Area Forecast Discussion
Issued by NWS Hastings, NE
FXUS63 KGID 241546
Area Forecast Discussion
National Weather Service Hastings NE
1046 AM CDT TUE MAY 24 2016
Issued at 1046 AM CDT Tue May 24 2016
A rather substantial fcst update has been published thru 6 pm.
Environmental assessment is still on-going. But what is know is
that early morning tstms are departing to the E with rapid
clearing over all but the Srn fringe of the fcst area. Sfc
analysis shows a diffuse pattern with svrl mesoscale features...
the most prominent of which are the low over SW KS and the outflow
boundaries over Srn KS. There appears to be an old remnant portion
of the cool front from SW-NE across the Sandhills and then back
into SW Neb into NE CO.
Confidence in what transpires today is low. Model depictions of
what might develop vary wildly and are of little use. For what
Model fcsts of dwpts may be svrl degs too high compared to
sfc/upr air obs...and this will impact instability fcsts. The
models appear to be eroding the outflow boundaries and rapidly
advecting dwpts of 65-70F into the fcst area.
Another complication is that the morning tstms were at the Nrn
edge of the cap which was at +9C at 700 mb. This isotherm/cap is
fcst by the RAP to lift N to hwy 6 by 4 pm and I-80 by 7 pm. This
WAA can be see in the 00Z/12Z RAOBs at DDC.
For now...our current expectation is that a few tstms will
develop this afternoon/eve...with the best chance over S-cntrl
Neb. With temps near 80F and dwpts in the low-mid 60s and mid-lvl
lapse rates 7-8 C/km...MLCAPE will be 1500-2500 J/kg. Deep layer
shear will be sufficient (35-40 kts) for well-organized tstms.
Storm mode is also a bit uncertain...but it looks like primarily
multicell...but supercells cannot be ruled out either.
.SHORT TERM...(Today and tonight)
Issued at 443 AM CDT Tue May 24 2016
The next 24 hours is going to be a rather tough forecast due to the
ongoing convection to the south and other finer mesoscale features
that have yet to be realized. Main focus over the next 24 hours is
going to be development of thunderstorms and the severe potential
associated with these storms. The low-end severe threat and
flooding will be ongoing this morning across north central Kansas.
In the upper levels, we remain under southwesterly flow aloft, with
our main feature being a low-amplitude shortwave embedded in this
mean flow ejecting out over the Central Plains later today. The
timing of this shortwave does seem favorable for severe weather to
develop later this afternoon. At the surface, a low should develop
over eastern Colorado/western portions of the Central Plains later
today. There is a little uncertainty with the placement of this low
and could ultimately be a big game changer for our severe potential.
However, with the boundary in place later today and ample
instability ranging around 4000 J/kg of most unstable across a
majority of the forecast area. Bulk shear (0-6 km) values are around
40 knots. Low level shear is not all that impressive until later
tonight after 00Z, but with the boundary around during the afternoon
we will have that in place to make up for the lack of low level
environmental shear. Supercells will be possible within these
environmental conditions. Large hail and damaging winds will be
possible along with isolated tornadoes, especially in the vicinity
of the boundary. The exact location of this severe potential is in
question until the finer mesoscale features become more clear across
the forecast area. Thunderstorms will likely continue overnight and
develop into a more complex MCS of storms and grow larger in overall
coverage. The MCS is more likely develop across northern parts of
the forecast area tonight, or in other words parts of
central/northern Nebraska. Thunderstorms appear to be on the trend
to develop early this afternoon, but confidence remains low for the
exact timing for the start of this event. Current thinking is the
boundary will line up in a north-south orientation through the heart
of the forecast area (along/near highway 281) and storms could start
to fire along this boundary early in the afternoon. Lots of
uncertainty but this is the best first guess until the boundary
lines up later today and that upper level shortwave ejects out into
the plains. Some of the higher resolution models like the NCEP 4 km
WRF-NMM has essentially nothing across our forecast area today,
which is a little disheartening given the 30-50 PoPs in the forecast
at this time indicating thunderstorms today/tonight.
.LONG TERM...(Wednesday through Monday)
Issued at 529 AM CDT Tue May 24 2016
To make a long story short, the upper level longwave mean trough in
the western United States will persist through the long term as a
stationary or nearly stationary boundary hangs around or near our
area. Abundant moisture will be available as most people can tell by
the dewpoints in the 60s recently, so this means several days of
potentially inclement and severe weather, along with near normal to
a bit above normal temperatures. Highs will generally be in the 70s
and 80s and lows in the 50s and 60s.
.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Wednesday
Issued at 623 AM CDT Tue May 24 2016
The terminals will be in (or near) MVFR conditions through at
least mid morning before ceilings increase slightly to VFR.
Conditions will likely fluctuate today with ongoing convection
making this a rather difficult forecast. The ongoing convection
now should work over and delay thunderstorm activity later today.
Thunderstorms are anticipated later but the timing is in question.
Look for updates and follow the forecast closely as this is an
evolving forecast as the finer mesoscale details become clearer
over the next several hours. Confidence is higher for
thunderstorms tonight after 00Z as a cluster of storms will likely
push through the forecast area.