Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 180438

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1138 PM CDT Tue Apr 17 2018

Issued at 939 PM CDT Tue Apr 17 2018

An intense, negatively tilted mid-level trough is emerging into
the central High Plains this evening with an associated surface
low located over central KS as of 02z. Ahead of this synoptic
system, 00z regional soundings sampled quite steep mid-level
lapse rates attendant to an EML plume and strong capping
inversion. Recent radar and satellite data indicate considerable
implied forcing for ascent beginning to spread from central into
eastern NE as suggested by cooling cloud tops and the development weak
reflectivity echoes. Consensus of latest convection-allowing
model guidance is suggestive that the bulk of precipitation will
occur north of I-80 overnight with a fairly quick change over from
rain to snow across northeast Nebraska. A burst of convection,
including a few thunderstorms, is possible initially as the cap is

The current forecast of 1" to 3+" of snow in the winter weather
advisory area appears reasonable based on latest numeric guidance.
A mixture of light rain and snow or all light snow appears
probable as far south as I-80 toward 12z Wednesday. However,
accumulations should remain less than an inch.


.SHORT TERM...(Tonight through Friday)
Issued at 311 PM CDT Tue Apr 17 2018

WV imagery this afternoon depicting a deep trof extending northward
from the central Rockies into British Columbia getting shoved
eastward in part to building upstream ridge off the west coast.

Somewhat complex weather is still being advertised through tonight.
Synoptic scale lift increases overnight via DPVA and isentropic
upglide. RAP13 progs snow developing early this evening over western
SD/NE panhandle under upper trof deformation zone, then spreading
into n-cntrl NE around midnight. Thermal profiles suggest as the
area of snow approaches the CWA, the environment will be more
supportive of a snow/sleet/freezing rain mix over northeast NE and w-
cntrl IA before making a change over to all snow early Wednesday
morning. Looks as if snow accumulations over the northern CWA may be
a bit more than previously anticipated, with amounts now ranging
from 1 to 2 inches possible by Wednesday morning. And because there
is a threat for some ice accumulations, plan on posting a winter
weather advisory north.

Meanwhile, isolated elevated convective activity appears possible
late this evening along and south of I-80. A surface low is progged
to be centered over western KS early this evening with a thermal
boundary just to the north extending from central NE into central
IA. CAMS show instability parameters modestly increasing over the
southern CWA with isolated cells forming along axis of increasing
boundary layer moisture convergence coincident to low/mid layer
frontogenetic forcing. Believe it is reasonable to assume some cells
may be able to produce some small hail given rather steep mid layer
lapse rates atop pooling moisture.

All precip activity show be clear of the CWA by mid morning

.LONG TERM...(Friday night through Tuesday)
Issued at 311 PM CDT Tue Apr 17 2018

Another strong upper circulation crossing the central Plains this
weekend will be the focus for the next round of precipitation.
Precip chances begin Friday night and continue into late Saturday
night. Thermal profiles do suggest the potential for a brief period
of a rain/snow mix early Saturday morning over the northern CWA, but
the dominate type will be rain.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1138 PM CDT Tue Apr 17 2018

A band of showers with embedded thunderstorms from central into
northeast NE as of 0430z will spread east/northeast overnight.
Rain is expected to change over to snow fairly quickly at KOFK
with ceilings lowering to MVFR or IFR. At KOMA and KLNK, showers
and isolated thunderstorms will become more probable by around 08z
with a potential mix or change over to light snow toward 12z
Wednesday. Gusty northeast winds will shift to north and then
northwest with the passage of a surface low through northeast KS.
The precipitation should end by mid morning with continued MVFR
ceilings through Wednesday afternoon.


NE...Winter Weather Advisory until 1 PM CDT Wednesday for NEZ011-012-

IA...Winter Weather Advisory until 1 PM CDT Wednesday for IAZ043.



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