Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/24/19

Area Forecast Discussion

National Weather Service Louisville KY

 927 PM EDT Tue Apr 23 2019

.Forecast Update...
Issued at 927 PM EDT Tue Apr 23 2019

An east-west cold front has moved through southern Indiana and is
now edging into northern Kentucky. With the setting of the sun the
atmosphere is quickly stabilizing and convective inhibition is
increasing. The earlier storms, which weren`t particularly
widespread at their peak, have diminished to just a few cells. This
should continue for the rest of the night; widely scattered showers
and an isolated thunderstorm or two.

Issued at 539 PM EDT Tue Apr 23 2019

Storms that fired over western Kentucky have been struggling to
maintain themselves as they head east into central Kentucky. Bulk
shear is very weak and the latest SDF AMDAR sounding (over an hour
ago) shows capping in the 7k-10k` layer. Most cumulus clouds on the
visible satellite loop aren`t very impressive, though a look out the
window shows some moderate cu piling up northwest of the weather
office.

SBCAPE is around 1000 J/kg along and a couple counties either side
of the Ohio River just ahead of the incoming cold front, and DCAPE
is above 800 J/kg east of I-65 in that corridor. Low level lapse
rates are steep. So, if convection can get going, some gusty winds
could still occur with the heaviest local downpours. Latest radar
scan shows a cell going up over western Breckinridge County, so
we`re not out of the woods yet.

&&

.Short Term...(This evening through Wednesday)
Issued at 300 PM EDT Tue Apr 23 2019

Latest GOES-Derived instability (CAPE) along the Ohio River is
nearing 1000 J/kg, close to what the HREF model has for this time. A
weak inversion at 700 mb (per latest AMDAR soundings) is keeping
development from occurring so far today. As instability peaks to
around 1500 J/kg on the HREF in the 5-7 PM time frame, we expect
development to begin by then. Still no change in the expected
weather hazards from earlier forecast...peak gusts of 35-45 mph in
storms and small areas of heavier rainfall where any training of
cells occurs this evening.

That activity could linger well into the overnight as colliding
boundaries keep things active farther into central Kentucky. The
cold front behind this first wave of activity will also linger as it
stalls out in the vicinity. General troughiness over the Midwest
looks to shoot some vortmaxes our way Wednesday, likely allowing for
more development along residual outflow boundaries and that front.
Given precipitable water values moving up to around 1.5 inches by
afternoon and these boundaries/this extra forcing, decided to bump
up rain chances for many in the area.

Temperatures are a little more in question for highs Wednesday,
given the difficulty in located morning cloud cover as well as those
boundaries. For now have around 70 in southern IN ranging to near
80 in southern KY.

.Long Term...(Wednesday night through Tuesday)
Issued at 330 PM EDT Tue Apr 23 2019

Wednesday night, an area of low surface pressure will be centered
over the Ohio Valley in the area the stationary front was, but by
this time, the front will have weakened to a point of pretty much
nothing. The CWA will maintain wind energy in the mid-levels and a
good moisture feed from the Gulf of Mexico. This provides most of
the CWA with high chances of seeing rain showers, and a decent
chance of a rumble or two of thunder. The chances drop off somewhat
in the Lake Cumberland region.

As a closed off low, over the Dallas, Texas area, heads towards
Tennessee, it will begin to push the precipitation through the CWA
from west to east. Chances of precipitation early Thursday drop
somewhat before intensifying in the evening hours. This will shift
the heaviest rainfall towards the Lake Cumberland area overnight
Thursday.

On Friday, skies clear and the sun comes out until Saturday
afternoon. Southern Indiana will be the first to see clouds and rain
chances move in from the northwest, if the GFS is correct. The Euro
delays this until later in the evening and shows the event having
less overall rainfall by moving out of the CWA Saturday night. The
GFS has a moist cold front moving through mid-day Saturday. With
this, thinking areas near the Ohio River could get less than a tenth
of an inch. The area will likely see some more rain around Tuesday,
but the guidance isn`t very well aligned.

Temperatures are going to be nice this week. Highs will run in the
70s until after the weekend when things bump up to near 80. Lows
will stay in the 50s for the most part with Saturday morning
dropping into the 40s.

&&

.Aviation...(00Z TAF Issuance)
Updated at 736 PM EDT Tue Apr 23 2019

A cold front draped along the Ohio River sparked widely scattered
thunderstorms earlier during the heat of the afternoon. The cells
are weakening now and that should generally continue through the
early evening hours, with LEX standing the best chance of a stronger
storm moving through. The remainder of the night will then be quiet
with perhaps a few showers but prevailing VFR conditions.

Tomorrow that front will still be stretched out east-west, likely
right along the length of Kentucky. It will have weakened some but
scattered afternoon showers and a few storms can still be expected,
increasing in coverage as we get into the evening hours.


&&

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

$$

Update...13
Short Term...RJS
Long Term...KDW
Aviation...13




Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 807 PM PDT Tue Apr 23 2019

.SYNOPSIS...23/116 PM.

Afternoon temperatures across inland areas will remain above
normal through the week while a weak onshore flow will help to
keep coastal areas cool. Temperatures across the region will be
near normal next weekend. There is a slight chance of mountain
thundershowers Thursday and during the weekend.

&&

.SHORT TERM (TUE-FRI)...23/806 PM.

***UPDATE***

Overall, a very quiet evening across the forecast area. Latest
satellite and surface observations indicate clear skies across
most of the area, except for some low clouds/fog over the LA
coasta and some mid/high level clouds developing over Ventura
county. Currently, no winds of any significance are noted.

Forecast-wise, the main concern in the immediate short term is the
development of the marine layer stratus and fog. Latest AMDAR
soundings indicate marine inversion around 900 feet this evening.
With H5 heights increasing overnight, do not anticipate much
deepening despite the forecast development of an eddy. However
will expect clouds to work their way up the coastal plain
overnight/Wednesday morning to the South Coast of SBA county.
Based on MOS and high resolution models, Central Coast should
remain stratus-free through Wednesday morning. Other than this
possible stratus, no significant forecast issues are present.

Overall, current forecast appears to have good handle on the
immediate short term. Therefore, no updates are planned at this
time.

***From Previous Discussion***

Temperatures for coast/valleys peaking today as onshore flow
increases through the rest of the week. Already seeing some marine
layer clouds off the LA Coast today and expecting those to expand
westward overnight, possibly getting as far west as Pt Conception
by Wednesday morning. Probably not too much inland push yet but at
least enough to cover the coastal plain and some of the coastal
valleys.

Cooler onshore flow will set in Wednesday and last through the end
of the week bringing temps back to near normal by Friday. Low
clouds will push a little farther inland each night and also push
north up the SLO/SB coastal areas by Wednesday afternoon and night.

Models have started to show some rather robust instability across
the Ventura/SB mountains starting Thu and a fairly shallow but
significant increase in moisture between 850 and 700mb, the source
of which is unknown at this time so confidence is not particularly
high. But if these factors come together there would likely be
some convective activity the latter half of the week.

.LONG TERM (SAT-TUE)...23/216 PM.

Not too much change in the pattern over the weekend. The ridge
aloft remains in place but a cutoff upper low will be approaching
from the west Sunday that will continue the cooling trend through
Monday. Models in surprising agreement on the track and strength
of the low which is expected to move through the area Monday
morning. As it does it will likely deepen the marine layer over
3000` and possibly generate some light showers or drizzle,
especially in LA County. There is some instability with it as it
moves through south of Pt Conception which would provide
additional support for the showers and can`t rule out thunder
chances, though too low confidence to include at this time.
Current forecast of partly cloudy Monday may be optimistic
depending on the timing of the upper low passage. And temps may be
too warm, especially if showers develop and clouds linger into the
afternoon.

Heights rise Monday night and Tuesday as the low moves into AZ.
However, models maintain a very strong onshore flow so even if the
marine layer clears out faster than Monday temps will remain near
to slightly below normal.

&&

.AVIATION...23/2311Z.

At 2300Z, the marine inversion at KLAX was based at 1000 feet.
The top of the inversion was 2100 feet with a temperature
of 26 degrees Celsius.

Overall, moderate to high confidence in 00Z TAF package. High
confidence in return of CIG/VSBY restrictions to coastal sites
south of Point Conception, but only moderate confidence in timing
and flight category. For all other sites, high confidence in CAVU
conditions through TAF period.

KLAX...Overall, moderate confidence in 00Z TAF. Timing of MVFR to
IFR change may be +/- 2 hours of current 03Z forecast. Timing of
IFR to MVFR change may be +/-4 hours of current 16Z forecast.

KBUR...Overall, high confidence in 00Z TAF. There is a 10-15%
chance of MVFR VSBYs 11Z-17Z.

&&

.MARINE...23/806 PM.

For the Outer Waters, high confidence in current forecast. Winds
and seas will remain below Small Craft Advisory (SCA) levels
through Saturday. On Sunday, there is a 50% chance of SCA level
winds developing across PZZ670 in the afternoon and evening hours.

For the Inner Waters north of Point Sal, high confidence in
current forecast. Winds and seas are expected to remain below SCA
levels through Sunday.

For the Inner Waters south of Point Conception, high confidence in
current forecast. Winds and seas are expected to remain below SCA
levels through Sunday.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

No significant hazards expected.

&&

$$

PUBLIC...MW/RAT
AVIATION...RAT
MARINE...RAT
SYNOPSIS...Kj

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