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Displaying AFOS PIL: AFDLUB Received: 2018-10-12 09:32 UTC

FXUS64 KLUB 120932

Area Forecast Discussion
National Weather Service Lubbock TX
432 AM CDT Fri Oct 12 2018

Plenty to consider this forecast with widespread moderate to heavy 
rain expected late tonight into the first half of the day Saturday, 
and the coldest air of the season late weekend into early next week 
when many spots may experience their first freeze.

Early this Friday morning mild and moist conditions were in place, 
supporting widespread cloud cover and even patchy fog at spots on 
the Caprock. Steady isentropic upglide was also generated isolated 
showers across roughly the southeast 1/2 of the CWA as of 0830Z. The 
best shower chances will gradually shift eastward, but may linger 
through the first half of the day across the southern and eastern 
zones. The warm advection will fade through the morning as winds 
veer and this will allow any fog to diminish and the low clouds to 
gradually lift/scattered, though mid-level cloud cover may persist. 
Modest drying and downslope flow (along with some insolation?) will 
allow temperatures to warm into the upper 60s to lower and middle 
70s. However, an upper trough traversing the Midwest will push a 
backdoor cold front into the FA this afternoon. In addition to a 
northerly wind shift, the front will stunt the warming across the 
northeast zones this afternoon, while south of the front parts of 
the South Plains and southern Rolling Plains may warm into the 
middle 70s. Just enough heating and destabilization may be in place 
ahead of the front this afternoon for isolated to widely scattered 
convection to develop.

Slim rain chances will linger into this evening before the remnants 
of Tropical Storm Sergio (currently approaching Baja California) 
race up and over the region. This will cause rain, and perhaps a few 
thunderstorms, to blossom over the South Plains. The rain will 
quickly advance from southwest to northeast across West Texas, with 
the best chances occurring late tonight, after midnight, through the 
first half of Saturday. The quick moving nature of the system will 
help to limit rain totals, but an efficient rain process should 
still secure widespread 0.5 to 1.5" totals, with locally 2+ 
inches. There remains uncertainty where the heaviest rain will
fall with the GFS and NAM both favoring the northwest South 
Plains into the southeast Texas Panhandle, while the ECMWF and CMC
favor the Permian Basin into North Texas. Better 
moisture/instability would tend to favor the southern spots, 
though it will depend on the exact track of Sergio along with the 
position of the surface front, which could focus the heavier 
rain. Regardless, even with relatively moist soils, the limited 
duration/amounts/rates should keep the the flooding risk in check,
with only nuisance flooding expected.

A bit of a lull in precipitation chances will follow Saturday night 
before the next much stronger cold front barrels into the South 
Plains on Sunday. This will occur as a sharp positively tilted 
trough sinks through the Rockies. Current NWP have the front 
sweeping through the Texas Panhandle Sunday morning, then quickly 
through the South Plains during the afternoon. Shallow moisture 
riding up and over this strong front will yield widespread cloud 
cover and the potential for precipitation, though relatively dry air 
aloft and dry advection on gusty northerly winds near ground level 
should keep any precipitation light. The coldest air of the season 
will follow with NWP showing 850 mb temperatures of -2C to -4C 
overspreading most of the Caprock by 12Z Monday. This strong cold 
advection will likely drop temperatures to or below freezing for 
much of the Caprock. In addition, if precipitation persists, a light 
wintry mix will be possible, generally north and west of Lubbock 
Sunday night into Monday morning. Have carried a rain/snow mention 
in the grids, but given the expected shallow saturation it could 
very well be drizzle and/or freezing drizzle. Whatever falls, any 
amounts should be light, though it could still cause a few 
problems if/where temperatures fall into the 20s. 

Surface ridging will linger through the middle of next week keeping 
temperatures well below average. Places that don't see a freeze 
Monday morning will have another opportunity Tuesday morning. 
Additionally, a cutoff upper low will linger over the Desert 
Southwest through much of next week. Downstream of the low southwest 
flow aloft could keep at least low shower chances in the region 
much of the week, though relatively dry low-levels will temper
these chances.