Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 220006 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 706 PM EST Sun Jan 21 2018 .SYNOPSIS... Southerly flow will keep warm air and a chance of rain in the region tonight. On Monday, a cold front will swing up the Ohio Valley, pushing a better chance of rain showers across the region during the afternoon and evening. A quick shot of light snow will be possible on Tuesday. A weak upper level disturbance will offer a slight chance of a snow shower Wednesday. High pressure will then offer dry conditions through the end of the week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Mid/upper level low to move through the central plains tonight. As this occurs the mid level flow over the Ohio Valley will continue to back with e-w oriented sfc warm front shifting north into the southern Great Lakes this evening. Low level moisture to remain in place with low clouds through most of the night. As better mixing comes into play expect some improvement to low clouds mainly over the southeast. Will diminish pops over the southeast of the FA late tonight. Mild temperatures to continue wit lows from the lower 40s northwest to the mid 40s Southeast. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Mid/upper level low and deepening surface low to eject northeast from the plains into the upper MS VLY Monday and the Great Lakes Monday night into Tuesday. In the warm sector the morning to start out dry with increasing chances for pcpn as forcing associated with 60kt low level jet comes into play during the afternoon. Will ramp up pops to categorical across the west early in the afternoon and then shift east into the early evening. Thin ribbon of very marginal instby develops into far southern counties ahead of the front. A rumble of thunder is not out of the question but due to limited chances/coverage have not mentioned in forecast at this time. On the warm side of the system, temperatures look to be close to 20 degrees above normal with highs Monday from the lower 50s northwest to the mid 60s southeast. Cold front to sweep east across the region Monday evening with dry slot working into the area. Pcpn will diminish and then re- develop late as wrap around associated with mid/upr level low develops. Have kept all pcpn rain through the night based on thermal profiles. Expect lows from the upper 30s northwest to near 40 southeast. && .LONG TERM /TUESDAY THROUGH SUNDAY/... On Tuesday morning, nearly-stacked low pressure will be centered over the lower peninsula of Michigan -- with the surface low expected to be a little further north than the mid-level low. The weather pattern will remain very amplified as this system moves ENE, but on the back side of the low, flow is expected to be pseudo-zonal rather than meridional. At the surface, an early-Tuesday-AM cold front will be well ahead of the longitudinal position of the surface flow. Thus, flow behind the front going into Tuesday morning will exhibit a wind shift, but only veering to the WSW by morning. As cold advection continues on this flow through the day, wind directions will gradually veer from WSW to WNW. This cold advection will lead to temperatures that struggle to warm on Tuesday, especially in the northwestern half of the forecast area -- where nearly steady temperatures are forecast. Some warming is a little more likely in the southern and southeastern sections of the ILN CWA, and max temps were actually raised slightly for these locations. In either case, the cold advection will still be a far cry from what was experienced behind cold fronts that passed through in previous weeks. Overall, max temps will actually be very close to -- or even slightly above -- normal (middle 30s to lower 40s) for Tuesday. In terms of precipitation for Tuesday, after a break behind the cold front, forcing associated with the mid-level low center and enhanced low-level RH will combine with some deeper mixing to allow for showers to develop across the southern Great Lakes and northern Ohio Valley. PoPs with this have been left mostly unchanged as the forecast appears to be on track, with 60 percent chances in the northern CWA dropping to 20 percent chances in the southern CWA. At some point, temperatures will cool enough to allow for rain showers to switch to snow showers. With some differences in how the models are handling the amount of saturation in the boundary layer, the timing of the switch from rain to snow is somewhat uncertain. Not a big deal either way, as accumulations beyond a few tenths appear unlikely. Finally, but far from least important, is the issue of wind on Tuesday. The pressure gradient associated with the low will be relatively strong, and mixing will allow some higher winds to be tapped -- as opposed to the more isothermal sounding profiles expected for Monday. Gusts have been increased slightly again, topping out a few knots on either side of 30, with the highest values in the northern ILN CWA. Behind the Tuesday system, the coldest air aloft will be moving through the area on Wednesday morning. This sets up Wednesday as the coolest day of the week, especially as surface winds will remain neutrally-advecting at best, and the cloud forecast has become more pessimistic. In fact, beyond just clouds, models have come in with a band of jet-induced precipitation (likely in the form of light snow if it occurs) moving somewhere through the Ohio Valley during the day. Would like to see more persistence and placement consistency before doing too much with this, but will add a 20-PoP for now. Broad surface high pressure will move east into the area later on Wednesday and into the second half of the week, as the upper pattern gradually switches from troughing to ridging over the eastern half of the CONUS. This will bring dry conditions and gradually warming temperatures through Friday. Behind the departing surface high, and with troughing developing over the plains, moist flow from the Gulf is expected to move into the Ohio Valley again over the weekend. Overall model agreement in this pattern remains strong across several GFS/ECMWF runs, though GFS ensemble plots suggest the depth/timing of the upstream trough is perhaps a source of inconsistency in exact timing and placement details for the incoming rainfall. So, without getting into specifics that far out, conditions appear warmer than normal with rain expected -- with a cold front eventually cooling things off at the tail end of the long term forecast period going into Monday. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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Our region will continue to be influenced by a southerly flow pattern well ahead of a weather system moving east across the Central Plains tonight. Models are still indicating that low level moisture in the form of mainly MVFR ceilings will lift north overnight as the flow begins to buckle ahead of the weather system to our west. Any shower activity in the WAA pattern should be spotty and early on, followed by a return to VFR conditions. A strong low level jet will develop overnight as well, encroaching from the west. This has prompted the mention of non-convective LLWS in the terminals. On Monday, surface low pressure will rotate east/northeast toward the mid Mississippi River Valley and the Western Great Lakes through the day. Ahead of the low and its attendant cold front, a plume of moisture in a focused area of low level convergence will spread showers from west to east across the terminals between 18Z and 00Z. VFR conditions will drop to MVFR in showers. Some pockets of IFR ceilings can not be ruled out. In addition, surface winds will increase from the south and will become gusty up to 25 knots. Non-convective LLWS should wane by 19Z as the shear differential between 2000 feet and the surface decreases. For Monday night, low pressure will move east/northeast across the Great Lakes. A cold front will push east across the terminals between 00Z and 06Z Monday. Precipitation will taper off behind frontal passage, with the likelihood of VFR conditions developing in the dry slot right behind the front. OUTLOOK...MVFR ceilings likely Tuesday with possible MVFR visbilities. MVFR ceilings may linger into Wednesday.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...AR NEAR TERM...AR SHORT TERM...AR LONG TERM...Hatzos AVIATION...Hickman

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