Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 171128

Area Forecast Discussion
National Weather Service Houston/Galveston TX
628 AM CDT Sat Mar 17 2018

.AVIATION [12Z TAF Issuance]...

After an initial burst of IFR/LIFR visibility and ceilings earlier
in the night, the situation has stabilized generally near the
MVFR/IFR threshold, as winds have stayed up just enough to largely
wipe out any fog and support ceilings rising to around or above
1000 feet. While we may stay here for much of the morning, expect
a gradual improvement to VFR at all sites but GLS for the
afternoon. But, without a real significant change in environment,
think we`ll end up more or less back in the same spot tonight.

Short range models are in pretty strong agreement in the
development of storms far to our west later today. But there is
disagreement for any potential impact on our area. At this time,
even the most aggressive would require only a VCTS at CLL and UTS
late this evening. So, for now, will leave precip mentions out of
the TAFs with an eye to more definitively answer this question
later today.



.PREV DISCUSSION /Issued 424 AM CDT Sat Mar 17 2018/...

.NEAR TERM [Through Today]...

GOES East RGB Nighttime microphysics imagery is winning again as
it continues to depict low stratus and fog pushing inland off the
Gulf. Northward extent of this cloud cover has reached just south
of a Temple to Longview line. Sea fog has filled in most coastal
areas along the Upper Texas Coast so marine dense fog advisory is
in effect. Surface analysis has a stalled Pacific front over north
Texas stretching back to west Texas. Warm sector remains moist
with dewpoints in the 60s hence the low clouds and fog development
over SE Texas. Water vapor imagery shows a weak short wave trough
and jet streak approaching the Big Bend and Trans-Pecos. The
evolution of this jet streak will play a big role in convective
trends for today.

Latest HRRR/WRF-ARW/Tx Tech WRF runs initiate convection over the
northern reaches of the Hill Country and push convection east
towards central Texas mid/late afternoon. HRRR and WRF-ARW want to
bring this convection near Madisonville to Crockett late in the
evening. This deserves to be watched but think SPC day 1 outlook
has a good handle on the situation with keeping the higher severe
weather threat to the north near dryline/front triple point in the
NWS Fort Worth CWA.

Closer to SE Texas, the atmosphere should be capped with boundary
layer flow from the southwest and weak ridging south of where the
main jet streak moves into Texas. Capping is tough to diagnose
with out a 00Z CRP sounding but 06Z-07Z AMDAR soundings over
Houston do show some capping at 850-800mb with temperatures 14-16C
in that layer. Most likely we will see the cap hold but dully
noting that most short range model soundings show little capping
this afternoon. For now will trust the data we have and go with 20
PoPs for today with higher chances tonight for Madison/Houston

.SHORT TERM [Sunday Through Monday]...

The combination of two upper level troughs, one over northern
California and the other in the Pacific which will cross the Baja
will affect Texas on Sunday. Forcing from these troughs will
likely help weaken the cap over the area but higher moisture will
be pushed east of the region. With little surface forcing,
forecast will go with 30-40 PoPs thinking some scattered activity
will be possible with the jet streak but cap may be just strong
enough to limit activity despite large scale lift.

A Pacific front does push through on Monday and there may be a
small chance of showers and storms with the front early Monday
morning. Otherwise dry conditions are expected for Monday. Given
the pattern with west to northwest flow, expect the airmass to be
well mixed supporting some adiabatic heating in the process. High
temperatures in the mid 80s will be possible and likely have low
80s on Galveston Island with the offshore flow. Dewpoints will mix
lower than what models suggest so low RH values will be possible.
Fire weather discussion below highlights the fire concern.

.LONG TERM [Monday Night Through Saturday]...

Tuesday the real cold front pushes through with 850mb
temperatures falling from 12-16C on Monday to 5-8C on Tuesday.
Tuesday will be cooler so have high temperatures in the low 70s.
It will be another dry day so will need to watch fire weather
concerns but RH values should be higher given high temperatures in
the 70s. The coldest morning should be Wednesday morning as high
pressure builds over the region for maximum radiational cooling

The end of the week will feature upper level ridging and return
flow off the Gulf. There may be a few showers on Friday but too
low of confidence to really mention in the forecast. The upper
level pattern does become more zonal next weekend so any fronts
that approach the area will likely stall.



Light to moderate onshore winds are still expected through the
weekend, with warm and moist air moving over relatively cooler water
resulting in sea fog on the waters. A dense fog advisory is already
in place on Galveston Bay and the adjacent nearshore waters, and
have just extended down the coast as visibility degrades there. The
potential for sea fog will likely continue through the weekend with
only brief periods of improvement in the afternoon, until more
lasting relief comes with the cold front Monday.

The Galveston Beach Patrol reported strong rip currents yesterday,
and with not much change in the environment expected, a Rip Current
Statement remains in place today for any residents or Spring
Breakers heading to a Gulf-facing beach this weekend.

After Monday`s front sweeps through the waters, caution flags are
likely on Tuesday and a small craft advisory is possible. Improving
conditions are expected mid-week as the pressure gradient behind the
front relaxes. Potential for a tighter gradient, stronger winds, and
higher seas may return towards the end of the work week as another
front begins to develop in the Great Plains.



Elevated fire weather conditions are expected Monday behind a cold
front as very warm temperatures will help push minimum relative
humidity values below 30 percent across the region and potentially
even below 20 percent. Additionally, some breezy northerly winds
will become established. Around College Station, winds may briefly
approach red flag thresholds in the afternoon. Despite KBDI and ERC
values that are relatively low, fine fuels will dry rapidly with
these low humidity values and even 100 hour fuels are near or below
the 50th percentile. Along with the heat and limited rainfall this
weekend, control issues may emerge where fuels are lighter and
densely arranged.

Low RH and breezy conditions will continue Tuesday, but with cooler
temperatures, RH values will not fall nearly as severely, only to 30
to 35 percent. Similarly low minimum RH values are currently
forecast for Wednesday, but high pressure moving across the area
will result in light winds and be a mitigating factor on that day.




College Station (CLL)  86  67  85  60  81 /  20  30  30  20   0
Houston (IAH)          85  68  83  68  84 /  20  20  40  30  10
Galveston (GLS)        79  69  78  69  82 /  20  20  20  20  10



TX...High Rip Current Risk through this evening for the following
     zones: Brazoria...Chambers...Galveston...Matagorda.

GM...Dense Fog Advisory until 1 PM CDT this afternoon for the
     following zones: Coastal waters from Freeport to the
     Matagorda Ship Channel out 20 NM...Coastal waters from High
     Island to Freeport out 20 NM...Galveston Bay...Matagorda



NEAR TERM...Overpeck
SHORT TERM...Overpeck
LONG TERM...Overpeck
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