Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
332 am EST Monday Nov 30 2015
high pressure will keep dry conditions and cool but seasonable
temperatures across the region through tonight. Then low pressure
will track across the Great Lakes on Tuesday bringing above normal
temperatures and rain. A cold front will cross the region Wednesday
which will bring temperatures back to normal with some rain or snow
showers Wednesday night and Thursday. High pressure then builds back
in for the weekend with dry conditions and above normal temperatures.
Near term /through tonight/...
as has been the story over the last day+... some low cloud cover
continues to hang around near the lower Great Lakes. This is
resulting from low-level moisture /enhanced by the lakes/ trapped
below a sharp inversion above 850 mb per the 00z buf sounding. As
the surface high over New England slides off the coast today and
pressures fall across the middle-west ahead of the next storm system...
winds will turn more east-southeasterly today. The result will be
increased downsloping across the region which will finally scour out
any remaining low-level moisture and send it toward the Canadian
side of Lake Ontario. Thus temperatures will run several degrees
warmer today under mostly sunny skies and light downslope flow.
By tonight... middle/high cloud cover will increase and thicken from
south to north as flow turns more southerly and warm air advection increases across
the region ahead of the next approaching storm system moving into
the Midwest. The better chances for steady rain hold off until
Tuesday (more on that in the short term section)... but wouldn't rule
out some isolated/scattered showers making it into the area by the
later part of the overnight. Temperatures tonight will follow a non-
diurnal trend... as we quickly cool under clear skies early... then
increasing warm advection and cloud cover will allow temperatures to
climb after midnight.
Short term /Tuesday through Thursday/...
Tuesday and Tuesday night a nearly vertically stacked low will move
from the upper Mississippi Valley to the upper lakes. At the surface
a warm front will lift across the lower lakes Tuesday morning
followed by a cold front Tuesday night. This system will bring a few
periods of showers to the region...although overall quantitative precipitation forecast will be
Looking at the details...isentropic upglide will be on the increase
by daybreak Thursday along and ahead of the surface warm front. This
will allow a few scattered showers across western and central New York by
early Tuesday morning...reaching as far north as Lake Ontario. These
warm advection showers will spread quickly northeast across the
north country during the morning. Temperatures will be on the rise
already at daybreak Tuesday in the increasing low level warm
advection. It will be a close call across the north country...but it
still appears surface temperatures will warm to above freezing just prior
to the onset of showers. Elsewhere temperatures will be well above freezing
by the time any showers begin.
Tuesday afternoon and evening the cold front or cold occlusion
approach western New York...and large scale ascent will also increase as
DPVA and height falls spread downstream of the middle level closed low
and diffluent upper level flow spreads into the lower lakes. Precipitable water
will reach 1 inch which is about 2 Standard deviations above normal
for the first day of December. The forcing and moisture will come
together to produce a few periods of showers Tuesday afternoon and
evening regionwide...however the relatively weak and diffuse nature
of the forcing will keep quantitative precipitation forecast on the light side. A surge of warmer
air will arrive just ahead of the frontal boundary with 850mb temperatures
rising to +8c...supporting highs in the middle 50s on the lake plains
of western New York aided by downslope flow. The warm air will reach as
far east as The Finger lakes...but cold air damming will likely hold
Lewis County and the Saint Lawrence valley to around 40.
Overnight Tuesday the front will move east across the area with
showers ending across western New York by late evening...then tapering off
farther east after midnight. A well defined dry slot will move into
western New York after midnight with at least partial clearing. Low temperatures
will be mild with only weak low level cold advection behind the
first frontal boundary. Expect lows in the low to middle 40s.
By Wednesday model guidance begins to diverge...with the GFS and NAM
showing an expansive dry slot taking hold of the entire County Warning Area. The
Canadian Gem and European model (ecmwf) bring a weak wave northward along the frontal
zone across eastern PA/New York during the day. This wave would slow the
passage of the frontal zone and possibly bring more showers to areas
from The Finger lakes eastward into central New York and the north
country. Given the model uncertainty will hold onto chance probability of precipitation
across eastern areas through Wednesday afternoon...with a mainly dry
forecast from the Genesee Valley westward where a good deal of
sunshine should be found in the dry slot. The model consensus is for
a slower arrival of wrap around moisture...which will not reach
western New York until Wednesday evening. Temperatures will still be mild
on Wednesday with highs in the 45-50 degree range in most areas.
Wednesday night the sharp middle level trough and associated wrap
around moisture will cross the lower lakes. This will bring an
increase in cloud cover and showers from west to east. The greatest
coverage of showers will be found in areas of lake enhancement off
both lakes. Off Lake Erie initial southwest flow will Put Lake
enhancement across the Niagara Frontier before sinking southward
across the southern tier overnight as boundary layer flow becomes
westerly and finally northwest by Thursday morning. Expect a similar
trend later Thursday night east of Lake Ontario with initial lake
enhancement near Watertown pushing south across the Tug Hill to the
southeast corner of the lake by Thursday morning. On Thursday
lingering weak lake effect showers southeast of the lakes will
Cold advection Wednesday night will bring ptype concerns into play as
850mb temperatures drop to around -6c. Boundary layer temperatures will lag...with
lower elevations not dropping to the freezing mark. Expect the lower
elevations to see a rain/wet snow mix overnight Wednesday night and
Thursday...with some of the higher terrain changing to all wet snow.
The above freezing temperatures should prevent any snow accumulation
at lower elevations. The higher terrain east of both lakes may see
some minor accumulations on the order of a coating to an inch.
If Buffalo is able to get through Wednesday night and Thursday
morning with no measurable snow...this year will shatter the record
for the latest first measurable snow as no potential for snow is
apparent in long term forecasts through at least the 10th of
December. The previous record for first measurable snow is December
3rd...set in 1899.
Long term /Thursday night through Sunday/...
benign weather will rule the long term with temperatures warming to
well above average again.
Looking at the details...a surface ridge will build into the Ohio
Valley and middle Atlantic on Thursday night and Friday before building
north into the lower lakes and New England Saturday and Sunday. Both
the GFS and European model (ecmwf) drop a middle level trough across Quebec and into New
England on Friday...but this system will be moisture starved with
any small chances of precipitation likely relegated to the higher terrain
of New England well east of our area. With this in mind have
maintained a dry forecast Friday through the weekend.
Temperatures will rebound to above average on Friday with highs in
the middle 40s across lower elevations. Even warmer temperatures are
expected over the weekend with high pressure surface and aloft
providing sunshine and 850mb temperatures moderating to +6c or better. This
should support highs in the lower 50s at lower elevations.
Aviation /09z Monday through Friday/...
area of MVFR ceilings along near Lake Ontario continue to impact
kbuf/kiag/kroc/kart this morning. Overtime this morning...
increasing easterly to east-southeasterly winds will erode this low
stratus deck and shift it to the north side of Lake Ontario. The
result will be improving conditions across the taf sites with mainly
VFR conditions expected to prevail by this afternoon.
Clouds increase from south to north tonight ahead of the next
approaching storm system. Rain chances will hold off until early
Tuesday morning... with ceilings likely lowering to MVFR with the onset
of precipitation... especially across the higher terrain.
Tuesday...rain. Mainly MVFR.
Wednesday...mainly MVFR. Rain or snow showers likely.
Thursday...mainly VFR. A chance of rain or snow showers early.
high pressure to remain in control through Monday... keeping winds
and wave minimal.
A low pressure system will then track across the Great Lakes Tuesday
through Thursday resulting in a period of brisk southwesterly winds
ahead of the storm and west to northwest winds behind it. Small
Craft Advisory conditions will likely develop on area waters as this
weather system moves through.