Area Forecast Discussion
Issued by NWS Houston/Galveston, TX
Issued by NWS Houston/Galveston, TX
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729 FXUS64 KHGX 170512 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 1212 AM CDT Fri May 17 2024 ...New AVIATION... .SHORT TERM... (This evening through Friday Night) Issued at 242 PM CDT Thu May 16 2024 As of the time of writing (2PM CDT), a strengthening MCS is approaching the area from the NW, with large-scale development aided via the approach of a robust midlevel trough which continues to swing westward into the Southern Plains. The continued approach of this system, and its eventual impacts on SE TX throughout the remainder of the afternoon and evening, presents both a severe weather and a potentially significant flash flooding concern. As indicated by recent SPC mesoanalysis, environmental conditions ahead of the system`s approach remain favorable for both heavy rain and severe storms. This includes: - Abundant moisture availability, with total PWs of 1.8 to 2.2 in across portions of the area and a steady low-level jet continuing to supply the region with warm, moist Gulf air. - Ample instability, with SB CAPE values in the region of 3000 - 4500 J/kg across portions of the area as well as limited convective inhibition (CIN) and mid-level lapse rates of 7-8 degC/km. - Effective layer bulk shear of approximately 50-60 knots, with forecast soundings indicating a favorable backing directional shear profile. - A pocket of effective layer helicity of approximately 200 m^2/s^2 across portions of the Greater Houston area, supporting the isolated tornado risk. - Forecast Downdraft CAPE (DCAPE) values of approximately 700-1100 J/kg over the next several hours. As such, we continue to keep a close eye on the radar over the next 4-6 hours. Stronger storms may produce large hail and strong wind gusts, as well as the aforementioned isolated tornado threat. Thunderstorm activity should become widespread over the next 1-2 hours as the complex pushes roughly from the NW to the SE, first reaching the Brazos Valley and advancing towards the coast as we head into the evening. Development will be further aided by the presence of a stalled warm frontal boundary, which is expected to sit just north of the I-10 corridor and extend to the east into the Piney Woods region. Given this setup, along with the significant ground saturation in place from recent rainfall, has resulted in the WPC placing the region (roughly NE of metro Houston) in a High Risk area for Excessive Rainfall. High resolution models indicate the potential for 3-6" of new rainfall across the area through this evening, with some locally higher amounts in excess of 6" possible where the strongest storms set up. In addition to flash flooding, this rainfall (and the subsequent runoff) will contribute and/or exacerbate flooding along area rivers, streams, and creeks. Further south and southwest, we continue to anticipate the potential for 2-4" of new rainfall for metro Houston and lower (0.5-2") amounts closer to the coast. Storms should generally push through the Brazos Valley between around 3-5PM, metro Houston around 5-7PM and the coast around 7-9PM. Some lingering showers may persist further into the evening, particularly along the coast. The warm frontal boundary will sag southward with the complex, likely stalling out near the coast. Tomorrow, the approach of a weak shortwave along with the presence of a stalled boundary near the coast will result in another round of scattered showers and storms. This will not present nearly as significant as a severe weather/flooding threat as today, but will nonetheless produce some additional measurable rainfall (especially along and south of the I-10 corridor). Cady && .LONG TERM... (Saturday through next Wednesday) Issued at 242 PM CDT Thu May 16 2024 Quieter weather conditions are expected in the long term period. A warming trend with near to above normal temperatures is expected as ridging aloft builds over Mexico. The NAEFS/GEFS standardized anomaly table maintains 1 to 2 standard deviations above normal for 500mb heights from next Monday through the end of the week. This adds confidence that hot conditions will return into our area. With sfc high pressure to our east, a southerly warm and humid airmass will continue to filter in, resulting in hot and muggy conditions through the week. Highs will generally range into the upper 80s to mid 90s. Overnight lows mainly in the low 70s. A cool front will attempt to move across the region by mid-week. Given the strong influence of the ridge aloft; any precipitation will need to fight the amount of dry layer at mid-levels. Have only included around 15 percent of PoP across our far northern counties for Wednesday and Thursday. JM && .AVIATION... (06Z TAF Issuance) Issued at 1158 PM CDT Thu May 16 2024 MVFR with occasional IFR CIGS will fill in over SE Texas during the early morning hours of Friday. Expect CIGS to gradually lift after sunrise, eventually returning to VFR levels later in the day. Areas south of I-10 may see scattered showers and isolated storms throughout the afternoon as another disturbance passes overhead. Rain chances taper off Friday evening. 03 && .MARINE... Issued at 242 PM CDT Thu May 16 2024 A few showers and storms can be expected this afternoon and evening ahead of a disturbance and a frontal boundary moving through SE TX. The best precipitation chances will be on Friday along the aforementioned boundary. Moderate onshore winds and seas around 3 to 5 ft are expected tonight. Small Craft Should Exercise Conditions are in effect for all Gulf waters. Winds may reach advisory levels at times. A brief window of offshore winds are expected by Friday as the boundary moves through the waters. This boundary will possibly stall over the coast through Saturday. Dry weather with light to moderate onshore winds and low seas are expected for the remainder of the period. JM && .HYDROLOGY... Issued at 242 PM CDT Thu May 16 2024 Areas of showers and thunderstorms are expected to continue to affect portions of Southeast TX through early tonight. Periods of heavy rainfall is expected with this activity through this evening with some rainfall rates of 2 to 3 inches per hour are possible. Rainfall totals are estimated to be 3 to 6 inches with isolated higher amounts for areas north of I-10 and 1 to 3 inches with isolated higher amounts elsewhere. Flash flooding can be expected as well as rises in rivers, small streams, creeks and bayous. Runoff and rainfall over the rivers upstream can result in further rises along the rivers over the next few days. Minor to major river flooding continues for parts of Southeast Texas, particularly along portions of the Trinity and Brazos rivers. The following river points are either currently in flood stage or are forecast to reach flood stage (as of Thursday afternoon): - Trinity River (Liberty): Major Flood Stage - Trinity River (Goodrich): Minor Flood Stage rising to Major - Trinity River (Riverside): Moderate Flood Stage - Trinity River (Moss Bluff): Moderate Flood Stage - Trinity River (Crockett): Minor Flood Stage - East Fork San Jacinto (New Caney): Minor Flood Stage rising to Moderate - Navasota River (Normangee): Minor Flood Stage rising to Moderate - Brazos River (Rosharon): Minor Flood Stage - Menard Creek (Rye): Rising to Minor Flood Stage - Brazos River (Sugar Land): Rising to Minor Flood Stage Soils are already saturated from the previous rounds of rainfall in the Piney Woods and this is where we expect the highest rainfall totals once again, so we could see the rain become runoff fairly quickly and caused additional responses along area rivers/creeks. Please be sure to stay up to date on the latest forecast information. Please monitor updated forecasts via the NWS AHPS website and/or the new NWS NWPS webpage (https://water.noaa.gov/) as the river flood threat continues. Cotto && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 65 82 67 89 / 60 10 10 10 Houston (IAH) 68 83 69 91 / 70 30 10 10 Galveston (GLS) 69 81 74 84 / 60 30 20 10 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...None. GM...Small Craft Should Exercise Caution until 4 AM CDT Friday for GMZ335. Small Craft Should Exercise Caution until 10 AM CDT Friday for GMZ350-355-370-375. && $$ SHORT TERM...24 LONG TERM....JM AVIATION...03 MARINE...JM