Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 182036 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 436 PM EDT Tue Jun 18 2019 .SYNOPSIS... Through Wednesday weak high pressure will linger across the Lower Great Lakes...while a stalled out frontal boundary will remain draped across Pennsylvania. Weak impulses sliding eastward along the front may generate some widely scattered showers across far interior sections at times through early Wednesday...with increasing daytime heating then allowing showers and perhaps a few thunderstorms to expand a bit across areas inland from the lakes Wednesday afternoon into Wednesday evening. Low pressure advancing into the Lower Great Lakes will then bring a widespread soaking rainfall Thursday into Thursday night which could be heavy at times. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 430 pm a cumulus field persists inland from the lakes... however shower coverage within this region remains very spotty on area radars...with any echoes confined to interior portions of the Southern Tier and Finger Lakes. Still could see a few additional showers and perhaps an isolated thunderstorm develop within the above areas through early this evening given SBCAPES of 500-1000 J/kg and the potential for localized convergence/lift along lake breeze boundaries and terrain features...however coverage will likely remain fairly limited. After that there should be a relative break for at least part of the night... before a few more isolated showers become possible across the Southern Tier as an impulse along front currently causing showers and t-storms over central Indiana to central Ohio slides along PA/NY border...as is hinted at by a majority of the higher resolution models (WRF-ARW, NMM, NSSL- WRF and even NAM- nest). On Wednesday, diurnal instability and local convergence from lake breezes, terrain, and differential heating will support a chance of a few showers or an isolated thunderstorm especially in the afternoon and evening hours, mainly inland from the lakes. Stable lake shadows will likely keep most lake plain locations dry. High temperatures will be in the upper 70s in most areas, but it will be cooler along the immediate lakeshores as lake breeze circulations develop. Still appears that most of the diurnal showers will taper off Wednesday evening. Then late Wednesday night, larger scale ascent in form of pva/q-vector convergence ahead of approaching shortwave trough and warm air advection/moisture flux convergence in advance of approaching sfc-H85 lows will support increase in showers and possibly a thunderstorm toward western portions of forecast area. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... Thursday, a surface low will be found near Ohio, this within a progressive, zonal shortwave trough that will eventually merge with an upper level low well to our east this weekend. Ahead of this low, a southerly stream will transport deep moisture northward, with PWATS rising to near 1.5 inches during the day over our region. While moisture will surge northward, it will not become very warm...with temperatures at 850 hPa around 10-13C. The surface low is forecasted to track eastward across Pennsylvania, and the greater warmth and instability will remain along and to the south of this low. In light of this, will narrow in the area for heavy rain, and thunderstorms to the southern two tiers of counties in our CWA. While moderate rain is still possible to the north of the thruway, the position of the surface low (which will continue a steady eastward track), greatest instability, and southward push of the axis of deeper moisture will allow the removal of heavy rain. Still with the upper level shortwave passing through, deep accent will allow for rain showers for the entire region and will continue with the categorical PoPs. Rainfall of over an inch is likely south of the NYS thruway Thursday- Thursday night, while closer to the Saint Lawrence Valley total rainfall will average around a quarter of an inch. This surface low will track towards the Jersey Shore Thursday night. This will carry the bulk of the rain showers eastward, though moist cyclonic flow aloft will maintain chances for light rain showers or drizzle deep into the overnight time period. A northerly wind behind the surface trough aloft may bring some lower ceiling heights, and areas of fog across the hills of the Southern Tier. High temperatures on Thursday will range from the upper 60s, to lower 70s or about 5 to 10 degrees below normal. A late night push of drier and cooler air will allow for temperatures to drop into the mid 50s late. && .LONG TERM /FRIDAY THROUGH TUESDAY/... After Thursday`s rains...Friday will become much nicer with a surface low now over New England and heading out to sea. Under cyclonic flow aloft, a dry northerly flow will bring increasing amounts of sunshine and much lower humidity. There will likely be a decent cumulus field forming through the afternoon under the cyclonic flow, though there should still be plenty of sunshine. Temperatures through the afternoon will be in the 60s, with highs peaking around 70F. Saturday and Sunday an upper level ridge will begin to amplify over our region, with 500 hPa heights peaking Sunday around 576-580 dm. This upper level ridge and strengthening lower level inversion will limit any shower or thunderstorm activity, while also allowing for day to day warming into the mid 70s Saturday and around 80F Sunday. The ridge axis will slide to our east Sunday night and this will allow for increasing chances for showers and perhaps a thunderstorm. The greatest chances will be Monday and Monday night as an upper level trough axis swings across the region. The GFS is much sharper with this trough than the operational ECMWF/Canadian and much of the GFS`s 12Z ensemble members. If a slower progression to this trough occurs, then a sharper trough as suggested by the GFS could be possible with prospects for stronger thunderstorms Monday night/Tuesday. Monday will likely still remain warm, with temperatures well into the 70s to lower 80s, with Tuesday behind the trough a few degrees cooler. && .AVIATION /21Z TUESDAY THROUGH SUNDAY/... Daytime VFR cumulus clouds will fade into the evening. Overall VFR conditions will continue into Wednesday morning, though should see some fog (IFR/MVFR conditions) and an isolated shower at KJHW late tonight into Wednesday morning. Additional showers could develop over more areas during peak heating on Wednesday afternoon, though again especially at KJHW. Conditions Wednesday afternoon into Wednesday night should remain VFR. Outlook... Thursday...MVFR/IFR with periods of rain and a chance of a thunderstorm. Friday...MVFR/VFR. AM chance of showers. Saturday and Sunday...VFR. && .MARINE... Weak surface high and weak pressure gradient will reside across the Lower Lakes through Wednesday maintaining light winds and minimal wave action. A low pressure is expected to track across the Lower Great Lakes on Thursday, but the exact track and strength of the low still is uncertain. Winds and waves may approach Small Craft levels Thursday into Friday depending on the track and eventual strength of this system. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...JLA/JJR NEAR TERM...Hitchcock/JLA/JJR SHORT TERM...Thomas LONG TERM...Thomas AVIATION...JLA MARINE...AR/JLA

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