Area Forecast Discussion
Issued by NWS Amarillo, TX

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000
FXUS64 KAMA 180509 AAB
AFDAMA

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
1209 AM CDT Thu May 18 2017

.AVIATION...
Gusty southwest winds will be common from the mid morning through
the late afternoon. Winds will decrease and veer more to the west
early this evening. Skies are expected to remain VFR.

&&

.PREV DISCUSSION... /Issued 638 PM CDT Wed May 17 2017/

AVIATION...
For the 00Z TAFs, sfc dryline will remain generally east of the
terminal sites for this fcst cycle. Southwest winds will diminish
early this evening, and increase again by mid to late Thursday
morning as the sfc pressure gradient tightens. VFR conditions are
anticipated through late Thursday afternoon.

Andrade

PREV DISCUSSION... /Issued 509 PM CDT Wed May 17 2017/

DISCUSSION...
Vigorous upper low that brought severe weather Tuesday has shifted
northeast into Iowa while the next broad upper low spins over the
Great Basin. A brief period of height rises is noted today as
flow aloft slowly becomes more southwesterly ahead of the
approaching Great Basin closed low. Moisture has been scoured out
of the Panhandles with dry conditions expected along with
continued breezy southwesterly winds this afternoon.

For Thursday... models are in fairly good agreement that the
Great Basin low will move over the Rockies and begin to slow with
some very subtle negative tilting. As this occurs, surface
cyclogenesis is progged over northeast NM and southeast CO which
will help bolster low level moisture return. The biggest question
at this time is how far west will the dryline with 60 plus
dewpoints be able to retreat. The ECMWF is the most agressive
bringing it all the way back into the central Panhandles by 21z.
The GFS keep is just east of the OK/TX line with the NAM just west
of the line. For now, going more with the NAM as this model has
handled the dryline position fairly well as of late. Moreover, as
an initial wave moves off the periphery of the upper low and
convergence increases along the dryline, thunderstorms are
expected initiate most likely around mid-afternoon and move
northeast at 35-45 mph. Conditions will be favorable for severe
storms along and east of the dryline with primary mode initially
being discrete supercells. MLCAPE around 3000 J/kg along with deep
layer shear upwards of 50 knots is expected as an upper level jet
streak advances over the dryline. Large hail will be the primary
threat initially, however isolated tornados are possible with any
ongoing discrete storm after 00z as a 40-50 knots LLJ ramps up
resulting in more directional hodographs from 0-3km. The area near
the triple point region of the developing surface low will be the
most favorable for enlarged hodographs which will hopefully be
just north and east of the far northeastern zones. Storm motion
will most likely result in storms shifting east of the Panhandles
prior to the highest tornado potential, however, large to very
large hail is possible for the far eastern Panhandles as storms
will intensify rapidly.

A pacific front will move through the Panhandles late Thursday as
the main upper low slowly starts shifting east. This should help
push the dryline just east of the Panhandles Friday, but keeping
a chance of a few showers and thunderstorms as upper dynamics are
supportive and enough uncertainty exist with the exact position
of the dryline. The 500mb trough axis finally traverses the
Panhandles late Friday into early Saturday with a more robust
front in its wake. This front may kick off a few showers or storms
but should be brief and fairly tame as moisture will be limited.

Saturday should be mostly dry with below normal temperatures
post-frontal. Upper flow expected to become more zonal over the
weekend with a subtle perturbation in the flow late Sunday. This
may help spark a few storms in the northern zones Sunday afternoon
and evening.

For the extended... a warming trend is expected with temperatures
near or above normal by early next week. Long range deterministic
guidance show an upper trough moving south out of Alberta Canada
with the trough axis extending all the way into the southern
plains by Tuesday. There are large discrepancies in the timing of
this feature, but it does look like an unseasonably strong front
may push through the region as the trough shifts into the OH
valley region. Moisture availability is questionable, but it does
look like showers and storms will be possible with this frontal
feature.

Ward

&&

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

&&

$$

15/29



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