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Area forecast discussion 
National Weather Service Buffalo New York
435 am EDT Sat may 30 2015

the weekend will get off to a warm and humid start but a cold
front will drop across the region this evening and bring much
cooler temperatures on Sunday. There will be widespread showers
and thunderstorms with this front...with the potential for heavy
rainfall lasting through Sunday.


Near term /through tonight/...
today will start off similar to yesterday with humid conditions and
above normal temperatures which will quickly rise into the 80s by
early afternoon. Scattered showers along the leading edge of a 40 knots
low level jet will exit up the St Lawrence Valley. This will leave our
region mostly dry through the morning hours...though a stray
shower cannot completely be ruled out.

Diurnally driven instability will increase ahead of a cold front
this afternoon. Showers and thunderstorms should first develop
across interior sections with the southwesterly flow helping keep
the lake plains boundary layer mixed which will delay the
development of any showers. Convection will still need a focus...and
with the front still well upstream across southern Ontario province
it will probably be lake breeze or terrain boundaries that do this.

Despite fairly impressive consensus model quantitative precipitation forecast...high resolution
guidance (hrrr/WRF/arw) shows areal coverage relatively scattered in
nature. This does not diminish the potential for locally heavy
rainfall. Precipitable waters to 1.75 inches and quantitative precipitation forecast guidance supports localized
rainfall of 1 to 2 inches from some thunderstorms this afternoon.
Areas most likely to see these amounts are east of Lake Erie in
western portions of the southern tier...and east-southeast of Lake Ontario from
Wayne to Lewis counties. Given the dry antecedent conditions and
localized nature of heavy not have the confidence to issue
a Flood Watch.

Winds aloft will not be that strong...with 850mb winds only about 25
kts this afternoon when convection develops. There is always a
chance for a few strong to severe pulse storms...but flooding
appears to be the primary concern for this afternoon and evening.

Model consensus brings the front through this evening...which will
bring large scale forcing when the cooler air undercuts the warm
moist airmass. Thus there is a higher confidence (nearly certain) in
measurable precipitation tonight with a widespread showers and some
embedded thunderstorms. Temperatures are much cooler behind the
front...with temperatures likely to fall into the upper 40s to middle
50s by daybreak Sunday. Patchy fog is also possible as the moist air
mass mixes with the cooler air and gets squeezed by the developing


Short term /Sunday through Tuesday night/...
a complex storm and moisture laden storm system will continue to
evolve through this time period. On Sunday the surface baroclinic
boundary will lie from New England southwestward across the
southern Middle Atlantic States and back towards the middle west. A
surface wave riding slowly along this baroclinic boundary from the
Ohio Valley will send another wave of rainfall across the region
on Sunday. Precipitable waters Sunday will average 1.50 to 1.75
inches...indicating the moisture rich environment. Sharp
isentropic lift in the middle levels northeast of the surface wave
and the still present right entrance region of an upper level jet
will provide for broad lift across the eastern Great Lakes
region...with this lift producing a period of rain showers through
the day. Favorable conditions for rain showers Sunday will slowly
push eastward through the day as the upper level jet and surface
wave slide eastward. By Sunday night the areas most prone to rain
showers will be central portions of New York state. However with
the surface wave stalling over Pennsylvania Sunday night...all
areas of the County Warning Area will have at least likely probability of precipitation.

Instability will be marginal for thunderstorms Sunday and Sunday
night...with what instability to be had this day lying across the
southern tier. Will place thunder chances here...while just calling
it plain rain showers across the remainder of the region.

We have not had a widespread, long duration synoptic precipitation
event of this magnitude in quite some time. Rainfall amounts Sunday
and Sunday night will average around a half an inch of
precipitation...with a few areas upwards to three quarters of an
inch. All told by the end of the weekend an inch to two inches of
rainfall is likely across the County Warning Area. With the very dry conditions and
low creek and stream flows river flooding is not a big concern at
this point...and would only become a concern in areas where storms
train and produce locally significant amounts.

By Monday the middle level shortwave will be east of the region.
However at the surface a wave of low pressure will still be near the
region and will advance from western Pennsylvania towards the
eastern middle Atlantic region. A northwest flow behind this surface
low and easterly flow ahead of the surface low will provide for
ample low level convergence across the region. A moisture rich
environment will remain and light rain showers will again develop
across the eastern Great Lakes region on Monday. The poor lapse
rates and little surface instability on Monday will not make for a
favorable environment for thunderstorm development.

Rain showers may not taper off as quickly Monday night. Though the
surface low will be tracking across New England Monday night...and
upper level shortwave trough will advance towards our region from
the central Great Lakes. This feature will continue chance probability of precipitation
across the region Monday night.

On Tuesday this upper level shortwave trough will cross the eastern
Great Lakes region. A cold pool associated with this trough will
increase lapse rates through the day such that low top showers will
develop through the daytime. Moisture will be found greatest towards
the east...from the Genesee Valley eastward there will be a chance
for a brief shower. Clouds will likely start the day thick across
the eastern Great Lakes region...with clearing slowly edging
eastward through the afternoon hours. A much drier airmass behind
this shortwave will clear skies Tuesday night...making for a chilly
night under good radiational cooling conditions.

Temperatures this time period will average well below normal...with
highs Sunday and Monday in the 50s. A few low 60s are possible near
the state line where the surface boundary may edge northward enough
to allow for warmer air to reach into the southern tier. Tuesday
under cloudy skies and 850 hpa temperatures of only +4 to +5c
daytime highs will still remain in the 50s to around 60. Lows
Tuesday night will drop back into the 40s...5 to 10f degrees below


Long term /Wednesday through Friday/...
ridging aloft and surface high pressure finally build in across
western New York for the second half of the work week. With a drier
airmass moving in on Wednesday...expect most locations to finally
clear out nicely after a gloomy start to the week. Nice weather will
remain with US Wednesday and Thursday as high pressure crosses the
region. Friday will be the next chance for some rain
showers...albeit small with a few thunderstorms possibly blossoming
on a lake breeze boundary Friday afternoon.

Temperatures will also recover through the second half of the week
as southerly flow develops on the back side of the high pressure and
warm air advection pushes 850 mb temperatures back into the low
teens celsius above zero. The warming trend will bring 70s back to
the forecast on Wednesday with middle 80s possible by Friday.


Aviation /09z Saturday through Wednesday/...
expect the vast majority of time to be dry through 16z. Widely
scattered showers or thunderstorms may briefly lower visibility/ceilings
but coverage will be sparse through this morning.

Diurnal instability convection will develop this afternoon...first
across interior sections but then becoming more widespread across
the entire region late afternoon and evening as a cold front
approaches. This is likely to produce numerous showers and
thunderstorms...but there is low forecast confidence in timing the
exact location of any storms. Thunderstorms may lower visibility 2sm or
less in heavy rain...and could have an extended impact on flight
operations 21z through 03z Sunday.

The front will drop across the region between 03z and 06z Sunday
which will lower ceilings late Saturday night to IFR or lower
following the wind shift. Showers will linger with perhaps some
embedded thunderstorms.

Sunday...slowly diminishing showers...with IFR/MVFR ceilings
Monday through Wednesday...mainly VFR.


southwest winds will increase ahead of a cold front with the
strongest winds across the Saint Lawrence River where a Small Craft
Advisory has been issued.

Behind the cold front... winds and waves will increase across the
lower lakes tonight and Sunday as north then northeast winds develop
in a cold air advection regime. Small craft advisories have been
issued for most of the waters starting late tonight. Winds will
diminish on Monday when the northerly flow is expected to diminish.


may 2015 will go down as one of the warmest Mays on record...and
possibly one of the driest for Buffalo and Watertown. A moisture
laden cold front will cross the region to end the month...and
showers and thunderstorms along this feature may remove climate
sites from a top 10 driest may's on record. Below are the warmest
Mays on record.

Buffalo rank mean temperature year
1 64.3 1991
2 63.8 2012
3 63.4 1944
4 62.8 1998
5 62.3 2015 (through 5/29)
6 62.2 1975

Rochester rank mean temperature year
1 63.7 1911
2 63.6 2015 (through 5/29)
3 63.2 2012
4 63.2 1944

Watertown rank mean temperature year
1 60.5 2012
2 60.0 1998
3 59.3 1975
4 58.8 2015 (through 5/29)
5 58.8 1960
6 58.3 1991

May has also been a dry month. Outside of a few localized heavy
thunderstorms many locations are well below normal for the month.
Below is monthly precipitation for the driest months on record for
our three climate sites.

Buffalo rank precipitation year
1 0.53 1877
2 0.54 1934
3 0.60 2005
4 0.83 2015 (through 5/29)
5 0.90 2012
10 1.11 1926

Rochester rank precipitation year
1 0.24 2007
27 1.52 2015 (through 5/29)
28 1.55 1876
29 1.59 1954
30 1.64 1926

Watertown rank precipitation year
1 0.70 1965
2 0.87 2005
3 0.88 1980
4 0.90 1974
5 0.99 1966
6 1.04 2015 (through 5/29)
7 1.08 1972
8 1.09 1951
9 1.14 1949
10 1.16 1962

Again with thunderstorms in the forecast to close out the month
none of our three climate sites may have a top ten driest may on
record. However all three sites may continue the stretch of below
normal precipitation months. Below are listed the latest month
for when precipitation recorded was above normal for each of our
three climate locations.

Buffalo - October 2014
Rochester - February 2015
Watertown - August 2014


Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory from 4 am Sunday to 8 am EDT Monday for
Small Craft Advisory from 2 am Sunday to 2 am EDT
Monday for loz030.
Small Craft Advisory from 8 am Sunday to 8 am EDT Monday
for loz042-043.
Small Craft Advisory from 4 am Sunday to 5 am EDT Monday
for loz044-045.
Small Craft Advisory from 10 am this morning to 8 PM
EDT this evening for slz022-024.



near term...apffel
short term...Thomas

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