Sunrise 5:43 AM   Sunset 7:56 PM Moonrise 1:19 AM   Moonset 9:25 AM

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FXUS61 KBTV 291739 AFDBTV

Area Forecast Discussion National Weather Service Burlington VT 139 PM EDT Mon Apr 29 2024

SYNOPSIS
Outside some rain in New York and light sprinkles elsewhere, today is expected to be mostly dry. Our next system will impact the region late Monday night into Tuesday with showers likely, followed by another batch of afternoon showers and perhaps a rumble of thunder. Temperatures will hold in the 40s to lower 50s tonight and warm into the 50s north to near 70 degrees south through Tuesday. Quieter weather is expected for the latter half of the week, with a warming trend across the region.

NEAR TERM /THROUGH TUESDAY/
As of 123 PM EDT Monday...Showers across the region have begun dissipating this afternoon. Satellite imagery shows mostly cloudy skies, although there are a few pockets of clearing and higher clouds that may allow for a little bit of sunshine to filter through. Main adjustment with this update was to lower temperatures a few degrees since things have been slower to warm than initially forecast. Otherwise, the forecast remains on track.

Previous Discussion...Today, the region will warm towards seasonal norms in the upper 50s to mid 60s, except in the lower Connecticut River Valley, which could climb up the 70s. Mainly north flow will remain today, with some diversions around terrain features. We'll be at the eastern periphery of a warm conveyor belt, and so moisture will arc over the strong ridge to our south. The exact placement is in question, but there's also a very narrow tongue of dry air at 850hPa. The air is very dry at lower than -30 C dewpoints, but the layer is so thin that it's reasonable to assume some rain will make it past over northern New York at least. Amounts a few hundredths at most.

On Monday night into early Tuesday morning, a strong warm front will slide northeastwards. A strong surface high in far northern Quebec Province will try to maintain dry air across northern Vermont as deep, tropical moisture overruns the relatively dense, stable air mass. Strong upper divergence along the frontal feature will result in an FGEN band at the boundary of dry, seasonable air and humid, late Spring-type air. A weak surface low will develop while an upper trough acts to break the strong upper ridge that's remained in place resulting in good surface convergence alongside the FGEN band. Ingredients appear to come together to produce a narrow strip of moderate to heavy rain with the warm front just south of the international border.

Then we monitor how far north new low pressure gets across the Mid- Atlantic and what it means for our instability. The air behind the warm front is very warm, and could create a gradient of about 50 north to about 70 south. If warm air advects far enough north, we will weakly destabilize across the region as PWATs climb higher to about 200 percent of normal. High resolution guidance depicts at least 2 rounds of precipitation, likely as a result of wind profiles that would support backbuilding convection. However, an important caveat, is that if we can't get the convection, then we don't get the backbuilding. The NAM12 forecasts southeast flow that would keep conditions more stable as well and limit convection. Given how weak the surface low is expected to be at 1010mb or higher, tracking where exactly that will be is going to be tough. For now, the forecast leans heavily on high resolution ensemble data.
Precipitation will likely continue into the overnight hours. For additional details on hydro, please see the discussion below.

SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/
As of 338 AM EDT Monday...Widespread rain and thunderstorms during the day will decrease in coverage overnight Tuesday, tapering off into showers by Wednesday morning. Weak high pressure builds in from the Great Lakes, resulting in a rather pleasant day with quiet weather, light winds and partial sunshine on Wednesday. Daytime highs would likely be cooler across the northern Adirondacks and east of the Green Mountains, reaching only the mid 50s to near 60.
On the other hand, southern locales in the CWA should reach into the 60s. For perspective, the average high temperatures for the first day of May across North Country are in the low to mid 60s.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
As of 338 AM EDT Monday...Overall, the second half of the work week features a gradual warming trend with mostly quiet conditions.
Models depict a weak shortwave trough sliding southeastward across Vermont on Thursday, so there could be some showers and cooler temperatures east of the Greens. But overall, the weather pattern looks quite quiet across North Country as we begin the month of May.
This coming weekend does look potentially unsettled, but there remains considerable spread in the global guidance. The overall upper level pattern favors the development of an omega block somewhere east of the Mississippi River, book ended by a meandering closed low centered near Manitoba/Ontario and a anomalously deep trough that is slow to exit the Canadian Maritimes. At this time, there is just about equal odds of a toasty weekend, especially for our western zones and an unsettled period with widespread rain and thunderstorms. So there is low forecast confidence in how the weekend will transpire at this time so stuck very close to blended guidance. Additionally, given the lack of confidence in any significant storms, let's spend some time to discuss the potential for heat risk heading into the first weekend of May.

The experimental NWS heat risk website does indicate the potential for minor heat risk for individuals particularly sensitive to heat across the St Lawrence Valley on Friday on Saturday. The URL is https:/ www.wpc.ncep.noaa.gov/heatrisk. Global ensemble guidance indicates the potential for anomalous H5 ridging, with 850mb temperatures potentially as much as 10C above climatological normal across portions of far western NY. This would put our far western zones, i.e. St Lawrence county in the closest proximity to this anomalous ridge. At this time, the potential of apparent temperatures or heat indices reaching the mid 80s remain low but non zero. The in-house Dynamic Ensemble-based Scenario for IDSS (DESI)
tool that aggregates deterministic and ensemble guidance currently gives a 3 percent chance for heat index values to reach or exceed 85 degrees for Massena on Friday and Saturday, which puts the NWS heat risk tool output into context. A word of caution against jumping onto the early season heat bandwagon is the potential for much cooler maritime influence from the New England coast, as a anomalously 850mb cool regime associated with a closed off low across the Canadian Maritimes could pivot further westward and shunt the heat risk concerns west of our CWA Nonetheless, those with outdoor plans for the first weekend of May should keep abreast of the latest forecast. After all, summer is knocking on our doorsteps.
Forecast wise, have stuck rather close to blended guidance given the amount of uncertainty at this time frame. But we will monitor the trends through the week if any upward adjustments to the temperatures need to be made and message it on various platforms given the overall lack of acclimatization to early summer heat at this point in the shoulder season.

AVIATION /18Z MONDAY THROUGH SATURDAY/
Through 18Z Tuesday...Primarily VFR conditions across the region this afternoon, with the exception of KSLK and KRUT with ceilings at or below 1000 ft. Precipitation this afternoon has ended, with a brief dry period before the next round approaches.
Approaching 06z Tuesday, precipitation will spread over the region from southwest to northeast. Rainfall rates may be moderate in some of the heavier showers, with reduced visibilities possible. MVFR ceilings will be possible after this precipitation, especially across northern New York terminals. Winds this afternoon into the evening will become variable and terrain driven, generally less than 10 knots.

Outlook...

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

HYDROLOGY
There is a marginal risk for excessive rainfall for Tuesday into Wednesday over the Adirondacks and much of Vermont. The northern half of our forecast area received a respectable amount of rain Sunday, with widespread 0.50" to 1.00" across the northern Champlain Valley and the northern half of Vermont. The southern half and St. Lawrence Valley mainly saw variable readings between a few hundredths and 0.25".

Beginning overnight Monday into Tuesday night, multiple rounds of precipitation will be possible. A warm front will lift north during the predawn hours Tuesday. Along the front, moderate to locally heavy rain is possible, producing 0.2 to 0.5 inch of rain. After some clearing, afternoon showers and a few thunderstorms are likely to develop. Multiple rounds of moderate to heavy showers could produce an additional third to two thirds of an inch. Locally higher rainfall amounts will be possible. With some trees still dormant and lingering summit level snow, there could be some areal flooding on low lying farm fields, poor urban drainage basins, and across ditches. Dry conditions over the last couple weeks has allowed river levels to fall. At this time, it does not appear that there will be enough precipitation and snowmelt for river flooding, but we will closely monitor.

BTV WATCHES/WARNINGS/ADVISORIES
VT...None.
NY...None.

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