Flash Flood and Hail in Texas, May 13, 2018

Area Forecast Discussion
National Weather Service Lubbock TX
344 PM CDT Sun May 13 2018

.DISCUSSION...
It looks like we may be entering a fairly active (and more typical
of mid-May) stretch of weather, supported by a prolonged period of
southwest flow aloft and a dryline wandering the region. This will
occur as the upper low across the Great Basin lingers there as it
slowly fills. Eventually the low will be dislodged and dissipate
around mid-week, but it will quickly be replaced by another upper
low moving in from the eastern Pacific which may be a little more
progressive than this current low (not a tough thing to do). In the
brief transition between western lows, a shortwave ridge will
traverse West Texas on Thursday, with a temporary interruption to the
southwesterly flow aloft.

The difficulty in this pattern is figuring out what days present the
highest chances for convection, and exactly where that convection
will be. Starting with this afternoon, it isn't quite as hot as the
past few days, but it is still toasty with 1930Z temperatures mostly
in the lower to middle 90s. The dryline was mixing through the I-27
corridor and it should halt again near the edge of the Caprock
late this afternoon before returning back westward this evening.
Moisture and instability levels east of the dryline are improved
from the past few afternoons with the 19Z SPC objective analysis
showing 3000-4000 J/kg of MLCAPE in the Rolling Plains, with
fairly minimal CIN as opposed to recent days. Deep layer shear
isn't overly impressive at 25-30 knots, but given the instability,
storms that can get rooted in the boundary layer could quickly
become severe and produce large hail and damaging winds. Most
high-res guidance continues to suggest scattered storms will fire
along the dryline by late afternoon, though the 12Z GFS, NAM and
TTU-WRF are less optimistic on coverage in our CWA later today.
Given relatively weak wind fields and convergence on the dryline
and minimal upper support, confidence in storm
development/coverage isn't high, but anything that goes will have
a severe threat.

Tomorrow will bring a similar setup though we may receive a glancing
shot of upper support as shortwave energy ejects into the central
High Plains. The best storm chances locally may be Tuesday as the
recent NWP suggest a convectively aided front may dip into the South
Plains and stall while a weak subtropical disturbance approaches
from the west. Many of these details could change, but at this point
it looks like a decent shot for convection late Tuesday afternoon
into Tuesday evening. Throughout this period, fairly stout late day
instability coupled with modest deep layer shear will support a
severe weather risk. The storm chances become less clear late
Wednesday into Thursday as the upper ridge passes (after a brief
period of northwesterly flow), but with a residual boundary
potential in/near the area we have maintained slight chance PoPs for
parts of the area. Southwesterly flow and a potentially active
dryline will return to the region late week. Beyond that, the 12Z
GFS and ECMWF suggest a portion of the western trough will emerge
into the central High Plains with a cold front moving into the South
Plains Saturday or Saturday night. Confidence in these details is
low but we have maintained 20-30% PoPs and reflect a modest cooling
trend.

&&

.FIRE WEATHER...
Hot and dry conditions were present west of the dryline across the
southwest Texas Panhandle and western and central South Plains where
RH values ranged from 7 to 14%. Winds have been rather tame to this
point but may become gusty through the late afternoon and early
evening, creating elevated to briefly critical conditions. For this
reason a Fire Danger Statement (RFD) remains in effect for this area
through 9 pm. After decent overnight recoveries tonight for all but
the southwest Texas Panhandle, Monday will bring a similar setup
with hot and dry conditions west of the dryline across the southwest
Panhandle and western South Plains. Wind will again be the limiting
factor, though widespread elevate fire weather conditions will
occur. Additionally, isolated to scattered thunderstorms will be
possible along and east of the dryline later this afternoon and
evening and again Monday afternoon and evening. Improved
moisture/instability levels will support strong to severe
thunderstorms which will include strong and erratic winds and
pockets of wetting rains.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&

23

Hazardous Weather Outlook
National Weather Service Lubbock TX
1135 AM CDT Sun May 13 2018

TXZ021>044-140445-
Parmer-Castro-Swisher-Briscoe-Hall-Childress-Bailey-Lamb-Hale-
Floyd-Motley-Cottle-Cochran-Hockley-Lubbock-Crosby-Dickens-King-
Yoakum-Terry-Lynn-Garza-Kent-Stonewall-
1135 AM CDT Sun May 13 2018

This Hazardous Weather Outlook is for the South Plains, Rolling
Plains and the far Southern Texas Panhandle.

.DAY ONE...This Afternoon and Tonight

There is a risk of severe thunderstorms this afternoon and
evening mainly east and north of a Silverton to Lorenzo to
Guthrie line. Hail to the size of tennis balls and wind gusts to
70 mph are the primary threats.

A rangeland fire danger statement is in effect for elevated fire
weather conditions along and west of a Dimmitt to Brownfield line
this afternoon to mid-evening.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Mainly afternoon and evening strong to severe thunderstorms will
be possible through much of the upcoming week particularly east
of the Highway 385 corridor.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening.