Area Forecast Discussion
Issued by NWS Hastings, NE

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837
FXUS63 KGID 301144
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
644 AM CDT Tue May 30 2017

.UPDATE...
Issued at 644 AM CDT Tue May 30 2017

Have removed the "slight chance of sprinkles" from the official
forecast for this morning in some KS zones. As previously
discussed in the since-removed "early this morning" paragraph,
some spotty sprinkles/light high-based showers did eventually
develop this morning, but they initiated slightly east of our KS
zones in northeast KS and appear to be moving away. Satellite
trends and short term model data show little chance of
redevelopment back to the west, so will run with a dry forecast
CWA-wide today except for the small chance for KS thunderstorms
this afternoon.

&&

.SHORT TERM...(Today and tonight)
Issued at 435 AM CDT Tue May 30 2017

While not truly guaranteed dry across our entire coverage area
(CWA) through the next 24 hours, the vast majority of our domain
will likely remain so. From a "weather impact" perspective, the
primary concern is still a brief window of opportunity for a few
strong (probably non-severe) storms within our far southern CWA in
KS this afternoon, but compared to 24 hours the potential for
legitimate severe storms has both diminished somewhat and also
shifted slightly south-southeast of our area. So all in all, most
folks should end up considering this another in a string of fairly
pleasant late-May days, with plenty of sunshine, overall- lighter
breezes than yesterday and high temps climbing a few ticks
warmer.

Taking a look at the current/recent weather scene as of 08Z/3AM:
At least so far, it`s been another quiet/mostly clear and fairly
cool night (by late-May standards) across the entire CWA. In the
bigger picture of the mid-upper levels, water vapor satellite
imagery and short term model data clearly show our area still
under the influence of northwest-flow, directed between a large-
scale trough centered over the Great Lakes/southeast Canada and a
ridge axis stretched over much of the western CONUS. While the
majority of forcing associated with the trough is focused to our
northeast, a likely convectively-enhanced small-scale disturbance
has fostered a complex of showers/non-severe storms migrating
eastward across southern KS, well-south of our CWA. At the
surface, broad /non-descript high pressure/ridging is clearly the
main story this morning, as we remain well north of a loosely-
defined quasi-stationary front draped from the High Plains
southward-then-eastward across parts of OK into MO. While skies
are currently clear/mostly clear nearly CWA-wide, infrared
satellite imagery and even a few airport sensors reveal the recent
development of a few high-based shallow cumulus clouds mainly
within the southeast quad of the CWA, likely a result of meager
mid-level moisture advection nudging in from the west. Temp-wise,
lows are on track to bottom out a few degrees cooler than
yesterday morning in most places, with the majority of the CWA
likely ending up 45-51, and a few typically-colder spots such as
Ord possibly into the low 40s (which is nearly 10 degrees below
normal for the date). For those who enjoy low moisture/humidity
levels, we have frankly been getting spoiled of late with values
currently well down into the upper-30s to mid-40s range, pretty
dry for late-May.

Now looking ahead forecast-wise through late Tuesday night...

Today (through 7PM):
As mentioned at the top, for the vast majority of the (if not the
entire) CWA, this should be a rain-free and rather pleasant day.
In the mid-upper levels, we remain under the aforementioned
northwesterly flow, but the very beginning stages of a pattern
change will start to occur in the form of subtle mid-level height
rises as the northeast CONUS trough finally starts to shift east a
little. At the surface today, broad high pressure also remains the
main influence, as we continue to reside north of a frontal
boundary generally stretched from Wyoming then southeast-east
across central KS into MO. Over our local area, modest mixing will
again result in a day of prevailing northwest breezes, although
southern zones especially KS may average more westerly than
northerly through at least the first part of the day. For sure,
breezes/gustiness will be a little lighter than the past few days,
but it won`t be calm by any means either, with most areas
averaging sustained speeds 10-15 MPH/gusts up to around 20 MPH
especially this afternoon, and the overall-highest speeds mostly
favoring our northern half. Under prevailing sunny-mostly sunny
skies, high temps were nudged up 1-2 degrees from previous
forecast most areas, aimed upper 70s most areas but ranging from
mid 70s far north to low 80s in KS. Dewpoints/humidity levels will
remain rather low, especially as mixing kicks in this afternoon,
with mid-afternoon dews in most Nebraska areas expected to be
upper 30s, with perhaps upper 40s in our southern KS zones. As for
very limited precip chances, models such as the NAM/RAP continue
to show some modest instability (mixed-layer CAPE perhaps as high
as 500-1000 J/kg) building in our far southern zones in KS this
afternoon along/near a subtle west-east frontal zone. While 24
hours ago it looked somewhat probable that at least strong, if not
marginally severe storm potential might exist along this boundary
within our far southern CWA, the latest trends have diminished
this potential, showing that it would mainly focus at least
slightly south- southeast of our CWA, if it even occurs at all.
While we support SPC removing the Marginal Risk that previously
existed in our south, will continue a strong storm mention in the
Hazardous Weather Outlook (HWOGID) for our far southern row of KS
counties as there remains a small chance a few storms could brush
this area mainly during the 3-6PM time frame before departing to
the south-southeast.

This evening/overnight (through 7AM Wednesday):
Like the daytime hours, the vast majority of the CWA (if not the
entire) should remain dry, but especially for our far western and
perhaps also far southern zones this could be difficult to
guarantee, especially very late in the night toward sunrise. In
the mid-upper levels, the northeast CONUS trough continues to
slowly ease its influence, allowing subtle/weak disturbances
undercutting the ridge to our west to start approaching the area.
For the evening (pre-midnight) hours, confidence is pretty high in
the going dry forecast, as any possible afternoon activity in KS
should be gone by then, leaving the entire CWA under clear-mostly
clear skies and light breezes turning more easterly. Then late in
the night and toward sunrise, models such as the NAM/GFS both
suggest that perhaps our far western counties (mainly in Nebraska)
and perhaps also our KS zones could see some spotty shower/weak
thunderstorm activity flare up as perhaps up to a few hundred J/kg
of elevated instability starts returning northeastward along the
nose of a fairly weak low level jet/isentropic lift regime.
Considered adding at least a basic sprinkle mention to the
official forecast to hint at this possibility, but ultimately
decided to leave it dry for now, albeit with a "silent "/non-
zero precip chance around 10 percent. Next few shifts will have to
watch this closely, but all things considered the best chances of
possible late night/early Wed AM convection (if it in fact
develops at all) should in theory favor areas just west of our
CWA. Turning to temps, while clouds may start to increase from the
west especially late, overall it should be another mostly clear
night with light, mainly easterly breezes. This should yield
another coolish night for this time of year, and nudged down lows
1-2 degrees from previous forecast most areas, aiming for fairly
similar values to those of this morning, with most areas between
the mid-40s and low-50s.

.LONG TERM...(Wednesday daytime through Monday)
Issued at 435 AM CDT Tue May 30 2017

Overall a fairly benign weather pattern appears to be in store for
the local area through the extended periods with seasonable
temperatures and only a few small chances for thunderstorms expected
from time to time. This will largely be a consequence of an upper
level ridge of high pressure which will be over the plains for much
of the weekend and upcoming work week...with a few weak disturbances
trying to break through the ridge and bring small chances for
thunderstorms.

Expect the first...and possibly strongest...disturbance of the
period...to undercut the ridge and emerge out of the southwest on
Wednesday. Because of the southerly trajectory...the main forcing
will be across north central Kansas where showers and thunderstorms
should increase in coverage during the daytime hours. While the
atmosphere is modestly unstable...with 1500 Joules of CAPE and
modest 0-6 KM shear values...the forcing from this disturbance will
be weak...and widespread strong or severe storms are not
anticipated. That said...across our southern zones...could see a few
storms approach severe limits if they are able to initiate during
the late afternoon and evening hours.

Otherwise...additional small chances for thunderstorms can be
anticipated from time to time through the extended periods...with
the focus of these storms centered around different weak
disturbances/passing waves. Very late in the period...models are
attempting to break down the upper level ridge over the local area
next Monday or Tuesday...which should help support additional more
widespread shower and thunderstorm activity...but given the timing
and strength differences in the models...opted to cap given precip
chances at 50 percent for the time being.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Wednesday)
Issued at 644 AM CDT Tue May 30 2017

Confidence remains rather high in continued VFR
ceiling/visibility and precip-free conditions, with only limited
mid-level cloud cover at times. Toward the very end of the period
early Wednesday morning, there is mounting evidence that
especially KEAR could have a few showers/non-severe thunderstorms
nearing from the west-northwest, but with better chances for this
occurring beyond the current valid period will omit any formal
precipitation mention. Surface winds will average light/variable
both right away this morning and again through most of the
evening/overnight hours. For this afternoon, winds will be
lighter than recent days, but they could still get a touch breezy
from the northwest, albeit with gust potential mainly under 20kt
for the most part.

&&

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

$$

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



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