textproduct: Binghamton

WHAT HAS CHANGED

A slight northward expansion of the severe thunderstorm potential. Also, there is slightly more concern for heavy rain and fast runoff in the Catskills and Poconos Monday evening/night. Placed more emphasis on the drop in temperatures Monday night into Tuesday morning with winds remaining stronger than previously thought during this time.

KEY MESSAGES

1) Wind Advisory continues for today and tonight.

2) Severe thunderstorm potential Monday afternoon and evening with the main threats being damaging winds and tornadoes. Brief heavy rain could also lead to localized flash flooding and smaller stream headwater flooding.

3) Rapid drop in temperatures with the passage of the cold front Monday night where 20-25 deg F temperature falls in 3-5 hours are possible...increasing the risk of a flash freeze.

4) Accumulating lake effect snow in the snowbelt region of northern Onondaga/Madison and Oneida Counties Tuesday night.

DISCUSSION

KEY MESSAGE 1...

A strong southerly flow is expected to pick up this afternoon and continue through the overnight hours into early Monday morning. The strongest winds, around 40 to 50 mph, are expected across the elevated locations above 1400 feet of the southern tier of NY, north central tier of PA and the downsloping areas of the Finger Lakes.

These gusty south winds are in response to a rapidly tightening sfc pres gradient induced by a large area of high pressure off the New England coast and an approaching deep low pressure system from the west. At this time it appears the strongest winds will occur later today and tonight over western NY and portions of central NY and north-central PA. However, winds will still be quite gusty east of I- 81 during this time...gusting 30 to 40 mph. The winds will also remain on the gusty side through the day Monday with periodic gusts 30 to 40 mph throughout the region and even into the lower elevation valley areas where the winds will be able to mix down to the surface.

KEY MESSAGE 2...

Our primary focus of attention will be on the threat of severe thunderstorms Monday along with heavy rain leading to possibly a few instances of localized flash flooding.

Northeast PA and portions of central NY continue to be under the threat for severe thunderstorms Monday afternoon and evening. A very strong, amplifying trough is expected to dig into the OH/TN valley area Monday morning while at the same time causing the ridge to the east to amplify and draw northward a very warm and slightly unstable air mass along the East Coast. The amount of warming that will occur...850mb temperature around +10 deg C and surface temperatures into the lower to mid 60s...will contrast significantly with the incoming air mass on the back side of the system...850mb temps around -12 deg C and sfc temps in the upper 20s...to create a very strong surface baroclinic zone that will help focus the convection on.

The upper level forcing with this system is expected to be quite intense as well. An embedded short wave pushing to the east will create a weak negative tilt to the trough and also move eastward with a strong area of PVA the enhance the vertical lift. The jet dynamics are also conducive to additional upper level forcing/lift as much of the Northeast US is within the right entrance region of a 160kt jet streak.

This event will be dominated by the intense amount of shear...with roughly 60-70 kt of 0-6 km bulk shear and 0-1 km shear values exceeding 40 kt. ML CAPE values roughly 100-200 J/kg could be bumped up a little higher if the area can scour out the cloud cover in the late morning and early afternoon. If there is more clearing that anticipated at this time, some of the convection that initiates ahead of the cold front could allow for more cellular storm types. However, most of the focus will be on the linear convection that is expected to develop in west central PA late Monday morning and lift to the east/northeast through the afternoon across southern/central NY and ne PA. This could actually be a situation, if the instability does not increase, where the line of "storms" may not have much in the way of lightning and could be mostly low- topped.

The primary threat will be damaging winds along the line, but embedded quick-spin up tornadoes cannot be ruled out given the extreme amount of shear. The threat for severe storms will move east of the eastern Catskills after 8-10 PM.

The additional threat with this storm system will be the centered around the potential for heavy rainfall rates that may lead to some instances of flash flooding. There are a number of factors that will likely limit the threat...namely the fast progression of the system and the relatively low residence time of heavy rain/deep moisture over much of the region. The heaviest plume of deep moisture looks to become situated well to our east with ne PA and central NY within an area of PWs around 0.75 to 1 inch. However, if locations east of I-81 see a round of convection in the morning and then more rainfall with the line of storms that move through in the late afternoon and evening hours, the two rounds of rain, combined with saturated soils and even some lingering snow pack melting, could cause issues in some locations. At this time it looks like the threat is limited, but we do remain in a Marginal Risk Outlook from WPC.

KEY MESSAGE 3...

Behind the cold front a very cold air mass for this time of year will move in quickly and cause surface temperatures to drop 20-25 deg F in a 3-5 hour window (between 8PM and midnight). There is some concern for a flash freeze in this situation given how quickly the air temperatures drop behind a rain-producing front. A limiting factor in this situation will be related to the fact that the ground temperatures overall are much warmer than even a couple weeks ago. Road surface temperatures will likely be in the 50s or higher on Monday given 2m sfc temperatures in the 60s. Winds will also be quite breezy through morning and daytime hours on Tuesday which will help to dry out the wet roads before the cold air really settles in.

With all of that being said the threat is likely fairly low, but not zero. So, there will continue to be some concern for icy spots on the roads Tue morning and through the day.

KEY MESSAGE 4...

Snow showers are expected to kick up behind the front on Tuesday but be very disorganized in nature even though there will be a lake effect component. Temperatures at 850mb advecting in will range from -16 to -19 deg C and initially work with a mostly westerly flow off of Lake Ontario to place snow showers into the Tug Hill plateau on Tuesday. However as the primary upper trough shifts eastward the flow will become more nwly, which will favor an upstream lake connection with Ontario into locations along the NY Thruway between Syracuse and Utica. The mixed layer depth will be modest, around 8 kft with a weak to moderate lift within the favorable DGZ. At this time it appears the most favorable time for accumulating snow will be Tuesday evening through Wed morning. As much as 4 to 6 inches is possible, but confidence is still on the low side given that the event is still beyond 48 hours. As we get closer to this time frame a Winter Weather Advisory for LES may be needed.

AVIATION /00Z MONDAY THROUGH FRIDAY/

VFR conditions are expected initially but conditions will fall to MVFR and Fuel Alt overnight at most terminals like what has already happened at AVP and BGM. SYR will potentially hang onto VFR until after 12z. PoP up showers will be possible overnight with low confidence that any particular location will be impacted. The main concern will be Monday afternoon when a strong cold front will move through with rain and thunderstorms. Some of the thunderstorms may become strong to severe. Prob30 groups were added for the best estimated timing of the line of thunderstorms. There is some uncertainty on timing, so modifications are likely with future updates. With the front, IFR restrictions will be possible.

Southerly winds will remain gusty throughout the overnight and morning hours with peak gusts of 25 to 35 kts. Following the front, winds will become more west to northwesterly but are expected to remain gusty. Winds will have potential to be stronger than forecasted when the main line of showers and storms moves through.

A strong low-level jet will lead to low-level wind shear (LLWS) at all terminals. For most terminals, LLWS is expected until 18 to 21z. After that, any LLWS will likely be convectively driven so it was left out of the TAFs as guidance keeps it in slightly longer. The LLWS will be delayed at RME and will end earlier there as well at SYR.

Outlook:

Monday Night through Tuesday Night...Rain changing to snow with restrictions possible. Widespread snow showers become more localized as lake effect snow over SYR and RME late on Tuesday. With winds staying gusty, blowing snow will also be possible.

Wednesday...Mainly VFR.

Thursday...Mainly VFR; a low chance for spotty rain/snow showers.

Friday...A chance for additional showers.

BGM WATCHES/WARNINGS/ADVISORIES

PA...Wind Advisory until 8 AM EDT Monday for PAZ038-043. NY...Wind Advisory until 8 AM EDT Monday for NYZ015>018-022>025-036- 044-055.