Area Forecast Discussion
Issued by NWS Hastings, NE

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189
FXUS63 KGID 222205
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
505 PM CDT Thu Aug 22 2019

.SHORT TERM...(This evening through Friday night)
Issued at 504 PM CDT Thu Aug 22 2019

Apologize for the late issuance...this forecast has been a real
headache in terms of trying to determine short-term details with
any degree of confidence.

Focusing solely on the first 36 hours here, the main issues are a
number of nagging/more-uncertain-than-usual rain and thunderstorm
chances. Will state up front that this is an UNUSUALLY-FRUSTRATING
and tricky weather pattern from a rainfall forecasting
perspective. While it`s pretty much a given that we will see off-
and-on rain chances through Friday night (and beyond as covered
below), trying to highlight the more "exact" details such as rain
chances, timing and amounts is proving to be a pain. What we are
more sure of is that widespread cloud cover will continue to
plague us right on through Friday (and likely into Saturday), and
at least patchy fog (perhaps some drizzle?) will likely redevelop
tonight into Friday morning. With Friday expected to be a fairly
similar day to today in terms of fairly widespread low clouds,
expect temperatures to end up similar as well.

Overview of the recent/current weather scene as of 430 PM:
Things would have likely been more straightforward today if not
for a pesky mesoscale convective vortex (MCV) that is currently
highly-visible on radar/satellite imagery over the eastern Custer
County area. Mesoscale forcing from this feature has sparked up a
small complex of strong thunderstorms currently centered near Blue
Hill that is slowly tracking east. So far this activity has
remained sub-severe, but small hail/gusty winds heavy rainfall are
certainly possible. Meanwhile, outside of this primary area of
storms, the vast majority of the coverage area (CWA) has simply
observed a cloudy/mostly cloudy day with an abundance of pesky low
clouds and morning fog. While just enough sunshine has broken out
to boost a few southern locations such as Phillipsburg/Hebron
over the 80-degree mark, most of our CWA is on track to top out no
warmer than 74-78. In the mid-upper levels, our tricky weather
pattern is being supported by a parade of subtle/low amplitude
disturbances kicking out eastward ahead of a larger-scale trough
centered over the Northern Rockies. At the surface, our CWA
remains north of an east-west front stretched through central KS,
giving our area mainly east-southeast breezes around 10 MPH with
occasional higher gusts.

Now looking ahead forecast-wise through these next 3 day/night
periods...

This evening/tonight:
Right off the bat, we are watching the small cluster of strong
storms near Blue Hill for at least marginally-severe hail and/or
winds. Models struggled mightily to pick up on this activity today
as the failed to properly initialize the aforementioned MCV, but
this should continue tracking east and eventually moving out
and/or weakening. Despite not being in a formal SPC Marginal Risk
of severe, the threat of severe through mid-evening is not exactly
zero, as mixed-layer CAPE is a solid 1000-2000 J/kg across most
of the CWA, despite weak deep layer shear only around 30KT. While
most of the CWA will probably remain mainly dry overnight, opted
to carry at least 20-30 rain chances/PoPs all areas through the
night as additional subtle disturbances arrive from the west, with
the overall-highest chances far west late tonight. Even if most
places do not see any true measurable rain, expect at least patchy
fog to re-develop late this evening and overnight, along with
possible patchy drizzle under the widespread low clouds that will
either remain in place or redevelop. Am not currently expecting
widespread/impactful dense fog, but as evidenced this morning at
least hit-and-miss instances cannot be ruled out. If anything,
southeast breezes should be a touch steadier than last night. If
anything, low temps were nudged up very slightly, with most areas
aimed into the mid 60s.

Friday daytime:
In many ways, expecting a similar day to today, especially in
terms of at least light AM fog giving way to rather stubborn and
widespread low clouds, with perhaps some limited sunshine here or
there in the afternoon. Like today, there could easily be a sneaky
MCV around, along with other subtle disturbances tied to the
larger-scale flow. As a result, have at least small rain/storm
chances all areas through the day. Breezes look a touch stronger
than today, with sustained 10-15 MPH/gusts to around 20 MPH common
(especially afternoon). Lowered highs very slightly, but overall
expect similar to today with mainly mid-upper 70s in Neb zones and
low 80s more common in KS.

Friday night:
In theory, perhaps a more widespread chance for rain/storms
especially within our western zones, with lower chances remaining
east of the Highway 281 corridor. These higher chances are driven
by stronger forcing arriving from the west as the larger-scale
trough starts to kick eastward into the Plains. Have introduced
"likely" rain chances to western zones (although still only 60
percent officially), as this could still trend higher as it nears.
Again, we are not outlooked for severe storms by SPC, but will
likely have to watch especially our far west for at least strong
storm and localized heavy rain potential. Low temps similar to
tonight with mainly mid-60s.

.LONG TERM...(Saturday daytime through Thursday)
Issued at 504 PM CDT Thu Aug 22 2019

General overview of this 6-day period:
With as many nagging rainfall/thunderstorm uncertainties that
abound in the short term covered above, at least the first few
days of this time frame are very much prone to the same issues. In
short, there are several, halfway-decent, off-and-on chances for
rain between Saturday daytime and Monday as several upper
disturbances continue to affect the region. Beyond Monday, while
our forecast continues to be littered with a number of mainly
small (20-30 percent) chances, the raw model data from the latest
ECMWF/GFS strongly suggests that most of this time frame will
likely be dry, as our region becomes more influenced by broad mid-
upper level ridging extending northeastward from the southwestern
CONUS. In fact, would not be at all surprised to see some of these
day/night periods (such as Monday night-Tuesday) eventually carry
a completely dry forecast. One thing adding confidence to this
pattern change of sorts to a drier regime is that both ECMWF/GFS
are fairly insistent on a decent cold frontal passage Monday-
Monday night, that should scour out appreciable instability for at
least a few days.

Temperature-wise:
As is almost always the case, confidence is higher in temperatures
through these longer term periods than in rain chances. As a
result, confidence is high that this period as a whole will
average slightly-below normal by late-August standards. More
specifically, high temperatures on most of these days are only
aimed into the mid-upper 70s in most of the CWA (especially Neb
zones), with KS zones more prone to at least low 80s. That being
said, it maybe isn`t looking "quite" as cool as previously
advertised on a few days, and highs have trended upward 1-3
degrees with this latest forecast for days such as Tues and Wed.
The overall-warmest day currently looks to be Sunday, but even
then we are only talking low-mid 80s in most Neb zones and perhaps
upper 80s in our far southwest. Overnight lows on most nights
should average in the 60s for Sat- Sun nights, with cooler 50s
then more prevalent through much of next week.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Friday)
Issued at 1240 PM CDT Thu Aug 22 2019

The next 24hrs will be a cloud and vis forecast. Expecting clouds
to rise and maybe scatter out late this afternoon and MVFR/IFR
ceilings will move back in later this evening. Guidance brings
the LIFR back in tomorrow morning.

&&

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

$$

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



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