Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Hastings NE
1217 PM CDT Tuesday Apr 21 2015
issued at 654 am CDT Tuesday Apr 21 2015
Infrared satellite shows overnight altocu has diminished and moved southeast
..but another large area is heading southeast through South Dakota. Timing tool
brings it into our northern counties by 15z. So sky cover was increased
with this update.
A couple other notes. The 06z NAM came in more robust with
potential for a few sprinkles with this evening's frontal passage.
Cloud depth/instability is greater and would support precipitation
generation. Sprinkles may need to be added to the forecast.
Watch the NE winds with the frontal passage this evening. The 06z NAM
also shows a tight pressure gradient immediately behind the front. The
forecast may need to better reflect a period of brief gusty NE winds.
Short term...(today and tonight)
issued at 403 am CDT Tuesday Apr 21 2015
Aloft: northwest flow through tonight with an anomalously deep low slowly
lifting from the Great Lakes into Ontario...and a West Coast ridge
that makes slow but steady progress into the intermountain west. WV
imagery shows a very subtle shortwave trough diving S out of
Saskatchewan into the Dakotas. This trough will continue around the
backside of the Great Lakes low and head into the Midwest tonight.
The next shot of cool air will be delivered by this trough.
Surface: a weak/subtle low was over Montana. This low will move south-southeast
and across Nebraska today along with its trailing cool front. Frontal
passage will this afternoon-eve. A piece of central Canada high pressure
will break off drop S and settle over the region tonight.
Today: overall p/cloudy and breezy with patches of middle-level altocu
drifting through and/or developing with daytime heating. Highs will
be a little warmer than normal.
Sustained winds and gusts were increased above MOS with deep
mixing. Also used the mix-down tool to lower dewpoints this afternoon.
Tonight: diurnal altocu dissipate leaving clear skies. Good
radiating. The usual cold spots in the North Loup River Valley will
drop into the middle 20s...and possibly into the lower 20s.
Long term...(wednesday through monday)
issued at 403 am CDT Tuesday Apr 21 2015
The upper level low pressure system over Southern California and
visible in water vapor imagery this morning will become the focus
for shower and thunderstorm activity across the local area
beginning Thursday...with unsettled weather forecast to continue
for several days before a ridge of high pressure builds across the
intermountain west early next week...eventually bringing warmer
and drier air to the region. With plenty of divergence in long
term models...uncertainty in timing and overall rainfall chances
is fairly high...but most areas should at least see some shower
activity later this week.
While Wednesday is expected to start off on the cool side as an
area of surface high pressure will be centered across the local
area...expect southerly flow on the backside of this system to
begin to advect moisture northward late in the day as this high
shifts to the southeast. That said...with fairly light winds
forecast...even below normal temperatures Wednesday afternoon
should feel fairly nice.
As the moisture pool deepens across the local area late
Wednesday/Thursday...expect the aforementioned upper level low to
begin to spread its influence across the local area by
Thursday...resulting in increasing chances for shower activity
across the local area. While the instability is fairly low...on
the order of only a couple hundred joules of cape and mainly
limited south of Interstate 80...could see some isolated
thunderstorms develop as well...but severe storms are not
anticipated given the underlying airmass. Otherwise...cloudy and
occasionally showery conditions can be expected for Friday as
models are in fair agreement tracking this upper level low across
Kansas Friday afternoon/evening.
Thereafter...the flow will remain a bit messy as yet another
disturbance in the southern branch of the jet stream may impact
the local area later in the weekend before high pressure
eventually builds across the intermountain west. Given the
uncertainty in this solution...did not alter blended model
solutions significantly and kept thunderstorms out of the forecast
as instability is very minimal. Depending on how far east the
upper level ridge advances early next week will have a significant
impact on temperatures...with the ec not nearly as aggressive taking this
ridge into the plains...but presently have lower to middle 70s
forecast to start the new work week per model blends...which would
be about 5-10 degrees above seasonal norms for late April. That
said...the ec is much cooler...keeping afternoon temperatures near
or below climatology for the next 7 days.
Aviation...(for the 18z kgri/kear tafs through 18z Wednesday afternoon)
issued at 1122 am CDT Tuesday Apr 21 2015
VFR conditions are forecast through the taf period. An area of low
pressure will drag a cold front across the forecast area this
afternoon allowing for wind gusts to increase to the low to middle
20s. Winds are expected to taper off after sunset and will become
more northeasterly. An are of middle clouds over South Dakota is working its
way into NE and will bring few to scattered skies to the taf sites later