Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 161817
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1217 PM CST Mon Jan 16 2017

.UPDATE...
An active morning with low-topped convection, and at least one
cell showing mini-supercell characteristics has resulted in damage
from Fort Bend County, through northwest Harris County, and into
Montgomery County. Perhaps due to the low tops, these storms
exhibited little to no lightning. In the late morning hours, the
convection has wound down, with showers running across the
northern part of the area.

Farther south, the sun has started to break out and temperatures
have been rising rapidly, necessitating an increase in the
temperature forecast. Between the higher temperatures and
dewpoints in the mid to upper 60s, expecting to see the
development of another round of convection. Concentrated the
highest rain chances towards the northern area of outflow from
this morning`s convection, with the expectation that differential
heating should reinforce whatever outflow boundary may remain from
the morning`s storms.

Suspect that the southern outflow boundary may provide focus for
convective development as well, though it is not receiving the
same love from the models. The 16Z HRRR does eventually show some
precip here, but not until midnight when the front is moving into
our northernmost counties. So, there just may not be quite enough
to get things going on this boundary. Since high res guidance
still seems to be a bit slow on warmer temperatures, it may not
quite have a perfect handle on the convective environment. Rather
than go dry, I conservatively bled a lower chance of rain back
towards the Houston metro.

Luchs

&&

.PREV DISCUSSION... /ISSUED 521 AM CST Mon Jan 16 2017/

AVIATION...
An area of showers and thunderstorms will affect most of the
Houston metro and points northward through mid morning. There is a
potential for isolated stronger storms. The strongest were west of
KSGR at 1115Z and could affect KSGR, KIAH, and the temporary
forecast site at KDWH between 14Z and 17Z (give or take an hour).
Not confident that the area of showers and storms will work its
way much further to the south. Models still showed a break from
the MVFR/IFR conditions this afternoon before ceilings and/or
visibility lowers again after 00Z. Sea fog may become a threat
again for KGLS, KLBX, and KHOU after 06Z tonight.

40

PREV DISCUSSION... /ISSUED 402 AM CST Mon Jan 16 2017/

DISCUSSION...
At 3 AM, an area of weak of low pressure was located over central
Oklahoma with a weak warm front extending SE from the low
across southern Arkansas. A cold front extended SSW of the
surface low and lies across central Texas. A line of showers and
thunderstorms extends N-S across SE Texas and this will persist
for much of the morning. There is sufficient shear to support some
marginal wind gusts or isolated tornadoes this morning, especially
over the NW zones. The line will progress slowly east today while
individual storms within the line move NNE. This will allow storms
to train today especially over the western zones and could produce
some locally heavy rain. Upper level winds are diffluent with PW
values near 1.40 inches. There are enough parameters in place to
spark some interest in hoisting a flash flood watch but it`s been
dry and most areas should be able to handle 1 to 2 inches of rain
(isolated 3 inch totals) so will forego a flash flood watch today.

A deep upper level trough over Baja CA will remain nearly
stationary through Wednesday night. The upper low will slowly fill
as it meanders to the east toward the central plains through
Thursday. PW values remain between 1.30 and 1.50 inches through
Tuesday with a series of weak upper level disturbances embedded in
the SW flow aloft. Most of SE TX will experience intermittent
showers and thunderstorms. A cold weak front will cross or try to
cross SE TX Mon night through Wed night. Initially thought the
best chance for precip would be along the boundary but it`s
looking more likely to focus behind the front with isentropic
upglide. Have gone with likely PoPs everywhere but have tapered
higher PoPs to the NW and lower at the coast.

Rain chances will continue Tuesday night into Wednesday as a
weak disturbance approaches and fcst soundings show a nearly
saturated profile. Showers and thunderstorms are expected to
increase Wednesday night into Thursday as the upper low shifts
east and jet dynamics becoming increasingly favorable. Fcst
soundings over the SE half of the region look super saturated with
PW values peaking at 1.60 inches. Could get more heavy rain late
Wed night into early Thursday. Some drying is expected Thursday
afternoon with drier conditions expected Friday. Another fast
moving short wave will cross the southern plains on Saturday. Not
sure how much moisture will make it back into SE TX but will
maintain 20/30 PoPs late Fri night into Saturday. A dry northwest
flow aloft will develop Sun/Mon with conditions turning drier and
cooler. 43

MARINE...
After starting out with advisory conditions between 20 and 60 nm of
the coast, the winds will gradually diminish later this morning and
through Tuesday. The potential for fog develop increases late
Tuesday and early Wednesday as easterly winds are expected near the
coast. A frontal boundary is also expected to drift toward the coast
but remain inland both Tuesday and Wednesday which may further aid
in fog development. Otherwise, chances for thunderstorms will
increase later today through Thursday. Southwesterly winds are
expected to develop by Friday and end the thunderstorm and fog
threat.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      73  57  61  52  65 /  70  60  60  70  70
Houston (IAH)              79  64  69  59  72 /  40  50  60  70  70
Galveston (GLS)            76  64  69  63  69 /  20  50  40  60  60

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 4 PM CST this
     afternoon for the following zones: Waters from Freeport to
     the Matagorda Ship Channel from 20 to 60 NM...Waters from
     High Island to Freeport from 20 to 60 NM.

&&

$$

Discussion...25



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