Scientific Forecaster Discussion
fxus63 klbf 222055
Area forecast discussion
National Weather Service North Platte NE
255 PM CST Fri Nov 22 2019
Short term...(this evening through Saturday night)
issued at 254 PM CST Fri Nov 22 2019
Near term concerns revolve around exiting light precipitation across
portions of Frontier, Hayes, and extreme southeast Lincoln counties.
Satellite analysis depicts a mid-level disturbance moving west to
east from the plains of eastern Colorado into western Kansas. This
feature is associated with a larger trough situated across the inter-
mountain west. This system will slowly move east with time with
embedded shortwaves expected to bring about more light rain/snow
chances, mainly for areas to our south and east, through the day
Friday. Subsidence and drier air behind this departing system will
quickly bring an end to all precipitation across the local area over
the next few hours with continued sunny to mostly sunny skies for
areas north of Interstate 80. Elsewhere, cloud cover will remain
more stubborn in closer proximity to the h5 cutoff. Lows tonight
will fall into the upper teens to mid 20s.
Much quieter weather arrives for Saturday as shortwave ridging
builds into the area behind a clearing cool front. Winds will turn
out of the west-northwest, adding a modest downsloping component.
This combined with h85 temperatures warming a couple degrees will
lead to a rather mild day. Will see daytime highs climb above normal
values for late November standards, ranging from the low 50s across
the far northeast counties to the upper 50s over southwest Nebraska
with dry weather expected. Weak shortwave moves in late Saturday
night into early Sunday but with ample dry air in place, will only
lead to an increase in upper-level clouds across the region. Lows
Sunday morning will fall to the upper 20s to low 30s.
Long term...(sunday through friday)
issued at 254 PM CST Fri Nov 22 2019
Beginning 12z Sunday. A very complicated weather story looks to
unfold in the extended, with concerns for some sort of impacts to
the busy Holiday travel week. Sunday picks up right where Saturday
left off with dry conditions expected though various shortwaves
within the general northwest flow look to encroach on the area.
Little in the way of moisture advection is expected ahead of these
quick moving perturbations, thus no change to the sensible weather
for Sunday. Temperatures at h85 look to remain steady if not warm
slightly, leading to a similarly warm Sunday. Did go with a general
blend netting highs in the mid 50s to low 60s but even this appears
cooler than most nwp guidance. The first potential for precipitation
arrives late Sunday into early Monday as a cold front associated
with a strong surface low located over the upper Midwest into Great
Lakes region drops into the area. As this front drops south, mid-
level frontogenesis in concert with weak lobes of energy within the
generally zonal flow may be able to squeeze out an isolated light
rain/snow shower with the favored location of this occurring being
along the Nebraska/South Dakota border into the central sandhills.
Moisture quality, however, continues to be meager and so confidence
in occurrence is low for now. With the area seeing colder air arrive
from Canada, will see a noticeable cool down as highs on Monday only
reach the low 40s northwest to low 50s south.
A stronger trough will move into the Pacific northwest early Monday
morning and dive into The Four Corners region by early Tuesday. As
it does, will see it take more of a neutral tilt before ejecting
onto the plains by early Tuesday. Upslope flow will lead to a
continuation of precipitation chances through the overnight hours
with rain becoming snow Monday evening with cold air building in.
Strong cyclogenesis will begin Tuesday morning to the south, leading
to a resurgence in northerly flow locally and thus persistent cold
air advection into the area. Discrepancies within the models on
where this surface low develops remain large, especially with where
the frontal boundary stalls and surface low forms across the plains.
Have seen a northward trend in consecutive gefs runs with placement
for the low with early thinking favoring Interstate 44 corridor from
the Thursday night run to now honing in on an eastern Colorado to
western Kansas placement with the morning run on Friday. Meanwhile,
the deterministic run of the GFS has favored the Interstate 44
corridor with the last 3-4 runs. The deterministic European model (ecmwf) is in
general agreement with the GFS thinking of a further south track
with the eps somewhere in the middle. The system doesn't appear to
be very well stacked vertically, leaving the greatest low-level
forcing displaced from the strongest mid and upper-level forcing.
That said, do have "chance" pops across much of the area for the
first part of the day on Tuesday. Thinking greatest quantitative precipitation forecast and thus
snow accumulations will reside in the area of strongest upslope flow
with this favoring southwest Nebraska. For now, thinking snow
accumulations of 1-3" possible across this area though these may
change in subsequent forecasts so stay tuned. Winds look rather tame
through this evening with h85 flow never exceeding 20-30 knots and
the precise track of the surface low will have large implications on
this so consider this medium confidence at best for the time being.
High temperatures on Tuesday and Wednesday will likely top out in
the 30s to low 40s.
Shortwave ridging builds in during the day on Wednesday leading to
mostly dry weather expected. A few weak lobes of energy embedded
within the southwest flow will move through the area bringing a few
areas of "slight chance" pops but there appears no real organization
to this activity so expect most locations to remain dry leading up
to the Thanksgiving Holiday. Mid-level height rises continue into
the day on Thursday, leading to general low-end chances of
precipitation owing to additional weak vorticity advection. A large
scale trough moves onto the West Coast Thursday with implications
towards the Post-Holiday weekend for the local area. With decent
agreement between the global models regarding timing, thinking
greatest potential for travel impacts will fall on Friday night into
Saturday, but specifics remain foggy for now.
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1115 am CST Fri Nov 22 2019
Light snow over far southwest Nebraska affecting kiml and toward
kmck will taper early this afternoon. Low/mid clouds extending to
koga and klbf will lift by 23/00z, leading to VFR. Southwest
surface winds transition to northwest overnight.