####018007766#### FXUS64 KHUN 041512 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1012 AM CDT Sat May 4 2024 ...New NEAR TERM... .NEAR TERM... (Rest of Today) Issued at 1011 AM CDT Sat May 4 2024 Temperatures are currently in the upper 60s to lower 70s primarily. A good deal of cloud cover is in place over portions of Jackson and DeKalb counties and also from Limestone into Colbert counties. In between, a substantial amount of sunshine is in place. Precipitation is mainly confined to near a weak surface low that currently is in place over north central Georgia. The forcing with this feature should remain far enough to the east to keep it from producing activity in our area. One additional area of scattered showers is also present in central Tennessee that is associated with a weak upper level trough axis extending southwest from a weak low at 700 mb over southern Indiana. Expect this to be the main driver of additional showers and possible thunderstorms this afternoon into the early evening hours. However, models don't really move this trough axis much to the south this afternoon, so confidence in even scattered coverage has lessened near and south of the Tennessee River overall. The exception to this could be northeastern Alabama into portions of southern middle Tennessee, where a higher chance (30 to 50 percent) may occur this evening, as a diurnal heating boundary sets up from north to south through the area. We should see cloudy conditions return fairly quickly towards into the early afternoon hours over much of the area, except maybe portions of Cullman county and further south. Lowered temperatures overall today given current temperatures and expected cloud cover through the day. Highs should make it into the lower 80s in locations that are currently seeing more sunshine (mainly near and south of the Tennessee River). Elsewhere, expect highs to be cooler, only reaching the mid to upper 70s. && .SHORT TERM... (Tonight through Monday night) Issued at 418 AM CDT Sat May 4 2024 The general synoptic pattern across the TN Valley will remain largely unchanged tonight and Sunday, with light/moist southerly flow expected to persist in the low-levels beneath a zonal flow regime aloft. There are some indications that another weak mid- level vort max (perhaps convectively-induced) may track eastward across our region late this evening, and with some agreement from the 00Z CAMs on an increase in convection, we have included a low- medium chance POP between 3-9Z. This activity will in all likelihood exit the region prior to sunrise on Sunday, with a warm/humid but dry start to the day followed by development of isolated afternoon showers and storms as temps rise into the m-u 80s. Over the course of the day tomorrow, another shortwave trough is predicted to lift northeastward from the Red River Valley of OK/TX within the flow around a strong upper low tracking east- northeastward from the Great Basin into the central Rockies. Due to the motion of the upper low, a well-defined lee cyclone will evolve across eastern MT throughout the day, forcing a warm front to spread northeastward across the TN Valley late Sunday night/early Monday morning. Deep lift generated by the warm front and approaching shortwave trough will produce a fairly widespread coverage of rain and storms that may begin across our western zones as early as 00Z Monday before spreading further northeastward. Although mid-level winds will back to SW and increase to 15-25 knots preceding the arrival of the trough, shear does not appear strong enough at this point to warrant concern for organized storm structures. Most NWP guidance suggests that the effective warm front will lie across the OH Valley by 12Z Monday, with remnants of nocturnal precipitation expected to spread northeastward and out of the region during the late morning. A 500-mb shortwave ridge to the east of the upper low (discussed in the paragraph above) will translate across the region, yielding a lower but non-zero coverage of showers and storms Monday afternoon and night. Low- level SW flow will strengthen in the wake of the warm front, with dewpoints expected to rise into the u60s-l70s. && .LONG TERM... (Tuesday through Friday) Issued at 418 AM CDT Sat May 4 2024 Latest long range guidance from the global models suggests that the presence of a mid-level ridge will continue to limit the coverage of warm sector showers and thunderstorms across the TN Valley on Tuesday, with a breezy, warm and humid day expected as highs rise into the m-u 80s. However, by Tuesday night, we will need to keep a close eye on thunderstorm activity to our northwest that should develop along a Pacific cold front/dryline that will surge eastward ahead of an occluding cyclone across eastern MT/western ND. There are some indications that frontal convection across southern portions of MO/IL may evolve into a broken MCS Tuesday evening that could potentially track southeastward into the local area early Wednesday morning and may feature a risk for strong-severe storms as mid-level westerly flow will likely increase to 35-40 knots prior to its arrival in our region. However, a more reasonable scenario is that the initial MCS will not reach our region due to the development of another weak area of low pressure across the southern High Plains that should eject northeastward into MO by Wednesday evening. In this case, redevelopment of thunderstorms would occur along the path of the surface low (across MO) early Wednesday afternoon that could potentially grow upscale into a larger and more significant MCS that would reach our region late Wednesday night/early Thursday morning. This convective system would be entering an environment of even stronger deep-layer shear (with WSW flow aloft of 45-50 knots) and moderate-high levels of instability driven by surface dewpoints in the lower 70s beneath a plume of steep lapse rates aloft. Thus, a notable risk of severe thunderstorms producing large hail and damaging winds may materialize during this timeframe. A third and final round of storms may occur on Thursday night/Friday morning prior to the eventual passage of a cold front that should bring a drier/cooler airmass into the region by next weekend. && .AVIATION... (12Z TAFS) Issued at 559 AM CDT Sat May 4 2024 The remnants of nocturnal rain/storms continue to spread eastward and out of northern AL early this morning, with clearing mid- level clouds across the western half of the area supporting development of patchy, locally dense fog in a few locations. We will indicate IFR conditions in a 1-hr long TEMPO group for MSL and MVFR conditions at HSV, where brief development of BR/FG could occur thru 13Z. Diurnal warming of the moist boundary layer will encourage development of a sct-bkn Cu field by 16Z, but coverage of afternoon showers/storms appears too low to include in the TAFs attm. However, a slightly greater coverage of convection may occur btwn 3-9Z, which is when a weak mid-level disturbance will track eastward across the TN Valley. Outside of convection, light SSW winds and mostly clear skies may allow for the development of patchy BR/FG once again early Sunday morning. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...KTW SHORT TERM....70 LONG TERM....70 AVIATION...70 ####018007893#### FXUS63 KJKL 041512 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1112 AM EDT Sat May 4 2024 .KEY MESSAGES... - Shower and thunderstorm potential lasts through the next 7 days. - Above normal temperatures are forecast through most of the next week. A cold front should pass late in the week and bring readings down to near or below normal. && .UPDATE... Issued at 1112 AM EDT SAT MAY 4 2024 A short wave trough is currently rotating through the region. The best coverage of convection has been across far southeastern Kentucky, with more widely scattered shower activity popping up further northwest. Forecast soundings do not reveal much of a cap this afternoon, and even with the exit of this short wave trough early this afternoon, 500 mb heights are still dipping later, as we still remain in a broad trough. As such, have adjusted PoPs mainly for the next few hours, attempting to capture the radar trends a bit better. There should be an uptick once again through peak heating, although coverage should be mainly scattered, with more modest forcing and instability in place. High temperatures in the mid to upper 70s look on target, although did lower these a bit across far southeastern Kentucky, given the better convective coverage and cloud cover in place. Updates have been sent. UPDATE Issued at 855 AM EDT SAT MAY 4 2024 Issued an update primarily to get forecast grids in tolerance with neighboring offices. Otherwise, the current forecast for this morning looks satisfactory. UPDATE Issued at 700 AM EDT SAT MAY 4 2024 The forecast overall is looking pretty good early this morning. Isolated showers and storms area moving through portions of the area, per the current forecast, and should gradually increase in coverage through out the day, especially this afternoon during peak heating. The latest obs were used to establish new trends in the forecast grids, but as mentioned earlier, things are in pretty good shape so far. The pre-first period that was included with the 4 am forecast package will need to be removed in an hour or so, but until then, things should be good as is. && .SHORT TERM...(Today through Sunday) Issued at 449 AM EDT SAT MAY 4 2024 Isolated rain showers were ongoing at time of forecast issuance early this morning, and were beginning to slowly increase in coverage, especially north of the Mountain Parkway. This trend is expected to continue through sunrise this morning. Once the sun is up, isolated to scattered showers are expected to fire across eastern Kentucky. The primary challenge in the short term portion of the forecast will be how widespread will showers and storms become today. To answer that question, the latest model data was consulted and revealed that in spite of ample moisture and instability being in place, the lack of a clear cut triggering mechanism will limit shower and storm coverage today. With several models all supporting this scenario, the HRRR, NAMNEST, and CAMS in particular, it made sense to go with much lower precip chances for today than previously forecast. The same scenario looks reasonable for Sunday as well. The 6Z analysis showed a stationary front in place from the eastern Great Lakes into southwestern Indiana and then across Missouri where it merged with a surface low situated over southeastern Nebraska. A weak trough of low pressure was also analyzed over central Kentucky, just south of the Ohio River, but due to the weakness of this feature, it appears it will not offer enough lift to spark widespread convection today. Instead, it looks like todays showers and storms will be diurnally driven, and will peak in coverage this afternoon into early this evening, before quickly tapering off after dark, when instability will also quickly wane. Another frontal boundary extended southwestward through Kansas into far western Oklahoma and then further west out to Nevada. A well defined dry line was also in place extended southward from a surface over the Oklahoma pan handle through eastern New Mexico and across extreme western Texas. This set of boundaries and surface lows will be the focus for severe weather across the southern Plains later today. Temperatures will continue to run above normal over the weekend, with todays highs maxing out in the upper 70s, and Sundays max readings in the upper 70s and lower 80s. Tonights lows should fall to around 60, with only minimal ridge valley differences due to extensive cloud cover and little radiational cooling expected. No significant weather concerns are expected at this time, with only garden variety thunderstorms on tap today and tomorrow. Winds should be generally from the south or southwest and 5 to 10kts today and tomorrow, and light and variable tonight. .LONG TERM...(Sunday night through Friday) Issued at 449 AM EDT SAT MAY 4 2024 The long term period continues to look wet. Prevailing large scale flow aloft will be persistent from the west southwest through at least Thursday, while low level flow is out of the southwest off the gulf. This pattern of warm/moist advection will favor precip whenever there are triggers/forcing mechanisms. A wavering frontal boundary will approach from the northwest at times, but being largely parallel to the upper level flow until near the end of the period it is not likely to make a forceful passage until then. This will leave us in a modestly humid air mass with surface dew points mainly in the lower to mid 60s. The main drivers for precip will be mid/upper level waves along with diurnal heating/destabilization cycles. The mid/upper level waves with the most agreement in the models are ones that would affect us on Monday, and also Wednesday night into Thursday, and these time frames contain the highest POP area wide at mainly 70%+. There are some model discrepancies in the Thursday-Friday time frame concerning timing of an eventual cold frontal passage. In the 00Z deterministic/operational runs, the GFS is faster than the ECMWF with the passage of the primary cold front, and this results in lower forecast confidence. The current forecast is a model blend, but temperatures are likely to end up being either warmer or colder, depending on timing of cold fropa. Also, a faster fropa would result in the POP dropping off faster, and a slower passage would allow precip to linger longer. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) ISSUED AT 700 AM EDT SAT MAY 4 2024 MVFR CIGs at SME and SYM to begin the 12Z forecast period, with JKL, LOZ, and SJS holding at VFR. Isolated showers and storms were moving through the area at TAF issuance. These will continue to gradually increase in coverage through out the day, especially this afternoon and early this evening during peak heating and instability. The rain is not expected to be widespread, but enough showers and storms will be around to warrant VCTS mention at each TAF airport later today into early this evening. Winds will be generally from the south or southwest at 5 to 10 kts today and light and variable overnight. MVFR fog could affect that TAF sites toward the end of the TAF period due to any rainfall that is received at those locations, but confidence is not high at this time. Brief periods of IFR could also occur at any TAF site during a thunderstorm, but outside of that, MVFR or VFR will be most common. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GEOGERIAN SHORT TERM...AR LONG TERM...HAL AVIATION...AR