Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/20/21
Area Forecast Discussion
National Weather Service La Crosse WI
645 PM CDT Sun Sep 19 2021
.SHORT TERM...(This evening through Monday)
Issued at 245 PM CDT Sun Sep 19 2021
Focus is on thunderstorm potential on Monday.
Breezy southerly flow will keep temps quite mild overnight tonight
with lows only in the 60s to near 70 in spots. Attention then turns
to an approaching cold front associated with a mid-level trough
crossing the northern plains on Monday. Guidance indicates possible
stratus development Monday morning ahead of it with continued low-
level moisture transport.
Lift with the shortwave trough along with strong frontal forcing
leads to high confidence that an area of showers and storms will
move from west to east by Monday afternoon. The system will be
progressive, but rain amounts in the 0.75 to 1.50 inch range are
forecast with local amounts in excess of 2 inches possible given the
anomalous moisture/pwats to 1.75 inches along the front.
As for severe weather potential, instability will be a limiting
factor, as soundings generally show a skinny CAPE profile with
SBCAPE up to 1000 to 1500 J/kg and fairly weak low to mid-level
lapse rates. This may serve to limit peak updraft intensity. The
CAPE is forecast to be higher farther south into IA with the RAP
showing only a narrow instability axis to the north ahead of the
front. The stronger mid-level flow/deep shear largely still is
forecast to lag the front/instability axis, but 30-40 kts of bulk
shear in the 0-3 km layer with a sizable amount of bulk shear in the
0-1 km layer along the front would favor organized, stronger
convection if updrafts are intense enough. Timing of the front looks
favorable to take advantage of the diurnal max in instability, but
significant destabilization is uncertain given impacts from possible
low cloud development Monday morning and the rather weak lapse
rates. Overall, given the set-up, expect mainly showers and sub-
severe storms, but isolated severe storms are possible later in the
afternoon. However, if greater destabilization can be realized, the
severe weather risk could increase. The primary threat would be
strong winds. Secondary threats include small hail, and a
conditional low risk of a tornado given the 0-3 km shear profiles.
.LONG TERM...(Monday night through Sunday)
Issued at 245 PM CDT Sun Sep 19 2021
The trend has been to move the showers and thunderstorms out
earlier, thus will continue highest chance of precipitation during
the evening. A marginal threat for severe storms continues into
the early evening due to the limited instability available with
sufficient shear in the 0-3km and 0-6km layers. The area should be
able to handle the rainfall as we are about 1 to 2 inches below
normal for the month. The high rainfall rates on an 1 inch an hour
could cause impacts to travel. Showers and isolated thunderstorms
exit the eastern part of the forecast area after 06Z.
By 12Z Tuesday, the 500mb trough has dragged the cold front
through the forecast area. The main area of precipitation has
exited the region, however lagging trough energy lingers into the
afternoon. Some hint of shower re-development. The forecast
soundings have a small window where convective temperatures are
reached, but this shuts off quickly. With moisture much more
limited (precipitable water less than 0.5") locally, showers
should be spotty and mainly north of I90. Northwest winds will
usher in cooler temperatures, thus temperatures that start out in
the 50s will only make it to the 60s for highs. Surface high
pressure builds in overnight and will need to assess fog
potential. Surface winds are light and 850mb winds are still in
the 10 to 20 mph range. In addition, cold areas/bogs should dip
into the 30s Wednesday and Thursday morning with local
frost/freeze conditions possible. Temperatures in the 60s into
the 70s for highs Wednesday through Friday. Friday, a cold front
will push through. It may not be completely dry, however much of
the area should remain dry. 850mb temperatures drop, however
ahead of the front, mixing may support temperatures 3 to 7 degrees
warmer than what is currently forecast which is in the 10th
percentile of NBM. Should the front speed up, the temps would work
out, but if slower, may be too cool. We see less agreement for
Saturday/Sunday as the GFS has us under the influence of the
eastern side of the ridge and the EC has us cooler with the
trough. The current NBM is on the side of the warmer temps. The
EPS trend has had a 20 degree spread over the last week, so it`s
been jumping around a lot too. Will see how the most recent trends
go. They can agree that is will be a fairly dry period at RST/LSE
into the weekend with spotty precip chances more in the
Taylor/Clark areas.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 645 PM CDT Sun Sep 19 2021
MVFR to IFR stratus spreads northward after 06Z and encompasses
most of the area by sunrise. These low clouds lift through the
late morning and scatter out in the afternoon. An approaching cold
front moving from west to east brings widespread showers and
occasional thunderstorms west of a MDZ-LSE-OLZ line before 00Z.
The showers and storms continue to spread eastward Monday evening
and exit early Tuesday morning. Winds remain from the south
through at least midday Monday before veering to the northwest
behind the aforementioned cold front. Wind speeds subside tonight
before increasing to 10-20G30kts ahead of and behind the front.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...JM
LONG TERM...Zapotocny
AVIATION...Skow
Area Forecast Discussion
National Weather Service Bismarck ND
947 PM CDT Sun Sep 19 2021
.UPDATE...
Issued at 925 PM CDT Sun Sep 19 2021
Main forecast update was for pops this evening. Convection has
been trying to fire from southern Emmons into Logan county over
the past hour. This is in narrow area of increasing mid level
lapse rates. This is also within a tight gradient area with no
MLCape to the northwest (Bismarck) and decent MLCape, but capped
to the east (Ellendale) However, within this area (Linton to
around Jamestown) MUCapes are around 500-1000J/kg. Wind profiles
area strong but erratic. Bulk and effective shear is around 50
knots here. Surface winds are northerly and then weak as you rise
above the cold front and veer to the southeast, south and then
southwest before increasing quickly as you rise into the mid
levels. HRRR Updraft helicities have backed off over this area
since late this afternoon. Thus we think the threat of severe
storms continues to diminish and looks more and more unlikely as
we go through the late evening hours. The main threat would be a
locally strong to severe gust given the strong winds aloft and
inverted V type sounding this evening at Bismarck. Updated text
products will be sent shortly.
UPDATE Issued at 551 PM CDT Sun Sep 19 2021
At 6 PM CDT a cold front was situated from around Grand Forks to
Mobridge SD, then back west to and area of low pressure north of
Rapid City SD. Along this frontal boundary, including the James
River Valley there remains quite a bit of instability aloft, with
strong shear (40-50 knots) in place, but with some low level
capping remaining near the surface. This area seems to have the
greatest potential for some strong to severe storms this evening,
if there is enough forcing for ascent. Currently the Daytime
cloud phase RGB satellite imagery is not showing much in the way
of agitation within the cu field over the southern James River
Valley. There does look still be a window of a couple hours for
potential development this evening. Will need to monitor. Farther
west, the RGB imagery is showing a little more vertical
development over far southwest ND and into southeast Montana.
However, this area is behind the cold front and the shear is quite
strong, the profile for severe convection is not favorable. As
you move east of here into far south central ND, and eventually to
the JRV mentioned above, there may be a brief window for a strong
to possibly severe storm as we go through the early evening
hours. What we also will need to monitor is a period of strong
environmental winds, currently over western ND moving eastward
through the southwest and south central this evening. Shower
activity may help mix down the stronger winds aloft. And if there
is some elevated convection, it`s not out of the question that we
could get a severe wind gust this evening south central into the
JRV. Late tonight, as the upper trough approaches, there will be
another band of showers moving through from west to east.
&&
.SHORT TERM...(This evening through Monday)
Issued at 329 PM CDT Sun Sep 19 2021
A cold front looks to bring showers, a few thunderstorms, and
breezy to windy conditions through tonight. Surface cold front
currently in western ND will continue to push eastward through
tonight. Ahead of this front will be dry with some breezy
conditions. This could bring some near critical fire danger at
times through the early evening. A line of showers will then
shortly follow this front, as currently seen in eastern MT. Look
for these showers to also push eastward through this evening and
tonight. As this front enters into the more moist and
conditionally unstable eastern portions, a few thunderstorms may
develop. Shear is fairly strong along this front, while some sr
helicity will also be present. DCAPE will also increase somewhat
ahead of the front. The result could be an isolated stronger storm
for southeastern portions later this evening into the early
overnight hours. With the amount of wind along the front, strong
winds will be the main threat although some hail up to the size of
a quarter is possible. The other impact from this front could be
a brief period of strong winds this evening. Pressure rises are
fairly decent this evening, with strong winds aloft all along the
front. The result could be some brief advisory level winds,
especially in the southwest. Confidence is not high enough for any
highlights at this time. Behind this front temperatures will cool
into the 40s tonight, with 50s across the east.
Post frontal conditions then look to be found for Monday. Look for
temperatures to be cooler and generally in the 60s. Breezy
northwest winds may also linger across much of the area. The
unsettled northwest flow could also provide for a few lingering
showers on Monday, mainly in southern portions. An isolated
thunderstorm is possible, mainly in southeastern portions.
.LONG TERM...(Monday night through Sunday)
Issued at 329 PM CDT Sun Sep 19 2021
Overall look for dry conditions with near to slightly above normal
temperatures during the long term period.
A broad trough pattern looks to linger for Monday night through
Tuesday. The result though will be cooler and dry conditions with
highs in the 60s and lows in the upper 30s to 40s. Weak ridging
then builds in for Wednesday, bringing warmer and dry conditions.
This will lower RH values and bring increased southwesterly winds.
This could at least elevate the fire danger and perhaps bring some
near critical fire danger. A weak and mainly dry front then looks
to move through Thursday and Friday. This will cool temperatures
back to near normal readings, although dry and breezy conditions
could continue to elevate the fire weather danger. Another upper
level ridge then builds back in for the weekend. This looks to
warm temperatures and bring continued dry conditions. Low RH
values could again elevate the fire weather danger, although winds
should remain on the lighter side with this ridge.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 925 PM CDT Sun Sep 19 2021
Strong winds and showers and thunderstorms will move east across
the forecast area tonight. The best chances for thunderstorms will
be this evening at KBIS and KJMS. Generally showers expected at
remaining TAF sites with a very small risk of thunder. With
uncertainties high, at this time only carried a VCTS at KJMS. We
will also see a period of strong northwest to north winds directly
behind the cold front this evening, generally lasting for no
longer than 3-4 hours, before diminishing. Late tonight into
Monday morning, MVFR ceilings are expected at KJMS and possibly at
KBIS. North to northwest winds diminish late tonight then increase
again on Monday with winds gusting 15 to 25 kts Monday afternoon.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...TWH
SHORT TERM...Anglin
LONG TERM...Anglin
AVIATION...TWH
Area Forecast Discussion
National Weather Service Dodge City KS
644 PM CDT Sun Sep 19 2021
...Updated Aviation...
.SHORT TERM...(This evening through Monday Night)
Issued at 128 PM CDT Sun Sep 19 2021
A surface trough was positioned near the Kansas/Colorado line
early this afternoon. Southwest surface winds were most pronounced
across the western half of the area, and temperatures had reached
the upper 80s from Liberal to Elkhart by noon. As we have yet to
reach peak heating, the upper 80s will likely be reached over the
central Kansas counties while a few models suggest as warm as the
mid/upper 90s (96-97 degrees) over the extreme southwest by the
end of the afternoon. The radar mosaic was showing returns moving
east across southeast colorado, associated with mid level
accas/elevated showers and trailing a zone of weak 850 mb
moisture transport over western Kansas. The convection allowing
models have for the last 24 hours or more suggested thunderstorms
developing in the higher terrain and advecting eastward with the
westerly momentum this afternoon. Relatively steep mid level lapse
rates of 7.5-8 C/km are in place as far east as the highway 283
corridor. On the limiting side is the relatively lacking moisture,
which model soundings mix out into relative deep inverted V-type
soundings suggesting isolated strong wind gusts as DCAPE values
ramp up rapidly from west to east. Convection, if it develops at
all, since the recent HRRR seems to be more suppressive, should
become much more isolated eastward toward the eastern half of the
area by mid evening.
A breezy overnight with wind gusts in the 30+ mph range as a low
level jet develops at the top of the boundary layer. There may be
a relative weakening of the surface winds briefly as a cold front
approaches in the morning, however as winds turn north behind the
cold front, windy conditions will continue for much of Monday. A
dry - cold air advection airmass will temper the rate of warming
over much of the area, with model consensus favoring upper 70s to
around 80s over most of the area.
.LONG TERM...(Tuesday through Sunday)
Issued at 128 PM CDT Sun Sep 19 2021
Even cooler temperatures are expected Tuesday afternoon as the drier
airmass settles over Kansas with the absence of the downslope
heating. Pacific high pressure becomes centered over the central
Plains by Tuesday evening. Surface winds may still be breezy out
of the north at 10 to 15 mph with higher gusts through the day,
and light by Tuesday night. A trending drier airmass is expected
going forward into the week, although Monday night and early
Tuesday could bring some northwest flow instability showers to the
area. A broad upper ridge develops again over the Rocky mountain
range and breaks down as split flow develops with a strong upper
jet positioning itself from western Canada into the northern
Plains while an upper low cuts off over California. This makes for
a relatively non-eventful pattern of near normal high
temperatures and relatively pleasant evenings given the lower dew
points. Another dry front might be possible late in the week,
perhaps Friday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 642 PM CDT Sun Sep 19 2021
VFR flying conditions for all terminals this TAF period. Gusty
south winds will persist across southwest KS through the overnight
period, with 50 kts of southerly LLWS also developing at all
terminals roughly from 03-11Z. Early Monday morning, winds will
begin to veer to northerly as a strong cold front passes through
southwest KS. Winds behind the front will be considerable, with
sustained winds in the 25-30 kt range and gusts of 35-45 kts
possible. These strong winds will begin to relax late in the
period, but still remain quite gusty.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 66 81 53 73 / 20 0 20 0
GCK 62 77 51 71 / 20 0 20 0
EHA 62 80 51 73 / 10 0 10 0
LBL 63 82 52 74 / 20 0 20 0
HYS 66 77 51 71 / 20 0 10 0
P28 70 87 57 75 / 10 0 20 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Russell
LONG TERM...Russell
AVIATION...Springer
Area Forecast Discussion
National Weather Service Lincoln IL
900 PM CDT Sun Sep 19 2021
.SYNOPSIS...
Issued at 844 PM CDT Sun Sep 19 2021
Scattered showers over southern IL will advance north toward
through east central IL tonight, with a few thunderstorms possible.
A break in the rain is possible for most areas later Monday
morning into afternoon, before a cold front brings more widespread
rain thunderstorms to the area Monday night and Tuesday. For
Wednesday, much cooler temperatures arrive, lingering through the
end of the week.
&&
.UPDATE...
Issued at 900 PM CDT Sun Sep 19 2021
A sheared 500 mb wave evident on water vapor imagery entering
southern IL this evening, will be the focus for scattered showers
and possibly a few thunderstorms as it shifts northeast across
eastern IL later tonight and Monday morning. With the best lift
focused near and east of I-57, this is where likely pops are
maintained, tapering to only slight chance west near the IL River
Valley. Precipitable water values see a marked increase as
moisture associated with the wave moves overhead (sampled at
1.35" on 00z ILX sounding), with both RAP and HRRR showing an
increase at CMI from 1.25" early this evening to near 2" after
midnight. As a result, these showers will be capable of producing
locally heavy rainfall rates. A few hundred J/kg of CAPE are
available so isolated rumbles of thunder possible. Forecast lows
are unseasonably warm in the upper 60s to lower 70s thanks to
increasing cloud cover and a steady southeast wind around 10 mph.
&&
.SHORT TERM...(This evening through Monday)
ISSUED AT 304 PM CDT Sun Sep 19 2021
An upper level shortwave and surface trough will progress toward
IL from the south this evening, triggering periodic showers and
storms through tonight. The better chances of precip will remain
confined to areas east of I-55, in a corridor of stronger DPVA.
The wave will be weakening in general the farther it progresses
toward northeastern Illinois/Indiana, but the complex of rain is
still expected to linger into Monday morning for our eastern
counties. A break in the rain is likely in the wake of that
system, from Monday mid-morning through late afternoon.
A deep upper trough and associated cold front will approach our
western counties toward late Monday afternoon, but the consensus
of guidance are keeping precip west of IL through 00z/7pm Monday
.LONG TERM...(Monday night through Sunday)
ISSUED AT 304 PM CDT Sun Sep 19 2021
An extensive line of showers and storms will advance across
Illinois Monday night. The cold front is progged to reach the
western edge of Knox County to Schuyler County toward 06z/1am,
and roughly to near I-57 by 12z/7am Tues, then out of our
southeast CWA by 18z/1 pm. SPC has updated the Day 2 Severe
Weather Outlook to include a Marginal Risk of Severe for our
areas west of Springfield to Morton to Lacon - for the Monday
night time frame. The frontal dynamics are projected to be
relatively strong with moderately unstable air ahead of the
front. In the 8 pm to 2 am time frame, any storms could produce
some damaging winds, with isolated large hail.
As indicated earlier, the front looks to depart our SE counties
toward 18z, so it`s possible that a damaging wind threat will be
included in the Tuesday morning time frame for our eastern
counties. The afternoon will see decreasing precip trends, but the
delay in the passage of the 500 mb trough until late Tuesday night
into Wednesday morning will keep the potential of scattered
showers in the forecast for areas east of I-57.
GEFS ensemble solutions show good clustering that 850 mb temps
will drop from +19C Monday night to +4C by Tuesday night. That
will provide below normal temps for the first time in a while.
Tuesdays highs will be in the low 70s in most of our CWA except
east of I-57, with upper 60s to low 70s for highs on Wednesday.
Thursday could be as cold as Wednesday due to the extended
guidance now in consensus that the upper low will cut off from the
prevailing flow and linger over Indiana/Ohio. In that scenario,
plenty of chilly air will linger in Illinois.
Warmer conditions are projected for Friday under ridging at the
surface and aloft. However, additional troughing into the western
Great Lakes Saturday and Sunday will temper any additional
warming.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 611 PM CDT Sun Sep 19 2021
An upper level disturbance moving in from the south is the main
feature this cycle. This will initially send MVFR ceilings
northward after midnight, with ceilings likely lowering to IFR
prior to sunrise as moisture increases. Rain showers will be
focused over eastern IL, so CMI and DEC have predominant showers
mentioned with only VCSH farther west. Isolated storms are
possible but probability too low to include. As the system shifts
northeast, an improvement to MVFR then VFR ceilings from the
southwest is expected Monday afternoon. Southeast winds around 10
kt will be common tonight, veering south midday with 20-25 kt
gusts for the afternoon.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...25
SYNOPSIS...Shimon
SHORT TERM...Shimon
LONG TERM...Shimon
AVIATION...25
Area Forecast Discussion
National Weather Service Louisville KY
749 PM EDT Sun Sep 19 2021
...Updated Forecast and Aviation Discussion...
.Forecast Update...
Issued at 745 PM EDT Sun Sep 19 2021
Have a widespread swath of light rain across the region right now,
with very little lightning. A stronger band is moving across eastern
KY. The 4k NAM, HRRR, and RAP each have some handle on this band in
the east...holding it together into our Bluegrass counties late this
evening. Given its progressive nature, not worried at this time
about flood potential there.
Had given some thought to hoisting a flash flood watch...given
several models showing a narrow north/south oriented swath of 2-4
inch rainfall totals, somewhere in the vicinity of the I-65 corridor
or points westward, through Monday morning. A lot of features argue
for this watch: high precipitable water airmass in place, which of
late has been enough for some fairly high rainfall totals; the 00Z
ECWMF Extreme Forecast Index has that same north/south region in
with a better chance for high numbers; the 12Z HREF 24-hour LPMM
rainfall totals have a narrow swath of 2.5-4" in that region; CREST
soil moisture shows some soils that wouldn`t take too much more rain
to become saturated. The argument against is the more recent hourly
hi-res CAM guidance, RAP/HRRR, have backed off on that plume of
higher rainfall...instead making only isolated totals over 2".
All of that said, will monitor the updates on the RAP/HRRR as well
as the incoming 00Z NAM later this evening and may still pull the
trigger on a swath of a Flash Flood Watch. For now, forecast QPF is
on the high end of the guidance envelope...with totals averaging
around an inch or a little more through Monday morning in the focus
region mentioned above.
&&
.Short Term...(This evening through Monday)
Issued at 310 PM EDT Sun Sep 19 2021
General western trough/eastern ridge pattern set up over the CONUS
today, while a weak upper low associated with the remnants of
Nicholas spins over the ArkLaTex region sending waves of energy
towards the lower OH Valley. As the upper trough progresses eastward
and deepens over the central Plains into Monday, expect the lower MS
Valley circulation to open up and lift northeastward over the area
in advance of the upper trough while the upper ridge is displaced
farther east. In the lower levels, a southerly 25 - 35 kt LLJ is
pumping ample moisture into the region with SPC Mesoanalysis
indicating PWATs of 1.8 - 2.0 inches working in over southwest
portions of the forecast area.
Current radar imagery shows scattered to widespread showers pushing
into southern KY while a narrow line of showers and storms
progresses northwest across central KY on the nose of the 850 mb
jet. MRMS estimates suggest isolated rainfall amounts of 1 to 2
inches in the initial line of storms while the showers across
southern KY consist of a more light to moderate rainfall with totals
generally between 0.1 - 0.3 inches so far. As we move through the
evening hours, expect the broken line of showers and storms to
continue lifting NNE towards the I-64 corridor over the next couple
of hours while over southern KY the more widespread showers very
gradually spread northward.
Expect a lull in precipitation tonight before a second round of
showers and a few embedded thunderstorms begins to push northward
across the area overnight with precip chances continuing through
Monday before tapering off in the late afternoon. Hi-res guidance
indicates the heaviest rainfall may occur between 20/09-15Z
generally west of a Burkesville, KY to Madison, IN line where the
best moisture will be located.
The main weather related hazards over the next 36 hours will be
heavy rainfall leading to localized flooding issues as well as cloud-
to-ground lightning. Expect these showers and storms to be very
efficient rainers as model soundings indicate tall and skinny CAPE
profiles, high moisture content (PWATs ~ 2.00" and RH ~ 90%), and a
deep warm cloud layer with freezing heights generally between 13 -
14 kft. Overall expect additional rainfall amounts of 1 - 2 inches
through Monday (locally higher amounts possible), with highest
amounts expected west of I-65.
.Long Term...(Monday night through Sunday)
Issued at 250 PM EDT Sun Sep 19 2021
Increased cloud coverage and precip chances will be the highlight
for the first half of the long term. A significant upper level
shortwave will be located over the Plains Monday evening, digging as
it pivots to the southeast and towards the Ohio/Tennessee Valley.
When doing so, the shortwave will be elongated from north to south
across the Midwest and will deepen enough to form a closed low over
the Ohio Valley by Wednesday morning. Associated sfc cold front will
likely be extending from the Great Lakes down to the Gulf States,
and looks to pass through our region sometime on Wednesday.
Ahead of the front, tropical like airmass will be in place due to
deep SSW flow, possibly raising PWATs beyond 2 inches and near the
daily maximum from BNA and ILN sounding climatology on Tuesday.
We`ll likely see showers and storms take place on Tuesday as daytime
heating nears convective temperatures. Model soundings show tall and
skinny CAPE profiles, with modest sfc instability (around 1000 J/kg)
and weak speed shear and unidirectional flow. Increased cloud cover
associated with the shortwave will help limit our instability and
lapse rates, but effective shear will slightly increase as the front
approaches, so can`t rule out some organization of convection
along/near the FROPA. However, currently think flash flooding may be
the primary concern to watch for. PoPs look to linger along and
slightly behind the frontal boundary, so will keep slight and chance
PoPs in the forecast through Wednesday evening.
Deep NNW flow on the western flank of the departing shortwave and
post frontal airmass will bring dry wx back into the forecast early
Thursday morning. Additionally, this cool post-frontal flow will
also allow temperatures to possibly drop into the upper 40s and near
50F Thursday and Friday mornings. Max temps for Thursday could
remain in the 60s, with below normal temps forecast to stay around
for Friday and through next weekend as well.
&&
.Aviation...(00Z TAF Issuance)
Issued at 740 PM EDT Sun Sep 19 2021
Impacts: MVFR to IFR CIGs and VIS in rain showers and fog with
potential embedded TS. Gusty SE winds 18-22kt Monday afternoon.
Discussion: Remnants of Nicholas will send showers, moderate to
heavy at times, with possible embedded thunder from south to north
across the region throughout most of the TAF period resulting in
MVFR to IFR conditions. Current radar shows a line of TS moving NE
from LOZ toward LEX with time of arrival at LEX between 02-03Z, if
it holds together. Winds will also pick up out of the SE Monday
afternoon with gusts 18-22kt possible. Rain showers begin to taper
off early Monday evening with VFR conditions likely at all sites
except HNB.
Confidence: Low to medium confidence on exact timing of IFR
conditions. Medium to high confidence in MVFR conditions and winds.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...RJS
Short Term...JML
Long Term...CJP
Aviation...CG
Area Forecast Discussion
National Weather Service San Francisco Bay Area
429 PM PDT Sun Sep 19 2021
.SYNOPSIS...Mostly sunny and mild this afternoon. Red Flag
Warnings go into effect at 11 pm for the North and East Bay hills
as well as the East Bay interior valleys through 8 pm Monday for
drying offshore winds. Otherwise sunny and warmer Monday and
Tuesday regionwide under fall offshore wind pattern. Slight
cooling trend by Wednesday but continued dry and seasonable
through the work week.
&&
.DISCUSSION...as of 2:03 PM PDT Sunday...Skies have cleared out
behind last nights frontal passage with just some lingering clouds
over the ocean and a few instability clouds over the hills this
afternoon with mild temps warming into the upper 70s and lower 80s
inland. All focus will shift to developing offshore winds and
associated Red Flag Warning as well as a noted warming and drying
trend for Monday and Tuesday.
Todays forecast focus has been on the Red Flag Warning that covers
the North/East Bay hills and East Bay valleys from 11 pm tonight
through 8 pm Monday. As expected any rainfall of note was
confined to northwest Sonoma county down to coastal Marin.
Interior North Bay and the heart of the Bay Area generally saw
trace amounts or less than a tenth which is not considered a
wetting rain or enough to have an appreciable impact on the fine
fuels let alone the heavier drought impacted fuels. So the areas
of most concern will be the Napa hills across the North Bay as
well as the East Bay hills/valleys where stronger winds, low
humidity values and dry fuels are most likely to line up.
For tonight northerly winds will develop over the Napa hills
before midnight and then spread over the rest of the Bay Area
hills overnight into Monday morning. Initially most of the strong
winds will be confined to the higher ridges above 2000 feet before
slowly mixing down closer to the 1000 foot elevation. We can
expect to see some gusts to around 50 mph for Mt Saint Helena and
Diablo but more significant rainfall was observed around those
higher peaks last night. The initial burst of winds will arrive
with humidity readings quite moist, thus the period of strongest
winds will not line up with the lowest humidity but rather the
initial energy of the winds will be spent drying the fine fuels
out. Without getting too esoteric its also worth noting the 10
hour fuel stick values are remaining fairly high, even for those
locations that didn`t see rainfall so fuel conditions are not too
extreme going into the event which is supported by the latest ERC
fuel chart readings as well. Nonetheless the synoptic weather
pattern features a fairly typical mid-September offshore wind
event. From sunrise through about 10 am winds should be peaking in
strength regionwide and riding on-top of the nighttime inversion
layer right around 1000 to 1500 feet in elevation. As the morning
inversion breaks some of those winds will mix down to the lower
elevations of the North/East Bay as well as the coastline. As this
occurs we should see rapid spike in temperatures before noon on
Monday as readings quickly approach 80 degrees, even near the
coast and bays. Persistent but fairly light offshore flow to
continue through Monday afternoon but the main impact will become
hotter temps regionwide with widespread upper 80s to mid 90s as
humidity values lower into the teens.
Offshore flow to continue Monday night but as the sun goes down we
dont expect any strong wind speeds. Thus for now and in coordination
with neighboring offices will plan to let the Red Flag expire at
8 pm Monday evening. That being said we expect little or no
humidity recovery Monday night into Tuesday morning, especially in
the hills with readings staying from 18-30% overnight keeping
conditions near critical.
The offshore flow should ease by Tuesday morning but the stage
will be set for another hot day with widespread readings in the
upper 80s and 90s. Were at the time of year when things become
more isothermal and the hottest temps can actually be closer to
the coast under offshore/downslope flow. No expectation of any
heat products as the dry airmass will allow good radiational
cooling under the longer Sept nights.
Will be watching a midweek shortwave that will turn the wind
pattern back to onshore by Weds morning and induce a modest
cooling trend. This feature will get rid of the inland 90s but
still expect comfortable temps in the 70s and 80s for Weds.
Models then take the midweek shortwave and drop it towards the
Central Valley before potentially it turns into a weak cut-off
low by late in the week. Nearly all the models are now indicating
this potential with the likely result of little appreciable impact
of note for the Bay Area though some solutions indicate an
outside chance of some showers for the Central Coast though that
remains doubtful. The North Bay and greater Bay Area will likely
be on the dry northeast side of the upper low with fair and nice
wx.
Longer range solutions suggest as that feature finally kicks out
towards Nevada dry high pressure will build later next weekend
with continued dry and seasonable weather.
&&
.AVIATION...as of 04:29 PM PDT Sunday...For the 00z TAFs.
Satellite imagery shows stratus remains along the coast from
Sonoma County down through the Monterey Bay as well as some
scattered cumulus and a line of passing high clouds. VFR
conditions are expected to prevail as dry offshore flow sets up
tonight and persists through the forecast period. As northerly
winds strengthen overnight, there is a possibility of LLWS (mainly
in the North and East Bay) late tonight into early tomorrow
morning. Breezy northwest winds this afternoon in the wake of a
cold front with most sites around 10 to 20 kt into this evening
before surface winds diminish tonight. Occasional higher gusts
overnight may mix down to the surface from the offshore flow
aloft, but no widespread consistent stronger winds are
anticipated.
The latest HRRR smoke model is showing an increase in total smoke
beginning just at the end of this taf package from south to north.
Expect reduced slant range visibility starting late tomorrow
afternoon.
Vicinity of KSFO...VFR. Breezy W/NW winds this afternoon at 15 to
25 kt diminishing this evening. Increasing offshore winds aloft
overnight may lead to some LLWS on and off into early Monday
morning.
KSFO Bridge Approach...Similar to KSFO.
Monterey Bay...VFR prevailing, though satellite does show some
stratus moving into the Monterey Bay. There is the chance of SCT
to BKN cigs developing over the terminals early this evening.
Should this occur, expecting clearing to occur by early Monday
morning. Breezy onshore winds this afternoon around 10-15 kt
diminishing overnight. As mentioned above, HRRR smoke model shows
increasing smoke beginning late tomorrow afternoon.
&&
.MARINE...as of 04:21 PM PDT Sunday...Northwest winds with
stronger gusts continue to strengthen Sunday and into Monday.
Hazardous seas conditions will develop over much of the waters,
particularly for smaller vessels. Seas remain mixed with a short
period northwest swell and a weak longer period southerly swell.
An additional longer period northwest swell will arrive around mid
week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Red Flag Warning...CAZ507-510-511
SCA...Mry Bay until 9 PM
SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
&&
$$
PUBLIC FORECAST: RWW
AVIATION: AS
MARINE: DK
Visit us at www.weather.gov/sanfrancisco
Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea
Area Forecast Discussion
National Weather Service Nashville TN
751 PM CDT Sun Sep 19 2021
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
Showers continue to diminish as we head into the evening. Most of
the existing activity is occurring east of I-65, and the most
recent HRRR suggests that this trend will continue during the next
several hours, with some regeneration toward morning. The 00Z
sounding from OHX shows a modestly unstable environment, but
plenty of available moisture. Hourly grids look to be holding up
well. Flash Flood Watch remains in effect for all of Middle
Tennessee until Monday evening. No forecast changes are planned
at this time.
&&
.AVIATION...
00Z TAF DISCUSSION.
BNA/MQY/CKV/CSV...A strong upper trough situated to our west is
helping pull abundant Gulf moisture into Middle Tennessee, with
widespread, mainly light showers ongoing. Ceilings are generally
MVFR across the region. Look for ceilings to gradually deteriorate
during the next several hours as showers become more prevalent
overnight and tomorrow.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Monday evening for Bedford-Cannon-
Cheatham-Clay-Coffee-Cumberland-Davidson-De Kalb-Dickson-
Fentress-Giles-Grundy-Hickman-Houston-Humphreys-Jackson-Lawrence-
Lewis-Macon-Marshall-Maury-Montgomery-Overton-Perry-Pickett-
Putnam-Robertson-Rutherford-Smith-Stewart-Sumner-Trousdale-Van
Buren-Warren-Wayne-White-Williamson-Wilson.
&&
$$
DISCUSSION......08
AVIATION........08
Area Forecast Discussion
National Weather Service Pocatello ID
125 PM MDT Sun Sep 19 2021
.SHORT TERM...Tonight through Tuesday night. Early afternoon radar
imagery was showing a broad band of showers working east through the
region with the advancing upper trough. The trough axis is expected
to clear east into the Wyoming border region by early evening with a
moderately strong west flow and scattered showers trailing behind
the trough this evening. Thus a Lake Wind Advisory will remain in
effect for American Falls Reservoir through 8 PM. A drier NW flow is
expected to overspread the area late tonight as wind speeds diminish
across the upper valley but remain breezy in the Burley area. As the
winds decouple, we do expect to see overnight lows drop to near
freezing in the upper valley, Shoshone, and Pocatello regions Monday
morning and thus the Frost Advisory will remain in effect. A ridge
of high pressure is expected to expand across Washington and Oregon
late Monday into Tuesday which should promote lighter winds and
drier conditions. The downside here is the potential for yet another
frost/freeze situation Tuesday morning. Warmer temperatures follow
Tuesday afternoon as the ridge expands east into Idaho. Huston
.LONG TERM...Wednesday through next Sunday. A large/longwave ridge
of high pressure remains expected as the dominant wx enforcer across
most of the wrn US through the long term period, supporting mostly
clear/sunny skies, light winds, and a slight warming/drying trend
with highs back into the 70s to near 80 by next weekend.
Deterministic models continue to bring one solitary shortwave trough
through the ridge Wed night, now splitting it with a weak/dry
frontal passage possible for the CWA and the srn branch potentially
closing off into a low down over NV/CA. Cluster analysis suggest
some slight uncertainty with regard to timing in the ensembles, but
no significant trends have been noted and no significant impacts are
expected other than perhaps kicking up the winds just a bit Wed/Wed
night. 01
&&
.AVIATION...Showers and isolated t-storms (and breezy conditions)
will continue through this eve along/behind an advancing cold front,
but generally VFR conditions are expected for all major terminals
after about 21z/3pm. Tonight/Mon AM, we will need to be on the
lookout for our first shot at early season fog/low stratus. Most
guidance does not support development, but the HRRR and HREF suite
suggest some potential in the 08-16z/2am-10am window. NBM maxRH
projections are also near 100% for valleys/low elevations, and we
have seen widespread rainfall today. Confidence is low (and winds
will need to drop off in line with lower HREF/NAM guidance), but
have hinted at some VCFG in all TAFs except KSUN for now. If this
scenario does manifest, we really have no idea if fog vs. low
stratus will be favored. Future shifts will continue to evaluate and
refine timing. Otherwise, high pressure with mostly clear/sunny
skies and light winds will take over for much of the upcoming week.
01
&&
.FIRE WEATHER...Rain/high elevation snow/isolated t-storms will wind
down by this eve (perhaps lingering into Mon AM in Zone 411) as our
current low pressure system pulls away. For the entire upcoming
week, high pressure will dominate with a gradual warming/drying
trend. Deterministic models continue to bring one solitary shortwave
trough through the ridge Wed night, now splitting it with a weak/dry
frontal passage possible for the CWA associated with the nrn branch,
and the srn branch potentially closing off into a low down over
NV/CA. Cluster analysis suggest some slight uncertainty with regard
to timing in the ensembles, but no significant trends have been
noted and no significant impacts are expected other than perhaps
kicking up the winds just a bit Wed/Wed night. Currently they are
expected to remain below Red Flag criteria, but even if the forecast
trends stronger afternoon RH values are currently expected to remain
above critical thresholds throughout the week. Otherwise, fire
personnel should be aware of those colder temps for the next couple
days, including readings below freezing for many areas Mon/Tue
mornings! 01
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory continues until 8 PM MDT for IDZ054.
Frost Advisory from 3 AM to 9 AM MDT Monday for IDZ051>055.
&&
$$
Area Forecast Discussion
National Weather Service Reno NV
1217 PM PDT Sun Sep 19 2021
.SYNOPSIS...
After a cool start Monday with frosts and freezes in some
valleys, high pressure will control our weather much of this week.
This means warming temperatures with dry conditions persisting.
Gusty winds are possible at times, such as on Wednesday, however
no strong wind events are expected this week. There is a chance
of showers next weekend however confidence remains quite low.
&&
.DISCUSSION...
* TEMPERATURES: Ensemble guidance generally showing ridging to be
the dominant weather driver this week. As such after a cool
start Monday into Tuesday morning, we should see daytime temps
warming to just above normal mid to late this week. Near-
freezing temps are likely in rural and suburban valleys Monday
morning, with just isolated spots of that Tuesday morning.
* WINDS: Cold front rolling through today will keep W/NW winds
breezy into this evening, with lake recreation and localized
road travel impacts. Gusts on the order of 30-40 MPH possible
across the E Sierra, for example. NE flow takes effect Monday
with some breezy periods on Tahoe and along the Sierra crest,
otherwise no impact. We`ll likely see an increase in W/SW winds
of 25-35 MPH gusts on Wednesday as quick little upper wave
passes by, with some spots of critical fire weather and road
travel impacts. Roughly 40% of ECMWF EPS members showing
stronger gusts over 35 MPH along Sierra Front, so worth keeping
an eye on. Behind that wave, a period of E/NE winds is likely
Thursday-Friday.
* SMOKE: With a turn to more N/NE winds, we`re smoke free on the
east side through Monday night per latest HRRR Smoke models.
Starting Tuesday NAM3km guidance showing a light W/SW flow
kicking in over the Sierra, and that could be enough to send
smoke that`s bottled up on the west slopes over to our region.
Mammoth has the highest risk of seeing appreciable smoke impacts
but can`t rule out haze over Tahoe, W Nevada either. That may
persist into Wednesday as well but this far out confidence is
quite limited.
* ANOTHER WEEKEND STORM? There are several ensemble members
showing potential for light precipitation next weekend, as a
weak upper trough develops off the CA coastline. Basically a
50/50 split in the ensemble clusters showing a trough outcome
versus the ridging holding on over CA/NV. To that point NBM QPF
guidance along the Sierra crest from Mammoth to Donner Pass
ranges from zero to 0.5" of precipitation Saturday-Sunday.
Anyways, just like this past storm don`t count on anything
meaningful rainfall-wise, but don`t count it out either. NBM
guidance also showing a small chance of t-storms over E Sierra.
Not a big wind pattern with less than 10% of ensembles showing
appreciable wind gusts over 35 MPH next weekend.
-Chris
&&
.AVIATION...
Cold front moving through will continue the breezy W/NW winds
through this evening, especially over the Eastern Sierra near MMH
and eastward to around BIH, HTH, and TPH. Gusts on the order of
30-35 knots possible with rough rides likely. Sierra crest
observations near Mammoth earlier showing 65-70 kt gusts.
Winds will subside and turn more N/NE tonight and into Monday.
East of the Sierra into Nevada this pattern isn`t generally
significant for wind impacts, with just some low-end 20kt gusts
here and there.
With that NE flow smoke and haze are not expected for the E Sierra
and W Nevada through at least Monday night. However that could
change stating Tuesday as flow over the mountains turns light SW.
That could bring any smoke bottled up on the west slopes over
onto our side. MMH has highest risk of MVFR or worse in smoke/haze
Tuesday but can`t rule out some haze for TVL, TRK, and even into
RNO, CXP, MEV, and NFL.
-Chris
&&
.FIRE WEATHER...
Winds remain breezy this afternoon behind the cold front, but are
corresponding with higher humidity. The greatest areas of concern
through this evening will be the lower elevations of the Eastern
Sierra and Mineral County, which tend to funnel the northwest winds
efficiently and also will have min RH values in the 12-20% range.
Winds will turn NE-E overnight and will be gusty for the Sierra
crest and into western slopes where our neighboring offices have Red
Flag Warnings in effect.
After a couple of cooler days, a warming and drying trend will begin
Tuesday onward. A weak passing system may enhance westerly winds on
Wednesday, but at this point it appears critical conditions will
remain isolated. -Dawn
&&
.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory until 11 PM PDT this evening for Pyramid Lake
in NVZ004.
Lake Wind Advisory until 5 PM PDT this afternoon for Lake Tahoe
in NVZ002.
CA...Lake Wind Advisory until 5 PM PDT this afternoon for Lake Tahoe
in CAZ072.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno