Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 271042
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
642 AM EDT Thu Apr 27 2017

.SYNOPSIS...
Summer conditions will remain across the region today with air
temperatures peaking in the 80s, a bit of humidity in the air and a
light south wind. A cold front will send showers and thunderstorms,
some of which may produce damaging wind gusts and heavy rainfall,
across the region late this afternoon and evening. Cooler, yet still
above normal temperatures will remain through the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Water Vapor imagery this morning displays a long wave trough across
the mid-Mississippi Valley, with two shortwaves, one over MN, with a
second over IA/IL. It`s this second shortwave that will track
northeastward today, and maintain the negative tilt to the upper
level trough. While the shortwave will become less evident
through the day, its axis will cross the Eastern Great Lakes
region this evening.

Surface observations display a broad area of low pressure over the
central Great Lakes, with a cold front dropped southward over the
lower Mississippi Valley.

Ahead of this cold front a southerly flow will bring summer`s warmth,
while also increasing moisture. Temperatures at 925/850 hPa of 20-
21C/17-18C will be some of the warmest values recorded for late
April based on Buffalo`s sounding climatology (since 1948) and with
the light southerly flow we should see afternoon temperature
approach record values across the region. These record temperatures
include...84F at Buffalo (1984)...86F at Rochester (1990)...and 85F
at Watertown (2009). In addition, if forecasted highs for our three
climate stations verify then today will be a top ten warmest April
day. The warmest April day...94F/Buffalo, 93F/Rochester,
89F/Watertown looks to be out of reach. What may limit the
warmth today will be if the mid and high clouds stream in
faster, and also with the ground being very wet, and vegetation
starting to become green there will be energy going to
evapotranspiration.

Summer-like warmth will remain into the evening hours before a cold
front and showers/t-storms roll through and mark an end to the brief
warm spell. Low temperatures tonight will drop back into the upper
40s across far WNY, while lower 50s will be the low temperature from
the Genesee Valley eastward.

For these showers and thunderstorms...it will remain dry well into
the afternoon hours as the cold front and associated precipitation
slowly advances eastward with the upper level flow nearly parallel
to the frontal boundary. There likely will be a pre-frontal band of
showers and thunderstorms forming this afternoon across Ohio that will
reach Chautauqua County between 4 and 6pm. This band of showers and
storms will pass eastward, reaching the eastern Lake Ontario region
during the evening hours. A second and less robust band of showers
will likely lie along the cold front that will push across WNY
during the evening hours, and later east of Lake Ontario.

Severe potential...These storms will have a potential to become
severe with damaging wind gusts the primary concern. Moisture
pooling ahead of the cold front will elevate PWats to over an
inch/nearing 1.50 inches while also increasing surface dewpoints to
around 60F. These dewpoints, and the very warm airmass will produce
MUCAPE values of 1000 to 2000 J/KG across the region. In addition
increasing speed shear (0-6km bulk shear of 40 to 50 knots) will
allow for thunderstorms to grow and potentially produce damaging
downdrafts. Aiding in the development of the storms will be
coinciding passage of the upper level trough axis which should
further destabilize the atmosphere. Greatest risk for damaging winds
will be across WNY, while eastward and across the Eastern Lake
Ontario region the late evening arrival and loss of daytime
instability will allow for weakening to the storms.

Heavy rain will remain a threat for all areas this evening. PWAT
values over an inch will allow for good downbursts of rain.
Activity, likely heaviest along the pre-frontal trough will likely
maintain an eastward flow, allowing storms to continue to move which
would limit the flooding risk.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Weak surface high pressure will build behind a cold front on Friday,
providing dry weather. There will be some upstream convection, with
model guidance advecting some high clouds associated with this
across the region Friday afternoon. Temperatures will be
considerably cooler Friday, with highs mainly in the upper 60s to
lower 70s, except a bit cooler along the immediate lakeshores due to
the lake breeze.

There will be a baroclinic zone between high pressure across south-
central Canada and off the Southeast coast Friday night through
Saturday night. This will promote the development a frontal boundary
which will roughly extend from the mid-west to the Ohio Valley.
Model consensus keeps this boundary and most of the showers and
thunderstorms associated with it to our south and west during this
time. However, there is a chance some showers will hold together
long enough to reach Western New York, but for the most part any
showers should be brief. Model guidance continues to disagree on the
specifics of these waves.  The forecast will maintain low chance
PoPs late Friday night through Saturday, then bring drier conditions
to the North Country Saturday night with surface pressure forecast
to ridge into that region.

Regarding temperatures, there is still some uncertainty, but
increasing confidence that our region will be on the cool side of
the front during the time period. Even so, temperatures should be
near or slightly above normal for late April with highs in the lower
60s to around 70 on Saturday. Forecast hedges warmer than consensus
guidance for low temperatures since there will be quite a bit of
high clouds from upstream convection which will hinder radiational
cooling.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Our weather for the second half of the weekend into the first half
on next week will be influenced by an unseasonably deep stacked
surface and mid-level cyclone. This storm system will develop over
the heart of the country on Sunday then slowly deepening while
tracking north to near the vicinity of Lake Michigan by Monday then
further north tracking across Quebec Tuesday and Wednesday.

On Sunday, a southerly low level jet ahead of this developing system
will shift a warm front from PA north into Western NY. This front
will help trigger at least a broken band of showers and possibly
some thunderstorms on Sunday with the exact movement of this front
being the determining factor in temperatures. Model guidance differs
a bit in the placement of this front, with at least the Southern
Tier likely to break into the warmer (70s) air. A northeasterly flow
will keep the North Country in the 50s, with  the most uncertainty
between the two where 60s is most likely though it could be warmer
or cooler depending on the position of the front.

By Sunday night, the 00Z GFS/ECMWF both lift the boundary to our
north, with a 988mb surface low near Wisconsin. This would place our
region back into the warm sector, with increasing chances for a
return of summer-like temperatures for Monday. While there still is
a chance our region will remain on the cool side of the boundary, it
appears more likely than not consensus guidance is too cold with
highs likely to top 80 in many areas on Monday.

An associated cold front is then forecast to move across the area
late Monday. This front should trigger another threat of showers and
thunderstorms as decent surface based instability and strong shear
is forecast during the afternoon hours. Will have to keep an eye on
Monday for a severe threat. This is mentioned in the Hazardous
Weather Outlook.

Cooler weather can then be expected behind the cold front on Tuesday
along with a chance of some showers and gusty winds. Strong cold air
advection behind the front will low 850mb temps below 0c which will
translate into very cool temperatures Tuesday afternoon only topping
out in the 50s which is below normal for this time of year. This
strong cold air advection will also support very gusty winds with a
50+ knot low level jet streaking across the eastern Great Lakes. The
track of the low and current forecast strength of the low level jet
could support possible advisory level wind gusts but if the low
level jet verifies stronger than a late season high wind event may
be possible. This is also included in the Hazardous Weather Outlook.

Cool temperatures then look to remain in place Tuesday night and
again Wednesday with continued cold air advection as the mid-level
trough axis shifts east across our region. There will be low to
slight chances of showers as well with winds slackening off. Lows
Tuesday night look to dip into the upper 30s to low 40s then highs
on Wednesday only rising into the low to mid 50s.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
For the 12Z TAFs primarily VFR flight conditions will be across
the Eastern Great Lakes region through the TAF cycle. A cold
front will bring a line, or perhaps two lines of showers and
thunderstorms across the region. Timing looks best between
20-21Z across the west, with activity reaching KART around 03Z.
This line of storms will remain for just a few hours over the
TAF sites, with possible brief, and localized MVFR flight
conditions within heavier storms.

Southerly winds today will veer to more of a southwest to westerly
flow for tonight. Some patches of MVFR flight conditions will be
possible later tonight behind the cold front.

Outlook...

Friday...Mainly VFR.
Saturday...VFR/MVFR with a chance of showers.
Sunday...VFR/MVFR with a chance of showers and thunderstorms.
Monday...MVFR to locally IFR with showers and thunderstorms likely.

&&

.MARINE...
Fading weak high pressure will maintain light winds and minimal
waves on the lakes this morning. By afternoon a cold front will be
crossing Lake Erie, bringing a line of showers and thunderstorms
across the eastern Great Lakes. Weak cold air advection behind this
cold front will increase waves some, to around 2 feet later tonight
and into Friday, before another area of high pressure expands across
the lakes for the start of the weekend, with non small craft boating
conditions.

Looking a bit further out, strengthening easterly winds may bring
SCA to the western lake waters for Sunday. Another, stronger storm
system may bring another round of thunderstorms early next week,
with gale force winds possible behind a cold front on Tuesday.

&&

.CLIMATE...
The last days of April will finish with above normal
temperatures, warm enough that it will send our climate sites
towards a top 10 warmest April on record. The degree of
anomalous warmth has been greater towards the west, where
climate site Buffalo may reach the warmest April on record.
Below are the warmest Aprils on record.


Buffalo

Rank....Value (F).....Year

1........51.3.........1921
2........51.1.........2010
3........51.0.........1955
4........50.9.........2008
5........50.8.........1878

Current April average temperature through April 26th: 49.6F


Rochester

Rank....Value (F).....Year

1........52.6.........1878
2........52.5.........1921
3........52.4.........2010
4........52.3.........2008
5........51.4.........1915

Current April average temperature through April 26th: 50.4F


Watertown

Rank....Value (F).....Year

1........49.1.........1987
2........48.7.........1955
3........48.7.........2010
4........48.3.........1968
5........48.2.........2008

Current April average temperature through April 26th: 46.6F

Temperature records for Buffalo and Rochester begin 1871, while
Watertown`s history is a bit shorter, with temperature records
beginning in 1949.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...THOMAS
SHORT TERM...APFFEL
LONG TERM...APFFEL/SMITH
AVIATION...THOMAS
MARINE...THOMAS
CLIMATE...THOMAS



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