textproduct: Burlington

WHAT HAS CHANGED

As of 1045 AM EDT Tuesday...

Light showers are starting to develop. No lightning has been observed at this time. A few rounds of thunderstorms will be possible, with a stronger storm or two capable of gusty winds.

KEY MESSAGES

As of 238 PM EDT Tuesday...

1. Warm and humid weather will promote a few strong storms before a cold front drives cool weather back south.

2. A period of cool weather is expected the remainder of the week.

3. A pair of weak systems will drive rain chances late Saturday night into early next week.

DISCUSSION

As of 238 PM EDT Tuesday...

KEY MESSAGE 1: The latest thinking from the Storm Prediction Center is to reduce the likelihood of severe weather in the forecast. A marginal risk outlook (Level 1 of 5), is now forecast for today. A few strong storms may develop as a result of strong heating into the 80s with dewpoints in the lower 60s. CAPE of about 1000-1500 J/kg will be possible, and there is also modest wind flow with 40 knots of 0-6km bulk shear. Lapse rates are marginal, and there is not much of a lifting mechanism in place today. Coverage of showers and thunderstorms will be greatest in southern and eastern Vermont, with relatively little outside these regions during the afternoon. The main threat from any thunderstorm will be sending stronger winds aloft to the surface.

Thunderstorm potential won't end with the sunset this evening. We're in the season of piece meal frontal boundaries now. The first piece arrives after sunset. Although surface instability will decrease, the radiation of heat and mid-level warming should produce a sharp inversion. Mid-level instability will increase along and ahead of the front that will also coincide with a subtle upper jet and vorticity max. Precipitation will expand northeast across the Adirondacks. However, it will struggle as terrain shadowing and dry air entrainment break up activity heading into Vermont.

However, the front will not yet be through the region until Wednesday. So another warm, humid night it expected with upper 50s to upper 60s tonight. A theta E boundary will cross mid-morning, and cold produce some tiny, spot showers, and then the wind shift finally crosses in the afternoon, which could also produce a localized shower. Southern Vermont will still be in the 80s, but most of the region will be in the 70s behind the theta E boundary. If any activity can overcome strong mid-level drying in southern Vermont, then a shower or two could briefly produce a few flashes of lightning, but this isn't expressly noted in the current forecast.

One last thing to note for Wednesday will be the breezy northwesterly flow behind the system as the dry air filters in. With afternoon mixing, it'll bring in 20-25 mph gusts and RHs sinking to 30-40%. This may be most relevant in south-central Vermont, which hasn't seen quite as much rain over the last 3-4 days.

KEY MESSAGE 2: A rather strong batch of cold air will come in from the north, and it will linger for awhile as the 1030mb surface high is slow to move. Looks like we may be talking frost headlines based on present low temperatures as the Adirondacks and Northeast Kingdom enter the temperature-defined growing season. Min temperatures for Wednesday night and Thursday night feature low to mid 30s for these regions, and low to mid 40s for the rest of the area. Part of the reason why we'll observe such cool weather at night will come from the very dry air mass overhead. Even with afternoon temperatures in the 60s, minimum relative humidity values appear likely to drop significantly during the day. Thursday's cooler temperatures will likely keep values closer to 25-35%, but Friday looks especially dry around 20-30%. There'll be steady winds Thursday, and light and variable winds on Friday.

Even as high pressure begins to depart, it lifts towards the Gulf of St. Lawrence rather than simply going off into the Atlantic. So colder north flow will trend to cool, maritime east-southeast flow. Conditions will be dry underneath this strong high. It'll be supremely pleasant weather through Saturday afternoon.

KEY MESSAGE 3: A weak, 1013mb low pressure will track towards the Great Lakes region, and it will struggle mightily against the now 1035mb surface high in the Canadian Maritimes. Guidance is consistent on a warm front lifting northeast in association with the surface low but also decelerating and decaying. A sharp gradient in rainfall amounts is expected with steady rain setting up near or south of our forecast area and dry the farther northeast you get. Some guidance has the warm front and associated precipitation collapsing before it even reaches the Northeast Kingdom of Vermont. The latest 12z GFS doesn't even allow the warm front to make it to our region of responsibility.

Another area of low pressure will move towards James Bay, and it will come with a well-defined upper trough that will begin to acquire a negative tilt on. Yet another weak surface low will start developing near Long Island. This will set the stage for strong confluence while a moisture feed out of the Gulf and Atlantic are positioned nearby. The doubling up of these features appears to last for a very short time, and given that it's relatively small, any disconnect would disrupt precipitation efficiency. Regardless, this feature will be progressive. A few showers cold linger into next Tuesday as the backside of the upper trough makes it in during the morning.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18Z Wednesday...Conditions are mainly VFR for the next several hours. Spotty showers and thunderstorms will be possibly, mainly at KRUT from 19z-21z, and then a separate batch is possible at KMSS, KSLK, and KPBG from about 03z-07z. Any shower or storm could briefly reduce visibility to 2-4SM for 10-30 minutes. Ceilings will mostly remain at or above 5000 ft agl with scattered cumulus. More appreciable drops in ceilings will be possible after 06z with ceilings trending towards 1500-4500 ft agl. Winds throughout the period will be southwesterly at 7-15 knots with intermittent gusts of 20-25 knots possible, mainly at KMSS. 2000 ft agl winds increase between about 04z and 12z, with west winds at 35-45 knots, and LLWS will be possible for almost every terminal. Flight conditions will generally improve after 12z Wednesday, but there could be some bouncing or pauses between several weak boundaries sliding southeast into Wednesday along with a shift to west or west-northwest winds.

Outlook...

Wednesday Night: VFR. NO SIG WX. Thursday: VFR. NO SIG WX. Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX. Friday Night: VFR. Slight chance SHRA. Saturday: VFR. Chance SHRA. Saturday Night: VFR. Chance SHRA. Sunday: VFR. Chance SHRA.

MARINE

As of 238 PM EDT Tuesday...

A Lake Wind Advisory remains in effect for the Broad Waters of Lake Champlain. Sustained winds have been lacking much of the day, but have increased over the last couple hours. A few gusts have hovered just under the 25 knot criteria as well. Given the proximity to that threshold and cold water, the Lake Wind Advisory will remain up. Some stronger wind gusts will be possible on Lake Champlain around midnight following a boundary, and then again once winds shift from south or southwest to north later on Wednesday. Waves will likely range about 1-3 feet.

BTV WATCHES/WARNINGS/ADVISORIES

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