Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/05/19

Area Forecast Discussion
National Weather Service Louisville KY
841 PM EDT Wed Sep 4 2019 .Forecast Update... Issued at 841 PM EDT Wed Sep 4 2019 The cold front has passed south of the area, and dew points are slowly dropping off on a steady N wind across much of the area. For instance, already seeing the upper 50s at SDF/LOU. In contrast, southern KY is still holding onto lower 70s dew points. These values should drop off into the 60s pretty quickly this evening, however there is some concern that some fog may form across southern KY toward dawn given the lingering low level moisture. A mitigating factor could be the light but persistent N surface winds so don`t fog to become dense, but will keep fog mention in the forecast. Forecast looks on track this evening, and mainly just updated the grids for latest obs and trends. && .Short Term...(This evening through Thursday) Updated at 310 PM EDT Wed Sep 4 2019 AMDAR and model soundings as well as GOES Sounder data show quite a bit of elevated instability across the region, as well as enough moisture to work with for storms to develop...however the low-levels of the atmosphere are fairly well capped by a strong inversion. The question mark for any late afternoon development will be whether we can get enough convergence along a cold front moving southeast across the region...combined with differential heating boundaries as well as the surface heating to get to a point to break that cap. Most hi-res near term models are arguing against that development, with 18Z soundings from ILN/OHX both showing convective temperatures well into the 100s, will not carry any pops tonight. With loss of heating tonight, expect any type of cumulus field to diminish...though we may see some thin low stratus develop overnight with moisture trapped under that inversion. Will lean on the optimistic side for now...having the cold front clear through enough of the region to have those clouds form more south of our KY/TN border overnight. With the assumption the clouds will be gone in the morning, Thursday should be a very pleasant day. Highs will rise into the upper 70s to lower 80s across the area, but a steady north wind should help dewpoints fall into the 50s for many places by late afternoon. .Long Term...(Thursday night through Wednesday) Updated at 320 PM EDT Wed Sep 4 2019 Another dry cold front looks to come through the area Friday...not really bringing a change in airmass, as we should see temperatures return to normal for the weekend. Rain chances will be limited again by capping aloft, and what looks to be even less available moisture than the front we have today. Despite temperatures near normal for the weekend, dewpoints again getting into the upper 50s to low 60s should make each day relatively comfortable. As we get into the next work week, the GEFS mean fields show a ridge developing over the Deep South. Should this occur, it looks to keep the storm track to our north with temperatures warming up each day. The GFS and Euro both allude to this pattern as well, but the CMC keeps more troughiness aloft over our region. Will hedge a little toward climo 20 pops by Wednesday, given that model difference and some weak signals in the GEFS QPF fields by then. We also have a slight chance early Monday, with a warm front lifting north over our northern CWA, as we transition into that pattern. && .Aviation...(00Z TAF Issuance) Updated at 733 PM EDT Wed Sep 4 2019 A steady N wind is expected overnight behind a departing cold front. These winds and the drier air behind the front should keep fog formation in check, although can`t rule out some MVFR fog at BWG toward dawn. Otherwise, steady N or NNE winds continue on Thursday with a few flat cumulus around 3 K feet. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...BJS Short Term...RJS Long Term...RJS Aviation...BJS
Area Forecast Discussion
National Weather Service Phoenix AZ
510 PM MST Wed Sep 4 2019 .UPDATE... Updated 00Z aviation discussion. && .SYNOPSIS... Seasonably hot weather will persist through the week with excessive readings this afternoon, and only a few degrees of cooling through the end of the week. A small weather disturbance may spark a few storms through much of the area late this afternoon into Thursday morning, however drier air will steadily spread through the region into the weekend. A stronger weather system and frontal boundary will approach the region next week with fairly good rainfall chances through south-central and eastern Arizona, as well as much cooler temperatures. && .DISCUSSION... Latest streamline analysis depicts a mean layer southeasterly flow around the Monsoon High, which has migrated eastward into the southern Plains. Meanwhile, a pocket of drier air is evident on water vapor imagery across central Arizona. Further to the south and west, thunderstorms across the northern Baja Peninsula are indicative of a weak inverted trough, which extends into southwestern Arizona. Between the aforementioned trough near Puerto Penasco and the anticyclone further east, the pressure gradient is relatively strong, resulting in an anomalous u-component to the steering flow, particularly across southern Arizona. This will favor propagation of convection as far westward as southeastern California this afternoon and evening. Across the Phoenix Metro area, latest ACARS flights indicate a mid-level isothermal layer, which will reduce CAPE this afternoon. Consequently, a lack of convection further upstream across Gila County will reduce the potential for an outflow boundary triggering additional storms in the lower deserts. However, the intense diabatic heating with temperature approaching 110 degrees should at least should be sufficient for isolated to scattered air-mass storms to initiate. DCAPEs approaching 1500 J/kg suggest that any storms that develop will be capable of producing strong winds and patchy blowing dust. Latest consensus from both the HREF and local CAMs generally highlight areas further west from Phoenix westward for thunderstorm activity. This is likely due to the broader ascent from the inverted trough and widespread instability (MUCAPE approaching 1000 J/kg). Higher PWATs will also translate into an increased threat for flash flooding as far west as JTNP. Shower activity will likely linger into Thursday morning across southeastern California before dissipating in the afternoon and PoPs were raised in these areas. Consensus from the CAMs again points to isolated storms across southwestern Arizona and southeastern California Thursday afternoon. && .PREVIOUS DISCUSSION... Confidence is moderate to high that more resounding dry air through the entire atmospheric column along with general subsidence will spread into the region Friday and Saturday. Quite a pattern shift is still being advertised among all operational and ensemble members starting next week, although there is rather significant differences in timing and depth of northern stream waves entering the SW Conus and Great Basin. Recent iterations of the GFS remain quicker and less amplified with a series of shortwaves progressing into the western US while the ECMWF carries more depth to troughing becoming established through the western Conus (while ensemble members cover a wide range of outcomes). A few consistent facets carry over all model output 1) stronger subtropical ridging will temporarily be eroded with H5 heights falling to near 586dm and consequently temperatures depressed back near or slightly below normal, and 2) unusually early season height/pressure falls associated with this trough will force stronger low level southerly flow through the eastern half of Arizona drawing moisture north from Mexico. Some of this moisture and potentially subtle waves may be associated with the long decayed remnants of TS Fernand crossing westward from the Gulf of Mexico. Regardless, models suggest ample cooling aloft with this trough, and along with dynamical forcing, forecast soundings actually look quite enticing for the eastern portions of the CWA during this transition season type event. Have bumped up POPs generally for the entire Sun- Tues time frame as model output indicates the potential for multiple rounds of convection aided by deep upslope flow and dynamical influences. Given all the uncertainty describe above, could not really pinpoint a specific time frame more likely for rain/storms; though conceptually with the forcing, instability, and stronger shear parameters, prospects are excellent for at least one convectively active day around and east of the Phoenix metro during the first part of next week. && .AVIATION...Updated at 0009Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Very isolated convection will affect the Phoenix terminals for the next few hours, with an isolated cell developing E-NE of FFZ and additional cells possible with outflows later this evening. Confidence on deep convection affecting any of the terminals is low because of weak midlevel stability and drier conditions relative to the last few days and further west. Thus, we have included VCSH for now through 03Z at KIWA and KSDL with a 02-04Z period for KDVT and KPHX, the latter of which would be due to outflows from the S-SW and/or east if either materializes. Winds will most likely favor south to southwesterly headings at most of the Phoenix terminals this evening except KIWA where more south- southeasterly headings will be favored. Light and variable or easterly winds will return overnight through tomorrow morning, with winds most likely veering to the south-southeast by late morning or early afternoon. If winds do veer to the southwest tomorrow, it will not be until very late in the afternoon. Southeast California/Southwest Arizona including KIPL and KBLH: Isolated to scattered thunderstorms with broken 10 kft ceilings will continue to affect SW Arizona and SE California for at least the next few hours, with VCTS included through 02-03Z at KIPL and BLH. Although storms are generally remaining south of both sites, outflows from the southwest at KIPL and southwest to southeast at KBLH will be possible, with gusts to 25-30 knots and blowing dust possible. Some hi-res models suggest convection may continue into the evening and overnight hours with a potential inverted trough moving in from Sonora, but the ongoing convection may stabilize the atmosphere enough to prevent this from occurring or temper coverage significantly. For now we have just VCSH through 05Z at KBLH and 08Z at KIPL, but this is a low confidence forecast that will likely change significantly with the next TAF cycle. In the absence of convective outflows, winds should return to south- southeasterly headings below 10 knots overnight through tomorrow afternoon with lower chances of convection tomorrow. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Saturday through Wednesday: Seasonably hot temperatures will persist through Saturday, however much cooler weather will arrive next week as readings fall near or slightly below average with an incoming storm system. There will be a sharp gradient between relatively dry air to the west and relatively moist air from Phoenix eastward. The storm system next week will could result in fairly widespread wetting rains over higher terrain area in the eastern districts while southerly winds periodically become gusty around a frontal boundary. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST this evening for AZZ530- 532-534-536-537-540>544-546-548-550-551-553-555-556. CA...Excessive Heat Warning until 8 PM PDT this evening for CAZ567- 569-570. && $$ DISCUSSION...Hirsch PREVIOUS DISCUSSION...MO AVIATION...Hopper FIRE WEATHER...MO
Area Forecast Discussion
National Weather Service Blacksburg VA
759 PM EDT Wed Sep 4 2019 .SYNOPSIS... A cold front in the Ohio Valley will move southeast this evening, crossing the Mid- Atlantic Region tonight into Thursday. Hurricane Dorian will move slowly north, along the southeast Atlantic coast into Thursday night before exiting the Outer Banks on Friday. && .NEAR TERM /THROUGH THURSDAY/... As of 230 PM EDT Wednesday... Subsidence/dry air continuing to hold across the region this afternoon with a weak downsloping component helping to confine most cumulus to the far northwest ahead of the upstream cold front. Latest analysis does show a decent ribbon of instability just in advance of the boundary to our northwest, but appears any convective development will be slow per limited convergence for now. Latest short term solutions basically agree on only isolated coverage at best until perhaps mixing decreases and the 85h front edges into northeast sections this evening. This could result in some convective development east of the mountains before the low level boundary slides through after midnight. Developing northeast flow in the wake of the front may also undercut warm air aloft by daybreak resulting in some low clouds espcly Blue Ridge east as moisture pools a bit below the inversion. Lows a bit milder tonight but still appears enough dry air per current dewpoints, and subsidence to allow most to fall back into the 60s with some 50s in the deeper valleys. Front folds south of the area Thursday while Dorian slides north/northeast to off the South Carolina coast late in the day. Guidance depicts bands of deeper moisture working to the northwest of Dorian on increasing easterly flow aloft. However at the same time will continue to see some dry advection kick in behind the front on northeast flow, with forecast soundings indicating deeper moisture having a hard time overcoming residual pockets of dry air through the column. This may tend to delay any rainfall outside of very light passing showers until late in the day and mainly across the piedmont. Thus only going with low pops increasing over the southeast in the afternoon with some spotty chances elsewhere as some light rain possibly sneaking through within the onshore flow. May even see a few more showers over the southwest as well where could get heating on the periphery of the cool pool. Otrw more clouds east to start with moisture overspreading the region if can completely overcome the dry air. Will become breezy as well espcly south/east as the jet to the north of Dorian increases and enough mixing likely helps bring down some 20-30 mph gusts far southeast by late in the day. Highs tricky pending the degree of clouds and just how fast cooling at 85h arrives from the north. For now trended on the warmer side of Mos (70s to low 80s) given potential for at least a few sunny breaks. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 245 PM EDT Wednesday... The biggest challenge during this portion of the forecast will continue to be any impacts the region will have from the northwest extent of Hurricane Dorian. The latest official forecast cone track has the center of Dorian skirting the coast of South Carolina on Thursday and passing over the Outer Banks of North Carolina on Friday. During the portion of this progression where Dorian is near the SC/NC border, its position and size would place the far northwest section of its rain shield across the far southeastern and then eastern sections of the forecast area during the Thursday afternoon and Thursday night part of the forecast. Precipitation totals are still forecast to be less than a quarter of an inch across this part of the forecast area with wind gusts approaching 30 mph. For the latest information regarding Hurricane Dorian, you can visit A secondary area of isolated to scattered light rain showers is possible across far southwest Virginia, south into the Northern Mountains of North Carolina on Thursday afternoon. Here northeast flow on will advect moisture in the area of the old weak and washed out frontal boundary. This combination may be just enough for some light precipitation in this area. As Dorian reaches the Outer Banks on Friday, its distance from us will have increased enough to slacken the pressure gradient, and winds will decrease through the day. Precipitation, will be isolated at best across the far eastern and northeastern sections of the region during the morning. Friday night through Saturday night drier air will work its way into the area from the northwest. Temperatures during this portion of the forecast will average a few degrees above normal. Confidence in this portion of the forecast is moderate. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 130 PM EDT Wednesday... Synoptic flow across the area will transition to zonal flow by the end of the weekend. Heading into early next week, an upper level ridge is expected to build over the Ohio River Valley, transitioning our pattern aloft to a northwest flow. This northwest flow is expected to bring a cold front into the region by Monday afternoon where it will stall, and/or wash out over the region. This feature is expected to bring isolated showers to primarily northern parts of the area on Monday. On Tuesday the center of surface high pressure is expected to shift east of the region, bringing low level flow back tot he south across the area. This flow will help advect slightly higher moisture levels into the region. The presence of the washed out front, will help act as a focus for isolated to scattered coverage of shower and storms. The greatest focus will be the Northern Mountains of North Carolina where both differential heating and upslope components will help maximize coverage across this region of the forecast area. For Wednesday, the 850mb flow becomes westerly. This will help to minimize convection in the east thanks to downsloping, with an upslope component in the west keeping isolated to scattered coverage of showers and a few storms in the west. Temperatures during this portion of the forecast will experience lows a few degrees above normal and high temperatures around normal for this time of the year. Confidence during this portion of the forecast is moderate. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 745 PM EDT Wednesday... Much of the TAF valid period will remain VFR, despite the formidable and ominous Hurricane Dorian looming off the GA/SC coast this evening and drifting slowly north toward the SC coast. A weak cold front located to our north will essentially dissipate in the face of large scale subsidence around the outer periphery of Dorian. Cumulus clouds and isolated showers popped up along the front mainly just north of the I-64 corridor and on up toward DCA. All but the northeastern most activity has dissipated at this point. A weak area of high pressure aloft is sandwiched in between the weak front to our north and Hurricane Dorian to our southeast. Meanwhile, the large cirrus shield associated with Dorian has spread as far north as a TNB-BCB-LYH line and should make further progress into Thursday toward the western border of the CWA at which point it should stop drifting any further west. Variable/southeast winds generally less than 10kts this evening will begin to respond to the approaching Dorian and back to the northeast and east overnight and increase in speed with low end gusts commencing shortly after 12Z Thu across much of the area. The easterly flow will increase the marine layer moisture and likely result in a shallow layer of low clouds developing across much of the region, especially along/east of the Blue Ridge after daybreak or early in the morning. At this time, it appears that these cloud ceilings could be in the mid to high end range of the MVFR category. This should persist throughout much of the day, especially east of the Blue Ridge, but may scatter out some west of the Blue Ridge. Meanwhile, a thick deck of cirrus/cirrostratus should reside above in the 200-250 range through much of the TAF valid period. Fog development in the morning is more questionable than normal as a result of increased wind flow and clouds. However, do feel that BCB and especially LWB should remain far enough removed from the effects of Dorian for one more night to decouple and see some MVFR to potentially LIFR fog conditions for a few hours near daybreak. /Confidence in Forecast Parameters/ Ceilings - Moderate, Visibility - Moderate to High, Winds - Moderate to High. .Extended Aviation Discussion... Periods of sub-VFR cigs could continue espcly Blue Ridge east into Thursday night within the onshore northeast flow around Dorian. Bands of showers may also work into the KDAN vicinity Thursday night with possible brief vsby restrictions at times pending the future track of the hurricane. While the latest model guidance keeps Dorian well off to our east, there still will likely be enough wind to affect aircraft operations espcly east of the mountains Thursday night into Friday. Aside from Dorian, the overall trend after Friday morning will be for VFR conditions as weak high pressure builds in behind the exiting storm. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/PM NEAR TERM...JH SHORT TERM...DS LONG TERM...DS AVIATION...JH/RAB