Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/04/19

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 911 PM MDT Fri May 3 2019

.UPDATE...
Issued at 847 PM MDT Fri May 3 2019

Colorado remains under a moderate northwest flow this evening with
some banded streaks of mid level moisture. Overall, the
atmosphere is rather dry but there is an exiting jet streak across
far northern Colorado with northeast Colorado under favorable
right entrance region of jet. There have been a few showers that
have been trying to get going associated with the jet, but
fighting the overall dryness. Could be a few sprinkles along the
northern border areas until midnight and also across Elbert and
Lincoln counties. Expect some low clouds developing across
Lincoln county later tonight so will increase cloud cover in those
areas overnight. No other changes needed.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 235 PM MDT Fri May 3 2019

Dry and stable northwest flow aloft continues this afternoon, with
a healthy cap showing up around 600mb on recent ACARS aircraft
soundings. Only isolated to scattered fair-weather flat topped
cumulus streaming across the area. An upper level speed max draped
across the CO/WY/NE state lines early this evening will push east,
putting the forecast area under the right entrance region of the
jet after midnight. QG motion will turn upward, and southerly flow
around the surface high over the Great Plains will pull up
moisture into the southern portions of the forecast area. Some
hires models showing the potential for some showers over this
location, so went ahead and added higher PoPs after midnight over
southern Lincoln County. Warm advection and cloud cover will allow
for much warmer overnight low temperatures, especially over the
eastern plains.

Upper pattern allows for slight broad troughing from the north
while a jet max rounding weak ridging over the Desert Southwest to
impact the area Saturday. The increase in moisture at the surface
will combine with slight cooling aloft for an unstable airmass,
mainly remaining east of a surface trough along the urban
corridor. Shear profiles and warmer surface temperatures to boost CAPE
values over 1000 J/kg near, south, and east of Limon will allow
for thunderstorms, some strong, to form in the afternoon. Main
impacts will be strong gusty outflow winds and hail up to an inch.
West of this, moisture will be much less and if any storms might
form, it would will be over the high terrain where very low CAPE
will lead to very weak and isolated storms.

.LONG TERM...(Saturday night through Friday)
Issued at 235 PM MDT Fri May 3 2019

Setting up for Saturday evening, return moisture around the
Central Plains surface high will bring an increased chance for
showers and thunderstorms for Saturday evening, especially over
the far eastern plains. Generally, ML capes across the models are
in the 300-600 J/kg range with values from prev model runs holding
consistent with an axis of near 1000+ j/kg on the CO/KS border.
Latest runs bring higher capes values westward onto the Palmer
Ridge region for Sat eve, so will increase pops Saturday night for
those zones. Expecting mostly gusty weak storms along the Palmer
and foothills with potentially severe level storms out east closer
to the KS border.

Rex block feature currently over the eastern Pacific begins to
release the surface low on an eastward trajectory towards the SO
CA coast Saturday. Out ahead of the trough, the upper ridge over
the southwest US and southern Great Basin gradually amplifies
bringing a brief warming and a dry period to the central Rockies
Sunday and Monday. Mid and upper level QG fields indicate weak
subsidence for both Sunday and early Monday with fairly strong
positive surface omega bringing mostly dry conditions and above
average warmth. Consistent with previous runs, the weak upper
ridge maximizes early Monday. Ahead of the well advertised
approaching cold front set for early Tuesday, south to
southeasterly sfc flow brings strong to potentially severe CAPEs
back onto the southeastern plains and Palmer region late Monday
afternoon and evening. NAM and GFS indicate an axis of ML
1200-1600 J/kg Monday for points east of a Sterling to Fort Morgan
to COS line. Will keep the scattered pops going for this Monday
night period as we could see a few severe level storms Monday
evening, especially with the best synoptic level QG ascent
approaching. For temps, latest guidance has trended slightly
cooler for both Sunday and Monday, but will expect highs ranging
from 75-80degF for Monday.

As typical with CO weather, a fairly rapid and sharp change
arrives late Monday into early Tuesday as a Canadian cold front
pushes southward into northern CO. Mid and upper QG fields begin
the good trend of ascent from Monday evening all the way through
Wednesday morning. This environment of mid and upper level ascent
will be extended due to a secondary southward moving wave of low
pressure on the backside of the first trough pulling out of CA.
This will keep the entire southern and central Rockies in a cool
and unsettled period. Cross sections and fcst soundings show a
saturated to near saturated environment throughout entire column
from Tuesday morning all the way thru midday Friday with a period
of brief drying on Thursday. QPF values across a few of the long
range models bring a bullish 0.75 to near 2.00 inches of precip
across the plains through this timeframe, but believe attm those
are well overdone due to cool temps, weak to brief moderate
synoptic lift, minimal convection, weak to moderate flow aloft and
low-end specific humidities. In general, we`re looking at a good
May-like cool and moist period Tuesday through Friday with low
clouds, light showers and persistent weak easterlies at the
surface.

At this time not drawn to any hydro issues across the lower
elevations as the 850-500mb layer spec humidities ride in 2.0-3.5
g/kg range from Tuesday through Friday. NAEFS Mean Precip H20 not
flagging high standardized anomalies at this time in the western US
and Rockies.

For the high country in this Tuesday through Friday period will look
for moderate snow accumulations to the tune of several inches
primarily on west facing aspects and locations above 10000ft. Snow
levels will gradually fall into the 5500-6500ft range which could
bring some accumulations to the foothills and portions of the
Palmer Divide Wednesday night into late Thursday morning, with
rising levels into Friday. CWA-wide, will keep higher chances for
precip and showers with temperatures holding 12-17 degF below
seasonal average.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 847 PM MDT Fri May 3 2019

Still some mid level moisture over terminals this evening in
associated with exiting jet streak but not expecting more than a
possible sprinkle. Surface winds will continue to shift southeast
and then southerly overnight before becoming light and variable
on Saturday morning. No impacts expected.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Entrekin
SHORT TERM...Kriederman
LONG TERM...Fredin
AVIATION...Entrekin



Area Forecast Discussion

National Weather Service Honolulu HI

 351 PM HST Fri May 3 2019

.SYNOPSIS...
A humid and unstable southerly flow ahead of an out of season
cold front will produce isolated showers, some briefly heavy
through this evening. The rather strong front will move down the
island chain late tonight into early Sunday, bringing a period of
heavy showers, gusty winds, and possibly thunderstorms. Drier and
cooler northwest winds will fill in behind the front Saturday
night into Monday, with trade winds unlikely to make a return
until Thursday.

&&

.DISCUSSION...
A humid and unstable southerly flow is in place this afternoon.
Low level winds are veering southerly as an out of season cold
front, which currently reached buoy 51101 210 miles northwest of
Kauai, approaches from the northwest. Recent aircraft data and
afternoon soundings show that aside from a weak warm layer
between 12,000 and 20,000 ft, the advancing upper level trough
driving the front has essentially wiped out the inversion. Heavy
showers have been periodically flaring along a diffuse band of low
level moisture near Maui County and Oahu today. However, the bulk
of this moisture has lifted north of the islands, and the weak
warm layer aloft combined with the increasing southerly flow has
helped to keep heavy shower activity isolated and somewhat brief
over any given location. An isolated, briefly heavy shower could
pop up over any of the islands through the rest of the day.

Southerly winds will shift out of the southwest and increase
tonight as the front nears the islands. Scattered showers will
pass over most islands, and the humid southerly flow will keep dew
points elevated around 70, leading to somewhat uncomfortable
sleeping weather. The GFS model shows an area of prefrontal
convergence generating some enhanced shower activity over and
around Kauai during the middle of the night, with the front
reaching the island in the predawn hours. Expect a line of heavy
showers and/or thunderstorms to accompany the front.

The unusually strong May front will bring a period of heavy
rainfall, gusty winds, and possibly thunderstorms down most of the
island chain on Saturday. The consensus of the guidance has the
front clearing Kauai not long after sunrise, reaching Oahu by late
morning, moving to Maui County during the afternoon and evening,
then on to the Big Island Saturday night. During this time, a
compact and potent upper low will drop southward toward the state.
A jet stream along the southern flank of the upper low will move
over the islands and produce forcing that could generate organized
deep convection. Though the greatest amount of forcing and
coldest air aloft will be just northeast of the state, a line of
heavy showers or thunderstorms along the front could be capable of
producing strong and gusty winds from Kauai to Maui. While rain
rates could be impressive along the front, heavy showers are not
expected to last long enough in any one place to produce a
significant flash flood threat. There is also the potential for
downsloping southwest to west winds to gust over 40 mph ahead the
front on Oahu and parts of Maui County, but we do not anticipate
the need for a Wind Advisory for lower elevations. At higher
elevations, a High Wind Warning has been issued for the high
summits on the Big Island, and a Wind Advisory is now in place
summit of Haleakala on Maui.

On Sunday, the front will likely weaken near the Big Island as the
compact upper level low passes north of the state. The GFS and
ECMWF models show a surface low passing just north of the state,
along with a secondary band of moisture that could produce
another round of showers and gusty northwest winds from Oahu to
Maui.

Very cool conditions by May standards are expected to fill in on
the northwesterly flow Saturday night into Monday. The latest
guidance drops dew points into the upper 50s, and daytime high
temperatures will likely remain in the upper 70s, which is highly
unusual for early May.

There is no real sign of trade winds until Thursday. As the upper
level low fills and lifts off to the northeast Tuesday and
Wednesday, it will leave a weak area of low pressure north of the
state. This will produce generally weak west to northwest winds
over the islands and will likely lead to somewhat dry conditions.

&&

.AVIATION...
Increasing moisture and instability from an approaching surface
front and disturbance aloft continue to feed showers around the
islands and coastal waters, though significantly fewer than this
morning. Conditions have improved enough that all AIRMETS for
mountain obscuration have been dropped. VFR conditions will
continue to prevail through this evening. Brief to TEMPO MVFR
conditions in lower ceilings and showers will occur over the
individual islands with greater frequency and coverage tonight
through Saturday, likely prompting AIRMET Sierra to be reissued.
Winds will veer toward the south through tonight as the surface
and upper-level features get closer.

As the upper-level low digs closer to the islands tonight,
turbulence aloft will become an issue, likely warranting AIRMET
Tango over and around Kauai, then Oahu Saturday.

&&

.MARINE...
An approaching front will bring unsettled weather this weekend
that could include heavy showers, thunderstorms and locally gusty
winds. Sustained winds from the southwest to northwest with the
frontal passage may briefly reach Small Craft Advisory criteria
over some of the coastal waters.

South to southwest winds are expected tonight and tomorrow as the
front draws closer to the region from the northwest. The front is
expected to move quickly down the island chain Saturday, reaching
Kauai by early Saturday, Oahu by the afternoon, Maui County during
the evening and the Big Island Saturday night into Sunday. Behind
the front, northwest winds are expected. A low settling in north
of the islands Monday will help winds to become west Monday. The
low responsible for the front will dissipate north of the islands
as we head into the middle of the week, resulting in lighter
winds.

The current small northwest swell is expected to persist through
Saturday. The approaching low will send a moderate sized short-
period northwest swell toward the islands Saturday night through
Monday, with surf expected to remain below advisory levels as the
swell peaks Sunday night. A small long-period northwest swell is
possible around the middle of next week, as is a small short-
period northeast swell. Relatively small south and southwest
swells will arrive in the islands through the middle of next week,
with an uptick in swell energy expected today into the weekend,
and then again early next week.

See the latest Oahu Surf Discussion (SRDHFO) for additional
details on surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 8 AM Saturday to 6 PM HST Sunday for
Haleakala Summit.

High Wind Warning from 6 PM this evening to 6 PM HST Sunday for
Big Island Summits.

&&

$$

DISCUSSION...Wroe
AVIATION...TS
MARINE...M Ballard




Area Forecast Discussion

National Weather Service Louisville KY

 936 PM EDT Fri May 3 2019

.Forecast Update...
Issued 935 PM EDT Fri May 3 2019

Forecast remains largely on track. Some minor updates were made to
the timing of precipitation based on the latest observations and
model trends. Still appears the best chances for measurable
precipitation will be along and south of the Ohio River, with the
bulk of it coming during the daytime hours.

Also introduced patchy fog to the entire area after midnight given
trapped low-level moisture in the boundary layer and fairly wet
soils across the region. Many KY Mesonet sites are reporting surface
RHs in the 90% range already. Widespread cloud cover should keep it
from becoming dense.

&&

.Short Term...(This evening through Saturday)
Issued at 300 PM EDT Fri May 3 2019

...A Rainy Saturday in Store...

As of 245 pm, light showery activity was still slowly moving east
over east central KY.  Expect these showers to completely clear the
area by this evening.  Also of note was an area of congested cu with
good moisture convergence on mesoanalysis over southern IN.  This
would be a potential area for light showers to develop late this
afternoon/evening, however, AMDAR soundings do show low and mid
level inversions so convective development isn`t real likely.

For tonight, expect a mainly dry overnight period with cloudy skies.
As low level moisture is trapped under a low level inversion, patchy
fog may form especially over portions of south central and east
central KY with the lightest winds. Overnight lows in the upper 50s
to lower 60s are forecast.

For Saturday, light rain showers are expected to slowly move into
the region around or just before sunrise.  Light rain showers should
hold off in the Louisville area until after sunrise.  Expect these
rain showers to be scattered in nature through mid morning.  By mid
to late morning, more steady rains will arrive with the best chance
for widespread rain and isld-sct t-storms Sat afternoon. By early
Sat evening, convective activity should break up a bit with
scattered showers and storms expected in the Louisville area.  The
12Z model guidance did overall trend down in precipitation coverage
and duration throughout the day with the focus on south central KY
receiving the longest period of rain on Sat.  Sat doesn`t look like
a complete washout for southern Indiana/north central Kentucky but
on and off rains will persist throughout much of the late morning
through afternoon time frame. Will need to watch the evening model
guidance to determine if the slightly drier trend holds for Sat or
if models come back north with this system and give a wetter
solution as they did on the 0Z model suite.  High temps should range
from the mid 60s to lower 70s on Sat.

.Long Term...(Saturday night through Friday)
Issued at 315 PM EDT Fri May 3 2019

Saturday Night through Sunday Night...

Mid-level trough axis is forecast to swing through the region
Saturday night and exit off to the east on Sunday with zonal flow
returning to the region.  Light rain showers look to end from west
to east Saturday night with mainly dry conditions for Sunday and
Sunday night.  Lows Saturday night should drop into the lower-mid
50s with highs on Sunday warming into the 70-75 degree range.  Lows
Sunday night should drop back into the lower 50s.

Monday through Friday...

In the long term period, high latitude blocking across northern
Canada is expected to persist throughout much of next week.  A
rather confluent zonal flow is expected over the eastern US Monday
and into Tuesday which should bring a brief reprieve to the
unsettled weather conditions.  However, while the high latitude
block pattern remains in place across Canada, we`ll see a return of
lowering heights across the desert southwest with a downstream
confluent, flat ridge flow over the Ohio Valley.  Several
disturbances will roll through the mean flow and bring periods of
active weather from the Plains through the Ohio Valley for the
second half of the work week.

While Monday looks to be dry, there is a bit of uncertainty about
how dry Tuesday will be.  Some of the models keep much of the
unsettled weather to our west and northwest, while others bring it
back into the Ohio Valley.  Have generally leaned to a blend of the
GFS and Euro here, but overall, Tuesday may end up being more dry
than wet if we get a deeper trough in the SW US which would give us
a slightly stronger ridge in the east.

By mid-week, a fairly decent mid-level short wave trough is expected
to eject out of the southwest and through the Plains.  This will
likely lead to strong/severe convection out in southern Plains, with
remnant convective clusters rolling eastward toward our region. Best
chances of rain look to be in the Wednesday Night through Friday
period as the mid-level trough swings through the region.  For now,
have kept the blended PoP in the forecast which agrees with the
latest 12Z model trends.

Temperatures through the period will be seasonal for early May with
daytime highs in upper 70s to the low 80s Monday through Wednesday,
with mainly upper 70s for Thursday.  Some cooler weather may arrive
by Friday with readings ranging from the upper 60s over southern IN
to the lower 70s over southern KY.  Lows through the period will
generally be in the 50s/60s.

&&

.Aviation...(00Z TAF Issuance)
Updated at 700 PM EDT Fri May 3 2019

Dry forecast is expected overnight, but cig/vis forecast remains
complicated. Most observations across central KY and southern IN are
coming in VFR, and model blends have come in a bit more optimistic
in regards to cig/vis conditions for the short-term, with most
IFR/MVFR criteria occurring after midnight as low level moisture
moves in. Have leaned the forecast toward the more optimistic side
of guidance for now. Rain showers, with perhaps some isolated
thunder across central KY, will move in tomorrow after sunrise.
Expect IFR/MVFR cigs through the daytime tomorrow, with visibilities
ranging from VFR to as low as IFR in the heavier showers/storms.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...DM
Short Term...AMS
Long Term...MJ
Aviation...DM



Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 827 PM PDT Fri May 3 2019

.SYNOPSIS...03/817 PM.

Extensive low clouds will develop over coastal and valley areas
tonight into Saturday morning. The interior should clear by
Saturday afternoon but coastal areas may not as quickly. Low
pressure will move in on Sunday bringing increasing clouds and
cooler temperatures into the early week. There will be a chance
of showers on Sunday into Monday.

&&

.SHORT TERM (FRI-MON)...03/827 PM.

An upper level low pressure system, cutoff from the prevailing jet
stream and currently 1000 miles west of Los Angeles, will move
eastward and be centered near the Central California coast by
Sunday. As it approaches the coast on Saturday, it will deepen
the marine layer while strengthening the onshore pressure
gradients. ACARS data showing the marine layer depth around 1300
feet this evening across the LA Basin, but should deepen to around
2000 feet by Saturday morning. As a result, expecting low clouds
to spread into most valley locations south of Point Conception,
including portions of the Santa Clarita Valley. Low clouds are
expected to be slower to clear on Saturday afternoon, and may
linger near some beach areas all day. Some mid level moisture
and instability will likely generate some cloud buildups over
the Ventura mountains on Saturday afternoon, but no precipitation
is expected.

Onshore winds will be on the increase across interior sections
Saturday afternoon into evening, as the LAX-Daggett pressure
gradient strengthens to around +7 mb onshore. As a result, wind
gusts between 25 and 35 mph across the mountains and Antelope
Valley, except isolated gusts to 45 mph in the foothills.
Temperatures will begin to cool a few degrees across interior
sections on Saturday due to the stronger onshore flow and
deeper marine layer.

*** From previous discussion ***

By Sunday, clouds at all levels will be prevalent and while a
gloomy day is more likely than not, wouldn`t be surprised to see
more breaks in the clouds than currently in the forecast. Drizzle
will also be possible over the weekend, with the best chances on
Sunday. A weak and small frontal boundary will move through SLO
and SBA Counties on Sunday, and may interact with the marine layer
and some mid- level moisture to produce a few showers. If any
showers result, amounts will be light and under one quarter of an
inch. Temperatures will cool even more on Sunday...especially
over the interior where a healthy 10 degree drop is anticipated.
The stronger pressure gradients will result in gusty southwest
winds over the interior sections, but looks to stay just under
advisory strength at this time.

The latest computer projections continue to show the low wobbling
into southern California on Monday, but due to the cutoff-
spinning-top nature of this system and still some significant
spread in the ensembles, will have to move forward with this idea
with some reservation. Showers will remain a possibility, with the
focus shifting more into Ventura and LA Counties. Any showers
still look light. Cool conditions will continue as well.

With 500 MB temperatures expected to be around -20C overhead on
Sunday and Monday, the potential for a thunderstorm or two is not
zero, but all the convective parameters are still too low to
mention thunderstorms in the forecast. Not expecting any snow
issues with snow levels at 6500 feet and above.

.LONG TERM (TUE-FRI)...03/221 PM.

Assuming the low will move to the east on Tuesday, as to the
majority of the computer projections, Tuesday and Wednesday will
remain mostly dry. Mostly is the key word as moist northerly flow
will keep chance of showers going in the mountains. Over the
lower elevations, increasing onshore pressure gradients should
maintain a moist lower layer like a marine layer, although the
inversion should be quite week.

An upper level trough should spawn off of a low currently over
Alaska, and drop through western Canada and into the Great Basin
by late Wednesday. From there, the computer projections and
ensembles diverge greatly. Half of the solutions have the low
wobbling west and right over southern California Thursday through
next weekend. This would result in showers and maybe
thunderstorms. The other half keep the low to the east which would
result in enhanced northerly by mostly dry flow. Without much more
to go on, 20-30 PoPs look very appropriate with cooler than normal
conditions.

&&

.AVIATION...03/2359Z.

At 2345Z, the marine inversion was around 1300 ft deep at KLAX.
The top of the inversion was around 3400 ft with a temperature
around 16 degrees C.

Moderate confidence overall in the 00Z TAFs. Low clouds with
IFR/MVFR cigs/vsbys are generally expected to return to
coastal/valley areas south of Point Conception overnight into
Saturday morning. Brief LIFR conditions are possible overnight
across the coastal locations north of Point Conception. A slight
deepening of the marine layer is expected across the LA Basin by
Saturday morning, likely approaching 2000 feet.

KLAX...Moderate confidence overall in the 00Z TAF. VFR conditions
will prevail through early this evening. MVFR cigs are generally
expected to affect KLAX between 05Z-20Z but onset and dissipation
of the low clouds may be off +/- an hour or two. There is a 20
percent chance of MVFR cigs lingering through Saturday afternoon.

KBUR...Moderate confidence overall in the 00Z TAF. VFR conditions
will prevail through this evening. Low clouds with IFR/MVFR cigs
are expected to move into KBUR between 09Z-18Z but onset and
dissipation of low clouds may be off +/- an hour or two.

&&

.MARINE...03/756 PM.

For the Outer Waters...Moderate to high confidence in the current
forecast. Winds and seas should remain under Small Craft Advisory
(SCA) thresholds through Wednesday. However, there is a 30%
chance for SCA level gusts through late this evening.

For the Inner Waters N and S of Point Conception...Generally high
confidence in the current forecast. Winds and seas should remain
under SCA thresholds through Wednesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (MON-FRI).

No significant hazards expected.

&&

$$

PUBLIC...Gomberg/Kittell
AVIATION...Gomberg
MARINE...Smith
SYNOPSIS...Stewart

weather.gov/losangeles