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Area forecast discussion
National Weather Service Buffalo New York
924 am EDT Mon Sep 23 2019

Synopsis...
a cold front will advance across our region today, bringing gusty
winds and rounds of rain showers. As we enter astronomical autumn,
temperatures will still remain late Summer-like with above normal
warmth through tonight...and rain showers tonight becoming
concentrated east of the lakes where cold air aloft generates a Few
Lake enhanced precipitation. Cooler weather, and near normal
temperatures will be across the region Tuesday before we again warm
to above normal temperatures by mid-week.

&&

Near term /through tonight/...
the first few hours of astronomical autumn will feel Summer-like as
a strong southerly flow is maintaining temperatures in the upper 60s
to mid 70s across the region. A broad area of high pressure is
centered over the southeast United States, while a cold front is
advancing across the central Great Lakes. Between these two features
the deep southwesterly flow is not only maintaining the warmth, but
also transporting deep moisture northward...with precipitable waters nearing 1.75
to 2.00" ahead of the front.

Regional radars display initial showers this morning now
reaching far wny, and the Saint Lawrence valley. Quantitative precipitation forecast is light
with regional observations generally under a tenth of an inch of
rainfall. A gusty wind is accompanying this activity,
especially northeast of Lake Erie. This light activity will push
across the region this morning, with no thunder expected.

There will be several concerns today as winds aloft remain strong.
These winds however will keep clusters of showers moving, that
despite the precipitable waters nearing +3 SD, prolonged heavy rainfall is not
expected.

Synoptic winds...

A surface wave forming along this upstream cold front will deepen in
part due to a pv Max dropping around an upper level low over the
Great Lakes. As the surface low tracks across southern Canada this
late morning...and with the cold front passage within a rather tight
pressure gradient southwest to westerly winds will gust upwards to
40 mph across the lake plain. Winds will likely be strongest late
morning to mid afternoon...just behind the cold front when lapse
rates between the surface and 750 hpa begin to increase to 8 c/km.

Convective winds...

While overall instability is not overly impressive...with just
several 100 j/kg of MUCAPE...the lingering strong winds aloft could
present a problem if much convection along the cold front gets
going. The 0-6 km bulk wind shear will be near 60 knots and if
convection (with or without thunder) can grow into the 40 knot low level jet 4-
8k feet above the surface some convective gusty winds could
accompany the frontal passage...with strongest gusts likely to our
east where daytime heating will be maximized. Much of our region
will be outlined in a marginal risk for severe storms today by Storm Prediction Center.

The cold front will cross the region from west to east late this
morning and mid afternoon. Showers and thunderstorms will form
along this frontal boundary. Temperatures will linger in the
70s ahead of the front...still some 5 - 10f above normal.

Behind the front we will transition to cooler air advecting across
the Great Lakes and generating lake enhanced rain showers. 850 hpa
temperatures will lower to near +6c late tonight over both Lake Erie
and Lake Ontario. This should generate a lake response...that will
also be enhanced by moist cyclonic flow aloft around an upper level
closed low.

Within the cold air advection...temperatures will lower into the low
to mid 50s overnight.

&&

Short term /Tuesday through Thursday night/...
during the course of Tuesday a closed upper level low over the Saint
Lawrence valley will make its way eastward to Maine...where it will
become increasingly vertically stacked on top of its attendant surface
low along the Maine coastline. Meanwhile...surface high pressure and
drier air will ridge northeastward into our region from the Ohio Valley.
The consequent transition from cyclonic to anticyclonic flow and dry
air advection will result in lingering lake-effect and orographically-
driven showers east and southeast of the lakes diminishing from west
to east over time...with morning clouds also gradually giving way to
some partial sunshine. The above said...there will still be enough
cloud cover around and temps aloft will remain cool enough (850 mb
temps of +4c to +8c) to keep daytime highs confined to the 60s...making
for a marked departure from the midsummer warmth of the previous
weekend.

Ridging at all levels will then crest across our area Tuesday night
into early Wednesday...before drifting eastward to eastern New York
and New England Wednesday afternoon. This will result in dry and quiet
weather for this 24 hour period. With good conditions for radiational
cooling expected...lows Tuesday night will range from the mid 40s
across interior portions of the southern tier and north country to
the lower to mid 50s along the Lake Erie lake plain...with readings
then quickly rebounding into the 70s areawide on Wednesday as a good
southwesterly return flow/warm advection regime sets up on the backside
of the departing ridge.

Wednesday night and Thursday broad/flat troughing will dig eastward
across the Great Lakes and northeast...with an attendant surface low
traversing northern Quebec province and easing a trailing cold front
across our area between later Wednesday night and Thursday morning.
At this point both moisture return and synoptic forcing along the
frontal boundary and leading edge of the upper trough both appear to
be sufficient to warrant a continued likelihood of some showers across
our region during this time frame...with strong dry slotting/cool air
advection in the wake of the front then resulting in shower chances
rapidly diminishing from west to east Thursday afternoon. As for temps...
lows mostly in the mid to upper 50s Wednesday night will be followed by
cooler highs in the upper 60s to lower 70s on Thursday...with readings
held in check both by the morning timing of the front and ensuing cool
air advection in its wake.

Finally...this period will come to an end with a tranquil night Thursday
night as high pressure and cooler/drier air crests across our region...
with the dry nature of the airmass helping to preclude any real lake
response in spite of favorably cool 850 mb temperatures of +4c to +6c.
Expect low temperatures to again range from the mid 40s across interior
portions of the southern tier and north country to the lower 50s along
the Lake Erie lake plain.

&&

Long term /Friday through Sunday/...
moving on into the longer term portion of the forecast...Friday looks
to be a virtual repeat of Wednesday...as high pressure drifts from
our region to the eastern Seaboard and a good southwesterly return
flow/warm air advection pattern sets up on its backside. This will
result in a dry day...with temps surging back into the lower to mid
70s in most areas.

After that...timing differences persist with regard to the arrival
of the next frontal system over the weekend...with the GFS remaining
much faster and stronger with this feature than the gefs ensembles
and its Gem and European model (ecmwf) counterparts. With the latter cluster of guidance
still looking more reasonable...have continued to steer the forecast in
that direction for now...with relatively minimal precipitation chances
and a notable trend back to well above normal temperatures indicated
for the weekend.

A look further down the Road...ensemble model consensus strongly
suggests that temperatures will average well above normal through at
least the middle of the ensuing week when the calender will turn to
October. The ensemble mean of the gefs...the operational European model (ecmwf) and
the Canadian forecast system are in solid agreement that a broad sub
tropical ridge will be in place across the eastern portion of the
country. Much of the 'blame' for the persistent sub tropical ridge
over the eastern U.S. Can be placed on a strong blocking ridge that
has been...and will continue to be...centered near 150w over the
open Pacific. This has kept a wave number 5 longwave pattern intact
across the northern hemisphere which in this case has supported warm
weather over the eastern half of our continent.

850 mb temperatures are forecast to be in the mid teens Monday and
Tuesday and possibly make it into the upper teens c by mid week.
This warm weather forecast is also supported by both the 6 to 10
and 8 to 14 day temperature outlook by the climate prediction center
(cpc) that is advertising a high likelihood for above normal temps
throughout the eastern half of the country. The early autumn warmth
should be accompanied by mainly dry weather. Any way you slice it...
we should expect a very warm start to the month of October.

&&

Aviation /14z Monday through Friday/...
a cold front will cross the region today. Light showers will
continue to track east of kroc this morning. Mainly VFR conditions
are expected however MVFR cigs are starting to show up ahead of the
next round of rain along the cold front. Showers and a possible
thunderstorm will spread across western New York late this morning into
the afternoon, moving east across the north country this afternoon.
As the cold front passes today showers will bring lowering ceiling
heights to MVFR, and possibly IFR across the hill tops of the
southern tier (including kjhw).

Precipitation will remain possible through 21-00z, after which
precipitation will become concentrated to the east/southeast of the
lakes as much cooler air aloft flows down upon our region. Here lake
enhanced rain showers will fall from a strato-cu deck at MVFR...that
will lower to IFR across the southern tier.

Outlook...

Tuesday...mainly VFR...except a chance of showers/MVFR east of Lake
Ontario.
Wednesday...VFR.
Wednesday night and Thursday...mainly VFR with showers likely.
Friday...VFR.

&&

Marine...
a cold front will cross our region today. Ahead of the front
southwesterly winds will increase to 15 to 25 knots, building waves
to the northeast of both lakes. Small craft advisories will be in
effect for this on the lakes...including the upper Niagara River.

After the front crosses the lake waters this afternoon, winds will
veer to westerly and tonight northwesterly...sending the higher
waves to along the southern shorelines of the lakes. This will
maintain Small Craft Advisory on the lakes tonight and into the first half of
Tuesday. High pressure will then build south of the lakes Tuesday
night with much lighter winds over the lakes.

&&

Buf watches/warnings/advisories...
New York...beach hazards statement until 8 PM EDT this evening for nyz010-
019-085.
Marine...Small Craft Advisory until 11 am EDT Tuesday for lez040-041.
Small Craft Advisory until 8 PM EDT this evening for
lez020.
Small Craft Advisory until 5 PM EDT Tuesday for
loz043-044.
Small Craft Advisory until 11 am EDT Tuesday for loz042.
Small Craft Advisory until 2 PM EDT Tuesday for loz045.

&&

$$

Synopsis...hsk/Thomas
near term...hsk/Thomas

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