Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 261724

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1224 PM CDT SUN JUN 26 2016

12z soundings show PW values near 2.00 inches with convective
temps between 85-88 degrees. Despite the mstr and low Tc,
shra/tsra have had difficulty developing probably due to some
confluence at 300 mb. Will continue to carry VCSH for most TAF
sites and amend to TSRA if stronger convection can develop. NAM12
is aggressive with regard to mstr/instability on Monday afternoon
and the GFS is somewhat supportive. Will introduce SHRA for KIAH
tomorrow aftn and this may need to become TSRA. Both the GFS and
the NAM show an inverted V tomorrow aftn so if storms develop, a
few could put out some stronger winds. 43



A handful of showers and a thunderstorm are currently moving
slowly inland across the coastal areas. Only a few tweaks were
made to the previous forecast. Expanded the area of 20% PoP to
include morning showers over the marine zones. Isolated to
scattered showers and thunderstorms are forecast to develop across
coastal zones this morning and spread further inland throughout
the afternoon. Highs today are forecast in the upper 80s near the
coast to the low/mid 90s inland, with heat index values in the low
to mid 100s.



Upper air analysis shows upper low between Del Rio and Midland TX
and upper level ridge over the Arklatex. The CRP and LCH 00Z
soundings showed around 2 inches of precipitable water. Surface
analysis at 08Z showed weak high pressure over much of SE Texas
allowing for near calm winds. Today the upper level low should
meander across west Texas with the upper ridge slowly weakening
over the Arklatex as ridging builds over the 4 corners region.
Ascent from the upper low and subsidence from the ridge will again
fight it out over much of SE and E Texas today. Precipitable water
values are forecast to decrease closer to 1.8 inches today so
there may be less activity today than yesterday. Forecast will go
with 20/30 PoPs for widely scattered showers and perhaps an
isolated thunderstorm.

Upper level pattern will undergo a bit of a transition with the
upper level ridge over the S Rockies becoming more established
Monday into Tuesday. This will allow for northerly flow aloft with
a broad trough developing over the Great Lakes. This will support
a frontal boundary working into SE Texas from the NE. The front
could stall across the area late Tuesday through Wednesday and be
the primary focus for showers and thunderstorms. Along the
boundary precipitable water values increase to around 2-2.1
inches. Upper level winds will be light from the N to NE so storm
motions will be quite slow Tuesday into Wednesday. Given the
stalling boundary and high moisture, there is certainly a higher
threat for heavy rainfall during this time. Instability may also
increase so there could also be an isolated strong/severe storm
with a downburst wind threat to go along with the heavy rainfall
and lightning. The hail threat looks small since wet bulb zero
heights may be too high and instability may not be high enough to
support vigorous enough updrafts.

Chances of thunderstorms look to decrease for the end of the
week. Precipitable water values are forecast to decrease to under
1.8 inches Thursday through Saturday. The upper level pattern
still remains favorable for a wet pattern given the NW to N flow
aloft and the ridge remaining over the S Rockies and W Texas.
Since capping and subsidence from the ridge will be limited, the
forecast will keep at least 20/30 PoP for the end of the week.
Again with at least some instability and high moisture, there
looks to be a small threat for heavy rainfall and downburst winds
for the end of the week. This threat will be lower than for the
Tuesday/Wednesday time frame.

Overall forecast confidence remains moderate since there is
reasonable agreement between the forecast models. The ECMWF may be
building a flat ridge over the southern U.S. for the end of the
week which would suggest even lower rain chances for the end of
the week. The ECMWF is also stronger than the GFS with the ridge
going into the Independence Day holiday. Overall the models are in
agreement with the current ridge weakening with NW flow developing
and the frontal boundary being the focus for thunderstorm activity
Tuesday into Wednesday.


Light to occasionally moderate onshore flow will continue through
Monday then will become light and variable Tuesday as a weak cold
front reaches the coast then stalls and washes out. Onshore flow
will increase Friday and Saturday as gradient tightens between
deepening low pressure over West Texas and increasing high pressure
ridge over the Gulf of Mexico. 18


College Station (CLL)      91  76  94  76  91 /  30  10  20  20  50
Houston (IAH)              94  75  95  76  92 /  30  10  40  20  60
Galveston (GLS)            90  80  90  80  89 /  20  10  20  20  50




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