Area Forecast Discussion
Issued by NWS Hastings, NE

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199
FXUS63 KGID 252304
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
604 PM CDT WED MAY 25 2016

.SHORT TERM...(This evening through Thursday night)
Issued at 418 PM CDT Wed May 25 2016

Unfortunately, due to the overall-complexity of this forecast (at
least slight thunderstorm chances in each and every day/night
period)...this forecaster is running out of time to give this
discussion full "justice" given the Enhanced Risk of severe
weather advertised by SPC for Thursday afternoon/night. Want to
caution though, that despite the potential for an active/dicey
Day 2 period, as always nothing is set in stone and there is still
time for mesoscale details to either lower or increase this
overall severe risk. Also, and more importantly given that it
occurs right away in these next 8 hours or so, we cannot
completely "ignore" the Marginal/Slight risk setup that could
yield at least a few severe storms within the CWA late this
afternoon/evening.

Taking a look at the recent/current scene as of 330 PM, today has
turned out reasonably close to expectations, especially regarding
the fact that the entire CWA has remained dry/storm-free thus far
behind the morning convection. However, especially the southeast
half of the area has been cloudier than anticipated thanks to a
fairly robust development of stratocumulus, while sunshine has
been more prevalent in the northwest. As a result of these clouds,
high temps will likely fall at least a few degrees short of early
morning expectations, with most places topping out in the 70s
versus low 80s. In the mid-upper levels, water vapor imagery and
short term model data reveal continued broad southwesterly flow,
with a low-amplitude wave kicking eastward across western NE/KS to
the south of a parent closed low centered over the northern MT
area. At the surface, a few somewhat subtle boundaries are
present, most notably a generally west-east outflow boundary
draped across northern KS with a warmer/more unstable airmass to
its south, and also a generally northeast-southwest oriented weak
cold front aligned through central Nebraska, marked by a switch to
a more westerly wind component. Thus far, lack of forcing and
capping has kept convection at bay.

Now briefly looking ahead forecast-wise through these next 36
hours:

Late this afternoon-tonight:
Kept precip chances (POPs) on the relatively low-side, but various
models including high-res 4KM WRF`s and the latest HRRR suggest a
decent chance that storms currently forming in western NE will
eventually march east into the CWA. The question is, will they
remain relatively sparse/isolated or possibly congeal into a small
complex/MCS. That is yet to be seen, but in general the better
storm chances should favor the western half of the CWA, mainly
during the 5-11 PM time frame. Given mixed-layer CAPE up to around
2000 J/kg and deep-layer shear of 30-40 knots, at least brief
supercell structures cannot be ruled out. As for the outflow
boundary to the south, it seems that the main severe focus should
remain just to our south in central KS, but this could be a close
call and bears watching as well. Took a bit of a gamble and ended
thunderstorm chances around midnight as forcing
departs/instability wanes, as unlike previous nights there is not
a strong low level jet. However, suppose some very spotty
activity is not out of the question especially in KS zones late
tonight so this bears watching. Given fairly light surface winds
and the expected lack of late-night rain, added a generic mention
of "patchy fog" to roughly the southern two-thirds of the CWA. Low
temps tonight ranging mid 50s northwest to low 60s southeast.

Thursday-Thursday night:
As mentioned, this "could" be a fairly widespread severe weather
event mainly late afternoon/evening if things come together just
right, but models do vary enough on timing/placement of initial
convection that nothing is a sure thing. Overall though, the
ingredients are there for a legit severe threat with supercells,
given ML-CAPE values possibly up around 3000 J/kg, deep-layer
shear 40-50kt, stronger forcing than today as a stronger shortwave
trough swings into the Plains out of the Central Rockies, and
also stronger low-level shear as a warm front extends generally
east-northeast across the CWA from a roughly 995mb surface low
and centered over west-central KS. In addition, we will again see
a stout 40-50+kt low level jet ramp up toward evening, which will
further enhance low level shear/helicity. If any storms are
reasonably discrete (as opposed to clusters/lines), the chance
exists for a few tornadoes, with a strong one not out of the
question. Although at least a hail threat could persist through
the night, the main higher-end severe threat, should it
materialize, should focus during the typical 4 PM-midnight time
frame. Not to be overlooked, at least localized 2+ inch rainfall
amounts are possible if not likely, with a flash flood risk in
play. One of the unknowns at this point is whether the main warm
front will remain down near the KS line or possibly lift north
closer to I-80, and these details will hopefully become clearer
over the next 12-18 hours. Made minimal changes to both high and
low temps, with highs mainly upper 70s/low 80s and lows Thursday
night mainly upper 50s/low 60s.

.LONG TERM...(Friday daytime through Wednesday)
Issued at 418 PM CDT Wed May 25 2016

Have to keep this shorter than usual, but the bottom line is that
at least slight thunderstorm chances continue each and every day
and night. At the most basic sense, this means that several rounds
of rainfall could result in a slow, but steady increase in
flooding potential across the area, possibly trending from more
isolated to more widespread. Something to watch for sure.

From a severe weather sense, we are admittedly very focused on
Thursday right now, but want to make it clear that we cannot
ignore Friday either. Although mesoscale details are far from
clear, this is the day that the main southwestern upper low swings
into the Plains. If things trend more favorable for severe storms,
would not be at all surprised to see SPC "upgrade" parts of the
CWA from the current Marginal Risk designation for Friday.

Despite the continuation of at least small storm chances, the
majority of the weekend has the potential for being reasonably
dry in the wake of the departing system from Thursday-Friday.
Still though, enough instability exists for at least strong storm
potential mainly afternoon/evening. Fortunately, deep layer shear
looks somewhat weaker with time, which should in theory limit the
overall severe threat.

Looking into next week, there are hints that maybe, just maybe, we
could be looking at a somewhat quieter/drier pattern change by
mid-late week transitions from more southwesterly to more
northwesterly, but this is far enough out in time that uncertainty
is high.

Temps through the period are fairly typical of late May, with
highs mainly 70s to near 80 and lows mainly 50s to near 60.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Thursday evening)
Issued at 600 PM CDT Wed May 25 2016

Scattered thunderstorms may reach the terminals after dark,
however better chances for convection and severe weather exist on
Thursday primarily during the afternoon and evening hours. Look
for winds to be fairly light and variable during the TAF period,
with stronger winds during thunderstorms. There is some potential
for reduced visibilities in fog tonight in presence of light winds
and lowlevel moisture.

&&

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

&&

$$

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



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