Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 271102
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
602 AM CDT Thu Apr 27 2017

.DISCUSSION...
The April 27-28, 2017 12 TAF discussion follows:

&&

.AVIATION...
Unrestricted ceilings and visibilities are expected to continue
through most of the TAF period. Light and variable winds are
expected to become southerly and gusty--especially across western
terminals by mid-morning.

High-based showers and perhaps isolated thunderstorms are
forecast to move into west central Oklahoma mid-afternoon, and
will quickly progress eastward through the northern half of
Oklahoma. These will be capable of producing gusty winds.
Confidence in impacting a given terminal is too low to include in
TAFs, except at KPNC. Nevertheless, there will be a brief window
of opportunity at KCSM/KHBR to KOKC/KOUN from approximately 20 to
02 UTC.

A cold front/northwesterly wind shift will enter northwest
Oklahoma toward the end of the TAF period. There is a chance of
low ceilings behind the front, but confidence is too low to
include in TAFs for now.

Mahale

&&

.PREV DISCUSSION... /issued 424 AM CDT Thu Apr 27 2017/

DISCUSSION...
Primary forecast challenge continues to be the potential for
severe weather and heavy rainfall late Friday into early Sunday.

For today, a shortwave trough--currently located across
Colorado/New Mexico--will shift east-southeastward into
Kansas/northern Oklahoma. Scattered showers and thunderstorms will
be possible, mainly north of I-40, as the wave traverses near the
border. A cold front/northerly wind shift associated with this
wave will enter Oklahoma tonight and progress southeastward
through Friday morning.

For Friday, there is still low confidence on surface-based
convective initation late afternoon/early evening. Model consensus
still indicates mid-level heights will rise between 21-03Z across
southern Oklahoma/north Texas. In addition, most convective-
allowing models that have come into the range (3 KM NAM/HRW WRF-
ARW) do not indicate any convective initation through 00Z;
however, the HRW-NMMB does have some convection in far southeast
Oklahoma/adjacent western Arkansas.

Nevertheless, some guidance does indicate a triple point may
develop somewhere in western north Texas. With the lack of large-
scale ascent, it still appears the best location for surface-based
convective initation will be near and northeast of a triple
point. Environmental conditions will be favorable for supercells
with all potential hazards for cells that stay along and south of
the warm front.

There is also a somewhat bimodal distribution for the location of
the warm front. Both the GFS and ECMWF now have the 65F
isodrosotherm to I-44 by 00Z. On the other side, many convective-
allowing models are farther south and east with the warm sector.
From the surface fields of the models, this discrepancy might be
(at least partially) due to the impact of tonight`s cold front
(i.e., the location of the warm front may depend on the strength
of today`s shortwave and the southward push of the attendant cold
front). Either way, locations near the Red River and north Texas
have a high confidence of being in the warm sector with the
potential northern limit of the warm sector near I-44.

By late evening into the overnight, increasing isentropic ascent
(augmented by a strengthening low-level jet) will result in
widespread showers and thunderstorms, along and north of the warm
front. Elevated instability/effective bulk shear will result in
severe weather potential even north of the front with large hail
being the primary hazard; however, there will be an attendant
tornado threat in vicinity of the warm front due to increasing 0-1
km shear.

Flooding will become an increasing hazard Friday night into
Saturday-especially across central, east central and southeast
Oklahoma. Isentropic ascent of a very moist, unstable airmass will
be favorable for high rainfall rates. Therefore, opted to issue a
Flood Watch for Friday evening through early Sunday morning,
where confidence is highest for heavy rainfall.

Significant precipitation should come to an end by early Sunday;
however, wrap-around showers will be possible across northern
Oklahoma into Sunday afternoon. Strong cold air advection,
limited solar insolation, and lingering showers will keep
temperatures well below average for Sunday afternoon. Lows will
drop into the 30Fs and 40Fs by Monday morning across the area.

Beyond Monday, both the ECMWF and GFS indicate the Plains will
transition toward mean northwest flow aloft. Embedded shortwaves
within the flow may bring an occasional front with chance of
showers/storms; however, the overall pattern will be unfavorable
for severe weather.

Mahale

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  69  54  76  55 /  10  20  10  80
Hobart OK         76  52  78  52 /  10  10   0  70
Wichita Falls TX  80  58  84  62 /   0   0  10  50
Gage OK           72  47  72  44 /  30  20   0  70
Ponca City OK     65  50  72  50 /  20  50  10  80
Durant OK         73  60  80  69 /   0  10  30  60

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Flood Watch from Friday evening through Sunday morning for
     OKZ025-026-028>032-040>043-047-048.

TX...None.
&&

$$

17/10/10


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