Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/01/20

Area Forecast Discussion
National Weather Service Des Moines IA
638 PM CDT Tue Jun 30 2020 ...Updated for 00z Aviation Discussion... .DISCUSSION.../Tonight through Tuesday/ Issued at 301 PM CDT Tue Jun 30 2020 Synoptic Overview: Main features of interest over the next 36 hours are the short-wave perturbation moving up the Mississippi River Valley and deep trough becoming negatively titled over the Rockies. At the surface there is a broad low pressure system centered over Kansas and Nebraska. Influence of the pressure gradient from this does extend into Iowa, leaving most of the upper Midwest in a southerly flow regime. There is not a pronounced warm front with this system, but there is a stronger cold front trailing it that can be seen in the temperature and dewpoint analysis. Overnight an MCS developed in front of the nose of the low-level jet in conjunction with the short-wave producing torrential rainfall over eastern Missouri and wester Illinois. Now that the low-level jet has weakened, this feature has stalled but still continues to produce the torrential rainfall. Today and Tomorrow: With relatively weak H5 flow over the mid and upper Mississippi River Valley this morning and afternoon, the short-wave perturbation will stall and behave like a closed-low, which will leave stagnant rain shower activity over western Illinois and eastern Missouri, and parts of southeast Iowa. A few CAM solutions do depict some back building of the convection into the Davis and Wapello counties, the extreme southeast portion of the forecast area. The heaviest rainfall for Iowa will look to be in the Keokuk and Burlington area. Rainfall rates in our southeast area will need to be monitored closely if more convection develops and stalls in our southeast counties. However, radar trends over the past few hours have not been showing an increase convection, and actually has dwindled considerably in our southeast. Most guidance solutions do not bring the precipitation associated with this short-wave and MCS much further west of U.S. Highway 63. However, interaction with the larger trough out west has complicated the forecast for the rest of the day, late this evening and overnight. The trough is what will eventually help to increase the flow across the upper Midwest and eventually progress the MCS north and east, but not before it causes problems in areas surrounding the Mississippi River. Strong PV anomaly that has been sitting over the western CONUS the past few days is now starting to propagate across the Rocky Mountain region. The deep H5 trough has developed a negative tilt in the past 12-18 hours, and has sent a stronger shot of CVA into the High Plains and Central Plains late this morning and has allowed for further deepening of the surface cyclone. As the the 50-60 kt jet at H5 rounds the base, the vort max and bulk of the CVA will eject into the northern Plains this afternoon and evening, lifting the trough northward into the southern Canadian Provinces. However, the height falls from this propagation now appear to be extending further eastward, and will clip far western and northwestern portions of the forecast area late this evening. As a result, the convection potential that yesterday looked to remain in eastern Nebraska and Dakotas will now have potential to work its way through Iowa late tonight. As the trough lifts, the associated surface low develops a bifurcation point, with a secondary surface low developing in the Dakotas and lifting northward with the parent trough, as the southern end of slides eastward and breaks away from it. While it will not be as stagnant as this morning`s short-wave and subsequent MCS, the surface low propagation will slow. Convergence will increase as it crosses into Iowa along with the trailing cold front. CAM guidance has convection entering Iowa after 06z this evening. The HRRR appears to to be depicting the most robust convection, concentrating a stronger convective cluster moving eastward from Sioux City toward Fort Dodge, and then diving southeastward. Other CAM solutions are bit weaker and more widespread with convection along the cold front. Instability will not be hard to come by. HREF mean during the afternoon ahead of the convergent zone characterizes the warm moist airmass with SBCAPE values between 3500 and 4500 J/kg, and maintains MUCAPE values in western Iowa over 2000 J/kg late into the evening and overnight hours. For surface parcels though will have over -150 J/kg of CIN that it will need battle, MU will only have to battle -50 to -70 J/kg of CIN. There may some struggle to initiate new updrafts at times, but the surface low and cold front likely will provide extra forcing needed to beat this. The wind shear, or lack there of, will be the main component that largely hinders the severe potential. 0-6 km bulk shear values in most model solutions struggle to reach 20 kts this afternoon and evening ahead of the boundary. With the weak shear environment, it is interesting how this morning`s HRRR cycles depicted a somewhat organized convective cluster. Perhaps if a stronger cold pool develops this may provide better support to a convective cluster. But, the overall parameter space of the environment does not support a highly organized system. Model soundings this evening do depict DCAPE values in excess of 1000 J/kg, which certainly could foster the development of a few downbursts with convection that perhaps produce isolated severe wind gusts. The bigger concern this evening could perhaps be heavy rainfall, especially with any convection coming from the west that meets up with stagnant MCS. Overnight and through Wednesday morning, GFS and NAM depict warm cloud depths between 3500-4000m, with PWATs pushing 1.75 to 1.90 across most of central Iowa. While this system is expected to move at a faster speed than the MCS over the mid Mississippi River Valley, a new convective complex may still not be overly progressive. HREF mean QPF is about 1-1.75 inches across western, southwestern, and southern Iowa in the next 12-18 hours. A few individual CAM members of the HREF have 2-3 inches on the high side. In this environment, amounts this high are possible in localized areas. However, as mentioned above regarding concerns about thunderstorm potential, there will be CIN that updrafts will have to fight. If robust convection fails to initiate, and storms quickly become stratiform on the backside of the low and cold front, rainfall amounts could be less. For rainfall totals, this is currently the source of greatest uncertainty. Flash Flood guidance across most of the area with high QPF is 2.75 - 3.00 inches in 6 hours. Given HREF mean QPF and uncertainty associated with convection, have decided to hold off from issuing a Flash Flood Watch for counties in our area. If flash flooding does occur, it will likely be very localized. If there is an upward trend in the precipitation forecast in the next few hours, a short fused watch may be needed. Overall, the bulk of the area in the highest QPF will be able to handle a decent amount of rain. Should robust rain showers and thunderstorms hold up to the southeastern extent of the forecast area (Wapello and Davis Counties), there could be additional issues there. Over the last few hours though, Davis and Wapello Counties have not had any rain accumulations, which is helpful in reducing the flooding threat. Extended: Beginning Thursday afternoon, amplified thermal ridge develops across the central Plains and into the mid Mississippi River Valley. Low- level flow will remain southerly, brining in hot humid gulf air. This will likely make for oppressive heat over the holiday weekend, with heat indices pushing the mid to upper 90s. There will not be any major forcing through the weekend, but air mass thundershowers are certainly possible given the theta-e rich air that will be in place across the region. At this time, it looks like the heat will stay just below headline criteria through the weekend. Beyond the official forecast period, more heat is in the forecast and could become problematic. && .AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/ Issued at 638 PM CDT Tue Jun 30 2020 Primary concerns this TAF cycle will be thunderstorms and associated restrictions. Plenty of high level clouds remain over Iowa with FEW/SCT ceilings below FL030 in some places. There could be intermittent MVFR at the central Iowa airports this evening, but went prevailing VFR. Thunderstorms are just beginning to develop over central Nebraska and will move into central Iowa after midnight into Wednesday morning. Highest chances of impacts would be at DSM and OTM with storms perhaps just brushing FOD. For MCW and ALO, thunderstorms may end up missing these terminals and removed from ALO this cycle and may do the same for MCW next cycle. After storms pass through, conditions should improve from north to south through the day back into VFR. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION...Krull AVIATION...Ansorge
National Weather Service Kansas City/Pleasant Hill MO
641 PM CDT Tue Jun 30 2020 .Discussion... Issued at 326 PM CDT TUE JUN 30 2020 The MCV that moved through Missouri overnight is now centered over northwest Illinois this afternoon and is slowly weakening as it moves into northern Illinois towards the southern tip of Lake Michigan. Scattered showers and thunderstorms have accompanied this MCV and the cold pool has helped to reinforce an outflow boundary that is generally bisecting Missouri from northwest to southeast. Convergence along this boundary, CAPE values of ~3500 J/kg, and a weaker secondary shortwave moving out of the Ozark Plateau has resulted in storms firing along portions of this convergence zone over Central Missouri as well as across southwest Missouri. Initial thinking was that this boundary may drift back to the west but boundary looks pretty steady this afternoon with no real push westward. The weaker secondary shortwave trough has kicked up some showers with isolated thunder over portions of southeast Kansas and southwest Missouri. As we head into the overnight hours, we could see this activity perk up as the LLJ starts to increase over eastern Kansas and far western Missouri. Further to the elongated trough over the northwestern states rotating northward and its associated cold front will kick off storms across central Nebraska later this evening. The resulting MCS will push eastward before dropping southward. The first question of the day will be just where the MCS will drop south and how long it will hang together before weakening. CAM models are coming more in line with this complex dropping southward into Missouri, but discrepancies on timing and the general location of the line are still a concern. Current thinking is that the MCS will follow the 1000-500 mb thickness which matches up well with the aforementioned outflow boundary, generally from northwest Missouri southeastward to southeast Missouri. The main question is how far west will this line extend as some models such as the HRRR keep the western edge clipped and eastern Kansas and far western Missouri would not see much, if anything, overnight. The NAM Nest is a little more aggressive and develops convection along the outflow boundary ahead of the incoming MCS. After they merge the MCS takes a more southern route and the western edge of the line would go through eastern Kansas and western Missouri. The second question of the day will be how this overnight system will impact temperatures and the resulting heat indices tomorrow afternoon. Lingering showers and thunderstorms tomorrow morning will allow for a cooler start to the day with clouds possibly lingering into late morning to early afternoon. As clouds scour out, temperatures should recover fairly rapidly and we could see heat indices quickly climb into the lower 100s. The longer the clouds linger, the less likelihood we will see heat indices near heat advisory criteria. For now have gone with a Special Weather Statement to highlight the possible heat indices of 100-105 degrees tomorrow afternoon and will hold off on issuing a Heat Advisory given the uncertainty. However, future forecast updates may warrant issuing an Advisory if confidence builds. As a broad upper ridge builds over the central conus the rest of this week, heat and humidity will remain a concern, especially headed into the holiday weekend. && .Aviation...(For the 00Z TAFS through 00Z Wednesday Evening) Issued at 640 PM CDT TUE JUN 30 2020 Mostly VFR with some MVFR conditions possible during the overnight hours. Model trends indicate the possibility of showers and thunderstorms rolling through the area during the early AM hours Wednesday. Storms are expected to traverse the area from north to south. Vertical profiles and forecast models continue the trend of a shallow moist layer favorable for nocturnal low level cloud development. Also continuing is the trend of diurnal cumulus development over the area during the late morning and early afternoon which may bring MVFR ceilings. Finally, during the second half of the forecast period a low pressure center slowly traverses the area from east to west. This results in winds shifting from southeasterly to easterly. && .EAX WATCHES/WARNINGS/ADVISORIES... KS...Heat Advisory until 8 PM CDT this evening for KSZ057-060. MO...Heat Advisory until 8 PM CDT this evening for MOZ053. && $$ Discussion...Pietrycha Aviation...CDB/Pesel
Area Forecast Discussion
National Weather Service Lincoln IL
855 PM CDT Tue Jun 30 2020 .SYNOPSIS... Issued at 309 PM CDT Tue Jun 30 2020 Periods of showers and thunderstorms will continue across central and southeast Illinois through Wednesday evening, some of which may be strong and produce heavy rain. After that, we will be in a pattern that favors only isolated afternoon storms, as well as hot and humid weather, through the holiday weekend. && .UPDATE... Issued at 854 PM CDT Tue Jun 30 2020 Trends in nearly all of the high resolution models are looking drier overnight in our forecast area. An MCV centered over eastern Iowa is expected to shear out and drift to the NW away from Illinois later tonight. The vortex is still triggering an axis of showers/storms in west-central IL near Schuyler County, and the SW flank of the MCV may remain active with rain/storms along the Mississippi River Valley, per the NAM4K and HRRR. Despite the models dry trends, spurious showers could bubble up at times, as indicated by channels of cooler cloud tops across central IL. Therefore, have not completely removed PoPs for now, but did reduce them to slight chance 15-20% in most of the area. The best chances of any measurable rain overnight will reside in our SW row of counties, closest to where the Hi Res guidance has an axis of precip overnight, so have kept a corridor of Chance PoPs (30-50%) there. A late night/early morning storm complex could come into western Illinois, per older runs of the HRRR and NAM4K, but more recent output has that wave dissipating as it arrives near our western counties. We had a larger area of likely PoPs in our W CWA to account for that complex, but we have reduced that area with the evening update, with further reductions possible if the models continue their dry trends. No other noticeable changes were made to the forecast, with muggy lows in the upper 60s to low 70s likely. && .SHORT TERM...(This evening through Wednesday night) ISSUED AT 309 PM CDT Tue Jun 30 2020 Flash flood watch has been extended for a few more hours, now through 10 am Wednesday. Radar loops continue to show a well defined MCV spinning just south of Macomb this afternoon. Northern portion of the rain shield has diminished to scattered activity rotating around this MCV, while more widespread heavy rain and thunderstorms have been tracking from eastern Missouri into south central Illinois. Infrared satellite imagery showing colder cloud tops with these areas about to merge with a separate convective cluster over far southern Illinois. With the focus shifting down there, rain chances in our area for this evening have been cut back some. Main period of concern begins around midnight, as redevelopment begins in west central Illinois. As this occurs, an MCS that is expected to develop Nebraska and South Dakota this evening will track southeast. High-res models are a mixed bag as to how much this MCS will play a factor in our area, with the NAM Nest most likely to bring it this far northeast. A good chunk of the watch area has already been hammered by the earlier convection, though mainly on the fringes of our forecast area, so it would not take much more rain to cause issues. MRMS estimates have shown 2-3 inches across Scott and western Morgan Counties, as well as south of Springfield and west of Flora. With the timing uncertainty, it was decided to extend the watch a bit longer, until 10 am. Temperatures today have been significantly held down with the rain, struggling to get out of the upper 60s/lower 70s in the southern CWA. With an earlier stop to the rain on Wednesday, we should have enough time to recover into the mid-upper 80s, though that was lowered a few degrees from the previous forecast. .LONG TERM...(Thursday through Tuesday) ISSUED AT 309 PM CDT Tue Jun 30 2020 A rather stagnant pattern will remain in place late this week and early next week. The upper level ridge over the central U.S. will become more of a broad west-east configuration, favoring mainly dry conditions with only a few afternoon pop-up storms through the weekend. As the ridge flattens, longer range models show an upper wave sliding along top. This will lead to a slightly better chance of storms Monday and Tuesday. Temperatures through the period will be fairly uniform: Highs in the lower 90s, lows near 70, and afternoon heat index 95 to 100. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 659 PM CDT Tue Jun 30 2020 An MCV rotation remains centered in SE Iowa with storms redeveloping on the southern flank advancing into Schuyler County headed to the SE toward SPI. While IR satellite images indicate some cooling of the cloud tops, no strong storm threat is anticipated in the next 3-6 hours. The only MVFR ceilings remaining are at CMI, closer to the stationary front draped from NW Illinois to NE Vermilion County. High resolution models indicate SPI will have the best chance for periodic rain/storm threat tonight, with more isolated chances at the other TAF sites. The eventual track of the MCV will control where additional thunder potential with concentrate later tonight and Wed morning. There is some indication in the forecast soundings that IFR clouds may develop later tonight through just after sunrise. Added that to SPI, but only went down to MVFR at the other terminals for now. && .ILX WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Wednesday morning for ILZ040-047>052- 061-066-067-071-072. && $$ UPDATE...Shimon SYNOPSIS...Geelhart SHORT TERM...Geelhart LONG TERM...Geelhart AVIATION...Shimon
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
935 PM CDT Tue Jun 30 2020 .UPDATE... Updated for evening discussion. && .DISCUSSION... The convection for the day has ended. Regional radars showed an outflow boundary dropping south through western Tennessee that a few hi-res models suggest will spawn some convection in our northeast most zones around sunrise. Wl maintain pops there toward sunrise but elsewhere no additional development is expected and pops have been removed the remainder of tonight. Temperatures were on track to bottom out a couple of degrees warmer than normal again in the middle 70s. /22/ Prior discussion below: Rest of this afternoon - Wednesday: Rest of this afternoon- tonight: Convection has been been slow transpire this afternoon due to morning stratus/rain showers that persisted into the afternoon. Any convection that does develop will likely be more in the northern areas that have warmed into the low 90s & a better thermodynamic/microburst environment reside. However, to the south, these areas have been cooler, outside of the Pine Belt & less potential. Due to that, any organized stronger storms will have the best potential in the ArkLaMiss Delta. Expect any showers & storms to wind down by early evening. However, synoptic flow will become more out of the northwest & perturbed flow will help an MCS develop across the Ozark/Tennessee Valleys. For now, this looks like most of the convection or any type of overnight MCS will be more into the Mid-South into northern Alabama. However, it is possible it might sneak in across north Mississippi & Golden Triangle, generally after midnight to just before daybreak . Also can`t rule out some morning showers across the south but likely less coverage than this morning across central & southwest Mississippi before daybreak. Wednesday: The region will become entrenched in northwest flow with synoptic ridging developing further to the west over the central Plains. The subtropical ridge over the Gulf of Mexico will begin to weaken, which will only help better northwest flow regime to setup. This pattern will bring in a juxtaposition of copious lapse rates/thermodynamics & microburst potential. High moisture laden air, with PWs approaching 2 inches & dewpoints in the mid 70s, will support a warm & muggy environment. Thermal profiles will be similar with heat & humidity reaching in the low-mid 90s & heat indices climbing into the lower 100s & approaching 105 degrees along & west of Interstate 55. Due to that, kept the combined "Limited" for heat stress in the HWO/graphics Wednesday & into Thursday. With high warmth & humidity, a very favorable thermodynamic setup will favor N-NW flow MCS potential (i.e. 7-7.5 deg. mid- level lapse rates, widespread 7-10+ microburst composite parameters & SBCAPE/DCAPE upwards of 5000+ J/kg & 1500+ J/kg). This setup favors scattered isolated to severe organized downdrafts/cold pools/line segments into late afternoon. HREF guidance continue to prog a MCS diving down out of the Ozarks/Tennessee Valley & potentially making it down into the Mid- South & north Mississippi before early Wednesday evening. The new 12Z HRRR continues to trend in that direction & the 12Z Euro shows consensus with the HRRR/ARW/NMM. Due to that, mentioned this area in the HWO text/graphics for late Wednesday afternoon, generally after 4PM, for "Marginal" severe for isolated severe storms, with most potential into the evening hours & through Thursday. Even though the 12Z HRRR has most convection into the evening, wanted to account for faster convective cold pool motion & extremely favorable MCS environment. /DC/ Wednesday night through Monday: Mid level ridge from the Southern Plains into the mid MS valley will put much of the area in an active northerly flow by Wednesday night. Shortwave dropping out of the Midsouth will likely be already fueling strong convection over north MS/west TN/north AL late Wednesday afternoon. 30-40 knots of deep layer shear with continued instability (1500-2500 J/kg CAPE, 7C/km and upper 20s vertical totals) during the evening should lead to upscale growth/MCS development over north into eastern MS Wednesday night with primarily a damaging wind threat. Will continue the marginal severe threat, similar to the area outlooked by SPC, but continue into Thursday as the parameter space continues to support this sort of activity. While the majority of the convection will remain in the east, proximity to mid level ridge over western sections will help max temperatures rise into the mid 90s Thursday. This with dewpoints in the mid 70s will result in heat indices around 105, so will continue limited dangerous heat risk in the HWO for these areas. The mid level flow will gradually weaken moving into the weekend, but the continued cyclonic nature will support higher than average rainfall chances, mainly during the afternoon/evening. The heat should not be as much of a problem as maximums stay around 90. /GG/ && .AVIATION... 00Z TAF discussion: Radars showed very little convection in our area at 2330Z. HBG-PIB may see a brief TSRA/SHRA before 02Z. Otherwise, some guidance suggests early activity over our ne affecting GTR by 12Z Wed with no additional development elsewhere until Wed aftn. VFR conditions are expected to prevail away from TSRA activity through Wed aftn. A possible exception is in cntrl MS 12-15Z when MVFR cigs may develop before lifting above 3kft. /22/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 75 93 75 90 / 10 25 29 68 Meridian 75 93 74 89 / 14 40 48 81 Vicksburg 76 93 76 92 / 11 15 16 51 Hattiesburg 76 93 75 90 / 10 31 18 64 Natchez 75 92 74 91 / 13 13 6 32 Greenville 76 92 75 91 / 9 17 35 62 Greenwood 76 92 75 90 / 13 34 51 72 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...None. LA...None. AR...None. && $$ 22/DC/GG
Area Forecast Discussion
National Weather Service North Platte NE
610 PM CDT Tue Jun 30 2020 .SHORT TERM...(This evening through Wednesday night) Issued at 321 PM CDT Tue Jun 30 2020 The forecast is following the short term model blend for likely thunderstorm chances this evening east of highway 83 throughout ncntl Nebraska. This is a little west of the previous forecast and is based on post frontal thunderstorms forming in addition to storms developing along a cold front which is slowing up across cntl Nebraska this afternoon. Storm activity should last about 6 hours and exit ncntl Nebraska to the east around midnight tonight. The rest of the forecast Wednesday and Wednesday night is dry as a result of Pacific high pressure building through the region. The models and latest SPC analysis indicate 4000-5000J/KG of MLCAPE across ncntl Nebraska this afternoon. A belt of increasing winds aloft across ern WY/Colo will move in this evening supporting deep storm development but the directional shear appears limited. This would seem to support splitting storms and competing updrafts. SPC suggested supercells at the onset of storm development evolving into a more linear mode as the MCS shifts east later this evening. Both the NAM and RAP model soundings show moisture deepening along the nearly stationary front. The deepening moisture should weaken the cap by 22z-00z this aftn/evening. .LONG TERM...(Thursday through Tuesday) Issued at 321 PM CDT Tue Jun 30 2020 An upper level ridge of subtropical high pressure centered over the nrn Gulf of Mexico this morning will build north through Texas and into Nebraska this week. The GFS and ECM both show an attendant plume of subtropical moisture moving north with the ridge. The result is a more moist environment supporting what appears to be ordinary thunderstorm development across Nebraska. The new forecast has more scattered thunderstorm chances Thursday through Tuesday. Winds aloft should remain fairly weak at less than 15kt. A modest increase in winds aloft is possible next Tuesday as the ridge weakens with the approach of a nrn stream disturbance. The temperature forecast is for highs in the 90s Thursday and beyond. This is consistent with h700mb around 11C. Steady south winds are in place associated with a broad area of weak low pressure forming across the cntl and nrn Plains. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 610 PM CDT Tue Jun 30 2020 Scattered thunderstorms will move through north central Nebraska this evening (mainly from KBBW to KONL), resulting in tempo visby and cig drops, along with gusty erratic winds. Otherwise, VFR will continue through the forecast period. Gusty winds are the main aviation weather concern, primarily through sunset tonight (northwesterly) and again tomorrow afternoon (southerly). && .HYDROLOGY... Issued at 321 PM CDT Tue Jun 30 2020 Radar shows the cold front slowing up across ncntl Nebraska and the rapid refresh models are pooling moisture behind this front. Precipitable water will exceed 1.5 inches at the onset of scattered thunderstorms early this evening. Storm cover should expand throughout ncntl Nebraska this evening. The deep southerly flow aloft and elevated CAPE of 2500J/KG shown in the RAP and NAM models should support splitting storms and perhaps some HP echo training. The RAP and HRRR are showing signs of a expansive area significant rainfall with locally heavy rainfall totals of 1.5 and 2.5 inches. The locally heavy rainfall would probably lead to flooding in some areas. The Flood Watch in effect across Holt and Boyd counties has been expanded south and west to include Custer county and areas north to the South Dakota border. && .LBF WATCHES/WARNINGS/ADVISORIES... Flood Watch until 5 AM CDT Wednesday for NEZ006>010-026>029-038. && $$ SHORT TERM...CDC LONG TERM...CDC AVIATION...Snively HYDROLOGY...CDC
...Updated Mesoscale Forecast Discussion...

.MESOSCALE DISCUSSION... Issued at 847 PM CDT Tue Jun 30 2020 Thunderstorms have slowly intensified and increased in coverage over the past hour with a few severe hail reports in central NE. The surface front is well-defined as a fine-line in radar imagery from KUEX and at this time (just prior to 9 PM) is just nosing into Knox county, extending south to near the western Boone county line, and then south southwest from there. Low pressure over Kansas has helped to back surface winds ahead of the front and increase low-level convergence along the boundary. At the same time, water vapor imagery shows a well-defined cooler/drier mid- level airmass has been lifting northeast and has helped to destabilize near the front. The front will continue moving east for the next several hours, and expect a continued increase in storm coverage and intensity through 11 PM. At some point, the question becomes whether an organized cold pool will develop and push east out of these storms, and the current belief is that this will happen over the next 2 hours or so. As the cold pool and cold front propagate east and southeast, they will interact with a pool of deep boundary layer moisture and ample instability. Most model guidance maintains greater than 3000 J/kg of MLCAPE into the early morning hours. Forecast soundings indicate that it should be quite easy for a cold pool to lift parcels to the LFC within the very moist environment, and thus expect a forward propagating MCS to organize and move initially east and then southeast across the area. Severe potential will exist despite a general lack of deep layer shear ahead of the front...owing mainly to the favorable thermodynamics, and while some large hail will be possible it appears that the greatest hail threat will be early this evening with a transition to more of a damaging wind potential. Much of this echoes earlier forecast thoughts, and for the most part the forecast is largely unchanged. The main change would be an increased potential for the MCS to impact a good chunk of southwest Iowa and southeast Nebraska. && .DISCUSSION... Issued at 342 PM CDT Tue Jun 30 2020 Forecast Summary: There is a fairly decent shot of thunderstorms tonight as a potent shortwave rotates around upper low in the northern Rockies. Strong, damaging winds will be the main threat, especially in the northern half of eastern Nebraska and western Iowa. Then a trend toward warmer temperatures will take us through the weekend with mid level ridging building into the region. Tonight and Wednesday: Widespread low clouds have persisted across eastern Nebraska and western Iowa this afternoon, holding temperatures to the middle and upper 80s for the most part. However a soupy environment characterized by dew points in the mid and upper 70s made it feel more like the middle 90s in many areas. It also contributed to instability as SBCAPE values over 5000 J/kg were noted on RAP analysis. The atmosphere remains capped this afternoon, and should remain that way until system approaches from the west. Shortwave was noted on water vapor imagery rotating northeast through eastern Wyoming at mid afternoon. Diffluent flow and cooler mid level air was spreading into western sections of South Dakota and Nebraska, and was approaching surface front extending from persistent MCV in western North Dakota into central Nebraska. MLCAPE was maximized along this boundary where 5000 J/kg was noted over top of increasing moisture convergence. Effective shear was maximized near and west of frontal zone, and is forecast to migrate east with boundary this afternoon and evening. Continued low level warming under cooling mid levels should lead to scattered convection along frontal boundary shortly. Models have been fairly consistent in this scenario. How things progress this evening is still somewhat in question as solutions vary by a couple of hours on timing of southeast movement into our area. The HRRR has been consistent in development of storms, but has trended slower in regards to advancement into northeast Nebraska. Have followed this somewhat slower progression of storms into our area. Expect convection to begin shortly well west of our area where it will percolate for several hours into the early evening before nudged eastward by advancing shortwave and developing cold pool. It appears supercellular storms with the threat of large hail and possibly tornadoes will remain generally west of our area before storms congeal into a line and advance east and southeast. The main threat then will be damaging winds as instability remains high and low level jet increases. Storms will likely enter western parts of Knox through Boone counties by 7 or 8 PM, then race east and southeast to reach the Omaha and Lincoln areas somewhere in the 10 PM to 2 AM timeframe, and western Iowa Midnight and later. Damaging winds will be possible much of the night. Expect main activity to be east of our CWA before 12Z, however latest trend of HRRR suggests lingering instability behind this line will be tapped for additional development near and northwest of Interstate 80, which may linger through the morning. Additional development Wednesday afternoon is a concern for southeast Nebraska and southwest Iowa where models indicate frontal boundary will set up during peak heating. Strong instability will be available, but only modest shear and low level convergence. Will introduce a chance for storms there for Wednesday afternoon. Thursday through Tuesday: Mid level ridging builds into the Plains from West Texas area on Thursday and holds through much of the weekend. This pattern will promote warming of mid and low levels which should squash most convective attempts. However, low level moisture streaming into the High Plains will fuel occasional rounds of convection there which may hold together as they march east during the overnight hours to affect at least our western CWA. And with 70s dew points remaining in eastern Nebraska and western Iowa, instability will be high each afternoon, so can`t rule out a pop-up storm from time to time. Otherwise expect highs to average the lower 90s each afternoon right through Tuesday. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 707 PM CDT Tue Jun 30 2020 Primary forecast concern through this TAF is thunderstorms as a large line of storms is likely to impact all TAF sites at some point in the next 10 hours. There is a good likelihood that the storms will produce strong wind gusts as they arrive, with some potential for strong thunderstorm outflow to precede the storms themselves. Gusts greater than 50 kts and some hail are possible. Otherwise, confidence is low, but could see some low-end MVFR cigs or perhaps even IFR around sunrise through mid morning before scattering out. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ MESOSCALE...Barjenbruch DISCUSSION...Dergan AVIATION...Barjenbruch
Area Forecast Discussion
National Weather Service Nashville TN
637 PM CDT Tue Jun 30 2020 .UPDATE... FOR EVENING DISCUSSION. && .DISCUSSION... A few pre-Independence Day fireworks across the south already late this afternoon with several spots seeing trees down and torrential rainfall. We`re not quite done, however. Latest radar trends, as well as hi-res guidance, suggest the storms in west KY will continue to push southward into Middle TN over the next several hours. The good news is that most of the atmospheric energy that could be used to fuel these storms has been expended. For this reason, we`re only expecting these storms to be `general` in nature and sub-severe. Doesn`t mean a gust of 40 mph or so isn`t out of the question, but that should be the exception rather than the rule. If you have evening plans along and west of I-65, bring an umbrella. Forecast update out shortly. && .AVIATION... 00Z TAF DISCUSSION. BNA/MQY/CKV/CSV...Surface ridge is now situated to the immediate east of Middle Tennessee this evening while an upper trough approaches from the west. Most of the earlier storms have diminished so that there is a dearth of echoes in the vicinity of the terminals. Scattered POP`s remain in the forecast this evening and overnight, and the HRRR does suggest some additional activity forming and moving across the mid state. Expect stronger convection late tomorrow morning through the afternoon as the upper trough slides down the NW flow aloft into Middle Tennessee and we add some daytime heating. The best time for storms appears to be Wednesday afternoon, so we`ll focus our energies there, although scattered cells may affect the terminals outside peak- heating hours. Also, look for MVFR ceilings to develop overnight and last into the morning owing to this moisture-laden air mass. && .OHX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION......Unger AVIATION........08
...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday) Issued at 354 PM CDT Tue Jun 30 2020 Surface obs at 20Z showed temperatures in the upper 90s across parts of central KS and a very moist air mass in place with dew points in the low and mid 70s area-wide. Heat index values continue to climb this afternoon so an advisory will remain in place until 8 PM. Water vapor imagery this afternoon continues to show a large upper trough to our northwest, which is expected to trigger convection in the Dakotas and Nebraska this evening as it pivots northward. Model guidance on the probability of precipitation in northeastern Kansas tonight remains varied with some convective allowing models (CAMS) extending the tail end of the convection to our north all the way to I-70, while others (including the HRRR) keep storms north and east of the area. Our environment overnight will remain very unstable aloft with the RAP showing near 4000 J/kg of elevated CAPE. Shear will increase slightly as the LLJ gets going so thunderstorms should survive if they move in. However, a stout low level inversion should help to limit severe potential unless the MCS becomes well organized, at which time we would need to watch for a damaging wind risk. In terms of POPs for tonight, I decided to go with 40 percent chances in far northeastern Kansas to account for the possibility of storms making it this far south, and slightly lesser chances closer to I-70. Either way, increased cloud cover is expected tomorrow morning due to the complex of storms traversing the region. An area of surface low pressure will be in place over the CWA tomorrow and will gradually weaken with time. Models continue to show and hot and very humid air mass remaining in place and our current forecast heat index values again approach advisory criteria, especially in east-central KS. Thus, we have issued another Heat Advisory tomorrow afternoon for east-central counties. .LONG TERM...(Wednesday night through Tuesday) Issued at 354 PM CDT Tue Jun 30 2020 The upper level pattern in the long-term will be dominated by expansive ridging aloft. This generally points toward a very hot forecast this time of the year. In addition to the heat, there will be nearly daily chances for isolated to scattered storms if enough lift from instability can be realized. With the lack of a more potent forcing mechanism late this week and this weekend, will keep chances for storms low at this time with many locations likely to be dry most days. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 619 PM CDT Tue Jun 30 2020 VFR conditions are expected through much of the evening and overnight hours. Southeasterly winds will decrease to around 10 kts within the next hour. Main challenge for the forecast period is a complex of thunderstorms progged to move across southern NE overnight which may push a frontal boundary into the terminals around 10Z, shifting winds to the east/northeast. Furthermore, MVFR stratus and isolated storms may accompany the frontal passage. Confidence is too low to introduce any thunderstorm mention. Marginal LLWS is possible from 04-09Z. Diurnal Cu around 1.5-2.5 kft is expected by mid-morning, especially at the Topeka sites. && .TOP WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM CDT this evening for KSZ008>012-020>024- 026-034>040-054>056-058-059. Heat Advisory from 1 PM to 7 PM CDT Wednesday for KSZ040-054>056- 058-059. && $$ SHORT TERM...Teefey LONG TERM...Teefey AVIATION...Baerg