Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 210449
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
1149 PM CDT Fri Apr 20 2018

.AVIATION...

For the 06Z TAFs:

MVFR and IFR conditions will prevail through the morning hours as
showers and thunderstorms continue to push through the Panhandles.
In the wake of these showers, the lower levels in the atmosphere
will remain very saturated, so ceilings and visibilities will be
impacted until late this morning. Wind speeds will start to shift
and slowly become more northerly by late morning. At this time we
should see ceilings rise more steadily into MVFR. KAMA and KDHT
will be the first to go back to VFR in the early afternoon hours,
but KGUY may stay in MVFR throughout this TAF cycle. Overall,

Guerrero

&&

.PREV DISCUSSION... /Issued 659 PM CDT Fri Apr 20 2018/

UPDATE...
Will allow the wind advisory to expire at 7 pm. Winds have
decreased across the southwest Texas Panhandle. Storms tonight are
expected to remain below severe limits, but some hail up to one
half inch in size and gusty winds will still be possible as they
move northeast across the region.

PREV DISCUSSION... /Issued 622 PM CDT Fri Apr 20 2018/

AVIATION...
A band of showers and thunderstorms will move across the TAF sites
at the start of the period. Conditions may get down into the IFR
range with the stronger activity. Most of the rain should move
east of the TAF sites by late this evening. Low clouds in the IFR
range are expected to move back across the TAF sites overnight.
These clouds will slowly lift through the day on Saturday, but GUY
and DHT may get stuck in MVFR cigs through the end of the
forecast. Southeast winds will be replaced by northerly winds
Saturday morning.

PREV DISCUSSION... /Issued 311 PM CDT Fri Apr 20 2018/

DISCUSSION...
Current observations show a line of storms developing in north
central Panhandle out ahead of the main upper level low pressure
system centered over the Four Corners region. This in-conjunction
with a south to north localized boundary as seen on the visible
satellite image is helping to develop localized convection out
ahead of the boundary downstream of the first perturbation in the
mean 500 hPa cyclonic flow. Small hail around dime size has been
reported with these storms as they continue to move east. Some
further development is possible further south into the east-
central TX Panhandle as the first mid level perturbation works its
way east. Back toward the western Panhandles, skies are beginning
to clear out ahead of a stronger perturbation rounding the base
of the upper level low in-conjunction with a dryline moving east.
In particular, strong southeasterly surface flow sustained at
25-35 kts has steadily been advecting low level moisture into the
region, which may help the stages of low level convection
initiation later on.

Given the current conditions, areas across the southwestern TX
Panhandle in particular will have the best chance of storms
reaching severe criteria later this afternoon under the mostly
clear skies with good directional shear in the meso-scale model
profiles. Best chances of seeing sub severe to near severe
convection will be from a line from Hereford north to Dalhart.
Some complications to the severity of storms for this forecast for
parts of the western Panhandles include the timing of the mid
level features including the cold pocket aloft to match low level
conditions currently being observed and the ability of deep mixing
within the atmospheric profile as SBCIN in still present. With
MUCAPE values of around 500 J/Kg across the western Panhandles
currently with effective shear increasing to 40-50 kts later
today, some organized convection is possible. Latest hi-res model
guidance out ahead of the curvature vorticity along a more
significant perturbation rounding the base of the upper level low
pressure system shows favorable conditions for localized lift for
convection initiation, especially in the SW TX Panhandle for the
afternoon hours. Severe criteria hail and gusty winds will be the
main threat. However, the focal point of localized max helicity
values of 200-300 m2/s2 moving into the southwestern Panhandle
along the mid level vort max suggest that a tornado cannot be
completely ruled out, especially during initial storm
development. Eventually as storms progress eastward, they will
become more linear going forward into the evening hours as we lose
daytime heating and the wind profile becomes more uni-
directional.

Rainfall with embedded thunderstorms will continue into the day
on Saturday as the main upper level system shifts to the east-
southeast. A cold front will work its way south across the region
during the second half on Saturday as winds shift from
southeasterly to northerly. Wrap around moisture will bring
additional chances of precipitation, especially for the eastern
Panhandles along the front into Saturday evening. Precipitation
will begin to clear out of the entire region by early Sunday
morning. High temperatures on Saturday will be below normal.

Going from Sunday into the remainder of the forecast period,
northwesterly mid level flow will return to the region. According
to the latest global model guidance, a low amplitude ridge over
the western Rockies will help develop a trough pattern
downstream. This will bring several mid level perturbations across
the central Plains with additional chances of precipitation into
the region, especially in the eastern Panhandles starting Tuesday
evening. Temperatures will be near to below average going into
next week.

Meccariello

&&

.AMA Watches/Warnings/Advisories...
TX...None.
OK...None.

&&

$$


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