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Area forecast discussion 
National Weather Service Buffalo New York
1026 am EDT Tuesday Jun 30 2015

Synopsis...
low pressure over the central Great Lakes will lift northeastward
across southern Ontario and Quebec through Wednesday...while
bringing a few rounds of showers and thunderstorms to our region.
In the wake of this system...high pressure and dry weather will
then build across the Great Lakes and northeast for both Thursday
and Friday.

&&

Near term /through tonight/...
broad/diffuse low pressure currently sprawled across the central
Great Lakes will become somewhat better organized as it slides
into southern Ontario today...then lifts into Quebec province
tonight. In the process...this feature will swing its attendant
warm front across western and north central New York through early
this afternoon...followed quickly by a trailing pre-cold-frontal
trough this afternoon and evening.

Latest observations show the warm front across the southern tier and
slowly lifting northward. Along and to the north of this
feature...scattered showers and isolated thunderstorms continue to
press northward across northern Pennsylvania and upstate New
York.

The surface warm front will continue to push northward and cross
western and north central New York by this afternoon...while
continuing to produce scattered to numerous showers...along with
some embedded thunder as some weak to modest elevated instability
spreads north into our region from the Ohio Valley.

By midday/early afternoon...a decent middle level shortwave will be
pivoting into our region from the Ohio Valley...in conjunction with
a pre-cold-frontal surface trough. In the presence of daytime
heating and increasing diurnal instability...these features will
trigger the development of a second round of showers and
thunderstorms somewhere over far western New York by early this
afternoon...with this round of convection then working east across
the remainder of the region through the rest of the afternoon and
early evening hours.

In the wake of this trough...our region will then remain in the
warm sector of the low right through tonight...with its trailing
cold front only approaching our western doorstep by Wednesday
morning. With the lack of an additional well-defined surface-based
focusing mechanism to focus convection...and diurnally-driven
instability also on the wane with the loss of daytime
heating...convective chances should generally trend downward a bit
for the nighttime hours.

With respect to the potential for severe storms...the short term
guidance continues to insist on the potential for anywhere from
1000-1500 j/kg of SBCAPE to develop within the warm sector this
afternoon...however this will be highly contingent on sufficient
daytime heating developing...which remains rather questionable at
this time given the amount of cloud cover currently expected to be
in place. Coupling this with 0-6 km bulk shear values of only
about 30 knots...feel that the potential for stronger to severe
storms will be fairly limited across our region today... with the
better probabilities for such remaining to our south and east
where somewhat better shear and a better Reservoir of instability
should both be in place.

&&

Short term /Wednesday through Friday night/...
showers will be largely be winding down from west to east Wednesday
night as a cool front slides across the state. While the bulk of the
precipitation should end Wednesday evening with the passage of the
front...the axis of the middle-level trough will remain upstream and as
such cannot rule out a few showers or perhaps some patchy drizzle as
the weak middle-level lift interacts with the limited moisture left
behind the front. Lows will run in the middle to upper 50s.

Any lingering low clouds should quickly diminish Thursday morning
however as cooler and drier air advects in from Canada...allowing
for plenty of sunshine on Thursday with temperatures running
slightly cooler than average...in the low 70s. The only catch is
that with the axis of the middle-level trough still making its way
across the forecast area on Thursday...we may see a few brief
showers pop up across The Finger lakes and southern tier in the
afternoon...but no substantial rainfall is expected.

The middle-level trough will complete its transit of the area Thursday.
With weak upper level ridging and surface high pressure building
across the lower Great Lakes Thursday night...expect a clear and
cool night with radiational cooling allowing readings to drop into
the low to middle 50s. A few of the more sheltered locales in the
southern tier and north country may even dip just below the 50
degree mark. High pressure will remain in control through the rest
of the period though a return to southerly flow as the diffuse high
shifts to the East Coast will allow for a return to more seasonable
temperatures and slightly higher humidity Friday with highs in the
middle to upper 70s and lows Friday night running close to
climatology...within a couple of degrees either side of 60.

&&

Long term /Saturday through Monday/...
the Fourth of July weekend should be largely dry and
uneventful... but as is usually the case for long Holiday
weekends...mother nature cant help but to keep some 'flies in the
ointment'.

A weakening middle level trough and attendant wind shift frontal
boundary will pass over our forecast area on Saturday. From this
Vantage Point there does not appear to be enough lift and low
level moisture to support widespread precipitation...but a couple showers
and thunderstorms will be possible. Have thus lowered probability of precipitation a
little to low chance from continuity.

The good news is that any precipitation from the weak synoptic system
should be out of our forecast area by nightfall...as the
progressive trough will move east across the Saint Lawrence valley
and Adirondacks. This should support favorable conditions for
another round of fireworks displays Saturday evening.

Weak high pressure is then forecast to build across the lower
Great Lakes late Saturday night and Sunday. This should favor
Sunday as having the nicest weather of the long weekend...as ample
sunshine will be accompanied by moderately warm and humid early
Summer conditions with high temperatures generally within a few
degrees of 80.

On Monday...a strengthening southerly flow between exiting high
pressure and a cold front over the upper Great Lakes will advect
increasingly moist and unstable air across our region from the
Ohio Valley. While the majority of the day will be problem-
free...there will be the risk for a shower or thunderstorm during
the afternoon. The highest chance for any convection will be found
from The Finger lakes region westward to Lake Erie.

&&

Aviation /15z Tuesday through Saturday/...
broad/diffuse low pressure sprawled across the central Great
Lakes will become somewhat better organized as it slides into
southern Ontario today...then lifts into Quebec province tonight.
In the process...this feature will swing its attendant warm front
across western and north central New York through early this
afternoon... followed quickly by a trailing pre-cold-frontal
trough this afternoon and evening.

Showers and isolated thunderstorms will end in Genesee Valley and
southern tier by 15z...Finger Lakes by 16z...and north country by
17z. Most cloud decks will be 3-5k feet...with 2-3k feet ceilings across
the western southern tier this morning and again tonight.

Outlook...
Wednesday...VFR/MVFR with scattered to numerous showers and
thunderstorms.
Thursday and Friday...VFR.
Saturday...mainly VFR with a chance of showers and thunderstorms.

&&

Marine...
low pressure over the central Great Lakes will lift northeastward
across southern Ontario Quebec province through Wednesday...with
high pressure then building southeastward across the Great Lakes
Thursday and Friday.

While winds will freshen a bit in advance of a warm front today
and behind a cold front on Wednesday...at this point it still
appears that prevailing conditions should remain safely below
advisory levels right through the rest of the work week. This
stated... locally higher winds/waves will still be possible within
any thunderstorms today through Wednesday.

&&

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

&&

$$

Synopsis...Franklin/jjr
near term...Franklin/jjr
short term...wood
long term...rsh
aviation...Franklin/jjr
marine...Franklin/jjr

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