Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/22/19

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 914 PM MDT Wed Aug 21 2019

.UPDATE...
Issued at 900 PM MDT Wed Aug 21 2019

The majority of the storms have dissipated this evening and the
severe threat has diminished. An outflow boundary may still
provide enough forcing to generate storms to the southeast of
DIA. In addition, southerly winds along with an outflow boundary
coming southward out of the Cheyenne, WY area may convergence to
generate a few storms in Larimer and Weld Counties. These storms
should be done by 1am. Otherwise, there will be near normal lows
with clouds clearing out.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 221 PM MDT Wed Aug 21 2019

East winds around a large surface high over the Great Lakes will
help keep low level moisture across northeast Colorado. Dew points
are expected to stay in the mid to upper 50s with precipitable
water values around an inch. With surface temperatures in mid 80s,
surface based CAPEs are 1500-2500 J/kg. The 12Z sounding at DNR
and AMDAR soundings show a strong cap around 650mb. Storms are
expected to continue to form over the mountains and foothills
where they should be able to bust through the cap. Storms are then
expected to slowly track east-southeast. Models indicate storms
will have a tough time surviving north of I-70 and east of line
from Akron to Limon because of the cap. Lowered PoPs over the
northeast corner, but kept 40-60 PoPs for the Front Range and near
by plains. Some of the storms should be strong to severe with
hail, strong winds, and very heavy rain. Convection is expected to
end by 06Z as the airmass stabilizes.

On Thursday, an upper level trough will move into the Northern
Rockies. This will turn flow aloft southwesterly and bring drier
air to the mountains. There may be enough lift to produce a few
week showers and storms over the mountains. Models show an area of
convergence somewhere along the Front Range to the near by
plains. This should help trigger storms. ML CAPE climbs to
1500-3000 J/kg over the Front Range and eastern plains Thursday
afternoon. Southeast winds will be stronger over the plains and
result in better shear. This should lead to a few of the storms to
be strong to severe with large hail, damaging winds, and heavy
rain. Temperatures are expected to be slightly warmer with highs
in the mid to upper 80s across northeast Colorado.

.LONG TERM...(Thursday night through Wednesday)
Issued at 221 PM MDT Wed Aug 21 2019

Further disorganization and weakening of the summer subtropical
ridge will take place over the weekend as the supply of mid and
upper level moisture to the Rockies essentially gets shut off by
dry northwesterly flow aloft. Hot and dry conditions are expected
for the weekend and into early next week ahead of potentially much
cooler temps for NE Colorado for the middle to latter portion of
next week. Potential critical fire weather concerns may exist for
Sunday and Monday.

Starting with Thursday evening, the weak ridge axis over the
state Thursday will flatten into early Friday as a Pacific short
wave trough treks over the northern US Rockies along the US/Canada
border. This will leave the state under drier, moderate westerly
zonal flow aloft. This trough will send southward the first of
three cooler surges to northeast Colorado in the extended period.
By midday Friday this cool front, associated with the northern
trough, will enter the northeast plains. At this time the front
looks nothing more than a strong northerly wind shift while aiding
to keeping temps slightly cooler in the 80s across the lower
elevations. Would also expect a lower cloud deck to develop over
the plains for late Friday night into early Saturday under stable
west-northwestly flow aloft. For Saturday, with dry conditions in
the mid and upper levels, this cooler morning airmass should be a
stabilizing feature for much of the day, however temps will
quickly rebound back into the 90s as the boundary layer mixes with
dry and warm mid-level temps by midday.

Heading into Sunday, as the upper trough which brought the cooler
surge moves across the northern US plains states, slight
strengthening of the upper ridge develops over the entire western
US in it`s wake. This will allow for moderate to strong dry
northwestly flow aloft to dominate the state. This should bring a
hint of a dry, blue-sky, Septemberlike day to the region Sunday.
This ridge should also fend off any northerly advection of
tropical moisture out of the Baja region from Tropical Depressing
TEN-E which is projected to move northwestward well off the Baja
coast. Will need to monitor potential critical fire weather
concerns for Sunday as low RHs and potentially stronger
northwestly winds are likely, especially across the mountains and
foothills.

As moderate northwest flow dominates the Rockies, another weak
impulse of energy rides southeastward across the northern US
plains states behind a closed upper low over southern Manitoba.
This will force another slightly cooler wind shift onto NE CO late
Monday into early Tuesday. With the dry ridge continuing to
dominate the Rockies, will keep PoPs in the isolated category with
gusty afternoon storms Tuesday. Any critical fire weather
concerns on Sunday will also be there for Monday as potential dry
and gusty conditions may be present ahead of this late Monday,
early Tuesday surge, especially over the higher terrain.

With a dominant deep upper trough projected to hold over SE
Canada into mid-week, the third and coolest surge of the extended
spreads onto the high plains, including eastern CO, late Tuesday
into early Wednesday. This surge, forced southward from strong
northwesterly flow aloft over southern Canada and the northern
US, may bring daytime highs down into the 70s for Wednesday along
with the potential for higher PoPs. This is far off in time, but
if this upper pattern over N America materializes, the potential
for cooler temps across the northern states and high plains states
may increase for this mid to late next week timeframe.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 900 PM MDT Wed Aug 21 2019

Strong southerly flow has developed this evening with outflow
boundaries around the area. One of these outflow boundaries may
still produce gusts up to 35 knots so I kept the TEMPO in there
for another hour. The chance for storms has diminished tonight.
Southerly flow will continue for much of the night and will become
southeasterly tomorrow morning. Storms will be possible in the
afternoon on Thursday with wind gusts and lower ceilings the
primary threats.

&&

.FIRE WEATHER...
Issued at 221 PM MDT Wed Aug 21 2019

Elevated fire danger conditions may materialize for Sunday and
Monday. Dry and stable conditions under moderate northwesterly
flow aloft are expected in this timeframe. At his time, the main
areas set for potential critical fire conditions would be the
mountains, high parks and eastern foothills as afternoon winds
over 25 mph combined with low relative humidities may develop.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Danielson
SHORT TERM...Meier
LONG TERM...Fredin
AVIATION...Danielson
FIRE WEATHER...Fredin



Area Forecast Discussion

National Weather Service Buffalo NY

 1021 PM EDT Wed Aug 21 2019

.SYNOPSIS...
A cold front will push through the region tonight. While this could
spark a few more scattered showers or thunderstorms, it will bring
an end to a stretch of warm and muggy conditions. A weak wave of low
pressure may produce a few more showers Thursday, mainly south of
the Thruway. We will then experience spectacular weather Friday
through the upcoming weekend with little cloud cover...comfortable
temperatures and low humidity.

&&

.NEAR TERM /THROUGH THURSDAY/...

Radar imagery showing a few widely scattered showers across
Chautauqua County. Otherwise the rest of the area is mainly dry
late this evening with varying amounts of cloud cover.

A cold front will then gradually push to the south across our
forecast area overnight. Other than a very modest 30kt low level
jet and some convergence near and ahead of this boundary...
there really is not much forcing to support widespread pcpn. A
strong H25 jet will pass to our north...but it will be in the
`wrong` place to give any additional lift from the upper levels.
It is interesting to note though...that most if not all of the
guidance packages are grossly under estimating the strength of
the UL jet. Aircraft measurements from across Minnesota this
morning measured winds >160kts with this jet...but upper air
soundings have only been able to `capture` winds of 115 to
120kts. As mentioned though...the position of the jet is more
important and this is not favorable for significant weather
production. In any case, the passage of the low level frontal
boundary may continue to support a few scattered showers
overnight, with the highest chances over and east of Lakes Erie
and Ontario where the lakes provide better nocturnal
instability.

Thursday will feature improving conditions for areas north of the NY
Thruway. Farther south, the latest guidance is now more aggressive
with a weak baroclinic wave moving along the frontal zone. This wave
may bring a few showers to the Southern Tier and western Finger
Lakes, with plenty of cloud cover lingering. Otherwise...it will
become increasingly comfortable as dew points in the lower 60s
during the morning will drop through the 50s during the afternoon.
Meanwhile...afternoon highs will reach the mid 70s at lower
elevations and around 70 on the hills.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
The first taste of fall-like conditions will be felt across the
forecast area during this period. Cold air advection continuing
behind the front will keep in place a much cooler airmass for Friday
and also Saturday. How cool will it be? Well, H850T are forecast to
fall from +11C to +7C Thursday night, that`s chilly (single digits
at H850) for August standards.

Friday, with a cool NNW`erly flow filtering in across the region and
much warmer lakes, it will result in a conditionally unstable
airmass for any lake effect processes. However, with only a thin,
shallow layer of moisture left and strong subsidence any lake
response will be very limited, if anything at all. The most likely
scenario, with steep low level lapse rates, will be some diurnally
driven flat fair weather cu. With that said, look for dry weather
across all locations, with a mixture of afternoon clouds and
sunshine. With a much cooler air mass in place, look for highs in
the upper 60s to low 70s, which will roughly be 5-8F below normal
for this time of year.

Friday night, Canadian sourced high pressure will provide light
winds and clear skies overnight. In fact, it will be an excellent
night for star gazing, if you get a chance head outside and make use
of a telescope if you have one. The only thing weather wise will be
some interior valley fog across the Southern Tier and to a lesser
extent east of Lake Ontario in the Black River valley. With clear
skies and excellent radiational cooling look for lows to fall back
in the upper 40s to low 50s by daybreak.

Saturday, more of the same as cool NNE flow will reside across the
forecast area with highs only expected in the upper 60s to low 70s.
Saturday night, another spectacular night is on tap with clear skies
and light winds. Lows will generally be found in the low 50s, with a
few pockets of upper 40s across interior sections of the Southern
Tier and east of Lake Ontario. Sunday, a gradual warming trend
begins as the broad Canadian sourced high slowly slides east. This
will allow return southerly flow to develop across our region which
will encourage a return to near normal highs, mid and upper 70s.

Sunday night, the center of the surface high pressure slides further
east to New Brunswick and Prince Edward Island. However, it will
continue to maintain dry conditions as we head into the new work
week. Also, it won`t be as cool overnight with lows expected in the
50s to low 60s by sunrise Monday morning.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A return to above normal temperatures is likely during the long
term period.

Otherwise, medium range guidance is not in good agreement and
diverge with respect to how quickly the ridge slides further
east and out to sea, and how quickly the next trough and
associated moisture approaches from the west. The GFS remains
fastest with this overall scenario and brings increasing chances
for convection into our region. Meanwhile, the ECMWF lies on
the other side of the guidance envelope and keeps the ridge
intact and our region totally dry through Tuesday. Keeping this
in mind, have held POPs to only a chance showers and
thunderstorms for the time being with all the uncertainty beyond
Monday.

With the above said, the combination of general airmass modification
and strengthening warm air advection will lead to a day-to-day
warming trend through this period with highs climbing into the low
to mid 80s.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...

A few scattered showers continue late this evening across
Chautauqua County. A very small and persistent patch of MVFR
CIGS coming off Lake Erie also continue near KBUF. Otherwise VFR
will prevail for the rest of the area through the midnight hour.

Overnight a cold front will move slowly southeast across the
region, with a few more scattered showers possible. Low stratus
may develop for a few hours behind the cold front late tonight
and Thursday morning, with MVFR to IFR CIGS possible across the
higher terrain while the lower elevations stay mainly VFR. A
weak wave of low pressure will ripple along the front Thursday,
and this may bring a few additional showers to the Southern Tier
and western Finger Lakes with mainly VFR CIGS/VSBY.

Outlook...

Friday through Monday...Mainly VFR with nothing more than Southern
Tier valley fog producing local IFR conditions each late night and
morning.

&&

.MARINE...
A southwesterly flow will be in place across the region this evening
ahead of a cold front will become WNW behind the cold front later
tonight, with a brief period of stronger winds centered near
daybreak Thursday. This will produce marginal Small Craft advisory
conditions on Lake Ontario.

WNW winds over the shorter fetch of Lake Erie will build waves 2-3
feet tonight and Thursday, while a longer fetch and slightly
stronger wind flow over Lake Ontario will bring waves up to 4-5 feet
on the southern Lake Ontario shoreline. Small craft advisories have
been issued. Winds and waves will diminish Friday, with good boating
conditions expected over the weekend.

&&

.TIDES/COASTAL FLOODING...
A strong cold front will cross the Lower Great Lakes this evening.
Strengthening west to northwesterlies in the wake of the front will
increase wave action and combine with already high lake levels to
produce significant shoreline erosion and flooding late tonight
through late Thursday afternoon. A Lakeshore Flood Warning is
now in effect for Wayne, northern Cayuga and Oswego counties.
Since winds will be more westerly and not as much onshore, the
lakeshore flood watch was dropped for Niagara, Orleans and
Monroe counties.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning from 5 AM to 5 PM EDT Thursday for
     NYZ004>006.
MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Thursday for LOZ043-
         044.
         Small Craft Advisory from 2 AM to 2 PM EDT Thursday for
         LOZ042.
         Small Craft Advisory from 8 AM to 8 PM EDT Thursday for
         LOZ045.

&&

$$

SYNOPSIS...Hitchcock/RSH
NEAR TERM...Hitchcock/RSH
SHORT TERM...AR
LONG TERM...AR/JLA
AVIATION...Hitchcock
MARINE...Hitchcock/JLA/RSH
TIDES/COASTAL FLOODING...RSH/JLA