Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/19/20

Area Forecast Discussion

National Weather Service Cleveland OH

 948 PM EDT Sun Oct 18 2020

.SYNOPSIS...
Low pressure over northwest Quebec will drift east through the
evening with a cold front settling south into the area
overnight. This boundary will stall across southern Ohio on
Monday as high pressure builds east across the Great Lakes on
Tuesday. Low pressure will track northeast across the Upper
Great Lakes Tuesday night into Wednesday, lifting a warm front
back north across the area.

&&

.NEAR TERM /THROUGH MONDAY NIGHT/...
930 pm update...
We have made some minor adjustments on timing with the precip
chance forecast with the latest radar and HRRR trends. The
adjustments are not significant and the main weather story
going forward will be wet and soggy late tonight and much of the
day Monday.

Previous discussion...
Area of rain across extreme NE OH into NW PA will progress
eastward through early evening then we should see all locations
briefly dry. Cold front will continue to make steady progress
into the region overnight. It appears the front reaches NW OH
around sunset and then makes a very slow move to the east. The
first wave of low pressure moving along the front will arrive
overnight with occasional showers expected after midnight Lows
tonight should remain in the 40`s, maybe a few lower 50`s along
the lakeshore.

The cold front looks as if it will stall across southern Ohio
but it may wobble northward on Monday as the next ripple of low
pressure rides the boundary. So hopefully there will be a brief
decrease in the shower coverage Monday morning. Rain chances
should increase from the south late in the afternoon. It will be
a cool day with 50`s common. If the steady rain does not sag
southward with the frontal boundary a few locations could see
highs in the upper 40`s.

The second ripple of low pressure should bring another round of
showers to most of the CWA Monday night. Rain may start to taper
off from west to east by sunrise. Lows Monday night will once
again hold in the 40`s, with a few spots around 50 along the
lakeshore.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
A longwave upper level trough will reside over much of the CONUS
with shortwaves propagating along it throughout the short term
period. On Tuesday morning, some lingering showers may persist over
the area as the stationary front slowly moves south and high
pressure begins to move over the area. The surface high should allow
for a brief period without any precipitation Tuesday afternoon into
the early overnight hours as areas of increased moisture also push
east out of the area.

Overnight Tuesday, models suggest another shortwave propagating
along the longwave trough. Subsequently, a surface low pressure
develops over the Midwest and moves northeast into the Ohio River
Valley. This will lift a warm front across the area late Tuesday
night/early Wednesday morning, bring warmer temperatures into the
area. An 850 mb low level jet of 50 to 60 knots will occur with the
passing of the warm front, allowing ample moisture to also move into
the area. With ample moisture, source of lift at the surface and
upper level support, widespread rainfall is expected with the
passage of the warm front. With the increase temperatures and
moisture, models are suggesting minor instability building over the
area, making isolated thunder possible. The associated cold front
with that low pressure will move across the area Wednesday
afternoon, allowing showers to taper off by Wednesday evening into
the overnight hours.

High temperatures on Tuesday will be in the upper 50s with overnight
lows dipping into the low 50s. On Wednesday, high temperatures will
peak in the mid 60s to low 70s before the passage of the cold front.
Overnight lows will again dip into the low to mid 50s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
A rather active pattern is expected to persist into the long term
period as the long wave trough continue to stretch across the CONUS.
On Thursday, a surface high pressure should bring a brief hiatus to
shower activity as low level moisture moves out of the area.
Southwesterly winds will usher in above normal temperatures, with
highs in the mid 70s across the area.

As nice weather resides over our area, an upper level longwave
trough begins to deepen along the West Coast, which will be the next
impactful system to our area for the end of the work week into the
weekend. In association with the upper level trough, the ECMWF/GFS
are in agreement with a surface low developing near the Oklahoma
Panhandle and tracking northeast towards the Great Lakes region.
This will bring an associated cold front across the area late Friday
night/early Saturday morning. Both the ECMWF/GFS have slowed the
passage of this cold front with the latest guidance, so exact timing
is still uncertain. The Canadian model is in complete disagreement
and suggests a much faster low pressure that moves through Friday
afternoon. With this system, widespread showers are expected with
isolated thunder. Temperatures will again be above normal on Friday,
but with the passage of the front, will cool down to below normal on
Saturday and persist at below normal temperatures through the
duration of the long term forecast. Overnight lows will follow a
similar trend with prefrontal overnight lows being in the 50s then
dropping to the low 40s post frontal.

&&

.AVIATION /00Z Monday THROUGH Friday/...
VFR conditions this evening will quickly deteriorate to
widespread IFR late tonight into Monday morning. A cold front
will move through the region and ceilings and visibilities will
quickly drop behind the frontal passage. Winds will start out
from the south or southwest before the passage and become
northerly to northeasterly by late tonight 5 to 10 knots.
Guidance show widespread IFR ceilings and visibilities by
Monday morning. There is some potential and guidance showing
LIFR ceilings for MFD, CLE, and ERI but not confidence enough to
mention in actual TAFs at this time for later Monday morning.
IFR will continue all day Monday with widespread light rain and
showers through out the day.

Outlook...Non-VFR conditions likely Monday night through
Tuesday with low ceilings and rain showers.

&&

.MARINE...
Have cancelled the Small Craft Advisory for all zones across the
lake as winds and waves have quickly decreased to below Small
Craft criteria.

Late tonight, a cold front will move across the lake, allowing
winds to shift to become north to northwesterly and quickly
weaken, dropping below Small Craft Advisory criteria. This cold
front is expected to become stationary just southeast of the
lake, resulting in sustained winds of 10 to 15 knots from the
northeast, briefly strengthening to near 20 knots from west to
east overnight Monday as a weak low pressure moves northeast
along that stationary boundary.

Another low pressure develops over the Midwest and moves northeast
over the western Great Lakes, resulting in winds shifting and
becoming south to southwesterly across Lake Erie. This will be the
next chance a Small Craft Advisory may be needed as winds are
expected to increase to 15 to 25 knots for all zones near the
lakeshore. After the cold front moves across the lake, winds again
weaken behind it and conditions are rather calm across Lake Erie for
Wednesday and much of Thursday.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...None.

&&

$$
SYNOPSIS...MM
NEAR TERM...Griffin/MM
SHORT TERM...Campbell
LONG TERM...Campbell
AVIATION...Griffin
MARINE...Campbell/Kahn



Area Forecast Discussion

National Weather Service Des Moines IA

 1048 PM CDT Sun Oct 18 2020

...Update Regarding Light Snow Potential Monday Morning...

.UPDATE...
Issued at 1047 PM CDT Sun Oct 18 2020

A vorticity max swinging through the enhanced upper-level flow
continues to be monitored this evening, associated with an area of
frontogenetical forcing maximized near H85. During the afternoon,
12z guidance solutions displayed a great amount of spread with
respect to snowfall, and the location of where a potentially higher
band could set up. 12z GEFS members had started to draw this further
southward, where the better moisture supply would be located at. 00z
CAMs continue to show divergence in their solutions. 00z HRRR, ARW-
WRF and Hi-Res NMM have a dry slot that punches through, leaving
little in the way of precipitation, and moreover, no ice
introduction with dry air in what would be the DGZ. On the other
hand, NAM Nest, NSSL-WRF bring in more moisture, near the area of
best frontogenesis. As a result, this places a band of 1.0 to 1.5
inches of snow between Interstate 80 and Hwy. 20. The 00z
operational NAM takes this band further north, between Hwy. 30 and
Hwy. 18. Given the dry conditions that have been ongoing, especially
across west-central Iowa, the HRRR like solutions may be a better
representation with its drier output. However, radar late this
Sunday evening has been showing widespread areas of reflectivity,
but likely this is virga given that the ASOS and AWOS observations
are not reporting anything at the surface. This could perhaps mean
that the atmosphere is slowly working toward saturation if this
continues on. The question, is will there be saturation in the right
spot to allow for ice introduction, or will this only allow for rain
to be the dominant precipitation type? The moisture profile
overnight will need to me monitored closely for this. For now, have
not made any changes to the snowfall forecast for Monday morning,
and will allow the 00z GEFS and other ensembles members to come in
that may provide a better opportunity to address this uncertainty.
The key takeaway, is that the morning commute may be impacted by
light snow showers. This includes portions of Interstate 80, as well
as Interstate 35, Hwy. 30, and Hwy. 20. Road surface temperatures
still remain above freezing, and the winds will be light. This will
help drastically reduce the chances of roads becoming slick, but
certainly do not be caught off guard if snow is falling. Otherwise,
if we miss out on snow completely, still expecting areas of rain
showers early through mid morning across the forecast area for areas
along and north of Interstate 80.

&&

.DISCUSSION.../Tonight through Sunday/
Issued at 300 PM CDT Sun Oct 18 2020

General Summary...

An active pattern will be in place over the region throughout the
forecast period, resulting in multiple opportunities for rain/snow
and even some thunder towards the middle to end of the work week.
Temperatures will remain on the cold side of normal to start the
work week, moderating by mid week back into the 50s/60s and even low
70s through mid-week, and then back into the 40s to end the week.
Any snowfall seen over the next few days will be short lived with
most accumulations on elevated or grassy areas and then melting
through the daytime hours.

Monday through Tuesday...

Unfortunately this is not a high confidence forecast window,
especially Monday morning as the next wave of precipitation moves
through. Within upper level northwest flow, we`ll see a few things
come together to provide lift tomorrow morning including left exit
jet region aloft, low-mid level isentropic lift, frontogenetical
lift (albeit less than this morning), and mid-upper level vorticity
advection to name a few. There will also be a bit of an influx of
mid level moisture not too dissimilar to last night/this morning. The
lynch pin for snowfall and snowfall amounts will be snowfall rates.
Within any areas of enhanced snowfall, wet bulb processes will
likely keep low level temperature profiles in favor of snowfall with
a fair amount of near-surface dry air around. Should that be the
case, surfaces more prone to snowfall accumulation could see an inch
or more in portions of central Iowa. Currently the forecast hedges
towards the lower end with many areas north of I-80 around an inch
with the anticipation of a transition to rain/mix limiting
accumulations. Another wild card to keep an eye on would be overall
placement. GFS/GEFS members tended to be on the southern end of
available solutions, but did not fully buy in with majority of
guidance a little further north. Should the 12z GFS/GEFS prevail,
current forecast snowfall and rain may need to come south a county
or two. Suffice it to say, forecast confidence through Monday
morning is medium at best.

Tuesday will see another upper level short wave slide through the
region along with a broad surface low to pass NW/N of the state. As
a result, there will be both upper level (open wave) and low level
support (southerly flow/isentropic lift) to yield another window of
rain/snow opportunities. In this case, the best chances for snow
will reside across far northern Iowa where around an inch or less
will be possible while the remainder of the state should simply see
period of rain. Once again, any snow that sticks will be short lived
and melt off through the day, limiting impacts.

Wednesday through Sunday...

The active weather pattern will continue within this period,
including the likely return of thunder to the forecast. Southerly
flow/WAA will be ongoing through the first couple of days within
this period, allowing highs to return back into the 50s Wednesday
and 60s/low 70s for most on Thursday. There is strong consensus of a
deeper open 500mb wave to dig into the west, turning our upper flow
southwesterly. Within that, a surface low is expected to develop
along the Colorado front range and then race northeast from southwest
KS across Iowa and into Wisconsin. As a result, a warm front will
lift northward during the latter half of Wednesday and settle into
southern Minnesota by Thursday afternoon. Precipitation within this
time frame will be rain, including some thunder potential. Quickly a
cold front will then pivot around and sweep across the state
Thursday evening/overnight and provide another opportunity for
elevated thunderstorms and some brief snow behind the front.
Certainly cannot rule out some small hail with any thunderstorms.

Friday into the weekend, cold air returns, dropping highs back into
the 40s. Synoptic guidance diverges through the weekend, but tends
to depict another potential surface low developing in western Kansas
and racing northeastward Sunday.

&&

.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 636 PM CDT Sun Oct 18 2020

Main concern will be regarding a mix of rain and snow showers over
the next 18-24 hours. Currently have high confidence in the
occurrence of precipitation for central and northern portions of
Iowa. Not exactly confident on how much of it will be snow, and
what the impacts of snow could be on visibility, and even if snow
does occur where exactly will the band of greatest accumulation,
if any, fall. With the current forecast, forcing seems to be most
favorable at FOD for snow compared to other terminals. However, a
modest shift could cause the snow to completely miss FOD. Expect
a wintry mix of rain and snow to impact DSM, ALO, and MCW at some
point, but at this time not seeing large impacts to visibility or
ceilings. Overall, low-end MVFR conditions expected at most sites
during the early morning hours on Monday. A brief period of IFR
cannot be completely ruled out, but at this time not seeing a
strong enough signal to include in the TAFs. Winds are not
expected to be an issue.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Krull
DISCUSSION...Curtis
AVIATION...Krull




Area Forecast Discussion

National Weather Service Quad Cities IA IL

 949 PM CDT Sun Oct 18 2020

.UPDATE...
Issued at 949 PM CDT Sun Oct 18 2020

Area radars showed an area of reflectivity producing snow or a
rain snow mix in southeast NE moving eastward. This was occurring
in an area of low level F-Gen in the right entrance region of an
upper level jet streak moving into the Great Lakes. This feature
should continue to translate eastward across southern IA into
southeast IA and west central IL after midnight. The 18Z GFS was
way overdone with widespread QPF for this feature, but the 00Z
NAM, RAP and several high res models have latched onto this
feature to some degree, with more narrow banding. Have updated
the forecast to introduce slight chances for rain or a rain snow
mix late tonight across the south, with some concern that the dry
air in place and weakening trend of the forcing may limit anything
from reaching the ground.

&&

.SYNOPSIS...
Issued at 330 PM CDT Sun Oct 18 2020

It`s a cold mid October afternoon with temperatures in the 40s and a
steady NW wind dropping wind chills into the 30s. The light
precipitation during the morning and early afternoon has since moved
off to the east. There were reports of a few hour period of all snow
this morning behind the cold front with some locations picking up an
early first measurable snow. The Dubuque Airport had 0.4" and 0.2" -
0.3" was reported in Cedar Rapids and Marion.

&&

.SHORT TERM...(This Evening through Monday)
ISSUED AT 330 PM CDT Sun Oct 18 2020

Tonight

Cold temps are expected tonight with lows in the mid/upper 20s north
to mid 30s far south. Otherwise, it will be quiet with light winds.

Monday

A shortwave trough, currently depicted in mid-level water vapor
imagery over NW Montana, is forecast to quickly track to the ESE
tonight into Monday. Ascent in the left exit region of an upper jet
streak, and from a narrow corridor of mid-level frontogenesis, may
lead to a band of light precipitation over parts of Iowa and
Illinois. Model consensus has the most likely track over areas north
of I-80 during the afternoon. But due to some uncertainty on the
exact placement and intensity of the band, capped precip chances at
50% until confidence increases.

While most model guidance paints light QPF in the counties along and
north of I-80, the ECMWF is a dry outlier for the afternoon period.
HREF QPF/dominant p-type is furthest north and has a band of light
snow generally along and north of highway 30.

Precipitation Type: Top-down thermal profiles suggest the potential
for a rain/snow mix or brief period of all snow, favored to the
north of I-80. This detail is washed out in the model blend`s
typical diurnal hourly temp trend, which yields rain as the dominant
p-type. However, the aforementioned cold thermal profiles aloft and
sub-freezing surface wet-bulb temps would support mostly snow. For
this reason, trended afternoon hourly temps toward CONSRaw model
data to introduce the potential for a rain/snow mix. If the
development of this band of precip becomes more likely in later
forecasts, a trend to all snow for a period in the afternoon may be
necessary.

Warm ground should prevent snow accumulations on pavement, but a
period of steady snow could lead to minor slushy accumulations on
elevated surfaces and the grass. Uttech

.LONG TERM...(Monday Night through next Sunday)
ISSUED AT 330 PM CDT Sun Oct 18 2020

Monday night and Tuesday...Expect most of the precip to be east of
the CWA by the start of the period, making for a seasonably chilly
night in the lower 30s, with a few upper 20s in spots. Tuesday,
advancing trof aloft acrs the mid CONUS to induce return flow
warming, but more may be realized aloft in the H8 to H7 mb layer
making for a large inversion aloft. Limited mixing at the sfc may
make for highs only in the low to mid 50s acrs much of the area.
Veering and increasing low level jet(LLJ) to southwest at 25-35 KTs
will look to advect a convergent elevated THTA-E plume ahead of the
incoming upper trof axis acrs the CWA, enough so to produce sctrd
showers to increase as the afternoon progresses. Enough mid layer
MUCAPEs of 100-200 J/KG to support some embedded thunder late
afternoon into Tue evening mainly acrs the southeast third or so of
the CWA. Depending on saturation aloft, thermal profiles some of
these possibly producing small hail, but not enough shear and
instability for anything significant. A good elevated moisture feed
indicated by PWATs of 1-1.2 inches suggest areas in forced
convergent swath along and south of a Burlington IA to Princeton IL
line may get from a quarter, to three quarters of an inch by Wed
morning. More embedded thunder than currently expected will produce
some localized swaths up to an inch.

Wednesday...The Tuesday system moves off, then 130-140 KT upper jet
energy digs down southward along the Pacific Northwest to reload
western Intermountain longer wave troffiness into the end of the
week. Backing steering flow acrs the midwest to a west-southwest
orientation aligns and concentrates LLVL baroclinicity somewhere from
the southwestern plains, up acrs the local area and into the GRT
LKS. As the main warm front organizes along and south of the area,
another round of increasing LLJ jet energy from the southwest will
moist/THTA-E advect, with convergent swaths inducing more elevated
showers acrs the area as Wed afternoon progresses. Also another
round of incoming mid layer MUCAPEs supportive of embedded
thunderstorms will look to spread up from the south by late
afternoon, and then take focus acrs the central and northern CWA
overnight into early Thu morning.

Where the prime convergent axis along and north of the LLVL warm
front sets up could be an area/strip of moderate to heavy rainfall,
if currently progged precipital water feed(PWAT`s) of 1.1 to 1.4 are
close to what occurs. Thus areas along this axis may see similar
rainfall amounts as the PWAT`s indicate, even with some locally high
spots pushing 2 inches by Thu morning. But where this axis lays out
still at question and how much of the local CWA is in it. But right
now ensemble placement suggests from along the NE/KS border region,
into the southern heart of the GRT LKS making the northern half of
the CWA at risk of getting some good rains. Embedded elevated
thunder in this axis too until deeper saturation may limit lightning
flash by early Thu morning. The heavier rain axis may lay out just
to the northwest of the CWA, but again a bit early on this for more
confidence. Back to Wed highs, return flow warming into the mid 50s
and even 60s.

Thursday and Friday...With plunging jet energy to the west,
southwesterlies will look to amplify acrs the plains and into the
western GRT LKS. This may allow for a temporary bath in full on warm
sector by Thu if the warm front can make it to acrs WI into eastern
MN. If currently advected LLVL temps and thicknesses are anywhere
in the ballpark, we may get well up into the 70s on Thu, with even
some 80s possible in spots. Unseasonable sfc DPTS possible too in
the upper 50s to low 60s at least. While most of Thursday during the
day may then be dry, breezy and warm, an in sweeping strong front
from the west as the upstream upper trof pushes this way may make
for a long fetch, along and post-frontal precip scenario Thu night
into Friday depending on mass field and forcing progression. This
process may produce another round of seasonably decent rainfall of
at least moderate amounts, again depending on the progression speed
of the passing front...does it occur mainly Thu night or linger well
into Friday?

Saturday and next Sunday...A cool dump with below normal temps will
look to follow the late week system. First half of the weekend
currently looks to be dry, but will then have to watch sunday with
long rang signs of an overrunning system with precip-type issues to
resolve.   ..12..

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 623 PM CDT Sun Oct 18 2020

VFR conditions will prevail tonight with light northwest winds and
high level cloud cover. A band of rain may set up across southeast
Iowa, impacting the BRL terminal after midnight with periods of
MVFR ceilings. Monday will see another axis of precipitation move
the region, likely in the form of snow or a rain/snow mix. This
has been included at all sites, but is most likely to impact CID
and MLI. While accumulating snow is not likely on paved surfaces,
visibilities and ceilings may drop to IFR thresholds, but for
now, a period of prevailing MVFR conditions is included in this
late forecast period.


&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...Sheets
SYNOPSIS...Uttech
SHORT TERM...Uttech
LONG TERM...12
AVIATION...Sheets



Area Forecast Discussion

National Weather Service Reno NV

 303 PM PDT Sun Oct 18 2020

.SYNOPSIS...

A persistent pattern of dry and mild conditions will continue into
the middle of the week. Temperatures begin a cool down by Thursday
as a dry cold front dips south across the region. Additional cooling
and breezy north winds are possible next weekend with some slight
chances for light rain and higher elevation snowfall.

&&

.SHORT TERM...

Not much change to weather pattern into Wednesday for most locations
across northeast CA and western Nevada. A ridge of high pressure
off the California coast will keep us in a persistent dry and mild
pattern with afternoon temperatures 5-10 degrees above average
through Wednesday. Lows will remain seasonably cool to chilly with
large diurnal swings for valleys with dry air, light overnight
winds, and around 14 hours (~6 PM - 8 AM) of radiational cooling.

Regarding smoke in southern Mono County, smoke modeling continues
to bring additional particulates into Mammoth Lakes this afternoon
and evening with smoke settling into the Long Valley Caldera and
points south and east tonight. On Monday, while many areas of Mono
County will see north to northeast flow, the HRRR still brings
stubborn west winds to the Mammoth area in the afternoon as west
winds on the western slopes of the Sierra push through Mammoth
Pass. Tuesday and Wednesday, blended guidance (NBM) indicates
additional westerly winds over Mammoth Mountain so I`m afraid more
smoke continues to be possible if the Creek Fire remains active.
-Snyder

.LONG TERM...Thursday through next weekend...

Thursday`s front looks dry and somewhat shallow with main impact
8-15 degrees of cooling. Increased north to northeast winds in the
lowest few thousand feet AGL are also possible behind the front
with the cooler post-frontal air pooling against the eastern Sierra
and tightening the surface pressure gradient.

By next weekend, a secondary and likely colder trough moves in.
Being a week out, uncertainty lies mainly with how deep the trough
digs across Nevada/California with about a third of ensembles
still holding onto a weaker, farther east trough. Overall, seeing
an additional backdoor cold front with increased north/northeast
winds seems what`s most favorable at this point. Also, with
temperatures falling off more, a widespread freeze for the lower
valleys is increasingly likely by early next week.

The inland trajectory of the trough shown by multiple ensemble
systems does not favor a big precipitation potential. Initial early
estimates looking at about a 20% probability of receiving at least
a wetting rain (0.10") sometime next weekend. As of now, slight
chances for rain and high elevation snow showers are in the forecast
for next weekend. -Snyder/Fuentes

&&

.AVIATION...

Modest west-north gusts up to 15-20 kts are occurring this afternoon.
Lighter winds are anticipated for most areas Monday, though places
that favor NW flow, such as KCXP, KMEV, KMMH, and KHTH may be a
bit breezy once again Monday afternoon.

Otherwise, smoke impacts from the Creek Fire continue in the Sierra,
mainly south of Yosemite. Slantwise visibility reductions and terrain
obscuration due to smoke are likely, with KMMH likely seeing MVFR-
IFR CIG/VIS restrictions for many hours through Monday.

A pair of backdoor cold fronts are looking possible the week ahead,
the first Wednesday into Thursday and the second Saturday into
Sunday. This will bring an increase in northerly winds and could
potentially kick up dust as well. The first front looks dry, with
the second bringing perhaps a 20% chance for precipitation.
-Snyder/Dawn

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno




Area Forecast Discussion

National Weather Service San Diego CA

 856 PM PDT Sun Oct 18 2020

.SYNOPSIS...
Warm and dry weather will prevail through Wednesday, with patchy low
clouds and fog over coastal areas nights and mornings. A noticeable
change will occur later this week as an upper trough moves in from
the north. This will usher in much cooler weather beginning on
Thursday, and continuing into the weekend. A much deeper marine
layer will spread moisture and cooling well inland, and may result
in some light precipitation along and west of the mountains.
Dry and Gusty Santa Ana winds are possible early next week as the
trough swings east.


&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

A mix of high and low clouds covered the CA Bight and portions of the
coastal zones this evening. The higher clouds were making it
difficult to assess the low cloud coverage. The 00Z Miramar sounding
had a weak 3.5C inversion perched near 1200 FT MSL. Winds were weak
westerly below the inversion and northwesterly 15-30 KTS above. A
weak onshore trend was noted in sfc pressure gradients to the
deserts.

The main forecast concern for tonight will be the possibility of
fog. At this time factors affecting fog formation are not as well
aligned as the last couple of nights. Light winds and small dewpoint
depressions favor development, but sfc winds and additional high
clouds do not. A slight drying trend has occurred at coastal
sights and winds are now NW not southerly. Most runs of the hourly
HRRR runs have not developed any appreciable fog either. 900 MB
winds are solidly NW as well, unlike last night when 850 MB height
contours over the CA Bight were cyclonic and those winds were very
light. Given these trends, the high clouds, and latest guidance,
fog may occur, but will probably be more patchy and farther
inland than the last couple of nights. No forecast changes this
evening.

From previous discussion...

-Forecast Highlights-

* Warm through Wednesday, turning much cooler late week
* Light rain possible next weekend coast to mountains
* Santa Ana wind potential October 26-28

Southern California weather continues to be dominated by an upper
ridge of high pressure and this will continue through mid week.
This will keep warm temperatures going through Wednesday, running
some 5-10 degrees above normal overall. So the lower deserts will
continue to see afternoon temps reaching near 100, but there is an
end in sight! Before getting to that detail, will mention that
dense fog could re-develop this evening, impacting parts of the
coast and mesas.

Now to the changeable weather ahead. Global models and their
ensembles show a big pattern change to take shape late this week.
Our upper ridging will be replaced by an upper trough. One
longwave trough will be diving southward from the north, possibly
phasing in with a closed low over the Pacific this weekend with
the trough axis eventually moving across Southern California.
Timing/strength is uncertain but the consensus shows this to be
Sunday into Monday.

Light rain could develop ahead of this trough with GFS and EC
ensemble mean showing chances increasing this weekend with the
best chance of light rain being Sunday, October 25. There is a
large spread in rainfall amounts, ranging from nothing to over a
half an inch. We believe less than 0.25 inches is most likely with
light rainfall rates, but will continue to monitor trends. Of
greater importance will be a potential Santa Ana wind event
developing behind the trough as cold surface high pressure builds
southward into the Great Basin. Just like rainfall, there is a
spread in possibilities, but at least a moderate Santa Ana wind
looks possible in the October 26-28 timeframe, so stay tuned.

&&

.AVIATION...
190340Z...Coastal Areas...Low clouds will continue to spill onto the
coast and push about 5-10 miles inland overnight. Bases will be 400-
800 feet MSL with vis reduced down to 1-3 miles, locally less than 1
mile on higher coastal terrain, including KCRQ. Scatter out expected
16-18Z Monday with beaches possibly clearing a bit later in the
morning.

Elsewhere, mountain breezes diminishing through the night with FEW-
SCT mid to high level clouds with unrestricted vis through Monday.

&&

.MARINE...No impactful marine weather through Wednesday.

&&

.FIRE WEATHER...
Above average temperatures, extremely dry conditions, low daytime
RH, and gusty late day and evening westerly winds winds will
continue elevated fire weather conditions well inland and over the
mountains through midweek.

Much cooler conditions Thursday through the weekend, will combine
with higher RH to ease fire weather conditions a bit more.

A deep marine layer Friday through Sunday may produce some light
precipitation west of the mountains at times, however significant
wetting rains are not forecast at this time. The next chance for
Santa Ana type winds looks to be early next week.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC...10/Gregoria
FIRE WEATHER...10
AVIATION/MARINE...APR