Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 141042
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
642 AM EDT Mon Oct 14 2019

.SYNOPSIS...
An upper level low will bring moisture and cooler air across our
region today, with narrow bands of lake effect rain to the east of
the Great Lakes. These bands of lake effect rain will weaken this
afternoon, and end all together later tonight as drier air builds
back into our region. It will be quiet Tuesday with high pressure
nearby before a strong area of low pressure brings gusty winds, rain
and possibly thunder mid-week.

&&

.NEAR TERM /THROUGH TONIGHT/...
This morning an upper level low continues to spiral across Ontario
Canada, reaching near James Bay. A surface low is found at the
surface under this upper level low, and this surface low has swung
another cold front towards our region....with this front now
crossing WNY.

Temperatures aloft will dip to just below zero Celsius at 850 hPa
this morning, and this will create instability over the still warm
lakes. Lake rains, enhanced by orographic upslope processes will
become likely across the Southern Tier...and the Boston Hills
before diminishing during the afternoon hours. Not the greatest
set-up with still some drier air in the lower levels, but a
tenth of two of an inch of rain is possible.

East of Lake Ontario as the surface trough passes we should like-
wise see a few scattered showers that become better organized this
morning with the arrival of cooler air aloft. Like Lake Erie, as
inversion heights fall this morning bands of rain will not become
heavy...with just a tenth or two of an inch of rain possible before
drier air begins to weaken the lake bands this evening.

Tonight surface high pressure will advance towards our region from
the Ohio Valley. This feature will bring drier air northward, that
will end the lake effect precipitation from west to east...though
lake clouds will likely persist through much if not all of the
night.

It will become chilly under this surface high tonight, however
the traditionally cooler spots of WNY will likely be under lake
clouds...limiting frost potential here. Elsewhere mainly clear
skies are expected and patches of frost will be possible across
the Genesee Valley and Finger Lakes region, though not
widespread enough at this time to hoist any frost advisories.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Overall theme of forecast for the balance of the work week has not
changed; dry and warmer on Tuesday followed by widespread showers
with potential thunder late Tuesday night into Wednesday, then
cooler and windy with increasing lake effect later Wednesday through
Thursday. Though the pattern is amplified, it is also progressive,
so this cooldown mid week will be quickly replaced by another push
of above normal temperature by next weekend. Based on amplifying
ridge enveloping much of the eastern CONUS by day 7, that warm up
may have some staying power into early next week.

Starting off on Tuesday, high pressure will be centered over central
Pennsylvania. Could be some frost away from immediate Great Lakes
shorelines. Lingering lake effect still possible downwind of eastern
Lake Ontario with wnw cloud bearing flow and inversion top temps of
+2c (delta t/s 17c based on water temps of 60F/15c). Inversion is
under 5kft, so looking at light activity. Winds backing more sw will
end the lake effect by mid aftn east of Lake Ontario. Highs Tuesday
should reach around 60F, maybe a smidge warmer on the lake plains
and a few degrees cooler over the higher terrain in the Southern
Tier and also on the Tug Hill.

Upper low upstream on Tuesday evening gradually deepens, but
associated sfc low looks weaker than what was shown last couple
days. Even so, cold front tied to the low still looks strong and
convergence along front remains sharp. Those factors along with
theta-e ridge just ahead of front on 40-50 kt low-level jet should
result in swath of showers just ahead of front. Rain should not move
in until very late Tuesday night over western NY. Certainly possible
that though forecast instability is meager, strong low-level forcing
and low-level jet may result in some thunder as the front moves
through late Tuesday night into Wednesday morning. Setup would be
one of higher shear, lower CAPE. Not completely out of the question
stronger wind gusts could occur in the more organized showers and
thunderstorms as shown in favorable forecast SHERB numbers (severe
hazards in environments with low buoyancy). In addition to the gusty
winds, model guidance continues to suggest a solid 0.50-0.75" of
rain with this front.

As alluded to before, the sfc low later Wednesday is weaker and so
at least just behind the front, think gradient synoptic s veering w
winds will stay more in the 15-30 mph range. After a lull behind the
front, cooler air does begin to filter in so will see gradual lake
response increase later in the afternoon, first downwind of Lake
Erie then eventually into Wednesday night downwind of Lake Ontario.
Forecast soundings show lake equilibrium levels 5-8kft early
Wednesday afternoon increasing to around 15-20kft by Wednesday
evening before stabilizing around 10kft later Wednesday night into
Thursday morning.

Overall, these values look lower than they did last couple days.
This could be due to weaker sfc low and more of an emphasis Wed
night and beyond on quickly deepening Nor`easter off the coasts of
MA to ME. Shift in focus has diminished the extent of deeper
moisture farther west of that system across Lake Erie and Lake
Ontario. H85 temps still bottom out around -3C Wed night into Thu so
so over-water instability is more than sufficient to justify
categorical pops downwind of the lakes with delta t/s 18-20c.
Suppose the lower lake equilibrium levels may result in lower chance
of graupel/lightning, but not enough to remove from the forecast
just quite yet. Strongest cold air advection occurs late Wed aftn
though Wed evening. With winds in the mixed layer at that time of 35-
40 kts, think this period is the best probability in seeing gusts
over land that may reach wind advy criteria. Again though, main sfc
low focusing well to our east may limit that as well. We`ll have to
see if these trends hold up, but models are certainly becoming
locked onto the Nor`easter instead of the low sliding by to our
north. Have kept with non-diurnal temp curve late Tuesday night
through Wed night, as temps should be more or less steady over
western NY on Wednesday with only small rises toward Finger Lakes
and east of Lake Ontario.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Stacked storm system over northern New England moves toward Atlantic
Canada Thursday into Thursday night. A deep cyclonic flow of chilly
air will remain over the Lower Great Lakes which will continue to
support a fairly strong lake response...with lake to cloud base
delta t values averaging 15 deg c. H85 temps only down to -3c will
not be low enough to support any snow...but the resulting lake
driven convection could include some heavier rain showers.
Otherwise...it will be a poor day to be out and about as a gusty
northwest wind and fairly widespread lake driven rain showers within
the ongoing cold advection will prevent many areas from climbing out
of the 40s.

Surface ridging will start to cross the Lower Great Lakes Thursday
night. This will lower the limiting subsidence inversion to under 5k
ft while the bulk of the synoptic moisture above 5kft will be
stripped away. Leftover rain showers southeast of both lakes will
taper off as a result (esp off Lk Erie) with temperatures generally
dropping into the upper 30s and lower 40s.

Ridging at all levels will cross our forecast area Friday and Friday
night. While there may still be a few nuisance lake showers east of
Lake Ontario Friday morning...overall scenario will promote fair dry
weather. It will remain on the chilly side of normal though with
highs only into the lower 50s. Most efficient warm advection should
become established over our region Friday night into Saturday with
temps likely rising overnight heading toward temps into the mid 60s
by Saturday afternoon.

An even nicer day is being advertised on Sunday...as a burgeoning
sub tropical ridge over the Southeast coast will help to pump our H5
hgts to near 580dm...levels more typical of late summer. H85 temps
may get into the mid teens by late Sunday. If this were to verify...
a large swath of our forecast area would experience max temps of 70
or better.

As mentioned earlier, warmth will very likely continue beyond this
period into the start of the new work week. The anomalously strong
East Asian jet, which as of last evening was beginning to emerge off
the eastern coast of Russia per 00z RAOBS, will ultimately be
responsible for this warmth as they often lead to troughiness over
the Inter-mountain region which teleconnect to burgeoning ridges in
the East. These features also effectively cut off any intrusions of
cold air. Eventually though the jet will help propel a stronger
system toward the Great Lakes, so another push of colder air could
be in the offing as we head toward middle of next week. Obviously
details will change, but that is how the general pattern looks at
this point.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
For the 12Z TAFS VFR flight conditions are found.

Showers will become better organized as cool air flows over Lake
Erie just past 12Z, and later Lake Ontario resulting in lake
instability forming lake effect rain showers. These showers are
most likely to the east of Lake Erie (KJHW) and later this
morning east of Lake Ontario (KART).

These showers will diminish through the afternoon and evening
hours...with lake clouds within an MVFR or low end VFR flight range
remaining through the end of tonight.

Brisk westerly winds today will back and become lighter tonight as
surface high pressure ridges towards our region from the Ohio Valley.


Outlook...

Tuesday...Mainly VFR.
Wednesday...Showers likely with areas of MVFR. Gusty
Winds.
Thursday...A chance of lake effect showers and MVFR CIGS east
of the lakes, otherwise VFR.
Friday...Mainly VFR. Slight chance of a lake effect shower east of
Lake Ontario.

&&

.MARINE...
A cold front pin-wheeling around an upper level low is advancing
across the Eastern Great Lakes this morning. Cold air advection
behind this front will increase waves on the Lakes, with both winds
and waves reaching small craft criteria. Small craft advisories will
in place now for both Lakes, with winds and wave diminishing this
evening and overnight as surface high pressure pushes towards the
lakes.

Colder air coming in aloft will bring the potential for waterspouts
through midday.

Winds and waves will be light Tuesday with the surface high nearby
before increasing once again as a deeper and colder storm system
passes through the Eastern Great Lakes midweek.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for LEZ040-
         041.
         Small Craft Advisory from 11 AM this morning to 5 AM
         EDT Tuesday for LOZ043-044.
         Small Craft Advisory until 2 AM EDT Tuesday for LOZ042.
         Small Craft Advisory until 2 AM EDT Tuesday for LOZ045.

&&

$$

SYNOPSIS...Thomas
NEAR TERM...Thomas
SHORT TERM...JLA
LONG TERM...JLA/RSH
AVIATION...Thomas
MARINE...Thomas


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