, including 500-1500 J/kg of ML CAPE, 35-45 kt of 0-6km shear and 20- 30 kt of 0-1km shear. Hodographs are sharply curved and favorable for rotating updrafts. Some of the limiting factors with this event could be the stable clouds that are currently in place and look to be fairly stubborn to scour out east and south of the Finger Lakes. The convection that gets going in wrn NY may meet this stable air and become mostly elevated above the boundary layer if the clouds stick around.

The strong-severe thunderstorms will roll through the area between approximately 7 PM to around 2 AM Thu. There is a threat of heavy rain and flash flooding as well, with the persisting weaker storms holding on through the overnight.

KEY MESSAGE 2... The second conern is for flash flooding. There is a slight risk of excessive rainfall that could lead to rapid runoff and flash flooding across the region tonight due to heavy showers and thunderstorms.

A wave of convection, currently developing in southern Ontario, will gather energy and speed this evening and push into the region tonight. These thunderstorms will focus along a warm front and combine with the steering flow nearly parallel to the front to produce back-building storms that could train over the same area once the front sags south into the southern tier of NY.

The environment is primed for deep moist convection with PWs around 1.5 to 2 inches and a persistent LLJ from the southwest pulling in moisture to help regenerate the storms to the west as they move eastward.

A Flash Flood Watch has been issued for a large portion of central NY and the northern tier of northeast PA beginning at 4 PM today and continuing through 8 AM Thu.

Locations north of Cortland and Oneonta saw a fair amount of rainfall this morning, anywhere from 0.5 to 2.5 inches, which has left many areas saturated and very sensitive to additional rainfall. Rainfall rates will be the main concern where rates upwards of 1.5 to 2 inches in an hour could cause flooding problems in the sensitive areas and around 2 to 2.5 inches in an hour in other locations could cause flash flooding...especially in urban areas and heavy terrain.

The showers and weak storms will persist into the overnight, but slowly drop south with time. The question will be how quickly/slowly the entire system moves south. The slower it moves the more problems are likely. The quicker it moves out, the less hydro issues expected. The current forecast has most of the heavier precip out of the area before 6 AM.

KEY MESSAGE 3... The upper ridge slowly drops south on Thursday as the upper low rotates east/newd. The wave pattern gradually becomes flatter with time and the air mass drier and cooler. This pattern will be favorable for quiet and dry weather with seasonal temperatures in the 70s during the day and 50s/low 60s at night. There does appear to be non-zero chances for rain in the afternoon, or at the very least diurnal cumulus clouds Friday and Saturday before more clearing possible Sunday into Labor Day.

AVIATION /19Z WEDNESDAY THROUGH MONDAY/

MVFR/MVFR fuel alternate CIGs will linger from near ELM and ITH south and east to BGM and AVP. BGM will be lower, mainly LIFR to IFR much of the afternoon under the marine layer influence. The MVFR CIGs may scatter out at times at ELM and ITH, as they are on the edge of the lower cloud deck. Otherwise, mainly VFR conditions will persist at RME and SYR through around 23z.

After around 23/00z this evening pop up showers and thunderstorms look to develop across portions of Central NY. At first coverage may be more isolated to scattered in the early evening, so addressed this potential with TEMPOs in the TAFs at SYR, RME, ITH...with ELM and BGM being a little later after 01z. Heading into the late evening and overnight there looks to be a period of heavy rain and thunderstorms that is forecast to drop NW to SE across the area. The best consensus on timing of this heavy thunderstorm cluster/line is 01 to 05z at RME and SYR, 02 to 08z at ELM and ITH and 04-08z at BGM. As this line moves through there could very well be IFR/LIFR conditons with heavy rain, reduced visibility and very gusty winds. There could even be isolated hail with a few storms. The storms reach AVP between 03-07z, and could continue until 10z before transitioning to light rain. After the storms end at all locations there will likely be a period of light rain, drizzle and low CIGs lingering into mid morning Thursday. Then, conditions begin to lift and scatter out by late Thursday morning or early afternoon.

Surface winds will be south-southeast into this evening, under 10 kts, veering more southwesterly overnight. Winds will be gusty and erratic in any thunderstorms that occur. Winds turn west-northwest Thursday morning, between 5 to 15 kts.

Outlook...

Thursday Afternoon... Mainly VFR, although scattered showers and thunderstorms could bring restrictions at times.

Thursday Night...Chance for showers, with associated ceiling restrictions possible.

Friday through Monday...Low operational impact. Chance of early AM fog each day.

BGM WATCHES/WARNINGS/ADVISORIES

PA...Flood Watch through Thursday morning for PAZ038>040. NY...Flood Watch through Thursday morning for NYZ015>018-022>025- 036-037-044>046-055>057-062.