Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 231531

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1031 AM CDT Fri Sep 23 2016


Sufficient moisture continues to filter into the area, keeping rain
chances higher over the coastal waters and along the coast.
12Z soundings at CRP and LCH are keeping precipitable waters up
around 1.70 to 2.00 inches for this morning. Moisture will be in a
surplus for this afternoon and into the evening. A convective
temperature around 84 degrees should also be met today with the help
of daytime heating. Raised PoPs a bit to match current radar trends.

Onshore flow is helping to push showers developing over the coastal
waters over the coastal counties. A weak coastal trough has helped
aid storm development right along the coastline.  This coastal
trough is acting as a boundary, where onshore winds are from the
southeast, and winds to the north of the boundary are from the east.
The change in wind direction along with a change in wind speed, is
acting as a zone of convergence. This area of convergence, will also
provide lift as indicated by both European the GFS omega fields over
the coastal counties early this afternoon. Cloud cover along with
the scattered showers will help to keep high temperatures a bit
cooler for this afternoon. Adjusted temperatures a degree down to
account for this.




MVFR to VFR ceilings in place across the Southeast Texas
terminals this morning are expected to transition to VFR by mid-
morning, with patchy IFR/MVFR fog at Conroe also expected to
dissipate around this time.

Beyond low ceilings and visibilities this morning, the main
aviation concern will be timing SHRA/possible TSRA near the
terminals. Scattered SHRA near Angleton and Galveston now will
expand inland with heating today. Convective temperatures are in
the low to mid 80s and expect shower coverage to increase near the
inland terminals 15-17Z as these temperatures are reached. Have
included TEMPO groups for SHRA midday with enhanced coverage
possible near the Houston terminals along a weak seabreeze. MVFR
ceilings and visibilities will be possible with stronger activity,
as well as gusty and variable winds. Expect SHRA/TSRA to end by
early evening with loss of heating, but another round of showers
is expected to spread inland towards the Houston terminals from
the Gulf early Saturday morning. Otherwise, southeast winds 10
knots or less are expected to prevail through the period.



Mid-upper level ridging over the northern areas this morning with
moist low level flow from the Gulf across the southwestern area
and on into the Hill Country. Showers becoming more numerous over
the Gulf waters and expanding into the coastal counties up to
around I-10. The low level flow will drag in greater moisture
today and by mid morning expect scattered showers and isolated
thunderstorms to have spread well inland. Rich plume of low level
moisture from the central Gulf will flow into the region in
advance of longwave trough that will be advancing southeastward
today and Saturday before stalling. This keeps the moist
environment in place with strongest moisture advection focused
more toward the Hill Country/Central TX area. By late Sunday the
trough should be cutting off and drifting southwest...this may
spare SETX from the threat of very heavy rain but still not out of
the woods on heavy rain Sunday/Monday. PW 1-8-2.1" with
respectable instability but relatively light forcing today through
Saturday then only slightly more favorable forcing followed by a cold
front (timing is certainly in question on the front...will it
reach the area Monday as upper low sags southwest - or will it
stall just northwest of the area) Monday or Tuesday. Models have
been having a great deal of trouble with the trough`s evolution
and it continues...on a more positive note as the speed max moves
into the Pacific northwest today by 12z Saturday models should
have a much better sample on the upper air pattern and should
have a more reliable forecast. If the area is going to receive
heavy rainfall it should be in the Sunday through Monday time
frame as things stand now. Tuesday is a very low confidence
forecast - the front could be through the area and dry by
afternoon or stalled near the coast and wet. Eventually Wednesday
the surface ridging should be pushing south and drier air should
be intruding into the region with a corresponding lessening chance
for rainfall. Temperatures should continue to run above normal
through Sunday then dip back toward normal. Lows by Wednesday
morning could easily be in the 60s and possibly even around 60
(low chance but possible if ensemble guidance is to be believed).

South to southeast winds around 10-15 knots are expected to
persist through Sunday, but may approach caution criteria late
tonight and again Saturday night as a frontal system approaches
Texas. This onshore flow will continue to push deeper Gulf
moisture onto the Upper Texas Coast, resulting in periods of
showers and thunderstorms this weekend. There is still
considerable uncertainty regarding the timing of the cold front
as it moves into Texas on Sunday (and whether or not it will make
it off the Upper Texas Coast). With mid and upper level flow
continuing to look unfavorable for the front to make considerable
progress across Southeast Texas, expect onshore flow to continue
through Monday as the front stalls inland. However, winds look to
back to the east/northeast by late Monday as a weak surface low
develops over the southwest Gulf.

Increasing winds tonight and Saturday night combined with
elevated astronomical tides may result in tide levels approaching
2.7-3.0 feet above MLLW at high tide along the coast. Another
period of elevated tides is possible early to mid next week as
east to northeast winds become established.



College Station (CLL)      94  76  92  75  89 /  40  10  50  20  60
Houston (IAH)              92  77  91  76  89 /  40  20  40  30  60
Galveston (GLS)            90  82  88  81  85 /  40  30  40  40  50



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