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

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298
FXUS64 KFWD 141008
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
408 AM CST Sat Jan 14 2017

.DISCUSSION...
Main headline for this forecast continues to be the Sunday
evening/night through Monday morning time frame when some strong
to severe storms and heavy rain are expected to affect North and
Central Texas. There are still some timing/location uncertainties
with this system, but confidence is high that most locations will
receive rainfall and that a few strong/severe storms will occur.
Otherwise, we`ll have one more day of dealing with this pesky
stationary front which will keep cool and damp conditions around
today.

The stubborn shallow Arctic front that has affected our area for
the past couple of days has managed to sink as far south as San
Marcos, TX and remains draped roughly along I-10 to the west and
northeastward toward Texarkana to the east. This cold airmass is
only around 1000 ft deep and temperatures are actually around 50F
or higher in the inversion layer immediately above. Low clouds,
mist, and drizzle will continue through the morning as we remain
socked in to overcast skies with the front remaining nearly
stationary through most of the day. Have sided with some of the
coolest guidance for high temperatures this afternoon as
temperatures should struggle to warm more than a few degrees
especially in areas situated well north of the frontal zone. The
good news is that the cold advection has become nearly neutral
preventing the low 30s temperatures in our northwest from falling
below freezing, so no issues with freezing precipitation are
expected even where temperatures are currently near freezing.
Later this afternoon, a few warm advection showers will be
possible, but am expecting less coverage than yesterday. The
highest PoPs will be located in our northwest areas where warm
advection will be the strongest.

As a strong upper low nears the region tonight, the front will
finally begin lifting back to the north as a warm front. Have
stuck to the slowest guidance especially the NAM regarding the
front`s retreat as the NAM has the best handle on the front`s
current position and has shown to be far better at resolving this
very shallow arctic air mass over the past 48 hours. Temperatures
should remain steady or even warm a few degrees overnight as the
front moves northward and winds turn to the east and eventually
southeast. Strong warm advection will continue to result in some
isolated/scattered showers during this time. It`s difficult to get
a good handle on the warm sector environment for Sunday afternoon
and evening especially since the timing of the front`s northern
retreat is in question in the first place. However, the most
likely scenario should consist of dewpoints climbing into the 50s
and low 60s area-wide Sunday afternoon with temperatures ranging
from the low 60s in the northwest to the low 70s in the southeast.
Those numbers immediately indicate that instability will be in
question, especially since most of the area should still be
overcast through the day which will reduce surface heating.

Strong warm advection should be able to generate showers and
storms especially west of I-35 on Sunday afternoon. While there is
no shortage of wind shear given the approaching upper low and jet
max, limited instability should put a damper on the strong/severe
storm threat during this time. Given the strong shear and widely
curved hodographs, any shower or storm will likely be rotating,
but the lack of instability, particularly in the low levels,
should continue to preclude a tornado/severe threat during this
time. The main concern regarding strong/severe storm potential
will arrive Sunday evening/night as a line of storms generated
along a Pacific front in West TX impinges on the area. Latest
guidance puts this line at our western counties early Sunday
evening, near I-35 around midnight, and across our eastern areas
by daybreak. The main concern with this activity will be the wind
threat given the environmental wind speeds of 50-60 kts in the
925-80mb layer to begin with. This momentum could easily be
transferred to the surface by this convective complex. Wouldn`t be
surprised to see a bowing segment or two within the line given
that 30-40 kts of shear would be concentrated in the lowest 3 km.
The main area of concern will be along/west of I-35 where
instability is a bit more favorable and upper support will be
stronger. By the time the complex gets east of I-35, the upper low
will be lifting northeast along with the strongest support, and
expect the line to slow down and weaken as it enters our eastern
areas Monday morning.

Am growing less concerned about the flood threat with this system
as it appears to be faster moving than previously thought,
although a localized flood threat will still exist as the system
should be an efficient rain producer given the very high PWs for
this time of year. If the system does slow down or begin to stall
across our eastern areas, this may end up being the more favorable
area for some flood issues. Overall, am still expecting rain
totals of around 1-2" on average over our entire area with some
localized higher amounts.

Monday`s forecast will depend heavily on Sunday night`s system. At
this time, it appears that thunderstorms will still be possible
in our southeast on Monday afternoon along the modified Pacific
front that will accompany the line of storms Sunday night. As this
moisture boundary becomes stalled in our eastern counties, it
could assist in providing a focus for convective initiation again
Monday afternoon. Instability may be more favorable in this area
during this time, but the strong upper support from the upper low
will be displaced a few hundred miles to the north which will
likely hinder the strength of thunderstorms Monday afternoon.
Otherwise, a trailing cold front behind the Pacific front will
move through the area late Monday and Tuesday. Have left a mention
of showers and storms across the southeastern half of the area on
Tuesday but there may not be enough moisture left by this time
for additional activity.

Confidence in the extended portion of the forecast is fairly low
given the uncertainties that still exist even through the first 4
days. An active pattern is expected to continue with additional
upper troughs moving through the Central and Southern Plains
Wednesday through Friday. The GFS is more aggressive than the
ECMWF with moisture return on Wednesday and Thursday, and as a
result is developing showers and storms for the southern and
eastern portions of the forecast area. The ECMWF is a bit farther
south with the track of the upper level features keeping us cut
off from the better moisture content through the end of the week.
Have introduced some low PoPs with low confidence at this time.

-Stalley

&&

.AVIATION...
/ISSUED 1139 PM CST Fri Jan 13 2017/
A frontal boundary extended south of a KPSN (Palestine) to KHYI
(San Marcos)line as of 05Z (11 PM CST). Expect north flow to
prevail at all of the TAF sites for the next 36 hours. All of the
TAF sites are IFR and some LIFR conditions are possible overnight
and Saturday morning. Areas of fog and patchy drizzle are
possible through Saturday. Scattered showers are expected mainly
during the afternoon and evening hours Saturday and an isolated
thunderstorm will be possible. More widespread showers and
thunderstorms are expected Sunday.

58


&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    47  47  65  56  67 /  30  20  40  90  40
Waco                51  51  68  59  67 /  20  20  50  90  50
Paris               54  50  65  59  66 /  30  20  20  90  90
Denton              46  46  63  51  65 /  30  20  50  90  30
McKinney            49  47  64  56  66 /  30  20  30  90  40
Dallas              49  49  67  58  67 /  30  20  40  90  40
Terrell             55  51  67  59  66 /  20  20  30  90  70
Corsicana           56  52  69  61  68 /  20  20  30  90  70
Temple              54  53  71  59  67 /  20  20  50  90  50
Mineral Wells       43  43  62  47  66 /  40  20  70  80  20

&&

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

$$

82/26



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