Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 242103
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
403 PM EST Sat Feb 24 2018

.SYNOPSIS...
Strengthening low pressure will track from the Upper Great Lakes
region tonight into Ontario on Sunday. This will result in above
normal temperatures over the weekend with a period of rain, possible
thunderstorms and windy conditions late tonight and Sunday. A dry
and mild period of weather is expected early next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
Regional radars showing a sharp cut-off on the northern fringe of
the widespread precipitation area moving across Pennsylvania, with
just areas very close to the Pennsylvania border getting a glancing
shot of rain this afternoon. High pressure anchored to our north
keep the remainder of the area, with even some sunshine across the
North Country and the Saint Lawrence Valley.

Dynamic mid level system currently lifting out of the southern
Rockies will steadily shift northeast over the next 24 hours,
reaching the upper Great Lakes by Sunday morning. Strengthening of
this system with time underneath favorable upper jet dynamics will
bring a corresponding deepening of the attendant surface low,
projected to eventually track north into the upper Midwest overnight
and eventually to near James Bay by the end of the day Sunday.

While the strongest dynamic forcing remains to our west/northwest in
closer proximity to the main height falls and surface low track, a
large region of modest large scale ascent will emerge downstream
under a lead area of isentropic lift and eventually accompanying the
trailing frontal convergence. This will support a period of
precipitation which will move across the region from southwest to
northeast tonight, entering far western New York just before
midnight, with widespread rain across the entire region by daybreak
Sunday. Main axis of higher theta-e advection streaming up from the
Ohio valley may briefly sneak north overnight and early Sunday,
providing a small window for possible elevated convection.

Downsloping will result in temperatures rising into the upper 40s to
near 50 degrees across the lake plains overnight, and across most of
Western New York through daybreak Sunday. The notable exception will
be across the Saint Lawrence Valley and eastern portions of Lewis
county where temperatures will be much slower to warm tonight as a
northerly component remains in place. In these locations, some spots
will be below freezing with the arrival of precipitation with rapid
mid-level warming, resulting in a period of freezing rain. Any
freezing rain would be short-lived, but still could result in up to
two tenths of an inch of icing in spots due to the moderate to heavy
rainfall rates. Any icing southwest of a Watertown to Lowville line
will be minimal due to warming from downsloping. A winter weather
advisory remains in place as outlined below.

There continues to be a concern for strong to damaging downsloping
winds late tonight across favored southeast component downslope
areas north and west of the Chautauqua Ridge and northern Tug Hill
and Black river Valley. Favorable low level wind direction combined
with a 60 knot plus low level jet may likely offset stabilizing of
atmospheric column due to precipitation. Wind headlines are outlined
below.

Sunday, attendant cold front blasts through early Sunday afternoon
in the 17z-19z time frame. Deep layer drying commences within the
ensuing cold air advection during this time. Progressive onset of
strong gusty conditions immediately in the wake of this frontal
passage, as the advective process and ensuing growth to the diurnal
mixed layer taps the existing strong wind field just off the
surface. Wind gust magnitude will carry strong dependence on the
degree of turbulent mixing, as greater isallobaric forcing will be
lacking given the surface low trajectory well off to our north. An
immediate greater wind gust response may accompany the frontal
passage under brief stronger isentropic descent, but any spike in
downward momentum transport tied to the front will be brief, on the
order of just a couple hours or so. Given the wind magnitude aloft,
looking at wind gusts between 50 to 60 mph with the strongest winds
focused just downwind of Lake Erie. Although this event looks to be
a marginal high wind event, feel a warning for areas from the
corridor from Buffalo to Rochester is warranted due to likely
impacts from downed trees due to the recently thawed ground and
saturdated soil conditons. Other areas will likely see wind gusts
closer to 40 to 45 mph. The steady cold air advection regime will
bring a non-diurnal temperatures curve with the warmest temperatures
ahead of the front with temperatures falling into the 40s by late
in the day.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH WEDNESDAY NIGHT/...
After the turbulent conditions of Sunday...Sunday night will feature
a return to much quieter weather along with diminishing winds as high
pressure over the Ohio Valley ridges northeastward across our region.
Under modest cold air advection...low temperatures will settle back
into the lower half of the 30s...though such readings will still be a
solid 10 to 15 degrees above late February normals.

Quiet and dry weather will then continue for the next 48 hours of
this period...as the aforementioned surface ridge slowly drifts
eastward and eventually off the mid-Atlantic coastline. At the same
time our temperatures will also remain at well above late winter
normals...with daytime highs only settling back to the mid 40s to
lower 50s on Monday...before climbing back up a solid 5 degrees
higher on Tuesday as somewhat milder air works into the region on
the backside of the eastward-migrating surface ridge. The above
stated...an onshore flow will keep areas immediately northeast of
the lakes cooler both days.

As we move on into Wednesday and Wednesday night...a weak wave of
low pressure will slide eastward across the Canadian Maritimes while
sliding a weak cold front southward into Lake Ontario and Northern
New York...with this boundary then stalling and/or falling apart
Wednesday night as its parent low slides farther away from our region...
and as a new (and more significant) low pressure system organizes
over Illinois. The front could touch off a few scattered light showers
across the Saint Lawrence Valley and North Country during this time
frame...with the remainder of the region otherwise expected to remain
dry. As for temperatures...unseasonably mild temperatures will continue
out ahead of this boundary...with Wednesday`s highs likely to climb
into the upper 40s to lower 50s east of Lake Ontario and to the mid
to upper 50s in most other locations...though areas immediately
northeast of the lakes will again be cooler due to another day of
onshore low-level flow.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
While temperatures will average above normal throughout this
period...there will be a distinct day to day cooling trend. Along
with the higher than normal temperatures...there is high confidence
that it will be quite unsettled through at least Friday night.

The main culprit for the inclement weather will be a newly formed
closed low that is forecast to track from the Upper Mid West to the
Virginia coast during the course of this time frame. While guidance
has come into better agreement with the existence and general track
of this feature...there are still uncertainties as to how far the
system will move off the coast by the weekend. For what its worth...
the GFS ensembles are the fastest with moving it out to sea.

When we open this period on Thursday...a dynamic storm system will
be in the process of drifting east across Illinois and Indiana. As
the system moves east...a tight H925-70 baroclinic zone will become
established near and just southwest of our forecast area. An
anomalously strong southeasterly low level jet in advance of the
large storm system will advect abundant (PWAT values nr 1") Atlantic
based moisture up and over the burgeoning warm frontal boundary...
while there may be some bonus lift from a coupled H25 sub tropical
jet. This will result in widespread rain over our region Thursday
and Thursday night...with high confidence for at LEAST an inch of
rain in the process. There will be the potential for up to two
inches of rain...so hydro issues will be a concern. For what its
worth...there could be an occasional mix of wet snow across the
North Country as some colder air will try to advect into the region
from New England.

The large storm system will become occluded as it will pass by to
our south late Thursday night and Friday. While this will remove a
lot of the lift over our region...rich Atlantic moisture will
continue to be transported back to the west by the anomalously
strong and persistent easterly flow. Upslope and residual
frontogentic forcing will be the main source to generate the
precipitation...which will be weaker in intensity. Colder air being
wrapped into this system will allow some of the rain to mix with or
change to wet snow...but with max temps in the vcnty of 40f...do not
anticipated appreciable snow accumulations.

Confidence in the forecast will drop off considerably later Friday
night and Saturday...as the exiting speed of the closed storm system
will come into play. While scattered mixed showers can be expected
Friday night...will lean more on the GEFS ensembles by being
optimistic with just slgt chc pops on Saturday.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
Northern edge of large precipitation shield extending through the
Ohio Valley will remain right along the New York State and
Pennsylvania border through this afternoon. 3k-4k foot ceilings
will remain across the area this morning, expect for IFR
ceilings along the Southern Tier. Some drier air advecting in on
a northerly component could bring ceilings up a bit through
this afternoon with improvement to MVFR along the Southern Tier
and possibly to VFR by late afternoon.

Expect mainly VFR conditions this evening, followed by active
weather starting around midnight. This will include a period of
heavy rain, and possibly even a thunderstorm. There also may be
LLWS late in the period as a low level jet moves into the region.

Outlook...

Sunday...Rain ending with improvement to VFR. LLWS early. Windy.
Monday through Wednesday...Mainly VFR.

&&

.MARINE...
A strong area of low pressure tracks northeastward across the Great
Lakes on Sunday. This system will bring a round of high end advisory-
worthy conditions, with gale force wind gusts possible.

After this, a moderate southwesterly flow will result in near-
advisory conditions across eastern portions of the lakes Sunday night
into Monday. Then high pressure will build across the lower Great
Lakes late Monday and Tuesday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory from 1 AM to 10 AM EST Sunday for
     NYZ007-008.
     Wind Advisory from 4 AM to 1 PM EST Sunday for NYZ007-008.
     High Wind Warning from 9 AM to 6 PM EST Sunday for NYZ001>003-
     010>012-085.
     High Wind Warning from 2 AM to 6 PM EST Sunday for NYZ019.
MARINE...Small Craft Advisory from 6 AM to 6 PM EST Sunday for LEZ020.
         Small Craft Advisory from 2 AM to 11 PM EST Sunday for
         LEZ040-041.
         Small Craft Advisory from 6 AM to 6 PM EST Sunday for
         LOZ030.
         Small Craft Advisory from 2 AM Sunday to 4 AM EST Monday
         for LOZ043>045.
         Small Craft Advisory from midnight tonight to 11 PM EST
         Sunday for LOZ042.

&&

$$

SYNOPSIS...TMA
NEAR TERM...TMA
SHORT TERM...JJR
LONG TERM...RSH
AVIATION...TMA
MARINE...TMA


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