Area Forecast Discussion
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FXUS64 KLUB 292133

Area Forecast Discussion
National Weather Service Lubbock TX
333 PM CST Tue Nov 29 2016

Continental upper level low pressure trough will translate eastward
across the area overnight. An upper level impulse remains cohesive
northwest of Clovis, New Mexico late this afternoon and even has
generated very high-based virga showers into Parmer County in the
southwest Texas Panhandle. This impulse is forecast to fill and open
this evening while passing overhead, with majority of solutions
continuing to indicate very little chance for meaningful showers. We
can`t completely eliminate the idea of a spritz of a rain shower
reaching the ground mainly west or northwest of Lubbock, but our
forecast will remain dry given the expected weakening of the
impulse. A weak surface cold front should gain a little momentum
overnight with cooler and drier northerly low level flow, though
surface winds will weaken later tonight. A chilly morning will start
the day Wednesday with sub-freezing conditions most of the area
other than perhaps parts of the Rolling Plains. We continue to trend
a little below guidance for the typically colder spots on the

Drier air and confluent upper pattern will follow late tonight and
Wednesday. A trailing upper level speed max associated with an
already weak channeled impulse dropping south-southeast through
eastern Idaho may eventually scoot across our area on Wednesday.
A weak surface high pressure ridge will span the area through
Wednesday morning before giving way to the next version of lee-side
cyclogenesis and returning modest 10-20 mph or so southwesterly
breezes Wednesday afternoon. Highs Wednesday will be slightly cooler
than today most areas owing to a chilly start, except eventually
should climb a little warmer than today across our west or northwest
counties. RMcQueen

The main concern in the extended revolves around an approaching
upper level storm system and the prospects for precipitation,
potentially of the wintry variety for at least the northwest
zones, late Friday into Saturday (and perhaps beyond).

Before then, quasi-zonal flow and dry conditions will follow
Wednesday through at least early Friday. Breezy downsloping winds
and near full insolation should help secure a mild day on Thursday,
with temperatures peaking near or slightly above average. Surface
ridging will then gradually begin to build into the region on
Friday. Although cold air advection is not expected to be that
impressive, increasing cloudiness well downstream of the gathering
storm system over/near the Baja will result in cooler temperatures
locally with highs only in the upper 40s to middle 50s.

In addition, increasingly moist low-mid level meridional flow being
drawn over the cool surface ridge will cause clouds and rain chances
to blossom, particularly across the southeast zones Friday
afternoon. Precipitation chances will further expand across the
area Friday night as isentropic upglide is maximized. It appears
the best window for widespread light to moderate precipitation in
the South Plains region will be Friday night into Saturday before
large scale lift wanes. The latest guidance does suggest most of
the CWA should remain mild enough for a cold rain to be the
primary mode. However, enough cold air, along with wet-bulb
effects, may be present across the southwest Texas Panhandle into
the northwest South Plains to bring a risk for a little wintry
precipitation (freezing rain, sleet and/or snow, depending on the
depth of the cold air and strength of any elevated warm layer).
Still many things to be resolved yet, but there is high enough
confidence to insert the mention of a possible wintry mix across
the northwest zones in the HWO in addition to the forecast.

The latest NWP is now in pretty good agreement that the upper low
near/over the Baja Saturday will gradually weaken and eventually
open as it ejects northeastward Sunday and Monday. The low may sink
far enough south that lift and precipitation chances come to end
late Saturday/Saturday night into Sunday, though they could then
briefly renew as what remains of the system ejects somewhere
nearby Sunday night or Monday. Given these trends we have raised
PoPs further Friday night and Saturday, curtailed them a bit
Sunday and added a rain mention across the eastern zones Monday.
The clouds and precipitation will keep it cool on Saturday with
highs struggling to make it into the lower and middle 40s.

A gradual moderating trend should follow into early next week as
drier conditions return under westerly to southwesterly flow
aloft. However, it does appear a more significant dump of cold
air (emanating from up around Alaska) could be in the offing by
the middle of next week. It will be something to keep an eye on
after the Friday/Saturday/Sunday system.




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