Area forecast discussion
National Weather Service Buffalo New York
402 am EDT sun may 19 2013
Synopsis...
high pressure centered just off the New England coast will continue
to drift slowly eastward today...while continuing to pump warmer air
into the area. Aside from a few light showers across the north
country today...conditions should remain mainly dry through
tonight...before a frontal boundary stalls out over the region for
much of the work week and acts as the focus for periods of showers
and thunderstorms.
&&
Near term /through tonight/...
as of 0745z...a narrow broken band of sprinkles continues to lift
northeast across the County Warning Area...and is now situated from just east of
Toronto...southeast to Rochester and the central southern tier. This
band of sprinkles is associated with an area of enhanced middle level
moisture and associated warm air advection...and will continue to
lift northeastward across the remainder of The Finger lakes region
and into the north country through middle morning. Otherwise...expect
dry weather to continue through middle morning...with most areas just
seeing varying amounts of middle and high cloud cover. The one
exception to this will be across the southern tier...where an area
of lower stratus has edged north into areas along the New York/PA border
as Atlantic moisture continues to increase on the prevailing
southeasterly low level flow. While this should not get too much
further north due to downsloping effects on the north side of the
Allegany plateau...where the stratus has developed it will likely
persist until diurnal heating/mixing helps to erode this later on
this morning.
After that...expect mainly dry weather to continue through the
balance of the morning and afternoon hours...albeit with continued
varying amounts of middle and high cloud cover given the overall weak
to modest warm air advection pattern. The one potential exception to
this will be across the north country...where the short term
guidance continues to suggest the best combination of warm air
advection/isentropic lift and deepest moisture will be in
play...with enough of each present to generate some spotty light
showers. Have thus continued with some low chance probability of precipitation for this
region...while keeping the remainder of the region dry per the
seemingly more realistic Gem/European model (ecmwf) solutions.
This evening...expect mainly dry conditions to continue to prevail
as the best swath of warm advection/associated moisture shifts
eastward and out of the area...which should lead to a corresponding
decrease in middle and high cloud cover through the early overnight
hours. Later on in the night...cloud cover will begin to increase
again from the north as a weak frontal boundary over Ontario
province begins to sag southward toward our region...however expect
any shower chances associated with this to remain in the slight
chance range given both its slow approach and the unfavorable time
of day...and mainly confined to the north country at that.
With respect to temperatures...850 mb temperatures will climb to between
+10c and +13c today...with the warmest air found across far western
New York. Coupled with a southerly downslope flow...this should be
enough to boost highs back into the middle to upper 70s across the bulk
of the County Warning Area today...save for two areas. The first of these will be
across the higher terrain of the southern tier and north country
where temperatures should remain confined to the lower 70s...and the second
will be along the immediate Lake Ontario shore from Rochester over
to the Niagara River where an east-northeasterly onshore flow will
help keep highs confined to the 60s. With a continued southerly flow
and surface dewpoints remaining in the middle-upper 50s...rather mild
overnight lows will then follow for tonight...with readings ranging
from the middle-upper 50s in interior portions of the southern tier and
north country to the lower 60s across the lake plains.
&&
Short term /Monday through Wednesday night/...
an anomalously deep and expansive upper level low over the northern
plains at the beginning of the week will keep a downstream ridge in
place over the lower Great Lakes into Wednesday. This will guarantee
above normal temperatures for this short term period...but the flip
side to this Coin is that we will likely experience fairly unsettled
weather as well. The timing of showers and thunderstorms will
certainly be a challenge though...as many of these will either be
diurnally driven or tied to impulses within the upper level flow.
The details...
While a fairly strong ridge will be in place over the upper Ohio
Valley and lower Great Lakes on Monday...high pressure over James
Bay will push a weak frontal boundary south across Lake Ontario.
This front will encounter a Summer like airmass as dew points are
expected to climb into the lower 60s while 850 mb temperatures in the vicinity of
15c will encourage near surface temperatures to climb into the low 80s (mid 80s
in some valleys). This combination will lead to convective available potential energy of 1000-2000
j/kg...with the most unstable air expected over The Finger lakes and
southern tier.
Keeping this in mind...the general synoptic subsidence from the
aforementioned ridge should help to suppress any convection for a
large portion of the day. A fair amount of heating through the
midday hours may be able to overcome this though...especially given
the presence of the weak frontal boundary and favorable low level
thermodynamics. A little higher up...am not impressed with the
forecast middle level lapse rates and the NAM BUFKIT profiles are
suggesting a weak cap around 10k feet. While these are not conducive for
widespread convection...if sbcapes of 1000-2000 j/kg can be realized
then this should not pose too much of a problem for scattered storms
to develop during the course of the afternoon. A closer look at the
underlying airmass suggests that a very weak wind field will be in
place through 10k feet...and with precipitable water values in the vicinity of 1...
that should heighten the chance for slow moving downpours within any
convection that does develop. Otherwise...Monday will be summery
with mainly dry conditions for the bulk of the day.
The weak frontal boundary will slowly settle south of the region
Monday night. While the threat for thunderstorms will generally
cease with the removal of diurnal heating...impulses dropping down
the front side of the 500 mb ridge (along and north of surface front) will
keep the chance for showers in place. It may also be uncomfortably
humid for parts of the forecast area...pending the progression of
the surface frontal boundary. The southern tier stands the highest
chance for experiencing a summery night.
The presence of the nearly stalled frontal boundary in the vicinity of
our forecast area will keep unsettled conditions in place for
Tuesday and Tuesday night. Confidence in the timing and extent of
this precipitation will be low as the mainstream guidance differs on the
placement of the front. We will lean more on the European model (ecmwf) solution...
which hangs the front up over our area. Will thus keep likely probability of precipitation
in play south of Lake Ontario for Tuesday/Tuesday night while using chance probability of precipitation
across the north country.
The blocking upper level low that was found over the northern plains
at the start of this period will finally open up and become absorbed
within a digging longwave trough over eastern Canada. This will
knock down whats left of any 500 mb ridging over the lower Great Lakes
and allow broad surface low pressure to settle over our region. The
result will be more showers and thunderstorms. Will use high chance
probability of precipitation for now given the amount of uncertainty within the various
packages.
&&
Long term /Thursday through Saturday/...
it will be much cooler during this period...as a longwave trough
over eastern Canada will dig south across New England and the lower
Great Lakes. Temperatures will drop below normal by Friday and will
further cool as we head into the Memorial Day weekend.
In terms of precipitation...there will be another chance for showers and
thunderstorms Thursday and Thursday night when a shortwave from the
Central Plains will pass towards our region. Upper level height
falls and low level convergence ahead of a cool pool of air will
bring showers and perhaps some thunderstorms. Instability will not
be as great Thursday...compared to Tuesday and Wednesday.
The European model (ecmwf) will phase this Central Plains low with a shortwave
dropping southward from eastern Canada. This phasing will develop a
trough that will drive a cold front across the region Thursday
night. Behind the cold front high pressure and much drier and cooler
air will filter across the eastern Great Lakes. High pressure will
then build across the lower Great Lakes for Friday and Saturday.
&&
Aviation /08z Sunday through Thursday/...
as of 08z...a narrow broken band of sprinkles continues to lift
across the Genesee Valley and western Finger Lakes and will continue
to lift northeastward through middle morning...however this will have
no impact on aviation interests with varying amounts of middle/high
level cloud cover and VFR conditions otherwise expected. The one
possible exception to this will come across portions of the western
southern tier...where some lower MVFR ceilings over PA have spread
across the New York/PA border and will affect locations from kjhw east to
kelz through the early morning hours...before slowly dissipating by
middle-late morning with renewed daytime heating.
During the daylight hours...the combination of increasing moisture
and weak warm air advection could touch off a few scattered showers
east of Lake Ontario...however these should remain light enough to
keep ceilings/visibilities VFR. Farther west...expect dry VFR weather to
prevail under continued middle and high cloud cover. Tonight...VFR
conditions are expected to continue with middle and high clouds
thinning out from west to east this evening...before increasing
again from the north late as a weak frontal boundary over Ontario
province begins sagging southward.
Outlook...
Monday...mainly VFR...with a chance of MVFR in scattered afternoon
showers/thunderstorms.
Tuesday and Thursday...scattered to numerous showers and
thunderstorms with associated MVFR/IFR...otherwise VFR.
&&
Marine...
quiet conditions will remain in place across the lower lakes through
tonight...with relatively light to modest southeasterly to southerly
winds and minimal waves. After that...generally light winds will
continue through much of next week...albeit with an increasing risk
of showers and thunderstorms as a frontal boundary takes up
residence across the lower lakes region.
&&
Buf watches/warnings/advisories...
New York...none.
Marine...none.
&&
$$
Synopsis...jjr
near term...jjr
short term...rsh
long term...rsh/Thomas
aviation...jjr
marine...jjr
