Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 171801 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 101 PM EST Sun Dec 17 2017 .SYNOPSIS... Weak weather disturbances crossing the Ohio Valley today and tomorrow will bring clouds and a little rain or drizzle to much of the area as temperatures remain mild in the 40s. While clouds will likely hang on into Tuesday, temperatures will warm into the 50s ahead of the next weak cold front which will slip through the area rather quietly on Tuesday evening. This front will bring cooler temperatures and a little sunshine for Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Water vapor satellite imagery shows shortwave over mid MS Vly this morning. This s/w will eject northeast and run into the mean ridge position over the region and deamplify and shear out. Forcing will be weak and airmass is starting out rather dry. Expect to see a good deal of virga on the radar with a light rain event developing this afternoon. Will continue to have pops ramp up to likely where band of light rain is expected to develop generally along and south of the I-70, once the column saturates later this afternoon. Have used a blended approach for temperatures with MAV guidance appearing too high given light rain and clouds. Generally expect highs of 40 to 45 degrees today. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... Wave departs this evening with scattered light rain quickly ending but clouds continuing to thicken/lower as weak warm advection on swly boundary layer flow continues in the wake of the wave. In fact, forecast soundings suggest low level moisture will continue to deepen past 2km this evening as next subtle ripple in midlevel height field approaches. Combination of weak vertical motion in/above this deeper low level moisture field will induce patches/areas of drizzle and fog, particularly later tonight into much of Monday. Introduced a PoP for measurable drizzle or even very fine/light rain given maintenance of low level moisture field in excess of 1.5km into Monday evening. With saturated surface temp/dewpoint traces, think the temp curves will be muted on both Monday afternoon and Monday night, so tightened those up considerably. Monday night may not see any fall, and despite current forecast indicating steady temps overnight or perhaps dropping a degree, would not be at all surprised if temps Monday night actually went up a degree or two given most recent data trends. Bottom line - the Monday and Monday night periods will see plenty of stratus, light fog, and patches/areas of drizzle - most of which will diminish with time through Monday night. On Tuesday, height falls dropping through the northern Great Lakes will allow a weak cold front to slip toward the area. Continued southwesterly low level flow will allow temperatures to respond into the 50s, particularly with a few breaks of sunshine possible on Tuesday afternoon, though still expect mostly cloudy skies with any breaks confined to the later part of the afternoon. Front slips through quietly /dry/ on Tuesday evening with modest low-level cold advection signal and temps back below freezing Tuesday night. Wednesday will feature high pressure moving directly over the area with good subsidence/drying which should allow for more sunshine although it will be cooler, with highs back in the lower 40s. Will need to watch southern stream shortwave trough/surface low coming out of the southern branch of the western CONUS split flow regime. Bulk of deterministic/ensemble data has taken this system and its rain shield south of the area, though enough members grazing nrn KY with a bit of light rain to keep an eye on this system into mid-week. && .LONG TERM /THURSDAY THROUGH SATURDAY/... While Thursday is a relatively high confidence dry forecast as high pressure pulls away into New England and a large upper trough advances eastward from the central Plains, confidence in this portion of the forecast degrades very quickly. GEFS/EPS plumes continue to indicate a tremendous amount of spread in the details despite a slowly increasing signal of a cold front/low pressure shifting through the Great Lakes Friday afternoon through Saturday morning. There`s a great deal of variety in the timing of the front, orientation of the boundary, and whether a frontal wave will form on the boundary or a dominant surface low will deepen through the Great Lakes and swing the cold front through with much more brute force. There`s solutions ranging from a very potent surface low developing through WI/MI which allows highs on Friday well into the 50s with nearly similar dewpoints, and then a strong frontal surge with hints of CAPE and need for thunder consideration. Other solutions continue to be seen of a much slower/strung out frontal passing that takes far longer and entrains very deep moisture from the Gulf of Mexico, and hints at a heavy rain/flooding threat Friday night into Saturday. Still further, there have been members/runs showing a rain-to- wet snow scenario for Friday night/Saturday morning, or a band of rain passing quietly through and then the front clearing for a quiet/dry Saturday. Just not seeing any ensemble movement to a preferred solution, so will hit rain chances highest on Friday night, with a trend to cooler temperatures for Saturday and perhaps some rain/snow mix or brief wet snow. Given ensemble spread that exceeds the natural variability, continue to expect a very low confidence forecast in this time period for a few more days. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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Mid level shortwave to weaken as it moves through the Ohio Valley this afternoon into this evening. This combined with a relatively dry airmass in the low levels will lead to VFR CIGs around 5000 feet with areas of light rain. This mid level shortwave to move off to the east this evening with rain ending.Increasing low level moisture will result in MVFR and then IFR CIGs late with patchy drizzle. These low CIGs will be slow to improve Monday morning. OUTLOOK...MVFR/IFR ceilings and MVFR visibilities possible Monday evening.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Binau NEAR TERM...Binau/AR SHORT TERM...Binau LONG TERM...Binau AVIATION...AR

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