191 
FXUS63 KOAX 282321
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
521 PM CST Thu Jan 28 2021

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 430 PM CST Thu Jan 28 2021

Tonight and Friday...

Moist low level warm advection across and north of snowpack
expected to produce advection fog under deck of low stratus. Some
indications of thinning stratus deck across southern portions of
CWA late tonight, which could lead to some radiation fog. Kept 
temperatures on the low side of guidance, based on trends. 
Snowpack and whether or not there are breaks in clouds will
dictate whether minimum temperatures drop into the teens or lower
20s.

As H5 ridging increases, increasing subsidence, likely will see a
thinning of stratus deck, though low level moist advection will
continue. Due to potential for clouds kept temperatures slightly
cooler than 50 percentile temperatures, with lower to mid 30s
common.

Saturday and Sunday...

Actually beginning late Friday into early Saturday, lower
tropospheric moist isentropic ascent increases in advance of
progressive H5 trough/closed low. Atmospheric moistening increases
with PWAT one to two standard deviations above normal for January.
Perhaps models haven't completely ingested remnants of infusion of
mid-level moisture from atmospheric river bringing copious
precipitation to western U.S. Increased QPF toward 75%, as well as
PoPs. Some disparity in atmospheric temperature profiles between 
various models. 00Z GFS and GEFS were the outliers, with warmer 
temperature profiles; however, more consistency in ECENS, Canadian
and NAM. Thus feel profile will support a greater area of wintry 
precipitation,especially freezing drizzle/light freezing rain
early on versus liquid. Evaporational and dynamic cooling could
allow transition to snow more quickly, with EC and NAM depicting
more rapid transition to lower tropospheric wet-bulb at or below
zero by mid- to late afternoon on Saturday. Bottom line, hold on,
precipitation type, snow and ice totals likely to change. At
present, do not feel amounts of either snow or ice will reach
warning criteria levels.

Aside from snow and ice, some concern of what rain falling on snow
will do to smaller rivers and streams across southeast Nebraska.
Area dominated by mainstem, so impact will be localized. For now,
only mentioned in HWO.

Sunday Through Tuesday...

Some lingering light snow and clouds on Sunday, with low level
cold advection and additional new, fresh snow and ice keeping
temperatures in the 20s. Upper H5 ridging increases Monday and
Tuesday, thus expect warming to temperatures at or above normals,
or lower to mid 40s.  

Wednesday and Thursday...

Another progressive wave expected to move across the Nation,though
showing some stagnation across the central plains. Disparity in 
timing of the deterministic and ensemble members; however,next
chance of significant precipitation expected Wednesday through
Thursday. Ensemble plumes hinting at some potential for QPF
greater one half inch or greater, and snowfall of 3 inches or
greater.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 509 PM CST Thu Jan 28 2021

Latest models maintain enough low level moisture to result in
flight restrictions at all terminals. Therefore expect IFR with
occasional LIFR conditions to prevail through tonight and into
Friday afternoon. 

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

DISCUSSION...Fortin
AVIATION...DEE