761 
FXUS64 KLUB 081745
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
1145 AM CST Fri Jan 8 2021

.AVIATION...
Low CIGS and fog was quickly lifting early this afternoon at KLBB
and KPVW. Conditions are expected to return to VFR in the next few
hours or so. KCDS will also return to VFR later this afternoon.
Additional fog and low CIG development is expected early Saturday
morning to the south and west of KLBB and KPVW. Some of these
lowered flight conditions may reach into the terminals but it is
unclear at the moment how far down CIGS and visbys will go.

&&

PREV DISCUSSION... /issued 321 AM CST Fri Jan 8 2021/ 

SHORT TERM...
Low stratus clouds have begun to expand south and west out of the 
Texas Panhandle and southwest Oklahoma into the Rolling Plains and 
South Plains as of 3AM CST. Low level clouds will be stubborn to 
lift through the morning hours, if at all in some spots. Surface 
high pressure will push east through the day as upper level ridging 
aloft gradually flattens across the southwest US. Clouds will 
struggle to mix out as a robust inversion keeps winds aloft from 
mixing down toward the surface. There should be some partial 
clearing by mid afternoon especially on the Caprock. Temperatures 
will range from 5-10 degrees below normal both today and tomorrow. 

A window of clearing skies later this evening into early Saturday 
morning, will drop temperatures into the low 20s for most locations 
by early Saturday morning. But high clouds in upper level west-
northwest flow aloft will be present by sunrise Saturday. Increasing 
southeasterly surface flow during the day tomorrow will reinforce 
moisture out ahead of the potent storm approaching our area in the 
early morning hours Sunday.

LONG TERM...
Confidence is increasing in the potential for widespread heavy
snow across much of the forecast area Saturday night and Sunday.
Models continue to be in very good agreement with the evolution of
a stout upper level low progged to move from the Pacific northwest
today to the 4-corners midday Saturday to southeastern New Mexico
at sunrise Sunday. The NAM continues to be an outlier with its
faster progression and less robust QPF while the SREF mean, the 
Canadian, the GFS, and the ECMWF are in remarkable agreement. 
Positives toward heavy snow for this event include a moist sub- 
cloud layer at the time of the arrival of the mid-level lift and 
moisture (less time spent moistening several thousand feet of air 
mass allowing precipitation to reach the ground), ample mid and 
upper level moisture, strong mid and upper level lift for about a 
12 hour period, favorable temperatures in the precipitation 
development region for dendritic growth, and a temperature profile
and surface temperatures that support an all-snow event (rather 
than beginning as rain or mixing with sleet, for example). This 
pattern matches one of four patterns identified as potential heavy
snow patterns by Lambert in his 1993 TTU master's thesis and 
supported by more recent work by Jeff Vitale of WFO Lubbock. 
Lambert identified this pattern as having the greatest chance to 
produce heavy snowfall, the highest average snowfall, and the 
most widespread heavy snow of the four patterns. While matching 
this pattern is not a slam dunk for heavy snow, it gives a 
historical reference supporting the meteorological parameters 
listed above in favor of widespread heavy snow, defined for our 
forecast area as 4" or more during a 12 hour period or 6" or for 
24 hours. Will ramp precip chances up further this morning and 
will run with the WPC forecast for snowfall which yields in excess
of 4" for all but the northeastern corner of the forecast, the 
axis of heaviest snow extending from Friona to Lubbock to Jayton. 
The typical caveat applies this morning with the storm just now 
coming onshore to be sampled by the upper air network this morning
as well as the possible shifts southward and slower with these 
types of systems. Given the increased confidence will issue a 
Winter Storm Watch for all but Hall and Childress counties for 
Saturday night and Sunday.

The remainder of the forecast period looks to be relatively quiet
with the bulk of upper level energy in the northern jet stream
well to our north. Northwesterly flow aloft overhead downstream
from ridging over the West Coast will temper the warming trend
behind the departing storm system as will the expectation of snow
cover across the forecast area. 

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Saturday evening through Sunday 
afternoon for TXZ021>024-027>044.

&&

$$

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