Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 180107 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 907 PM EDT Sat Jun 17 2017 .SYNOPSIS... It will be warm and humid overnight as southerly flow continues. A cold front will move east across the Great Lakes and Ohio Valley Sunday into Sunday night, resulting in showers and thunderstorms. Cooler, but near normal conditions, will return behind the front for the beginning of the work week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Shearing MCV that is now crossing into Ohio from Indiana caused a brief uptick in showers across eastern IND into NW Ohio but this activity is on the wane as the MCV continues to deamplify and it further elongates. Attention of course turns to expanding convection over IL/IA/MO and trying to decide what coverage/impacts this convection will have later on in the night for the WFO ILN CWA. 18.00Z sounding from KILN was modestly unstable /SBCAPE to 1700 J/kg/ albeit with very weak shear /effective shears below 20kts/. Lapse rates aloft were weak...an underwhelming severe weather sounding for late June. However...upstream /KILX/ sounding had decidedly stronger mid level flow and thus effective shear with similar instability...and storms per radar mosaics in IL showing some structure/organization as forced ascent increases there amidst shortwave trough energy. Up until about 22Z...just about every stormscale model run from the past 12 hours had shown current IA/IL activity would split with a line segment across northern IND/southern MI, and a much beefier segment sinking southeast along the ribbon of extreme instby well to our SW. However...more recent HRRR runs have shown a little stronger/deeper push of convection into west central Ohio after 2 AM with the northern line segment...so there is still concern for an isolated strong/severe threat in this area overnight. Confidence...however...is very low on how this all materializes through the night considering increased forced ascent and flow battling instby toward the bottom of the diurnal cycle. Any strong/severe threat would be wind-based, as low level shear remains generally weak and instby likely not robust enough to support large hail. Forecast update focused on generally adding detail to rain chances and timing...focusing a higher chance across west central ohio in the 2-4 AM timeframe /could be a stronger storm here/. Then general increases in rain chances over the rest of the west 1/3 of the CWA very late in the night as the northeastern fringe of the southern line may attempt to move into southeast Indiana/nrn KY/swrn OH after 4 or 5 AM. This not likely to be strong/severe.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... On Sunday, the cold front will move east/southeast into our area. Convection allowing models suggest that showers/storms may first develop near the frontal boundary across our west by early afternoon, followed by perhaps another area in a prefrontal convergence region over our east. As such, have likely PoPs for showers/storms west, with categorical PoPs for the eastern zones. Best instability will be over the east, with at least moderate deep layer shear expected. This will provide the possibility for storms to become strong/severe. Again, best threat for severe storms is poised for our eastern zones. Damaging winds will be the main severe weather threat with the possibility of isolated large hail. With pwat values approaching 2 inches (150-175% of normal for mid June), locally heavy rain will be a concern along with subsequent flooding issues. Will mention all these threats in the HWO. Synoptic scale winds will pick up due to diurnal mixing and a tightening pressure gradient. Highs will range from the lower 80s west to the mid/upper 80s east. For Sunday night, the front will make its way east/southeast, and should be just about out of the area by 12Z Monday. Likely/categorical PoPs should push east/southeast during the evening, followed by a lingering chance of showers for the main overnight hours. Lows will range from the lower 60s northwest to the upper 60s southeast. && .LONG TERM /MONDAY THROUGH SATURDAY/... At the onset of the forecast period, a cold front will be east of and moving away from the forecast area, with just a slight chance of a lingering shower in the southeast at daybreak. Upper level trough digs in behind the surface front and some instability showers appear to be in the offing for the afternoon, particularly along the I-70 corridor closer to the "cooler" air aloft. The air behind the front will be nicely cooler and right at or just below seasonal normals through about Wednesday night. The best part of this particular forecast is dewpoints in the upper 50s to around 60 through this time, increasing late next week as surface flow turns southerly and the upper level flow becomes more zonal. With the increasing surface moisture, southwest flow, and higher propensity for disturbances to be passing over the region in the zonal upper flow, precipitation chances increase accordingly. This may begin as early as Wednesday night as a warm front appears to be noted in the European model. Beyond this, a broad-brush approach was used to denote the higher chances for thunderstorm potential. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... Showers associated with a weakening/shearing mesoscale convective vortex over eastern Indiana will remain north/west of the terminals this evening. Just some brief mid cloud under some thin cirrus for the next 6-9 hours. Later tonight...after about 06Z...confidence deteriorates with regards to how upstream convection over Iowa/Illinois moves and how it holds together. Latest storm scale models are inconsistent on whether terminals see any thunderstorms in the 06Z-12Z timeframe. Continued to play a dry forecast through 12Z based on the amalgam of data, with VFR conditions continuing. Should convection hold together, most likely impacted terminal would be KDAY with some MVFR restrictions and some gusty winds. On Sunday morning...approach of cold front should act to thicken clouds/lower cigs somewhat while showers/storms begin to develop and increase in coverage/intensity. Bulk of activity is expected in the afternoon hours and given high available moisture a direct hit by a thunderstorm core would almost certainly bring IFR vsby/cigs for a brief time, but with confidence low on specific timing, but high on coverage of showers/storms, will go with prevailing showers and VCTS with MVFR restrictions. Front will swing east by early evening bringing an end to any showers/storms. Winds tonight will remain above 8kts in most locations as southwesterly flow maintains ahead of approaching cold front. Gusty swly winds to continue on Sunday in advance of the front, with 20+kt gusts likely at all sites immediately ahead of the front. OUTLOOK...Thunderstorms moving out Sunday night. Thunderstorms are possible again Tuesday night into Wednesday, and again Thursday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hickman NEAR TERM...Binau/Hickman SHORT TERM...Binau/Hickman LONG TERM...Franks AVIATION...Binau

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