Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 202023
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
323 PM CDT Fri Jul 20 2018

.SHORT TERM...(This evening through Saturday)
Issued at 320 PM CDT Fri Jul 20 2018

The main issue in the short term revolves around low confidence
chance for shwrs/tstms through early evening.

Early afternoon water vapor satellite reveals what appears to be
a weak shortwave in the NW flow over central NE. This wave,
combined with weak WAA and isentropic ascent, have led to the
development of scat shwrs and at times some tstms as well.
Activity has trended weaker over the past couple of hours as this
forcing becomes more displaced from the better instability. Models
in general, including CAMS, have struggled with this activity
with NAM/GFS both dry. RAP/HRRR have shown activity within our
CWA, but haven`t had the best handle on location and intensity (at
least initially). The model struggles along with pattern
recognition (NW flow) leads to low confidence POP forecast
through the evening.

With that said, RAP/HRRR have been relatively consistent in
showing decreasing intensity/coverage as the afternoon wears on,
and this is consistent with latest radar trends. I believe this is
tied to the timing/track of the weak wave in central NE, so we
may have peaked in terms of our tstm potential. However, radar and
sfc analysis indicates a weak front/convergence zone near the
KS/NE state line. SPC mesoanalysis page indicates an eroding cap
from LBF down to MCK, and this is where visible satellite shows a
developing CU field. Will continue a slight chc POP through the
early evening to account for a rogue tstm or two that may try to
develop, similar to last night. Agree with SPC Marginal Risk area
in that, IF a tstm develops, it could become strong to marginal
severe given MLCAPE 2000-3500 J/kg and effective shear
unseasonably strong for this time of year around 50 kts or
greater. It is important to note that this severe potential is
very conditional on tstm development, which may not occur at all.
Just didn`t feel comfortable with a dry forecast this aftn/eve
given the pattern.

Overnight should be quiet with lgt and vrbl winds. NAM indicates
uncapped elevated instability across the S/W zones overnight
within very weak WAA near H7, but RAP/HRRR do not have this and
will side with them and maintain a dry overnight forecast. Can`t
rule out some very patchy light fog by dawn with the sfc ridge
axis over the N/E.

.LONG TERM...(Saturday night through Friday)
Issued at 320 PM CDT Fri Jul 20 2018

There is high confidence in mostly below normal temperatures in
the extended, but precipitation timing and chances are low
confidence due to weak nature of upper level waves within the NW
flow.

Generally speaking, expect fairly persistent troughing from south
central Canada to the Great Lakes to the SE US, with a persistent
ridge over the SW US. This results in mainly NW flow for the
Central Plains which often means an abundance of weak shortwaves
and several chances for precip as well as mostly below normal
temperatures. Ensemble and deterministic data is in relatively
good agreement in this pattern, so confidence on the general
temperature pattern is high. Precipitation timing, coverage and
amounts is another story though. Timing of these waves will be
difficult to pin down much more than half a day or day in advance,
so confidence in sensible weather features past Sunday is low.

The strongest waves, and best chances for shwrs/tstms, appears to
be Sunday night into Monday morning and Tuesday night into
Wednesday associated with cold fronts. Neither of these tstm
chances scream strong or severe weather at this time, but as we`ve
seen the past couple of days the NW flow can provide an
opportunity for strong shear and forcing. So the actual severe
potential will largely depend on timing and moisture/instability
availability, which as mentioned above remains uncertain.

Temperatures on Sunday will range from the mid 80s in central NE
to near mid 90s north central KS. Temperatures will then cool
behind the cold front Sunday night, with highs primarily in the
80s for the rest of the week, or around 4-8 deg below normal.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Saturday)
Issued at 1250 PM CDT Fri Jul 20 2018

Significant Wx: Possibly an iso/brief -TSRA, but CIG or VSBY
reduction unlikely

Rest of today thru 00Z: Iso shwrs/stms remain poss into
afternoon, with best/longest chc at GRI. Have gone VCTS for next
few hours. This activity is high based (CIGs above 10K ft) so any
flight cat restrictions are unlikely. Wind will be lgt out of
E/ESE.

Tonight: VFR. Clearing skies with winds becoming lgt and vrbl
around sunset.

Sat thru 18Z: VFR. Clear or mostly clear skies. Winds remain lgt
and vrbl or perhaps E/ESE


&&

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

$$

SHORT TERM...Thies
LONG TERM...Thies
AVIATION...Thies



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