Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/02/20

Area Forecast Discussion
National Weather Service Lincoln IL
856 PM CDT Tue Sep 1 2020 .SYNOPSIS... Issued at 255 PM CDT Tue Sep 1 2020 A slow moving front will bring showers and thunderstorms to portions of the area through Thursday. The best chance will be confined to areas south of I-72 Wednesday and then south of I-70 on Thursday. Dry weather and lower temperatures are expected Friday into Saturday. && .UPDATE... Issued at 856 PM CDT Tue Sep 1 2020 Rich moisture across the region with current dewpoints from the upper 60s west of I-55 to the lower 70s to the east should result in fog development across the area overnight as higher level clouds clear out. Widespread rain that fell today should help supply moisture, especially west of I-55 where many areas received over an inch. Otherwise, have trimmed PoPs east of I-55 late this evening and overnight based on recent trends, but also added slight chance PoPs in the northwest due to approaching showers associated with approaching surface cold front. Lows should reach as low as 63 in Galesburg, but otherwise range up to as warm as 70 in Lawrenceville. && .SHORT TERM...(This evening through Wednesday) ISSUED AT 255 PM CDT Tue Sep 1 2020 A nearly stationary frontal boundary is draped from near Kansas City across the Peoria area and into NW Indiana this afternoon. Dew points in the upper 60s to lower 70s are in place south of the front and quickly drop through the 60s into the 50s north. Meanwhile, outflow boundary from earlier storms has moved across the I-57 corridor and has helped kick off new line of thunderstorms early this afternoon from roughly Shelbyville to Danville. Latest RAP shows fairly modest instability in place across east central Illinois with MLCAPE around 500-700 J/kg. Given expansive cloud cover and weak flow, do not anticipate any significant further destabilization this afternoon. Still, deep layer shear values of 30-40 kt mean storms will bear some watching this afternoon. Any low end severe threat should be fairly short lived over the next couple hours only as what little instability that is present is overturned by ongoing convection. On Wednesday, effective front is expected to push south of the I-72 corridor and will serve as the focus for additional isolated to widely scattered storm development. Further north, lower dew points do start to creep back into portions of central Illinois north of I-72, with values into the lower to mid 60s. Temperatures will warm into the lower to mid 80s area wide Wednesday afternoon. .LONG TERM...(Wednesday night through Tuesday) ISSUED AT 255 PM CDT Tue Sep 1 2020 Upper pattern will be characterized by a broad and flat longwave trough spanning much of the country with a compact shortwave moving along the international border across the northern Great Plains into Great Lakes Thursday. Attendant surface low will stay over Canada, but a trailing cold front will sweep across the Midwest, crossing central Illinois Thursday night. At this time, no precip is expected with the front, but 850mb temps fall from around 15-16C ahead of the front to 9-10C behind the front. Meanwhile broad surface high will spread from the Great Plains across the Midwest Friday and Saturday. This should amount to temps falling back to near or slightly below seasonal norms with otherwise fair weather to close the week and start the weekend. Upper pattern begins to amplify over the weekend with a strong ridge building across the west coast and trough deepening downstream centered over the Midwest. Another shortwave trough will dig across the Upper Midwest Saturday night into Sunday. Warm advection ahead of the wave will moderate temps Sunday with temps back into the lower to mid 80s, but this will be short lived as yet another cold front pushes across the region later Sunday. There remains large differences in how far south this front pushes and placement of later storm tracks, thus extended forecast has broad brushed chance PoPs given the uncertainty but well below normal temperatures appear possible if the more southerly solutions verify. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 653 PM CDT Tue Sep 1 2020 Expect diminishing showers affecting the central IL terminals this evening as scattered showers and isolated thunderstorm potential move eastward. Mention of SHRA/VCSH confined to KDEC and KCMI until 03Z-04Z. Primarily VFR conditions initially, then cigs and vsbys likely to reduce to IFR or MVFR with locally worse conditions overnight as fog and low clouds develop. Improvement in conditions should develop rapidly from 14Z-18Z as diurnal heating dissipates morning fog. Winds S 6-9 kts initially, becoming light and variable overnight, then increasing out of the west after 14Z after a front moves eastward through the area. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...37 SYNOPSIS...Deubelbeiss SHORT TERM...Deubelbeiss LONG TERM...Deubelbeiss AVIATION...37
Area Forecast Discussion...UPDATED
National Weather Service Shreveport LA
1013 PM CDT Tue Sep 1 2020 .UPDATE... Convection continues to slowly advance eastward across North Central Texas, and the first band is finally beginning to enter East and Northeast Texas. Two more distinct areas of intense thunderstorms trail south of Interstate 20 back to the west of the first band. The intensity has decreased with the loss of daytime heating and as the storms encounter more stable air near the ArkLaTex. However, the development of a low-level jet tonight should help to sustain the convection during the overnight hours. There is a quite a bit of uncertainty regarding the southeastward extent of this activity. Some of the models suggest a more northeastward track, basically in line with the Flash Flood Watch. Other models, notably the HRRR suggest a more southeastward track, followed by a turn to the south after daybreak. The HRRR may be on to something as radar and satellite loops do show some south and southeast propagation. However, confidence is still low, so will maintain the highest pops generally northeast of a line from Tyler TX to Prescott AR. PoPs were removed from the far eastern zones over North Central Louisiana. CN && .PREV DISCUSSION... /issued 703 PM CDT Tue Sep 1 2020/ UPDATE... See below for 02/00z Aviation Discussion. Heat Advisory will be allowed to expire at 00z this evening. There is quite a bit of uncertainty regarding the eventual track of the convection ongoing across North Central Texas as it moves into East Texas later tonight, and this will have implications in where an advisory might be needed for Wednesday. Some of the model guidance turns this complex more to the southeast, while others keep which matches very well to our Flash Flood Watch from Mineola TX to Hope AR. Therefore, a re- issuance of the Heat Advisory will be left to the midnight shift. CN AVIATION... For the 02/00z TAFs, a temporary lull in the convection will occur early in the period before another complex of strong thunderstorms moves into East Texas, Southwest Arkansas, and Southeast Oklahoma beginning around 02/05z. There may be yet another brief break for some locations around sunrise before another round of showers and thunderstorms develop in the same areas before noon Wednesday. KTXK, KTYR, and KGGG will likely be the TAF sites most affected by thunderstorms during the period. MVFR ceilings are expected to develop areawide during the overnight hours. Flight conditions will gradually improve except at sites where thunderstorms are ongoing. CN PREV DISCUSSION... /issued 215 PM CDT Tue Sep 1 2020/ SHORT TERM.../Tonight through Wednesday Night/ Finally beginning to see some widespread convection moving into our northwest zones, roughly north and west of the I-30 Corridor this afternoon and it has taken a strong southeastward moving outflow boundary to direct this precipitation into our region. Rainfall amounts have not been too excessive as of yet, nothing like our neighboring counties in Southeast Oklahoma and Southwest Arkansas have had to deal with earlier this morning with high water rescues, widespread flooding and several inches of rainfall. This evening into the overnight hours, several CAM suites are picking up on the outflow boundary to our northwest and rather intense convection developing later this evening into the overnight hours with the development of a southwest to northeast oriented 30-35kt low level jet max oriented parallel to the surface outflow boundary. This coupled with continued deep southwesterly flow aloft with ripples in this flow moving north and east towards the Middle Red River Valley overnight through Wednesday, providing the necessary upward forcing for scattered to numerous showers and thunderstorms with an increasing flood threat. For this reason, have added some counties south and west into Northeast Texas to the existing Flash Flood Watch which remains in effect through 00z Thu. The latest run of the 12z NAM is hinting at an axis of 8+ inches from just northwest of Smith County to just northwest of Texarkana beginning this evening and continuing through the day Wednesday. While this appears to be a worse case scenario, cannot ignore the potential given the players mentioned above. The upper trough will move out of the Four Corners Region of the Country overnight tonight and will attempt to become cutoff from the westerlies as it meanders across the Upper Red River/Tx Hill Country during the day Wednesday before slowly ejecting eastward Wednesday Night. Current FFA will likely need to be extended in time beyond 00z Thu but will let future shift make the call on just where it needs to be extended depending on rainfall over the next 24 hours. The same goes for the current Heat Advisory which remains in effect through 7 pm this evening. Uncertain on counties/parishes along the I-20 Corridor needing an extension to the Advisory into Wednesday but I could easily see our southern and eastern third needing the extension. Will allow future shifts to make this determination based on how much debris cloud cover we are dealing with on Wednesday from nocturnal convection overnight. 13 LONG TERM.../Thursday through Monday Night/ An upper-level trough from the Red River Valley of north Texas into Oklahoma and Missouri to linger through the weekend while slowly drifting south east. Instability associated with the upper-trough to maintain periods of convection through the weekend with a continued flash flood threat persisting each day. A frontal boundary will move through the region on Friday evening introducing a reinforcement of slightly cooler air across the region. Temperatures late in the week into the weekend to range from highs in the 80s to lows in the upper 60s to around 70. Rain chances to diminish through the weekend as the upper-trough shifts east and weak ridging builds in its wake. /05/ && .PRELIMINARY POINT TEMPS/POPS... SHV 79 88 75 89 / 30 50 40 40 MLU 77 95 75 93 / 10 20 20 20 DEQ 72 80 70 84 / 80 90 60 60 TXK 74 82 72 83 / 70 80 60 50 ELD 76 85 72 88 / 30 50 40 40 TYR 75 85 74 88 / 70 70 60 50 GGG 75 86 74 89 / 50 60 50 40 LFK 78 94 76 94 / 30 30 20 40 && .SHV WATCHES/WARNINGS/ADVISORIES... AR...Flash Flood Watch through Wednesday evening for ARZ050-051- 059>061-070. LA...None. OK...Flash Flood Watch through Wednesday evening for OKZ077. TX...Flash Flood Watch through Wednesday evening for TXZ096-097- 108>112-124-125. && $$ 09/33
Area Forecast Discussion...UPDATED
National Weather Service San Angelo TX
659 PM CDT Tue Sep 1 2020 .AVIATION... /00Z TAFS/ Scattered to numerous thunderstorms are moving east-northeast across the eastern Big Country, and across Coleman and Brown Counties this evening. Additional development of showers and thunderstorms is anticipated through late evening and tonight, mainly to the south across parts of the eastern half of West Central Texas. Localized strong, gusty winds are possible in and near the storms. Brief reductions in ceilings and visibilities are expected in the locally heavy rain accompanying the convection. Currently carrying a mention of thunderstorms in the KABI and KSJT TAFs, with VCTS at our other terminals. Will monitor radar trends and update TAFs as needed. Outside of convective activity, VFR conditions are expected, and winds will be primarily from the south tonight. On Wednesday morning, winds will become north at KABI and KSJT, but should remain generally from the south at our southern terminals. 19 && .PREV DISCUSSION... /issued 257 PM CDT Tue Sep 1 2020/ SHORT TERM... (Tonight and Wednesday) Current water vapor imagery shows an upper level low digging into southern Colorado and northern New Mexico...with southwesterly flow aloft in place across West Central Texas. At the surface, an outflow boundary from morning convection extended from the D/FW Metroplex westward across the northern Big Country. Isolated to scattered showers and thunderstorms are developing across the Big Country back down into the Heartland. High res model guidance and CAMs continue to develop numerous showers and thunderstorms through the remainder of the afternoon and into the overnight a shortwave trough in the southwest flow approaches from the west. In addition, current RAP analysis shows MLCAPE values of 2500+ J/KG along with 25- 35 knots of bulk shear across the northern half of our area. Thus, strong to severe storms are possible this afternoon and tonight with large hail and damaging winds the main hazards. SPC does have roughly the northern half of our CWA in a slight risk for severe storms. Also, heavy rainfall leading to localized flash flooding will also be possible given PW values of 1.9-2.1 inches across the Big Country and Heartland. The upper level trough axis will linger across the area on Wednesday leading to scattered showers and storms in the afternoon, with the highest rain chances across the eastern half of the CWA. Temperatures on Wednesday will only be in the 80s and lower 90s with the cloud cover and rain in the area. 42 LONG TERM... (Wednesday Night through next Tuesday) By Wednesday evening, models depict the axis of the upper level trough that will move into the area tonight along our eastern border or just east of our area. So, expect the scattered showers and thunderstorms if they develop tomorrow afternoon to be largely across the eastern half of the CWA, but could still have a few lingering showers and storms farther west. The upper low continues to slowly move east on Thursday, making it into eastern Texas. This would normally end rain chances, but with as much moisture as we will still have available, and the center of the upper ridge well west of our area, we could see a few showers/storms Thursday, so will keep a Slight Chance to Chance going on Thursday as well. The low then weakens, and is expected to slowly drift back to the southwest, grazing our southeastern counties. Because of that, will have to continue some PoPs through Saturday, but will show mainly Slight Chance PoPs through Friday and Saturday. The forecast then dries out for Sunday and Monday. Temperatures are expected to be fairly typical for this time of year through this weekend with highs in the upper 80s to mid 90s, with lows from the upper 60s to lower 70s. 20 && .PRELIMINARY POINT TEMPS/POPS... Abilene 71 86 68 90 / 60 70 40 30 San Angelo 72 89 70 93 / 50 50 30 20 Junction 75 91 71 93 / 60 50 50 30 Brownwood 71 87 69 90 / 70 80 60 50 Sweetwater 70 86 69 92 / 50 50 20 20 Ozona 72 91 71 93 / 40 30 30 20 && .SJT WATCHES/WARNINGS/ADVISORIES... None. && $$
...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday) Issued at 340 PM CDT Tue Sep 1 2020 Showers depart this evening with fog possible tonight and seasonable weather for Wednesday. Upper level lift associated with a departing northern stream wave was slowly decreasing over the forecast area, and with it the low clouds from west to east. To the west, an upstream PV lobe has dived southward towards the Four Corners region, detaching from the more vigorous polar jet and becoming embedded in a much slower sub- tropical jet. This feature meanders eastward over the next few days, gradually filling and being swept up with the next northern stream wave on Thursday. The resultant southwest flow and weak undulations in the mid- level flow ejecting from this western trough interacting with a complex, quasi-stationary lower tropospheric baroclinic zone have been responsible for periods of light showers over the eastern half of the forecast area today. Convection thus far has been shallow and short-lived, likely owing to a +10 C H700 warm nose. Some RAP forecast soundings depict a risk for deeper updrafts by late this afternoon at peak heating, but weak mid-level flow should result in poorly organized storm structures that would pose little more than a lightning risk. The threat for rain shifts south of the I-35 corridor tonight, with skies gradually clearing from west to east. While not the most ideal setup, the combination of light winds and recently wetted soils may result in overnight fog across much of the area. High clouds streaming northward from convection in OK/TX also may dampen fog prospects in the eastern forecast area; therefore, focused the highest fog potential between Clay Center and Topeka. Areas southeast of this region may see fog early in the evening, but there is considerable uncertainty with how the fog will behave towards sunrise as the clouds thicken. Will need to watch trends closely overnight. The ill-defined H925-H850 boundary meanders southward towards southeastern Kansas tonight into Wednesday as weak H300 ridging and an attendant surface high slide through the region. Forcing for ascent along the boundary lessens with the weakening of the sub-tropical jet and synoptic ridging building across the Northern Plains. Therefore, have kept the forecast dry for the day on Wednesday. Increasing sunshine and a downslope-modified H850 airmass should result in highs reaching the mid to upper 80s. .LONG TERM...(Wednesday night through Tuesday) Issued at 340 PM CDT Tue Sep 1 2020 The longer term forecast looks dry through the weekend with seasonal temperatures giving way to much cooler weather. The first in a series of strong Canadian cold fronts dives southeastward during the day on Thursday, but the parent upper trough rapidly progresses out ahead of the front, resulting in a dry frontal passage. With an amplified and progressive pattern in place, the trailing surface high passes east of the area by Friday morning, with return flow and WAA ensuing by the afternoon. Highs look to reach the upper 80s to low 90s for the first two days of the Labor Day weekend with southerly flow well-established. The medium range ensemble guidance diverges significantly on the timing of the next cold front late in the holiday weekend, with a 24+ hour spread amongst the various GEFS/EC members. Thus, confidence in the temperature and precipitation forecast for Labor Day is quite low. A fall-like change in temperatures awaits behind this front with polar air possibly lingering for much of the next week. Raw temperature guidance has some locations only reaching the 50s and 60s for highs and lows falling into the 40s. We may be flirting with record low max and min temperature values, which are around the mid-50s to low 60s for max temps and the upper 30s to low 40s for min temps. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 625 PM CDT Tue Sep 1 2020 Main concern for the forecast is with visibilities due to mist and fog, especially after 09Z. Forecast soundings show shallow saturation with nearly calm winds so have gone with mvfr to ifr vsbys at this time from 10Z-13Z. High clouds may inhibit vsbys falling to ifr or lifr, so will continue to monitor this evening. VFR conditions are expected after 14Z Wednesday. && .TOP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Skow LONG TERM...Skow AVIATION...53