Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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523 FXUS61 KBUF 092154 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 554 PM EDT Tue Jul 9 2024 .SYNOPSIS... Our stretch of fair dry weather will come crashing to an end later tonight and Wednesday...as the remnants of Beryl will make its way out of the Mid West. A soaking one to two inches of rain can be expected in many areas by Thursday morning...with higher amounts possible east of Lake Ontario and even moreso across the Adirondacks. Along with tropical downpours on Wednesday...there will be the risk for strong to severe thunderstorms...mainly across the western Southern Tier and for portions of the Finger Lakes. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... ...Significant Rains AND increased severe weather threat continues from the Remnants of Beryl on Wednesday... Late this afternoon, radar shows spotty showers and a few thunderstorms across Western NY. These are mainly instability driven, and will taper off later this evening. Conditions will significantly deteriorate during the course of tonight though...as the remnants of Beryl over the Lower Ohio valley will push northeast. A tropically enhanced warm front extending to the east across Pennsylvania will approach our region in the process. A modest 25 to 30kt low level jet impinging upon this boundary will combine with forcing under the nose of an 80kt UL jet to lift a deepening tropical airmass to generate increasingly widespread rain as we progress through the overnight/wee hours Wednesday morning. PWAT values will surge to 2.25" by daybreak...so some heavy rain will be possible...particularly within any embedded thunderstorms. The focus of the rain late tonight will be over the western counties with sites west of the Finger Lakes most likely to experience the heavier downpours. Wednesday will most certainly be the most unsettled day of the week... as the center of whats left of Beryl will track across the far west end of Lake Erie to southernmost Ontario. Meanwhile...the aforementioned eastward extending warm front will gradually advance across our forecast area. The deep tropical moisture will focus near and north of the advancing warm front where widespread moderate to heavy rain is expected. Daytime rainfall amounts are forecast to range from a quarter to a half inch across the western Southern Tier to an inch most elsewhere. Embedded thunderstorm activity could locally double that amount. The good news is that the threat for excessive rains has diminished across the sloped terrain of the Southern Tier...but on the flip side...the risk remains in place for the more populated areas from Buffalo...Batavia and Rochester to the Eastern Lake Ontario region. Six hour FFG guidance for this particular area is in the vcnty of 2.25"... so the risk for widespread hydro concerns will be minimal. The forecast rainfall should easily double the flow in most area tributaries (north of the Southern Tier)...but this would only bring most rivers/streams to half bankfull. Any concern would be more directed at urban areas of areas with terrain (sloped sfcs). The exception would be over the Eastern Lake Ontario region where some creeks could climb to three quarters bankfull. Updated WPC forecast clips Lewis county with a moderate risk for excessive rainfall, leaving most of the forecast area in a slight risk. The main concern would be for flash flooding or general flooding, instead of flooding at river forecast points since rainfall amounts will vary by location and may not fall all in the same basin. As for the potential for severe weather...the Storm Prediction Center has outlined much of western New York within a slight risk area. This aligns with the progression of the tropically enhanced warm front where a notably enhanced amount of shear will be present. Bulk shear values of 40-50 kts and veering low level profiles will support supercells and a non-zero threat of tornadoes...along with clusters that will include tropical rain loaded downdrafts (ie localized straight line wind damage risk). 18Z HRRR hints and convection developing early Wednesday afternoon and moving from west to east across the area through around 8 p.m. This would likely be the timeframe for the greatest severe weather risk. Wednesday night will remain very unsettled...particularly over the Eastern Lake Ontario region. The center of the tropical remnants will drift across the far western counties...while the axis of deepest tropical moisture and associated will be slowly exiting via the Thousand Islands and St Lawrence valley. This could produce an additional inch to an inch and a half rain for the Eastern Lake Ontario region...bringing 24 hour amounts to nearly three inches. The highest amounts are expected to be over Lewis county. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... By Thursday morning Beryl`s elongated remnant surface low will be centered across the Lower Great Lakes and Upper Saint Lawrence Valley...with this continuing to fill as it tracks into Southern Quebec through the course of the day. While its attendant axis of deep tropical moisture (and widespread moderate to heavy rains) will be well to our east by this time...the continued close proximity of the remnant low will keep clouds and at least some scattered lighter showers going across the eastern Lake Ontario region through the day...with upslope flow and wraparound moisture also producing a few more of these across far western New York. In between...largely dry weather should prevail across the Finger Lakes. This disparity in cloud and pcpn coverage will also be reflected in the temperatures we`ll experience...with highs ranging in the 70s across far western New York and the North Country...and in the upper 70s to lower 80s in between. It will also remain on the muggy side...with surface dewpoints remaining in the mid to upper 60s. Thursday night surface high pressure and drier air will ridge northeastward into our region from the Ohio Valley. This will help to bring an end to any lingering scattered showers...with fair dry weather otherwise prevailing. Lows will dip into the upper 50s to mid 60s as surface dewpoints drop back a little more...making for at least somewhat more comfortable conditions compared to the preceding few nights. Friday and Friday night the aforementioned surface ridge will remain draped across our region...while a weakening mid-level trough passes by just to our north and west. In the process this latter feature will brush our region...and this coupled with diurnal heating/ destabilization and developing lake/orographically-forced circulations could be enough to pop some widely scattered convection across the Southern Tier and interior Finger Lakes during Friday... with this activity then weakening with the loss of heating and sliding eastward Friday night. Have covered this potential with some slight chance PoPs for now...with dry weather otherwise anticipated. As for temps...highs on Friday will bounce back to the lower to mid 80s for the most part...with lows in the lower to mid 60s then following for Friday night. It will also be at least somewhat humid...as surface dewpoints will generally be in the lower to mid 60s. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Guidance is starting to trend drier for Saturday as a shortwave ridge moves into the area. A few showers can`t be ruled out for eastern areas as a shortwave trough exits to the east. The next trough tracks into the area on Sunday, bringing the next potential for showers. Some timing issues still among the guidance with shower onset time from early Sunday morning through Sunday night. Thunderstorms will also be possible as instability increases through the second half of the weekend. Shower potential will continue into the new work week as a few shortwave troughs track across the area within a quasi-zonal flow over the region. Guidance is also slower with a cold front tracking southeast across the Great Lakes and into the forecast area for the first half of the work week. Again though, there is plenty of uncertainty among guidance for timing and shower coverage. Per usual certainty will start to increase closer to the period and as higher resolution models start to cover any specific day. Daytime temperatures will be some 5 to 10 degrees above normal for the period. Depending on the actual cold frontal passage, temperatures later in the period, on Monday and/or Tuesday may end up being cooler. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... Through the rest of the day expect continued VFR conditions along with thickening high and mid level cloud cover. While it will mostly be dry...a couple showers and thunderstorms will be possible across interior sections of the Southern Tier...Finger Lakes...and North Country. Tonight and Wednesday the remnants of Beryl will approach from the southwest. This will bring continued thickening and lowering cloud cover...and eventually periods of moderate to possibly heavy rain late tonight and Wednesday...along with some scattered thunder storms. This will result in flight conditions lowering to MVFR/IFR. Wednesday afternoon and evening...enough instability could develop to bring a risk of some strong to severe thunderstorms...with this risk greatest south of a rough KBUF-KROC-KFZY axis. The main threat with any such storms would be strong wind gusts. Outlook... Wednesday night...MVFR/IFR with widespread rain diminishing. Thursday...Improvement to MVFR/VFR with leftover scattered showers. Friday...Mainly VFR with a low chance of showers and thunderstorms across the Southern Tier/Finger Lakes. Saturday...Mainly VFR with a low chance of showers and thunderstorms well inland from the lakes. Sunday...Mainly VFR with a chance of showers and thunderstorms. && .MARINE... Wednesday will be quite unsettled, as the remnants of Beryl will move through with times of heavy rain and possibly some gusty thunderstorms. The active weather will be accompanied by moderate to occasionally fresh northeasterlies which are likely to require small craft headlines for at least portions of Lake Ontario. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...RSH NEAR TERM...Apffel/RSH SHORT TERM...JJR LONG TERM...JM/SW AVIATION...JJR MARINE...RSH/TMA/Apffel