Area Forecast Discussion
Issued by NWS Hastings, NE

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098
FXUS63 KGID 212349
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
649 PM CDT Mon Aug 21 2017

.MESOSCALE DISCUSSION...
Issued at 528 PM CDT Mon Aug 21 2017

We cont to monitor potential for initiation of tstms. The cool
front currently extends from just N of LXN to just S of OLU (just
N of I-80). The RAP/NMM/WRF-ARW/RGEM are too aggressive... already
indicating tstms should have developed. So that leaves the NAM/GFS
which are later suggesting initiation between 00Z-03Z just W-NW-N
of the CWA. If this occurs...they should move into areas N and W
of the Tri-Cities before 03Z.

If initiation occurs...these storms will be in the post-frontal
air mass where deep layer shear will be increasing from 25 up to
35 kts.

We will be warning on 50 dBZ cores that reach 35K ft and 60 dBZ
cores that reach 23K ft.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 242 PM CDT Mon Aug 21 2017

Much of the focus today has involved keeping an eye on the high
cloud deck and the eclipse, but will also need to talk about the
expected weather over the next 7 days.

17Z Discussion --- Current water vapor imagery and upper air
analysis shows an active northern stream continues over the
region although the better forcing looks to be a little north of
us. A subtle mid level should move through west to east later this
afternoon. While the flow is weaker across and to the south of
our CWA, there is vort max to our southwest that could affect the
southeast part of the CWA later today. One other thing of note on
satellite is the sub-tropical tap that starts south of the Baja
region and has been streaming NNE through KS and SE Neb. This is a
big contributing factor to the eclipse-hampering cirrus in our
area. At the surface at 10 am, low pressure was situated over west
central Neb with a warm front extending ENE. Fog/Stratus deck was
taking its time burning off north of the warm front, but ODX has
gone from a quarter mile to 10 miles between 14 & 15Z

Primary question will be the extent of any convection firing later
this afternoon and into tonight. The shortwave noted above should
help drag the surface front into and through the CWA, starting in
the northwest CWA between 22-00Z and exiting the southeast part
of the CWA by sunrise Tue. The best instability should occur a
little to the north of our CWA but ML CAPE will still be in the
1000-1500 j/kg range in the northern half of the CWA. Deep layer
shear not as impressive with 20 kt 0-6 km shear progged at 00Z.
Will continue to monitor real time radar and CAM models for
convective initiation. Earlier runs of the HRRR have shown this to
occur around 4 pm in our northwest. HRRR does show some
convection along the front across much of the CWA during the
evening and overnight, however the bulk of this remains in our far
northern CWA and into NE Neb closer to the better forcing.

1930Z Update... Storms have indeed initiated along an outflow
boundary across northeast Neb and are just to the north of our
CWA. Latest HRRR guidance now showing this activity will push
southward through the CWA the remainder of the afternoon and
overnight, exiting the southern CWA just before sunrise. Deep
layer shear still lacking but enough instability that a few
strong/severe storms cannot be ruled out.

Tuesday should be quiet in terms of the active weather as the
surface front pushes well south with high pressure dropping into
northeast Neb. Will be a bit cooler with highs in the lower 80s,
but even more noticeable will be the lower dewpoints which should
be in the mid 50s, about 15 degrees lower than what we are seeing
today.


.LONG TERM...(Tuesday night through Monday)
Issued at 242 PM CDT Mon Aug 21 2017

Quiet conditions continue Wed and Thu as mid level ridge builds
into the Rockies before that pattern reverts to something similar
to the last few days for the weekend as the next wave moves onto
the PAC NW coast and dampens the ridge. Superblend producing Pops
during the day Thursday but don`t see a lot of evidence for that.
Tstm chances do return by Thu night into the weekend with series
of wave passages. If models are correct, the ridge then builds
back into the Rockies again early next week, lowering our
precipitation chances. At least early next week, high temps remain
in the lower 80s as the ridge axis remains far enough west of
here to keep the hotter temps at bay.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 648 PM CDT Mon Aug 21 2017

Significant Wx: Low probability of IFR TSRA tonight.

Tonight: Cold frontal passage 02Z-03Z. Predominantly VFR with
multi-layered CIGs at or above 10K ft. A few CU around 4K ft will
be possible thru the night with some developing into sct TSRAs.
Lgt S winds will shift to the N after frontal passage. Confidence:
Medium

Tue: VFR SKC or becoming SKC before 17Z. N winds 8-12 kts becoming
NE. Confidence: High

&&

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

$$

SHORT TERM...Ewald
LONG TERM...Ewald
AVIATION...Kelley



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