Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/06/21
Area Forecast Discussion
National Weather Service Gray ME
1035 PM EDT Sun Sep 5 2021
A weak passing wave from the west will result in scattered
showers tonight. Another trough will arrive late on Monday with
showers and thunderstorms possible, especially across the north.
High pressure will result in pleasant conditions on Tuesday
before another frontal boundary approaches by the middle of the
week with additional showers possible on both Wednesday and
Thursday. Hurricane Larry will pass well offshore this week but
building long-period swells are expected, which may result in
increased rip currents.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
1030 PM Update...Much of the forecast area in the warm sector
between a warm front near our border with Caribou`s CWA and a
weak cold front located across eastern NY. Drizzle and light
rain continue on the coast and central ME but this activity will
gradually move northeastward overnight. Showers located across
VT will move into western zones over the next two hours, perhaps
with a rumble of thunder. However most of the forecast area
should be dry by late tonight. Areas of fog are then likely.
Strong short wave trough approaches our northern zones Monday,
with a chance of strong thunderstorms, mainly across northern
and central zones during the afternoon and early evening hours.
650 PM Update...Just a few minor adjustments to PoPs this
evening based on latest radar imagery. Increased then across
southeastern NH and southern ME to categorical based on latest
radar mosaic loop. Otherwise, the rest of the forecast is in
Clouds will continue to thicken and lower tonight amid warm,
moist return flow w/ departing high. Showers have been very
limited in coverage today, becoming a bit more widespread
tonight with greater forcing moving in. With the WAA and clouds,
tonight will be 10-15 degrees warmer than last night. Fog will
likely develop in the usual CT Valley locations after midnight.
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
The main item Monday will be the chance for thunderstorms, some
strong, during the afternoon hours. Amid the longwave pattern
aloft, a sharp shortwave will punch the trough negative. This
will bring good forcing amid a region experience cooling aloft
from the front overnight. The contrast between warm lower levels
and cooling upper levels will create ample lapse rates in the
mid and low levels. There is some question on how unstable the
lower levels get through the morning, but any breaks in the
clouds should bump temps into the mid-70s.
HRRR and NAMnest runs have been consistent in painting single
cell showers and storms developing into a broken line segment
across the northern tier of counties (ME and NH). These showers
and storms will have 50-60kts of 0-6km shear to work with, as
well as the mid/low lapse rates 6-7 c/km. This certainly points
to a small hail or gusty wind threat for storms that form along
the vort passing through. MLCAPE remains marginal, but with
other parameters in place, can`t rule out these storm attributes.
Showers and storms move off to the east overnight, with just a
few upslope showers possible in the higher terrain left in brisk
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Overview: A continued active pattern is expected through much of
the upcoming week as a series of relatively weak disturbances
cross through allowing for several rounds of showery weather
under broad upper-level troughing. While there will be several
opportunities for a scattered showers, no major systems are
currently expected and there will be plenty of pleasant weather
mixed in between. Temperatures will remain near to slightly
below normal for early September.
Impacts: Hurricane Larry is expected to continue to move towards
Bermuda through the upcoming week before turning more northward by
Thursday. Although this system is expected to remain well offshore,
long-period swells will likely begin to approach the Gulf of
Maine by the middle to end of the week. High astronomical tides
combined with building seas may result in some dune overwash
and beach erosion.
Forecast Details: High pressure will build to the southwest of New
England on Tuesday allowing for increasing sunshine throughout the
day and pleasantly warm high temperatures into the lower to middle
70s for locations outside of the mountains. Skies will remain mostly
clear on Tuesday night and this combined with weakening winds should
allow for some decent radiational cooling. As a result, expecting
lows to range from the 40s across the north to 50s elsewhere. On
Wednesday morning a deepening area of low pressure will be centered
over the Northern Great Lakes, which will send a surface warm front
northward through New England. Flow will increase out of the south
during the day, which will allow dewpoints to climb into the 60s as
high temperatures reach the upper 70s to lower 80s across
southwestern ME and southern NH. Heights will fall during the
day with increasing chances for showers and thunderstorms from
west to east during the afternoon and evening hours. Wednesday
night will be a mild one as the additional cloud cover,
lingering showers, and high dewpoints keep most locations into
the 60s. A cold front will gradually cross through New England
late Thursday with additional scattered showers expected
throughout the day. Dewpoints will gradually fall from north to
south late in the day as winds turn more northwesterly. We will
then dry out on Thursday night with gradually clearing skies,
allowing for low temperatures to range from the 40s in the north
to the 50s elsewhere.
On Friday we will remain under weak 500 mb troughing with cyclonic
flow, which will result in a non-zero threat for a few scattered
showers to develop. The best chance for showers currently looks to
be across the north where some upslope flow will be present. The
Atlantic ridge and departing cold front will help to keep Hurricane
Larry well offshore through the end of the week, although it will
likely be close enough to result in increased seas across the Gulf
of Maine. This combined with relatively high astronomical tides of
around 10.6` Wednesday through Friday in Portland, may result in
some beach erosion and dune overwash issues in addition to dangerous
rip currents and high surf. This will need to be watched some as the
timing of the frontal passage will help to determine how close Larry
gets to our coastline before turning more easterly into the open
North Atlantic. Broad high pressure will then build back into the
area for the upcoming weekend with mostly tranquil weather and
continued cool temperatures expected.
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Short Term...Ceilings will lower tonight to MVFR and then IFR
across most TAF sites. -SHRA and BR can be expected through 12z
Mon, with conditions improving to VFR. Some thunder and showers
will be possible at inland TAF sites Mon afternoon, with a W
wind shift in the evening and overnight hours.
Long Term...VFR conditions expected on Tuesday as high pressure
to our southwest keeps skies mostly sunny under light southerly
flow. Scattered showers and thunderstorms are then expected on
Wednesday and Thursday as a frontal system crosses through,
which may result in brief flight restrictions. More prolonged
MVFR ceilings will also be possible on Wednesday across some
coastal terminals such as KRKD as southerly flow brings in
moisture from the Gulf of Maine. VFR conditions will return on
Friday as high pressure builds back into the area.
Short Term...A few gusts up to 25 kt will be possible this
evening as a front approaching with increasing southerly winds.
The front passes Monday morning, with another disturbance
passing inland during the afternoon. Otherwise, conditions are
expected to remain below SCA criteria, with waves generally 2 to
Long Term...High pressure to our southwest will keep winds and
seas below SCA criteria on Tuesday. Southerly winds will then
increase on Wednesday ahead of an approaching frontal boundary
with SCA conditions likely as winds gust up to 25-30 kts and
seas build to 4-7 feet. Distant Hurricane Larry will then begin
to allow for increasing seas towards the end of the week with
seas of 6-12 feet possible across the outer waters and 4-8 feet
across the bays.
Area Forecast Discussion
National Weather Service Houston/Galveston TX
646 PM CDT Sun Sep 5 2021
A line of showers and thunderstorms ahead and along a weak cold
front will approach SE TX this evening. The line has begun to
weaken and not sure how far south the line will get this evening.
Still plenty hot and there is decent CAPE and PWATs in advance of
the front so will carry VCTS for northern TAF sites and see how
things evolve. Leaned toward the HRRR which shows the line
weakening and then blossoming again after 09z further south
affecting the Houston terminals for the morning push. Will carry
VCSH after 09z through the morning. Will carry a VCTS for central
and southern TAF sites for Monday afternoon but confidence with
additional development is low as models dry things out quickly
after 18z. 43
.PREV DISCUSSION... /ISSUED 308 PM CDT Sun Sep 5 2021/
Showers have had a hard time getting started so far today, though
that is expected to change for the Houston Metro/I-45 eastward as
a weak front droops into the region. Though the rain setup does
not overall look particularly impressive, the strongest cell or
two may manage some isolated heavy rain.
The deeper we go into the new week, the lower rain chances will go
as some drier air filters into the region and high pressure
attempts to build back. Along with the lower rain chances, we`ll
also see above average temperatures with highs away from the Gulf
looking to rise into the middle to upper 90s multiple days.
Finally, we will continue to keep an eye on Invest 91L and its
potential for development as it lifts northward across the Gulf
over the next several days. Confidence though, is increasing that
this feature will be kept well to our east.
SHORT TERM [Monday Through Monday Night]...
The remainder of this afternoon`s weather pattern will be very
similar to what we saw yesterday. Despite higher PW air along our
eastern counties again today, subsidence still seems to be winning
out and our radar remains quiet inland. With high pressure overhead
and light SW flow, the sea-breeze will begin to push inland over the
next few hours and at most might kick up some isolated showers along
our coastal areas before dissipating around sunset. Meanwhile, a
front currently passing through DFW`s area will sag further south
and is expected to reach our northern counties by late this evening.
Therefore, isolated to scattered showers and storms are expected
along the frontal boundary as it pushes south overnight and reaches
the coast by morning. WPC has placed our eastern and northern
portions of our CWA in a marginal risk for excessive rainfall
tonight, but as the front becomes more E/W oriented, it`s low-level
moisture transport will weaken, so not expecting much of a risk
By tomorrow, the frontal boundary will be stalled across our
southern CWA and act as a focus for showers throughout the day. With
daytime heating, coverage and intensity of these showers are
expected to increase throughout the day and peak late afternoon.
Rain chances will also be enhanced by a broad tropical trough in the
Central Gulf expected to migrate north and bring a surge of deep
tropical moisture along the northern Gulf Coast. Forecast soundings
show PWs climbing to 2.1-2.2 inches and CAPE peaking at ~2200 J/kg.
Therefore, WPC has placed our southeastern counties in a marginal
risk for excessive rainfall. Any training storms and slow moving
storms are capable of producing heavy rainfall tomorrow. By the
evening with the frontal boundary still stalled across our southern
counties, PoPs will remain near 30-60% overnight.
Regarding temperatures, tonight will be warm and muggy again with
lows reaching the mid to upper 70s inland and near 80 along the
coast. Tomorrow`s high temperature are expected to reach the lower
to mid 90s, a slight cool down thanks to the FROPA. But for tomorrow
night, optimistically, our northernmost counties will reach the
lower 70s and perhaps even the upper 60s for our most rural sites..
LONG TERM [Tuesday Through Sunday]...
By Tuesday morning, there will likely be precious little left of
the upper trough/weak front that was the story of the short term
forecast. We may have some lingering vorticity left aloft in a big
gap in the subtropical ridge, but it will be entirely cut off from
the main trough heading towards the Canadian Maritimes. We could
still see some showers and storms on Tuesday around the coast,
particularly if the boundary doesn`t make it as far south as
progged in the model guidance.
For the rest of the week and into the weekend, the main story will
be the rebuilding of the subtropical ridge, and the filtering in
of some drier air from the north behind the weak front. Both of
those will allow for afternoon temperatures to shoot up above
seasonal averages and into the middle to upper 90s away from the
coast (and even to around or just above 90 to the Gulf). While the
surface pressure gradient won`t be too tight, we should see enough
onshore flow - especially in the wake of 91L - to keep overnight
lows from falling out of the 70s...so if you like it a bit cooler,
we look to get the worst of both worlds there with both above
average temps overnight and during the day.
This setup should effectively cut off rain chances, at least over
the vast majority of the area late in the week. With high pressure
and precipitable water progged to fall to around or even below an
inch, convection seems a long shot. Depending on how deep the
drier air manages to work, guidance suggests we could still
squeeze out some showers/storms over the nearshore Gulf waters and
maybe, maaaaaaaybe right on the immediate coast, but that should
be about it.
As some deeper Gulf moisture returns to the region late in the
weekend or early next week, we should see higher humidity and
perhaps even some rain chances creeping back into the picture.
The potential fly in the ointment for this forecast? Invest 91L.
My forecast reflects the increasing confidence that the bulk of
the Gulf moisture (and any tropical cyclone, if there is one),
will ride east of the incoming boundary and get caught up in the
last little bit of influence from the passing northern stream
trough and take that break in the subtropical ridge right up into
the North/Northeast Gulf coast and Southeastern states. This seems
pretty clearly the most likely scenario, and the one that the
deterministic guidance strongly favors. But there are a couple
lonely members of the GEFS that really have something against
Freeport/Matagorda, and take 91L as a tropical cyclone over their
way. This very much has "SoYoureTellingMeTheresAChance.gif"
energy, but theoretically, yes, it is still on the table. We will
continue to monitor things and start raising a ruckus if things
change for our area - we just ask you recall that it is peak
hurricane season and are prepared accordingly.
Light to moderate winds are expected through the first half of the
week along with seas below three feet. Showers and thunderstorms
will be possible as a weak front drops into Southeast Texas
tonight and tomorrow, then rain chances will be relatively low for
much of the coming week along with a general land/seabreeze
diurnal pattern. Deeper Gulf moisture pushing back into the area
may start to boost rain chances at the end of next week. Mariners
should closely monitor the forecasts regarding potential tropical
cyclone development in the Gulf of Mexico towards the middle of
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 75 94 72 96 70 / 30 20 10 10 0
Houston (IAH) 78 94 75 94 74 / 30 50 40 20 10
Galveston (GLS) 80 91 79 90 79 / 30 40 60 30 20
Area Forecast Discussion
National Weather Service Lake Charles LA
1000 PM CDT Sun Sep 5 2021
.UPDATE...The previous forecast remains on target with only a
minor update to the precip grids conducted to reflect current
.PREV DISCUSSION... /issued 623 PM CDT Sun Sep 5 2021/
For 09/06/2021 00Z TAF Issuance.
Some scattered convection and associated cloud cover around the
region this evening. Expect some of this activity to begin to
fizzle out following sunset... But, a diffuse and slow moving
frontal boundary will sink towards the area overnight, so will see
a reintroduction of VCTS and lowered CIGS accordingly. TEMPO
groups may be added later, but high res guidance suggests activity
should remain fairly scattered. Additionally, given the weakness
of the boundary, winds will remain light and variable through much
of the night enhancing the potential for the typical patchy BR/FG
development after midnight. Some question of how far south the
boundary makes it, but likely will see at least some northerly
winds pick up after daybreak tomorrow as it stalls and washes out
nearby. With the stalling of the boundary, will also see a
continuation of vicinity type activity through the day. Most
guidance prevails VFR... Though any increased convective coverage
and activity directly over the terminals will result in more
PREV DISCUSSION... /issued 344 PM CDT Sun Sep 5 2021/
SHORT TERM [Today through 12Z Wednesday]...
Showers and thunderstorms will be expected to continue developing
(primarily for southern areas) for the remainder of this afternoon
into this evening. A few storms will be possible for Central LA
through the evening. Storms will dissipate after sunset but an
approaching frontal boundary from the north will lead to forced
uplift and formation of storms in our area during the overnight
hours. The HRRR is showing some storms making their way through
our area starting around 04Z and progressing towards the coast by
12Z. PWATs 2.00-2.25 inches will be expected heading into Monday.
The frontal boundary will be expected to stall over our area
Monday into Wednesday. Precipitation chances will be enhanced by
daytime heating. WPC has our area in a Marginal Risk of Excessive
Rainfall through the period. A significant amount of moisture
present in our area along with the stalling frontal boundary means
that there will be persistent chances for showers and
thunderstorms over the next few days. Areas that get sustained and
persistent rainfall could see flooding.
LONG TERM [Wednesday through Sunday]...
As we start the long term period, our weak frontal boundary is
progged to be meandering/washing out in vicinity of the forecast
area, while another, more substantial cool front is noted to our
northwest, extending from the Mid-South through the ArkLaTex. At the
same time, the much talked about area of disturbed weather currently
over the wrn Caribbean/Yucatan Peninsula is progged to be moving
newd across the cntl Gulf as a trof of low pressure. Combo of these
features, along with plentiful Gulf moisture in place across the
area (forecast soundings indicate PWAT values as high as 2.2 inches,
mainly over lower Acadiana) should lead to scattered/numerous
showers/storms by Wednesday afternoon, primarily over the sern zones.
By Thursday, the reinforcing front should be slipping into the
forecast area, squeezing sufficient moisture for further convection
to mainly the coastal areas and lower Acadiana. The main impacts of
the front for now appear to be a nice lowering of dewpoints across
the nrn zones, making for a more pleasant afternoon despite temps
into the mid 90s.
With the front slipping off the coast by early Friday, dry weather
looks on tap for the early portions of the weekend. Wake up temps
are progged by guidance to be in the mid/upper 60s (a degree or two
below seasonal norms) for a large portion of the forecast area
By Sunday, the front washes out and return flow begins moistening
the lower levels again...look for widely scattered showers/storms to
also return to the region.
Weak onshore flow and low seas will prevail this evening outside
of scattered thunderstorms. Storms will become more widespread
Monday through Wednesday as a frontal boundary stalls across the
region. Winds will alternate between offshore and onshore through
the first half of the week depending on the exact location of the
.PRELIMINARY POINT TEMPS/POPS...
AEX 74 89 68 92 / 70 40 10 30
LCH 76 89 72 90 / 60 60 40 50
LFT 76 89 73 91 / 40 80 40 60
BPT 74 90 71 91 / 60 60 40 40
Area Forecast Discussion
National Weather Service Elko NV
257 PM PDT Sun Sep 5 2021
.SYNOPSIS...Strong high pressure bring hot afternoons and dry
weather to the region for the next few days. Daytime temperatures
will be approaching record highs on Tuesday and Wednesday.
.SHORT TERM...Tonight through Tuesday evening.
Amplified ridge will be locked over the Intermountain West region
for the next two days. Some record high temperatures are expected
by Tuesday, like Winnemucca, Eureka, and Ely. With the dry nearly
cloud free air mass, large diurnal swings are expected with
morning lows in the 40s and 50s. The air will not be free of smoke
particulates, although the amount of smoke from the Dixie fire
has lessened (still plenty of smoke). The HRRR smoke model keeps
the smoke/haze across northern Nevada, but better air exists over
Nye and White Pine counties.
.LONG TERM...Tuesday night through next Sunday
Guidance continues to have a fair amount of agreement only through
Wednesday night with respect to weather conditions remaining
quiet. Wednesday should be the warmest day of the long term with
highs mostly in the 90s, potentially rivaling records in some
locations across the CWA.
The center of the high pressure looks to shift south and eastward
over the course of the second half of the week. Temperatures
slowly trend down as relatively cooler air has the opportunity to
advect into the region, and we may see highs that are only in the
70s and 80s accompanied by overnight lows in the 40s and 50s as we
get to the weekend. These temps are closer to what we would
expect for this time of the year.
Lower confidence lingers around what the resulting weather
conditions will be. Pulses of mid-level moisture may help in the
development of some dry thunderstorms beginning Thursday, with a
mix of dry thunderstorm and shower activity on Friday, onward.
There isnt anything at this time supporting any confidence
behind rainfall totals, but it looks like the best chance for some
much needed rain accumulation could be in northern Nye and White
Brief periods of MVFR visibility is possible from smoke and haze
from KWMC-KBAM-KEKO. Otherwise VFR dominates with the sky cover
mostly cloud free.
Transport winds will be light for the next few days with dry
conditions prevailing. The hazy conditions persist, particularly
across northwest Nevada.
Isolated dry lightning remains a possibility late in the week.
This bears watching given the forthcoming hot and dry afternoons
and receptive fuels across much of the region. While some moisture
may creep into eastern Nevada, cluster analysis keeps an elongated
subtropical high core over the southwest CONUS. This pattern does
not favor moisture advection into eastern Nevada.
Area Forecast Discussion
National Weather Service Marquette MI
728 PM EDT Sun Sep 5 2021
.SHORT TERM...(This evening through Monday)
Issued at 416 PM EDT SUN SEP 5 2021
Water vapor imagery and RAP analysis show a mid-level trof over
Ontario and across the Great Lakes region. The mid-level low that
was centered over far ne Manitoba 24hrs ago has opened up, but its
well-defined vort max is diving sse and is nearing nw Lake Superior
attm. Convection has been increasing underneath it and its
associated mid-level cold pool. Closer to home, cool, cyclonic flow
under troffing and some instability have been supporting isold to
sct shra development today. So far, no lightning has been detected
with any of the shra here or upstream. With the rapid increase in
diurnal cloudiness during the morning, temps currently are mostly in
the 60s F, but a few lwr 70s are noted s central.
As vort max and cold pool aloft (500mb temps around -21C) passes
across the fcst area this evening, shra coverage/intensity will
peak. As was the case with previous model runs, latest runs show
greatest instability over Lake Superior where the relatively warm
lake waters boost sfc/mixed layer Td. Instability diminishes inland
from the lake with very little to almost none noted well inland.
Over Lake Superior, SBCAPE generally peaks in the 500-1000j/kg
range, shifting w to e in the 21z-06z time frame, essentially
corresponding to the passing 500mb cold pool. Per the Szilagyi
waterspout nomogram, conditions may sneak into waterspout potential
thru the evening hrs due to convective cloud depths to around 20kft
and water sfc to 850mb delta-T increasing to around 13C. Although no
mention of thunder was included in fcst, wouldn`t be surprised if a
couple of the shra manage to be deep enough to generate a lightning
strike or two. Shra will mostly end from w to e during the night,
but will probably linger over the e into Labor Day morning due to
marginal overlake instability. With increasing breaks in the cloud
cover, especially interior w half, and diminishing winds,
traditional cold spots should see temps fall toward 40F. Temps will
range up to the mid 50s near Lake Superior.
Lingering isold light shra will end over the e by aftn. Otherwise,
expect a dry Labor Day as weak shortwave ridging arrives btwn the
departing trof and the next approaching shortwave reaching the
Canadian Prairies. 850mb thermal trof will be departing to the e.
Before shifting farther e, expect some diurnal cu to blossom in the
morning over the w before dissipating. However, high clouds will
already begin increasing as strong waa/isentropic ascent regime
spreads toward the Upper Lakes in response to the next approaching
shortwave. Expect lake cloudiness and an expansion of diurnal
cu/stratocu e with later departure of the thermal trof. Those clouds
will begin clearing out during the aftn. High temps will range from
the mid 60s to lwr 70s F.
.LONG TERM...(Monday night through Sunday)
Issued at 331 PM EDT SUN SEP 5 2021
Ridging near the four-corners region and eastern US troughing
amplify this week. The primary feature of interest is a surface low
that develops and intensifies as it tracks east-northeast through
the Upper Great Lakes region on Tuesday into Tuesday night. This
seasonably strong surface low results in thunderstorm chances and
gusty winds as it tracks through our area. Gales seem increasingly
likely across eastern Lake Superior Tuesday night. Seasonably cool
weather is expected through Thursday with warm air advection
returning on Friday. Weekend forecast is uncertain, but more zonal
flow should result in temperatures closer to seasonal averages.
Sky cover and precipitation chances increase early on Tuesday as a
surface low develops over northern MN and tracks east-northeast. The
low track is still somewhat uncertain, but model guidance seems to
continue the northward trend noted yesterday. 00Z ECMWF and 00Z CMC
guidance track the low north of Lake Superior with 00Z GEFS guidance
tracking over the lake. A middle of the road approach is favored at
this time considering warm lake temperatures imply a preferred
baroclinic zone along the north shore. 12Z NAM/GFS guidance seems to
be in good agreement showing the surface low occluding over Lake
Nipigon then meandering east-southeast near the shoreline.
Irrespective of the exact location, an occluding low that lingers
across N/NE portions of Lake Superior before tracking northeast
toward James Bay seems increasingly likely. Operational guidance
indicates the surface low deepens to ~990mb and the NAEFS continues
to highlight MSLP values being at or near climatologic minimums.
Gales are therefore increasingly likely, particularly over eastern
Strong winds may provide the most widespread impacts of Tuesday
storm system, but widespread precipitation is also expected. With a
low track farther to the north, our CWA is deeper into the warm
sector where isolated to scattered thunderstorms should occur. The
final hours of the 12z HREF (especially the NAM nest and NSSL)
indicates a thunderstorm complex tracking southeast from the
arrowhead of MN early on Tuesday morning within a strong warm air
advection regime. While I`m not confident in thunderstorm location,
a strongly forced line of elevated storms seems increasingly likely
across the west in the morning. More mixed layer thunderstorm
development seems increasingly likely across the east in the
afternoon. Digging into specifics of the near-storm environment may
be futile at this time, but the typically too aggressive 3km NAM
shows a plume of 3000+ J/kg MUCAPE rooted around the 825 mb layer.
Bulk shear in the cloud bearing layer doesn`t appear particularly
impressive (~30 knots), but should be adequate for a hail threat.
Elevated storms don`t typically pose much of a damaging wind threat,
but stronger storms may mix the ~50 knot LLJ down toward the
Seasonably chilly weather continues through Thursday with lake
effect clouds and showers expected for NW wind belts. Subtle
shortwaves embedded within NW flow aloft combined with diurnal
heating may locally enhance lake effect showers. Adjusting surface
parcels to ~17C water temperatures yields a few hundred J/kg of
skinny CAPE that might be enough for thunderstorms. A warmer air
mass moving in on Friday will bring an end to lake effect
clouds/precip. Model guidance diverges this weekend with difference
primarily related to amplitude of incoming shortwave and
associated cold front. 12Z ECMWF advertises a much stronger cold
front compared to GFS/CMC/UKMET guidance. Forecaster confidence
is low for next weekend, but the flow regime should become more
zonal with time indicating more seasonable temperatures.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 727 PM EDT SUN SEP 5 2021
Cool, cyclonic flow was resulting in sct shra and a few tsra across
the, west, north and eastern Upper Peninsula this evening. Impacts
to TAF sites will be brief with possible MVFR CIGs and brief
gusty winds. The rest of the TAF period is looking like VFR
conditions for KSAW and KIWD. For KCMX low level moisture
combined with a heating after sunrise should produce a period of
MVFR CIGs before mixing lifts the cloud bases to VFR later in the
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 416 PM EDT SUN SEP 5 2021
Thru tonight, low pres over James Bay will only drift e while a high
pres ridge over the Dakotas and Manitoba shifts to MN and northern
Ontario. Under a cool air mass and relatively tight pres gradient,
nw winds of 15-25kt will generally prevail across Lake Superior this
evening with some gusts up to 30kt over the e half. Conditions this
evening may also become marginally supportive of waterspouts to
occur with some of the showers moving across Lake Superior,
particularly from nw of the Keweenaw to s central portions of the
lake. Winds will slacken some over the w overnight as high pres
ridge moves closer. With the high pres ridge arriving on Labor Day,
expect winds mostly under 15kt over the w half of Lake Superior.
Winds will diminish to mostly under 15kt e during the day. On Tue,
deepening low pres will track e across northern Ontario, passing
just n of Lake Superior. Ahead of it during Mon night, southerly
winds will ramp up to at least 15-25kt, strongest across eastern
Lake Superior. These southerly winds may even gust to 35kt gales
over the e half of the lake late Mon night/Tue morning. As the cold
front associated with the low crosses Lake Superior, expect w winds
of 20-30kt to develop Tue, then shift nw Tue night into Wed. It`s
looking increasingly likely that the nw winds will increase to 35-
40kt gales Tue night thru Wed morning, at least over the e half of
Lake Superior. Wind will then slowly diminish w to e Wed aftn/night
with winds under 20kt across Lake Superior by sunrise Thu as high
pres ridge moves closer to the area. Winds are then expected to
remain under 20kt on Fri.
Beach Hazards Statement until 9 PM EDT this evening for MIZ006.