Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Buffalo New York
720 am EDT Sat Jul 12 2014

Synopsis...
high pressure that brought US several beautiful days with
comfortable conditions has since drifted off the East Coast...so now
warmer and gradually more humid air will start to circulate back
across the region. This will set the stage for some unsettled
weather late tonight into Tuesday...as a series of frontal systems
will combine with the increasingly unstable air to produce a few
rounds of showers and thunderstorms.

&&

Near term /through tonight/...
high pressure along the East Coast will provide our region with
another sun filled day...but unlike the past several...today will be
warm and become increasingly more humid. The clockwise circulation
around the fair weather feature will pump more summery air out of
the Ohio Valley...where temperatures on Friday topped out in the middle
80s. Similar temperatures can be expected this afternoon across Our
Lake plains and in the valleys...with readings closer to 80 near the
Lake Shores and across the higher terrain.

The day will not be without a minor concern though...that being the
potential for isolated showers in The Finger lakes region. Increased
low level moisture advecting north from Pennsylvania will help to
destabilize the air in that area this afternoon...but a weak middle
level cap and unimpressive lapse rates (<5 degree c/km) above 700 mb should
minimize this potential. Will use slight chance probability of precipitation for this region.

The high off the coast will lose its grip on our weather tonight as
a warm frontal boundary over lower Michigan is expected to support
the development of a complex of thunderstorms. These storms will
make their way east across the lower Great Lakes after midnight...
reaching our far western counties (west of general valley) during the
wee hours of Sunday morning. The bulk of the effect of these storms
though should not be felt until after daybreak.

Temperatures tonight will continue their general upward trend...as
readings will be nearly 10 degrees higher than those from this
morning with lows generally in the middle to upper 60s outside of the
southern tier.

&&

Short term /Sunday through Tuesday night/...
on Sunday...an open wave of low pressure will lift from the vicinity
of Lake Huron to near the southern tip of James Bay through the
course of the day. In the process...it will push its attendant warm
front across the region Sunday morning...before slowly pivoting its
trailing cold front into the region during the afternoon.

At this point...it appears that we can potentially expect two rounds
of convection on Sunday. The first of these should work across the
area through the morning/midday hours in association with the warm
front/attendant middle level shortwave/40-50 knot low level jet and
should be primarily elevated in nature...with second round more
surface-based in nature and coming during the afternoon/early
evening hours in association with the trailing cold front. In both
instances...enough lift...moisture...and instability appears to be
present to warrant high likely probability of precipitation for much of the day.

As has been mentioned in this space for a few days...the biggest
threat from the convection will come in the form of locally heavy
rainfall given that precipitable water values will be pushing 2
inches. This stated...there will also at least some risk for strong
to severe storms as well during the afternoon given the moderately
strong and near-unidirectional west-southwesterly flow aloft...with
this potential strongly contingent on the amount of destabilization
we will actually experience. Provided sufficient destabilization can
occur /as suggested by the NAM/...enough shear would be in place to
support the development of some bowing line segments and supercells
with strong damaging winds being the primary severe threat...as
indicated by Storm Prediction Center in their new day 2 convective outlook. This
stated...the development of sufficient instability for this still
appears rather questionable at this point...as leftover debris
clouds and showers could well result in a less unstable airmass as
suggested by the GFS and European model (ecmwf)...which would result in a much lower
overall severe risk. Given this uncertainty...for now will elect to
just highlight this potential in the severe weather potential statement...while holding off on any
mention of enhanced wind wording within the forecast itself.

Sunday night...any convection should die down fairly quickly during
the evening with the loss of daytime heating...and the passage of
the aforementioned cold front/subsequent arrival of somewhat drier
air. This stated...with a general large-scale cyclonic flow
remaining intact through the night...will still retain some lower
chance probability of precipitation for some spotty additional convection overnight.

Once we get into the Monday and Tuesday time frame...the forecast
picture becomes more muddled as the 00z guidance continues to
exhibit significant differences in the handling of both the
burgeoning upper level trough that will be in the process of digging
across the Great Lakes and northeast...and that of any attendant
surface features. In a nutshell...the 00z GFS remains much faster
and more progressive than the other guidance...and essentially
swings the core of the upper trough into the lower Great Lakes and
New York state by Tuesday. Consequently...it pushes an attendant
secondary surface wave across the region later Monday and Monday
evening along with a second round of our convection...with our
region locked in the cool cyclonic flow around the upper low by the
start of Tuesday. In contrast...the European model (ecmwf) and Gem remain some 24
hours slower with the arrival of both the upper low and its surface
wave...with a mainly dry day on Monday followed by the next
potential round of convection on Tuesday. Meanwhile...the NAM lies
between these two extremes...albeit a little closer to the European model (ecmwf) and
Gem solutions.

At this point tend to favor the slower European model (ecmwf)/Gem Camp...as these
models have been much more consistent over the past 24 hours and
enjoy wpc support...and also simply look much more realistic in
comparison to the faster and what appears to be overly progressive
GFS. With this in mind...have continued to trend the forecast toward
a drier Monday...with just some lingering lower chance probability of precipitation left
across our southeastern periphery in an attempt to account for the
continuing forecast uncertainty and out of respect for previous
continuity. Subsequently...have also gone somewhat wetter later in
the Monday night and Tuesday time frame in association with the
second surface wave/cold front...though have kept probability of precipitation confined to
the high chance range for now given the continued model
discrepancies.

Should the above scenario verify...the greatest potential for
additional rainfall early next week will come on Tuesday...when
there could also be a secondary severe threat given both increasing
shear and dynamics on the eastern flank of the approaching upper
trough. This stated...this potential will again be highly dependent
upon the amount of instability that will actually be realized...with
current model projections suggesting that the best instability may
actually remain to the south and east of our forecast area.

With the approach of the upper trough and its attendant cool pool
and the passage of what should be multiple cold fronts...
temperatures during this period should exhibit a general downward
trend. Expect highs ranging within a few degrees of 80 on Sunday to
drop back into the 70s area wide by Tuesday...while nighttime lows
initially in the lower to middle 60s fall back into the 50s by Tuesday
night. At the same time...fairly humid conditions on Sunday will
also trend substantially less so by Tuesday night...with dewpoints
initially in the middle and upper 60s falling back into the 50s.

&&

Long term /Wednesday through Friday/...
in the extended portion of the forecast...the core of the upper
trough and its attendant cool pool will meander across the Great
Lakes region on Wednesday...before gradually lifting out into
northern Quebec Thursday and Friday. This will result in deep
troughing over our region giving way to a quasi-zonal flow by the
end of the period...with seasonably cool temperatures on Wednesday
moderating back closer to normal levels by Friday. More
specifically...850 mb temperatures averaging around +8c on Wednesday will
recover back to between +10c and +12c by Friday...which should
translate into highs of around 70 on Wednesday climbing back to
the middle to upper 70s by the end of the work week. Meanwhile...
nighttime lows will generally range through the 50s...though some
upper 40s will be possible across interior sections of the southern
tier and north country both Wednesday and Thursday nights.

In terms of precipitation chances...with the upper trough/cool pool
overhead...expect diurnal heating to bring at least a low chance of
some instability showers to just about anywhere on Wednesday. In
addition...some lake-effect rain showers may also be possible very
early in the day Wednesday and again Wednesday night with the waters
of lakes Erie and Ontario now fairly warm...though have elected to
not add this kind of detail to the forecast just yet given the
still-distant Vantage Point. After that...precipitation chances
should gradually diminish through the remainder of the period as the
main upper low pulls away from our region...and as such have
indicated a mainly dry forecast for the bulk of Thursday and
especially Friday.

&&

Aviation /11z Saturday through Wednesday/...
VFR conditions will remain in place through at least this evening...
as high pressure centered along the New England coast will still be
in control. While there may be an isolated shower or two over parts
of The Finger lakes region this afternoon...no organized convection
is expected.

Tonight...a complex of thunderstorms will form in the vicinity of a
warm front over lower Michigan. While these storms are forecast to
make their way across the lower Great Lakes during the wee hours of
Sunday morning...the bulk of the night will feature fair weather
with continued VFR conditions for the taf sites across our region.

Outlook...
Sunday...MVFR in showers and thunderstorms early...then general
improvement is expected for the afternoon.
Monday...mainly VFR with a chance of a shower or thunderstorm.
Tuesday...VFR to MVFR in scattered showers and thunderstorms.
Wednesday...mainly VFR with a chance of showers.

&&

Marine...
high pressure along the New England coast will extend back across
the lower Great Lakes today...keeping light winds and negligible
waves in place across lakes Erie and Ontario.

Conditions will deteriorate later tonight and Sunday as a complex of
thunderstorms is forecast to develop in the vicinity of the warm front
over lower Michigan. The storms will move east across the lower
Great Lakes late tonight and Sunday morning...possibly producing
wind gusts in excess of 35 knots. There will also be the chance for
a second round of thunderstorms Sunday afternoon. Recreational
boaters are thus encouraged to take advantage of the fair weather
today...as Sunday could be quite unsettled.

While there will be the chance for a shower or thunderstorm over the
lakes on Monday...a greater chance for storms will come Tuesday when
a fairly strong cold front will move through.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...rsh
near term...rsh
short term...jjr
long term...jjr
aviation...rsh
marine...rsh

National Weather Service Glossary of Abbreviations