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 140526 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 1126 PM CST Sat Mar 13 2021 .AVIATION... MVFR cigs are expected overnight as low level moisture gets drawn into SE TX. Winds will diminish later tonight as the front nears the region and the gradient begins to relax. A moist layer grows to around 850 mb and that looks sufficiently deep enough for some streamer showers to develop between 10-12z and have added a VCSH for area TAF sites for the pre-dawn hours. A cold front will approach from the west Sunday morning and this feature will trigger a band of showers and isolated thunderstorms to move across SE TX. MVFR cigs for much of the day with a mix of MVFR and VFR cigs developing from west to east in the afternoon. As skies clear Sunday night, think there will be some fog development especially after 06z. 43 && PREV DISCUSSION... /ISSUED 220 PM CST Sat Mar 13 2021/ DISCUSSION... Onshore flow is increasing ahead of a cold front expected to arrive in Southeast Texas tomorrow, and we`re already seeing some isolated showers roll by east of Houston. This front will bring showers and an isolated thunderstorm as it moves across the area Sunday. While there`ll likely be a small cooldown, it will be short-lived as winds quickly become more onshore. The progressive pattern continues with another mid-week front poised to move through on Wednesday. SHORT TERM [Through Sunday Night]... Obs around the area show temperatures a good 5-10 degrees above normal for mid-March, which is not a terrible surprise with solid onshore flow in place ahead of a cold front that will cross much of Texas overnight, and be set to cross our area tomorrow. Precipitable water is not very high just yet, but we`ve got enough moisture to kick up some isolated light showers east of the Houston metro this afternoon. Gradually, streamer showers should become more common as moisture continues to pool in the pre- frontal environment, though for most we`ll be mainly mired in low clouds and moderate southeasterly flow. Some sea fog may continue to be a threat near the coast and over the nearshore waters, but thinking that winds will be strong enough to limit fog potential to even less than we saw last night - for more on the impact over the waters, check the marine section below. Look for the front to be right on our doorstep early Sunday morning, and make its way across the area through the day. Expectations are that the front should reach the coast later in the afternoon. In general, we`ll see at least a broken line of showers on and near the front, but as we will be pretty divorced from the better dynamic support, there`s not much suggestion we`ll see more of that. Instability with the front is pretty meager, but that plus mechanical forcing along the front may give an updraft enough oomph to get us isolated lightning, so I`ve got some mention of thunder right on the front as it moves through. The front comes through quickly enough that I make things noticeably cooler across the area for high temps, but any delay means I might be too cool on the coastal plain...we shall see. Small changes in timing could make for a pretty significant difference in temps closer to the coast tomorrow. Rain should wind down by Sunday night in the wake of the front, and while cooler air will be making its way into the area, I`m not expecting anything drastic here. Winds look to return pretty quickly to being onshore by early Monday morning as the front stalls just offshore, cutting off the influx of cooler, drier air. LONG TERM [Monday Through Saturday]... Sunday`s cold front will become washed out along the coast and push back northward as a warm front throughout the day on Monday. This means the return of onshore flow and warmer temperatures as highs quickly bounce back to the low 80s for Monday afternoon. Overnight temperatures for Monday and Tuesday night will be in the low 60s. This onshore flow will also steadily increase moisture and instability in advance of the next cold front which will pass through on Wednesday. Before that though, GFS/ECMWF are hinting at afternoon showers/thunderstorms going for Tuesday as PW values will range from 1.2"-1.4" along with suitable daytime heating with highs back in the low 80s and plenty of instability as CAPE will be around 1500 J/kg. Instability is expected to further increase ahead of Wednesday`s front. A 500mb low pushing in from the Western CONUS will help generate lee cyclogenesis as a surface low develops just west of the TX/OK Panhandles on Tuesday night/Wednesday morning. As this low slides eastward across the Central Plains, it will push a cold front through the region on Wednesday morning/early afternoon. GFS/ECMWF are in agreement on a low-level capping inversion along with increasing CAPE going into Wednesday morning. ECMWF is a bit heavier on the CAPE with values maxing out around 2500 J/kg compared to the near 2000 J/kg max on the GFS. While both models agree on a weak upper-level trough swinging down, there is a bit of disagreement on the jet streak placement. Since it is expected to be weak either way, upper-level support will be limited at best. With plenty of lift from the front, that will be enough to generate some thunderstorms as it passes through. PoPs rapidly taper off going into Wednesday late afternoon/evening as there is model consensus on the area drying out rather quickly (although the ECMWF dries us out juuuuust a little bit faster). Either way, skies will clear out following the front as dry air filters in. Temperatures cool down quite a bit and become below normal for some locations. The second half of the work week will be absolutely pleasant! Expecting lows to drop into the 40s/50s from Wednesday night through at least Saturday night and highs in the mid- to-upper 60s for Thursday and Friday. Highs in the 70s return for Saturday as CAA comes to an end due to surface high pressure pushing off to the east and placing the region back into onshore flow. Looking a bit beyond the forecast period, there is model consensus on upper-level ridging returning in the latter portion of next weekend and the temperature trend following this is an upward one. AVIATION [18Z TAF Issuance]... VFR beginning to emerge across the area, and though some MVFR remains, expecting that to scatter/lift by 18Z. One exception may be GLS, where IFR visibility remains at the airport. Fog is retreating/dissipating, though, so the TAF just shows lingering last gasp of this influence at 18Z and quickly goes to VFR. Tonight, moisture expected to be high enough for streamer showers, so have inserted some VCSH late this evening/overnight. Approaching cold front still lies beyond the forecast period for most sites, but have introduced the front`s arrival at CLL and made some hints in the IAH extended. MARINE... Although the sea fog has dissipated this afternoon, it is expected to build back in tonight until the next cold front arrives and washes out the fog on Sunday. Small Craft Exercise Caution conditions are expected this afternoon as onshore winds are expected to build ahead of this approaching front. Exercise Caution conditions might need to be upgraded to Small Craft Advisory for a few hours overnight due to strengthening winds near 20 knots and seas building to 6 feet with occasional seas near 7ft for our 20 to 60 miles offshore waters. This next front is expected to push offshore and into our nearshore waters by Sunday afternoon and evening where winds will briefly switch to offshore. However, once this front dissipates, southerly winds are expected to resume on Monday and persist until the next frontal system arrives on Wednesday. && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 58 66 45 82 60 / 60 70 0 0 0 Houston (IAH) 66 71 50 81 63 / 50 80 10 10 0 Galveston (GLS) 64 67 59 72 65 / 20 90 30 10 10 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...NONE. GM...NONE. && $$ Discussion...99 Aviation/Marine...99
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