Area Forecast Discussion
Issued by NWS Cleveland, OH

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051 FXUS61 KCLE 272338 AFDCLE Area Forecast Discussion National Weather Service Cleveland OH 738 PM EDT TUE SEP 27 2016 .SYNOPSIS... An area of low pressure will move from the Upper Lakes overnight into the Ohio Valley by Wednesday. This feature will meander over the region for several days providing cloudy skies, rain, and isolated thunderstorms. && .NEAR TERM /THROUGH WEDNESDAY/... The dry slot over the region will push east overnight. Energy moving in advance of an upper low dropping south from the Lake Superior this evening will help develop some clouds over the area. The clouds will progressively fill in overnight as a strong vort max moves in. This feature along with height drops will begin to support shower activity mainly in our western counties. Believe the showers should hold off until daybreak given how much dry air needs to be overcome to support measurable rain. Winds will come down overnight as the mixing is reduced. Temperatures will drop down into the lower 50s. Some area will touch the upper 40s, but given more wind and encroaching clouds than last night most areas should remain in the 50s. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As stated above the rain chances will start Wednesday morning mainly in the west and gradually spread east through late morning. The height falls associated with the upper low are impressive, which will help steepen the lapse rate over the area. Temperatures will struggle to reach the upper 60s given cloud cover and showers, but this will be sufficient to support thunder. Best timing will be early afternoon when the vort max moves in. The upper low will become cut off right over the Ohio Valley through late week. Generally speaking conditions under this set up are cloudy skies with on and off showers with isolated thunderstorms during peak heating (or timing of best divergence aloft and/or convergence along the moisture axis). The exact placement and evolution of this feature and the surface low could have big impacts on the rainfall forecast. The location of the mid level moisture advection from the Atlantic combined with the placement of the left exit region of the upper level jet, deformation zone, and vorticity max will help develop large bands of rain that could extend into southern PA. On the flip side a dry slot could move in and bring a break to the rain for portions of the CWA. The favored location at this time looking at the impressive forcing aloft is the north and eastern counties Thursday into Friday. These areas could see hours of moderate to heavy rainfall. Overall most areas should see an inch of rain through the end of the week with the potential for notably more. The slow movement of the low could lead to excessive rainfall problems should banding develop over the area. Will have to see how the models come in-line over the next 24hrs. Temperatures will be challenging as well. There will be warm advection moving in Thursday and Friday as we develop a strong moisture feed from the mid Atlantic. However the upper level low will support notably cooler temperatures. Believe we could see a bigger temperature gradient from West to East as the exact placement of the low and surface features come into line. For now have temperatures generally in the 60s. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Fall is upon us and the overall pattern is shaping up to remind us this season is here. Vertically stacked low right on top of the local forecast area will slowly meander around the eastern Great Lakes through the forecast period. The upper level low sort of gets cut off and begins the slow shift east as amplification of the broad upper level ridge encompassing three fourths of the United States and Canada begins to shift east. The stacked low will keep a relatively cool pool of air over the forecast area along with pumping a conveyor belt of moisture in from the Atlantic Ocean. This flow of moist air could bring quite a bit of rainfall to the eastern portions of the forecast area early in the extended periods. However, one caution is how extensive the dry slot interacts with the conveyor belt and pushes the moisture further north and out of our area. So, this all remains to be seen in how the storm system winds down by the weekend. As mentioned, with the cool pool over the area and potential for showers, we will not see temperatures climbing much out of the 60s through the first half of the extended periods. Eventually, as the upper level low pulls out, some warm air advection will take place and restore temperatures back into the 70s. Otherwise, overnight lows will be consistently in the 50s. && .AVIATION /00Z Wednesday THROUGH Sunday/... Low across Lake Superior will spiral southward to the Ohio Valley where it will linger for days. VFR conditions on the fringes...but as we get some of the deeper moisture into the area late morning/midday...Non-VFR conditions will take over...from vsby issues in RA and/or from lowering ceilings. Western terminals will likely be the focus for the steadier showers on Wednesday. IFR possible in the heavier rain. Thunderstorms possible in the afternoon. Winds will shift counter- clockwise around the dial over the next 24 hours. Low confidence in the exact timing of the impactful changes though. OUTLOOK...Periods of non-VFR through Sunday. && .MARINE... Massive upper level and surface low will slowly work their way southeast across the lake over the next 24 hours. The low will continue to cause winds to gradually diminish overnight from west to east. Will continue the small craft advisory in the west into the evening and the east late tonight. We will likely need to reissue the small craft advisory once again Thursday and continue it until Friday when the winds finally start to diminish again. Otherwise, lake will be quiet for the duration of the weekend. As the upper level low settles in over the area, there will be a chance for waterspouts through the rest of the week. This should begin during the day tomorrow as the showers move into the local area. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...None. PA...None. MARINE...Small Craft Advisory until 3 AM EDT Wednesday for LEZ146>149. Small Craft Advisory until 10 PM EDT this evening for LEZ142>145. && $$ SYNOPSIS...Jamison NEAR TERM...Jamison SHORT TERM...Jamison LONG TERM...Lombardy AVIATION...Oudeman MARINE...DJB/Lombardy is the U.S. government's official web portal to all federal, state and local government web resources and services.