Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 160027 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 827 PM EDT Fri Mar 15 2024 .KEY MESSAGES... - Temperatures will remain about 5 to 10 degrees above normal through Saturday night. - A cold front sags south through this evening with lingering showers and any thunderstorms diminishing. - A deep trough passing aloft brings a threat of some rain/snow showers on Monday. - Hard freeze conditions Monday night could kill any cold sensitive vegetation that has emerged prematurely due to early season warmth. && .UPDATE...
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Issued at 827 PM EDT FRI MAR 15 2024 The NBM has trended a degree or two higher with dew point temperature forecasts late tonight into Saturday morning, while also trending toward at least partial clearing toward the pre-dawn hours. Given these two trends, expanded the duration and areal extent of fog for the morning hours Saturday. Otherwise, the only other change was to remove any further mention of thunderstorms from the grids and text forecasts for the remainder of this evening. Hourly observed trends were blended into the forecast as well.
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&& .SHORT TERM...(This evening through Saturday night) Issued at 435 PM EDT FRI MAR 15 2024 Late this afternoon, the axis of a shortwave trough extended from near the Ontario and Quebec border to the Central Great Lakes while a more southern shortwave was moving across the Lower OH Valley region. Further northwest an upper level low was working across Manitoba with an associated shortwave trough to the south toward the US/Canadian border. A sfc low associated with this system was tracking from Manitoba into portions of Ontario with a cold front trialing southwest to near the ND and MT border with Canada. Closer to home, a surface cold front continues to sag south and southeast across eastern KY and was located from near Charleston WV to JKL to Rockcastle County. Showers were most prevalent near and south of this boundary although some showers were located near the front aloft further to the north. Meanwhile, a sfc ridge of high pressure was centered over the Central Plains and extended toward portions of the MS Valley. This evening and tonight, the shortwave moving across the OH Valley will cross eastern KY through tis evening, moving east of the area by late this evening followed by a more moisture starved shortwave overnight. In advance of this, the cold front that is sagging south and southeast across eastern KY should sag into VA and TN by mid to late this evening with the sfc ridge of high pressure building east into the OH Valley behind it. The axis of this ridge of high pressure will sag south of eastern KY through the day on Saturday. This will occur in advance of the upper low moving from Manitoba into Ontario and the trailing shortwave trough working across the upper MS Valley and into the Great Lakes region and the associated cold front that should drop southeast of the western and central Great Lakes through the day on Saturday. The upper low is progged to move to Quebec through the end of the period while the trailing shortwave trough rotates across the Great Lakes and into the OH Valley. This will help push the cold front across the Commonwealth on Saturday night. A much colder airmass than what has been experienced recently will arrive behind the front as the period end with 850 mb temperatures forecast to drop to the 0C to 5C range at that point with further cooling and cold air advection continuing into the start of the long term period. Limited instability remains across the region at present with MUCAPE analyzed in the the 100 to 250 J/kg range with effective shear in the 20 to 25 KT range though these values will be diminishing over the next few hours. Lighting has not been detected across the region so far this afternoon, however, with the limited instability remaining, an isolated storm or too cannot be ruled out ahead of the boundary. However, mainly just showers are expected with chances diminishing from northwest to southeast through this evening. Precipitation free weather will follow for the balance of the near term period. Although the airmass behind the front crossing the region at this time will cooler than what was experienced earlier this week, temperatures will remain a few degrees above normal, by about five degrees through Saturday. Mild weather will above normal temperatures will persist into Saturday night ahead of the secondary boundary. .LONG TERM...(Sunday through Friday) Issued at 447 PM EDT FRI MAR 15 2024 The 15/12z model suite is in reasonably good synoptic agreement Sunday morning but does show some deterioration, especially after Wednesday. On Sunday morning, a broad and deep upper level low will be found over Eastern Canada, dipping down into the Great Lakes. A moisture-starved cold front front, originating from an ~995 surface low over southern Quebec, is seeping southeastward along the periphery of the aforementioned upper level trough into the Ohio Valley where there is near zonal flow aloft. Additionally, a prominent 500H vorticity lobe extends from the vicinity of the surface low over Southern Quebec through the southern Great Lakes to the Upper Midwest/Manitoba where a potent shortwave trough will be traversing the periphery of the parent upper level trough. Meanwhile, an ~556 dam closed low is spinning atop Arizona. The cold front will slip south of eastern Kentucky during the day on Sunday, while heights aloft start to subside in advance of the shortwave trough diving southeast from the Upper Midwest. A busy west northwest breeze will advect drier air in through the day, leading to falling dew points (values in the 20s can be expected for many by Sunday evening). BUFKIT GFS mixed-layer momentum transfer values support gusts in the 15 to 20 mph range around peak heating. Meanwhile, cold air advection will keep the day`s highs muted, primarily in the mid 50s north of I-64 to the mid 60s in the deepest valleys near the Virginia border. No measurable precipitation is expected with the front; rather, just anticipate a period of more abundant cloud cover. The upper level shortwave trough (and attendant vort lobe) will carve deeply into the Ohio Valley on Sunday night through Monday Night as it rides around the base of its parent trough. Uncertainty remains as to how much moisture will be available to this system, which may be dependent, at least in part, on how much moistening of the air mass occurs over the Great Lakes. The 12z NAM12 solution falls on the moist side of guidance with more than ample moisture for deep convection and equilibrium levels above -20C. Such a scenario combined with 850 mb temperatures falling to around -10C would lead to the potential for squally snow showers with the possibility for lightning. Conversely, the Canadian and ECWMF soundings are much drier and would support little more than some patchy cloud cover and perhaps some light flurries. A 20 to 30 PoP was maintained across most of eastern Kentucky to account for this potential and can be trended up or down depending upon whether the moister or drier solutions prevail. Regardless, Monday`s temperatures will be cold with highs ranging in the upper 30s to lower 40s for most locations -- a far cry from what we have experienced this week. Those chilly temperatures will be compounded by a cold northwesterly breeze which could gusts to between 20 and 25 mph. Monday night is shaping up to be the coldest night of the period with lows easily in the 20s. Lows in the teens cannot be ruled out for colder locations if skies are able to clear early in the night. Looking ahead to Tuesday, the low level flow will quickly turn more westerly ahead of a second, albeit weaker, upper level shortwave trough riding around the parent upper level trough. This system tracks slightly further to the east than the previous shortwave, but will drop another cold front into eastern Kentucky from the north or northeast on Tuesday night or Wednesday morning. While a sprinkle or flurry cannot be ruled out with the boundary, no measurable precipitation is forecast. Ahead of the front, temperatures will make a quick rebound on Tuesday back to between 50 and 55 for most locations. The core of the chillier air with the second front will only brush our area and will likely be felt more as a reinforcing shot of drier air rather than the return of a colder air mass (due to modification by the strong spring sunshine). Thus expect temperatures to to warm several degrees further in the mid 50s to lower 60s on Wednesday with a subsequent ridge-valley split of 27 to 40 on Wednesday night. Later in the week, forecaster confidence drops as model solutions diverge with respect to the closed low initially over the Desert Southwest and possible interaction with a northern stream shortwave trough coming ashore the Pacific Coast. In most cases, a low pressure system is depicted to develop and pass through the eastern CONUS, though the track remains highly uncertain. Therefore, the NBM forecast was retained for Thursday and Friday and shows PoPs increasing to likely levels while temperatures rise back to near or above normal levels. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) ISSUED AT 733 PM EDT FRI MAR 15 2024 A mix of IFR and MVFR cigs will prevail through ~06z with light north to northwest winds, with skies undergoing partial clearing thereafter generally from north to south. Assuming partial clearing occurs before sunrise, which looks increasingly probable, fog development with a deterioration to LIFR or lower is likely at most if not all TAF sites. Fog will burn off around 13z-14z Saturday morning, with VFR conditions prevailing thereafter. The light north to northwest winds will decouple later tonight, with a light west to southwest wind developing Saturday afternoon. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...CMC SHORT TERM...JP LONG TERM...GEERTSON AVIATION...CMC

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