National Weather Service Raw Text Product

Displaying AFOS PIL: AFDFWD Received: 2018-10-12 12:17 UTC

FXUS64 KFWD 121217

Area Forecast Discussion
National Weather Service Fort Worth TX
717 AM CDT Fri Oct 12 2018

/12Z TAFS/

Widespread rainfall is moving across parts of North Texas this
morning but is mainly confined to the Red River counties north of
the major airports. Most of the moisture is elevated at this time
so ceilings are generally VFR areawide. Continued moistening of
the lower levels where rainfall occurs and through advection will
result in lowering cigs through the day. We'll prevail VFR cigs
with VCSH through this morning and have a brief period of
prevailing -RA around midday. This timing may need to be adjusted
through the morning. Otherwise, showers will likely persist for
much of the day as a weak front slides southward by this evening.
Cigs will likely lower to around 2500 ft after dark with continued
lowering through the overnight hours. Additional areas of rain are
expected to develop late overnight and we'll have prevailing SHRA
with IFR cigs by early Saturday morning. There will be sufficient
instability for a few lightning strikes through the day, but
showers should generally prevail over thunderstorms. Trends will 
be similar through the day at Waco, although the onset of 
precipitation may be a little later into the afternoon.



.SHORT TERM... /Issued 354 AM CDT Fri Oct 12 2018/
/Today and Tonight/

Water vapor imagery shows high level moisture streaming into the
Southern Plains ahead of Tropical Storm Sergio in the eastern
Pacific along with a strong shortwave trough moving through the
Central Plains. These two features will help strengthen the mid
and upper level wind fields across the Plains today. In response,
low level southerly flow will strengthen and help pull Gulf of
Mexico moisture northward. Abundant mid and high cloud cover is
already in place across the region indicative of the increase in
moisture aloft from the eastern Pacific.

Strong isentropic ascent in the 295-310 K layer is ongoing across
much of Central and North Texas and is already resulting in some
spotty showers across our northwest counties. With continued
moistening, the coverage of showers should increase through the
mid morning hours with the best chances across the northern half 
of the region. There will be enough instability aloft for a few 
rumbles of thunder through the afternoon, but showers will
generally prevail. Most of the precipitation will move off to the
northeast late this afternoon as the northern stream shortwave
quickly moves eastward and the low level jet veers and weakens.

A cold front will slide southward this evening and should make 
its way into the I-20 corridor prior to midnight. We'll hang onto
some low rain chances right along the front through late evening.
During the overnight hours, the remnant mid level circulation of
Sergio will spread into West Texas. An ill-defined surface low
over far West Texas will deepen overnight and should be centered
somewhere north of Midland by early Saturday morning. Ahead of
this feature, strong low level warm advection will again ramp up
aided by a 45 kt low level jet. Unlike this morning, low level
moisture will already be in place and a rapid development of
showers and thunderstorms is expected across West Texas. This
activity will spread eastward into our western counties prior to
sunrise Saturday. We'll have high PoPs mainly west of I-35 for the
late night hours into early Saturday morning. The aforementioned
cold front will begin to spread back northward during this time.
Right now, it doesn't appear that we'll be dealing with any severe
weather overnight tonight, but that potential into the day
Saturday will be discussed further below.



.LONG TERM... /Issued 354 AM CDT Fri Oct 12 2018/
/Saturday through Friday/

...An active weather pattern will bring a threat for heavy 
rainfall and flash flooding to North and Central Texas this 
weekend and early next week, and at least a low potential for 
severe weather on Saturday. Some of the coldest temperatures 
since last April are slated to descend upon the region on Monday 
and Tuesday...

Saturday and Sunday...
The main feature of interest this weekend will be the remnant 
circulation of Tropical Storm Sergio, which will effectively 
dictate where the heaviest rainfall and any severe weather threat 
sets up. Sergio is presently just off the Baja California Sur 
coast early this morning and is forecast to come ashore a little 
later this morning. 

Global model guidance over the last few nights has consistently
forecast a somewhat coherent low-level circulation to survive the
500 mile trek over the extremely rugged terrain of Sonora and
Chihuahua as it crosses over the Sierra Madre Occidental. Recent
runs of the HWRF similarly show a 925-850 mb circulation emerging
across the High Plains of west Texas Saturday morning and
subsequently tracking across the Low Rolling Plains and into
southeastern Oklahoma Saturday evening. This lends some confidence
to the global guidance from the GFS, FV3, and ECMWF, all of which
depict a similar scenario. 

While our airmass is currently still recovering from the frontal
intrusion last weekend, PWATs are forecast to climb back into
near-record territory tonight and into Saturday morning as
moisture to our west sloshes back overhead. Strong low-level flow
associated with Sergio's remnant circulation (35-45 kts in the
925-850 mb layer) will facilitate poleward moisture fluxes into 
the region as very strong lift overspreads the area. Given all of
this, I've bumped PoPs upwards across all of the forecast area
Saturday and into Saturday night, painting the highest chances 
(80-90%) north and west of a Lampasas to Canton line. Given the
very dynamic and moist environment, heavy rainfall will be a
threat, and flash flooding--at least on a localized basis--is a
concern over this region. Due to some lingering uncertainties 
associated with the low-level circulation's track, however, 
confidence was not quite high enough to hoist a Flash Flood Watch 
for Saturday and Saturday night. We'll let the day shift digest 
some additional guidance, but if trends continue, one may be 
warranted for roughly the northwestern half of the CWA. 

In addition to the flood threat, there is a conditional severe
weather risk on Saturday. Overnight model guidance continues to
suggest that at least a portion of our forecast area will make it
into the warm sector Saturday afternoon, with MLCAPE values
increasing into the 1000-1500 J/kg range. The GFS appears too
aggressive with this northward instability return, but SREF
guidance shows decent probabilities of >1000 J/kg readings
developing mainly west of I-45 and south of I-20 during the 
afternoon and evening hours. Deep layer shear values of 40-45 kts 
and long-looping hodographs resulting in SRH values in excess of 
250+ m2/s2 support a threat for supercells with an associated risk
for a tornado or two (where surface winds remain locally backed),
in addition to damaging wind gusts and perhaps some hail. Two 
mitigating factors will be a notable lingering subsidence 
inversion above 600 mb, and the presence of copious rainfall 
across North Texas which could encourage more of a southward push 
of the effective cold front through the day. We'll continue to 
monitor this potential closely today and tonight. 

Sunday night through Wednesday... 
After a brief reprieve from the action on Sunday, a strong cold 
front will blast through the region Sunday evening and overnight. 
Strong ascent will continue well into the post-frontal airmass as 
North and Central Texas will remain favorably positioned within 
the right entrance region of a 100-120 kt upper-level jet through
this period. Rain is expected to become widespread Sunday night
and into Monday and PoPs will be high (80-100%) during this
timeframe. Temperatures will fall through the 40s and even into
the upper 30s across our far northwest counties by Monday morning.
Combined with a biting 15-25 mph north wind, and Monday is shaping
up to be an extremely raw and unpleasant day. 

Embedded pockets of heavy rainfall will develop through Tuesday
night as waves of ascent pass overhead. Widespread rainfall totals
of two to four inches, with localized amounts in excess of 5
inches will be possible, which will lead to additional bouts of
flash flooding and eventually main stem river flooding. 

Rain chances will gradually diminish by Wednesday and Wednesday
night as the main jet core moves off to our northeast and overall
forcing for ascent decreased. We'll keep chance PoPs going through
this period, however, for most of the area. 

Thursday and Beyond... 
It doesn't look like we'll ever really dry out in the extended
portion of the forecast as additional ripples in the broad
cyclonic flow to our west pivot overhead. We'll advertise chance
PoPs across the region through Friday to account for the
development of additional precipitation, but the flood threat
should be minimal at this point. Temperatures through the end of
the week look to remain in the 60s for most of the region. 



Dallas-Ft. Worth    69  60  71  62  71 /  80  70  90  60  60 
Waco                75  64  77  68  77 /  50  50  80  50  70 
Paris               62  56  67  60  71 /  60  20  90  80  60 
Denton              67  58  68  60  69 /  90  70  90  60  50 
McKinney            67  57  69  61  71 /  80  50  90  70  60 
Dallas              69  61  71  63  74 /  80  60  90  60  60 
Terrell             69  60  76  66  75 /  60  40  80  60  60 
Corsicana           72  62  80  67  78 /  60  50  80  50  70 
Temple              80  66  78  70  80 /  30  40  70  40  70 
Mineral Wells       68  60  70  58  68 /  90  90  90  50  60