textproduct: Burlington

WHAT HAS CHANGED

As of 306 AM EDT Sunday...

No major changes with this forecast update as we continue to anticipate a gradual pattern change from drier and warmer to increasing chances of showers and thunderstorms each day through the midweek.

KEY MESSAGES

As of 306 AM EDT Sunday...

1. Showers and thunderstorms will return to the region this week as a series of shortwaves cross the Northeast, likely resulting in isolated to scattered heavier downpours.

2. Eventually drier air with warming temperatures arrive for late week into early next weekend.

DISCUSSION

As of 306 AM EDT Sunday...

KEY MESSAGE 1: High pressure is currently over Nova Scotia early this morning, resulting in broken cloud cover flowing into northern New York and Vermont from the west with light and variable winds at the surface. Temperatures are expected to continue their gradual fall towards the 50s to mid 60s this morning, featuring some isolated valley fog. A shortwave trough will reach northern New York from the west this afternoon, though the pre-existing drier air mass in place and high pressure locked in to our east will keep any resulting precipitation limited to a few showers or thunderstorms. As temperatures increase into the upper 70s to mid 80s this afternoon, models are indicating some modest instability (surface CAPE 500-1000 J/kg) and precipitable water values approaching 1.25-1.50 inches. This could result in a few of the showers or storms offering briefly heavy downpours in isolated spots, but we've been dry for days so this is not expected to immediately cause issues. Then, another mainly dry night tonight with lows in the mid 50s to mid 60s is looking likely, a low temperature range that is expected to persist each night into the midweek.

On Monday, the shortwave will shift eastward. Temperatures will be able to rise into upper 70s and 80s, increasing surface instability (around 1000 J/kg) and producing more widespread showers and thunderstorms than Sunday with 50-80% chance of precip in northern New York and 5-50% chance of precip across Vermont, highest in the afternoon. While we'll lack an upper level feature, precipitable water values may approach 1.40-1.60 inches and localized heavier downpours could occur. Shower activity should dwindle with sunset, though about 20-40% chance of some lingering activity in northern New York and southern Vermont. Precipitation amounts are forecast as high as 0.25-0.50 inches Monday and Monday night across the Adirondacks, likely higher in isolated heavy downpours. Now through Monday evening, the probability of reaching a total rainfall of 1 inch or more is around 25-40% at some of the higher peaks of the Adirondacks. We'll want to watch any place that gets consecutive days of heavy downpours, particularly across northern New York, but the threat is highly conditional. The Weather Prediction Center has northern New York outside of the Champlain Valley under Marginal (at least 5%, a 1 out of 4 scale) Risk of rainfall exceeding flash flood guidance. As of this morning, river forecasts show some slight rises, but nothing near bankfull or Action Stage.

Then on Tuesday, we'll see another trough move through the region, though deterministic global models continue to disagree on the strength and extent of this feature. The GFS keeps the upper wave mostly open, progressive, and aloft, occasionally closing off a weaker upper low across southern New York and eventually developing a coastal surface low off the mid-Atlantic by late Tuesday night. The ICON model is in fair agreement with the GFS. The ECMWF continues to push for a strong, closed, vertically stacked low pressure system drifting through the Northeast Tuesday and Tuesday night. Meanwhile, the Canadian model also favors the GFS's open wave on Tuesday, then starts to close and deepen the low pressure like the ECMWF does late Tuesday night. Whichever direction we go, showers and thunderstorms are looking increasingly likely on Tuesday (55-95% chance precip) and Tuesday night (50-80% chance precip). Some model solutions are projecting surface CAPE values around 1000- 1500 J/kg. Precipitable water values peak near 1.75 inches on Tuesday, so again localized downpours will be possible in surface convergence and upper level divergence. If the stronger closed upper low solution verifies, we may see more widespread heavy downpours. Overall Tuesday-Tuesday night precipitation expectations are 0.25- 1.00" across northern New York (highest amounts in St. Lawrence County) and 0.05-0.65" across Vermont (highest amounts in southern and south-central Vermont). Any areas that saw heavier downpours on Sunday or Monday will need to be watched. By Tuesday, the WPC has the Marginal (at least 5%) Risk of excessive rainfall over the entire forecast area. Because of all these additional showers, thunderstorms, and general moisture/clouds around, highs Tuesday will come back down just a couple degrees, in the upper 70s to mid 80s.

On Wednesday, our main question becomes: how long does the upper trough linger across our area? Regardless of the clear model differences, most solutions have precipitation lingering through the day Wednesday, 55-90% chance of showers and thunderstorms, with highest confidence in southern portions of our area, closest to forcing. Precipitation likely won't be as convective as previous days, though pwats nearing 1.20-1.75 inches are possible. After several days of showers and thunderstorms, additional rain likely won't be quite as welcome. Chance of 24 hour totals at or above 1 inch Tuesday night and Wednesday alone are 20-55%, highest across southern Vermont. Wednesday is another period that the WPC has our entire area under Marginal Risk of excessive rainfall. Precipitation should limit temperatures on Wednesday, reaching widespread 70s.

KEY MESSAGE 2: A highly amplified pattern continues for the CONUS mid to late week with anomalously strong ridge acrs the Rockies and prevailing mid/upper lvl trof over the Great Lakes into the NE CONUS. As initial deep/closed 7-5H cyclonic circulation slowly moves offshore by Friday, a narrow mid/upper lvl ridge axis is progged to impact our cwa for late week into the upcoming weekend. The combination of cyclonic flow, lingering deep layer moisture in the 1000 to 500mb layer, along with pw values in the 1.0" to 1.25" on Thursday wl keep us unsettled with additional showers likely. The probability of thunder is <25%, given the moist adiabatic sounding profiles and limited instability on Thurs. Highest pops wl be acrs the favorable east-northeast upslope areas of central/northern VT and northern Dacks with less acrs the downslope shadow regions. Progged 925mb temps btwn 16-18C support highs lower 70s to near 80F most locations on Thurs. Eventually mid/upper lvl ridge builds into our cwa on Friday with some clearing skies and warmer temps. Progged 925mb temps warm several degrees to 20-22C, supporting highs well into the 80s. The flow remains relatively progressive, given the highly amplified pattern with next deep full latitude trof approaching our cwa late Sat into Sunday with additional threat for more showers/storms. Plenty of time to sort out the details, for now have increasing pops and slightly cooler temps for next Sunday.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Through 12Z Monday...First light on the GOES-19 vis imagery shows mid/upper lvl clouds advecting from south to north across our taf sites as VFR conditions prevail. This will be the theme today across our sites with intervals of mid/upper level clouds. There is a 30% probability of a scattered shower impacting MSS/SLK between 18-22z this afternoon, but conditions should remain VFR. The combination of multiple days removed from rainfall and additional clouds and some bl mixing should limit fog development again overnight. VFR will prevail at all sites for the next 12 to 24 hours with developing south-southwest winds 4 to 8 knots.

Outlook...

Monday: VFR. Slight chance SHRA, Slight chance TSRA. Monday Night: VFR. Slight chance SHRA, Slight chance TSRA. Tuesday: VFR. Likely SHRA, Chance TSRA. Tuesday Night: Mainly MVFR, with areas VFR possible. Likely SHRA, Slight chance TSRA. Wednesday: Mainly MVFR, with areas VFR possible. Definite SHRA, Chance TSRA. Wednesday Night: Mainly MVFR, with areas IFR possible. Chance SHRA, Slight chance TSRA. Thursday: MVFR/IFR conditions possible. Chance SHRA, Chance TSRA.

BTV WATCHES/WARNINGS/ADVISORIES

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