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Area forecast discussion 
National Weather Service Hastings NE
540 am CDT Thursday Sep 3 2015

Update...
issued at 540 am CDT Thursday Sep 3 2015

After further consideration and a look at the latest trends in
very short term models such as the rap13/hrrr...have opted to pull
the morning "slight chance of sprinkles" from much of the County Warning Area.
That's not to say that the chance of a rogue sprinkle/light shower
is truly "zero" during the next few hours...especially within the
far southeast County Warning Area in closest proximity to weak northeast Kansas
convection...but have lost confidence enough in the earlier-issued
sprinkle chance that was mainly focused over Central/Northeast
counties. As a result...the entire daytime forecast is now
officially void of any precipitation mention.

Update issued at 449 am CDT Thursday Sep 3 2015

Quick update to mention a couple notes over-looked in the
original morning discussion:

1) although have portions of mainly our Kansas County Warning Area topping out with a
heat index right at 100 this afternoon (5 degrees short of
technical advisory criteria)...have opted to not include this
in the hazardous weather outlook (hwogid) given that it barely
meets the 100-degree mentionable threshold...and more-so that this
heat is "nothing new" or noteworthy to that area given the last
few days.

2) technically...actually have a very small portion of the
southwestern County Warning Area (furnas/Phillips/Rooks area) barely meeting the
meteorological definition of "near-critical" fire danger criteria
this afternoon...which is defined locally as the overlap of 25
percent-or-lower relative humidity and sustained winds/gusts of 15+ miles per hour/20+ miles per hour.
However...will also keep this out of the severe weather potential statement product given that it
only affects an extremely small area...and that there is still
some lingering late-Summer "green-ness" to vegetation despite the
recent dry spell.

&&

Short term...(today and tonight)
issued at 420 am CDT Thursday Sep 3 2015

In many ways...these next 24 hours will likely strongly resemble
the last 24 hours...as another seasonably hot day is in store in
the presence of steady southerly breezes that if anything will
probably average a few miles per hour stronger than yesterday (especially in
the afternoon/evening). However...there are at least a few
differences expected in these upcoming 24 hours than the past 24
hours:

1) although am by no means expecting a widespread coverage of
measurable rain...there is at least "some" large-scale support
for isolated to possibly scattered showers/storms primarily late
tonight...and primarily within the northwest 1/2 of the County Warning Area where
20-30 percent precipitation chances (pops) have been assigned. Prior to
late tonight...certainly cannot say that precipitation chances are truly
"zero"...but have deemed measurable potential to be less than 15
percent...and thus have maintained a forecast void of shower/storm
chances until tonight. That being said...have introduced a "slight
chance of sprinkles" for this morning (non-measurable
expectations) mainly within the Central/Northeast County Warning Area just in case
a few of the recent rap13/hrrr runs are catching onto something
with a few of their latest runs.

2) although still expect most of the day to average no-worse than
partly cloudy...it appears there probably will be a bit more
middle/mainly high cloud cover drifting over than
yesterday...especially during the afternoon. As a result...despite
very similar low-level thermal fields to yesterday...think maximum
temperatures could be held down very slightly.

Taking a look at the here-and-now as of 08z/3am...another
balmy/uneventful night so far...with the only radar echoes even
close to the County Warning Area consisting of a few high based sprinkles near
Gothenburg a few hours ago that have since faded. At least thus
far...the last several runs of the GFS producing showers/storms in
southern zones early this morning has not materialized.
However...well to our east...a smattering of light showers has
sprung up in the southwest Iowa/northwest MO area...within the exit
region of a decent veering 30-40 knot low level jet evident at 850
millibars. In the larger scale of the middle-upper levels...very
similar to 24 hours ago...as fairly weak west-southwest flow aloft
is over the local area...which resides along the northern edges of
a Southern Plains ridge...and well-southwest of a large trough
starting to exert greater influence on the far northwest Continental U.S..
embedded within the weak flow aloft locally...a very weak wave is
evident drifting northeast across western Nebraska...but with warm middle
level temperatures and the terminus of the low level jet aimed well to
the east...this feature is producing little more than a smattering
of middle-high clouds. At the surface...again much the same
story...as a generally north-south trough axis resides over
western Nebraska to the Kansas/Colorado border area. To its east...a modest
pressure gradient is promoting steady 5-10 miles per hour south/southeast
breezes over much of the County Warning Area...with some slightly stronger speeds
in southeast counties with aided mixing from the low level
jet...and a bit lighter/variable regime in far northwest areas
such as Ord...which has predictably dropped all the way down to 62
degrees at last ob. Meanwhile...the majority of the County Warning Area is still
holding onto readings in the low-middle 70s...and the majority of the
area is expected to ultimately realize lows in the 65-70
range...assuming that a decent little drop occurs right around
sunrise as it did yesterday. On a side note...Hastings Airport
needs to drop to at least 70 degrees or a record warm low for Sep.
3rd might come into play (71 in 1980, 1937).

Now looking ahead forecast-wise over these next 24 hours...

Early this morning (through around 7am): will continue to
officially carry a dry forecast cwa-wide...but will need to keep
an eye out for 1) the possibility of a few random weak
sprinkles/light showers popping up almost anywhere...2) the
possibility that a few weak showers popping up over northeast Kansas
could try building back west into our Kansas zones within the low
level jet axis.

Today (through around 7pm): nearly kept the entire County Warning Area void of any
precipitation mention whatsoever...but with at least a few consecutive
rap13/hrrr runs suggesting that some high-based sprinkle activity
could flare up mainly in Central/Northeast counties through middle-
day (including over the Tri-Cities area)..."gave in" and
introduced a baseline "slight chance of sprinkles" to these
areas...just in case any weak elevated Theta-E advection
associated with the weak disturbance passing across central Nebraska
can manage to kick off anything. Would be surprised though if more
than a tiny fraction of the County Warning Area sees anything though.
Meanwhile...in the larger scale today...the very weak wave
currently over the area departs to the northeast while a more
noticeable wave currently over the 4-corners area gradually slides
northeast...reaching the Wyoming/co/neb border area by day's end.
Within this County Warning Area...the only noticeable effect of this disturbance
through nightfall will be somewhat more middle-high cloud cover than
yesterday...as forcing should remain insufficient to pop
legitimate afternoon convection except off to our west closer to
the High Plains surface trough. Speaking of the surface...if
anything the local pressure gradient should be a touch
tighter/stronger today given the approach of the incoming
shortwave disturbance. As a result...expect most of the day
(especially this afternoon) to average at least a touch breezier
than yesterday most places...with the majority of the County Warning Area seeing
several hours of sustained 15-20 miles per hour speeds/gusts to around 25
miles per hour...and Kansas zones more favored to average around 5 miles per hour stronger
than this. Temp-wise...as earlier mentioned...given expectation of
somewhat greater cloud cover...foresee highs being very slightly
"cooler"...and thus basically took yesterday's observed values
and knocked them down 1 degree. This still means a toasty day
ranging from near-90 northeast...middle 90s central and upper 90s to
100 southwest.

This evening/tonight: again...far from a "great" chance of
rain...but there is just enough evidence to support a slight
chance (20 percent) of showers/non-severe storms within the
majority of the County Warning Area...with a 30 percent chance in few northern
counties north of I-80. Although have brought slight chances into
far western counties before midnight...the better chances focus
Post-midnight. Technically though...maintained a precipitation-free
forecast for a few far eastern/southeast counties. In the larger
scale aloft...the obvious instigator is the aforementioned
shortwave disturbance that tracks from the Wyoming/co/neb border area
around sunset...northeastward into western or central South Dakota by
sunrise Friday. Although the track of this wave takes it just
west- northwest of the County Warning Area...and thus in theory keeps the best
rain chances slightly outside the County Warning Area as well...the presence of
another decent low level jet axis setting up directly overhead
during the night could...1) maintain some evening convection off
to our west into the County Warning Area and/or 2) promote new isolated to
scattered showers/storms developing directly over the County Warning Area within
the low level jet axis. Needless to say...the latest 06z NAM is
not as aggressive bringing rain chances into the County Warning Area as the 00z
GFS...and thus have certainly kept probability of precipitation on the low-side. Should
any storms materialize...cannot completely rule out a brief
stronger storm with gusty winds and small hail...but the combo of
weak shear and instability likely averaging well-under 1000 j/kg
should keep any storms from becoming severe. At the surface...with
a continued decent pressure gradient and some limited mixing under
the low level jet...expect breezes to generally remain up in the
10-15 miles per hour range most areas most of the night with some higher
gusts. This should in theory help keep most areas a few degrees
miler on overnight low temperatures...and made little change
here...aiming most of the County Warning Area into the 68-71 range.

Long term...(friday through wednesday)
issued at 420 am CDT Thursday Sep 3 2015

Despite multiple small chances for thunderstorms through the
extended periods...think that the majority of the local area will
stay dry the majority of the time...with multiple weak disturbances
bringing only periodic...mainly small...chances for thunderstorms
through the end of the forecast period.

Overall...temperatures will likely be in focus to start the extended
periods...as continued unseasonably warm September weather is
anticipated across the region in a west southwesterly flow pattern
aloft. Expect the main upper level low across the Pacific northwest
this morning...to eventually swing out of the upper level trough to
our west and into the northern plains late in the weekend.

This upper level low will steer an associated weak cold front across
the Central Plains late Sunday...with temperatures expected to drop
a few degrees and settle closer to climatology by Monday afternoon.
This front could also provide the trigger for a better shot of some
shower/thunderstorm activity Monday afternoon through Tuesday
afternoon as it lifts northward...with the best chances for more
active weather generally existing to the east/southeast of the local
area.

The bigger cool off will have to wait until the middle of next
week...though...when a second cold front...with notably cooler
air...crosses the Central Plains Wednesday morning. As a
result...temperatures are expected to fall below normal by Wednesday
and Thursday of next week...when afternoon temperatures will
struggle to climb out of the 70s across much of the local area. This
cold front and associated upper level fragments of energy...should
also result in additional chances for some shower and thunderstorm
activity...but confidence in coverage and intensity is low at this
time and hence kept overall chances for precipitation close to
blended values given by models for the time being.

&&

Aviation...(for the 12z kgri/kear tafs through 12z Friday morning)
issued at 540 am CDT Thursday Sep 3 2015

High confidence in VFR ceiling/visibility through the
period...with only varying degrees of middle-high cloud cover. There
is an outside chance of a shower/thunderstorm in the general area
of both terminals mainly during the latter 6 hours late
tonight...and have opted to hint at this slim possibility with a
"vicinity thunderstorm" (vcts) mention at this time.

As for low-level wind shear (llws)...the early morning round has
largely wound down/weakened and thus will not be carrying a
formal mention going forward in the 12z tafs. Once again late
tonight there could be another round of low level wind shear...but at this time it
still appears a bit marginal in strength (bulk shear difference
between the surface and roughly 1000 feet is barely 30kt)...and as a
result let later taf issuances address whether it's worthy of
eventual inclusion.

As for surface wind...it will again maintain a southerly
direction throughout the period with sustained speeds largely
below 12kt this morning but then averaging near/above 12kt through
the majority of the afternoon and overnight hours...with gust
potential up to around 22kt at times.

&&

Gid watches/warnings/advisories...
NE...none.
Kansas...none.
&&

$$

Update...pfannkuch
short term...pfannkuch
long term...Rossi
aviation...pfannkuch

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