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 192309 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 609 PM CDT Mon Apr 19 2021 .AVIATION... Light rain showers have expanded in coverage this evening and will be adding a VCSH to most TAF sites this evening. Short term guidance has no idea that precipitation is ongoing so not much confidence moving forward with this TAF package. Fcst soundings keep ceilings VFR overnight with mid level drying for tomorrow. A cold front will move through the area tomorrow and tomorrow night with a wind shift at KCLL around 21z and KIA around 03z. MVFR ceilings are expected to develop in the wake of the cold front tomorrow night. 43 && .PREV DISCUSSION... /ISSUED 340 PM CDT Mon Apr 19 2021/ DISCUSSION... SHORT TERM [Through Tuesday Night]... The quiet weather pattern continues today thanks to surface high pressure sitting over Southeast Texas. As the high slides off to the east, winds will transition from easterly to southeasterly. Temperatures today will be slightly below normal with highs in the low-to-mid 70s. For tonight, temperatures will be a bit warmer than the previous night since CAA has come to an end. Overcast clouds moving in overnight will initially keep temperatures on the mild side, but these will depart after midnight allowing temperatures to drop into the low 50s. It`s worth mentioning that some hi-res models are indicating isolated rain showers developing after sunset due to upper-level divergence from a departing jet streak, but with plentiful dry air in the lowest 3km above the surface, any precipitation that falls will evaporate before it reaches the ground. Thus, PoPs will remain less than 10% throughout the night. Southwesterly winds kick in and skies clear out on Tuesday morning as surface high pressure continues its eastward trek. Resultingly, afternoon temperatures will be slightly warmer with highs approaching the 80 degree mark at most locations. The southwesterly winds will gradually decrease our PW values down into the 0.6 inch to 0.8 inch range, so our moisture profile looks relatively slim ahead of our next cold front that will pass through the region on Tuesday afternoon/evening. Since there will be dry air out ahead of the front, models are in agreement that this will be a dry FROPA. With sufficient CAA persisting through Tuesday night, temperatures will be at least 10-15 degrees below normal with lows ranging from the low 40s to the low 50s across Southeast Texas. LONG TERM [Wednesday Through Monday]... Wednesday morning puts us in a decidedly post-frontal environment, as a surface high sits over the Red River Valley. The cold advection does not look particularly strong, but we also weren`t starting from the warmest, most humid place either, so Wednesday still looks to be unseasonably cool and dry. Of course, we are now arriving in the time of year where your reaction to that sentence depends wholly on how you feel about heat and humidity. For this Wisconsin-raised forecaster, a sunny day with highs in the upper 60s to 70s with dewpoints ranging from the upper 30s to lower 50s sounds downright wonderful! But your mileage may vary. Spring being a season of transition, this setup won`t stay static, particularly since the flow aloft is relatively zonal. Wednesday night will see winds veer to become more easterly, picking up a connection with more humid Gulf air. Meanwhile, a surface low should be starting to spin up over New Mexico underneath what looks like it will be a pretty robust shortwave trough dropping off the Rockies. This will keep the pressure gradient fairly tight, for the back half of the week, aiding the return of deep moisture over the area. Depending on how quick moisture return is, we could see some low chances for showers as early as late Thursday afternoon down by Matagorda Bay closer to the deep moisture axis. However, by Friday morning, the potential for showers will spread across our area. Depending on how significant capping is, we could see some afternoon convection on Friday, particularly if we see some pre- frontal surface troughing as a focus mechanism, as hinted at in at least some of the guidance. The other focus will come later Friday night into Saturday as the front sweeps through. Though the timing is not best, there looks to be enough instability that we could sustain some existing, organized severe weather for some time right on the front. SPC does have the western half or so of our area in what is the equivalent of a slight risk area for Friday night, and that seems a reasonable forecast. For what is a Day 5 forecast, there`s only so much that can be divined from what will eventually be driven by mesoscale details. Speaking of mesoscale details, the GFS has a party with them...or at least the best approximations of them it can resolve with the frontal convection. There`s really zero point in trying to speculate on details or specific timing, but it`s probably worth being on the lookout for some kinks in the forecast as the front rolls through. Peering into early next week, there doesn`t appear to be much cold advection behind the front to speak of, so this may well be a situation where the increasingly powerful sun overwhelms any potential cooling behind the front, and we actually end up with warmer temperatures after the front passes. Indeed, that`s just what I have in the forecast. My sweet, spring children, summer is coming. AVIATION [18Z TAF Issuance]... VFR conditions will persist throughout the TAF period as surface high pressure sits overhead. Light easterly winds will gradually transition over to southeasterly before becoming light and variable overnight. For the coastal sites (GLS and LBX), wind gusts are possible up to 15 knots through sunset. Hi-res models show isolated to widely scattered rain showers after sunset, but low-levels are too dry for any rain to reach the surface so no mention of VCSH in any of the TAFS. In the overnight hours, an OVC cloud layer around 10,000 ft will move into the region. These clouds will clear out Tuesday morning with southwesterly winds kicking in around 5-7 knots. Southwesterly winds will prevail until FROPA which will occur just after 00z on Wednesday for the northern sites, so this will be covered in the upcoming TAF packages. MARINE... Light to moderate easterly winds prevail this afternoon as surface high pressure drifts eastward across the region. Winds should continue to veer overnight, becoming southeasterly for tomorrow. A cold front will cross the coastal waters Tuesday night with moderate north winds developing in its wake. At their strongest, these winds will have the potential to exceed the SCEC threshold, and caution flags may be needed late Tuesday into Wednesday morning. Later in the week, developing low pressure to the northwest will keep the pressure gradient over Southeast Texas pretty tight, holding up wind speeds. This will stretch the potential for caution flags deep into the week ahead of another cold front on Saturday. With more moisture available, showers and thunderstorms will be more of a consideration as that front approaches. FIRE WEATHER... Dry conditions will persist through Tuesday with RH values in the afternoon hours for today and tomorrow dropping into the 30-40 percent range. Although there are steep low-level lapse rates in place, light winds are present aloft and at the surface as high pressure sits overhead. As the high pressure moves off to the east, winds will gradually transition from easterly through southerly to southwesterly by Tuesday. A cold front will pass through the area on Tuesday afternoon but with low moisture in place, this will be a dry frontal passage. Those in the northern portion of the CWA will want to be particularly aware of the timing for this front, as it may come early enough to cause a wind shift closer to the period of peak fire behavior for the day. In the wake of this front, conditions will be even drier for Wednesday as a new surge of colder, drier air from the north moves in with RH values dropping to 30 percent in the afternoon hours. && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 50 79 42 69 48 / 10 0 0 0 0 Houston (IAH) 54 80 48 72 51 / 10 0 0 0 0 Galveston (GLS) 64 73 56 71 61 / 20 0 0 0 0 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...NONE. GM...NONE. && $$
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