Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 171153
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
653 AM CDT Thu May 17 2018

.SHORT TERM...(Today and tonight)
Issued at 404 AM CDT Thu May 17 2018

Upper level trough shifts east today across the Great Basin toward
the western slope. This will take the shortwave ridge over our area
today, which will help keep us dry during the day, and shift this
east, putting us within southwest flow tonight, opening us up to
perturbations being kicked out of the base of the trough.

Ongoing convection that was to the north of the CWA overnight is
seeping into the far northern CWA. Isentropic features are a factor
in the production of these thundershowers, with enough CIN to limit
the vertical extent of these small convective cells. However, 450-
550 J/kg of MUCAPE may aid to keep convection going, although
vertical growth is weak. PWAT sits at about 0.9 inches, so the tiny
areas where it might rain might get quite the local downpour. I may
throw in a 20 percent POP in our far north/northeast to account for
this possibility through this morning.

Thunderstorms will probably erupt in the lee of the Rockies along a
distinct theta-e ridge as there will be considerable height falls in
response to the approaching mean trough. Increasing low-level
moisture and strengthening low-mid level lapse rates will also aid in
the spawning of these storm, with enough support for severe storms.
These storms will drift east and will be supported by a reasonably
strong 40-50kt low-level jet over the High Plains. Numerical models
generally point toward at least a good chance of measurable rainfall
tonight for most of the CWA, but it does look like a late show,
mostly after midnight, creeping in from the west.

For high temperatures today, I went with BCConsShort, which places
temps in the mid 80s which is generally near to slightly above what
guidances are giving us. For tonight, Superblend looks acceptable
with lows at or slightly below guidance. If it rains, and there is a
good chance it will, I do not want to be higher than guidance.

Severe weather is not out of the question, especially in our western
CWA, but by the time storms arrive in our area, they will likely be
outflow dominant and will lose at least some of the severe
potential that existed farther west.

.LONG TERM...(Friday through Wednesday)
Issued at 404 AM CDT Thu May 17 2018

Main forecast concern is the potential for strong-severe storms Fri-
Sat along with nearly daily rain chances in the extended.

Friday: Showers/t-storms will likely be ongoing across the area in
the morning. This activity should dissipate by around midday but
could play a role in how the aftn-eve plays out. Current thoughts
are that convection will redevelop W/SW of the area by mid-late
aftn, then shift into W/S portions of CWA in the eve as it grows
upscale and then into the rest of CWA overnight. SPC has maintained
a "Slight" risk for most of CWA in latest Day 2 outlook. MUCAPE 1000-
2500 J/kg (highest SW of Kearney to Smith Center), 0-6km bulk shear
25-30kts, and a srly LLJ of 35-45kts helping to sustain activity
overnight could lead to some large hail and damaging wind gusts. The
highest risk will be over the S/W CWA, closer to highest instability.

Saturday: Could be a bit of a repeat of Fri in that activity will
likely be ongoing in morning, with redevelopment expected in the
aftn along a cold front. Location of this front and any potential
for severe wx will largely depend on how the morning activity plays
out. The SE/E CWA stand the best chc to see some clearing/warming
and combination of weak-mod CAPE and modest shear. As a result,
these areas are in the "Slight" Risk on latest Day 3 outlook from
SPC. Areas that don`t see strong/severe storms will still have
potential for add rain Sat aftn-night, esp. N of the KS/NE state
line. Total QPF for late week/weekend has trended down slightly, but
still expect many areas in NE zones to pick up 1-2" with locally
higher amounts poss. Lighter amnts forecast for KS zones.

Sunday: Any lingering shwrs in the early morning should be limited
to the far NE CWA. Sfc and upper level ridging should provide dry
conditions for the rest of the day. However, it will feel quite
chilly due to CAA on steady N breeze and remnant cld cover. Going
highs (upper 60s to mid 70s) could easily be 5-10 deg too warm if
latest GFS is anywhere close as to how long clds linger.

Next week appears active as yet another upper level trof establishes
itself across the W CONUS on Mon , then deamplifies as it shifts E.
This will once again result in multiple weak waves getting flung
into the central Plains, especially for the middle of next week.
Could start to see some precip chcs creep back into the CWA as early
as Mon as WAA will help lift the front that passes this weekend
return N. This front appears to stall out generally from the central
High Plains to near or over our CWA then ESE to the Mid Miss. River
Valley as it is caught between high pressure over Great Lakes and
lee troughing over the central High Plains. Therefore, at some sort
of precip chances appear poss each day next week.

We`re heading into the climatological peak severe weather season
locally and while severe chances next week certainly are not zero,
nothing particularly widespread/significant stands out at this time.
Model progs indicate seasonably high moisture/instability as Gulf
should be "open", but mid-upper level winds remain rather weak
and/or displaced further W, resulting in rather weak deep layer bulk
shear locally. Obviously, this may change some as we get closer and
any boundaries could locally enhance the shear, but thought it is
prudent to note given the time of year. PWATS in the 125-175% of
normal range and nearly daily chance of convection suggests some
potential for hydro issues for parts of the area, esp. if soils are
primed this weekend. Something to watch as we head into next week.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Friday)
Issued at 648 AM CDT Thu May 17 2018

First concern will be convection just north of terminals that will
be skirting east. Should remain north, but KGRI may be rather
close to a lightning strike or two through 15Z. Next issue will be
storms rolling in near or after 5/6Z. By the time storms make it
in, severe threat should be largely over, although heavy rain is
quite possible. Although most storms should be outflow dominant
late tonight, gusty winds are still possible, especially at KEAR.

&&

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

$$

SHORT TERM...Heinlein
LONG TERM...Thies
AVIATION...Heinlein



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