Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/10/24

Area Forecast Discussion

National Weather Service La Crosse WI

 1052 PM CDT Thu May 9 2024

.KEY MESSAGES...

- Frost advisory for parts of north central Wisconsin

- Showers and storms will move southeast across the region
  Friday afternoon and evening. A few strong storms are possible
  with small hail and gusty winds being the primary threat.

- Periodic rain chances persist through the weekend and into
  next week. Temperatures will trend warmer than normal with
  Sunday appearing to be the warmest day with highs in the upper
  70s to lower 80s.

&&

.DISCUSSION...
Issued at 600 PM CDT Thu May 9 2024

Tonight: Cooler, Some Frost

Decaying showers and clearing skies later tonight along with
decreasing winds and temperatures dropping into the lower to mid
30s should allow areas of frost to develop, especially for
Taylor County. In coordination with neighbors, did include
Trempealeau, Jackson, Clark and Taylor Counties in a frost
advisory.

Friday Afternoon and Overnight: Showers and Storms

As we head into the afternoon and onward cloud cover will begin to
build ahead of an incoming 850mb shortwave caught in the northwest
flow regime. As the wave progresses through our area during the
afternoon and early evening, the 09.15z RAP shows a fairly robust
low-level jet behind it to 40-50 kts. This in combination with
MLCAPE of up to 1000 J/kg will help to initiate a line of showers
and storms that will quickly push southeast along with the
aforementioned low-level jet. In this case, instability appears to be
the limiting factor with strong (around 50 kts) 0-6 km bulk shear in
place. However, with fairly steep lapse rates and an inverted-v
subcloud layer, cannot rule out some gusty winds to 50 mph or some
small hail with any stronger storms when considering the freezing
levels of around 6kft. Consequently, SPC has a marginal (level 1 of
5) risk for severe storms for much of our area on Friday. Showers
and storms will quickly progress southeast through the forecast area
and will move out of the local area later into the evening.

This Weekend and Next Week: Warmer Trend with Some Shower & Storm
Chances

Northwest upper-level flow will be in place for the weekend with the
aforementioned departing shortwave trough departing leaving room for
a weak ridge to build into the region allowing for a warming trend
to take hold with surface southwesterly flow. As a result, the inter-
quartile range of for high temperatures at La Crosse on Sunday in
the 09.13z NBM is 80 to 85 degrees. Additionally, with the 09.12z
GFS/NAM showing fairly well mixed low-levels it could be a day with
overachieving warming but will feature lower dewpoints. With fairly
modest instability (1000-2000 J/kg of MUCAPE) present at peaking
heating on Sunday will have to watch for any subtle forcing
mechanisms that could set off any convection. Currently, the 09.12z
NAM/GFS shows some subtle vorticity advection associated with a weak
wave that progress through northern MN and into northwestern WI. As
this synoptic forcing pushes into the aforementioned higher
instability, a stronger 800-900mb frontogenetic signal is noted in
both the 09.12z GFS/NAM which when combined with modest precipitable
waters of around 1 inch and marginal 850mb moisture transport could
set off pulse convection across portions of the region. With any
potential convection for Sunday being outside of the range of the
short-range CAMs, hard to put confidence into localized
thermodynamics and shear profiles too much but the severe threat
with any storms appears to be minimal at this point in time with 0-
6km bulk shear values appearing very low across portions of northern
WI.

As we head into next week, northwest flow turns more quasi-zonal
with a couple of weaker short-wave troughs hinted by deterministic
guidance. However, still lots of uncertainty with how these systems
will manifest. Consequently, generally expecting a calmer period
into the first half of next week at this point in time with fairly
pleasant temperatures and occasional shower/storm chances in
accordance with the NBM. However, the EC ensemble has fairly low
probabilities for measurable precipitation (0-40% chance) early next
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1050 PM CDT Thu May 9 2024

Latest trends has been for IFR to LIFR fog to develop south of
AUM to DLL line over the next few hours and last until 12-13Z.
VFR conditions are then forecast through mid-afternoon before a
front sweeps through, which may bring periods of lower
visibilities in any stronger storms. Winds will be light from
the north to northwest overnight, increasing to 10 to 15 kts
from the west by early afternoon before veering to the
northwest with the passage of the front--gusting upwards of
20-25kts (higher in any storms).

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory from 2 AM to 8 AM CDT Friday for WIZ017-029-033-
     034.
MN...None.
IA...None.

&&

$$

DISCUSSION...Naylor/Skow/Zapotocny
AVIATION...Skow




Area Forecast Discussion

National Weather Service Des Moines IA

 628 PM CDT Thu May 9 2024

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Lingering shower chances into this evening, mainly along and
  east of I-35. Few showers/storms possible again Friday
  afternoon and evening.

- Fantastic spring conditions Saturday. Sunshine and 70s.

- Chances for showers and storms return early next week. Severe
  threat low.

&&

.DISCUSSION...
Issued at 200 PM CDT Thu May 9 2024

The presence of a broad, decaying trough overhead has sustained
shower activity over the forecast area through the day. The focus
has generally been within a diffuse zone of low level convergence co-
located with mid-level fgen forcing. RAP analysis shows pockets of 0-
3km CAPE pushing 100 J/kg beneath a cool airmass aloft. The enhanced
stretching potential combined with high background vorticity may
support a few funnels or brief landspouts. Dry air has really eaten
into the westward extent of the precip, much more so than suggested
by hires guidance. Thus the rest of the day has trended drier at
many locations, save for about the eastern third of the cwa which
stands the highest chance to see additional measurable
precipitation before the rainfall exits tonight.

Additional precip chances return Friday afternoon and evening
as a compact shortwave slides through the Great Lakes region and
sweeps a surface frontal boundary across the state. Synoptic
forcing contributions are not well phased on the south/west
periphery of the wave, and combined with dry boundary layer
conditions should limit the spatial coverage and depth of the
convection. Soundings show inverted-v profiles and steep low
level lapse rates up to ~800mb so a few brief elevated wind
gusts are possible, but overall the threat of any strong to
severe convection is low.

Make plans to get outside on Saturday as fantastic spring conditions
are forecast. A passing surface ridge axis beneath building heights
aloft will lead to dry conditions and subsidence through much of the
atmospheric column, giving way to plentiful sunshine and highs in
the 70s. Rain chances return early next week as cutoff upper low is
kicked out of the Four Corners region. Forcing mechanisms and
convergence still look rather diffuse, so it is difficult to
pinpoint a particular period for higher PoPs or to provide more
detail on potential precip amounts. The deterministic EC is
also more aggressive with impinging dry air on the northern
periphery of the upper low as it crosses the central Plains, a
trend that is also reflected in the EC ENS guidance with a fair
share of members now advertising no QPF over the northern half
of the forecast area. Flow aloft is very lethargic with 500mb
winds less than 20 kts. Any convection will be highly
disorganized and likely pose little severe threat.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 628 PM CDT Thu May 9 2024

Scattered convection moving into southeast sections at 2320 and
diminishing. Have dropped -shra most areas sans OTM where VCTS
is possible between 00 and 01z. Have left out for now. Patchy
MVFR cigs continue with VFR returning aft 02z most areas. Some
early morning MVFR BR from MCW to ALO and should lift by 13z.
Some mixing expected aft 20z most areas from the west northwest,
through end of period. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Martin
AVIATION...REV




Area Forecast Discussion

National Weather Service Greenville-Spartanburg SC

 1017 PM EDT Thu May 9 2024

.SYNOPSIS...
A cold front will continue to push east of the area, before another
system approaches Friday. Showers and thunderstorms are possible
Friday afternoon, before dry high pressure builds in from the north
through the weekend.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 1000 PM: The forecast is on track. Temps are falling
slightly faster than expected, thanks to clear skies. But clouds
will quickly spread back in from the west due to ongoing convection
over MS/AL. The clouds should slow the downward temp trends. Latest
guidance hasn`t really trended up or down much on fog potential. So
no significant changes made with the evening update.

Otherwise, mostly clear skies this evening should permit good
radiational cooling for a time. Some dry advection will begin
overnight as weak sfc low passes by to our north, pulling very weak
sfc front through the area. This will promote just enough drying to
maintain a dewpoint depression of a few degrees in the foothills and
upper Piedmont, and furthermore some gradient wind is expected to
persist. Thus, the likelihood of radiation fog/stratus looks small
in those areas and mins will remain several degrees above normal.

Mountain valleys are likely to see some fog, along with the
SE CWA border where that weak front doesn`t reach and instead
may serve to pool moisture. A couple hundred joules of CAPE may
persist there thru daybreak. An MCV or other remnant of convection
looks to round the base of the main trough in the morning and some
guidance depicts a round of showers passing thru the Piedmont at
that time. Partly cloudy skies will permit the return of warmer
temps, again being a few degrees above normal. 700-500mb lapse rates
will increase as main shortwave swings in, and isolated convective
development is not out of the question over the mountains. For
the aforementioned Piedmont areas, guidance members differ as
to how soon low-level airmass change begins; GFS for example
maintains poor low level lapse rates above the PBL and develops
only small diurnal instability. The NAM depicts favorable lapse
rates thru a deep layer and develops 1000 J/kg or more of CAPE in
the afternoon. All models depict strong deep layer shear, perhaps
60+ kt, so if timing of the shortwave trends slightly slower or
the low level lapse rates improve, we could see an isolated severe
threat develop mainly southeast of I-85 or east of I-77. The setup
warrants only a chance PoP in our south and east; FV3 and HRRR
show short updraft helicity streaks from a lone cell.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 1245 PM Thursday...An upper shortwave axis continues to swing
east of the area Fri night as a cP air mass mixes into the lower
levels. This airmass will slowly modify warmer over the weekend as a
small scale ridge gives way to another diving Canadian h5 trof Sat
afternoon. This trof looks to bring it/s own moisture and will
probably produce some rain showers across the NC mtns Sat afternoon
into the evening. No good chance of thunder during that time as sfc
td/s drop into the 40s and potential instability remains nil or
quite low. Drier conds with warming temps across the FA Sun as a
broad sfc high builds over the area from the west. Generally, both
days will be rather pleasant with highs a couple degrees below
normal Sat, then back to normal levels on Sun. Mins will likely fall
a couple degrees below normal each night.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 120 PM Thursday...A more springtime pattern returns during the
ext range. The latest guidance contines to show a subs zone becoming
displaced by waves of srn stream energy while a mlvl trof/low
travseres the MS to OH valleys. The surface response indicates an
opening GOM flow, which will supply a good amt of moisture to a
broad frontal system each day. Onset precip timing Mon is suspect
with the majority of models indicating a later timeframe than the
moister insitu wedge pattern progged by the latest GFS. In any case,
thunder probabilty remains low with non-conducive llvl thermal
profiles. By Tue, expect a better chance of afternoon thunderstorms
as a wavy cold approaches from the west and sfc dewps rise into the
u50s to l60s. The pattern remains uncertain, yet possibly active
into Wed as another round of srn stream energy may be pushing east
across the GOM coastline by then. High Temps remain near normal Mon,
then drop abt 5 degrees below normal Tue with the best chance of
widespread precip and cloud cover. Highs rebound to normal values
Wed. Lows begin the period near climo, then warm abv normal Tue/Wed
nights.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Mainly just a few high clouds this
evening, with lingering light winds out of the SW (except for
NW at KAVL). Overnight, thicker mid and high clouds are expected
to stream in from the SW due to convection over the central Gulf
states, which combined with just enough mixing, could limit fog
potential. With that said, very moist soils and low levels may
combine to produce patchy fog or LIFR stratus across portions of
the lower Piedmont as well as the mountain valleys sheltered from
NWLY flow. Guidance is still not hitting cigs or vsby restrictions
all that hard, and with the mixed signals of clouds/wind/moisture,
will continue to just show few LIFR clouds and/or 6sm BR for the
early morning hours Friday. If trends in the clouds and wind trend
lower, potential for the stratus and fog will go up. Whatever does
develop, should dissipate early Friday morning. Spotty light rain
may cross the southern Upstate, but should stay mostly south of
the area and looks too low for any TAF mention. In the aftn, a
cold front will slip across the mountains and into the Piedmont,
which may trigger a few showers and isolated TS before pushing
east of the area. While better coverage of showers will be near
the TN/NC border. The NC TAF sites will feature PROB30 for the
SHRA potential. Given less confidence on TS, will not mention for
now. The Upstate sites look largely dry Friday aftn. Winds should
toggle from SW to WNW behind the front with gusts generally in
the 18-22 kt range.

Outlook: Drier and likely VFR conditions can be expected this
weekend. Moisture returns late Monday with active weather possible
by Tuesday.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$

SYNOPSIS...SBK
NEAR TERM...ARK/Wimberley
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...ARK




Area Forecast Discussion...Updated

National Weather Service Lincoln IL

 731 PM CDT Thu May 9 2024

.KEY MESSAGES...

- A threat for isolated lightning strikes will persist through
  the middle of this evening south of I-74.

- A low-end lightning threat will accompany a line of showers
  crossing central Illinois from late Friday evening into early
  Saturday morning.

- In the Monday-Tuesday time frame, there is a 20-40% chance of
  greater than a half inch of rainfall in 24 hours. Should this
  occur, one impact would be additional runoff into area rivers
  already running high.

&&

.UPDATE...
Issued at 731 PM CDT Thu May 9 2024

Latest surface map shows the frontal boundary has slipped
south past I-72. A couple batches of showers are working their way
through, one immediately behind the front, and another stretching
from near Quincy to northern Indiana. This, and a third area of
showers in southeast Iowa, is associated with an upper shortwave
currently swinging southeast across Iowa. Latest high-res guidance
suggests this Iowa batch of rain may hold together enough to
warrant keeping some low PoP`s going past midnight across the
Illinois River valley. Elsewhere, rain chances should gradually
wane. No lightning has been observed as of late, though some
heavier 40-50 dBZ showers were near Jacksonville this hour. Have
lingered a mention of isolated thunder across the I-72 corridor
for another hour or two.

Geelhart

&&

.DISCUSSION...
Issued at 313 PM CDT Thu May 9 2024

A frontal boundary which was nearly stationary this morning has
lifted northward slightly early this afternoon, with winds along
I-74 backing somewhat in response. Around 250-750 J/kg of MLCAPE
resides along a narrow axis from about Lincoln to Mattoon-
Charleston where the sky has cleared somewhat, and we have seen a
handful of showers reaching 40-50 dBZ or so with a few lightning
strikes. The threat for lightning should persist no later than
mid-evening as the frontal boundary pushes southward, MLCAPE
decreases and the atmosphere stabilizes.

A 500-mb short wave trough diving southward out of the upper
Midwest helping to drive some of this afternoon and evening`s
shower activity should pivot east into Indiana by early Friday
morning. Weather during the day should be fairly quiet, with the
next mid-level short wave and associated mid-level jet coming out
of the upper Midwest on Friday evening. An associated weakening
line of showers is forecast to move through central Illinois from
northwest to southeast from late Friday evening through early
Saturday morning, with around 100 J/kg of MUCAPE forecast by the
HRRR indicating at least some probability of lightning especially
Friday evening.

Look for breezy northwest winds gusting to 20-30 mph on Saturday
behind the departing short wave trough. Temperatures kick up a
notch on Sunday under short wave ridging as a mid-level low moves
out of the Colorado Rockies into the high Plains. This low is
responsible for a chance of fairly widespread rainfall in the
Monday-Tuesday time frame. The probability of SBCAPE > 250 J/kg
and sfc-500 mb shear is below 5%, with severe weather
probabilities low. Enough CAPE should be around to support some
thunder, however. NBM probabilities show about a 20-40% chance of
greater than a half inch of rain in a 24 hour period in the
Monday-Tuesday window.

Notable model variability exists in timing and strength of troughs
beyond Tuesday. Though mid-range precip chances are included
throughout Wednesday and Thursday, there`s a decent chance of at
least one dry period occurring in that stretch.

AAT

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 605 PM CDT Thu May 9 2024

Band of MVFR to occasionally IFR ceilings has been sagging
southward this evening, associated with a cold front that roughly
extends from KIJX-KDNV. Lower visibilities have generally been
associated with heavier showers immediately north of this front.
General trend for the next several hours will be for ceilings to
remain below 2,000 feet in most areas except for KPIA, where more
of an increase to 5,000 feet is imminent. However, HREF guidance
hints at some potential for IFR ceilings (30-50%) after 08Z. More
of a general improvement is expected after 15Z.

North/northeast winds overnight will generally trend more toward
the northwest Friday morning.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$




Area Forecast Discussion

National Weather Service Indianapolis IN

 917 PM EDT Thu May 9 2024

.KEY MESSAGES...

- Light showers possible Tonight
- Decreasing clouds and cooler on Friday
- Passing showers Saturday...before several rounds of showers/few
  non-severe t-storms, next Monday and onward
- Slightly below normal to seasonable temperatures Thursday through
  Saturday...to slightly above readings next week

&&

.FORECAST UPDATE...
Issued at 917 PM EDT Thu May 9 2024

Very minor adjustments made to going forecast this evening.

Secondary cold front is just about through the area this evening,
with the upper trough axis to follow over the next several hours. A
few light sprinkles/showers are present across portions of central
Indiana, with slightly more organized band of widely scattered
showers associated with the upper trough beginning to move into the
area. CAMs expect this to weaken a bit overnight, understandably,
but it should persist enough to merit low to middling chance PoPs
north through the night, particularly north/northeast, with a
sprinkle mention most of the rest of the area.

Have removed what was left of the thunder mention for the evening as
modest pooled instability is ahead of the boundary and departing, as
well as steadily diminishing in the typical diurnal fashion.

Low clouds should persist through the night and likely into tomorrow
morning before beginning to lift as mixing increases during the day.
There is a non-zero chance for a few very shallow convective
sprinkles or showers tomorrow, but confidence too low to mention for
now, with low level dry advection ongoing and forecast sounding
instability profiles slight and shallow.

&&

.SHORT TERM (This evening through Friday)...
Issued at 259 PM EDT Thu May 9 2024

Synopsis:

Surface analysis early this afternoon shows low pressure just west
of Indianapolis. The broad low was providing cyclonic circulation
across the region. A warm front extended east from the low, to
southern OH and WV. This low also had a cold front associated with
it, stretching west across Central Illinois to southern IA. Aloft,
an active pattern remained in place. A large, broad, upper trough
was in place from Quebec across the upper Midwest and continued to
another upper low near UT and NV. Ahead of this trough across
Indiana, a quick flowing westerly flow was in place. Water vapor
showed moisture in place over MI and northern IN, ahead of the upper
trough, while subsidence was in place over IL and central and
southern Indiana.  Radar this afternoon shows some scattered light
showers across Central Indiana, beneath the stratocu deck. A few
showers and thunderstorms were found across northern Indiana and
Michiana. These showers were ahead of the mid and upper trough.
Abundant cloud cover was still found across Central Indiana, but
some clearing and heating was found over Knox county, pushing
northeast. Plenty of moisture remained available as dew points
remained in the lower 60s across our area.

Tonight...

The surface low over Central Indiana is expected to quickly push to
Ohio this evening and then reach the middle Atlantic states
overnight. This will allow for the development of a northerly
surface flow of cooler air overnight. Meanwhile aloft, the
previously mentioned surface trough will be sagging across Central
Indiana trough the evening. Ongoing heating, combined with the
cyclonic flow and approaching upper trough is expected to continue
to develop scattered light rain showers across Central Indiana late
this afternoon and early evening. SW central Indiana will need to be
watched for possible thunderstorm activity. Clearing arriving in
Knox county is allowing for additional heating that could trigger
additional afternoon and early evening thunderstorms. HRRR suggests
that as this cloud shield continues to lift northeast thunderstorms
develop in combination with the arrival of the surface cool front.
Will try to keep the Thunder mention at those southern locations,
however a stray rumble of embedded within a shower will also be
possible.

Overnight, the upper trough will exit to the south and any
associated forcing will be lost. Cold air advection will be in play
as falling thicknesses are noted. This results in the formation of a
stratus deck overnight, with a trapping inversion found aloft as
seen within the forecast soundings. Thus overall, scattered late
afternoon and evening showers are expected to continue with light
rain amounts. Best thunder chances will be across far southern
Central Indiana in association with any clearing and extra heating
that occurs. Then expect cloudy and cooler conditions overnight as
cold air advection is in play. Expect lows in the upper 40s and
lower 50s.

Friday...

Models suggest the previous upper trough will quickly depart on
Friday, allowing northwest flow along with moderate ridging to build
across Indiana through the day. Surface high pressure over the
plains is suggested to build a ridge axis across Indiana through the
day, originating from the southern plains. Forecast soundings start
the day with saturation within the lower levels due to the passed
system, cold air advection and the trapped lower level moisture.
However as the ridging builds, the lower levels are shown to mix out
as the inversion aloft rises. This will allow for decreasing
cloudiness in the morning followed by some high CU development
during the afternoon. Cool northerly winds but with some afternoon
sunshine will allow highs in the upper 60s to be reached.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 259 PM EDT Thu May 9 2024

Friday night through Sunday...

Northwesterly flow aloft will promote at least weak ridging this
weekend...on either side of a passing northern-stream, plunging
short wave in the late Friday night-Saturday timeframe.  This
quickly-passing feature should shake out some widely scattered rain
showers from pre-dawn to afternoon hours on Saturday...with perhaps
a rumble of late day thunder and moderate rainfall rates in isolated
convection over eastern zones.

Ample sun should otherwise prevail through the weekend. Seasonably
low humidity will be the backdrop to slightly below normal maximum
temperatures Saturday in mainly the 65-70F range, under the passing
lower heights and west-northwest gusts as high as 20-30 mph...to
more seasonably mild conditions Sunday in the 70s as lighter breezes
return from the west-southwest.

Monday through Thursday...

A rather typical late spring pattern will prevail over much of the
next workweek...as lower heights retracted to Canada allow a small
yet progressive short wave to cross the central US to the Ohio
Valley.  Solid ribbon of Atlantic and eastern Gulf of Mexico
moisture is expected to boost precipitable water values to 1.25-1.50
inches over much of the Midwest.  The overall disturbed pattern
should promote a few rounds of showers and thunderstorms...which so
far appear will be best organized in the late Monday to Tuesday
night timeframe.  Total rainfall would likely be under an inch for
most areas, with perhaps heavier amounts across southern
counties...although ultimately this would be determined by wherever
corresponding surface low pressure and associated boundaries would
focus any heavier rains.

Severe weather is so far not expected with primarily overcast skies
likely limiting instability despite above normal dewpoints...and
vertical wind shear likely low per the overall weak nature of the
passing wave.  Temperatures trending from near to slightly above
normal...will be led by overnight lows in mainly the mid to upper
50s...courtesy of noticeable humidity amid the often southerly
breezes.  The normal max/min at Indianapolis for the long term is
73/53.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 731 PM EDT Thu May 9 2024

Impacts:

- MVFR conditions much of the night into Friday morning.

Discussion:

A large upper trough and secondary cold front are passing through
the area this evening, bringing a few lingering showers primarily to
northern portions of the area, and continuing to keep low stratus
trapped across much of the region. Some sites have briefly returned
to VFR this afternoon, but expect all to deteriorate again to low
end MVFR if they have not already over the next couple of hours.

LAMP guidance is fairly optimistic in MVFR ending overnight, but
this is not well supported by forecast soundings, and the presence
of a second vort lobe and climatological progression of overnight
low ceilings suggests restrictions will continue into Friday morning
before returning to broken VFR ceilings midday onward. Will depict
some slow improvement later tonight.

Winds will begin the period somewhere between 310-030 degrees
depending upon the site, with all quickly becoming primarily
northerly in the first few hours. A few gusts to near 20KT may
persist at a couple of sites over the first hour or two, but these
will quickly subside, with sustained winds largely 5-10KT overnight
into tomorrow. Winds will back a bit during the day to a more
northwesterly heading by late in the period.

There is potential for some light fog at LAF, but most areas should
see unrestricted visibility.

&&

.IND WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

UPDATE...Nield
SHORT TERM...Puma
LONG TERM...AGM
AVIATION...Nield




Area Forecast Discussion

National Weather Service San Francisco CA

 823 PM PDT Thu May 9 2024

...New UPDATE...

.SYNOPSIS...
Issued at 108 PM PDT Thu May 9 2024

Temperatures peak today along the coast with a incoming southerly
surge cooling the coastal regions on Friday. Interior regions see
temperatures peak on Friday, before a slight cooldown begins over
the weekend. Coastal regions cool to around the seasonal average
temperatures by early next week.

&&

.UPDATE...
Issued at 812 PM PDT Thu May 9 2024

Onshore winds have returned in dramatic fashion. The temperature
dropped 16F in an hour at the Half Moon Bay Airport. In fact,
that site looked like it would challenged its daily record of 80
early, reaching 77 degrees at 12:15 PM, however the cool down came
shortly after and the area is now back to dealing with a cool
fog, per usual. This sharp cool down was limited to coastal areas
and portions of the adjacent valleys. With strong high pressure
aloft, the marine layer is still quite shallow. The Ft. Ord
profiler is measuring it below 300 ft. This means that inland
areas will still be dealing with heat tomorrow, but coastal areas
will get some relief. Synoptic winds will gradually shift onshore
tomorrow afternoon, bringing a slight cool down to the rest of the
area over the weekend. The humidity will also increase as the
winds return to an onshore breeze.

&&

.SHORT TERM...
(This evening through Friday)
Issued at 108 PM PDT Thu May 9 2024

The peak of the heat event has started with highs today ranging from
the low to mid 70s at the coastal regions, to the low to mid 80s at
the Bayshore and near Santa Cruz, to the upper 80s across the
interior valleys. The interaction between a strong ridge building
into British Columbia and the Pacific Northwest with a weak cut-off
low in the Great Basin is creating offshore flow across the region,
but this pattern is also one that will tend to create a "southerly
surge" of coastally trapped winds. Indeed, the high resolution HRRR
is showing a southerly surge coming up the Central Coast today,
abating overnight before a second surge travels farther north across
the California coast, beyond the Golden Gate and Point Arena. Those
two southerly surges will bring some relief to the coastal Central
Coast later today, and to the coastal regions tomorrow, with
Friday`s coastal highs expected to hover around the upper 60s to
lower 70s. The surges will also provide the only substantial chances
for cloud cover near the coastal areas impacted. That is little
comfort to those inland, where high temperatures will continue to
rise on Friday with the warmest spots bumping into the lower 90s.
Even the City, which does see some relief from the approaching
southerly surge, is expected to top out in the upper 70s tomorrow.

The region will generally see a Minor HeatRisk today and Friday,
with a Moderate HeatRisk for the interior regions of the North Bay,
East Bay, and South Bay. This corresponds to a low to moderate risk
of heat-related illnesses for vulnerable populations (children, the
elderly, pregnant women, people without adequate cooling, and people
with certain medical conditions). Here`s a reminder of some heat
safety tips:

* Stay hydrated and drink plenty of fluids.
* Wear lightweight, light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 108 PM PDT Thu May 9 2024

As the upper level ridge weakens as it moves through the Pacific
Northwest over the weekend, onshore flow will begin to reassert
itself. Coastal regions will continue to cool down and reach
seasonal average highs of around the upper 50s to lower 60s by the
early part of next week. The interior will continue to remain warmer
than seasonal averages, but not as warm as the forecast for Friday,
with highs generally in the low to mid 80s by the early part of next
week. Ensemble model clusters are in agreement over a new ridge
expected to approach the Pacific Northwest by Tuesday, but its
evolution after that point remains unclear.

&&

.AVIATION...
(00Z TAFS)
Issued at 428 PM PDT Thu May 9 2024

VFR through the TAF period for most terminals, except Monterey
Bay terminals. Models show the southerly flow tonight with a
return of stratus near the Salinas Valley and along the coast,
mostly near Monterey Bay. Low to moderate confidence that MVFR
ceilings will develop tonight, but if they do, expect near 09-11Z.
Winds will start to shift overnight but will relatively light. A
return of N/NW winds are expected by late Friday morning.

Vicinity of SFO...VFR through the period. Moderate northerly winds
will turn westerly this evening before becoming N/NE again by early
Friday morning. By Friday afternoon, winds will return to onshore
and breezy.

SFO Bridge Approach...similar to SFO.

Monterey Bay Terminals...VFR through early tonight but models show
MVFR ceilings returning near the terminals. Therefore, included a
SCT group for KMRY and BKN group for KSNS, as there is higher
confidence for KSNS experiencing MVFR CIGs.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 428 PM PDT Thu May 9 2024

Light to moderate winds continue over the waters from the high
pressure that sits in the north, but winds will become more
southerly along the Big Sur and Monterey Bay region this evening.
Otherwise, gentle breezes out of the north and northwest continue
through the weekend first portion of the weekend. Dry weather
continues through the forecast period as high pressure dominates.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...SO
MARINE...SO

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