Area Forecast Discussion
Issued by NWS Houston/Galveston, TXVersions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000 FXUS64 KHGX 230437 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 1137 PM CDT Sat May 22 2021 .AVIATION [06Z TAF Issuance]... SHRA activity has diminished around most terminals this evening, with a mix of VFR and MVFR conditions currently being reported in the most recent surface obs. Flight categories in the immediate term will be dependent upon sky cover...deck heights seem to be holding at around 1500-2500ft but coverage varies from SCT to OVC. That being said, MVFR conditions should largely be the story overnight and well into tomorrow. Scattered SHRA are expected to develop offshore tomorrow and later expand inland, though coverage should be concentrated in areas further west than today as the axis of strongest moisture concurrently pushes westward. Have continued with VCSH wording for the time being given expected coverage of any developing showers & storms. Brief patchy fog may once again be possible with ample near-surface moisture remaining in place and lighter winds overnight. Cady && .PREV DISCUSSION... /ISSUED 348 PM CDT Sat May 22 2021/ DISCUSSION... As the low that was Invest 91L continues to hang out over Texas, it will continue to bring us some breezy onshore flow along with a good bit of showers and thunderstorms. For most of the area this will not be a significant issue, as rain rates are expected to be fairly low. Closer to Matagorda Bay, however, we may see a change to locally heavier rainfall as a moisture axis becomes more stationary in that vicinity. Because of the copious amounts of rain that area has already seen, it will take less rainfall to cause issues, so a flash flood watch has been issued from late tonight through Sunday night. SHORT TERM [Through Sunday Night]... Widespread cloud cover and scattered rain will continue to move across southeast TX this afternoon and early evening. This activity is associated with a MCV (former Invest 91L) located over west- central TX. Low to mid-level instability is limited (5-6.5 C/km); however, with some daytime heating and forcing, a few lightning strikes cannot be ruled out. Models suggest some stretching potential west of I-45; however the better potential is just west of our forecast area (near I-35). Vorticity is weak in our region, but cannot rule out isolated weak funnel clouds developing over our far west/northwestern zones. Tight pressure gradient relaxes this evening, allowing wind speed to decrease to 10-15 mph or less. Rain should taper off this evening, before another round of showers returns early Sunday. Upper ridge over the Southeastern CONUS retrogrades westward, pushing a fetch of deep low to mid level moisture farther west (mainly west of I-45). In fact, this deep south to southeast flow will keep PWATs near 2.0 inches late tonight into late Sunday, resulting in scattered to numerous showers and isolated thunderstorms throughout the day, mainly west of I-45. There is still uncertainty on where the axis of heaviest precipitation will fall. At the moment, HiRes models and ensembles bring the convergence zone/moisture axis across our far southwestern counties (Colorado, Wharton, Matagorda and Jackson). Rainfall totals of 1 to 2 inches can be expected with locally higher amounts likely. Again, any flood threat will be dependent on where the heaviest precipitation axis falls. Given that soils are already saturated, have issued a Flash Flood Watch for our far southwestern counties until early Monday morning. LONG TERM [Monday Through Saturday]... By Monday morning, an upper ridge over the Southeast will be attempting to build its way to the west over our area. Lingering vorticity will likely prolong scattered rain chances through Monday, and will likely enhance diurnal convection on Tuesday, giving us one more day of enhanced rainfall in at least parts of Southeast Texas. More summerlike subtropical ridging should take hold on Wednesday, but it is not exceptionally strong. Between that and plenty of moisture on continued onshore flow, late morning and afternoon showers/storms should probably be expected Wednesday, though things may start to get turned off later in the week as the ridge and subsidence beneath it grows stronger. As one might expect with stronger ridging, we`ll also be looking for a warming trend deeper into the week as we look for less rainy and likely more sunny conditions - especially in the second half of the work week. MARINE... As the low pressure system formerly known as Invest 91L continues to spin over Central Texas, elevated winds and seas will continue across the area, though winds can be expected to very slowly diminish into tonight. The small craft advisory will be able to fall off first for the bays, as they respond most quickly to decreasing winds. However, SCEC conditions should remain on those waters into tonight. On the Gulf, elevated seas will take a longer time to subside, and so the small craft advisory there will continue tonight. Periods of showers and thunderstorms will accompany this system with rain chances lasting through the weekend. Tide levels will continue to run above normal as well. TROPICAL... Invest 91L moved onshore along the middle Texas Gulf Coast last night, and continues to make its wave across Central Texas. Lingering impacts from this low pressure center are discussed above in the AFD. Subtropical Storm Ana was named last night - it is of no threat to Southeast Texas, as it is located near Bermuda and drifting slowly far away from our area. Since these two events happened very close together, there may be a little confusion for some. To clarify, Ana is unrelated to the low pressure center in our area. && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 82 70 80 67 78 / 70 40 60 40 50 Houston (IAH) 81 70 80 69 79 / 70 30 40 30 40 Galveston (GLS) 80 74 80 74 80 / 60 30 30 40 40 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Flash Flood Watch through Monday morning for the following zones: Coastal Jackson...Coastal Matagorda...Colorado... Inland Jackson...Inland Matagorda...Wharton. High Rip Current Risk until 1 AM CDT Sunday for the following zones: Bolivar Peninsula...Brazoria Islands...Galveston Island...Matagorda Islands. Coastal Flood Advisory until 7 AM CDT Sunday for the following zones: Bolivar Peninsula...Brazoria Islands...Chambers... Coastal Brazoria...Coastal Galveston...Coastal Harris... Galveston Island...Matagorda Islands. GM...Small Craft Advisory until 4 AM CDT Sunday for the following zones: Coastal waters from Freeport to Matagorda Ship Channel TX out 20 NM...Coastal waters from High Island to Freeport TX out 20 NM...Waters from Freeport to Matagorda Ship Channel TX from 20 to 60 NM...Waters from High Island to Freeport TX from 20 to 60 NM. && $$ Discussion...99 Aviation/Marine...99
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