textproduct: Burlington

WHAT HAS CHANGED

As of 215 AM EDT Saturday...

Increasing chances for 1" or greater rainfall in northern Vermont Sunday night into Monday morning.

KEY MESSAGES

As of 215 AM EDT Saturday...

1. Much of the weekend will be dry, then rain Sunday evening through the overnight hours is expected.

2. Scattered showers on Monday will give way to another drier period Monday night into Tuesday.

3. Near seasonable temperatures with a chance of showers mid to late next week.

DISCUSSION

As of 215 AM EDT Saturday...

KEY MESSAGE 1: Surface high pressure is building into the region today, which will maintain a slightly cooler than normal air mass with abundant dry air aloft. The low humidity pattern will flip beginning Sunday afternoon, and especially evening, as this high exits to our east and increasing moisture transport from the southwest occurs ahead of an occluding area of low pressure moving into the eastern Great Lakes.

It continues to appear that weakly unstable air aloft will support moderate rainfall rates (as high as an inch/hour), and a few rumbles of thunder at times. The heavier showers should tend to be at the nose of a strengthening nocturnal low level jet (850 millibar winds increasing to around 30 knots or so). The placement of the heavier rain is rather uncertain at this time and will tend to be wherever a north-south moisture gradient sets up overnight. The latest guidance shows a broad consensus in portions of northern/northeastern Vermont, but given large spread in recent forecast cycles of where heavier footprints of rain will fall we have maintained a blend showing roughly 0.5" of rain in much of our region. The event total 75th percentile looks like reasonable higher end rainfall amounts, showing potential for swaths of rainfall in the 1-1.5" range in Vermont with less potential in the Adirondacks and points west. If heavier rain occurs farther south, the southwesterly low level flow will support locally heavier totals in the vicinity of the Green Mountain National Forest. Antecedent dry conditions and lack of a stationary boundary or setup for training showers are limiting factors for flash flood risk, such that a marginal (level 1) excessive rainfall outlook looks reasonable for our region. The steady rain will exit to our east towards Monday morning with the departure of isentropic lift and a broad area of surface low pressure into the region.

KEY MESSAGE 2: A deeper area of low pressure over northern Quebec will be dragging a weak cold front through the area during the day on Monday. In the wake of the early morning rain, there will be plenty of shallow moisture/elevated dew points such to support scattered to numerous showers during the day ahead of this front. Any modest heating will increase instability, although shallow cloud tops are expected due to a wedge of warm, dry air aloft and limit downpour intensity with low chances for thunder. As drier air continues to filter through on deepening west-northwesterly flow, rain chances will become orographically forced with otherwise increasing sunshine through the later part of the day.

KEY MESSAGE 3: Pretty much remain in a broad cyclonic flow that is dominating the Great Lakes-NY-New England. Heat ridge remains mainly across southern-southwest tier of CONUS. Our CWA is far enough from the periphery of the ridge that we stay largely influenced by the northern stream flow with seasonable temperatures and a chance of showers now and then. The best chance for showers will be late Wed- Thu with a northern stream system.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Through 06Z Sunday...Calm and variable winds will continue as high pressure nudges in from the northwest. Outside of any variable winds, northerly flow aloft will prevail through the TAF period. Clouds are clearing after sunset with some patchy fog possible in the climatologically favored terminals. Winds likely will decouple at most sites and have trended favored sites towards prevailing fog tonight at SLK/MPV with intermittent IFR fog potentially at EFK/RUT and vcnty of KBTV.

Fog will lift between 12-13Z where it develops. Winds will become prevailing from the north-northwest after sunrise tomorrow with mostly clear skies.

Outlook...

Sunday: VFR. Slight chance SHRA. Sunday Night: Mainly MVFR, with areas IFR possible. Definite SHRA, Slight chance TSRA. Monday: Mainly MVFR, with areas IFR possible. Likely SHRA, Slight chance TSRA. Monday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Tuesday: Mainly VFR, with local MVFR possible. NO SIG WX. Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. Chance SHRA.

BTV WATCHES/WARNINGS/ADVISORIES

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