Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 241420

Area Forecast Discussion
National Weather Service Hastings NE
920 AM CDT SUN JUL 24 2016

Issued at 920 AM CDT Sun Jul 24 2016

Just published the first forecast update of the day, mainly to
increase and expand-northward the chances of measurable rain
(PoPs) in our southern zones...

The initial overnight forecast tried to confine rain chances today
to only our KS zones, but radar trends along with some very
limited help from a few higher-res models such as the HRRR/NSSL
WRF clearly suggest that at least scattered showers/isolated
storms will in fact drift at least slightly north of the state
line into our southern Neb zones yet this morning. This weak
convection is pretty clearly tied to a mid level mesoscale
convective vortex (MCV) currently centered over west-central KS,
interacting with a weak-but-noticeable convergence zone evident
between 850-700 millibars. According to forecast soundings, this
high-based weak convection is probably only tapping into a few
hundred J/kg of most-unstable CAPE. Models such as the RAP13
slowly drift this MCV east-northeast through the day, eventually
exiting the vicinity of our southeastern CWA by mid-late
afternoon. Given that this limited forcing will be hanging around
for several more hours, it`s almost impossible to rule out
isolated/scattered convection across our south. For now, have
confined all mentionable (15 percent or higher) PoPs for the day
to areas generally south of a Geneva-Beaver City line, but would
also not be shocked to see some of this rain try creeping a bit
farther north and will be keeping a close eye on this.

As for severe weather chances this afternoon/tonight, they seem
fairly small and we have noted that SPC has kept the official
Marginal Risk area just barely south of our CWA (at least thus
far). That being said, with instability potentially increasing
closer to 1000 J/kg in our south assuming at least limited
sun/heating, it`s not out of the question that a few strong to
perhaps marginally severe storms could actually materialize mainly
within our KS zones later this afternoon into this evening.

Related to the aforementioned tricky rain chances, considerable
cloud cover could be an issue much of the day as well, which could
temper high temps a bit as well (not that most folks would
complain!). Will not make any changes yet, as like yesterday some
afternoon sun could easily put highs right back on track, but
something to keep in mind as well.


.SHORT TERM...(Today and tonight)
Issued at 329 AM CDT Sun Jul 24 2016

The weather pattern has transitioned more zonal and more seasonal
conditions are settling in early this morning. Temperatures and
dewpoints are cooling behind a cold frontal boundary located from
roughly KHJH to KGCK. The front will continue to advance south
early this morning and a few showers and storms are possible ahead
of the boundary which may skirt our southern zones for a time.

A cooler, more seasonal airmass will settle across our region and
temperatures will be more typical for this time of year with highs
in the mid 80s to lower 90s. Conditions will be noticeably less
humid as well with dewpoints in the 50s and 60s. Just not looking
for much in the way of convection today once the boundary moves
south of our area and surface high pressure builds in. Heading into
tonight another round of convection is possible in the vicinity of
the boundary to the south and along the high plains aided by upslope
flow and this activity may affect portions of our southern zones.

.LONG TERM...(Monday through Saturday)
Issued at 329 AM CDT Sun Jul 24 2016

Primary forecast concern through the long term continue to lie with
thunderstorm chances.

Generally zonal flow in the upper levels is expected to be in place
to start of the period Monday morning, as broad ridging sits over
the desert SW/Rockies and a trough slides through the Great Lakes
region. At the surface, a frontal boundary meandering around the
area looks to be draped across northern/central KS, with mainly
light easterly winds in place across the CWA. Could see some
lingering precipitation across southern areas to start the day with
a subtle wave moving through, but thinking most of the daytime hours
will be dry. The east-southeasterly winds remain in place through
the day, topping out around 10-15 MPH. Only made minor adjustments
to the temp forecast, with highs expected to range from the mid 80s
to low 90s. As we get into Monday night, seriously considered
removing PoPs completely from the forecast. It`s roughly split down
the middle between models keeping it dry/keeping precip chances in.
Overall forcing is on the weak side and not really a notable surface
boundary expected to be in the area. Capping doesn`t look to be as
strong as the past several days, and some models show a weaker-end
LLJ developing overnight. Decided that with a couple models still
showing some scattered QPF around to keep 20 PoPs going.

Tuesday/Tuesday night, models in good agreement with the overall
picture, showing little change in the upper level pattern.
Zonal/slight northwesterly flow expected to be in place, with the
center of the upper high remaining over the desert SW. Precipitation
chances are driven by the next upper level shortwave disturbance,
and similar to Monday night, models vary with how much activity
there ends up being during the daytime hour. While continue to carry
some low PoPs during the day, thinking at this that most locations
may end up being dry. The better chances come post 00Z and through
the overnight hours, when activity that starts over western SD/NE
slides southeast through the region. Carrying 30-50% chances across
the CWA, with the higher values across the north-northeastern
sections. Potential that stronger capping building in during this
time frame will limit the overall coverage the further south you go,
though not all models (like the NAM) show that being much of a
factor. At this point, the potential for strong/severe weather looks
to be a bit better through Tuesday night. MLCAPE values of 1500+
j/kg are possible (the NAM is quite a bit higher), and deeper layer
shear looks to improve. Entire CWA has been included in the SPC Day
3 Marginal Risk outlook. Large hail/damaging winds would be the
primary hazards...will insert mention in the HWO. Outside of the
thunderstorm chances, southerly winds may be on the breezy side with
speeds around 15 MPH. Temperatures expected to be a touch warmer
than Monday, with highs forecast in the lower/mid 90s. Southern
areas may see heat index values near 100 degrees.

Wednesday through Saturday, the unsettled pattern looks to continue,
and overall confidence in mainly preciptiation chances is pretty
low. Northwesterly flow remains in place aloft, if anything becoming
a touch more amplified with time as the high over the westerly CONUS
builds. Periodic shortwave disturbances passing through will
continue to bring chances for thunderstorms to the region, but
because of timing/location differences between models, difficult to
pin down a lot of details. PoPs remain in the 20-40% range. This
pattern keeps the brunt of the warmest airmass to the west of our
CWA, with highs through this time frame forecast to be in the 80s.


.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Monday morning)
Issued at 526 AM CDT Sun Jul 24 2016

Vfr conditions are forecast through the taf period. Clouds will be
remain at mid and high levels and any convection should be
limited later tonight primarily to the south of the terminals.


.GID Watches/Warnings/Advisories...


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