Area Forecast Discussion
Issued by NWS Wilmington, OH

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463 FXUS61 KILN 251051 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 651 AM EDT Sun Aug 25 2019 .SYNOPSIS... Surface high pressure will drift away from the region today with moisture increasing from the south by late tonight. Widespread showers are expected Monday with precipitation chances lingering through Tuesday. Drier and cooler conditions are expected past midweek. && .NEAR TERM /THROUGH TONIGHT/... Tranquil weather will once again persist through the entirety of the near term period, with seasonably warm temperatures expected for the day today. Highs will generally top out in the low/mid 80s. Surface high pressure centered over the eastern Great Lakes will drift further away from the Ohio Valley through the day as the mid/upper level ridge axis traverses the region as well. This will initiate stronger moisture advection into the area -- initially only in the upper levels in the form of denser/thicker cirrus which will gradually overspreads the local area from the south and west throughout the day. Any precipitation chances will hold off until later tonight. && .SHORT TERM /MONDAY/... Although the near term period will be a quiet one, the same cannot be said about the short term period. Past midnight tonight, the nosing of a seasonably modest LLJ (courtesy of 850mb-925mb winds of about 30kts) will allow for a tremendous moisture transport to evolve into initially the southern and western third or so of the ILN FA through the heart of the overnight period. During this time period, PWATS will go from about 1" to nearly 2" in only an 8-10 hour period (especially for the Tri-State area). This will initially manifest itself in an increase in cloud cover, with progressively lower and lower CIGs to move in from the southwest in the predawn hours on Monday. The rapid saturation of the profile, in conjunction with midlevel energy progressing northeast from the Tennessee Valley to the Ohio Valley, will allow for widespread showers to overspread the ILN FA Monday morning into the afternoon. While an isolated rumble of thunder cannot be completely ruled out, the poor lapse rates and nearly saturated profile will likely keep thunder limited -- even during the typical diurnally- favored time period in the afternoon. Have seen an uptick trend in precipitation coverage and amounts in several deterministic and ensemble solutions for the Monday time period (with the operational GFS on the lower end of the GEFS QPF envelope) -- so have increased PoPs and QPF accordingly to trend toward a more widespread rain event. The onset of precipitation will likely be occurring before daybreak across parts of northern Kentucky and perhaps extreme southeastern Indiana into southwestern Ohio. There are some subtle timing differences in the various solutions regarding exactly how quickly the precipitation moves in and how fast the initially drier profile is able to be overcome. Nevertheless, will see widespread showers overspreading the local area through Monday morning and afternoon -- with indications of amounts between 0.50"-1.0" very likely near and west of the I-75 corridor into parts of north-central KY by Monday evening. The heaviest and most widespread activity will initially be focused across the Tri-State area before progressing north/east through the day. Rainfall amounts are likely to taper somewhat from SW to NE -- with parts of central OH more likely to see around 0.25-0.50" through the day (specifically afternoon/evening for these locations). With the overspreading of thicker cirrus and cloud cover by late tonight, will see generally warmer temperatures than has been the case the past several overnight periods as lows only bottom out in the low to mid 60s from NE to SW. Highs on Monday will be held considerably below seasonal norms with the expectation for thick cloud cover and widespread showers throughout nearly the entire daytime period for some spots. Temps will top out in the lows 70s (SW/W) to the mid/upper 70s (NE/E). Although a gradual tapering off of the precipitation is expected toward Monday evening, will likely see some scattered showers linger in parts of the ILN FA even through Monday night before a cold front approaches with renewed precipitation chances Tuesday afternoon/evening. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... A broad upper level trough will remain across the Great Lakes region through much of the week. Mid level short wave energy will rotate through the base of the trough Monday night into Tuesday, helping to push an associated cold front east across the Ohio Valley. This will lead to an increasing chance of showers through the day on Tuesday. Instability will be fairly marginal, but with increasing wind fields through the day, will allow for at least a chance for some embedded thunderstorms. Highs on Tuesday will be in the upper 70s to lower 80s. Drier air will try to move in behind the front Tuesday night but some additional mid level short wave energy will pivot across the region through the day on Wednesday. This may be enough to produce a few showers through the day but think the wetter GFS may be overdone. Will therefore maintain a dry forecast for Wednesday at this time. Highs on Wednesday will again be in the upper 70s to lower 80s. Surface high pressure will build east across the Ohio Valley Thursday into Friday. This will result in dry conditions. A weakening frontal boundary will push south into the region Friday night into Saturday, leading to a slight chance of showers. Temperatures through the remainder of the long term period will remain slightly below normal with highs in the mid 70s to lower 80s for Thursday through Saturday. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... Other than a few passing cirrus, mainly clear skies are expected through the morning hours. A FEW VFR Cu may again develop/expand this afternoon as thicker cirrus gradually overspreads the region from the southwest through the day. Between 06z-12z, a tremendous increase in deep layer moisture will allow for rapid saturation of the profile progressively from southwest to northeast early Monday morning. This will occur coincident with a shield of SHRA fcst to move north into the southern Ohio Valley by daybreak. As of right now, this is only included in the KCVG and KLUK fcsts late in the period. Expect IFR CIGs and potentially MVFR VSBYs to overspread the southern terminals through Monday morning before these restrictions spread further north/east through the afternoon hours. With a nearly saturated profile developing in the low levels, do think that CIGs between 800-1200ft will evolve for at least brief stretches Monday morning (in a several hour period after 12z) -- especially for KCVG, KLUK, and potentially even KDAY. Light northeasterly winds will go more easterly later today but remain generally 10kts or less. A shift to more east- southeasterly will evolve tonight before relaxing somewhat and going more southeasterly Monday morning. OUTLOOK...IFR CIGs possible Monday. Thunderstorms are possible on Monday and Tuesday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...KC NEAR TERM...KC SHORT TERM...KC LONG TERM...JGL AVIATION...KC

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