Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/31/22
See below for an aviation forecast discussion for the 00Z TAFs.
&&
.SHORT TERM...(This Evening through Saturday Night)
Issued at 235 PM CST Fri Dec 30 2022
A broadly progressive mid level flow pattern will continue for the
short range. A couple of weak waves are forecast to move through the
flow, but overall moisture looks pretty scant and really am having
trouble seeing any measurable pcpn through the period. The main
issue this weekend may well be areas of fog overnight and early in
the day due to relatively weak winds and plenty of snow cover to
enhance low level moisture. Tough to say exactly where to put fog so
will rely on models to some degree. In this persistent low level
pattern will stick with and not stray too far from NBM temps, which
is to stay near seasonal norms.
.LONG TERM...(Sunday through Friday)
Issued at 235 PM CST Fri Dec 30 2022
Really, not a lot to add to the extended discussion that hasn`t
already been hashed out of the last 3-4 days. Deterministic guidance
remains in its own camps, with the GFS having the more northerly
track (though this has shifted south slightly) and the EC the more
southerly track and the Canadian leaning towards the EC. Ensembles
follow the trends of the deterministic guidance, with fewer EC members
bringing moisture into the CWA compared to this time yesterday.
While the GFS is the more northerly track, profiles for KABR/KATY
show less of a warm layer influence on p-type, with any freezing
precipitation generation being the response to a lack of ice in the
dendritic growth zone. As such, NBM 4.0 has lowered probabilities for
mixed precip, and even GEFS ensembles have trended towards almost
exclusively snow (though Watertown still has a small probability for
ice). The caveat to this is the NBM 4.1 which has some not-
insignificant ice probabilities to our south. Will stick with
blended guidance (NBM 4.0) which maintains mainly snow as the p-
type. As for snow totals, confidence is low, GEFS plumes are still
all over the place, and the NBM 4.0 and NBM 4.1 show significant
differences in mean snowfall potential. Confidence in winds is also
low, with placement of surface highs nearly over the CWA in the EC
and a gradient across the state in the GFS. Peak sustained wind in
NBM 4.1 is only 20kts for our more favored locations, and at these
temperatures blowing snow model would require over a 1/2" per hour
rate to get reduced visibility to even consider blowing snow
impacts. Since that is the worst case and most of forecast areas NBM
4.1 winds are sustained at 10 to 15kts, at this point will not
include any mention of blowing snow.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 600 PM CST Fri Dec 30 2022
Terminals KABR,KATY,KPIR,KMBG
Low clouds and fog across northeast South Dakota (KABR/KATY) and
west central Minnesota are expected to fill in and spread west
toward the KPIR/KMBG terminals over central and north central
South Dakota overnight. Expect LIFR, or perhaps even VLIFR, at
times in dense fog and very low stratus.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 6 AM CST /5 AM MST/ Saturday for
SDZ003>011-016-017-021-036-037.
MN...None.
&&
$$
UPDATE...Dorn
SHORT TERM...TDK
LONG TERM...Connelly
AVIATION...Dorn
AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
837 PM EST Fri Dec 30 2022
.SYNOPSIS...
A storm system and associated weak cold front moves across the
area for New Years Eve, bringing the next chance for rain.
Drying out and remaining warm Sunday through early next week.
Rain chances increase once again by the middle of next week with
a second, stronger cold front approaching the region.
&&
.NEAR TERM /THROUGH SATURDAY/...
As of 835 PM EST Friday...
Latest analysis reveals an inverted/coastal trough along/just
offshore of the coastal Carolinas this evening. To the west, a
weak cold front extends from western QC/ON into the lower and
middle MS Valley, with a secondary weak sfc low lifting along
the front over the Tennessee valley.
Forecast is in good shape at this hour. Clouds have increased as
expected this evening, and will continue to thicken and lower
overnight. Light isentropic overrunning along the coastal trough
will bring some light showers to coastal NE NC and southside
hampton Roads after midnight. A second area of weak shallow lift
will result in some sprinkles or very light rain over the VA
piedmont mainly south of US-460 late tonight, but otherwise
expect inland areas to remain dry tonight.
WAA will also allow for fog to develop late, mainly along and
just west of the encroaching coastal front, as it lifts N along
the coastal plain into Saturday morning. Patchy fog will be
possible farther inland to the west of I-95, but expect
widespread fog to develop late tonight, and quite possibly
becoming dense in spots along the SE coast per HRRR and NARRE
trends. Not confident enough to get into any fog headlines at
this stage, but could very well need them along the coast
overnight. Lows tonight into the 40s.
Fog lingers through the morning Saturday before beginning to
lift by late morning- early afternoon, as more widespread rain
moves into the piedmont, and winds become S/increase to 5-10
mph.
A main area of low pressure moves through the Ohio Valley
and into the interior Northeast Saturday, as the secondary low
lifts across the mid-south, reaching, then crossing the local
area through Sat night. Both lows eventually phase Sat night
over the Northeast, which shunts a cold front through the area.
Made some minor modifications to PoP timing with the evening
update. First batch of light overrunning showers lift along the
coastal front over the coastal plain late tonight, while some
spotty light showers or sprinkles lift across the piedmont. As
the main slug of isentropic upglide/overrunning moisture arrives
and lifts across the area ahead of the approaching upper trough
tomorrow afternoon and evening, pushed likely to categorical
PoPs across the region from NW to SE from late Saturday morning
through Saturday night. A few rumbles of thunder cannot be
ruled out across far E/SE portions of the FA by Sat evening, as
the secondary low drags a warm front and some weak (mainly
elevated) instability into the area. However, a weak in-situ
wedge should keep much of any modest instability confined to our
south.
Any showers taper off from SW to NE by around midnight. Overall,
numerical guidance continues to lower total QPF, which now
stands ~0.3-0.7" (highest across the SE half of the area). Some
locally higher amounts are possible, again mainly across the SE
one-third of the area. Highs Sat in the upper 50s NW to upper
60s SE. Clouds begin to clear just as we ring in 2023 Sat night
into Sunday morning, with expected overnight lows in the mid 40s
NW to lower 50s SE.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 255 PM EST Friday...
High pressure remains centered offshore through mid-week. Dry
weather returns New Year`s Day with mostly sunny to partly cloudy
skies. Given sunshine, W downsloping winds, and any cool air lagging
behind the weak cold front, expect highs to be above guidance on New
Year`s Day in the mid 60s N to upper 60s to near 70F S. Mostly sunny
early Mon with cirrus moving in from W to E during the afternoon.
Again, went above guidance for Mon given SW winds and sunshine as
well as thickness values supporting warmer temps. Highs Mon in the
mid 60s NE to upper 60s to around 70F SW. Lows in the upper 30s to
lower 40s Sun night and mid 40s (lower 40s over the Eastern Shore)
Mon night due to clouds increasing overnight.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 255 PM EST Friday...
The ridge amplifies over the East Coast Tues before shifting
offshore late Tues through Thurs. This will result in above normal
temps continuing through mid-week. Low pressure tracks well NW of
the area through the W Midwest Tues. The trailing cold front will be
slow to cross the area with at least one more low likely forming
along the front from mid-late week. However, confidence on location
and timing of the secondary low remains low. Nevertheless, PoPs look
to increase Tues evening, continuing through early Thurs, with the
best chance of showers Wed (likely PoPs). Given days of WAA,
dewpoints rise into the lower 60s Wed which may allow for some
storms to develop. However, given that this will be early Jan and
confidence in the position and track of any secondary low remains
low, will hold off for now in adding thunder to the forecast. The
cold front pushes through Wed night with a return to near normal
temps by late week.
Highs in the upper 60s to near 70F Tues, upper 60s to lower 70s Wed,
mid 50s NW to lower to mid 60s SE Thurs, and mid to upper 40s NW to
lower to mid 50s SE Fri. Lows in the mid to upper 50s (perhaps 60F
in spots) Tues night, mid 40s NW to lower 50s SE Wed night, lower to
mid 30s NW to lower 40s SE Thurs night, and mid to upper 20s NW to
lower to mid 30s SE Fri night.
&&
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
As of 705 PM EST Friday...
VFR conditions across area terminals early this evening will
give way to gradually deteriorating flying conditions through
the night, with poor flying conditions expected on Saturday.
Increasing clouds this evening tonight, particularly after
midnight, with CIGs remaining mainly VFR until around midnight
for most terminals, except for MVFR and some spotty showers
developing along the immediate coast). After 06z/1 AM EST,
expect IFR/LIFR CIGs to develop E VA/NE NC along an encroaching
coastal front, with lowering CIGs spreading farther inland by
sunrise. There will likely be 1-2 hours of MVFR CIGs between the
VFR and IFR/LIFR transition. Fog will also develop after
midnight, initially near the coast, with fog also spreading
inland into Sat morning. Some patchy drizzle/light rain possible
across the piedmont overnight, but otherwise remaining mostly
dry tonight.
Lowest VIS/CIGs look to be along and E of the I-95 corridor
where areas of fog appear likely, with guidance trending toward
dense fog likely developing along the coastal terminals after
08-10z. VIS and CIGs look to drop into LIFR (LCL VLIFR) late
tonight through mid- morning Saturday. As rain moves in from
the west, expect fog will diminish a bit by late morning/early
afternoon inland and from mid to late aftn along the coast.
However, expect CIGs to remain in IFR/LIFR range through the
day. Winds remain light and variable (or calm) overnight, and
become S 5-7 kt by Sat afternoon.
Outlook: IFR/LIFR conditions continue through early Sunday
morning as a cold front crosses the region. VFR conditions look
to return through Sunday morning. VFR conditions then persist
through the middle of next week, as high pressure rebuilds over
the mid-Atlantic from the W-SW.
&&
.MARINE...
As of 255 PM EST Friday...
Upper air analysis shows a trough over the central CONUS and a
strong ridge off the SE coast. Surface high pressure, centered just
offshore this afternoon, will slowly translate eastward tonight as
weak surface low pressure along the Gulf Coast begins to lift NE.
Local winds are generally S 5-10 kt, with southern waters showing
more of an easterly component. Waves are 1 foot or less with seas 2-
3 ft.
The surface low is forecast to move into the Ohio Valley by Saturday
morning and into western NY by the evening, bringing a cold front
across the area overnight. Warm advection over the cooler waters
will bring the chance for marine fog tonight into Saturday.
Southerly flow increases to 10-15 kt by late Sat afternoon and
averages ~15 kt in the rivers, bay, and sound with 15-20 kt offshore
from the evening into the overnight ahead of the front. Winds become
W ~15 kt behind the boundary but models continue to show little in
the way of cold advection and only marginal chances for winds above
SCA thresholds. Seas are forecast to increase to 3- 4 ft on Saturday
with guidance continuing to show the potential for seas to build to
4-5 ft well offshore. Waves increase to 2-3 ft Saturday night before
falling back to 1-2 ft by Sunday. Will hold off on any SCA headlines
for the Atlantic waters with this forecast given the tendency for
wave guidance to over perform reality in SW flow events.
High pressure builds in behind the front with generally tranquil
weather expected through Tuesday before another system impacts the
region mid to late week.
West winds will gradually diminish to 10-15 kt by late Sun aftn-Sun
evening, and become SW 5-10 kt Sun night. Seas will subside to 2-3
ft by Sun night. Sub-SCA conditions are expected on Mon/Tue.
&&
.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.
&&
$$
SYNOPSIS...RMM
NEAR TERM...MAM/RMM
SHORT TERM...RMM
LONG TERM...RMM
AVIATION...MAM/RMM
MARINE...RHR
AREA FORECAST DISCUSSION
National Weather Service Bismarck ND
938 PM CST Fri Dec 30 2022
.UPDATE...
Issued at 936 PM CST Fri Dec 30 2022
Stratus and areas of fog continue to expand across much of central
and eastern North Dakota this evening, as well as portions of
western ND. Adjusted the forecast based on latest imagery and
trends. Thus far will hold off on any fog headlines with observed
visibility greater than 1-2 miles and web cam imagery not
indicated a need yet. Will continue to monitor.
UPDATE Issued at 548 PM CST Fri Dec 30 2022
Main forecast challenge tonight will be low stratus and fog
expanding across much of the area, lingering central and east
Saturday morning and possibly into the afternoon some areas.
Utilized a blend of the HRRR and NBM 4.1. Will definitely be
making adjustments to sky cover and fog coverage through this
shift this evening based on observations and trends.
&&
.SHORT TERM...(This Evening through Saturday)
Issued at 213 PM CST Fri Dec 30 2022
Relatively weak zonal flow persisted aloft, which will aid in
returning stratus and fog tonight across much of the state.
Southerly flow at the surface continues ahead of a weak low that
will cross the state tomorrow, bringing a slight chance of light
snow across areas near the International Border.
This afternoon, stratus had eroded over most of western and
central North Dakota, lingering in the far north and the James
River Valley. Patches of stratus are still present in south
central North Dakota where the dew point depression remains fairly
small. It looks likely that stratus and fog will again develop as
temperatures cool later this evening. High-res guidance has been
bullish on developing stratus as early as late this afternoon,
however this may be a bit early and widespread development should
wait until what little boundary layer mixing exists diminishes
with loss of insolation.
Tomorrow, cloud cover and fog should be focused mainly central to
east as the surface low should clear out the west. Added a slight
chance of light snow along the low over far northern North Dakota,
but any accumulations should be very light.
.LONG TERM...(Saturday Night through Friday)
Issued at 213 PM CST Fri Dec 30 2022
There is a chance of accumulating snow in southeast North Dakota
Monday and Tuesday, but the probability of heavy snow remains
below 30%.
Cool high pressure will be in place on Sunday in the wake of the
previous shortwave. Afternoon forecast highs range from 15 to 25.
A deep trough will dig out of the Four Corners region with a
shortwave and surface low moving out of Colorado on Monday. The
track of this Colorado Low has been somewhat questionable this
past week, but seems to be converging on a southward track,
influenced by a northern stream shortwave which should phase with
the Colorado wave and ultimately keep it south of most of North
Dakota. Southeast North Dakota remains under modestly higher
probabilities from recent ensemble runs to receive accumulating
snow, with LaMoure, Dickey, Logan, McIntosh in the 15-25% range to
see greater than 6 inches. There isn`t a large drop off in
probabilities from 2 or 4 inches up to at least 6 or 8 inches,
which speaks to the likelihood of a strong northwest gradient in
snowfall accumulation, where areas may see heavy snow or nearly
nothing, and the probability of something in between is low. While
low visibilities with blowing snow would be a concern if this
northern track does produce snow in southeast North Dakota, the
fact that most guidance keeps snow south of the South Dakota
border (and therefore the greater pressure gradient), the
conditional probability of blowing snow looks low at this time.
The forecast behind this system is dry for now with northwest flow
possibly leading to some ridging takes hold. Cool temperatures
prevail under this flow as well, with CIPS analogs favoring below
normal temperatures through the middle of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 548 PM CST Fri Dec 30 2022
IFR to LIFR conditions in stratus and fog will quickly
redevelopment this evening over central and eastern terminals of
KJMS, KMOT, and KBIS. KDIK will also see a period of MVFR to IFR
stratus this evening before conditions improve there overnight as
winds become more westerly. KXWA should remain VFR. Conditions
will improve for KMOT and KBIS after 15Z Sat morning, and for KJMS
after 18Z Sat afternoon.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...NH
SHORT TERM...AE
LONG TERM...AE
AVIATION...NH
Area Forecast Discussion
National Weather Service Grand Forks ND
958 PM CST Fri Dec 30 2022
.UPDATE...
Issued at 955 PM CST Fri Dec 30 2022
Fog is the main issue overnight into Saturday morning. After
initially seeing some spots in the 1/2 to 1/4SM range in fog near
00z, there has been a slight increase in south-southeast winds
into the 10-20 kt range in E ND, where HRRR and NBM suggested the
best chance for low vsbys overnight. Lowering vsbys in fog
certainly still possible overnight but less clear if we will get
into dense fog range. Areas of fog covers much of the fcst area
and will leave as is. Temps not dropping much overnight.
UPDATE Issued at 602 PM CST Fri Dec 30 2022
Per NBM and consort vsby forecasts tonight it will be a foggy one
for many areas with potential for dense fog with highest
percent chance west of the Red River. Considerable low level
moisture stuck in the boundary layer with a light south wind.
Areas that did clear out a bit this afternoon (DVL and PKD) will
cool down to the dew pt and likey fog in too. Expanded fog mention
to inclue most of the forecast area into Saturday morning.
&&
.SHORT TERM...(This evening through Sunday night)
Issued at 127 PM CST Fri Dec 30 2022
Key Messages:
1.) Mostly quiet weather will continue for the short term period.
2.) Snow and freezing drizzle are possible at times through
Sunday night. Widespread impacts are not anticipated at this time.
Discussion...
The surface pattern is dominated by a weak pressure gradient over
our area, contributing to weak southerly winds this afternoon. A
thick stratus deck continues to linger around the area. Within
this stratus, areas of flurries are possible however impacts will
remain minimal.
For Saturday, a weak shortwave-clipper will progress through the
region. Dry midlevels should inhibit precipitation impacts. At the
moment, the greatest chance for snow is closer to the
international border, especially around the Turtle Mountains.
Sunday will feature more of the same of the recent pattern. Mild
temperatures with little to no accumulating snow/rain. The pattern
does begin to shift as we approach the long term period as we
shift to southwest flow.
.LONG TERM...(Monday through Friday)
Issued at 127 PM CST Fri Dec 30 2022
Primary focus continues to be on the track/evolution of the system
early next week and any potential for winter travel impacts.
Regarding the system Monday into Tuesday: Trends have started to
favor a southern track placing the highest probability for warning
impacts south of our CWA (though there is still 10-20% chance based
on combined ensembles in our far southern CWA). The probability for
3" or greater snowfall is also south of our CWA based on the ECMWF
ensemble, but GEFS still maintains probs for 3"+ in the 30-50% range
along and south of the I-94 corridor in our CWA. This southern shift
in NBM reflects the ECWMF ensemble tends and makes sense considering
the larger scale/progressive mid level flow across the CONUS and
less amplified ridging to the east. As the pattern is set up a
stronger system farther north needs more amplified ridging ahead of
it to slow it down and turn north. Ultimately we still have some
potential for winter impacts within our area (particularly in our
south), and I don`t want to completely discount the possibility for
additional shifts in track or even mesoscale forcing on a smaller
scale that could still lead to localized warning impacts. A lot can
still change at this range.
Progressive mid level flow continues through the long range with
shortwave ridging followed by westerly zonal/split-flow by the end
of next week. No impactful weather is anticipated through the rest of
the long range periods and NBM favors dry conditions/no measurable
snowfall. While a few days may feature highs in the single
digits/lower teens this is still not outside of what could be
considered "seasonal", and any nights that clear out have potential
for lows in the negative temperatures in the single digits mid to
late next week (again not outside of seasonal ranges). Colder arctic
air will remain bottled up in northern Canada and without an
amplification of the mid level pattern we are not likely to see
deeper cold arrive during the next 7 days.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 602 PM CST Fri Dec 30 2022
Poor flying conditions into Saturday either due to IFR ceilings
and/or IFR vsbys in fog, potential for LIFR. Improvement may be
slow on Saturday.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
&&
$$
UPDATE...Riddle
SHORT TERM...Perroux
LONG TERM...DJR
AVIATION...Riddle
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
459 PM CST Fri Dec 30 2022
...AVIATION UPDATE...
.DISCUSSION...(This evening through Friday)
Issued at 248 PM CST Fri Dec 30 2022
Key Messages:
* Nice weekend with above normal highs in the 40s south central
Nebraska to near 50 over north central Kansas.
* Big Monday into Tuesday storm system, but plenty of uncertainty
regarding storm track. At this time the heaviest snow appears to
be north of our area, perhaps more of a freezing rain event for
much of our area (possibly a pretty impactful freezing rain
event).
* Colder for several days next week on the back side of this
storm system.
Weekend...
There will be zonal flow across the middle of the country and then
a bit of upper ridging as the next upper trough digs over the
west coast. This will make for a warmer than normal weekend. Any
remaining snow cover should melt except for some of the bigger
piles and drifts.
Monday into Tuesday Winter Storm System...
The same model trends from the past few days continue. The GFS and
GEFS continue to be the furthest northwest with the 500 mb upper
low track, the 12/30 12Z GFS taking the upper low from northeast
Colorado towards Valentine, NE. On the other hand, you have the
12/30 12Z ECMWF that takes the 500 mb upper low more easterly out
of Colorado on a track along the NE/KS state line towards Nebraska
City, thus giving our forecast area much more wintry
precipitation, especially freezing rain. The Canadian model falls
somewhere in between.
A long look at the 50 ECMWF ensemble members indicate that the
ECMWF deterministic run is more in line with the furthest
southeast cluster of ensemble storm tracks, while over half of the
overall ECMWF ensemble storm tracks are further northwest.
Consequently, with only the southern most ensemble members getting
heavy snow down into the heart of our forecast area, it is
currently more likely that the heavy snow will be north of our
area and thus freezing rain may be our biggest concern with this
system. It`s still far enough out that things could shift south
towards the more southern model solutions, which could give us an
impressive and memorable winter storm event of both ice and snow.
However, at this time at least some ice issues are the primary
concern with the snow probably being more of an issue across our
far northern zones and points north from there. Keep up to date
with the latest forecast and hopefully we will start having more
certainty regarding the storm track by this weekend.
The storm will likely last into Tuesday, which will be colder on
the back side of this system. There does appear to be wind with
this winter storm, but not as much wind as we have had with some
of our recent storms, probably more in the 20 mph gusting 30 mph
range. However, this is more than enough wind to cause problems if
we do end up getting an icing event.
Wednesday and Thursday...
We should be colder and likely below freezing for highs for
anywhere that has fresh snow cover, but we are not going back into
the deep freeze with this one.
Friday...
We should moderate fairly quickly as an upper level ridge moves in
pushing highs back above freezing.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday)
Issued at 445 PM CST Fri Dec 30 2022
The forecast challenge for tonight will be if the area sees and
BR from the melting snow today. The NAM is the most aggressive
and saturates the SFC. The HRRR SFC vis product is only show 6 to
8sm in BR. The RAP and GFS hint at some moisture at the SFC, so
will go with 6SM BR for now. Forecast mid-level ceilings tonight
along with SFC winds becoming more southwesterly should keep FG at
bay. A weak LLJ will be over the area tonight which will cause
some sheer, but not enough to put a LLWS remark in the TAFs.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
DISCUSSION...Wesely
AVIATION...Beda
Area Forecast Discussion
National Weather Service Lincoln IL
815 PM CST Fri Dec 30 2022
.SYNOPSIS...
Issued at 311 PM CST Fri Dec 30 2022
Rain east of I-57 will gradually come to an end Friday night,
while dry conditions will continue west. Aside from a slight
chance of showers Saturday evening with a weak warm front, dry
weather is forecast to continue through at least Monday morning
when the next system approaches from the southwest.
&&
.UPDATE...
Issued at 813 PM CST Fri Dec 30 2022
Light to moderate showers continue roughly along and east of a
Pana to Rantoul line this evening and will persist several more
hours. Precip should exit the state by around midnight. Meanwhile,
surface high is centered near Quincy this hour and will gradually
spread east across central Illinois overnight. At least patchy
fog development remains a concern within the weak winds and humid
boundary layer conditions, though guidance has been backing off on
the fog threat some. Latest NBM shows probs of visibility less
than a mile generally at 20-30 percent or less across the forecast
area.
&&
.SHORT TERM...(This evening through Saturday)
ISSUED AT 311 PM CST Fri Dec 30 2022
DESI`s cluster analysis suggests good agreement in the upper level
synoptic pattern in the short term, with only two 500hPa height
clusters for days 1 and 2 each showing a continuation of SW flow
across the MS Valley ahead of a negatively tilted trough meandering
gradually east. The moisture axis which mid level water vapor
imagery suggested stretched northward into IL from the Gulf of
Mexico is projected to finally exit our area, bringing an end to the
precipitation in our SE counties, late tonight. However, a weak
perturbation diving southeast along the back of the upper trough
could spark a couple showers Saturday afternoon before dryer air
filters in from the west. The CAMs depicting simulated
reflectivities across our west have these showers mainly west of
I-55 - in areas that will have theoretically received little rain
from our current weather maker. Behind these showers, temperatures
are forecast to climb tomorrow afternoon/evening as warm air
advection begins to gradually overspread the Midwest well in
advance of the next storm system taking shape to our west. Though
it`ll be cool tomorrow relative to our past couple days of warm
weather, our highs are forecast to be in the mid to upper 40s
which is around 10-12 degrees above climatological normal; for
reference, the average high on December 31st is 35F in Lincoln.
Both high and low temperatures tomorrow will be a challenge, though,
as cloud cover remains a source of uncertainty. With some rain
continuing in our far southeast counties overnight, cloud cover
should inhibit surface cooling for radiation fog, though saturation
of the column by falling rain could be sufficient for patches of
reduced visibilities, especially early in the night; further west
where low cloud cover is more limited, radiational cooling could
bring temperatures down to the dewpoint and result in fog,
depending on whether winds become light enough. Largely due to the
NAMNest and HRRR which bring visibilities down to less than a
quarter mile in spots, HREF guidance forecasts a gradient in
probabilities for sub 1 mile (1/4 mile) visibilities from 50%
(40%) in our E to around 20% (10%) in our W CWA for early tomorrow
morning. Depending on whether this fog materializes and how long
it takes to burn off, especially east of I-55 where a greater
depth of the column could be saturated, temperatures may cool less
and warm less than forecast tonight and tomorrow.
.LONG TERM...(Sunday through Friday)
ISSUED AT 311 PM CST Fri Dec 30 2022
Main concerns during the extended forecast period are:
1. Flooding Potential
2. Severe Potential
Deterministic models and their ensembles remain in general agreement
in the upper pattern through the weekend, with uncertainty becoming
more apparent by Monday, when a couple distinct scenarios become
plausible as a storm system evolves across the Great Plains. Zonal
500hPa flow across the Midwest is forecast to come to an end by this
time, as each cluster solution suggests amplification of the Rossby
Wave with ridging east of the Plains and a trough somewhere between
the Great Basin and Western/High Plains. The differences between
the clusters is primarily driven by timing of the trough`s eastward
progression, with the EPS driving the slower solution and the
Canadian and GFS ensembles dominating the faster scenario.
Thereafter, uncertainty in what happens with the upper large-scale
pattern and hence any surface weather-makers increases, with the
European ensemble generally tending towards a more quickly
weakening trough over the Midwest/Great Lakes.
Surface cyclogenesis appears likely on Monday, but where and how
quickly it occurs will be a function of the upper trough`s strength
and location. The deterministic CMC and GFS, which each are near the
center of the cluster phase space and hence represent fairly well
the mean of the grand ensemble for at least the upper level pattern
for Monday and Tuesday, each have a surface cyclone forming beneath
a 500mb vort max ejecting northeastward out of the Plains into the
Midwest Monday evening. The ECMWF and GFS have this low tracking
through eastern IA, while the CMC has it crossing central/western
IL. Ultimately, the exact track will matter a whole lot for both
rain amounts and potential for strong thunderstorms, along with
temperatures.
1. Our first concern with this system will be flooding potential. A
potentially robust LLJ developing ahead of the surface cyclone is
expected to advect an impressive low level moisture plume into the
MS and Ohio Valleys from the Gulf of Mexico, with the mean of the
EPS suggesting PWATs around 300% of normal by Monday evening. In
fact, southeast IL will have around a 60-70% chance for PWATs
greater than 1.50" (the record for Jan 2 in Lincoln is 1.05"). Both
the GFS and CMC have a swath of 2" or more of precipitation falling
in a single 6 hour period Monday evening, though they disagree on
where this will occur which is probably the reason that NBM has a
broad area of probabilities from 15-25% for greater than 2" of rain
across central IL. FFG is around 2.25" in 6 hours or 1.75" in 3
hours, so how quickly this rain falls will bear watching, especially
given some of the frost depths measured this morning; theoretically,
the warm weather between now and the time of heaviest rain will
completely thaw the ground across the board, but if it doesn`t then
even non-urban surfaces may act hydrophobically and flooding could
be a bigger threat than it currently appears.
2. Severe potential for this system is not looking overly
impressive, though still a lot of uncertainty exists. The grand
ensemble (GE) mean suggests 100 to 150 J/kg of SBCAPE overspreading
central IL Monday afternoon and evening, while the 90th percentile
has close to 400 J/kg in our far south CWA. The GFS has around 50 kt
of 0-6 km shear over Lincoln during the same time frame, which
should be sufficient for sustained convective activity. However, the
location and strength of the surface low will largely govern how
much shear (and instability) our area experiences, and given
instability is looking lackluster we`ll need to have quite a bit of
shear to overcome that for organized thunderstorms capable of
generating severe weather. The SPC has kept the northern extent of
their day 4 convective outlook just south of our area, clipping just
the far southern tip of the state, and with this we agree. As model
agreement increases and details in the evolution of this system
become apparent with time, we`ll have more to discuss in regard to
severe potential.
Otherwise it`ll likely be breezy Monday going into Tuesday as
surface pressure gradients tighten with the passage of the low to
our northwest. The GFS and EPS ensembles have peak 6 hour wind gusts
increasing to 35+mph during this time period, so south/southwest
gusts to 40 mph (outside of thunderstorms) appear a distinct
possibility Monday night and/or Tuesday. Behind the front, which is
projected to cross the region Tuesday or Tuesday night, cold air
advection will bring an abrupt end to the 25+ degree above normal
temperatures we`ll have to start the work week with overnight lows
Wednesday morning expected to drop into the low 30s and perhaps even
the 20s west of the IL River. By Wednesday afternoon, 75% of the GE
have 850mb temperatures less than -4C. Additionally, a number of
ensemble members have sufficient low level moisture that should
enough sunshine occur for steep lapse rates off the surface, parts
of the area could see snow showers on Wednesday and perhaps even on
Thursday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 521 PM CST Fri Dec 30 2022
Showers continue across portions of east central Illinois this
evening but should taper off by late this evening. High pressure
will build in from the west overnight allowing light northwest
winds to become light and variable. Fog and low stratus will then
develop overnight. Fog is expected to be thickest where the rain
is currently occurring. Winds will set up out of the SE Saturday
and expect conditions to improve back to VFR by late morning.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Deubelbeiss
SYNOPSIS...Bumgardner
SHORT TERM...Bumgardner
LONG TERM...Bumgardner
AVIATION...Deubelbeiss
Area Forecast Discussion
National Weather Service San Diego CA
230 PM PST Fri Dec 30 2022
.SYNOPSIS...
A strong cold front moving down the West Coast tonight will bring
increasing chances for rain over and west of the mountains Saturday
afternoon. Strong winds and heavy rain will move across the region
Saturday night when road flooding is most likely. A Flood Watch is
in effect for all coastal, valley and mountain zones Saturday night.
Gale Warnings were issued for the Coastal Waters. Next week will
remain active as a series of Pacific disturbances make landfall on
the West Coast.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
*** Flood Watch issued from 6 PM Saturday to 2 AM Sunday ***
Details below.
A deep cloud layer blanketed most coastal, valley and mountain areas
below 5,500 feet this afternoon. In contrast, the higher mountains
and the deserts were sunny.
The band of rain and mountain snow over northern CA this morning
crept a little farther south this afternoon. At 2 PM the southern
edge of the precipitation band had reached Lake Tahoe. The rain band
and the associated AR will trek southward tonight and Saturday,
crossing Southern California Saturday night. The timing and
intensity of this cold front hasn`t changed.
The rain here in SoCal will start to increase in coverage midday
Saturday, mostly in Orange and San Bernardino Counties. The highest
rain amounts on Saturday will be on the south and southwest facing
mountain slopes of the San Bernardino County mountains where strong
southerly 850 mb winds of 20-30 kt will produce orographic rain
amounts of a 1/2" from the LA County line eastward to Crestline.
This includes Lytle Creek and I-15 in the Cajon Pass. Rain shadowed
areas of the Inland Empire will not see much if any rainfall on
Saturday, anywhere from a trace to a few hundredths of an inch. The
same goes for southern San Diego County near the Mexican Border, and
all desert areas Saturday.
The AR then moves across SoCal Saturday evening. It will move across
SBD and ORA counties in the evening, and then across Riverside and
San Diego Counties through midnight with a core IVT of 400-700
kg/m/s. The HRRR and WRF model rain rates in the San Bernardino and
Santa Ana Mountains of 0.50"-0.80"/hr are most likely between 7 PM
and Midnight Saturday. A Flood Watch has been issued for all
coastal, valley and mountain areas from 6 PM Saturday to 2 AM
Sunday. This is when road flooding and mud/debris flows will be most
likely.
HRRR and WRF rain totals of 2-4" are projected on the south and
southwest facing slopes of the San Bernardino Mountains. Elsewhere
the southwest facing slopes in San Diego, Orange and Riverside
Counties should see 1.5-3 inches. Coastal and valley areas will see
0.75-1.5 inches. The high deserts around 0.50" and the lower deserts
from 0.25-0.50 inches.
This will be a warm storm with snow levels above 7,500 feet so most
of the precip will fall as rain. Snow impacts will mostly be
confined to areas above 8,000 feet where several inches will
accumulate. Snow levels fall to 6,000 feet late Saturday night with
the passage of the cold front, but by then the heaviest
precipitation will have moved east.
The San Diego River at Fashion Valley is forecast to reach 7.8 feet,
high enough for water to flow over the low water crossings at
Fashion Valley Road, Avendia Del Rio and Camino De La Reina.
A High Wind Watch is in effect for the San Bernardino Mountains and
High Deserts from 10 AM to 10 PM Saturday.
The storm will move quickly east Sunday morning followed by a brief
period of dry weather into early Monday. Another shortwave in the
Pacific jet will bring rain chances back into SoCal Monday night and
Tuesday. This is a weaker system, but still has plenty of moisture
for another round of widespread rain and mountain snowfall. A lower
snow level (5000-5500 ft.) should result in few inches of snow below
7,000 feet.
There are more perturbations in the strong zonal jet crossing the
Pacific later next week, so rain and snow chances remain in the
forecast through next Friday.
$$
.AVIATION...
302130Z...Coast/Valleys/Mountains...Widespread BKN/OVC clouds will
continue through Sat with variable bases 1500-3500 ft MSL and areas
of terrain obscurations layered at times to 25000+ feet MSL. Local
VIS 2-4 miles will occur due to ISOLD -SHRA and BR below the clouds.
South/southwest winds 15-25 kt with gusts 30-40 kt will develop in
the San Bernardino County Mountains after 17Z Sat and spread to the
Riverside County and San Diego County Mountains after 20Z Sat.
Deserts...SCT-BKN clouds at/above 10000 feet MSL will continue
through Sat with unrestricted VIS.
&&
.MARINE...
A storm system from the northwest will bring strong winds and
hazardous seas Saturday evening through Sunday evening. Northwest
winds of 20 to 30 kt with gusts 35 to 40 kt are expected over the
waters. A Gale Warning has been posted for the outer and inner
waters. Combined seas of 10-15 feet are likely Sunday, highest in
the outer waters, with the dominant periods 8-10 seconds.
&&
.BEACHES...
A west-northwest swell of 10-15 feet from 280-290 degrees at 8-10
seconds will produce high surf at the beaches Sunday through Monday,
with 5 to 8 feet in Orange County and 6-9 feet in San Diego County.
A High Surf Advisory is in effect Sunday through Monday. The
relatively short period of the swell will be the limiting factor
despite high seas in the coastal waters. Surf will gradually
diminish Monday.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from Saturday evening through late Saturday night
for Orange County Coastal Areas-Orange County Inland Areas-
Riverside County Mountains-San Bernardino County Mountains-
San Bernardino and Riverside County Valleys-The Inland
Empire-San Diego County Coastal Areas-San Diego County
Mountains-San Diego County Valleys-Santa Ana Mountains and
Foothills.
High Surf Advisory from 4 AM Sunday to 6 PM PST Monday for
Orange County Coastal Areas-San Diego County Coastal Areas.
High Wind Watch from Saturday morning through Saturday evening
for Apple and Lucerne Valleys-San Bernardino County
Mountains.
PZ...Gale Warning from 8 PM Saturday to 8 PM PST Sunday for Coastal
Waters from San Mateo Point to the Mexican Border and out
to 30 nm-Waters from San Mateo Point to the Mexican Border
Extending 30 to 60 nm out including San Clemente Island.
&&
$$
PUBLIC...Moede
AVIATION/MARINE/BEACHES...Maxwell