Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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812
FXUS64 KOUN 240446
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1046 PM CST Thu Nov 23 2017

.DISCUSSION...


&&

.AVIATION...
VFR conditions will prevail throughout the TAF period. Light south
to southwest wind will increase 12 to 20 knots Friday afternoon in
central and southwestern Oklahoma. A weak front will turn winds to
north and speeds under 12 knots in northwestern Oklahoma late
Friday afternoon.

&&

.PREV DISCUSSION... /issued 934 PM CST Thu Nov 23 2017/

UPDATE...
No significant updates this evening.

DISCUSSION...
The grids appear to be in good shape. Have bumped up cloud cover a
little bit with the cirrus moving in from the northwest, but
otherwise no significant updates are needed this evening.

PREV DISCUSSION... /issued 733 PM CST Thu Nov 23 2017/

DISCUSSION...

AVIATION...
VFR conditions will prevail throughout the TAF period. Light south
to southwest wind will increase 12 to 20 knots Friday afternoon in
central and southwestern Oklahoma.

PREV DISCUSSION... /issued 215 PM CST Thu Nov 23 2017/

DISCUSSION...
Weather impacts over the next several days will be minimal. A blend
of the models sufficed for most periods/elements, although we did
adjust wind, temperatures, and relative humidity for a few periods.
Elevated fire weather conditions are still possible on Friday
afternoon and again early next week.

Latest visible satellite imagery shows thin cirrus moving
southeast across the region on the eastern periphery of anomalous
ridge in the west. Several locations in western Oklahoma and
western north Texas have reached the low/mid 70s already early
this afternoon, and the upward trend in temperatures should
continue tomorrow. A more pronounced/warmer plume of
downsloped/adiabatically warmed air will move overhead tomorrow as
west-southwesterly ~850 hPa flow strengthens, and this will
support temperatures of 70 degrees or higher for nearly all
locations in our forecast area. Lower 80s seem probable across
southwest Oklahoma and most of our western north Texas counties in
this pattern. We increased temperatures closer to the high end of
guidance, and may need to increase further, especially if cirrus
remains thin. More locations across western and perhaps even
central Oklahoma could approach 80 degrees.

Late in the day a weak cold front will move into northwest
Oklahoma and then progress through the area overnight. Post-
frontal air mass will be slightly cooler (by about 10 degrees
compared to the previous day) albeit still at least 5 degrees
above normal for this time of year. No precipitation will
accompany this front, although its passage may be coincident with
a period of thicker cirrus.

The overall amplified upper flow pattern is expected to continue
into early next week. Models suggest the western ridge will dislodge
and deamplify, shifting eastward over our area early next week ahead
of a deepening trough in the west. From this point forward, medium
range ensemble spread grows and deterministic runs of the GFS and
ECMWF continue to be out of phase. ECMWF continues to be
slower/deeper with closed 500 hPa low on Tuesday, while GFS
maintains a more open wave and moves it and its associated cold
front through quicker. This has major implications for our
temperature forecast on Tuesday, as well as timing of clouds/precip.
Any precipitation in this pattern should be low probability and
light given prolong period of northwesterly flow and anomalously low
PWATs well south in latitude into western Gulf. This will
result in modest moisture return at best. Nevertheless, we
adjusted spatial coverage of low probabilities including a larger
area back to the west and north compared to previous forecast.
This is more in line with the slower ECMWF/EPS and a good number
of GFES ensemble members. Confidence remains low though given
model disagreements.

BRB

FIRE WEATHER...
A few periods of low end fire activity may occur over the next
seven days, supported by marginal meteorological conditions and
dry/dormant fuels.

Elevated fire weather conditions could occur Friday afternoon
across mainly southwest Oklahoma and western north Texas where
winds could be sustained around 15 mph during the afternoon. RH
could fall to as low as 20 percent. A wind shift to northerly
associated with a frontal passage will progress through overnight.

For the most part, post frontal winds and low RH values will be
misaligned Saturday. A slight increase in initial activity may be
possible, but elevated fire weather thresholds may be difficult to
achieve.

Anomalously warm temperatures return Sunday and Monday, and by
Monday afternoon south-southwesterly winds strengthen
significantly. Moisture return should be gradual and modest
and so RH values may be low enough Monday afternoon to support
elevated to near critical fire weather conditions. ERC values will
probably remain near or just above the 75th percentile during
this period. If moisture returns quicker, this would mitigate fire
weather concerns, or at least confine them to western Oklahoma
and western north Texas.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  44  76  46  65 /   0   0   0   0
Hobart OK         44  79  47  66 /   0   0   0   0
Wichita Falls TX  43  80  48  69 /   0   0   0   0
Gage OK           46  79  41  64 /   0   0   0   0
Ponca City OK     42  76  45  65 /   0   0   0   0
Durant OK         41  73  47  70 /   0   0   0   0

&&

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

$$

26/09/09



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