Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/21/17
Area Forecast Discussion
National Weather Service La Crosse WI
643 PM CDT Sun Aug 20 2017
.SHORT TERM...(This Evening through Monday Night
Issued at 315 PM CDT Sun Aug 20 2017
High Impact Weather Potential: Several rounds of showers and
thunderstorms are still expected to impact the area through Monday
night. Depending on how things unfold, there is a small risk for a
few strong to severe storms, perhaps late tonight but particularly
Monday evening south of Interstate 90. Heavy rainfall is also
possible pending evolution of storms, though the overall weather
pattern is rather progressive.
A rather quiet day out there weather-wise, with subsidence in the
wake of an earlier convective complex crossing Iowa holding things
in check. Earlier clouds have been replaced by some sunshine for
many areas, with dew points creeping upward through the 60s to
near 70 and resulting in increasing CAPE values toward 2k J/kg or
better. For the moment, however, there`s just not much of any
forcing to work on that instability, though a cold front is
working east out of central Minnesota. We`ll be watching that
boundary the next few hours with possible scattered convective
development, though help aloft is rather paltry as is both low
level and deep layer shear, with the better shear in the post-
frontal environment. Additionally, per RAP forecast soundings,
things look increasingly capped given a lack of better boundary
layer moisture, so we ultimately may not see much of anything
through this evening.
The setup changes to a more favorable one overnight as that frontal
boundary washes out while a redeveloping warm front sets up across
central Iowa. Per multi-model consensus, looking like a pretty good
shot of low/mid level moisture transport will impinge upon that
boundary later tonight, suggesting convection should blossom east
out of northwest Iowa with time. Confidence in just how far north
coverage will reach isn`t the highest but the greater risk will
be south of I-90 closer to the nose of best low level jet
convergence. Uptick in effective shear toward 30 knots may allow
some degree of storm organization, with maybe a risk for some
damaging winds and maybe hail over mainly Iowa given pretty decent
elevated mixed layer overspreading the area. With that said, will
really have to watch trends into the evening as persistent
convection into northern MO might be hinting that our forcing
boundary will end up farther south.
We may then take a break for much of Monday in the wake of any
morning convection as another push of subsidence works into the
area, particularly if overnight storms get a little better
organized. With that said, will have to closely watch the warm front
and where it ends up, as some convection could bubble along that
boundary through the day. Gut feeling based on the pattern is that
the front will get shunted southward into central or even southern
Iowa, so we may well end up dry with potentially some breaks in the
cloud cover for eclipse viewing time.
Another ramp-up of better moisture transport through the late
afternoon and overnight hours should deliver a second bout of
showers and storms for much of the area, helped by the passage of a
better shortwave. Slightly better shear profiles could support a
severe threat for a few hours Monday evening, particularly south of
I-90 once again. Also, the setup remains conducive for some brief
heavy rains with any of this convection the next 36 hours with PWAT
values pushing 2 inches and deep warm cloud depths, though the
progressive nature of any storms should (in theory at least) keep
things in check from a flooding perspective. Additionally, guidance
continues to trend faster and faster with the exit of convection by
Monday night, as high pressure and much drier air make a very quick
approach before sunrise Tuesday.
.LONG TERM...(Tuesday through Sunday)
Issued at 315 PM CDT Sun Aug 20 2017
A return to some great late summer weather remains on track
Tuesday into at least Thursday as broad Canadian high pressure
works through the region, in concert with upper troughing. Looking
like another stretch of below normal temps along with dew points
mixing through the 40s and low 50s, and some morning lows likely
to push 40 degrees (if not a touch colder) for some of the
traditional colder locales and lots of upper 40s-lower 50s
elsewhere. Not bad at all for late August!
Thereafter, strengthening return flow into Friday and the weekend
suggests we will eventually pick up additional precipitation
chances, perhaps initially on Friday with the onset of better
thermal and moisture advection, and then toward later Saturday or
Sunday with hints of a stronger upper trough and cold front crossing
the area. Of course, exact timing remains to be seen, but the
overall trend of near to continued below normal temperatures looks
to stick through the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 643 PM CDT Sun Aug 20 2017
A cold front extends from northern WI through southern MN as of
20.23Z. Will be watching an area of weak convection along this
front for possible strengthening as it drops southeastward this
evening. KRST/KLSE could be impacted, but confidence in timing and
more so convective coverage/additional development is low, precluding
mention in the 00Z TAFs. Better chances for more widespread showers
and storms exists overnight and will keep previous forecast
timing for VCTS. Additional convective activity is possible late
in the period, but will focus on the first 12 hours for now.
Barring heavier showers/storms, ceilings should remain above 3000
ft agl through the period with no restrictions to visibility.
Winds will be light and if not variable, favor a southerly
direction at KLSE and a northwesterly direction at KRST through
tonight, then shifting back to the south tomorrow.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...Rogers
Area Forecast Discussion
National Weather Service Cleveland OH
916 PM EDT Sun Aug 20 2017
.SYNOPSIS...
High pressure over the region tonight will move east of the area on
Monday. Low pressure will move northeast across the Great Lakes
Tuesday, bringing a cold front across the region Tuesday night.
High pressure will build east across the region Wednesday
through the first half of the weekend.
&&
.NEAR TERM /THROUGH MONDAY NIGHT/...
Have been trying to keep up with the precip that has formed on
the nose of some warm air advection aloft. Storms remain
isolated to scattered in nature and should keep heading
northeast. Latest HRRR and RUC moves this activity out over the
warm waters of the lake and keeps it going thru 06z or so. Will
go with 20 or 30 pops where needed. Have increased sky cover
not only tonight but tomorrow. The new guidance is also showing
possible precip toward daybreak over the west end of the area.
Have gone ahead an added a mention to the forecast for the
entire day Monday. Other minor changes as well.
Previous...Lower confidence forecast tonight through Monday
night as several upstream MCS` will impact the weather across
the region. Return flow will continue to feed into the region as
high pressure is now centered east of the forecast area. Low
level moisture increase reflected in visible satellite picture
as expansive cu field blankets much of western Ohio this
afternoon. Some signs of isolated convection beginning on latest
radar scans, as 1000-2000 j/kg SBCAPE creeps up into the
southern part of the forecast area. Although forcing is minimal,
with upstream MCV approaching the area from the west, will opt
for a few hours of slight chance pops through the evening hours.
Will terminate pops around 03Z time frame, however some
guidance suggests convection may sustain a bit longer.
Nevertheless, any shower activity is expected to be very
isolated and concentrated from near Marion to Canton.
Forecast picture becomes a little more obscure late in the overnight
into Monday. Upstream MCV will cross IN and move into OH during the
overnight. Models are developing convection off of the trailing
flank of this MCV somewhere in northern IN. Currently forecasting
this activity to remain upstream, however cloud debris from this
convection could move into the area through the morning hours. The
debris clouds should diminish into the afternoon hours, with diurnal
cu developing across the area. Pops will slowly increase during the
afternoon on Monday, with slight chance pops for most locations.
Atmosphere will become very unstable, with models suggesting up to
2500-3000 j/kg by late afternoon. Forcing remains conditional,as
upstream MCS remnants may track towards the area during the
afternoon. If this comes to fruition, a low end severe risk is
possible, with low/mid level flow beginning to increase a bit, with
20-30 kts of low level shear. Most likely, if any convection forms
it would most likely be after 21Z, but it is still very low
confidence with uncertainty in the upstream evolution tonight/Monday
morning. No major changes to high temps tomorrow, with uncertainties
in cloud cover/precip.
Main cold front/upper trough will move toward the region Monday
night. Kept slight chance/low chance pops around through the night,
but the bulk of precip activity will remain west of the area until
12Z Tuesday.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Tuesday begins with models showing low pressure moving into
southeast Ontario from the central lakes. A trailing cold front
will extend southwest across the lakes to west of Chicago.
Moisture will be moving into the area from the southwest ahead
of this boundary and will continue with chance pops most places
through the morning and likely pops northwest. The front will
moves across the area through the afternoon and early evening
bringing showers and thunderstorms to most. Have boosted pops to
categorical for all areas through the afternoon with precip
ending from the northwest through the evening hours. Wednesday
begins dry however models show wrap around moisture dropping
across the area through the afternoon. With 850mb temps down
around +9C moving over the warm lake as well as general
instability provided by daytime heating below colder air aloft
will have 20% pops in place for the area and chance pops for
showers se of the lake. Will drop lake effect pops to 20%
Wednesday night and Thursday as high pressure builds in. Tuesday
temps near normal. Wednesday and Thursday will be below with
highs in the low to mid 70s.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
Little change in the extended with a large area of high pressure
remaining the dominate weather feature. By Wednesday evening large
area of Canadian high pressure centered over the Northern Lakes. The
high moves slowly across the lakes and moves off the New England
Coast late Sunday. Expect mostly sunny conditions, highs mainly in
the 70s and lows mainly in the 50s. Model timing on the next
system still a little in doubt. ECMWF brings the next wave of
convection Sunday night while the GFS holds off until Monday. For
now will just go low chance pops in the West Sunday night.
&&
.AVIATION /00Z Monday THROUGH Friday/...
Lot`s of mid and high level clouds floating across the area. As
predicted earlier by the guidance a few storms have popped up
over the southwest end of the area. These could impact FDY and
possibly MFD so will go with a brief mention those two sites.
The activity should diminish after the sun sets. More precip
could impact the area toward daybreak and again late tomorrow
afternoon. This activity depends on what happens upstream
overnight so confidence is low. Will go with a vicinity mention
tomorrow morning at FDY and TOL but will keep the afternoon dry
for now. There should be a lot of mid and high level clouds on
Monday. Light and variable flow is expected overnight. The
clouds should keep fog from becoming widespread but some patchy
MVFR fog is again possible. Southwest flow under 10 knots is
expected on Monday with onshore winds again developing at ERI.
OUTLOOK...Non-VFR likely in scattered showers/tstms on Tuesday
and Tuesday night.
&&
.MARINE...
Marine wx looks fairly tranquil tonight through dawn Tuesday
and again Thursday through Friday with high pressure affecting
the region. Monday night into Tuesday morning models show low
pressure moving through the central Great Lakes toward
southeastern Ontario. This will increase the pressure gradient
across Lake Erie causing southwest winds to increase to 15 to 25
knots Tuesday. The associated cold front will drop across the
lake Tuesday afternoon and evening turning winds northwest. Wind
speeds will drop a bit to 15 to 20 knots however northwest flow
will keep waves up on the lake. Wednesday high pressure will
build from the west slowly relaxing the gradient however waves
will remain up through much of the day before dropping off
Wednesday night. Expect a small craft advisory will be needed
from Tuesday morning into Wednesday night.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...None.
&&
$$
SYNOPSIS...Greenawalt
NEAR TERM...Greenawalt/Kubina
SHORT TERM...TK
LONG TERM...DJB
AVIATION...Kubina
MARINE...TK
Area Forecast Discussion
National Weather Service Cheyenne WY
532 PM MDT Sun Aug 20 2017
.SHORT TERM...(This evening through Tuesday Night)
Issued at 235 PM MDT Sun Aug 20 2017
A few showers/thunderstorms are expected to continue through early
this evening for the southeast Wyo mountains, and adjacent valleys
including Laramie. There is potential for some additional activity
to develop over the high plains after 00z as a shortwave begins to
traverse the northern Rockies. The HRRR suggests this, but GFS/NAM
both remain mostly dry tonight. We introduced low-end PoPs along/E
of I-25 given decent low-level moisture with dew points in the 50s
for these areas. Light, moist southeast flow will allow stratus to
develop over the NE Panhandle overnight, possibly encroaching into
east central WY in the Platte River Valley. Forecast soundings are
suggesting some potential for fog, especially via the NAM. 12z GFS
quite a bit drier though, so opted to leave this out of the latest
forecast and let the evening shift re-evaluate. Any fog or stratus
over southeast Wyoming should erode very quickly by 15z as a front
causes winds to shift to the northwest. The Panhandle sites should
take longer to clear out on Monday AM, so Wyoming is looking quite
good for the Great American Eclipse. Precipitation chances will be
low with most of the energy aloft going to the north & east. Upper
level ridging will build into the area on Tuesday, keeping chances
for precipitation low outside of the high country.
.LONG TERM...(Wednesday through Sunday)
Issued at 320 PM MDT Sun Aug 20 2017
Models in good agreement for late this week and into next weekend
showing a strong upper level ridge to the south of Wyoming
dominating the weather pattern. As is typical with late August,
the polar jet will become a little more active along the United
States/Canada border. Models indicate that each Pacific upper
level trough will remain well north of southeast Wyoming with the
bulk of the cool air. Some cooler air may move into the High
Plains this weekend as the upper level high builds further to the
west, allowing northerly flow aloft to increase as a cold front
moves southward across the plains. Expect daytime temperatures to
be near or slightly above normal through the end of the week, and
then it may cool off a bit by Sunday as that cold front moves
southward.
As for precipitation, Wednesday and Thursday look to be
the most favorable days to see at least scattered showers and
thunderstorms in the afternoon and evening hours. Models continue
to show a weak upper level low near the Calif coastline ejecting
northeast, which will help advect subtropical moisture northward
into Wyoming and Colorado midweek. Kept POP between 25 to 35
percent during this period across most of southeast Wyoming and
western Nebraska. Models indicate less instability for Friday and
Saturday, but still can not rule out a few showers and
thunderstorms mainly in the mountains and near the Black Hills
north of Lusk and Chadron Nebraska. Most locations will be dry so
kept POP between 10 to 20 percent into the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 529 PM MDT Sun Aug 20 2017
Main concern for this TAF period will be the potential for low
clouds and fog over the Nebraska plains late tonight. Latest hi-
res guidance indicated decent fog potential in light moist upslope
SE flow. For now, kept ceilings MVFR in stratus for KBFF and KAIA
while bringing IFR into KSNY between 08 and 10Z. Any fog and
stratus should begin to burn off after sunrise with VFR expected
by 15Z. Elsewhere, other than a few isolated evening showers over
SE WY, expect VFR to prevail for the TAF period with light winds.
&&
.FIRE WEATHER...
Issued at 235 PM MDT Sun Aug 20 2017
Fire weather concerns are expected to remain low over the next few
days with RH values generally above 15 percent and winds remaining
light.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...CLH
LONG TERM...TJT
AVIATION...DEL
FIRE WEATHER...CLH
Area Forecast Discussion
National Weather Service Des Moines IA
929 PM CDT Sun Aug 20 2017
...Update for Near Term Trends and Eclipse Sky Cover...
.UPDATE...
Issued at 929 PM CDT Sun Aug 20 2017
Currently monitoring trends over southern Minnesota and northeast
Nebraska this evening as short term models/CAMs show
thunderstorms developing in the next 2 to 3 hours. Already,
thunderstorms have developed along the surface boundary over
southeast Minnesota, which the CAMs are not showing presently.
While it may seem odd that we are looking at it, the Ash RGB,
which can help to differentiate low level water vapor, showed some
sort of low level moisture or boundary moving northward into the
front with convective initiation shortly thereafter. This area is
characterized by nearly 2500 J/kg of MLCAPE that is almost
uncapped, but shear is rather weak per SPC mesoanalysis. Farther
to the southwest over northeast Nebraska, there is a boundary
apparent in the GOES-16 low level water vapor imagery. In the Ash
RGB, there is a different boundary moving northward toward the
one identified in the low level water vapor and is just north of
a Yankton to Hawarden line at 222z. This will be an area along
with northeast Nebraska to monitor with the GOES-16 1-minute
mesoscale sector 1 over Iowa now through 12z for convection that
should move across Iowa tonight. Have updated PoPs through 12z
with a blend of current forecast, HRRR, and CONSShort to better
refine expected thunderstorm timing.
As for the eclipse, updated sky cover through 21z Monday with
probably a net zero change over the forecast area, but that
doesn`t mean no change. One concern is what happens with the
thunderstorms overnight and the clouds they may leave behind
tomorrow. Another is that GOES-16 mid level water vapor currently
shows a plume of moisture from central Mexico moving up into
Colorado and Kansas. This will move over Iowa tomorrow as shown
by the HRRR simulated IR, but these clouds may end up just being
higher level clouds. A blend of the Superblend/HRRR/CONSShort
provided generally 45-55% of clouds over southern Iowa, which is
a slight improvement with higher probability of clouds over
northern Iowa.
&&
.SHORT TERM.../Tonight through Monday/
Issued at 318 PM CDT Sun Aug 20 2017
Convective trends will highlight the concerns into Monday, but
confidence is not high. MCS remnants from overnight are still
festering from SW Iowa into MO and it continues to survive longer
than models have anticipated with most not handling current weather
well. The HRRR and ESRL HRRR seem to have the best current
projections, but even they are too aggressive pushing the cluster
off to the SE by 21z. Current RAP objective analysis continues to
show this MCS driven by H85/H7 frontogenesis and warm/theta-e
advection into 0-2km moisture convergence over NW Missouri so feel
this will continue to be a focus as the low level jet matures into
the night. The mean wind and Corfidi vectors suggest movement would
keep this out of our forecast area, or just brushing far SW
sections, with the NCAR ensembles providing a reasonable solution.
Although the MLCIN and convergence are currently unfavorable for
development anytime soon, most models suggest nocturnal development
will occur this evening somewhere over NW Iowa. Using the HRRR 305K
isent surface as a guide since it seems to have the best handle at
the moment would suggest this would occur in or near our far NW
corner as the current SD/MN mid clouds ooze into Iowa with timing
similar to last night, 02-03z. This area is also highlighted by a
GOES 16 elevated derived CAPE axis. The question will be whether
there will be enough separation between the two MCSs for them both
to have significant inflow, especially with what seems to be suspect
effective shear this far south and east. Have fairly good confidence
that this northern area will materialize to at least some degree so
have likely PoPs north later tonight as suggested by the CAM
consensus.
Looking ahead into tomorrow, most models suggest what MCSs are in
place would dissipate or exit into midday looking to re-charge into
the afternoon. It appears as though the surface based genesis area
would be similar to where the weak boundary is currently, over
northern Iowa. Instability looks to be high with at least moderate
deep shear, so a jump to severe in the 21-00z window as suggested by
most guidance and the Day 2 SPC outlook seems quite realistic. All
modes of severe weather look possible considering the degree of
instability, especially into and shortly after peak heating.
.LONG TERM.../Monday night through Sunday/
Issued at 318 PM CDT Sun Aug 20 2017
Bottom Line up Front...
Continuing severe weather threat greets us at 00z Tue, with
moderate to heavy rainfall threat overnight tomorrow night. The
rest of the long term looks to be dry, with slightly below normal
temperatures.
Tuesday...
00z Tue to 06z Tue will bring the most active weather in the long
term. Located somewhere across north-central Iowa will be a cold
front attendant to strengthening sfc low pushing across northern
Lake Michigan. Ahead of the front, in the WAA sector, LLJ
continuing to surge moisture as GFS and NAM continue to suggest
PWATs of 2 inches spread across Iowa into southern Wisconsin. All
modes of severe weather will remain on the table at 00z Tue. As is
climatologically favored, instability will begin to wane with
loss of daytime heating... so am expecting storms to undergo
transition from being svr wx producers to moderate/heavy rainfall
producers. Carrying over issues discussed in short-term, not great
agreement among model members at this time. Hopefully by next
update, when hi-res models dig in and system has shown its hand
more, can have some better consistency among solutions. At this
point, confidence there that somewhere may receive 1 to 2 inches
of rain between 00z and 12z Tue, but the location of the swath of
heaviest rain is difficult to get pinned down. Suggestion at this
time is towards eastern Iowa.
Behind this system, run-to-run consistency extremely strong in a
deep, broad area of high pressure that will push significant CAA,
subsidence, and dry air entrainment into Iowa...setting us up for
a sunny afternoon on Tuesday.
Wednesday and Beyond...
Strong high pressure to take control for the rest of this week.
By Wednesday afternoon, position of high should be somewhere near
northern Minnesota, and by Friday afternoon, high should be
somewhere near northern Michigan...returning a southerly (SE)
component to the low-level flow. As expected, trends continue to
be slightly stronger, cooler, and slower with the high, so have
slowed down temperature increases by next weekend, hedging closer
to persistence. Widespread area of 850mb temps -1 to -2 std dev
over the upper Midwest support forecast temperatures of around 5
or so degrees below normal.
&&
.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 646 PM CDT Sun Aug 20 2017
Primary concerns this TAF period will be thunderstorms that are
expected to form later this evening and overnight and additional
thunderstorms Monday.
For tonight, have upped from VCSH to VCTS for timing of
convection with slight changes in timing from 18z TAFs. Hard to
nail down exact impacts since storms are around at least 6 hours
away. Beyond the thunderstorms arriving tonight and dissipating
tomorrow morning, short range models show thunderstorms
developing later tomorrow afternoon. At this far our, did not have
the confidence to include any mention and will leave to future TAF
issuances.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Ansorge
SHORT TERM...Small
LONG TERM...Kotenberg
AVIATION...Ansorge
Area Forecast Discussion
National Weather Service Quad Cities IA IL
716 PM CDT Sun Aug 20 2017
.UPDATE...
Issued at 641 PM CDT Sun Aug 20 2017
Updated forecast to cut back on precip chances most areas until
late tonight. Next couple of hours still offer a small chance for
a shower in portions of the far eastern cwa with departing
convectively enhanced shortwave, and also in the far south with
elevated warm advection... but in both cases the lift is waning
so nothing more than just 20 pop or isolated coverage. Otherwise,
will have to await the development of convection to our west
late this evening into the overnight and potential upscale growth
as it tracks e/se.
With light winds, decreasing clouds and abundant low level
moisture we may be looking at fog developing and becoming more
prevalent into the overnight. If trends continue favorable
for fog development will need to add into the forecast with a
later update.
&&
.SYNOPSIS...
Issued at 312 PM CDT Sun Aug 20 2017
A band of shower continued to push northeast through the early
afternoon hours, and extended from far northeast Iowa into
northern Illinois. Strong thunderstorms persisted across areas
from southwest Iowa through northern Missouri. There were some
passing breaks in the cloud cover through early afternoon.
Temperatures varied widely, ranging from the low 70s to mid 80s.
&&
.SHORT TERM...(This Evening through Monday)
ISSUED AT 312 PM CDT Sun Aug 20 2017
The main forecast issues in the short term period are
timing/coverage/intensity of showers and storms.
In the near term, there have been some breaks in the cloud cover
south, with latest HRRR runs developing storms near and south of
the Quad Cities during the late afternoon/evening. Have bumped up
pops slightly across the southeast, but not optimistic that
instability will rebound enough to overcome the capping in place,
as a cirrus shield is already moving into those areas.
Looking ahead, the various CAMS have been fairly persistent in
tracking an MCS into the forecast area late tonight into tomorrow
morning. SPC has upgraded the far western counties to a slight
risk, which looks to be the favored area for more intense storms
toward daybreak before an expected weakening trend with eastward
progress Monday morning. The main threats will be damaging wind
gusts around 60 mph, and large hail. Flash flooding potential is
not looking as favorable overnight/Monday morning, with the system
expected to be progressive enough to preclude significant hydro
issues. Later Monday into Tuesday may be a different story with
the second round.
After the morning showers and storms, there will likely be a lull,
ahead of redevelopment in the late afternoon/early evening.
Eclipse viewing is not expected to be ideal with cloud coverage of
50 to 70 percent from late morning through early afternoon. Parts
of eastern Iowa would be favored for initial storm development
during the late afternoon, with a threat for large hail/damaging
winds. Higher coverage of storms is expected later Monday night.
.LONG TERM...(Monday Night through Sunday)
ISSUED AT 312 PM CDT Sun Aug 20 2017
Widespread thunderstorms expected Monday night then a dry and
pleasant stretch of weather the remainder of the work week.
Monday night and Tuesday: Widespread showers and thunderstorms can
be expected Monday night, then ending Tuesday morning as the strong
cold front exits to the southeast. Strong forcing will be arriving
Monday evening as a significant upper level trough/height falls
dives southeast into the Midwest/Great Lakes. A strong cold front
will also be approaching from the northwest, which will be
interacting with PWAT`s over 2 inches, and an unstable airmass with
SBCAPES of 3000-4000 j/kg ahead of the front. Deep layer shear
increases during the evening as westerly mid level winds increase to
45 knots. CAM`s models suggest this event to be mainly multicell
clusters/lines which would support damaging winds and large hail.
SPC has a slight risk of severe storms across much of the dvn cwa.
These storms will also produce torrential rainfall and 2-3 inches of
rain is possible especially where storms repeat over the same area.
I will continue to mention "heavy rainfall" in the grids for Monday
night.
Tuesday night through Friday: Northwest flow aloft will be locked in
place for the remainder of the work week. A sprawling Canadian high
pressure will set-up-shop across the Midwest/Great Lakes providing
clear skies and comfortable temperatures. Highs in the 70s and lows
in the 50s will be common, which is at least several degrees below
normal for late August. I would not be surprised if lows dip into
the 40s at some locations for a couple of nights.
Next weekend: Zonal flow returns with a small chance for showers or
storms especially in our northern counties. However, the models keep
the bulk of the rain to the west and north of the cwa. Temperatures
should rebound to near normal readings.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 641 PM CDT Sun Aug 20 2017
Initial concern will be with the potential for fog development
tonight. Satellite trends are supportive of decreasing clouds
rest of this evening. This along with light winds and abundant
moisture look favorable for at least patchy fog mainly after 06z.
If winds remain calm then could see more widespread areas of fog
as being suggested by some recent guidance. Given these trends I
have added fog mention (MVFR/IFR) at the terminals. There is a
low potential for LIFR/VLIFR at MLI and DBQ terminals near/north
of a frontal boundary.
Next concern is with timing/location of storms overnight into
Monday morning. Some of the latest hi-res models continue
to support increasing storm development/coverage late evening
into the overnight to our west tracking e/se with increasing
warm advection and lift ahead of an approaching shortwave.
Hi-res guidance is favoring Hwy30 to I-80 on south for greatest
coverage which seems reasonable based on location of 850 mb
thermal gradient and strongest warm/moist advection. As result,
have gone with prevailing shower mention with VCTS at all sites
except DBQ where have gone with just vcsh wording. Timing looks
to be generally aft 09z-10z through 16-17z. Expecting periods of
MVFR with pockets of IFR in the showers and storms.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
UPDATE...McClure
SYNOPSIS...RP Kinney
SHORT TERM...RP Kinney
LONG TERM...Haase
AVIATION...McClure
Area Forecast Discussion
National Weather Service Indianapolis IN
1144 PM EDT Sun Aug 20 2017
.UPDATE...
The AVIATION Section has been updated below.
&&
.SYNOPSIS...
Issued at 253 PM EDT Sun Aug 20 2017
A few upper waves will bring chances for thunderstorms tonight into
Monday, before a cold front brings better chances for rain Monday
night into Tuesday evening. Dry conditions will then prevail mid
week into next weekend. Hot and humid conditions to start the week
will give way to below normal temperatures mid week on.
&&
.NEAR TERM /Tonight/...
Issued at 932 PM EDT Sun Aug 20 2017
No significant changes made and will still carry chance pops
across north half of area overnight but with low confidence.
Early evening southern IL/IN thunderstorms have died. Scattered
showers NE IL/NW IN tied with upper shortwave over southern Lake
Michigan continue eastward track with no strength/coverage growth.
Operational HRRR has developed this shower and storm area over
multiple runs and carry the convection SE across central Indiana
overnight. Observed mesodata shows axis of decent CAPE pointing
towards this shower area while low level lapse rates remain fairly
steep and moisture convergence aligns with CAPE axis. Thus all
parameters point toward upscale growth potential. Problem has been
this was supposed to have started by 00Z and 01Z and upscale
growth has yet to occur.
So potential is there, models suggest it could occur, we have a
mention for storms in the forecast, so will keep it there, but
again not excited that it will come to fruition given the upper
support is starting to pull away and stabilization has begun.
&&
.SHORT TERM.../Monday through Wednesday/
Issued at 253 PM EDT Sun Aug 20 2017
Models are close enough that the model blend initialization
was accepted for most items.
There could be some lingering convection across the far north at the
start of the Monday period so will keep some slight chance PoPs
there early. After a brief lull, more scattered convection is
possible as yet another upper disturbance moves in. Looks like the
best forcing remains north, so will keep PoPs across the northwest
2/3 of the area or so and keep them in chance category or lower,
with the highest PoPs in the afternoon when instability is highest.
Next concern is then sky cover for the eclipse. Have real concerns
that mid and high clouds will impact the event and reduce the
chances of having a good view. Models have been trending up sky
cover at 18Z with each run. However, confidence is low in sky cover
for the eclipse window as timing of any convection and exact
location of thicker high clouds is hard to pinpoint. Will keep skies
partly cloudy (50-70% coverage of opaque clouds) for now.
A cold front will then approach the area Monday night and move
through Tuesday. Forcing will be decent with upper jet support and
decent 850mb flow. However, timing for convection isn`t that great
as front moves in when instability is lower due to time of day. Rain
could be in the weakening phase as it moves in Tuesday morning then
get stronger again south of the area when instability is maximized
later Tuesday afternoon. For now though timing looks good enough for
the threat of strong to severe storms across mainly the southern
half of the area Tuesday afternoon.
Still feel there will be enough rain around to measure at least 0.01
inch most areas so will keep the blend`s likely category PoPs
Tuesday.
Will keep some low PoPs Tuesday evening to account for any lingering
rain behind the front. High pressure will then build in and bring
dry conditions later Tuesday night through Wednesday.
Model blend temperatures look good. Heat indices could reach around
100 Monday afternoon if cloud cover is thin enough.
&&
.LONG TERM /Wednesday Night through Sunday/...
Issued at 201 PM EDT Sun Aug 20 2017
Splendid stretch of late summer weather for the extended period as
the Great Lakes and Ohio Valley reside under a broad upper trough
and strong high pressure at the surface for much of the period.
With dry low level flow from the north then east...expect days
full of plentiful sunshine and mainly clear nights with no
threats of rainfall. High temperatures will be pleasant...ranging
from the mid 70s to lower 80s Thursday through Saturday. Nights
will have a distinct autumn feel with temperatures dropping as low
as the lower and middle 50s.
Heights aloft will recover with the upper trough shifting off to
the east by Sunday. The region will remain under the influence of
a surface ridge...but low level flow will transition to southerly
on the back side of the high...resulting in temperatures warming
into the lower to possibly middle 80s on Sunday. Not entirely out
of the question that a potential for isolated convection would be
present by late weekend with moisture being advected north into
the Ohio Valley...but chances too remote at this point for
inclusion into the forecast.
&&
.AVIATION /Discussion for 210600z TAFs/...
Issued at 1143 PM EDT Sun Aug 20 2017
Brief visibility restrictions possible in thunderstorms predawn
hours...otherwise VFR conditions expected. Winds will be below 10
knots through the period and mainly from the south or southwest.
Scattered thunderstorms over eastern Illinois will track east into
the north half of Indiana through predawn hours. These may briefly
drop visibility into IFR range if in the core of a storm
otherwise expect VFR conditions to prevail. More storms may be
possible during peak heating Monday afternoon as weak trough which
is expected to develop convection west of the Mississippi river
early this morning will be moving across central Indiana. Presence
of the upper wave nearby and sufficient moisture at low levels
will be enough to generate some cumulus by late morning. One
negating factor in cumulus development may be abundant cirrus
debris from Iowa early morning convection which would then delay
cumulus development here until early afternoon Monday.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...50
NEAR TERM...Tucek
SHORT TERM...50
LONG TERM....Ryan
AVIATION...Tucek
Area Forecast Discussion
National Weather Service Northern Indiana
828 PM EDT Sun Aug 20 2017
.SYNOPSIS...
Issued at 216 PM EDT Sun Aug 20 2017
A more humid airmass will continue to build into the area tonight
and Monday with a low chance for showers and thunderstorms. Lows
tonight will drop to near 70 degrees, with highs on Monday into
the 80s. A strong cold front will drop through later Monday night
into Tuesday with showers and thunderstorms likely. Drier and
cooler air will then filter in behind this system midweek through
next weekend.
&&
.UPDATE...
Issued at 804 PM EDT Sun Aug 20 2017
Convectively enhanced vort max across northern Illinois will
continue to push eastward across northern Indiana overnight into
early Tuesday morning. A wing of more pronounced low level
theta-e advection has resulted in a few isolated showers/storms
across far southeast portions of the forecast area over the past
few hours, in more favorable proximity to steeper mid level lapse
rates. Broad area of stronger low level theta-e advection across
central Indiana will lift northward late evening/overnight as low
level flow becomes augmented by approaching MCV. Isolated storms
have been developing along this theta-e gradient/weak warm front
to the south/southwest of the local area this evening. Still
cannot completely rule out a few stronger storms late
evening/early overnight across especially west/southwest portions
of the forecast area where MUCAPEs are maximized. Latest HRRR
trends of more of focus on southwest portions of forecast area may
carry some validity given richer low level low level theta-e
air/maximized elevated CAPE overnight. May tweak PoPs slightly to
reflect this trend, but previous forecast of low-mid chance still
seems reasonable.
&&
.SHORT TERM...(This Evening through Monday)
Issued at 216 PM EDT Sun Aug 20 2017
Zonal flow will continue across the northern tier of the US tonight
into Monday with uptick in low level southwest flow supporting
increasingly humid/warm conditions. This northeastward influx of
moisture/instability in tandem with a series of low
amplitude/convectively aided shortwaves to track east on southern
fringe of westerlies will also bring chances for showers/storms back
into the forecast tonight/Monday, mainly west of I-69. The first
feature to watch is a dying MCV now near the IL/IA border. The
leftover perturbation will translate east through the lower Lakes
tonight. Downstream theta-e advection near a diffuse warm front
lifting north from central IL/IN may be enough to generate a
period of showers/thunder late this evening into early Monday
morning. Opted to introduce PoPs as a result, though only in the
20-40 percent range given subtle timing difference in latest CAMS
solutions...with stronger LLJ focus also displaced well west of
the FA.
Attention tomorrow will turn to the next MCS to likely emerge back
into IA/srn MN later tonight. The expected orientation of the
instability gradient and propagation vectors hint at the possibility
of this system tracking east into the area by sometime in the
afternoon with renewed storm chances. Model guidance is on board
with moderate surface based destablization in advance of this
feature as temps warm into the 80s, with little CIN and sfc
dewpoints near 70F. Deep layer shear not looking all that impressive
but could see some enhanced flow if a more pronounced MCV develops
and holds together east. The chances of this occuring are somewhat
low however as convective complex likely outruns better low level
inflow and weakens with eastward progression. Held onto chance
PoPs regardless as any outflow could generate afternoon convection
given ample instability. If this line/MCS is more organized a
wind threat could materialize. Mainly dry/humid with highs in the
mid/upper 80s otherwise on Monday.
&&
.LONG TERM...(Monday Night through Sunday)
Issued at 216 PM EDT Sun Aug 20 2017
The best opportunity for rain/storms still appears to be later
Monday night into Tuesday morning as an upper trough amplifies
southeast toward the Great Lakes and ingests monsoonal moisture
from the Four Corners. An associated pre-frontal sfc trough and a
series of low amplitude waves will provide the focus as large
scale ascent/height falls overspread during this time.
Precipitable water values pushing 2 inches and a deep warm cloud
layer hints at the potential for some locally heavy rainfall. The
severe threat looks relatively low by this time however given the
poor diurnal timing.
Renewed convection by peak heating Tuesday afternoon will likely
latch onto this pre-frontal trough/composite outflow toward the Ohio
River Valley. This should limit the coverage/intensity of convection
along the main cold front progged to drop through the local area
from nw to se Tuesday afternoon/evening.
Much drier/cooler air will filter in for the middle of the week
behind this system on the leading edge of an expansive high pressure
system. This feature will settle overhead by the end of the week and
next weekend with temps gradually modifying.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
Issued at 804 PM EDT Sun Aug 20 2017
Weak low level warm front and MCV combination should lead to
isolated scattered shower/storm development late this evening into
the overnight hours. Confidence in thunderstorms affecting
terminals is on the low side however given late timing of approach
of MCV and greatest elevated instability west/southwest of
terminals. Low level flow will strengthen late evening/overnight
and given some northward retreat of low level theta-e boundary
with warm front, scattered showers are a possibility in the 06Z-
12Z timeframe. Some lull in precip chances expected Monday
morning as the old MCV tracks east of the area, but will need to
watch potential of upstream Corn Belt convection to possibly begin
to affect northern Indiana Monday afternoon. With a good deal of
uncertainty for Monday afternoon, will keep TAFS dry at this time.
Otherwise, increasing low level moisture and light near sfc flow
may promote some patchy fog formation late tonight/early Monday,
but will keep conditions VFR at this time.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
UPDATE...Marsili
SYNOPSIS...Steinwedel
SHORT TERM...Steinwedel
LONG TERM...Steinwedel
AVIATION...Marsili
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Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
817 PM CDT Sun Aug 20 2017
.SHORT TERM...(This evening through Monday)
Issued at 312 PM CDT Sun Aug 20 2017
Uncertainties are abound in this forecast, with how far north we
will see convection tonight along with coverage of any storms Monday
afternoon. Then you throw in the eclipse and the added pressure on
getting a good handle on sky cover (which we don`t) and you get a
forecast where there isn`t as much confidence in as one one like
over the first 24 hours.
Frontal boundary at 3pm stretched from near Fairmont, MN to the Rice
Lake, WI area. Temps are in the low-mid 80s with dewpoints around 70
ahead of the boundary. This is resulting in a rather unstable
environment, with the SPC meso analysis showing around 3k j/kg of
sbCAPE along the boundary. But the 12z MPX soundings shows why we
just have not been able to sustain any surface based convection
today and its is the relatively stable layer of air between h85 and
h7. Convective trigger temp on the MPX sounding was 88 and we are
just not going to quite get there. Still, given the degree of
instability, can not rule out something like what the 12z NSSLwrf
and HRRR show happening around 00z, with a line of storms developing
along the front out toward Rochester over toward EAU, so have pops
for this evening limited to this area.
For tonight, there will be a focus for convection to the northeast
of the surface low developing along the Neb/KS border. Lots of
spread with where storms develop tonight as there are a couple of
regions of focused moist ascent. One along the 85-h7 theta=e
gradient from about Redwood Falls to the Twin Cities, and to the
north of the surface warm front, which will be down in IA. Favor the
idea of convection north of the warm front being the main show
tonight, with an MCS tracking across IA. This should really limit
the amount of moisture return we see into MN, so not really buying
into the convection the HRRR shows for south central MN, with the
HopWRFs and NMM/ARW looking a bit more realistic.
What happens with this convection will be key to what we see for
potential storms and severe weather Monday. The front working across
the area now will be stalling out from south central MN up into
central WI. We`ll likely again see dewpoints pool up to around 70,
with continued steep mid level lapse rates, so we will again see a
large degree of instability. Forcing looks a bit better Monday, with
the upper jet strengthening to our north, with right entrance region
setting up over southern MN. In addition, we`ll have a strong trough
dropping down from Canada, with mid-level flow picking up in
response. Favored pops tomorrow along where the NAM and GFS show the
CAPE gradient setting up, which is from about St. James, MN to
Ladysmith, WI. If we get storms to go, CAPE/shear parameters
certainly pose a severe threat and agree with the northward shift to
severe probabilities made to the updated Day2 convective outlook.
For clouds and the eclipse, with incoming trough and jet, along with
potential for overnight convection nearby, think it is fair to say
that we will be hoping from some breaks in the cloud cover as
opposed to worrying about the passing of the occasional cloud.
.LONG TERM...(Monday night through Sunday)
Issued at 300 PM CDT Sun Aug 20 2017
Showers and thunderstorms may be ongoing near the front across
southern MN into western WI at the beginning of the long term
period early Monday evening. The strong/severe threat will likely have
shifted southeast already with an abundance of development ahead
of the front. Any lingering activity will be pushed well to the
southeast by the early overnight hours as much drier air arrives.
A deep trough across the eastern U.S. and surface high pressure
over the Upper Midwest will bring another round of below normal
temperatures for much of the week. Highs in the upper 60s to mid
70s and lows in the 40s and 50s are expected.
The next system approaching from the west will spread warmer and
more humid air northward across the Plains late week, arriving
here next weekend. High chance PoPs continue for this feature due
to relatively good consistency between the models.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 802 PM CDT Sun Aug 20 2017
Main concern is for thunderstorms overnight. Think most of the
activity will be in Iowa, but did include a VCTS at MKT. Left
precip mention out of the remainder of the TAF sites. This
activity will be focused along a frontal boundary draped across
southern MN. Thinking highest chance for storms in southern MN is
from 08Z to 12Z. Otherwise a VFR forecast period. RAP does
indicate BKN040 across a portion of the area through much of the
day tomorrow. Winds will be northwesterly under 5 knots tonight,
becoming southeasterly tomorrow but remaining light.
KMSP...For now, not confident in storms nearing the metro
overnight to include a mention in the TAF. But will be evaluating
this potential closely ahead of the next issuance.
/OUTLOOK FOR KMSP/
TUE...VFR. Wind NW 10 kts.
WED...VFR. Wind N 5 kts.
THU...VFR. Wind SE 5 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&
$$
SHORT TERM...MPG
LONG TERM...BORGHOFF
AVIATION...SPD
Area Forecast Discussion
National Weather Service Pueblo CO
251 PM MDT Sun Aug 20 2017
.SHORT TERM...(This evening through Monday)
Issued at 236 PM MDT Sun Aug 20 2017
Showers and thunderstorms will be found mostly from around the I-25
corridor and westward this evening. However, the HRRR does show
some isold pcpn being possible over some of the southeast plains.
Most of the pcpn is expected to end by midnight, but as a weather
disturbance moves northeastward through NM tonight and into southern
CO Mon morning, there could be some additional showers moving into
southern CO late tonight and into Mon morning. Much of the pcpn
associated with the disturbance is expected to be near the southern
CO border, with the best chances probably acrs eastern Las Animas
and Baca counties.
Mon afternoon, showers and tstms are expected to develop over and
near the higher terrain, and along the I-25 corridor, while much of
the southeast plains is expected to be dry. Temps on Mon are
expected to be a little cooler than today.
There is a lot of cloud cover that is expected to continue working
its way northward over CO tonight and into early Mon. However, at
this time it appears that some drier air may work its way into
southern CO later in the morning to bring a decrease in the cloud
cover.
.LONG TERM...(Monday night through Sunday)
Issued at 236 PM MDT Sun Aug 20 2017
Not much change to the forecast thinking through the extended
period. Active weather looks likely through the middle part of the
work week before drying out towards the weekend.
Monday night...expect scattered showers and thunderstorms to be
ongoing across much of southern Colorado Monday evening, spreading
east across the Plains and dissipating late overnight. Models in
good agreement with a cold front dropping south behind an upper
disturbance late Monday night into Tuesday morning turning flow
northeasterly in the low levels.
Tuesday through Thursday...a weak upper level disturbance over
southern California will combine with high pressure over New
Mexico to force moisture and energy northward over Utah into
Colorado through the middle of the week. At the low levels, flow
looks northeasterly upslope on Tuesday, transitioning to
southeasterly upslope Wednesday and Thursday. The increased
moisture, disturbances aloft and upslope flow at the surface will
set the stage for potentially widespread showers and thunderstorms
across the region. Initial development is forecast over the
mountains, spreading east across the Plains through the late
afternoon and overnight hours. Main threats will be locally heavy
rainfall and lightning, but small hail and gusty outflow winds may
also be possible with stronger cores. Flash flooding may be
possible on area burn scars and over urban areas prone to
flooding. These will need to be monitored closely. Temperatures
will be cooler with highs generally in the lower to mid 80s
through this period.
Friday through Sunday...high pressure is forecast build northward
over the Great Basin while an upper trough takes shape over the
Ohio Valley. This will force flow aloft across Colorado out of the
northwest. Drier air will move into the area on Friday which will
limit thunderstorm development with more isolated activity
generally over the mountains. By Saturday and Sunday, much will
depend on how much moisture and energy move over the upper ridge
to the west and drops south across Colorado. Models hinting that
Saturday could see more widespread thunderstorm activity,
including possibly strong to severe, but this is a long ways out.
Mozley
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 236 PM MDT Sun Aug 20 2017
VFR conditions are expected the next 24 hrs. There will be the
possibility of showers/tstms at KCOS, KPUB and KALS this evening,
and then again Mon afternoon, although KCOS should see a better
chance than the other sites.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...28
LONG TERM...MOZLEY
AVIATION...28
Area Forecast Discussion
National Weather Service Springfield MO
552 PM CDT Sun Aug 20 2017
.SHORT TERM...(This evening through Monday)
Issued at 217 PM CDT Sun Aug 20 2017
Convection is ongoing along the MO/AR border driven or triggered
by outflow boundaries. Another area of convection now over
northern MO is also expected to move southeast over the next few
hours. Evolution of this northern area of storms is a little more
up in the air, but HRRR does develop convection along a trailing
outflow boundary into our west central and central MO counties by
early evening. Some storms may also form along and nw-se oriented
boundary west of KSGF toward 00z. A strong instability/modest
shear environment will support a continued mention of isolated-
scattered strong/severe storms in our messaging with large
hail/downburst winds the main concerns. Looks like storms will
diminish by late evening.
Heat index values are reaching up to around 105 deg F over our
western counties at this time. No changes are planned to today`s
heat advisory.
For Monday, more of the same with lots of low level moisture in
place, some scattered convection will still be possible. Eclipse
viewing will be a roll of the dice, with clouds likely to hamper
some areas. 18z forecast grids for Mon has 50-60% coverage in
general.
.LONG TERM...(Monday Night through Sunday)
Issued at 250 PM CDT Sun Aug 20 2017
A cold front will move through the area Tuesday with a good chance
for rain/tstms. Rain chances will initially push into our
northern counties late Mon night and spread quickly into the rest
of the area Tue morning. Overall instability looks hampered by
cloud cover at this point so the severe risk looks marginal. We
will need to monitor for heavy rain and flooding potential, but
given the progressive front, probably not looking at a widespread
flooding risk. WPC marginal day 3 (Tue) risk for excessive rain
looks appropriate.
It looks like a nice stretch of weather behind the front. We
could see at least a couple of nights with lows in the 50s with
lower dew points/humidity in a deep nw flow pattern and sfc high
pressure ridging. Some moisture return may lead to a return of a
chance of thunderstorms by Sunday as we transition to a weak zonal
upper level flow.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 547 PM CDT Sun Aug 20 2017
Outflow boundary from this mornings convective complex has nearly
stalled out and was located from near Schell City to Greenfield to
Kimberling City. Convection has fired up in an area of instability
on the eastern edge of the outflow boundary over Cedar county
northwest of SGF. Am going to mention VCTS on the BBG TAF for a
couple hours this evening, but will leave SGF/JLN without mention
of CB or VCTS at this time. Expecting mainly VFR conditions
through the period, but areas which get under any thunderstorms
could drop into MVFR/IFR.
&&
.SGF WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT this evening for MOZ066-077-088-093-
101.
KS...Heat Advisory until 7 PM CDT this evening for KSZ073-097-101.
&&
$$
SHORT TERM...DSA
LONG TERM...DSA
AVIATION...Lindenberg
Area Forecast Discussion
National Weather Service Shreveport LA
938 PM CDT Sun Aug 20 2017
.DISCUSSION...
Updated forecast earlier this evening with cancellation of heat
advisory at 7 PM and added pops across our far northern zones
where daytime convection persisted into the early evening hours.
However, convection has all dissipated as of this mid evening
update and will allow the current forecast to continue on track
through the overnight hours. Any decision on an additional heat
advisory for Monday will be left to midnight shift with fresh
model data to consider. Otherwise, diminishing cirrus clouds this
evening should set us up for mostly clear skies on Monday morning
so our solar eclipse watchers should hopefully have good viewing
to start by late morning, but cumulus development later in the day
may obscure peak time viewing for the eclipse a little after 1 PM.
/19/
&&
.PREV DISCUSSION... /issued 517 PM CDT Sun Aug 20 2017/
AVIATION...
Dealing with some scattered convection at this time which may
influence the TXK/ELD/GGG/TYR and LFK terminals over the next 1-3
hours, otherwise, expecting VFR conditions to prevail through the
next 24 hours. CU/Mid Level AC and Cirrus debris should give way
to mostly SKC during the overnight hours before we see the cu
field begin to condense once again between 14-16z areawide on
Monday. Cannot rule out some ceilings at this height as well
beyond 16z and continuing in and out throughout the afternoon
hours on Monday. Some isolated to widely scattered afternoon
convection will be possible on Monday, mainly after 17z or so but
coverage does not warrant a mention in this package.
Winds will be light and variable through the night except for an
occasional stronger gust associated with a random outflow boundary
through 03z or so with a return to south to southeast winds during
the day Monday mainly less than 10kts.
13
PREV DISCUSSION... /issued 313 PM CDT Sun Aug 20 2017/
DISCUSSION...
Shwrs/tstms have developed across portions of N LA/E TX. The HRRR
model data seems to be initializing very well, and the latest run
indicates that convection will diminish around 00Z. Have left PoPs
out of the overnight forecast as a result.
Monday will be another hot day, although most likely not as warm
as today. Some areas very close to Heat Advisory criteria, but
have decided /in collaboration with surrounding offices/ to hold
off on issuance and defer to the midnight shift. There appears at
least a decent shot that the solar eclipse will be visible from
most areas, as far as cloud cover is concerned. Areas that will be
most prone to obstruction due to cloud cover will be along and
north of I-30. Convection may also be an issue for some, as we
will likely see some isold to possibly sct development around
midday through sunset.
Similar conditions are expected for Tuesday, but Wednesday will
bring some changes. Upper ridge will build back in over the
Rockies, allowing the upper trof over the nern CONUS to deepen as
a disturbance rounds the base and sweeps a cold front into our
region. Good chances for shwrs/tstms will accompany the front as
it slowly drifts swd through Friday. Front will stall s of our
area and begin to move back nwd during next weekend, keeping our
fcst wet through the end of the pd. Increased coverage of
convection and cloud cover will most likely knock our temps back
down to below seasonal normals. /12/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 77 96 76 95 / 10 30 10 10
MLU 76 95 75 94 / 10 30 10 20
DEQ 75 93 74 94 / 20 30 10 30
TXK 75 94 75 94 / 10 30 10 20
ELD 75 95 75 94 / 10 30 10 20
TYR 76 94 75 94 / 10 20 10 10
GGG 76 95 75 94 / 10 30 10 10
LFK 75 96 74 95 / 10 20 10 30
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
19/13/12
Area Forecast Discussion
National Weather Service Las Vegas NV
205 PM PDT Sun Aug 20 2017
.SYNOPSIS...An area of low pressure off the southern California
coast will pull moisture northward into the region overnight,
resulting in rain showers and isolated thunderstorms developing late
tonight and lasting through Monday. Daily thunderstorm chances will
persist through Wednesday before conditions gradually dry out late
in the week.
&&
.DISCUSSION...Initial influx of moisture has been northward through
Arizona today. There has been isolated thunderstorms in northern
Mohave County with scattered coverage along and just east of the
county line in Coconino and Yavapai Counties. Elsewhere, seeing less
vertical extent in the cumulus field over Inyo County/southern
Sierra Nevada then previous days.
In the big picture, a quasi-stationary upper low will remain off the
southern California through Monday. All 12z models agree that the
additional moisture needed to support precipitation and associated
jet dynamics/diffluence east of the upper low that will be providing
the lift for showers/embedded thunderstorms will be delayed until
late tonight. Latest operational HRRR and ESRL experimental HRRR
indicate lines of rain showers and probably some embedded
thunderstorms developing south of Las Vegas between 2-5 am Monday
morning. Those bands along with new development slated to lift north
through Las Vegas Monday morning. Again, viewing of the solar
eclipse likely will be obstructed by passing clouds/precipitation.
Air mass forecast to become more unstable Monday afternoon with
isolated/scattered thunderstorms possible within the entire forecast
area. Time heights suggesting low levels of the atmosphere will
remain somewhat dry meaning any stronger cells would likely produce
gusty winds and be less of a flash flood threat. Some some hail
possible as well with part of the area under 25-35kts 0-6km Bulk
Shear.
Tuesday/Wednesday...Upper low still to our west with models depicting
a 60-70 kts jet across southern California/southeast Nevada and
northwest Arizona. Moisture parameters not overly impressive but
with less cloud cover surface heating will help destabilize the
atmosphere each day for continue threat of isolated/scattered
thunderstorms mainly across southern Nevada, northwest Arizona and
Inyo County. Gusty wind and hail would be threat with storms.
Beyond Thursday, models continue to advertise drying with
temperatures warming through the weekend.
&&
.AVIATION...For McCarran...Winds this evening will begin to veer
from southeasterly to a typical south/southwest drainage with speeds
up to 10 knots. Overnight into Monday morning, scattered showers
will likely develop in the vicinity and over the terminal.
Confidence is only moderate on arrival of nocturnal showers with an
approximate start time between 10z-12z. Scattered showers are
expected to linger through Monday morning/afternoon, with embedded
thunderstorms possible during the afternoon. Winds should stay
fairly light through the morning with an easterly/southeast
direction favored, however confidence is not high as nearby
showers/thunderstorms may produce sporadic wind gusts. Increasing
cloud cover expected early this evening with overcast conditions
working in overnight with bases likely between 9-10 kft.
For the rest of southern Nevada, northwest Arizona and southeast
California...An areawide southwest to southeast wind between 10-20
knots expected through the evening. Winds should favor a diurnal
flow regimes overnight, with the exception of sporadic wind gusts
from nearby showers/virga. Through the rest of the afternoon/early
evening, isolated thunderstorms will be limited to NW Arizona and
southern Sierra. Late tonight and into Monday a chance of isolated
to scattered shower activity is expected for most areas with the
exception of KDAG where shower activity is less likely. Accompanying
the showers will be broken/overcast sky conditions a CIGs down to 9
kft at sites south and east of Interstate 15.
&&
.SPOTTER INFORMATION STATEMENT...Thunderstorm activity will
increase late tonight through Monday with thunderstorm chances
lingering Tuesday and Wednesday over much of the area. Spotters are
encouraged to report any significant weather or impacts according to
standard operating procedures.
&&
$$
Discussion...Pierce
Aviation...Boothe
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