area forecast discussion National Weather Service Louisville Kentucky 125 PM EDT sun may 19 2013 ..updated aviation discussion... Forecast update... issued at 1145 am EDT sun may 19 2013 Convection this morning across south-central Kentucky was on the northern side of a weak warm frontal boundary. These storms produced quite a bit of lightning, very heavy rain, and small hail. Activity is diminishing with outflow moving in all directions away from the old convective complex. Can see the outflow on radar and satellite heading north toward the Ohio River. This may trigger new development. However, an upper-level ridge axis and associated capping is moving in from the west-northwest. This is evident in the capping of cumulus across portions of western Kentucky. This will continue to push east through the day. With this in mind, believe the best chance for any additional isolated to scattered convection will be across south-central Kentucky northeastward through the Blue Grass, where capping aloft is less. Made a few adjustments to near-term forecast to align with observations and blend with the afternoon forecast, which looks on track. && Short term (now - monday)... issued at 258 am EDT sun may 19 2013 The upper level low that has helped plague the area with scattered showers and a few storms over the weekend is now located over southeast Kentucky. Meanwhile, a weak warm frontal boundary is situated from central MO to central Tennessee. This brings the boundary across western Kentucky where some scattered to broken mid level clouds reside. There are also some very light returns that are resulting in sprinkles at best near the surface. Models have been depicting light quantitative precipitation forecast with this boundary for several days, however think that even the light quantitative precipitation forecast is overdone and may go with just some scattered sprinkles through the morning hours across the southwest cwa, into the central County Warning Area. Otherwise, expect a dry morning. Will have to continue to monitor fog development, with some locally dense spots possible. A few obs have gone down to a half mile at times already. Do think that the scattered to broken upper level clouds will Hurt fog potential some as we near dawn, so will only mention in the severe weather potential statement unless conditions warrant a more significant product. The upper low is forecast to wobble over eastern Kentucky today while an upper level ridge axis builds over central and western portions of the state. A nice subsidence inversion looks to accompany this ridge as evidenced on forecast soundings across the western two thirds of the County Warning Area by afternoon. Therefore, will only keep iso-scattered (30%) pops in the eastern County Warning Area this afternoon where ridge does not build in until tonight. Will go dry across western portions of the state as any potential precipitation with the warm front should be shunted by the inversion. Will see partly to mostly cloudy skies by afternoon as diurnally driven cu develop, however will see a warm up. Look for low to mid 80s west and around 80 east. Any lingering showers or storms will die off with the loss of heating this evening. Upper ridge will hold over the area keeping things dry. A light southerly flow will encompass the area which should keep temps mild so only expecting lows in the mid and upper 60s. Also think the noticeable gradient winds will keep fog formation potential in check. Upper ridge axis will hold through the day on Monday as well, continuing to keep the County Warning Area dry. Will see a continued increase in temperatures as 850 mb temps in Jump Up around 18 c with only partly cloudy skies and steady south-southwest wind. Will go nearer the slightly cooler NAM guidance in the mid and upper 80s. Mav guidance is going with upper 80s and low 90s in many spots, but with the amount of greenery, recent rainfall, and at least scattered cu, hard to imagine we will get that warm. Just an interesting note, a high in the low 90s at sdf on Monday would put the record of 91 (1934) in jeopardy. Right now the forecast calls for 89. Stay tuned. Long term (monday night - saturday)... issued at 257 am EDT sun may 19 2013 A stacked upper low over the mid-Missouri Valley at the start of the long term will slowly drift to the east to the Great Lakes by Thursday morning and then get absorbed into a deep upper trof sweeping through southeast Canada. Correspondingly at the surface, low pressure will advance from South Dakota to Michigan, pulling its cold front through the Ohio Valley sometime Thursday or Thursday evening. Meanwhile, a large dome of high pressure over the Atlantic will Pump Gulf of Mexico warmth and moisture northward ahead of the approaching storm system. The result will be unseasonably warm, muggy conditions with shower and thunderstorm chances. Although the best chances for severe storms on Tuesday will remain to our west, we could still see some strong pulsers here in the afternoon or evening. A few strong storms will again be possible on Wednesday as the plains system approaches. Total totals and sweat numbers are actually higher on Tuesday, likely due in part to steeper mid level lapse rates. Progged surface instability is also stronger on Tuesday. However on Wednesday there will be better upper level divergence along with a 500 mb speed Max and stronger 850hpa winds as well. Wednesday also should have higher 1000-850 rh, which could serve as moisture to fuel storms but may also cause greater cloud cover and, as a result, decreased insolation and less surface based instability. Canadian high pressure will invade from the north Friday/Saturday, bringing much drier and cooler air to the region. Tuesday will be the warmest day of the long term with afternoon readings peaking in the middle and upper 80s. Greater relative humidity and shower coverage on Wednesday should limit high temperatures to around 80. Thursday through Saturday we'll enjoy highs in the 70s. && Aviation (18z taf issuance)... issued at 125 PM EDT sun may 19 2013 A weak upper low continues to meander around east Kentucky today, with a weak frontal boundary across the Tennessee Valley. These two disturbances will provide focus for isolated to scattered showers and storms through the afternoon. Will continue with just scattered shower coverage around Lex with isolated thunder. VFR conditions will prevail through the afternoon and evening hours with a steady south-southwest wind between 5 and 10 mph. Fog may become a concern again once again tonight. However, surface winds are expected to stay up a bit, which could limit fog, particularly dense fog, production. && Lmk watches/warnings/advisories... in...none. Kentucky...none. $$ Update...........mjp short term.......bjs long term........13 aviation.........Mjp