Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 270809 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 409 AM EDT Mon Mar 27 2017 .SHORT TERM...(Today through Tuesday) Issued at 407 AM EDT MON MAR 27 2017 This morning the surface analysis shows a weakening frontal boundary to our west and another surface low across western OK. This weakening surface boundary to the west is having little influences on surface winds or temperatures. The bigger influence on temperatures this morning has been with the breaks in the clouds which is leading to some temperature splits. Also the fog is locally dense which could also be holding back temperatures to an extent. This surface boundary will likely lift north through the day, as more of a warm front if anything. Therefore we remain in the warm airmass across eastern KY today. The locally dense fog is expected to lift through the early morning hours. All eyes turn to the aforementioned surface low in western OK and upper level short wave expected to lift into the midwest through the day. This will induce height falls through the day from west to east across the Ohio and Tennessee Valleys. Also this will induce a LLJ that will creep north today and lead to further lift and moisture. It does look like we will see breaks in the clouds early in the day and this could lead to modestly unstable environment. Cloud cover will also be the caveat as it could rob the potential destabilization. Given the previously mentioned LLJ and increasing winds with height we will have sufficient shear in place across the region for strong storms. The shear is more unidirectional and therefore think storm mode will be more multicell or perhaps line segments. Model soundings do show a EML in the mid levels with better reflection in the 00Z NAM. Given this and dependent on low level lapse rates nearing the 8 C/km through the day will be enough to support marginally severe wind risk. Also the EML, reasonable shear, and low freezing levels at or below 10 KFT will support marginal hail risk as well. Given some of the caveats and climatology think the marginal risk from SPC is reasonable. The best chances of seeing stronger storms right now would be along and west of the I-75 corridor. However, many of the CAMs suggest a line segment could in fact move northeast along and near the I-64 corridor this afternoon. Therefore did increase POPs across that area this afternoon, but This will have to be monitored in subsequent updates. This Surface low is expected to move into the Ohio Valley tonight and overall best lift will come tonight where height falls will be maximized. Therefore did opt to bring the CAT POPs through tonight into the overnight from west to east. POPs will wane through the day on Tuesday, as the upper level wave moves east and front pushes across the region. This wave will dampen out and front will weaken therefore not expecting a big airmass change. .LONG TERM...(Tuesday night through Sunday) Issued at 405 AM EDT MON MAR 27 2017 The models are in decent agreement aloft at the start of the extended portion of the forecast with questions arising quickly by the end of the week as spread increases. They all depict a weakening wave departing to the east of Kentucky early in the period - pushed along by a northern stream trough pivoting through New England. This leaves ridging behind over the Ohio and Tennessee Valleys ahead of a deep trough rolling east through the Southern Plains. Already at this time, though, the models are slightly out of step - the ECMWF further east and north with the core of its trough compared to the GFS and laggard CMC. These differences are steady state through Thursday as the individual models move their trough centers north and east into the Central Plains while ridging slips east of our area and mid level southwest flow commences over Kentucky bringing some energy through by evening. The broad trough will progress into the Ohio Valley on Friday as the GFS hangs back when compared to the more progressive and weaker ECMWF. As this occurs, a general weakening of the trough itself will spread its energy more broadly through the region with its 5h axis passing later that night. Another bout of ridging follows for the weekend over Kentucky while the next broad and deep trough plows its way through the Desert Southwest. With the models still settling into a stable solution will favor a general blend - accepting the broader trend as represented by their consensus. Sensible weather will feature a generally mild to warm period of weather through the extended due to eastern Kentucky finding itself in the midst of ridging aloft and mainly on the warm side of the wx system moving across the region through the rest of the week. While there may be some fluctuation or brief movement south of a cold front to the north of the state on Wednesday, this will occur in an environment of rising heights and climbing low level thickness yielding a mild and near normal day with temperatures hindered more by cloud cover than any advection. Thursday will see warm and increasingly humid conditions as low pressure lifting to the northwest of the area will bring its warm sector over the state along with a threat of showers and thunderstorms. The fairly slow movement of this relatively stacked low will linger the shower and thunderstorm chances for the area through the day Friday, though temperatures will be down a bit from Thursday - but still mild. By Saturday, the low will be well east of the area and result in some CAA on northwest winds for our area as high pressure moves in to dry out the region. This high will gradually moderate through the latter part of the weekend, but readings will not get too far from normal for this time of year. The best chances for any severe weather appears to be Thursday afternoon and evening as the upper system, and its winds, will be stronger than on Friday with more instability available ahead of the system`s occluding cold front. Made some minor - terrain based - changes to lows for most nights of the extended considering the times that appear favorable for inversions and radiational cooling of the sheltered valleys. As for PoPs - did not deviate much from the consensus guidance as it appeared reasonable for the main wx system and its structure passing through from Thursday into Friday night. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) ISSUED AT 122 AM EDT MON MAR 27 2017 Coverage of showers have decreased this hour, but not out of the question that a shower will move over SYM. That said, the upstream ob at IOB stayed VFR based on the obs and therefore opted to keep SYM VFR. Some guidance still suggests a layer of stratocu is not out of the question overnight, but the trend in the guidance has been VFR CIGs. This will be tough to forecast given the scatter holes in the cloud deck seen in the IR SAT. These holes in the clouds will also lead to fog particularly in the valleys and areas that saw rain today. Given the latest guidance did opt to keep the TAF sites VFR for now. Then the challenge will be how much convection develops and where for this afternoon. Right now will add showers and VCTS to all sites at 18Z and some of these will probably linger into the evening. The winds are expected to remain light generally out of the south and southwest through the TAF period. However, any stronger thunderstorm that develop this afternoon could contain gusty winds. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...DJ LONG TERM...GREIF AVIATION...DJ

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