Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 220653 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 253 AM EDT Sat Apr 22 2017 .SYNOPSIS... As an area of upper level low pressure moves into the southeastern states, cool conditions are expected over the Ohio Valley today, warming slightly on Sunday. A continued warming trend is expected going into the new week, with drier and sunnier conditions on Monday and Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... An initial wave of precipitation, extending south-to-north across the entire ILN forecast area, is currently working its way east -- soon to exit the region. The intense bright banding radar echoes (50+ dBZ) are proven by observations not be representative of any significant precipitation. However, PoPs will need to be kept high in the eastern CWA for the next hour or two. Surface observations indicate that the slowly-southward-moving surface front is already most of the way through Kentucky, with the ILN CWA in a regime of cool NE flow from the surface through about 850mb. At 700mb, there is still a wave yet to come through, with some warmer and moister air yet to pass south of the region. As this wave moves through, and the 700mb boundary shifts south, additional precipitation is expected to spread into the southern third of the ILN CWA between 10Z-15Z. The northern extent of the precipitation shield (as forecast by recent HRRR runs) matches nicely with this 700mb feature, with precipitation expected roughly from Ripley County IN through Hocking County OH -- and potentially some heavier pockets in the southern one or two tiers of ILN counties. There will be a significant lack of moisture as the day progresses, with subsidence expected to become prevailing on the north side of the lumbering mid-level low moving into the southeastern states. With surface high pressure moving into the southern Great Lakes, a gradual shift toward less cloudy conditions is expected from NW to SE, clearing about halfway through the ILN CWA -- resulting in a gradient in sky cover from Portsmouth OH (mostly cloudy) to Celina OH (mostly clear) by evening. With the lack of precipitation further north, max temps will actually be flipped from their usual north-to-south orientation -- mid 50s in the northern CWA and lower 50s in the southern CWA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Elongated surface high pressure is expected to position itself from Iowa to Lake Erie tonight, as surface low pressure begins to develop in the deep south. A gradient will thus exist between very different air masses -- warmer and wetter in the southern Appalachians, and cool and dry in the northern Ohio Valley and southern Great Lakes. Outside of the chance of a few light showers in the far southern ILN CWA, most of the forecast area should be well within the drier air mass, with clearing skies tonight. Persistent NE flow will keep radiational cooling conditions from becoming ideal, limiting the chances for frost, even as temperatures may get close to 40 degrees by Sunday morning. This pattern will change very little on Sunday, as the main driver of the scenario -- the mid-level low in the southeastern states -- will not be moving very fast. By Sunday afternoon, there may be just enough 850mb-700mb moisture wrapping NW/W into the forecast area to allow for a few showers in the southeastern third of the CWA. That will present another day with an unusual temperature gradient, as temperatures will likely be warmest in the NW CWA, where mostly clear conditions are expected. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Upper level low will slowly move southeast from the Tennessee River Valley to the southeast United States coastline Sunday night into Monday. As this occurs, the threat for showers will end across the southeast CWFA while clearing takes place there as well. More sunshine and airmass modification will boost temperatures into the upper 60s to the lower 70s on Monday, which isn`t too far from normal. For the period Monday night into Tuesday, upper level low will push northeast near the coastline of the Carolinas. We will see weak high pressure across our region. With another day of airmass modification and developing southerly flow, highs will warm into the mid and upper 70s. For the period Tuesday night into Wednesday night, weak ridging shifts east, along a frontal system to push east/southeast through the region. This will bring the next chance of showers and thunderstorms. Thursday may end up being dry in the wake of the front. However, the frontal boundary is expected to lift north as a warm front Thursday night into Friday as upper level flow begins to amplify. This will bring another chance of showers and thunderstorms, particularly for western locations. Discrepancies occur in the long range models as we head into Friday. The ECMWF wants to push another frontal system into the region while the GFS dries the Ohio Valley out in the wake of the warm front. It does not bring the next frontal system into the region until next Saturday. Have decided to keep forecast dry given stark differences. Temperatures will be warm by the end of the week with lower to mid 80s forecast. && .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/... One area of rain is currently moving east through the TAF sites, though conditions have generally remained VFR. This rain will mostly clear the area over the next few hours, leaving the northern TAF sites dry. Another chance of rain is expected for KCVG/KLUK after 11Z, and some MVFR ceilings may be possible before or during the rain. However, overall, flight conditions are not expected to deteriorate significantly. With drier conditions in the forecast for the rest of the TAF sites, this represents a change in the previous forecast, as it now looks like most of the second area of rain will remain south of KDAY/KCMH/KLCK. Once the rain has passed, some VFR mid clouds will likely persist. Winds are expected to be out of the NE through the period, sustained at around 10 knots, with gusts up to around 20 knots at times. OUTLOOK...No significant weather expected. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Hatzos LONG TERM...Hickman AVIATION...Hatzos

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