153 FXUS64 KHGX 030548 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 1148 PM CST Wed Jan 2 2019 .AVIATION... Radar imagery is continuing to show the first band of showers push southeastward this evening, currently stretched across LBX and HOU. This first round of rain should continue to push off to the east of all terminals over then next hour or two. Anticipating a short break in the rain through about 09Z, when another round of light to moderate rain should fill in starting across the northern terminals before spreading southeastward. Most of the precipitation should end by the early afternoon hours, clearing at CLL around 19Z and eventually GLS closer to 00Z. Overall, confidence is low on the progression of the rainfall, as short term guidance has really struggled to initialize well with current radar imagery. Ceilings should remain at IFR/LIFR criteria through the morning and into the early afternoon, slowly rising and scattering out by the evening hours. Visibilities should also improve in a similar progression as the rainfall shifts east of the terminals tomorrow afternoon. Sustain NW winds are anticipated to range between 09-16kts, with gusts higher near 25 kts at times. Hathaway && .PREV DISCUSSION... /ISSUED 921 PM CST Wed Jan 2 2019/ DISCUSSION... At 8 PM, a weak area of low pressure was over the western Gulf with a weak meso-low in the Brazos Valley. An 850 mb low was over SW TX and 850 mb dew points were 13-14 C. At 300 mb, a strong upper ridge was near southern FL with a deep upper trough extending from the upper midwest into the southern Rockies. Upper level winds were split over SE TX and lift was enhanced with a 125 kt speed max over northern Mexico. Isentropic upglide coupled with a broadly diffluent upper flow and a weak coastal trough will continue to generate periods of light to occasionally moderate rain. Rainfall today has averaged 1-2 inches with some isolated totals approaching 3 inches. Soils are saturated and the impact from todays rain far outweighs the magnitude of the rainfall. Because there appears to be so much runoff, feel it's best to maintain the Flash Flood Watch overnight. Don't think the area will get much more than 0.50-1.00 inches of additional rainfall but that might be enough to generate some minor flooding. 43 PREV DISCUSSION... /ISSUED 604 PM CST Wed Jan 2 2019/ AVIATION... MVFR/IFR ceilings and visibilities persist area wide. Radar imagery shows two main bands of showers and isolated thunder, one oriented over our northern terminals and the second stretched over the metro terminals. Light rain is continuing to fall over the coastal TAF sites as well. Overall, coverage should continue to fill in over the next few hours through approximately 03Z. This round of precip will provide the best chance for moderate to heavier rainfall and isolated thunder. Anticipating a short break during the overnight hours until the early morning around 09Z, when a second round of precipitation moves in from west to east. This second band should contain lighter precipitation. As a result, ceilings and visibilities will remain rather low, fluctuating between MVFR to LIFR ceilings during the early morning hours. Short term guidance shows most of the precipitation shifting east of all terminals by the afternoon hours between 20-23Z. Winds behind the cold front will be out of the northwest between 8 to 15 kts, with gustier conditions closer to the coast. Hathaway PREV DISCUSSION... /ISSUED 350 PM CST Wed Jan 2 2019/ DISCUSSION... A gray and dreary day across Southeast Texas today will continue into tonight. The rain that has fallen so far will further saturate soils for more rain tonight, and so the flood watch will continue for now. Look for rain to clear out through the day tomorrow, and then we will see fair weather for several days - until a weak front arrives on the scene early next week. After another brief shot at rain, fair weather returns for much of next week. NEAR TERM [Through Tonight]... Periodic bouts of rainfall have dominated the day not just across Southeast Texas, but all of North and East Texas. Fortunately, the heaviest rain so far has fallen just to our north and just to our east, but a storm total of between half an inch and an inch in bands that swipe the northwest part of the Houston metro, and another around/just north of Bryan/College Station. In Harris County, localized spots have seen up to 1.5 inches total. And though no such reports have been received in the other band, it's likely similar there. All in all, the rainfall so far is certainly not enough to cause flooding on its own. However, soils were already fairly saturated, and this continuous rain will not help matters. Radar indicates stronger convection up around B/CS, where lightning is being observed, but also in a band of rain that looks to have stronger convective cells offshore. Indeed, that offshore band looks to have set up a very strong training signature, and could cause issues in Chambers or Jefferson County should it drift downstream. This increase in intensity has been anticipated, and the strongest impacts may be driven by rainfall beginning now and into tonight. There are still no indications that we'll see the typical flooding threat caused by short, but extremely intense convective rainfall. Instead, we'll see nigh continuous rainfall, and with the wet soils and dormant vegetation, expect the rain to be more efficiently converted to runoff. This could cause issues near small streams, typical low spots that see collection of drainage, and other locations with poor drainage. SHORT TERM [Thursday Through Friday Night]... Expect rain/drizzle/fog to linger through the day Thursday, but things should start to clear out for all but the far east by evening. By Friday morning, look for skies to be largely clear west of I-45, with partly cloudy skies to the east, gradually becoming clear across the entire area. Expect drier and cooler air to flow in as the upper low bowling balls its way off to the east, and though the forecast doesn't explicitly forecast any freezing temps, it's certainly not impossible way up in the northwest on Thursday night. Mitigating the temperature fall will be the fact that the upper low itself has been Pacific in origin, and the incoming air mass will be streaming in on winds that are more westerly than northerly. So, once the coldest air trapped in the core of the upper low moves on, things should rebound relatively quickly. LONG TERM [Saturday Through Wednesday]... An upper ridge builds in over the weekend, accelerating the warming trend. Adding to things will be the drifting of the surface ridge to our east, re-establishing onshore flow. Low temps should shoot right on by seasonal averages, and by next Monday, widespread high temperatures around or above 70 degrees look likely. However, also by Monday, the upper ridge will have moved off to the east, and the next trough in the northern stream will dig into the Central Plains. It will be supporting a clipper shooting through the Great Lakes, and trail a front - albeit almost surely a weak one - down into Texas. Look for that front to arrive at some point Monday night. While the GFS is a bit faster than the Euro, there seems to be a broad consensus between the two on the broader timeframe. The Canadian is a bit slower still, but even then it posits a Monday night/Tuesday morning frontal passage. Guidance also seems to generally agree that the front will not generate much in the way of precip for us, and that should probably be expected with a front tied to a Great Lakes clipper. Still, some slight chance to chance PoPs seem reasonable given that we'll have plenty of time for onshore flow to build a reserve of moisture for the area. Indeed, the GFS progs a pretty impressive 1.5-1.75 inches of precipitable water ahead of the front. After that, fair weather returns for much of the rest of the week until a lee cyclone crossing the Plains will bring us our next front and a shot at precipitation. MARINE... Winds 15 to 20 knots across most of the area and have made some changes to the SCEC to extend it as winds in the wake of the frontal push should max out near 20 knots and linger well into Thursday. Winds in Galveston bay have been bouncing around between 12-14 and 18-20kts. Winds and seas should start coming down Friday morning as high builds in to SETX. Low tide Thursday night/early Friday morning will probably warrant a Low Water Advisory for that low tide before recovering. 45 HYDROLOGY... Main concerns will probably be over the Cypress, Spring basins, Cedar Bayou and the East Fork of the San Jacinto and Trinity river channels. Given the expected rainfall today and Thursday. Greater amounts should focus in the eastern counties and earlier rains today have done a good job of saturating the soils along the upper reaches of the Spring/Cypress basins. Minor flooding will probably be the main impact...possibly moderate along the Trinity and/or the East Fork. 45 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 43 41 46 34 56 / 100 90 90 10 0 Houston (IAH) 51 48 50 37 55 / 100 100 90 10 0 Galveston (GLS) 54 52 53 42 54 / 100 90 90 10 0 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Flash Flood Watch through Thursday morning for the following zones: Austin...Brazoria Islands...Brazos...Burleson... Chambers...Coastal Brazoria...Coastal Galveston...Coastal Harris...Fort Bend...Galveston Island and Bolivar Peninsula...Grimes...Houston...Inland Brazoria...Inland Galveston...Inland Harris...Madison...Montgomery...Northern Liberty...Polk...San Jacinto...Southern Liberty...Trinity... Walker...Waller...Washington. GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 3 AM CST Thursday for the following zones: Galveston Bay...Matagorda Bay. Small Craft Advisory until 3 AM CST Thursday 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. Small Craft Advisory until 6 PM CST Thursday 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...43 Aviation/Marine...08