Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 190621
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
121 AM CDT MON SEP 19 2016

.SHORT TERM...(This evening through Tuesday night)
Issued at 410 PM CDT Sun Sep 18 2016

Instead of our more "traditional" short term discussion time frame
that focuses only on the first 24-36 hours, decided to extend
this one out to include the entire first 72 hours given that we
have a fairly "clean break" between a dry weather regime early in
the week and a wetter/more unsettled pattern mid-week into this
weekend (as covered in the long term section below).

So, getting on with the short term weather situation through
Tuesday night, the bottom line is that the vast majority of this
time frame will almost undoubtedly be dry for the vast majority
of the CWA, and in fact the official forecast has kept all
precipitation chances/PoPs below mentionable (15 percent or
higher) thresholds. As a result, the number one story these next
few days will be a continuation of our sudden return to noticeably
warmer, more summer-like temperatures with highs both Monday-
Tuesday well into the 80s and even some low-90s especially in
southern zones. Will state that one possible (key word "possible")
caveat to our very "quiet" short-term forecast is at least an
outside shot of some light fog tonight mainly near our far eastern
edges, and then possibly a chance for somewhat more
widespread/noticeable fog on Monday night/early Tuesday morning.
However, with confidence in occurrence currently on the low side
both nights and with the Monday night setup still about 36 hours
away, opted to keep any formal fog mention out of the official
forecast for now.

Taking a look at the current scene as of 20z/3PM, other than
maybe south-southwesterly winds gusts being a touch higher at
times than indicated in the original early-AM forecast issuance
(with gusts up to around 25 MPH at times mainly in the northeast
half of the CWA), things have been very much as expected with
widespread sunshine and high temps solidly into at least the low-
mid 80s all areas, and likely some upper 80s in our far
western/southwest fringes. In the mid-upper levels, water vapor
satellite imagery and short term model data clearly reveal rising
heights/ridging building in aloft in the wake of the disturbance
that brought rain/storms to mainly southwest zones last evening,
which has now departed well southeast into the southeast CONUS. In
its wake, broad west-northwest flow has overtaken the Central
Plains, as we lie well south of the primary west-east upper level
jet segment stretched near the Canadian border. At the surface,
the modestly-breezy south-southwest winds this afternoon are being
focused between departing high pressure to the east, and ahead of
a north-south oriented trough axis extending well-southward into
the Central Plains from a fairly strong surface low centered over
Manitoba. This trough axis is generally separating predominantly
southerly breezes with dewpoints in the 50s/60s over our CWA from
more westerly winds with drier dewpoints only in the 30s/40s over
western Nebraska.

Finally getting to some fairly brief daily/nightly details through
Tuesday night:

This evening/tonight:
First off, despite some instability noted in our far eastern zones
late this afternoon/early evening, lack of forcing (as evidenced
by rising mid level heights) and lack of low-level convergence
will keep any possible convection at bay. In response to the
aforementioned low pressure well to our north shifting eastward,
the aforementioned surface trough currently draped just to our
west will gradually shift east across the CWA overnight, allowing
generally 5-10 MPH breezes to turn more westerly with time. As
earlier mentioned, some models hint at light fog near our far
eastern border late tonight, but the increasingly-westerly wind
direction should largely prove detrimental to this. As for low
temps, if anything nudged down very slightly, as despite warmer
air moving in, temps have seemed to fall at least a few degrees
cooler than expected these past few nights. Thus am aiming for
mid-upper 50s most areas, but low 50s far north and low 60s far
southeast.

Monday/Monday night:
Confidence in our going dry forecast remains rather high as we
remain in quasi-zonal flow aloft, well to the south of the strong
upper jet near the Canada border, and with much more influence
from a broad southern CONUS ridge. That being said, a weak cold
front will sink southward into the CWA on Monday before largely
washing out/retreating on Monday night. This front will result in
winds turning more northerly and eventually easterly in most of
the CWA during the day, but with speeds only 5-15 MPH. Not a lot
of cool air behind the boundary by any means, but its presence
will set up a modest north-south gradient in high temps, ranging
from mid-upper 80s in most Neb zones, to low 90s near/south of the
state line. As covered, light east-southeast breezes Monday night
could prove conducive to at least "some" fog development and this
will need watched. Low temps aimed very similar to those of
tonight.

Tuesday/Tuesday night:
The flow aloft starts transitioning more southwesterly with time,
as the first mid level shortwave trough of the week makes its way
toward the Central Plains from the southwest. While confidence
remains high in a dry/very warm day, the dry forecast for Tuesday
night may not necessarily be "guaranteed", as there are at least
subtle hints of a few warm air advection showers/weak storms in a
few models, and this will need watched as it gets closer.
Otherwise, for most of the CWA, this will likely be the
warmest/hottest day of the week, and if anything slightly nudged
highs upward, with most of the CWA topping out 89-93 in the
presence of steady southerly breezes gusting 20+ MPH. With steady
south winds continuing into the night, Tuesday night (calendar day
of the 21st) has the potential to feature near-record warm low
temperatures around 70 degrees in much of the CWA.

.LONG TERM...(Wednesday daytime through Sunday)
Issued at 410 PM CDT Sun Sep 18 2016

Although this 5-day period features the vast majority of more
"interesting" weather contained in the current 7-day forecast,
mainly centered around at least two (possibly more) halfway decent
chances for showers/thunderstorms, these days are obviously also
farther out in time and thus naturally carry a lower degree of
confidence in the details compared to the short term periods
described above. As a result, will be sticking more to the basics
here.

Very general overview:
We will gradually transition from our dry/above normal
temperature regime of these next few days to a more unsettled and
likely slightly below normal temperature regime by the weekend.
There are basically two distinct windows of opportunity for
showers/storms...one focused on Wednesday afternoon/night as a
leading shortwave trough ejects well out ahead of the main trough
setting up over the western CONUS, and then late in the week/into
the weekend as the main, potentially rather deep and highly-
amplified upper level system slowly tracks eastward into the
central CONUS from the west. The potential is certainly there for
a few decent rounds of rainfall during this time frame, and
possibly even some strong/severe storms given increasing, albeit
largely unidirectional deep-layer shear. That being said, very
early indications of instability parameters from the ECMWF/GFS
suggest that there is not yet an "obvious" severe storm event
lurking in this time frame, and thus we will have to keep a close
eye on this time frame as it nears in case one eventually
materializes. Will now take a rather quick look at day-to-day
trends:

Wednesday/Wednesday night:
This 24 hours sees the invasion/passage of the aforementioned lead
wave, which progressively tracks through from southwest-to-
northeast. Ahead of the wave, southerly breezes will persist and
unless clouds are more abundant than expected, another warm day
with highs well into the mid-upper 80s is expected. Then, compared
to earlier runs, the latest 12z ECMWF/GFS runs are more aggressive
in breaking out potentially widespread convection during the
afternoon/evening along/ahead of a surface trough and cold front.
PoPs were increased 10-20 percent in most areas, but am not yet
willing to go "likely" 60+ percent values this far out.

Thursday/Thursday night:
At least in the mid-upper levels, the CWA seems to be in a bit of
a break/lull in between disturbances during this time. However,
with low level jet forcing in play, cannot rule out
at least some showers/storms especially Thursday night.

Friday-Sunday:
With many fine details yet to sort out, the main story of this
3-day time frame is that an expansive, slow-moving upper level
trough is progged to very slowly track out of the western into the
central CONUS, and thus modest (but still less than "likely") PoPs
are advertised in nearly every period. Unless timing slows as it
sometimes does with these sort of systems, the majority of
rain/storm potential should focus between Friday night-Saturday
night, during which time some areas could see some decent rain. As
this gets closer, look for PoPs to go up considerably as
confidence in timing increases. Very preliminarily, Sunday
daytime has been introduced to the forecast as dry, but this is
"out the window" if system timing slows hardly at all, so please
don`t count on it remaining that way. Although probably not quite
as warm as earlier in the week, highs on Thursday-Friday are still
expected to reach the 80s before cooler highs in the 70s arrive
over the weekend.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Monday night)
Issued at 116 AM CDT Mon Sep 19 2016

VFR conditions are expected to continue through the TAF valid
period. Skies will be clear to mostly clear. We will see a trough
axis pass through that will turn the winds gradually from
southwest early this morning, to northerly by around lunch, and
then easterly by this evening. There will be some marginal low
level wind shear around this morning.

&&

.GID Watches/Warnings/Advisories...
NE...None.
KS...None.
&&

$$

SHORT TERM...Pfannkuch
LONG TERM...Pfannkuch
AVIATION...Wesely



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