Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Omaha/valley NE
556 am CDT Sat Apr 19 2014

Short term...(today through monday)
issued at 310 am CDT Sat Apr 19 2014

Increasing chances of precipitation...especially tonight through
Sunday night main focus in short term.

Early morning satellite imagery showed modestly strong upper low
moving eastward near Canadian/U.S. ND border at 08z. Although this
system will send a weakening cold front into northwestern zones this
afternoon...southern open trough near California/Arizona border and any moisture/energy
ejecting out ahead of it appears to be main weather influence for
our forecast area. Although there is a small chance of showers
ahead of front in northern zones this morning and possibly thunderstorm
development in vicinity of weakening/slowing front northern zones this
afternoon...appears better convection chances will be west-southwest zones this
evening as middle level moisture arriving ahead of southern trough
interacts with afternoon heating allowing late afternoon development near or
SW of area. That area has been suggested for development...especially
by NAM/GFS which has also influenced the sref members...for a
couple of days now. Moisture and shear...however...are not overly
impressive for our forecast area...but if we can manage to heat toward or
above forecast maximum temperatures near 80...modest convective available potential energy will develop with
strong/isolated severe storms possible for a few hours. Made little/no
changes to maximum temperatures today...guid/prev forecast look good.

If the expected small complex of storms develops near/SW of forecast area
this evening...would expect it to spread/develop into eastern/northestern
zones toward morning in southwesterly upper flow as low level jet veers to
southwesterly. Thus expanded likely probability of precipitation from western zones this evening east-northeast
through 06-07z. Relatively high probability of precipitation seem in order then for Sunday
as southern trough moves into western Kansas/western OK region. Forecast a diurnal
late morning/early afternoon lull in higher probability of precipitation before any heating
interacts with middle level moisture/trough to bring an increase in
expected coverage by aftn/evening. Airmass will be mild so any
breaks in overcast/precipitation should allow heating into 70s...especially
southeastern zones. Still could be a small area where readings fail to get
out of low 60s but at this time confidence in placement not great enough
to change highs any northern zones. Forecast deep shear even weaker for
area on Sunday with instability less...so strength of storms do
not currently look like they will be an issue.

Although southern trough and associated moisture/lift will influence mainly
southeastern 2/3rds of area Sunday night...another stronger trough in northern
steam moving along Canadian border Sunday night will send a
reinforcing push to cold front into northern zones late. This could bring an
additional shower/isolated thunderstorm threat behind main precipitation area which
is expected to be shifting into southeastern zones by Monday morning.
Would expect all zones to dry out Monday afternoon and that period was
continued dry...with highs a degree or two either side of 70.

Long term...(monday night through friday)
issued at 310 am CDT Sat Apr 19 2014

After a quiet period Tuesday active weather still on tap for area
Tuesday night through Thursday as deepening upper trough sets up
across northern rockies. Warm advection precipitation likely to spread over
forecast area Tuesday night into Wednesday period as a very strong low level jet develops
in response to deepening upper trough. If precipitation is widespread
enough Wednesday...which has been suggested by European model (ecmwf) for several runs
now...temperatures could struggle to reach mex numbers which were
a category or so warmer than European model (ecmwf). For now left previous forecast/model
blend in place which were generally near or a little below mex.
Widespread precipitation Wednesday could also alter coverage of severity of
storms over forecast area but upper system strength alone will probably allow
at least some of the area becoming under slight risk area in Wednesday-
midday Thursday period. How efficient/quickly upper low clears out low
level moisture Thursday will greatly influence probability of precipitation/possible thunderstorm
strength that day...and with some possibility of it lingering for
a while Thursday...will probably keep some mention in severe weather potential statement. Cooler but
dry weather expected then by the end of next week as upper trough
axis shifts east of the forecast area.

&&

Aviation...(12z tafs for kofk...klnk and koma.)
Issued at 551 am CDT Sat Apr 19 2014

VFR conditions are expected through 00z as a cold front moves into
the area and becomes stationary by late afternoon. MVFR ceilings and
visibilities likely at times through the remainder of the period as
stalled front acts as focus for convection.

&&

Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&

$$

Short term...chermok
long term...chermok
aviation...fobert