Forecast Discussion for Dallas/Ft. Worth, Texas

FXUS64 KFWD 182050

Area Forecast Discussion
National Weather Service Fort Worth TX
350 PM CDT Thu Oct 18 2018


The high pressure circulation across the Florida Peninsula will
continue to advect moist, Gulf air into Texas through the night.
Given the cool, dense air is still settled across the state, warm
air advection will once again lead to another wave of
precipitation, mainly west of Interstate 35. There will likely be
the presence of weak instability across Central Texas overnight,
leading to the threat of isolated storms. Rain rates outside of
any storms will likely not be significant, generally less than
half an inch before 7am. If thunderstorms occur, there will be a
threat for slightly higher rainfall amounts around sunrise. For
that reason, a Flash Flood Watch will be in place beginning 6 AM
and last through the day tomorrow.

Lows tonight are expected to be a few degrees warmer compared to
last night. The warmest temperatures will be across the Brazos
Valley, where upper 50s are expected. Winds will remain out of the
north/northeast, between 5-10 mph.



/Friday Through Thursday/
The ejection of the upper level low over the southwestern US into
the Plains will result in increasing isentropic lift and warm
advection above a shallow frontal layer. Winds just above the
frontal inversion will become southerly at speeds of 20-25 knots
resulting in good moisture flux and precipitable water values
surging toward 2 inches across much of North Central Texas.
Theta-E values will also increase and models are in better
agreement in bringing MUCAPE values of a couple hundred J/KG
in across the southern CWA, and saturated EPV progs suggests
CSI/CI will also be present well into the heart of north Texas.
While the threat for thunderstorms will be limited to primarily
the southern and southeastern zones, the increased instability
combined with the surging moisture content suggests that either
bands of heavier rainfall or cellular convective cells will be
possible Friday.

The actual QPF guidance from the models is not as clustered as
I`d like to see and it is possible that some of the drier
forecasts of less than an inch everywhere will be the ones that
pan out. However, there is a signal in several of the models
highlighting all of the ingredients we look for to anticipate
heavy rainfall across the southwestern into the central zones of
the CWA that can`t be ignored. This coincidentally is the region
that has seen the highest amount of rainfall in the last week and
soils just aren`t capable of holding any more rain. We have issued
a flash flood watch in this region to highlight this potential of
heavy rainfall. These heavy rain ingredients suggest some
locations may see more than 3 inches if and where any banding sets
up, but in general the average amounts still look only like 1-2
inches over the watch area. We do expect rivers, creeks, and
streams to be very sensitive to any additional rainfall which
would cause flooding. While widespread rain is expected Friday in
areas outside of the watch, locations farther to the north have
not seen as much rainfall and this round is not expected to be as
heavy there as moisture content and instability diminish which
should keep rainfall rates low. Temperatures will be cooler
Friday due to the rainfall and weak northeasterly surface winds
continuing. Most locations will spend the day in the 50s with low
60s in the east and southeast.

The bulk of the rain will come to and end from west to east Friday
evening as the shortwave moves off to the east and the isentropic
lift ends. This will also send a cold front into the area with
much drier air filtering into the region Saturday. Still a few
showers are possible along the front as it moves through the
region Saturday morning, but by late Saturday the entire area will
be rain free with some sunshine filtering in through the lingering
high clouds. Dry and cool weather looks to prevail Sunday and
Monday and these look like pretty nice days compared to what we`ve
been through in the last week. Highs will generally be near 70
Saturday and in the 60s on Sunday and Monday. Lows will drop into
the 40s.

Unfortunately the rain will return by the middle of next week as
another trough moves toward the region. The weekend front will
stall across south Texas and therefore that rich moisture will be
quickly drawn back northward. We will bring the chances of rain
back Monday night, and show them increasing Tuesday and Tuesday
night. While confidence is high in the chance of rainfall
Wednesday, what is still in question are the amounts. That`s
because rainfall amounts are contingent on whether a tropical
system will develop in the eastern Pacific Ocean and gets drawn
northward by the upper trough into Mexico. Should this occur it
would provide strong upper level dynamics for lift and result in a
swath of widespread heavy rainfall across Texas. We`ve seen both
the operational GFS and ECMWF flirt with this scenario on
occasional runs and we know from climatology that this is a
pattern setup that has produced many instances of 10+ inches of
rain. Again, we will not start advertising or anticipating this
until we get better consistency with the possible tropical system
(that hasn`t organized yet), but we`re watching this closely as
it`d be a worse case scenario after all of the rain we`ve already
seen. Temperatures in the midweek period should stay cool with
the frontal boundary remaining to our south with ongoing rain.

The good news is that a more progressive upper level pattern will
organize later in the week into the following weekend. This will
get us back to normal - with a period of drier weather in between
successive systems.



.AVIATION... /Issued 1254 PM CDT Thu Oct 18 2018/
/18Z TAF Cycle/

Early afternoon precipitation is confined to areas east of KACT,
and will continue to mainly drift to the northeast away from the
TAF terminals. Although precipitation has not been impressive this
morning, weak isentropic ascent continues across the region, and
for that reason, VCSH will remain in the forecast.

A gradual uptick in precipitation is likely this evening as the
next wave of precipitation develops to our southwest. This is
likely to impact both KACT and all the Metroplex TAF sites
overnight through tomorrow. Although the KACT forecast has non-
thunderstorm precipitation falling overnight, there may be just
enough instability for an isolated lightning strike within the
heaviest precipitation. Given there are some model discrepancies
as to the placement and amount of instability, will hold of on
adding a mention of lightning. This will have to be revisited in
later forecast cycles.

MVFR conditions will move in tonight, and likely persist through
the rest of the day tomorrow. Not much change in the speed and
direction is expected, generally remaining out of the
north/northeast below 10 mph.



Dallas-Ft. Worth    56  58  55  70  50 /  50 100  70  20   0
Waco                55  60  58  68  52 /  60 100  80  40   0
Paris               52  56  54  69  47 /  30  90  70  10   0
Denton              54  58  55  71  49 /  60 100  60  10   0
McKinney            55  58  55  70  49 /  40 100  70  10   0
Dallas              56  60  56  71  51 /  50 100  70  20   0
Terrell             56  59  56  69  51 /  30  90  80  20   0
Corsicana           56  60  55  67  50 /  30  90  80  40   0
Temple              56  61  58  65  54 /  60 100  70  40   0
Mineral Wells       54  59  55  70  48 /  80  90  50  20   0


Flash Flood Watch from Friday morning through Friday evening for



NWS FWD Office Area Forecast Discussion