Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
257 PM EDT Tuesday Sep 30 2014
an upper level disturbance will bring clouds and scattered showers
to southern and western New York tonight and early Wednesday.
Lingering clouds will break with a return to mild and warm weather
on Thursday. A strong cold front is then expected to cross the
region on Friday...bringing a greater likelihood of showers followed
by much cooler temperatures for the upcoming weekend.
Near term /through Wednesday/...
surface low moving southeast into western PA will open up into
surface trough...with scattered light rain showers across the
southern tier and some sprinkles across the rest of western New
York. The north country should avoid any possibility of precipitation
tonight and Wednesday.
An inverted trough will become established across western half of
the state with scattered sprinkles possible through the night and
early Wednesday. This trough will also draw moist air from Lake
Ontario and expected to produce patchy fog overnight...especially
from the Lakeshore to the escarpments south of the lake.
High pressure north of Lake Ontario will move toward the Saint
Lawrence valley on Wednesday and will ridge southward with drier air
and bring about a clearing trend late in the day on Wednesday.
Temperatures will range mostly in the middle 50s overnight with a
moderating influence from Lake Ontario and the thicker cloud cover.
Highs on Wednesday will be a little shy of todays temperatures with mainly
upper 60s to low 70s...the warmer spots across the north country
where clouds will be thinner and more sunshine.
Short term /Wednesday night through Friday night/...
our prolonged stretch of Indian Summer weather will come to an end
during this period as a strong Pacific jet racing across British
Columbia will push a deepening longwave trough across the center of
the country...which in turn will dislodge ridging over the lower
Great Lakes. This process will eventually lead to the development of
an anomalously deep closed low over the Great Lakes region. By the
time the associated pattern changing surface cold front makes its way
across our forecast area...temperatures will have averaged above
normal for nearly two weeks.
The semblance of a Rex block (ridging over Quebec/cutoff low over
new england) found over the St Lawrence Valley Wednesday night will
push east to the Canadian Maritimes during the day Thursday. This
general scenario will promote fair dry weather for our region
Wednesday night...then a second reinforcing ridge will build across
the lower Great Lakes in its immediate wake to supply US with a
beautiful day on Thursday. Subsidence associated with the ridge will
combine with a deepening southerly flow to support widespread
afternoon temperatures in the middle 70s. Sites across the Genesee
Valley and in the downslope areas near the iag Escarpment should
make it into the upper 70s.
A 130kt h25 jet over the northern rockies Thursday evening will dig
into a deepening longwave trough over the northern plains during the
overnight...which will support the consolidation of a surface low over
the upper Great Lakes. This will intensify a downstream low level
jet over Michigan...which in combination with ridging to our east
will keep a very warm southerly flow in place over our region. The
result will be a warm dry night with min temperatures generally
within a few degrees of 60. These readings will be some 15 degree f
above normal early Oct values...or close to where we should be for
On Friday...a feed of 80-100 winds at h25 will continue to pour into
the longwave trough over the Mississippi Valley. This will encourage
the development of a cut off low near The Arrowhead of Minnesota
while the associated surface low will lift due north. The movement of
the deepening surface low should be a clue as to the downstream flow
over our region. An anomalously strong 50kt southerly low level jet
over the lower Great Lakes will not only support one more warm day
over our forecast area...but will also keep the eastward progression
of the surface front and its associated precipitation to a crawl. Have thus
continued the trend of slowing the advancement of the showers...in
this case by some 3-6 hours. The bulk of the day should thus be rain
free for sites east of the Genesee Valley...with likely probability of precipitation not
expected for the far western counties until late. Again...many areas
will experience maximum temperatures in the middle to upper 70s.
The cold front...which will be on our doorstep stretching from Lake
Huron to Central Lake Erie Friday evening...will grudgingly push
across our forecast area during the course of Friday night. The low
level forcing from the cold front will be accompanied by a
relatively narrow 3 hour window of enhanced lift supplied by the rr
entrance region of a cyclonically curved 120kt h25 jet over southern
Ontario. Will hold onto the high likely probability of precipitation with this package...but
as the confidence in the timing of this frontal passage becomes
greater...can easily see probability of precipitation being raised to categorical. Given
lapse rates of less than 6 degree c/km...will continue to leave out the
mention of any thunder. That being said...there should be deep
enough lift and sufficient moisture to support some heavier showers.
850 mb temperatures that will be in the vicinity of 12-14c ahead of the front
Friday evening will plunge to around 2c (wrn counties) by daybreak.
This should enable temperatures over the far western counties to bottom out
at normal levels (40s).
Long term /Saturday through Tuesday/...
temperatures will average near to below normal during this period as
a persistent longwave trough will be centered over Ontario and the
Great Lakes region. The core of the coldest air associated with this
trough will be over the Great Lakes region during the second half of
the weekend. As the negatively tilted longwave rotates poleward
across eastern Canada early next work week...a near zonal Pacific
flow will promote a modification of the airmass over Great Lakes.
For Saturday...the surface cold front will push away from our region via
the St Lawrence Valley while a shortwave ridge will build across the
lower Great Lakes and our forecast area in its wake. This ridging
will work against organized lake driven shower activity...even
though 850 mb temperatures near 2c will supply plenty of instability over the
lakes. Will carry likely probability of precipitation for the morning across the north
country with generally low chance probability of precipitation elsewhere. The bulk of the
midday and afternoon should basically be precipitation free...but chilly as
temperatures will climb into the upper 50s to lower 60s.
The cyclonic flow found above 10k feet will work to the surface Saturday
night as the aforementioned ridging will push east. This will
encourage the development of some lake driven rain showers east of
Lake Erie and particularly east of Lake Ontario in the vicinity of the tug.
Low temperatures will range from the 30s across the southern tier to the lower
40s most elsewhere.
As the core of the negatively tilted upper level trough advances to
the north on Sunday...the low level flow will back and this will
send increasingly disorganized lake effect rain showers to parts of
the iag Frontier and across The Heart of Jefferson County. 850 mb temperatures
straddling the zero degree isotherm will suggest daytime highs will
only be in the 50s.
A broad area of low pressure is forecast to drift across the Great
Lakes and southern Ontario on Monday. This will bring the chance for
some showers to all of our region...although the bulk of the day
should be precipitation free.
Finally for Tuesday...low level ridging over the Mississippi Valley
will drift east across the upper Great Lakes and Ohio Valley while
the aforementioned surface low will work its way down the St Lawrence
Valley. The exiting surface low will once again pose the opportunity for
some badly needed rain showers.
Aviation /19z Tuesday through Sunday/...
a few showers will pass across the region late today. Will maintain
vcsh as this activity is expected to be scattered south of Lake
Ontario. The exception will be across the southern tier which will
lie closer to the upper level shortwave and cold pool aloft. The
north country should remain VFR through this taf period.
Tonight clouds will lower south of Lake Ontario as winds veer around
to northeasterly. A still convergence boundary in the low levels may
serve as a focus for sprinkles and low MVFR or IFR clouds south of
Lake Ontario as the northeast winds maintain ample low level
Clouds will thin and dissipate later on Wednesday with VFR overall.
Wednesday through Thursday...VFR...except for localized IFR in
southern tier valley fog between 06z-15z each day.
Friday...VFR lowering to MVFR with showers becoming likely.
Saturday...MVFR with a chance of showers.
an upper level low...and weak surface low will dive southeastward
across Pennsylvania today tonight. A light wind will become
northeasterly tonight and increase to around 15 knots on Lake
Ontario...and 10 knots on Lake Erie. These stronger winds on Lake
Ontario will bring waves 2 to 4 feet tonight. Weaker winds will
allow for 1 to perhaps 2 foot waves on the eastern end of Lake Erie
Waves and winds will diminish through the day Wednesday as high
pressure again builds across the lower lakes region.
Late in the week...a strong area of low pressure is expected to lift
across the Great Lakes region on Friday...while swinging a strong
trailing cold front across the lower lakes. The tightening pressure
gradient associated with the low will lead to a period of stronger
winds...with advisory-level winds and waves becoming possible.