Area Forecast Discussion
Issued by NWS Hastings, NE

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569
FXUS63 KGID 231142
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
542 AM CST Thu Feb 23 2017

...Back to Temps Much More Typical of Late Feb with a Winter Storm
and Much-Needed Precip in the Transition...

.SHORT TERM...(Today and tonight)
Issued at 426 AM CST Thu Feb 23 2017

Aloft: WV imagery and aircraft data showed a modest shortwave
ridge over the Cntrl/Nrn Plns...and a trof over the Wrn USA. A
well- defined upr low was embedded within the trof moving E along
the ID/UT border per IR satellite. This low is fcst to fade while
a new low forms over NE CO as lee cyclogenesis continues. The new
low will eject into Neb this afternoon with the GEM/GFS/EC/NAM
tracking it along I-80. It will be along the IA/Neb border by
12Z/Fri.

Surface: Low pres was over the GtLakes with a cool front
extending SW thru IL-MO-KS to developing low pres over CO. This
front will remain stationary today while the low deepens over SE
CO. This low will become mobile this afternoon with the 00Z models
clustered on its arrival at DDC by 00Z...MCI by 06Z and near the
confluence of the IA/MO/IL borders by 12Z/Fri.

Today: M/cldy and much cooler...especially over S-cntrl Neb were
ODX will be almost 30F colder than yesterday. Overall...much of
the day will be quiet and dry. The precip will cont filling in
from the Sandhills thru Wrn Neb...and the leading edge of this
will begin infringing on the fcst area after 3 pm. Meanwhile...sct
shwrs and elevated tstms will form late afternoon over KS and
drift NE into the fcst area.

Thunder: expanded thunder to further N into S-cntrl Neb to better
coincide with SPC D1 outlook. While thunder is certaintly
warranted for 150-500 J/kg of elevated CAPE with greatest amts
over N-cntrl KS...attm do not believe there is enough instability
to get severe hail. Some smaller hail certainly is possible.
HWO also updated.

Ptypes are iffy to start this event. Low stratus is moving in
from the N and this is retarding nocturnal cooling. Believe CAA
should lower temps enough for initial pcpn to fall as snow from
LXN-ODX this afternoon. The rest of the fcst area will start as
rain or rain shwrs. The BL will be warm and there will be a mid-
lvl warm nose to be erased.

Tonight: The pcpn band should really fill in and/or move in...
enveloping much of the fcst area. Rain will gradually changeover
to snow from NW-SE.

There is a lot of uncertainty on pcpn potential over N-cntrl KS
...but given that the mid-lvl low will track along I-80...N-cntrl
KS will be largely dry-slotted. Pcpn will be transitory and amts
will be considerably lighter.

Models: Coordinated with WPC and their QPF was used exclusively.
The NAM conts its bias of being too far N with the QPF. We`ve seen
it in every system this season. So this fcst was heavily weighted
toward the GFS.

Snow Amts: they really depend on how quickly rain changes to snow
and how much snow melts on contact. The ground is not cold after
this 8 day stretch with high temps of 60F or better each day.
Using WPC QPF and GFS thermal profiles with fairly low snow:liquid
ratios...we now have 1-2" in the Tri-Cities by daybreak Fri with
2-5" N and W of the Tri-Cities.

Based on storm totals (see LT section below)...have added another
row of counties to the Winter Stm Wrng and another row to the
Advy...plus Gosper/Phelps Counties. This may not be the final
changes to the headlines (Advy/Wrng areas). This is based on the
latest info we have at this moment. We need to see how things
evolve.


.LONG TERM...(Friday through Wednesday)
Issued at 359 AM CST Thu Feb 23 2017

The main issue for the extended forecast will be potential snow
amounts for Friday.

Friday morning snow amounts will be something to pay attention
to. We`ll be essentially watching the deformation band as the low
pulls off to the east. The position of the 700 mb low over eastern
Nebraska suggests that at least our far north could stand to get a
few more solid inches of snow before all is said and done. This
will set us up for storm total snow of 5 to 8 inches of snow from
the Winter Storm Warning area for 5 counties along and north of
Highway 92, to 3 to 4 inches for tri-cities, to below an inch for
our north central Kansas, with the winter weather advisory
continuing into Friday/Friday evening for near Interstate 80 and
farther north, meeting up with the aforementioned winter storm
warning. Continuing the thought that the NAM is biased
north/northwest in the cold sector, with the GFS/ECMWF having a
better grasp, placing some solid winter storm snow amounts over
our north, especially 6 or 8 inches near Ord and Greeley.

I kept precipitation type snow, because once we turn to snow, the
overwhelming cold air throughout the column from strong cold air
advection should prevent any changeover back to rain, even in our
south. I kept some blowing snow in for Friday into Friday evening
as I nudge sustained speeds toward CONSMOS and used CONSRAW for
wind gusts, which could be over 30 mph in some spots.

The wind should finally start slacking off Friday evening and
should let up enough to allow the winter products to go. Most of
any snow should wrap up Friday afternoon as the system is
consistently forecast to move precip out by Friday evening. I also
lowered high temperatures on Friday, as most will not even make it
to 30, considering the strong cold air advection, sky cover, and
potential snow on the ground.

We will generally have subsidence behind this system, eventually
flattening upper flow, but turning a bit more southwest over our
area as another wave(s) advance(s) into the Central Plains. We
generally have low pops in the Monday night and Tuesday night time
frame as temperatures modify into the 40s/50s next week. At this
point this hardly looks like a big deal.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Friday)
Issued at 542 AM CST Thu Feb 23 2017

Significant Wx: IFR CIGs thru 12Z with VSBYs decaying to IFR in
SN beginning roughly 00Z. De-icing/plowing ops will be required.

Today: IFR CIGs arrived as expected. Sct SHRAs develop around 21Z
with steadier RASN moving in from the NW. Can`t rule out brief
LTG/TSRA but it`s too soon to include in the TAFs. RA changes to
SN toward 00Z. NE winds gust up to 29 kts at times. Confidence:
High

Tonight: IFR CIGs/VSBYs in steady SN. Could see TEMPO 1/2SM SN
VV002 sometime btwn 00Z-07Z. Wet snow accumulates on RWYs. SN
intensity begins to decrease by 09Z. Winds become N-NNW gusting
25-35 kts. Confidence: High

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from 6 PM this evening to 9 PM CST
     Friday for NEZ048-049-060>064-072-073.

     Winter Storm Warning from 6 PM this evening to 9 PM CST Friday
     for NEZ039>041-046-047.

KS...None.
&&

$$

SHORT TERM...Kelley
LONG TERM...Heinlein
AVIATION...Kelley



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