Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Omaha/valley NE
628 PM CST Friday Dec 19 2014
Short term...(tonight through monday)
issued at 310 PM CST Friday Dec 19 2014
Chances for drizzle and fog the next couple of nights...then
rain/snow chances Sunday night into Monday...remain the primary
Low clouds and patchy fog were hanging tough across eastern Nebraska
and western Iowa today. However some clearing was noted in central
Nebraska working east. This will likely get into parts of northeast
Nebraska this evening...but persistent southerly flow and moist low
level atmosphere points to a reinforcement of clouds/fog overnight.
Forecast soundings are similar in moist/cloud depth compared to this
morning. However weak warm advection in a deep layer just above
cloud top suggests some patchy drizzle will be possible in the
eastern two-thirds of the County Warning Area from about 04z to 12z. Temperatures
will slip below freezing all areas...so freezing drizzle is likely.
However expected limited coverage and amounts suggest impacts will
be minimal. Similar situation is forecast Saturday night but
favoring the southeast third of our area.
Clouds should persist for the most part on Saturday as light
southerly low level flow and weak warm advection aloft continues.
Thus temperatures will only slowly rise into the middle and upper 30s
from morning lows in the middle and upper 20s.
Saturday night lows will not be quite as cool as low level moisture
gradually increases. Still looking at lows in the 20s or low 30s.
Southerly winds will increase on Sunday as upper trough begins
moving into the plains. Broad warm advection regime ahead of this
trough over top of surface front will lead to increasing chances for
precipitation beginning in our west in the evening and spreading
across the County Warning Area overnight. Forecast soundings and partial thicknesses
combined with surface temperature forecasts point to mainly a rain event
through sunrise Monday. NAM is coolest of model solutions and would
change rain to snow in west central Iowa before ending.
Precipitation should be ending Monday morning as surface front lifts
northeast of the County Warning Area along with warm advection Wing aloft. However
could see lingering rain in our east and southeast. Cold advection
follows during the day Monday with 850 temperatures dropping below 0c most
of the County Warning Area. Middle level impulse rotating from South Dakota into
northeast Nebraska in the afternoon may ignite snow showers there.
Temperatures Monday should hit highs in the morning north and early
afternoon south before falling as stronger cool advection invades.
Long term...(monday night through friday)
issued at 310 PM CST Friday Dec 19 2014
Aforementioned shortwave dropping into northeast Nebraska Monday
afternoon will slide through the rest of the County Warning Area Monday night
before exiting on Tuesday. Continue light snow chances will result
during this time.
Then attention turns to a potentially potent storm system scheduled
to arrive Friday. Ahead of this system...shallow upper ridging will
be moving into the plains. Northwesterly surface winds through
Wednesday will keep temperatures on the cool side...but more
sunshine should help moderate temperatures somewhat. By
Thursday...influence of approaching trough will turn winds to the
southeast or east with increasing middle and high clouds.
Upper system should begin affecting our area Thursday night. GFS is
weaker than European model (ecmwf) with this system and just brushes northeast
Nebraska with light snow Thursday night. European model (ecmwf) has a more wound up
surface low with a favorable snow-producing track through eastern
Kansas into northern Missouri...and paints about a half inch of quantitative precipitation forecast
across most of eastern Nebraska and southwest Iowa from Thursday
night into Friday...most of which will be in the form of snow. Other
model solutions as well as ensembles of GFS/European model (ecmwf) are offering wide
variation in potential outcomes...so have below normal confidence in
late week forecast. For now will highlight the chance for snow...but
will have to watch this one for potential impacts for a travel-heavy
Aviation...(00z tafs for kofk...klnk and koma.)
Issued at 617 PM CST Friday Dec 19 2014
Light southerly flow is expected across the area during the
period...and this is likely to keep the low clouds locked in
place. MVFR ceilings this evening will become IFR overnight...and even
vlifr by early Sat morning. We will also see visibilities drop as
well...though the clouds overnight should keep visbys generally
above 1 mile. Some improvement is expected by Sat afternoon though with
cloud bases increase to MVFR and visby restrictions diminishing.