Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 181803

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1203 PM CST Mon Dec 18 2017

Sub-par flying conditions for the general aviation community
tonight through early Tuesday. A inland-lifting warm frontal
boundary will maintain afternoon MVFR ceilings then lower decks
into IFR (possible LIFR) cats with the warm front`s inland
passage. While thunderstorms are not out of the question...most of
these storms may remain elevated with a few maybe becoming more
surface-based. Have left thunder out of the TAFs for now and have
gone with drizzle or light rain. Light precipitation will
periodically occur tonight through the overnight Tuesday AM
hours...lowering decks within rain with areas of fog developing
where it is not raining. There is a risk that dense coastal sea
fog will form this evening and...if this is the case...coastal
terminals (including HOU and possibly IAH) may experience (V)LIFR
visbies within such a scenario. 31


.PREV DISCUSSION... /ISSUED 959 AM CST Mon Dec 18 2017/

Morning surface analysis shows a warm front having lifted to near
Platform BQX to just south of Buoy 42035 this morning, with
continued northward progress expected during the day. Near and
south of this warm front, roughly 500-1000 J/kg of MLCAPE (per
SPC Mesoanalysis) has encouraged isolated thunderstorm
development. Main updates to the forecast this morning include
adding a mention of isolated thunderstorms to the forecast for
the southern two tiers of counties and the coastal waters as the
warm front and better instability push inland. Also lowered rain
chances through the remainder of the morning to better reflect
radar trends with overrunning and forcing from the warm front
resulting in scattered showers and isolated thunderstorms to
spread inland through the afternoon. Expect highs in the 60s today
across the region under mostly cloudy to overcast skies.


PREV DISCUSSION... /ISSUED 445 AM CST Mon Dec 18 2017/

Areas of fog, dense at times, was noted across northern parts of
the area early this morning. Patchy sea fog is starting to
develop in the Gulf and this will likely expand and become more
dense in the next 12-24 hours.

Based on the latest rigs & buoy obs, it appears that the warm
front is situated just north of 42019 this morning. Latest
guidance suggests it`ll make slower northward progression than
what we were thinking yesterday. It appears the boundary might not
approach the coast until late afternoon now, so trimmed POPs down
some northwest of Highway 59/69. Concerned the numbers south of
there could be a touch too high as well based on some of the
hires data, but will let the 50-60% POPs ride there for now.

Look for some showers and thunderstorms to initiate south of the Big
Bend area overnight complements of an upper impulse making its up
in the southwest flow aloft. These showers and thunderstorms will
probably clip our nw/n zones late tonight into Tuesday morning.

Large scale lift will increase during the day Tuesday and Tuesday
night as the upper trough situated over southern Arizona & New
Mexico makes its way across north Texas. Look for shra/tstms to
continue across the NW half of the area thru much of the
day...eventually building further southwestward into a thin line
of storms along a surface front. This boundary should push
ese through the region between 5pm-11pm Tue. Parameters are still
in place for the possibility of some strong/severe cells. (There
should be more instability to tap into than what we saw Saturday
night). Areas of sea fog will be an issue coastal areas, outside
of rainfall, later today until the front pushes thru late Tue

Wednesday is looking nice with lows in the 50s & highs in the 70s
along w/ msunny skies. Thursday also looks dry and warm, though
it`ll be a transition day with onshore winds resuming and an
increase in clouds and moisture levels.

A stronger cold front, and associated precip in advance of the
windshift, should push thru southeast Texas during the day
Friday. There remains some fairly significant differences in
opinion between models as to this fronts strength in regards to
temps in its wake. Some, like the ECMWF even bring a warm front
quickly back through se Tx late Saturday. Instead of chasing run-to-
run guesses this far out, the extended fcst (from Saturday and
beyond) was left essentially the same. The set up remains
favorable for a couple of reinforcing shots of colder temps making
their way into the region going into next week. But overall
forecast confidence in timing & specific details hasn`t improved
much, and probably won`t do so for at least a few more days. 47

Generally light east and then southeast winds will prevail across
the coastal waters through tonight. This pattern will remain
favorable for the development of sea fog late this afternoon/tonight
across the bays/nearshore waters. This potential for sea fog will
likely stay in place through until late Tues...when the next cold
front is expected to move across SE TX. A light/moderate offshore
flow will prevail in the wake of the front through Weds.

Onshore flow should return early Thurs, and wind speeds should be
strengthening to SCEC criteria Thurs night/early Fri. Models are
now pushing this second stronger front into the coastal waters by
Fri night. Moderate/strong N winds will fill in behind this front
Sat. SCEC/SCA flags will likely be needed at that time. 41


College Station (CLL)      63  61  72  53  72 /  30  70  70  70   0
Houston (IAH)              68  63  75  59  73 /  40  40  40  70   0
Galveston (GLS)            65  65  73  62  71 /  40  20  30  60   0




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