FXUS64 KAMA 171749 AAA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
1249 PM CDT Tue Jul 17 2018

For the 18Z TAFs, isold tstms are fcst to develop later this
afternoon and evening across mainly the OK Panhandle and parts of
the northern Texas Panhandle. Have included VCTS at KGUY from 21Z
until 01Z as this site appears to have the greatest threat of
having at least nearby tstms. Otherwise, outside of tstms, VFR
conditions are expected through 18Z Wednesday.



.PREV DISCUSSION... /Issued 617 AM CDT Tue Jul 17 2018/

For the 12z TAFs...
VFR conditions expected to prevail next 24 hours. Thunderstorm
threat expected to lie northeast of a line near GUY to LTS, where
instability will be higher on moist side of surface boundary.
Position of this boundary may be displaced southward if it is
overtaken by outflow boundary currently moving south through
western Kansas. Will include VCTS this afternoon at GUY. DHT
and AMA expected to remain in drier, more stable air.


PREV DISCUSSION... /Issued 433 AM CDT Tue Jul 17 2018/

Latest upper level analysis indicates broad cyclonic flow
stretched out over almost all of the southern CONUS. An upper
level trough is pushing into the northeast states while the
monsoon moisture plume is evident across the southwest. A
relatively dry mid/upper level airmass continues continue to
advect northwest to impinge on the monsoonal flow and shift its
influence further north and west. Meanwhile, a fairly vigorous
shortwave which is not being handled well by short/medium range
guidance has helped develop an MCS now moving rapidly southeast
through southwest NE and northwest KS. An outflow boundary is
quickly moving south from this activity, and is now almost
through KGLD. The big questions with this feature is how far south
will it make it before stalling, as this could help initiate
thunderstorms if it is able to move into the OK/TX Panhandles
later this morning. Definitely will be something to keep an eye
on. Otherwise, a weak sfc boundary detected based on a subtle
wind shift and Td increase in the surface obs is currently draped
from near Guymon to Canadian. This feature is not expected to
move too much through the morning (although this could change
based on evolution of aforementioned outflow boundary). It seems
this boundary will help initiate convection this afternoon as
convective temperatures are reached. However, increasing
subsidence as upper level high pressure strengthens should keep
overall storm coverage lower today, especially south of the
surface boundary where instability will be very limited due to
ample mixing. Even in the better moisture north of the boundary,
MLCAPE should stay below 1000 J/kg. Moreover, storms today should
stay pretty tame, with heavy rain being the main threat. Can't
completely rule out some microburst winds given steep low level
lapse rate and high LCL in the afternoon, but will depend on
updraft strength. Storms should not last much beyond early

Model guidance seem to have decent agreement on evolution of upper
high pressure through the weekend. 200mb anticyclonic flow should
become better established over NM/AZ today through tomorrow. This
will result in weak northwest flow aloft across roughly the
northeast half of the outlook area, which could help steer storms
off the higher terrain and into the northwest zones as early as
this evening, with possible repeats Wednesday through Friday
evening. Only included slight pops for far northwest zones during
this time as confidence is not high that storms will move in quick
enough before losing day time heating. Also, even though
effective shear is slightly better at around 25 knots, instability
will be limited as near surface moisture quality looks modest at
best, with dry and weak subsident air aloft. One other thing to
note before moving on is that guidance tries to advance weak
surface fronts towards the northern zones behind shortwaves
passing to the north both Wednesday and late Friday, with the NAM
being most agressive. For now keeping north of the area, except
late Friday when boundary should have enough push to make it into
the area.

The final item of note is that temperatures are still expected to
trend up, with 100 to 104 being common Wednesday through possibly
at late as Sunday. Medium and long term guidance, including
the ensembles, suggest a 596-598 dam 500mb high will shift back
east being more squarely over West Texas Thursday through
Saturday before shifting back to the west. Moreover, near advisory
criteria temperatures will be possible each afternoon for some
locations on Caprock, and likely for the Palo Duro Canyon floor
where afternoon temperatures are already forecasted to be above
104 Wed through the weekend.

Rain chances should increase going into early next week if current
model solutions verify and northwest flow resumes. Temperatures
should also trend down some.



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