960 FXUS64 KHGX 030357 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 957 PM CST Fri Dec 2 2016 .UPDATE... The well-advertised rain event for Southeast Texas has begun today, with the first wave of rain showers moving through. The most intense rain has come over the offshore waters, and is where a small handful of CG strikes have occurred. Mesoanalysis has shown significant low level shear and helicity, and this has largely been reflected in the resultant cells, as even small showers have shown weak rotation, particularly over the waters closer to the surface trough axis. Whether or not this has translated to waterspouts is unknown, with no reports received. But as a result, there has been a sensitivity to potential for landfalling waterspouts/tornadoes right on the coast this evening. However, to this point, this threat has not seriously emerged. This may be shown by examining effective SRH, rather than defined 0-1km or 0-3km SRH, which has been significantly lower. Despite the favorable kinematic environment, it does not seem to translate well to the inflow layer of our cells this evening. Rainfall so far has been relatively light, despite isolated cores of 1-2 inch per hour instantaneous rain rates. These cores are too small and moving too quickly, and thus precip so far does not appear to exceed half an inch. Still, there is a long weekend with plenty of rain ahead, and the expectation was already for this evening to be a relatively low contributor to the total rainfall. Thus, the potential for eventual excessive rainfall is not changed at this time. Changes to the forecast have been relatively minimal, as the focus has been more on mesoanalysis and radar meteorology. Fortunately, the forecast from this afternoon has been tracking relatively well. The biggest changes have been to PoPs, in an attempt to blend current rainfall with hi-res, short term guidance in the near term. Into tomorrow, the forecast weights to the more broad- brushed previous forecast, as confidence in CAMs highlighting the true areas of heaviest rainfall decreases. Luchs && .PREV DISCUSSION... /ISSUED 554 PM CST Fri Dec 2 2016/ AVIATION... Low forecaster confidence level on the 03/00Z TAFS. Looking for mainly periods of SHRA possibly embedded with TSRA this evening, with activity becoming more widespread/numerous during the overnight hours and on into tomorrow. Majority of the 00Z TAFs have MVFR ceilings overnight with IFR conditions possible during the day tomorrow. IFR/LIFR ceilings and visibilities are likely with any hard to time strong SHRA/TSRA. Winds (both speed and direction) will be tricky and will depend on when/where any boundaries set up. Generally have gusty east winds for much of the area tonight through tomorrow morning becoming northeast inland and east to southeast near the coast tomorrow afternoon. 42 PREV DISCUSSION... /ISSUED 346 PM CST Fri Dec 2 2016/ DISCUSSION... All of the ingredients for what is setting up to be a high rainfall event are coming into place. The coastal surface trough axis is currently just offshore...with the greatest rain coverage occuring over the northwestern Gulf this afternoon. Bands of precipitation are coming onshore and these bands will continue to increase in areal coverage through the evening hours. The main threat with these bands will be isolated tornadoes embedded within them as lower level winds significantly turn within the lowest couple of kilometers. A developing warm frontal boundary moving up towards the upper Texas coastline through the weekend will maintain the isolated tornado threat through Saturday...or until the lower level winds back more northeasterly with this boundary's north(east)ern approach. The main threat throughout the weekend will evolve from isolated (near coastal) tornadoes and locally heavy bouts of rain leading to minor flooding issues to more areawide flooding. Antecedent dry soils and rivers well within banks will keep the immediate flash flooding threat at bay but...by Saturday afternoon or evening or once soils become more saturated...the flooding threat will move to the forefront. Thus...a Flash Flood Watch may need to be issued for the remainder of the weekend into Monday. Once all of the forecast meteorological parameters were analyzed in relation to flash flooding...from the near 2 inch pw offshore air mass being efficiently pumped in on moderate mid-level flow/ location of theta E axis in relation to the vicinity warm frontal boundary as well as well as decent upper level forcing going into Sunday (e.g., better jet positioning of RRQ/LFQ as the upper low enters the Big Bend region)...there is a good potential for an eventual regional flash flooding event. The coastal trough will shear out with the upper low's northeastern passage Monday...ending precipitation from west to east through the day. Moderate northwest to westerly winds in the wake of this low will scour out skies and advect in a much drier air mass across the region early Tuesday. Early week diurnal temperatures in the morning interior 40s/coastal low to mid 50s will still warm into the daytime 60s under a weakening northwest wind Tuesday...onshore breezes Wednesday. Rain chances (primarily showers) will briefly increase through Wednesday and peak pre-sunrise Thursday downstream of a late day into morning cold frontal passage. A continental-in- origin cold...dry air mass will descend into eastern Texas late next work week and significantly chill the weather out. Late period winter-like conditions under clear skies...north to east breezes with minimum Ts in the 30s and days slowly warming into the low to mid 50s. 31 MARINE... At 3:00 PM the coastal warm front was located from near the Sabine to the Upper Texas offshore waters to the Lower Texas coastline. The high resolution models move this boundary slowly toward the coast overnight tonight. There is a chance that some isolated strong storms may produce isolated strong wind gusts and waterspouts later this afternoon through tonight mainly east of the frontal boundary. Other impacts for tonight include winds gusting between 20 and 30 knots and seas approaching 10 feet (mainly beyond 20 nm). Winds and seas should diminish on Saturday as the frontal boundary moves onshore. Periods of showers and thunderstorms will continue to be a hazard through Monday. Moderate winds may approach advisory levels on Monday as the main storm system moves east of the area. 40/08 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 51 53 48 55 50 / 90 100 80 80 70 Houston (IAH) 53 61 54 61 54 / 90 100 90 100 90 Galveston (GLS) 63 68 65 67 61 / 80 100 90 100 90 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Coastal Flood Advisory until 6 AM CST Saturday for the following zones: Brazoria...Chambers...Galveston...Harris. GM...Small Craft Advisory until 6 AM CST Saturday for the following zones: Coastal waters from Freeport to the Matagorda Ship Channel out 20 NM...Coastal waters from High Island to Freeport out 20 NM...Galveston Bay...Matagorda Bay...Waters from Freeport to the Matagorda Ship Channel from 20 to 60 NM...Waters from High Island to Freeport from 20 to 60 NM. && $$ Discussion...25