Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000 FXUS64 KHGX 281204 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 704 AM CDT Sun May 28 2017 .UPDATE...
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Quick update to pull mention of isolated (20 PoP) rain chances to the coast for the remainder of the morning hours and into the afternoon. An outflow boundary continues to push southwest into the forecast area from decaying thunderstorms along Interstate 20 and with surface pressure rises behind this boundary on the order of 4-5 MB over the past 3 hours, expect the boundary to continue propagating into the northern half of the forecast area through the morning hours. This boundary (in addition to a possible sea breeze) may serve as a focus for shower development with additional heating later this morning into the early afternoon hours ahead of an approaching cold front currently stretching from the Davis Mountains to D/FW Metroplex. No other changes made to ongoing forecast. Huffman
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&& .PREV DISCUSSION...
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/ISSUED 434 AM CDT Sun May 28 2017/ SHORT TERM (Today through Monday)... Hot and humid conditions will again blanket Southeast Texas today, but the arrival of a cold front this afternoon and evening will herald in a somewhat cooler and much wetter period this week. Temperatures as of 4 AM CDT are in the upper 70s and low 80s and with not much change expected over the next few hours owing to elevated onshore flow and an overcast stratus deck, this warm start will mean not much heating is needed to push afternoon temperatures back into the upper 80s to low 90s today. This will help push afternoon heat index values into the low 100s again today in many locations and residents are urged to take frequent breaks and drink plenty of water if working outdoors. Similar to yesterday, several record high minimum temperatures are in danger of being tied or set again today and those records for first order climate sites are included in the climate section below. Regional radar mosaic early this morning shows a thunderstorm complex slowly pushing south of the Red River towards Interstate 20 along a cold front. While this complex is expected to continue weakening as it moves east/southeast and encounters a capping inversion located between 950 and 800 MB, aircraft soundings out of Dallas/Fort Worth showed that the capping inversion evident on the 00Z FWD RAOB had begun to weaken and lift... raising concerns that this complex may persist farther to the southeast than what model guidance currently indicates. As a result have added 20-30 PoPs to the extreme northern counties through the remainder of the morning. May also see a few streamer showers push onto the coast this morning from the Gulf. Thunderstorm chances will increase dramatically this afternoon with the arrival of the cold front as the capping inversion in place over the region erodes through the day. The combination of moisture pooling along the front and diurnal heating (even with mostly cloudy to cloudy skies in place) should be enough to contribute to significant instability (MLCAPE values exceeding 4000 J/kg) for strong to severe thunderstorm development. In addition, steep mid-level lapse rates evident on 00z RAOBs (8.4-8.9 C/km) may only lessen slightly through this evening and will only further serve to accelerate updrafts along the front. 0-6 km bulk shear during this time still appears to remain minimal (generally 20 knots or less), which will help limit overall thunderstorm organization. However, given a considerable dry layer of air between 750-450 MB enhancing evaporational cooling and downdraft acceleration, lack of thunderstorm organization does not appear to hamper the severe weather threat for today and concerned that thunderstorms that develop along the front will be capable of damaging winds and possibly large hail. Best chances for this threat to materialize appear to be north of a Columbus to Cleveland line. Will also have to keep an eye on the possibility for locally heavy rain and isolated minor to flash flooding issues along the front with precipitable water values increasing to 1.6-1.9 inches and anticipated west to east storm motions indicating the potential for training along the frontal boundary. Through Monday, could see widespread 1-2 inch rain amounts across the region but locally higher amounts in excess of 2-4 inches will be possible. Current timing for the cold front has it arriving into the Brazos Valley and Piney Woods regions mid to late afternoon and the Houston metro after midnight, but this timing is highly dependent on outflow not driving the cold front farther south faster than what model guidance currently indicates. As a result, the front may push into the Houston metro tonight faster than anticipated (possibly bringing an isolated damaging wind threat with it). Showers and thunderstorms are expected to persist along the front as it continues to push south during the overnight hours, with the frontal boundary pushing near or just off of the Upper Texas Coast by sunrise. A shortwave trough lifting out of Mexico and moving across the region Monday morning looks to result in a thunderstorm complex developing over South Central Texas and moving east as well as ongoing convection flaring along the cold front during the morning hours. This would renew the threat for at least locally heavy rain and gusty winds. The location of the cold front tomorrow morning will be highly dependent on how the thunderstorms that develop along it behave today. Continuing to advertise the front stalling somewhere in between Interstate 10 and the coast and resulting in highest rain totals over the southwestern counties Monday morning, but if the front is able to push off the coast as the shortwave arrives it may limit how far inland rain chances exist. Diurnal heating and the passing shortwave will result in rain chances persisting through the day on Monday with high temperatures only in the low 80s. Huffman LONG TERM (Monday night through Saturday)... Subsidence in the wake of the passing shortwave may be enough to temper rain chances (at least briefly) Monday night before increasing during the day Tuesday as a series of waves move across the region in the west/southwest flow aloft. With little overall change in the expected pattern through mid to late week, periods of showers and thunderstorms capable of at least locally heavy rain will continue through the work week. Weak mid-level flow and deep layer saturation (1000-500 MB relative humidities in excess of 75 percent at times) raise the concern for isolated instances of minor or flash flooding, especially along any residual boundaries from previous rain events. For now, have continued to advertise 30-50 PoPs in the extended portion of the forecast with refinements to locations and forecast rain amounts likely as mesoscale features become evident. Huffman MARINE... Southeasterly winds offshore and south-southwesterly nearshore near 15 knots. These moderate winds will continue this morning then gradually diminish. SCEC currently up until 6 am and will let it expire at that point. South winds today should back to the southeast as frontal boundary-enhanced by outflow sags into the northern CWA. Seas changing little or diminishing slightly over the next few days in response to lighter wind fields. Possible showers and thunderstorms could become focused near the coast or just offshore Monday morning...possibly strong storms as well. Models really struggling with deep convection placement late Monday through Tuesday and it may be so mesoscale driven that trying to pinpoint storms as far south as coastal waters is unreliable at best. S/W passing by to the north should lead to increased southeasterly flow late Tuesday and probably maintain it through Saturday. ECMWF continues to point to some sort of low pressure system taking shape in the Western Gulf and drifting north toward the coastal waters Sunday then just meandering about...which of course isn`t good news this time of year. If so stronger easterly flow possible with impacts of elevated tide levels. Again stay tuned. 45 MARINE... Surge of stronger winds passing through the region with MVFR ceilings. Areas along and north of CXO seeing some breaks to VFR but these may well fill back in toward sunrise. MVFR ceilings should prevail through mid morning north and late morning to early afternoon south where richer/deeper moisture is evident. May see a few spotty showers develop this afternoon but main focus for storms will likely be along the slowly sagging frontal boundary (possibly outflow reinforced) late afternoon for CLL/UTS areas. CAMs continue to highlight a band of precip extending from well southwest of CLL to near or north of LFK at 00z. Will likely continue to carry the VCSH/VCTS north with a TEMPO for CLL late afternoon into the evening hours. Overnight storms and boundary should sag slowly or stall and remain a focus for storms. Will need to keep an eye out to the southwest for more organized circulation to develop near SAT and shift towards the region. Could have significant impacts Monday morning. 45 CLIMATE... Near to record high minimum temperatures are possible at all of the first order climate sites this morning. A listing of the current records is provided below. May 28 LOCATION RECORD HIGH MINIMUM YEAR City of Houston 81 1996 Houston Hobby 79 1996 College Station 77 1996 Galveston 81 1996 It was very warm yesterday with all 4 official sites either tying or surpassing the record high minimum temperatures. CLL 77 Tied IAH 80 Tied HOU 79 Record (previous 78-1996) GLS 81 Record (previous 80-2000) Huffman/45
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&& .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 90 70 81 69 85 / 50 80 50 30 50 Houston (IAH) 91 74 81 72 85 / 30 60 80 50 60 Galveston (GLS) 85 77 80 75 83 / 20 60 80 60 50 && .HGX WATCHES/WARNINGS/ADVISORIES...
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TX...NONE. GM...NONE.
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&& $$ Discussion...14

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