Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/03/20

Area Forecast Discussion

National Weather Service Honolulu HI

 359 PM HST Thu Apr 2 2020

.SYNOPSIS...
Winds will decrease and veer southeasterly tonight as deep low
pressure intensifies far north-northwest of the state. Isolated
showers will diminish early this evening as land breezes develop.
High clouds will move up from the southwest and shower chances
will increase over the western end of the island chain late
tonight. Winds will turn more southerly on Friday and the weekend,
drawing up deeper moisture that will likely fuel increased shower
activity and possibly a few thunderstorms. Wet conditions are
expected to linger over portions of the state through the first
part of next week.

&&

.DISCUSSION...
A somewhat unstable east to east-southeast low level flow is
producing spotty showers across mainly island interior sections
this afternoon. Low level background winds are decreasing and
veering due to deep low pressure developing far north-northwest of
the state. A broad upper level trough covers much of the central
north Pacific and is maintaining somewhat unstable conditions with
essentially no inversion according to the afternoon soundings and
recent aircraft data. For now, low level moisture remains below
April normal, and afternoon sea breezes have managed to trigger
only spotty, mainly interior showers, a few briefly heavy.

The deep low will continue to drop toward the islands tonight.
This will cause winds to continue to shift out of the southeast
and allow land breezes to clear out most areas this evening. Later
tonight, the deep low will cause the subtropical jet stream to
lift northward over the state, leading to increasing high clouds
and possibly generating showers over waters to the southwest of
the islands. Some of these showers could reach as far north as
Kauai and Oahu late.

As the deep low settles about 850 miles northwest of the state on
Friday, shower chances will increase as south to southeasterly
winds draw deeper moisture over the islands. The state will be
under the outer portion of the upper level trough surrounding the
low with the subtropical jet stream overhead, possibly leading to
enough instability to trigger isolated heavy showers and a few
thunderstorms, mainly during the weekend. As the low edges closer
to the state on Sunday, shower chances should increase, especially
in the moist, convergent flow across the western end of the
state. In addition, the southerly flow will push dew points up to
around 70, bringing an increase humidity.

Early next week, area of convergence on the flank of the low will
push to the east. The latest runs of the GFS and ECMWF show this
feature maintaining wet conditions for the western end of the
state on Monday but have diverged on motion of the convergence
band on Tuesday and Wednesday. Confidence is therefore low in the
extended forecast, though portions of the island chain will likely
experience active showers and no trade winds through the middle
of next week.

&&

.AVIATION...
A trough to the northwest of Kauai will continue the light flow
pattern across the islands through the remainder of this
afternoon. Sea breezes will limit shower activity to the island
interiors. Elsewhere, expect partly cloudy skies and VFR
conditions. Sea breezes should dwindle by sundown, leaving light
and variable winds overnight with isolated showers.

No AIRMETS are in effect at this time.

&&

.MARINE...
A surface high far northeast of the area and a surface trough
northwest of Kauai will continue to produce gentle to locally
fresh east to southeast winds across Hawaiian waters through
tonight. A front slowly approaching the state Friday will cause
the wind direction to veer slightly more toward the south on
Friday and over the weekend. Over the western coastal waters,
winds are expected to become southerly by Friday. Meanwhile over
the eastern coastal waters, winds will remain out of the
southeast, but is expected to strengthen on Friday. Winds could
even reach Small Craft Advisory speeds tomorrow over the Big
Island windward waters and Big Island leeward waters off South
Cape.

Over the weekend and into early next week, the front or resulting
convergence zone is expected to stall somewhere over the western
coastal waters. This will bring the chances for heavy rain and
possibly a few thunderstorms over the area waters.

A new NNW swell building Saturday will produce moderate surf
along north and west shores over the weekend, but is expected to
remain below the advisory threshold. As the weekend swell
subsides, a west-northwest swell will slowly build, peaking
around Monday night followed by a northwest swell on Wednesday.
Surf from these swells will also remain below the advisory level.

Swells from the southeast Pacific are partly blocked by the
islands of French Polynesia, but our current southeast swell is
coming through a narrow swell window. This swell will continue to
drop tonight through Friday. A small south-southeast swell is
possible early next week. Surf along east shores will slowly
subside as trade winds weaken.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Wroe
AVIATION...Thomas
MARINE...Kino




Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 909 PM CDT Thu Apr 2 2020

.UPDATE...
900 PM CDT

Going forecast is in good shape, but did nudge PoPs up just a bit
later this evening/overnight. Shortwave ridge axis is just about
cresting overhead at this hour, with broad cyclonic mid-level
flow starting to push eastward. A series of weak/subtle
disturbances are embedded within this flow, and will provide a
glancing blow of forcing for ascent later this evening to the
region. Subtly-enhanced jet divergence atop of an area of modest
low-level warm advection seems to be driving the zone of showers
which are drifting out of eastern Iowa at this hour, and this
should continue to lift northeastward this evening. Recent RAOBs
and AMDAR VAPOR soundings do show the layers above 700 mb have
moistened up nicely over the last few hours, with some lingering
dry air below. All things taken together seem to support a brief
potential for showers spreading into the region around/just after
midnight, with activity weakening/fizzling through the late
overnight hours as forcing wanes. Have noted a few straggling
lightning strikes to our west, but do think this activity will be
short-lived with a lack of a steeper lapse rate plume and stronger
forcing for ascent with eastward extent. Updated products have
been transmitted.

Carlaw

&&

.SHORT TERM...
219 PM CDT

Through Friday...

Temperatures are warming nicely (to around 60) across inland
areas this afternoon under mostly sunny skies. While skies have
been mostly sunny, expect higher level cloudiness to increase
over the area later this afternoon in advance of our next weather
system. Skies will thus become mostly cloudy across the area for
tonight. A weak mid-level disturbance, noted in the GOES 16 water
vapor imagery over northern MO and southern IA, is expected to
shift across our area tonight. As it does so, we could have a few
light showers develop over northern IL tonight. Overall, this will
not be a big deal, but we do have some low end chances for rain
overnight, primarily across northern IL.

On Friday we will be awaiting the arrival of a cold front
approaching western IL late in the day. Since this front will not
move into our western areas until Friday evening, it appears most,
if not all of the day Friday will be precipitation free for the
area. Instead, it appears the primary threat for rain should hold
off until Friday evening. While it is looking dry, there is
likely to be more cloud cover around. In spite of this, warmer
conditions are expected thanks to a thermal ridge featuring 925 mb
temperatures around 11C advecting northward ahead of the
approaching front. This should yield afternoon high temperatures
into the mid 60s inland from Lake Michigan. Close to the lake,
however, onshore winds are likely keep temperatures in the upper
40s to low 50s.

KJB

&&

.LONG TERM...
310 PM CDT

Friday Night through Thursday...

A slow moving cold frontal passage will bring rain showers to the
area Friday night into Saturday, followed by quiet conditions
through Sunday night. Next work week will be mild and unsettled
with thunderstorm chances in the first part of the week and then
turn cooler later in the week.

Friday Night through Sunday Night:

A narrow plume of anomalous PWATs (about 150-200% of normal) for
the time of year of a bit upwards of 1" will be drawn northward
with the approach of slow moving cold front from the northwest. A
weak frontal wave may initially slow the eastward progress of the
front and associated showers. Lower and mid-level convergence and
transient frontogenesis along with very modest height falls will
drive primarily anafrontal (post-frontal) rain showers. Confidence
is high in rain occurrence for the Friday night period, so
indicate categorical PoPs gradually translating east-southeastward.
Can`t completely rule out some embedded thunder, however it
appears sub-slight chance mention as instability will be very
meager. Relatively steep lapse rates will maximize above 600 mb,
so lifting would have to be high up in the column. With
probabilistic thunder products sub-mentionable over the area and
better chances off to the west/southwest of west/southwest CWA
area, opted to remove thunder mention.

There may be some embedded moderate rainfall rates depending on if
f-gen is more than transient, with upside potential in rainfall
amounts in a narrow swath given presence of well above normal
column moisture. NAM hints at this sort of potential, though
guidance is mixed. For now, WPC QPF totals around 1/4" appear
reasonable and will be able to add detail as needed with
subsequent updates. Expansive high pressure ridge building in from
the northwest will give the front and associated rain/showers an
extra push during the day on Saturday, so there should be fairly
quick drying from northwest to southeast across Illinois counties.
As such, added some temporal resolution to the PoP grids. Saturday
will be 10-15 degrees cooler than Friday away from the lakeshore
in the lower to mid 50s and only mid-upper 40s lakeside as winds
turn north to northeast behind the front. It appears that Saturday
evening through Sunday night will then be dry (minor exception of
last showers exiting far southeast early Sunday evening). Sunday
will feature partly cloudy skies and moderate back to the mid-
upper 50s inland, but stay chilly lakeside in the 40s under
continued northeast surface flow.

Castro

Monday through Thursday:

Medium range guidance continues to develop a long wave trough
along the west coast early next week, with a broad downstream
upper ridge across the eastern CONUS. With quick southwesterly
flow aloft, surface low pressure is progged to develop out of the
Plains and progress northeast to the western Great Lakes region
through mid-week. In the process, a warm front lifts across the
region, bringing warmer (potentially 70+ degrees on Tuesday) and
more humid air into the region. Shower and thunderstorm potential
also increases, with a few periods of unsettled weather likely
Monday into early Wednesday.

The pattern is rather messy and thus uncertain as depicted in the
guidance and ensembles, with a few to several short-waves
traversing the area and large variance on timing. Surface pattern
and timing of waves of showers/storms and associated cloud cover
will also dictate exactly how mild it gets and possible lakeside
cooling. It will take some time to sort out specific details, so
confidence is on the low side. Depending on the timing and overall
evolution, there may be overlap of stronger flow aloft with
sufficient moisture and instability to bring a stronger
thunderstorm risk somewhere over the region. It appears that
initial cold front passage will occur Tuesday night into
Wednesday, possibly followed by a reinforcing shot of cooler air
to close out the period. Some guidance indicates a rather stout
cold shot for this time of year.

Ratzer/Castro

&&

.AVIATION...
For the 00Z TAFs...

There are no major aviation weather concerns over the next 24 to
30 hours outside of a brief window for some showers overnight
tonight.

Light east to southeasterly winds will prevail through the TAF
period, although a somewhat more chaotic/variable wind field may
develop as an area of light showers moves northeast across the
region late tonight/very early Friday morning. While we are
currently seeing several in-cloud lightning flashes across north-
central Missouri, all indications point to a lack of
electrification potential as this activity spreads farther
northeast. Anticipate that any lingering showers should move out
of the region or fizzle by daybreak Friday, leaving behind a mid-
level cloud deck through the day. Could see some occasional
southeast wind gusts to 15 kts develop Friday afternoon with
heating.

The next weather feature of interest will be a sharp cold front
which--at this time--looks to move through the Chicago-area
terminals just outside the extended ORD/MDW TAF window. Cigs
should be on a quick downward trend Friday evening, but the better
chances for precipitation and IFR cigs looks to occur right around
or just after 04.06z and have left this mention out of the current
TAFs as a result.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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