textproduct: Burlington

WHAT HAS CHANGED

As of 215 AM EDT Sunday...

Isolated flash flood threat remains for late today into early Monday with the upcoming low pressure system due to potential for slow- moving showers and thunderstorms. Best potential for any localized flash flooding is across the northern Adirondacks and St. Lawrence Valley of New York.

KEY MESSAGES

As of 215 AM EDT Sunday...

1. Moderate to locally heavy rainfall through Monday with an isolated risk of flash flooding.

2. Seasonably warm and wet for the second half of next week and next weekend.

DISCUSSION

As of 215 AM EDT Sunday...

KEY MESSAGE 1: Interesting synoptic setup with vertically-stacked low pressure system centered across Indiana early this morning. A positive tilt mid-level trough extends newd from the closed low across sern Michigan into sern Ontario. This positive tilt trough should serve as a slow-moving focus for convergence and deformation, with ongoing showers and embedded convective activity likely to spread northeastward during the daylight hours today (Sunday). While best precipitation focus should be across the International Border into Ontario, may see some bands of moderate to locally heavy rainfall lifting across the St. Lawrence Valley later this morning into the afternoon hours. Combination of rich moisture (PW values 1.9 to 2.0) and some training thunderstorm potential with SBCAPE values 500-1000 J/kg does bring potential for widespread 1-2" rainfall with locally higher amounts across St. Lawrence and Franklin Counties today. The 00Z HREF Probability Matched Mean QPF guidance suggest a few locations could see rainfall amts exceeding 2" thru 12Z Monday. Topographically, it is relatively difficult to get flash flooding in the St. Lawrence Valley given flat terrain, and QPF values suggest only an isolated threat. Will continue to message this isolated threat via the Hazardous Weather Outlook. Narrow CAPE profiles with modest mid-level lapse rates suggest there isn't a severe threat with this activity. Have included heavy rainfall wording only into the forecast grids.

Abundant clouds across the St. Lawrence Valley and the Adirondacks will keep high temperatures generally in the 74-78F range this afternoon. Rain generally holds off across Vermont thru early evening, and partial sunshine allows temperatures to reach the lower 80s in most locations from the Champlain Valley ewd.

For tonight and Monday, wave low moving newd across the Eastern Great Lakes and across the St. Lawrence Valley will eventually allow the baroclinic zone to shift ewd as as cold front tonight into Monday. It appears the bulk of the widespread shower and embedded thunderstorm activity will be 06-18Z Monday from the Champlain Valley ewd associated with strengthening low-level frontal convergence and right entrance region of impressive 90-100kt 250mb jet for this time of the year. Have indicated 80-100% PoPs overnight into Monday morning, gradually diminishing thereafter as best dynamic support and PWATs shift east of our forecast area. Overall rainfall amounts from the Champlain Valley ewd are expected to range from 0.5" to 1", with some locally heavier amounts possible due to thunderstorms. Flash flooding is not currently expected in VT. Highs on Monday will generally range from the upper 70s to lower 80s.

KEY MESSAGE 2: A typical mid to late summer set-up is in store for the second half of the upcoming week and next weekend. A strong Bermuda high pressure system (nearly 600 dm) is forecasted to situate across the western Atlantic with an elongated but not highly amplified trough across the northern US. This will keep the longwave pattern Thursday through Sunday relatively the same with several rounds of shortwave energy aiding the longwave trough from falling apart. The North Country will be in a peculiar spot between the ridge and main upper level trough which should help bring warmth, moisture, and the occasional shortwave trough overhead. Basically, this means that we should see periods of showers and possibly a few thunderstorms daily with temperatures hovering within a few degrees of normal (generally low to mid 80s). No significant storm systems appear likely on the horizon given we have no distinguishable surface features to produce convergence/lift and modest flow aloft. High PWAT values in the 90+ percent range will allow any showers or thunderstorms that develop to be heavy rainers but they will be scattered at best and short- lived, meaning flooding isn't a concern at this time.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Through 12Z Monday...We've already begun to see a few showers move through KMSS this morning but the latest radar trends show a noticeable break for much of the morning. Widespread rainfall is on track to move into northern New York this afternoon with rain slowly pushing eastward through the evening. It will likely take until 06Z before rain moves into the Vermont terminals while northern New York should see rainfall between 18Z and 00Z. MVFR to brief IFR conditions are possible within this rain given a very moist environment and visibility reductions will likely be tied to convective elements embedded within the showers. Winds will be from the south at 10 to 20 knots ahead of the rainfall with winds diminishing below 10 knots at the onset of the rain showers. Wind shear is likely to develop as winds weaken with winds at 2000 ft around 40 knots.

Outlook...

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

CLIMATE

Possible heavy rainfall tomorrow into Monday could approach daily rainfall record levels. Below are the current daily precipitation total records that may be broken at our area climate sites.

Record Precipitation:

August 2: KMSS: 1.31/2020

BTV WATCHES/WARNINGS/ADVISORIES

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