Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 212029 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 429 PM EDT Wed Aug 21 2019 .SYNOPSIS... A cold front will push through the region tonight. While this could spark a few more showers or thunderstorms...it will bring an end to a stretch of warm and muggy conditions. We will then experience spectacular weather Thursday through the upcoming weekend with little cloud cover...comfortable temperatures and low humidity. && .NEAR TERM /THROUGH THURSDAY/... During the remainder of the afternoon...our forecast area will find itself within an unstable airmass well ahead of an approaching cold front. A well established lake shadow downwind of Lake Erie will keep the BUF metro area and much of the IAG Frontier free of any rainfall...while there will be the risk for some widely separated showers and storms most elsewhere. Any convection that does fire up before 6 PM will likely do so along and just ahead of a strengthening lake breeze boundary. As of 1730z...this line of enhanced Cu stretched from near Batavia southwest along the Chautauqua ridge to about Ripley. As this mesoscale forcing mechanism pushes east...it will encounter SBCAPEs averaging 1500 j/kg. Fortunately bulk shear values will only range from 20 to 25 knots...so there will not be a significant risk for severe weather. PWAT values in the vcnty of 1.5" though could encourage pockets of locally heavy rain...mainly over the Southern Tier and Finger Lakes region. That being said...the coverage for the possible convection should not be nearly as widespread as that from early this morning. Otherwise it will be warm and humid for the rest of the afternoon with 70 degree dew points being accompanied by temperatures that will largely range from the low to mid 80s. A cold front will gradually push to the south across our forecast area tonight. Other than a very modest 30kt low level jet and some convergence near and ahead of this boundary...there really is not much forcing to support WIDESPREAD pcpn. A strong H25 jet will pass to our north...but it will be in the `wrong` place to give any additional lift from the upper levels. It is interesting to note though...that most if not all of the guidance packages are grossly under estimating the strength of the UL jet. Aircraft measurements from across Minnesota this morning measured winds >160kts with this jet...but upper air soundings have only been able to `capture` winds of 115 to 120kts. As mentioned though...the position of the jet is more important and this is not favorable for significant weather production. In any case...will use chc pops for showers and thunderstorms. Thursday will feature improving conditions...as a cooler and notably drier airmass will gradually push across our region in the wake of the overnight cold frontal passage. While a brief shower cannot be ruled out across the Southern Tier...dry air advecting south in the mid levels and a developing subsidence inversion should keep any shower activity to a minimum. Otherwise...it will become increasingly comfortable as dew points in the lower 60s during the morning will drop through the 50s during the afternoon. Meanwhile... afternoon highs will be in the low to mid 70s. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... The first taste of fall-like conditions will be felt across the forecast area during this period. Cold air advection continuing behind the front will keep in place a much cooler airmass for Friday and also Saturday. How cool will it be? Well, H850T are forecast to fall from +11C to +7C Thursday night, that`s chilly (single digits at H850) for August standards. Friday, with a cool NNW`erly flow filtering in across the region and much warmer lakes, it will result in a conditionally unstable airmass for any lake effect processes. However, with only a thin, shallow layer of moisture left and strong subsidence any lake response will be very limited, if anything at all. The most likely scenario, with steep low level lapse rates, will be some diurnally driven flat fair weather cu. With that said, look for dry weather across all locations, with a mixture of afternoon clouds and sunshine. With a much cooler air mass in place, look for highs in the upper 60s to low 70s, which will roughly be 5-8F below normal for this time of year. Friday night, Canadian sourced high pressure will provide light winds and clear skies overnight. In fact, it will be an excellent night for star gazing, if you get a chance head outside and make use of a telescope if you have one. The only thing weather wise will be some interior valley fog across the Southern Tier and to a lesser extent east of Lake Ontario in the Black River valley. With clear skies and excellent radiational cooling look for lows to fall back in the upper 40s to low 50s by daybreak. Saturday, more of the same as cool NNE flow will reside across the forecast area with highs only expected in the upper 60s to low 70s. Saturday night, another spectacular night is on tap with clear skies and light winds. Lows will generally be found in the low 50s, with a few pockets of upper 40s across interior sections of the Southern Tier and east of Lake Ontario. Sunday, a gradual warming trend begins as the broad Canadian sourced high slowly slides east. This will allow return southerly flow to develop across our region which will encourage a return to near normal highs, mid and upper 70s. Sunday night, the center of the surface high pressure slides further east to New Brunswick and Prince Edward Island. However, it will continue to maintain dry conditions as we head into the new work week. Also, it won`t be as cool overnight with lows expected in the 50s to low 60s by sunrise Monday morning. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... A return to above normal temperatures is likely during the long term period. Otherwise, medium range guidance is not in good agreement and diverge with respect to how quickly the ridge slides further east and out to sea, and how quickly the next trough and associated moisture approaches from the west. The GFS remains fastest with this overall scenario and brings increasing chances for convection into our region. Meanwhile, the ECMWF lies on the other side of the guidance envelope and keeps the ridge intact and our region totally dry through Tuesday. Keeping this in mind, have held POPs to only a chance showers and thunderstorms for the time being with all the uncertainty beyond Monday. With the above said, the combination of general airmass modification and strengthening warm air advection will lead to a day-to-day warming trend through this period with highs climbing into the low to mid 80s. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... VFR conditions will be found across the region this afternoon and evening...although a developing lake breeze boundary should help to re-ignite some thunderstorms well south and east of Buffalo and Rochester. Tonight...a cold front will gradually push across the region. While this feature should generate more scattered convection...the vast majority of the area should continue to experience VFR weather. The exception will be across the Southern Tier and possibly the North Country...where late night fog and stratus could lead to MVFR to IFR conditions. Thursday will feature VFR weather as high pressure over central Canada will gradually build south across the Upper Great Lakes. Outlook... Thursday through Monday...Mainly VFR with nothing more than Southern Tier valley fog producing local MVFR/IFR conditions each morning. && .MARINE... A southwesterly flow will be in place across the region this afternoon ahead of a cold front with waves building to 2-4 feet on Lake Erie. A cold front will swing across the Lower Lakes this evening and early overnight, with waves and winds increasing within the cold air advection environment. WNW winds over the shorter fetch of Lake Erie will build waves 2-3 feet tonight and Thursday, while a longer fetch and slightly stronger wind flow over Lake Ontario will bring waves up to 5 feet or greater on the southern Lake Ontario shoreline. Small craft advisories have been issued. && .TIDES/COASTAL FLOODING... A strong cold front will cross the Lower Great Lakes this evening. Strengthening west to northwesterlies in the wake of the front will increase wave action and combine with already high lake levels to produce significant shoreline erosion and flooding late tonight through late Thursday afternoon. A Lakeshore Flood Warning is now in effect for Wayne, northern Cayuga and Oswego counties. Since winds will be more westerly and not as much onshore, the lakeshore flood watch was dropped for Niagara, Orleans and Monroe counties. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Lakeshore Flood Warning from 5 AM to 5 PM EDT Thursday for NYZ004>006. MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Thursday for LOZ043- 044. Small Craft Advisory from 2 AM to 2 PM EDT Thursday for LOZ042. Small Craft Advisory from 8 AM to 8 PM EDT Thursday for LOZ045. && $$ SYNOPSIS...RSH NEAR TERM...RSH SHORT TERM...AR LONG TERM...AR/JLA AVIATION...RSH MARINE...Hitchcock/JLA/RSH TIDES/COASTAL FLOODING...RSH/JLA

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