Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 190957
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
457 AM CDT TUE JUL 19 2016

.SHORT TERM...(Today and tonight)
Issued at 456 AM CDT Tue Jul 19 2016

The main stories of these next 24 hours involve the eventual
departure of lingering showers/non-severe thunderstorms this
morning, and then our attention turns to the first round of
several days of advisory/watch worthy (and possibly eventually
warning-worthy) heat. Admittedly, spent a good chunk of this shift
coordinating with various neighboring WFO`s regarding how best to
handle the heat headline situation, but the bottom line is that a
potentially "marginal" Heat Advisory has been issued for this
afternoon, with the earlier-issued Excessive Heat Watch remaining
in place from Wednesday afternoon-Friday afternoon. We want to
make it very clear that the worst of the heat will NOT arrive
today, and that is why today is "only" an advisory versus a
warning. It is possible that one or more days from Wednesday-
Friday could eventually be upgraded to a warning, but the
consensus of most neighboring offices was to let the Watch stand
for now and let day shift do another round of coordination to
handle possible upgrades (see below for a few more comments on the
headline situation, including within the "Long Term" section).

Taking a look at the current/recent scene as of 430 AM: As
expected, shower/thunderstorm activity did in fact make into
especially western/northern sections of the CWA overnight, but has
struggled considerable to push into most southern/eastern counties
except for the passage of an associated outflow boundary that has
pushed out through nearly the entire CWA. By far the majority of
measurable rain has been northwest of Greeley-Elwood line. While
the vast majority of this overnight activity has been sub-severe,
earlier in the night the initial surge of outflow resulted in
fairly widespread 40-55 MPH winds mainly in far western counties
including some small tree branch damage reported in Edison. In the
big picture of the mid-upper levels, water vapor satellite imagery
and short term model data clearly reveal that the much-discussed
high pressure system/ridge is exerting increasing influence on the
local area, and is currently centered over the KS/OK border area.
Despite rather toasty mid level temps (evident by 12-14C at 700
millibars), the combination of steep lapse rates and forcing
within the axis of a generally 30-40 knot low level jet that is
steadily veering southwesterly is promoting the ongoing,
generally northeast-southwest axis of fairly weak convection over
parts of the CWA. Under considerable mainly high level clouds, low
temps are expected to hold up in the 68-74 range, but with some
variation depending on the presence or lack of rain-cooled air.

Now looking ahead forecast-wise through these next 24 hours:

Today (including early this morning):
It is becoming increasingly-apparent that showers/weak storms will
be slower to depart the CWA than expected 24 hours ago, and thus
have lingered rain chances (PoPs) through the mid-late morning
hours for especially the northern half to one-third of the CWA.
That being said, may have to update and even put some low post-
sunrise PoPS as far south as our KS zones, as at least
spotty/pesky weak convection seems to be flaring up in the wake of
the passing outflow boundary. Eventually though, rain should
gradually pull out of the entire CWA this morning as forcing from
both the low level jet and the associated mid level disturbance
departs more off to our east/northeast. Then, the story for the
afternoon turns to temperatures/heat. Admittedly, given the
extensive morning clouds and the presence of the southward-
shifting outflow, there is a bit more doubt than 24 hours ago
regarding just how hot it will really get today (especially within
the northern half of the CWA). However, even hi-res short term
models are pretty insistent that skies should gradually clear and
winds will increase out of the south for this afternoon, with
sustained speeds generally 15-20 MPH with higher gusts. As a
result, made little change from previous forecast regarding both
temps/dewpoints. Actual highs are aimed into the mid 90s most Neb
zones, and more so upper 90s in KS. Resultant peak heat index
values are generally expected to be "near" 100 degrees. Without
going into too much "behind the scenes" detail, will fully admit
that normally we would not issue a Heat Advisory for these values
given that our normal criteria is 105+. However, given that
previous day shift had earlier placed this afternoon into a Watch,
it was pretty much unavoidable that it needed converted to a
marginal Advisory, and besides a more serious Warning was just not
justified for today. Again, would not be surprised to see this
Advisory struggle a bit in some areas, but it`s out and will be
allowed to ride for now.

This evening/tonight:
Confidence remains fairly high in a dry/balmy night, and although
some convection could affect western/north central NE, would be
fairly surprised to see any of this activity get within 50 miles
of the edges of our CWA. In the mid-upper levels, the dominant
ridge remains anchored over the KS/OK/AR/MO border area, with a
slight northward shift of mid-level height rises shunting the jet
stream and associated weak disturbances rounding the top of the
ridge a bit farther north compared to the current night/morning.
Thus, in theory the local area remains dry and capped. Assuming
that convective outlow is not an issue, breezes overnight should
remain steady and southerly at generally 10-15 MPH with some
higher gusts. Despite mainly clear skies, low temps should
struggle to fall very efficiently, and have lows holding up in the
mid-70s most areas, with maybe some low 70s in typically cooler
west-central/northern counties. Technically, the Heat Advisory
continues through the night, mainly due to the limited relief that
these above-average low temps will provide (average lows for
mid/late July are in the 60s).

.LONG TERM...(Wednesday DAYTIME through Monday)
Issued at 446 AM CDT Tue Jul 19 2016

A broad area of high pressure across the center of the country will
extend its influence into the central plains for much of the work
week resulting in an unseasonably warm and humid airmass across the
region. With this fairly stagnant and hot air in place...expect
dangerous heat index values to become the norm for several
days...and an excessive heat watch remains in effect for the entire
forecast area Wednesday afternoon through Friday evening.

While there will be a few ripples in the upper flow rolling
intermittently off the high plains through the end of the
week...only very isolated and elevated convection is anticipated
starting Thursday night...as instability will be limited and cloud
bases are forecast to be above 10kft according to model soundings.
If some thunderstorms are able to develop...however...severe wind
gusts will be likely as classic inverted-V soundings are evident
in model data during the afternoon and early evening hours each day.

As the main upper level ridge shows some signs of breaking down over
the upcoming weekend...only minor relief is expected for
Saturday...with the cooler and more seasonal air not expected to
settle in behind a passing cold front until late Saturday night or
even Sunday. This shift in the upper level pattern will then result
in a more zonal flow and more seasonal temperatures through the end
of the extended period.

Overall...hot and primarily dry conditions are expected across the
region through at least Saturday...with some minor temperature
relief coming late in the weekend into early next week.
Precipitation wise...there are very small chances for convection
across the local area each day...starting Thursday evening...but most
locations are expected to remain dry as convection in this pattern
is anticipated to be very high based and isolated across the
region.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Tuesday night)
Issued at 115 AM CDT Tue Jul 19 2016

Confidence is reasonably high in VFR visibility and especially VFR
ceiling through at least the vast majority of the period. By far
the main question marks/caveats come right away during the first
6-9 hours, as there is increasing evidence that KEAR, and perhaps
KGRI also, will be affected by at least a brief period of
thunderstorms as a linear complex/cluster moves in from the west.
For now, went with a TEMPO group for KEAR mainly for gusty winds
to around 30kt where confidence is higher that storms will hit,
but will keep KGRI just a generic "vicinity" (VCTS) for now. In
addition to storm chances, have maintained a mention of low level
wind shear (LLWS) through the first 7 hours at both sites as
south-southwest winds of up to around 40kt within the lowest 1500
ft will create 30+kt of overall shear difference between the
surface and that level. Once the storm/low level wind shear
concerns subside beyond the first 6-9 hours, most of the remainder
of the period should be fairly straightforward with VFR/storm-free
conditions and breezy south winds with afternoon gust potential
into the 20-25 kt range. Low-level wind shear could again become a
concern late in the period Tuesday evening, but there is still
plenty of time to address this in later TAF issuances.

&&

.GID Watches/Warnings/Advisories...
NE...Heat Advisory from 1 PM this afternoon to noon CDT Wednesday for
     NEZ039>041-046>049-060>064-072>077-082>087.

     Excessive Heat Watch from Wednesday afternoon through Friday
     evening for NEZ039>041-046>049-060>064-072>077-082>087.

KS...Heat Advisory from 1 PM this afternoon to noon CDT Wednesday for
     KSZ005>007-017>019.

     Excessive Heat Watch from Wednesday afternoon through Friday
     evening for KSZ005>007-017>019.

&&

$$

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


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