DFW FORECAST DISCUSSION
000
FXUS64 KFWD 180451
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1151 PM CDT Wed Oct 17 2018


.AVIATION...
/06Z TAFs/

Low VFR cigs will continue to prevail overnight and into the
morning hours across DFW area airports, while MVFR cigs will prevail
at Waco. Waco could see some sporadic low VFR cigs as dry low
level air tries to entrain from the north-northeast through mid
morning Thursday. This will be due to a south to north sloping
frontal inversion which is deeper across DFW and closer to 850mb,
whereas Waco`s inversion is more shallow. During this time period,
the area will be in between mid level shortwave disturbances.

The next mid level shortwave disturbance currently over the Texas
Coast will slowly migrate northward through the day Thursday. By
afternoon, cigs everywhere will be in the MVFR category as showers
increase from the south. Waco will likely see these showers by
late morning/midday, while DFW may be delayed more during the
mid-late afternoon hours. Rain coverage should increase across the
entire area by 00z Friday and beyond with both vsbys and cigs
falling. Low MVFR cigs with occasional heavier showers causing
vsbys to fall to IFR are expected across the DFW Metro airports
Thursday evening, while RUC soundings show Waco going down into
IFR even on cigs.

Otherwise, light northerly winds around 5 knots overnight will
veer northeast or even east-northeast 6-9 knots by Friday
afternoon as a secondary shallow surge of cool air arrives from
the north. By Thursday evening, northeast winds 4-6 knots will
prevail.

05/

&&


.DISCUSSION... /Issued 328 PM CDT Wed Oct 17 2018/
I`ll just skip ahead to the part of the forecast that everyone
wants to know about - the sun will be back this weekend. We know
it still exists because our visible satellite shows the bright
white cloud cover blanketing the entire region.

The water vapor satellite continues to show the cut off upper
level low responsible for the prolonged rain event spinning
across the southwestern US. Isentropic upglide continues over much
of the northern half of the CWA, but the best lift and heaviest
rain is primarily the western zones this afternoon. Hi-res and
synoptic models are all in good agreement in showing the best lift
and rainfall chances tonight will be across the northwestern
zones through about midnight before tapering off and shifting
northwest. While rainfall rates should remain below 0.35" per
hour due to limited instability (which should limit flash
flooding) there still is the potential for 1-2 inches of rain
across the NW CWA through tonight. Fortunately this region is not
quite as saturated as other parts of the CWA, but still flooding
of low-lying areas, creeks, and rivers is a concern. Elsewhere
across the CWA, rain will be lighter with little or no rain
expected across the eastern zones into Central Texas tonight.
Temperatures will hold nearly steady near their current readings
all night.

Models are coming into good agreement in ejecting the bulk of the
PV anomaly in the Desert SW out into the Plains this weekend.
This will be both good news and bad news. The bad news is that it
will cause our low level winds above the frontal inversion to
increase out of the southeast resulting in a renewed vigor of the
isentropic lift, and perhaps more concerning, greater moisture
flux with precipitable water values increasing from the current
values of 1.5 inches to near 2 inches during the day Friday. While
traditional upright instability continues to look low (limiting
the thunderstorm threat), models do show slantwise instability is
available with some high res models forecasting frontogenesis to
increase. The result is that some of the models are now outputting
higher QPF Thursday night into Friday with the upper end amounts
of 3 to 5 inches across parts of the northern and western CWA.
Since there is still a lot of spread among the QPF guidance, we
will hold off on issuing a flood watch at this time, and we will
keep average QPF in the 1-2 inch range through Friday night.
However we will continue to monitor these trends in the data
overnight and will have to consider the resurrection of a flood
watch for part of the area. The primary region we`re concerned
about is along and west of the I-35 corridor, and the time frame
is Thursday afternoon through Friday.

The good news is that the ejection of the energy associated with
the upper low will help to send another cold front into the region
with much drier air in the lower levels. This will result in the
chance of rain ending from north to south on Saturday with some
sunshine possible in the afternoon too. We`ll still keep some
high clouds in the region, but Sunday should be a partly sunny and
dry day for the entire area. High temperatures Saturday will be
in the upper 60s to near 70, but as the cooler air filters into
the region, Sunday`s highs will only be in the low to mid 60s.
Lows will also be seasonably cool and in the 40s.

Unfortunately another upper level trough will develop off of the
coast of California early next week. This will bring the return of
southwesterly flow aloft and southerly flow just above the frontal
inversion to the region again. Isentropic lift and moisture
advection will bring the chances of rain back to the area starting
late Monday, but especially into Tuesday and Wednesday. The ECMWF
has sped up its timing of the upper level features to match the
GFS forecast, so we have increased PoPs Tuesday and Wednesday.
Rainfall at this time looks to average 1-2 inches, however both
the GFS and ECMWF do show a landfalling eastern Pacific hurricane
in Mexico during this time period. This system (should it exist)
would likely enhance the upper level dynamics over the state and
increase the risk for heavy rainfall. Obviously because it`s a
tropical system that hasn`t formed yet, it`s too early to say for
sure whether this will occur, but it bears watching. Otherwise
temperatures look to cool Tuesday and Wednesday due to the rain
over the area.

TR.92

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    52  61  54  59  55 /  60  60  60  80  50
Waco                52  60  56  60  56 /  20  70  50  70  50
Paris               53  63  52  57  53 /  40  20  40  70  60
Denton              52  61  53  58  54 /  70  70  70  80  40
McKinney            53  62  53  57  54 /  60  60  60  80  50
Dallas              53  62  55  59  56 /  50  60  60  80  50
Terrell             53  64  55  59  55 /  30  50  50  70  60
Corsicana           52  63  54  60  55 /  20  50  40  70  60
Temple              51  58  56  60  56 /  20  70  50  70  50
Mineral Wells       50  58  53  58  54 /  80  70  80  80  40

&&

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

$$

05/25

NWS FWD Office Area Forecast Discussion