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Forecast Discussion for FWD NWS Office
FXUS64 KFWD 200011

Area Forecast Discussion
National Weather Service Fort Worth TX
711 PM CDT Sun Aug 19 2018

Lift associated with the Plains upper low has shifted east of the
of North and Central Texas along with the focus for additional
thunderstorm development. Isolated thunderstorms may occur over
the next couple of hours while surface instability lingers into
the early evening, otherwise VFR conditions and overall quiet
weather can be expected. Additional showers and perhaps a few
isolated thunderstorms may redevelop late tonight and early Monday
as a cold front moves in from the northwest. A shift to northwest
winds will be the primary concern in the Metroplex, which is
expected around 8 or 9 AM Monday morning. The front should make
its way into the KACT area around midday Monday.



.SHORT TERM... /Issued 332 PM CDT Sun Aug 19 2018/
/Rest of Today and Tonight/

An upper low is situated across western Kansas at this hour, with
an attendant surface low spiraling across eastern parts of the
state. A band of persistent mid and upper level cloud cover is now
situated across parts of the I-35 corridor, and has cut back on
insolation just a bit this afternoon. That said, recent
mesoanalysis reveals lingering inhibition is dwindling at this
hour as temperatures rise into the mid 90s, and this is
corroborated by recent ACARS soundings. While the brunt of large
scale forcing for ascent associated with the aformentioned low
will remain north of the Red River, very modest height falls are
overspreading much of North Texas at this time. Hi-resolution
guidance has been all over the map today regarding the placement
of the better convective chances, but it seems reasonable to
expect a gradual uptick in thunderstorms within the main 850-700
mb theta-e/moist axis which stretches from Grayson to Comanche
counties early this afternoon. Somewhat greater coverage is
anticipated across our far northeast counties which sit closer to
the better forcing. Another area of locally maximized chances is
possible within a zone of enhanced near-surface convergence, which
presently stretches from the Metroplex, southwestward towards
Hamilton. While temperatures are a bit lower than this time
yesterday, the strongest storms will once again carry a threat for
localized strong to severe downbursts with DCAPE values pushing
1200-1500 J/kg.

This activity will wane with the loss of heating this evening, but
a moist axis will remain entrenched from I-20 northward tonight.
Another round of stronger isentropic ascent is forecast to develop
after midnight and impinge upon this reservoir of enhanced
moisture/instability. This could result in the development of
another round of showers and storms late tonight focused across
parts of North Texas as the main cold front approaches. We`ll
advertise an area of 30-40% PoPs here overnight to account for
this potential, although the depth of the lingering moist layer
may detract from the overall coverage of additional precipitation.
Some modest increase in the mid-level wind field will occur at
this time as well, so if the moisture profile increases
sufficiently, a stronger storm can`t be ruled out.



.LONG TERM... /Issued 332 PM CDT Sun Aug 19 2018/
/Monday Onward/

The true cold front will be making progress through North Texas
on Monday morning, although it appears its passage will be fairly
dry for a majority of the area. This will be due to relatively
limited convergence along the frontal boundary, along with a lack
of dynamic forcing aloft which will remain displaced to our north.
With only weak convergence along the front and an abundance of
surface based CIN through the morning hours, am anticipating very
limited rain coverage before noon. However, as destabilization
occurs throughout the day, inhibition will erode ahead of the
front while hot temperatures and moisture pooling combine to yield
SBCAPEs in excess of 2500 J/kg. As a result, areas along/ahead of
the front during the afternoon hours will be at risk for
scattered storms, some of which will likely be strong with a
potential damaging wind threat. At this time, initiation looks
most likely across Central Texas near a Killeen/Waco/Corsicana
line, and areas downstream to the southeast will have a 30-40%
PoP. Storms will continue across our far southern zones through
Monday evening before coming to an end overnight.

The cold front will likely slow down or stall just south of the
forecast area as it outruns any support to drive it farther
south. A low-level moisture axis should remain positioned along
it with dewpoints remaining near 70, while areas to the north see
dewpoints scoured into the low 60s or upper 50s. This will mean a
slightly cooler and less humid Tuesday at least for most of North
Texas, although relief in Central Texas may be limited to simply
a return to near-normal temperatures.

There are still some significant discrepancies in model guidance
through the midweek time period, although increased upper ridging
will be the prevailing tendency during this time. The main feature
we`ll need to monitor is a northeastward pivot of our old frontal
zone and resultant intensifying warm advection across parts of
northwestern Texas on both Wednesday and Thursday. Very strong
isentropic ascent is likely to occur late Tuesday night and into
Wednesday morning, although the operational GFS and ECMWF differ
significantly in its placement. The southern GFS solution suggests
an overnight redevelopment of showers and storms across our
northwestern zones, while the ECMWF places the strongest ascent
over 100 miles farther north due to its more aggressive expansion
of the upper ridge. I will maintain a dry forecast favoring the
ECMWF during this time period, although some PoPs will be needed
if a southern trend appears in model guidance. A similar scenario
can be expected again Wednesday night into Thursday, when strong
warm advection should fuel a complex of storms somewhere in
Oklahoma. It remains unclear at this time whether our Red River
counties will be affected, although there is certainly a nonzero
potential for convection to spread into our northern zones
Thursday morning.

Since I`ve trended toward the drier ECMWF through the middle of
the week, I`ve also trended towards its warmer temperatures which
would place some areas back around the century mark by Thursday
or Friday. It appears the upper ridge will remain in control
during the end of the week and into next weekend, which will mean
a return to typical August with near-normal temperatures and
minimal chances for rainfall.



Dallas-Ft. Worth    77  95  74  94  72 /  40  10   0   0   0
Waco                80  99  75  98  72 /  30  20  10  10  10
Paris               74  91  68  90  67 /  40  20   0   0   0
Denton              73  94  69  93  70 /  40  10   0   0   5
McKinney            75  94  69  93  69 /  40  10   0   0   0
Dallas              80  96  75  95  74 /  40  10   0   0   0
Terrell             77  95  71  94  70 /  40  10   5   0   0
Corsicana           78  98  74  96  71 /  30  30  10   5   0
Temple              77  98  74  98  72 /  50  30  20  10  10
Mineral Wells       72  94  70  95  70 /  40  10   0   0  10





NWS FWD Office Area Forecast Discussion

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