Area Forecast Discussion
Issued by NWS Hastings, NE
FXUS63 KGID 250544
Area Forecast Discussion
National Weather Service Hastings NE
1244 AM CDT WED MAY 25 2016
.DISCUSSION...(This evening through Next Tuesday)
Issued at 332 PM CDT Tue May 24 2016
Aloft: The longwave trof was over the Wrn USA with SW flow over
the Plains. The deterministic global models and ensemble means are
in very good agreement that this pattern will not change thru next
Tue. That means active wx with daily opportunities for tstm
activity...but some days will produce more than others. Tstms
will be mostly determined by low-amplitude/subtle shortwave trofs
and/or the nocturnal low-lvl jet. One of these trofs will be
moving by to the NW tonight into tomorrow. The upr low off CA will
be kicked thru the Desert SW Thu as the next low drops into the
backside of the Wrn trof. This low will open up and lift across
the Cntrl Plains Fri night into Sat. This low should cause a
significant increase in tstm activity.
Surface: The cool front that became stationary from SW-NE across
the Plains a couple days ago was ill-defined in places due to
multiple tstm episodes...but it extended roughly from low pres
over SW KS N-NE across Neb into the Dakotas. This front was just N
and W of the fcst area...from SW Neb across the Sandhills. It
appears that the upr trof fcst to brush the fcst area will force a
sfc low to develop tonight and lift into the Dakotas tomorrow. The
circulation around this low should shove whats left of the front E
of the fcst area by daybreak Thu. Lee cyclogenesis will then occur
Thu as the upr low approaches. This low will lift NE into the Nrn
Plains Sat. But there won`t be much of a cold sector with this
Now into tonight: There are svrl negative factors against
convective initiation anytime soon. Believe the tstm threat will
be delayed. This afternoon and early evening should be dry most
1) Vis satellite shows no cu field. Dwpts are lower than
currently modeled and this has resulted in more CIN and less
instability. Dwpts have remained in the mid-upr 50s. The models
are trying to surge the mid-upr 60s in here...and obs show them
confined S of the outflow boundaries over Srn KS and OK.
2) There is a shortwave ridge/subsidence over the region. However
...there is a small darkening WV imagery over Wrn KS and this is
where one storm is initiating at 315 pm within an increasingly
agitated cu field.
3) Another issue is the cap. This morning`s tstm activity was just
N of the +9C isotherm at 700 mb. That isotherm is fcst by the RAP
to be up to Hwy 6 right now. This could also limit development.
The low-lvl jet will strengthen against tonight...with associated
convergence/WAA and moisture transport. This should initiate sct
tstms. MLCAPE will be 2000-3000 J/kg. Deep layer shear will
actually drop off tonight as low-lvl winds attain similar speeds
to the mid-upr lvls...but some directional shear will remain.
Overall fcst confidence is low...but where storms develop they
will have the potential to be svr with flash flooding also
Beyond tonight...trying to pin down details in this fcst is like
chasing after the wind. The entire fcst hinges on tstm development
which has fairly low predictability in this pattern. And what`s
more...future tstm development largely depends on previous tstm
development. So all we can say with any confidence is that tstms
are possible every day. As mentioned above...some days will be
more productive than others.
Thu-Fri: convective initiation appears likely Thu night along the
front that will be stationary across Nrn KS.
.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Wednesday night)
Issued at 1238 AM CDT Wed May 25 2016
The terminals will begin in VFR conditions, and these conditions
should persist through much of the TAF period, except for the time
period when thunderstorms transition through the forecast area.
These storms will likely bring the terminals down to MVFR
conditions for both ceilings, and in the heavier rain visibility
will be reduced as well. Thunderstorms should be moving out later
this morning with nearly all day in VFR conditions. Thunderstorms
will likely be done around 7 am for both the terminals.