Subj : HVYRAIN: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 19 2023 07:50:58 FOUS30 KWBC 190750 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 250 AM EST Sun Feb 19 2023 Day 1 Valid 12Z Sun Feb 19 2023 - 12Z Mon Feb 20 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST ARIZONA AND SOUTHERN NEW MEXICO... A compact, highly anomalous closed low has dropped west of Baja California pushing standard deviation over 3.5 and well into 99th percentile for this time of the year. Already CIRA LPW PW values are starting to increase along the southeast side of the circulation with strengthening southwesterly flow bringing mid-level moisture across northwest Mexico initially, with sfc to 700mb moisture lifting north. Eventually, total PWat values will reach 1.25" along Baja CA into the lower elevations of Sonora, bringing 2-3 standard deviation moisture values into the region.=20 The inner core of the core will slide northeast into the California Bight and strengthen flow along the atmospheric river with .75 to near 1" total PWat values into the higher plateau across northeast Sonora, southeast Arizona, southwest New Mexico.=20 This is near record moisture for the date and even near monthly record with both GFS and ECMWF all-time period maxima in IVT (moisture transport) accounting for the acceleration of the low level winds. Winds in the 850-700mb layer will strengthen along 700mb vorticity stripe across Northern Old Mexico as the right entrance of the polar jet strengthens over the southern Rockies throughout the day (reaching 150kts along the CO/NM border at 22.00z). The overall acceleration will support IVT values over 500 kg/m/s. While the moisture is solid, it will not be unstable with CAPE values expected below 25 J/kg throughout the length of the atmospheric river stream. In fact, the forcing is going to limited toward orographic ascent and given the axis of upper level right entrance ascent is narrow, the expected band of showers is expected to be similarly narrow and weakly anti-cyclonically curved. Now, the plume may be narrow but it will strong convergence along the westward facing north-south ranges of far Southeast AZ, southern NM, and Sonora. The persistence and record moisture will support consistent moderate rainfall within the orography with up to .1-.2"/hr rates occasionally peaking near .25". This will support 24hr totals of 1.5-2" with perhaps isolated 2.5-3" along the highest peaks (8-10Kft) where winds are stronger and the moisture depth remains sufficient. There remains latitudinal spread in the placement of the narrow band, mainly driven by the amount of shortwave ridging along/ahead of the closed low. The NAM and its hi-res CAM family members are driving the axis further north to affect the Chiricahua and Guadalupe Mts in AZ, southern Black/Pintos Altos Rangesin NM. With these sort of maxim totals, the suite is driving HREF probability signals further north into SE AZ/SW NM indicative of Marginal Risk category for Excessive Rainfall. However, global models (GFS/ECMWF) and other hi-res CAMs such as the FV3CAM, ARW and Canadian Regional further south focusing on the mountains of northeast Sonora. Satellite trends along with model to model comparisions, suggest a flatter solution shedding energy into the Southern Plains a bit faster. This results in the plume staying at the Mexico boarder and south, until around the Rio Grande Valley, where it lifts a bit to direct the plume into the Southern Sacramento Range in NM as well as intersecting the Franklin Range and Sacramento Mtns near Guadalupe Pass in TX. While this is favored, the northern solutions cannot be fully ignored and as such small adjustments were made to the Marginal Risk particularly with orographic ascent being the dominant forcing for prolonged anomalous rainfall totals throughout the day. Flash flooding is not expected given the lower rates; however, atypical flooding within washes emanating from the mountain ranges is probable. The best forcing will be diminishing around the 20.12z time frame, as the upper-level right exit region will start to dominate as the closed low approaches, the AR will also focus further south into higher terrain of S Sonora.=20=20 Gallina Day 2 Valid 12Z Sun Feb 19 2023 - 12Z Mon Feb 20 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....Southeast AZ/Southwest NM/Western Texas Panhandle... The northwest Mexico Atmospheric River from Day 1 period will have low potential to still be ongoing at the 20.12z end valid time.=20 Best forcing should be diminishing by 20.06z, as the favorable right entrance of the upper level jet streak over N NM/CO has shifted into the Southern Plains, concurrently the jet streak rounding the eastern periphery of the closed low near the California Bight will be drifting across Sonora providing=20 upper-level decent likely suppressing remaining shower activity.=20 Additionally, low level flow, moisture plume will be directed further south across S Sonora toward Sinaloa, and not likely to track through the higher terrain of the Sierra Madre Occidental to affect AZ/NM any further. Flooding may still be ongoing at 20.12z toward 18z accounting for this lingering light rain, as well as, water still washing out of the higher terrain that fell in the Day 1 period. Gallina Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8ISA4_ook6_VIVg_3GioN8iSJxuxlz9psgG9Qy1t4ypi= x9QDZH4ACBu6jiSRc4OPiZj2qqYmdK1yuq8SLedeUoRX8l0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8ISA4_ook6_VIVg_3GioN8iSJxuxlz9psgG9Qy1t4ypi= x9QDZH4ACBu6jiSRc4OPiZj2qqYmdK1yuq8SLede63P9GD0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8ISA4_ook6_VIVg_3GioN8iSJxuxlz9psgG9Qy1t4ypi= x9QDZH4ACBu6jiSRc4OPiZj2qqYmdK1yuq8SLedevDhSL_8$=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) .