Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/28/17

Area Forecast Discussion
National Weather Service Wilmington OH
750 PM EDT Fri Oct 27 2017 .SYNOPSIS... A cold front will move through the region today, with rain and cooling temperatures coming in behind it. After the precipitation ends on Saturday morning, much cooler conditions will be in place over the weekend and into early next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Adjusted temperatures downward by a bit this evening as readings below 40 were eking into Indiana counties ahead of schedule by several hours. This is likely due to the rain falling and cooling the column in short order to a moist adiabatic profile. The rain will take its time in moving through the CWA and get a push in the late overnight period to clear out from west to east by daybreak over much of the area. The cooler temperatures had me change the mixed ptype timing as well, given that the inclusion of snow as a mixed precip occurred at and below 37 degrees for this forecast. Previous in-depth discussion still valid and speaks to the core of the development of the overnight forecast: The basics of the forecast are straightforward -- a gradual spreading of PoPs from west to east, with 100-percent chances of precipitation for every grid point in the forecast area. Winds shift to the WNW (and may remain slightly gusty for a while) along with a steep drop in temperatures that will continue into the overnight hours. Though precipitation amounts of several tenths of an inch (over a half inch in the SW ILN CWA) are possible, heavy rain is not expected. One thing that is notable is that the front is forecast to slow and lose some definition as the night progresses, which is likely one reason why precipitation amounts should be heavier further to the west. Two wrinkles to the forecast involve the potential for wintry precipitation. There have been several spots with enhanced radar echoes over Indiana today, along with a few reports of sleet mixing in with the rain. Looking at HRRR soundings, there does appear to be a narrow cool layer at around 925mb that will slowly advect west along with the greatest ascent. Though said ascent may be gradually weakening with time, and thus this part of the forecast is not of the highest confidence, there does appear to be a chance for some sleet to mix in during the late evening / early overnight hours, primarily in the western half of the forecast area. Nothing beyond a nuisance accumulation is expected. The second concern is the possibility of a change to snow on the back side of the band of precipitation. PoPs were adjusted carefully based on 12Z WRF-ARW/WRF-NMM projections, in order to keep the cut-off timing as sharp as possible. Nonetheless, temperatures should be dropping into the 30s before this occurs, at least where temperatures will be coldest in the western half of the ILN CWA. This has forced the inclusion of a rain/snow mix in the final hour or two in which precipitation will be possible. The most likely scenario will be for most locations to not receive any accumulations from this mix. However, even along the back edge of the precipitation, there may be some slightly heavier waves -- recent HRRR and RAP runs have indicated this. Thus, it appears possible that there could be some isolated tenth-or-two accumulations (if the warm antecedent conditions do not melt everything that falls). Another cause for uncertainty, though, is that sounding profiles may be somewhat isothermal -- which could keep hydrometeors just on the warm side of the freezing mark as they fall. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... The surface cold front will be east of the ILN CWA by Saturday morning, but precipitation (likely a little lighter than during the overnight hours) will still be ongoing (possibly with a brief mix with snow on the back edge, as discussed earlier). The cut-off will continue moving west to east during the morning, with virtually the entire CWA dry by noon or just after. Cold advection will be the story for the rest of Saturday, with enough cold air moving in to steepen lapse rates and develop low stratocumulus clouds across much of the forecast area (though there could be some breaks in the sky conditions in the first few hours behind the precipitation). Highs will thus be unlikely to get any higher than the mid 40s, and lows Saturday night will be within a degree or two on either side of the freezing mark. The area of the coldest air at 850mb will be moving over the ILN CWA at around 12Z Sunday morning. As lapse rates continue to be steep, even overnight, there will be a chance of flurries (possibly some light rain or sprinkles) late in the overnight and into Sunday morning. Only trace amounts are expected either way. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Deep H5 trof will located over the Ohio Valley at 12Z Sunday. H8 caa and a flow off Lake Michigan should combine with the upper support to produce a few sprinkles or flurries Sunday morning. Temperatures will remain well below normal on Sunday with highs only in the mid to upper 40s. The upper low lifts and fills Sunday night. With the clouds breaking, lows could fall to or below freezing. The H5 flow goes zonal and the models continue to struggle to find consensus on the forecast for Monday. All the extended models swing a H5 vort through Monday, but their timing and placement are all different. Will continue to go dry on Monday. Temperatures will moderate, with highs reaching the lower to mid 50s. A high pressure system builds in for Tuesday with high temperatures remaining in the lower 50s, but then another H5 trof swings out of the MS valley and brings a chance of rain for late Tuesday night into Wednesday. Lows Wednesday morning will be around freezing in Central Ohio, so there could be some mixed pcpn for the morning commute. The rain overspreads the region on Wednesday, then pcpn chances linger for the rest of the forecast period, as broad sly flow at the sfc keep moisture working north. Temperatures should be warm enuf during the period for the pcpn to be all rain. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Have seen a few IFR cigs and jumped the gun on this phenomenon for the better part of the overnight period with this area of rain. While cigs may drop this low, vsbys are hanging tough in the VFR category early this evening. Tried to time the onset of rain a little better in CMH/LCK and felt the need to linger pops a little longer into the morning hours than previous forecast had. Expect a scattering of cloud cover after the precip ends later tonight, then to go bkn-ovc in the late morning given the cold pool overtop of the region, right between 2-3kft. Will maintain a watch on the progression of the area of rain and hopefully clear the western edge a little earlier overnight, even as the latest forecast delayed this feature given most models had solid area of QPF still found along the I-75 corridor at 12z. OUTLOOK...MVFR ceilings may continue through Sunday morning. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Franks/Hatzos SHORT TERM...Hatzos LONG TERM...Sites AVIATION...Franks
Area Forecast Discussion
National Weather Service Louisville KY
1200 AM EDT Sat Oct 28 2017 .Forecast Update... Issued at 1159 PM EDT Fri Oct 27 2017 The LVX radar tonight shows a very sharp back edge to the precipitation with portions of southern IN and far west central KY dry. However, regional radar does show another light area of precipitation further back to the west. Pops were adjusted to taper them more quickly across the northwest portion of the forecast area, but have not removed them completely due to the returns showing up to the west. No snow reports have been seen yet, but there is still a brief window where we could see some flakes. Other than the pop update, only minor tweaks were made to the forecast. Issued at 855 PM EDT Fri Oct 27 2017 Surface cold front has just pushed through LEX, with mild temps giving way to cold rain within the last hour. Temps along and west of the I-65 corridor have already dropped into the upper 30s/lower 40s, and we expect that cold air to continue to overspread central Kentucky through late evening. Still a brief window overnight where the soundings show deep enough saturation and low-level temps are just cool enough to get a few snowflakes to the ground, but the soil temps are much too warm for any accumulation other than on grassy or elevated surfaces. Previous forecast has a good handle on these trends, so no update planned beyond tweaking hourly details. && .Short Term...(This evening through Saturday night) Issued at 310 PM EDT Fri Oct 27 2017 Surface cold front currently is bisecting the forecast area this afternoon. The front was located just east of the I-65 corridor. The edge of the colder airmass is not too far behind it, lagging about 30-40 miles or so. Out ahead of the front, southerly winds have allowed temperatures to spike into the upper 60s to the lower 70s. With cloud cover rapidly increasing across the region, high temperatures in the east will be met shortly, while temperatures across central and western KY will continue to fall throughout the afternoon. Regional radars show an increase in shower activity. Scattered showers continue to blossom across western TN and these will move northeastward into the Bowling Green area in the next few hours. Post frontal band of precipitation extends from near Indianapolis southwestward to Memphis. This band should expand a bit as it moves eastward into our region later this afternoon. As we head into the evening and overnight hours, the cold front will continue to plow on off to the east and colder air will advance into the region from the west. Short term high resolution model data continues to show increasing deep-layer forcing over the region. This is in response to a jet streak rotating through the upper Ohio Valley. The jet streak looks to stretch out and develop into to distinct jets, one over the Great Lakes, and one over the northern TN valley. This would place much of southern IN and central KY in the left entrance region of the Great Lakes jet, while also in the right exit region of the northern TN valley jet. With the jets stretching out, mass evacuation looks to be fairly efficient aloft, resulting in upward motion. The thermal gradient will also tighten resulting in stronger frontogenetical forcing. The combination of these forcing features support an increase in shower activity this evening. Some moderate to heavy rainfall is likely as these features push through and a solid 0.50-1.0 inch of rainfall looks possible through early Saturday morning. As we move into the overnight period, forecast becomes a bit more complicated as influx of colder air pushes in from the west and makes an attempt to catch up to the back edge of the precipitation shield. The NAM solutions have been the most aggressive with this over the past few days, while the more coarse GFS has been slightly warmer with its profiles. This is still the case this afternoon with the latest data, though the higher res 3km NAM and HRRR solutions keep the colder air a little more confined to the north. Current indications are that we`ll see the column cool overnight for the back edge of the precipitation to mix with snow and possibly end as a period of snow. The best chances for this to occur will be along and west of the US 127 corridor, mainly over southern IN and portions of north-central KY. The switchover looks to be late tonight, probably after 2-3 AM and will linger through around sunrise. Further east, toward the I-75 corridor, thermal profiles have trended a little warmer during the overnight hours and really do not cool sufficiently until after sunrise, when most of the precipitation will be exiting the region. With that said, our overall forecast has not changed all that much. We believe that we could see a slushy accumulation of snow in some areas...mainly along and just east of the I-65 corridor. Combination of warm ground temperatures and surface temperatures above freezing look to result in little if any impacts. Lows tonight will range from the lower 30s over SW In with middle 30s over our central and eastern sections. For Saturday, precipitation will quickly move eastward during the morning hours. Current thinking is that we`ll get dry slotted for a while in the morning allowing some sunshine. However, steep lapse rates and a little heating will quickly lead to a strato-cu field developing during the afternoon. Highs of 40-45 look attainable across SE IN down into the Bluegrass region. Highs in the 45-50 degree range look possible in areas west of I-65. For Saturday night, cold cyclonic flow is expected across the region. It appears that we`ll have some low cloudiness persist in the NW flow across our northeastern half of the CWA. A few snow flurries probably will fall out of those clouds. Further west, clearing skies will allow temperatures to fall and patchy frost will be possible out in areas west of I-65. Lows look to cool down into the 32-37 degree range. .Long Term...(Sunday through Friday) Issued at 330 PM EDT Fri Oct 27 2017 Sunday through Tuesday Night... Upper trough axis will start to pull east and lift away from the area. Skies will start off partly to mostly cloudy and then partially clear throughout the day. Temperatures will remain below normal with highs in the mid-upper 40s across our eastern sections with upper 40s to around 50 in the west. Dry conditions look likely as we head into Sunday night. Though, some mid-high level cloudiness may start to streak in from the west/northwest. In addition, a light southerly wind looks to return and that may keep temperatures warmer than previously forecast. As of now, we plan on going with lows in the lower to middle 30s. Will probably see some frost, and a few sheltered valleys could see a light freeze. Heading into Monday, a large scale trough axis looks to remain centered just to our west. The flow will be mainly zonal across our region and a sheared out perturbation within the main flow will cross the area. Moisture is just not all that impressive, but enough will be around for some mid-high level cloudiness and perhaps a few sprinkles here and there. This feature will shift eastward Monday night with quiet weather continuing into Tuesday. Clouds will increase Tuesday night however as the next weather system to our south and west takes aim at the region. Highs Monday look to warm into the lower-mid 50s in the north with upper 50s to around 60 in the south. Lows Monday night look to cool into the mid 30s. Highs on Tuesday will warm into the lower 50s in the north with mid- upper 50s across southern KY. Current forecast suggests that dry conditions are expected for trick or treaters Tuesday evening. Temperatures will likely be in the 40s across the region and overnight lows will dip to around 40 or so before rising toward morning. Wednesday through Friday... Broad upper level troughing is expected to be in place across the central US on Wednesday as a large ridge builds across the central Pacific into Alaska. A disturbance will move out of the southern Plains and streak across the Ohio Valley on Wednesday bringing rounds of showers. As we move into Thursday and Friday, mid-level heights are expected to build across the southeastern US and SW Atlantic. As this occurs, the ridge over the Pacific and into Alaska looks to grow and eventually experience a wave break of sorts. This will end up helping significant troughing off the western US coast. For the Ohio Valley, a broad southwest flow will remain in place aloft with several weak perturbations streaking through. In general, the sensible weather pattern can be classified as unsettled with chances of showers and possibly a few storms on Thursday and into Friday. There is some signaling that the flow may flatten out a bit by Friday allowing some cooler air to push back into the region. Model cross sections show a bit shallow depth cold air dropping southward, while low-level wind fields remain southwest to west. So for now have backed off temps slightly for Friday with highs mainly in the lower 60s in the north with middle 60s down south. Beyond Friday and into Week Two... Hemispheric pattern looks to remain fairly active as we go into the first weekend of November. Upper air pattern is likely to see a deep trough off the California coast with a general ridge pattern over the southeastern US. A broad W/WSW flow will be seen across the Ohio Valley with the main storm track located to our north. A few perturbations within the flow will bring episodic bouts of precipitation to the region. While temperatures look to remain generally above seasonal averages, brief warm ups prior and cool downs after perturbation passages will be seen. The cold looks to be centered mostly across the northern High Plains with the warm concentrated along the Gulf Coast and into the SE US. Organic techniques along with updated signal analysis suggest the hemispheric pattern will amplify a bit as we head into the second weekend of November. There are hints of another pattern shift around that time which could spell a period of volatile weather in the central US spreading eastward into the Ohio Valley (roughly in the 11/14-17 time frame). && .Aviation...(00Z TAF Issuance) Issued at 705 PM EDT Fri Oct 27 2017 Strong cold front pushing through central Kentucky, and now just on the doorstep of LEX. Will be a close call initializing wind there, but other terminals are already around to NW or even NNW. Rain shield now making slow progress, and by 01-02Z should have all terminals into fuel-alternate ceilings with TEMPO IFR cig/vis expected for much of the night. Could see a few snowflakes flying after midnight, mainly at SDF and LEX, but probability is too low to mention in the TAF. Conditions will improve fairly quickly Sat morning as a dry slot scours out some of the low clouds. Only exception is LEX, which will stay in precip through midday, and not recover to VFR until mid/late afternoon. Winds will be light out of the NW. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...EER/RAS Short Term...MJ Long Term....MJ Aviation...RAS