Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 242118
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
418 PM CDT TUE MAY 24 2016

.Mesoscale Update...
19z KAMA sounding shows similar low level moisture depth as the 12z
sounding and mixing now up to just above the top of this layer and
we initially started to mix out. Hot/dry air to the west of the
dryline and attendant surface pressure falls have caused winds ahead
of the dryline to turn more southeasterly and confluence along the
dryline to increase. Sharpening dryline is setting up from just east
of Liberal to near Borger to near Amarillo. Deepening cumulus field
has formed along and behind the dryline with glaciation noted in
satellite and weak echos have recently shown up on radar from near
Fritch to just west of Tulia.

There has been little change in earlier thinking other than minor
adjustments to the position of the dryline. Also, we have a better
handle on residual boundaries across the area. The most prominent is
an outflow from overnight convection which now extends from near
Dodge City southeastward across northeast Beaver County to near
Gage. East of this (including a small portion of Beaver County) low
level shear is enhanced with slightly backed winds. This boundary is
nearly stationary. Other mesoscale features include bands of
northwest to southeast oriented enhanced cu, probably associated
with areas of enhanced low level moisture. One is oriented
downstream of developing convection near Borger. We will need to
monitor this closely for possible enhancement of low level shear in
case these enhanced cu fields are more baroclinic than they
currently appear.

Another concern is retreat of the dryline later this evening and the
potential to involve a larger portion of the central Panhandle.
Similar to last night, cool outflow from convection if it becomes
extensive enough, will augment/accelerate the retreating dryline and
may be enough for at least marginal severe threat further west
including the city of Amarillo.

BRB

&&

.Prev Discussion... /Issued 110 PM CDT TUE MAY 24 2016/

Aviation...
Skies should remain VFR through this forecast. Thunderstorms will be
possible near the AMA TAF site this afternoon, but at this point it
looks like they will be just east of AMA. Gusty southerly winds will
decrease tonight after sunset. Winds will then veer some toward
sunrise.

Prev Discussion... /Issued 1254 PM CDT TUE MAY 24 2016/

Mesoscale Update...
.Severe weather expected today across the eastern Panhandles...

* Synoptic Overview: Water Vapor loop shows a complex pattern in the
  western United States, with a broad trough and embedded shortwaves.
  One fairly potent shortwave trough is now located in southern
  Nevada and is slowly moving east. Mid-level momentum will
  overspread much of New Mexico through the day and spread into the
  Texas Panhandle by early evening. Subtle mid-level height falls are
  expected to begin across the region by afternoon and provide more
  large scale ascent, albeit still quite weak, than was seen
  yesterday.

* Mesoscale: 15z hand surface analysis shows that low level flow has
  veered across much of the Texas and Oklahoma Panhandles with the
  exception being in the Southeast Texas Panhandle. A moisture
  discontinuity is present along this confluence zone which extends
  from near Lipscomb to Borger to Palo Duro Canyon. This is the
  beginning of what is expected to be a sharpening dryline later this
  afternoon. Latest surface observation at Amarillo ASOS has a
  temperature of 81 and a dew point of 61. Modifying the 12z sounding
  for this T/Td show that mixing is nearly extending into dry layer
  above a shallow moist layer. The dew point at Amarillo should begin
  to fall quickly within the next hour or two and the dryline will
  become much sharper in the vicinity of Amarillo. Temperatures west
  of the dryline are expected to warm considerably with mid 80s
  already observed in the western Panhandle. Typical diurnal density
  cycle related to this warming and falling surface pressures should
  result in a fairly significant isollabaric response and backing of
  low level flow east of the dryline by mid afternoon and continuing
  into early evening. This will 1.) ensure low-level moisture
  continues to be advected westward, 2.) result in increased low-
  level moisture convergence along the dryline to aid in convective
  initiation, and 3.) increase low level shear and enhance the
  tornado potential. The finer scale details of this process are not
  completely clear at this point and additional updates will be
  needed based on observational trends. One of the more challenging
  aspects of this forecast will be depth of moisture and how that may
  change throughout the day. Most of the short term model guidance
  suggests a fairly pronounced northward surge of higher 850 mb
  theta-e values across the eastern Texas Panhandle. The nose of this
  low-level theta-e axis may reach far southwest Kansas by early
  evening when the most likely time for tornadoes may occur as
  boundary layer starts to stabilize and low level jet increases
  causing an increase in 0-1 km shear. Another mesoscale aspect worth
  noting that may become particuarly important later today is an
  outflow boundary from overnight convection in Kansas that is now
  moving slowly south across Beaver County extending east-southeast
  to just north of Gage and further into Oklahoma. Stratus is more
  extensive north of this boundary with easterly surface winds
  enhancing low level shear.

* Threats: All modes of severe weather are expected, including large
  hail, damaging winds and tornadoes. At first glance at the short
  term guidance the most likely area for tornadoes to occur will be
  across the far northeast Texas Panhandle, Beaver County in the
  Oklahoma Panhandle, and extending north and east from there outside
  of our forecast area. This is due to proximity/timing of the nose
  of the low-level theta-e ridge, potential enhanced low level shear
  along and north of advancing outflow boundary, and tendency for
  stronger low level jet by evening as boundary layer begins to
  stabilize. We will refine the specific area of this threat later
  today. The primary threat will be large hail and soundings have
  evolved to be more favorable for very large/giant hail compared to
  prevous days. RAP/HRRR soundings across the eastern Panhandles show
  strong instability with MLCAPE in excess of 2,500 J/KG. What is
  particuarly concerning about the hail threat is the amount of CAPE
  in the hail growth zone and the increased flow from the top of the
  HGZ to the anvil layer compared to previous days. 1.5 PVU isotachs
  suggest stronger tropopause level flow with further south extent in
  the Panhandles as upper jet overspreads west/central Texas into
  southwest Oklahoma this evening. In the most persistent sustained
  updrafts in this thermodynamic environment, very large hail bigger
  than baseballs seems quite possible. We are also concerned about
  locally heavy rain for areas that received significant amounts two
  days ago. PWATs are not as high but slow moving supercells may
  produce locally heavy rainfall amounts and could cause flooding.

* Timing & Location: Convective initiation time based on modifying
  the 12z KAMA sounding for expected dew points ahead of the dryline
  and temperatures later this afternoon suggests thunderstorms may
  begin to develop shortly before 3 PM. Organization may be slow
  since deep layer shear is somewhat marginal and there is an
  imbalance between shear and instability with CAPE being so high.
  Storm motions should be northeasterly at around 20-25 knots before
  storms mature/become supercellular, turn right and slow down.
  Mature supercell storm motions and speeds should be east-
  northeasterly or easterly at around 15 knots based on Bunkers right
  moving vectors. Location of this initiation will be dependent on
  location of the dryline. Again, there is uncertainty with this
  given uncertainty with the depth of the moisture. We will sample
  this with a special 19z sounding, but it is entirely possible that
  the dryline does not mix east off the Caprock and remains over/near
  Amarillo, extending northeast to near Spearman. We will provide an
  update after analyzing the 19z sounding.

* Summary: Large hail, damaging winds, and isolated tornadoes could
  occur with any storms that form this afternoon across the eastern
  Texas and Oklahoma Panhandles and persist into the evening. Large
  hail, possibly very large, is the primary threat. The tornado
  threat should be maximized in the northeastern portion of the area
  from around 7 PM and 10 PM. Locally heavy rainfall with slow moving
  storms could cause flooding, particularly in areas that received
  significant rainfall on Sunday. Primary uncertainties are where the
  dryline will sharpen and thus where convective initiation is most
  likely, and where/when the best tornado potential will be. We will
  provide updates throughout the day based on observational trends
  and short term guidance.

BRB

Prev Discussion... /Issued 543 AM CDT TUE MAY 24 2016/

Aviation...
12Z Issuance...VFR conditions expected for all sites through the
period. Low clouds off the Caprock should thin out this morning and
thunderstorm chances later in the afternoon, after 21Z, shouldn`t
affect the taf sites. Gusty southwest winds will be up to 30kts today
and stick around until 02 to 06Z.

Beat

Prev Discussion... /Issued 519 AM CDT TUE MAY 24 2016/

Discussion...
For today, a fairly broad upper level trof over wrn us witll retain
SW flow in place across the srn high plains. Surface winds will
increase and become SW on the Caprock later this morning, causing the
surface dryline to move east across wrn and most of cntrl zones and
eventually slow down and stall somewhere across ern half of the fcst
area later this afternoon. The combination of sufficient moisture
east of the dryline, strong daytime heating and attendant atmospheric
instability, the dryline itself acting as a sfc boundary to help
initiate sfc based tstms, a high cape environment east of the
dryline, decent shear, all suggest that another round of tstms will
develop later this afternoon and continue through the evening hours
east of where the dryline parks itself. Some storms will become
severe, with large hail the dominant primary severe weather threat,
although damaging winds and isolated tornadoes will also pose a
secondary threat. Have painted slgt chc to chc pops ern third of fcst
area for starters this afternoon and evening and also mentioned
psblty of severe in grids and appropriate zones.

A brief break from tstms seems likely on Wednesday and Wednesday
night as the dryline temporarily moves into Oklahoma. No pops during
this period.

A near repeat performance of this afternoon`s and evening`s severe
weather potential looks plausible for Thursday afternoon and evening
across the ern third of the fcst area as an upper level low pressure
system tracks across the srn and cntrl high plains durg this time
period. Slgt chc pops for tstms were incorporated into the grids
along with psblty of severe.

As the upper level low pressure system continues moving across to the
north of the OK and TX Panhandles on Friday, continued slgt chc pops
across nrn and ern sections based on projected path of the storm
system itself.

Dry weather is then anticipated area wide Friday night through
Saturday night. However, the wrn states upper level trof reloads for
Sunday into early next week with the major long range numerical
weather models indicating this to occur. Therefore, have slgt chc to
chc pops from Sunday through next Tuesday across the area in accordance
with the expected continuation of some semblance of a wrn states
upper level trof.

Andrade

&&

.AMA Watches/Warnings/Advisories...
TX...Flash Flood Watch until 4 AM CDT Wednesday for the following
     zones: Collingsworth...Donley...Gray...Hemphill...
     Lipscomb...Ochiltree...Roberts...Wheeler.

OK...NONE.

&&

$$

6/15



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