Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 170918
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
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  83  66  89  71 /  20  20  20  20
Hobart OK         87  64  93  70 /  30  40  20  20
Wichita Falls TX  89  65  94  71 /  20  40  10  20
Gage OK           86  64  91  65 /  40  50  20  20
Ponca City OK     85  65  87  70 /  10  10  20  20
Durant OK         88  68  90  70 /  10  20  20  20

&&

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

$$

10/17



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