Area Forecast Discussion
Issued by NWS Burlington, VT

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272 FXUS61 KBTV 242341 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 741 PM EDT Mon Jul 24 2017 .SYNOPSIS... An upper level low pressure system will keep showers and clouds around through Tuesday morning. Drier weather moves in late Tuesday with high pressure and remains in place for a day or two. A cold front will bring a renewed threat of showers and storms on Thursday. Fair weather then returns for Friday into the weekend with temperatures near seasonal late summer norms. && .NEAR TERM /THROUGH TUESDAY NIGHT/... As of 706 PM EDT Monday...Steady rainfall has shifted east of VT early this evening. However, closed mid-level low - quite evident on WV imagery east of Lake Ontario - will shift slowly ewd overnight bringing additional UVV and bands of shower activity. Abundant low-level moisture will also result in patchy drizzle and/or fog, yielding a rather murky night. Winds will generally be light. All those clouds won`t allow temperatures to fall much overnight (maybe 5 degrees), with early AM lows in the 50s for the entire area. Tuesday, troughiness slowly gets pushed out to the southeast as upper level ridging tries to build to our west. The good news -- we should end the day with a good deal of sun and drier conditions. However, the bad news is that I really mean the end of the day. Up until mid/late afternoon, murky conditions with lots of clouds and a few light showers will be around. The very late day sun will allow temperatures to top out in the upper 60s, especially in northern areas where clearing happens first. Tuesday night, high pressure builds over the region. Calm, clear and drier airmass will allow for good radiational cooling, especially outside of the larger valleys. We should see temperatures drop into the 40s for many colder spots in eastern VT and the `Dacks. The NAM MET guidance has Saranac Lake going down to 36F (brrr) degrees. Don`t think it will be quite that cold, but 39-41F is quite reasonable for that notoriously cold location. With the wet ground, patchy dense fog is also expected in the river valleys and sheltered valleys. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... As of 320 PM EDT Monday..1025mb high pres directly overhead at 12z Weds morning will provide region with dry conditions and near normal temps. Have continued with previous forecasters idea of patchy valley fog thru 13z...before mixing increases and fog dissipates. Otherwise...progged 850mb temps between 10-11c by 21z weds support highs lower 70s mtn towns to near 80 warmer valley locations. With plenty of sun have trended toward the warmer side of guidance. Weds night...mid/upper level clouds increase as winds turn southerly ahead of our next surface boundary. Best 1000 to 500mb rh fields and forcing stays west of our cwa...so anticipating a mainly dry night. Temps fall quickly early...but level off or increase slightly after midnight with clouds and gradient flow increasing. Mainly mid 50s to l/m 60s depending upon location. Have mention schc/chc pops nw sections by 12z Thursday. Clouds/winds should confine fog/br to the immediate ct river valley on weds night. Thursday...Mid/upper level trof digs across the northern Great Lakes into the NE Conus with associated surface cold front. Still some uncertainty on timing of system with gfs 3 to 6 hours faster than the latest 12z NAM solutions. Timing of boundary will play an important role on amount of instability and magnitude of convection. Slower arrival would support greater instability with CAPE values between 1200-1800 j/kg...combined with 0 to 6 km shear of 35 to 45 knots...indicating a pre-storm environment favorable for stronger storms with some organization. Meanwhile...faster GFS shows less destabilization with CAPE values of 400 to 800 j/kg...mainly over northern NY...with plenty of clouds limiting sfc heating over VT. Both solutions show favorable deep layer shear associated with 700 to 500mb wind max of 35 to 45 knots...in fast mid level flow...just lacking instability with potential 5h energy. Some of the stronger convective elements would be capable of producing locally heavy rainfall given pws between 1.75 and 2.0 and the progged forcing associated with potent 5h energy. Meanwhile...12z ECMWF is completely different with much slower and deeper trof with 996mb low pres developing over central NY. This scenario would support a general widespread rainfall with embedded convective elements. Will continue with idea of chc to likely pops for showers with isolated to scattered thunder potential. Too much uncertainty for enhanced wording...but time frame should be watched for potential stronger convective elements. Temps on Thurs are tricky with potential for morning showers followed by some sun...before more aftn showers/storms arrive with progged 850mb temps climbing to near 14c. Will mention highs l/m 70s mtns towns to lower 80s warmest valley locations. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 320 PM EDT Monday...Mid/upper level trof continues to influence our cwa on Thurs night into Friday and depending upon timing...showers with embedded storms could linger into midday Friday. Will continue to mention chc/likely pops during this time period...as plenty of uncertainty with timing/magnitude of trof and associated surface low pres/boundary continues to be advertised in model solutions. Cooler and drier air eventually returns by the weekend...as surface high pres builds into our cwa. Progged 850mb temps between 9-11c Friday support highs mainly 70s...but if ecmwf surface pres was to verify easterly winds and much cooler temps would be possible...especially eastern/central vt. Have played mid of the road with superblend guidance and will fine tune as event become closer. For the weekend...eventually 1020 mb high pres builds from the Ohio Valley/Great Lakes...with building mid/upper level heights. This will provide a mainly dry weekend with seasonable temps. Highs mainly in the upper 60s to mid/upper 70s with lows mid 40s to mid 50s and much lower humidity values. Expect some areas of patchy fog in the deeper/protected valleys of northern NY and parts of central/eastern VT. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Through 00Z Wednesday...Complex forecast with VFR to MVFR conditions starting the period. Expect plentiful moisture in the low levels and low level jet of 15-20kts to subside around 06Z to allow for fog development. Expect MVFR conditions to deteriorate to IFR and LIFR at KMPV and KSLK mainly between 06Z- 11Z. Rest of the terminals are expected to see MVFR conditions with periods/TEMPO of IFR through Tuesday morning. The mid-level trough will continue to affect the region, putting the North Country in NE flow by Tuesday morning, expect low level clouds to be slow and stubborn to scour out. Expect MVFR cigs through most of Tuesday. Models indicate cig lifting and clearing out in the mid to late afternoon. Outlook... Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. NO SIG WX. Wednesday Night: VFR. Chance SHRA. Thursday: VFR. Likely SHRA...Chance TSRA. Thursday Night: VFR. Chance SHRA. Friday: VFR/MVFR. Chance SHRA. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Nash NEAR TERM...Banacos/Nash SHORT TERM...Taber LONG TERM...Taber AVIATION...KGM

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