Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Buffalo New York
357 PM EDT sun Apr 20 2014

Synopsis...
high pressure will drift off the East Coast Monday but not before
providing one more dry and warm day. A cold front will cross the
region late Monday night and Tuesday with a period of rain showers.
This front will usher in cooler temperatures for the middle of the
week before some rebound for Thursday and Friday.

&&

Near term /through Monday/...
abundant sunshine continues this afternoon with just a few very thin
cirrus passing over the lower lakes. Temperatures have warmed nicely
into the middle and upper 60s in many inland areas...with local lake
breezes keeping the lakeshores much cooler.

Tonight high pressure will drift off the New England coast. A few
weak middle level shortwaves will traverse the westerly flow aloft
through southeast Canada...and combine with increasing middle level
warm advection and moisture to produce a few middle/high clouds
overnight. The clouds will be more prevalent near the Canadian
border. Expect lows in the lower to middle 40s on the lake plains with
middle 30s in the cooler southern tier valleys and Lewis County.
Southwest return flow will increase some overnight...so expect
temperatures to rise late tonight as mixing and low level warm
advection increase.

On Monday ongoing deep southwest flow and warm advection will boost
850mb temperatures to around +9c by middle afternoon across western New York and
about +7c across the north country. We have noticed over the past
several years that warm airmasses during the pre green-up stage of
Spring will often deliver warmer temperatures than forecast by model
guidance...due to lack of transpiration from plants and trees. With
this in mind have gone above even the warmest guidance...with highs
in the middle 70s at lower elevations away from lake influences...with
middle to upper 60s east of Lake Ontario. Some of the warmer locations
of the Genesee Valley may reach the upper 70s.

Gradient onshore flow will keep the Lake Erie shore cooler and also
areas northeast of Lake Ontario cooler. Mesoscale model guidance
such as our 6km workstation WRF suggest the synoptic scale southwest
flow will not be quite strong enough to prevent a lake breeze from
developing along portions of the South Shore of Lake Ontario. This
appears most likely from Monroe County east to Oswego County where
the synoptic flow is a little weaker...so have gone with cooler
temperatures along the lakeshores of those counties.

Finally...there may be two small areas where winds become a little
breezy tomorrow...due to more unique mesoscale processes of the
Great Lakes. BUFKIT profiles suggest 20-25 knots of wind a few
thousand feet of the deck. These stronger winds will not impact
lakes Erie or Ontario...where a dome of cooler and stable lake air
will result in much lighter surface winds. Immediately downwind of
these stable lake domes...the stronger winds will essentially
downslope off the stable lake domes...following isentropic surfaces
to the surface. This often produces small corridors of somewhat
stronger winds from about the buf Airport northeast into Genesee
County...and also across central and northeast Jefferson County.
Winds may gust to around 20 knots in these two areas on Monday.

&&

Short term /Monday night through Wednesday night/...
clouds will thicken and lower Monday night with rain showers
advancing toward western New York as a middle-level trough amplifies
while shifting east across the western Great Lakes. Ahead of this
amplifying trough surface low pressure will shift east across the
lower lakes and deepen. Southwesterly winds ahead of the low and
thickening cloud cover will keep mild temperatures overnight ranging
in the middle to upper 40s.

Tuesday morning a cold front extending south from the low will cross
western and central New York bringing rain showers. Southwesterly
moisture transport vectors just ahead of the front will increase
precipitable waters to just over one inch which is about +1.5sd for middle to late
April climatology so heavy rainfall is not expected. Quantitative precipitation forecast is a little
higher with 12z runs and is expected to range 0.20-0.40 inches. Weak
northwest moisture transport off the lakes combined with cold air
advection and a trailing surface trough will keep chances for
scattered rain showers in the forecast behind the cold front through
the remainder of the day and into Tuesday night. The thick cloud
cover and showers will keep temperatures a bit cooler than
previous days with highs only ranging in the low to middle 50s.
Overnight Tuesday BUFKIT profiles continue to show weak synoptic
lift and low level moisture remaining likely associated with the
trailing surface trough which will continue chances of showers.
Overnight lows will fall back into the middle 30s with lower 30s found
across the interior southern tier and Tug Hill. This brings a
possibility of some snow flakes mixing with any lingering rain
showers across the hill tops.

Wednesday into Wednesday night modified Arctic sourced high pressure
will settle across the Great Lakes region. Lingering cloud cover
will be around early Wednesday but middle-level drying and subsidence
associated with the high pressure will work to clear out skies with
full sunshine breaking out by the afternoon hours and clear skies
overnight. 850mb temperatures around -5c will limit diurnal heating and
keep our surface high temperatures limited to only the middle to upper 40s
despite full sunshine developing in the afternoon. Clear
skies...light winds and a drier airmass will help overnight temperatures to
fall into the low to middle 30s with a possible threat of patchy fog
early Thursday morning.

&&

Long term /Thursday through Sunday/...
a progressive middle-level flow is forecast for late in the week with a
low amplitude trough across the West Coast which will build a ridge
over the Great Lakes. All 20/12z model packages are in fair
agreement that the Great Lakes ridge will quickly shift off the East
Coast on Friday being replaced by an extended period of troughiness
into the weekend. The late week ridging and surface high pressure
will bring dry weather on Thursday with temperatures recovering back
up to near late April normals.

Thursday night and Friday the western trough builds across the
western Great Lakes and centers over the lower Great Lakes. In a
similar pattern to what we will see on Tuesday...a surface low and
cold front will cross western and central New York bringing another
round of rain showers. A warm and moist southwest and west flow will
help boost temperatures above normal with the leading band of rain showers
Friday. This will keep middle overnight low temperatures in the 40s across
western New York but the warm and moist air will not quite reach the
Eastern Lake Ontario region where lows will still dip into the 30s.
Highs Friday will climb into the low to middle 60s for much of the area
but a little cooler east of Lake Ontario.

Friday night through Sunday a now slower moving middle-level trough of
cool air will keep unsettled weather over next weekend. Chances of
showers and near to slightly below normal temperatures are forecast
for Saturday and Sunday as northwest flow will keep reinforcing cold
advection across the Great Lakes region. Saturday night temperatures
may drop to near or just below freezing especially across inland
locations and hilltops with a chance for some snow and rain showers
overnight.

&&

Aviation /20z Sunday through Friday/...
VFR conditions will prevail for the 18z taf cycle. Very thin scattered
cirrus will continue to drift across the region through the rest of
today. Overnight a series of weak middle level disturbances will pass
by just north of the region and bring a modest increase in middle/high
clouds with the most concentrated cloud cover near the Canadian
border. This will continue through Monday with periods of middle level
clouds crossing Lake Ontario and the Saint Lawrence valley...with
more sunshine near the PA state line.

Outlook...
Tuesday...areas of MVFR with showers...improving to VFR late.
Wednesday...a chance of a rain or snow shower with MVFR
early...otherwise VFR.
Thursday...VFR.
Friday...mainly VFR with a chance of showers.

&&

Marine...
surface high pressure will drift off the East Coast through Monday
and remain near enough to keep relatively light winds over the lower
lakes. The Cold Lake waters will also stabilize the air over the
lakes with lighter winds during the afternoon than over land areas.
Local lake breezes will produce onshore winds again Monday
afternoon.

A cold front will cross the region from west to east Tuesday
morning. Winds will increase behind this front with conditions
possibly approaching Small Craft Advisory criteria on Lake Ontario
Tuesday night and Wednesday.

&&

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

&&

$$

Synopsis...Hitchcock
near term...Hitchcock
short term...Smith
long term...Smith
aviation...Hitchcock
marine...Hitchcock