Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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315
FXUS64 KOUN 171737
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1237 PM CDT Thu May 17 2018

.DISCUSSION...
The 18Z aviation discussion follows....

&&

.AVIATION...
A small cluster of thunderstorms over far northwest Oklahoma will
move slowly east early this afternoon. It is currently expected
to diminish and dissipate by late afternoon, although it is
possible that it could survive and continue east into north-
central Oklahoma by evening.

A much larger area of showers and thunderstorms is forecast to
develop this afternoon over the High Plains of New
Mexico/Colorado/Texas, and move quickly east. If this storm area
develops as expected, it will move into western Oklahoma around
00Z, and pass across KWWR, KCSM, and KSPS by 06Z. There is a
possibility that KLAW may also see TSRA toward 06Z, but the system
is expected to diminish substantially by the time it reaches that
area.

Winds will be light from the east and southeast through tonight,
before strengthening tomorrow morning from the south to
southeast. Gusty winds are, of course, expected near the stronger
thunderstorms.

CmS
&&

.PREV DISCUSSION... /issued 1038 AM CDT Thu May 17 2018/

DISCUSSION...
Scattered strong/severe thunderstorms have developed along a mid-
level convergence line extending from southwest Kansas into the
Texas Panhandle, just west of Ellis County, Oklahoma. Short-range
models suggest that this convection will die out quickly late this
morning, which seems highly improbable, given current
radar/satellite trends. It is unclear how far south this
convection will develop, since building cumulus is visible all the
way to the Red River. We have updated the forecast to account for
the most probable evolution of this precipitation. The update also
includes some minor adjustments to temperatures and dew points.

CmS

PREV DISCUSSION... /issued 554 AM CDT Thu May 17 2018/

DISCUSSION...
The May 17-18, 2018 12 UTC TAF discussion follows:

AVIATION...
Generally expect unrestricted ceilings and visiblities at most
terminals through the TAF period with brief visibility reduction
possible with convection.

Patchy fog may briefly impact KPNC this morning. Otherwise,
scattered showers and thunderstorms are expected to develop across
western Oklahoma this morning. The most likely terminals that
could see temporary impacts are KCSM and KWWR. There is a lower
probability that terminals farther south and east (KOKC/KOUN/KLAW)
could be impacted by the remnants early this afternoon.

Additional showers and thunderstorms are expected to move
eastward from the Texas panhandle into western Oklahoma this
evening. Once again, KCSM and KWWR are the most likely terminals
that could be impacted. These thunderstorms could be strong to
severe with gusty, variable winds and hail. There is a chance
convection could affect KLAW and KSPS as well, but confidence is
too low to include in these TAFs for now.

Outside of thunderstorms, winds will generally remain from to
east to southeast through the TAF period and are forecast to
become gusty across western terminals later this morning.

Mahale

PREV DISCUSSION... /issued 418 AM CDT Thu May 17 2018/

DISCUSSION...
Rain/storm chances and possible strong to severe thunderstorms
with heavy rainfall remain the primary forecast challenges.

The biggest changes to the previous forecast was to add 20-40%
rain chances today across western Oklahoma and western north Texas
as well as to add patchy/areas of fog before 9 am this morning
east of a Cherokee to Guthrie to Seminole to Ardmore line.

Some fog has formed near Ponca City, Blackwell, and Chandler in
the past few hours with visibilities generally 1/4 to 3 miles.
Thus, added the mention of patchy/areas of fog. Locations near
Ponca City, Blackwell, Perry, and Medford where storms with heavy
downpours occurred yesterday afternoon have the highest potential
for locally dense fog (visibilities 1/4 mile or less). Doubt fog
will get too dense or widespread in these areas to warrant the
issuance of a Dense Fog Advisory.

Today, latest CAMs/models including the NAM12/HRRR/HRRRX have been
consistently depicting the formation of high based elevated
showers and storms over the far eastern Panhandles into western
Oklahoma and possibly western north Texas after 6 am this morning.
This appears to be a result of mid level (between 500 and 700 mb)
isentropic lift just east of the mid-level ridge axis. Added rain
chances to the forecast to account of this activity. Severe
potential from this activity appears to be low due to marginal
instability (MUCAPE below 1500 J/kg). Gusty winds and small hail
are possible with this activity that should weaken this afternoon
as isentropic lift weakens.

Highs today may be tricky due to some rain/storms in western
Oklahoma and western north Texas with mid/high level cloud cover
spreading eastward. Generally went towards the cooler side
of guidance. Latest model dewpoints may be too low over the next
several days.

After 6 pm today into tonight, some strong to severe thunderstorms
will be possible across western Oklahoma and western north Texas.
Fairly strong shear (0-6 km bulk shear 30-40 kt) and moderate
instability (1000-2500 MLCAPE) support organized storms in the
form of multicells and supercells. Storms that form this afternoon
near the dryline over the Panhandles/west Texas will likely
congeal into lines/clusters by the time they cross the 100th
meridian into far western Oklahoma and far western north Texas.
Thus, think multicells will be the main mode of severe weather
which could lead to a few reports of damaging winds up to 70 mph
along with hail generally half dollars or less. If storms remain
supercells, large hail potential would increase. Tornado potential
appears to be very low due to high cloud bases and LCLs generally
above 6000 ft AGL, though low level shear will increase to near
20 kt after 7 pm. Locally heavy rainfall is possible with rainfall
rates 1-4"/hour possible. Storms are expected to weaken through
the night as they move eastward into a more stable environment
with less CAPE and higher CINH. Not sure how far east storms get
before completely dissipating tonight. A low chance of gusty winds
from heatbursts could occur as storms weaken tonight.

On Friday, think most areas will remain dry during the daytime
hours with warmer surface temperatures, higher surface dewpoints,
and increasing low level winds. There is a signal from latest
models that some elevated/high based storms may occur mainly
during the morning hours east of a Cherokee to Oklahoma City to
Atoka line.

Friday night, another round of severe storms may occur similar
to tonight. Increasing 700 mb temperatures from models suggest
that any storm development would be more sparse compared to this
evening/tonight. A few strong to severe storms will be possible
with damaging winds, large hail, and locally heavy rainfall as the
main hazards. If storms occur, they should generally weaken
through the nighttime hours as they move east/northeast into a
more capped/less unstable environment.

Saturday, warm, humid, and breezy conditions are expected.
Rain/storm chances will remain very low until late afternoon
and nighttime hours. Highs should be near or above 90F in
many locations.

Saturday night, rain/storm chances will increase areawide as a
cold front moves southward. Storm coverage should be higher
compared to today and Friday, especially as mid level cap weakens.
Some strong to severe storms will be possible along with heavy
rainfall as storms may not move very quickly. Kept rather high
rain chances (30-70%) across the area.

Sunday through Wednesday, chances for showers and thunderstorms
are forecast to continue across parts of Oklahoma and north Texas.
Decreasing shear supports mainly unorganized slow moving storms.
A few strong to severe storms with heavy rainfall are possible
during this time frame due to abundant nearby moisture and some
instability. Noticed the latest ECMWF and GFS model depicted
surface dewpoints near or just above 70F next Tuesday. Cooler
temperatures on Sunday are expected behind cold front passage with
a warming trend towards the middle of the week. Rain chances
may decrease towards next Wednesday due to some mid/upper
level ridging.

MBS

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  86  66  89  71 /  10  20  20  20
Hobart OK         87  64  93  70 /  20  40  20  20
Wichita Falls TX  90  65  94  71 /  10  40  10  20
Gage OK           88  64  91  65 /  70  50  20  20
Ponca City OK     86  65  87  70 /  10  10  20  20
Durant OK         87  68  90  70 /  10  20  20  20

&&

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

$$

23/26/23



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