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 100443 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 1043 PM CST Sat Jan 9 2021 .UPDATE... Hi-res models continue to arrive increasingly colder/wetter in our north, and even the globals still hint at some potentially big numbers. Have spent this evening trying to adjust for this, but there are still a couple concerns about the big numbers some of the guidance is popping out. First, while it hasn`t been terribly warm of late, I wonder how much snow will have to be wasted in order to bring ground temps down enough to get some solid accumulation. If we can get some high initial snow rates, this may not be as big a concern. But if snow is a bit slow in coming in, we will waste time and snow on even creating a ground environment conducive to accumulation. Additionally, because snow looks to begin this afternoon and temperatures will be near the high end for snow at this time, snow-liquid ratios are going to be low...real low. It`s hard to believe those totals pushing 10 inches in a 10:1 ratio snow map when it seems more likely to me the SLRs will be down towards 6. (Also, 6:1 snow sounds absolutely excruciating to shovel. Hard pass.) So, long story short, the warning area is still looking at totals of roughly 1-4 inches. But, there is definitely potential for more, especially in Houston County. Adjusting for SLR, the HREF probability-matched mean in parts of that county are more like 5-7 inches. It`s no surprise to anyone who`s spent a winter down here, but there is a LOT of uncertainty here. Be sure to check in frequently for the latest information tomorrow. && .AVIATION [06Z TAF Issuance]... VFR conditions continue this evening, but will begin to deteriorate from the west around 09z. Rain has started moving towards the TAF sites and will continue to draw near tonight. Upper air profiles are showing a good indication of winter precipitation as well tomorrow afternoon for the northern flying areas. Right now, CLL/UTS/CXO have RASN in the forecast but the situation is dynamic. Outside of that, MVFR/IFR ceilings are expected to move in through the night. At this time, conditions are not expected to improve until Monday morning. && .PREV DISCUSSION /Issued 548 PM CST Sat Jan 9 2021/... .SHORT TERM [Tonight through Sunday Night]... Winter storm system is still on schedule to move eastward across the state tomorrow through late tomorrow night. Current south Texas cloud cover will be moving into our southwest and western counties later this afternoon and the rest of the area tonight, and look for areas of rain/showers to develop late tonight but more likely tomorrow morning. These rain areas along with the chance of some thunderstorms mainly near/along the coast will be on the increase as the day progresses as the surface low develops/strengthens along the lower to middle coast and intensifies as it moves generally eastward across our coastal waters in the afternoon through evening hours. As winds shift to the northeast and north across our area, temperatures will be falling, and model soundings are still forecasting a transition from rain to show across our northern counties beginning as early as the mid to late afternoon hours tomorrow. After coordinating with adjacent offices, have upgraded our Winter Storm Watch to a Winter Storm Warning where 1 to 4 inches of snow with locally higher amounts can be expected. Because, the far northern edges of both Polk and San Jacinto counties have some potential to get similar snowfall amounts, have gone ahead and placed them under a Winter Storm Watch. These two counties might need to be upgraded to a warning later tonight or early tomorrow morning if model trends continue. Speaking of model trends, we are still seeing a large range of potentially higher snowfall amounts (>4 inches) across our far northernmost counties, and our expected amounts might need to be raised in future updates if we begin to see any model convergence toward these higher totals. As noted over the past several days, there will likely be a sharp gradient of snow accumulations, and any slight storm track deviations and/or mesoscale forcing could become a significant player as to where the 1 to 4 inch or higher totals end up. Further to the south where temperatures will stay too warm for any winter precipitation (it will end up being a cold, cold rain), rainfall totals for this event are anticipated to average around one inch with higher totals mainly near the coast and offshore locations that will be closer to the surface low (especially near the Matagorda Bay area). Also expect breezy/windy conditions to develop as this system moves on through, especially for locations closer to the coast and especially offshore. .LONG TERM [Monday Through Saturday Night]... In the wake of this frontal system, a high pressure should build over the region. CAA and clearing skies will allow temps Monday night and into Tuesday morning to steadily drop into at or near freezing levels. North of I-10 and outside of the Houston metro area, temps will be below freezing for several hours overnight. South of I-10, temps will be at or near freezing overnight. Along the coast, more cloud coverage and moderation from The Gulf will help keep overnight temperatures in the mid to upper 30s. For Tuesday night, overnight temperatures will only be a few degrees warmer compared to Monday night, but areas north of the beltway will still be at or near freezing overnight. After that, high pressure should settle in over our region for several days and temps will gradually warm back to the 60s by Wednesday. Global models indicate a low pressure system sitting over the Baja Peninsula for several days with zonal flow sending short- wave ripples across SE TX. The only impacts expected from this would be increased cloud coverage. The Euro shows this Baja low merging with a developing front on Friday and pushing east, but any precip would develop well east and offshore of our CWA. The GFS is more aggressive with this front developing on Friday, however it does not interact with the Baja low and precip still remains east and well offshore of our CWA. KBL .MARINE... Northeasterly winds will transition to more easterly winds today. As a coastal low begins to develop late tonight and early Sunday morning, winds will begin to increase in our SE offshore waters with possible SCEC conditions tonight transitioning to SCA early tomorrow morning. In the wake of this coastal low, winds will become southeast and increase to near 25 knots. As the cold front pushes off Sunday evening and early Monday morning, winds will continue to increase with gale force conditions possible beginning as early as Sunday night with seas forecast to range from 7-11 feet. With strong offshore winds, low water advisories are possible during this time frame. SCA conditions are expected to persist through Monday and offshore winds will continue through the middle of next week before transitioning to west/southwesterly winds by late Wednesday night and persisting through the rest of the week. KBL && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 37 39 32 44 28 / 40 90 80 10 0 Houston (IAH) 40 42 35 47 32 / 30 90 80 10 0 Galveston (GLS) 48 50 39 48 39 / 20 80 80 10 0 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Winter Storm Warning from noon Sunday to 6 AM CST Monday for the following zones: Brazos...Burleson...Grimes...Houston...Madison...Trinity...Walker...Washington. Winter Storm Watch from Sunday afternoon through late Sunday night for the following zones: Polk...San Jacinto. GM...Small Craft Advisory until 4 PM CST Sunday for the following zones: Coastal waters from Freeport to Matagorda Ship Channel TX out 20 NM...Matagorda Bay...Waters from Freeport to Matagorda Ship Channel TX from 20 to 60 NM. Small Craft Advisory from 3 AM to 4 PM CST Sunday for the following zones: Coastal waters from High Island to Freeport TX out 20 NM...Galveston Bay...Waters from High Island to Freeport TX from 20 to 60 NM. Gale Watch from Sunday afternoon through late Sunday night 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...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. SMALL CRAFT SHOULD EXERCISE CAUTION until midnight CST tonight for the following zones: Coastal waters from Freeport to Matagorda Ship Channel TX out 20 NM...Waters from Freeport to Matagorda Ship Channel TX from 20 to 60 NM. SMALL CRAFT SHOULD EXERCISE CAUTION until 3 AM CST Sunday for the following zones: Coastal waters from High Island to Freeport TX out 20 NM...Waters from High Island to Freeport TX from 20 to 60 NM. && $$ UPDATE...Luchs SHORT TERM...42 LONG TERM...KBL AVIATION...35 MARINE...KBL
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