Area Forecast Discussion
Issued by NWS Amarillo, TX

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000
FXUS64 KAMA 181843
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
143 PM CDT Fri May 18 2018

.AVIATION...
18Z TAF Cycle:

VFR conditions expected through most of the period (see last part
of discussion). Southerly winds will be gusty this afternoon.
Thunderstorms are expected to develop east of Amarillo to Guymon
between 21z and 23z moving east. Can`t completely rule out a brief
-TSRA at KGUY/KAMA, but confidence is fairly high that storms
will stay east of all terminals. Storms to the east could produce
outflow winds in the evening, so will need to watch for possible
amendments to account for winds shifts based on radar/obs. A weak
frontal boundary may try to sneak into the KGUY/KDHT terminals
overnight, shifting winds to the north. A strong low level jet may
result in low level shear at KGUY between 01z and 06z tonight,
prior to the arrival of the frontal boundary. Can`t rule out some
MVFR or even IFR cigs behind the frontal boundary during the
morning hours.

Ward

&&

PREV DISCUSSION... /Issued 417 AM CDT Fri May 18 2018/

DISCUSSION...A stalled upper level low is evident on water vapor
this morning across the intermountain west, with southwesterly
flow and downsloping winds expected through the day today. A
dryline is expected to sharpen as a result and progress as far
east as a Sturgis to Amarillo/Canyon line, with fire weather
concerns west of the dryline (see fire weather discussion below)
and a possibility of thunderstorm development east of it.
Assessing the environment east of the dryline, forecast skew-Ts
from model guidance have favorable parameters in place for strong
to severe thunderstorms. MLCAPE values are progged to be around
1500 to 2500 J/kg, with around 25 to 35 kts of 0-6km bulk shear
ahead of potential convective initiation. Winds are expected to
back with time towards sunset, favoring the northeastern
Panhandles, which should aid in increasing lower level helicity
values that could introduce lower level rotation in thunderstorms. However,
there is also a capping H7 to H8 inversion layer aloft that
parcels would have to overcome in order for convective initiation
to occur. All guidance, to include hi-res guidance, show that
coverage of convection may be less than what has was seen on
Thursday as a result with best chances favoring the northeastern
Panhandles. With all that being said, a slight chance to low-end
chance of thunderstorms are possible with those that develop
capable of being strong to severe. The main hazards with these
storms will be damaging winds (DCAPE values suggestive of up to 70
MPH) and large hail. A tornado cannot be ruled out due to the
aforementioned backing of the winds in the northeastern Panhandles
when the low level jet kicks in, with 15 to 25 kts of 0-1 km
shear possible.

A cold front is expected to dive south into the combined
Panhandles on Saturday, though model placement of this feature has
been difficult to pinpoint. In collaboration with neighboring
offices, have opted to progress this front through the
northwestern Panhandles through the early afternoon and clearing
the region by late Saturday evening. Enough heating ahead of both
the cold front, and possible dryline, could be enough to produce
an isolated thunderstorm in the eastern Panhandles. Any storms
that develop in the eastern Panhandles could be strong to
marginally severe. Beyond Saturday, the upper low will shear and
weaken as it moves northeast across the northern Plains and be
replaced by another deep upper low over the southwestern United
States that stalls once more across the intermountain west.
Thunderstorm chances are expected to continue through Thursday
next week as a result of this continued weather pattern.

Bieda

FIRE WEATHER...Elevated to critical fire weather conditions are
expected this afternoon and early evening across the western
combined Panhandles. This will be due to a dryline expected to
progress as far east as a line from Sturgis, OK to
Amarillo/Canyon, TX. A Red Flag Warning has been issued for the
extreme western combined Panhandles due to RFTI values ranging
from 4 to 6 owing to southwest winds of 15 to 25 MPH with higher
gusts as well as relative humidity values as low as 6 percent. In
addition, Haines 6 conditions can be expected with potential for
plume dominated fires (i.e., pyrocumulus) possible. Elevated fire
weather conditions are expected in the western half of Sherman
County south to Randall County, with the dryline set up across the
central part of these counties. A fire danger statement is in
effect for these aforementioned counties as a result. Thunderstorm
develop and moist air east of the dryline will preclude fire
weather conditions for the rest of the region today.

On Saturday, a southward progressing cold front will aid in
bringing showers and thunderstorms across most of the region.
Those regions that remain south of the front and west of a dryline
can once again expect elevated fire weather conditions.
Unfortunately, there is a great deal of uncertainty as to which
regions this may be as outflow boundaries from previous evening
thunderstorms as well as Saturday afternoon thunderstorms will
greatly determine forward progression. As of now, it would seem
the best chances for elevated fire weather conditions may occur in
the extreme southwestern and western Texas Panhandle. Beyond this
period, no further fire weather conditions are expected at this
time.

Bieda

&&

.AMA Watches/Warnings/Advisories...
TX...Red Flag Warning until 9 PM CDT this evening for the following
     zones: Dallam...Deaf Smith...Hartley...Oldham.

OK...Red Flag Warning until 9 PM CDT this evening for the following
     zones: Cimarron.


&&

$$

7/29



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