Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/19/23
Area Forecast Discussion
National Weather Service Grand Junction CO
618 PM MDT Wed Oct 18 2023
.SHORT TERM...(Tonight through Thursday night)
Issued at 150 PM MDT Wed Oct 18 2023
Northwest flow will remain in place today through Thursday as a
ridge of high pressure remains planted across the western CONUS
and even amplifies a bit. Some high clouds are seen on satellite
moving down the northern and central divide due to a shortwave
trough passing through the Midwest. Winds will be gusty at times
across southwest Colorado valleys as well as some high terrain
sites due to the passing wave. Due to the low relative humidities
in the mid teens across the south, localized near critical fire
weather conditions are possible across southwest Colorado this
afternoon when combined with the breezy afternoon winds. Patchy
smoke and haze was present this morning across portions of
southwest Colorado valleys due to nearby burns, so decided to add
this to the forecast the next couple days based on the HRRR smoke
model output, which seems to be doing a decent job. The warming
trend will continue with highs a few degrees warmer on Thursday
due to the building ridge slowly shifting eastward. Highs may not
reach record highs for mid October yet, but will be close in a
few places, with high temperatures around 15 degrees above normal
area wide by Thursday.
.LONG TERM...(Friday through Wednesday)
Issued at 150 PM MDT Wed Oct 18 2023
On Friday, the amplified ridge over the western CONUS begins to
translate eastward and eventually becomes centered over our region.
This pattern will continue to support warm advection. In fact, high
temperatures for Friday may break records at some locations. Over
the course of the weekend, a strong trough moves into the Pacific
Northwest. At least for our area, we may only see a general
uptick in the winds. There is decent model agreement that this
system will dive southeastward over the Great Basin on Monday, and
the associated jet aloft rounds the base of the trough at the
same time moisture reaches us in the southwest flow. This may be
enough for isolated to scattered precipitation. This would most
likely be limited to the higher elevations during the early stages
of the storm. There is some variability on where this trough
tracks, but it looks to close off in the Desert Southwest late
Monday. Exactly how far southwest the lows tracks varies from the
northern Baja to central Arizona before it progresses eastward.
This might not play a huge role in our weather, but in this
scenario, the main forcing will pass south of our area. The Four
Corners could benefit from some of this lift enhancement.
Regardless, the system will drag a cold front through the entire
region most likely on Monday. There will be some moisture and
therefore precipitation with this front. Winds will also increase
as we will be located in the tighter pressure gradient on the
front side of the low. Temperatures drop behind the front closer
to normal, which will definitely be a change from the record
warmth possible this weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 617 PM MDT Wed Oct 18 2023
VFR conditions with light terrain driven winds continue through
the next 24 hours.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&
$$
SHORT TERM...MDA
LONG TERM...KJS
AVIATION...NL
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
900 PM PDT Wed Oct 18 2023
.SYNOPSIS...18/133 PM.
High pressure aloft will continue over the region this week,
bringing dry offshore flow and much above normal temperatures to
Southwest California. A shallow marine layer will bring dense fog
to many areas near the beaches this morning and again Thursday
morning. By the weekend, stronger onshore flow will bring much
cooler temperatures to the area. Drizzle or light rain is
possible across parts of LA County early next week.
&&
.SHORT TERM (WED-SAT)...18/900 PM.
It was a hot day today in the valleys, lower mountain elevations
and the Antelope Valley. High temperatures reached or slightly
exceeded 100 degrees in a couple of places in the L.A. and Ventura
County valleys, including 101 degrees at Ojai and 100 degrees at
Van Nuys and Woodland HIlls. Locations such as Westlake Village
and Simi Valley came up just short with highs of 99 degrees. A
shallow marine layer kept it much cooler across most of the
coastal plain, despite abundant sunshine as low clouds cleared
reasonably early. However, portions of the inland Central Coast
got very warm today, and it did not take much of a rise in
elevation to experience very warm conditions across the coastal
plain in L.A. County as well.
The marine layer remained shallow, generally between 500 and 700
feet deep or so this evening. Low clouds and patchy dense fog
have moved into most coastal areas south of Point Conception this
evening, with the exception of the L.A. and VTU County coastal
plain more than about 6 to 8 miles of the beaches. Clouds should
overspread those areas before midnight or so. North of Pt.
Conception, skies remained mostly clear this evening due to some
weak low level NE flow, but low clouds and fog are expected to
spread into most coastal areas north of Pt. Conception late
tonight. Will likely issue a Dense Fog Advisory for all coastal
areas south of Point Conception, and may hold off for areas to the
north for now.
Expect low clouds to clear by mid to late morning in most areas
on Fri. With the shallow marine layer still in place, and with
little chance in heights or temps at 950 mb, expect max temps to
be similar on Thu to those that were recorded today, with perhaps
a bit of warming across interior sections of the L.A. and Ventura
County coastal plain.
***from previous discussion***
Will be keeping a close eye on the area of instability over
northern Baja tonight as models show that area moving towards the
northwest and possibly into the outer coastal waters. It`s a very
low confidence pattern but with potentially higher impacts on ship
traffic should convection develop. Hi res ensemble models
including the HREF, SREF, RAP, and HRRR still not showing any
precip from that tonight or tomorrow but given the expected
trajectory would place the chances of showers at around 10% with
isolated thunderstorms possible as well. With the upper high in
place over the southwest the instability should not get that close
to the mainland coast but could skirt some of the far offshore
islands like San Nicolas, or possibly even San Miguel. Forecast
soundings still showing CAPEs in the 800j/kg range and PW`s around
an inch so it`s worth keeping a close eye on tonight.
Offshore flow expected to weaken Friday and then turn onshore over
the weekend resulting in a significant cooler trend, especially by
Saturday.
.LONG TERM (SUN-WED)...18/208 PM.
Much cooler weather expected Sunday as onshore flow increases
ahead of the next upper low which most EPS/NAEFS solutions say
will be an inside slider. Highs Sunday expected to be 3-6 degrees
below normal in most areas with marine layer clouds at least along
the Central Coast and in LA County.
As the upper low drops south through California Sunday northerly
flow around the west side of the low will start bringing
increasing north winds to SLO/Santa Barbara Counties and
eventually into LA/Ventura Counties Sunday night into Monday. This
should clear out the marine layer for western counties but Monday
will likely start out pretty cloudy for LA County and possibly
eastern Ventura County with some morning drizzle possible. Better
chances for drizzle or even some light rain across the north
facing mountains around the Grapevine area as the northerly flow
pushes the moisture up the slopes. Therefore, best chances for any
measurable rain from this system will be in that area. Ensembles
are indicating anywhere from a trace to as much as a half inch
there, with the most likely outcome a quarter inch or less.
Probably the biggest impact from this will be the winds which will
likely reach advisory levels in the mountains, including the Santa
Ynez Range Sunday and Monday. Some of that wind will likely
surface into the valleys and some of the coastal areas as well.
The northwest push will eventually clear out the marine layer but
it may take most of Monday. After that through the rest of next
week there is a lot of uncertainty in the details but in general
the pattern looks cooler than normal with one or two more inside
slider type systems moving through.
&&
.AVIATION...19/0209Z.
At 2345Z at KLAX, the marine layer was 1000 feet deep. The top of
the inversion was around 1900 feet with a temperature 30 C.
High confidence in valley and desert TAFs.
Low to moderate confidence in coastal TAFs due to uncertainty in
the timing of cigs. Timing of cig arrivals tonight and clearing
tomorrow morning may be up to 2 hours later than forecast. There
is a 40% chance of LIFR cigs at KSBP from 08Z-15Z.
KLAX...Low confidence in the TAF. Timing of LIFR conditions may be
off 1-2 hours. High confidence any east wind component will be
under 6 kt.
KBUR...High confidence in VFR conds.
&&
.MARINE...18/248 PM.
In the outer waters, moderate confidence in forecast. Seas are
at Small Craft Advisory (SCA) levels currently and will continue
at or above SCA levels thru at least Thu night, with a 40% chance
they will continue thru Fri. Winds are expected to be below SCA
levels thru Fri, then SCA level winds are expected Fri night thru
Sun. The exception is the northern zone (PZZ670), where winds are
expected to stay below SCA levels thru Fri night, with a 40%
chance of SCA level winds Sat, and SCA winds are likely Sat night
and Sun.
Across the inner waters north of Pt. Sal, seas at SCA levels now,
and will continue at or above SCA levels thru at least Thu night,
with a 30% chance they will continue thru Fri. Winds are expected
to be below SCA levels thru Sun morning, then SCA level winds are
expected Sun afternoon.
In the SBA Channel, winds are seas are expected to remain below SCA
levels thru Fri. However this afternoon seas will be elevated,
with swells up to 6 feet. SCA level winds are likely across
western portions of the channel late Fri into Fri night, and
across most of the channel during the late afternoon thru late
night hours Sat and Sun.
Across the souther inner waters, winds and seas are expected to
remain below SCA levels thru Fri. There is a 30% chance of SCA
level winds across western portions Fri evening. SCA level winds
are likely during the afternoon and evening hours Sat and Sun.
&&
.BEACHES...18/249 PM.
For the Central Coast high surf is expected starting this
evening, due to very long period (up to 25 seconds) northwest
swell. West- Northwest facing beaches can expect surf of 5 to 8
feet today building to 7 to 11 feet in the evening. Thursday W-NW
beaches will see surf of 10 to 15 feet, with local sets to 20
feet, and SW facing beaches will see surf of 6 to 9 feet. Surf
should subside to below advisory level during the day Friday.
Minor coastal flooding is possible midday on Thursday.
For Ventura County, surf of 4 to 8 feet with local sets to 9 feet
is expected to start to develop after midnight tonight. High risk
of hazardous rip currents during this time. Surf is expected to
subside around Friday night. Nuisance coastal flooding is
possible midday on Thursday.
For Los Angeles County surf of 3 to 6 feet with local sets to 7
feet is expected to start to develop early tomorrow. High risk of
hazardous rip currents during this time. Surf is expected to
subside around Friday night.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect from 10 AM to 8 PM PDT Thursday for
zones 88-358-367-369>375-548. (See LAXNPWLOX).
High Surf Advisory in effect until 9 AM PDT Friday for zones
340-346. (See LAXCFWLOX).
High Surf Advisory in effect until 9 PM PDT Friday for zone
354. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for
zones 645-670-673-676. (See LAXMWWLOX).
&&
$$
PUBLIC...MW/DB
AVIATION...Phillips
MARINE...DB/Schoenfeld
BEACHES...Schoenfeld
SYNOPSIS...MW
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox
Area Forecast Discussion
National Weather Service Phoenix AZ
412 PM MST Wed Oct 18 2023
.UPDATE...00Z Aviation Discussion.
&&
.SYNOPSIS...
Well-above normal temperatures will continue through Saturday as
high pressure predominates across the Desert Southwest. Near or
record-breaking temperatures are possible Thursday and Friday,
especially across the Phoenix area. A noticeable cooling trend
will begin Sunday as a Pacific low pressure system moves through
the region and below-normal temperatures will be possible by the
middle of next week.
&&
.DISCUSSION...
Latest water vapor imagery and RAP streamline analysis reveal a
dry, easterly flow between a retrograding upper low west of the
Baja Peninsula and a building anticyclone across northern
California. Positive mid-level height anomalies are again
translating into a continuation of the widespread above normal
temperatures across the Desert Southwest.
Models remain in good agreement depicting the ridge amplifying
across the western CONUS Thursday. Latest NBM indicates an 80
percent chance of at least tying the record high of 101 degrees
for the date in Phoenix. The ridge is expected to slide eastward
Friday, resulting in a dry southwesterly flow. Meanwhile, the NBM
continues to trend warmer, indicating a deterministic high
temperature of 104 degrees for Phoenix, which would again break
the daily record of 103 degrees set in 2003. Somewhat cooler
conditions are anticipated Saturday as moisture and the remnants
of the Baja upper low move eastward through the Four Corners.
A more noticeable cooling trend is likely Sunday as heights lower
in response to deepening Pacific low pressure system. Initial
impact from this system will be widespread breeziness, though
ECMWF EFIs below 50 percent suggest only minimal impact.
Meanwhile, the cooling trend will continue through the middle of
next week as the trough sweeps through the Desert Southwest, and
there is a 60 percent chance of below normal temperatures by next
Wednesday. ECMWF Ensemble IVT is also unremarkable, given the lack
of a deep subtropical fetch. Consequently, latest trends in the
grand ensemble also suggest a decreased chance of significant
rainfall across the area. Nevertheless, the latest NBM indicates a
20 percent chance of measurable rainfall across portions of
eastern Arizona Monday/Tuesday.
&&
.AVIATION...Updated at 2315Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT;
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation impacts are anticipated throughout the forecast
period under clear skies. Diurnal tendencies will prevail across
the Phoenix metro TAF sites as the typical easterly shift takes
hold between 04Z-07Z this evening. At KIPL and KBLH, west to
northwest winds early this evening will become variable tomorrow
morning, with a slight preference towards east to northeast
directions. Otherwise, speeds will remain light AOB 7 kts across
all terminals.
&&
.FIRE WEATHER...
Above-normal temperatures will continue through the remainder of
this week with rain chances remaining near zero. Winds will
continue to follow typical diurnal trends with occasional
afternoon upslope breeziness. Dry conditions will remain in place
as MinRHs values are only expected to range between 10-15% for the
next several days. Overnight recoveries will be minimal to modest
at best with MaxRH values ranging between 25-45% through Friday.
Substantial cooling is anticipated for next week, with
temperatures dropping to near and even below-normal
&&
.CLIMATE...
Record high temperatures this week:
Date Phoenix Yuma El Centro
---- ------- ---- ---------
Oct 18 103 in 2003 103 in 1959 102 in 2003
Oct 19 101 in 2003 105 in 2003 103 in 2003
Oct 20 103 in 2003 105 in 2003 103 in 2003
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hirsch
AVIATION...Leffel
FIRE WEATHER...RW
CLIMATE...Young/18