Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 232117

Area Forecast Discussion
National Weather Service Omaha/Valley NE
317 PM CST Thu Nov 23 2017

.SHORT TERM...(Tonight through Sunday)
Issued at 312 PM CST Thu Nov 23 2017

Temperatures well above normal are forecast through the weekend,
with a cold front bringing breezy conditions Friday afternoon and a
bit of a cooldown on Saturday the caveats for the short term period.

Weak mid level ridging was over the Plains today, stretching from
the Baja into Nebraska. Main feature of note was a shortwave
trough moving onto the southwestern Canadian coastal region, which
is forecast to swing across the northern Plains on Friday,
pushing attendant cold front through eastern Nebraska and
southwest Iowa Friday afternoon.

Ahead of the front, warm temperatures will continue as downsloping
southwest low level flow helps warm surface temperatures under an
already unseasonably warm airmass characterized by 16C 850
temperatures Friday morning. Given airmass and some compressional
warming component ahead of cold front, expect temperatures to reach
the 60s for highs all of our CWA, with some 70s likely in southeast
Nebraska. Cold front is slated to be along I-80 around 18Z Friday,
with cooling effects felt in northeast Nebraska by then, but later
in the afternoon southeast of the Interstate. Also, strong northwest
winds approaching advisory levels will follow front Friday
afternoon. Straight model output may be a bit low given increasing
speeds with height and a modestly conducive momentum transfer regime
under cold advection and mostly unidirectional flow.

Gradient and mixing will decrease markedly Friday evening as high
pressure begins to build into the region. Clearing skies and light
winds should allow lows to settle back into the 30s with only light
winds continuing on Saturday keeping mixing at a minimum. Neutral
temperature advection is expected Saturday as well, thus our main
warming influence will be lots of sunshine. Highs should still
be above normal in the 50s.

Warmer airmass begins building into the region again on Sunday when
850 temps gain a few degrees over Saturday. However still relatively
light winds through the afternoon, so mixing will be limited despite
favorable southwest direction. Still lots of sun, though, so we`ll
keep highs at or above 60 as per going forecast.

.LONG TERM...(Sunday night through Thursday)
Issued at 312 PM CST Thu Nov 23 2017

We are still looking at a warm start to the work week before a
colder airmass settles into the region for Tuesday through Thursday.
Precipitation chances will remain low through the period as well.

Mid level ridging will expand across the Plains Sunday night before
flow becomes southwesterly with approach of strong trough swinging
into the Rockies. Models are coming in better agreement with timing
of the trough and its associated cold front. GFS is still faster,
bringing front into northeast Nebraska late Monday afternoon, with
ECMWF showing a later evening arrival. However both suggest our area
will remain in warm sector through heating of the day Monday, and
both indicate 850 temps approaching 20C ahead of front. This is a
warmer airmass than is expected Friday, so temps could potentially
top 70 in much of our area. However there remains concern with
thickening mid and high cloud cover dampening max warmup a bit. Thus
will maintain highs well into the 60s for now.

Cold front should clear our area Monday night with much colder
airmass to follow for Tuesday when we lose about 15C or more at 850.
A short-lived warming trend is likely Wednesday as mid level
shortwave ridging overspreads the area ahead of secondary trough
reinforcing colder airmass for Thursday.

With limited moisture with each of these systems, precipitation
chances are low through Thursday. However we are still watching the
Wednesday timeframe when ECMWF has been flip-flopping in showing a
significant surface low wrapping up in the Plains and spreading a
swath rain or snow in its northwest quadrant. 12Z runs from
Wednesday and this morning indicate parts of eastern Nebraska and
western Iowa would be affected by this, but the 00Z run last evening
suggested a track much farther south. GFS shows no support for
either solution, and this morning`s Canadian supports a farther
south track. Again, something to watch, but for now will follow
consistency between our going forecast and GFS/Canadian blend.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1109 AM CST Thu Nov 23 2017

VFR conditions will prevail thru the fcst pd.




LONG TERM...Dergan
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