Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/30/21
Area Forecast Discussion...UPDATED
National Weather Service Albuquerque NM
601 PM MDT Sun Aug 29 2021
00Z TAF CYCLE
Scattered thunderstorms will favor the northeast half of NM this
evening and overnight with isold MVFR cigs/vsbys and terrain obscurations
in the stronger storms with very heavy rain, hail and gusty downburst
winds. A quasi-line or cluster of storms is forecast to move swd
through portions of ne and east-central NM aft 30/00Z, which may
remain relatively intact through 30/06Z before possibly reaching KROW
thereafter. Potential for areas MVFR cigs/patchy br from the east
slopes of the central mt chain to the TX border 30/10Z- 15Z. As drier
mid-level air works in from the northwest on Monday, afternoon
thunderstorms will be isolated mainly mts and central highlands
.PREV DISCUSSION...243 PM MDT Sun Aug 29 2021...
Scattered to numerous thunderstorms across central and eastern New
Mexico will gradually diminish in coverage late this evening. Another
round of hit and miss storms is expected Monday and Tuesday as
temperatures warm a few degrees above normal. An increase in moisture
from the eastern Pacific may allow for an increase in thunderstorms
and heavy rainfall Wednesday and Thursday, especially for western and
central New Mexico. This influx of moisture will also allow for
temperatures to cool several degrees.
SHORT TERM...(TONIGHT THROUGH MONDAY NIGHT)...
Showers and storms have developed over the higher terrain as well as
over portions of east central NM where an outflow boundary has
already been expelled from the cluster of storms there. The HREF
suggested the east central plains would see this area of storms
initially then would be impacted this evening by another cluster
that was to progress through parts of northeast NM first. Several
runs of the HRRR also latched onto the idea there would be a cluster
that moved southward mainly between the central mountain chain and
the Pecos Valley this evening and overnight. The 18Z NAM also keeps
this evening/overnight cluster tracking over the same area, so there
is some consensus. Therefore will leave the Flash Flood Watch as is
but with the slow and erratic storm motion, any cell could produce
heavy rain and flash flooding if it hits a vulnerable area.
Otherwise, there may be some patchy fog from the east slopes of the
central mountain chain to the TX border late tonight and have added
that to the weather grids.
Monday should feature a bit of a downturn in activity with the
southwest mountains and central mountain chain the focus areas for
storms. The northwest and north central tend to dry out a little and
a weak lee trough will replace the low level east winds observed
this afternoon. Highs on Monday will be near normal, with the east
seeing a few degrees of warming over today`s highs. Lows will be a
few degrees above average.
LONG TERM...(TUESDAY THROUGH SUNDAY)...
Deterministic models as well as their ensembles are in very good
agreement with the H5 high building over NM on Tuesday. With pressure
heights rising to about 589dam and 700mb temperatures warming, high
temperatures will rise as well and are expected to be a few degrees
above late August normals for most of the area. With this high
overhead, PWATs will fall below an inch, and this will lead to a
relative downtick in storm coverage. Moisture won`t be completely
scoured out though, and isolated to widely scattered convection will
mostly favor the western and northern high terrain and adjacent
A pattern shift is expected starting Wednesday thanks to now Tropical
Storm Nora. Nora will be tracking northward along the west coast of
Mexico early this week and is currently forecast to be a tropical
depression by early Thursday as it nears the northern Gulf of
California area. Meanwhile, a trough moving inland into the PacNW
and increasing southwesterly flow ahead of it will allow for the
aforementioned H5 high to shift back to the east over OK and TX. This
opens the door for quite the tropical moisture plume courtesy of
Nora to develop over the southwest U.S. The moisture plume develops
over AZ first on Tuesday and then shifts into western NM on
Wednesday. By Thursday, the moisture plume develops over NM and PWATs
are forecast to climb to the 1.1 to 1.3 inch range with some models
(most notably the ECMWF) even forecasting PWATs higher. This is well
above the 90th percentile for early September which is around 0.99"
and could even rival daily record PWATs. What all this means is
precipitation chances will rise starting Wednesday and then become
more widespread over northern and central NM Thursday. And with these
anomalously high PWATs, heavy rainfall and flash flooding may become
a big concern. WPC is already highlighting a slight risk in the Day
3 ERO in southern AZ to account for this increasing moisture.
Confidence is then lower in the upper-level pattern Friday and
through the weekend. Deterministic models and their ensembles
keep the H5 high well to our east through the weekend, but they are
having a more difficult time in resolving the general troughing
pattern that sets up over the western CONUS. Still, the moisture
doesn`t look to be going anywhere so an active pattern looks to be on
tap as we head into early September.
Storm coverage has increased this afternoon, especially over east
central New Mexico, but the Northwest Plateau will remain mostly dry
with only a few cells. Locally heavy rain which could lead to flash
flooding is possible, as cell motion will be slow and erratic,
especially later this afternoon and evening as outflow boundaries
develop. There will likely be a decrease in the number and areal
coverage of storms on Monday except for the west central and
southwest high terrain where scattered to numerous storms are again
forecast. Tuesday looks to be the least active day with the center
of high pressure aloft over New Mexico and storms confined to the
central mountain chain westward. Both maximum and minimum humidities
decrease over northwest and north central New Mexico Monday and
On Wednesday, an upper trough moving into SoCal will nudge the upper
high far enough to our east to allow a stream of moisture into
Arizona, which will reach western New Mexico later in the day. The
plume progresses into central and northern New Mexico Thursday and
Friday and increases the potential for more widespread showers and
storms. Thereafter, model differences start to appear, although it
looks like at least isolated, if not scattered convection stretched
from the southwest mountains to the northeast plains will persist
through the weekend.
Fair to poor ventilation is featured Monday and Tuesday for many
areas across western and central New Mexico. Widespread poor rates
are forecast across the west and central Thursday and Friday.
Flash Flood Watch until 4 AM MDT Monday for the following zones...
Area Forecast Discussion
National Weather Service Bismarck ND
941 PM CDT Sun Aug 29 2021
Issued at 941 PM CDT Sun Aug 29 2021
Little change was needed to the overnight forecast once again, but
we did expand the slight chance of thunderstorms Monday afternoon
and evening further north and east, adding much of central ND into
the potential. Guidance suggests low-level moisture return beneath
steepening midlevel lapse rates on the leading edge of an elevated
mixed layer will yield considerable bouyancy by afternoon, while
deep-layer shear would favor potential organized, severe updrafts.
Synoptic-scale forcing and low-level convergence are both currently
forecast to be weak, so this represents a conditional severe-storm
risk, and some caution is advised in considering more aggressive
CAMs like the 00 UTC HRRR given those factors. However, evidence
is increasingly supportive of the need to begin communicating the
possibility that such a scenario could come to fruition, even if
it`s highly conditional on uncertain convective initiation.
UPDATE Issued at 609 PM CDT Sun Aug 29 2021
All we did with this update was blend recent observed trends and
NBM data into hourly forecast fields through the night, with very
little change. Expect diurnally-driven cumulus fields to wane as
the boundary layer cools and stabilizes this evening, leaving a
quiet and seasonably cool night.
.SHORT TERM...(This evening through Monday)
Issued at 219 PM CDT Sun Aug 29 2021
Current surface analysis places high pressure over northern
Wyoming into Montana, with low pushing over Ontario, keeping a
west to northwest breeze over much of our area. Upper level
analysis places trough sliding into the Great Lakes region, with
rather zonal flow to our west. A broad area of fair weather
cumulus has developed over our region, otherwise quiet weather
For tonight, clouds will diminish with the loss of daytime
heating. Thereafter, a quiet night is expected.
On Monday, the day will start out quiet. During the afternoon,
instability will be on the increase, particularly over the
southwest, with good shear in place. This sets the stage for the
possibility of a severe storm or two, but ample forcing to produce
a storm remains in question. Therefore, have gone with a slight
chance of thunderstorms, but if one does develop it could become
strong. Better chances remain well to the south of our area.
.LONG TERM...(Tuesday through Sunday)
Issued at 219 PM CDT Sun Aug 29 2021
On Tuesday ridging enhances over the area as upper low drops south
through British Columbia. Ridge slides east as the first of
multiple waves from this system push through the area, bringing
shower/thunderstorm chances. This system then slowly meanders
easterly bringing chances for precipitation through the week. As
for severe potential, the best chances continue to be Wednesday
when ample instability and shear are forecast to be in place
during the afternoon and evening hours. Will have to keep an eye
on this on future forecasts.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 941 PM CDT Sun Aug 29 2021
VFR conditions will prevail through the 00 UTC TAF cycle. A low
probability of thunderstorms exists in southwestern and central
ND Monday, mainly after 18 UTC, as instability returns. However,
uncertainty in forcing mechanisms for storms precluded us from
including any mention of them in the 00 UTC TAFs.
Area Forecast Discussion
National Weather Service Boise ID
828 PM MDT Sun Aug 29 2021
.DISCUSSION...HRRR smoke model has proved correct bringing the
smoke aloft back into our CWA from the southwest today. Monday
looks worse as HRRR shows near-surface smoke also increasing from
the southwest. Northern Harney County may be spared with westerly
flow aloft there keeping most of the smoke out, but Baker County
will be directly downwind of the Bull Complex Fire in north-
central Oregon and will receive some of that smoke. Aside from
the smoke our Idaho zones will be sunny and very warm again
Monday while Oregon zones begin to cool down as a weakening Gulf
of Alaska upper trough comes inland. A dry surface cold front
will pass through eastern Oregon Monday and western Idaho Monday
night, followed by cooler temps in all areas Tuesday. Current
forecast has this. No updates.
.AVIATION...Mainly VFR. Wildfire smoke layers over much of
southeast Oregon and southwest Idaho could degrade visibility at
times. Surface winds: variable 10 kt or less. After 30/1800Z,
becoming W-SW 10-20 kt with gusts to around 25 kt, except W-NW
5-15 kt in the Snake Plain. Winds aloft at 10kft MSL: SW 10-25 kt.
SHORT TERM...Tonight through Tuesday night...Conditions will
remain dry across the region through the period. A west to
southwest flow over the area will transport smoke, advancing
through southeast Oregon this afternoon, further into the region
tonight and Monday. The thicker smoke layers aloft and eventually
surface smoke will be south and east of a Burns-Ontario-Cascade
line by Monday. A trough will push into the Pacific NW on Tuesday
bringing cooler temperatures but with flow aloft remaining out of
the southwest would expect to at least keep smoke layers aloft.
Temperatures will be a few degrees above normal Monday, cooling
to several degrees below normal on Tuesday.
LONG TERM...Wednesday through Sunday...Southwest Idaho and
southeast Oregon will remain on the interface between a cool
upper level trough over southern British Columbia and Alberta
and a strong upper level ridge containing hot temperatures and
monsoon moisture to the south and east. Afternoons will feature
breezy west-northwest winds through the period. Temperatures will
be around 5 degrees below normal on Wednesday, warming to normal
PREV SHORT TERM...DG
PREV LONG TERM....KA
Area Forecast Discussion
National Weather Service Indianapolis IN
1144 PM EDT Sun Aug 29 2021
...Updated Aviation Discussion...
Issued at 942 PM EDT Sun Aug 29 2021
This evening, a broken line of thunderstorms continues across
northern sections of central Indiana, with isolated convection to
the south. The storms in the north are being forced by some
prefrontal convergence and some vorticity aloft. Storms have been
pulse like in nature with perhaps some gusty winds and small hail.
The forcing will continue tonight, especially north, closer to the
vorticity and the front. Will go with higher end chance PoPs there
tonight. Less forcing south will lead to slight chance or low end
chance PoPs there. Confidence is not has high in the south with the
weaker forcing and the latest trends in hi-res models to back off on
Mixed Layer CAPES of 2000-2500 J/KG will keep the threat of gusty
winds and small hail around.
Adjusted sky cover and hourly temperatures as needed based on latest
.Short Term...(This evening through Monday night)
Issued at 302 PM EDT Sun Aug 29 2021
CAMS are struggling a bit with convective initiation this afternoon.
Showers and thunderstorms have formed rather quickly over the last
hour and are more widespread than models were projecting. Despite
the persistency, thunderstorms are expected to remain below severe
levels though this afternoon and evening without any significant
dynamics. Current convection is mainly being diurnally driven in
the warm, moist environment as a weak influx of moisture continues
on the back side of high pressure dome. That will, however, change
tonight as a cold front drops into the forecast area. This
additional forcing could be enough to trigger some isolated strong
to severe thunderstorms (mainly north) overnight, which is
highlighted by the Marginal Risk per SPC. HRRR starts keying in on
re-initiation of convection around Mon 01/02Z over the northern
counties with cold front, eventually shifting southward toward
Monday/Monday Night... The aforementioned cold front will eventually
be met with the northward propagation of Ida on Monday morning,
stalling it a bit. The surge of moisture from Ida will eventually
overtake the southern third of central Indiana on Monday afternoon
with PWAT values approaching 2 inches and a Slight Risk in the
excessive rainfall forecast. Flooding will be a threat across the
southern tier of counties. Elsewhere, the effects of Ida will be
less pronounced over the northern portions of central Indiana. So,
will trend toward categorical Pops Monday afternoon over the
southern counties with likely Pops to the north.
With the cold front and extensive rainfall, the heat wave will
finally break on Monday as highs drop a bit into the mid to upper
80s. And, overnight lows Monday night will dip into the mid to
.Long Term...(Tuesday through Sunday)
Issued at 302 PM EDT Sun Aug 29 2021
The remnants of Hurricane Ida will be passing by central Indiana to
the southeast on Tuesday...with an abundance of clouds and continued
scattered to numerous showers impacting the region. Beginning early
Wednesday...the pattern will transition to dry and more seasonable
as Ida shifts off to the east and a broad high pressure ridge builds
The best chance for rain throughout the extended period will be on
Tuesday as what is left of Ida passes through the Tennessee and Ohio
Valleys. The track of the remnant low has solidified from middle
Tennessee into the central Appalachians...with the bulk of the broad
area of rain remaining to the southeast of the region. The diffuse
cold front however will still be in the southern half of the
forecast area on Tuesday with the potential for tropical moisture to
advect north into the area and interact with the front. A mid level
deformation axis will align north of the track of the remnant
low...likely aligning across southern Indiana and Ohio and
potentially impacting far southern portions of the forecast area.
While the potential for beneficial rainfall is there through Tuesday
night...any flood concerns will be localized considering antecedent
soil conditions which are quite dry over the last 6 weeks or so.
Any rain will depart Tuesday evening as the low pressure moves away
from the region. A broad high pressure ridge will expand into the
Ohio Valley beginning Wednesday and remain through the end of the
week. With a predominant E/NE low level flow...expect seasonable
temperatures with a nice drop in the humidity levels from what we
have felt over the last 10 days or so. Upper level troughing
initially midweek will lift out by Friday into the weekend with
heights rising. The ridge will center over the Ozarks and lower
Tennessee Valley over the weekend with central Indiana on the
periphery. Some discrepancies exist between long range guidance...
but the most likely scenario at this point is a frontal boundary
setting up north of the region over the weekend with just isolated
diurnal convection impacting the forecast area as southerly surface
flow returns. This front to the north may have a more substantial
impact locally by the tail end of the holiday weekend but confidence
is low in any specific solution at this time.
.Aviation...(06Z TAF Issuance)
Issued at 1144 PM EDT Sun Aug 29 2021
- Scattered convection should diminish toward sunrise, then more
convection Monday afternoon into Monday night.
- MVFR fog possible near sunrise, especially at KLAF.
DISCUSSION: Scattered convection should weaken overnight. Will
include VCTS for the first part of the TAFs, then allow for a lull.
More scattered to numerous convection will develop by Monday
afternoon and continue into Monday night with a cold front in the
area. MVFR or worse conditions are possible in convection.
Other than perhaps some brief MVFR conditions in fog near sunrise,
VFR conditions are expected for much of the TAF period outside of
convection. Winds may become variable during the day Monday thanks
to convection and the front in the area.
Area Forecast Discussion
National Weather Service Louisville KY
940 PM EDT Sun Aug 29 2021
Issued at 940 PM EDT Sun Aug 29 2021
In the near term, convection across southern Kentucky continues to
drift northward. Over the 15-20 minutes, we`ve seen it start to
weaken and gust out. We expect this activity to last for another
hour and mainly affect Logan/Simpson/Warren/Allen counties. Some
additional showers and storms will continue to move northeast
through Adair county and may get into southern Taylor, and perhaps
Casey county prior to diminishing. None of the storms are severe,
but brief heavy rainfall, some gusty winds, and lightning will be
the primary threats.
Moving to the overnight period, a surface cold front extending from
northern Missouri into central IL continues to move slowly
southward. Regional radars show some convection firing along it.
Earlier model runs in the day suggested that convection would
continue to grow along the front and drift southward overnight,
possibly getting into our southern Indiana counties. Much of the
guidance has backed off this idea now and really keep the best
chances of storms up near the I-70 corridor. Given the relative
good short term agreement, will back off PoPs tonight south of the
Ohio River, but will maintain at least a slight chance of
showers/storms across our southern IN counties. Overnight lows will
range from the upper 60s to the lower 70s.
Moving into tomorrow, we should start off mostly dry, though I can`t
rule out some renegade showers/storms in the morning across the
region. Convective activity should increase during the afternoon
hours as the frontal boundary to the north pushes down into the
region and tropical moisture from Ida works northward into the
There is a signal in the late afternoon data (Euro and 18Z GFS) that
suggest we could see the development of a Predecessor Rain Event
(PRE) across portions of the area tomorrow afternoon. A PRE is an
organized area of heavy rainfall that develops in connection with
water vapor originating in the vicinity of a tropical cyclone, but
this area of rainfall is separated from the tropical cyclone by a
large distance. In general, PRE`s are difficult for forecast models
to predict correctly, but there are several precursors that are
being predicted by the models for tomorrow afternoon.
We`ll be within the right rear entrance region of a 200 hPa jet, we
will be downstream of an approaching 700 hPa trough axis, we`ll have
a low-level front approaching from the north and we will be on the
periphery of an approaching tropical plume of moisture. Lastly, the
925 hPa theta-e ridge axis is forecast to be east of the area, along
Indeed, the 18Z GFS, the 12Z Euro, and even tonight`s 00Z HRRR runs
suggest that thunderstorms will develop across central/southern
Indiana tomorrow afternoon. These storms may slowly drift southward
with individual cells moving eastward. This could result in a swath
of training thunderstorms. With that plume of tropical moisture
advecting in from the south, PWATs should surge above 2 inches. This
would result in storms containing very heavy rainfall that could
result in localized flash flooding. As noted above, numerical models
often struggle with the placement of PREs, but given the pre-cursors
outlined above, it stands to reason that we may have a good shot at
getting one of these somewhere along and north of the I-64 corridor.
As of this writing there is still too much uncertainty to delineate
where widespread flash flooding could occur. While I do think the
area at most risk is mainly along and north of the I-64 corridor, it
remains uncertain if the highest risk will be across southern IN or
a little further downstream across SE IN, southern OH, and perhaps
This activity should weaken through the late evening hours, but
additional convection associated with the actual remnants of Ida
will then move into southern KY and spread northward across the
state overnight and into Tuesday.
The late afternoon model tends have continued to push the axis of
heavier rainfall with the remnants of Ida to the east. This is
likely due to the westerlies being a little stronger than earlier
predicted which is allowing the center of the system to pass a bit
more to our south and east. As of now, the best chances of heavier
rainfall still look to occur on Tuesday and continue through
Wednesday. The axis of highest QPF looks to favor areas east of a
Bowling Green to Lexington line. No headlines will be issued with
this forecast. However, if model trends continue to hold, a Flash
Flood Watch for portions of the region will be considered on the
.Short Term...(This evening through Monday)
Issued at 344 PM EDT Sun Aug 29 2021
Tonight, an approaching cold front, that is currently pushing
southeast through southeast Iowa, will continue pushing a line of
showers and thunderstorms towards the Lower Ohio Valley. Chances of
precipitation will continue increasing across the northern half of
the CWA during the overnight hours. This isn`t too exciting by
itself, but as the front begins to interact with the remnants of
Hurricane Ida, things get more interesting. As the outer bands of
Ida push moisture northward, the moisture will fan out along the
front and cause moisture to pool. PWATs will climb to around 2.5",
and with plenty of instability and warm temperatures, expect
efficient rainfall. This will likely result in very high rain rates
with thunderstorms along this front tomorrow afternoon. Flooding
could become an issue if showers remain over an area too long. Still
believe the areas along and north of Interstate 64 are most likely
to see these heavier showers.
After collaboration with neighboring offices and WPC, we decided
against a Flash Flood Watch. Recent dry conditions have caused low
river levels and dry soils. Flash flood guidance remains over 3" for
3 and 6 hour rainfalls across many of the possibly affected areas.
These will be evaluated during later shifts.
Under partly cloudy skies, temperatures will drop into the low to
mid 70s with a few rural areas possibly seeing the upper 60s.
Tomorrow, clouds continue to build through the day as precipitation
increases, but even with the clouds and rain temperatures should
reach the mid to upper 80s.
.Long Term...(Monday night through Sunday)
Issued at 317 PM EDT Sun Aug 29 2021
...Heavy Rainfall and Minor Flooding Possible Monday Evening into
Area of showers and storms with heavy downpours Monday afternoon
ahead of Ida and south of a cold front draped from northern Missouri
through central Illinois to northern Indiana will continue into the
evening hours over southern Indiana and north central Kentucky.
PWATS over 2" pooling along the length of the lower Ohio Valley
along with very weak shear indicates locally heavy downpours can be
There is good model agreement among operational runs and ensemble
envelopes over the first 72 hours of the forecast period taking the
center of Ida through the Tennessee Valley, putting us on the left
side of the track, which is typically where the heaviest rain occurs
in this pattern. We`ll also be located near the right entrance
region of an upper jet streak over the Great Lakes and that east-
west front over the Midwest will still be drifting towards us from
the north, eventually meeting up with Ida. Soundings show almost no
CAPE and continued weak shear as we get into Tuesday and Wednesday
with deep warm cloud depths of 13-15 thousand feet. Precipitable
water values will continue over two inches, especially south of the
There continues to be higher confidence in placement of the heaviest
rainfall amounts (storm total Monday evening through early Wednesday
morning) than there is in amounts. It still appears that the
heaviest rain will fall south of the Ohio River, especially southern
and eastern sections of central Kentucky. Recent progs have sped the
system up slightly, so where we previously had totals of 4-6" they
are now more in the 3-5" range. Still plenty of rain! Also it is
important to note that rainfall rate can be just as important, if
not moreso, as a flooding threat. If we do realize flooding issues
Tuesday-Wednesday it will likely be local flooding from intense
rates, and perhaps training, rather than from the overall rainfall
One thing that we do have working in our favor is antecedent
conditions. While there have been spotty summertime showers and
storms with heavy downpours recently, overall we have been on the
dry side...especially in the Lake Cumberland region and southern
Bluegrass where some of the heaviest rainfall is expected. The
Drought Monitor shows some areas of D0 across southern Indiana,
extreme north central Kentucky and southern Kentucky. Ensemble river
forecasts from the NAEFS and HEFS actually show very little river
flooding later this week...with a few spots possibly going into
minor flood. Looking at the year as a whole, rainfall has been near
to slightly above normal, which has allowed for plenty of green,
healthy vegetation that can help to soak up rainfall.
So, given all of the above, and after having spoken with surrounding
offices, will continue to advertise heavy rain in the forecast but
will hold off on a watch for now for the early Tuesday - early
Wednesday time period. Of course, each shift will continue to look
at things and make decisions accordingly. How much rain we get
tomorrow afternoon and evening, and where exactly is falls, will
have some bearing on choices regarding watch issuance and placement.
The rest of the forecast looks comparatively quiet as high pressure
noses down from Canada and translates to the East Coast. We may
start to see another system move in by the weekend...but for now
will keep PoPs low.
.Aviation...(00Z TAF Issuance)
Issued at 743 PM EDT Sun Aug 29 2021
Scattered convection is ongoing near and ahead of a cold front
across Illinois and Indiana, and weakening storms will approach
southern IN around 05z tonight. However, do not have confidence TSRA
will make it to HNB or SDF before weakening. Separately, ongoing
convection near the TN border may sneak into the vicinity of BWG in
the first hour of the TAF before storms diminish with sunset.
Otherwise, skies start the period relatively clear with increasing
clouds associated with decaying convection early Monday. TSRA
impacts are much more likely Monday afternoon and evening,
especially the northern 3 terminals (HNB/SDF/LEX). Some of these
storms will be capable of gusty winds and torrential rainfall.
Issued at 327 PM EDT Sun Aug 29 2021
The remnants of Hurricane Ida are expected to bring heavy rain to
the Ohio and Tennessee valleys through at least Tuesday night and
possibly into Wednesday. In addition to local flooding during the
heavy rain, minor river flooding may follow the rain for a few days
later this week.
At this time the forecast calls for 3-5" of rain generally along and
south of the Ohio River...with 2-4" possible north into southern
Indiana. Today`s 6hr FFG values are 2-4", and 1hr values are 1.5-
2.5". Flash flood guidance numbers are fairly uniform across the
area. Those numbers will likely change as we experience shower and
thunderstorm activity this afternoon through Monday evening ahead of
the main event. It`s also important to keep in mind that flash flood
guidance is the amount of rain, over a given time period, that will
cause small streams to flood. Locations with poor drainage, low
spots, and urban cityscapes may begin to flood at values below flash
Fortunately most area rivers are very low as we go into this event.
Nevertheless, rivers will have to be watched as this system moves
through. Right now the most likely basins to experience heavy rain
and potential minor flooding include the Cumberland, Barren, Green,
Rolling Fork, Salt, Kentucky, and Licking. Heavy rains are expected
in the upper Ohio basin and may cause a reaction in the Ohio River
in central Kentucky as the water moves downstream. Contributions
from tributaries flowing into the river from the south will add to
the overall volume of water in the mainstem Ohio.
Issued at 1130 AM EDT Sun Aug 29 2021
The remnants of Hurricane Ida are expected to bring heavy rain to
the Ohio and Tennessee Valleys Tuesday, possibly lingering into
Wednesday in eastern parts of the region. Daily rainfall records may
be in jeopardy.
Rainfall Records for August 31:
Bowling Green 1.83" in 2017 (ahead of former Hurricane Harvey)
Lexington 2.09" in 2013
Louisville 1.21" in 2018
The wettest August day on record at Bowling Green is 3.53" set on
the 5th in 1975.
The rainfall record for Lexington on September 1 is 2.04" set in
2017 (ahead of former Hurricane Harvey)
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
905 PM EDT Sun Aug 29 2021
A front stalled near the Blue Ridge Mountains will retreat
northeastward as a warm front overnight. A cold front will
slowly approach from the Great Lakes Monday into Monday night.
This front will stall overhead during the middle of the week as
the remnants of Ida approach from the Tennessee River Valley.
The cold front and remnants of Ida should move offshore late in
the week, giving way to building high pressure for next weekend.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Latest analysis shows a stalled frontal boundary lingering along
the Blue Ridge as high pressure remains displaced across the
southeastern US. Meanwhile, a weak shortwave continues to push
eastward across the CWA this evening. A few earlier showers and
thunderstorms across the Alleghenies have dissipated as a
capping inversion has developed albeit the decent amount of
surface CAPE remaining. More so, areas along and east of the
Blue Ridge have been more stable throughout much of the day. The
latest HRRR has captured the dying showers quite well and
aligns more or less with the current thinking. The stalled
boundary will gradually lift northward overnight through
tomorrow as a warm front. While general stability should hold
throughout much of the overnight hours, some of the HREF/CAMs
have spotty showers/thunderstorms redeveloping overnight due to
the shortwave advection interacting with the boundary. More so,
there remains a theta-E ridge across eastern portions of the
area. Thus, do think that there could be spotty
showers/thunderstorms that redevelop overnight, but should be
rather short lived. Otherwise, expect mostly dry, yet humid
conditions overnight with areas of patchy fog developing. Lows
expected in the upper 60s to mid 70s.
.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
A cold front approaching from the Great Lakes will slowly move
toward and eventually into the Mid- Atlantic Monday into Monday
night. There is uncertainty in the extent of any early morning
cloud cover and shower activity, and that will play a role in
how unstable it gets and how strong or widespread thunderstorms
will become later in the day. There is a bit of a modest
enhancement to the flow aloft expected, so storms may have a bit
more organization to them. Gusty to damaging winds and a few
instances of flooding are possible.
By Tuesday, the remnants of Ida will be moving northeastward
across the Tennessee River Valley. Meanwhile, Monday`s front
will be stalling overhead. This likely sets the stage for
scattered to numerous showers and thunderstorms, with the
probability of more widespread and potentially heavy rain
increasing markedly after midnight Tuesday night.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Please reference the National Hurricane Center for the latest
details on the track and strength of Ida.
Ida will likely continue to be steered northeast by an
approaching trough during the middle of the week. It is becoming
increasingly likely that our region will be affected. There is
an increasing flood/flash flood risk with a potentially prolonged
period of heavy rainfall from showers and thunderstorms Wednesday
into Wednesday night. The track will determine the placement,
extent, and severity of flooding and/or severe thunderstorm and
tornado threats. There is also a threat for tidal flooding
depending on the track of the remnants. Mainstem river rises and
additional flooding is possible late in the week even after the
heaviest rainfall has gone.
The remnants` track and intensity is still a bit uncertain. It
should be moving away by Thursday. This will set the stage for a
couple of refreshing days as Canadian high pressure surges
southward. Daytime temperatures will be in the upper 70s and lower
80s with dew points in the 50s. Overnight lows will be in the 50s to
around 60, with some 40s possible in the mountains. Return flow may
result in a slight warming trend by Saturday, but precipitation is
forecast to hold off at this time.
.AVIATION /01Z MONDAY THROUGH FRIDAY/...
Generally VFR conditions early this evening under a light
southerly flow. However fog is expected to develop mainly after
midnight tonight and can be locally dense in nature. Do think
fog/low stratus affects the terminals overnight but to what
extent is unknown. Have MVFR/IFR CIG/VSBYs in the forecast but
am most confident in restrictions at MRB/CHO. Elsewhere,
confidence on restrictions remains low. In any case, any fog/low
stratus should burn off by 12-13Z with VFR conditions returning.
Additional showers and thunderstorms are possible Monday
afternoon and evening and Tuesday afternoon, perhaps becoming
more widespread later Tuesday night as the remnants of Ida
approach. Please refer to the National Hurricane Center for
details on Ida.
Wednesday`s forecast will depend on the remnants of Hurricane Ida,
but heavy rain, thunderstorms, and low ceilings are all possible.
Improving conditions should arrive by Thursday.
Generally light flow is expected through Tuesday, though
periodic showers and thunderstorms could result in locally gusty
winds, higher waves, and lightning strikes.
Winds may increase Wednesday into Thursday as the remnants of
Hurricane Ida pass through the region, but details remain uncertain
at this time. Please refer to the National Hurricane Center
for details on Ida.
Slightly above normal tide levels persist. While most sites
should remain below minor flood stage, anamolies at Annapolis
have continued to rise. Observations have followed the CBOFS
forecast quite well, which signals Annapolis getting into minor
flood stage late tonight. Therefore, have issued a Coastal Flood
Advisory just for Annapolis through 06Z.
Anomalies should decrease a little for the first part of the
week, but increasing southerly winds ahead of the remnants of
Ida could result in tidal flooding around midweek.
MD...Coastal Flood Advisory until 2 AM EDT Monday for MDZ014.
Area Forecast Discussion
National Weather Service Shreveport LA
1006 PM CDT Sun Aug 29 2021
The first outer rainband associated with Hurricane Ida continues
to diminish in strength as it slides westward across the ArkLaTex
at this hour. None of the activity in this rainband reached severe
criteria, though it was responsible for producing steady rainfall
and gusty winds as high as 35 kts.
The RAP13 and HRRR agree that this rainband will continue to
weaken and should dissipate entirely by 04Z. There is some
disagreement regarding rainfall coverage and timing with
subsequent rainbands, as the totals will depend heavily on Ida`s
track and speed, however the latest guidance is trending towards
lowered probabilities of tropical storm force winds and reduced
rainfall accumulations, keeping the bulk of the moisture to the
east of the Four State Area. Revised PoP grids with the best
possible short term compromise through 12Z, maintaining PoPs for
the current rainband, and trending values downward for the
Based on the latest trends, the Flash Flood Watch and Tropical
Storm Warning have been cancelled, effective immediately. /26/
.PREV DISCUSSION... /issued 630 PM CDT Sun Aug 29 2021/
Mainly VFR conditions expected across area terminals through the
forecast period with the exception of MVFR ceilings possible
across MLU beginning late 30/09Z as tropical cyclone Ida moves
through western Mississippi. Ida will support elevated north to
northeast winds of up to 15 knots with higher gusts on Monday
across the MLU/ELD/SHV/TXK terminal sites with lesser values
across the east Texas terminals. Otherwise, rainband convection
could bring tempo thunderstorms across Louisiana and Arkansas
terminals this evening. /05/
.PRELIMINARY POINT TEMPS/POPS...
SHV 76 90 74 96 / 30 50 10 10
MLU 75 80 72 93 / 80 90 50 20
DEQ 73 91 71 94 / 20 30 10 10
TXK 75 90 72 94 / 20 40 10 10
ELD 72 86 69 92 / 50 70 30 10
TYR 75 92 75 95 / 10 10 0 10
GGG 73 92 72 95 / 20 20 10 10
LFK 74 93 74 97 / 20 30 10 30
LA...Flash Flood Watch through Monday evening for LAZ014-021-022.
Tropical Storm Warning for LAZ014-020>022.
For frequently asked questions about the Area Forecast Discussion
Area Forecast Discussion
National Weather Service Sacramento CA
214 PM PDT Sun Aug 29 2021
Hot and very dry today and Monday turning cooler through the
rest of the week. Gusty southwest to west winds early this week
will bring critical fire weather conditions to the northern
Sierra and southern Cascades.
GOES-West fire temperature product is showing intense heat
signatures associated with the Caldor Fire this afternoon. A
brief period of critical fire weather conditions is expected late
this afternoon over ridgetops, as trough forms off the Coast. Wind
gusts up to 20 mph has been observed so far across the high
Sierra and southern Cascades this afternoon. Valley afternoon
highs will will range from the upper 90s to around 103, resulting
in moderate heat risk.
Ensembles and cluster analysis indicate that an upper trough will
gradually deepen into mid-week. This will switch the wind pattern
to more onshore, which will gradually thin out the smoke the rest
of today, especially for the Delta/Southern Sacramento Valley per
latest HRRR smoke model. A stronger onshore flow/southwest winds
will get going Monday, which should push the smoke eastward out of
the Valley and much of the foothills.
The deepening trough will bring increasing fire weather concerns
to the northern Sierra and southern Cascades early to mid-week.
The strongest winds are expected in the afternoon and evening
hours. Southwest to west wind gusts of 20 to 35 mph are possible.
These winds combined with very low humidity and extremely dry
fuels will lead to critical fire weather conditions. A Red Flag
Warning has been issued for the northern Sierra and southern
Cascades as well as portions of the eastern foothills from 11 AM
Monday through 11 PM Tuesday, given the potential for rapid spread
of new or existing wildfires. Elevated fire weather conditions
may continue into Wednesday due to locally gusty winds and low
humidity. Practice fire safety.
Highs will remain above seasonal normals through Monday. Then,
temperatures will cool back into the mid 80s to mid 90s during the
.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...
Cluster analysis is in good agreement troughing over the region
will likely remain in place at the start of the extended forecast
period. By early next weekend, some differences emerge in forecast
model solutions. There is some indication of a closed low
developing, generally located off the Central Coast of California.
This could potentially lead to below average temperatures across
the region. Interior Northern California could see temperatures 5
to 10 degrees below climatology. Breezy onshore winds are also
possible at times in the afternoon and evening hours, particularly
through the Delta and higher elevation terrain.
Areas of MVFR possible due to area wildfire smoke. Gusts 15 to 30
kts vicinity Delta and high Sierra. Elsewhere, winds generally
under 12 kts.
Red Flag Warning from 11 AM Monday to 11 PM PDT Tuesday for
Burney Basin and Northeast Plateau in Shasta County Including
Northwest Lassen NF north of Lassen NP-Eastern Portion of
Shasta/Trinity NF-Northern Motherlode From 1000 to 3000 Ft.
Includes portions of Nevada-Yuba-Placer-Amador and ElDorado
Units-Northern Sierra Foothills from 1000 to 3000 Ft. Includes
portions of Shasta-Trinity and Butte Units-Northern Sierra
Including Lassen NP and Plumas and Lassen NF/S West of the
Sierra Crest (West of Evans Peak-Grizzly Peak-Beckworth Peak)-
Northern Sierra Including the Tahoe and ElDorado NF/S West of
the Sierra Crest-Southern Motherlode From 1000 to 3000 Ft.
Includes portions of Calaveras-Tuolumne Unit-Stanislaus NF West
of the Sierra Crest.
Area Forecast Discussion
National Weather Service Las Vegas NV
1216 PM PDT Sun Aug 29 2021
.SYNOPSIS...Hot temperatures and isolated thunderstorms are
expected through Monday with Excessive Heat Warnings in effect for
much of the region. Moisture will be increasing through the middle
of next week aided by the remnants of Nora. This moisture will lead
to better chances for shower and thunderstorm activity in Mohave
County today, expanding west and north into southern Nevada through
.DISCUSSION...Through next Sunday.
Typical monsoon pattern expected with storms firing over the higher
terrain of Clark, Mohave and San Bernardino Counties into this
evening and again Monday afternoon/evening. Gusty outflow winds and
brief heavy rain main concern with storms. Did blend in a higher
percentage of the camPoPs for the rest of today through Monday.
Above normal temperatures persist with an excessive heat warning
covering parts of our area through Monday evening.
Tuesday afternoon through Wednesday still looks to be our most
favorable period for showers and thunderstorms as additional
dynamics come into play. Models all show a weak disturbance situated
near 30N/120W early Tuesday morning. Stronger trough entering the
Pac NW poised to draw this feature inland across the area late
Tuesday afternoon through Wednesday. Developing jet streak and
associated divergence aloft will provide some additional lift. As
for models. GFS and its ensemble members continue to support a
wetter scenario for southern Nevada and eastern California with
highest QPF values still plotted across northwest Arizona. Believe
latest NAM and EC and its members continue to underplay the
situation as associated dynamics will be overspreading PW values
between 1" and 1.5". WPC Day 3 QPF (5 pm Tue - 5 pm Wed) depicting
0.50"-1.25" for the eastern half of Mohave County. The Colorado
River Valley, southern Nevada and eastern California mostly a 0.50"
or less. No hydro headlines will be issued with this package as
discussed in a collaboration call with WPC and AZ offices.
Residual moisture Wednesday night and Thursday will keep additional
chances for showers and thunderstorms largely confined to Mohave
County, but can not rule out a few storms lingering over eastern
Nevada. Mainly dry conditions with temperatures near normal Friday
into the Labor Day Weekend. The exception is in Mohave County where
lingering moisture could still ignite a few showers and
.AVIATION...For McCarran...Light winds favoring an easterly
direction will remain before giving way to some southeasterly winds
this afternoon around 22-23Z. Expect winds around 10-12 knots with
some occasional gusts around 15-20 knots lasting through 01-02Z.
Thereafter, winds will shift to more of a south-southwest direction,
eventually becoming light and variable overnight. Low confidence,
but there is a very small chance for an isolated storm to develop
just south of the Las Vegas Valley along the McCullough Range which
may bring lightning within 15 miles of KHND. Not anticipating any
storms to develop in the Las Vegas proper this afternoon, but will
be possible tomorrow afternoon. Some FEW to SCT aoa 12 Kft is
expected, primarily along the higher terrain this afternoon with
more cloud cover possible tomorrow.
For the rest of southern Nevada, northwest Arizona and southeast
California...Isolated to scattered thunderstorms are possible later
this afternoon and again tomorrow across southeastern portions of
our region, including in and around the Colorado River Valley. Low
confidence on storms impacting KIFP and KEED directly, but vicinity
thunderstorms maybe within 15 miles at times both afternoons. Main
concern would be strong outflow winds impacting the terminals,
potentially bringing gusts up to 30-40 knots. FEW to SCT aoa 12 Kft
will be possible in this region.
Further north and west, expect light winds following typical wind
patterns. Skies will be mostly clear with some FEW aoa 12 Kft across
some of the higher terrain in the western Mojave Desert. Although,
haze from distant wildfire smoke will reduce slant range visibility
at times, especially across the Sierra, western Mojave Desert and
parts of the southern Great Basin. Less confident on the potential
for smoke/haze to impact KBIH tonight, with some signal of smoke
coming in from the north-northeast, the smoke may not make it to the
Owens Valley overnight tonight. If it does, the HRRR Smoke indicates
it may be more dense, dropping vsbys to around 4-5 SM.
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
For more forecast information...see us on our webpage:
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