Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/02/16

Area Forecast Discussion

National Weather Service La Crosse WI

 529 PM CST Thu Dec 1 2016

.UPDATE...
Issued at 322 PM CST Thu Dec 1 2016

With the latest RAP soundings, showing a saturated sounding up to
1.5 km and some omega (ahead of a short wave trough moving south
through Minnesota) in this layer, added drizzle to the forecast
through midnight tonight.

&&

.SHORT TERM...(This evening through Friday)
Issued at 220 PM CST Thu Dec 1 2016

At 2 PM, a closed low was located over eastern Ontario and western
Quebec. With this low moving away from the area, much of the area
has been dry this afternoon. The only thing that we will have to
watch tonight is a weak short wave moving south through northern
Minnesota. The radars have been pretty quiet with this system.
However, there was a recent report of unknown precipitation at
Aiken MN. With the soundings not showing much lift across the
region, opted to keep the forecast dry for now.

The only other issue tonight looks to be the low temperatures.
With persistent cloud cover and neutral temperature advection,
the MOS temperature look too cold. As a result, did a trajectory
analysis to see where this air mass was this morning. This
revealed that this air mass was over northern Minnesota and the
temperatures were near 30F this morning. Due to this, opted to
raise the low temperatures closer to these values tonight.

.LONG TERM...(Friday night through Thursday)
Issued at 220 PM CST Thu Dec 1 2016

From Saturday night into Sunday evening...the 01.12z models
continue to show that a short wave trough will move east through
the region. Soundings continue to show that the temperatures aloft
and at the surface will be cold enough for the precipitation to
start out as snow. However there is some indication in the NAM
that there may be a lack of icing initially which could could
result in maybe some patchy freezing drizzle. With surface
temperatures warming into the mid and upper 30s on Sunday, the
boundary layer will sufficiently warm for the snow to change to
either a mix of rain and snow or to all rain. As far as snow
totals, the SPC plumes show that most of the models have snow
totals ranging from a dusting to maybe up to a half inch.

Beyond Monday, the models continue to show a wide variety of
solutions. Some show that the northern and southern streams will
phase over the region. This would result in a strong low moving
through the Midwest. Meanwhile, other models show no phasing at
all. In this scenario, we would be split and would see no
precipitation at all. With the 01.12z ECMWF was running 3 hours
late due to a power failure, did not get a chance to look at that
model at all.

As far as the temperatures, the models continue to show that the
850 mb temperatures will plunge into the -10C to -15C range. While
this will be cold, it is not that unusual for December. The models
continue to show a large spread with standard deviations up to 7.
This is a result of uncertainty on the snow extent across the
region. If the ground remains snow free, high temperatures would
range from the mid-20s to the mid-30s. If we become snow covered,
we would see high temperatures anywhere from the teens to the
mid- 20s. Due to this uncertainty, just stayed with model blends
for now.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 529 PM CST Thu Dec 1 2016

No significant changes are expected to occur through Friday. The
area of low pressure south of Hudson Bay will remain nearly
stationary which will maintain the low level cyclonic flow over
the Great Lakes Region. With lots of low level moisture stuck in
this flow, the clouds will remain in place with little movement in
the ceiling heights expected for an extended period of MVFR
conditions. There could also be a little bit of drizzle this
evening as a mid level short wave trough rotates over the area.
Not expecting this to produce any visibility restrictions, so for
now, will keep this out of the forecasts.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

UPDATE...Boyne
SHORT TERM...Boyne
LONG TERM...Boyne
AVIATION...04




Area Forecast Discussion

National Weather Service State College PA

 1011 PM EST Thu Dec 1 2016

.SYNOPSIS...
A large and deep storm system will move slowly through Quebec over
the next couple of days keeping a prolonged period of cool
northwest flow over the local area. High pressure will build in
for a brief time Sunday before the next frontal system approached
early next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
No big changes late this evening as lake effect regime continues
tonight. Lake clouds and flurries hugging areas along and north of
the PA/NY border this evening are showing a slight southward
drift. Latest HRRR in good agreement with this trend for the
overnight...as backing flow upstream flow evidence in northeast
Ohio should bring this to fruition. Expect an increase in snow
shower activity after midnight across the north. Boundary layer
and sfc marginally cold and bands not expected to become very
organized. However...a light accumulation will be seen over my
northern tier overnight. Some sprinkles still mixed in in areas
where lighter precip rates occur.

Mins will be fairly uniform throughout...ranging from the lower
30s northwest to the lower to middle 30s elsewhere.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
The cold NW flow will remain air in place for Friday, but again
the cold air is unimpressive so NW snow shower activity is not
expected to amount to more than nuisance amounts. With high temps
expected to be above freezing, most areas will ave a hard time
making any snow stick at all.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
As low continues to move further east into the Canadian Maritimes,
lake effect snow showers over the NW mtns will gradually wind down
on Sat. But one last shortwave Fri night could be enough to extend
snow bands into parts of the central mtns for a time.

Sunday brings a brief respite as high pressure moves over the
state. By late Sunday into the overnight, a period of light snow
is possible as a northern stream shortwave races through the
region with a burst of warm advection. QPF looks to be on the
order of a tenth of an inch or less, but occurring overnight many
places could see their first coating of snow of the young season
by Mon morning.

Another ridge moves through on Monday as progressive weather
pattern becomes more active. On Tues there is decent agreement in
bringing the SW US upper low up through the OHIO Valley as a
shearing out shortwave and diffuse surface low. Unless cold air
damming traps enough chilly air in the low levels to make for some
freezing rain, the precip type with this midwest system looks to
be mainly rain.

The end of the week brings some model disagreement with the
GFS/GEFS being faster than the ECMWF with the next large upper
trof and frontal system. Either way, precip looks like a good bet
around the Thu/fri period as all solutions eventually bring this
trough through. So predictability is increasing, but timing issues
remain. Best bet for precip at this point is mainly rain over the
SE as decent push of warm air lifts ahead of the system, with a
rain/snow mix further north where warm air will not infiltrate as
much.

Behind the trough, looks like a chilly weekend in store with a
potential sharp dropoff in temps.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Widespread MVFR to low end VFR CIGs will persist through the
overnight over the favorable cold advection/upslope region from
KBFD to KJST (and possibly extending briefly at times into the
KUNV/KAOO areas), with VFR, BKN-OVC conds across the east
scattering out late across the Lower Susquehanna Valley
airfields - KMDT, KLNS, KMUI and KTHV.

An initial mean WSW wind flow in the boundary layer will keep
lake effect snow showers mainly north of the PA/NY border through
05Z Friday.

Last several runs of the HRRR and BUFKIT time/height
cross-section continues to show a slight (10-15 degrees) veering
to the mean wind within the sfc-850 mb layer (to about 280-285
deg) which will cause the bands of enhanced lake effect snow
showers to shift slowly south from the Western Southern Tier
counties of NY, into NW Pa at times late tonight and Friday.
Thus, IFR vis reductions appear likely, and will become more
persistent at KBFD very late tonight into Friday.

Outlook...

Fri-Sat...MVFR CIGS and ocnl SHSN accompanied by IFR vsbys at KBFD/KJST.
Mainly MVFR to low-end VFR cigs and VFR vsbys at KAOO, KUNV and
KIPT. Sct-Bkn VFR Cigs and VFR vsbys expected to continue at KMDT
and KLNS.

Sun...Slight chance of light snow/reduced vis at night.

Mon...No sig wx expected.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Gartner
NEAR TERM...DeVoir/Gartner
SHORT TERM...La Corte/Gartner
LONG TERM...La Corte/RXR
AVIATION...Lambert/Gartner




...Update to aviation forecast discussion...



 .SHORT TERM...(This evening through Friday)
Issued at 208 PM CST Thu Dec 1 2016

A quiet weather pattern will persist through tonight and tomorrow
with generally zonal H300 flow in place tonight, transitioning to
more southwesterly flow tomorrow as a broad longwave trough moves
into the western CONUS. Trended towards the ADJ/MOS guidance for
lows tonight given the minimal changes in the air mass and last
night`s lows. There is some uncertainty with regards to low temps
in the south with both the NAM and RAP developing a patch of
altostratus over SE KS that barely skirts the CWA. Weak northerly
surface flow should keep highs tomrrow similar to today with
increasing clouds late ahead of our weekend storm system.

.LONG TERM...(Friday night through Thursday) Issued at 208 PM CST
Thu Dec 1 2016

For the long term, we are continuing to deal with the evolution of
the long wave upper trough over the central US, timing and impact
of shortwave energy and the eventual first intrusion of arctic air
into Kansas early next week.

All operational models continue to spread moisture north across
the southern plains northeast of an upper low over northern
Mexico and breaking out precipitation by Friday afternoon south of
Kansas. The moisture, weak lift and mainly light precipitation
continues spreading north across eastern Kansas on Saturday.
Meanwhile, a shortwave in the northern stream is forecast to cross
the central plains Saturday night and Sunday morning shifting the
moisture and precipition east of the area. The models have been
somewhat consistent with this weak system over the past couple of
days. Much of the precipitation should be rain, but there is a
risk of a wintery mix especially early Saturday and Sunday
mornings, but winter weather impacts are not expected.

The models are in fair to poor agreement with the movement the
northern Mexico upper low and the eventual arrival of the arctic
air in northeast Kansas. We are confident that the upper low will
be kicked out by shortwave energy moving south on the western side
of the large upper trough early next week. As the upper low
approaches, light rain is forecast to develop and it should
remain liquid until the arrival of deep cold air behind the front.
With respect to the arctic air, the models have been very
inconsistent with the passage of the front. The 12Z GFS is now the
most aggressive with the cold air which is totally different than
yesterday. The new GFS has the cold air being drawn down behind
the exiting upper low over the Missouri Valley Monday night while
the old ECMWF and Canadian are much slower with boundary not
drawing the cold air into the exiting upper low. The end result is
low confidence with the timing of arrival of the cold air, but
there is high confidence that it will arrive between Monday night
and early Wednesday. After the deeper cold air moves in, the
precipitation type should be snow. Given the high degree of
uncertainty, will forecast low to moderate pops for light
snow/rain in the extended from late Monday night through early
Wednesday. At this point, there is no clear indication that the
snow would be impactful or not given the low confidence in the
various model solutions.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 459 PM CST Thu Dec 1 2016

VFR conditions are likely through the TAF period with light winds.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Skow
LONG TERM...Johnson
AVIATION...Barjenbruch