598 FXUS61 KBTV 161710 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 110 PM EDT Thu Jul 16 2020 .SYNOPSIS... Surface high pressure moving eastward into the Gulf of Maine will maintain mostly dry and warm conditions across the North Country today. Breezy south wind conditions will also develop as a frontal system makes its way eastward across the Great Lakes region. This frontal system will bring widespread rainfall tonight into Friday morning, with a few embedded thunderstorms anticipated. Rainfall amounts of a half to three-quarters of an inch are possible, likely highest along the international border. The weekend will be drier and trend much warmer with higher humidity and heat indices. Valley heat indices in the mid 90s are expected Sunday. && .NEAR TERM /THROUGH FRIDAY/... As of 1014 AM EDT Thursday...Cloud cover is being stubborn across much of Vermont this morning. High resolution guidance from this morning depicted our mixing heights increasing this morning to help scour out some of the cloud cover but instead we have strengthened our low level inversion based on latest RAP mesoanalysis. Nevertheless, satellite does show pockets of less clouds over the Adirondacks which should shift eastward through the afternoon hours. The 12Z NAM3 is being aggressive with depicting convection across the St. Lawrence Valley this afternoon but the model soundings depict any instability associated with this convection to be elevated. This should help to produce efficient rainfall but won't produce any hail or strong wind gusts as out lapse rates are beginning to trend toward moist adiabatic as we see moisture stream into the region. Overall, the forecast is in good shape and just tweaked the sky and temp forecast to reflect current trends and increased PoPs a little earlier for the St. Lawrence Valley. Previous Discussion...Ridge of high pressure along coastal New England remains our controlling weather feature today, despite variable cloudiness expected thru the day. GOES-16 10.3-3.9um product indicates widespread low stratus across s-central and ern VT, which will be slow to mix out this morning. However, with increasing southerly gradient flow, PBL eventually mixes out bringing a period of partly sunny conditions to the North Country late morning/afternoon. Already seeing abundant mid-level clouds moving ewd from the shortwave trough over the southern Great Lakes region. Channeled flow in the Champlain Valley results in south winds 12-20 mph around BTV, with gusts up to 25-30 mph. Have issued a Lake Wind Advisory for Lake Champlain with sustained winds of 15-25kt over the water. High temperatures this afternoon generally reach the upper 70s to lower 80s, and locally into the mid 80s across the St. Lawrence valley. Progressive mid-level shortwave trough brings increasing mid- level cloudiness later this afternoon across the St. Lawrence Valley and nrn Adirondacks, followed by potential for widespread showers and a few embedded thunderstorms during the evening/overnight hours. Have indicated 70-90% PoPs shifting from west to east across the forecast area, highest during the pre-dawn hours Friday. Some continued indication in NAM/GFS model soundings for a swly low-level jet of 40-45kt overnight at 4-5kft, and this allows PW values to increase to 1.7-1.9". As such, could be some brief heavy rainfall with any embedded convective elements overnight. That said, MUCAPE values remain around 500 J/kg, so severe threat remains low. All in all, mid- level trough is progressive enough that we should avoid any flooding concerns, but generally looking at 0.5-0.75" basin- averaged rainfall. Currently, appears highest rainfall will be across nrn areas, and this will bring much needed rainfall to the St. Lawrence Valley, where precipitation deficits remain large during the past 2-3 months. Lows tonight generally upper 50s to mid 60s, highest in the Champlain Valley as PBL remains well-mixed (Champlain Valley winds hold 10-20 mph much of tonight). Will see a gradual decrease in coverage of shower activity from west to east during the day Friday. That said, daytime heating may bring a renewed threat of thunderstorms, mainly central/ern VT during the early-mid afternoon hours. Should see highs on Friday from the mid-upper 70s across central/ern VT, near 80F in the Champlain Valley, and 80-85F in the St. Lawrence Valley where the best potential exists for prolonged sunshine on Friday. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/... As of 258 AM EDT Thursday...A relatively warm Friday night due to lingering low-level moisture. Clouds decreasing overnight with the North Country waking up to 60s Saturday morning. For the afternoon, it will be quiet, but bordering on hot for Saturday. Deep-layer ridging and dry mid-level air will shift across the North Country during the day. An inversion layer positioned 8000ft above sea level. So not even elevated heating off terrain should produce convection. We should still see some fair weather cumulus dot the sky. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 258 AM EDT Thursday...Westerly flow aloft becomes more southwesterly, allowing continued warming with muggier air in place. With that, we should see better instability allowing for storms along the high terrain, along with lee-side troughing that could support convection from lake breeze interactions towards New York. Temperatures should warm into the upper 80s to mid 90s as 925 hPa temps climb up to 26 C. There could be a fly in the ointment. There is a shortwave trough riding over the ridge Sunday, and some guidance is suggesting convection that develops along the feature Saturday evening might seep down into the North Country as opposed to remaining north. Will continue to lean towards NBM output for the time being. Piecemeal frontal passage takes place Sunday night into Monday. The nocturnal timing will not help us get the most out of the frontal passage, but most should see at least some precipitation. Afterwards, a longwave trough will nudge southwards over the Great Lakes region. West to northwest mid-level flow should prevent moist southerly flow from bringing oppressive heat back northwards and with thicknesses should be lower overall. 925 hPa temps remain in the upper teens Celsius. So it should still be seasonably warm (+2 to 4 F above normal), but nothing oppressive in sight for now. Anticipate a series of weak waves to ride confluent flow between the Bermuda High and the troughing centered over the Great Lakes, but there is some disagreement between global models on the finer details. && .AVIATION /17Z THURSDAY THROUGH TUESDAY/... Through 18Z Friday...A mix of MVFR and VFR ceilings prevail across the North Country this afternoon ahead of an approaching warm front. Conditions will likely deteriorate as we head into the evening and overnight hours as we begin to see moisture surge into the region with ceilings dropping to 1500 to 2500 ft by 12Z on Friday. Isolated pockets of IFR conditions will be possible, especially at KSLK during the morning hours initially behind the warm front until a cold front swings through. We are expecting convection to move into KMSS between 22Z and 00Z and spreading eastward into Vermont just prior to 12Z. We could see some embedded rumbles of thunder but we are generally looking at some decent rain makers tonight and again on Friday. Visibilities look to stay above 6SM but some stronger showers or thunderstorms could briefly drop visibilities to 3-5SM. Wind shear will also be a concern tonight into the early morning hours as a strong low level jet moves overhead. We will likely lose our gusty winds between 6Z and 14Z when we will see 40-50 knots of wind at 2000 ft. This will likely lead to some decent turbulence during the morning hours across much of northern New York and Vermont. Conditions will slowly improve throughout the day on Friday as precipitation ends from west to east and ceilings begin to slowly improve and the stronger winds aloft exit to the east. Outlook... Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SHRA. Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Monday: Mainly VFR, with areas MVFR possible. Chance SHRA. Monday Night: VFR. NO SIG WX. Tuesday: VFR. Chance SHRA. && .MARINE... South winds will increase to 15-25 knots this morning as pressure gradient increases between a departing high pressure system across the Gulf of Maine, and a frontal system across the Great Lakes. Waves will build to 2 to 4 feet by this afternoon, likely highest across the northern portion of the broad lake. May see a continuation 15-25 knot winds through much of tonight as low pressure shifts eastward into northern New York. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos/Clay SHORT TERM...Haynes LONG TERM...Haynes AVIATION...Clay MARINE...Banacos