Severe Thunderstorm Warning 151, NWS Hastings, NE

AREA FORECAST DISCUSSION
National Weather Service Hastings NE
625 PM CDT Wed Jul 29 2020

...Aviation Update...

.SHORT TERM...(This evening through Thursday)
Issued at 225 PM CDT Wed Jul 29 2020

Primary concern for the short term includes ongoing tstms and hydro
issues in the southeast CWA along with possible MCS moving across
the west/southwest tonight.

Current water vapor imagery and upper air data showing large upper
low located over southern Hudson Bay with trough extending into the
northeastern CONUS. Ridging continues across the western half of the
country although an upper low has pushed through the ridge and was
centered just west of the MT/WY/SD border. A lead wave sliding
eastward has resulted in heavy rain producing tstms today across the
eastern half of our CWA.  At the surface, a stationary front
stretched across the SD/NE border to a sfc low in the NE panhandle.
A lee trough stretched south of the low along the front range. Good
low level moisture return the past 24 hours as dewpoints have
climbed into the upper 60s to lower 70s across the entire CWA. The
eastern half of the CWA has remained mainly cloudy while clearing to
the west will help destabilize things as the day wears on.

As noted above, expect an MCS to move in from the west this evening.
CAMS models have been fairly consistent with this from run to run.
Looks like it should move into the western CWA about 00Z, affecting
the west and SW CWA. Deep layer shear and instability parameters
look sufficient for severe potential with damaging winds the primary
threat but cannot rule out some large hail as well. 0-1 km shear is
progged to be fairly weak so do not anticipate a tornado threat. An
additional round of tstms are possible across the west overnight as
models have more storms moving in around midnight or a little
earlier.

Precip threat doesn't end with this as we will remain under cyclonic
flow with the broad upper low to our NW working slowly across the
Plains Wed night and Thursday. Tstms will be scattered in nature and
do not expect much in the way of severe on Thursday but precipitable
water values remain fairly high and could have hydro issues based on
how much rain falls today and tonight.

.LONG TERM...(Thursday night through Wednesday)
Issued at 225 PM CDT Wed Jul 29 2020

The precip is expected to come to an end starting Thu night into the
day on Friday as the upper low noted above dives south across the
region as an open wave. Latest operation models in decent agreement
showing the 500mb trough axis stretching east/west across central KS
by 00Z Friday. Light precip may linger overnight Thu as this feature
continues to drop south and by Friday I expect mainly a dry day.

The ridge over the Rockies is then progged to reestablish itself
placing us between this high amplitude ridge to our west and
troughing east. For the most part still expect dry weather the
majority of the extended period although as has been noted the past
few days, not out of the question for a wave or two to drop down the
backside of the trough and clip us.

With the ridge a little ways to the west, we won't see the hot
temps usually noted in July/Aug. Expecting upper 70s to mid 80s
which is actually a few degrees below average for this time of
year.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday)
Issued at 624 PM CDT Wed Jul 29 2020

Fairly high confidence in VFR ceiling/visibility through the
majority of the first 6-10 hours, but beyond that, confidence is
at least medium-high in several hours of MVFR/IFR ceiling and
perhaps MVFR visibility (especially centered in the 10-17Z time
frame). As for rainfall/thunderstorm chances, normally dislike
blanketing an ENTIRE TAF period with a generic "vicinity
thunderstorm" (VCTS) mention, but this just seems to be one of
those rare cases where it is justified. Overall though, the "best"
chance for steadier rain/possible storms appears to favor the
mid-morning through mid- afternoon on Thursday. The reason for
the persistent VCTS mention is that at least isolated activity
looks possible at almost any time, especially this evening and
then again during the day Thursday. Will obviously adjust/amend
with TEMPO/prevailing groups as needed. Not anticipating any
severe storms at the terminals, but brief heavy rain, gusty winds
and small hail cannot be ruled out. As for winds (and not
accounting for any thunderstorm outflow effects), not expecting
big issues, as prevailing speeds should largely hold under 12KT,
with direction transitioning from easterly this evening to
northerly on Thursday.

&&

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

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

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