Forecast Discussion

Forecast Discussion for BUF NWS Office
541
FXUS61 KBUF 181859
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
259 PM EDT Thu Jul 18 2019

.SYNOPSIS...
A few isolated showers and thunderstorms will occur inland from the
lakes today. Oppressive summer heat and humidity will then build
into the region Friday through the weekend with a few brief rounds
of showers and thunderstorms. A cold front is expected to cross the
area by Sunday night, allowing for a break from the heat and
humidity by early next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
A humid airmass remains across the eastern Great Lakes this
afternoon. High pressure extends southwest from the Canadian
Maritimes and weak subsidence is across the region. Leftover
moisture from the tropical airmass has led to a cumulus field across
the region. A few showers and thunderstorms are possible east of
Lake Ontario where a weak disturbance tracks across the Ottawa
Valley. Can`t rule out an isolated shower or thunderstorm along a
lake breeze, inland from the lakes.

Any activity from the this afternoon will diminish this evening and
partly cloudy skies and dry conditions will persist through the
first part of the night period. High pressure will move east along
the east coast late tonight and southwest flow will increase across
the region into Friday morning. A 592 dm ridge over the central
and southeastern U.S. will build northward and a 30kt westerely
low- level jet will ride the top of the ridge into the eastern
Great Lakes through Friday morning. This will advect +20C 850
hPa temperatures into western NY early Friday morning and east
of Lake Ontario by Friday afternoon. This surge of warm air will
also carry the potential for showers and thunderstorms to move
into western NY early Friday morning. An increase in instability
from activity across the Mid-West this afternoon will head
towards the region Friday morning. Hi-res guidance is shunting
most of this activity into Ohio but it may clip the Southern
Tier. Another shortwave trough across Ontario will also bring
the potential for showers to clip the North Country early Friday
morning. Mild and muggy tonight with low temperatures in the
low 70`s to upper 60`s across the Southern Tier and east of Lake
Ontario.

The talked about oppressive heat and humidity arrives Friday with
high temperatures expected to climb into the upper 80`s to low 90`s.
The highest temperatures will occur across the Lake Plains and
Genesee Valley. A gusty southwest wind will keep areas downwind of
the lakes on the cooler side but still hot. Adding fuel to the fire,
dewpoints will climb into the mid to upper 70`s, abnormal for
western and north central NY. This will result in heat index values
of 105-110 across the Lake Plains and Genesee Valley and 95-104
across the rest of western and north central NY. Heat Headlines are
in effect including Excessive Heat Warning for the Lake Plains and
Genesee Valley and Head Advisories elsewhere. These headlines begin
10 AM Friday and continue through 6 PM Saturday.

The heat and humidity will produce an abundance of instability
during the day. Showers and thunderstorms will likely form earlier
than normal along differential heating and/or lake breeze
boundaries. Yes, that means cloud cover will be around and may
inhibit some places from reaching their full potential for high
temperatures but there should be enough breaks in the clouds and
warm air advection to raise our temperatures to oppressive levels.
Moderate shear of 20-30kts and instability may cause some storms to
become strong to severe late Friday morning through Friday afternoon.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH MONDAY NIGHT/...
...Dangerously Oppressive Heat Continues A Little Longer...

An expansive 594dm sub tropical ridge extending from Bermuda back
across the eastern half of the country to Baja California will
continue to bathe the majority of the country in a sweltering sauna
of heat and high humidity through at least the first half of the
weekend. Interestingly...the ridge is not especially unusual. Rather
it is the `perfect storm` of several variables coming together...
primarily anomalous temperatures below 10k ft and extraordinarily
high PWAT values coinciding with the thermal solstice. Its one thing
to have H7/H85 temperatures 2 to 3 STD above normal...and its quite
another to have that occur during the climatological max period of
the year. These values have return intervals of 10 to 20 years for
this point in summer. THAT in itself is impressive.

All of that being said...ensemble guidance (GEFS/SREF) continues to
hammer home the forecast of 20-22 C air at H85 for Friday night and
Saturday with some deterministic guidance as high as 24c. Unlike
Friday when there could be some MCS remnants in the morning to delay
insolation...cloud cover on Saturday should not be an issue in
getting the heat started. Additionally...we will get a head start on
the dangerous heat due to the fact that Friday night will be at
least 5 deg f warmer than the previous night. Specifically...mins
Friday night will ONLY be in the mid 70s across the western counties
with max temps Saturday ranging from the upper 80s across the North
Country...higher terrain and lake cooled areas to 90-95 inland
across the lake plains. When mid 70 dew points are factored in...
heat indices will Saturday afternoon will generally range from 100
to 105. This will EASILY support widespread heat advisories with the
very real threat for Excessive Heat Warning conditions.

In regards to pcpn...there will be two areas of convection to
contend with Friday evening. The first will be leftover lake breeze
driven thunderstorm activity across the Southern Tier...and the
second will be a blossoming area of potentially strong storms
supported by a convectively enhanced shortwave moving southeast from
southern Ontario. Will use high chc to likely pops to cover the
latter...but both areas will either die off or pass through the
region by 06z. The important note with the convection is that it
will occur within/near an EML plume...something that we have been
pointing out for the past several days. The origin of this elevated
instability can be seen on this mornings KLBF and KABQ soundings.
During the course of the next 36 to 48 hours...this instability
(lapse rates >7 deg c/km) will be advected across the northern
plains to the Great Lakes (as per HYSPLIT trajectory forecasts at
the 700-500mb level). This will certainly have the ability to
enhance the above described convection (esp. activity coming out of
Srn Ontario) and drive up the risk for strong damaging thunderstorm
wind gusts. The moisture rich environment and `fat CAPE` profile
will also aid in ramping up greater than normal cloud to ground
lightning strikes. Will use some enhanced wording for the Srn Tier
for this risk.

Mainly dry weather is then expected from the second half of Friday
night through the bulk of Saturday. While there will be the
potential for some showers and thunderstorms south and east of
Buffalo and Rochester late Saturday afternoon...the next round of
convection will be largely driven by the first of two cold fronts
that will be approaching from southern Ontario. The first of these
fronts will pass through the region Saturday night and will take the
edge off the heat for the second half of the weekend. The second
front will usher in the true relief for the new work week...but
thats getting ahead of ourselves.

The initial cold front will press south across our region Saturday
night. Will carry high chc pops during the first half of the night
for the associated convection with diminishing pops for the
overnight into Sunday morning. Steep mid level lapse rates may still
be in place early...so will have to remain vigilant for more strong
thunderstorm activity.

As the first fronts stalls over Pennsylvania on Sunday...the
secondary cold front will make its across Lake Ontario. Subsidence
between the two boundaries SHOULD provide a six hour period of mainly
convection free weather over the region...but timing this relatively
narrow window will be difficult. May just broad brush chc pops for
now and await more clear cut guidance before fine tuning. In either
case...temperatures will be several degrees lower on Sunday with the
mercury topping out in the mid to upper 80s. While it will still be
quite warm...lower humidity levels should help to make things a
little more tolerable.

High pressure centered over the northern plains Sunday night will
settle south across the Mississippi Valley Monday and Monday night.
This will usher cooler and notably drier air across all of the Great
Lakes region...allowing our temperatures to drop back to below
normal levels.

&&

.LONG TERM /TUESDAY THROUGH WEDNESDAY/...
What a difference a week makes! There is increasing confidence that
we will be able to enjoy near to BELOW normal temperatures during
this period. The ECMWF and GEFS ensemble are in lock step agreement
that an amplified pattern will be in place across the country during
this period...one that will feature an anomalously strong ridge in
the west and a deep longwave trough in the east. This will support a
prolonged flow of Canadian cooled mid summer air with low double
digit H85 temps only allowing daytime highs to climb to between 75
and 80f.

Meanwhile...a massive surface high will generally reside over the
Upper Mid West. This will promote fair dry weather across the
region...although a weak frontal passage on Thursday could generate
a few nuisance showers.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
A few isolated showers and thunderstorms may develop this afternoon
along and inland of lake breeze boundaries, with the best chance of
this east of Lake Ontario. Any thunderstorm may produce local/brief
MVFR to IFR, but VFR will prevail the vast majority of the time.

The isolated showers and thunderstorms will end this evening.
Another area of showers and thunderstorms will approach from
Southern Ontario late tonight, possibly reaching the area by
daybreak Friday with another round of local/brief MVFR to IFR
conditions in the heavier showers. At this time, activity looks
confined to KJHW Friday morning. Showers and thunderstorms will form
along lake breeze boundaries and differential heating boundaries
Friday. These storms have the potential to become strong to severe
with brief reductions in cigs/vsbys and gusty winds if near
terminals. Highest risk for strong storms will be across KJHW.

Outlook...

Friday through Monday...Mainly VFR with a chance of a few brief
rounds of showers and thunderstorms with associated local MVFR to
IFR.
Tuesday...VFR conditions expected.

&&

.MARINE...
Winds will remain light today and tonight, generally 10 knots or
less. Southwest winds will increase Friday and Saturday, averaging
15 knots on lakes Erie and Ontario. This will produce choppy
conditions at times, although winds and waves will likely remain
below Small Craft Advisory levels.

There will be a chance of a few scattered thunderstorms at times
Friday through the weekend. Any thunderstorm may produce locally
higher winds and waves.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Heat Advisory from noon Friday to 6 PM EDT Saturday for
     NYZ006>008-010>012-019>021-085.
     Excessive Heat Warning from noon Friday to 6 PM EDT Saturday
     for NYZ001>005-013-014.
MARINE...None.

&&

$$

SYNOPSIS...Hitchcock/HSK
NEAR TERM...HSK
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...Hitchcock/HSK
MARINE...Hitchcock/HSK

NWS BUF Office Area Forecast Discussion