Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 210546
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1246 AM CDT Fri Apr 21 2017

.DISCUSSION...
The 06Z aviation discussion follows....

&&

.AVIATION...
Numerous thunderstorms, several severe, have developed north of a
stalled front (that was from near KAQR-KADM-KSPS at 0540Z). There
are many different scenarios that may occur overnight into Friday,
making the forecast extremely difficult. The HRRR model has, for
several hours, latched onto the idea that a convective system will
form over the Panhandles around 0800-0900Z, then sweep east across
Oklahoma early Friday morning as a squall line. Since this is
plausible, and consistent, have opted to include a modified
version of this forecast in the TAFs. If the convective complex
fails to form, or forms later than expected, the TAFs will need to
be modified accordingly.

The front itself is expected to move back north a short distance
during the day Friday (although if the squall line forms as
expected, it will be forced back south by early afternoon). A
reinforcing surge of cool air will then push the front southeast
late Friday afternoon and evening. This will likely generate new
thunderstorms across the eastern half of Oklahoma, some severe,
which will move out of southeast Oklahoma late in the evening.

Winds will be highly erratic overnight, especially in the vicinity
of thunderstorms.

CmS
&&

.PREV DISCUSSION... /issued 647 PM CDT Thu Apr 20 2017/

DISCUSSION...
The 00Z aviation discussion follows....

AVIATION...
A stalled front from near KADH west-southwest to KSPS will move
little through about 21/2100Z. Numerous showers and thunderstorms
are expected to form by 21/0300Z near/north of the front over
western Oklahoma and north Texas. These storms will then expand
and spread east-northeast as the evening/night progresses, with a
few areas of torrential rain and hail. Strong winds will also be
a concern overnight with the stronger storms. The storms will
likely be so widespread tomorrow morning that some of the TAFs
have prevailing storms with TEMPO "no significant weather", which
is the reverse of the normal forecast pattern. As the front gets a
shove from the north late tomorrow afternoon, mainly after
21/2100Z, winds will turn more northerly and increase at most
sites. The showers and storms should move out of central/western
Oklahoma a few hours after the end of this forecast period
(22/0000Z).

The ceiling and visibility forecasts are very low confidence,
because the widespread convection is expected to produce numerous
exceptions to the "rule" in the forecasts. Winds should be close
to the forecasts, except near the stronger storms that will
produce their own temporary wind fields.

CmS

PREV DISCUSSION... /issued 258 PM CDT Thu Apr 20 2017/

DISCUSSION...
Increased POPS across most of the forecast area (overnight and
Friday morning), especially southwest Oklahoma. Also added a few
counties across southwest Oklahoma, including the cities of
Lawton, Duncan, and Paul Valley to the Flood Watch.

A cold front continues a slow southward push this afternoon,
and is currently located from near Seminole to Pauls Valley to
Duncan and Wichita Falls.  The airmass ahead of the front is
rather warm with dewpoint temperatures in the mid to upper 60s.

A few storms may develop along or just behind the front late
this afternoon/early evening, but storm coverage should be
isolated. If storms can form, severe weather is certainly
possible.

By mid to late evening, scattered to widespread showers and
thunderstorms are expected to develop. The first storms may
form across southwest and west central Oklahoma. Elevated
instability and effective shear will support some rotating storms
which will enhance the risk of large hail. Several rounds of
precipitation may occur, and this may result in flooding and flash
flooding, especially overnight into Friday morning.

On Friday, the cold front is expected to drift northward during
the day in response to an approaching trough. How far north the
front will lift remains uncertain. Regardless, severe weather
chances will remain until the front pushes back southward late
Friday afternoon and night.

Cool and dry weather is expected this weekend with warmer
temperatures returning early next week. Storm chances will
increase again by late next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  46  60  41  68 /  30  10   0   0
Hobart OK         45  63  40  69 /  10   0   0   0
Wichita Falls TX  48  64  42  71 /  20  10   0   0
Gage OK           41  60  37  69 /  20   0   0   0
Ponca City OK     44  58  38  67 /  60  10   0   0
Durant OK         50  62  43  70 /  70  10   0   0

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Flood Watch through this evening for OKZ007-008-012-013-018>020-
     023>031-038>040.

TX...None.
&&

$$

23/03/23


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