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FXUS63 KGID 271130

Area Forecast Discussion
National Weather Service Hastings NE
630 AM CDT Tue Jun 27 2017

.SHORT TERM...(Today and tonight)
Issued at 349 AM CDT Tue Jun 27 2017

This Morning:
Patchy fog has developed across the area. Short-term models did a
decent good job picking up on this potential. Visibility has been
variable and highly dependent on the wind speeds. Nevertheless, I
went ahead and issued a dense fog advisory until 9 AM. If trends 
continue, there is a chance that this will need to be expanded 
northward later this morning. Fog should mix out by 8-9am as 
southerly winds increase. 

This Afternoon and Early Evening: 
Speaking of winds, a tightening pressure gradient should produce
sustained southerly to south-southeasterly winds of 20 to 30 MPH 
with gusts around 35 MPH west of Highway 281. The HRRR and RAP 
only have sustained winds of 15 to 20 MPH this afternoon, although
given the strength of the pressure gradient, I think that they 
may be underdoing it a bit. Winds will decrease a bit in the 
evening as mixing decreases, but will remain breezy until 
thunderstorms roll through overnight. 

Late Evening and Overnight: 
Thunderstorms are expected to develop across western Nebraska late
this afternoon ahead of an upper level shortwave trough moving
into the region. Locally, we will remain capped until this forcing
pushes these storms into the area...most likely after 02Z. We will
still have ample instability (1500-2500 j of MUCAPE) and shear
(35-45 kt of 0-6km bulk shear) to maintain severe storms. Because
of this, we could see some large hail as the storms arrive, but
wind will should quickly become the main threat as storms merge
into an MCS aided by a 50-60 kt low-level jet. The latest
NAM/GFS/EURO all take the bulk of the activity through the
northern parts of the area, along the edge of the instability
gradient and where there is a bit better convergence at 850mb. For
this reason I mostly kept the likely PoPs north of I-80. That
said, the NAMnest and NCAR WRF Ensemble still bring activity down
the Platte River, so I don't think that we will miss out entirely. Activity
should clear the area by tomorrow morning as a weak front makes 
its way through the area. 

.LONG TERM...(Wednesday through Monday)
Issued at 349 AM CDT Tue Jun 27 2017

Overview...Several chances for thunderstorms with appreciable 
moisture stand out. With so much of the forecast area having seen 
below normal rainfall thus far through June, hopefully we can get 
some appreciable moisture out of at least one of these upcoming 
opportunities. The better rain chances will be Wednesday night 
especially south of the Platte River, then Thursday evening near the 
sfc front but hard to pinpoint, and then finally with yet another 
shortwave Sunday afternoon/evening.

We do expect a warm up getting us closer to seasonal temperatures 
but still perhaps a few degrees below normal on most days. Normal 
highs are now generally in the mid to upper 80s over south central 
Nebraska to around 90 over north central Kansas.

Wednesday...A sfc trough will track southeast across the forecast 
area through the day and will largely be southeast of the forecast 
area by late afternoon when there is the best chance of firing 
thunderstorms along this sfc boundary. Therefore...will call for dry 
conditions on Wednesday with any sfc based convection likely firing 
east of our forecast area. 

Wednesday night...the low level jet will really get cranking after 
dusk with what models are indicating will be a strong 50 kt 850 mb 
southerly wind across much of Kansas. This 850 mb jet will nose 
right into our forecast area, probably north central Kansas or far 
south central Nebraska leading to strong convergence and a good 
chance of thunderstorm development after dark. Our rain chances may 
not be high enough. Models differ on the convective initiation and 
how widespread this event will be, but are fairly similar with the 
pattern. This pattern looks good to me to really dump on an area of 
two to three counties in width with some training elevated 
thunderstorms leading to a localized flash flooding threat under the 
zone where these storms develop. Given the storms will be elevated, 
believe that large hail and flash flooding will be the primary 
threats. There is a lot of elevated instability and wind shear is 
more than sufficient. Can not rule out a few strong wind gusts 
making it to the sfc, but that may be more rare given storms will 
likely be elevated. Not everyone, will get wet, and we will need to 
see where that couple county wide convergence zone will set up.

Thursday...Confidence in precipitation chances is honestly a bit low 
as we'll have to see how Wednesday night convection impacts the sfc 
frontal boundary. Best estimate is that the sfc front will be 
southeast of our forecast area, which could limit our rain chances. 
However, an upper level trough will be swinging through the central 
and northern plains and could provide enough support for afternoon 
and evening thunderstorms even on the north side of the sfc front, 
but models are hit and miss on this happening. The best chance for 
thunderstorms will be along the sfc front wherever it ends up being 
located after the Wednesday night storms.


.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Wednesday)
Issued at 625 AM CDT Tue Jun 27 2017

Fog and low stratus is in the process of mixing out this morning.
Conditions have improved to MVFR and should improve to VFR over
the next two hours.

Still expecting gusty south-southeasterly winds this afternoon and
evening. Gusts will reach 25 to 30 kts. 

Scattered thunderstorms are expected to move through the area
between 02Z and 08Z. Some of these storms could be severe. It
appears that wind gusts will be the main threat. 

LLWS is possible late tonight as the low-level jet increases to
around 50 kts. 


NE...Dense Fog Advisory until 9 AM CDT this morning for NEZ041-

KS...Dense Fog Advisory until 9 AM CDT this morning for KSZ006-007.



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