Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 240520

Area Forecast Discussion
National Weather Service Hastings NE
1220 AM CDT Thu May 24 2018

Issued at 939 PM CDT Wed May 23 2018

Have refreshed our forecast and Hazardous Weather Outlook (HWOGID)
within the past 30 minutes to reflect our latest thinking for the
overnight hours...

A brief look back:
Late this afternoon/early evening we dealt with a few isolated
severe storms driven primarily by daytime/diurnal heating and
instability (most severe hail reports were from Phillips County
KS). This convection has long since died off, and over the last
few hours the focus for strong/severe activity has focused (as
expected) to our west over western Nebraska.

Rest of tonight:
The vast majority of the CWA (except for perhaps the far western
fringes) should remain storm-free through at least midnight.
However, agree with the previous forecaster that the overnight
hours could feature almost "random" isolated thunderstorm activity
almost anywhere, especially after 3-4 AM, as weak disturbances in
west-southwest flow aloft interact with a modest 30-45kt low level
jet, and with elevated CAPE/instability in the 850-700 millibar
layer averaging roughly 500-1000 J/kg. With deep-layer shear
remaining fairly weak at around 25kt-or-less, am not expecting
organized severe storms, although a few instances of small
hail/gusty winds cannot be ruled out. Although SPC has formally
placed/kept much of the western half of our coverage area (CWA) in
a Marginal Risk through the night, we have geared our local- level
thinking more toward the non-severe side, and this is reflected in
the latest HWO. That being said, we will need to closely monitor
the western NE convection just in case it tries growing upscale
into more of an organized wind threat. Even so, current
radar/short term model trends largely suggest that any organized
severe storm threat overnight should continue to focus at least
slightly west-northwest of our CWA.


.SHORT TERM...(This evening through Thursday)
Issued at 237 PM CDT Wed May 23 2018

Aloft: RAP analyses/WV imagery and 12Z RAOBs show the Rex block
remains over Wrn N America. The low was over ID/WY with SW flow
over the Plns. The Rex block will finally break down over the next
24 hrs...but that does not mean an end to the summer wx. Models
are tightly clustered on the low drifting into MT tonight and into
the Canadian Prairies tomorrow. As this occurs...the flow will
remain SW over the Cntrl Plns...but a trailing trof from the low
will move over the Plns from ND to Wrn KS by 00Z/Fri.

Surface: The CWA was in the warm sector. Low pres was over MT
with a warm front extending SE into the mid-MS Vly. High pres was
over the GtLakes. The rgn will remain in the warm sector thru
tomorrow as the low lifts to Lk Winnipeg. As it does so...a
trailing sfc trof will drift from the lee side of the Rockies into
Cntrl Neb and NW KS... extending from ONL-LXN-CBK.

Now thru mid-evening: Isolated tstms. MLCAPE 1500-2000 J/kg but
0-6 km shear is very weak (20 kt). So expect outflow dominant
ordinary cells.

Tonight: Any evening storms will die shortly after sunset with no
help aloft. With no change in the situation...could small/isolated
shwrs and possibly a tstm or two redevelop after 3 AM...similar to
this morning. Most locations will remain dry.

A mild and muggy night with dwpts in the 60s. Temps will not fall
below 70F until after midnight.

Thu: Possibly similar to this AM with small isolated shwrs
associated with high-based ACCAS. Isolated tstms could develop
along the sfc trof. With temps 87-92F and dwpts in the 60s...
MLCAPE is fcst near 2500 J/kg. 0-6 km shear will be 15-25 kt
across the CWA (lowest E/highest W). Any tstms that develop could
turn svr...but tstm coverage will not be widespread.

Temps similar to today (87-92F).

.LONG TERM...(Thursday night through Wednesday)
Issued at 237 PM CDT Wed May 23 2018

Aloft: The last 2 runs of global models and the EC/GFS ensemble
means are in excellent agreement that the Westerlies will remain
far to the N over Canada thru next Wed. Low-amplitude NW flow will
occur Fri behind Thu`s trof. A ridge will then build over the
Cntrl USA Sat downstream of a low that moves into the Wrn USA and
cuts off over UT. Neb/KS will be on the W side of the ridge with
weak SW flow. Predictability regarding when cut-off`s open up or
become mobile is low...but present indications are that a trof
approaching the W coast could force the low to lift into the Nrn
Rckys Tue and the Nrn Plns Wed as a remnant trof. The tail end of
this trof could affect the CWA.

Surface: Very weak high pres will build over the Cntrl Plns Fri-
Sat. It is then fcst to drift E of the rgn Sun. A large high will
sink from Canada into the GtLakes Mon-Wed. This scenario will
maintain Multiple days of return flow.

Temps: The heat is on. Welcome to an early summer. Widespread
low-mid 90s Fri-Mon...then possibly cooling back into the 80s-low
90s Tue-Wed as heights fall a bit.

Precip: Mostly dry. There will be the typical isolated tstms that
fire daily well to the W within the lee trof. The weak flow and
lack of forcing will keep nearly all of it well to the W of the
CWA...but can`t completely rule out a rogue storm or two making it
to areas W of Hwy 183. If the upr trof moves thru here Tue or Wed
that would increase the risk of sct tstms.


.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Friday)
Issued at 1213 AM CDT Thu May 24 2018

VFR is forecast for the TAF period. The LLJ will setup once again
tonight and looks strongest out west, so will put a mention of it
in the EAR TAF. Chance for TSRA overnight with LLJ, don`t have
high confidence that they will impact TAF sites so left out a
mention for now.




LONG TERM...Kelley
AVIATION...Beda is the U.S. government's official web portal to all federal, state and local government web resources and services.