Area Forecast Discussion
Issued by NWS Houston/Galveston, TX
FXUS64 KHGX 010514
Area Forecast Discussion
National Weather Service Houston/Galveston TX
1114 PM CST Wed Nov 30 2016
Gusty northerly winds have come down and become light to calm
across the area. Forecast continues to call for VFR and these
winds to turn easterly and increase to around 10 knots by mid-day
GLS briefly went to IFR with haze earlier this evening. If
real...was likely something transient like smoke. Temperature-
Dewpoint spreads are too wide (currently 20 degrees at GLS) to
expect fog tonight. Similarly, some guidance began to introduce
some light fog in spots at the end of the period tonight. At this
time, still expect spreads to be too great for much in the way of
fog formation and left it out.
.PREV DISCUSSION... /ISSUED 922 PM CST Wed Nov 30 2016/
Surface analysis has high pressure over much of Texas which has
allowed for winds to become calm. Skies remain clear so there
should be good radiational cooling tonight with the dry
airmass. Min temperatures look on track for 30s/40s for the area.
Forecast trends for temps have been adjusted to account for more
rapid cooling for rural areas north of Houston. Otherwise the
forecast looks on track.
Weekend forecast still looking on track for the potential of a
prolonged rain event. WPC is forecasting 5 day rainfall totals of
basically 2 to 5 inches of rain. Most of this will occur in the
last 3 days so basically looking at 1-1.5 inches of rain a day.
There very well could be some isolated higher amounts along the
coast and that will remain a forecast challenge going forward. The
point being that it may not be until the late Sunday/Monday time
frame that we could remotely discuss the possibility of a flash
flood watch. Looking at NASA SPORT LIS soil moisture image, soil
remains dry with a range of 15-30 percent soil moisture. Trends
for the past week has been a loss of 2 percent which doesn`t seem
like much but there is not much more moisture to be loss either.
WCRFC 3 hr gridded flash flood guidance mirrors these dry areas
but still suggests that even 4 inches of rain in 3 hours could
cause flooding concerns. So even though forecasted rainfall
amounts could reach 5 inches in a few spots, enough of that
rainfall could be spread out enough as not to cause flooding
problems. It would not be until the end of the rain event that
issues could arise. But all it would take would be a more
convectively active period of rainfall with higher rain rates that
could increase the potential for flooding. At this time it make
sense to forgo any mention of a flash flood watch and let the
forecast play out since soils are dry.
PREV DISCUSSION... /ISSUED 525 PM CST Wed Nov 30 2016/
VFR across the area as drier air has been moving in on brisk
offshore flow. Those northerly winds are diminishing, and in many
locations should be (near) calm overnight, then veer easterly
tomorrow. While not quite as brisk, winds should increase back to
around 10 knots by mid-day.
PREV DISCUSSION... /ISSUED 255 PM CST Wed Nov 30 2016/
Surface high pressure was located over Central texas this
afternoon. Clear skies and considerably cooler temperatures are
expected tonight. Another sunny day is expected Thursday as the
area of high drifts east of the region. An east wind will develop
by Thursday night on the backside of the high pressure system and
a coastal trough will begin to develop off the Lower Texas Coast.
The east wind will persist through Saturday morning and tide
levels will increase and some minor coastal flooding will be
possible along the Bolivar peninsula late Fri into Saturday.
At the upper levels, a deep upper trough will begin to slowly
move across the Southern Rockies. Moisture levels begin to rise
Friday evening with PW values reaching 2.00 inches by 06z Sat (Dec
3rd). This is close to the maximum value for this time of year. At
this time (and there is uncertainty), it appears the coastal
trough will lie from about Palacios to Hou Hobby to Beaumont and
the heaviest rain should fall along that axis with lighter amounts
to the north of this feature. There are several upper level
disturbances embedded in the SW upper flow that will enhance
rainfall from time to time on Saturday as well. There should be a
break in the precip on Sunday but a weak upper level disturbance
coupled with weak isentropic upglide should maintain rain chances
but amounts look a bit lighter on Sunday.
A much stronger disturbance will move toward the region on Sunday
night and Monday morning. This feature should again bring a good
chance of shra/tsra to SE TX. PW values remain around 1.80 inches
so again some healthy rainfall totals will be possible. Jet
dynamics look strongest on Sunday night into Monday as the upper
low out west finally moves east. Upper level winds become
increasingly divergent and SE TX will lie in a RRQ by Mon 18z.
Went above the SuperBlend for Sun night/Monday morning as rain
chances look to remain high. Subsidence should kick in quickly
Monday afternoon as the strong disturbance moves east. Would
expect the rain to end quickly during the afternoon. A mid week
warm-up should ensue next Tue/Wed in the wake of Monday`s system
and ahead of the next cold front. Speaking of the next cold front,
it should move through the region next Wednesday evening. It will
usher in some very cold air with high temps next Thu/Fri
struggling to warm out of the 50`s. A potential areawide freeze
will be possible next Friday morning. 43
Post cold frontal north winds will weaken through the early evening
hours...below offshore water caution criteria around midnight. Amped
up seas will significantly fall through the overnight hours...an
average 3 to 4 feet by sunrise Thursday. Surface ridging moving off
to the northeast Thursday will establish an easterly fetch by
evening. A developing (near) coastal trough of low pressure will
pucker up a northeasterly pressure gradient Friday...leading to at
least afternoon caution level flags...advisory by Friday evening.
This strong northern Gulf easterly fetch will persist through at
least Monday...pulling in a heightened long period swell under wind
driven winds. The likelihood of areawide frequent thunderstorms will
make for hazardous (Friday through Monday) maritime conditions.
Another hazard will be coastal water beach run-up. During times of
late week near 2 foot high tides...overall water levels will exceed
3 feet. Water levels of between 3.3 and 3.8 feet Friday and Saturday
will push water into the dunes/low-lying areas and possibly overwash
sections of the Blue Water Highway in Brazoria County as well as
Highway 87 along the Bolivar Peninsula. 31
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 39 65 46 68 52 / 0 0 10 30 70
Houston (IAH) 40 67 47 69 55 / 0 0 10 30 70
Galveston (GLS) 54 65 58 69 63 / 0 0 10 50 70