Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 240633 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 233 AM EDT Mon Oct 24 2016 .SYNOPSIS... Cold northwesterly flow will persist into the middle of the week, generating plenty of cloud cover, but only limited shower activity southeast of the lakes. Temperatures will continue to run below average. && .NEAR TERM /THROUGH TODAY/... The shortwave that caused the rainfall across the Southern Tier during the evening hours has moved off to the east early this morning, taking with it the shower activity. However, as can be seen on regional satellite imagery, cold cyclonic flow remains in place across the region, and this is generating widespread lake effect clouds downwind of the Great Lakes, with a few showers noted upstream across northern Lower Michigan. While we should remain dry through the rest of tonight, northwest 1000-850 mb winds will return cooler air to the region, with 850 mb temperatures tumbling back to near -5c during the day. This will cause equilibrium levels to rise above 10kft, and as a result we should see at least some scattered lake effect rain showers southeast of the lakes, mainly across areas aligned with Georgian Bay and southern Lake Huron. The cold air advection that will be responsible for the lake clouds and showers will also serve to keep temperatures nearly steady through the day, in the upper 40s to around 50. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... For the first 48 hours of this period...our weather will continue to be dominated by persistent upper level troughing...the core of which will only slowly drift from eastern Quebec Province to the Canadian Maritimes. This feature will feed a continued northwesterly to northerly flow of colder Canadian air across our region...which will result in temperatures averaging solidly below normal right through midweek. More specifically...expect daytime highs mostly in the lower to mid 40s both Tuesday and Wednesday...while nighttime lows mostly ranging through the 30s Monday night will drop off into the upper 20s and lower 30s Tuesday night...likely resulting in a killing freeze in most areas where the growing season has not already ended. Precipitation-wise...the persistent northwesterly to northerly flow of Canadian air across our region will also lead to the potential for some lake effect precipitation southeast and south of the lakes. This stated...the combination of the shortening fetch...a fairly low (5-6 kft) capping inversion...and less than impressive moisture below this level should all help to keep any such activity fairly limited/scattered in nature. As such...have kept PoPs confined to the 20-40 range...with the highest values southeast of Lake Erie Monday night and early Tuesday... where and when moisture will be a little bit more favorable. Ptype with the lake effect precip will be predominantly rain showers by day... mixing with or changing to snow each night/early morning as the boundary layer cools. Any lake effect activity lingering into Tuesday night will come to an end during the day on surface-based ridging settles directly overhead along with increasing large-scale subsidence and shear. Wednesday night the axis of the surface ridge will grudgingly drift east into New England...while a developing storm system over the Upper Midwest slowly pushes into the western Great Lakes. The developing warm air advection regime out ahead of this next system will initially drive a west to east increase in cloud cover during the night...before leading to the possibility of some showers across far western New York late. While the bulk of these should be in the form of plain rain given the strengthening warm air advection regime...interior sections of the Southern Tier may well remain cold enough to support a brief mix at the onset of the precipitation. Given the still somewhat-distant time frame...have elected to keep this in the form of a general rain-snow shower mix for now...though the degree of warming currently portrayed aloft would ultimately be supportive of other precipitation types. On Thursday...the surface low will continue to slowly deepen while lifting northeastward into Southern Ontario...while pushing its attendant warm front across areas south of Lake Ontario. Coupled with height falls aloft and deepening synoptic-scale moisture...this will lead to a likelihood of precipitation spreading across our region from southwest to northeast...with the continued warm air advection regime supporting rain showers as the predominant precip type. This stated...high temperatures will remain a bit below average thanks to thicker cloud cover and increasing precipitation coverage... with readings generally remaining confined to between 45 and 50. && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... A progressive low amplitude flow will remain in place across the country during this period. The center piece for this pattern will be a 100kt H25 jet straddling the Canadian border....which will effectively block any anomalously cold air to the north. This will encourage temperatures across the Lower Great Lakes to average within a couple degrees of normal. As we open this period Thursday night...a compact area of low pressure over Southern Ontario will start to push northeast away from the region. In the process...this initial storm system will start to transfer a bulk of its energy to a coastal low off New England. We can anticipate rain showers as a result of this scenario...particularly over the Eastern Lake Ontario region. The negatively tilted H5 trough will deepen enough to generate a stacked low in the vcnty of northern New England/Maine on Friday... while weak sfc based ridging will extend from the Upper Great Lakes to the Ohio Valley. This will place our region within a cyclonic flow of moist chilly air so that scattered rain showers can be expected. A minimal lake response should enhance the coverage and possibly the intensity of these showers southeast of Lake Ontario. The aforementioned weak ridging is forecast to push east across the Lower Great Lakes Friday night and Saturday. This will enable our weather to improve somewhat...but with low confidence in the guidance and significant differences between the various ensembles...will carry slight chc pops. On Sunday...the weak ridging will exit across New England while the next southern stream shortwave is forecast to approach from the Ohio Valley. This would support the next round of precipitation... although as mentioned...confidence will be lower than normal due to significant discrepancies in the ensemble packages. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... Shower activity has shifted south of the PA border with the passage of last evening`s upper level disturbance and conditions have returned to VFR across the forecast area. Persistent cold cyclonic northwesterly flow across the Great Lakes will continue to generate plenty of VFR cigs across the forecast area through the TAF period, and a few lake effect rain showers will be possible at times across the far western Southern Tier, as well across areas south of Lake Ontario. Cigs may drop to MVFR in these showers, but otherwise cigs will remain VFR elsewhere through the TAF period. Outlook... Tuesday and Tuesday Night...Mainly VFR. Wednesday...VFR. Thursday...MVFR/IFR with rain showers likely. Friday...MVFR with a chance of lake effect showers. && .MARINE... Brisk west-northwesterly flow continues across the lakes, as the area remains with a tight pressure gradient between a deep low pressure system centered to the north of Maine and high pressure over the Ohio Valley and central Great Lakes. Winds will relax somewhat tonight as a short wave trough moves through. The downtime for the small craft advisory conditions will likely be short lived as a northwest flow will increase behind the system. Strong cold advection will assist in keeping winds up into at least Monday night on Lake Erie and through Tuesday on Lake Ontario. High pressure will briefly ridge across the lake on later Tuesday but another fast moving storm system will arrive Wednesday night into Thursday. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory until 9 AM EDT Tuesday for LEZ040-041. Small Craft Advisory until 6 PM EDT Tuesday for LOZ042>044. Small Craft Advisory until 9 AM EDT Tuesday for LOZ045. && $$ SYNOPSIS...WOOD NEAR TERM...WOOD SHORT TERM...JJR LONG TERM...RSH AVIATION...WOOD MARINE...TMA/WCH is the U.S. government's official web portal to all federal, state and local government web resources and services.