Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/18/24
Area Forecast Discussion
National Weather Service La Crosse WI
946 PM CDT Sat Aug 17 2024
.KEY MESSAGES...
- Scattered showers ending this evening. Dry start to the new week.
- Warming for Sunday. Temps mostly at/above normal for the new week.
&&
.DISCUSSION...
Issued at 130 PM CDT Sat Aug 17 2024
OVERVIEW: the upper level trough responsible for much of the
scattered showers across the area today eases east tonight/Sunday -
allowing for high pressure at the surface to build in. The upper
level pattern continues to shift moving into the new week with the
models showing strong continuity (within and between themselves)
with edging an upper level ridge axis from the plains to across the
upper mississippi river valley by Wed. How long the amplified ridge
lingers and/or flattens out/becomes more zonal is uncertain. WPC
cluster analysis shows a mixed bag of potential outcomes with a
fairly even distribution of GEFS/EPS members in the 4 clusters. The
sensible weather outcomes would still favor at/above normal temps
while holding the storm track across the north (but not necessarily
dry).
PCPN CHANCES: current scattering of showers will decrease in
coverage, gradually end this evening with loss of daytime heating
and shifting of upper level trough eastward.
A weak ripple a loft could shift across the region on Sunday, but
most models favor sfc high pressure winning the day, keeping it dry.
The dry conditions would then persist for the start of the new work
week.
Long range guidance starts to top the ridge with bits of shortwave
energy for the later half of the week. While the brunt of the upper
level forcing may hold north of the local area, associated sfc
boundaries could provide a focus for pcpn development. In addition,
an MCV or two could push across the ridge from nocturnal convection
over the plains. Nothing clear cut at this time but warrants at
least low end chances (20%) from time to time for now.
TEMPS: with the ridge building in, so will warmer air - although not
looking "hot". Both the GEFS and EPS suite of ensemble members
suggest temps at or few degrees above normal though much of the new
week. Dewpoints aren`t climbing much either, so humidity looks to be
held "in check". Ensembles start to trend warmer moving into the
weekend, but also show larger spreads in potential outcomes. As
mentioned earlier, the models aren`t quite sure whether more ridging
will persist or broader zonal flow will return - thus the range of
temps.
&&
.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 946 PM CDT Sat Aug 17 2024
Fog potential will be the main TAF consideration through the
overnight hours and into Sunday morning. With ongoing dewpoint
depression trends favoring some fog formation at KRST, decided to
introduce MVFR visby reductions at the TAF site. Questions remain
how low visbys can go with the 18.01z RAP showing winds off the
deck to 10-20 kts which should work against more substantial
visby reductions. However, when considering some probabilities
(10- 40%) for IFR visbys in the 17.12z HREF, would not totally
dismiss the potential for IFR reductions at KRST. Otherwise,
conditions into Sunday afternoon remain VFR with few to sct low-
VFR cumulus. Winds generally remain from the north at 5-10 kts.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Rieck
AVIATION...Naylor
Area Forecast Discussion
National Weather Service Boston/Norton MA
1048 PM EDT Sat Aug 17 2024
.SYNOPSIS...
Dangerous rip current continue due to distant Ernesto through
Sunday. Spotty showers possible across western/central MA and
CT tonight. Otherwise dry with low clouds and fog. Low clouds
slow to erode on Sunday due to persistent onshore flow. A slow
moving frontal system moving in from the Great Lakes will bring
several opportunities for showers and thunderstorms Sunday
evening through Tuesday. Locally heavy downpours are possible,
but severe weather potential is very low. Drier weather for the
middle portion of the week with cooler than normal temperatures.
Warming trend for Friday into the weekend but with continued
generally dry weather.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Stratus was located over the coastal waters east of MA late
this evening, and is expected to move onshore overnight.
Scattered showers over northern NJ and southeast NY state should
also arrive later tonight as well. The last few runs of the
HRRR seems to have the right idea, but perhaps is not perfect
with the timing. Generally liked the focus across portions of CT
and western and central MA, so used that idea to tweak rainfall
chances overnight.
Minor tweaks to temperatures to reflect observed trends.
730 PM Update:
Starting to see stratus re-develop and/or return back landward
from the coastal waters now that the sun is starting to set and
the boundary layer begins to cool. The trend will be for
continued SE to NW advance of stratus in general thru late
evening/midnight. Still an open question on the extent of fog,
but I think odds are against dense fog coverage. MOS products
seem to hit the potential the hardest, but recent GFS LAMP
output is starting to back off on the visbys. I`d feel somewhat
more confident about about larger dense fog coverage if the
near- surface lapse rates were more inverted/stable than what
the NAM/RAP/HRRR indicates in the lowest 2000 ft AGL. Nonetheless,
a pretty gray evening is expected with light southeast winds.
Though there are a few showers in the lower Hudson Valley,
they`re moving into the surface ridge axis and dissipating as
they do so, and I`d expect that to continue with dry weather by-
and- large.
Previous discussion:
Highlights
* Dangerous Rip Current Risk continues.
* Low clouds and stratus return. Spotty light showers across
central/western MA and CT.
Cyclonic flow in place with a trough parked over the Great Lakes
region. A shortwave trough will lift from the eastern Great
Lakes/Mid Atlantic this evening into New England tonight. A
broad low is located over the central/eastern Great Lakes while
we remain under persistent onshore flow.
Anticipating dry and quiet weather for much of the region
tonight. Will gradually see PWATs increasing to roughly 1.5 to
1.75 inches across western/central areas tonight. This is also
where we will have a roughly 15-25 kt southerly low level jet
impinging on the region. Did adjust our precip chances based on
this setup, but think best shot for showers is across western
MA and CT. Main concern is we are quite removed from strong
forcing, which is why activity overnight may be spotty in
nature. Wondering if some guidance hinting more at a more
widespread drizzle vs showers. At this point given the moisture
available went with showers. Low temperatures in the 60s.
One thing we will need to keep a close eye on is the stratus
deck advecting onshore across eastern areas. Some pieces of
guidance, GLAMP/HRRR, show patchy dense fog moving in. Did lower
our visibilities a bit in the latest update, but did not go as
low as latest GLAMP/HRRR at this time. Will need to monitor as
night progresses.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Highlights
* Dangerous Rip Current risk continues due to distant Ernesto.
* Spotty AM showers across western/central areas diminishing.
Dry for much of Sun. Near to slightly cooler than seasonable
temperatures.
* Showers along with isolated thunderstorms spread in from west
to east Sun Night into Mon.
Cyclonic flow lingers across the Great Lakes and New England
through this timeframe. The trough over the central/eastern
Great Lakes early on Sun will slowly slide into the eastern
Great Lakes/Mid Atlantic by early Mon. Another shortwave lifts
from the Mid Atlantic late on Sun into New England Sun Night. A
slow moving frontal system will gradually slide into Upstate NY
on Sun/Sun Night.
Clouds slow to erode across southern New England on Sun due to
persistent onshore flow, but thinking improvement will be faster
than on Sat given there should be better mixing within the
boundary layer. In addition, think any lingering showers/drizzle
across western/central areas Sun AM will exit as the first
shortwave moves off to the northeast. High temps may be a few
degrees warmer than today given the better mixing and skies
clearing a tad bit faster. Highs range from the mid 70s to low
80s. Main concern along south facing beaches continues to be the
high risk for rip currents due to the increased swell from
distant Ernesto.
Return of more unsettled weather late Sun into Mon as another
shortwave lifts into the region. Will have a better shot for
more widespread showers as the broad low moves into Upstate NY.
Will see PWATs increasing to roughly 1.5-2 inches as the trough
approaches and southerly flow increases. There is a bit more
instability available with a few hundred J/kg of MUCAPE in
place. Not out of the question there are some heavy downpours
given the environment, but think risk greater during the day
Mon. See the Long term section for more of these details. Lows
in the 60s.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
Highlights:
* Slow-moving frontal system brings mostly cloudy weather and
several opportunities for showers/t-storms Mon and Tue.
Severe weather potential is low, but localized downpours
leading to isolated instances of flooding could be possible.
Temps seasonable but humid.
* Drier weather with cooler than normal temps Wed and Thurs.
* Continues dry Fri into the weekend, but with a warming trend.
Details:
Monday and Tuesday:
This is the more active period of weather in the long-term forecast
period. Mid/upper level trough and its associated surface frontal
system initially over NY/PA to slowly progress eastward and offshore
through Tue. Although the forecast PoPs (Likely/Categorical Mon,
then solid Chance for Tue) are pretty broad-brushed, guidance seems
to convey some agreement in there being multiple opportunities for
showers and embedded t-storms in this timeframe. One is with an
approaching warm front which moves in Mon AM to early aftn with a
related rise in deep moisture/PWAT values (to around 1.5 to 1.7
inches). We then should see more broader warm-sector-airmass showers
and embedded t-storms for Mon aftn to evening, and while not
everyone will see rains in this general timeframe, there will be
showers and storms around. The final period of showers and storms,
perhaps energized by disorganized trough energy over the lower mid-
Atlantic region, comes in on Tue before the cold front slips
offshore later Tue aftn or early night.
Convective instability for both days looks to be tempered by reduced
diurnal heating from lots of cloud cover, and wind shear also isn`t
supportive of organized severe weather. However there should be
enough instability for lightning, with forecast MUCAPEs in the 500-
1000 J/kg range. With several opportunities for showers and t-storms
in this period, infused by elevated PWATs and warm cloud depths
around 11-12 kft, localized instances of flooding could need to
be monitored in this period; but with that said, models show
varied placement of QPF bullseyes and that makes it difficult to
provide any location or timing specifics at this juncture.
Particularly for Tue, consideration will also have to be given
to where prior heavy rain footprints took occur/where FFG is
locally reduced, which are obviously unknown at this time.
Trained machine- learning progs also indicate limited/marginal
potential for excessive rainfall.
Temperatures in this period should run near to slightly cooler than
normal (could see highs only in the 70s, with upper 60s/low 70s
Tue), but it won`t feel that way with elevated humidity levels until
the cold front clears us out by Tue evening.
Wednesday and Thursday:
Cyclonic flow aloft associated with a shot of anomalously cool 925-
850 mb temps then settles in over the Northeast states, with surface
high pressure supplying MUCH drier conditions. Overall a pretty
pleasant stretch of weather that may feel more like a typical day in
mid-September than mid-August. Will have to watch for
nighttime/early morning fog potential with a pattern of clear skies,
light winds favored each night and wetting rains from early in the
week. Highs mainly in the 70s both Wed and Thurs, with lows in the
50s, perhaps some mid/upper 40s NW MA and the sites which typically
radiate well at night under clear/calm conditions.
Friday into Next Weekend:
Drier stretch of weather continues into this forecast period as
broad high pressure shifts seaward over the mid-Atlc waters. Warming
trend closer to above normal temps then becomes more favored by late
in the week into the weekend.
&&
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight: High confidence in trends, moderate in timing.
Gradual deterioration toward IFR/LIFR conditions (occurring
soonest with the worst categories S/E of I-95), mainly in
stratus. Development of fog is still a low-confidence prospect
and with GLAMP now starting to back off on reduced visbys, its
coverage may end up being more sparse than last night/this
morning. Light E/SE winds.
Sunday...Moderate confidence.
IFR stratus to start will slowly lift to MVFR with some spotty
VFR as onshore flow continues. Though we may mix enough in
eastern areas where we lift those lower ceilings more firmly to
VFR levels. Spotty AM showers out in western areas. SE winds
5-15 kts.
Sunday Night...Moderate confidence.
Return of IFR to LIFR stratus and fog with persistent onshore
flow. Showers and isolated thunderstorms spreading in from west
to east as the night progresses. E to SE winds around 5-10 kts
or less.
KBOS TAF...High confidence in trends, moderate in exact timing.
Gradual deterioration to MVFR stratus decks, then a return to
IFR decks later tonight which continue into the early Sunday
morning hrs. Slow improvement to MVFR on Sun due to persistent
onshore flow. SE winds 5-8 kt.
KBDL TAF...High confidence in trends, moderate in exact timing.
Borderline MVFR ceilings linger heading into this evening.
Spotty rain showers along with ceilings lowering to MVFR/IFR
conditions roughly through 05Z. Slow improvement to higher MVFR
levels on Sun due to prolonged southeasterly flow.
Outlook /Monday through Thursday/...
Monday: Mainly MVFR, with local IFR possible. SHRA, scattered
TSRA.
Monday Night through Tuesday: Mainly VFR, with local IFR
possible. Chance SHRA, isolated TSRA.
Tuesday Night: VFR. Chance SHRA.
Wednesday through Thursday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Sunday Night...High confidence.
Expecting persistent SE flow at 5-10 kts through the vast
majority of the period. Wind gusts remain generally below 20 kts
as well. Seas remain elevated due to the powerful swell
associated with Ernesto. This keeps 5-7 ft seas across the outer
waters through Mon, so have extended the Small Craft Advisory.
This is also the case for the nearshore waters across coastal
Rhode Islands where 3-5 ft seas linger. Rain showers along with
thunderstorms could spread into the waters Sun Night.
Outlook /Monday through Thursday/...
Monday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers, isolated thunderstorms.
Monday Night through Tuesday: Winds less than 25 kt. Seas up to
5 ft. Chance of rain showers.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers.
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft.
Wednesday Night through Thursday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents from 6 AM EDT Sunday through Sunday
evening for MAZ007.
High Risk for Rip Currents through Sunday evening for MAZ022>024.
RI...High Risk for Rip Currents through Sunday evening for RIZ006>008.
MARINE...Small Craft Advisory until 8 PM EDT Monday for ANZ235-237.
Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254>256.
&&
$$
SYNOPSIS...Loconto/BL
NEAR TERM...Belk/Loconto/BL
SHORT TERM...BL
LONG TERM...Loconto
AVIATION...Belk/Loconto/BL
MARINE...Loconto/BL
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
944 PM CDT Sat Aug 17 2024
...New MESOSCALE UPDATE...
.MESOSCALE UPDATE...
Issued at 943 PM CDT Sat Aug 17 2024
Convective activity has shifted out of the forecast area and just
some remnant convective debris is left across the south half.
Several updates were made earlier to capture temps that were
impacted by precip/cooler outflow so things are pretty much on
track. Will updated to capture temp tweaks shortly.
Focus will shift to Sunday, it will be HOT as we will reside in the
lower level thermal axis. It sure looks like it will be the hottest
day of the year for most locations with Highs peaking in the 98-102
range with some 100-105 very possible. As for storms, it`s not a
slam dunk as the atmosphere, as often the case with volatile
situations, will be right up to a point that could go either way. In
the "either way" I`m referring to is just enough to convect and we
get very windy storms which in-turn establish deep enough cold
pools to develop additional cells and we ultimately get an organized
cluster. The other way would be there`s too much dry air and limited
lower level convergence that doesn`t overcome any capping resulting
in few to no convective cells. While each scenario remains on the
table, the latest 00z CAMs are favoring convection. While
instability is not anticipated to be extreme, there`s other elements
of the likely environment that are very rare for us. First will be
storms developing in 98-104 degree temps. From this, there will be
very steep lapse rates in the 0-3 and 0-4 km layers that will allow
for efficient momentum transfer to the surface. Also between 700-
400mb there will be strong flow of 30-40kts. I`ll add in dry air in
the mid levels as well which will all for more evaporative cooling
as we should see Dcape values in the 1200-1600 j/kg range. So, with
all that, the signal we see from the HRRR and NAM3km with strong
downdraft wind signatures are very telling. Compiling all of this
offers the potential for a more widespread wind event along with
some potential for sig type wind gusts as well. Still more details
to cover, but wanted to offer the potential and some background as
to why. Lastly, timing looks to be later and main time window for
this appears to be 4p to midnight. /CME/
&&
.DISCUSSION...
Issued at 231 PM CDT Sat Aug 17 2024
Tonight through Monday...
Tonight: Convection should persist through early evening, but wind
down before midnight. In the wake, a quiet night will be in store,
with some potential patchy fog in low-lying areas or locations that
receive rainfall. With increased boundary layer moisture,
persistence forecast, with seasonably warm lows in the mid-upper 70s
(74-78F) are expected.
Sunday-Monday: An active period of excessive heat & severe storms is
expected Sunday, before a frontal zone moves through, finally
breaking the grip of the heat & more seasonable & dry conditions
move in next week. Synoptic & sfc pattern will consist of deep mid-
level ridge centered over west TX to the southwest states while mean
longwave trough persist east of the MS River Valley. This will keep
perturbed northwest flow & a frontal zone is expected to sink
southward into Sunday. Moisture & deep mixing is anticipated in
advance of the frontal zone moving in. Guidance indicates efficient
mixing up to 850-700mb layer. There are indications combined with
this deep mixing, favorable thermo profiles (i.e. 28-30C vertical
totals & DCAPE nearly 1800-2000 J/kg) & 25-40kt bulk shear in the
mean 0-2 to 0-6km layer, southward moving organized convective
clusters could contain some higher end gusts near 70mph at times &
quarter size hail. Convective allowing models (CAMs) indicate some
potential of gusts in excess of 50-60kts, so strong to severe storms
remain a low-medium chance, where advertised "Slight" risk looks on
track. The convective outlook area has been brought further
southwards towards I-20, which seems to be in agreement with most
guidance. With convective storm onset in the mid-late aftn
timeframe, mainly between 2-4PM, high boundary layer moisture ahead
of the boundary will lead to continued dangerous heat stress again
into the aftn to early evening hours. With seasonably warm highs in
the 98-102F range & excessive heat potential more expansive, the
"Significant" area was expanded east along I-20 & southeast, with
the "Extreme" taken out of the Delta, with less oppressive
conditions today, while pulled eastward near east MS due to ongoing
persistent dangerous heat & expected conditions Sunday. Heat
headlines were maintained from mid-morning to early evening , with a
heat advisory in east-northeast MS & a Excessive Heat Warning areal
configuration with similar but slightly larger coverage. The
Excessive Heat Warning may be able to be adjusted to the northeast
but some earlier convective coverage makes this potential a low
confidence forecast. Will led later shifts decide on any further
adjustments. Expect storms to persist into the evening hours but
could linger a little later closer to midnight. For now, timing
looks mostly intact but may be able to be refined as confidence
increases. Timing looks to be mid-late aftn & persist into the
evening, with rain & storm chances in the isolated to scattered
range (15-40%).
As heights in the ridge to the west begins to fall, there will be
continued surges of drier & less oppressive airmass beginning to
move in the region into next week. This will help highs become more
seasonable in the low-mid 90s & lows in the mid-upper 60s north of I-
20 to upper 60s to near 70F in the south into Tuesday morning. Some
storms are possible but become more focused into the Hwy 84 corridor
into Monday aftn to early evening. Can`t rule out an isolated strong
storm in southwest MS & portions of northeast LA on Monday. /DC/
Tuesday through Friday...
Post frontal passage will bring relief from the oppressive
heat/humidity of the previous week. Upper/mid-lvl ridge will
primarily encompass the Southern Plains/CO/NM area, placing the
ArkLaMiss region on the periphery of the ridge. As a result,
northwest to northerly flow allows for dewpoints to fall into the
upper 50-mid 60s range across the area, lowering humidity for the
area. Afternoon high won`t be as hot either, as upper 80s/lower 90s
temps are expected. Low temperatures will more likely resemble early
fall than summer, as low temperatures are expected to range in the
60s midweek to near 70 degrees by late week. /SW/
&&
.AVIATION...
(00Z TAFS)
Issued at 635 PM CDT Sat Aug 17 2024
Precip/storms have moved to our south and TAF sites will remain
VFR for the period. By Sunday afternoon, the northern half of the
area will see WNW winds with some gusts as we heat up. Storm
chances will increase late, but that looks to be mainly after 21z
and will hold off on including in the TAFs until timing/location
fit better. /CE/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 76 100 74 92 / 0 20 40 20
Meridian 74 101 71 93 / 0 30 30 10
Vicksburg 76 101 74 92 / 0 20 30 20
Hattiesburg 76 100 75 95 / 10 10 30 20
Natchez 76 100 75 92 / 10 10 30 30
Greenville 75 100 72 90 / 0 20 30 20
Greenwood 75 100 72 92 / 0 10 20 10
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for MSZ018-
019-025>029-032-034>037-040>044-047>066-072>074.
Heat Advisory from 10 AM to 8 PM CDT Sunday for MSZ030-031-033-
038-039-045-046.
LA...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for
LAZ007>009-015-016-023>026.
AR...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for ARZ074-
075.
&&
$$
CME/DC/SW
AREA FORECAST DISCUSSION...CORRECTED
National Weather Service Jackson KY
1033 PM EDT Sat Aug 17 2024
.KEY MESSAGES...
- Below normal temperatures are expected Sunday through Wednesday
behind a cold front passage late Saturday night.
- Showers and thunderstorms will remain possible Sunday and
Monday, especially in the afternoon and early evening, with a
drying trend for Tuesday into Wednesday.
&&
.UPDATE...
Issued at 1029 PM EDT SAT AUG 17 2024
Updated grids, especially PoPs and sky for latest trends form the
regional radar loops. Dropped overnight lows just slightly after
impacts of evening convection. Lows may have been met, at least
until the cold front pushes through the area later tonight. Temps
may actually rebound just slightly through the remainder of the
night. Active night, but intensity of storms have been gradually
decreasing with time. However, there are still some respectable
storms out there with breif, locally heavy rainfall and intense
lightning. These last cluster of storms will continue to pass
through eastern Kentucky over the next few hours. Will see
considerably less activity overall, but the threat of at least
some minimal (isolated) convection will continue through the
overnight period for portions of the area. Another round of
showers and storms is expected to impact the area tomorrow.
Trends have been for slightly less activity Sunday and even less
on Monday. The hrrr has been fairly consistent with convection
being focused in the southwest tomorrow. Will continue to
evaluate. Updated grids and zones have been issued.
UPDATE Issued at 513 PM EDT SAT AUG 17 2024
Did a quick update to do a fairly big overall update to the PoPs
given the line of storms rolling through parts of eastern Kentucky
late this afternoon and evening. These have been strong to severe
at times and will continue to track southeast. Outside this
overall minor update for other elements.
&&
.SHORT TERM...(This evening through Sunday night)
Issued at 505 PM EDT SAT AUG 17 2024
We are seeing a notable upper low push across the Great Lakes this
afternoon and this will reflect down to the mid-levels with embedded
shortwaves riding through the associated trough axis across the
Ohio valley. We saw a notable boundary where cumulus first
developed this afternoon and this has overall been one of the main
focus areas for convection this afternoon. Some of these storms
have been spiting at times given the somewhat straight and
concave up hodographs noted in the SPC mesoanalysis. There
remains a risk of severe storms through the remainder of the
afternoon and perhaps into the early evening before storms should
loose better daytime heating. Outside this very little changes
were needed for the near term forecast this afternoon.
Tonight, most of the convection will relent through the evening, but
some of the CAMs indicate possibly a bit more in the way of showers
and thunderstorms into the late night hours. However, CAMs have been
all over the place in the way of where convection will be and
haven`t been managing the convection this afternoon well. This leads
to a fair amount of uncertainty. Given this went more toward a
southeastward trend with PoPs through the evening and overnight.
This seems to be reasonable given the more cold pool look this is
taking on. The highest PoPs will be early in the evening before
tapering from west to east through the night. This trend will have
to be watched given the uncertainties and lack of CAM support.
Outside this overnight lows will be in the mid to upper 60s.
Sunday, we will see increasing chance of showers and thunderstorms
through the afternoon and evening. This as a mid-level trough
deepens in the Ohio Valley and it ushers in northwest flow at the
surface leading to PoPs in the 60-70 percent chance range mainly
during peak heating hours. However, given the northwest flow
regime these showers and perhaps a thunderstorm could continue
into the evening and perhaps the night, but the HREF suggests
overall the trend would be downward for showers through the night.
This will have to be looked at closer in additional updates.
.LONG TERM...(Monday through Saturday)
Issued at 412 PM EDT SAT AUG 17 2024
The extended period will start off quite active, as an area of low
pressure moves through the area on Monday. We will see showers and
scattered thunderstorms rumbling through as the trough moves off to
the east. The rain should taper off late in the day, and be out of
the area by early Monday evening. After that, a large and well
developed ridge of high pressure will settle over the region, and
will bring dry and very pleasant weather to eastern Kentucky the
rest of the week. A much cooler air mass will advect into the region
on northwest winds through the middle of the week. In fact, we could
see daytime highs in the mid to upper 70s Monday, Tuesday, and
Wednesday, making it feel more like fall than mid-summer. With clear
skies, light winds, and strong sunshine, the air mass will finally
begin to modify on Thursday. Highs on that day should rebound to
more normal highs in the lower 80s. Thursday and Friday should be
even warmer, with highs on each of those days reaching the mid to
upper 80s.
With ridging overhead, and light winds and clear skies expected,
conditions will favor ridge valley temperature splits most nights.
Some valley locations may fall into the upper 40s Tuesday night and
Wednesday night, with low to mid 50s everywhere else. We could also
see patchy valley fog each night, especially early on after the rain
event moistens everything up. The only weather hazards to speak of
would be cloud to ground lightning that will be possible with any
thunderstorms on Monday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 841 PM EDT SAT AUG 17 2024
Thunderstorms are currently passing through the area. Flight
conditions have been predominantly VFR outside of thunderstorms.
Bases of these storms have been relatively high, above 030 AGL.
However, there has been some very strong gusty winds associated
with the strongest storms and VSBYS lower to less than a mile
with a direct hit from any thunderstorm. Storm motion is quite
high. Thus the decreases in flight categories will be short lived.
Storms will continue to work through the area during the evening
hours before dissipating. The stronger storms at TAF issuance were
generally located south of the I-64 corridor, and that continues
to be the case. Expect a lull in activity through the overnight,
though some isolated to widely scattered convection can not be
ruled out at any time. The next best round of showers and
thunderstorms will arrive during the day Sunday, where at this
time our southwestern most terminals, KSME and KLOZ appear to be
most impacted. Winds will be light, around 5 kts from the west,
southwest but will veer out of the west-northwest Sunday at 5-10
kts. Of note however, is that winds will be variable and gusty in
the vicinity of any storms.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...RAY
SHORT TERM...DJ
LONG TERM...AR
AVIATION...RAY
Area Forecast Discussion
National Weather Service San Francisco CA
549 PM PDT Sat Aug 17 2024
...New AVIATION...
.SYNOPSIS...
Issued at 1102 AM PDT Fri Aug 16 2024
Seasonal to slightly cooler than normal temperatures will continue
through the weekend into next week. Increased coverage of early
morning marine layer stratus, fog and drizzle is likely this
weekend. Less than 10% chance for thunder on Saturday.
&&
.UPDATE...
Issued at 539 PM PDT Sat Aug 17 2024
Satellite is showing some clouds still moving over our area
bringing chances of some light rain near the northern parts of our
area and along the coast. Therefore, our radar remains in
"precip" mode to capture any convection. Currently, no lightening
activity, as most of that is further northern California. No
changes were made to the forecast, as conditions remain on track.
SO
&&
.SHORT TERM...
(This evening through Sunday)
Issued at 259 PM PDT Sat Aug 17 2024
Upper-level troughing continues to be the name of the game. Said
upper-level trough is responsible for a non-zero (<10%) chance of
thunderstorms today across the North Bay in addition to gusty
conditions through gaps and passes. While our region is not
experiencing critical fire weather conditions, it is imperative to
remain vigilant when it comes to exercising fire weather safety as
grasses remain dry and winds will easily spread fire. Temperatures
will be near normal with tomorrow being slightly warmer than today.
Stratus is expected to fill valleys and low-lying areas tonight,
receding back to the coastline by tomorrow afternoon.
&&
.LONG TERM...
(Sunday night through next Friday)
Issued at 259 PM PDT Sat Aug 17 2024
As the upper-level low fills, temperatures will continue to warm up
through Tuesday. A brief, gradual cooldown will take place Wednesday
through Friday as troughing is expected to take shape. Uncertainty
with the forecast primarily lies in the amplitude of the trough -
will it be a cutoff low or will it be an open wave? If it is a
cutoff low, it will linger longer, the North Bay will have better
chances for measurable precipitation, and onshore winds will
noticeably increase. If it is an open wave, it will move through
quicker with the better chances of precipitation confined to the
north. Either way, any kind of troughing offshore will promote
moist, onshore flow, which is a good thing.
&&
.AVIATION...
(00Z TAFS)
Issued at 548 PM PDT Sat Aug 17 2024
It`s a complex pattern resulting in largely variable weather
conditions this afternoon, it`s VFR inland while it`s a mix of
MVFR and localized IFR (including fog, mist) along the immediate
coast. Higher dewpoint air i.e. higher water vapor has arrived
across much of the forecast area, surface dewpoint temperatures
are in the lower to mid 60s. Additionally a layer of cool air
advection aloft with the offshore trough of low pressure has moved
in mostly between 925 mb (~2500 feet) and 850 mb (~5000 feet)
resulting in low clouds with a mix of stratus/stratocumulus and
periodic light drizzle/light rain along the coast. SFO Airport
reported a trace just after 4 pm for example. For the 00z TAFs, dry
weather is forecast specifically at the terminals
Cool air advection aloft has weakened and deepened the marine
layer temperature inversion per recent profiler data at Bodega
Bay, Fort Ord and Point Sur. A loss of northwest winds and upwelling,
including a still steep August sun angle and heat input into sea
surface temperatures has also reduced the lower level temperature
inversion to sea surface temp difference. The amount of stratus
returning tonight including the development of IFR will rest
largely on clear sky aloft for radiative cooling and if there`s
any additional cool air advection. The 00z TAFs carry a combination
of MVFR-IFR ceilings for tonight and Sunday morning, diurnal surface
warming should help lift ceilings most locations to MVFR-VFR
Sunday afternoon.
Vicinity of SFO...North-south band of low clouds /MVFR/ with
higher dewpoint air is adhering to the SF Peninsula for the
evening. Post sunset cooling will be a combination of residual
cool air advection and radiative cooling supporting a continuation
of ceiling at the terminal for the overnight hours and Sunday
morning. The RAP model is forecasting IFR during the evening,
kept in inherited 18z TAF IFR ceiling forecast for 06z this
evening. KHAF has reported a low ceiling & visibility in fog,
thus LIFR-IFR is there on the other side of SF Peninsula. IFR
06z-16z Sunday then improving to MVFR-VFR thereafter for the
remainder of the morning and afternoon. West wind near 12 knots
decreasing to 5 to 10 knots tonight and Sunday morning, increasing
to near 15 knots Sunday afternoon.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Same as the Bay Area, largely variable
weather conditions here this afternoon. Low clouds moving in over
KWVI with IFR ceiling reported, KSNS and KMRY holding onto VFR for
the time being. Low clouds will initially run into late afternoon
diurnal surface warming and vertical mixing with surface temperatures
in the lower 70s over the southern Monterey Bay. With the weakened
marine layer temperature inversion on recent Fort Ord profiler data,
00z TAFs currently advertise tempo MVFR ceilings, however may need
to amend for IFR if the low ceilings over the northern Monterey Bay
hold together as the ceilings move south and east. Ceilings mixing
out by late Sunday morning with generally MVFR-VFR conditions during
the afternoon. Onshore winds 5 to 15 knots during the period.
&&
.MARINE...
(Tonight through next Thursday)
Issued at 259 PM PDT Sat Aug 17 2024
Light to gentle breezes are anticipated across most of the marine
zones tonight. The exception will be across the northern San
Francisco and San Pablo Bays where intermittent moderate breezes
are forecast. Primary swell will continue to roll in from the west
and northwest with wave heights ranging between 2 and 6 feet.
Fresh to moderate breezes are expected Sunday afternoon into next
week, especially near and south of Point Sur. In response, seas
will increase to 6 to 8 feet across southern zones and low-end
marine headlines may be needed Sunday afternoon and into early
next week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...Bain
Visit us at www.weather.gov/sanfrancisco
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Area Forecast Discussion
National Weather Service Nashville TN
713 PM CDT Sat Aug 17 2024
...New AVIATION...
.UPDATE...
Issued at 634 PM CDT Sat Aug 17 2024
As of 630pm, there were no storm in Middle Tennessee, but a storm
over far southern KY had sent a nice outflow boundary down toward
Dover and Lafayette. The afternoon has been very hot and very
sunny. Thanks to strong subsidence between storms to our east and
an approaching front to our northwest, the air has dried out
considerably this afternoon with dew points dipping to 60 at BNA
while the temperature surged to 99.
The low dew points have dropped cape values down below 1000 J/kg,
thus no storms and really no clouds. But, a band of much higher
dew points and cape values was upstream ahead of the cold front.
These greater moisture and instability values will slide into
Middle Tennessee over the next couple of hours, and as the front
approaches, scattered thunderstorms are expected to develop. HRRR
shows this and the NAMNest really blows it up along the front. A
few storms could still produce gusty winds and heavy downpours.
Unfortunately, the coverage will be lower than we previously
hoped, so many people wanting some rain will not get it, and it
looks quite dry through the coming week. The best chance this
evening will be across the Upper Cumberland.
The forecast data was recently updated to reflect the hot temps
and low dew points. Also, hourly pops were updated with lower
expected coverage.
&&
.SHORT TERM...
(Rest of today through Sunday)
Issued at 1033 AM CDT Sat Aug 17 2024
A weak upper trough has come through Middle Tennessee already
this morning, and there`s another one positioned to our immediate
west that will come through later on. In addition, a rather
pronounced surface boundary will soon begin inching its way across
the mid state. Already, the instability needed for additional
convection is in place, and the dynamics will be there with the
surface and upper patterns being what they are. Most of Middle
Tennessee remains under a marginal risk of severe storms today &
tonight, with a portion of northeast Middle Tennessee under a
slight risk. So the next several hours may be somewhat busy
weatherwise, but the activity looks to diminish during the
overnight hours, with maybe some lingering cells over the
Cumberland Plateau early Sunday. Temperatures tomorrow will be
several degrees cooler than today owing the air mass change coming
with the fropa.
&&
.LONG TERM...
(Sunday Night through next Saturday)
Issued at 1033 AM CDT Sat Aug 17 2024
Rain chances after tomorrow will be virtually nonexistent. High
pressure will dominate our weather pattern next week, with
temperatures hovering below seasonal norms until maybe Friday.
Even looking out to 240 hrs., there is only high pressure. So once
this weekend`s active weather system departs the region, we`re
headed back into a dry pattern for the foreseeable future.
&&
.AVIATION...
(00Z TAFS)
Issued at 713 PM CDT Sat Aug 17 2024
VFR generally thru 18/24Z. CSV obs since 17/1853Z, AMD NOT SKED
removed. Convection moving thru SE/SC KY. Lightning activity
noted, but if SEWD progression continues, low confidence per more
stability across our area to mention prevailing shwrs/tstms,
mentioned only vcnty shwrs. Convection should dissipate by 18/04Z.
MVFR patchy fog formation possible all terminal sites
18/09Z-18/14Z. Shwrs/tstms possible SRB/CSV after 18/18Z, but low
confidence prevailing shwrs/tstms, mentioned only vcnty shwrs.
&&
.PRELIMINARY POINT TEMPS/POPS...
Nashville 72 89 68 86 / 40 20 0 0
Clarksville 69 87 65 84 / 40 10 0 0
Crossville 64 80 61 77 / 50 50 10 10
Columbia 71 90 66 87 / 20 10 0 0
Cookeville 66 80 63 78 / 50 40 10 10
Jamestown 65 79 62 77 / 50 70 20 20
Lawrenceburg 70 89 66 86 / 20 10 0 0
Murfreesboro 70 89 67 86 / 40 20 0 0
Waverly 69 88 66 86 / 30 10 0 0
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Rose
LONG TERM....Rose
AVIATION.....JB Wright
Area Forecast Discussion
National Weather Service New York NY
1030 PM EDT Sat Aug 17 2024
.SYNOPSIS...
A weak low tracks slowly eastward through the Great Lakes region
tonight, and approaches Sunday. Meanwhile another low develops
during Sunday over southeastern Pennsylvania and eastern
Maryland. This low then deepens Sunday night into Monday and
tracks northeast bringing a cold front across the area late
Sunday night into Monday. A secondary frontal passage moves
through Tuesday. High pressure builds in for the middle and end
of the week.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Forecast generally on track. Made some adjustments to PoPs
over the next few hours to account the latest radar trends.
There is still the potential for one round of moderate to heavy
rainfall late tonight into early Sunday morning. The Flood Watch
remains in effect for NE NJ into the Lower Hudson Valley at 06z
and continues through into Sunday night. The 00z HRRR has backed
off on its depiction from earlier of a more organized band of
heavy rain across the watch area early Sunday morning. Heavy
downpours may end up more scattered, but would like to see the
rest of the 00z CAMs before making any changes to the rest of
the forecast. Rainfall rates may peak late tonight around 1
inch per hour. Isolated flash flooding is also possible a little
farther to the east, into New York City and Putnam and
Westchester counties, with poor drainage and urban flooding
possible.
With the upper ridge remaining into the western Atlantic,
showers will continue to struggle to move eastward across Long
Island and CT with many locations remaining mostly dry out east
through the night.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
A Flood Watch is in effect from late tonight, 06Z Sunday,
through late Sunday night, 06Z Monday, for the potential for
scattered flash flooding, urban and poor drainage flooding, and
possibly fast responding streams of northeastern New Jersey.
Rainfall rates could be near 1 inch per hour, and at times
approach 2 inches per hour. Total rainfall in the watch area
will be around 2 inches to 2.5 inches with locally as much as 3
inches possible. This will be with a slow moving frontal system
and with training showers and isolated thunderstorms, as the
flow nearly parallels the trough. Also, precipitable waters
increase to just over two inches Sunday, and warm cloud process
increase along with a 20-230kt low level jet during Sunday and
into Sunday night. This system will be slow moving eastward as
downstream riding remains across the western North Atlantic. An
then during Sunday a frontal wave develops near the mid Atlantic
coast, across southeastern Pennsylvania into the Delmarva. This
low provides lift for heavy rainfall as this low tracks slowly
northeast to east across northeastern New Jersey into New York
City and then to the northeast of the area during Monday.
&&
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
The area remains under a large-scale trough with vorticity
maxima moving through Monday night and into Tuesday. As the
trough tries to lift during the day on Tuesday, additional
energy descends from the north to allow for another round of
forcing. At the surface, this should translate into the form of
a secondary frontal passage that brings another round of showers
with possible embedded thunderstorms, especially Monday night
into Tuesday morning. Any residual showers should diminish into
the afternoon on Tuesday with the passage of the surface cold
front.
There is still some uncertainty as to how quickly the trough
lifts with the upper-level energy rotating over New England,
but consensus has been that the trough departs late Wednesday
into Thursday and ridging begins to move over the area from the
west. At the surface, a relatively strong high pressure system
builds into the Mid- Atlantic and Northeast from Wednesday
through the weekend. This will provide fairly calm and dry
conditions through the rest of next week.
This high pressure will be accompanied with primarily N/NW winds
and a much cooler airmass. The airmass should be fairly
anomalously cool for middle to late August. High temperatures on
Tuesday and Wednesday may not rise out of the upper 60s to low
70s for much of the area. Even coastal areas, highs will only be
in the low to maybe middle 70s. Lows Wednesday night and
Thursday night will likely be fairly chilly, with some locations
for the interior and outlying areas possibly dropping into the
low 50s or upper 40s, depending on the strength of any
radiational cooling. Temperatures will gradually moderate into
late week and the weekend with highs by Friday and Saturday
rising back into the upper 70s to low 80s.
&&
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
A frontal system slowly approaches the terminals through the
TAF period.
VFR to start for NYC terminals on north and west with MVFR with
some local IFR further east. Conditions should slowly lower to
MVFR overnight at all terminals. Scattered showers are possible
at any time through 09z, especially from KISP and KBDR on west.
More widespread showers 09-15z, possibly heavy at times, are
expected especially NYC terminals on north and west.
MVFR conditions are likely to continue through Sunday evening
although there could be some brief improvement to VFR at times
in the afternoon. Showers remain possible into Sunday evening,
especially along and west of the Hudson River corridor. Further
east, a brief shower is possible, but the most widespread shower
activity likely holds off until after 00z Monday.
There could be an isolated thunderstorm early Sunday morning,
mainly NYC metro terminals on north and west. Potential for
thunderstorms increases a bit Sunday afternoon/evening for the
same terminals and have included a PROB30 for this time period.
Winds will mainly be SE around 10 kt or less through the TAF
period. Coastal terminals could see winds a few kt higher at
times, especially Sunday afternoon. There is also a chance for a
few gusts 15-20 kt Sunday afternoon.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Timing of return to MVFR may be off by 1-3 hours. Amendments
for changing flight categories likely through the TAF period.
Isolated thunderstorms possible 10-16z Sunday.
Timing of PROB30 TSRA Sunday afternoon and evening may be off by
several hours with adjustments likely.
OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY...
Sunday night: Showers with possible thunderstorms. MVFR to
occasional IFR conditions.
Monday: Showers with possible thunderstorms, especially
afternoon and evening. MVFR or lower at times.
Tuesday: Mainly VFR. A chance of showers with MVFR possible. NW
wind gusts 15-20 kt.
Wednesday-Thursday: VFR.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90
&&
.MARINE...
Rough ocean seas and long period swells, 12 to 15 second, will
persist this weekend and into early next week as distant TC
Ernesto passes well offshore in the open Atlantic. This will
also lead to rough conditions around inlets. Please refer to the
National Hurricane Center for official forecasts regarding
Hurricane Ernesto. A Small Craft Advisory is in effect for the
ocean zones, and was extended through Monday night.
Elevated wave heights on the ocean zones will allow for SCA
conditions to continue Monday night and possibly into the day on
Tuesday with some marginal wind gusts near 20-25kt with the passage
of a cold front. Late Tuesday, wind diminish and wave heights should
fall below 5 feet. Sub-SCA conditions are then expected with high
pressure moving into the area by mid-week.
&&
.HYDROLOGY...
A Flood Watch is in effect late tonight into late Sunday night
for Northeastern New Jersey and into the Lower Hudson Valley
west of the Hudson River.
Locally heavy rainfall is possible late tonight, and again
during Sunday into Sunday night, particularly west of the NYC
metro and Hudson River. The threat of heavy rainfall expands to
the east into Western Long Island and portions of southern
Connecticut, and with the slow movement of low pressure and
lower rainfall amounts and rainfall rate was not confident
enough to go farther to the east with the Flood Watch.
Total rainfall amounts from tonight through Monday night range
from around a half inch east to around 2 inches from NYC metro
on north and west. Locally higher amounts, possibly up to 3
inches, are possible across northeastern New Jersey into the
Lower Hudson Valley. Isolated to scattered instances of flash
flooding are possible across the more flood prone areas of NE
NJ and adjacent areas of the Lower Hudson Valley, and perhaps as
far east as NYC. A more widespread threat for localized flash
flooding, along with nuisance flooding of urban and poor
drainage areas, sets up on Monday.
No hydrologic concerns Tuesday through next weekend.
&&
.TIDES/COASTAL FLOODING...
A high rip current risk is in place through Monday. This is due
to SE to S long period swells from Hurricane Ernesto.
Ocean seas are forecast to be highest Sunday into Monday, with
heights up to 6-7 ft. There is potential for high surf along the
ocean beaches during this time frame as well as beach erosion.
A new moon on the 19th as well as swell from distant Hurricane
Enersto will elevated tide levels Sunday into early this week.
Minor coastal flooding is expected with high tide Sunday
evening across the back bays of Nassau and Western Sound along
the southwest CT and S Westchester coast. Have issued a Coastal
Flood Advisory for these locations. Localized minor coastal
flooding is possible across southern Queens, Southern Brooklyn
and lower NY Harbor. Locations may just touch minor benchmarks
and a statement has been issued. Additional minor flooding is
possible for high tide Monday evening and statements/Advisories
will likely be needed for similar locations as with high tide
Sunday evening.
Please refer to NHC for official forecasts regarding Hurricane
Ernesto.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Coastal Flood Advisory from 10 PM Sunday to 1 AM EDT Monday
for CTZ009.
NY...Coastal Flood Advisory from 10 PM Sunday to 1 AM EDT Monday
for NYZ071.
Flood Watch from 2 AM EDT Sunday through late Sunday night for
NYZ067-069.
High Risk for Rip Currents through Monday evening for NYZ075-080-
081-178-179.
Coastal Flood Advisory from 7 PM to 10 PM EDT Sunday for
NYZ179.
NJ...Flood Watch from 2 AM EDT Sunday through late Sunday night for
NJZ002-004-006-103>108.
MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ350-353-355.
&&
$$
SYNOPSIS...MET/MW
NEAR TERM...DS/MET
SHORT TERM...MET
LONG TERM...MW
AVIATION...DS
MARINE...MET/MW
HYDROLOGY...MET/MW
TIDES/COASTAL FLOODING...
Area Forecast Discussion
National Weather Service Pocatello ID
133 PM MDT Sat Aug 17 2024
.SHORT TERM...Today and Sunday.
Looking at current satellite imagery, there continues to be a deep
upper level low centered just off the coast of Oregon. Over
northern Utah, there is a trough with ample moisture moving
northeast into our area.
Look for isolated to scattered showers and thunderstorms, mainly
over our southern areas along the Utah border later this afternoon
into the evening. Expect gusty winds around 40 mph and up to 50
to 55 mph as well small hail and moderate to heavy rainfall under
thunderstorms. Our southern areas are under an excessive rainfall
outlook along the Utah border. Again, this is the area where
thunderstorms are most likely as well as be the strongest.
Tonight into tomorrow, models show us in the same pattern with an
upper level low off the Oregon coast. Models show moisture still
moving up from Utah combined with lingering moisture. Look for
isolated mostly afternoon showers and thunderstorms over most of
our forecast area. Look for scattered showers and isolated to
widely scattered thunderstorms along the Wyoming border in our our
area mainly Sunday afternoon. The biggest thunderstorm hazard
will be moderate to heavy rainfall. Our eastern areas bordering
the Wyoming border are in an Excessive Rainfall Outlook for
tomorrow afternoon. Small hail and gusty winds are likely as well
with thunderstorms tomorrow afternoon.
Expect temperatures today and Sunday near normal for this time of
year, mid to upper 80s with some lower 90s across our lower
elevations.
Wyatt
.LONG TERM...Monday through next Saturday.
Models continue to show lingering moisture in the area with
isolated to scattered showers and isolated to widely scattered
thunderstorms Monday afternoon. Our eastern areas along the
Wyoming border are under an Excessive Rainfall Outlook on Monday
too. Models show a drying trend Tuesday through early Thursday.
Models then continue to show moisture moving back in the area late
Thursday into next weekend. Temperatures will start the week near
normal if not slightly above normal and will stay that way
through Wednesday. Thursday temperatures will start trending
downward and look to be 4 to 8 degrees below normal by next
weekend.
Wyatt
&&
.AVIATION...
VFR conditions expected over the next few hours with mostly clear
skies. Increasing clouds and moisture will overspread the region
later this afternoon and into the evening. Hi-res CAMs bring a brief
period where showers, perhaps a few thunderstorms, will be possible
until around 18/04-06Z. There`s quite a bit of variability however
amongst the various models so don`t have a good feel for how things
will transpire. Nevertheless, the forecast has VCSH everywhere
except KSUN. Winds will become gusty out of the south in the SNake
Plain over the next few hours. During the overnight, precip moves
out, winds lessen and skies clear allowing VFR to prevail.
McKaughan
&&
.FIRE WEATHER...
Moisture and clouds will surge northward this afternoon out of Utah
bringing increasing chances for showers and some thunderstorms to
southern and eastern portions of the forecast area. Winds will
increase out ahead of this over the next few hours but RHs will also
surge with the increasing moisture so no concerns for Red Flags.
Sunday will see additional shower and storm development in the
afternoon hours but tstm coverage looks isolated in nature so no
need for any red flags that day either. Could see a bit better tstm
coverage on Monday with deeper moisture before things dry out into
the middle part of the week.
McKaughan
&&
.AIR QUALITY...The HRRR smoke model continues to show improvement
in air quality throughout today across Custer County as the upper
level flow becomes more southerly. By this evening the vast
majority of central and east Idaho should be experiencing good air
quality, as long as there are no new fire starts. This pattern
should stay in place through Sunday and much of Monday.
Wyatt
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Portland OR
202 PM PDT Sat Aug 17 2024
.SYNOPSIS...A strong low pressure system offshore will bring
widespread wetting rain to the area this afternoon into tonight,
with concerns for localized flash flooding near ongoing
wildfire burn areas. There is also a chance of thunderstorms
across the area today, a few of which could produce severe wind
gusts and large hail from the Cascades west to the I-5
corridor. Showers taper off on Sunday, yielding a return of mild
onshore flow through much of next week.
&&
.SHORT TERM...Now through Sunday Night...Not much change in the
overall thoughts from this morning. A Severe Thunderstorm Watch has
been issued for most of the counties along the I-5 corridor eastward
to the Cascade crest, where the strongest thunderstorms are expected
to occur. The watch is currently in effect through 9 PM tonight.
Water vapor satellite imagery reveals a large and well defined upper
level low offshore of the Pacific Northwest this afternoon, while
diffluent southerly flow aloft is present across western Oregon and
Washington on the periphery of this feature. As of 1:45 PM, numerous
showers and strong thunderstorms have developed across parts of
southwest Oregon and are moving northward towards Lane County. RAP
analysis shows areas of 500-1000 J/kg of MUCAPE across the Oregon
Cascades along with effective bulk shear increasing to 35-45 kt
early this afternoon.
Southerly flow will pivot a bit more southeasterly over the course
of the day, helping to advect rich mid level moisture and enhanced
instability into the region to set the stage for widespread wetting
rain showers with embedded thunderstorms across the area this
afternoon and evening. The trigger for this activity will be a
potent, negative-tilt shortwave trough which will lift northward
across the area this afternoon, coincident with peak heating.
Temperatures will warm into the low to mid 80s in the interior
valleys and into the 70s in the higher terrain today prior to the
arrival of this feature, contributing to destabilization
characterized by MUCAPE values of 500-1500 J/kg across much of the
area away from the coast this afternoon. Additionally, strong mid
and upper level wind fields will provide ample shear values to
support organized updrafts for any thunderstorms that develop.
Finally, all of this will occur within the left exit region of a 90
kt jet streak rounding the base of the large scale trough, providing
additional forcing for ascent across northwest Oregon and southwest
Washington.
Given all of the favorable factors described above, SPC
maintains a rare slight risk for severe thunderstorms across
the Cascades today, with a marginal risk extending westward to
the I-5 corridor. For some historical context, we have to go
back nearly four years to September 2020 to find the last time
any portion of our forecast area was included in an SPC Day 1
slight risk. The primary severe threat will likely be damaging
thunderstorm wind gusts of 60+ mph given a well mixed sub cloud
layer contributing to DCAPE values of 700-1100 J/kg. That said,
can`t rule out the possibility of some large hail to the size of
quarters, especially farther south over Lane County where cells
may tend to be more discreet early in the event. SPC maintains
a 15 percent chance of both severe modes for areas in the slight
risk, and a 5-15 percent chance in the marginal areas. This
means that any point in the Cascades slight risk area will have
a 15 percent chance of a severe thunderstorm occurring within 25
miles today, with a corresponding 5-15 percent chance within 25
miles of any point in the marginal risk area. In terms of
timing, hi-res guidance has been fairly consistent over the past
several runs in depicting showers and thunderstorms popping up
across Lane County around 1-2 PM this afternoon and then
spreading northward and reaching the Mt Hood and Portland areas
approximately 4-5 PM. Activity then continues into the evening
and starts to ramp down in intensity after sunset through about
midnight.
Shifting gears to the heavy rain/potential flooding aspect of
today`s activity, the forecast remains largely on track with
what has been depicted in previous model runs. Yesterday`s
sounding from SLE showed a precipitable water value over 1.1",
with additional moisture streaming into the area today looking
to send PWATs above 1.25" and perhaps as high as 1.50" according
to the higher end of guidance, which would be right around the
maximum values of mid August climatology. Given the ample
moisture and forcing, hi-res guidance continues to depict
rainfall rates mostly topping out around 0.75" per hour, though
latest HREF guidance does show a 5-10 percent chance of rates
locally as high as 1 inch per hour starting to show up over some
areas this afternoon. As such, will keep the Flash Flood Watch
intact along the length of the Oregon and south Washington
Cascades this afternoon into tonight. The primary areas of
concern remain the recently burned areas associated with ongoing
wildfires, but will have to also keep an eye on burn scars from
past years give the slight uptick in probabilistic guidance for
rainfall rates. Flood concerns in the inland valleys should
remain more limited in scope to some localized ponding of water
in areas that happen to see heavier rainfall rates over a
prolonged period of time, but widespread flooding concerns are
not expected in the lowlands.
Showers will ramp down in intensity and eventually taper off
from south to north through late this evening as the bulk of
the energy associated with the upper level trough shifts north
of the area into Washington. Could certainly see some lingering
shower activity into the day on Sunday and perhaps some isolated
thunderstorms into Sunday morning across southwest Washington,
but any additional rainfall will be minimal. The region will
start to settle back into a benign onshore flow regime by later
Sunday afternoon, with highs remaining in the upper 70s to
around 80 in the interior valleys. DH/CB
.LONG TERM...Monday through Friday...Little change in the
long term forecast as ensemble guidance continues to favor
mean upper level troughing over the NE Pacific through much of
next week. This will keep western Oregon and Washington in a
stable onshore flow regime through the period, bringing
seasonably mild temperatures with morning cloudiness and
afternoon highs generally in the upper 70s. The proximity to the
upper level trough will also yield continued chances for
sporadic shower activity and perhaps some minimal thunderstorm
potential at times, but no significant rainfall or strong
thunderstorm potential is expected beyond this weekend. /CB
&&
.AVIATION...VFR conditions prevail at 21Z Sat, now seeing start of
next round of convection as a shortwave lifting north across
western Oregon expected to trigger more robust thunderstorms this
afternoon into the evening hours. Hires models show most active
thunderstorms over the Cascades during this time. But valley
locations as well have a chance for thunderstorms. Approximate
timing for stronger batch of thunderstorms at TAF sites: KEUG 21Z
Sat-01Z Sun, KSLE 22Z Sat-02Z Sun, KPDX 23Z Sat-03Z Sun. After that
thunderstorm chances drop but not quite end until about 09Z Sun.
Predominantly VFR conditions throughout, though passing
thunderstorms could briefly reduce visibilities below 6SM due to
heavy rainfall. Gusty erratic winds will be possible as
thunderstorms pass through, with a 5-14% chance of severe convective
wind gusts up to 60 mph. Frequent lightning will also be possible.
PDX AND APPROACHES...Thunderstorms and showers reach KPDX around
00z Sun through about 03Z Sun, then chances drop but not quite end
until about 09Z Sun. Predominantly VFR conditions throughout,
though passing thunderstorms could briefly reduce visibilities
below 6SM due to heavy rainfall. Other impacts of thunderstorms
covered above.
&&
.MARINE...Expect benign conditions over the waters through mid next
week. Winds remain N/NW this evening then turn SW late tonight/early
Sunday as surface low pressure moves through the waters. Showers
pass through all waters on Saturday, with around a 20% chance of
isolated thunderstorms. Low pressure remains over the NE Pacific
through mid-week, maintaining SW winds. Winds are expected to
remain at 10 kts or less with gusts up to 15 kts; wind-driven
seas of around 4 feet. /mh /Sala
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$
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Area Forecast Discussion
National Weather Service Phoenix AZ
440 PM MST Sat Aug 17 2024
.UPDATE...Updated 00z Aviation Discussion...
&&
.SYNOPSIS...
Thunderstorm chances increase today with the best chances favoring
the high terrain areas of Arizona and across southeast Arizona.
Isolated thunderstorms will be possible across south-central
Arizona with gusty winds and blowing dust being the primary
concerns going through this evening. Drier conditions are favored
early next week before thunderstorm chances increase again during
the middle part of next week. Temperatures will warm up early next
week with excessive heat conditions possible.
&&
.DISCUSSION...
The subtropical ridge of high pressure that`s been over the region
continues to gradually shift eastward and is now centered over
eastern New Mexico. Meanwhile, a strong trough situated off the
coast of the Pacific Northwest is leading to downstream
amplification of the ridge as it shifts into the Southern Plains.
Locally, this has resulted in better southeasterly flow aloft,
importing better moisture into the region that will help increase
our thunderstorm chances for today.
Early afternoon satellite and radar trends shows more robust
convection ongoing across northern Arizona and Utah as a notable
vort max pushes through that region, while CU development is ongoing
across southeast Arizona with a few isolated thunderstorms now
popping up. Thunderstorm chances today will be greater today across
south-central Arizona given the better moisture that is now in place
with the 12Z PHX sounding recording a PWAT value of 1.66" and
surface dew points now in the upper 50s to low 60s. HREF paintball
plots support continued thunderstorm development across southeast
Arizona through the rest of this afternoon with southeasterly
steering flow helping to propagate thunderstorms toward south-
central Arizona. Across south-central Arizona, uncertainty quickly
increases in regards to thunderstorms being able to survive as they
push northwestward from southeast Arizona. Forecast soundings
suggest a favorable environment conducive to thunderstorm
development and strong outflows with favorable CAPE values upwards
of 1000-1500 J/kg and inverted-V profiles supporting high DCAPE
values to around 1500 J/kg. However, there is a good deal of
uncertainty around whether or not a strong/deep enough outflow
boundary can survive into south- central Arizona and overcome the
CIN to spark new thunderstorm activity. Previous iterations of the
HRRR had supported the idea of new thunderstorm development
occurring into the Valley, but the latest runs continue to back
off on this. Nevertheless, any thunderstorms that were to develop
across south-central Arizona this evening would be capable of
producing strong downbursts. Aside from thunderstorm chances,
strong outflows from southeast Arizona could lead to some areas of
dense blowing dust between Phoenix and Tucson.
Going into early next week, the subtropical ridge will continue to
strengthen and gradually shift westward with global ensembles
indicating 500 mb heights climbing upwards of 596-598 dm during the
Monday/Tuesday timeframe. This will lead to temperatures warming up
to around 108-114 degrees across the lower deserts with the hottest
temperatures currently focused across the Valley. The warming
temperatures will promote Major HeatRisk primarily around the
Phoenix metro as well as the San Carlos/Globe areas during this
time. Thus, an Excessive Heat Watch has been issued for the
aforementioned areas.
Moisture will decrease for the start of the new workweek and thus
lead to lower thunderstorm chances before global ensembles show
moisture increasing again midweek. There is uncertainty in exactly
how this pattern will evolve, but there are indications that an
inverted trough move across northern Mexico may potentially
support greater thunderstorm chances during the middle part of
next week.
&&
.AVIATION...Updated at 2330Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Main aviation weather concern will be the potential for gusty
thunderstorm outflow winds heading into this evening. Westerly
winds aob 10 kts will prevail into early this evening before an
outflow boundary from thunderstorm activity currently affecting
southeast AZ pushes through the metro area. Based on the latest
trends, it appears the main outflow boundary will push through
between the 02-04z timeframe, with wind directions switching out
of the S-SSE with potential gusts in excess of 25 kts as well as
areas of blowing dust. Confidence of actual thunderstorm activity
directly affecting the area terminals continues to remain low and
thus not mentioned in the TAF package. Conditions should improve
by the late evening hours with winds resuming the typical diurnal
tendencies with easterly winds overnight through early Sunday
morning before switching out of the west by the late morning hours
with speeds aob 10 kts. Convective cloud bases will remain aoa 10
kts with FEW coverage becoming SCT to occasionally BKN coverage by
early this evening.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns are expected during the next 24 hours
under generally clear skies. Winds at KIPL will follow the typical
diurnal tendencies while winds at KBLH will favor the south to
south-southwest. Wind speeds will generally remain aob 10 kts,
although afternoon gusts upwards of 20-25 kts will continue to be
favored at KBLH through early this evening and once again for
Sunday afternoon.
&&
.FIRE WEATHER...
The greatest thunderstorm chances this weekend will remain
primarily confined to the Arizona high terrain and southeast
Arizona, but isolated chances for thunderstorms along with strong,
erratic outflows will be possible across south-central Arizona.
MinRH values will be in the 15-25% range with fair to good
overnight recoveries of 30-60%. Drier conditions with lower
thunderstorm chances will start off the new workweek before
thunderstorm chances are favored to increase during the middle
part of next week. Outside of thunderstorm outflows, winds will
tend to follow their typical diurnal patterns with some afternoon
upslope gusts of 20-25 mph possible.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Monday morning through Tuesday evening
for AZZ534-537-540>551-560-562.
CA...None.
&&
$$
DISCUSSION...Smith
AVIATION...Lojero
FIRE WEATHER...Smith
Area Forecast Discussion
National Weather Service Topeka KS
609 PM CDT Sat Aug 17 2024
.KEY MESSAGES...
- Showers and thunderstorms are possible (30 to 50 percent)
Sunday afternoon and evening, some of which could be strong.
- Below normal temperatures are expected to start off the
workweek.
- The forecast has highs back into the 90s heading into next
weekend.
&&
.DISCUSSION...
Issued at 222 PM CDT Sat Aug 17 2024
An upper ridge remained centered over the southern high plains
per the 19Z water vapor imagery. The ridge axis extended north
over the northern plains and a closed upper low was noted off
the coast of OR. A shortwave looked to be lifting northeast
through UT. Surface obs showed weak high pressure ridging into
northeast KS from the north.
Main challenge with the forecast is timing the weak disturbances
rounding the upper ridge. And then there may not even be a wave
spark convection per the isolated storms across central NEB which
appear to be a result of some modest warm air advection in the mid
levels. The 12Z operational models are converging on a common idea
of a shortwave diving southeast Sunday afternoon and evening. There
is a good response to this wave seen in the isentropic surfaces with
increasing lift and saturation in mid levels. So confidence in
isolated to scattered showers and storms is increasing and have POPs
in the 30 to 50 percent range by Sunday evening. NAM and RAP
forecast soundings suggest elevated CAPE values could be around 1000
J/kg. Combined with bulk shear around 50KT with effectively a
straight line hodograph, there is some potential for organized
updrafts and severe storms.
By Monday models build a stronger surface high into the central
plains with some drier air. This brings into question whether there
is enough moisture for precip Tuesday night and the operational
models have backed off on QPF. This has resulted in the NBM coming
in with POPs less than 10 percent for Tuesday night and into
Wednesday. Then the upper ridge axis begins to slide east over the
central plains limiting the chances for shortwave energy to affect
the area. So the only chances for precip in the forecast is on
Sunday and Sunday night.
The stronger surface ridge Monday should bring below normal temps
for the first of the workweek. Then temps are forecast to warm as
the upper ridge moves overhead and southerly return flow
redevelops. This should push highs back into the 90s by
Saturday. The NBM reflects these trends nicely and have not
made and changes.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 607 PM CDT Sat Aug 17 2024
VFR at terminals with light easterly winds overnight and
increasing high clouds by sunrise, limiting overall fog
development at KTOP. Added a mention of VCSH aft 17Z at all
sites with some uncertainty on timing and coverage of showers
and isolated TSRA during the afternoon. Mid clouds around 10 kft
are most likely with showers given lack of low level moisture
with this system.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Wolters
AVIATION...Prieto
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
510 PM MDT Sat Aug 17 2024
.KEY MESSAGES...
- Thunderstorm chances overnight and Sunday, with potential for
strong/severe thunderstorms on Sunday.
- Warm and generally dry conditions to start begin the work week.
- Fire weather conditions will become a concern late Monday
afternoon and again Tuesday afternoon across the western parts
of our CWA.
&&
.DISCUSSION...(This Evening Through Saturday)
Issued at 111 PM MDT Sat Aug 17 2024
Current 500hpa analysis shows upper low spinning across the Great
Lakes region with high pressure located across nrn New Mexico/srn
Colorado. Ridge axis extends northward through central WY with
much of the CWA located in northwest flow aloft between the two
features. Water vapor imagery shows fairly potent s/w lifting
northward through NV/UT with abundant convection associated with
feature. At the sfc, weak boundary located across northeast WY
dropping southeast through the Neb panhandle. West of this
feature, sfc winds are generally westerly with lower dwpts, while
to the east, southeast winds are found with sfc dwpts in the low
to mid 60s.
850hpa low level jet increases into the 35-45kt range overnight
across the SC part of the state. This is also about the time the
aforementioned s/w moving through the NV/UT area moves into the
region. Ensembles are showing mean 0-6km shear AOA 50kts in the
06z-09z Sunday time frame...with increasing probabilities for
lightning strikes (as seen in DESI). MUCAPE values are still in
the 1.0-1.5k J/kg range (again...all aloft and not surface based)
during this time. Also noticed that with the new Day1 SPC outlook,
the MRGL outlook has been re-drawn to include a large part of SC
SD. One question that remains is will the boundary that remains in
place from northeast WY through the Neb panhandle also be a
focusing mechanism for storms as the s/w lifts into the region.
The HRRR has been fairly persistent in developing isolated
convection across the srn Black Hills separate from the expected
elevated convection across the sc part of the state. With the
boundary and s/w moving over, developing lolvl jet, the
probabilities are non-zero.
Thoughts then turn to Sunday proper. Will be dealing with any leftover
convection across the sc part of the state, and if the atmos and
recover quick enough for stuff to re-fire during the afternoon. By
21z Sunday a narrow corridor of MUCAPE values from 2k-3k J/kg
will exist from the Black Hills to south central SD. Ensembles
shows sfc dwpts in the low 60s in the corridor during the
afternoon. However shear looks meager at best with 35 to 40kts
seen. With an easterly sfc upslope wind cant discount something
developing over the Black Hills, with isolated plains convection
developing.
The first half of next week will be defined by the upper 500hpa
ridge staying in place across the nrn plains. Temperatures will
remain above normal for the middle of August. Models are
highlighting various impulses moving over the ridge, which will
bring isolated/widely scattered showers/storms to the region.
&&
.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 509 PM MDT Sat Aug 17 2024
VFR conditions are expected through the forecast period. Isolated
thunderstorms are possible across southwestern and south central
South Dakota late tonight.
&&
.FIRE WEATHER...
Issued At 111 PM MDT Sat Aug 17 2024
While a brief recovery in RHs is expected for Sunday across
northeast WY, they will once again fall to sub 20% values on
Monday, especially across western Campbell Co WY. With the upper
ridge in place through the middle of next week, the dry airmass
and low RH values will spread into the Black Hills region for
Tuesday afternoon...leading to the potential for elevated fire
weather concerns.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION/KEY MESSAGES...Hintz
AVIATION...10
FIRE WEATHER...Hintz