000
FXUS64 KOUN 210047
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
747 PM CDT Fri Oct 20 2017

.DISCUSSION...


&&

.AVIATION...
Scattered MVFR ceilings later tonight will become more widespread
across much of central Oklahoma from Kansas to Texas before
sunrise and last into Saturday afternoon. Moderate and gusty south
winds will persist overnight. A cold front will enter northwest
Oklahoma after 19Z Saturday. Showers and thunderstorms will
increase after 212400.

&&

.PREV DISCUSSION... /issued 316 PM CDT Fri Oct 20 2017/

DISCUSSION...
Severe weather Saturday afternoon/evening continues to be the
primary forecast concern for this forecast period.

For this afternoon/early evening, a few sprinkles/showers will be
possible as an upper-level low passes by the area. Additional
showers will be possible across southeast Oklahoma due to
isentropic ascent/warm air advection. No significant weather
impacts are expected through Saturday morning.

For Saturday afternoon, a cold front is expected to enter
northwest Oklahoma by early to mid afternoon a as mid-level trough
ejects into the Plains. Thunderstorms are expected to develop
along the front from north central Oklahoma, southwestward into
west central Oklahoma. Instability and shear will be sufficient
for severe thunderstorms with forecast effective bulk shear >40
knots and MLCAPE >2500 J/kg, including supercells with large hail
and damaging wind gusts with the given parameter space.

Thunderstorms along the cold front are expected to quickly grow
upscale into a quasi-linear convective system as it shifts
southeastward into central Oklahoma due to strong, linear forcing
and shear vectors becoming parallel to the front. Damaging wind
gusts will become the primary threat after this transition.

A surface low and quasi-dryline/trough structure may develop
across southwest Oklahoma and adjacent parts of western north
Texas, which may serve as a secondary focus for convection.
Nearly all convective-allowing models (HRRRX/NSSL WRF/HRW WRF-
ARW/HRW NMMB) do initiate convection along this trough axis,
ahead of the cold front.

Any cells that develop along the trough across southwest
Oklahoma/western north Texas have the potential to remain
discrete/supercellar longer before becoming undercut by the cold
front. Enhanced low-level wind shear/localized backing near this
triple point may increase the tornado threat if storms remain
discrete/supercellular across this area. These storms would have a
greater threat for significant hail due to greater instability.
The SHIP (Significant Hail Parameter) is ~2, which indicates an
environment favorable for significant hail.

Showers/storms will exit by Sunday morning; cooler and drier air
will advect into the region for Sunday in the front`s wake.

A brief warm-up is expected Monday afternoon before another cold
front passes by late Monday. A dry frontal passage is expected due
to limited moisture. Cooler weather with highs in the 60Fs to near
70F are expected Tuesday.

Warmer weather is expected Wednesday and Thursday ahead of another
cold front that will arrive late Thursday. The air mass behind
this cold front might be the coldest so far this season with highs
only in the 50Fs Friday afternoon. Many locations may experience
a freeze by next Saturday morning.

Mahale

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  77  68  76  50 /  20  10  40  90
Hobart OK         78  67  77  48 /  20  10  70  50
Wichita Falls TX  80  69  83  53 /  20  10  30  90
Gage OK           75  65  76  42 /  10  10  20  10
Ponca City OK     77  69  75  48 /  10  20  70  80
Durant OK         79  67  81  57 /  30  20  20 100

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&

$$

12/09/09