textproduct: Burlington

WHAT HAS CHANGED

As of 245 PM EDT Tuesday...

Frost Advisories have been issued for the St. Lawrence Valley and eastern Clinton County in New York, as well as for Franklin, Lamoille, Chittenden, Washington, Orange, eastern Rutland, eastern Addison, and western Windsor Counties in Vermont from 2 AM to 9 AM Wednesday.

KEY MESSAGES

As of 245 PM EDT Tuesday...

1. Seasonably cool and dry weather will continue through late week, with patchy frost tonight, and likely Wednesday night.

2. Still a large spread in potential outcomes associated with coastal system and if any rain/wind impacts our forecast area this weekend.

DISCUSSION

As of 245 PM EDT Tuesday...

KEY MESSAGE 1: High pressure is settling in across the region with clearing skies. The center of the high is actually to our north in southern Quebec, but we will still enjoy the clear and calm weather that is associated with it. Fair weather terrain cumulus will dissipate this evening with a few high clouds remaining across southern Vermont associated with a stationary boundary well south of the region in the Mid-Atlantic. Patchy fog and frost are expected tonight as clearing skies set up for good radiational cooling. Temperatures will dip below 40 degrees for majority of the area, outside of the wider valleys of southern Vermont. Widespread near freezing temperatures will be possible across the Northeast Kingdom, central Vermont, and the Adirondacks. Pocket mid to upper 20s will be likely in isolated portions of the northern Adirondacks. Frost Advisories have been issued for the St. Lawrence Valley and eastern Clinton County in New York, as well as for Franklin, Lamoille, Chittenden, Washington, Orange, eastern Rutland, eastern Addison, and western Windsor Counties in Vermont from 2 AM to 9 AM Wednesday. Frost will be less likely in areas near Lake Champlain, due to the surrounding warmer water temperatures helping to moderate the surrounding air. It should be noted that, as of 9/21, these products will no longer be issued for the Adirondacks and Northeast Kingdom, as median date of the first autumn freeze has passed. Thus, the growing season is considered ended in these areas.

Through the mid to late week, temperatures will slowly creep up a degree or two each day towards Thursday, with highs in the mid to upper 60s, as the high drifts to the east. Portions of the eastern Greens may see below normal temperatures continue Wednesday with a cold air damming setup. Frost potential will continue Wednesday night, though radiational cooling will be a touch weaker resulting in less areal coverage of any potential Frost Advisories. Fog chances will also see less coverage Wednesday night, though patchy fog in the climatologically favored valleys of eastern Vermont and the Adirondacks will still be possible. Clouds begin to build Thursday into Friday as a nor'easter off the southern New England Coast meanders. There is still a large degree of uncertainty with regards to the evolution of the system, as it pertains to cloud cover and precipitation chances. Currently it looks like Friday should remain dry for now with PoPs below 30%. Regardless, a tightening pressure gradient will develop across our area resulting in some breezy to channeled winds potentially Friday afternoon.

KEY MESSAGE 2: The long term forecast challenge is evolution and movement of deeply closed off sfc to 250mb cyclonic circulation and potential impacts to our cwa. Latest guidance continues to indicate a large spread in potential solutions between individual deterministic models and associated ensemble members, especially with regards to sfc low pres track and placement of precip. The 12z trends in guidance shows embedded short wave being captured in the cyclonic circulation, which helps to retro-grade sfc low pres westward toward the Mid-Atlantic/SNE coast by Sunday. The 12z ECMWF/ICON are most aggressive with advecting deep layer moisture back into parts of our cwa, while GFS/CMC shows better potential over central/eastern VT. The challenge will be a very sharp nw-se moisture gradient btwn coastal system and strong/dry high pres anchored over southern Canada. Could see band of moisture rotate around cyclonic circulation toward VT on Sat/Sunday and fall apart when they encounter deeper dry layer over our region. Latest WPC pop grids have cutback on precip chcs by 15% to 30%, which seems a little unreasonable given current trends. Feel these should be increases based on latest data, with highest probability of measurable precip acrs central/eastern and southern VT on Sat into Sun.

Did note as the gradient increases between coastal low pres and sfc high pres, progged 925mb to 850mb winds increase at 30 to 45 knots, which wl support a few gusts in the 20 to 35 mph range, especially higher trrn and aligned north to south valleys. Temps mostly in the 60s on Saturday/Sunday, and warm into the upper 60s to lower 70s by early next week. Lows in the mid 30s to mid/upper 40s, but could be warmer with more clouds/precip this upcoming weekend.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Through 00Z Thursday...VFR conditions will generally persist for the next 24 hours, except for some patchy fog formation tonight in the climatologically favored areas. Conditions at all terminals will remain VFR through the evening. The fog will begin to form after midnight and it should reach MPV and SLK by around 7-8Z. It is possible at EFK later in the night, where a few intervals of IFR could occur. Fog will form over the Winooski River right next to the runway at BTV, but whether it will drift onto the runway for a few brief periods of time remains uncertain (maybe a 25 percent chance of an instance of IFR). Any fog lifts by around 13Z and VFR conditions will persist for the rest of the day. Winds will generally go light/variable and calm tonight, before increasing into the 5-15 KT range out of the north/northeast tomorrow.

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. Slight chance SHRA. Saturday Night: VFR. Slight chance SHRA. Sunday: VFR. Slight chance SHRA.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Frost Advisory from 2 AM to 9 AM EDT Wednesday for VTZ002-005- 006-008-010-016>020. NY...Frost Advisory from 2 AM to 9 AM EDT Wednesday for NYZ026>028- 087.