Area Forecast Discussion
Issued by NWS Oklahoma City, OK
FXUS64 KOUN 201733
Area Forecast Discussion
National Weather Service Norman OK
1133 AM CST Fri Jan 20 2017
.AVIATION...20/18Z TAF Issuance...
IFR/MVFR ceilings will continue to dissipate and shift northward
as the surface low continues to move northeastward across Kansas.
KWWR and KPNC remain the TAF sites impacted by MVFR Fog and
IFR/MVFR ceilings. Both sites should begin to clear between 1830
and 1930Z. After which and for the remaining sites, VFR
conditions are expected to prevail through the period. West and
southwest winds will continue to increase, with gusts nearing 30
kts at several sites, primarily those in western Oklahoma and
north Texas this afternoon. Winds will remain out of the
southwest, relaxing, overnight, becoming light by morning. Mid to
high clouds will begin to increase in coverage in the later
portion of the TAF period as stronger surface low approaches off
the western high plains Saturday morning.
.PREV DISCUSSION... /issued 1029 AM CST Fri Jan 20 2017/
Visibilities in northern Oklahoma have generally risen above 1/4
mile, and the Dense Fog Advisory was allowed to expire on
schedule. Some not-dense fog remains in the Enid area, but even
there the visibilities are increasing. Low clouds and the remains
of the fog should gradually erode from the south, giving a mainly
clear mid-to-late afternoon.
The rest of our forecast area has already cleared, with only a few
scattered clouds. Temperatures are already rising into the 50s and
60s F, and we expect a mild afternoon over the entire area.
The current forecast appears to be in good shape, so no changes
are currently planned for this morning.
PREV DISCUSSION... /issued 503 AM CST Fri Jan 20 2017/
AVIATION... /For the 12z TAFs/
IFR to VLIFR visibility is present at most observations across
northern Oklahoma and some in central Oklahoma. Fog and/or low
ceilings will diminish this morning across all but far northern
Oklahoma, including Ponca City, where at least MVFR conditions may
persist through midday. Deep mixing will contribute to gusty
southwest winds this afternoon across much of the area. Fog is
possible at northern TAF sites toward the end of the TAF period
(Saturday morning) but confidence was too low for inclusion at
PREV DISCUSSION... /issued 325 AM CST Fri Jan 20 2017/
Synoptic scale features of note currently seen in observational data
include 1.) a departing closed upper low in the central Plains, 2.)
shortwave trough approaching the Four Corners region, 3.)
deepening/digging trough and attendant strong mid-upper speed max
approaching the west coast. Each will have some impact on our
weather over the next few days, although high-impact/hazardous
weather seems unlikely.
The most immediate concern is residual low-level moisture and
fog. Surface dew point gradient is fairly substantial from west
to east across the forecast area, and with light southeasterly
winds areas of fog have formed early this morning across mainly
the northeastern half of the forecast area. High level
moisture/cirrus that is a precursor to aforementioned shortwave
across Arizona and New Mexico is likely helping to temper
radiative cooling and should prevent a more widespread fog event
through mid-morning. Nevertheless, some areas will see dense fog.
Despite lee surface pressure falls to our west, surface pressure
anomalies further west are negative with departing shortwave
forcing surface low in the Great Lakes region. So, light easterly
or southeasterly winds are expected through the morning and until
lee surface low moves eastward with the ejecting upper shortwave.
This, coincident with deeper mixing tomorrow afternoon, could
result in gusty southwest winds possibly gusting to near 40 mph
in far western Oklahoma.
Attention then turns to the digging western CONUS trough.
Deterministic and ensemble guidance is in good agreement with the
evolution of this trough as it move across the area. The
exception is the NAM which continues to be out of phase with
nearly all other guidance in being too quick and open with this
system. Our forecast disregards this outlier solution. High
clouds should thicken and lower Saturday. By Saturday afternoon,
increasing ascent and moisture should be sufficient for some
showers across western north Texas and western Oklahoma, spreading
east and expanding in coverage late in the afternoon and through
the evening. For the evening and overnight, there may be a tight
gradient of precipitation probabilities. Current model guidance
suggests deformation and strongest ascent along with deepest
moisture across the northern portion of the area, so this is where
we have confined the highest probabilities. Small differences in
where this system tracks and/or how closed off it becomes will
have implications on placement of higher probabilities. We`ll
refine this as our confidence grows.
For the rest of the forecast period the weather should be fairly
uneventful with the biggest challenge and uncertainties being
temperatures. Backtracking some, temperatures today should warm
at least to what statistical guidance offers (low to possibly mid
70s across the south and 60s across much of the rest of the area).
Slightly cooler but still above normal temperatures are
anticipated Saturday, followed by a modest cool down Sunday to
around or slightly above normal since the departing system will be
too low in latitude to tap reservoir of arctic air at much higher
latitudes. Monday, we could see notably warmer temperatures well
above normal again depending on timing of a brief period of
ridging before broad troughing/height falls arrive Tuesday. We may
have to adjust temperatures up quite a bit Monday depending on
trends as this gets into a period of greater uncertainty as spread
among medium range guidance grows. Regardless of timing and
amplitude, the general signal is for a positively tilted broad
trough passing through. This trough will probably have trouble
generating precipitation in the absence of deep moisture return,
and may be more successful at bringing in modified arctic air and
below average temperatures by mid week.
Although meteorological conditions are not expected to be met for
critical fire weather conditions, there are a few opportunities
over the next several days for elevated to near critical fire
weather. Today, deep mixing and momentum transfer south of a
eastward moving surface low will bring sustained southwesterly 20
foot winds of around or slightly above 20 mph to portions of
western north Texas and western Oklahoma. However, minimum
relative humidity values are expected to remain above 25 percent.
ERC-G values are in the average range across this area.
Much above normal temperatures are again anticipated on Saturday,
although relative humidity values will again fail to fall to
critical levels. Winds will be lighter than today, but may still
be sufficient for a brief period of elevated to near critical fire
weather conditions across western north Texas.
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 68 41 66 41 / 0 0 10 60
Hobart OK 68 38 65 39 / 0 0 30 30
Wichita Falls TX 72 43 70 43 / 0 0 30 20
Gage OK 64 31 58 33 / 0 0 30 40
Ponca City OK 62 36 61 38 / 0 0 0 60
Durant OK 73 48 70 45 / 0 0 20 40