Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/25/24
Area Forecast Discussion
National Weather Service Denver/Boulder CO
753 PM MDT Wed Apr 24 2024
.KEY MESSAGES...
- Slight Risk of severe thunderstorms Thursday, east of a line
from Sterling to Akron, including large hail, damaging winds and
isolated tornadoes. A marginal risk south and west of this
area.
- Cool and unsettled Friday into the weekend, with accumulating
moderate snowfall in the mountains, widespread rain showers over
the plains
&&
.UPDATE...
Issued at 742 PM MDT Wed Apr 24 2024
One thunderstorm is still doing its best to persevere in a
generally hostile environment along the CO/NE border this evening,
with just a couple of weak, high-based showers noted elsewhere.
Not expecting much overnight tonight with just some chance PoPs in
the far northeast corner overnight.
As better moisture streams into the area overnight, there should
be some development of stratus/mist in the eastern plains, along
with some patchy fog. Have also added a little bit of fog into
the grids across southern Weld county into the DIA area where
guidance the HRRR has hinted at this the past few cycles.
Otherwise, only some minor adjustments were made to the forecast
grids this evening. The previous forecast was largely in good
shape.
&&
.SHORT TERM /Through Thursday/...
Issued at 324 PM MDT Wed Apr 24 2024
Northern border shower activity is running a couple hours ahead of
schedule. The edge of the drier air is lifting northward and there
does appear to be more stable air upstream west of the Front
Range, so the end of this over the mountains may also be faster,
in the early evening or sooner. On the plains the showers will be
encountering the south winds that could keep them going longer,
although there`s not really more moisture out there yet. Further
south, there`s just a slight chance of very light showers, we`ll
probably just have virga.
A surface low will develop early Thursday on the broad shear zone
on the edge of the southerlies on the plains, probably starting
near Denver but then drifting eastward. Moisture will be
increasing in the southerlies tonight. There is a stratus deck
from western Kansas into Texas that will advect into the northeast
Corner of Colorado tonight, and it will likely develop westward
late tonight. The increase in moisture is gradual at first, but
richer air will arrive by Thursday morning. Between the wind
speeds and the existing stratus deck, it looks like this will
probably be off the ground instead of producing fog.
Thursday`s severe potential is complicated by this cloud deck and
the fact that the moist air is considerably cooler and should be
capped, at least for most of the day and possible into Thursday
evening. So the question becomes where there will be both enough
moisture and heat, or enough convergence to break the cap. If we
can get convection rooted in that moisture, it`s a pretty
favorable supercell environment with mainly a large hail threat. I
see two severe scenarios, both of which are questionable, and both
of which could happen together.
One is on the west edge of the better moisture, extending on the
north side of the surface low, probably across northeast Weld, or
possibly Logan or Morgan counties. This area could be the sweet
spot which has increased moisture but still gets warm enough.
While CAPEs in this area won`t be as high as further east, it`s
still a supercell environment and this area might have the best
potential for tornadoes early in the life of the storm with a more
backed low level wind field. This would most likely be for a
couple hours during the late afternoon. The second scenario would
be that the dryline convergence is enough to overcome a weak cap.
Most of the convective allowing models we`ve seen like this idea,
and insist on it happening in the late afternoon. This seems like
it might be too fast given the model soundings we`ve seen which
are mostly still pretty cool in the moist air in the late
afternoon. It may take increasing convergence along with peak
heating/moistening into the evening if that`s going to happen.
This would be more likely on the east side of the low, east or
northeast of Akron, and a few hours later. In this case also, the
severe threat is probably just a couple of hours and then we`re
dealing with elevated convection over the cooler moist air.
Behind the low during the afternoon, we`ll have a relatively dry
environment, though still probably enough moisture/instability for
some higher based weaker storms. The bulk of that may wait for
evening as well with some cooling aloft and moisture advection
from the north/northeast behind the low.
For now, minimal changes have been made as this was the general
forecast scenario we`ve had going. The main question remains the
heating of the moist air late Thursday.
&&
.LONG TERM /Thursday night through Wednesday/...
Issued at 324 PM MDT Wed Apr 24 2024
As the backside of the cyclone brings northwest flow to the
northeastern plains, the threat of severe storms could continue
through midnight. Counties such as Logan, Sedgwick, and Phillips
have the greatest chance of additional severe storms while
elsewhere instability decreases overnight. Although a nocturnal
threat of severe weather isn`t new, those areas listed above
should remain weather aware Thursday evening until midnight. Light
snow prevails throughout elevations above 9k ft overnight into
Friday morning. With increasing snow and mid-level cloud cover
across the region Friday, this forecast package includes an
adjustment to afternoon highs as well Friday night lows. The next
trough axis approaches Utah quickly but Friday afternoon may
become a break in additional precipitation before the next
shortwave trough enters western Colorado. Therefore, kept a chance
of scattered PoPs (40-50%) along the urban corridor Friday
afternoon. WPC Super Ensemble QPF fields display at least
0.50-0.75 inches over majority of the CWA Friday night into
Saturday morning. It is likely areas across the mountains could
receive periods of light to moderate snowfall. If traveling to
mountain passes, prepare for winter travel conditions. Snowfall
rates could approach 1-2 inch/hr above 10k ft especially by
Saturday afternoon. Heavy rainfall will likely occur across the
lower elevations Saturday as precipitable water values 0.7-1
inches. Numerous showers continue through Sunday morning. It is
possible these showers will remain less convective as daytime
heating will be limited.
Our region will transition into zonal flow by Monday and weak
lingering mid-level moisture could lead to isolated showers
throughout Jackson and Grand counties. By Tuesday, dry conditions
continue across the region.
&&
.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 524 PM MDT Wed Apr 24 2024
VFR conditions should prevail through the TAF period. A broad
Denver cyclone has been observed again this afternoon with the
main boundary/wind shift located between BJC and DEN. Current
expectation is for this to remain fairly steady-state through the
next couple of hours, and then gradually weaken later this evening
as drainage flow establishes.
Next forecast challenge comes early Thursday as models hint at
some potential for a brief period of fog or very low stratus
tomorrow at DEN. BUFKIT profiles would favor fog, but the
majority of guidance keeps this just north/northeast of the field
in southern Weld county.
Finally, there`s still some uncertainty in the winds and overall
convective/shower potential Thursday afternoon, with DEN
reasonably close to the dryline. Will need to re-evaluate with
tonight/tomorrow AM hi-res guidance to get a better feel, but a
broad period of VCTS/VCSH is likely. Eventually may see some lower
cigs develop after 00z as well.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Hiris
SHORT TERM...Gimmestad
LONG TERM...AD
AVIATION...Hiris
Area Forecast Discussion
National Weather Service Dodge City KS
704 PM CDT Wed Apr 24 2024
.KEY MESSAGES...
- Severe weather risk on Thursday for areas along and east of
highway 83.
- Fire weather risk on Thursday for areas along and west of
highway 83.
- Potential fire and severe weather risk for Saturday as well.
&&
.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 103 PM CDT Wed Apr 24 2024
18z obs and RAP upper air analysis shows a widespread cloud deck
across southwest Kansas with the last areas of morning
convection well to the south and east. 500 mb winds have a ridge
across the Rockies with an embedded shortwave developing in the
front range and a large closed low still well off the Pacific
coast of California.
For tonight the position of the longwave trough/upper low should
quickly move into the Colorado river basin in the desert
southwest which will push the upper level ridge eastward into
the central plains. With this we will also see a layer of warmer
air in the mid levels with many models showing around 8-10 (C)
700 mb temperatures which will be important to monitor as it
will affect our storm chances on Thursday. Ahead of the warm
front we should have a 700 mb shortwave coming out of the front
range from eastern Colorado through central Kansas and with good
moisture advection along the front and wave we should see an
area of thunderstorms develop mainly after midnight for areas
along and east of highway 83. These storms should move quickly
to the east into central Kansas by morning and with low CAPE
values forecast this rain and storm should stay below severe
limits.
Thursday the SPC has put an enhanced risk of severe weather for
areas along and east of highway 83. Three things we have been
noticing so far that could mitigate the risk is how much
thunderstorm outflow/clouds/colder air hangs around from what we
get tonight in our eastern zones. Also the warm mid layers at
700 mb will produce a strong cap all across southwest Kansas
with the 25th percentile temperatures at 8 (C) and 90th at 9-10
(C) suggesting a >90 % chance of a strong cap. With temperatures
in the mid levels that warm we would need the areas with
moisture to get to near 90 degrees to break the cap which is not
looking promising at this point. Also models are lagging the
forcing at 500 mb until well after 00Z to also help break the
CAP. Some CAMs have been showing no convection at all however if
a storm can break the CAPE the bulk shear and CAPE values would
support supercells capable of hail greater than 2 inches and
damaging winds. If supercells can stay discrete through 7 pm the
low level jet will increase and introduce a tornado threat and
we can`t rule out a strong tornado potential. This is what would
be call a classic conditional severe weather risk.
Fire weather threat west of highway 83 will be the result of a
dryline moving in from the west and reaching to the Scott City-
Liberal line and southwest winds will be 20-30 mph with relative
humidity values falling to below 15%.
Thursday night any convection that develops will race to the
north and east as the 991 mb surface low moves into southwest
Nebraska and the dryline/cool front moves to the east.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 208 PM CDT Wed Apr 24 2024
Friday the low from the surface to 500 mb will move into central
Nebraska and will sweep drier air through southwest Kansas.
Winds will increase through the day especially for areas along
and north of K-96 with wind speeds at 20-30 mph with higher
gusts.
Saturday will have both severe and fire weather potential in
southwest Kansas. Medium range ensemble models have an upper low
moving from the four corners region Saturday morning to
southeast Colorado by late afternoon. Moisture profiles have the
highest levels in central Kansas with the drier air for much of
southwest Kansas along and west of highway 283. Elevated to
critical fire weather potential is high (>80%) as winds will be
out of the southwest at 20-30 mph with higher gusts. Severe
weather at this point looks to be mainly along and east of
highway 281 with the greater potential more into central Kansas.
After Saturday ensemble upper air forecasts go more zonal and we
will go dry and warmer for the middle parts of next week.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 700 PM CDT Wed Apr 24 2024
Aviation weather conditions will deteriorate this evening with
widespread IFR/LIFR conditions developing particularly in the
09-15Z time frame...later up north toward HYS and earlier down
south toward LBL terminal as the warm front lifts north. The
forecast at HYS terminal is particularly challenging in that a
large cluster of thunderstorms will develop overnight near or
just east of HYS, which will likely spread an outflow boundary
south across HYS some time in the 09-13Z time frame. This
thunderstorm outflow boundary will likely result in an easterly
wind (if not slightly northeasterly) and may reach as far as DDC
mid-morning, however we will keep winds at DDC out of the
south-southeast Thursday morning. HYS will likely remain in the
low stratus and IFR/LIFR flight category much of the day
Thursday.
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 1 PM CDT /noon MDT/ to 9 PM CDT /8 PM
MDT/ Thursday for KSZ061-062-074-075-084-085.
&&
$$
SHORT TERM...Tatro
LONG TERM...Tatro
AVIATION...Umscheid
Area Forecast Discussion
National Weather Service Goodland KS
813 PM MDT Wed Apr 24 2024
.KEY MESSAGES...
- Significant severe weather is possible Thursday for most of
the area with the main threats being tornadoes and very large
hail. The threat is conditional as a cap could prevent storms
from forming.
- A Fire Weather Watch and Red Flag Warning is in effect
Thursday south of I-70 and west of Highway 25 for low humidity
and strong winds.
- Blowing dust is also possible Thursday afternoon for near and
south of the I-70 corridor.
&&
.UPDATE...
Issued at 722 PM MDT Wed Apr 24 2024
Confidence is increasing in overnight convection affecting
portions of the east and northeast counties. RAP soundings
indicate an increasing environment for strong to marginally
severe hail occurring with MUCAPE around 1400 j/kg, effective
shear of 40-45 knots, EBWD shear in excess of 40 knots and lapse
rates of around 8 C/km which should bring about the potential
for hail around quarter size. PWATS are also in excess of 1 inch
which would support a very heavy rain threat as well. Would be
surprised if flooding becomes a concern due to the antecedent
dry conditions along with fast storm motion. However if
backbuilding does become an issue than may need to watch this
more closely.
Confidence also does continue to increase in the potential for a
significant severe weather event Thursday afternoon. Virtual all
CAMS are now convecting along the dry line during the afternoon
hours which is quite the change vs what was seen last night
where everything was capped. It appears that the reasoning for
this is due to the low stratus being favored a bit further north
and east. A slight concern I do have is regarding upper level
cirrus potential as RH values in the 400-200mb level do show
around 30% RH values during the afternoon hours and signals of
cirrus is also seen in RAP soundings. If this is the case this
may be one of the many factors that may limit convective
initation or sustained of any updrafts. Others are if the CAP
is to strong and any potential impact that any outflow from
overnight/morning convection may have; especially regarding the
tornado potential. Despite all the continued uncertainties that
do continue to shadow this event, the potential is there for a
few intense supercells with very large hail and perhaps a
significant tornado threat as 0-3 SRH values are around 200-225
and 0-1 SRH around 100 and does steadily increase into the later
afternoon and early evening hours.
Regarding location for tomorrow; have been noticing a slight
westward trend with where guidance wants to place the dry line.
Similar signs were seen with last week`s severe event where the
NAM was the relatively most accurate with the location of the
dry line and other guidance were playing catchup. I feel the
same thing is again applying in this scenario as well. Reasoning
for this may be due to the undoing of soil moisture across the
area; yes we have been dry lately but the area is coming off of
a wetter past year; SPORT soil moisture also does support this
theory as soil moisture has slightly improved over the past
week. Overall current expectations is that the dry line does end
up developing a bit further west perhaps around the Highway 27
corridor, creating a slightly larger warm sector.
&&
.SHORT TERM /THROUGH FRIDAY/...
Issued at 248 PM MDT Wed Apr 24 2024
Tonight, the 850 mb LLJ will strengthen and shove more moisture into
the CWA. At the surface, easterly winds will cause upslope flow,
leading to stratus and patchy to locally dense fog. This fog may
begin around 10Z and potentially last until 18Z. The stratus will
linger around longer than the fog and potentially cap the severe
environment tomorrow afternoon/evening.
Also tonight, a shortwave looks to fire off a few showers and storms
around 7Z. Small hail and some gusty winds are possible (5% chance),
but confidence for severe weather is less than 2%. These showers
and storms are expected to form near the eastern Colorado border and
move east. The precipitation will exit the CWA in the late morning.
If these showers and storms linger and are fairly strong, this
precipitation could deplete the environment of ingredients for the
later storms.
After 18Z, southerly winds will pick up with gusts up to 35 kts in
the southerly portions of the CWA. Depending on where the dryline
sets up, locales to the west will be much more dry. RH values to the
west of the dryline will drop into the lower teens. This will create
critical fire weather conditions for locations south of I-70 and
west of Highway 25. Most locations will only briefly see the
critical conditions, but there is high (80%) confidence that Greeley
county will see prolonged critical conditions. If the dryline stalls
out farther to the east and north, surrounding counties will have a
good shot at hitting Red Flag Warning criteria, hence why the Fire
Weather Watch has been left in place.
Blowing dust will also be possible (~20-50% chance) in locations
along and south of Highway 36. Along the Kansas Colorado border will
see the best conditions for blowing dust. Visibility reductions down
to 2-3 miles are possible in plumes of blowing dust. Brown-out
conditions cannot be ruled out.
The dryline will be the trigger for the severe weather in the
eventing. SPC has added an Enhanced risk to the southeastern CWA for
Thursday afternoon-night. This is based on a hatched/significant
hazard for 30% chance of hail and 10% chance of tornado. For this
event, the environment will be highly primed for tornado and hail
hazards, but there will likely (60%) be a hefty inversion that will
work to cap the updraft potential. If the cap does break, isolated
discrete to clusters of severe storms will form and all hazards will
be possible, with a focus on tornadoes and hail. The entire Tri-
State area will have potential to see severe weather, but chances
increase farther to the southeast.
Storms are expected to start firing around 18-21Z with the highlight
of the severe storms being 21Z-06Z. The prime location for the
severe storms will be in the southeastern CWA and the storms will
move to the northeast. After 06Z, the severe weather threat will
lower over the following 6 hours. During this time, we will begin to
get the wrap-around precipitation from the northwest. These are
expected to just be showers with a few weak thunderstorms embedded
within. Less than 0.5 inches of QPF is expected with this system
with most of that falling north of highway 36.
As the low pressure system leaves the area on Friday, strong
northwesterly winds are expected to follow. Gusts up to 40 kts are
already expected due to the pressure rises.
Temperatures overnight tonight and tomorrow night will cool to
around 50. High temperatures tomorrow will be highly dependent on
the dryline location and extent of the stratus. Under the stratus,
highs will only reach the upper 60s to lower 70s. In the southwest,
behind the dryline, low to mid 80s are forecast. Friday will be a
bit more uniform with the northwestern CWA only warming into the mid
60s and the southern CWA reaching into the mid to upper 70s.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 254 PM MDT Wed Apr 24 2024
A low pressure system will lift to the northeast across north
central Kansas and south central Nebraska Friday evening. Overnight,
there will be a 20-50% chance of showers and a few thunderstorms
across areas mainly along and east of Highway 26.
Another low pressure system will lift to the northeast, out of the
Four Corners region Saturday, bringing additional chances of
precipitation to the area. Chances (40-80%) for showers and
thunderstorms will increase west to east through the day as the
system moves across the CWA. Saturday night into Sunday, shower and
thunderstorm chances continue as wrap around moisture impacts the
region. Winds are also expected to increase on the back of the
system.
Zonal flow sets up over the region on Monday and Tuesday.
Expect a drying out period during this time and a warm up.
Monday highs will be mainly in the low to mid-70s. Afternoon
highs on Tuesday will be in the 70s and 80s.
&&
.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 511 PM MDT Wed Apr 24 2024
Breezy conditions will continue into the evening hours. The main
concern, especially for the first portion of this TAF period
will be stratus and patchy fog as moisture advects into the
area. Currently, thinking stratus will be the main aviation
concern as fog may be patchy in coverage as wind may lead into
the "dissolving" of fog so will utilize VCFG for this. IFR to
LIFR appears to be likely at each terminal. Some nocturnal
convection may impact KMCK tonight around 06Z so will use VCTS
until confidence increases in terminal being affected. Thursday
afternoon may see some storms, perhaps severe during the
afternoon hours with all hazards on the table. Exact timing due
to initation issues exists currently so remain aware for
updates.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Fire Weather Watch from Thursday afternoon through Thursday
evening for KSZ013-027-028-042.
Red Flag Warning from noon to 8 PM MDT Thursday for KSZ041.
CO...Fire Weather Watch from Thursday afternoon through Thursday
evening for COZ253-254.
NE...None.
&&
$$
UPDATE...Trigg
SHORT TERM...CA
LONG TERM...Wekesser
AVIATION...Trigg
Area Forecast Discussion
National Weather Service Gray ME
1050 PM EDT Wed Apr 24 2024
.SYNOPSIS...
Dry high pressure then moves into and across the region tonight
through Saturday. A warming trend can be expected over the
weekend with chance of showers Saturday night or Sunday. Warmer
weather is then expected early next week for most areas except
possibly the coastal plain.
&&
.NEAR TERM /OVERNIGHT/...
1050 PM Update...Another round of very minor tweaks using latest
00Z hires guidance. At this time, the only clouds remaining over
the area are a few stubborn patches of cumulus near the Whites,
but these are fast eroding right on schedule. Did go a bit more
deterministic and lowered sky coverage further to denote the
strong clearing trend. Winds are just starting to become less
gusty, and more of a steady breeze... with this trend continuing
over the next few hours.
702 PM Update...Just a few minor tweaks to T/Td/sky trends
overnight with latest hires guidance coming in. Overall very
little change of consequence. At this time, the cold front is
slipping offshore with gusty northwest winds 25-35 and a
clearing trend. over the area.
Previously...
A cold front will pass through the area through the evening,
kicking up some winds as well as dropping temperatures
overnight.
After midday clearing, scattered showers have again developed
over the area. This is associated with lift from the passing
cold front, and should taper into the early evening. Some light
snow is also expected through early evening along the US/CAD
border. Mixing taps into some low level winds through late
evening, creating gusts up to 35 mph. Winds should lose gust
factor around midnight, with breeze continuing. Temps fall due
to this CAA, with widespread values around freezing or off into
the 20s across the mountains.
&&
.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
Wave that enhanced winds Wed evening will have moved out for
Thursday, with just a few gusts early. As mixing kicks in amid a
very dry airmass, will likely see RH values fall into the 20s
and teens through the afternoon. Limited moisture through the
column should prove for a nearly full sun day. Temperatures will
be cooler however, and struggle to warm outside of direct sun
insolation. HRRR is depicting a seabreeze beginning early
afternoon, and this should bring a wind shift to coastal
communities around 2pm along with a bit more humidity as temps
fall off a couple degrees.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
We`ll start off the long term period 12z on Friday with a 1030+
millibar high pressure center overhead. A cool crisp morning
will give way to a sunny afternoon but with below normal
temperatures.
Deep layer ridging builds Friday night allowing for the fair
weather to continue. Radiational cooling is likely Friday night
and therefore sided with MOS guidance for lows.
Deep layer ridging slowly moves eastward on Saturday but still
should provide for a fair weather day with temperatures
returning to the 60s. A warm front approaches from the west
Saturday night with the chance of showers late. However, the
ridge aloft will hold firm so capped the PoPs some as it`s
entirely possible that any period of showers Saturday night and
Sunday could be brief. It still should remain cloudy Sunday with
low level onshore flow in place, but larger scale subsidence
should keep chances of rain low.
The same general setup looks to be in the cards for Monday but
there is more uncertainty in temperatures as onshore flow may
penetrate deeper into Maine and portions of NH. The best chance
of 70+ degree readings will be over southwestern NH while lower
temperatures are expected as one moves eastward. There is also a
chance that some showers will spill over the ridge axis.
The best chance of measurable rainfall will come Tuesday and/or
Wednesday as the ridge finally breaks down and allows a trough
to approach from the west. Showers and perhaps a few
thunderstorms will be possible then.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Short Term...VFR with gusty NW winds through mid evening. MVFR
ceilings through late this afternoon for HIE. Some gusts may
approach 30 kt accompanying showers. Some LLWS is possible as
surface winds settle before winds aloft. Winds slowly slacken
overnight. Lighter winds Thursday, with primarily SKC
conditions. Can`t rule out some valley fog developing Thursday
night.
Long Term...VFR prevails Friday through Saturday with high
pressure overhead. Scattered -SHRA arrives Saturday night
through part of Sunday with possible lower ceilings although the
any rainfall would likely be brief at one location. The same is
expected for Monday although chances of rain will be lower.
&&
.MARINE...
Short Term...NW winds increase this evening as a cold front
crosses the waters. Some gusts to 35 kt are possible, but bulk
of these winds should be 30kt or less. These winds slacken below
SCA criteria Thursday morning, with seas slowly lowered to 3 to
4 ft through the day. A seabreeze may form during the afternoon,
turning winds onshore for the bays/harbors.
Long Term...Winds and seas to remain below thresholds hazardous
to small crafts as high pressure builds over the waters Fri-Mon.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ150-152-
154.
Small Craft Advisory until 4 AM EDT Thursday for ANZ151-153.
&&
$$
UPDATE...Casey
NEAR/SHORT TERM...Cornwell
LONG TERM...Ekster
Area Forecast Discussion
National Weather Service Reno NV
329 PM PDT Wed Apr 24 2024
.SYNOPSIS...
Cooler weather along with periods of showers and thunderstorms will
persist through early Saturday. Potential thunderstorm risks include
gusty outflow winds, dangerous lightning, and localized heavy rain
and/or small hail. Please be aware of rapidly changing conditions if
recreating outdoors. Drier weather and a slow warming trend are
expected to return on Sunday and persist into Tuesday.
&&
.DISCUSSION...
According to the latest RAP analysis, an upper air low is currently
residing to the west of the southern CA and the northern Baja
Peninsula causing a southerly to southwesterly flow over the CWA
this afternoon. The latest radar imagery along with surface
observations show some isolated to scattered showers and storms
along and east of a line from Sonora Pass, CA to Lovelock, NV as
well as in northern Washoe County that are moving generally north-
northeast. Going through tonight, models depict the upper air low
passing eastward through southern CA and south of the CWA until it
reaches the southern tip of NV by tomorrow morning. At the surface,
models show showers and thunderstorms continuing in eastern and
southern portions of the region through the rest of the day and into
the night with a frontal boundary moving through the area. The most
impressive looking storms in NV currently look to be east of the REV
CWA and in LKN`s CWA at this time which is where the highest 0-6km
bulk shear of around 30 kts is present. Models are showing pockets
of around 500 J/kg of SBCAPE later this afternoon and evening in
Mono and Mineral Counties, so best chances for thunderstorms look to
be in this portion of the region. Storms are not anticipated to be
severe, but they may contain some brief downpours, small hail,
and gusty winds. Portions of Mineral and Lyon counties may see up
to almost an inch of QPF by tomorrow morning with these showers
and storms with southern Mono County and eastern Churchill
counties coming in with about 0.50 inches of QPF. Other counties
that see precipitation such as Pershing and Washoe may see a few
tenths of an inch at most. Will monitor conditions, but not
anticipating any hydro issues with this rainfall.
On Thursday, models show the CWA having a divergent flow aloft in
the morning that becomes west-northwesterly by the evening hours as
a Pacific Northwest upper air trough moves over to control the upper
air flow in the northwestern CONUS. Forecast guidance then has the
axis of the trough passing over the CWA on Friday morning allowing
for the CWA to take a northwesterly flow by the afternoon and
evening hour. By Friday night into Saturday morning, forecast models
have the base of the trough digging down over AZ/southern CA causing
a north-northwesterly upper air flow over the CWA being underneath
the rear portion of the trough. At the surface, temperatures look to
take a cooling trend on Thursday and Friday due to cloud cover
inhibiting daytime heating. Guidance also is still showing a 50-90%
chance for widespread showers beginning in the latter half of
Thursday and going through Friday night with a 15-30% chance of
thunderstorms and/or ice pellet showers. Portions of the Sierra
above 6500-7000 feet may see some accumulating snow with the colder
temperatures. The latest NBM probabilities of 4 inches or more have
come down a bit as they are around 10%. What also came down a bit is
Thursday`s daytime winds though they still look to be on the
breezy side gusting up to around 35-40 mph in northwestern NV. The
latest NBM probabilities of 45+ mph wind gusts look to be around
20-40% with higher elevations having the best potential. QPF
values for late Thursday and going into Friday night are forecast
to range from around a few hundredths to around 0.5 inches in
eastern Pershing county. Severe weather is not anticipated on
Thursday or Friday though we will monitor conditions in case this
changes as small hail and gusty winds cannot be ruled out with
storms particularly on Friday. By Saturday morning, precipitation
chances look to begin to taper off within the region.
Going through the rest of the weekend, ensemble guidance shows a
weak ridge moving over the CWA by late Saturday and continue into
Sunday. A generally zonal flow is then seen on Monday over the CWA with
another trough starting to develop off the coast of southern BC
during the evening hours. Models then start to differ in their
upper air solutions going forward starting on Tuesday as the GFS
has the trough moving southward and turning the CWA`s flow aloft
to southwesterly by late afternoon and evening hours of Tuesday.
The latest run of the ECMWF as an alternative solution delays this
progression of the trough until Wednesday. Will have to wait for
models to come into better agreement in future runs for this far
out to have a better handle on the upper air pattern in the middle
of the week. But at the surface, a warming trend looks to begin
on Saturday and continue into next week at least through Tuesday
and potentially Wednesday. Drier conditions are also expected
going into the midweek after the Saturday morning`s precipitation
chances depart the region. As for winds, some models show winds to
potentially gust up to around 35-45 mph on next Wednesday along
the CA/NV border with a relatively tight surface pressure gradient
in the forecast. Will continue to monitor this going forward as
more forecast details become clearer.
-078
&&
.AVIATION...
VFR conditions are expected through the remainder of the today and
going into tomorrow for most of the REV TAF sites. Exceptions
include KTRK which expects some fog to develop between 09-16Z which
will cause IFR visibilities. Also: will be monitoring conditions at
KMMH with showers and thunderstorms expected to continue within
Douglas, Mineral, and Mono counties through most of today though not
expecting precipitation seen at the site to lower visibilities at
this time.
More widespread showers will migrate into the Sierra and western
Nevada by Thursday into the start of the weekend with a bigger
trough. Ahead of the main trough, FL100 winds increase resulting in
enhanced westerly surface winds (25-35 kts) on Thursday afternoon.
-078
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
Area Forecast Discussion
National Weather Service San Diego CA
900 PM PDT Wed Apr 24 2024
.SYNOPSIS...
A deep marine layer; gusty winds in the mountains and deserts; and
cooler conditions will prevail through Friday. Patchy drizzle or
light rain is expected each night and morning west of the mountains.
Gusty southwest to west winds will peak each afternoon and evening
in the mountains and deserts through Friday. Winds will weaken
through the weekend. Drier and warmer with a shallower marine layer
expected early next week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.Evening Update...
High clouds are streaming in over the high desert as low clouds
fill in much of the coastal basin this evening. Latest HRRR model
guidance indicates drizzle and light showers will develop mainly
after midnight, lasting until the mid morning hours. Winds have
been gusty this evening as the trough axis moves over Southern
California. Peak wind gusts have been mainly near 30-40 MPH across
mountains and deserts, with highest gusts near 60 MPH in the San
Gorgonio Pass and near In-Ko-Pah in San Diego County.
Graypril will continue for much of the day on Thursday for those
west of the mountains, especially away from the coast per latest
HREF model guidance. The deep marine layer will maintain itself
into Friday, so the chance for drizzle and light showers will once
again occur Thursday night into Friday morning. Winds will also
continue to be gusty across the mountains into the deserts on
Thursday and Friday as well. Friday will see the strongest winds
with these areas seeing peak wind gusts 40-55 MPH. Not all is
lost, as a brighter and warmer weekend is in store!
.Previous Discussion (133 PM PDT Wednesday)...
Low clouds are expected to fill in the coastal basin again
tonight into Thursday morning. Deep marine layer moisture combined
with lift from a low pressure system passing through Southern
California and Northern Baja will generate areas of drizzle and
light rain this evening and overnight. The greatest coverage is
expected to be in the coast and valleys in San Diego County and
along the coastal mountain slopes. Any accumulations for the coast
and valleys will be light, with 0.10 inches or less expected. On
the coastal mountain slopes, around 0.25 inch is expected. Marine
layer low clouds may become patchier Thursday night into Friday
morning, but areas of drizzle or light rain are still possible.
Dry conditions expected for the weekend into early next week.
Gusty southwest to west winds are expected in the mountains and
deserts through Friday. Peak winds gusts will be 50 to 65 mph. Gusts
could locally reach up to 75 mph through the San Gorgonio Pass.
Winds will peak each afternoon and evening. Winds will gradually
decrease in the the weekend, with weaker winds expected early next
week.
Cooler conditions expected for inland areas Thursday, with a few
degrees of warming on Friday for the coast. High temperatures will
be as much as 10 to 15 degrees below average on Thursday for the
mountains and valleys. A warming trend is expected for Saturday
through Monday with not much change on Tuesday. Weak high pressure
aloft is expected to prevail but there are some model differences
for early in the week which would impact the strength of the onshore
flow and the depth of the marine layer. This uncertainty creates
greater spread of the high temperature forecasts for locations in
the coast and valleys. If the warming develops, high temperatures
would be near average for most locations on Sunday with high
temperatures on Monday and Tuesday 3 to 7 degrees above average.
&&
.AVIATION...
250400Z...Coast/Valleys...Widespread BKN/OVC stratus will prevail
through 18Z Thu with bases 2000-4000 ft MSL and tops to 6500 ft MSL
and with higher terrain obscured. Local VIS 3-5 miles will occur
below the clouds in -DZ/-SHRA, mainly 09Z-18Z Thu. SCT/BKN stratus
will prevail with bases 2500-5000 ft MSL 18Z Thu-03Z Fri, with
increasing stratus again after 03Z Fri.
Mountains/Deserts...Areas of terrain obscurations will continue
at times along the coastal mountain slopes through Thu evening
with cloud tops to 7500 ft MSL and (09Z-18Z Thu) areas of -DZ/-SHRA.
Areas of west winds with surface gusts 30-50 kt will occur from the
mountain crests east through the mountain slopes and into the
deserts through Thu evening. VIS will be unrestricted on the desert
slopes/deserts.
&&
.MARINE...
No hazardous marine conditions are expected through Thursday night.
Stronger winds and choppy seas arrive Friday morning and continue
into Saturday morning, likely generating hazardous conditions,
especially in the outer waters. There is a period Friday night
(mainly mid-evening to a little after midnight) when there is
around a 25 percent chance of gale force winds near San Clemente
Basin Buoy. There is a gale watch in effect from 5 PM Friday
through 3 AM Saturday for this possibility, though there is
high confidence of winds reaching Small Craft Advisory strength.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 11 PM PDT Friday for Apple and Lucerne
Valleys-Coachella Valley-Riverside County Mountains-San
Bernardino County Mountains-San Diego County Deserts-San
Diego County Mountains-San Gorgonio Pass Near Banning.
PZ...Gale Watch from Friday afternoon through late Friday night for
Waters from San Mateo Point to the Mexican Border Extending
30 to 60 nm out including San Clemente Island.
&&
$$
PUBLIC...APR
AVIATION/MARINE...Maxwell