Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 172149
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
449 PM CDT Thu Aug 17 2017

.SHORT TERM...(This evening through Friday night)
Issued at 449 PM CDT Thu Aug 17 2017

The main focus of these next 24 hours is on the potential for at
least a few strong thunderstorms during the overnight hours into
perhaps mid-morning Friday, but am not really expecting much of a
severe storm or heavy rainfall threat, although it`s hard to
completely rule out a "rogue" severe storm either. Otherwise,
confidence is actually pretty high that the vast majority of the
coverage area (CWA) will be dry through this evening and again
Friday afternoon through Friday night.

Taking a very quick glance at current/recent weather:
Today has turned out very much as expected with plentiful
sunshine, westerly to southerly breezes and high temps mainly mid
80s in Nebraska zones, and near-90 in KS zones. In the mid-upper
levels, we are under west-northwest flow aloft and currently in a
"break" between departing/incoming waves.

This evening/tonight:
While the vast majority (if not all) of the evening hours should
remain dry for the pre-midnight hours, at least small
shower/thunderstorm chances gradually invade the CWA from west-
to-east as the night wears on (mainly post-midnight) as the next
low-amplitude shortwave trough brushes in from the northwest and
interacts with increasing elevated instability/moisture advection
within the axis of a 30-40kt southwesterly low level jet.
Unfortunately, various models (including higher res) vary
considerably on the likelihood/coverage of convection, but have
focuses the highest PoPs (40-50 percent) in north-northeast zones.
All areas stand at least a small chance, however. There is just
enough elevated instability to work with (perhaps up to around
1000 J/kg) that it may be impossible to completely rule out a
marginally severe storm with quarter size hail, but most storms
should remain at least slightly sub-severe and have geared our
local Hazardous Weather Outlook this direction. Brief heavy rain
possible, but would be surprised if more than very isolated areas
saw more than one-half inch. Low temps tonight aimed mainly 60-65.

Friday-Friday night:
Will keep thunderstorm chances going (perhaps a few strong
storms?) for roughly the eastern half of the CWA for the morning
hours as the aforementioned upper wave passes by, but in its wake
and behind a weak surface cold front that will turn breezes
northerly at 10-15 MPH, any precip chances should shut down by the
afternoon hours. Technically, SPC clips our extreme east-southeast
zones with a Marginal Risk of severe, but with the main surface
cold frontal convergence expected to be at least slightly east-
southeast of our local domain by late afternoon/evening, would
tend to expect to see this risk area pulled at least slightly
outside our area on future updates. With plenty of afternoon sun,
behind the departing wave, high temps look very similar to today
with mid-80s north to around 90 south. Friday night looks dry as a
brief period of low amplitude ridging works overhead. Overnight
winds look fairly light/variable, with low temps a touch cooler
than tonight with more in the way of upper 50s north/low 60s
south.

.LONG TERM...(Saturday daytime through Thursday)
Issued at 449 PM CDT Thu Aug 17 2017

General overview of this 6-day period:
Overall we are looking at a relatively consistent weather pattern
featuring near-normal temperatures (mainly within 5 degrees
either side of normal) and various, off-and-on chances for
showers, thunderstorms. At least for now, the only day/night
forecast periods that are void of any mentionable (20+ percent)
precip chances (PoPs) for the entire CWA are Saturday daytime and
Tuesday night, although especially late Saturday afternoon may not
necessarily stay that way.

Temperatures:
Each day looks to feature highs somewhere in the 80s in Nebraska
zones, with more in the way of upper 80s to mid-90s in KS zones.
However, a gradual cooling trend is evident with time, with the
first 3 days (Sat-Mon) a little on the warmer side than Tues-
Thurs. Overnight lows look to be mainly 60s.

Precipitation/thunderstorm chances and general overview of upper
air pattern:
At least through Tuesday, both the GFS/ECMWF are in pretty decent
agreement on a quasi-zonal flow pattern with various, mainly low
amplitude disturbances working through. For the final few days of
the forecast next week, models diverge with the ECMWF indicating
more of a northwesterly flow regime on the interface between a
western ridge/eastern trough, while the GFS hangs more onto quasi-
zonal. In either case, the forecast remains littered with various,
mainly fairly low-confidence shower/thunderstorm chances. Overall
though, the evening/overnight hours of Saturday evening through
early Tuesday morning feature the overall-highest chances, due in
part to the current timing of passing waves, and also the enhanced
effects of the nocturnal low level jet on encouraging the greatest
storm coverage overnight. There is enough instability present
through most of this time that could foresee at least 2-3 days
being placed in a Marginal Risk type setup from SPC as they get
closer, but for now the only "official" severe risk from them is
for our western zones for Saturday evening, which seems reasonable
from our local perspective as well. The potential for additional
severe storm chances will be assessed further with time.

.ECLIPSE...

A total solar eclipse will occur Monday, Aug. 21st around 1 PM
CDT.

Before getting into this, want to make sure anyone reading this
acknowledges a "reality check" that this event is still 4 days
away and we are not overly-confident on the finer details. With
each passing day this confidence will increase, especially over
the weekend as Monday comes into the time range of various
shorter-term, higher resolution computer models. That being
said...

Precipitation/thunderstorm chances:
As it currently stands, a consensus of two of our primary longer
range models (ECMWF/GFS) suggest that the majority of our coverage
area (CWA) should be dry during the daytime hours, likely in a
"break" between somewhat better chances for showers/thunderstorms
both Sunday night and Monday night. This is obviously good news
for most folks, but it`s also probably a bit too soon to declare
it "guaranteed dry".

Sky cover/clouds:
Despite the overall lack of rain chances, this type of west-
southwest flow aloft pattern, along with the presence of both a
departing and incoming mid level disturbance that are relatively
close in time and space, will likely make a "highly confident"
cloud forecast rather dicey for a few more days yet. As best we
can tell for now, "partly cloudy" is the most likely scenario for
most of our area, as we surely cannot make a declaration yet of
"pristine sun" or, conversely "plentiful clouds". If anything
though, any clouds appear to be mainly of the higher/thinner
variety, which is better news than lower overcast stratus. Stay
tuned...

Temps/winds:
In other departments, it still looks to be seasonably warm day
with afternoon highs mainly upper 80s Nebraska and low-mid 90s KS.
It does look to be a touch breezy from the south, with sustained
speeds at least 10-15 MPH and some gust potential to 20+ MPH.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Friday)
Issued at 102 PM CDT Thu Aug 17 2017

General overview:
VFR ceiling/visibility expected to prevail, with a low probability
of a passing shower/thunderstorm late tonight/early Friday
morning. Low level wind shear (LLWS) looks to also become an issue
late tonight/early Friday. Read on for more specifics...

Ceiling/visibility/rain potential:
Confidence is high in VFR conditions with about the only possible
caveat being a brief visibility reduction if a passing
shower/thunderstorm happens to move over. Confidence is not
overly-high regarding shower/thunderstorm potential tonight but
felt it was at least worth a generic "vicinity" (VCTS) mention
from mainly 07-12Z. Not anticipating severe storms, but small
hail/gusty winds probably not out of the question.

Winds/LLWS:
Surface winds should not be a big issue, with prevailing speeds
largely under 12kt, although directional changes will occur from
westerly this afternoon, to southerly overnight, to northwesterly
behind a passing cold front late in the period. At least marginal
LLWS is a concern mainly 07-12Z as the low level jet increases,
setting up 30+ kt of shear between the surface and mainly 1,000
ft AGL as winds at that level accelerate to 40-45kt.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&

$$

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


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