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Area forecast discussion
National Weather Service Buffalo New York
713 PM EDT Tue Oct 22 2019

much cooler air will overspread the region tonight and lead to the
development of some lake effect rain northeast of the lakes, which
will then wind down from southwest to northeast later Wednesday and
Wednesday evening as high pressure and drier air builds into the
region. Another cold front will then slowly sag across the region
Thursday and Friday while bringing some additional scattered
showers, with cool and mainly dry weather then following for the
first half of the weekend.


Near term /until 6 am Wednesday morning/...
an area of low pressure located over Lake Superior this evening was
pushing a cold front through central New York with a secondary
trough pushing into western New York. Widespread showers in
advance of both features. It won't be until the lake induced
instability forms and upstream moisture from the central and
western Great Lakes rotates towards the eastern Great Lakes
tonight that lake effect rain showers develop across Lake Erie.
The rainfall ahead of the frontal boundary and trough will
depart the Tug Hill region late tonight while the lake effect
forms across the Buffalo Metro.

Favorable lake effect conditions will continue into Wednesday
morning. A southwest flow of 30-40kts will also bring the lake
effect showers as far northeast as the Rochester Metro by Wednesday
morning. Rainfall amounts will be localized due to the nature of the
band and amounts of up to a quarter to half inch are possible within
the band. There will be some clearing outside of the lake effect
activity however southwest winds will average 10-15 mph through the
night hours. Low temperatures will reach the upper 30's across the
higher terrain to the low to mid 40's across the lake plains and
possibly the upper 40's under the influence of the lake band. Lake
effect will just be starting late tonight northeast of Lake Ontario.


Short term /6 am Wednesday morning through Friday Night/...
Lake induced rain showers will already be in place northeast of Lake
Erie as we open this period on Wednesday morning. A well aligned 240
flow of -1c 850 mb air will place a well defined band of steady rain
over the Buffalo Metro area with a 30-40kt cloud bearing flow
extending the activity northeast to the western suburbs of
Rochester. A cap in the vcnty of 8kft and lack of background
synoptic deeper moisture and lift should keep the band from
producing significant rainfall amounts...although the rain showers
could be moderately heavy at times during the first few hours of the
day. As the base of a shortwave trough passes east of our
region...subtle warm advection during the afternoon will further
lower the limiting cap below 5kft. This should substantially weaken
the lake effect showers...although the axis of the activity will
move very little as winds persist from the southwest.

Off Lake Ontario...the base of the aforementioned shortwave trough
will still be the west as the day begins. A moderately sheared
airmass within a general 240 flow will focus disorganized lake rain
showers near or immediately north of Watertown...although an upslope
flow will support scattered showers throughout much of the Eastern
Lake Ontario region. Once the base of the mid level trough passes...
the lake response should become more pronounced across the northern
half of Jefferson County and Thousand Islands region. Given the
'late' start and shorter fetch...forecast rainfall amounts in this
region (as compared to lake erie's activity) should be significantly

Outside of these two lake effect areas...cold advection strato-cu
within the cyclonic flow during the early morning will thin out
during the course of the day as weak warm advection becomes
established. This will especially be the case across the southern
tier and Finger Lakes regions...where partial sunshine may make an
appearance all day away from the influences of the additional lake
moisture. Temperatures in the low to mid 50s will be quite close to
where we should be for the later stages of October. However, gusty
southwest winds, reaching 30 to 35 mph at times especially from the
Niagara Frontier toward Rochester and along the eastern shoreline of
Lake Ontario, will add a chill to the air.

Lake effect will end on Wednesday evening with continual warm air
advection, lowering inversions and anticyclonic flow as sfc ridge
expands from southeast Continental U.S. To the mid Atlantic states. Attention
later Wednesday night into Thursday morning will be on broad and
flat troughing sweeping across the Great Lakes. Weak sfc cold front
tied to the upper level trough will remain moisture starved as it
limps across our forecast area later Thursday. While it will
generate a fair amount of cloud cover...the paltry mid level
moisture and general lack of forcing continue to only warrant
slight to low chc pops, with best chances closer to Lake Ontario.
Looks like with gusty SW wind, though not as strong as what occurs
on Wednesday, temps on Thursday may be able to warm into the lower
60s, especially toward Finger Lakes.

Forecast confidence remains on the lower side later Thursday night
and the various guidance packages continue to have
timing issues with the next shortwave trough moving in from the
nations mid section. Whether this trough is more amplified or
flatter has bearing on if showers impact mainly western New York or more
over the southern tier into eastern New York. Maintained continuity and
kept chc pops to avoid significant flip flopping. Temps on Friday
should reach around 50f or into the lower 50s. Behind this system
does appear we'll see a Minor Lake response off Lake Ontario with
WNW winds sfc-850 mb and sufficient instability as 850 mb temps drop to
around 0c to -2c, leading to Delta T/S toward 13c with Lake Ontario
water temps of 52f (11c).


Long term /Saturday through Tuesday/...
any limited lake response off Lake Ontario will end later Saturday
afternoon as surface high pressure and associated dry air move into
the eastern Great Lakes. Looks like another day with highs mainly
into the lower 50s, with upper 40s across higher terrain.

Medium range guidance continues to diverge Saturday night and
Sunday. The latest 12z/22 European model (ecmwf) and Gem bring a substantial southern
stream system through the Ohio Valley and eastern Great Lakes
Saturday night into Sunday with the Gem on the quicker side of the
two. Meanwhile, recent GFS runs keep this system more suppressed
over the southeast states and mid Atlantic, only grazing our
southern and eastern forecast areas with any light quantitative precipitation forecast. Given the
consensus between the European model (ecmwf) and Gem and recent pattern/model trends,
have continued to increase probability of precipitation for later Saturday night and Sunday.
If the surface low track ends up passing to our northwest such as
the European model (ecmwf) solution, it may turn fairly mild on Sunday despite the
clouds and showers.

Following this system weak high pressure will build into the Ohio
Valley and New England from Monday through Tuesday. The GFS is again
faster with the next trough coming into the Great Lakes, and again
appears too fast when compared to European model (ecmwf)/Gem solutions and ensemble
means. Given this, kept the Monday through Tuesday period dry and
turning gradually cooler.


Aviation /23z Tuesday through Sunday/...
a cold front will cross the region early tonight. Rainfall will
taper off from west to east through the evening hours while clouds
hang around the region. Lake effect rain showers are expected
east of Lake Erie in vicinity of kbuf to kroc after 04z. Lake
effect rain showers will develop near kart Wednesday morning and
continue through the afternoon. Low-end VFR/high-end MVFR cigs
expected within the lake bands. Outside of lake bands, VFR
conditions expected. Gusty southwest winds expected Wednesday
with gusts around 30-35 kts from kbuf-kiag-kroc late morning-
early afternoon.


Thursday...mainly VFR with a chance of showers.
Thursday night and Friday...MVFR/VFR with scattered showers.
Saturday and Sunday...mainly VFR.


a round of stronger southwest winds will develop on Lake Erie and
Western Lake Ontario this evening, then spread across the rest of
Lake Ontario during the course of Wednesday. This will result in
another round of advisory-worthy conditions that will last into
Wednesday night or Thursday, with the strongest winds and higher
waves persisting the longest at the eastern ends of both lakes.

Small craft headlines are outlined below.

Looking further out in time, winds and waves will steadily diminish
from later Thursday through the end of the week as the pressure
gradient slackens across the lower Great Lakes.


Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory until 5 PM EDT Thursday for lez040-041.
Small Craft Advisory from 5 am to 11 PM EDT Wednesday for
Small Craft Advisory from 8 am Wednesday to 2 am EDT
Thursday for loz043-044.
Small Craft Advisory from 8 am to 11 PM EDT Wednesday for
Small Craft Advisory until 5 PM EDT Thursday for loz045.



near term...hsk/tma

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