423 
FXUS63 KOAX 120916 AAA
AFDOAX

Area Forecast Discussion...UPDATED
National Weather Service Omaha/Valley NE
416 AM CDT Thu Apr 12 2018

.SHORT TERM...(Today through Saturday)
Issued at 404 AM CDT Thu Apr 12 2018

A very complex forecast continues as a powerful storm system 
takes aim at the region early this weekend.

Main forecast change for this cycle, in collaboration with our 
neighboring offices, was to remove all mention of freezing rain. 
Point forecast soundings indicate a transition over to sleet before 
turning over to snow with little in the way of any freezing rain. 
Any long duration sleet event will have a significant impact on
lowering total snowfall amounts.

Otherwise, no changes have been made to the Winter Storm Watch 
that was hoisted Wednesday afternoon.  

A weak surface cold front continues to push south across the 
forecast area and is forecast to stall along the KS/NE border later 
this morning. Meanwhile, a lee cyclone will strengthen over the 
High Plains this afternoon ahead of a potent upper level trough 
which is forecast to close off over the Colorado Rockies by Friday
morning. Ahead of this, the lee surface cyclone will move 
east/northeast along the KS/NE border, pushing the stalled frontal
boundary northward as a warm front this evening. Ahead of the 
low, strong southerly winds over the Central Plains will transport
50's to lower 60's surface dewpoints into the southern portion of
our CWA through the evening. Elevated convection is possible later
this evening along and north of the warm front as veered 
nocturnal low-level jet increases. Best chances will be across
northeast Nebraska and west-central Iowa this evening. 

Strong vertical forcing for ascent greatly increases Friday as 
the mid-upper level low moves east across central Nebraska 
through the day Friday with the surface low moving into 
southeastern Nebraska during the same time. Very steep mid-level 
lapse rates are forecast as mid-levels cool on approach of the 
upper system. In addition, the warm sector should be modestly 
unstable with a very strong vertical wind shear profile by 
mid/late Friday afternoon. The NAM remains very aggressive in 
developing a convective line, and is the most western model, with 
storms firing along the MO river valley and surging them 
northeast. The GFS placement of the surface low seems too far 
removed northward and so have gone closer to a ECMWF placement. A 
narrow sliver of our far southeastern CWA remains in a slight risk
for severe storms Friday with the brunt of the strong convection 
remaining to our south and east.

Now onto winter talk. 

Rain should change over to snow from northwest to southeast 
beginning in our northwest as early as midnight Friday night into 
Saturday morning. As mentioned above, feeling is that there will be 
a transition over to sleet before becoming all snow which could 
lower overall snowfall totals. Will error on the side of caution and 
continue with model trends, keeping near a foot of total snowfall 
across our far northwestern counties as very impressive mid-level 
frontogenetic forcing remains over the area. Have lesser amounts
toward an inch or two as we head south toward the I-80 corridor. As
if a foot of snow isn't enough across northeast Nebraska, a 
strong Canadian high pressure system will press southward creating
a very tight pressure gradient across the region. Forecast winds 
speeds of 40-50mph with likely higher gusts will lead to blizzard 
conditions across northeast Nebraska where travel of any kind will
likely be impossible.

.LONG TERM...(Saturday night through Wednesday)
Issued at 404 AM CDT Thu Apr 12 2018

The big storm system will be pressing east of the area by 
Saturday night however winds may take some time to diminish as the
Canadian high quickly pushes south, keeping the tight pressure
gradient. This surface high moves overhead on Sunday and 
eventually upper level ridging builds overhead by early next week.
Return flow quickly sets up ahead of a quick moving upper trough 
progged to move into the forecast area Tuesday night into early 
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1143 PM CDT Wed Apr 11 2018

VFR conditions will continue through the period with high and mid
clouds expected. Winds may gust briefly before settling down 
shortly after 06Z and become northwesterly as a cold front moves 
through. Winds will then become easterly around 18Z in response to
a low pressure system moving into southwest NE. 


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Storm Watch from Friday evening through Saturday evening 
     for NEZ011-012-015>018-030>033-042-043-050-065.

IA...None.
&&

$$

SHORT TERM...Kern
LONG TERM...Kern
AVIATION...KG