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
381 FXUS64 KHGX 232230 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 530 PM CDT Sun May 23 2021 .AVIATION... Short term guidance is struggling to pinpoint the moisture axis so confidence in the details is rather low. Overall, the synoptic situation is clear, with high pressure to the east and lower pressures out west allowing for a continued onshore flow. Moisture levels remain near 2.00 inches so it`s plenty moist with the moisture directed at SE TX. CAMs want to shift the moist axis to the SW but time and again, it remains locked along the I45 corridor. Have broadbrushed VCSH and tempoed in the short term for SHRA. Ceilings are tough as well. Winds should decouple this evening so am expecting MVFR ceilings to redevelop and precip to wane but will IFR cigs develop? Probably out west near KCLL but the still expecting MVFR at KIAH and KHOU through morning. 43 && .PREV DISCUSSION... /ISSUED 343 PM CDT Sun May 23 2021/ DISCUSSION... If images were allowed in this discussion, this synopsis could probably be replaced with a Fry meme that says "Not sure if Houston or Seattle". Our flash flood watch continues over the Matagorda Bay area as the hardest hit area continues to see rounds of showers and thunderstorms. We`ve been lucky so far to avoid excessive rain rates today, but the potential to get storms producing excessive rain in this saturated area will remain through tomorrow afternoon. An end to this dreary weather, a return to a more typical diurnal pattern of scattered showers, and a warmup to high temperatures closer to 90 degrees are all in our future. But...we`ve got to make it through the next 24-36 hours first. SHORT TERM [Through Monday Night]... You know that when GOES can`t derive any pixels in your forecast area in its precipitable water product due to cloud interference, it`s probably pretty moist. A few pixels just outside the area range from 1.9 to 2.2 inches, which matches up fairly well with the modeled estimate of 1.9-2.1 inches in the SPC mesoanalysis. All in all, it`s pretty obvious why we`ve seen widespread light to moderate rain, with some sporadic cells with heavier rain across the entire area for the entire day. If anything, the moisture plume did not work quite as far down the coast as anticipated today. Because of this, gave a though to extending the flash flood watch in both time and area. Went ahead and worked with the neighbors in extending through Monday afternoon, but held off on expanding the watch up into Brazoria and Fort Bend counties. While they have seen more of the brunt of the "heavier" rainfall today, their antecedent rain was not quite as significant as down towards Matagorda Bay, and so this area has been generally able to handle the observed rain rates so far. That said, future shifts will have to keep an eye on conditions and see how things are behaving. As mentioned before, I did opt to continue the flash flood watch going through Monday. This morning`s HREF keeps the moisture plume pretty well in place, and again its heaviest rainfall is in the watch area. There is again a signal in the 3-hr probability matched mean product for 3 inches per 3 hours through the afternoon. Beyond the rainfall potential, I did not make much in the way of changes. The main one is to even further narrow the temperature range across the area, given the continued stretch of cloudy, rainy weather. Eventually...eventually...I think...deeper ridging will take hold over the area, shutting off the faucet and letting us get a break from the rain, an increase in temperatures, and yes, even a glimpse of this mythical thing known as sunshine. But that`s likely not happening today or tomorrow. Check for the long term section for some more optimism on that front. LONG TERM [Tuesday Through Sunday]... Southeast TX will continue to be positioned between a broad ridge centered over southeastern CONUS and a trough across the western CONUS. At the surface, deep southeasterly flow will continue to surge Gulf moisture inland, thus shower and thunderstorm chances for Tuesday and Wednesday. The best chance for this activity is expected during the day on Tuesday, thanks to diurnal heating and some forcing associated with a weak mid-level shortwave moving over north- central TX. Showers and thunderstorms should gradually taper off by Tuesday evening. Showers and thunderstorms on Wednesday are primarily diurnally driven with the best chance in the afternoon and early evening. Upper-level subsidence should strengthen after midweek as the sfc high and ridging aloft slightly moves westward into the region. This will decrease PoPs into the weekend; albeit afternoon spotty/isolated showers/storms cannot be ruled out towards the end of the long term period. A warming trend is expected with high temperatures reaching the mid to upper 80s towards the end of the week. Low temperatures will generally be in the 70s. AVIATION [18Z TAF Issuance]... "Difficult" is the polite term to describe the ceiling forecast for the rest of this afternoon. CIGs will probably range from mid-MVFR (015-020) to very clearly VFR (as high as 090!). Have tried best to match the forecast to reality, but amendments may be needed. Beyond that, the big picture idea of a dreary forecast is on track. Overnight, bring widespread MVFR back to the area - and some guidance hints at high IFR ceilings, so that may be something to watch for. Then tomorrow looks a whole heckuva lot like today. MARINE... Scattered to numerous light to moderate rain will continue to move over the Gulf waters and bays tonight and Monday. A few lightning strikes will be possible. Latest observations show east winds 15-25 kt and elevated seas from 6 to 8 ft over the offshore waters. Have extended the Small Craft Advisory for the 20-60 nm waters until Monday morning. Caution flags are in effect for the nearshore waters and bays until midnight, but will continue to monitor trends for possible extension. Southeast winds and seas should begin to diminish by late Monday, but tides will remain elevated. Precipitation chances continue through Wednesday. Surface high over the southeastern CONUS slightly moves westward after mid-week, bringing relatively dry conditions. HYDROLOGY... On top of the flash flood watch, we also have numerous river flood warnings in effect as rains quickly runoff of saturated soils and into area streams and rivers. The highest impact so far is on the Trinity, San Bernard, and Lavaca-Navidad watersheds. These rivers will likely see rises with further rainfall over the next day or so, and given the length of this rainy episode, will also take some time to come down from their crests. Continue to monitor the latest flood statements if a flood warning is in effect for your area. && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 68 79 69 82 71 / 60 90 30 70 20 Houston (IAH) 70 79 70 83 72 / 50 70 40 60 10 Galveston (GLS) 73 80 74 82 76 / 40 60 20 40 10 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...High Rip Current Risk until 1 AM CDT Monday for the following zones: Bolivar Peninsula...Brazoria Islands...Galveston Island...Matagorda Islands. Flash Flood Watch through Monday evening for the following zones: Coastal Jackson...Coastal Matagorda...Colorado... Inland Jackson...Inland Matagorda...Wharton. GM...Small Craft Advisory until 7 AM CDT Monday for the following zones: 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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