NWS Omaha, NE wrote its last area forecast discussion before the first event at Nov 17, 11:39 PM CST, 2 hours 21 minutes earlier.
Area forecast discussion, Nov 17, 11:39 PM CST, 2 hours 21 minutes before
Area Forecast Discussion
National Weather Service Omaha/Valley NE
1139 PM CST Thu Nov 17 2016
.SHORT TERM...(Tonight through Sunday)
Issued at 440 PM CST Thu Nov 17 2016
Apologize for running behind today...mainly due to additional
time spent on trying to pin down snow amounts/headlines for the
impending first winter storm of the season late tonight- Friday.
Summarizing the latest situation: while the majority of the CWA
(especially south of a Columbus-Mapleton IA line) is expected to
see very little if any snow accumulation, a sharp increase in snow
amounts is expected as one goes farther north/northwest of the
aforementioned line. In general, those areas that were already
slated to receive at least 0.5" of snow in the previous forecast
were increased an average of 1 to 1.5" inches from previous
forecast. This means that much of northeast Nebraska is now pegged
for at least 2-4 inches of fairly wet/slushy snow, with locally
higher amounts of 5-6 inches most favored in the extreme northwest
counties. As a result, four counties have been upgraded to a
Winter Storm Warning while several more counties were added to the
original Winter Weather Advisory. With an expectation that snow
could start a bit sooner than previously expected, also backed up
the "start time" of both the Warning/Advisory to Midnight. In
addition to the good potential for accumulating snow (again,
mainly northeast Neb), the ENTIRE CWA will feel the effects of
strong northwest winds and noticeably colder-than-lately air, with
sustained speeds likely hovering a few MPH either side of 30
nearly the entire day Friday, with gusts up to around 45 MPH. As a
result, all counties in the CWA not in winter headlines have been
placed in a Wind Advisory valid 6AM-6PM Friday. While this
advisory may be a bit marginal especially in the far
south/southwest near the KS border, decided not to get "cute" and
just issue CWA-wide as all areas will be notably windy.
Taking a quick look at the current scene as of 22z/4PM, if
anything today has been a little cooler and windier than expected
across the majority of the CWA, as a cold front has invaded and is
currently extending southwest from a roughly 999 millibar low in
western IA. As a result, the most of the area already has breezy
north winds and temps down in the 40s to low 50s. A notable
exception is in far southeast Nebraska where warmer 60s and even
70s are still in place (Falls City was 73 at 4 PM). An even
stronger surface low (around 994 millibars) is currently noted in
the KS/OK/TX border area. In the mid-upper levels, the powerful
mid level low (vort max) is churning out of eastern CO toward
NE/KS.
Now looking ahead forecast-wise:
Tonight-Friday daytime:
This is clearly the paramount focus of this forecast, as
summarized in the opening paragraph above. Various models have
converged on a reasonably-consistent solution of the primary mid
level vort max tracking into the heart of central NE overnight,
then steadily departing across southern MN toward WI during the
day Friday. At the surface, the aforementioned strong low to our
southwest will ride northeast as well, reaching northeast KS by
around midnight, central/southwest IA by sunrise, and then
becoming more vertically stacked with the parent upper system as
it departs all the way into WI by day's end. Put simply, this is a
quick-moving but powerful system, with intense forcing in the form
of deep-layer frontogenesis and even some meager instability
(including upright). Starting out this evening, expect rain
showers to break out across mainly western portions of the CWA.
Cannot rule out a few lightning strikes, but have left any formal
mention of thunder out of the forecast. Toward midnight and
especially after, the colder air will start rushing in from
northwest-to-southeast, changing rain to snow (moderate to heavy
at times) mainly in northeast/east-central Nebraska. Some
convective elements (thundersnow) not out of the question. Although
the snow will be wet in nature, sustained winds increasing to
around 30 MPH with higher gusts should result in at least limited
blowing/drifting, especially in the Warning counties. All in all,
it could be a dicey AM commute anywhere in the Warning/Advisory
areas. Outside the winter headlines and farther south, there may
be a bit more precip potential than previously thought at least as
far south as I-80, but for the most part this should stay as rain
with little if any snow accumulation. Actual low temps tonight
aimed near-30 far northwest to near-40 far southeast. After
sunrise, accumulating snow will continue for at least a few more
hours in northeast Nebraska, but should gradually diminish in
intensity as the parent system pulls away to the northeast. That
being said, counties such as Knox/Cedar could easily see another
1-3" of snow accumulation after 6 AM. Again, cannot rule out some
light snow even as far south as the OMA/LNK metro areas, but
unless things shift further south just do not anticipate
legitimate accumulation here. By noon or so, even the far
north/northeast CWA should pretty much be down to flurries, with
little if any additional accumulation. However, northwest winds
will howl CWA-wide all day long in the intense pressure
gradient/cold air advection regime behind the departing low. As a
result, at least for now will let the winter headlines ride
through 00z/6PM mainly just in case lingering blowing snow is an
issue. However, would not be surprised to see these winter
headlines potentially ended early and converted over to a Wind
Advisory as well. As for actual high temps, it will feel MUCH
colder with highs ranging low 30s northwest to low 40s southeast.
Wind chill values will commonly be in the teens/20s most areas for
most of the day!
Friday night:
By sunset, all precipitation should be long gone, with high
pressure taking over both at the surface and aloft. Although winds
will remain quite breezy in the evening, they will lighten
steadily with time, and average only 10-15 MPH post-midnight. Lows
will be rather cold, and are aimed from teens north to mid-20s
southeast.
Saturday-Saturday night:
ALthough still chilly, pretty much "guaranteed dry" and not as
windy. Daytime breezes generally only 5-15 MPH from the northwest
before switching to south-southeast Saturday night. Under mostly
sunny/clear skies, high temps are aimed mid-30s north to mid-40s
south. Although not necessarily reflected in the forecast, some
places might be colder Saturday night than Friday night but for
now all areas aimed into the low-mid 20s.
Sunday daytime:
Still dry and a bit warmer with southerly breezes. High temps
should improve a solid 5-10 degrees versus Saturday, and will run
with low-mid 40s north to low-mid 50s south.
.LONG TERM...(Sunday night through Thursday)
Issued at 440 PM CST Thu Nov 17 2016
Continued dry conditions are expected for the latter half of the
weekend, with models remaining in good agreement showing the upper
level ridge axis sliding east through the Plains. At the surface,
winds are expected to be southerly for most of the CWA, though a
weak trough axis may bring more westerly winds to northern portions.
A warmer air mass advecting in from the west looks to bring a bump
up in temperatures, with forecast highs ranging from near 40 in the
far north to lower/mid 50s in the south.
As we get into Monday, models still in good agreement showing the
upper level pattern turning more southwesterly, as the next system
digs south into the Rockies. The daytime hours remain dry, with
precipitation chances on the increase through Mon evening/overnight,
and continuing on into Tue-Tues evening as the system crosses the
Central Plains. At this point, model thermal profiles continue to
support keeping the precip type as liquid, but colder air isn't far
off to the west. Will be something to watch in the coming days. As
far as temperatures go, highs look to reach the mid 40s-mid 50s for
Monday, and may end up at least a touch cooler for Tuesday, but
plenty of uncertainty present.
The forecast for the middle of the week, including Thanksgiving Day,
is dry. Models are currently in pretty good agreement showing
ridging building in across the region in the wake of Tuesday's
system. Not looking to be a significant swing in temps either way
for Wed-Thurs.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1128 PM CST Thu Nov 17 2016
Showers and isolated thunderstorms are rapidly overspreading
northeast Nebraska as of 0530z with a change over to all snow
anticipated by 10z at KOFK. Expect IFR ceilings to prevail there
through 12z with winds strengthening from the northwest at 25 kts
with gusts to 35 kts. Precipitation should end by mid morning at
KOFK with ceilings lifting to MVFR by early afternoon. At KOMA and
KLNK, precipitation coverage and duration remain much more in
question. Therefore, have opted only only include a VCSH mention
at this juncture. Ceilings should gradually fall to MVFR overnight
before rising to VFR by late morning at KLNK and late Friday
afternoon or early evening at KOMA. Similar to KOFK, winds will
strengthen from the northwest at 25 kts with gusts to 35 kts and
continue through the day.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Wind Advisory from 6 AM to 6 PM CST Friday for NEZ015-033-034-
043>045-050>053-065>068-078-088>093.
Winter Weather Advisory from 3 AM to 6 PM CST Friday for NEZ018-
030>032-042.
Winter Storm Warning from 3 AM to 6 PM CST Friday for NEZ011-012-
016-017.
IA...Wind Advisory from 6 AM to 6 PM CST Friday for IAZ043-055-056-
069-079-080-090-091.
&&
SHORT TERM...PFANNKUCH
LONG TERM...ADP
AVIATION...Mead