Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 212327
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
627 PM CDT Tue Mar 21 2017

.SHORT TERM...(tonight through Friday)
Issued at 250 PM CDT Tue Mar 21 2017

Early after water vapor imagery indicated weak shortwave trough
moving southeast through IA this afternoon. This was responsible
for the strong frontogenetical band of snow over the northern CWA
this morning. Upstream, height rises will start to advance east
over the central and northern Plains tonight. This should lead to
low- to mid-level WAA/isentropic ascent overnight. Short term
models are in fair agreement in this leading to saturation after
midnight and eventually light precipitation. The models though
differ on the extent of this precipitation. The NAM appears to wet
and we prefer a solution closer to the GFS/EC, which would
generally just have some light amounts in the northwest CWA /NE
NEb/. Thus have lowered/removed pops over the central and southern
CWA. Point forecast soundings indicate that this precipitation
would generally be in the form of light snow and we will include
some half inch accumulations near the SD border.

This band of clouds will likely lift to the northeast and we may
see a few peaks of the sun on Wednesday afternoon. Clouds will
again increase on Wednesday night though as a strong nocturnal LLJ
develops ahead of the potent Great Basin trough. This will likely
lead to deeper moisture into the area, but despite the better
moisture and steeper lapse rates aloft increasing mid-level
temperatures will likely limit overall precipitation threat. Will
include some chance of showers, but it may end up being more
drizzle than anything else. This is likely to continue into
Thursday morning, but may tend to move east during the day.

With the upper level trough slowly shifting east through the
Rockies we will see a cold front move/develop into the northern
CWA on Thursday night. Confluent flow into this zone will lead to
increasing thermal gradient/frontogenesis with a band of rain
likely on the cool side of the boundary. Closer to the surface
and 850 mb boundary we may see a few rumbles of thunder as well,
especially as the low-level jet develops and enhances mass
convergence along this zone. This boundary will likely create a
strong thermal gradient across the CWA on Friday. It is difficult
to discern exactly where this boundary will setup with the GFS/GEM
farther northwest, the EC in the middle, and the NAM much farther
south. Given the early spring season we generally prefer a
solution closer to the EC, but the NAM is certainly possible as
well. Given the uncertainty though the current forecast will not
reflect the likely strong temperature gradient /mid 40s north to
potentially upper 60s south/ on Friday. Rain should continue
during the day on Friday along and northern of the low-level
boundary, with some chance of showers or a thunderstorm south of
the boundary.

.LONG TERM...(Friday night through Tuesday)
Issued at 250 PM CDT Tue Mar 21 2017

With the expected slow movement of the trough we will likely see
the chance of showers continue into the weekend as well along with
the cool temperatures. Any break in the chance of precipitation
will be short-lived however with another shortwave trough swinging
into the Plains with additional chances of showers into early next
week with continued below normal temperatures.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 608 PM CDT Tue Mar 21 2017

VFR conditions expected thru the fcst pd.

&&

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

$$

SHORT TERM...Boustead
LONG TERM...Boustead
AVIATION...DEE


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