Information is from the NWS Wilmington, OH Office

ILN Area Forecast Discussion/SKEW-T

FXUS61 KILN 211434

Area Forecast Discussion
National Weather Service Wilmington OH
1034 AM EDT Mon Aug 21 2017

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Weak disturbances in the upper flow will bring a chance of thunderstorms to northern Ohio today. A cold front will bring more organized showers and thunderstorms on Tuesday, then drier and cooler air moves in for the rest of the week.
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Latest runs of the models continue to suggest that vort maxs in the zonal H5 flow will act as the catalyst for convection across nrn IN/OH this afternoon. Tweaked the onset of the timing by an hour here or there, but still left the best PoP chances across West Central Ohio with lesser chances as you head south. Cloud develop today could hinder the eclipse viewing, but right now don`t expect a thick overcast deck. Adjusted the temperatures down a degree or two due to the eclipse and adjusted the hourly temperature trace.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... This evening, convection or decaying showers from the afternoon will start to come to an end as daytime heating is lost. Tonight a potent upper level system over the Hudson Bay will begin to wrap up into an upper level low and head south. Mid and upper level flow will quickly start to amplify as the newly formed low pushes southeast. Ahead of the main upper level system a wedge of PV will swing east helping to get showers and thunderstorms going Tuesday afternoon. SFC to 6 km bulk shear values at this time are around 40 kts (slightly higher on the NAM and slightly lower on the GFS). ML CAPE values on the GFS are only around 700 J/kg while the NAM has values approaching 2000 J/kg. Looking more in depth at forecast soundings reveals why. The GFS clearly shows a cirrus shield inhibiting the area from fully destabilizing. Also at this time the cold front has yet to enter our CWA. Therefore convection will be dependent on destabilization as surface convergence from the front will come later. Not surprisingly SPC has therefore kept the area in a slight risk given supportive bulk shear vectors and questionable instability. The primary threat still looks to be damaging winds (possibly some type of broken line forming). && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Showers and thunderstorms will linger into Tuesday evening, especially across southeast portions of our forecast area. However, as the cold front pushes off to our southeast and drier air begins to filter in behind the front, expect pcpn to taper off from the northwest as we head into Tuesday night. Surface high pressure will build down across the Great Lakes through the rest of the week. This will lead to mainly dry and cooler conditions. However, some mid and upper level short wave energy dropping down across the Great lakes on Thursday could lead to a few showers, especially across northeast portions of our area. Temperatures through the end of the week will be several degrees below normal with highs in the 70s and overnight lows in the 50s. We will start to get into some return flow through the weekend, leading to a slight warmup by the end of the long term period. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... Convection has fallen apart as it has moved into the area this morning with only some lingering low cigs at KLUK. This afternoon high res models then indicate showers and thunderstorms possibly forming across our northwestern zones along the nose of a weak LLJ. The RAP, HRRR, WRF DART, and NMM show convection in some form or fashion while the NSSL WRF and NAM 3 km are dry. For now have just added a VCSH for KDAY due to uncertainty in formation. Tuesday morning into afternoon more showers and thunderstorms will be possible ahead of an approaching cold front. OUTLOOK...Thunderstorms are likely Tuesday into Tuesday evening. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Haines NEAR TERM... SHORT TERM...Haines LONG TERM...JGL AVIATION...Haines

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