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Area forecast discussion
National Weather Service Buffalo New York
101 am EDT Sat Oct 19 2019

Synopsis...
it will be a beautiful weekend for viewing the peak of the fall
foliage...as high pressure passing to our east will provide US with
US with sun filled skies today and fair dry weather through Monday.
The pleasant weather will be accompanied by day to day warming with
temperatures climbing as high as the lower 70s across the western
counties for Monday. A dramatic change back to more seasonable Fall
weather will then take place for the remainder of the week.

&&

Near term /through today/...
an elongated area of high pressure will cross the region during the
remainder of the overnight. While this will support clear moonlit
skies for most of the region...850 mb temps lingering close to zero c
east of the Genesee Valley will continue to allow just enough
instability over the far eastern part of Lake Ontario to keep some
lake induced strato-cu over parts of Oswego and northern Cayuga
counties. As we move through the wee hours of the morning though...
a lowering subsidence inversion brought about by stronger warm
advection will gradually shut down this minimal lake response.

Otherwise...it will be one of the chilliest nights that we have
experienced so far this early fall. Temperatures away from the
immediate Lake Shores will fall into the low to mid 30s...with 20s
anticipated in some of the more sheltered southern tier valleys and
over a large portion of Lewis County. This will lead to widespread
frost...which could very likely officially end the growing season
for the entire region. A widespread frost advisory thus remains in
place for counties that have not already experienced a killing frost
or freeze.

After a frosty start...high pressure moving away to our east will
provide US with a spectacular day. Sun filled skies on Saturday will
help to send afternoon temperatures to near 60 across the far
western counties...while readings will only top out in the mid 50s
east of Lake Ontario. Interestingly...if we were able to fully mix
our airmass...temperatures would push well into the 60s to near 70.
A staunch 4 deg subsidence inversion will prevent that from
happening...but take heart...this kind of warmth is 'just around the
corner'.

&&

Short term /tonight through Monday night/...
Saturday night, an upper level shortwave will pass across the
upper Great Lakes, while a second shortwave and associated
surface low pressure move into the mid Atlantic states. This
will leave our area sandwiched in between these two systems, and
thus will continue with a dry forecast through the overnight.
It will not be as cool as the prior night with lows ranging from
the lower to mid 30s across the north country, to the upper 30s
and lower 40s elsewhere.

Sunday, the main energy associated with the shortwave moving across
southeastern Canada will remain to our north, while the surface low
over the mid Atlantic moves northeast off the coast of the Delmarva.
Easterly to southeasterly surface flow off the Atlantic on the
northern side of this surface low will advect some low level
moisture in off the Atlantic across the eastern half of New York state. This
enhanced moisture combined with a shallow weakening upper trough
crossing the region may provide enough forcing to produce some
showers mainly east and southeast of our area. However, a few of
these showers may be able to make it as far west as the borders of
our eastern most counties, with the best chance for any precip
occurring during the first half of the day. High temperatures will
be in the 60s south of Lake Ontario, with mid and upper 50s reserved
for areas east of Lake Ontario.

An upper level ridge and surface high pressure will build across the
region for Sunday night and Monday, bringing dry and comfortable
weather during this period. Following low temperatures Sunday night
that will be similar to Saturday night, strong southeasterly flow
will develop out ahead a cold front off to the west that will advect
even warmer air in across western and north central New York on Monday.
This should yield highs in the mid and upper 60s for most, with a
shot at 70 in the typically favored downsloping areas across western
New York.

Upper level ridge axis and surface high pressure will shift east
over New England Monday night. This will make way for the next
strong cold front draped from the upper Great Lakes southward across
the lower Ohio Valley to approach the region. Have slowed down the
eastward progression of the front just a bit more. This will keep
much of the area dry through the first half of Monday night.
Moisture will then continue to increase with showers becoming likely
west of the Genesee Valley by late Monday night, with any moderate
to heavier rain remaining to the west through this timeframe.
Increasing cloud cover and continued southerly flow ahead of the
boundary will keep lows much warmer, with mainly 50s south of Lake
Ontario, and 40s east of Lake Ontario due to the later onset of
thicker cloud cover.

&&

Long term /Tuesday through Friday/...
a mature, nearly vertically stacked low will move from near Lake
Superior into northwest Ontario province Tuesday, with an associated
cold front moving slowly east across the eastern Great Lakes. The
GFS is on the fast side of the guidance envelope and appears too
fast in relation to the European model (ecmwf)/Gem with the cold front. Even with the
expected slower timing, widespread rain will overspread the area
from west to east Tuesday. By the time this system reaches the Great
Lakes it will be occluded and in a weakening phase. A secondary wave
may develop along the advancing cold front and bring heavier
rainfall to the mid Atlantic and New England later Tuesday night and
Wednesday, but this feature will likely miss our area. Given this
expectation, rainfall amounts should stay under 1 inch with little
hydrologic impact from rainfall in our region.

The bulk of the rain will taper off from west to east Tuesday night
with the passage of the cold front. A broad mid level trough and
wrap around moisture may produce a few more scattered showers
Tuesday night. The airmass will grow cold enough to support lake
effect rain showers Tuesday night and Wednesday off both lakes Erie
and Ontario. At this early juncture, boundary layer flow appears to
be SW or WSW, which will direct the lake effect showers off Lake
Erie into the Buffalo area, and Lake Ontario showers into the
northern Tug Hill and Jefferson County.

The GFS and Gem both show another weak trough moving through the
eastern Great Lakes Thursday, which would support additional lake
effect rain showers northeast of the lakes. Meanwhile the European model (ecmwf)
brings high pressure a little farther north from the Ohio Valley to
the mid Atlantic, keeping our region dry. Given the model
uncertainty, for now kept low chance pops northeast of the lakes.

By Friday another complex trough will be moving through the mid
section of the nation. Medium range models begin to diverge with
respect to how and when this will phase with additional southern
stream energy. Regardless, the more active portion of this system
will stay to our south and west through most of Friday, with just a
chance of a few showers here.

Temperatures will not stray too far from average next week.
Wednesday looks to be the coolest day with highs only in the lower
50s at lower elevations and upper 40s higher terrain. Some modest
warming is then expected late in the week as southerly flow develops
ahead of the next system.

&&

Aviation /06z Saturday through Wednesday/...
high pressure overhead will move east of the region during the day
Saturday. This will keep mainly clear skies and light winds in
place. The only real cloud cover to contend with will be some
residual lake induced strato-cu over Oswego County...but that should
be largely gone by daybreak.

Otherwise...the only real issue for this taf period will be the
potential for some low stratus and fog across parts of the srn tier
before 13z. Enhanced infrared imagery shows that valley fog is already
developing across the southern tier. The stratus and patchy fog
could result in a few hours of MVFR to IFR conditions for sites like
kjhw and kelz.

Outlook...
Saturday night through Monday...VFR.
Tuesday...MVFR with areas of rain and fog.
Wednesday...mainly VFR with scattered lake effect rain showers
northeast of lakes Erie and Ontario.

&&

Marine...
high pressure will build eastward across the lower Great Lakes
overnight. The high will slowly drift east into New England on
Saturday and then off the Atlantic coastline on Sunday. This
will result in a period of fair weather and lighter winds across
the lower Great Lakes.

&&

Hydrology...
2-3 inches of rain fell in the Black River basin between late
Wednesday and Thursday and this has resulted in high levels. It
will remain below flood stage, but Black River forecast points
have (or are expected to) reach action stage. Boonville crested
earlier today and will begin to slowly fall tonight. Farther
downstream, Watertown is expected to reach action stage late
Saturday, and should crest below flood stage Sunday.

&&

Buf watches/warnings/advisories...
New York...frost advisory until 9 am EDT this morning for nyz001>006-010-
011-013-014-019-085.
Marine...none.

&&

$$

Synopsis...rsh
near term...rsh

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