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

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FXUS64 KFWD 261002 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
502 AM CDT Sun Mar 26 2017

.DISCUSSION...
A rather cool and dry air mass is in place across North Texas
early this morning. However, dew points in the mid to upper 60s
are just to our south. As a shortwave emerges from the Rockies,
this mT air mass will surge northward as an effective warm front.
Initially, there may be some mild reductions in visibility as the
dew points upstream currently exceed the surface temperatures
across our area, but no significant fog is expected. The evening
shift was keen to notice the depth of the moisture in South Texas
is greater than earlier progged. This is improving our confidence
in the quality of the boundary layer moisture that will be
available at peak heating this afternoon. A cap will likely
prevent convective initiation until late in the day when both
surface heating and arriving lift aloft gradually erode it. While
this may delay (or prevent) thunderstorm development, it will also
limit the depth of the mixing today. This will maintain ample
boundary layer moisture, and with temperatures soaring into the
80s with full sun, will result in MLCAPE values in excess of
2000J/kg.

Another player in our thunderstorm game is the dryline, which may
struggle to penetrate the unstable air within North Texas. The
boundary will initially develop as return flow creates a moisture
discontinuity on the High Plains of West Texas this morning. With
the deepening low in Kansas, the mid-level flow will be most
favorable for dryline propagation farther north. This will focus
the best moisture convergence within Oklahoma this afternoon. To
our west, the boundary may only progress about 100 miles between
mid-morning and late afternoon. It is unlikely to reach our
southwestern counties at all (at least until the front arrives
Monday morning). While surface heating may allow for isolated
cells deep within the unstable air late in the day, the portion
of the dryline within western North Texas may be inhibited by
greater heating on the dry side. Some guidance is impressed enough
with the instability and the forward motion of the boundary that
it can`t help but convect, but the consensus among mesoscale
guidance is for the initiation to be primarily across Oklahoma
with perhaps a few rogue cells south of the Red River late this
afternoon.

While this event remains conditional on the extent of the
development within North Texas, any storms that develop may
quickly become severe. Supercell structures will be favored, and
although the greatest hail growth potential will be farther north
where the mid-level air closer to the cyclone will be quite cold,
our rotating updrafts would be of such intensity that they could
produce very large hail in excess of 2 inches in diameter. The
tornado threat may increase into the evening hours as a low-level
jet in excess of 40 knots ensues and the best forcing aloft
arrives. Additional development may occur after the traditional
peak heating time period. The richer moisture may result in lower
LCLs, which will only fall further as the boundary layer cools.
With the dryline unlikely to make any additional progress after
sunset, buoyant (likely untapped) air will remain across much of
North Texas. The best forcing will be north of I-20, but as a cold
front eventually overtakes the dryline late tonight into Monday
morning, additional development will be possible farther south
within our CWA. The intensity of the convection will likely wane
after midnight as the boundary layer instability further
diminishes and the best forcing passes to the east. This will also
slow the surface boundary, which may never actually exit the CWA.

This will keep the Gulf moisture right on our doorstep. And as the
next more powerful system digs into the Four Corners, this
moisture will surge back across North Texas. As large-scale
forcing for ascent begins arriving on Tuesday, some showers and
thunderstorms may develop, particularly across western portions of
North Texas. In addition, dryline convection across West Texas
Tuesday afternoon will race eastward into the richer moisture.
This activity could impact our western zones late in the day into
the evening hours. A very unstable boundary layer and steepening
mid-level lapse rates will help the cells maintain their intensity
with large hail and damaging winds the primary threats late
Tuesday. If a sufficient cold pool is able to develop, a linear
MCS with an attendant wind threat may travel deep into North Texas
late Tuesday night into Wednesday morning. This could disrupt the
evolution of the activity the remainder of the day, or this
complex may blend seamlessly with additional rounds of heavy rain
and thunderstorms. Deep tropical moisture flux within and above
the boundary layer will provide a continuous supply of fuel as
subsequent rounds of lift arrive during the day Wednesday.
Precipitable water values approaching 2 inches, extraordinary
precipitation efficiency, and training echoes will all increase
the likelihood for areas of heavy rainfall and the potential for
flooding issues. Precipitation deficiencies in recent weeks may
reduce the flooding impacts, but this event has the potential to
produce some of the highest 24-hour rainfall totals we have seen
in 2017.

The rain chances will end on Thursday, but again, the interlude
between systems will be short. Another deep low will dig into the
Desert Southwest late in the week, taking a similar southerly
track to its predecessor. This may ruin outdoor plans for the
first weekend of April, but the spring rainy season has clearly
begun.

25

&&

.AVIATION...

/ISSUED 1149 PM CDT Sat Mar 25 2017/
Light mostly easterly winds will become southeasterly at 5 to 8
knots overnight. Low clouds over South Texas will spread northward
overnight and may move into the Waco area toward 12z and into the
Metroplex TAF sites after daybreak. Thus have indicated a TEMPO
BKN015 at KACT from 12 to 16z and a TEMPO BKN020 at the Metroplex
TAF sites for the 13 to 16z period.

Southerly winds will be on the increase Sunday as a lee side
trough deepens. Expect south winds 10-12 knots at 13z to increase
to 15-17 knots by 16z with some gusts of 25 knots possible through
the afternoon. Although a capping inversion will be in place,
isolated to scattered thunderstorms may form along the dryline by
mid afternoon mainly along and north of the I-20 corridor. Thus
have placed VCTS in the Metroplex TAF sites for the 21z through
00z period. Some MVFR ceilings should spread northward again
Sunday night, thus have indicated BKN020 at 04z at Waco and 06z
at KDFW.

58

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    84  59  80  57  81 /  30  30   5   0  20
Waco                84  60  83  60  81 /  20  20  10   5  20
Paris               80  59  76  54  78 /  10  60  20   0  10
Denton              82  56  78  54  79 /  30  30   5   0  20
McKinney            81  59  78  54  79 /  30  40  10   0  20
Dallas              84  61  81  59  81 /  30  40   5   0  20
Terrell             83  62  79  57  81 /  20  40  10   0  20
Corsicana           84  62  81  61  81 /  20  30  10   0  20
Temple              85  61  84  60  82 /  20  20  10   5  20
Mineral Wells       87  53  80  55  79 /  20  10   0   0  30

&&

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

$$

82/25



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