Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 270907
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
407 AM CDT Tue Jun 27 2017

.SHORT TERM...(Today and tonight)
Issued at 349 AM CDT Tue Jun 27 2017

This Morning:
Patchy fog has developed across the area. Short-term models did a
decent good job picking up on this potential. Visibility has been
variable and highly dependent on the wind speeds. Nevertheless, I
went ahead and issued a dense fog advisory until 9 AM. If trends
continue, there is a chance that this will need to be expanded
northward later this morning. Fog should mix out by 8-9am as
southerly winds increase.

This Afternoon and Early Evening:
Speaking of winds, a tightening pressure gradient should produce
sustained southerly to south-southeasterly winds of 20 to 30 MPH
with gusts around 35 MPH west of Highway 281. The HRRR and RAP
only have sustained winds of 15 to 20 MPH this afternoon, although
given the strength of the pressure gradient, I think that they
may be underdoing it a bit. Winds will decrease a bit in the
evening as mixing decreases, but will remain breezy until
thunderstorms roll through overnight.

Late Evening and Overnight:
Thunderstorms are expected to develop across western Nebraska late
this afternoon ahead of an upper level shortwave trough moving
into the region. Locally, we will remain capped until this forcing
pushes these storms into the area...most likely after 02Z. We will
still have ample instability (1500-2500 j of MUCAPE) and shear
(35-45 kt of 0-6km bulk shear) to maintain severe storms. Because
of this, we could see some large hail as the storms arrive, but
wind will should quickly become the main threat as storms merge
into an MCS aided by a 50-60 kt low-level jet. The latest
NAM/GFS/EURO all take the bulk of the activity through the
northern parts of the area, along the edge of the instability
gradient and where there is a bit better convergence at 850mb. For
this reason I mostly kept the likely PoPs north of I-80. That
said, the NAMnest and NCAR WRF Ensemble still bring activity down
the Platte River, so I don`t think that we will miss out entirely. Activity
should clear the area by tomorrow morning as a weak front makes
its way through the area.

.LONG TERM...(Wednesday through Monday)
Issued at 349 AM CDT Tue Jun 27 2017

Overview...Several chances for thunderstorms with appreciable
moisture stand out. With so much of the forecast area having seen
below normal rainfall thus far through June, hopefully we can get
some appreciable moisture out of at least one of these upcoming
opportunities. The better rain chances will be Wednesday night
especially south of the Platte River, then Thursday evening near the
sfc front but hard to pinpoint, and then finally with yet another
shortwave Sunday afternoon/evening.

We do expect a warm up getting us closer to seasonal temperatures
but still perhaps a few degrees below normal on most days. Normal
highs are now generally in the mid to upper 80s over south central
Nebraska to around 90 over north central Kansas.

Wednesday...A sfc trough will track southeast across the forecast
area through the day and will largely be southeast of the forecast
area by late afternoon when there is the best chance of firing
thunderstorms along this sfc boundary. Therefore...will call for dry
conditions on Wednesday with any sfc based convection likely firing
east of our forecast area.

Wednesday night...the low level jet will really get cranking after
dusk with what models are indicating will be a strong 50 kt 850 mb
southerly wind across much of Kansas. This 850 mb jet will nose
right into our forecast area, probably north central Kansas or far
south central Nebraska leading to strong convergence and a good
chance of thunderstorm development after dark. Our rain chances may
not be high enough. Models differ on the convective initiation and
how widespread this event will be, but are fairly similar with the
pattern. This pattern looks good to me to really dump on an area of
two to three counties in width with some training elevated
thunderstorms leading to a localized flash flooding threat under the
zone where these storms develop. Given the storms will be elevated,
believe that large hail and flash flooding will be the primary
threats. There is a lot of elevated instability and wind shear is
more than sufficient. Can not rule out a few strong wind gusts
making it to the sfc, but that may be more rare given storms will
likely be elevated. Not everyone, will get wet, and we will need to
see where that couple county wide convergence zone will set up.

Thursday...Confidence in precipitation chances is honestly a bit low
as we`ll have to see how Wednesday night convection impacts the sfc
frontal boundary. Best estimate is that the sfc front will be
southeast of our forecast area, which could limit our rain chances.
However, an upper level trough will be swinging through the central
and northern plains and could provide enough support for afternoon
and evening thunderstorms even on the north side of the sfc front,
but models are hit and miss on this happening. The best chance for
thunderstorms will be along the sfc front wherever it ends up being
located after the Wednesday night storms.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Wednesday)
Issued at 1221 AM CDT Tue Jun 27 2017

Mostly clear skies along with relatively light winds and
increasingly moist low levels will provide a brief window for fog
and stratus Tuesday morning. Short-term models support this trend
of low visibilities, particularly along and east of Highway 281. Therefore,
I`ve given a brief window of IFR at KGRI, and MVFR at KEAR.
Increasing winds should mix out the fog/stratus by 13z or 14z at
the latest.

This afternoon, southerly winds will gust to around 30 kts. The
pressure gradient tightens significantly 21 to 00Z, so I expect
that somewhat breezy conditions will continue into the evening and
overnight as well.

The next concern is the threat for thunderstorms Tuesday night.
Models show a complex of thunderstorms moving out of western
Nebraska and into the area in the 02-05Z timeframe, but there is
still enough uncertainty on exact timing/location that this isn`t
included in this TAF issuance

Lastly, there is a chance that we approach LLWS criteria Tuesday
night under a 50-60 kt low-level jet at 850mb. Of course, this
will depend on how much surface winds can decouple. Given the
complex forecast, I haven`t included it in this TAF and will re-
evaluate at 12Z.


&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Dense Fog Advisory until 9 AM CDT this morning for NEZ041-
     047>049-061>064-073>077-083>087.

KS...Dense Fog Advisory until 9 AM CDT this morning for KSZ006-007.

&&

$$

SHORT TERM...Mangels
LONG TERM...Wesely
AVIATION...Mangels



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