Area forecast discussion
National Weather Service Buffalo New York
716 am EDT Monday may 20 2013
Synopsis...
a southwesterly flow of warm and more humid air will continue across
the region for much of this week...while a frontal boundary also
stalls out across New York state and sets the stage for increasing
chances of showers and thunderstorms. The more unsettled conditions
will last through Thursday...before a cold front crosses the area
and Ushers in cooler and drier weather for the end of the week and
the Memorial Day weekend.
&&
Near term /through tonight/...
through middle to late morning...dry weather will continue across the
vast majority of the area. The bulk of any cloud cover will be found
across far interior portions of the southern tier/north country
courtesy of a slowly departing stratus deck...while areas further
north should continue to see a fair amount of sunshine under just
some passing cirrus. The one exception to the dry conditions will
come across the upper Saint Lawrence valley and portions of the
north country...where some scattered sprinkles/light showers will be
possible in association with a weak frontal boundary sagging
southward from southern Ontario and Quebec.
After that...expect some scattered convection to gradually develop
inland from the lakes through the early to middle afternoon hours...as
lake breeze circulations develop and interact with a more warm and
humid airmass...with the lingering weak/diffuse frontal boundary
across northern New York also acting as a second potential trigger.
Will continue to carry some low-Middle Range chance probability of precipitation to cover this
potential...with the greatest convective chances stretching from
interior portions of the southern tier eastward across The Finger
lakes...where available instability will be maximized. Closer to the
lakes...the stabilizing onshore flow will result in much lower
chances for convection...with these areas likely to remain largely
dry. Given the relatively weak wind fields that will be in place and
precipitable water levels approaching 1.5 inches...any storms that
do form today will be slow moving...and therefore capable of
producing localized areas of heavier rainfall.
This evening...any lingering scattered convection should quickly
exit into central New York and diminish with the loss of daytime
heating/instability...with fairly quiet conditions otherwise
expected for the first half of the night. Overnight...convective
chances will begin to increase again from northwest to southeast as
low pressure develops across the western and Central Lakes and sends
increasing moisture and lift eastward along the sagging frontal
boundary. With the short term model guidance having difficulty in
resolving/agreeing on the timing and placement of the resultant
areas of convection...for now have just indicated a general increase
in probability of precipitation back to the low chance range overnight.
With respect to temperatures...850 mb temperatures will continue to climb
to the +13 to +15c range today...and this should be enough to
support widespread highs in the Lower-Middle 80s away from lake
influences...with cooler readings found near the lakeshores...and in
the vicinity of the frontal boundary sagging into the north country.
A rather warm night will then follow for tonight...with readings
only dropping into the lower to middle 60s. With surface dewpoints also
rising into the lower 60s...it will also begin to feel somewhat
humid.
&&
Short term /Tuesday through Thursday night/...
a closed 500 mb low parked over the northern plains at the start of this
period will keep a warm ridge in place across our region through at
least Wednesday. This will not only supply US with some Summer like
warmth but will give US a taste of Summer humidity as well. While we
can say this with a high degree of certainty...it will continue to
be challenging to pinpoint the timing and extent of the showers and
thunderstorms that are expected during this time frame.
On Tuesday...the controlling ridge that up to this point had been
protecting most of the region with its associated subsident flow
will start to weaken. Meanwhile at the surface...a slow moving frontal
boundary will sag south from southern Ontario...likely stalling over
our western counties. Convection is likely to develop along and
south of this boundary where dew points in the low-middle 60s should
help to establish afternoon cape values >1000 j/kg away from the
lakes along with lifted indice's in the vicinity of -4/-5. The diurnally driven
convection will be aided by increasing amounts of low level moisture
out of the Ohio Valley...with precipitable water values possibly climbing over 1.5
inches. Given the lack of confidence on the frontal position...will
have to broad brush with likely probability of precipitation for the afternoon. Otherwise as
already mentioned...it will be warm and humid Tuesday with highs of
80 to 85 over the western counties and 70s east of Lake Ontario.
The showers and thunderstorms over the western counties will taper
off early Tuesday night as the boundary layer will partially
stabilize with the removal of diurnal heating. Middle level ridging
will become re-established over our forecast area during the night
as well...so this should also help in temporarily ending any precipitation.
Showers and possible thunderstorms should be a little more common in
the vicinity of the frontal boundary east of Lake Ontario during the
overnight though. Otherwise...this will leave a relatively warm and
humid night across the region...especially over the western counties
(south of Lake Ontario and the frontal boundary).
The early Summer airmass will remain in place across the forecast
area on Wednesday as the closed low over the northern plains will
gradually open up while keeping a moisture rich low level intact
from the Ohio Valley. This low level feed will be enhanced by broad
low pressure that will approach our forecast area from lower
Michigan. This should lead to more extensive cloud cover...which in
turn will minimize diurnal instability over our region.
Nevertheless...sbcapes of 500 j/kg should be more than enough to
generate some showers and thunderstorms with precipitable water values of >1.5
supporting some localized high quantitative precipitation forecast. Will once again broad brush with
likely probability of precipitation.
In terms of the potential for strong to severe storms...will
reiterate the thinking from the previous discussions. Middle level
lapse rates for both Tuesday and Wednesday are only in the vicinity of
6 degree c/km with equally unimpressive kinematic fields (ex. 0-3km
shear <25 M/s).
The aforementioned surface low will cross to our north Wednesday night
while its trailing frontal boundary will hang back to a frontal wave
in the vicinity of Western Lake Erie. This will keep showers and possible
thunderstorms over our region...but do not expect strong enough
forcing to support significant quantitative precipitation forecast.
On Thursday and Thursday evening...the wavy frontal boundary will
slowly drift across our forecast area. From the 00z model runs...
the GFS was some 3-6 hours faster with this passage than its
European counterpart. In any case...this will likely generate
another round of showers and thunderstorms with daytime temperatures
averaging some 10 degree f lower than the previous few days. This will
translate into early afternoon highs in the lower 70s for most
areas.
While Thursday night should prove to be noticeably cooler...there
will be some lingering showers with skies stubborn to clear. In
fact...most areas may keep their low cloud cover right through
daybreak on Friday. This will especially be true for sites east of
the Genesee Valley. Temperatures are expected to drop into the
40s...which will be at least 15 degree lower than previous overnight
lows.
&&
Long term /Friday through Sunday/...
the various medium range guidance packages are in strong agreement
that generally fair and seasonably cool conditions will be in place
during this period...including the bulk of the Memorial Day weekend.
A broad based ridge will be positioned over the nations middle section
and this will leave twin troughs off the coasts of Vancouver and
eastern Quebec...where cooler than average temperatures are
expected.
A more detailed look at our region reveals that we will have some
leftover low clouds and light showers Friday morning (mainly east of
Genesee valley) in the wake of the departing frontal system...but as
low level ridging builds south across the Great Lakes...our skies
will clear out. 850 mb temperatures will drop to around 5c...so Friday will be
much cooler with afternoon temperatures generally in the lower 60s (50s
across the north country).
Expansive high pressure will build south across the region from
Canada Saturday and Sunday...with 850 mb temperatures forecast to be in the
vicinity of 4c both days. This will keep the afternoons cool and the
nights chilly with some frost possible...mainly across the southern
tier and Eastern Lake Ontario regions.
A peek ahead to Memorial Day suggests that fair dry weather will be
in place with a moderation in temperatures to near seasonal levels.
&&
Aviation /11z Monday through Friday/...
as this morning progresses...any lingering stratus across interior
portions of the southern tier and north country should mix out/slide
off to our east...leaving behind general VFR conditions for the rest
of the day under passing cirrus and developing diurnal cumulus. This
afternoon...scattered convection should develop away from the
stabilizing effects of the lakes...some of which could produce very
brief and localized IFR/MVFR conditions. This said...most of the taf
sites should remain behind lake breeze boundaries and thus in more
stable air...with VFR conditions continuing.
Tonight...expect VFR conditions to continue to prevail for much of
the night...before some additional convection possibly pushes into
the area from the west late. With the timing and placement of this
very uncertain at this point...for now have just added vcsh to the
tafs to cover this potential.
Outlook...
Tuesday through Thursday...numerous showers and thunderstorms with
associated brief MVFR/IFR...otherwise VFR.
Friday...mainly VFR with a chance of showers.
&&
Marine...
through much of this week...winds will remain relatively light and
variable in direction due to a nearly stationary frontal boundary
that will remain draped across the region...as well as the daily
development of lake breezes. As a result...wave heights should also
remain minimal. Otherwise...after a mainly dry day today...shower
and thunderstorm chances will increase markedly for the Tuesday
through Thursday time frame.
&&
Buf watches/warnings/advisories...
New York...none.
Marine...none.
&&
$$
Synopsis...jjr
near term...jjr
short term...rsh
long term...rsh
aviation...jjr
marine...jjr
