Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 312038
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
338 PM CDT TUE MAY 31 2016

.SHORT TERM...(tonight through Friday)
Issued at 334 PM CDT Tue May 31 2016

Ending rain chances this evening, then the next chance for storms by
late week, are the primary forecast concerns.

Cold front tied to upper low in the northern plains had pushed
through southeast Nebraska and southwest Iowa during the early
afternoon. Significant drying of low levels was noted behind the
front as 40s dew points were advecting into northeast and east
central Nebraska and west central Iowa this afternoon. With upper
low currently in North Dakota and swinging east-northeast, biggest
push of drier and cooler air has already occurred, with a gradual
drying trend overnight under weak northwest surface flow.
Precipitation chances will die off early this evening in our
southeast given front to the south and upper support moving farther
away, along with loss of heating. A secondary shortwave rotating
around main upper could bring a shower to parts of northeast
Nebraska for a couple hours this evening as well.

A generally zonal flow pattern will follow Northern Plains low for
much of the rest of the week, stretching from the Pacific Northwest
coast to the Great Lakes. However a shallow trough within that flow
will remain over the Central/Northern Plains Wednesday and Thursday
before a stronger shortwave drops out of the Canadian Plains into
the Upper Midwest. This shortwave will drive another cold front into
our area on Friday, and will bring our next significant chance for
thunderstorms.

Ahead of it, a broad warm advection regime will set up in the Plains
on Thursday. Model output has been and still is showing theta-e
advection culminating in a mid-level precipitation signal over a
warm front lifting north through northeast Nebraska and southeast
South Dakota Thursday afternoon or evening. As we already have a
mention in current forecast, will maintain an afternoon chance of
thunderstorms in northeast Nebraska.

Better storm chances are slated for Friday as cold front works into
the region. Latest information suggests a slightly delayed arrival
from 24 hours ago, putting wind shift into northeast Nebraska during
the afternoon. GFS may be a bit aggressive in showing surface dew
points 65-68F just ahead of front, but still an axis of 1500 j/kg or
greater of mixed-layer CAPE, and 0-6km west to northwest shear
vectors near 40kt becoming perpendicular to frontal zone, suggests
any storms that fire could become supercellular with attendant
severe threat.

Temperatures should be a bit cooler the next couple of nights when
lows drop into the 50s. Highs will gain a few degrees each day ahead
of Friday cold front, climbing from the mid 70s Wednesday toward the
mid 80s Friday.

.LONG TERM...(Friday night through Tuesday)
Issued at 334 PM CDT Tue May 31 2016

Thunderstorms Friday night, then a mainly dry forecast into early
next week are the main points in the longer term.

Cold front entering northeast Nebraska Friday afternoon is forecast
by both GFS and ECMWF to move through the CWA by 12Z Saturday.
Continued convective development is likely given degree of
instability/shear/convergence along/ahead of front. By Saturday
morning, things should be well southeast of here, making for a
mainly dry day. However there is some indication scattered afternoon
convection could fire under steepening lapse rate environment. Will
keep out of forecast for now but watch for later trends.

The rest of the period through Tuesday should also be dry as north
then northwest mid level flow keeps moisture at bay. There will
likely be a time or two when shortwaves ride that flow and spark
scattered storms, as is common in northwest flow events, but timing
those this far out is futile. Otherwise gradually rising heights
early next week suggest highs will gain a category or three, from
the mid 70s Saturday to the mid 80s by Tuesday.

&&

.AVIATION...(18Z TAFS for KOMA...KLNK...KOFK through 18Z Wednesday)
Issued at 1220 PM CDT Tue May 31 2016

MVFR ceilings possible at KOMA and KLNK into the early afternoon...
then expect VFR conditions. Best chances for TSRA are east of the
TAF sites. North/northwest winds will decrease this evening.


&&

.OAX Watches/Warnings/Advisories...
NE...None.
IA...None.
&&

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...Miller



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