Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 190004 AAA
AFDOUN

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
704 PM CDT Fri Aug 18 2017

.UPDATE...
Removed rain chances tonight across all of the Norman forecast
area. Also, decreased cloud cover tonight.

&&

.DISCUSSION...
Showers and thunderstorms are no longer expected tonight.

Think sufficient capping and subsidence will not allow for any showers
and thunderstorms to form/occur tonight across nearly all of
Oklahoma and western north Texas. Latest HRRR/HRRRX model runs
concur.

Cannot completely rule out some patchy fog after midnight tonight
through 9 am Saturday morning east of a Marietta to Purcell to
Chandler line where surface dewpoints are highest, generally
71-76F as of 7 pm. Did not mention due to low confidence of
occurrence, especially as no rainfall and abundant sunshine
occurred in these locations today.

Products have been updated.

MBS

&&

.PREV DISCUSSION... /issued 656 PM CDT Fri Aug 18 2017/

DISCUSSION...
Aviation discussion for the 00Z TAFS is below.

AVIATION...
Expect VFR conditions through Saturday afternoon. Isolated
thunderstorms still possible Saturday afternoon at all TAF sites
but they were not mentioned in this set of forecasts.

PREV DISCUSSION... /issued 312 PM CDT Fri Aug 18 2017/

DISCUSSION...
As mentioned in the previous update (see below), we`ve removed
precipitation chances for portions of the area (mainly from
northwest and north-central Oklahoma southwestward through western
Oklahoma). Convective overturning from overnight MCS has left a
less than optimal thermodynamic environment for surface based
convection this afternoon across much of the area. 12z OUN and
Lamont soundings both modified for expected high temperatures show
significant convective inhibition from mid level warm layer and
with mid-level height rises/QG vector divergence, we won`t receive
any help from large scale ascent.

Previous forecasts were for a weak cold front to move into
northwest Oklahoma late this afternoon in an environment where
boundary layer moisture in combination with diabatic heating was
expected to be sufficient for thunderstorm formation. 19z hand
surface analysis shows the cold front to extend from roughly
Leavenworth, Kansas to along/near I-70 into west-central Kansas.
This will make southward progress but shouldn`t make it into our
area until later this evening. The majority of the convergence
associated with this, albeit weak, may be over our north-central
and northeast counties. So, we have retained low probabilities
across this area.

Further south, elevated convection occurred over north Texas
associated with the northern edge of mid-level moisture plume
seen in 7.3 micrometer GOES-16 imagery. This convection gradually
become more surface based but has stayed south of the Red River
and has generally decreased in coverage the last couple of hours.
South-central through east-central portions of the forecast area
remain quite moist and if there is anywhere in our area that sees
diurnal development later today it would probably be across these
areas. Thunderstorm development was noted in southwest Missouri
coincident with a low-level moisture axis that extends up from
eastern Oklahoma. On the far western edge some minor cumulus
development has been noted from near Chandler down to Seminole.
This could be the area where some isolated storms form. If storms
do occur across this area, isolated brief wind events may be the
main severe weather concern. Deep layer shear is quite weak for
storm organization/persistence, so a more substantial severe
weather threat is unlikely. Locally heavy rainfall may occur
if/where storms develop and this is noteworthy since much of the
area has received so much rain lately and flash flood guidance
values are relatively low.

For tomorrow, isolated thunderstorms could form just about
anywhere across the area just because boundary layer moisture is
expected to be so high and diabatic heating will be fairly
significant. There really isn`t much aloft to help force
convective development. Perhaps there may be some residual
boundary or enhanced low level moisture pocket that we can focus
in on with observational data tomorrow morning to refine spatially
where best chances are. For now, we`ve kept chances <20% so the
zones and point and click forecasts should read "isolated / 10%
chance". This seems more fitting for the situation.

There is a signal tomorrow night into early Sunday that some mid-
level moisture and modest ascent could force some warm advection
type elevated convection, primarily across northern Oklahoma.
This could linger into Sunday afternoon across portions of
northern Oklahoma. Isolated convective development Sunday
afternoon seems less likely than Saturday afternoon across the
southern half of the area given even warmer mid-level temperatures
with building mean ridging across the south-central and southeast
states.

Aside from some isolated convection across northwest Oklahoma late
Monday, the rest of the area should be dry on Monday. Tuesday into
Tuesday night looks like the next best chance of precipitation as
a shortwave trough and associated surface front passes through.
Slightly cooler weather should follow for Thursday.

Medium range guidance diverges some by Friday but there is some
signal for a shortwave trough across the central Rockies to
increase chances again late Friday, particularly across the west.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  72  97  74  95 /   0  10  10  10
Hobart OK         73  98  74  97 /   0  10  10  10
Wichita Falls TX  73  98  75  97 /   0  10  10  10
Gage OK           68  97  72  95 /   0  10  20  20
Ponca City OK     73  97  73  96 /  10  10  10  20
Durant OK         73  95  74  95 /  10  10  10  10

&&

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

$$

15/17



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