Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 231856
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
156 PM CDT Sun Jul 23 2017

...Update...

&&

.DISCUSSION...
We made minor adjustments to precipitation probabilities this
afternoon and evening based on latest trends, confining the
highest probabilities to roughly the southeastern quadrant of the
forecast area and significantly lowering chances across north-
central Oklahoma.

Latest visible satellite shows a very well defined MCV just east
of Amarillo with enhanced cu/tcu and new convective development
on its southwest flank. This MCV has also helped increase low
level convergence across the low rolling plains and far southeast
Texas panhandle, just west of our Texas counties. Other areas of
enhanced cu/tcu and weak convection is ongoing on the western edge
of deeper low level moisture in south-central Oklahoma, possibly
enhanced slightly by the Arbuckle Mts. To the north, weak remnant
convection and a band of mid-level clouds is sinking slowly
southward and limiting diabatic heating/destabilization.

Aloft, very weak high level flow is present between eastern trough
and amplifying western ridge. Neutral mid-level heights to
perhaps subtle height rises are expected over the area through
evening. Our afternoon and evening rain chances will be dependent
on a balance of lack of large scale ascent and perhaps subtle
large scale subsidence, diabatic heating/destabilization, and
mesoscale boundaries from morning convection. Current
observations and latest short term model guidance suggest weak
convergence maximized near I-40. We focused the highest
probabilities across this area and southward favoring the
southeast portions of our forecast area which should see 1.) the
highest instability, and 2.) less chance of subtle large scale
subsidence. Also, raised probabilities across our Texas counties
given enhanced convergence and trends in cu field just to the
west.

Weak deep layer shear will not be supportive of organized
convection. Short lived single cells or multicells will be the
dominate storm mode. As mentioned earlier, a hot well-mixed
boundary layer and dry mid-levels contributing to significant
theta-e differences in the vertical should support strong to
severe wind gusts with the most intense convection.

The changes to the Heat Advisory and Excessive Heat Warning
earlier seem to mostly be on track and we don`t plan on changing
either at the moment.

BRB

&&

.PREV DISCUSSION... /issued 1238 PM CDT Sun Jul 23 2017/

AVIATION...
23/18Z TAFs. VFR conditions are expected outside of scattered TSRA
through the period. Greatest chances for storms affecting
terminals will be after 21Z through about 03Z across central and
southwest portions of Oklahoma. Although greatest coverage storms
will likely stay south of KOKC/KOUN, will go ahead and include
TEMPO at those sights. TSRA left out of northern Oklahoma and KSPS
terminals with lower confidence of any impacts. Outside of TSRA,
winds will remain light.

PREV DISCUSSION... /issued 1026 AM CDT Sun Jul 23 2017/

.Update...

DISCUSSION...
Based on trends in the observations, we have adjusted the Heat
Advisory and Excessive Heat Warning. The emphasis for the most
dangerous heat has shifted south given relatively cool/dry outflow
from morning convection limiting potential for criteria to be met
across north-central Oklahoma. The northern end of the current
advisory/warning may still struggle to reach criteria and we will
monitor trends and make adjustments as needed.

Also made some adjustments to wind, precipitation probability,
and weather grids. Morning sounding modified for expected
afternoon temperatures shows a weakly sheared environment with
moderate instability. Single cells and multicells should become
fairly numerous later this afternoon, particularly near and south
of remnant outflow from morning convection where low-level
convergence is maximized. A hot well-mixed boundary layer with
min/max theta-e difference in the vertical of ~35k will support
downburst potential. Any severe wind gusts should be fairly
isolated and brief given weak effective shear and resultant short
life cycle of storms.

BRB

PREV DISCUSSION... /issued 528 AM CDT Sun Jul 23 2017/

DISCUSSION...

AVIATION...
A surface boundary across northern Oklahoma is expected to focus
scattered thunderstorms today. This boundary will move slowly
south and bring a chance for scattered thunderstorms into central
and southern Oklahoma overnight. Very gusty winds are expected
during the afternoon near thunderstorms. VFR conditions will exist
outside of storms.

PREV DISCUSSION... /issued 341 AM CDT Sun Jul 23 2017/

DISCUSSION...
The outflow boundary in northern Oklahoma along with a weak trough
to the northeast of Oklahoma will provide a focus for scattered
shower and thunderstorm development today and Monday. The boundary
will likely affect the northern half of Oklahoma today, although
a few storms could form most anywhere given the slight cooling
aloft with the upper trough in the Midwest. It will be extremely
hot and humid, and the surface boundary will allow surface
moisture to pool near it. The heat advisory and excessive heat
warning remain in effect for central and eastern Oklahoma today.
On Monday, the influence of the upper trough will still be to the
northeast of Oklahoma providing a similar, favorable atmosphere
along with the fading, but lingering surface boundary. Central and
southern Oklahoma may have a higher chance for rain and
thunderstorms than areas to the west. Because of the heat, gusty
winds will be likely with any storms today or Monday. Beyond
Monday, the upper ridge builds over Oklahoma once again bringing
very high temperatures and humidity once again during mid-week. A
break may arrive late Thursday or Friday when the upper flow
pattern gradually shifts to more north-south as the upper ridge
moves slightly to the west. A front could move into Oklahoma
Friday bringing rain and thunderstorms with it.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  74  95  75  98 /  30  30  20  10
Hobart OK         74  97  75  99 /  40  20  10  10
Wichita Falls TX  75  98  75 100 /  50  20  10  10
Gage OK           70  96  72  99 /  30  20  20  10
Ponca City OK     72  95  74  98 /  20  20  20  20
Durant OK         75  94  75  97 /  50  30  20  10

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Heat Advisory until 8 PM CDT this evening for OKZ019-020-025-026-
     028-029-040-041-046-047-050>052.

     Excessive Heat Warning until 8 PM CDT this evening for
     OKZ030>032-042-043-048.

TX...None.
&&

$$

12/11



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