textproduct: Burlington

WHAT HAS CHANGED

As of 245 AM EDT Wednesday...

Refined timing of precipitation for today. Steady rainfall is expected to continue this morning, gradually coming to an end from west to east this afternoon. Total precipitation amounts are on track.

KEY MESSAGES

As of 245 AM EDT Wednesday...

1. Expect a wet day today with several daily record precipitation amounts forecast to be broken. Outside of some ponding in poor drainage areas, no flooding is anticipated.

2. Cooler temperatures are expected the second half of the week with some patchy frost possible.

3. An unsettled pattern anticipated for days 4 thru 7 but the probability of widespread hazardous or significant weather is low.

DISCUSSION

As of 245 AM EDT Wednesday...

KEY MESSAGE 1: Today will be a cooler and wet day with steady rain anticipated to last much of the morning into the early afternoon. A frontal boundary (oriented SW to NE around the Saint Lawrence Valley as of 2 AM) will very slowly shift eastward through the day and into this evening. A wave of low pressure developing along the boundary (located over the Ohio River Valley as of early this morning) will ride northeastward along the boundary, serving as an additional focal point for convergence over our CWA today. The duration of today's rainfall will be prolonged by nearly boundary- parallel upper-level flow, which will limit the eastward progression of the frontal boundary to a very slow pace. Rain will eventually come to an end from west to east during the early afternoon hours in northern NY, and late afternoon to early evening hours in VT.

Rainfall rates today will intensify at times to 0.1-0.2 inch/hour during the daylight hours over central portions of our CWA. This is due to deep lift (enhanced surface convergence with a coupled jet structure aloft/strong upper-level divergence) occurring within a moist airmass (precipitable water values over 1.0 inch). Storm total rainfall amounts today will range from a 0.25-0.75 inch in the Saint Lawrence Valley and southeastern Vermont, to 0.75-1.25 inch over the northern Adirondacks, Champlain Valley, and northern Vermont. These precipitation amounts would break several daily precipitation records, including at Burlington, Plattsburgh, and Saranac Lake (see Climate section for more). Rivers will rise in response to these rainfall amounts, but forecasts from the Northeast River Forecast Center keep all of our area rivers well within banks, and no river flooding is expected.

With the front forecast to bisect our forecast area today, afternoon daily high temperatures will range from the 40s for northern NY and northwestern VT to the 60s in southeastern Vermont. With respect to 24 hour daily high temperatures, these have already been reached at midnight for much of our forecast area, and temps will fall for the remainder of the day for all except southeastern Vermont.

KEY MESSAGE 2: After the passage of today's cold front, temperatures Thursday through Saturday will be cooler than seasonal norms for early May. Highs will be in the 50s to around 60 for most of the area, and lows will be in the 30s to around 40. Broad cyclonic flow aloft will keep skies at least partly cloudy overnight with some 5- 15 knot winds just off the surface. This will prevent any strong radiational cooling nights with widespread frost development, but some patchy frost is possible. The best chance for frost will be Friday morning, though frost is not forecast in any areas that have started their "growing season". As per our frost- freeze program, the only area that has started the growing season at this point is the Champlain Valley. Therefore, no headlines are anticipated at this point. However, anyone with sensitive vegetation should monitor the low temperatures forecast over the next few days.

KEY MESSAGE 3: The synoptic scale pattern acrs the conus wl feature mid/upper lvl ridge acrs the west and deep trof from the Great Lakes into the northeast conus. This general west/northwest flow aloft with embedded s/w's and lobes of enhanced mid lvl moisture wl keep fa unsettled for upcoming weekend into next week. Latest 00z trends have tracked Saturdays system slightly further south with better dynamics/moisture, but mid/upper lvl trof passage and lingering moisture wl produce some scattered showers. Probably not a washout, but not completely dry either.

The highest probability and greatest confidence for another widespread rainfall is late Sunday into Monday, as global guidance has come into better agreement. A developing full latitude trof with phasing of northern and southern stream energy wl help in the development of sfc low pres over the Ohio Valley on Sunday. This low pres is progged to deepen as it tracks toward the ne conus late Sunday into Monday. Strong southerly flow and deep moisture advection, combined with favorable ulvl jet structure wl continue to place high likely pops into the fcst for late Sunday into Monday. Upslope flow and caa wl cont pops acrs the mtns on Monday into Tuesday, before sfc high pres finally builds back into our cwa by Weds. The warmest day looks to be Sunday, as waa ahead of sfc low pres advects progged 925mb temps btwn 10-14C, supporting highs well into the 60s to lower 70s. Much cooler air develops on the backside of low pres for early next week with highs only in the upper 40s to upper 50s expected, with lows in the mid 30s to mid 40s. Winds and clouds wl limit temps from falling too much.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Through 12Z Thursday...A very challenging taf package with regards to CIGS/VIS in the next 6 to 12 hours. Crnt radar imagery shows light to moderate rain expanding across our taf sites with a wide range of flight categories from LIFR at RUT to IFR at MPV, MVFR at SLK/EFK/MSS and VFR at BTV/PBG. Sounding profiles and upstream obs indicate most taf sites trend quickly to MVFR cigs/vis by 14z with intervals of IFR possible. As winds continue from the north/northwest, except northeast at SLK/PBG, expect intervals of IFR cigs to develop, especially BTV/RUT/PBG/EFK and slightly less potential at SLK/MSS due to wind direction. However, as surface low pres passes to our east, northwest flow develops and SLK should drop to IFR cigs by early this aftn. Have utilized tempo groups to walk flight categories toward IFR conditions today, while slowly improving conditions are anticipated by late today into tonight.

Outlook...

Thursday: VFR. NO SIG WX. Thursday Night: VFR. NO SIG WX. Friday: VFR. Slight chance SHRA. Friday Night: VFR. Chance SHRA. Saturday: VFR. Chance SHRA. Saturday Night: Mainly VFR, with local IFR possible. Chance SHRA. Sunday: Mainly VFR, with local MVFR possible. Chance SHRA.

CLIMATE

Daily Precip Records Date KBTV KMPV K1V4 KMSS KPBG KSLK 05-06 0.85|1894 1.55|1989 0.39|2010 0.84|1991 0.42|1991 0.75|2017

BTV WATCHES/WARNINGS/ADVISORIES

VT...None. NY...None.