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Area Forecast Discussion (AFD)

Issued by Amarillo, TX (AMA)

                            
000
FXUS64 KAMA 190511
AFDAMA

Area Forecast Discussion
National Weather Service Amarillo TX
1211 AM CDT Wed Jun 19 2019

.AVIATION...
06Z TAF Cycle

VFR conditions will prevail at all three TAF sites through 06Z
Thursday, except for some possible MVFR ceilings at the Guymon TAF
site around 12Z Wednesday. Mainly north to northeast winds
becoming east and southeast 5 to 10 knots or less or 5 to 15 knots
through 06Z Thursday.

Schneider

&&

.PREV DISCUSSION... /Issued 711 PM CDT Tue Jun 18 2019/ 

AVIATION...
For the 00z TAFs...
Scattered thunderstorms will pose a threat to the terminals
through around 03z.  Variable surface winds gusting above 35
expected near thunderstorms.  Following thunderstorms, variable
surface winds generally below 10 kt expected through the night.
Surface winds expected to settle to a northwest direction for much
of the day on Wednesday at speeds below 15 kt.  VFR conditions
expected next 24 hours, apart from brief visibility reductions in
thunderstorms this evening.

Cockrell

PREV DISCUSSION... /Issued 258 PM CDT Tue Jun 18 2019/ 

SHORT TERM...This Afternoon through Tomorrow...

Synopsis: Upper level troughing is noted across the central CONUS. A 
leading shortwave is now shifting east/northeast across the central 
plains, with a second more subtle shortwave in northern NM. Isolated 
to scattered thunderstorms are expected late this afternoon into the 
evening hours in conjunction with the upper level shortwave and a 
cold front. There is a cap, but it is not as strong as previously 
thought based on the 19z KAMA special sounding. Any storms that do 
develop could become severe with large hail and strong winds being 
the main threat. An isolated tornado can't be rule out this evening 
mainly in the eastern Texas Panhandle. Storm should be ending after 
the front moves through tonight. There is a chance of some very 
isolated diurnally driven storms Wednesday afternoon, with storms 
moving off the higher terrain and perhaps along a weak area over 
convergence near the caprock.  A few of these storms could become 
briefly severe with hail and wind, with a diminishing threat into 
the early evening. The following discussion will focus on today and 
tonight: 

Convective Initiation (CI): Convection has already initiated near 
Raton NM near a pre-frontal trough that is currently draped across 
southeast CO down into the western Oklahoma Panhandle and back up 
into southern KS. A cumulus field is also becoming more evident just 
south of the pre-frontal trough near KDHT to KDUX and will need to 
be monitored for additional initiation in the next 1-2 hours. The 
cap is a concern in the Panhandles and may limit convective 
initiation and sustainment, especially across the southern Texas 
Panhandle. The 19z special sounding showed 51 J/kg MLCIN which may 
limit coverage, but a few storms should be able to develop in the 
Panhandles, or at least persist as they move into the area from our 
west. Another area of attempted CI is along a low level theta-E 
gradient that is slowly shifting north near Plainview to Childress, 
and has an area of Tcu near Floydata as of 19z. The cap may be too 
strong for development in this area based on the convective trends. 
The subtle shortwave trough is noted in the mid level water vapor 
imagery now moving into north central NM, and this may result in 
additional convective development across the northern zones in the 
evening. These storms are expected to move east to southeast at 10 
to 25 mph. Another round of storms may develop overnight as the main 
cold front moves south and generates elevated convection in the 
eastern Texas Panhandle near the better theta-E axis.

Pre-Storm Environment: A band of moderate 500mb westerlies is noted 
across the northern zones which supports 25 to 35 knots of effective 
bulk shear. Further south, mid level winds are weaker and surface 
winds are still veered to the southwest, resulting in lower 
effective shear values of around 20 knots. These may increase some 
this evening as the low level jet increases. Plenty of insolation 
across the Panhandles supports a thermodynamic environment around 
1500 - 2000 J/kg MLCAPE. Temperatures should come up another few 
degrees which will increase MLCAPE, with some 2500 to 3000 J/kg 
possible. Steep lapse rates are also noted in the low and mid levels 
with EML that also could keep capping concerns. However, short 
term models continue to suggest that the cap will weaken enough for 
storms to survive. Low level moisture is characterized with a subtle 
moisture gradient of mid 50s dew points in the northeastern NM 
plains to low 60s dew points in the eastern half of the Panhandles. 
This moisture is fairly shallow so LCL heights are still moderate 
high, around 1500 to 2000 m. These may drop some this evening aided 
by some additional moisture advection with the low level jet.  

Convective Mode and Severity: Given plentiful instability and 
moderate shear in the northern zones, a few discrete storms capable 
of supercell structures will be possible. These storms may loose 
their supercell characteristics if they move southward out of the 
better shear, however some backing of the low level winds this 
evening and the increase in LLJ could offset this some. Upscale 
growth will likely be the result of the strengthening LLJ and better 
lift with the shortwave. Overall, the discrete storms will pose the 
main hail threat. Certainly can't rule out some golf ball to tennis 
ball size hail with the strongest discrete storms. Winds will become 
more of a threat if storms can grow upscale with DCAPE as high as 
1400 J/kg in the Texas Panhandle. The tornado threat is low due to 
lack of better low level shear and high LCL heights, however if 
surface winds can back enough this evening, an isolated tornado 
threat can't be ruled out. 

Ward

LONG TERM...

Upper level flow will transition from northwest to zonal on Thursday 
and then it will become more southwest by Friday as an upper level 
trough moves through the northwest U.S.  Thursday and Friday are 
expected to be dry with temperatures above normal as southwest 
surface winds increase.

Showers and thunderstorms may return to the northern and eastern CWA 
Saturday night through Sunday as a cold front moves into the region 
and stalls.  Several upper level short wave troughs will move 
through the southwest flow aloft which will help trigger the showers 
and storms.

The upper level trough then swings through the high plains by Monday 
which should take the rain with it.

The rain and cold front will help to drop temperatures back down to 
near normal for the weekend and then temperatures will warm again on 
Monday.

&&

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

&&

$$

11/2