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 202304 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 604 PM CDT Tue Apr 20 2021 .AVIATION... A cold front is moving across SE TX this evening and southern TAF sites should expect a window of VFR ceilings and a wind shift to north. Fcst soundings don`t show the same level of saturation as previously progged so will keep skies scattered and not show cigs in the TAFs. Winds will gradually subside tomorrow with generally scattered clouds with VFR conds. 43 && .PREV DISCUSSION... /ISSUED 317 PM CDT Tue Apr 20 2021/ SHORT TERM [Tonight Through Wednesday Afternoon]... Cold front marching south and bringing a quick cooldown with it. Gusty NNW-N winds will accompany the moderate to strong cold front tonight and persist into Wednesday though becoming more NE. Temperatures tonight look to fall into the upper 30s near Madisonville and mid 40s across the Metro...even Galveston Island temperatures will probably fall into the lower to mid 50s! (roughly 15-20 degrees below normal) Skies should get partly to mostly cloudy overnight with weak upglide in the 925-875mb layer then dry out after sunrise from northeast to southwest with the 850 front stalling out over the northern 1/2 of the region. A cool day on tap Wednesday with high temperatures in the 60s and possibly a few low 70s in the southwest areas. No precip expected with the frontal passage. 45 LONG TERM [Wednesday Night Through Tuesday]... Surface high pressure slides off to the east going into Wednesday night bringing back a southeasterly flow to the region. Still expecting another night of below normal temperatures though with lows in the upper 40s/low 50s. With the onshore flow comes an increase in moisture and an increase in temperatures! MaxT values will reach the low-to-mid 70s on Thursday and the upper 70s on Friday, the latter of which is seasonal for this time of year. With steady WAA, PW values increasing to 1.2"-1.4" by Thursday afternoon, and upper-level divergence, scattered rain showers are expected to develop initially in the western portion of the CWA and spreading eastward. The big story, which I`m sure you all are aware of, is coming up for Friday/Saturday. A shortwave trough out ahead of an upper-level trough will generate lee cyclogenesis. Developing surface low pressure in north TX will increase low-level moisture return with PW values increasing to nearly 2" by Friday afternoon. Resultingly, widespread showers and thunderstorms are expected Friday afternoon/Saturday morning. SPC does have the entire CWA outlined in a 15% chance of severe weather for Friday. With a strong inflow of low-level moisture and steep mid- level lapse rates supporting sufficient instability, I don`t have any reason to disagree with them. The probability of strong to severe storms will exist ahead of (Friday afternoon) and along the boundary of a "cold front" (Friday night/Saturday morning). This is still three days out, so it`s too early to set things in stone. The picture will become clearer once we get into the range of hi-res model/CAM guidance. Did you notice that cold front had quotation marks on it? That`s because it won`t really make a difference as far as temperatures go. 850mb temperatures won`t drop much following the front with values remaining in the 15-17 degrees Celsius range, so MaxT values for Saturday afternoon will be in the upper 70s/low 80s. The warming trend doesn`t stop there! MaxT values in the low-to-mid 80s are expected by Sunday and mid 80s for the early half of next week. The good news is that PoPs will be essentially zero from Saturday afternoon through Tuesday. Tuesday night/Wednesday morning is when models are hinting at another cold front moving through the region, although the GFS is much more progressive than the ECMWF the front off the coast by Wednesday afternoon. FROPA with the ECMWF doesn`t occur until Wednesday night. Showers and thunderstorms are expected with this FROPA as well due to instability and moisture building out ahead of it. Still too early to say on how "cool" we will get behind this front, but the GFS is the coolest of the two solutions. 26 AVIATION [18Z TAF Issuance]... VFR...guidance is not very bullish for MVFR ceilings post frontal but with the lagging 850 front and moist isentropic lift in the 925-875mb layer have swung forecast more in line with MVFR ceilings after 06z but ending by 10-13z. Gusty north winds in the wake of the FROPA gradually becoming NE Wed morning. 45 MARINE... Advisory conditions will become present in the wake of tonight`s cold front with moderate northeasterly winds prevailing through Wednesday morning. As high pressure moves off to the east, winds will become more easterly on Wednesday night. This will result in increasing seas with wave heights reaching 6 to 7 feet by Thursday and persisting into the weekend. Onshore flow redevelops by Friday and becomes moderate to strong as an area of low pressure develops in North Texas. Will have to keep an eye on the potential for coastal flooding for Friday and Saturday during high tide. Strong to severe thunderstorms will be possible on Friday through Saturday morning in association with an incoming cold front. This front will push through the coastal waters on Saturday afternoon with moderate north to northeast flow in its wake. Seas will begin to decrease following this front as well. The offshore flow does not last for long as surface high pressure quickly kicks out to the east. Onshore flow will return by Sunday afternoon. 26 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 41 64 47 72 60 / 0 0 0 10 50 Houston (IAH) 46 68 50 71 63 / 0 0 0 10 40 Galveston (GLS) 53 66 61 72 69 / 0 0 0 10 40 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...NONE. GM...Small Craft Advisory from 1 AM to 8 AM CDT Wednesday for the following zones: Matagorda Bay. Small Craft Advisory from 10 PM this evening to 8 AM CDT Wednesday for the following zones: Galveston Bay. Small Craft Advisory from 1 AM to 11 AM CDT Wednesday 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. && $$ Discussion...99 Aviation/Marine...99
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