Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/30/19

Area Forecast Discussion

National Weather Service Buffalo NY

 1030 PM EST Sun Dec 29 2019

.SYNOPSIS...
A large storm system over the Upper Mississippi Valley will lumber
to the east across the Upper Great Lakes during the next couple
days. This will result in a prolonged period of unsettled weather
for our region with periods of rain for most areas except a
troublesome mix of rain and ice across the North Country tonight
into early Monday. Colder weather will move in behind this system,
along with some modest lake snows east of the lakes late Tuesday and
Wednesday.

&&

.NEAR TERM /THROUGH MONDAY/...
Regional radar late this evening shows widespread rain over eastern
portions of New York, including the North Country, while rain has
become less widespread over much of western NY where some patchy
dense fog has even formed around Batavia. Still some light rain
over the North Country though, and with temps still around
freezing, the potential for freezing rain and some minor icing
continues there through the rest of the night.

Next area of widespread rain is pushing north across the Tennessee
and Ohio River Valleys with leading fringes of the rain now as
close as Erie, PA and even into Buffalo area. This area of rain
is within larger scale diffluence ahead of deep upper low over
the central CONUS and is enhanced by differential divergence due
to strong upper level jet from eastern TX into Upper Great
Lakes and 50+ kt swrly jet at 3-5kft per AMDAR data.

As for precip trends for the rest of tonight, though parent upper
low stays over the central CONUS, lead shortwave heads out toward
central Great Lakes late tonight which allows the low-level jet to
lift toward the Lower Great Lakes. All the while, convectively
enhanced compact sfc low currently over scntrl TN will lift
northward toward central Great Lakes while deepening. Still expect
the area of moderate rain upstream, or at least a portion of it, to
lift across western NY after midnight, then reach the North Country
toward daybreak on Monday. Some occasional light rain or drizzle
will precede this next round of steady rain. Temps over western NY
will rise through the night into the 40s to around 50F as low-level
jet arrives and we remain ahead of occluded front that is due to
sweep west to east across here by Monday afternoon.

Meanwhile, temps will remain right around freezing across the North
Country while the warm layer aloft up to +5c persists, so we will
continue with the potential for freezing rain and light icing. As a
result of near freezing temps though, subtle differences such as
elevation, and a northeasterly cool air funneling down the St
Lawrence Valley will make a big difference in how much icing occurs.
Also, only a portion of the rainfall will freeze when temperatures
are near freezing. As the second (lower in elevation) low level jet
reaches the North Country Monday morning, this should finally scour
out the cold surface air in a southeasterly downslope flow. A Winter
Weather Advisory remains in effect for up to a quarter inch of ice
accumulation. Icing will mainly occur north of Watertown in the
Thousand Islands region, east of the Black River Valley and possibly
on the Tug Hill.

In total including the rain that fell this afternoon, we are
expecing about an inch of rainfall across far Western New York
through late tonight. Fortunately, the lack of any snowpack across
most of the area limits the potential for any flooding. MMEFS
ensembles show a few of the higher model runs (1.5 inches or
greater) pushing a few of the Buffalo and Rochester area creeks to
action stage. This will result in rises on waterways, but the risk
for any flooding is very low.

On Monday, the large stacked storm system over the Upper Great
Lakes will push its surface occlusion across the western
counties of New York. An influx of notably drier mid level air will
bring an end to the widespread precipitation over the western
counties by late morning. However there may be a few showers along
the frontal boundary. Temperatures will be much above normal on
Monday, with temperatures rising well into the 50s ahead of the
occlusion before tailing back off into the 40s in the afternoon post
occlusion.

Thermal profiles will also cool a bit in Lewis County Monday
afternoon, where there will be colder boundary later temperatures
located to the east. As a result, rain may mix with sleet or snow in
Lewis county, but with sfc temps into the mid or even upper 30s by
that point, think the impact should be minimal so will not extend
the advisory at this time.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
A broad and vertically stack low over the Upper Great Lake will
gradually track east across southern Ontario-Quebec, then off into
New England during this period. Multiple shortwaves in the cyclonic
flow aloft will move through the region which will help to keep
scattered to numerous rain showers going. Rain showers will also
begin to mix with snow overnight Monday as the air mass grows colder
with time behind the cold front. The best chance of seeing any snow
will likely be found across the higher terrain east of both lakes.
This is where thermal profiles will be slightly colder overnight.
Any accumulations will be minor if any at all.

Tuesday, the vertically stack system approaches from the west and
sends a secondary cold front across the region. Deeper synoptic
moisture and lift, along with a potent shortwave pivoting around the
mid-level low will bring about an uptick in rain and snow showers
areawide. With the passage of this front, H850T will fall to -7/9C
over the course of the day. This should be just enough in
combination with deep synoptic moisture to begin to generate a lake
response. In terms of snowfall accumulations, accumulations overall
will be limited during the day Tuesday. This will mainly be because
boundary layer temperatures will barely be supportive of any
accumulations.The best chances of any measurable accumulations will
likely be found across the higher terrain of the Souther Tier where
an inch or less may be possible during the day. Meanwhile, east of
Lake Ontario the only potential accumulations will be found across
the Tug Hill. This will largely be due to the fact that the colder
air doen`t arrive until the later in the day into the evening hours.

Otherwise, highs on Tuesday will range from the low to mid 30s
across the higher terrain, to the upper 30s and lower 40s across
lower elevations before tuning colder.

Tuesday night, deep synoptic moisture in combination with the air
mass grows colder(H850T dipping to -10/-11C), a modest lake response
will be possible overnight. Look for accumulating lake snows first
east-northeast of both lakes, then as flow becomes more westerly it
will favor the typical snow belt areas east of the lakes. While this
doesn`t appear to be a major lake effect event at this point, there
likely will be some advisory-type accumulations and possibly a few
warning amounts. This will especially be the case across the higher
terrain east of both lakes (Chautauqua Ridge and Tug hill area)
where upslope flow will maximize accumulations between Tuesday night
and Wednesday. For now, will mention this in the HWO.

Lake snows will still be ongoing early Wednesday morning. However,
over the course of the day lake snows will slowly weaken as synoptic
moisture gets stripped away and equilibrium levels fall. As usually
is the case, lake snows tend to linger a bit longer than we
anticipate so current thinking is they will persist most of
Wednesday. With that said, it won`t be until surface-based ridge and
drier air builds into our region late in the day Wednesday into
Wednesday night that will put an end to the lake snows. With
increasing shear and lowering of the capping, along with developing
warm air advection aloft expect any remaining lake effect will
effectively shut down Wednesday night.

Otherwise, taking a look at temperatures highs on Wednesday should
peak areawide in the low to mid 30s. Lows Wednesday night, will
range from the mid to upper 20s across higher terrain and east of
lake Ontario to the upper 20s to lower 30s across lower elevations.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The surface ridge over the region at the onset of the period slides
off the east coast on Thursday with a warming southerly flow
developing. This will result in temperatures climbing into the low
to mid 40s for most areas.

Thursday night and Friday, low pressure developing over the mid-
Mississippi valley will move north across the western Great Lakes.
This system will bring another round of rain and snow showers
beginning Thursday night with temperatures in the low to mid 30s.
Precipitation transitions to all rain during the day Friday as
temperatures reach the mid to upper 50s.

Friday night as the low moves across Ontario into Quebec, cooler air
wrapping around the low will result in precipitation once again
mixing back to rain/snow although becoming more scattered in
nature as it does. Scattered rain/snow showers linger the
remainder of the weekend as the low moves off to the Canadian
maritimes.

Temperatures Friday Night and Saturday Night in the upper 20s to low
30s and daytime highs Saturday and Sunday in the upper 30s to around
40 will still all be above the norm.

&&

.AVIATION /04Z MONDAY THROUGH FRIDAY/...
Another area of widespread rain will cross the region overnight,
with cigs staying IFR to lower MVFR. Some freezing rain remains
possible at KART into the early overnight before temps begin to
warm. Have seen areas of fog across higher terrain and the lake
plains south of Lake Ontario this evening with some patches of dense
fog around Batavia. Expect this fog to persist through the overnight
though visibility may increase some as next batch of rain moves
across.

As a strong low-level jet crosses the region late tonight, expect
low level wind shear at some TAF sites. Expect steady rain to taper
off from west to east on Monday, with flight conditions gradually
improving to MVFR by late morning or early afternoon.

Outlook...
Monday night...MVFR/IFR in rain showers changing to a
mixture of rain/snow showers Monday night. Tuesday...MVFR/IFR in
rain/snow showers becoming all snow by Tuesday evening.
Wednesday...VFR to locally IFR in snow showers east of the lakes.
Thursday...VFR.
Friday...Mainly MVFR. Rain showers.

&&

.MARINE...
Easterly winds will be in place across the Lower Great Lakes
through tonight. These will be strongest across western Lake
Ontario where a Gale Warning is in place for late tonight and into
Monday. Small craft advisories are also in place for the nearshore
waters for all of Lake Ontario.

A deep storm system over the Upper Great Lakes on Monday will plow
its associated occlusion across the region during the course of the
day. Winds on Lakes Erie and Ontario will veer by as much as 90
degrees in the process...with somewhat weaker winds by the end of
the day being southerly on Lake Erie and south to southeasterly on
Lake Ontario.

Moderate to fresh southwesterlies will then be found on both lakes
Monday night as the aforementioned storm system will drift north
across the SOO.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory until 1 PM EST Monday for NYZ007-008.
MARINE...Gale Warning until 10 AM EST Monday for LOZ062.
         Small Craft Advisory until 1 PM EST Monday for LOZ042-043.
         Small Craft Advisory from 5 AM to 10 PM EST Monday for
         LOZ044-045.

&&

$$

SYNOPSIS...Apffel/JLA/RSH
NEAR TERM...Apffel/JLA
SHORT TERM...AR
LONG TERM...Levan
AVIATION...Apffel/JLA/RSH
MARINE...Apffel/JLA/RSH