Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
424 am EDT Wednesday Aug 20 2014
a warm front will lift northeastward across the eastern Great Lakes
region today. This front will bring showers and thunderstorms to the
region through Thursday along with a warm and muggy airmass. A few
showers or a thunderstorm may be leftover Friday and Saturday...but
much of the time will be rain free while continuing to remain warm.
Near term /through tonight/...
early this morning a warm front is found across Central Lake Erie
and towards the southern tier and western Pennsylvania. Behind this
warm front dewpoints are in the low to middle 60s across Ohio and
western PA...while to the north of the front across the Niagara
Frontier...Genesee Valley and Eastern Lake Ontario region dewpoints
remain in the 50s. Cloudiness in associated with the warmer air
pushing northward is found across wny...while to the east mainly
clear skies are found across The Finger lakes and Eastern Lake
Aloft a closed upper level low is found over the western Great Lakes
with a surface low also reflected at the surface over northern
Michigan. Water vapor imagery displays a few subtle convectively
augments vorticity maxes to the southeast of this upper level low.
For today expect shower and thunderstorm activity to increase as the
surface warm front slowly edges northward across the County Warning Area. Activity
should increase by late morning with isentropically lifted moisture
along the front in addition to instability from daytime heating. Also
aiding in low level lift for showers and thunderstorms will be low
level outflow boundaries from overnight convection to our southwest.
Precipitable waters rise towards 1.50 to 1.75 inches today within a very light
synoptic flow. This will bring the potential for heavy showers and
thunderstorms again to the region as slow moving activity will have
the potential to drop a heavy amount of rain in a short period of
time. This potential for heavy activity will be localized and will
just continue to mention this possibility in the severe weather potential statement product. While
we will remain unstable through the day...with sbcapes 500 to 1000
j/kg...modest lapse rates will likely only bring scattered
thunderstorms with widespread showers more likely.
This activity will push eastward this evening as the warm front and
focusing boundary shifts eastward. Behind the warm front there may
be enough late day instability...which when combined with the lift
of the nearing upper level low to bring chances for showers and
thunderstorms across wny this evening. By late overnight the bulk of
showers and thunderstorms should be towards the east in proximity to
the warm front...with just a few scattered showers over wny under
the upper level low.
Temperatures today will push to normal...or even above normal
despite the mostly cloudy skies. This be upper 70s to lower 80s for
the region...with 80s most likely towards The Finger lakes and
Eastern Lake Ontario region where some morning sunshine will be
found. Tonight a mild and muggy night is expected with lows in the
60s with a mostly cloudy sky.
Short term /Thursday through Saturday night/...
a split flow featuring a pseudo Rex block over the Great Lakes will
break down at the start of this period...as anomalously strong h25
winds racing out of the Desert Southwest will cross the northern
plains and kick out the downstream cyclone. A burgeoning ridge will
take shape over the Mississippi Valley in the wake of the departing
upper level disturbance...and this will lead to general improvement
over our region. In terms of sensible weather...our temperatures will
average above normal into at least the upcoming weekend with
moderately high humidity.
The ill defined remnants of an 500 mb low in the vicinity of Georgian Bay
Thursday morning will track to the east across Lake Ontario during
the course of the day. Meanwhile the associated weak surface reflection
will drag one last frontal boundary across the eastern portion of
our forecast area. The lift provided by these synoptic features...
combined with an unstable airmass will translate into more showers
and thunderstorms...with the most widespread activity being found
east of the Genesee Valley where the strongest forcing near the surface
front will be found. Precipitable water values of 1.5 to 1.75 will be a little
lower than the previous day...but light steering winds east of
Rochester will persist...so there will be a continued chance for
some slow moving moderate to heavy downpours. While the abundance of
cloud cover will hold temperatures down somewhat...a warm airmass with 850 mb
temperatures in the middle teens (c) should enable maximum temperatures to reach the
upper 70s to near 80. The moderately humid airmass will make it feel
warmer as well...especially after our recent stretch of Fall like
The shortwave and supporting 500 mb trough will push east-southeast away
from our forecast area Thursday night. This will encourage the
leftover showers to end from west to east during the course of night
while slightly drier air will allow temperatures to drop a few
degrees lower (up 50s-low 60s) than the previous night.
On Friday...an interesting synoptic pattern will take shape to our
west. An amplifying 500 mb ridge will be found over the Mississippi
Valley and upper Great Lakes...and this will overlay an area of
weakness in the lower levels. The middle level disturbance will sharpen
a thermal boundary that will be aligned from Lake Superior to
Central Lake Erie. While showers and thunderstorms will likely focus
in the vicinity of this boundary to our west...our forecast area should
be mainly rain free. Since a conditionally unstable airmass will
still be in place over our region though...cannot rule out a shower
or isolated thunderstorm...particular in the afternoon. Will thus
maintain low chance probability of precipitation from continuity.
From Friday night through Saturday night...the 500 mb ridge will
continue to amplify over the upper Great Lakes while a strong surface
high over eastern Quebec will settle across New England and eastern
New York. This blocking pattern will keep a thermal boundary in
place from Lake Huron to Lake Erie and western Pennsylvania...where it
will continue to focus mainly diurnally driven convection. The bulk
of our forecast area should thus be rain free...particularly east of
the Genesee Valley.
Long term /Sunday through Tuesday/...
there is high confidence that this period will feature above normal
temperatures and dry weather as a 593dm 500 mb ridge centered over the
Ohio Valley will extend north across the lower Great Lakes. At the
surface...high pressure will remain anchored in the vicinity of Cape Cod.
High temperatures during this period will be in the middle to upper 70s
Sunday and Monday...close to 80 in many areas Monday...and the lower
80s for most on Tuesday. Overnight lows will be within a couple
degrees of 60.
Aviation /09z Wednesday through Sunday/...
at 06z VFR flight conditions were found across the region as a warm
front penetrated deeper into wny from the Ohio Valley. The increase
in moisture behind this frontal boundary combined with several
pockets of energy aloft passing through the mean flow will trigger
showers and thunderstorms today and this evening. Most of the
activity will remain VFR through the day though brief MVFR in
heavier downpours is quite possible. Tonight within the moist
airmass some MVFR ceilings are likely across the southern tier along
with lowering visibilities.
Wednesday night and Thursday...occasional showers and thunderstorms
with attendant localized reductions to IFR/MVFR.
Friday and Saturday...mainly VFR with a chance of showers and
weak low pressure will move from the Central Lakes Wednesday morning
to near the west end of Lake Ontario by Thursday morning where it
will dissipate in place. A warm front extending from this low will
slowly pass northward across the lake tonight. The pressure gradient
will remain weak through the end of the week with relatively light
winds and flat wave action. A few thunderstorms are possible today
through Thursday which may produce locally higher winds and waves.