Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Albany New York
229 PM EDT Sat Jul 12 2014
high pressure along the Atlantic Seaboard will move out to sea
tonight as a return flow of increasingly moist humid air moves
into the region. A series of frontal systems will move through the
area Sunday into Tuesday with showers and scattered thunderstorms.
Our weather will improve midweek but turn cooler and less humid.
Near term /through Sunday/...
as of 230pm EDT...sct-bkn cumulus were across hir terrain. Isolated -shra
over fca. Middle level lapse rates remain around a lame 5.5c. Mu cape
around 1000 j/kg...still pockets of cin around. What jet forcing
there is will depart fca next 2 hours. Few if any triggers around other
than terrain and lake boundary's. Isolated rain showers and thunderstorm threat continues into
Otherwise high pressure has slid off Atlantic Seaboard...and return flow
will increase wm advection and low level moisture. Surface dew point are in the 60s
and will continue to gradually increase overnight making for a mild humid
night...with some patchy fog.
NAM/GFS in agreement as return flow of increasing moisture. With end
of diurnal heating forcing for any scattered convection should decrease.
Overnight NAM maintains elevated cape of 500 j/kg across northwest prtns
of fca...GFS has none. However toward morning surface warm front mvs into fca along
with a 500hpa short WV mvng across north tier. Will leave isolated -shra
overnight...otherwise conds will remain fair much of nt until clouds
arrive with surface warm front.
Sunday...potential for strong thunderstorms has diminished from pvs guidance.
Storm Prediction Center has removed fca from slght risk in dy 2 and shifted see text
west of fca. The GFS/NAM/Gem have weak surface low and associated fronts
mvng from Lake Erie NE into St Lawrence Valley. It pushes a surface warm front
through region during morning...then drags a cold front through during afternoon. A more
significant cold front moves to and lingers in St Lawrence Valley during
the day. However all guidance bring considerable cloudiness...and amount of
sunshine will delineate the degree of rain showers vs thunderstorms and strength
NAM cape values peak 600-1400 j/kg middle day...and fall in the afternoon
to around 500 j/kg. The GFS only has mu cape of 200-400 j/kg with
400-600 j/kg in the far southeast portions of fca. The alb model NAM sndg
has maximum cape with warm front at 15utc...then drops off to values around
800 j/kg the rest of the day. GFS has 300 j/kg in the
am...then drops to near zero rest of day. Precipitable water values hover around 2
in much of Sunday as dew point climb into the 60s in most areas to near 70.
18utc hires WRF indicates scattered-broken -shra mvng across fca increasing
durng the morning with embedded thunderstorms...and continue through the day. NAM 300hpa
divergence associated with passing jet maximum in ont/qb remains negative
over the fca much of the day (convergent)...with a maximum passing north
of fca toward evening sun. GFS has 300hpa divergence maximum ahead of cold front toward
evening in environment with little cape.
Sunday will end up warm and humid...with considerable clouds...sct-numerous
-shra and scattered thunderstorms...with potential for heavy downpours. Hi temperatures
will be upper 70s hir terrain to low 80s most of fca.
Short term /Sunday night through Monday/...
Sunday night into Monday...plenty of model discrepancy as either
a cold front will slide slowly across the region or become quasi-
stationary as suggested by the GFS. A compromise of the available
guidance suggests this front will become quasi-stationary south of
i90 and return back as a warm front on Monday. This will continue
the threat for showers and thunderstorms mainly for the southern
portions of our County warning forecast area. With nocturnal aspect Sunday
night...expectations are for the severe weather potential to
diminish as we lose the surface based parcels. That changes on
Monday with the return of the warm front an rooting the surface
parcels as a potentially another active day may be unfolding. Per
swody3 outlook...our southern regions are just outside of the
slight rise with the entire region into a general outlook. As for
temperatures through the period...guidance numbers are fairly
close with a blended approach utilized.
Long term /Monday night through Friday/...
active weather will be continuing at the beginning portion of the
On Monday night into Tuesday...a deep cutoff upper level low will be
moving from the Great Lakes towards southern Canada...with a surface
cold front slowly approaching from the west. There are significant
differences in the placement of the cutoff low at 500 hpa when
comparing the latest 00z GFS...ggem and European model (ecmwf). The European model (ecmwf) is the
slowest of all three models...and lags the cutoff behind the
longest...which would keep a threat of showers/thunderstorms in the
forecast through at least middle week.
As a result of the deep meridional flow ahead of the cutoff
low...there will be a strong southerly component ahead of this
system across our area for Monday night into Tuesday. This will
allow precipitable water values to reach around 2.00 inches...which is close to 2
Standard above normal according to climatology. With daytime temperatures in the 70s
to near 80 and dewpoints reaching the upper 60s to low 70s...there
will be plenty of moisture available for periods of heavy showers
and thunderstorms. We will have to watch the potential for locally
heavy rainfall...as local studies have shown these types of setups
to be conducive for widespread flash flooding across our area.
In addition...there will be the potential for strong to severe
T-storms...as the upper level dynamics shift closer to our
area...and puts our area in the right rear quadrant /right entrance
region/ of a cyclonically curved 130 knots jet at 250 hpa. The degree
of severe weather will ultimately depend on just how much instability is
available. It may be limited due to extensive cloud cover...and
flash flooding may wind up being a bigger threat than severe storms for
Depending on which model is correct...the cold front will cross our
area sometime between Tuesday and Wednesday morning. Once it
crosses our area...much less humid air will work into our region
from the west. With the upper low slowly filling in and weakening to
our north...cyclonic flow will start keep the threat of a shower in
the forecast through Wednesday...and possibly even for Thursday for far
northern areas. If the European model (ecmwf) is correct though...there still be some
heavy showers for eastern areas for Tuesday night into Wednesday
morning...as the front will be crossing through around that time.
Otherwise...the remainder of the week looks quiet with a mostly to
partly sunny sky...as surface high pressure builds into the area from
the west. The upper low looks to continue to weaken and lift across
Quebec...with drier... cooler and less humid air in our area during
the late week. Daytime temperatures will be in the 70s to low 80s...and
overnight lows in the 50s to low 60s.
Aviation /19z Saturday through Thursday/...
VFR conditions will prevail throughout much of the taf period
except for a period of MVFR...and possibly IFR...fog/low stratus
at kgfl and kpsf late tonight.
This afternoon...daytime heating has spawned broken cumulus around
5-7 kft across the region. With continued heating during the
afternoon cannot rule out a few widely scattered showers and perhaps
a rumble of thunder at all the taf sites if the cumulus can grow
tall enough to break a cap at 700 hpa. Have placed vcsh in the tafs
for all the sites until 00z as shower coverage will be widely
scattered at best and diminish with loss of daytime heating during
the evening. Winds will be out of the south generally between 3-8
Tonight into Sunday...as an upper-level disturbance approaches from
the Great Lakes region...high level clouds will be on the increase
starting initially scattered but becoming broken by 06z-08z. If the
high clouds take longer to move into the region...enough overnight
clearing may again allow for some MVFR/possible IFR fog at kgfl and
kpsf. A low stratus deck may also develop at kpou as low-level
moisture increases along a southerly flow up the Hudson River valley
but have gone with just sct030 after 08z for now as this cloud layer
is highly dependent on the how quickly the high clouds build across
the region tonight.
Showers associated with the upper-level disturbance may begin to
affect the taf sites late in the taf period Sunday and have placed
vcsh after 15z. Winds tonight will trend towards calm before
becoming south/southwest Sunday at 5-10 knots.
Sunday night through Tuesday night: moderate operational impact.
Chance of rain showers...tsra.
Wednesday: low operational impact. Slight chance of rain showers.
Wednesday night through thursday: no operational impact. No sig weather.
as high pressure slides offshore...the return flow will increase
low level moisture through the remainder of the weekend. This in
turn will also increase the potential for showers and
thunderstorms...some containing heavy rainfall.
Minimum relative humidity values this afternoon with generally fall between 40
and 50 percent...an recover to values at or above 90 percent.
Those values remain elevated on Sunday with values at or above 60
Light winds will become southerly at 10 miles per hour or less today into
tonight. The magnitudes increase through Sunday with 10 to 15 miles per hour.
no widespread Hydro problems are expected into tonight...but
then a series of cold fronts could bring several rounds of showers
and thunderstorms possibly containing heavy rainfall Sunday into
the middle week.
A warm front and higher moisture content will bring some
scattered showers and thunderstorms overnight into Sunday and
lasting through Tuesday.
These frontal boundaries associated with a strong upper level
trough west of the region could bring intermittent showers and
thunderstorms Sunday into the middle week period. Locally heavy
rainfall in the humid air mass could increase the threat for the
potential of isolated flash flooding with some impacts on the main
Stem rivers...small streams and creeks. At this point it is
difficult to pinpoint where the heavy rainfall will occur...but
some locations could receive several inches of rainfall from any
convection that repeatedly moves over the same areas.
For details on specific area rivers and lakes...including observed
and forecast river stages and lake elevations...please visit the
advanced hydrologic prediction service /ahps/ graphs on our website.