Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 212312

Area Forecast Discussion
National Weather Service Norman OK
612 PM CDT Fri Jul 21 2017

Aviation discussion for 00 UTC TAF is below.


VFR conditions and generally southerly surface winds are expected
to continue.



.PREV DISCUSSION... /issued 141 PM CDT Fri Jul 21 2017/

Uneventful weather continues, aside from dangerous heat indices
across mainly the eastern half of the area. The forecast remains
largely unchanged with only minor adjustments. Most notably,
slightly lower precipitation chances Saturday night into early
Sunday, and more confined to far northwest Oklahoma, and slightly
hotter toward the end of next week.

The Heat Advisory was not changed and generally highlights the area
where the most dangerous conditions exist (i.e., heat indices at or
above 105F) through Saturday afternoon. It`s worth noting that heat
indices will not be very much lower across western portions of the
state and some danger still exists for anyone involved in outdoor
activities. The western end of the advisory coincides with a pre-
defined criteria difference. The criteria west of Highway 81 is a
heat index of 110F or greater. But, the general theme for our entire
area is to continue to take precautions when spending time outside.

Latest GOES-16 experimental moisture channel imagery clearly shows a
large subsident region with dry mid levels associated with the
persistent anti-cyclone centered over our region. Aside from some
alto-cu across portions of central and southwest Oklahoma this
morning, clear conditions were observed.

Within a band of stronger westerlies at higher latitudes, a
shortwave trough is forecast by models to emerge onto the Canadian
Prairies today moving east-southeast to the Great Lakes by Sunday.
Meanwhile the broad persistent ridge will deamplify. This shortwave
will send a weak cold front southward into Kansas on Saturday.
Convergence along this boundary amidst a moist unstable environment
should result in thunderstorms forming during the afternoon from the
Colorado front range eastward across Kansas, but weak flow aloft
should keep the activity from forward propagating and moving into
our area. If cold pool development is significant enough to our
north, this will probably drive the effective front southward into
northwest Oklahoma a little quicker.

On Sunday, some form of a remnant weak synoptic surface boundary
and/or composite outflow across our forecast area should focus
isolated to scattered thunderstorm development during the afternoon
into the evening. Weak deep layer shear will mean that short lived
single cells or multicells will be the primary storm mode. During
the late afternoon and early evening, storms that form in an
environment characterized by a deeply mixed sub-cloud layer could
cause brief strong/severe wind gusts as they collapse but this
threat is expected to be very limited spatially and temporally.
Coverage will decrease as instability lessens into the night.

Another diurnal uptick in convective coverage may occur Monday
afternoon and evening 1.) near diffuse synoptic boundary and/or
convective outflow boundaries that may linger from previous day`s
convection, 2.) as a weak PV anomaly move southeast across Kansas
into northern and eastern Oklahoma, 3.) as PWAT values rise to
around 1.85 inches owing to slight deepening of low level moisture
shown in model forecast soundings. Deep layer shear will remain
weak so convective threats will probably be limited to isolated
brief strong/severe wind gusts at worst. To add to point #2 above,
the new 12z ECMWF shows a little deeper/broader shortwave trough
passing just to our north compared to the more compact high level
PV anomaly seen in the GFS 1.5 PVU pressure field. The ECMWF would
favor a little greater coverage of convection on Monday.

Medium range model guidance is in agreement that mid-level heights
build mid-week as western ridge amplifies significantly. Isolated
convection may be possible through Tuesday across the eastern
portion of the area, but becomes quite unlikely for the latter half
of the week. Temperatures will warm to above normal levels with many
locations at least approaching if not reaching or exceeding 100
degrees by the end of the week. We trended slightly higher than the
model blend closer to raw guidance for late week.



OK...Heat Advisory until 8 PM CDT Saturday for OKZ007-008-012-013-



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