Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 250248 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1048 PM EDT Mon Apr 24 2017 .SYNOPSIS... High pressure will move away tonight. Low pressure over the southeastern states will slowly push northward along the east coast over the next several days. This will spread showers into our region late tonight and Tuesday. It will then become summer-like by mid week, as the mercury will soar into the 70s for Wednesday and well into the 80s Thursday. && .NEAR TERM /THROUGH TUESDAY/... The axis of the large surface high will push east to the Canadian maritimes overnight, while a cut-off low over the southeast CONUS makes slow progress northward. Strengthening low-level southeast flow will develop north of the low, which in turn will advect increasing amounts of Atlantic moisture back up across our forecast area. This can be seen on radar moving into northern Pennsylvania late this evening, however it is very dry across Western New York so these showers should initially evaporate before moving into the region late tonight. Precipitation should blossom into some steadier shower activity Tuesday morning as better lift arrives and lower levels saturate out. The shower activity will diminish from west to east Tuesday afternoon and Tuesday night as the deeper moisture and better forcing slide off into New England. Rainfall amounts out of this system will be fairly light with totals less than a quarter inch in most areas. Otherwise, overnight low temperatures will be in the 40s, with highs Tuesday ranging from the upper 50s to mid 60s. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... A slow-moving cutoff low will continue to make its way up the East Coast as we move through Tuesday night and into Wednesday. While most of the shower activity should be tapering off as we move into Tuesday night, as the bulk of the deeper moisture and synoptic forcing will be moving off into New England, nonetheless there will be enough of a southeasterly fetch of Atlantic moisture to maintain at least a chance of showers across the eastern half of the forecast area through much of the night. Things should dry out as we move into Wednesday, and the low pressure system continues to fill as it moves off the coast of New Jersey. The moist southeasterly flow will give way to warmer and drier southerly flow that will help clear out lingering cloud cover while boosting temperatures into the 70s. We should see mostly clear skies Wednesday night into Thursday, as a sharply amplified upper level ridge transits the region. Warm air and downsloping southerly flow will keep temperatures in the mid 50s Wed night, with readings in the low 60s along the Lake Erie plain, making it feel more like July than April. Thursday will be the warmest day we have seen so far this year, as a combination of subsidence that will boost 850mb temps to in excess of +18C. The subsidence, abundant sunshine, and slight downsloping on south-southeasterly flow will translate to highs that should easily top out in the mid-80s for many locales, with temperatures potentially approaching 90 in the Genesee valley. Things get more interesting as we move into Thursday night and a cold front approaches the region. Convection occurring along a pre- frontal trough is forecast to move across the forecast area overnight. While there may be a potential for some of these storms to be strong and possibly severe, particularly across far Western New York in the evening, when instability will be maximized, vertical shear as depicted in the models is marginal for severe weather, and moisture is limited. In addition, should the front be held up by even a few hours, the pre-frontal trough will cross later in the night, when diurnal instability will be greatly reduced. Nonetheless, it is often the case that when we see a dramatic warmup such as the one expected Thursday, it is followed by a bout of severe weather...so this is a scenario that will bear close watching over the next couple of days... As a final note, high temperature records for April 27th are 84 at Buffalo (1984)...86 at Rochester (1990)...and 85 at Watertown (2009)...with it appearing increasingly likely that the records at Buffalo/Rochester will at least be approached if not threatened on Thursday. After that...modest cool air advection setting up behind the cold frontal passage will allow lows to fall back into the mid and upper 50s Thursday night...though such readings will still be some 15-20 degrees above late April normals. && .LONG TERM /FRIDAY THROUGH MONDAY/... The cold front mentioned in the Short Term Discussion above is forecast to be in the process of shifting across Central NY Friday morning then clearing to the east of the forecast area by Friday afternoon with while the tail end stalls just south of the NY/PA border. Have left a chance of showers with a slight chance of thunderstorms during the morning east of about a Watertown to Oswego to Wellsville line with a slight chance of a shower to the west of that line. Expect mainly dry weather for Friday afternoon with a narrow wedge of high pressure building in behind the front. The exceptions are a slight chance of a shower possible in the afternoon for the eastern Lake Ontario Region lingering behind the cold front as well as far western NY ahead of an approaching weak surface wave moving into the Ohio Valley. Friday night, the weak surface wave with associated 40kt low level jet will shift from the Ohio Valley to western NY. In this process it should lift the stalled front to our south back north as a warm front, stretching across western and central NY. As this system shifts along the stalled front it will bring a chance of showers Friday night and Saturday morning with a chance of thunderstorms possible in the Southern Tier Saturday afternoon where some instability is possible south of the warm front. Saturday night, a chance of showers will linger for all areas with the front still stretch across western and central NY. Sunday and Monday will feature more widespread chances of showers and thunderstorms as forcing and instability are enhanced by a low pressure system strengthening in the Midwest. Southerly flow ahead of this system will bump the stalled front a little further with moisture and instability interacting with the warm front causing the chance for showers and thunderstorms. The low pressure system looks to rapidly deepen on Monday while lifting over Michigan. A cold front associated with this storm will approach the forecast area Monday or Monday night bringing the risk for another day of showers and thunderstorms. Its still pretty far out to be more certain but there could even be a risk of severe storms as shear will be enhances ahead of the cold front. Temperature-wise, readings through will remain well above normal with daytime highs Friday through Sunday still expected to range between the mid 60s and lower 70s. Overnight lows look to run comfortably in the upper 40s to low 50s. As mentioned in a previous discussion, while temperatures are forecast above average, the exact magnitude of these departures will be highly dependent upon the exact position of the warm front. This feature will mark the dividing line between pleasantly warm spring conditions to its north and downright midsummerlike warmth to its south. Monday may be the warmest day of the period as the warm front lifts north of our region possibly setting the stage for another run toward 80 degrees should showers and thunderstorms hold off until late in the day. Looking out just beyond this period into Monday night/Tuesday. There could be a risk of strong gradient wind gusts in the wake of the front downwind of the lakes. This would be due to the track of the surface low following a favorable track and 50+ knot low level jet mixing in cold advection behind the front. This is a very early assessment so stay tuned for future updates. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... High pressure centered near Hudson Bay will extend to the south across New England into this evening, and this will allow for flying with nearly cloud free skies. There is high confidence in VFR conditions for most of the night, but then clouds will lower and thicken abruptly between 08Z and 12Z. Some light showers are likely, with cigs lowering to near MVFR Tuesday morning as the lower levels become saturdated. Showers will taper off from west to east Tuesday afternoon, with mainly VFR conditions. Outlook... Tuesday night...VFR. Wednesday...VFR. Thursday...VFR/MVFR with a chance of showers and thunderstorms. Friday and Saturday...Mainly VFR with a slight chance of showers and thunderstorms. && .MARINE... The northeasterly flow has diminished some this evening, with winds/waves expected to be just below small craft criteria on the western two-thirds of Lake Ontario. The largest waves will be in Canadian waters as the flow becomes more easterly. A general east to southeast flow will remain in place across the Lower Great Lakes Tuesday and Wednesday, as a very slow moving coastal low will be found along the coast of the Carolinas. Again, the choppiest conditions will be found in Canadian waters so no additional marine related flags are anticipated. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...TMA NEAR TERM...APFFEL/TMA SHORT TERM...WOOD LONG TERM...SMITH AVIATION...APFFEL MARINE...APFFEL/TMA

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