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

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FXUS64 KFWD 180918

Area Forecast Discussion
National Weather Service Fort Worth TX
318 AM CST Sat Feb 18 2017

An upper low can be seen on satellite exiting the ARKLATEX region
and heading for the Mississippi Valley. Typically we would
experience veered surface winds in the wake of the system.
Instead, a southerly fetch continues across North and Central
Texas due to the development of a deeper upper level trough along
the West Coast (which has already provided excessive rainfall
across California) and its resulting lee side surface troughing.
A deck of stratus quickly spread north overnight along the I-35
corridor within the deep fetch of low level moisture. The low
clouds and breezy conditions have kept temperatures above forecast
lows in most locations, with the exception being the far west
counties where drier air still lingers.

The trend this weekend will be continued above-normal temperatures
and increasing moisture in advance of the West Coast system. The
upper trough is progged to cross the Desert Southwest and
Northern Mexico over the next 24 hours, and continue east into
West Texas on Sunday. Forcing for ascent will arrive Sunday ahead
of the trough but should be meager during the morning hours. There
may still be warm/moist advection showers and perhaps a few
storms across the western counties in the morning, where chance
POPs will remain. Convection will likely increase in coverage as
it spreads east during the afternoon due to strengthening deep
layer forcing, added moisture and the development of surface
based instability.

There are still substantial model discrepancies with regard to
convective parameters and the overall chances for severe weather.
The NAM continues to be aggressive with both CAPE and shear when
compared to other models, with the most recent run indicating CAPE
at or above 2000 J/KG and bulk shear values on the order of 60
KT. The GFS indicates about half the CAPE advertised by the NAM,
but still shows bulk shear around 50 KT. This should still be
enough for at least a low-end severe threat with both damaging
winds and large hail. The best chance for strong to severe storms
would be during the 21Z to 03Z time frame when maximum
instability is in place.

The strongest ascent will occur after 00Z in a region near the
I-35 corridor and will spread east during the evening and
overnight hours. This may allow the ongoing scattered convection
in the late afternoon to grow upscale into a linear MCS as
activity spreads east. This may also lead to a transition from a
severe threat to a locally heavy rain threat as showers and storms
affect the eastern half of the region, where PWATs are forecast
to climb into the 1.3 to 1.5 inch range.

So at this time, it still appears that the severe threat will be
highest along and west of Interstate 35 during the afternoon and
early evening, while the localized heavy rain threat would be
highest east of the I-35 corridor during the late evening and
overnight hours. That said, we are still about a day and a half
away from the event and and will refine the details as the system
evolves and fresher model data arrives. One commonality in the
latest model guidance is the progressive nature of the system.
Thunderstorms should move east of the forecast area Monday
Morning, with perhaps some lingering stratiform precipitation
Monday afternoon.

A cut-off low will then develop at the base of the trough on
Tuesday and move southeast across the Gulf of Mexico through
Thursday. This will leave North and Central Texas beneath an upper
ridge, leading to warm and dry weather Tuesday through the end of
next week.



/ISSUED 1128 PM CST Fri Feb 17 2017/
An upper level low over southeastern Oklahoma at 05z, will
continue to move east northeast. Meanwhile upper level ridging in
the wake of the departing upper level low will leave the region
dry except for some possible patchy drizzle along the Red River
and to the east of I-35/I-35E between 10z and 15z. A southerly low
level jet has developed this evening which is bringing some MVFR
stratus north northwestward. Some IFR ceilings will be possible in
the Waco area toward and shortly after daybreak (09z-14z). Expect
VFR conditions to return 16-17z. South to southeast winds 10 to
15 knots will prevail through the TAF forecast period.



Dallas-Ft. Worth    75  58  75  60  73 /   5   5  50  70  30
Waco                80  60  76  59  73 /   0  10  50  70  30
Paris               66  55  76  60  68 /  10   5  20  70  60
Denton              73  56  73  58  72 /   5   5  50  70  20
McKinney            71  56  75  60  71 /  10   5  50  70  40
Dallas              76  59  76  61  72 /   5   5  50  70  30
Terrell             74  58  77  61  71 /   5   5  40  70  60
Corsicana           77  60  78  61  72 /   5   5  40  70  60
Temple              81  61  76  59  74 /   0  10  50  70  40
Mineral Wells       76  55  74  55  75 /   0   5  60  70  10




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