Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
812 PM EDT sun Sep 21 2014
much cooler weather will briefly settle in behind a secondary cold
front tonight and linger into Monday. Expansive high pressure will
then build across the area from Tuesday through the rest of the week
and provide western and north central New York with an extended
period of fine early Fall weather with temperatures warming above
Near term /through Monday/...
an upper level low will pivot across New York state tonight bringing
an expansive area of cloud cover and scattered showers. A secondary
surface cold front...extending from north of Toronto to the west end
of Lake Erie at 00z...will usher in much colder temperatures on the
back edge of the showers. Surface temperatures behind this front
across northern Michigan are running in the 40s to low 50s which
will advect southward and modify a bit crossing the lower lakes to
bring low temperatures in the upper 40s to lower 50s overnight.
Showers should diminish in coverage and intensity from west to east
behind the front late tonight as the upper level low lifts northeast
and drier air aloft advects overhead. However even though showers
will be winding down later tonight...low level moisture will be
trapped underneath a strengthening subsidence inversion...and
continued upslope flow with very Shallow Lake enhancement courtesy
of cold temperatures aloft will continue to result in widespread
cloud cover and possibly some scattered sprinkles across much of the
forecast area throughout the day Monday. The abundant cloud cover
and cold air flowing into the region will make for a chilly start to
the week with highs that limp into the low to middle 50s.
Short term /Monday night through Tuesday night/...
broad ridging will dominate the North American continent during this
time frame...with the concentration of greatest height anomalies
tracking from the foot of the Canadian rockies eastward across the
Canadian prairies to the Great Lakes region. This pattern will be
represented at the surface by expansive high pressure that will
monopolize the weather over much of the eastern Continental U.S.. while it will
be relatively cool to start the period...the eastward progression of
the aforementioned synoptic pattern will promote a gradual day to
day to warming trend that will send the Mercury to above normal
levels by middle week.
Breaking this down into some detail...
a longwave trough extending from Quebec and the St Lawrence Valley
southwards across the lower Great Lakes and Tennessee Valley Monday
morning will push east during the course of the day...while the
impressive western Continental U.S. Based ridge will move across the plains.
Plenty of middle level dry air will work across our region in the
immediate wake of the trough...yet a wealth of low level moisture
will persist. Relatively light winds below 5k feet will have a tough
time clearing out the associated cloud cover...so the bulk of the
day should be mostly cloudy. This will only emphasize the change to
much cooler weather from the weekend. 850 mb temperatures will bottom out
close to zero c Monday afternoon...with a lack of sunshine ensuring
that near surface temperatures will not climb out of the 50s f. This will be a
change of some 20 degrees from earlier in the weekend.
While the layer of low level moisture will thin Monday night...a
strengthening subsidence inversion from approaching strong high
pressure over the Ohio Valley should keep enough cloud cover trapped
to keep skies at least partly...if not mostly cloudy. A cyclonic
flow above h925 will not help matters either. Will increase sky cover
from continuity to account for this scenario.
On Tuesday...the center of the surface high is forecast to cross
directly over the lower Great Lakes. This will increase the depth of
an already on going warm advection process...which will not only
lead to a much milder day...but will likely generate a fair amount
of Alto-cu. In any case...we should be able to experience a little
sunshine with 850 mb temperatures increasing to around 8c supporting afternoon
maximum temperatures in the middle 60s f.
The Heart of the strong surface high will drift across New England
Tuesday night....then will become anchored in the vicinity of Nova
Scotia on Wednesday. How strong will the surface high be? Forecast mslp
values of 1036-37mb will translate to levels that are only
experienced in that area/at that time of year to a once in 30 year
return interval. In any case...this will put the brakes on the warm
advection. 850 mb temperatures will be held around 10c...so we can anticipate
Wednesday afternoon highs close to 70 along with a fair amount of
Long term /Wednesday through Sunday/...
simply put...the extended period of dry weather will continue into
(and likely through) next weekend while temperatures will average
above late September normals.
Strong consensus exists between the European model (ecmwf) and GFS based ensembles
that anomalously strong ridging will reign across eastern Canada and
the Great Lakes region. Again...the strength of this particular
ridge in its forecast location will rival those from the past 30
years. Its surface reflection will be that of a sprawling area of high
pressure that will be centered in the vicinity of the lower Great
The result of this will be a period of dry comfortable weather with
850 mb temperatures around 12c supporting afternoon highs that will generally
range from 70 to 75...while overnight lows will be within a few
degrees of 50 (40s southern tier and north country).
Looking further ahead...the ridge is not expected to break down
until the end of next weekend with dry weather persisting into at
least the start of next work week.
Aviation /00z Monday through Friday/...
VFR remains in place at 00z but MVFR ceilings and scattered showers
associated with an upper level low are just upstream. A secondary
cold front will cross western and central New York later tonight
with flow veering to west-northwest. Wrap-around moisture and cold air
advection across the lower Great Lakes will bring in lower stratus
with MVFR ceilings at area terminals with IFR ceilings developing across
higher terrain of the southern tier but mainly east of kjhw. Expect
lower ceilings to linger through the overnight hours with gradual
lifting to VFR/MVFR over higher terrain/ after 15z Monday...though
cloud cover will still linger through 00z Tuesday.
Monday night...VFR/MVFR over higher terrain/ with clearing overnight.
Tuesday through Thursday...VFR...except for localized IFR in
southern tier valley fog each overnight/early morning.
gusty southwesterly winds continue this evening ahead of a
reinforcing cold front pivoting east across Lake Erie. Freshening
northwesterlies behind this front and associated cold advection will
bring a substantial increase in wave-action along the south shores
of the lakes...particularly on Lake Ontario where waves will build
into the 4-6 foot range late tonight into Monday. The shorter
northwesterly fetch on Lake Erie should keep waves slightly
lower...in the 3 to 4 foot range.
Waves will gradually subside Monday night as an expansive dome of
high pressure builds across the Great Lakes. This high will slowly
move over the lakes through the rest of the coming week...resulting
in an extended period of tranquil conditions.
Marine...Small Craft Advisory until 8 am EDT Monday for lez040-041.
Small Craft Advisory until 2 am EDT Monday for lez020.
Small Craft Advisory until 1 am EDT Tuesday for
Small Craft Advisory until 8 PM EDT Monday for loz042.
Small Craft Advisory until 2 am EDT Tuesday for loz045.