textproduct: Burlington

WHAT HAS CHANGED

As of 530 PM EDT Wednesday...Updated pops to match current radar and lightning trends, lowered qpf for most areas, and removed heavy rainfall wording for VT, but kept in for northern NY, where instability is lingering and dwpts are near 70F. Crnt radar shows two clusters of thunderstorms splitting our cwa to the north and south, but do expect some activity to increase as better dynamics arrive toward 00z acrs northern NY.

KEY MESSAGES

As of 308 PM EDT Wednesday...

1. Gusty south winds continue today. Widespread rainfall will move in this evening and overnight, with periods of moderate to locally heavy rain expected along with some embedded thunderstorms.

2. Some scattered afternoon showers are possible each day Thursday through Saturday.

3. No significant weather Sunday through Wednesday. Moderating temperatures and dry weather expected early next week, then likely trending cooler with a low chance for showers.

DISCUSSION

As of 308 PM EDT Wednesday...

KEY MESSAGE 1: Continue to expect some active weather this evening and overnight across the north country. A low pressure system passing north of our region will bring surface fronts across our area. Rain will move in from the west during the afternoon hours as a warm front approaches. Increasing southerly flow is evident and will continue, especially over Lake Champlain where gusts over 30 kts have occurred and will continue into this evening. Lake Wind Advisory is in effect. Outside of Lake Champlain, highest gusts this afternoon will mainly be observed over the northern Champlain Valley, higher elevations of the Greens and Adirondacks, and over the northern slopes of the Adirondacks. Gusts will be strongest ahead of the steady rain, then will diminish as rain becomes widespread due to low-level stabilization. The increased southerly flow has bumped PWATS up to 1.5 to 2.0 inches, which is around 150 to 200% of climatological normal for our area this time of year. This anomalously moist air mass will support some periods of moderate to heavy rain this evening into tonight. Models are indicating rates will mainly remain under a tenth of an inch an hour, but some heavier showers and thunderstorms could produce brief rainfall rates up to a quarter to a half inch an hour. Overall, the flood risk this evening into tonight is low (WPC's Excessive Rainfall Outlook has our entire area in a marginal risk of rainfall exceeding flash flood guidance). However, if any heavier storms track over the same area, those areas will need to be watched closely. In addition to moderate to briefly heavy rainfall, some thunderstorms are anticipated this evening into early tonight. The surface based instability and overall severe threat will be limited by a maintained low level inversion over most areas. However, the environment is slightly more favorable over the southern Saint Lawrence Valley, where the development of some marginal SBCAPE is progged. The amount of surface based instability is still somewhat in question, but latest SPC Convective Outlook maintains the Marginal Risk for most of Saint Lawrence County, with the Slight Risk just clipping our area and extending to the southwest. The main threat from thunderstorms in northern New York will be gusty winds and locally heavy rainfall. The remainder of our forecast area remains within the General Thunder contour, and risk of severe weather outside of the Saint Lawrence Valley is low tonight. There are some indications from higher resolution models that coverage of showers could be lower than anticipated with our region becoming split between an area of showers passing to our north while another passes to our south where the better instability exists.

KEY MESSAGE 2: An upper level low in the area will keep chances for showers each afternoon continuing from Thursday through Saturday. Temperatures will be a bit cooler than seasonal normals with periods of instability-driven afternoon showers. Coverage of showers will be greatest over higher terrain. Meanwhile, the Champlain Valley and Saint Lawrence Valley will remain mainly dry during this timeframe.

KEY MESSAGE 3: As the big upper level low continues to depart slowly to the east Sunday in an Omega block pattern, the storm track behind it is favored to remain to our north with the upper level ridge suppressed to our south. As a result, we will be in a fairly dry northwest flow pattern through the middle of next week. There is very good clustering of temperatures and lack of precipitation on Sunday and Monday. Temperatures should warm from slightly below normal to near normal.

Much larger spread in temperatures and dew points is noted after that time, associated with the possibility of a surface cold front passing through from the north on Tuesday, which could bring substantially cooler and drier air into the region along with some lighter variety showers. A similar degree of uncertainty exists Wednesday but with temperatures shifted a bit warmer with more guidance showing a return to southerly low level flow. No huge swings in temperature are expected in this pattern, but fluctuations are possible.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...Scattered to overcast clouds with bases in the 2500 to 4000 feet range are generally expected over the next six hours. Aside from a shower in the vicinity of MSS at issuance time, no precipitation is expected until about 22-00Z. Showers will increase in coverage from the west towards 00Z and especially 02-06Z. These showers will be moderate to heavy at times, which will result in intervals of IFR visibility. While unlikely, some embedded thunderstorms are possible especially in the vicinity of MSS. Ceilings will tend to lower to low MVFR/IFR levels after 06Z as moisture is trapped below a strengthening low level inversion following the exit of these showers, but a shift in winds towards the west during the 12Z to 18Z period will help improve conditions.

Winds currently are 10 to 15 knots with gusts 20 to 25 knots out of the south or southeast at most terminals, except under 10 knots at MSS. Some LLWS is likely when surface winds weaken as the aforementioned jet strengthens, primarily outside of the Champlain Valley and from 03Z to 08Z.

Outlook...

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

MARINE

As of 219 PM EDT Wednesday...South winds 20 to 35 knots continue into this evening. Waves will build to 2 to 4+ feet by late tonight. Winds will be strongest this evening into the early overnight hours, then will decrease once steady rain develops. Winds on Thursday will be 15 to 20 knots in the morning, then become light and variable later in the day.

BTV WATCHES/WARNINGS/ADVISORIES

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