Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/01/23
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1201 AM EDT Mon May 1 2023
.AVIATION...
Diabatic heating and colder air aloft will sustain scattered rain
showers the first hour or two of the taf period. Center of upper
level close low system will then push into the area after 06Z
tonight. Modest signal that plume of better thetae advection will
impact southern sections of the forecast area through daybreak. Kept
a prevailing rain shower group but confidence is low. Dry slotting
is expected to keep much of the area precipitation free for a good
part of the day on Monday. Moisture advection will then increase
substantially after 21Z. Did include rain as a precipitation type at
onset, but expecting wet snowflakes to become the predominate
precipitation type by 02Z Tuesday. Northwest winds are expected to
increase markedly 20 to 30 knots with colder air moving in Monday
evening.
DTW THRESHOLD PROBABILITIES...
* High for cigs aob 5000 feet overnight.
&&
.PREV DISCUSSION...
Issued at 346 PM EDT Sun Apr 30 2023
DISCUSSION...
Cold-core low exhibiting deep-layer vertical continuity continues to
churn overhead today providing additional opportunities for
showers/thunderstorms through this evening. General tropospheric
tendency for ascent improves as the next filament of CVA lifts into
Southeast Michigan this afternoon in conjunction with steep low-
level lapse rates (approaching dry adiabatic). Relative dryness in
the boundary-layer marked by surface dewpoint depressions around 15F
limits instability and potential for more robust updrafts, but UVVs
should be capable of isolated downpours with some small hail at
times as freezing levels hover near 4 kft AGL. CAMs continue to
illustrate a scattered/pulsey mode with low confidence for strong or
overachieving cells attributed to capping issues near 700 mb as
currently evidenced by ACARS and (some) forecast soundings. Should
the stable layer hold, low equilibrium levels would keep convection
rather shallow in depth and limit the distribution and frequency of
lightning. No real wind concerns today given the relative lack of
effective shear today (less than 25 knots) as stronger flow remains
off toward the west.
Final reduction in heights arrives tonight as the system centers
over southern Lower Michigan with several weak shortwave features
embedded within the lower portion of the column. This should touch
off a few clusters of widely scattered nocturnal showers.
Reconfiguration of the occluded low ensues Monday as a southern
stream speed max lifting up the Mid-Atlantic coast gets absorbed
into the parent wave producing an increase in wavelength. This
disrupts the flow structure and shifts the vertical axis abruptly
eastward followed by a notable uptick in PWATs as return flow arcs
into the Midwest off the western Atlantic. Some nuisance showers are
possible midday Monday, especially for Metro Detroit, as the cold
pool aloft (minus 13C at 700 mb) traverses the CWA, enroute for the
eastern Great Lakes. High temperatures are not expected to break
50F, and thermodynamic profiles appear quite favorable for graupel
should showers materialize. Stratiform precip chances ramp-up Monday
evening and overnight as low-level convergence increases within the
broader cyclonic environment. Clear shift in the NWP space
indicative of cold/saturated profiles and favorable ascent through
the DGZ warrant increased wording for snowfall, especially west of I-
75 where freezing levels will be just a few hundred feet of the
surface. Accumulations are not particularly impressive give 2m temps
above freezing suggesting melting snowfall. In additional to the
below normal temperatures, LLJ bleeds into the southwest portion of
the region with 30-40 knot winds in the lowest 2 kft AGL which
should have no trouble translating into gusts given mixed-layer
support by persistent cold advection.
Dreary conditions continue Tuesday with renewed shower production
under the lingering influence of the PV anomaly. Morning shower
activity carries extended potential for snow component until slight
recovery in 0C heights midday. Ensembles offer varying narratives on
the rate of thermal recovery mid-late week, dependent on how far
east flattening central CONUS ridging can overcome the
retrograding/orphaned upper low that emerges over west-central
Ontario. As of now, core of the thermal ridge will remain west of
the Upper Mississippi through the workweek yielding higher
confidence in sustained below normal temperatures trends.
MARINE...
A broad upper-level trough will continue to meander over the central
Great Lakes into Monday with continued unsettled conditions with
periodic showers. Light southerly to variable flow will trend more
southwesterly into tonight and become moderate in strength Monday as
another area of low pressure off the eastern seaboard lifts
northwestward Monday while getting absorbed into the broader scale
upper-level trough. This low pressure will deepen to around 980 hPa
north of Lake Huron Monday along with an increase in initially
southwesterly winds.
Winds will then veer northwesterly Monday night with the passage of
the upper-level trough axis, with hazardous small craft conditions
beginning Monday afternoon across western Lake Erie and Lake St.
Clair amidst a tightening pressure gradient with the strong low
pressure north of Lake Huron. Small craft conditions will be delayed
until the arrival of northwest flow Monday night across Saginaw Bay
and around the tip of the Thumb in northwesterly flow as colder air
is ushered into the region. Marine conditions will improve by
midweek as the upper-level trough and surface low pressure finally
begin to release and weaken to the east with gradually building high
pressure and drying conditions.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 8 PM this evening to 4 PM EDT Tuesday for
LHZ421-422-441.
Lake St Clair...Small Craft Advisory from 10 AM this morning to 4 PM EDT Tuesday
for LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory from 10 AM this morning to 4 PM EDT Tuesday
for LEZ444.
&&
$$
AVIATION.....MR
DISCUSSION...KGK
MARINE.......IRL
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
901 PM PDT Sun Apr 30 2023
.SYNOPSIS...30/835 PM.
A late season storm will affect the area through Thursday or
Friday, with rapid cooling and increasing clouds. Monday into
Tuesday will bring areas of drizzle to the area, with periods of
light to moderate rain and possible thunderstorms forming late
Tuesday through Wednesday or Thursday. Drier conditions with some
warming expected for the end of the week.
&&
.SHORT TERM (SUN-WED)...30/838 PM.
An upper level low pressure system centered off the northern
California coast and associated trough will deepen across the
state overnight into Monday, leading to substantial height falls
across the region. This upper low will move southward over the
next three days, taking up residence southwest of Point
Conception Wednesday afternoon. Both the deterministic and
ensembles are in good agreement, leading to higher confidence in
the forecast.
This upper level trough combined with strong onshore flow (LAC-
Daggett pressure gradient peaking at +8.4 mb this afternoon) has
resulted in a deepening of the marine layer as well as a cooling
trend. Current satellite imagery already showing low clouds
surging quickly into the valleys this evening, with ACARS data
showing a marine layer depth around 2500 feet across the LA Basin.
The marine layer will continue to deepen rapidly overnight,
eventually reaching around 5000 feet on Monday. As a result, low
clouds will surge well inland into the lower coastal slopes
tonight into Monday. With the rapid deepening, there will be some
drizzle/light rain developing tonight and continuing through
Monday, especially across Ventura and LA counties. So, chance POPs
with patchy drizzle continue in the forecast. Along with the
cloudy and damp conditions, gusty winds will continue through
Monday evening. Currently, WIND ADVISORIES are in effect tonight
for the Antelope Valley foothills as well as southwestern Santa
Barbara county. These advisories will likely need to be
extended/reissued for the same areas Monday afternoon and evening.
*** From previous discussion ***
For Monday night through Wednesday, rain chances will be
increasing as the upper low moves towards the area. Based on
confidence in model solutions, have bumped up POPs noticeably above
current NBM numbers for this time period. Through Wednesday
evening, rainfall totals are expected to generally range between
0.10 and 0.50 inches and some minor nuisance flooding issues will
be likely. Given the unstable air associated with the upper low,
the threat of thunderstorms remains in the forecast for San Luis
Obispo county (Tuesday/Wednesday) and Santa Barbara county
(Wednesday). Snow levels will be dropping to the 4500-5500 foot
range, so there will be some accumulating snowfall across the
mountains. Overall, do not anticipate any significant hydrologic
issues, just some nuisance urban flooding and some possible travel
issues across the mountains.
.LONG TERM (THU-SUN)...30/157 PM.
For the extended forecast, models continue to exhibit good
synoptic agreement. The upper low moves across the area then
northeastward on Thursday. main focus will be the continued
impacts of the upper low on Thursday. Broad cyclonic flow will
prevail on Friday, followed by some transient ridging on Saturday
then cyclonic developing again on Sunday.
Forecast-wise, main concern will be the impacts of the upper low
on Thursday. The low will continue to generate precipitation
across the area through Thursday afternoon. When all is said and
done, rainfall totals will generally range between 0.33 and 0.66
inches with local amounts around 1.00 inch over the foothills.
Snowfall totals in the mountains will generally range between 4
and 8 inches with locally higher amounts above the resort level.
For Friday, the persistent cyclonic flow will keep things on the
cool side. At this time, the forecast is dry, but it would not be
surprising to see some isolated showers during the day on Friday.
For Saturday and Sunday, dry conditions will prevail. With higher
thicknesses and more sunshine, temperatures will rebound with
inland areas climbing into the lower to mid 70s.
&&
.AVIATION...30/2350Z.
At 23Z over KLAX, the marine layer was 2200 feet. The top of the
inversion was 3200 feet with a temperature of 20 Celsius.
High confidence in improved flight categories over the next 24
hours, compared to the previous 24 hours. Ceilings should expand
rapidly this evening and lower a few hundred feet, before
steadily deepening after 06-10Z. The most deepening will be over
the Los Angeles and Ventura County airports, where moderately
confident there will be periods with -DZ or -SHRA but low
confidence on timing and duration. Moderate confidence on timing
of ceiling changes (plus or minus 3 hours).
KLAX...Moderate confidence in ceiling heights and timing (plus or
minus 3 hours). Low confidence on timing and duration of any -DZ
or -SHRA. Moderate confidence in southeast winds prevalent 12-20Z
Monday, with a 20 percent chance of a few hours of east wind
component over 8 knots (highest chances 12-16Z).
KBUR...Moderate confidence in ceiling heights and timing (plus or
minus 3 hours). Low confidence on timing and duration of any -DZ
or -SHRA.
&&
.MARINE...30/900 PM.
Moderate confidence in Gales continuing across the Outer Waters
tonight, likely falling off to Small Craft Advisory (SCA) levels
late tonight or early Monday morning.
SCA conds will likely (50-70% chance) become more widespread
across the Inner Waters south of Point Conception Monday afternoon
to evening.
Gusty southerly winds may approach SCA levels ahead
of a late Wednesday into Thursday storm system.
There is a slight chance of tstorms over the northern waters
Tuesday and all waters Wednesday and Thursday.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 3 AM PDT Monday for zones
349-351. (See LAXNPWLOX).
Wind Advisory in effect until 10 PM PDT this evening for
zones 381-382. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for
zones 645-650. (See LAXMWWLOX).
Gale Warning in effect until 3 AM PDT Monday for zone 676. (See LAXMWWLOX).
&&
$$
PUBLIC...Gomberg/Thompson
AVIATION...Kittell
MARINE...Gomberg/Munroe
SYNOPSIS...RK
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox