Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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000
FXUS64 KOUN 210802
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
302 AM CDT Wed Jun 21 2017

.DISCUSSION...
Thunderstorms that drifted south from Kansas into northwest
Oklahoma earlier have dissipated. These were mainly diurnally
driven in the absence of any noteworthy synoptic scale forcing.
Quiet weather is expected early this morning. We`ll watch
surface observations again in southeast and south-central Oklahoma
for fog given low level moisture (low T/Td depressions once
again) and light easterly winds. Any fog should be light and
isolated/patchy.

A similar scenario to last evening is expected this evening with
regards to thunderstorms. Convection will form as diabatic
heating/destabilization occur during the afternoon near a surface
trough oriented southwest to northeast across the Johnson Mesa
and up through western Kansas. Storm clusters will move south
driven by weak north-northwesterly mean mid-level flow. The
thermodynamic/kinematic environment by mid to late evening when/if
they reach northwest Oklahoma may be marginally favorable for
strong to severe thunderstorms. The threat doesn`t appear to be
higher than previous evening and spatial coverage probably won`t
be greater either.

Stressed fuels from recent heat and lack of rain combined with
marginally breezy/dry conditions could elevate fire concerns
slightly this afternoon (see Fire Weather section below for
details).

An anomalous ~599 decameter 500 mb high over the Southwest United
States that brought impressive record high temperatures to that
area today should weaken and flatten out gradually as
strengthening and increasingly perturbed westerlies are shown in
model guidance across the northern states. Meanwhile, Tropical
Storm Cindy will move north on Thursday reaching the coast near
the Texas/Louisiana state line. High level clouds may increase
across the southeast portion of our area and the far southeast
portion could experience a few showers/storms on its outer
periphery as it moves northeast into the Arklatex through early
Friday.

Late in the weak, deepening Canadian trough will increase
westerlies aloft over the Central Plains. A series of shortwave
troughs embedded within and traversing the northern Plains are out
of phase in medium range deterministic guidance and this is a
little troublesome with timing of onset of cooler air mass. The
first of two cold fronts is stronger in GFS than ECMWF, and the
second is stronger in ECMWF than GFS. In either case, below normal
temperatures should arrive sometime this weekend.

Precipitation chances become tricky Friday through the weekend.
Mean northwesterly flow aloft will continue and diurnal
convection from the high terrain will probably make it into
western portions of our area each evening/overnight. We applied
this conceptual pattern recognition when making adjustments to
precipitation probabilities, but confidence is still low. Small
difficult to resolve/time shortwaves embedded within the flow
should be the driver for more significant convective systems.
We`ll better refine timing of higher probabilities as soon as
possible. One of the bigger adjustments we made was to lower
probabilities on Sunday behind the front as air mass should be
fairly stable, but this move may be risky given the trends toward
weaker boundary that weakens and/or stalls and becomes oriented
west-northwest to east-northeast across southern portions of the
area. MCS activity could track near or just north of this
boundary. For now, higher probabilities have been assigned to
Friday night through Saturday night.

BRB

&&

.FIRE WEATHER...
Deep mixing into channel of fairly dry air aloft should result in
dew points falling across western portions of the area. We have
nudged the forecast significantly toward the drier (and often
closer to reality in these scenarios) hi-resolution guidance
(i.e., WRF- ARW/NMM). This yields minimum relative humidity values
between 25 and 30 percent for a large portion of western Oklahoma
and western north Texas. Stronger mid-level flow over the
northern Rockies will support strengthening lee surface trough and
a low level response resulting in strengthening winds down into
our area. 15 to 20 knot 10 meter winds are expected. This results
in meteorological conditions that approach elevated thresholds.
Fuels are stressed from recent heat and no rain. Although still
mostly green, moisture content is likely low. ERC-G observations
from nearly a week ago were on the high end of normal and
forecasts from that observation time onward indicated near 90th
percentile possible. Of course, to be put in perspective, this is
90th percentile for typical June values, so not as big of a deal
as if this were late winter or early spring. Nevertheless, initial
attack fire activity may increase tomorrow.

A couple of factors limiting concern today: 1.) evening rainfall
across far northwest Oklahoma where they greatest alignment of
RH/wind/fuels existed for minimally elevated or near elevated
conditions. MRMS QPE shows much of Ellis County and western Harper
County received >0.25", with locally >0.75", and isolated pockets
of >0.25" as far south as Retrop and Granite. 2.) Uncertainty on
exact positioning of channel of dry air just above 850 mb that
will mix down (models are a little further east this cycle).

Slightly higher RH on Thursday and weaker winds should result in
less concern, although meteorological and fuel conditions may
still be supportive of some initial attack fire activity.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  93  68  92  71 /   0   0   0   0
Hobart OK         95  67  96  71 /   0   0   0  10
Wichita Falls TX  94  68  94  72 /   0   0   0   0
Gage OK           95  68  97  68 /   0  20   0  20
Ponca City OK     93  67  91  70 /   0   0   0  10
Durant OK         91  70  89  73 /   0   0  10  10

&&

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

$$

09/12



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