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

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000
FXUS64 KFWD 200432
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1132 PM CDT Wed Apr 19 2017

.AVIATION...
Strong low level southerly flow continues to feed the convection
in the Central Plains this evening. Winds have mostly decoupled
across North and Central Texas, but a 35 to 40 KT low level jet
will transport a deck of stratus northward across all TAF
locations during the overnight hours. Patchy MVFR CIGs have
already begun to develop over South Central and Southeast Texas.
These clouds will rapidly increase in coverage and spread north,
likely affecting KACT by 07Z and the Metroplex an hour or so
later. CIGs should mostly be MVFR but will probably drop into IFR
category in the early Thursday morning hours, at least
occasionally. Conditions will improve mid to late morning,
eventually becoming VFR again around the middle part of Thursday
afternoon.

30

&&



.PREV DISCUSSION... /ISSUED 350 PM CDT Wed Apr 19 2017/
Warm and moist southerly flow continues across the region
resulting in a typical springtime feel to the air today. A few
showers have developed within an axis of greater moisture across
the eastern zones, and this activity will continue through the
early evening hours before dissipating with the loss of daytime
heating. Most of the region will experience a tranquil, warm, and
humid evening as dewpoints remain in the mid to upper 60s. Low
clouds will stream back into the region late tonight and persist
into the late morning hours Thursday. Thursday will be another day
with above normal temps as highs reach the low to mid 80s.

A cold front that is currently in Kansas will move south through
the overnight hours and reach the far northwestern zones by mid to
late afternoon Thursday. The front is expected to stall in this
area as a strong shortwave approaches from the west. There is
sufficient moisture and instability for a few showers and
thunderstorms to develop along the front, but overall forcing for
ascent is weak. The isolated storms that do form along the front
will move slowly eastward and could affect the northwest CWA
during the evening hours. While hail and damaging winds can`t
totally be ruled out with these storms, bulk layer shear is likely
too low to sustain organized updrafts for long.

The severe weather forecast Friday and Friday night is a complex
one involving the timing and placement of synoptic features and
their impacts on mesoscale boundaries. The high level overview is
that there is a threat of severe weather simply because we have
the combination of ample instability and wind shear in place when
a cold front moves through the area. However, it is often the
mesoscale features that can either make or break the severe
weather risk, and Friday`s setup is one where the timing of lift
is not optimal, while the impact of the mesoscale boundaries is a
major question mark.

The first issue with the severe forecast is that the front on
Thursday night looks like it will make it down to I-20 in West
Texas with cool and moist northeasterly flow prevailing across the
Panhandle and into the Permian Basin. This wedge of cool and
moist air will likely serve to keep the dryline well west of our
CWA on Friday. All of the high res models are showing the dryline
essentially a non-player for storm initiation because it just
isn`t able to mix out the frontal inversion very quickly and
advance eastward during the day Friday. Of note the coarser GFS,
ECMWF, and Canadian models do bring the dryline to our doorstep,
but I am inclined not to trust that forecast. So without a
dryline nearby, storms may struggle to initiate in the warm
sector and impact our CWA.

The second big concern with the forecast is that the main
shortwave trough that provides the strongest lift will move across
Oklahoma late Thursday night and Friday morning with subsidence
dominating during the day Friday. A second round of forcing for
ascent will occur Friday evening and night, but this is the result
of increasing cyclonic flow aloft at the base of a sharpening
longwave trough, and not a typical compact shortwave.

So that brings us to the mesoscale uncertainty. The early Friday
shortwave trough will assuredly kick off widespread convection
across Oklahoma north of the stalled front. The rain and storms
will produce cold pools which could keep the stationary cold front
farther south and lingering across our northern area into the day
Friday. With subsidence during the day Friday, this could keep a
convergent boundary with a diminishing thermal gradient near or
across the Red River counties. This is going to be the boundary to
watch for afternoon storm initiation, and may provide an enhanced
region of low level vorticity for storm rotation. However, it is
impossible to know now whether the cold outflows from storms in
Oklahoma will be enough to keep this boundary farther south in our
area, or if it will lift to the north into Oklahoma. Either way,
the highest potential for any severe weather will be across the
northern part of the CWA because they will be closer to wherever
the old front is located. Again if storms can initiate near the
Red River Valley during the afternoon hours, they will have the
potential to produce severe weather in our CWA with large hail the
primary threat.

Once the front gets a renewed southward push as the upper trough
progresses eastward Friday night, it is likely that the front
will undercut the convection that develops along it. 0-6 km bulk
shear vectors align parallel to the frontal boundary which means
convection should become linear. Low values and parallel 0-3km
shear vectors also suggest that even though it will be a line of
storms, the damaging wind threat and QLCS tornado threat looks
very limited. This line will likely reach the Metroplex around
midnight and continue tracking southeast across the region
overnight and into early Saturday morning. Indications are that
the line will outrun the synoptic forcing and enter a less unstable
atmosphere resulting in a weakening and possibly even dissipating
trend Saturday morning as it reaches the far southeast zones.

Much cooler and breezy conditions will prevail behind the front on
Saturday. Skies will clear from northwest to southeast and it will
be a fairly nice day. Highs will range from the mid 60s north to
lower 70s south. The northerly winds will continue into Saturday
night so radiational cooling will not be optimal, but still lows
will drop into the 40s area wide. Sunday will be very nice with
lighter winds and lots of sunshine. Highs will reach the low 70s.
Lows Sunday night will again be in the 40s area wide.

A gradual moderating trend will occur next week as southerly winds
return. Temperatures will be near normal for the first part of the
week but by mid to late week it looks like above normal temps
return. Model guidance is still in very bad agreement late in the
week regarding the fate of the next system. The Canadian shows an
upper trough reaching the region Wednesday with a chance of
storms, the GFS shows this occurring on Thursday, and the ECMWF
holds it off until Friday.

TR.92



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    68  83  67  85  57 /   5  10  10  10  70
Waco                67  83  66  84  59 /   5  10  10  10  40
Paris               63  80  64  82  56 /  10  10  10  20  70
Denton              66  82  65  82  55 /   0  10  10  10  70
McKinney            66  82  65  83  56 /   5  10  10  10  70
Dallas              69  84  68  84  58 /   5  10  10  10  70
Terrell             66  83  67  83  58 /   5  10  10  10  70
Corsicana           66  83  66  84  60 /   5  10   5  10  50
Temple              66  83  65  85  61 /   5  10  10  10  30
Mineral Wells       63  84  63  85  54 /   0  10  10  10  50

&&

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

$$

30/91



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