Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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FXUS64 KFWD 191147
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
647 AM CDT Sat Aug 19 2017


.AVIATION...
/12Z TAFS/

VFR conditions prevail across North Texas this morning with light
south-southwest flow. Some patchy MVFR cigs are noted to the
southeast of Waco at this hour but none of the major airports
should be impacted. Main concern through the period will be
potential for scattered thunderstorms this afternoon during peak
heating. We have introduced a VCTS for the Metroplex airports from
20-23Z to account for this activity. Any thunderstorms that
develop this afternoon will have some potential for isolated
microburst winds in excess of 50 kt. Convection should diminish
this evening as boundary layer temperatures cool. VFR conditions
should prevail overnight into Sunday.

Dunn

&&

.UPDATE... /Issued 521 AM CDT Sat Aug 19 2017/
Very minor update to raise PoPs to 20% along and north of I-20 as
it is looking like scattered thunderstorms will develop during
peak heating this afternoon. As mentioned below, an isolated
severe wind gust will be possible with the strongest storms. No
other changes at this time.

Dunn

&&

.SHORT TERM... /Issued 346 AM CDT Sat Aug 19 2017/
/Today and Tonight/

Morning satellite imagery shows the clockwise flow of clouds
around a mid level ridge that is centered over south-central
Texas. North Texas will be on the northern periphery of the ridge,
far enough removed from stronger subsidence for at least some
isolated thunderstorms this afternoon. It will be a hot and humid
day across the region with temperatures in the upper 90s and heat
indices near 105 degrees. The main concern for this afternoon will
be the potential for isolated thunderstorms. There are no
significant disturbances crossing the area today, although some
weak isentropic ascent is expected into early afternoon mainly
along and north of I-20. As we heat up by midday, a fairly robust
cumulus field should develop given the amount of low level
moisture present. Latest runs of the HRRR and experimental HRRR
suggest that we will reach convective temperatures in the upper
90s by mid afternoon, and both sets of guidance develop scattered
thunderstorms at this time. Right now, we`ll have coverage at 10%
and mention isolated thunderstorms, but if the higher coverage
advertised by the HRRR guidance continues to show up in successive
runs, we may bump these up later this morning.

If thunderstorms do develop later this afternoon, forecast
soundings exhibit a deep inverted-V structure up to 750mb
suggesting the potential for isolated severe wind gusts with the
strongest cells, typical of summertime pulse convection.
Otherwise, weak flow aloft suggests slow moving thunderstorms
capable of locally heavy rainfall. Any activity that develops
this afternoon should come to an end this evening with mostly
clear skies expected overnight.

Dunn

&&

.LONG TERM... /Issued 346 AM CDT Sat Aug 19 2017/
/Sunday through Friday/

Very low afternoon thunderstorm chances will persist primarily
across East Texas and perhaps near the Red River where surface
dewpoints will remain the highest. Vigorous mixing elsewhere
looks to greatly limit buoyancy available for any updrafts.
Afternoon heat indices will once again approach and locally exceed
105 degrees for a brief period Sunday afternoon mainly across our
northeastern-most counties. As a result, coverage of 105+ values
continues to look small enough to hold off on the issuance of a
Heat Advisory.

The long awaited mid-level ridging finally looks to build back
overhead in full force on Monday, and we`ll indicate a dry
forecast during the afternoon. It`s possible a rogue shower or two
pops up during the peak heating of the day where parcels can
locally breach their LFCs, but this potential is too low to
warrant an explicit mention in the worded forecast for the time
being.

Somewhat increased moisture across the Upper Gulf Coast may
breathe some life back into the sea breeze, and will show low
storm chances across our far southeastern counties on Tuesday. At
the same time, yet another unusual summertime cold front will be
approaching the region from Oklahoma, although most precipitation
looks to hold off until Tuesday night and into Wednesday morning.
While the GFS continues to lag behind the other global models
with the progression of this front, it has come in line with the
ECMWF and Canadian, indicating a forward push all the way through
our CWA and into Central Texas by Thursday. Overall upper-level
support does not, however, appear to overly impressive and focused
at this time. As a result, convective development near and along
the front would be tied closely to near-surface convergence and
diurnal gains in instability.

With this in mind, we`ve nudged PoPs up a bit--mainly across our
southern and eastern counties--during the Wednesday-Friday time
frame, but have capped them at 50% at this juncture. Copious
amounts of tropical moisture look to arrive ahead of the cold
front, with PWATs climbing towards 2" by Wednesday and Thursday.
Cloud-bearing flow directed nearly orthogonal to the initiating
frontal boundary may help temper overall rainfall amounts as
individual storms drift away from the front, but slow storm
motions (less than 10 kts), and exceptionally deep warm cloud
layers certainly spell a potential for locally heavy rainfall. If
this front blasts through the region as the Canadian advertises,
however, much of the region would remain more or less
precipitation-free into the weekend, but this solution remains in
the outlier camp at this juncture.

With the potential for showers, storms, and abundant cloud cover,
started to nudge high temperatures downwards on Wednesday and
especially Thursday.

Carlaw

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    99  79  98  79  96 /  20   5  10   5  10
Waco                99  77 100  76  98 /   5   0   5   5  10
Paris               94  74  95  75  93 /  10   5  20  10  10
Denton              97  76  96  76  96 /  20  10  10   5  10
McKinney            95  72  96  76  95 /  20   5  10  10  10
Dallas              98  80  98  80  96 /  20   5  10   5  10
Terrell             97  74  97  75  96 /  20   5  10  10  10
Corsicana           98  77  97  76  96 /  10   5  10   5  10
Temple             100  75  99  75  98 /   5   0   5   0  10
Mineral Wells       98  73  96  74  96 /  20  10   5   5  10

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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