Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
728 am EDT Wednesday Aug 5 2015
a trough of low pressure...and cool air will drop across
the eastern Great Lakes region today. This feature will provide for
clouds across the region...and to the east of Lake Ontario
showers and perhaps a thunderstorm. Thursday will become a few
degrees warmer with seasonable temperatures remaining for the rest
of the week.
Near term /through tonight/...
this morning's water vapor imagery displays a broad upper level
trough of low pressure over eastern Canada. Several shortwaves
advancing around this low will maintain this upper level low's
influence over the eastern Great Lakes region today.
East of Lake Ontario...as 850 hpa drop to near 8c today over the
lake...the 850 hpa to lake surface temperatures will be unstable
continuing the threat of lake effect rain today east of the lake.
Weak surface convergence will focus these rain bands towards the Tug
In addition the cool pool of air aloft will create steep lapse rates
such that rain showers will develop as we warm today. Instability
showers will be greatest in coverage area east of Lake Ontario where
the coolest air aloft resides...and passing shortwave in the
afternoon should provide enough lift to warrant likely probability of precipitation. In
addition the lower freezing level may allow for some rumbles of
thunder across Oswego County and the north country this afternoon
and early evening.
Temperatures at 850 hpa ranging from near +8c near the Saint
Lawrence valley to +11c near the New York state/PA state line will bring cooler
than normal afternoon highs. Temperatures today will average about 5
degrees below normal with widespread 70s found. With the cool trough
overhead skies will remain mostly cloudy through the day. Greatest
number of breaks in the clouds will be towards the New York state/PA line.
Tonight lake rain showers will continue to be possible into the
evening hours. This activity still remaining near the Tug Hill
region will fade through the overnight hours as drier air associated
with an area of high pressure building over the Great Lakes region
disrupts the organization of the band of rain.
This drier air combined with the increasing stability of the lower
level of the atmosphere should decrease the cloud cover through the
Tonight lows will drop down to a chilly upper 40s well inland to low
to middle 50s across the lake plains. With light winds tonight as high
pressure nears the region some River Valley fog is likely over SW
New York state.
Short term /Thursday through Saturday night/...
the anomalously deep closed low responsible for the cool weather
leading into this period will open up and exit across the Labrador
Sea during this period. In its wake...a complex split flow will take
place over the eastern half of the continent with a near zonal flow
being found over the Great Lakes region. This will encourage a day
to day moderation in temperature...while surface based ridging will
virtually guarantee rainfree conditions up to at least the start of
High pressure centered over Hudson Bay on Thursday will nose south
across the lower Great Lakes to the middle Atlantic coast through
Thursday night. This will ensure fair dry weather over our forecast
area with comfortable daytime temperatures topping out in the middle
70s while overnight lows will generally back into the 50s. The
valleys of the southern tier and the foothills to the Adirondacks could
revisit the upper 40s.
On Friday...the area of high pressure will push east across New
England while weak warm advection will lift our 850 mb temperatures out of the
single digits to between 12 and 14c. This will encourage our Mercury
to climb into the upper 70s to near 80 Friday afternoon...which is
right where they should be for this time of year.
As the surface high moves to eastern Quebec Friday night...our region
will find itself sandwiched between a developing storm system off
the middle Atlantic coast and a shortwave over the upper Great Lakes.
This should result in at least one more dry period for our forecast
area...with continued warm advection and somewhat more cloud cover
leading to a milder night. Overnight lows should range from the low
60s across the lake plains to the middle 50s in the normally cooler
areas spelled out in the discussion for the previous night.
For Saturday...there will be more uncertainty in the forecast as the
aforementioned shortwave over the upper Great Lakes will track
across Lake Ontario. The various guidance packages differ on the
potential for showers...with the European model (ecmwf) being in the more pessimistic
Camp. Will defer to continuity for now and hold onto the slight chance
probability of precipitation for Saturday afternoon...but those with outdoor plans should
keep a close eye on updated forecasts as we progress through the
While low level ridging may still extend across our region Saturday
night...the shortwave crossing to our north could generate a few
showers across the Eastern Lake Ontario region. Have introduced low
chance probability of precipitation for that area while keeping slight chance probability of precipitation in place
Long term /Sunday through Tuesday/...
the split upper level flow found over North America will evolve into
a phased longwave pattern during this period...as a burgeoning ridge
will take shape over the Canadian and U.S. Plains. While this
process will keep a fair amount of uncertainty as to the timing and
extent of rainfall for this period...there is fairly high confidence
that our temperatures will average within a couple degrees of
An exiting shortwave over the St Lawrence Valley will give way to a
wedge of high pressure Sunday and Sunday night. This should favor
mainly dry weather over our forecast area...but again...guidance has
not been consistent with the nuances of this scenario so will hold
onto slight chance probability of precipitation.
As we push into the new work week...confidence in the overall
pattern actually increases as an amplifying ridge over the plains
will set the stage for a deepening downstream trough over the lower
Great Lakes. Meanwhile...a broad inverted trough stretching from the
Great Lakes south to the lower Mississippi Valley on Monday will
push east Monday night and Tuesday. Some of the European model (ecmwf) and gefs
ensemble members are suggesting that an organized surface low will
develop within this trough and lift out of the Ohio Valley on
Tuesday. Even if this scenario does not take place...there will be
an increasing chance for unsettled weather across our region as we
progress through the first couple days of the new work week.
Aviation /12z Wednesday through Sunday/...
VFR flight conditions are found across the region at 12z.
A cool pool of air aloft will drop across the region maintaining
ceilings...though clouds will generally have bases between 5 and 10k
feet. The greatest chances for showers will be east of Lake Ontario
today where showers will become likely and will carry
-shra in the kart taf. Some thunder is also possible east of Lake
Ontario today. Elsewhere the remaining taf sites south of Lake
Ontario should remain dry.
As we head towards tonight scattered Showers/Lake enhanced showers
will linger southeast of Lake Ontario. This activity will wane such
that by dawn Thursday morning much of the region should be
precipitation free with just a few patches of clouds...mainly east
and southeast of Lake Ontario.
Winds today will generally be westerly...with occasional gusts this
afternoon of 20 knots. Tonight winds will go light and variable as
high pressure meanders across the Great Lakes region.
Thursday through Sunday...VFR.
small craft advisories will remain in effect for Lake
Ontario today as a pool of cold air aloft drops over the lake.
Westerly winds will kick up 4 to 6 foot waves over central and
eastern portions of the lake today and this evening.
Southwest to westerly winds will also near small craft conditions on
Lake Erie this afternoon. Though lapse rates from the water surface
will not be as great as Lake Ontario...still believe that Small Craft Advisory
conditions will be meet and will issue a Small Craft Advisory for this lake to
account for winds nearing 20 knots and waves increasing towards 4
In addition to the winds and waves...there will continue to remain a
possibility of waterspouts today...especially on Lake Ontario. Large
water surface to 850 hpa temperature difference and equilibrium
levels rising to 25 to 30k feet should continue the possibility of
waterspout formation under this upper level low aloft.
High pressure will build towards the eastern Great Lakes region
tonight ending the threat of waterspouts...while also allowing for
winds and waves to diminish on the lakes.
Marine...Small Craft Advisory from 2 PM this afternoon to 8 PM EDT this
evening for lez040-041.
Small Craft Advisory until midnight EDT tonight for
Small Craft Advisory from noon today to 6 PM EDT this
evening for loz042.