Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 250355

Area Forecast Discussion
National Weather Service Norman OK
1055 PM CDT Sat Mar 24 2018



For the 06z TAFs:

Mid level clouds (~10,000 feet) will increase tonight as a weak
system moves in. Some virga or sprinkles/light showers may occur
at some locations across the area with this mid-level moistening.
There is a small chance that lower level moistening in north
Texas could cause some thunderstorms to form late tonight
(generally after 3am), and we have covered this with a TEMPO
group for SPS. Confidence is not high. Low level moisture return
could cause stratus by dawn, especially in northwest Oklahoma,
with continued moisture return eventually resulting in stratus in
central/northern Oklahoma by midday or afternoon. These ceilings
could lower further toward the end of the TAF period.
Shower/storms tomorrow afternoon/evening should be limited by
fairly strong capping inversion, and so probabilities were too low
to mention in the TAFs at this time.


.PREV DISCUSSION... /issued 1016 PM CDT Sat Mar 24 2018/



The forecast remains on track and changes were minimal.

Shortwave trough seen in water vapor imagery over New Mexico will
move our way. Mid-high level moistening will result in increasing
clouds and could be of sufficient depth for some virga,
sprinkles, or possibly light showers late tonight across much of
the area. Measurable amounts from this seems unlikely.

There is a small chance of elevated convection over western north
Texas and perhaps far southwest Oklahoma toward dawn. Confidence
isn`t high as southwesterly trajectories continue to transport
dry/warm elevated mixed layer into the area. In some of the model
forecast soundings there seems to be a transient thin layer of
moistening near the base of the capping inversion, and a couple
of the SPC CAM ensemble members generate elevated deep convection
in western north Texas (probably the members on the more moist end
of the spectrum). It seems unlikely that convection will develop,
but if it does, it should be after 3am.


PREV DISCUSSION... /issued 355 PM CDT Sat Mar 24 2018/

Primary forecast issues are the chances of rain and potential for
severe weather this week.

For tonight, a subtle shortwave trough/lobe of vertical vorticity
will approach from the southwest. As this wave approaches,
isentropic ascent may result in some elevated showers and
thunderstorms across western north Texas and far southern Oklahoma
early tomorrow morning. Elevated instability and vertical wind
shear will be favorable for some small hail.

As this wave departs, a dry line is forecast to sharpen across
southwest Oklahoma, southward into western north Texas tomorrow
afternoon. A dry line bulge may develop across western north Texas
in association with a 700 mb wind maxima.

The uncertainty is if there will be sufficient ascent to weaken
the cap for convective iniation in the afternoon. The 24/12Z GFS
is aggressive in convection when compared to other parameterized
and convecting-allowing models. The GFS seems overdone based on no
appreciable ascent to lift the cap. So for now, will only have a
slight chance (20%) of showers/storms. If thunderstorms develop,
supercells will be possible with effective bulk shear >40 knots
and MLCAPE of at least 1000-2000 J/kg.

By Sunday evening into Sunday night, another shortwave trough/lobe
of vertical vorticity may approach and increase the chance of
showers/storms through the overnight hours.

By Monday and especially Monday night, widespread showers and
thunderstorms are expected to develop with increasing meridional
flow and persistent isentropic ascent as the mid/upper-level low
from the southwest U.S approaches the Southern Plains.

Initial thunderstorms on Monday afternoon/evening could be severe
as as there will be sufficient instability and vertical shear.
These thunderstorms may initially develop along a dry line across
western north Texas, northward into southwest Oklahoma. These
thunderstorm may grow upscale into an MCS into the evening hours
as they move northeastward.

Heavy rainfall will become a threat Monday night into Tuesday with
the potential of training thunderstorms--especially across the
southeast where the duration of event will be longer; however,
there has not been any recent rainfall across southeast Oklahoma
over the last 5 days. In addition, the 3-hour RFC Flash Flood
Guidance has 3-4" across most the area. Therefore, even though
localized flooding will be possible, widespread flooding is not
expected at this time.

As a shortwave trough passes by the northern Plains, the attendant
cold front will pass by on Tuesday. This should gradually shift
the moisture/rainfall to the southeast on Tuesday, decreasing the
chance of rain by Tuesday night into Wednesday. Another shortwave
(this time from the northwest), may result a low chance of
showers on Thursday.

Abundant cloud cover, precipitation, and a post-frontal air mass
will result in cool temperatures Tuesday through at least
Thursday. High temperatures should be below average in this



Oklahoma City OK  73  47  66  62 /   0  10  20  30
Hobart OK         76  51  75  63 /   0  20  20  30
Wichita Falls TX  80  56  86  66 /   0  30  20  30
Gage OK           73  46  74  55 /   0   0  10  10
Ponca City OK     68  39  60  56 /   0   0  20  40
Durant OK         81  54  73  63 /   0  10  30  20




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