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Area forecast discussion 
National Weather Service Amarillo Texas
1242 PM CDT Wednesday may 6 2015

Aviation...
/18z tafs/ strong southwest winds will be the main aviation concern
during the valid taf forecast period. An upper level upper trough
over the central rockies is forecast to lift to the north this
evening...and be located over the northern plains Thursday morning.
Southwest surface winds have increased to around 25 to 30 kts
sustained. Further diurnal heating and resulting mixing processes can
tap into the stronger middle-level winds. So kama seeing at least a
40 knots gust is still likely so will continue the aviation weather
warning that is currently in effect until 01z. Drier air over the
terminals should keep any convection east of the terminals later
today...although kama would have the best chance at seeing an
isolated storm this evening. However believe convection will stay
east of there so have left out any thunder mention in the forecast.
Upper level energy passing over the Southern Plains may generate
another round of convection Thursday. However better chances for
convection should occur after 18z and hence have opted to keep any
mention of thunderstorms and rain out of the forecast. VFR conditions through the valid
taf forecast period.

Clk

&&

Previous discussion... /issued 626 am CDT Wednesday may 6 2015/

Aviation...
generally clear sky expected today with only high clouds overhead.
South southwest surface winds expected to gust to around 40 knots at all
terminals today as stronger winds aloft mix to the surface. An
aviation weather warning has been issued for Amarillo area airports
for gusts to 40 knots between 16z today and 01z Thursday. Some high-
based cumulus may develop near kama early this evening. Isolated
thunderstorms this evening expected to remain east of kama and other
terminals. VFR forecast continues next 24 hours.

Cockrell

Previous discussion... /issued 303 am CDT Wednesday may 6 2015/

Discussion...

Early this morning water vapor imagery shows a closed middle-upper low
moving northeastward across eastern Colorado. The Texas and Oklahoma
panhandles are now convection free as remnant earlier convection
across West Texas has formed into a large thunderstorm cluster in
central Oklahoma. After an inch or more of rainfall at most locations
the last few days...weak shortwave ridging in the wake of departing
shortwave will result in dry and warmer conditions today. The
exception may be in the far southeast section of the Texas Panhandle
where there is a low probability of late afternoon/evening
thunderstorms. A return to a more active pattern will occur for the
latter part of the week into the weekend including daily chances of
thunderstorms primarily across the eastern portion of the forecast
area. Although deterministic guidance generally agrees on spatial and
temporal details on the larger scale...the typical smaller scale
discrepancies will be important especially in this particular
pattern.

The dryline will sharpen this afternoon across the far southeast
part of the forecast area with fairly rich/deep moisture on its east
side. Dryline circulation may not be sufficient for much more than
isolated thunderstorms given middle level height rises/warming in the
wake of the aforementioned departing wave. Most of the sref members
using kf or sas convective parametrization show a sizable cap
remaining from 21z through 00z at the Childress BUFKIT point.
Convection-allowing models differ some with regards to coverage of
convective development tomorrow. The more aggressive models such as
the ttu-WRF seem to also mix the dryline further east out of the
forecast area. Meanwhile the Storm Prediction Center WRF is mostly void of convection in
our region. Cannot argue against the further east mixing of the
dryline as this would fit the pattern of fairly strong mean
southwesterly flow that is expected to continue into tomorrow
evening. Have scaled precipitation probabilities back some and
limited isolated thunder coverage to Collingsworth County for
tomorrow afternoon.

A particularly challenging scenario develops during the evening
hours when most short-term guidance shows the dryline retreating
northwest and a fairly substantial increase in low level moisture
across roughly the southeast third of the forecast area. This is
probably mostly in response to 500 mb height falls and its
corresponding surface pressure response in the Lee of The Rockies
from yet another approaching/deepening middle-upper trough over the
western Continental U.S.. behavior/timing of the retreating dryline could also
be augmented by cold pool if convection to our southeast is more
extensive than currently expected. There is enough concern for some
convective development late in the evening and overnight to retain
low end precipitation probability across southeast portions of the
area but the better signal for warm advection/isentropic ascent is
further east across southwestern through central Oklahoma. This will
likely be where the greatest coverage is overnight through early
Thursday morning.

Certainly by Thursday afternoon with diabatic heating of a
moistening boundary layer...convection of at least an
isolated-scattered nature would be expected across the area. This
would be enhanced by any small difficult to resolve shortwave
embedded within strengthening mean southwesterly flow. Once such
wave is shown in model guidance to cross the New Mexico mountains
and approach the panhandles by late afternoon followed by another
early Friday. Thereafter the medium range guidance disagrees some on
the timing of the main upper low. European model (ecmwf) is slightly faster than the
GFS. In either case this system strengthens considerably and
becomes negatively tilted which will induce a fairly dramatic
surface response with sub-1000 mb low likely somewhere from
southeast Colorado to the northwest Texas Panhandle by late
Saturday. This setup conceptually would raise concern for the
dryline mixing east into Oklahoma keeping our area dry...although
the far eastern portion of the Texas and Oklahoma panhandles may
remain east of the dryline and see a threat for severe thunderstorm
development. The threat may occur even further west depending on
spatial/temporal details on the larger scale that are yet to be
resolved.

For Sunday into early next week medium range model agreement is less
and ensemble spread is greater. The large scale pattern deamplifies
some with perhaps one more wave passing quickly through sometime
late Sunday into Monday. There seems to be a trend toward upper
ridging and drier weather by Tuesday.

Brb

&&

Ama watches/warnings/advisories...
Texas...none.
OK...none.

&&

$$

05

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