Area Forecast Discussion
Issued by NWS Hastings, NE

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721
FXUS63 KGID 272100
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
400 PM CDT WED JUL 27 2016

...Multiple Chances for Spotty Tstm Activity thru Early Next Week
with Much-Needed Rain Where it Falls and We Need to Watch
Potential for More Svr Wx...

.SHORT TERM...(This evening through Thursday)
Issued at 400 PM CDT Wed Jul 27 2016

Aloft: The Westerlies were zonal over the Nrn USA with
subtropical highs over the Desert SW and over the SE. The zonal
flow was in the process of amplifying. The low-amplitude shortwave
trof that aided last night`s tstms was E of the region. Another
extended down the Ern borders of MT/WY/CO...and this trof was
responsible for tstms that are on-going at this hour. This trof
will cross the Cntrl Plains this evening...initiating the
transition to NW flow. There is one more shortwave trof currently
over WA/OR. This trof will cross the Nrn Rockies tonight and
approach the Cntrl Plains tomorrow eve. Both of these trofs will
influence tstm development this afternoon and tomorrow.

Surface: A cool front extended from low pres near MSP across Nrn
Neb into WY. Its exact location has been masked by the pre-frontal
air contaminated by last night`s MCS. This front will cont to
steadily work its way S across the fcst area tonight...with Nrn
Plains high pres building in. The front will stall W-E somewhere
across cntrl or Srn KS tomorrow...with high pres maintaining
upslope flow into the higher terrain to the W.

As is usual...the fcst is very complex because it mostly hinges
on tstms that have yet to develop. There are a multitude of
possible scenarios as to how things could develop...and fcst
guidance is as varied as your imagination allows.

Amongst all the noise...these are the fairly modest signals we
can deduce...

This afternoon: a couple to a few tstms could develop over the
fcst area and last into this eve. While synoptic help is moving in
aloft...sfc obs show an area of low-lvl divergence over cntrl Neb
in the form of a mesohigh left behind last night`s MCS. These
factors offset each other and could lead to little or no tstm
development.

With temps in the 80s and dwpts in the 60s...MLCAPE will be
approx 1000-2000 J/kg. Model and SREF depictions are probably
overdone as their dwpts are too high by 3-5F. 0-6 km shear will be
25-35 kts from E-W. So if any storms to develop...they could turn
severe.

Warning threshold for 1" hail will be around 34K ft for the top
of 50 dBZ cores.

Single and multicell storm modes will be favored...but can`t
entire rule out an isolated transient supercell.

Tonight: Other sct tstms will develop out to the W over the high
plains this afternoon...within the lee trof and from E upslope
flow which is now established W of Hwy 281. Some of this activity
could creep in from the W tonight ...probably in a weakened sub-
svr state as there will be no low- lvl jet to sustain it.

Tomorrow: Multiple tstm clusters will be on-going during the day
near the Ern borders of MT/WY/SD. This activity will be moving SE
down the mstr/instability gradient...and could send an outflow
boundary down into Neb/KS. Tstms and tstm clusters will develop
and/or expand in the afternoon out to the W and some of this
activity could sneak into the Wrn half of the fcst area.

MLCAPE is fcst between 750-1250 J/kg...greatest over the Wrn and
Srn fringes of the fcst area. 0-6 km shear will be 30-40 kts...
more than sufficient for organized multicells and possibly
supercells...with the clockwise curved hodograph below 3 km.


.LONG TERM...(Thursday night through Wednesday)
Issued at 400 PM CDT Wed Jul 27 2016

The main concern for this period is the potential for severe
weather Thursday night. The SPC Day 2 Outlook has much of our area
in a Marginal Risk with the southwestern counties in a Slight
Risk. A mid-level shortwave is moving across the region that will
aid in thunderstorm development. Current guidance suggests that
generally isolated storms should develop out to our west and
northwest that consolidate into an MCS that moves through western
Nebraska and Kansas. The main question is where exactly this
development sets up. The NAM is more in alignment with the current
SPC outlook and has mainly our southwestern counties having a
greater chance of seeing precipitation while the 12Z GFS suggests
that it could impact a more widespread area of our CWA. Will have
to monitor model trends and hi- res guidance as the event nears.

Friday and Saturday there are additional slight chances for
precipitation but the overall severe threat is lower than
Thursday. Temps will be more pleasant with highs in the 80s. The
northwest flow pattern begins to transition into more zonal flow
across our area as an upper level ridge builds in. This will help
to bring in drier and warmer conditions across the area as highs
reach into the 90s Monday through Wednesday. Will have to watch
dewpoints as heat index values could reach above 100. Although
multiple weak shortwaves move across the area Monday through
Wednesday that provide at least slight chances for precip, most
areas should remain dry.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Thursday)
Issued at 1236 PM CDT Wed Jul 27 2016

Significant Wx: Sct IFR tstms possible this afternoon/eve.

This Afternoon: VFR with SCT CU forming around 4K ft. Slight
chance of an IFR tstm with hail and winds gusting to at least 40
kts after 20Z. Light NE winds. Confidence: low due to uncertainty
with tstm threat.

Tonight: VFR except around SCT IFR tstms which should be departing
to the SE of the terminals. Light NE winds. Confidence: medium

Wed thru 18Z: SCT-BKN VFR clouds mainly at or above 10K ft. Light
NE winds. Confidence: medium

&&

.GID Watches/Warnings/Advisories...
NE...None.
KS...None.
&&

$$

SHORT TERM...Kelley
LONG TERM...Petr
AVIATION...Kelley



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