Area Forecast Discussion
Issued by NWS Hastings, NE

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099
FXUS63 KGID 201716
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1116 AM CST Fri Jan 20 2017

.SHORT TERM...(Today and tonight)
Issued at 413 AM CST Fri Jan 20 2017

The biggest issue will be fog this morning. I have extended the fog
advisory another couple of hours to go to noon, considering recent
output from the HRRR, RAP, and SREF. Also, it`s a safer bet to go
later with fog advisories in January as the sun angle is still quite
low, and we still have a solid deck of stratus to contend with.

The synoptic trough over the intermountain west is becoming
increasingly negatively tilted today as another lobe of energy is
expected to swing through tonight. In the meantime, pretty much the
same as yesterday with stratus and areas of drizzle, with a small
chance of measurable rain creeping in with the next wave
approaching. Highs will be in the lower to mid 40s. The best
chance of any accumulating rain will be this evening between
roughly 6 pm and midnight. There is decent agreement among
numerical models for this. After the trough axis passes through,
chances of precipitation wane quickly after midnight, but there is
a small chance of some snow at the end of precipitation, but no
appreciable accumulation is anticipated. Lows tonight will end up
in the lower 30s.

Followed closer to CONSshort dewpoints through the short term as it
appears to initialize best, and CONSMOS winds tonight behind the
trough axis. SREF gives a strong signal for more fog development
tonight, but as wind shifts to the west behind the trough, I expect
fog intensity to wane toward 12Z Saturday.

.LONG TERM...(Saturday daytime through Thursday)
Issued at 430 AM CST Fri Jan 20 2017

General overview of this 6-day period:
This forecaster is making the flip from short-term and frankly is
examining these particular longer term periods closely for the
first time. At a quick glance, and needless to say, the
"highlight" of these periods remains the potential winter storm
event centered on the Monday night-Tuesday night time frame (more
on this below). Outside of this system (both before and after),
the majority of this 6-day period is looking relatively quiet and
largely precipitation-free, with the secondary story being a
modest cool-down from high temps well into the 40s to near-50
Saturday-Monday to more seasonably-chilly highs in the 30s by
Wednesday-Thursday.

Some comments on the Monday night-Tuesday night system:
Despite a plethora of usual model uncertainties the past few
days, this system has slowly-but-surely been gaining more
attention at is creeps closer in time. For what it`s worth, the
latest 00z runs of the ECMWF/GFS seem to be in reasonably-good
agreement for a system still being a solid 5 days out. Will go
into more detail below, but the basic story is that northern
portions of the CWA (especially northwest of the Tri Cities) would
seem to have a halfway-decent shot at at least an "advisory-
worthy" snow event, while southern areas (especially KS zones)
stand lower chances for truly impactful amounts (perhaps little if
any). All this being said though, the highest snow totals of all
(best potential for perhaps Warning criteria) still seem generally
favored to target just north of our CWA within the northern 1/2 to
1/3 of the state. At any rate, snow would not be the only
story/concerns with this system. Another issue (unlike with our
recent ice storm) would be the likelihood of fairly strong north-
northwest winds especially Tuesday afternoon into Wednesday, and
the obvious implications for added impacts in falling snow.
Although the official forecast grids do not yet reflect speeds
this strong, the potential for sustained 25+ MPH/gust 35+ MPH
speeds appears to be there. In addition, and also not explicitly
reflected in the current official forecast, it may not be a truly
"clean" transition from rain to snow in parts of the CWA either
during the first part of the event, with perhaps at least a brief
wintry mix occurring before the deeper cold air becomes more
dominant. As usual, despite the seemingly-better model agreement
than recent days, we have a LONG ways to go to pin down the
details of this mainly 5-days-out system. We are still around 2
days away from potentially hoisting any winter headline products
and also about 2 days away from advertising any "official" snow
amount forecasts. However, this system at least continues to have
enough potential to warrant a mention in our Hazardous Weather
Outlook (HWOGID) and will maintain this inclusion which was
started yesterday. For a system still this far out, I have already
said plenty, but for a bit more meteorological detail see the day-
by-day breakdown below.

With the "high points" covered above, will conclude with some
day-by-day details for those interested...

Saturday daytime:
After 2 straight days of being "socked in" under widespread low
clouds and/or fog, for most folks the biggest story Saturday will
be a return to at least partly cloudy/mostly sunny skies,
especially by the afternoon hours. In the mid-upper levels,
various primary models are in good agreement that the center of
the mid-level shortwave responsible for the fog/precipitation
chances in the short term will already be exited well off into IA
by sunrise Saturday. Right away in the first few hours of the
official daytime period (mainly 6-9 AM), cannot rule out a few
lingering sprinkles/flurries possibly still flirting with mainly
our far north/northeast zones but will leave out for now. In
addition, while not expected to be nearly as widespread/dense as
these past few mornings especially given that surface winds will
have turned light westerly by this time behind a passing trough
axis, the first few hours of the morning could at least feature
some lingering patchy fog and this has been added to the forecast.
Otherwise, as the day wears on, expect skies to largely clear
from generally southwest-to-northeast with fairly light westerly
breezes prevailing. High temps were nudged up very slightly
especially in Neb zones, aiming for upper 40s most Neb counties
and low 50s in KS.

Saturday night:
Finally, what should be a reprieve from fog for a change, as light
northwest winds actually increase a bit during the night in
response to a low pressure system passing to our south mainly
across OK. Any precipitation associated with this system should
remain a solid 75+ miles south of the extreme southern edge of
our CWA. Low temps aimed into the upper 20s most areas.

Sunday-Sunday night:
These 24 hours should be pretty much "guaranteed dry" as the local
area remains in between the departing southern system and the next
upstream trough to the west. Despite at least mostly sunny skies
most areas, temps look to be a few ticks cooler than Saturday
behind a weak cold front, but still well into the mid-upper 40s
most areas. The bigger difference from Saturday will be stronger
breezes, with sustained northwest winds up to around 20 MPH and
gusts 25-30 MPH. Breezes subside Sunday night and turn more
westerly.

Monday daytime:
Flow aloft over the local area starts turning more southwesterly
ahead of the next large-scale trough to our west, but the day
looks to remain precip-free and seasonably-mild as breezes pick up
a little from the south-southeast. High temps mid 40s north to low
50s south.

Monday night-Tuesday night:
See paragraph above for a general overview, but these 36 hours are
currently the "highlight" of the long term forecast. Generally
speaking, the latest 00z ECMWF/GFS agree that a strong mid level
closed low will pass through eastward somewhere between the KS and
SD borders during this time frame, with an associated strong
surface low deepening to anywhere from 987-995 millibars as it
also tracks east across the Plains. Although models are far from
set on a final solution/storm track, the last few ECMWF runs are
clearly more supportive of perhaps several inches of snow for
mainly northern portions of our CWA than the GFS, which tends to
only "brush" our northern zones with halfway decent snow potential
and next to nothing in our south. As already covered above,
whether it snows much or not there will likely be a decent blast
of strong northwest winds especially Tuesday afternoon into
Wednesday morning. High temps Tuesday could be very tricky, with
potential for quite a colder (northwest) to warmer (southeast
gradient, but for now will call for mid 30s northwest to mid 40s
southeast with falling temps likely during the afternoon. If
warmer air happens to hang on longer, then precip could favor rain
longer into the event and cut into snow totals, but plenty of
uncertainty here for sure.

Wednesday daytime-Thursday daytime:
At least for now, these last few days of the official forecast are
void of precip chances, although would not be surprised to see at
least a few flurries hanging on especially Wednesday morning
behind the departing system. The Canadian model is actually most
aggressive with the possibility of light snow hanging on into
Wednesday so this bears watching. Overall though, the main story
these two days will finally be a more solid return to "January-
like" temperatures, with high temps only low-mid 30s most areas.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Saturday afternoon)
Issued at 1114 AM CST Fri Jan 20 2017

Some challenges in the TAF this afternoon. There is still some fog
around. Visibility has been improving, but there are still pockets
of lower visibilities. The visibility will improve some this
afternoon, but there will be lower visibilities tonight again.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Dense Fog Advisory until noon CST today for NEZ039>041-046>049-
     060>064-072>077-082>087.

KS...Dense Fog Advisory until noon CST today for KSZ005>007-017>019.

&&

$$

SHORT TERM...Heinlein
LONG TERM...Pfannkuch
AVIATION...JCB



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