489
FXUS63 KGID 201811
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
111 PM CDT Sun Aug 20 2017

.SHORT TERM...(Today and tonight)
Issued at 456 AM CDT Sun Aug 20 2017

Biggest issues include what POPs do we have for tonight, and what
are our chances of severe weather, along with fog potential.

The last of the nocturnal storms are in the far eastern CWA this
morning and moving out soon. Although clearing is occurring in the
wake, a surface boundary will be draped across the CWA and will be
a focus of potential convection later on toward evening. We will
have considerable moisture pooling near the front with dewpoints
near 70 or in the lower 70s by late afternoon near the boundary.
I expect 3000+ J/kg for instability, but bulk shear should remain
generally below 30 kts, with possibly smaller scale effective
shear that will be greater. The lack of shear will lead me to
believe that this is more of a marginally severe situation, with
hail to quarters and wind gusts to 60 mph. However, if we get
storms popping early enough, hail could very well be bigger. There
is a great divide among models as far as our chances of precip go
tonight, with the MET guidance leaving us dry compared to a
likely POP advertised by MAV at GRI. We will not have quite the
same scenario as we did this past overnight, so our shot at rain
is not as much of a sure thing. It also appears that we won`t
quite get the support from the 850 mb jet as we did this past
night either. Overall, however, I do want to go higher than just a
slight chance of precip. Most activity will probably not fire
until about 5 to 7 pm or so, as the cap breaks late in the
afternoon/early evening.

SREF ensembles indicate a fairly high likelihood of some fog just
north of the stationary boundary toward our northern CWA late
tonight and I will include this in the forecast, as it appears to
be a reasonable conclusion.

.LONG TERM...(Monday through Saturday)
Issued at 405 AM CDT Sun Aug 20 2017

There seems to be increasing potential for fog Monday morning.
The SREF shows around 50% chance for visibilities less than 1
mile, mainly north of I-80. As such, we went ahead and included
patchy fog along and north of I-80 until 9AM Monday.

After this fog clears out, attention shifts to a compact upper-
level wave moving into the area from the southwest. This will
serve to increase cloud cover during the afternoon. This wave is
expected to phase with a northern stream trough and push a front
through the area which will bring us a chance for thunderstorms
during the later afternoon, evening and overnight. There is a
marginal risk for some of these storms to be severe, but the NAM
only shows around 1500 J/kg of MUCAPE and pretty limited shear,
so I think the better chances will be to our east.

See the "Eclipse Day" section below for more specific details on
the weather impacts for eclipse day.

After storms clear the area Tuesday morning, we are looking at a
dry and cooler stretch that should last through Thursday. High
temperatures should only reach the upper 70s to mid 80s each day.

Slight chances for rain and storms return Friday, with better
chances arriving Saturday and Sunday as multiple upper-level
shortwaves move through the region.

.Eclipse Day...

Rain & Storms:
The threat for rain and storms during the eclipse is low.
Overnight storms are expected to exit the area well before the
eclipse. There is a slight chance for storms to redevelop during
the afternoon, but they are expected to hold off until at least
after totality and probably until after 4PM for most of the area.

Clouds:
Cloud cover will be the biggest issue for the eclipse. Fog and
low clouds will clear out by mid-morning, but models have
continued to increase the cloud cover across the area from around
midday onward. The GFS still keeps the best mid-level saturation
and clouds just south of the path of totality, but high clouds may
be abundant. In a lot of ways, the NAM is even more pessimistic
as it stalls the warm front very near I-80 and has more saturation
and cloud cover in the mid-levels.

There will still be opportunities for breaks in the clouds, so
the our forecast still calls for partly cloudy skies for most of
the area at 1PM. All hope isn`t lost, but, to be completely
honest, I`m becoming concerned about the prospects of seeing a
cloud-free eclipse in central Nebraska.

Temperatures & Winds:
Temperatures will be in the mid 70s to mid 80s at eclipse time
and winds will be southwesterly at 10 to 20 MPH.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Monday)
Issued at 108 PM CDT Sun Aug 20 2017

We have some vicinity thunderstorms in the forecast for this
evening, but chances are fairly low for any given spot. We will
update should storms develop and become more of a threat. Will
need to watch out for some strong low level wind shear again late
this evening through early Monday morning. There could also be
some patchy fog around the area that could briefly impact
visibility for a few hours around sunrise, but too low of
confidence to include fog in the TAF at this point in time.

&&

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

$$

SHORT TERM...Heinlein
LONG TERM...Mangels
AVIATION...Wesely