Severe Thunderstorm Warning 190, NWS Hastings, NE

Area Forecast Discussion
National Weather Service Hastings NE
354 PM CDT FRI JUN 3 2016

.SHORT TERM...(This evening through Saturday night)
Issued at 355 PM CDT Fri Jun 3 2016

The main focus of these next 36 hours comes right away late this
afternoon/evening, as we deal with a conditional (meaning not
"for sure") risk of strong to severe storms along/near an
advancing cold front, primarily within the southeast half of the
CWA. Otherwise, confidence remains high pretty high in dry/storm-
free conditions from late tonight through Saturday (and beyond),
with the main story Saturday being breezy-to-windy northwest
winds.

As for the here-and-now as of 20z/3 PM, the radar scope remains
quite for at least a short time longer. In the mid-upper levels,
water vapor satellite and short term model data highlight a broad
shortwave trough sinking southeast through primarily the
Dakotas/MN, but starting to impinge on NE as well. Meanwhile, a
large-scale ridge dominates the western CONUS, while a slow-moving
closed low lurks well to our south over TX. At the surface, the
obvious player is a seasonably well-defined cold front roughly
bisecting the CWA from southwest-to-northeast, marking a
transition from gusty south-southwest winds ahead of it, to gusty
north-northwest winds behind it. Under generally partly cloudy
skies, temps this afternoon are on track to top out in the 81-86
range most places. Mesoscale analysis indicates anywhere from 1000
to perhaps 2000 J/kg mixed-layer CAPE centered above and extending
slightly behind the aforementioned frontal zone, but with fairly
modest deep-layer shear of only around 30kt.

Now looking ahead forecast-wise through these next three night/day
forecast periods:

Late this afternoon-tonight:
Again, the million dollar question is whether or not severe storms
are able to develop along/near the cold front. Agree with the
latest SPC Day 1 severe outlook in keeping a Marginal to Slight
Risk going for mainly the southeast half of the CWA, but want to
also make it clear that a few severe storms can also not be ruled
out to the south-southwest of the official Marginal Risk area if
things do happen to pop near the front (including our southern
zones in KS). We are just now starting to see a few storms start
to back-build down the front across northeast NE, and various
models suggest that the potential for at least isolated, if not a
broken line of storms, will develop over the next few hours into
our CWA as well. Very roughly, initial development would tend to
favor areas within 20 miles either side of an Alma-Hastings-
Osceola line, although at least spotty post-surface frontal
activity could also spring up north of this axis as well. If/when
storms form, they should track generally southeast at 10-15 MPH.
The environment is favorable for large hail up to around ping pong
ball size, and given the solid 25+ degree surface temp/dewpoint
depressions, severe wind gusts are fair game as well, especially
if storms do congeal into some sort of linear complex. By early
evening (roughly 00z/7 PM), the vast majority of thunderstorms
should be southeast of a Phillipsburg-Hastings-Osceola line,
although at least spotty light showers/sprinkles could linger
northwest of that line for a few more hours. Technically, have
slight storm chances (POPs) persisting through midnight in the far
southeastern CWA, but in reality, even these areas will probably
be storm-free a few hours earlier than this as forcing associated
with the aforementioned upper wave shifts off to our east-
southeast. Otherwise tonight, generally 5-10 MPH northwest breezes
will prevail, with low temps mid-upper 50s most areas.

Saturday/Saturday night:
Although a few rogue afternoon showers/weak storms could possibly
brush parts of eastern NE during the afternoon, confidence is
pretty high that this activity would remain at least a few
counties east of our CWA. As a result, a dry and mostly sunny day
is anticipated. However, it will not be the "nicest" of days, as
seasonably-deep mixing on the backside of the departing upper
trough will promote quite breezy (some would say windy)
conditions, with northwest winds averaging at least 15-20 MPH most
of the day and gusting to around 30 MPH. Although temps are
expected to be slightly cooler than today, it will still be warm
with highs aimed into the 79-81 range most places. On Saturday
night, continued dry conditions as the western CONUS upper ridge
starts to edge eastward more over the Central Plains. The enhanced
winds of the day should ease down to no more than 5-10 MPH
overnight, with low temps a bit cooler than tonight in the low-mid
50s.

.LONG TERM...(Sunday through Friday)
Issued at 355 PM CDT Fri Jun 3 2016

Overview of this 6-day period:
At least for now (key phrase "for now"), the one and only
official slight chance of showers/thunderstorms through this
entire 6-day period is on Wednesday night. Because of this,
confidence remains pretty high that the vast majority of the long
term remains dry and somewhat "summery", with highs on almost each
day aimed somewhere into the 80s. Although not yet set in stone,
the outright-warmest days/nights are currently slated to arrive
late next week, with highs on both Thursday-Friday possibly
flirting with 90 and overnight lows holding well up into the 60s.
That being said, the latest ECMWF run suggests that these solidly
above-average highs for late next week may not necessarily be a
sure thing (especially for Friday). As also already hinted, there
are also at least a few forecast periods (other than Wed night)
that may eventually require the introduction of at least slight
POPs, including as early as Monday night (per the GFS) and maybe
next Thursday/Friday (mainly per the ECMWF). However, confidence
is just too low at this range to justify precip chances for
anything other than Wed night.

Briefly glancing through these days in a bit more detail:

Sunday/Sunday night:
High confidence in dry conditions with upper ridging the dominant
influence. Compared to Saturday, not as windy with northerly
breezes generally only 10-15 MPH. Highs temps low 80s.

Monday/Monday night:
A dry forecast continues, but models agree on a shortwave trough
dropping southward slightly to our east, with at least one model
(GFS) suggesting limited potential for rain in our southern zones
Monday night. Something to watch. High temps low-mid 80s.

Tuesday/Tuesday night:
Breezes flip around to southerly behind a departing surface ridge.
Some weak energy may start to under-cut the ridge and at least
affect the Central Rockies/High Plains, but most of this activity
should remain to our west and the dry forecast persists.

Wednesday/Wednesday night:
The aforementioned weak/low-amplitude Central Rockies wave shows
hints of moving east into/near the local area, and there are
enough hints of convection Wednesday night to justify slight
chances area-wide for now, with plenty of adjustments likely
between now and then.

Thursday-Friday:
Dry forecast persists (at least for now) as the flow aloft becomes
extremely weak (by early June standards) as the large-scale upper
level pattern is dominated by a ridge, thus in theory resulting in
a warm-up into the upper 80s/near 90. However, the presence of
weak low pressure lurking within the large-scale ridge brings the
currently-dry forecast at least slightly into question. Plenty of
time to tweak this Day 6-7 period as it gets closer.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Saturday afternoon)
Issued at 1241 PM CDT Fri Jun 3 2016

Overview:
Confidence is actually pretty high in VFR ceiling/visibility
through the period, with only varying levels of mid-high cloud
cover. The main issues involve whether or not especially KGRI
could see a brief thunderstorm this afternoon, and also wind
direction/speed changes associated with a passing cold front.
More details follow...

Precipitation/thunderstorm potential:
At least isolated thunderstorm development is expected along a
passing cold front. As it currently appears, KEAR should be far
enough northwest to miss out on this activity, but it could be a
closer call at KGRI and have introduced a generic "vicinity
thunderstorm" (VCTS) group from 20-22z to account for this.

Winds:
Right away this afternoon, a transition from gusty southerly to
somewhat lighter, more westerly winds will be underway as a pre-
frontal trough moves in. By later this afternoon, winds will be
more established from a northwest direction with speeds generally
around 12kt before becoming lighter overnight. However, a
noticeable increase in northwesterly speeds will occur by mid-late
Saturday morning with gust potential to at least 25kt by the end
of the period.

&&

.GID Watches/Warnings/Advisories...
NE...None.
KS...None.
&&

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

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