Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 180858

Area Forecast Discussion
National Weather Service Hastings NE
358 AM CDT Sat Aug 18 2018

.SHORT TERM...(Today through Sunday night)
Issued at 345 AM CDT Sat Aug 18 2018

Primary focus is on approaching mid level wave and chance for
heavy rain starting later tonight and continuing into mid day

Current water vapor imagery from GOES-16 shows this wave moving
from Pacific NW across Idaho over the past 12 hours. 00Z height
falls ahead of the wave not overly impressive at 500 mb. Meanwhile
at the surface, high pressure remains over the region with a weak
pressure gradient resulting in light winds. Earlier convection
over Colorado has weakened in the past 6 hours, as noted by
warming cloud tops on the IR imagery, as the complex moved east
into KS. The only affect for us has been some high clouds moving
through. Dewpoints remain fairly high at this time with most
locations only a few degrees below the temperature. This combined
with the light winds means patchy fog possible the rest of the
overnight and an hour or two past sunrise. Based on current
observations, this chance looks better in the eastern part of the
CWA but visibilities have dropped for brief periods of time across
several locations so will keep patchy fog going everywhere.

With short wave ridging continuing today, expecting it to remain
dry and seasonable. That changes tonight with approaching wave
noted above. Models in fair agreement closing this wave off with
the low projected to be in northeast WY by 00Z tonight, and then
somewhere near our CWA by Sunday evening, finally exiting the area
during the daytime on Monday. Synoptic forcing looks pretty good
for this time of year as noted in the omega values as seen on a
time/height section over the central part of our CWA. As far as
the timing goes, most of the precip should hold off until after
sunset tonight as it moves in from the west. It will then
overspread the area overnight, with rain continuing off and on
Sunday and Sunday night. This is a slow moving system which should
result in decent rain amounts for much of the area. Precipitable
water values average around an inch for this time of year and it
appears we will be closer to 1.5 inches on Sunday. This combined
with the slow speed of the system, and the fact that we can expect
thunderstorms as well, means some locations may get more rain than
they might want. Will need to keep an eye on potential flooding
issues through Sunday night. The severe threat does not look as
high however. MUCAPE values not progged to be all that impressive
on Sunday and neither is the deep layer shear.

.LONG TERM...(Monday through Friday)
Issued at 345 AM CDT Sat Aug 18 2018

System noted above finally pushes to our east on Monday. Could
see wrap around showers during the daytime but these will end
west to east. Should quiet down Mon night and Tuesday as ridging
again dominates, before another weak wave slides through late Tue
night into Wed. Yet another small chance for tstms exists on
Thursday night, but not expecting widespread storms with any of
the mid week systems.

Regarding temperatures, today will once again be near normal for
this time of year which means the mid 80s. Much cooler Sunday and
Monday with plenty of cloud cover and rain. Mid/upper 70s for most
locations. A gradual warmup slated for the rest of the work week
with high temps once again near normal by Friday.


.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Sunday)
Issued at 1207 AM CDT Sat Aug 18 2018

Expect VFR conditions for most of the forecast period although
could see MVFR for a few hours this morning with patchy fog
forming as winds will stay light overnight with surface high
pressure over the region. Also, current dewpoint depressions
between 1 and 3 degrees over the area so could see a repeat of
past few nights. A few high clouds have drifted in from the
convection off to the southwest and this may hamper fog formation
a bit. Otherwise there may be a few thunderstorms rolling in from
the west towards the end of the forecast period but looks like
these may hold off until after 06Z.




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