Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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033
FXUS64 KOUN 230337 AAB
AFDOUN

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
1037 PM CDT Sun Apr 22 2018

.AVIATION...
23/06Z TAFs. Will keep MVFR forecast going first several hours of
forecast with moisture wrapping around on the back side of the
departing storm system. Otherwise, VFR conditions with occasional
VFR ceilings possible much of forecast period. Winds will veer
around to northeast and even southeast latter part of forecast as
surface ridge builds over region.

&&

.PREV DISCUSSION... /issued 628 PM CDT Sun Apr 22 2018/

AVIATION...
23/00Z TAFs. MVFR conditions are expected to spread over KPNC down
through KOKC/KOUN this evening into the overnight hours as
moisture wraps around departing storm system. VFR conditions
expected at this terminals toward and after 12Z. VFR expected
elsewhere through forecast period. Northerly winds will continue
and light through this forecast period.

PREV DISCUSSION... /issued 229 PM CDT Sun Apr 22 2018/

DISCUSSION...
A distinct upstream circulation from the primary closed low
circulation was seen clearly in moisture channel imagery around
midday over our east-central counties. Aside from some morning
light rain or drizzle across this area, primary impacts have been
to enhance cloud cover. Stratus is likely to persist across the
eastern portion of the area into the evening, gradually clearing
tonight.

As the closed low departs, a Pacific shortwave trough will amplify
tonight/early Monday over the northern Rockies. This feature will
then traverse much of the Plains states through Wednesday as it
moves southeastward. Forcing/mid-level frontogenesis will interact
with increasingly moist environment (PWAT ~75th percentile for late
April) to bring some needed precipitation. This should be primarily
anafrontal behind southward surging cold front, with limited
instability precluding a severe thunderstorm threat.

Using ensemble approach and adjusting slightly for trends (slower
system with less influence/phasing with northern stream wave), we
made minor changes to QPF initialization. This keeps 0.25"-0.50"
on average across drought-stricken western Oklahoma, with slightly
higher amounts Wednesday. On Wednesday, due to the slowing trend,
we have higher probabilities and greater QPF slightly further
north compared to previous forecasts. We also lowered temperatures
slightly in anticipating of greater precipitation and cloud
coverage.

Differences in medium range guidance emerge as this shortwave
departs. GFS is more confined with Great Lakes shortwave suggesting
little influence in our area, while ECMWF is more amplified and
brings a period of ascent to the area late Thursday and Thursday
night. Since ECMWF has support from at least one GEFS member, we
will maintain slight/low-chance probabilities of showers, mainly
focused across northern and eastern sections of the forecast area.
Meager moisture should limit coverage and also limit instability,
so thunderstorm chances appear to be low at best.

Confidence continues to decrease into the weekend. An amplified
upper flow pattern will continue with mean ridging building
across the area. As western troughing increases, southerly low-
level flow will bring moisture back. The deterministic GFS is
furthest east with the upper level ridge axis by Saturday and
shows a lead shortwave and precipitation across western sections
of the area. This is in contrast to the ECMWF/EPS and to some
degree GEFS mean. Given this, confidence is low that any
precipitation will occur over the weekend. As mid-level heights
build and we eventually end up on the windward side of the upper
level ridge axis, temperatures will warm significantly. We have
increased Sat-Sun temperatures above previous forecast given this
pattern.

BRB

FIRE WEATHER...
Soaking rains yesterday should hopefully accelerate greenup
across the entire area, thus we seem to have peaked with regards
to the fire season. Nevertheless, a warm/breezy pattern will
develop this weekend and elevated to near-critical fire weather
conditions could develop. High-end fire threats aren`t expected,
but depending on the state of the fuels, an increase in initial
attack activity could occur Saturday and Sunday.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  47  72  49  75 /  10   0   0  10
Hobart OK         43  74  49  75 /   0   0   0  20
Wichita Falls TX  46  75  51  80 /   0   0   0  10
Gage OK           42  73  48  66 /   0   0  10  30
Ponca City OK     47  72  47  72 /  10   0   0  10
Durant OK         50  73  51  76 /   0   0   0   0

&&

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

$$

23/11



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