Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 222350 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 750 PM EDT Thu Jun 22 2017 .SYNOPSIS... Showers and thunderstorms return to the region tonight and tomorrow. Locally heavy rainfall is possible with stronger showers and storms during the day Friday. A brief return to dry weather is expected on Saturday before more showers return for the early portions of next week. && .NEAR TERM /THROUGH FRIDAY NIGHT/... As of 719 PM EDT Thursday...Main change to the forecast for this evening`s update was to hold back precip chances a few hours based on latest radar and hi-res model trends. Still looking like around midnight for arrival time in the St. Lawrence Valley, but not until closer to 3-4AM for the Champlain Valley and points eastward. Ahead of that, quiet conditions will prevail with increasing mid clouds and light winds leading to low temps mainly in the 60s. Previous Discussion...Retreating warm front brings shower and thunderstorm activity back to the region this evening and overnight. Carrying pretty high pops later this evening and the remainder of the overnight. Strong warm advection bringing moisture rich air back into the region very quickly. PW values rapidly increase back into the 1.75-2.00" range with deep warm cloud depths suggests heavy rainfall a possibility. Overall progressive nature of the system with a big convective component in the afternoon hours suggests areal risk of flash flooding remains low in any given location so no watches at the moment. Isolated flooding remains possible given very moist soil conditions. Very challenging forecast for the daytime and evening hours Friday. Kinematically speaking wind fields are favorable for severe convection tomorrow. Deep layer shear in the 30-40 kt range along with large sweeping low-level hodographs suggest organized convection, including supercells. However, this is a highly conditional risk given sufficient instability is able to be realized. Morning shower activity, lots of low and mid- level moisture would suggest that the sun will have a tough time tomorrow developing any big CAPE. Despite good kinematic fields, if there`s no instability, organized convection will be limited, and pulse marginal severe at best would be the result, along with the heavy rainfall threat. If we see a lot of sun tomorrow and develop any meaningful amounts of instability a higher end severe threat would be expected. Will have to continue to evaluate the stability parameters in the forecast through tomorrow evening. Best shot at getting warm will be in the Champlain Valley where downslope southwesterly flow off the Adirondacks may help to clear out low level cloud cover. Have mentioned gusty winds and heavy rainfall in the forecast and hazardous weather outlook. && .SHORT TERM /SATURDAY THROUGH SUNDAY/...
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As of 300 PM EDT Thursday...Mid/upper level trof will deepen across the ne conus for the weekend with several embedded vorts. Atmosphere will have much better dynamics to work with...but moisture and stability profiles will be weaker than expecting less areal coverage of showers and embedded rumbles of thunder. Neither Sat or Sun will be a wash out...but will continue to mention low chc pops between 18z-03z each aftn. Instability ranges from 400 to 800 j/kg...with axis of highest values near the international border each afternoon/evening with strong mid/upper level westerly flow. Soundings show slightly better instability with steeper lapse rates on Sunday aftn with the potential for some localized gusty winds...but threat is limited based on available energy. Progged 850mb temps btwn 10-12c Saturday support mainly 70s with values falling btwn 7-9c on Sunday supporting highs mid 60s to l/m 70s warmer valleys. Lows mainly in the upper 40s to mid/upper 50s over the weekend. Depending upon areal coverage of precip...some patchy fog is possible in the deeper protected valleys. Mid level moisture associated with remnants of Cindy may produce a light shower early Sat morning across extreme southern Rutland/Windsor Counties and have continued to mention low chc to cover this potential.
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&& .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 300 PM EDT Thursday...Large scale synoptic pattern shows mid/upper level trof persisting across the Great Lakes into the ne conus. This general setup will support at or below normal temps with chances for unsettled weather is expected. Thermal profiles show limited instability with some afternoon heating producing daily cape values between 300-600 j/kg. A rumble or two of thunder is possible...especially when the strong dynamics arrive during peak heating hours...but overall severe threat is limited. Have tried to focus higher pops during the aftn/evening hours...except on Tues when better dynamics and deeper moisture is present associated with mid/upper level trof. Progged 850mb temps btwn 6-8c Monday/Tuesday support highs in the mid 60s to lower 70s. These low level thermal profiles slow warm back into the 9-11c by late next week...supporting highs back into the mid 70s to lower 80s. Overnight lows range mainly in the mid 40s mountain valleys to mid/upper 50s in the warmer urban areas of the Champlain Valley. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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Through 00Z Saturday...Mainly VFR except becoming MVFR toward 12z mainly KMSS/KSLK. Clouds are moving in this evening as a warm front now just past KBUF approaches from the southwest. The front will bring rain showers to the TAF sites in NY shortly after midnight reaching BTV in the pre-dawn hours Fri. There is a chance of thunder as instability is advected in aloft, but the risk is hard to pin down any one time or location to include thunder at this time. The main warm front moves northeast of the region 12-15z so expecting any showers and thunder to become scattered and shown as VCSH in the TAFs as surface based instability increases ahead of a cold front. The frontal passage is expected tomorrow night. Some chance of LLWS tonight at SLK/MSS for a few hours as surface winds go light with increasing low- level jet aloft. Surface winds will be generally light then increase from the south and southwest at 10-20 knots with some higher gusts possible during midday at BTV. Outlook... Friday Night: VFR. Chance MVFR SHRA...Slight Chance TSRA. Saturday: VFR. Chance SHRA. Saturday Night: VFR. Slight Chance SHRA. Sunday: VFR. Chance SHRA. Sunday Night: VFR. Chance SHRA. Monday: VFR. Chance SHRA. Monday Night: VFR. Slight Chance SHRA. Tuesday: VFR. Chance SHRA.
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&& .HYDROLOGY... An isolated flood threat on Friday. Last rainfall event recharged streamflow across the region, and storms Friday will be very efficient rainers given very high PW values and some possibility of training given the wind field. In addition some heavy rainfall overnight tonight may saturate surface conditions for Friday afternoon convection. Can`t really pin down any one location, and overall the system is pretty progressive so widespread flash flooding is not expected at this time. Storm total QPF of around an 1"-1.25" expected over central and northern VT and northern NY...with lesser amounts to the south. Don`t anticipate any mainstem river flooding at this time. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Manning NEAR TERM...Lahiff/Manning SHORT TERM...Taber LONG TERM...Taber AVIATION...Sisson HYDROLOGY...Manning is the U.S. government's official web portal to all federal, state and local government web resources and services.