Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 171806
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
106 PM CDT Mon Jul 17 2017

.UPDATE...
Issued at 437 AM CDT Mon Jul 17 2017

Decided to include a mention for the potential of localized
flooding in the HWO for this afternoon and tonight as any
convection that might develop will be very slow moving, and
combined with a moist environment and a slowly moving instability
axis to focus on, this could spell trouble in at least isolated
areas.

&&

.SHORT TERM...(Today and tonight)
Issued at 349 AM CDT Mon Jul 17 2017

Main challenge will be concerning chances of precipitation and to
what extent of any severe weather we may have a shot at. Also, high
temperatures may be challenging thanks to potential added sky cover
in our west, with a sharp gradient of cloudiness progressing east.

The main potential weather maker will be a closed upper low embedded
within a subtropical ridge. This low is coming out of the central
Rockies and into the western Plains, which could give us a shot at
some showers and thunderstorms, especially in our west. A resultant
surface trough to the west will encourage a bit more wind speed from
the south for Monday. With slightly higher, yet still modest bulk
shear along with modest instability, we may be in store for one or
two pulse-type marginal severe storms in our west/northwest, closer
to the trough. We could very well get a localized cluster of storms
to develop in our western CWA for Monday afternoon, with a strong
cold pool potentially shifting the storms perhaps far enough east to
include the tri-cities and beyond, but the strongest wind
aloft/shear will be well north of the area. Topped POPs out at 40
to 50 percent this afternoon/evening, as there is some agreement
of a localized cluster of storms developing, but timing and
placement are not all that predictable with such a small feature.
If anything, the progression east may not be as fast as some short
term models indicate, considering the trends the past couple of
days. However, I did not want to limit POPs to slight, as there is
decent agreement that initiation of convection will begin near
the CWA this afternoon, and gave my best guess of placement and
timing, as inflow is at least somewhat supportive of maintenance
of convection once it gets going.

Highs could be tricky with additional sky cover in our west, and
could be a tough call on perhaps a healthy temperature gradient.
Looks like the thicker clouds will enter late enough to not be all
that much cooler in our west, but perhaps up to 5 degrees cooler
than the rest of the CWA. Currently going with highs near 90 far
west to mid 90s southeast. Lows tonight will be rather warm with
the muggy conditions, bottoming out mostly near 70 to the mid 70s.

.LONG TERM...(Tuesday through Sunday)
Issued at 349 AM CDT Mon Jul 17 2017

The primary weather threat of the upcoming week will be the heat. It
still appears that Wednesday will be the warmest day, with high
temperatures in  the upper 90s and low 100s across the entire area.
In addition, it is looking like Thursday (and possibly even Friday)
will only be a degree or two cooler than Wednesday for most
locations. Heat index values may approach advisory criteria (105
degrees or higher) on Tuesday, but the best opportunity will be
Wednesday and Thursday. Therefore, we`ve decided to hold off on any
heat headlines for now.

Taking a look at precipitation chances, it looks like today and
Tuesday evening/night will be our best chances for rain/thunderstorms
until at least the upcoming weekend.

Lingering storms should exit the eastern half of the CWA by late
morning Tuesday. By Tuesday evening, a cold front should be located
across northern Nebraska. With increasing convergence along a 850mb
LLJ, I expect scattered storms to develop in this vicinity and
gradually move southward into central and south-central Nebraska.
The NAM shows 2000-3000 J of elevated CAPE and 30 to 40 kts of deep-
layer shear. Therefore, an isolated severe storm or two is certainly
possible.

Wednesday through Friday, the upper level ridge builds moves
overhead, which will severely limit our chances for rain and
thunderstorms in this area. Northern Nebraska, possibly as far south
as Ord, will have off and on thunderstorm chances, but unfortunately
central Nebraska and northern Kansas will likely remain dry.

Friday night into Saturday, a cold front will drop southward into
the area as the upper ridge starts to break down. As this front
stalls in the area, this will bring us multiple opportunities for
rain and thunderstorms, especially across Kansas, through the
weekend and hopefully into early next week.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Tuesday)
Issued at 1240 PM CDT Mon Jul 17 2017

Mainly VFR conditions are expected through the TAF period. The
primary concern is the potential for scattered thunderstorm
development this afternoon through tonight. Have maintained a
VCTS mention beginning at 21Z and expanding in coverage to the
east. Due to the potentially isolated nature of any convection
that does develop, have held off on introducing a TSRA mention
until something appears more likely to directly impact the TAF
site. Any locally heavy rainfall could reduce visibilities and
ceilings to MVFR or lower temporarily.

Winds this afternoon and evening will mainly be out of the south
and could gust up to 20-25kts at times.

Some marginal low level wind shear is also possible overnight with
a strong low level jet in place. Currently only have this included
for KEAR, but will need to be monitored if it looks like this may
need to be expanded eastward to include KGRI.

&&

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

$$

UPDATE...Heinlein
SHORT TERM...Heinlein
LONG TERM...Mangels
AVIATION...Petr



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