Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 11 2022 23:47:31 FOUS30 KWBC 112347 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 646 PM EST Sun Dec 11 2022 Day 1 Valid 01Z Mon Dec 12 2022 - 12Z Mon Dec 12 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CALIFORNIA COASTAL RANGES... ....Central and Southern California Coast... A compact mid- to upper-level low with a cold pool aloft will be dropping south down along the central CA coast from Sunday night into early Monday morning, bringing a new surge of onshore flow into the coastal ranges of central and southern California. Due to the cold pool aloft, a pool of 500+ J/kg of MU CAPE will also be available (as seen on recent SPC mesoanalyses), bringing greater heavy rainfall efficiency than one would normally expect out of 0.50"+ precipitable water values. With spots of effective bulk shear of 25 kts, short bands of showers or thunderstorms will be possible, which could be capable of producing hourly rain totals up to or exceeding 0.50"/hour. An additional 1 to 2 inches of rain will be possible locally, which could occur quite quickly. Given the heavy rainfall since Saturday, and localized burn scar considerations, these bands of heavy showers and thunderstorms may result in some isolated runoff concerns. Maintained the Marginal Risk from Point Arena southward to account for this possible threat. Roth/Bann/Orrison Day 2 Valid 12Z Mon Dec 12 2022 - 12Z Tue Dec 13 2022 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS... 2030 UTC Update... Made a slight adjustment to the eastern side of the Marginal Risk area due to some uncertainty in the forward speed of the area of showers and thunderstorms that gets ejected eastward. A Marginal Risk remained in place for the update. Bann ....Southern Kansas...Central Oklahoma...Northern Texas... A strong upper-level trough and associated cold front will be ejecting east out toward the central and southern High Plains Monday night and Tuesday morning. A strengthening southerly low-level jet is forecast to reach 50 to 60 kts Monday night ahead of the front which will yield very strong moisture transport/convergence and a return of at least an elevated pool of instability (MUCAPE of 500 to 1000 J/kg). The rapidly improving thermodynamic environment coupled with strong upper-level divergence arriving ahead of the ejecting upper trough will set the stage for a developing axis of rather organized convection at least in a broken fashion across the central and southern Plains with the latest guidance emphasizing an area from southern KS down through northern TX for the heaviest amounts. The convection will tend to be rather progressive, but the improving shear parameters and enhanced moisture transport will favor convective cells capable of producing 1 to 2 inch/hour rainfall rates going into early Tuesday morning. The 06Z to 12Z/Tuesday time frame is generally the window in which convection will be initiating and growing upscale, although some activity may begin Monday evening. A Marginal Risk area is maintained for this update. Orrison Day 3 Valid 12Z Tue Dec 13 2022 - 12Z Wed Dec 14 2022 .....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE LOWER MISSISSIPPI VALLEY... ....2030 UTC Update... Numerical guidance continued to support the large scale forcing advancing eastward across the Plains into the Midwest. There was a subtle slowing of the model QPF...so expanded the western portion of the Marginal Risk area to account for that possibility. It also allowed a bit more overlap with the Day 2 ERO. While there may be some uncertainty with respect to the exact speed...confidence remains above average confidence in the heavy/excessive rainfall threat. Bann ....Lower Mississippi Valley... A well-organized and strong outbreak of convection is expected to impact the lower MS Valley and northwest to central Gulf Coast region on Tuesday and extending through early Wednesday as a strong upper-level trough and associated closed low advances east out across the Plains and toward the Midwest. A strong cold front will be advancing steadily east through the lower MS Valley and will be encountering an increasingly moist and unstable airmass lifting north from the Gulf of Mexico with the aid of a 50+ kt low-level jet. This jet energy will be fostering PW anomalies reaching 2+ standard deviations above the mean along with 850/700 mb moisture flux anomalies in the 3 to 4 standard deviation range above the mean. Enhancing upper-level jet dynamics and strong mid-level flow will set the stage for strong shear profiles which coupled with the pooling of moderate instability (MLCAPE values of 1000 to 1500 J/kg) and aforementioned moisture profiles should yield a rather widespread area of organized convection. The concern will be for bands of locally repeating/training convection, including supercells, across the region which will be capable of producing multiple swaths of 2 to 4 inch rainfall totals. Some locally heavier amounts cannot be ruled out given the strength of the moisture transport. The convective threat should extend across the entire 24-hour period going into Wednesday morning, and in time the convection will become focused closer to the Gulf Coast as the convection transitions more into a QLCS in time and interacts with the nose of the low-level jet coming inland off the Gulf of Mexico. There will be concerns for areas of flash flooding for this period as the larger scale convective event unfolds and organizes. A multi-model consensus of the latest QPF and a look at the CSU ERO first-guess fields suggest generally above average confidence in the heavy/excessive rainfall threat. Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_0UlyfarMLM3LbRkp5xnuDvny1ZiQVGqbf4DpU1MhSKd= LBL8cJ93crRwqd9zu9kW3oGRDFZw4wloYcgnxNvRFEmeIEs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_0UlyfarMLM3LbRkp5xnuDvny1ZiQVGqbf4DpU1MhSKd= LBL8cJ93crRwqd9zu9kW3oGRDFZw4wloYcgnxNvRBrR_03s$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_0UlyfarMLM3LbRkp5xnuDvny1ZiQVGqbf4DpU1MhSKd= LBL8cJ93crRwqd9zu9kW3oGRDFZw4wloYcgnxNvRumJpIgc$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .