Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 242032
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
332 PM CDT TUE MAY 24 2016

...No Change in the Pattern thru Next Tue with an Active Pattern
Resulting in Daily Potential for Severe Tstms and Flash
Flooding...

.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
low.

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
areas.

Negative factors:

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
possible.

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 18Z KGRI/KEAR TAFS through 18Z Wednesday
Issued at 103 PM CDT Tue May 24 2016

Significant Weather: Sct IFR +TSRA. Potential for MVFR or IFR
stratus 09Z-15Z Wed.

This afternoon: VFR. Just a few altocu around 12K ft initially...
but sct cu should develop around 5K ft. A few IFR tstms could
develop nearby after 21Z. Winds are not behaving as model guidance
is expecting as the environment has been perturbed by tstm
activity. Winds could be anywhere between SSW-SSE 8-15 kts.
Confidence: medium

Tonight: VFR except in pockets of IFR +TSRA. There is some
potential for a bit of MVFR/IFR fog/stratus after 09Z. Winds
outside of tstms will be SE 5-10 kts. Confidence: Medium

Wed thru 18Z: Possibly MVFR/IFR fog/stratus to start. Any tstm
activity nearby should end early. Otherwise...VFR. Winds probably
SE 5-10 kts away from any tstm activity. Confidence: Low

&&

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

$$

FORECAST/AVIATION...Halblaub



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