NWS Area Forecast Discussion


000
FXUS64 KFWD 171809 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
109 PM CDT Fri Aug 17 2018


.AVIATION...
/18z TAFs/

Morning convection has ceased, with just a remnant mid-level swirl
in its wake noted in visible satellite imagery. There is a low
chance of an isolated shower/storm developing this afternoon
across North Texas, but the anticipated coverage is far too low to
warrant any mention of precipitation at this time. Additional
showers and storms should develop along a cold front, currently
inching into the I-40 corridor across Central Oklahoma. Much of
this surface-based thunderstorm activity should dwindle this
evening as it encounters increasing inhibition in the vicinity of
the Red River. Late tonight, a resurgence of the low-level jet is
forecast, fostering rather robust ascent focused roughly along the
I-35 corridor. There will be a brief window for VCTS as this
ascent impinges upon a bit more mid-level moisture towards
daybreak Saturday, but any activity will quickly fizzle through
the morning hours.

In the DFW extended TAF, the aformentioned cold front may be
approaching the D10 TRACON late Saturday afternoon with a
northeast wind shift. This would most likely occur just outside
the current extended TAF window. Showers and storms may also
accompany this feature, but a VCSH will suffice for now given
uncertainties in timing and placement of the best lift.

Carlaw

&&


.UPDATE... /Issued 1120 AM CDT Fri Aug 17 2018/
Early-morning elevated convection, forced by a modest low-level
jet, has fizzled across the northwestern portions of the
Metroplex, with just some renegade sprinkles and increased cloud
cover. A subtle fine line is inching south of I-20 at this hour,
and this could provide some focus for isolated convective
development this afternoon. That said, convergence along this
feature is weak, and this outflow will continue to diffuse as
additional mixing takes place through the afternoon.

A cold front is currently pressing southward into Central Oklahoma
at this hour, and will be moving south of I-40 this afternoon.
Moisture pooled ahead of this boundary should remain just north of
the Red River, allowing surface dewpoints across North Texas to
gradually mix out into the upper 60s to near 70 degrees. As a
result, the expectation is that heat indices today will generally
top out in the 101-105 degree range, with pockets of 105-108
degree readings peppering parts of North Texas this afternoon.
The isolated nature of these readings precludes the issuance of a
small Heat Advisory at this time.

The combination of weak convergence near the aformentioned
outflow, negligible forcing for ascent, and some modest forecast
convective inhibition today seems to point away from much in the
way of convection this afternoon. We`ll keep a low (10-20%)
mention of an isolated storm going this afternoon given PWATs
pushing 1.8-2" in places, but coverage is expected to remain quite
low. Any storms which manage to develop will carry a downburst
wind threat today with DCAPE pushing 1500 J/kg and 25-30 K
surface-600 mb theta-e deficits.

Carlaw

&&

.SHORT TERM... /Issued 412 AM CDT Fri Aug 17 2018/
/Today and Tonight/

The axis of a shortwave trough extends from the Great Lakes to
the Southern Plains and continues to generate convection north of
the region early this morning. This feature is weakening the
northeast flank of the upper ridge centered over West Texas,
which will leave the northern counties of North Texas vulnerable
to additional convective development this afternoon.

For this morning, isolated elevated thunderstorms still remain
possible along the Red River due to added lift from a 30 MPH low
level jet, but coverage should remain low and POPs limited to 20
percent. Better chances of development are expected this afternoon
and evening on either side of the Red River as stronger ascent
associated with the shortwave arrives during peak heating hours.
This warrants chance POPs along the Red River with slight chance
extending south to the I-20 corridor. Shear and instability will
be sufficient for some strong storms with gusty winds and
frequent lightning, with an outside chance of a damaging wind gust
or two. Storm motion will remain southerly, and any storm that
attempts to push south of the I-20 area will likely be diminished
by stronger subsidence and a strengthening capping inversion. Heat
indices will again approach 105 in a few locations along and east
of the I-35 corridor this afternoon, but convection and
associated loud cover should keep conditions just below advisory
criteria.

Another disturbance rolling out of the southern Rockies will
generate additional showers and thunderstorms to our northwest
tonight. Activity will weaken as it moves southeast, but
probabilities of storms lingering into the area are high enough to
keep slight chance POPs going into the overnight areas. Otherwise
warm and humid conditions can be expected with lows in the mid
and upper 70s.

30

&&

.LONG TERM... /Issued 412 AM CDT Fri Aug 17 2018/
The upper ridging that brought an end to our rain event earlier in
the week will continue retrograding into the Desert Southwest this
weekend. The northerly flow that will result will allow the
unsettled weather that has so far been confined to areas north of
the Red River to spill south into North Texas. The rain chances
Saturday will be primarily north of the I-20 corridor where
convective debris may shave a few degrees off afternoon
temperatures. However, across Central Texas, the summer heat will
continue unimpeded, and some locations may reach the century mark
on Saturday afternoon. In areas east of the I-35 corridor, where
dew points may still be in the upper 60s or lower 70s at peak
heating, the heat index could approach 105.

A nocturnal MCS may make a charge at North Texas early Sunday
morning, but the veered flow may keep the bulk of the activity
within Oklahoma. Regardless of its southern extent, if the
resulting outflow boundary is able to survive the day, it could be
the focus for renewed development Sunday afternoon. However,
intensifying lee troughing should enhance the southerly winds
across North and Central Texas, reducing the likelihood that the
boundary remains into the afternoon hours. The best forcing will
remain well to our north, associated with a deepening upper low
over the Central Plains, but strong surface heating and rich
boundary layer moisture could allow for a few strong storms late
Sunday afternoon.

The tail end of a potent shortwave will swing through North Texas
early Monday with an attendant cold front. The main event will
likely be focused from the Ark-La-Tex and points northeast, but
our radar scope may still be busy Sunday night into Monday
morning. With the departing trough, the front may lose its
southward push, particularly if the associated convection isn`t
particularly widespread. If the boundary stalls through Central
and East Texas, Monday afternoon/evening may be the main event for
those areas. Intensifying northerly flow aloft should finally
surge the boundary through all of Central and East Texas on
Tuesday. This is still August, and with abundant sunshine,
postfrontal temperatures will be in the 90s along and south of the
I-20 corridor. However, the reduction in humidity will make the
middle of next week noticeably more comfortable.

The rain-free period may end late next week, but with considerable
divergence among extended guidance, confidence is low in returning
rain chances. While there is the typical ensemble spread at day 7,
the GFS members overwhelmingly favor a Desert Southwest upper high
rather than the ECMWF`s more August-like Southern Plains ridging.
For now, will keep the end of the 7-day forecast dry, but with
this afternoon`s package, low PoPs may need to be introduced for
Friday next week.

25

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    99  78  97  78  95 /  20  20  10  20  20
Waco               100  76 100  78  99 /  10   5   5   5   5
Paris               96  73  94  75  91 /  20  40  30  50  40
Denton              98  76  96  77  95 /  30  20  20  20  20
McKinney            98  76  96  77  94 /  20  20  20  20  20
Dallas              99  79  98  80  95 /  20  20  10  20  20
Terrell             98  76  97  77  95 /  20  20  10  20  20
Corsicana           98  77  99  77  97 /  10  10   5  10  10
Temple             100  75  99  76  98 /   5   5   5   5   5
Mineral Wells       99  74  97  75  97 /  20  10  10  10  10

&&

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

$$

90/91

NWS FWD Office Area Forecast Discussion