Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/17/20
Area Forecast Discussion
National Weather Service Denver/Boulder CO
939 PM MDT Sun Aug 16 2020
.UPDATE...
Issued at 934 PM MDT Sun Aug 16 2020
Forecast is on track with no significant changes needed. LIght
easterly winds have pushed across the Continental Divide and are
bringing a bit more humidity to the fire areas, as well as pushing
most of the smoke more to the south and west, though there`s still
a plume over the Front Range foothills from the Cameron Peak fire.
In general, fire activity the next couple of days should be
dominated by upslope/downslope wind regimes with afternoon plumes
drifting mostly south and west but with less definition/more
dispersion than in previous days.
&&
.SHORT TERM...(This evening through Monday)
Issued at 335 PM MDT Sun Aug 16 2020
Current satellite and radar imagery shows isolated to scattered
convection over the eastern plains where better low level moisture
resides. MLCAPE is near 1000-2000 J/kg, but 0-6km bulk shear and
effective shear is rather weak (<25 knots) so looks like we`ll
just see a couple pulse strong/low end severe storms.
Smoke due to the existing wildfires continues to plague the area.
The highest concentration per the HRRR shifts the bulk of the
smoke across the mountains and high valleys tonight as the mid
level flow shifts southeasterly. That should help some of the I-25
Corridor, but hard to say how much of this smoke can scour/mix
out this afternoon and evening before inversions settle back in.
High mountain valleys will likely see the worst of it through
Monday morning.
Monday will feature a continuation of above normal temperatures
and mainly dry conditions. There is at least a little push of
moisture across the mountains and high valleys with the southeast
mid level flow tonight, but most of that will mix out tomorrow.
That said, we see a narrow corridor of isolated to scattered
showers and thunderstorms developing from Park County across the
Front Range mountains and foothills. An isolated storm or two
could drift off the Palmer Divide or Cheyenne Ridge late in the
day, but overall most convection will be tied to the higher
terrain.
.LONG TERM...(Monday night through Sunday)
Issued at 335 PM MDT Sun Aug 16 2020
It looks like a long week ahead for those who are involved in the
wildfire suppression industry. The medium and long range models
show no appreciable change in the upper air pattern over the
western United States through next Monday. The strong upper level
ridge centered over Utah today is forecast to be in the same
position come next Monday morning. This will hold the very warm
airmass in place over the state, generating afternoon high
temperatures well above normal through the week. On the plains,
this means more 90 degree readings each day.
The one thing that will be subtly changing through the week is
the amount of moisture rotating under the ridge. The GFS and ECMWF
hint at some afternoon shower development over the mountains each
afternoon of the forecast period. This will depend on how much
moisture is able to either move anti-cyclonically over the ridge
and move in from the north, or come into eastern Colorado from the
southern plains. There has been some thunderstorm activity over
the far eastern Colorado plains over the last couple days, so it
is possible that some of this moisture could make it back to
central Colorado by Tuesday afternoon. In either case, the chance
of thunderstorms over the mountains comes back into the forecast
Monday afternoon and continues through the week. These storms will
be more likely to be high-based with gusty winds and dry
lightning than producers of wetting rains. This will produce the
less than desirable situation where additional fire starts are
going to be possible, because the last few days have shown how dry
and ready to burn the mountain fuels are. On the plus side,
pressure gradients across the state will not be that strong, so
winds should generally be light to moderate, following diurnal
upslope and downslope patterns. The generally dry and stable
airmass should also allow for favorable flying conditions,
allowing air support to fire operations to continue.
&&
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 934 PM MDT Sun Aug 16 2020
VFR through Monday. There will be some smoke in the Denver area,
and especially over the mountains. There should be less over
Denver on Monday, but it could impact slant visibility over the
mountains. There`s some uncertainty about whether winds will
rotate through northwest Monday morning or just go light and then
pick up from the east or northeast around midday. Speeds should be
under 8 knots either way.
&&
.FIRE WEATHER...
Issued at 335 PM MDT Sun Aug 16 2020
Only moderate humidity recovery is expected in the existing
high country fires tonight. Fortunately winds will remain light.
The lighter winds will prevail through Monday with an upper level
ridge dominating our weather pattern. However, above normal
temperatures and extremely dry fuel conditions remain. There is
just a slight increase in humidity levels, but even then minimum
RH drops to 10-15% over most areas west of the Front Range. The
eastern slopes and plains will see a little higher humidity
readings closer to 14-22% for mins.
The next potential problem we`ll start to deal with as early as
tomorrow will be dry lightning. There is just enough moisture to
produce isolated storm coverage, but only light if any rainfall.
Most of these storms will be along the spine of the Front Range
and points east into the foothills, as it`s simply too dry
farther west to support convection.
Tuesday will continue with elevated fire danger and still very
low humidities expected in the afternoon with just a slight chance
for a late day shower or storm. Moisture levels will increase
during the week with a better chance for showers and
thunderstorms. But low level humidity levels will still drop in
the afternoons, and overnight recoveries will be modest. Any
thunderstorm activity will probably not be able to generate
appreciable amounts of precipitation, so the threat of dry
thunderstorm activity and additional fire starts will continue
much of the week.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Gimmestad
SHORT TERM...Barjenbruch
LONG TERM...Dankers
AVIATION...Gimmestad
FIRE WEATHER...Barjenbruch
Area Forecast Discussion
National Weather Service Des Moines IA
655 PM CDT Sun Aug 16 2020
...Updated Aviation Discussion...
.SHORT TERM.../Tonight through Monday Night/
Issued at 236 PM CDT Sun Aug 16 2020
Confidence: Medium to High
Currently have a thin band of showers and perhaps iso thunder over
the northeast/northwest areas of Iowa. Just southwest of there,
the HRRR is focusing more initiation over northeast Nebraska by 20
to 21z. This is expected to expand and drift south southeast into
the evening hours. We continue in a marginal risk over the far
northwest counties to about Denison with perhaps a small risk of a
wind gust this evening. The H850 trough and warm air advection
causing the convection will shift south of the region later this
evening while another weak "backdoor" boundary drops south
southwest into northeast Iowa and then heads south overnight. This
will result in cooler temperatures over the north/northeast while
the far south continues milder overnight. Lows tonight will drop
to the upper 50s to 60 north and in the lower to mid 60s in the
south. Some clouds will linger into early Monday morning before
high pressure over Minnesota drops south into southern Minnesota
by 00z Tuesday. With cooling trends aloft across the north, H850
temps will fall to around 11-12C over the northeast to the mid
teens southwest with some stratocumulus behind the boundary. Highs
Monday will be about 5 degrees cooler than today with the clouds
and southward advection of cooler air.
.LONG TERM.../Tuesday through Sunday/
Issued at 236 PM CDT Sun Aug 16 2020
Confidence: Medium
From Tuesday onward, a similar patter will repeat. High pressure
will pass south of the area with return flow and warm air
advection Tues night and Wednesday. With west southwest flow
beginning to persist for much of the week, temps will be on the
increase to seasonal or slightly above normal for Wednesday
through Friday with highs in the lower 80s north to the mid to
upper 80s south. Lows will generally be in the 50s to 60s. Toward
Friday into Saturday a stronger short wave will drop south across
the region and pull a cold front into Iowa. Ahead of this more
organized system, the chances for stronger storms will increase by
Friday into Saturday. There remains some uncertainty on timing
with the GFS about 12 to 18 hours faster than the Euro, though the
shear instability parameter space for both models suggests some
potential of severe weather. With the slower Euro solution, warmer
temperatures are likely to hold on longer into the weekend.
&&
.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 652 PM CDT Sun Aug 16 2020
VFR conditions to prevail throughout the TAF period. Might see a
stray storm at FOD and DSM this evening, but left out mention
attm as currently radar trends and latest hires model runs keep
anything that develops west.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...REV
LONG TERM...REV
AVIATION...Podrazik
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1150 PM EDT Sun Aug 16 2020
.AVIATION...
Prevailing VFR conditions throughout the taf period. Pocket of mid
level moisture will lift across central lower MI this morning,
leading to some increase in higher based cloud cover accompanied by
perhaps a few showers...mainly at MBS/FNT. A steady increase in high
based diurnal cu then expected throughout Monday under standard
diurnal destabilization. Sufficient instability will exist to support
a few widely scattered showers and thunderstorms mid afternoon
through early evening. The limited coverage precludes a defined
mention at this stage.
For DTW...Isolated thunderstorms possible Monday afternoon /18z-
22z/.
.DTW THRESHOLD PROBABILITIES...
* Low for cigs briefly at or below 5000 ft late morning/early
afternoon Monday.
* Low for thunderstorms impacting the terminal Monday afternoon.
&&
.PREV DISCUSSION...
Issued at 311 PM EDT Sun Aug 16 2020
DISCUSSION...
The mid level wave responsible for this mornings convection will
depart east of the forecast area over the next couple of hours. This
will allow for the mid level subsidence bubble in its wake (now
affecting most of central and western Lower Mi) to expand across the
rest of Se Mi by early evening, ending the risk of additional
showers. A seasonally strong upper jet max (100-110 knots) will dive
down into the wrn Great Lakes by Mon morning, within the base of the
amplifying long wave trough over nrn Ontario. There is some degree
of support from the NAM and HRRR in showing a region of mid level
moisture pushing into Se Mi late tonight/early Mon morning within
the lead edge of this upper jet max. Mid level lapse rates within
the moist plume suggest some isolated high based showers are
possible late.
Mid level height falls will overspread much of Se Mi and Lake Huron
on Monday as the upper trough continues to amplify as it dives
toward the ern Great Lakes. This will also force another surface
cold front into Se Mi. Although limited, model soundings suggest
there will be enough moisture for diurnal heating to initiate some
convection, isolated to scattered at best. While most of this should
be shallow, model soundings indicate at least some opportunity for
deep convection late Mon afternoon, especially given steepening 850
to 500mb lapse rates. Diurnal mixing will be supportive of highs in
the upper 70s to low 80s Monday.
The passage of the cold front will drive even cooler air into Se Mi,
with 850mb temps now forecast to drop to +8 to +9 C over Se Mi by
Tuesday morning. Mid level confluence will take hold across the
Great Lakes on Tuesday as the upper trough rotates across ern
Canada. This will support an expansive region of high pressure
building into the area from the west Tues and Tues night. Some
moisture flux off Lake Huron on Tues will support a fair amount of
diurnal cu. This and the cool airmass overhead will suppress daytime
highs to the 70s. Recent trends in the medium range model suite
maintain some degree of sfc high pressure/low level anticyclonic
flow across the southern lakes through the end of the week,
supporting a dry forecast. A gradual rebound in the heights and
return flow around the sfc high will lead to a modest warming trend
Thurs into the beginning of the weekend.
MARINE...
The cold front responsible for morning showers and storms has nearly
exited into Canada. Expect the front to fully clear by 20Z as the
final clusters of showers drift east over far southern Lake Huron
and western Lake Erie. Conditions are becoming unfavorable for
waterspout development, and winds will diminish to around 10 knots
overnight with the exception being northern Lake Huron. Daytime
showers and thunderstorms are possible with a secondary cold front
on Monday, although coverage will be sparse. Increased wave action
arrives Monday night given a more constricted surface gradient. A
Small Craft Advisory will probably be needed as max wave heights
exceed 5 feet from Port Austin to Port Sanilac catching the stronger
NW fetch with shore-parallel flow. Winds begin to weaken mid-morning
on Tuesday with mainly dry conditions expected through Thursday as
Corn Belt high pressure expands into the central Great Lakes. Model
consensus regarding the development of a low pressure system through
The Straits on Wednesday remains low.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
AVIATION.....MR
DISCUSSION...SC
MARINE.......KK
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
631 PM CDT Sun Aug 16 2020
...AVIATION UPDATE...
.SHORT TERM...(This evening through Monday)
Issued at 237 PM CDT Sun Aug 16 2020
Another frustrating and humbling 24 hrs ahead, with more finicky
storm chances and poor model performance.
The set up...
There is a minor midlevel short wave with an associated sfc cold
front draped across our north. Currently we are looking at a very
similar set up to Friday. Convection has already started to fire up
along the front to our west and to our northeast. This is a bit
concerning already that we might see a split across our CWA where we
end up getting the shaft. Models certainly haven`t had a good handle
on this, and still don`t. The hi-res models and the GFS are rather
splotchy, and the 18Z HRRR does have it splitting around us. As far
as timing goes, best chances of seeing severe weather is between now
and 10pm. Tricky, trigger-happy events like this are to be expected
during the summer time under a northwest flow regime like this...but
that doesn`t make it any less frustrating to forecast.
Regarding severe potential...
There is a severe thunderstorm watch in effect from now through 9pm
tonight. With favorable sfc and midlevel lapse rates, roughly 3k-4k
J/kg of CAPE, and 30-40 kts of shear, at least several strong if not
a few severe thunderstorms are possible. SPC has most of the area in
a slight risk except for the far southeast since storms are expected
to weaken and die off more by the time the front gets there. Severe
threats are expected to be up to tennis ball size hail and damaging
wind gusts to around 70mph.
Now for the rest of the particulars for today and tomorrow...
I did bump highs up a bit today given our recent trend of being just
slightly under done the last several days...though I was a bit
hesitant to do so, given the storm potential. Also brought dewpoints
up by a few degrees as well. For lows tonight, I kept fairly close
to the previous forecast, if not slightly warmer due to the
potential for heat loss to be mitigated by any storm cloud cover.
Tomorrow begins the start of a much quieter period with more
northerly flow aloft and northerly flow at the sfc. Expecting
modestly warm highs generally in the 80s and touching 90 in just a
few spots.
.LONG TERM...(Monday night through Sunday)
Issued at 237 PM CDT Sun Aug 16 2020
Admittedly since most of the time was spent working on the short
term, not a lot of focus was placed on the longer term. So
keeping things fairly generalized...
We look to be getting into a blocking pattern aloft where we are
sandwiched between an amplified ridge over the western CONUS and
a modest trof over the eastern CONUS. This will keep us in a
northerly flow regime aloft, and will also keep most of the week
dry. The only precip chances over the remainder of the 7-day
period are on Tuesday night and Thursday night. Tuesday is likely
the result of another minor midlevel short wave, and the PoPs
right now are below "likely" and will probably stay that way, but
at least this has been consistently in the forecast over the last
few days. Wednesday and Thursday look like they could be the
warmest days of the week, though not by much, with highs right
around 90 across the board. Thursday looks like repeat of Tuesday,
again with PoPs below "likely".
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 629 PM CDT Sun Aug 16 2020
The main focus is obviously the ongoing storms across the area.
Main impacts we`re seeing right now are large hail, damaging wind
gusts, and heavy rain reducing visibilities to less than a mile.
Once this front finally makes it through things are expected to
clear up rapidly on the back side. This is clearly evident on
satellite currently where the front is rather obvious with clear
skies all across western and northern NE.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
SHORT TERM...Shawkey
LONG TERM...Shawkey
AVIATION...Shawkey
Area Forecast Discussion
National Weather Service Grand Junction CO
628 PM MDT Sun Aug 16 2020
.SHORT TERM...(Tonight through Monday night)
Issued at 250 PM MDT Sun Aug 16 2020
Another dry day across the Western Slope with precipitable water
values only running 43 percent of the climatological normal for
mid August. The persistent area of high pressure is currently
centered just to our west with moisture riding around the
periphery of the high evident on satellite this afternoon. This
includes the far Southwest San Juan Mountains with just enough
moisture brushing the area and producing weak returns on radar.
No evidence of any rainfall reaching the ground with this activity
so gusty outflow winds will remain the primary threat through the
evening hours before showers diminish around sunset. Elsewhere,
the two major wildfires burning in our forecast area...Pine Gulch
and Grizzly Creek...continue to run hot with 90 to 100 degrees C
fire temperature estimated by satellite. Smoke from these fires
has been and will continue to plague the surrounding lower valleys
with the latest HRRR Smoke extending the poor air quality further
towards southeast Utah and southwest Colorado. Visibilities will
likely be reduced overnight as the smoke becomes trapped
underneath the inversions. Enhanced drainage may briefly enhance
winds in the Grand Valley and Glenwood Canyon, but overall the
high pressure should keep winds on the light side.
The smoke has also kept high temperatures slightly cooler than
guidance and this trend will continue on Monday. Regardless,
temperatures are still running above normal with triple digit
heat possible across portions of east-central and southeast Utah
as well as west-central Colorado on Monday. Monday will also see
the high reposition slightly, allowing for a gradual increase in
moisture. This will be most evident across southwest Colorado with
PWATs increasing to around 0.60 to 0.70 inches Monday afternoon.
Isolated to scattered showers and storms will develop but again,
the dry low levels evident in Bufkit soundings will keep the
potential for wetting rains low. The northern tier of the forecast
area will see critically low humidities with dewpoints only
projected to climb into the mid 20s to low 30s. Smoke will again
be an issue as the upper level flow remains the same, particularly
into the overnight hours.
.LONG TERM...(Tuesday through Sunday)
Issued at 250 PM MDT Sun Aug 16 2020
Little significant change indicated in the pattern during the
extended period. The high will wobble from the southern Great
Basin to the Southwest then back late in the period. As aptly
pointed out in the previous discussion, mid-level heights reach
their peak on Tuesday and the highest temperatures during the
period are expected to be reached then. Temperature forecasts
present a challenge for areas where smoke is most dense as this
has limited highs for some areas over the past several days.
Regardless, afternoon temperatures will continue to run well
above normal, though overnight lows will continue to be relatively
cool.
In terms of sensible weather, moisture gradually works inward
over the area from the periphery of the high which leads to an
uptick in shower and thunderstorm coverage from Thursday through
Monday. This activity will incrementally increase moisture in the
sub-cloud layer leading to a better potential for wetting rains.
Meanwhile, a slow rise in dewpoint levels combined with rainfall
should begin to mellow fire behavior on the Pine Gulch and Grizzly
Creek fires.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 551 PM MDT Sun Aug 16 2020
MVFR visibility is possible over the next 24 hours as smoke from
the wildfires settle into the Eagle and Colorado River drainages.
A smoke layer will be around as well but for the most part skies
will be clear to mostly clear.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&
$$
SHORT TERM...MMS
LONG TERM...NL
AVIATION...TGJT
Area Forecast Discussion
National Weather Service Green Bay WI
638 PM CDT Sun Aug 16 2020
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Monday
Issued at 237 PM CDT Sun Aug 16 2020
The latest RAP analysis and satellite/radar imagery show shortwave
energy moving across western Lake Superior early this afternoon.
Cumulus started to pop in the 10-11 am hour over the Upper
Peninsula and northern WI, and mesoanalysis shows that temps are
closing in on their convective temps over much of the area.
Surface-based instability is rising above 1000 j/kg over northern
WI where the high resolution models are indicating scattered
showers and storms developing during the rest of the afternoon.
With that sort of instability, dry mid-level air, and inverted V
soundings in the low layers, could see any storms have the ability
to produce brief strong, gusty winds. Will leave a mention in the
HWO. The area most likely to be impacted remains far northeast WI
into the northern Fox Valley and Lakeshore areas. Besides the
thunderstorm potential this afternoon, forecast concerns mainly
revolve around temps and fog potential.
Tonight...A few showers and storms will be ongoing over northeast
Wisconsin early in the evening. Intensity will relatively quickly
wane as diurnal instability is lost. Skies should then clear at
most locations thereafter. The exception will be over central WI
where some high res models show a few showers approaching central
WI after midnight in the left front quad of a jet streak. Not
confident in the details so will keep the area dry. Otherwise, the
jet energy may bring in some clouds at times, but that shouldn`t
have much of an impact on temps, which are projected to fall below
the cross-over temp at many locations across north- central and
central WI. So will add a patchy fog mention late tonight. Lows
ranging through the 50s.
Monday...High pressure will be gradually building towards the
region from the northern Plains. The atmosphere will be more
stable tomorrow, partly because of cooler low level temperatures.
As a result, should see some convective clouds build with heat of
the day, but precip chances are too low to mention. Highs ranging
from the lower to upper 70s.
.LONG TERM...Monday Night Through Sunday
Issued at 237 PM CDT Sun Aug 16 2020
Monday night into Tuesday night: A surface ridge is expected to
linger/becoming reinforced across the area through much of Tuesday,
allowing for lighter winds and mainly dry conditions. Tuesday night,
a nearly east-west oriented cold front is expected to slowly sag
south toward the northern part of the area. The main impact for
Tuesday night will be increasing cloud cover. Aloft, northwest flow
will linger across the area, allowing for somewhat cooler
conditions. High temperature will be in the mid to upper 70s for
most locations, with a few 80 degree readings south. Overnight lows
will drop into the 40s to around 50.
Wednesday through Wednesday night: The aforementioned cold front is
expected to sag southward into much of northeast Wisconsin late
Wednesday afternoon into Wednesday night. This reflects a much
slower progression than earlier model run had indicated. This front
is currently progged to drop slowly south through all of northeast
Wisconsin before departing to the south by late Wednesday night. The
front doesn`t have a lot of moisture to work with as the Gulf is
continuing to be cut off through much of the first part of the week.
The main area of moisture associated with this feature will drift
into the area from the northwest, across central Canada. With that
in mind, models are showing enough forcing and instability along the
front to touch of some showers and thunderstorms through this time
period. Only minor rainfall accumulations are being painted out by
the models as has been the trend over the past couple days. Lows are
expected to be in the 50s with highs warming into the 70s to around
80. Of course, temperatures could be held back a bit if cloud cover
is extensive during the day.
Thursday into Thursday night: Much of northeast WI is expected to be
between systems during this time period, which may give a brief
break in the precipitation. This is not a definite as the northwest
flow and afternoon heating may destabilize enough to allow for
afternoon shower and thunderstorm development. Cloud cover will
increase during the afternoon as well. Temperatures are expected to
moderate to some extent as the flow deamplifies very slightly. Will
still be in northwest flow, but not quite as aggressive. as the
upper-level flow flattens across the area. Lows will be mainly in
the 50s with highs warming into the upper 70s to low 80s.
Rest of the extended: Moisture is expected to increase across the
area toward the end of the week into the weekend, allowing for
increased chances for showers and thunderstorms. The upper-level
pattern may begin to amplify once again during this time period with
a stubborn ridge parked across much of the western CONUS. This would
allow several disturbances to pass through the area, allowing for a
bit more unsettled weather pattern for next weekend. The unsettled
weather along with the potentially amplified northwest flow will act
to keep temps a bit cooler as well. At this point, temperatures
would be near to slightly below normal. No major changes were made
from the model consensus.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 637 PM CDT Sun Aug 16 2020
Once the scattered showers and isolated thunderstorms
dissipate/clear the area this evening, generally good flying
conditions are expected for the rest of the TAF period. Diurnal
convective clouds will develop again tomorrow, but bases should be
VFR.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM.....MPC
LONG TERM......Cooley
AVIATION.......Skowronski
Area Forecast Discussion
National Weather Service Grand Rapids MI
1005 PM EDT Sun Aug 16 2020
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 308 PM EDT Sun Aug 16 2020
- Quiet weather next several days
&&
.UPDATE...
Issued at 1005 PM EDT Sun Aug 16 2020
The convective shortwave that helped to cause the thunderstorms
over WI has moved over northern Lake Michigan as of 945 pm. The
RAP model shows a small area of upper divergence and surface
convergence that is supporting this convection. The SPC SREF 3hr
calibrated thunderstorm forecast is tracking this area well. It
does show it weakening and moving onshore near Hart.
What concerns me is we have a 100 knot polar jet core over NE WI
now that will be over Lake Michigan by 3 to 4 am. The RAP (and
other models) show very strong upper divergence developing over
east central Lake Michigan at that point. Also the MU cape on the
NAM, SREF, and RAP model jump to near 2500 j/kg near the lake
shore. While that is happening a sort of meso-low seems to want to
develop near MKG. I have to wonder with all of that going on if we
would not get come convection developing. After all the south buoy
water temperature was 75 degrees an hour ago. The 5 pm run of the
RAP model sounding just off shore of Holland had only 35 CIN and
2400 surface based cape. There was some dry air near 500 mb but it
was mostly moist till 500 mb and than moist again to near 250 mb.
Since the latest hi- res models do not have much convection, I
have 20% pop near the lake shore during the early morning hours
just in case something does develop.
UPDATE Issued at 640 PM EDT Sun Aug 16 2020
I have updated our forecast (grids) to indicate showers are
possible near and west of US-31, north of South Haven from just
before midnight till just before sunrise. A thunderstorm would not
be out of the question. There currently is a shortwave touching
off some showers and thunderstorms over the Michigan Upper
Peninsula that is dropping southeast. Both the NAMNEST and RAP
model show 2000 to 2500 j/kg of MU cape from mid Lake Michigan to
the Lake shore from midnight till sunrise. The instability just
gets to US-31. Likely the warm lake and cold air at mid levels is
helping the cause for convective instability. The SPC SREF shows a
5 to 10 pct chance of thunderstorms over a same area at the times
I indicated above too. The HRRR, HRRR Experimental, HREF, RAP and
NAMNEst show convection associated with this making to the lake
shore after midnight tonight. I do no think this will be a big
deal but it is enough for a 20-30 pct pop near the lake shore
after midnight.
The bottom line is I have scattered showers near the Lake Michigan
shore overnight until around sunrise.
&&
.DISCUSSION...(This evening through next Sunday)
Issued at 308 PM EDT Sun Aug 16 2020
- Quiet weather next several days
No real impact weather to write about today as the front is
through and only a few chances for scattered showers exist next
week.
The first chance is tonight as shortwave trough axis digs into the
central Great Lakes and the large scale western CONUS ridge and
eastern CONUS trough pattern amplifies. Only light showers
expected across the northern zones.
Steepening lapse rates on Monday along with sufficient mid level
moisture will bring diurnal enhancement of cu and low chance of
showers away from Lake Michigan on Monday,
Another shortwave trough and surface cold front advances into Lower
Michigan on Wednesday with a low chance of showers. We expect most
places will remain dry this entire week and with the low humidity
and comfortable temperatures, it will be a perfect week for
outdoor activities.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 640 PM EDT Sun Aug 16 2020
I expect VFR conditions to rule our TAF sites for tonight through
Monday into Tuesday (and beyond). However there are 2 glitches.
The first glitch is a shortwave dropping southeast from western
Upper Michigan this evening. It may bring a few showers to the MKG
and GRR taf sites in the 06z to 09z time frame. I put VCSH to
cover this possibility. It would not be out of the question there
would even be an isolated thunderstorm but that chance is fairly
low.
The next glitch is the strongly digging northern stream jet core
is aimed at Southwest Michigan on Monday. There will be
instability inland Monday afternoon. So do expect scattered
showers and thunderstorms inland of US-131 Monday. I put VCSH for
our easter TAFS for that event.
Winds will be northwest around 10 knots Monday but should be
southwest around 5 knots toward midnight as the weak system moves
into the area.
&&
.MARINE...
Issued at 308 PM EDT Sun Aug 16 2020
We will watch for some wind gusts near 25 knots on Monday and
Monday evening otherwise winds and waves should be below advisory
criteria for small craft most of this week.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&
$$
UPDATE...WDM
SYNOPSIS...Ostuno
DISCUSSION...Ostuno
AVIATION...WDM
MARINE...Ostuno
Area Forecast Discussion
National Weather Service Marquette MI
754 PM EDT Sun Aug 16 2020
.SHORT TERM...(This evening through Monday)
Issued at 348 PM EDT SUN AUG 16 2020
Diurnal CU field across much of the UP developing this afternoon
with iso shra across much of the Upper Great Lakes region.
Temperatures have climbed comfortably into the 70s across the cwa as
developing lake breezes can be observed in GOES and sfc obs off
Superior and Michigan. These lake breeze convergent zones will serve
as the focus for anticipated convection heading into this evening.
CAMs downplayed the event a bit with this morning`s runs and the
HRRR continues to be less than amused at tsra chances. Capped
chances at 40% across the central and east this afternoon and
changed wx into coverage to mention iso to sct wording. Regardless,
will need to monitor the next few hours for convection interacting
with any lake breezes.
Tonight, a weak cold front is progged to pass over Upper Michigan.
Front should remain mostly dry, but some models have been hinting at
chances of light precip. Look for lows to fall into the 50s, with
some temps near 60 along Superior and into the 40s across the
interior.
Tomorrow, winds will gust into the teens from the north behind a
cold front passing late tonight. A few diurnal showers are possible,
but have left any PoP mentions out of the forecast for now. Look for
potentially hazardous beach conditions east of Marquette and highs
climbing to either side of 70...coolest west and warmest along Lake
Michigan.
.LONG TERM...(Monday night through Sunday)
Issued at 339 PM EDT SUN AUG 16 2020
Expect a generally seasonable stretch of weather for much of the
upcoming week. Overall upper pattern will be pretty amplified for
August standards with significant heat ridge centered over the
desert southwest. 50H height will exceed 600 dam into midweek with
ridge axis extending up into western Canada. Downstream upper
troughing will exist over eastern North America with northwesterly
upper flow prevailing across the Upper Great Lakes at least until
late in the work week.
Yesterday...it looked liked most of the week was going to be dry
with the best chance of rain not til Friday. Today`s model trends
are a little wetter but by no means a washout. Shortwave energy in
northwesterly flow will drop into the Upper Great Lakes on Tuesday
and Tuesday evening brings some scattered showers. Weak boundary
associated with that shortwave will then hang up over or just south
of the area through mid to late week acting as a focus for slight to
low chance diurnally driven shras and isolated tsra Wednesday and
Thursday.
By Friday...shortwave energy moving in off the Pacific will flatten
the northern extent of the western U.S. upper ridge. Friday into
Friday night still looks like the best chance for the most
widespread shra/tsra activity but if anything models are in less
agreement on how things will evolve Friday through next weekend.
Temperatures will be seasonable...generally in the 70s for highs
this week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 754 PM EDT SUN AUG 16 2020
VFR conditions are expected at KIWD/KCMX/KSAW thru this fcst period.
Cold front passing during the night will lead to gusty nw to n winds
to around 20kt at KCMX/KSAW on Mon.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 302 PM EDT SUN AUG 16 2020
A cold front is expected to pass over Lake Superior tonight as winds
become more northerly, gusting up to 25 knots across the east half
and 20 knots across the west through tomorrow. High pressure then
traverses over the lake through the rest of the week with lighter
winds blo 20 knots prevailing.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...JAW
LONG TERM...MZ
AVIATION...Rolfson
MARINE...JAW
...Updated Aviation Forecast Discussion...
.DISCUSSION...
Issued at 211 PM CDT Sun Aug 16 2020
Near term...
Scattered strong to severe storms are possible this
afternoon/evening along a weak cold front moving south through the
area late this afternoon into the evening evening. Some of these
will be capable of large hail/damaging wind.
Synopsis...
The region remains in persistent northwesterly flow aloft with a
strong ridge of high pressure to our west and persistent
troughing to our east. At the surface, high pressure remains
centered over central Missouri with southerly low-level return
flow extending across central/western KS and Neb. Within this low-
level return flow resides a moist airmass with 850mb dewpoints
near 14-15C in central Nebraska contributing to an increase in
instability to our west and more specifically, across
northeastern Nebraska nearest to the surface front where a narrow
axis of 65-70F surface dewpoints have pooled.
Tonight...
Model solutions continue to show scattered convection developing
near the frontal boundary by mid-afternoon and continuing south
through eastern Neb/southwestern Iowa in broken clusters along the
instability axis with RAP effective bulk shear values of 35-40kts.
Storms may be capable of producing large hail and damaging winds
but cannot rule out an brief isolated tornado. Convection should
be fairly progressive and south of the forecast area by 04-06z
tonight.
Monday and beyond...
Surface high pressure will build overhead Monday with highs forecast
in the mid to upper 80s. A weak disturbance moves overhead Tuesday
night when we have our next chance of light precipitation. A few
other subtle disturbances are forecast to move through northwesterly
flow aloft and could spark additional showers/thunderstorms later on
Thursday into Friday. Overall temperatures will be in the upper
80s with lows generally in the 60s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 631 PM CDT Sun Aug 16 2020
Scattered thunderstorms will continue for the first hour of the
TAF cycle, otherwise VFR conditions with light and variable winds
are expected through Monday.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&
$$
DISCUSSION...Kern
AVIATION...Kern