Area Forecast Discussion
Issued by NWS Amarillo, TX

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FXUS64 KAMA 181136

Area Forecast Discussion
National Weather Service Amarillo TX
636 AM CDT Tue May 18 2021

.AVIATION...12z TAF Cycle...

Localized dense fog has developed over KAMA along with with areas
of low clouds near KDHT to KHRX. The fog should not last much
beyond sunrise, but the MVFR/IFR stratus may hang around for a
good part of the morning. Thunderstorm chances also increase from
late morning into the afternoon. Adjusted timing for storms based
on latest data, with most of the activity expected in the
afternoon into early evening.



.PREV DISCUSSION... /Issued 318 AM CDT Tue May 18 2021/

SHORT TERM...Today through Tomorrow Night...

Synopsis: Another round of thunderstorms is likely today, possibly
starting up in the western Panhandles before the noon hour, then
spreading east through the afternoon. While the severe potential
is not as high as yesterday, a few severe storms are possible with
large hail up to ping pong ball size being the main threat.
Localized flash flooding concerns will continue as storm motion
will remain on the slower side (20 to 30 mph) combined with the
fact that many areas have seen over an inch of rain in the last
few days. The better storm chances shift more over the eastern
Panhandles on Tuesday, and while a severe storm can`t be ruled
out, it looks like the severe threat will be lower than today.

Details (Today): The H5 Low center has finally made it over
northern NM / southern CO, and continues to weaken as it moves
ever more slowly to the east. The latest RAP output keeps the low
spinning over north central and northeast NM through Wednesday
afternoon before finally lifting it north as a shortwave ridge
builds in over the southern Rockies. At the surface, low to mid
50s dew points were common across the Panhandles in the wake of
dissipating showers in western OK as of 0800z. Surface winds were
quickly veering from northeast to east southeast, and some low
clouds were forming over the southwest TX Panhandle per latest
GOES GeoColor RGB. With the upper low hanging out just to the
west, return flow will continue as a surface trough reforms near
the TX/NM state line. PVA will kick back up a notch later this
morning as the next lead disturbance currently in central NM
swings around the south side of the low and approaches our area.

Looking at several different model forecast soundings, all
indications suggest that the atmosphere will recover despite the
potential for low clouds. Theta-E advection in the H8 to H7 levels
will further support convective initiation as the dynamics arrive
late this morning (storms may be elevated early). Low level lapse
rates look a bit sluggish up to about 700mb, but temperatures
around 500mb are quite cold at -16 to -18 C. MLCAPE values are
generally around 1000 J/kg with effective shear around 30 knots,
and given the steep lapse rates from about 700mb to 500mb, would
not be surprised to see some ping pong ball size hail with any
transient supercell structures. Storm motion will be atypical as
storm top winds become southeasterly due to some negative tilt of
the upper wave. Thus, while storms should generally propagate east
with the lead wave, individual storm motion may be to the north
or even northeast. PWATs stay below 1 inch but may approach 90th
percentile values this afternoon. Storm motions being under 30mph
combined with possible training along remnant outflow boundaries
will support a localized flash flood threat.

The setup for tomorrow will be very similar to today, except
shifted more over the eastern half of the combined Panhandles.
Another wave ejects out just ahead of the main low center
resulting in strong PVA during the afternoon. Recovery may be more
problematic if low clouds become extensive as some model output
suggest, but CAMs are still initiating storms along a surface
trough as moisture advection continues to feed into the area. A
severe storms can`t be ruled out, but forecast soundings indicate
less instability and lower equilibrium levels, which will limit
effective shear.


LONG TERM...Thursday through Monday...

Shots at beneficial rains continue in the long term forecast periods.

Thursday looks to defy the above theme, however, as an upper trough
departs to the northeast. This should allow for some subtle brief
height rises, keeping precipitation at bay for around 24 hours.

Friday through at least Sunday look to be dominated by upper
troughing in the western CONUS, an upper ridge over the lower
Mississippi Valley, and consequent southwesterly flow aloft over the
Panhandles. This pattern should also bring plenty of moisture
northward from the Gulf of Mexico to the Panhandles, with recurrent
shots at precipitation as disturbances aloft translate over the
CWA. On the subject of thunderstorms, these should be possible given
progged MUCAPE values of at least 250 J/kg each afternoon and
evening. That being said, with warm moist advection extending as
high as 700mb and the upper ridge shifting westward with time,
looks like we may struggle to get the cold temperatures aloft
needed for instability sufficient for widespread severe
thunderstorms. Will need to keep an eye on things, however, should
those temperatures aloft trend cooler.


AVIATION...06Z TAF Cycle...

Showers and thunderstorms are moving out of the combined
Panhandles and are now well east of all terminals. Thunderstorms
are possible again later today and may occur a few hours earlier
than yesterday. Additionally, MVFR/IFR cigs are expected to form
later this morning, although there are some indications that this
cloud deck may not be as prevalent. For now including MVFR at all
sites mainly after 12z, but IFR can`t be ruled out and some may
not make it to MVFR if cloud cover ends up being more limited.
Winds will generally veer from northeasterly to southeasterly by
late afternoon.



.AMA Watches/Warnings/Advisories...



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