Area forecast discussion
National Weather Service Buffalo New York
326 am EDT Wednesday may 22 2013
Synopsis...
a southwest flow of warm and humid air will continue through most of
the week. There will be a chance for showers and thunderstorms
through Thursday...as moist unstable air interacts with an
approaching cold front. Noticeably cooler air will follow the front
on Friday.
&&
Near term /through tonight/...
aside from some isolated showers and thunderstorms over the Genesee
Valley and Finger Lakes...the bulk of the active convection has
shifted into eastern New York and New England. Otherwise...we are
seeing partly cloudy skies early this morning along with some patchy
fog...especially along the Lakeshore areas bordering Lake
Ontario where slighter cooler temperatures have resulted in higher
relatively humidities near the surface.
Later today...the main focus will shift to the surface low that will
heading east toward the lower Great Lakes. As this system approaches
western New York during the afternoon...the chances for showers and
thunderstorms will increase...especially across western New York
where added lift will be provided by the Lake Erie breeze and a 30
to 40 knot low level jet that will be working east across the
western part of the state. Regarding the potential for severe
weather...the stability parameters do not appear as if they will be
as good as they were on Tuesday...but favorable wind shear profiles
will still be in place across the lower lakes. As a result...Storm Prediction Center has
most of New York outlined within a slight risk for severe weather.
Regarding temperatures for today...followed the trend depicted by
the warmer GFS biased corrected forecast.
Tonight...the surface low is forecast to track north of Lake Ontario
while its trailing cold front stays just west of New York state. As
the surface low lifts to the north...the tight low level Theta-E
gradient is forecast to shift north into southern Ontario and far
southern Quebec. As a result...the steadiest rain will likely stay
north of the US/Canadian border. However...the modest low level jet
will still keep moist and somewhat unstable air over our County Warning Area.
Therefore...will maintain likely probability of precipitation for measurable precipitation.
&&
Short term /Thursday through Saturday night/...
after a stretch of middle Summer warmth and humidity...a subtle change
in the overall pattern will yield a noticably cooler and more
comfortable weather regime. Rather than experiencing temperatures
more typical of July...we can look forward to Mercury levels that
will average some 5 to 10 degree below normal. This will all come as a
result of the exiting of a sultry ridge off the East Coast...which
will be replaced by an exceptionally high amplitude flow over all of
North America. The pseudo-Omega block pattern will feature a ridge
over the nations middle section with twin troughs over British Columbia
and Quebec. The details...
A broad...complex area of low pressure extending from the Saint
Lawrence valley across the lower Great Lakes on Thursday morning
will slowly pivot to the East Coast by daybreak Friday. The lift
provided by 100m height falls and low level convergence within the axis
of elongated surface trough will lead to fairly widespread light rain
during the day...then a trailing deformation zone on the west side
of the exiting surface trough will keep the rain intact for Thursday
night. Will cover both periods with Cat probability of precipitation...but quantitative precipitation forecast is not
expected to be significant. Rainfall amounts for the 24 hour period
should average a quarter to a half inch.
As mentioned earlier...it will be much cooler on Thursday. 850 mb temperatures
that up to this point had been in the middle teens will tumble into the
single digits by Thursday evening...then to near zero by daybreak
Friday. This will translate into midday highs of 70 to 75 before
temperatures steadily fall in the rain during the afternoon through
Thursday night. Mercury readings by daybreak Friday could be 20
degrees lower in many areas than the night before....with overnight
lows generally in the middle to upper 40s.
On Friday...the backedge to the soaking rain will be found pushing
east from the Genesee Valley as the supporting 500 mb trough will be
crossing overhead. During the course of the day...the aforementioned
deformation zone will give way to much drier air from southern
Ontario...with the leftover showers and associated low cloud cover
giving way to increasing amounts of sun from west to east. This will
leave partly to mostly skies for the afternoon...although there will
be a feel of autumn in the air as 850 mb temperatures near zero c will
correspond to near surface temperatures in the 50s f.
It will then become downright chilly (if not cold) across the
forecast area Friday night. While a robust shortwave will drop
across the lower Great Lakes...a very dry airmass should still
encourage clear to partly cloudy skies. Temperatures will be maringally
cold enough for some lake induced cloud cover...but the amount of
dry synoptic air and presence of a strong low level inversion should
work against this potential. Temperatures should thus fall to near 40
across the lake plains with readings in the middle to upper 30s across
the southern tier and Eastern Lake Ontario region. This will lend to the
risk for some frost...so will have to keep this in the back of our
minds.
A large surface high centered near James Bay will nose south across the
Great Lakes Saturday and Saturday night. While some of the guidance
packages are suggesting the passage of a couple of middle level
shortwaves...the moisture starved airmass is not expected to support
any showers. Rather...clear to partly cloudy skies are anticipated
with below normal temperatures. Highs on Saturday should be within a
couple degrees of 60 while Saturday night will have the potential to
produce another frosty night away from the lakes.
&&
Long term /Sunday through Tuesday/...
seasonably cool and dry weather will prevail through the remainder
of the Holiday weekend...courtesy of high pressure that will be
parked across the Great Lakes. It will be quite chilly both Saturday
and Sunday nights with temperatures dropping into the low 40s across
the lake plains while 30s will dominate the colder spots of the
southern tier and north country. This will keep the threat of frost
in place for those colder areas
Daytime highs will gradually increase during the period as the
strong ridge over the central U.S. Will nudge eastward. Highs of 60
to 65 on Sunday will make their way to above normal levels (mid 70s)
by Tuesday afternoon.
&&
Aviation /08z Wednesday through Sunday/...
isolated showers and thunderstorms are lingering over the Genesee
Valley and Finger Lakes early this morning. Outside of this
activity...partly cloudy skies prevail with mainly VFR conditions.
The exception to this general trend will be near Lake Ontario where
slightly cooler air has resulted in higher relatively humidity and
MVFR to IFR conditions in patchy fog.
Low pressure heading east toward the lower lakes will bring
increasing chances for showers and thunderstorms this afternoon.
Once again...expect mainly VFR conditions to prevail...with brief
periods of MVFR in the vicinity of passing thunderstorms.
Outlook...
Thursday...scattered to numerous showers and thunderstorms with
associated MVFR/IFR...otherwise VFR. Friday...mainly VFR with a
chance of showers.
Saturday and Sunday...VFR.
&&
Marine...
relatively light and variable winds will prevail through early this
morning. Southwest winds will pick up a bit this afternoon and
tonight as an area of low pressure and its trailing cold front
approach western New York. After the front crosses western and
central New York on Thursday...the winds will veer to the northwest.
Small craft advisories may be needed Thursday night into Friday
as north to northwest winds pick up behind the departing front.
&&
Buf watches/warnings/advisories...
New York...none.
Marine...none.
&&
$$
Synopsis...tjp
near term...tjp
short term...rsh
long term...rsh/wood
aviation...tjp
marine...tjp
