Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
358 PM EDT Wednesday Jul 30 2014
the Fall like weather pattern that we have been in the past couple
days will gradually modify as we push through Thursday and Friday.
In the meantime...the cool unstable airmass will support an
occasional shower or thunderstorm...which could be enhanced by the
warmer waters of the lower Great Lakes.
Near term /through Thursday/...
the anomalously deep longwave trough that has been parked over the
eastern half of the continent the past 48 hours will gradually fill
and lift out to the northeast...but not until the end of the week.
In the meantime...the associated airmass will slowly modify from the
middle Summer sun...so we can at least look forward to somewhat higher
Digging a little deeper into the details...there are two more
shortwaves embedded within the deep cyclonic flow that will have to
rotate across our forecast area. The first will cross our region
during the first half of tonight...but with some middle level drying
and unfavorable diurnal timing...this feature is not expected to
generate much (if any) in the way of precipitation.
The second shortwave is notably more robust. It is currently (as of
20z) circulating southwest from Lake Superior and will make its way
across the lower Great Lakes late tonight and early Thursday. This
feature will interact with favorable mesoscale lake effect
parameters (conv cloud depth >30k feet and fairly steep lapse rates
through h70 to generate some showers and thunderstorms. The bulk of
this activity will come during the wee hours of Thursday morning
through the midday hours...after which time subsidence in the wake
of the shortwave and diurnal mixing will end the activity from west
to east. As with the convection that occurred earlier today...some
of the storms could contain some small hail.
Temperatures will remain below normal through Thursday. Overnight
lows tonight will be in the 50s away from the lakes...while daytime
highs on Thursday will range from 70 to 75. These values will be
more than 5 degree f below normal end of July normals.
Short term /Thursday night through Saturday night/...
the persistent broad upper level tough will remain across the
eastern Continental U.S. Into the upcoming weekend. While this generally should
keep a threat for showers and thunderstorms in play...models are in
good consensus showing a short period of flat ridging across New
York state Thursday night and Friday. This should provide a window
of dry conditions. Later on Friday precipitable waters and moisture transport
vectors show a surge of moisture north from the middle-Atlantic which
will bring a chance of showers and thunderstorms mainly to the
southern tier. By Saturday the upper trough will reload as the next
strong shortwave trough shifts across the Great Lakes. The
combination of this cooling aloft with increase in moisture will
bring a higher chance of storms Saturday. Forecast bulk shear looks
too low at this time for any severe threat.
In terms of temperatures...the core of the upper low is forecast to
shift from near James Bay to northern Quebec. This will pull the
coldest air within the trough northward. Warming over the lower lakes
along with a southerly flow near the surface will help boost
temperatures and humidity levels back to near average for
mid-Summer. Low temperatures Thursday night will dip into to the middle
to low 50s but by Saturday night expect overnight lows to only fall
into the low 60s to upper 50s. The shortwave ridging Friday will
help high temperatures push into the upper 70s and low 80s but an increase
in cloud cover and shower/storm coverage on Saturday should top out
temperatures about 5 degrees cooler.
Long term /Sunday through Wednesday/...
a full Continental U.S. 500mb trough will extend from the Great Lakes to the
northern Gulf on Sunday. The axis of the trough is forecast by
GFS/European model (ecmwf) to shift across the lower Great Lakes east to New England
by Sunday night. This combined with precipitable waters between 1.25 and 1.5
inches will keep a high chance of showers and thunderstorms in the
forecast through Sunday night. A short window of flat ridging and
surface high pressure looks to bring dry weather on Monday for most
of western and central New York. The upper flow pattern looks to
then again exhibit a deepening but this time progressive Great Lakes
trough Tuesday into Wednesday which brings back chances of
precipitation going into middle next week. A Pacific sourced upper flow
pattern will keep temperatures near average with highs ranging from
the middle 70s to near 80 and lows falling into the upper 50s to low
Aviation /20z Wednesday through Monday/...
while VFR conditions will be found across the bulk of western and
north central New York during the remainder of the afternoon...
there will be scattered thunderstorms over the region. This
convection will weaken and dissipate within a couple hours of
A new round of thunderstorms will develop over the far western
counties late tonight...when ceilings at kjhw are expected to drop to
IFR levels. The showers and thunderstorms will then drift east
across all of western and north central New York during the course
Thursday night and Friday...VFR.
Saturday and Sunday...mainly VFR with chance showers and
an unseasonably cool airmass over the warm waters of lakes Erie and
Ontario helped to generate some lake induced showers last night...
and during the course of the next 24 to 30 hours...will also be
favorable for the development of waterspouts.
This forecast is supported by the excellent guidance offered by the
szilagyi nomogram. Our 850 mb temperatures in the vicinity of 8c combined with a
convective cloud depth in excess of 30k suggests the possibility of
waterspouts. These have been in the forecast for some time now and
will remain in place. Any showers that develop will thus carry the
risk of also having a waterspout.
While winds and waves on Lake Ontario will remain below Small Craft
Advisory criteria through Thursday...southwest winds on Lake Erie
have increased to the point where a short lived Small Craft Advisory has been issued.
Winds on Lake Erie will then drop off rather quickly this evening...
with minimal winds and waves expected overnight and Thursday.
Mariners should be alert to short fused special marine warnings that
are based on heavy showers or thunderstorms that could bear
Marine...Small Craft Advisory until 8 PM EDT this evening for lez040-