Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/17/17


Area Forecast Discussion
National Weather Service Louisville KY
746 PM EDT Fri Jun 16 2017 .Forecast Update... Issued at 740 PM EDT Fri Jun 16 2017 Made some minor adjustments to fog grids this evening through tomorrow morning based on latest model data. Latest trends seem to indicate that the fog potential may not be as high as previously thought, mainly due to dry air aloft and increasing southwesterly winds around 1kft that could potentially mix down to the surface. Best chances for patchy fog still look to generally south and east of the Bluegrass Parkway. Still planning on keeping the forecast dry for the evening, though am closely monitoring some small potential for very isolated showers/storms in northwestern portions of the CWA in southern Indiana. Some isolated showers and thunderstorms have begun firing off near the KVWX radar within the past hour or so and are slowly drifting toward Dubois/Perry counties. Several outflow boundaries are being picked up by radar/satellite as well. A quick mesoanalysis of the environment reveals 1500-2000 J/Kg MUCAPE across portions of southern Indiana, however, capping is quite strong and should keep a lid on most convective activity. If the isolated activity holds together, it should arrive into Dubois/Perry counties shortly after 02z. Will continue to monitor and update the forecast if it appears activity will hold together into the late evening hours. && .Short Term...(This evening through Saturday night) Issued at 230 PM EDT Fri Jun 16 2017 Latest preliminary GOES-16 derived precipitable water indicates a narrow swatch of dry air over the region, stretching from central Tennessee into Central Kentucky and then northeast to western New York. This area is not moving much today, and AMDAR and current RAP soundings show a subsident airmass in place across much of the region. Thus have generally fair weather cumulus forming out there. Temperatures are warm under the good insolation, with dewpoints in the upper 60s to around 70, so the day is not overly perfect, but typical for mid June. Only other concern then would be chances for fog overnight. A look at the GFS flow aloft indicates a weak disturbance moving through the Midwest to our north tomorrow afternoon, and then another one approaching the region late Saturday night. Precipitable water is expected to increase between now and Saturday night as more moist air pushes against our dry plume. Usually the edges of these dry plumes are where convection gets fired during daytime heating, so the current forecast for isolated to widely scattered pops across southern Indiana seems reasonable, with just isolated chances along the I-65 corridor. Warm temperatures should go for that mostly dry forecast, with highs Saturday reaching the 90s for many locations. Saturday night, the hi-res models, and to a lesser extent the coarser ones, bring in a decaying line of storms ahead of a cold front late. So here again will keep in the higher rain chances over the northwest, southern Indiana, with a gradient into south central Kentucky. Night time lows will depend on how quickly, or if, showers/cold pool get into the region. .Long Term...(Sunday through Friday) Issued at 230 PM EDT Fri Jun 16 2017 The timing of precip Sunday will depend greatly on when/if rains move through here Saturday night. Long-wave troughing aloft will provide some energy for new development, with cold mid-level lapse rates. Any boundary from the late Saturday night development could serve as a focus as well for new development during the afternoon. As for severe risk, the wind profile shows more shear potential than with the last few days worth of convection, especially over the northern half of the area. Temperatures for highs here again will depend on location of these boundaries. One other thing to note, precipitable waters from the models look awfully high, especially given that the GFS/NAM/GEM all would argue for record values for mid June. Still expect at least above average moisture into the region, so heavy rainfall will come with any storms that fall. By Monday, most of the precip should be just over or east of central Kentucky, with the trough axis aloft swinging through here and ridging trying to build in for midweek. Models have been struggling with bringing in (or not) a frontal boundary and rains Tue night/Wed and then beyond that we are back to a series of disturbances moving through the flow making timing best rain chances difficult this far out. Will keep up with the slight chances for Wednesday and limit peak rain chances the rest of the work week to that 20-30 percent range. Monday should be the coolest day of the extended, and then we`ll flip back to above normal by mid week, though again they will depend on what should happen with that midweek system. && .Aviation...(00Z TAF Issuance) Issued at 700 PM EDT Fri Jun 16 2017 Latest guidance beginning to back off on fog development near the LEX/BWG terminals tomorrow morning due to drier air aloft and 10- 15kt southwesterly winds 1kft above the surface with the potential that some of it could mix down. Not completely sold that they will remain fog free tomorrow morning, so will at least include a TEMPO group for MVFR visibilities tomorrow morning. Otherwise, expect some strato-cu to redevelop across the region tomorrow morning and afternoon. Expect most of it to be in the VFR range, but could see some high-end MVFR cigs near BWG briefly tomorrow morning. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...DM Short Term...RJS Long Term...RJS Aviation...DM