Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/21/23
Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
315 PM AKDT Wed Sep 20 2023
.SYNOPSIS...
A long wave trough complex with a handful of embedded features
crosses the state through the close of the workweek with
unsettled, showery conditions in the west and steadier
precipitation overspreading the eastern Interior to the Brooks
Range shifting east through tomorrow. High pressure builds behind
the system with cooler, drier Arctic air bringing fair weather to
much of Northern Alaska by the end of the week. With high
pressure centered over the Interior heading into the weekend,
rainy weather is generally deflected to the periphery, mostly
along the North Slope and the Yukon Delta.
&&
.DISCUSSION...
Current Upper Levels and Analysis...
Looking through RAP analysis and the satellite feed this
afternoon...a three-pronged upper level trough complex stretches
from the Arctic coast through western Alaska down to dominant low
pressure over the Alaska peninsula. Generally showery weather with
lowered ceilings accompany the surface trough through the west,
with areas of fog showing on webcams and surface stations along
the Arctic Coast. Meanwhile a surface occlusion/warm front aloft
associated with the low pressure circulation near the southern
coast continues to push northward through the Whites with KAPD
reflecting this nicely. SE flow behind this feature continues
across the eastern Alaska Range, spreading precipitation through
the eastern Interior and toward the eastern Brooks Range tonight.
Precipitation chances diminish from west to east tonight and
Thursday with a Pacific ridge poking north into the Bering Strait,
tracking west into Alaska tonight into Thursday. The exception is
along the North Slope as low pressure north of Nuiqsut/Deadhorse
draws an onshore/upslope flow into the Brooks Range through
Thursday night. High pressure and dry weather generally prevails
heading into the weekend.
Model Discussion...
Large scale wind and pressure fields are in relatively good
agreement at the jet level across the major model suites through
the end of the day Friday, then start to show disagreement as the
long wave trough begins to interact with a weak rex block near the
central Canada/CONUS border. Middle and lower level fields show
more disagreement as multiple trough features interact, however
these impacts appear to remain primarily south of the Alaska
Range.
By this weekend, model differences center primarily around the
persistence of upper level ridging through central Alaska
extending to northwest Alaska. In general the ENS solutions favor
a more amplified pattern featuring a stronger ridge and deeper
trough lingering over the northern Alcan border...and another
through the Bering sea... vs the GEFS. The timing and position of
these features however are very similar, and the broad ensemble
suite suggests accumulations associated with troughing features to
the northeast and southwest would be light at any rate.
Central and Eastern Interior (AFG)...
Precipitation associated with low pressure along the southern
coast will continue to spread north through the central and
eastern Interior tonight. Noteworthy accumulations are expected to
remain mostly at elevation with valley liquid amounts generally
expected to be AOB 0.15". Snow levels remain around 2 kft, except
in the upper Tanana valley southeast of Fairbanks where warmer
temperatures aloft have snow levels closer to 4 kft. A briefly
gusty downslope wind is possible between around Dry Creek and Tok
in the upper Tanana Valley late tonight, but otherwise wind will
remain light and variable before returning out of the west and the
system departs on Thursday.
A cooler and drier Arctic airmass invades Thursday and Friday
although the mixing accompanying it should support valley
temperatures in the 40s with ceilings lifting and perhaps a few
peaks of sunshine. The dry trend continues into Saturday with high
pressure moving overhead.
West Coast and Western Interior (WCZ)...
Low ceilings and unsettled weather shift east while northerly
flow diminishes and shifts northwesterly as high pressure builds
across the West Coast tonight Thursday. Fair weather prevails
under high pressure thereafter. The exception is the approach of
the next coastal low from the west... odds are good that most of
the precipitation activity will remain south of the area over the
Bering Sea toward the Alaska Peninsula with high pressure centered
over the interior deflecting the system south, however the Yukon
Delta still likely sees spotty rain showers amounting to a few
hundredths Friday into the weekend along with a modest, increasing
offshore wind.
North Slope and Brooks Range (NSB)...
Low pressure north of the Arctic Coast keeps an onshore flow
along the coast west of Nuiqsut/Deadhorse where low ceilings,
areas of fog, and showers continue... and upsloping into the
eastern Brooks Range where up to 2" of snowfall potential exists.
This general set up shifts east over the next couple of days with
near-shore flow turning westerly and upslope snowfall diminishing
by Friday. The low lingers over the Arctic Ocean north of the
Alcan border into the weekend however with lowered ceilings...
marine fog... light showers... and cool, raw weather continuing.
Extended Forecast Days 4-7...
Blocky upper level pattern brings inherent uncertainty to the long
range forecast with a nebulous upper air pattern. Ensemble fields
however suggest ridging to the east and troughing to the west with
light precipitation amounts centered on the west and southwest. No
hazardous weather is expected.
Coastal Hazard Potential Days 3 and 4...
Elevated surf along the Arctic Coast at Utqiagvik develops this
evening spreads east of Utqiagvik late tonight and Thu and
continuing into Fri. Northwest winds increasing to 20 mph along
the Arctic Coast near Utqiagvik tonight will continue into Thu and
spread east along the Arctic coast, then turn west on Thu night
and continue into Fri.
&&
.HYDROLOGY...
Rivers steady or slowly falling as snow levels drop.
&&
.AFG WATCHES/WARNINGS/ADVISORIES...
AK...None.
PK...Small Craft Advisory for PKZ801-854.
Small Craft Advisory for PKZ802-850-853.
Small Craft Advisory for PKZ805-857.
Small Craft Advisory for PKZ806-807-816-817-856.
Small Craft Advisory for PKZ813.
Small Craft Advisory for PKZ851.
Small Craft Advisory for PKZ852.
Small Craft Advisory for PKZ858.
Small Craft Advisory for PKZ859.
&&
$$
AREA FORECAST DISCUSSION
National Weather Service Bismarck ND
1007 PM CDT Wed Sep 20 2023
.UPDATE...
Issued at 959 PM CDT Wed Sep 20 2023
Late this evening, we have started to see some lightning activity
develop with the radar echoes across the far south near the South
Dakota border, mainly over Sioux county and portions of the
southern James River Valley. A much larger complex of stronger
storms continues to slowly move towards the area from north
central South Dakota. Thus far, RAP mesoanalysis suggests the
MUCAPE gradient drops off quickly with northward extent, mainly in
the 100 to 250 J/kg range over far south central North Dakota, but
an axis of 500 to 1000 J/kg should continue to advect north from
South Dakota. Thus, storms and heavier rainfall should become
more and more likely across portions of the south over the next
few hours. For this update, just tweaked precipiation chances
through much of the day tomorrow based on some of the latest high
resolution guidance and radar trends.
UPDATE Issued at 628 PM CDT Wed Sep 20 2023
Currently, a broad area of light to moderate rain showers is noted
on radar over portions of western and much of central North
Dakota. This activity will continue to move off to the east
northeast through the evening. The next subtle short wave
(currently located in the vicinity of eastern Wyoming and western
South Dakota) will move up into south central North Dakota later
tonight. The high resolution models continue to show a number of
various different solutions with the 3 km NAM Nest and HRRR being
the most aggressive in developing a complex of showers and
thunderstorms across the south central after 03z or so. While
instability will be rather limited early, NAM soundings do suggest
some MUCAPE in the 1000 J/kg to 1500 J/kg range across the far
south overnight. Whether parcels can access this instability is
another question. Deep layer shear is forecast to generally range
from 30 to 40 knots here. Thus, there is a conditional risk for a
strong storm or two across the south central and southeast
overnight into Thursday morning. Small hail would be the most
likely threat, but some brief gusty winds are not out of the
question.
As an additional note, with various rounds of convective showers
and storms forecast over the next several days, we are likely to
see periods of heavy rain rates under the more intense showers
and storms (most likely over the southern half of western and
central North Dakota). This could lead to some locally heavy
runoff which may become problematic for some small streams, urban
areas, and low lying areas. For this reason, we still start to
message the potential in the Hazardous Weather Outlook for tonight
through the weekend. While we are not expecting any kind of large
scale flooding, it is not out of the question that we could see
some localized flooding depending on how this system evolves over
the next several days.
&&
.SHORT TERM...(This Evening through Thursday Night)
Issued at 249 PM CDT Wed Sep 20 2023
The short term is highlighted by increasing chances of
showers and thunderstorms this afternoon through Thursday, with
potential for a few stronger thunderstorms on Thursday afternoon.
This afternoon, deep troughing extended across the western CONUS,
with closed lows placed over both the Pacific NW and southern
California. Southwest flow aloft existed across the Northern
Plains in between this and ridging over the Great Lakes region. At
the surface, a broad surface high was centered over southeast
Saskatchewan, while a weak surface trough/boundary exists over
central North Dakota. On the west side of this boundary, a broad
line of rain showers continues from north central through
southwest North Dakota. A few isolated thunderstorms have
developed in central South Dakota as of 1930 UTC.
Shower activity is expected to diminish some through this
afternoon as the boundary moves east, before increasing again as
an embedded impulse moves north from South Dakota. Chances for
showers and thunderstorms increase through this evening and are
highest after midnight across south central North Dakota.
Instability is low enough to limit the severe thunderstorm potential,
although there could be a few stronger storms that could produce
gusty winds and small hail, mainly across the south central
tonight where there is the most favorable overlap of shear (30-40
knots) and instability (~500 J/kg).
As the trough to our west deepens and emerges as a somewhat
stationary closed low somewhere over eastern Oregon into Idaho,
impulses will continue to eject out of the trough base and into
the Northern Plains, bringing continual chances for precipitation.
Thursday currently has the highest likelihood of some stronger
thunderstorms as a continuation of tonight`s activity, with
precipitation chances expanding north through the morning and
afternoon. Strong southerly flow aloft is projected to overlap
with a swath of low- level warm air advection, steep lapse rates,
and instability on the order of 1000 J/kg. Weak bulk shear favors
pulse-y thunderstorms that could produce small hail and gusty
winds, especially as they collapse, although there are some
differences among deterministic guidance regarding the strength of
shear which will likely be dependent on where and when storms end
up. Can`t rule out an isolated severe storm if parameters end up
overlapping more favorably than expected, or if a pulse
thunderstorm manages to get strong enough for a brief period of
tine. Extended high- res guidance is beginning to advertise a
second round of thunderstorms moving through the southern half of
the forecast area Thursday night, but earlier convection could
mitigate the environment. CSU machine learning does have a low but
non- zero probability of severe hail across much of the area.
Lows tonight will range from the mid 40s far west to the upper 50s
southeast. Highs on Thursday have warmed up slightly for the James
River Valley, into the mid to upper 70s, with the remainder of the
forecast area in the upper 60s to lower 70s. Patchy smoke is
projected to linger across parts of the south tonight into
Thursday, with a few locations reporting reduced visibilities in
the 6 to 8 mile range today.
.LONG TERM...(Friday through Wednesday)
Issued at 249 PM CDT Wed Sep 20 2023
Wet and cooler weather through the weekend highlights the extended
period.
The deep upper low begins to surge east on Friday, bringing more
widespread and consistent chances for precipitation through most
of the weekend as the low moves into the Dakotas. Blended POPs
still has the highest and most widespread swath of precip chances
Friday night through Saturday as the main deformation band moves
north through the area, with the center of the low progged to be
over the Dakotas on Sunday, although there are still slight
differences in the speed amongst ensemble members.
Probabilities have remained fairly consistent over the past day,
with the highest rainfall totals favored across parts of the
southwest and south central, in an area from Dickinson to Washburn
and south. The probability of at least 1" of rain is still at least
50% along and south of Highway 2, with higher amounts to the
south, although probabilities are also below 50% in the eastern
James River Valley. The probability of at least 2" is maximized
around 60% in between Dickinson and Bismarck, with the potential
for at least 3" highest in this same area, around 40%.
Highs during this period (Friday through Monday) will generally be
in the 60s, with overnight lows in the mid 40s to mid 50s. With
the strength of the upper low, expect breezy winds with this
system, coming from the east on Friday and Saturday before
becoming northerly on Sunday.
Current blended guidance is advertising POPs tapering off from
west to east on Monday, although it is frequent for wrap-around
precipitation to persist longer than expected. Ensemble guidance
then favors ridging building in over the central CONUS in
response to a large upper trough developing off the West Coast,
which indicates a slight warming trend bringing highs back to the
upper 60s to lower 70s for the first half of the work week. No
notable precipitation signals for this period, although CIPs
Extended Analogs start skewing wet late next week so we could
potentially get more active again.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 628 PM CDT Wed Sep 20 2023
Currently, light to moderate rain showers are moving east
northeast across portions of western and much of central North
Dakota. This activity may cause brief visibility reductions into
MVFR categories. More showers and thunderstorms are likely to
develop later tonight across the south central, eventually moving
north northeast into the vicinity of the Devil`s Lake Basin
overnight and into Thursday morning. These showers and storms may
be heavier and are most likely to impact KBIS, KJMS, and KMOT.
Here, we could see brief visibility reductions into MVFR or even
IFR categories. We may then see a break in precipitation from mid
to late morning and into the early afternoon hours. More showers
and thunderstorm are then forecast to develop later in the
afternoon hours and through the end of the forecast period. The
one site that may not see many impacts from this activity will be
KXWA. Winds may become gusty and erratic in the vicinity of any
heavier showers or storms.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...ZH
SHORT TERM...Jones
LONG TERM...Jones
AVIATION...ZH
Area Forecast Discussion
National Weather Service Burlington VT
1037 PM EDT Wed Sep 20 2023
.SYNOPSIS...
High pressure is moving into the North Country, with several
days of pleasant weather expected. Cool nights and warm days
are expected, with seasonal fog in the river valleys likely the
next several days. A gradual warming trend is expected throughout
the rest of this week. A low pressure system will move up the
Atlantic coast, but some uncertainty remains on how far north
precipitation lifts into the region. At the very least, there
will be increasing cloud cover heading into Sunday and a halt to
the warming trend.
&&
.NEAR TERM /THROUGH THURSDAY NIGHT/...
1030 PM UPDATE...
Forecast remains very much on track so only made minor changes
to bring it up to date with current obs. Nighttime microphysics
satellite shows some patchy lower stratus development across
locations that have dipped below crossover temperatures.
However, webcams are now showing fog development yet so SLK,
which is currently at 41F, has a good chance of reaching the
forecast low of 32F. If it were to occur, this will be the
first 32 deg reading of the season for SLK. Looking at climate
history, the mean date for the first 32F or lower for SLK is
September 8. Existing Frost Advisories also remain in effect.
PREVIOUS DISCUSSION...
Surface high pressure building overhead will continue to be the
dominate weather feature over the next few days, bringing a
stretch of dry and pleasant weather. As skies clear towards the
overnight, good radiational cooling conditions are expected
across the region. Overnight low temperatures will fall into the
40s, with locations along Lake Champlain closer to 50. A Frost
Advisory is in effect for parts of northern New York as low
temperatures drop into the lower to mid 30s across portions of
the Adirondacks. Given the synoptic set up and the radiational
cooling tonight, fog development is expected across much of the
area, especially the favored river valleys.
Another beautiful late September day is in store for the region
tomorrow. Skies will be mostly clear with some fair weather
cumulus popping up, although skies might be a little hazy with
the HRRR showing some wildfire smoke aloft moving into the
Northeast. Temperatures tomorrow will be seasonable, although a
few degrees warming than today. Daytimes high will be in the
upper 60s, with the broader valleys reaching the low 70s.
Thursday night will be another great night for radiational
cooling and fog development, with overnight lows generally in
the 40s.
&&
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 343 PM EDT Wednesday...The quiet stretch of weather continues
into Friday as surface ridge of high pressure gradually shifts east.
Our forecast area will remain on the western periphery of the
anticyclone, with a southeasterly onshore flow in place. High
temperatures on Friday will be in the low to mid 70s. Going into
Friday evening, will see high clouds begin to spread overhead
associated with a low pressure system to our south, with clouds
expected to thicken and lower through the night. Lows will be in
the 40s.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 343 PM EDT Wednesday...The forecast trends more uncertain going
into the weekend with a coastal low pressure system advancing
northward up the East Coast. Models still don`t have a good handle
on what path the system will take after tracking over the Mid
Atlantic Coast, with potential interaction with northern stream
shortwave energy shunting the system south and east of our area
before being carried out to sea. This scenario would mean few
impacts to our area from the system outside of some increased cloud
cover and some rain for our southern counties. This scenario lines
up with the latest GFS/ECMWF deterministic forecasts, and is
supported amongst the ensemble guidance as well (GEFS and ECENS
showing only 20-30% chances of southern VT receiving over 0.1 inch
rain over the weekend, with even lower probabilities further north).
We are noting the NAM has a very different and much wetter forecast
for our area, but this is towards the end of the NAM forecast and we
are leaning away from this scenario at this time. Our current
forecast has most of our area dry through the weekend, except
southern Vermont, where we carry a 20-40 percent chance of showers
mainly Saturday night. However, this is subject to change as models
get a better handle on the forecast, so keep on top of latest
forecasts if you have plans this weekend.
The forecast for next week is looking very quiet as a surface ridge
sets up over Quebec. Have forecast temperatures near seasonable
norms for mid/late September and low chances of precipitation.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Through 00Z Friday... All terminals are currently VFR with mostly
clear skies and light winds. The VFR conditions will continue
through the overnight hours except where fog develops from strong
radiational cooling. Currently fog is expected to form at SLK, MPV
and EFK. There is high confidence of fog at SLK and MPV while there
is less confidence at EFK, but still enough to put fog in the TAF.
SLK could see fog around 04Z which is earlier than usual on
radiational cooling nights as the 00Z temperature is much closer to
its crossover temperature than normal at this point in the evening.
MPV and EFK will likely see fog after 06Z. The fog should lift
shortly after sunrise and all locations will improve to VFR through
the end of the TAF periods with mostly clear skies and light winds.
Outlook...
Thursday Night: VFR. Patchy BR.
Friday: VFR. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. Slight chance SHRA.
Sunday: Mainly VFR, with local MVFR possible. Slight chance SHRA.
Sunday Night: VFR. NO SIG WX.
Monday: VFR. NO SIG WX.
&&
.EQUIPMENT...
The KCXX radar will be down for radome repairs, with a return to
service around September 21st.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...Frost Advisory from 2 AM to 8 AM EDT Thursday for NYZ029-030.
&&
$$
SYNOPSIS...Kremer
NEAR TERM...Chai/Kremer
SHORT TERM...Duell
LONG TERM...Duell
AVIATION...Myskowski
EQUIPMENT...WFO BTV
Area Forecast Discussion
National Weather Service Quad Cities IA IL
653 PM CDT Wed Sep 20 2023
...AVIATION UPDATE...
.SHORT TERM...(This evening through Thursday Night)
Issued at 240 PM CDT Wed Sep 20 2023
Key Messages:
* Spotty showers and a couple storms in northeast Iowa through
early evening, followed by gradually increasing showers south
of U.S. Highway 34 tonight
* While still uncertainty in specifics for Thursday, confidence
is higher in rain in parts of northwest/north central Illinois,
including potential for locally heavy rain during the P.M. hours
in namely Bureau and Putnam Counties
A broad upper low sprawled across Iowa, Missouri, and western
Illinois will slowly creep east-northeast the next 24 hours. This
low is comprised of multiple MCV centers, including one over
northeast Iowa that will continue isolated showers in its
immediate vicinity. Early afternoon environmental and satellite
trends support some lightning within this north of Highway 30 the
rest of this afternoon. Locally heavy downpours and lightning are
the main notes with these. If some of this area were to clear
this evening, patchy fog would be probable tonight.
A more potent short wave circulation that has characteristics of
an MCV, is located in northeast Missouri this afternoon and is
progressing north-northeast. Despite its close proximity in space
and time, this upper disturbance has been cumbersome for short-
term models to handle both its track and evolution tonight into
Thursday. Observational trends support a little more western track
than some of the morning guidance indicated, which would yield rain
in the immediate Mississippi River Valley and points east,
especially late tonight and Thursday. The RAP has been consistent
with an even further west solution and providing a soaking rain as
far west as the Quad Cities on Thursday. Given the nature of this
system with a closed circulation and PWATs near the 90th
percentile for the of year, felt comfortable boosting PoPs from
the Mississippi River eastward, especially in our eastern-most CWA
Counties during the afternoon and evening on Thursday, where
synoptic- and meso-scale forcing are juxtaposed.
In terms of hazards and impacts, elevated lapse rates are
forecast to be very weak, resulting in MUCAPE profiles being tall
and narrow in the vertical (i.e. non-rapid updraft accelerations
and unlikely to be widespread thunder or severe). In the far
eastern counties (Bureau and Putnam in IL) and/or just
east-southeast of there, a signal exists in convection-allowing
models (CAMs) of localized heavy rainfall. This includes the 12Z
HREF local probability matched mean indicating a narrow 2-4
inches just east of the CWA. So will need to keep an eye on that,
as localized over-performing rain swaths can occur near slow-
moving mid-level lows with anomalous moisture, such as this wave.
Otherwise, lowered forecast highs for Thursday with the
anticipation of more and deeper cloud cover, especially southern
and eastern locations.
.LONG TERM...(Friday through Wednesday)
Issued at 240 PM CDT Wed Sep 20 2023
Key Messages:
* Unsettled weather pattern, however low confidence in specific
evolution; highest chances for rain currently Saturday night-
Sunday
* Depending on timing, a severe risk is possible in mainly eastern
Iowa later Saturday/Saturday night, and then an even lower
confidence in possibly locally heavy rain early next week
The disturbance for Thursday/Thursday Night noted in the Short
Term Discussion should be exiting the region early Friday. Some
brief suppression may be seen in its wake, but the pattern remains
moist and ensembles indicate low chances of rain on Friday are
warranted.
On the broader synoptic scale, a deep, closed low is expected to
progress from Montana on Friday into the Upper Plains by midday
Saturday. Ridging ahead of this provides subtle heights rises
over the area Friday night and during the day Saturday, with an
overall slower eastward progression of shower and thunderstorm
chances on Saturday. Supporting this outcome is also a subtropical
system that will move northward into the Mid-Atlantic states, and
often such a pattern can result in a slowing of system movement at
the same latitude. So have collaboratively trended down NBM
forecast PoPs for the Mississippi River and points east during the
day Saturday, and that trend may need to be the case for the
entire CWA in future shifts. By Saturday night into Sunday, height
falls do creep over the area as does a zone of forcing ahead of
the surface cold front. But these features do slow as the wave
gradually occludes during the middle portion of the weekend. Hence
why confidence is low on details. The system has a magnitude and
low-level moisture return worthy of a severe risk, but right now
that seems better aligned in peak heating and the hours just after
on Saturday toward the Mid-Missouri River Valley region.
Certainly plenty of time for things to shift.
Beyond, the then meandering upper low is naturally a challenge for
long range guidance to handle. Large discrepancies from model-to-
model and run-to-run with this and make blended or even
probabilistic data difficult to interpret still at this point.
Because of this, tough to stray much from the NBM forecast of
"chance of rain with slight chance of thunder" Sunday-Tuesday. If
the wave were to slowly move over our region and maintain its
anomalous depth (similar to last evening`s 00Z ECMWF run), there
there would probably be localized heavy rainfall. But just way
too much uncertainty with such a pattern in Days 4.5 to 6 to hang
our hat on.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 644 PM CDT Wed Sep 20 2023
A weak, slow moving weather system will track in from the south
overnight into Thursday, bringing occasional chances for showers
mainly to BRL and MLI. Brief MVFR ceilings and visibilities are
possible in the vicinity of any heavier showers. There is also
potential for shallow fog to develop late tonight into early
Thursday AM near CID, but have low confidence on coverage and
severity at this time.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
SHORT TERM...Friedlein
LONG TERM...Friedlein
AVIATION...Uttech
Area Forecast Discussion
National Weather Service Grand Rapids MI
959 PM EDT Wed Sep 20 2023
LATEST UPDATE...
Update
.UPDATE...
Issued at 959 PM EDT Wed Sep 20 2023
The upper pattern across the Lower 48 this evening is dominated by
a trough in the Pacific Northwest and ridging (or at least higher
heights) across the eastern third of the country. The main feature
of note for our weather tonight is a compact low/vort center
embedded within the higher heights over our area moving slowly
northward across Illinois. There is some light rain/drizzle across
Southern Illinois associated with the mid level vort, but any
precipitation is expected to remain south of our area per the HRRR
and the 12z HREF. The main affect from this vort on our area
tonight will be that mid and high clouds will remain in place or
even thicken. The clouds and a light southeast wind will keep
temperatures up a bit with lows expected to be in the mid to upper
50s in most areas. The values are slightly above normal for late
September.
&&
.SHORT TERM...(This evening through Thursday night)
Issued at 303 PM EDT Wed Sep 20 2023
- Isolated shower/storm Thursday afternoon north, marine zones
Thursday night
A weakening mid level wave will be located over WI during this
time. This feature may provide enough lift to support an isolated
shower/storm Thursday into Thursday night. The area will be in
the entrance region of the low level jet though, which may limit
the low level lift. Weakness in the stability and even slight
instability will be around so, an isolated storm is possible. The
latest SPC HREF LPMM QPF does show a few spots around Big Rapids
and Baldwin with afternoon QPF Thursday. We will feature very low
POPs for that location. Currently several models show a better
area of organized rain lifting northward through Southern Lake MI
Thursday night and they pull it westward into WI overnight.
Assuming that stays west of our area, only very low POPs are
needed for our marine zones Thursday night.
- Warming up
Gradual warm air advection will continue into Thursday as 925 mb
temps climb another degree or two, with much of the CWA in the low
20 deg C range during the afternoon. Mixing to that level allows
for max temps to reach 80 degrees. Many locations saw high temps
today in the 75 to 80 degree range. There will be some more clouds
around Thursday but that should not stop temperatures from
topping out around 80 degrees. The slightly warmer temperatures
are supported by the most recent ensemble model runs.
.LONG TERM...(Friday through Wednesday)
Issued at 350 PM EDT Wed Sep 20 2023
Models have been fairly consistent of late in showing a weak
blocking pattern over the Great Lakes as a result of low pressure
developing off the southeast coast of of the US. This block will
help to keep high pressure over the state along with above normal
temperatures as we head into Autumn this weekend.
The first chance of precipitation really doesn`t arrive until Sunday
night and even then chances aren`t high. The models (especially the
ECMWF) are trying to move the eastern US low away from the coast
which allows the Wisconsin low to drift in our direction. The ECMWF
is much more bullish on precipitation late Tuesday into Wednesday.
Whereas, the GFS takes the precipitation well south of the state.
Thus confidence isn`t exactly high on precipitation chances next
week.
One thing that will probably occur, though, is that we`ll begin to
pick up more of an easterly or northeasterly flow with time from the
high over Ontario/Quebec, which will send some cooler air into the
cwa. Even then, by the middle of the week, temperatures will still
be near normal.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 741 PM EDT Wed Sep 20 2023
VFR conditions will continue through Thursday. Winds will be
light and variable overnight. Cloud bases will be AOA 10 kft AGL.
&&
.MARINE...
Issued at 303 PM EDT Wed Sep 20 2023
Marginal conditions for small craft/beach hazards continue for
northern zones this afternoon. The pressure gradient weakens this
evening and that should result in diminishing winds. The next
increase in wind/waves may occur Thursday night...but it will be
offshore flow for most zones so the impacts will be limited.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&
$$
UPDATE...Duke
SHORT TERM...MJS
LONG TERM...MJS
AVIATION...Ostuno
MARINE...MJS
Area Forecast Discussion
National Weather Service North Platte NE
635 PM CDT Wed Sep 20 2023
...00Z AVIATION UPDATE...
.SYNOPSIS...
Issued at 323 PM CDT Wed Sep 20 2023
Key Messages:
- Active weather pattern expected Thursday through Saturday with the
greatest precipitation chances Thursday night through Saturday.
There is a small threat for storms tonight.
- Severe storms are possible Thursday evening then again Friday
afternoon through Friday night.
- Cooler and windy conditions expected Saturday afternoon through
Sunday.
- Seasonal and dry conditions Monday through Wednesday.
H5 analysis this morning had closed low pressure over northern
Washington State. Downstream of this feature, shortwaves were noted
over southern Alberta and northern Saskatchewan. A second closed low
was located over the LA Basin of California. Across the central
CONUS, weak disturbances were noted. The first over northern Utah
and a second over Wyoming. Another stronger disturbance was located
over the Ozarks. At the surface, a weak boundary was present from
around Valentine to North Platte and McCook Nebraska. This was more
of a moisture boundary with 60+ dew points east of this boundary and
40-50s dew points west of this boundary. Winds were light westerly
west of the boundary with light easterly winds east of the boundary.
Skies were mostly clear and 3 PM CDT temperatures ranged from 78
degrees at O`Neill to 89 degrees at Thedford.
&&
.SHORT TERM...(This evening through Thursday night)
Issued at 323 PM CDT Wed Sep 20 2023
Over the next 36 hours, upper level low pressure will drift south
from northern Washington state south into southeastern Oregon.
The east ward progress of this feature will be hampered by a
southeast to northwest ridge, oriented from North Dakota into
northern portions of Saskatchewan and northern Alberta. Over the
next 36 hours, there will be three possible episodes of
thunderstorm chances. For tonight: Currently there is some
agitated CU off to the west of the forecast area over the Cheyenne
Ridge, as well as some developing cloud cover over western
portions of the forecast area. Looking at the short range CAMS
today, two pockets of precipitation look possible. The first over
central into northeastern portions of the forecast area, and
second over the northeastern Nebraska Panhandle. Yesterday, we saw
thunderstorm development over the central Sandhills with surface
dew points in the upper 30s and lower 40s. With additional
moisture noted this afternoon and similar flow aloft, believe pops
are warranted here. Late tonight into early Thursday morning, a
second area of storms may develop and push into the forecast area.
The models are hinting at some decent mid level warm air
advection late tonight entering southwestern Nebraska. This mid
level lift will advect over a moistening boundary layer, leading
to possible development of showers/thunderstorms Thursday morning.
During the day on Thursday, low level moisture will continue to
advect into western Nebraska thanks to deepening low pressure over
eastern Wyoming into eastern Colorado. By 21z Thursday, a
distinct dry line will develop from the southern panhandle into
far southwestern Nebraska. This will serve as the focal point for
thunderstorm development Thursday afternoon. ATTM, the latest
NAM12, NAMNST, and 12z HRRR develop storms along the dryline
Thursday afternoon. As this activity lifts east, it will encounter
SB CAPES of 2000 to 3000J/KG and deep layer shear of 30 to 35
KTS. This will favor severe storms with hail and winds being the
main threats. One caveat to the severe threat is low cloudiness.
If stratus should persist into the afternoon, it will have a
limiting effect on severe potential Thursday afternoon and
evening. This stratus development is more favorable if...no warm
air advection storms materialize overnight tonight. So in short,
storms overnight tonight in SW Nebraska may limit severe potential
in the west and southwest Thursday afternoon/evening. Given the
uncertainties listed above, I have limited confidence in the
severe threat for Thursday/Thursday night.
.LONG TERM...(Friday through Wednesday)
Issued at 323 PM CDT Wed Sep 20 2023
On Friday, the upper level low will migrate east from
southeastern Oregon into far western Wyoming. Surface low pressure
will remain nearly stationary along the front ranges of Colorado
and Wyoming with robust southerly and southeasterly boundary layer
winds continuing. By late afternoon, a dry line will become
oriented from the southern panhandle into far southwestern
Nebraska. By late afternoon, a strong shortwave will approach the
Black Hills and the Nebraska Panhandle. Thunderstorm initiation
appears possible INVOF the dry line from the northern panhandle
into far southwestern Nebraska. The chance for initiation appears
to highest from north to south across the forecast area as mid
level temperatures are coolest across the Black Hills and this
area is in a more favorable position with relation to an
approaching H250 jet streak. That being said, coverage of
thunderstorms appears to be best in the north and northeast Friday
with more widely scattered to isolated coverage in SW Nebraska.
Now, if any storms do develop in SW Nebraska, available CAPE is
favorable for severe storms, however, deep layer shear of 50-65
KTS in SW Nebraska may a tad high and may lead to "orphan" storms
early on. Not ready to rule out the severe threat in the SW, but
it appears to be more focused further east and north of SW
Nebraska. Friday night into Saturday, the upper level low will
migrate from far western Wyoming into South Dakota. Storms should
clear the northeastern forecast area later on Saturday with a On Friday, the upper level
low will migrate east from southeastern Oregon into far western
Wyoming. Surface low pressure will remain nearly stationary along the
front ranges of Colorado and Wyoming with robust southerly and
southeasterly boundary layer winds continuing. By late afternoon, a
dry line will become oriented from the southern panhandle into far
southwestern Nebraska. By late afternoon, a strong shortwave will
approach the Black Hills and the Nebraska Panhandle. Thunderstorm
initiation appears possible INVOF the dry line from the northern
panhandle into far southwestern Nebraska. The chance for initiation
appears to highest from north to south across the forecast area as
mid level temperatures are coolest across the Black Hills and this
area is in a more favorable position with relation to an approaching
H250 jet streak. That being said, coverage of thunderstorms appears
to be best in the north and northeast Friday with more widely
scattered to isolated coverage in SW Nebraska. Now, if any storms do
develop in SW Nebraska, available CAPE is favorable for severe
storms, however, deep layer shear of 50-65 KTS in SW Nebraska may a
tad high and may lead to "orphan" storms early on. Not ready to rule
out the severe threat in the SW, but it appears to be more focused
further east and north of SW Nebraska. Friday night into Saturday,
the upper level low will migrate from far western Wyoming into South
Dakota. Storms should clear the northeastern forecast area later on
Saturday with a chance of wrap around pcpn lingering into Saturday
night across northern portions of the forecast area. As the system
exits Saturday into Sunday, gusty westerly winds will be possible
Saturday into Saturday night. Winds will relax on Sunday as high
pressure builds into the area. Ridging aloft will build into the
central plains early next week with dry and seasonal conditions
expected through Wednesday. chance of wrap around pcpn lingering
into Saturday night across northern portions of the forecast
area. As the system exits Saturday into Sunday, gusty westerly
winds will be possible Saturday into Saturday night. Winds will
relax on Sunday as high pressure builds into the area. Ridging
aloft will build into the central plains early next week with dry
and seasonal conditions expected through Wednesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 631 PM CDT Wed Sep 20 2023
VFR conditions are expected through the period outside of
convection. New development southwest of VTN will threaten the
terminal over the next few hours but impacts should remain brief
therefore will cover with a tempo group. Impacts are possible at
LBF as well, however, may exit the area prior to the beginning of
the new forecast period so will limit to VCTS. After convection
exits, only passing high clouds are expected with light winds
favoring the southeast at less than 10 knots. Expect increasing
wind gusts Thursday out of the southeast with peak speeds around
25 knots. Attention turns to addition rain and thunderstorm
chances during the late morning and afternoon, particularly for
VTN. At this time, greatest confidence in seeing activity remains
northwest of the terminal so will omit mention for now but later
forecasts may include mention. As low-level winds increase, low to
mid level stratus will increase with the greatest impacts likely
to occur just beyond the end of the valid period.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Buttler
AVIATION...NMJ
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1032 PM CDT Wed Sep 20 2023
.UPDATE...
Issued at 825 PM CDT Wed Sep 20 2023
Tweaked PoPs for the rest of the night to reflect current trends.
I think the CAMs, particularly the HRRR, are developing too much
convection over the next few hours, so I tweaked PoPs downward a
category across the entire area. This fades 20-50 PoPs from
eastern Missouri into southwest Illinois, and ~60 PoPs across
south central Illinois. This corresponds to an area of low level
moisture convergence which develops east of the Mississippi
River which the RAP develops between now and midnight, and lifts
north- northeast through the overnight hours into central
Illinois. This area of moisture convergence is also apparent in
the GFS, though it develops much less precip than the RAP, and
again seems more likely given the current trends.
Carney
&&
.SHORT TERM... (Through Late Thursday Night)
Issued at 220 PM CDT Wed Sep 20 2023
Compact midlevel low is currently over east-central Missouri. This
feature has predominantly been producing very light rain or
sprinkles over the past 6-12 hours along/ahead of it, and this
should continue through the overnight period. Best chances early
this evening for light rain will be along the Mississippi River in
eastern Missouri and southwest Illinois, moving northeastward
into south-central Illinois gradually through the night. Elevated
instability increases overnight so a few rumbles of thunder are
also possible. A southwesterly low-level jet strengthens late
tonight into Thursday morning, so isolated to widely scattered
(15-30%) showers are possible further to the southwest into
southeast Missouri and southwest Illinois predominantly. The low-
level jet weakens toward 1500 UTC Thursday, so expecting at least
a brief period of dry or at least mostly dry conditions across the
CWA during the late morning/early afternoon hours. A slight
uptick in coverage probably will occur in by mid/late afternoon
into the early evening as diurnal instability peaks. This is
mainly true in parts of western Illinois which will be on the
western periphery of the departing midlevel closed circulation.
There is also some slight chances (15-25%) further southwest
roughly along a west-east front front. This front is forecast to
slowly move northward Thursday night and could help provide the
focus for more showers and a few thunderstorms as the low-level
jet intensifies and a weak midlevel shortwave approaches from the
west.
Temperatures are forecast to rebound on Thursday, as thicker cloud
cover departs off to the northeast and low-level warm air advection
strengthens. Highs are forecast to top out in the mid 70s to low 80s
from north to south, slightly above normal for the date. Overnight
temperatures will remain on the mild side with lows both tonight and
Thursday night in the low to mid 60s.
Gosselin
.LONG TERM... (Friday through Next Wednesday)
Issued at 220 PM CDT Wed Sep 20 2023
(Friday - Friday Night)
The retreating warm front may be in at least northern sections of
the forecast area Friday morning, but should continue to move north
through the day. Attention will then turn upstream as
deterministic guidance continues to show signs of a subtle
vorticity maximum moving through the region within the quasi-zonal
flow aloft. This feature may help yield at least isolated to
scattered showers and a few thunderstorms within the warm sector,
but confidence is not particularly high in this scenario. Guidance
shows building upper-level ridging at least through the first
half of the day, which may suppress any development due to
increasing subsidence. Six-hour probabilities for measurable
rainfall max out in the 30-40% range over most of the area Friday
afternoon/evening on the grand ensemble, which looks pretty
reasonable.
Temperature wise, we are expecting more of the status quo to end the
work week. Slightly above normal values are favored, but
particularly at night due to persistent southerly winds and at least
some cloud cover Friday night.
(Saturday - Sunday)
Spread in the track and timing of a closed mid/upper level low
moving out of the northern Rockies and into the northern Plains this
weekend has continued to decrease. By 0000 UTC Sunday, this feature
is most likely to be located over the western Dakotas, which is
slightly further northwest than compared to what it looked like
24 hours ago. This means a slightly later arrival of the surface
cold front into the bi-state area, with an approach into central
Missouri most likely between 0600 and 0900 UTC Sunday. Ahead of
the front, dry weather is looking more likely with mid/upper level
ridging overhead and no real forcing mechanisms to help initiate
any convection within the warm sector. Therefore, reduced PoPs
quite a bit from the previous forecast, more toward slight
chance/low chance (15-35%) which agrees well with latest
probabilities from the grand ensemble.
Widespread showers and thunderstorms are forecast along the cold
front, aided by strong low-level moisture convergence and mid/upper
level diffluent flow aloft. However, this area of convection should
weaken considerably Saturday night due to a multitude of factors
including: 1) waning nocturnal instability, 2) weaker shear
(propensity for outflow to outrun storms; cold pool/shear
imbalance), 3) abating low-level moisture convergence, and 4)
surface cold front becoming less defined by 1200 UTC
Sunday/weakening convergence along the front. Some of the rain
along with a few thunderstorms are very likely (~80 percent) to
reach central Missouri, but chances gradually wane toward and
especially east of the Mississippi River. By Sunday morning, there
may be some remnant shower or weak thunderstorm activity, but
chances should tick up at least slightly by the afternoon as
diurnal instability increases. There is some uncertainty as to how
well-defined the cold front will be by Sunday afternoon. In fact,
some of the latest deterministic guidance suggest the boundary
may just wash out entirely.
Above normal temperatures will continue ahead of the cold front on
Saturday, with highs mostly in the upper 70s to mid 80s. Slightly
cooler readings are favored to end the weekend into next week,
closer to normal for late September.
At least low chances of rain will continue through the period, as a
majority of all ensemble members (80%) suggest the closed mid/upper
level low will get "trapped" beneath a very anomalous (+3 sigma)
ridge centered to its north west of Hudson Bay. This blocking high
will at least dramatically slow the eastward progress of the
mid/upper level low across the northern Plains/Upper Midwest, and
could even send it further to the south closer to our area heading
toward the middle of next week.
Gosselin
&&
.AVIATION... (For the 06z TAFs through 06z Thursday Night)
Issued at 1026 PM CDT Wed Sep 20 2023
Showers continue to rotate around an upper level low which is
passing over the Mid Mississippi Valley. VFR flight conditions are
expected to continue to prevail outside of these showers.
CIGS/VSBYS could drop to MVFR in the heaviest showers across
southwest into south central Illinois into early Thursday morning.
It is possible, depending on exactly how and where the heavier
showers develop, that they could briefly affect the St. Louis
Metro terminals, however confidence is low on the precise track of
the showers and height of the ceilings, which may pass just east
of the Metro Area. After the morning showers exit to the north-
northeast, scattered showers will continue to be possible through
the day, but VFR flight conditions are likely to continue.
Carney
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX
Area Forecast Discussion
National Weather Service San Francisco CA
846 PM PDT Wed Sep 20 2023
...New UPDATE...
.SYNOPSIS...
Issued at 1040 AM PDT Wed Sep 20 2023
NW to N winds are bringing wildfire smoke from NW California and
SW Oregon to the Bay Area. The HRRR model suggests the smoke will
stay with us for the next couple of days. Otherwise conditions
will be fairly standard for this time of year through the weekend with
morning stratus clearing by mid-day and near normal temperatures.
A Red Flag Warning is in effect for the North Bay Mountains
tonight into Thursday afternoon.
&&
.UPDATE...
Issued at 823 PM PDT Wed Sep 20 2023
Current obs show a mix of wind directions in the North Bay with
some onshore flow still present, especially across lower
elevations. RDD-SAC pressure gradient strengthening over the past
hour, suggesting northerly flow along ridgetops should be
imminent within the next couple of hours. RH below about 3200 feet
still well into the 60s and 70s south of Lake county and west of
the Vaca Range. Above 3200 feet in these areas, such as Mt. Saint
Helena, is drier with RH in the 40-50% range. Do expect lower RH
values to spread to lower elevations once the northerly winds kick
in, likely down to about 1500 feet, roughly where the top of the
stable marine layer resides based on the 00Z OAK sounding.
Otherwise the forecast and highlights look on track for the winds
to decrease Thursday afternoon with good RH recoveries Thursday
night/Friday morning.
&&
.SHORT TERM...
(This evening through Thursday)
Issued at 210 PM PDT Wed Sep 20 2023
Water vapor imagery shows a trough of low pressure moving into
the Pacific Northwest this afternoon, with a couple of weak
disturbances off the Central California Coast that are finally
shifting south as a result. Meanwhile, current visible imagery
shows that skies are predominately sunny, except for the
immediate coast, which remain blanketed in low clouds. As a
result, coastal areas are running between 5 and 10 degrees cooler
at this time than this time yesterday, while inland areas are
for the most part similar to their temperatures yesterday. Another
area of interest for today remains with the smoke that has
filtered into the area from our north. At this time, the majority
of our observing stations are reporting visibility between 4 and 6
statue miles in either haze or smoke. Given that the upper level
north to northwesterly flow will continue through the next 24 to
48 hours, expect the smoke from the fires in Northwestern
California and Southwestern Oregon to continue to filter into the
area.
Meanwhile, the weather main story for tonight and tomorrow will be
the developing offshore winds across North Bay. At this point in
time, the models are showing that the northerly gradient will
increase this evening, and then peak during the late night and
early morning hours. The 925 mbs winds increase to between 25 to
35 kts tonight between 9z and 12z, with 850 mb winds not quite as
strong. At this point in time, think some local gusts upwards of
45 mph will be possible at the gustiest locations over the peaks.
Given the lack of upper level support, not expecting these winds
to mix down into the valley tonight. In fact, valley locations
will likely be dealing with our marine layer low clouds, as the
Fort Ord profiler is showing that the marine layer is around 2500
feet deep this afternoon. The offshore winds will weaken during
the day tomorrow, but still expect dry conditions to prevail
across the higher elevations. Otherwise, expect conditions to be
similar to or slight cooler for the day on Thursday. Palmer
&&
.LONG TERM...
(Thursday night through next Tuesday)
Issued at 210 PM PDT Wed Sep 20 2023
Overall temperatures trending cooler than average through Tuesday
with highs expected to be in the mid to high 70`s inland and high
60`s along the coast. Weak upper-level shortwave ridging will warm
temperatures slightly on Saturday/Sunday but temperatures are only
expected to be a few degrees higher than the rest of the period. As
the shortwave ridge moves in overnight Thursday and during the day
on Friday, wind directions will shift from northwesterly to
westerly/southwesterly. This will help to clear smoke out of the Bay
Area.
Confidence is increasing that North Bay will experience some
precipitation between Monday and Tuesday. There is continued
potential for South Bay to receive some rainfall as well however
confidence is lower for South Bay than it is for North Bay. Model
guidance suggests that the most likely timing for precipitation will
be overnight Monday into Tuesday but beyond this the exact timing
and amount are still unclear. We will continue to watch this system
to see how it will develop.
&&
.AVIATION...
(00Z TAFS)
Issued at 647 PM PDT Wed Sep 20 2023
Wildfire smoke and haze continue to mix with coastal stratus, per
metar observations surface visibilities are 5-9 miles /MVFR-VFR/
and ceilings vary from 1600 ft to 2000 ft /MVFR/. The marine layer
depth varies from 2100 ft Bodega Bay, 2900 ft Fort Ord to 2700 ft
Point Sur. A 4.2 mb ACV-SFO pressure gradient is juxtaposed to a
3.1 mb SMX-SFO pressure gradient (both are underforecast by the
latest NAM and HRRR models approx 1 mb and 2 mb respectively),
SFO-SAC is onshore 2.4 mb. Pressure gradients initiate atmospheric
motion effecting near surface to surface winds and in this case
the advection of current stratus. Stratus clouds continue converging
along the coast from Point Reyes to Point Conception, the larger
scale pattern forecast to arrive from the northeast blending in with
the coastal stratus pattern overnight.
00z TAFs are adjusted to account for underforecast gradients and
winds, a very challenging forecast, for example near 3 mb SNS-SJC
pressure gradient currently, yet there`s still a northwest wind 10
knots at KSJC (vs southeast wind which is forecast to develop early
this evening, PG&E weather stations show southeast winds nearby).
As best can tell from model forecasts low level wind shear (LLWS),
including across the North Bay should be minimal tonight and Thursday
morning, thus at present time LLWS was not added to KSTS, KAPC 00z
TAFs.
Vicinity of SFO...VFR. Southwest wind 10 to 13 knots early this
evening, surface wind shifting to a light southeast wind by mid to
late evening; still waiting for KSJC wind to shift to southeast
direction. With surface cyclonic wind flow west of the SF Peninsula
early Thursday morning, wind shifting to light northeast direction
then by late afternoon shifting over to west wind near 10 knots,
though the late afternoon wind shift is a low confidence forecast.
SFO Bridge Approach...Reductions in slant range visibility due to
wildfire smoke and haze continuing, especially during sunset and
sunrise. Otherwise similar to KSFO.
Monterey Bay Terminals...MVFR-VFR and visible satellite imagery
shows stratus curling around the Monterey Bay reaching over to
KWVI and KSNS, while ongoing southwest wind & downsloping drying
wind at KMRY keeping VFR going so far. The marine layer depth per
Fort Ord and gradually easing southwest wind will eventually allow
stratus clouds /MVFR/ to reach KMRY, tempo MVFR 02z-05z this
evening. Otherwise KSNS already with MVFR stratus ceiling this
evening and a northwest wind. Stratus filling across the north
Central Coast, a favorable area for gradually arriving lower level
cooling, a greater deepening of the marine layer and mixing out
the lower level temperature inversion, including /not currently in
00z KMRY or KSNS TAFs/ patchy light drizzle with upslope cooling
winds tonight and Thursday morning.
&&
.MARINE...
(Tonight through next Monday)
Issued at 541 PM PDT Wed Sep 20 2023
Strong northerly winds today in the coastal waters with frequent
gale force gusts anticipated in the northern outer waters. Winds
and gusts will begin to diminish Thursday, becoming light to
moderate by the weekend. Northwesterly swell begins to diminish on
Thursday, with a new swell train arriving late in the weekend.
&&
.FIRE WEATHER...
Issued at 1040 AM PDT Wed Sep 20 2023
The Fire Weather Watch has been upgraded to a Red Flag Warning
from 11 pm tonight to 5 pm on Thursday. As a deep upper low drops
into interior CA from the Pacific NW, it will set up a short
window for some offshore winds early AM hours on Thursday. Peak
winds will be overnight tonight into Thurs morning with winds of
10 to 20 mph and gusts up to 30 mph. Relative humidity values
overnight will be marginal and not critically low, making this a
marginal case. By the morning, RH will drop to 25-30% in
conjunction to breezy north winds. Winds turn onshore during the
afternoon Thurs when RH drops further into the low 20s.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until 5 PM PDT Thursday for CAZ504.
PZ...Small Craft Advisory until 9 PM PDT this evening for PZZ540.
Gale Warning until 9 AM PDT Thursday for PZZ570.
Small Craft Advisory until 3 AM PDT Thursday for PZZ575.
&&
$$
UPDATE...Behringer
SHORT TERM...Palmer
LONG TERM....Kennedy
AVIATION...Canepa
MARINE...DialH
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Area Forecast Discussion
National Weather Service Paducah KY
620 PM CDT Wed Sep 20 2023
.UPDATE...
Issued at 609 PM CDT Wed Sep 20 2023
Updated aviation discussion for 00z TAFs.
&&
.SHORT TERM...(Tonight through Friday night)
Issued at 251 PM CDT Wed Sep 20 2023
Rain continues to inch closer to the region, reaching the far
western counties this afternoon. Surface high pressure and weak
forcing aloft has kept heavier rain out of the forecast and appears
to be somewhat verified today. RAP soundings have shown relatively
dry air aloft in and around this weak system. No significant
moisture is being observed to promote higher confidence in heavier
rain as the precipitation travels east. Therefore, expect light
showers to move east throughout the CWA this afternoon through
tonight with light accumulation of less than 0.1".
Tomorrow morning should yield drier weather as the main
frontogenetic forcing moves off to our north and east. However,
there is a chance the vorticity maximum associated with this mid
level disturbance might retrograde west to the north of the CWA.
This would keep some higher PoPs in our northern counties
throughout the day tomorrow, but no significant precipitation
amounts are expected. Temperatures will likely be in the low 80s
in the east with upper 70s across areas that experience more cloud
cover and rain.
General high pressure should eat away at the strength of this
disturbance into Thursday night and Friday morning with 500mb height
rises helping clear out any precipitation. Some stubborn cloud cover
might still exist due to lingering moisture in the wake of
precipitation-driven wet bulbing. Nonetheless, the main headline for
Friday is that the weather should be dry with temperatures in the
mid 80s.
.LONG TERM...(Saturday through Wednesday)
Issued at 251 PM CDT Wed Sep 20 2023
The ridge strengthens slightly on Saturday keeping us mainly dry
with continued lower to mid 80s. Then as the northwestern low moves
east over the Northern Plains and Northern Midwest precip chances
begin to increase Saturday evening onward. Things get a little more
uncertain from there as the low lingers but the exact placement is
uncertain. The EC moves the low south and east over our area by
Wednesday whereas the GFS keeps it over the Great Lakes. Temperature
wise we start to cool down on Sunday with highs back down into the
70s by Monday. Lows will generally still be in the 60s.
&&
.AVIATION...
Issued at 609 PM CDT Wed Sep 20 2023
Scattered light showers will continue to drift NNE this evening
and overnight. Can`t completely rule out an isolated lightning
strike. Some of this activity may linger into the first half of
the day tomorrow across mainly northern terminals. A few of the
heavier showers may produce very brief vsby reductions. Otherwise,
VFR conditions expected with primarily a mid cloud deck around
5-10kft. Some guidance is suggesting a little fog development
possible across southeast Missouri late tonight. There`s low
confidence in this though, and it`s contingent on clouds clearing
enough and winds becoming calm. Winds will range from easterly to
SSE and primarily between 4-8 kts through the period.
&&
.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&
$$
UPDATE...SP
SHORT TERM...SHAWKEY/JAB
LONG TERM...SHAWKEY
AVIATION...SP