Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 171754 AAC

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
1254 PM CDT Sun Sep 17 2017

For the 18Z TAFs, a low confidence forecast with potential for
amendments later today. IFR to MVFR cigs at KGUY and KDHT will
slowly lift and erode at KDHT this afternoon while improving to
MVFR at KGUY during this same time period. The greatest threat
for thunderstorms late this afternoon and evening will be at KAMA
followed by KDHT. Have incorporated mention of this element at
both sites, and omitted at KGUY due to low confidence in its
occurrence. Low confidence in whether IFR cigs will return at the
terminal sites late tonight so have only included a sct deck for
this issuance.



.PREV DISCUSSION... /Issued 1057 AM CDT Sun Sep 17 2017/

Adjusted max T grids down some across northern zones this
afternoon due to extensive low clouds in post frontal atmosphere.
Remaining forecast grids remain plausible at this time. Updated
products have been sent.


PREV DISCUSSION... /Issued 643 AM CDT Sun Sep 17 2017/

For the 12z TAFs...
Short broken line of thunderstorms currently north of AMA moving
east at 10 to 15 kt.  These will move east of AMA shortly.
Remaining terminals expected to not be threatened by thunder this

IFR and MVFR ceilings moving into northern terminals at this time
expected to persist through much, if not all, of the morning as
moist northeast low-level winds continue.

Scattered thunderstorms expected to redevelop this afternoon and
evening, with a good chance for all terminals to receive a direct

Another round of low clouds could materialize late tonight and
early Monday morning, but certainty of extent and timing is too
low to include in forecasts at this time.


PREV DISCUSSION... /Issued 535 AM CDT Sun Sep 17 2017/

With another day of southwest flow aloft, another shortwave is
progged to cross the area this afternoon. This shortwave will
bring added instability to the already moisture-rich profile
thanks to Hurricane Norma off the coast of the Baja Peninsula.
Short term models and CAMs are not in full agreement on just how
the day will evolve; however, all models are indicating storms
will likely form just to our south or west between 3pm and 6pm
and move through the Panhandles. Storm mode will likely be
supercells due to 35 to 50kts of bulk shear. CAPE profiles vary
between the models with the NAM being the most aggressive with
between 2000 and 3000 J/kg. With large amounts of CAPE in the hail
growth zone, large hail, up to golf ball size, will be possible.
Decent amounts of DCAPE and fast storm motions will mean damaging
winds could be possible for collapsing storms. Low level helicity
and hodographs show that a brief tornado could not be ruled out.
Storms should generally clear out of the area between 3am and 6am.

Meanwhile, the storms firing right now have been pulse
thunderstorms and should die off later this morning. Monday will
see a transition in the upper levels to zonal flow which will cut
off moisture from Norma as well as limit shortwaves from coming
across. This will also allow for downsloping winds on Tuesday
which will bring warm temps and strong winds, leading to elevated
fire weather conditions. Wednesday will see a frontal passage that
will bring temps back to seasonal norms. The end of the work week
and beginning of the weekend will see a return of southwest flow
as a positively tilted longwave trough pushes across the Rockies.
This will allow the return of shortwaves and thus thunderstorm


Moisture-rich air will keep humidity values above 20 percent
through Monday. With RH values dropping into the teens and strong
winds on Tuesday, short-lived elevated fire weather conditions
for the northwest half of the combined Panhandles will be likely.
RH values will return above 20 percent by Wednesday along with
lighter winds.



.AMA Watches/Warnings/Advisories...


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