Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/12/23
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
523 PM CST Sat Mar 11 2023
.SHORT TERM...(This Evening through Sunday)
Issued at 242 PM CST Sat Mar 11 2023
KEY MESSAGES:
1. Windy and cold Sunday, with scattered flurries possible.
2. Roller-coaster temperatures this week, with a cold Monday, warmer
Tuesday-Wednesday, then cooling down again late week.
3. Transition to colder air mass will bring our next chance of
wintry precipitation somewhere in the Thursday timeframe, possibly
starting as a mix before changing to more snow.
--------------------------------
REST OF THIS AFTERNOON: Low pressure responsible for our snowfall
today is currently still spinning over western ND this afternoon.
Light snow lingers over portions of our MN/IA counties as of 20Z,
mainly east of US Highway 59 (Marshall-Worthington-Sioux City). This
should continue to trek east and out of our forecast area through
the balance of the afternoon.
TONIGHT-SUNDAY: The low pressure tracks east through southern ND and
into central MN tonight, with the associated cold front pushing east
across our forecast area this evening. Post-frontal west-northwest
flow will increase in our far west by late evening, with stronger
winds advancing east and weakening slightly as they reach the I-29
corridor around 12Z, and continuing to weaken slightly as they
progress into southwest MN/northwest IA Sunday morning. Have seen
some gusts topping 40kt/46mph in southeast MT/northwest SD this
afternoon, and if we were able to fully tap into the 40+kt winds
atop the mixed layer per the latest RAP soundings, could see a
period of advisory level winds in areas along/west of the James
River Valley late tonight into Sunday morning, and will join our
neighboring SD offices with a Wind Advisory from midnight tonight
through 10AM CDT Sunday. Temperatures through most of this area have
warmed into the mid-upper 30s today, and did not receive much new
snowfall either, so while there could be some low drifting, would
not expect blowing snow to be a significant issue.
The colder air will be accompanied by additional stratus spreading
southward into the forecast area later tonight and Sunday, so after
a welcome sunny day for at least western portions of the forecast
area today, clouds will likely be rather abundant again on Sunday.
Not a lot of deep moisture for this to work with, but soundings
indicate the top of the cloud layer could tap into the DGZ, so
scattered flurries seem a possibility near/northeast of a Huron to
Sioux Falls to Spencer line. Colder temperatures and the gusty winds
will make for a blustery day, with highs only in the 20s, and wind
chills in the single digits-lower teens.
.LONG TERM...(Sunday Night through Saturday)
Issued at 242 PM CST Sat Mar 11 2023
MONDAY: Still a cold day with highs again in the 20s, but much less
wind with a surface ridge moving across the area, so will not feel
quite as brisk as Sunday.
TUESDAY-WEDNESDAY: Strong warm front moves across the CWA Tuesday,
with the wedge of warmest air, as much as +10C(!), building into our
southern counties Wednesday. If we were snow-free, this could result
in quite a warm-up, as full mixing could push temperatures well into
the 60s through the Missouri River Valley Wednesday afternoon. Alas,
most, if not all of the forecast area does have some snow cover to
overcome, and the question is how much impact this will have on
limiting our temperatures. Still seeing a broad spread among the NBM
membership, with as much as a 10F difference between the 10th and
90th percentiles on Tuesday, growing to 15-25F on Wednesday. For
both days, the NBM mean remains fairly close to the 50th percentile,
so feel comfortable leaving the forecast as is for now.
WEDNESDAY NIGHT-FRIDAY: Deterministic models are fairly similar in
timing a strong cold front through the forecast area late Wednesday
night-Thursday morning, as a deepening upper trough digs into the
northern Plains from central Canada. These deterministic solutions
alone would lead one to think we could be in store for another
significant precipitation system. However, examining the ensembles
shows that these deterministic solutions are relative outliers on
the high side, with the mean much lower, and a large majority of
ensemble members near or below this mean. That said, it looks like a
pretty good chance for at least some light precipitation, but with
very high uncertainty on amounts at this range.
Late week confidence is much higher that cold air will again settle
into the region, with highs Friday-Saturday potentially as cold, or
colder, than we see to start off the week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 521 PM CST Sat Mar 11 2023
Back edge of MVFR stratus trying to push east of I-29 early this
evening. A secondary reinforcement of this stratus may be possible
keeping stratus near the I-29 corridor for a couple more hours
before clearing.
A secondary cold front arrives later tonight bringing 40+ mph
winds through the Tri-State area into Sunday morning. Also
expecting more stratus to drop southward towards midnight,
thickening through the overnight and remaining overcast for a good
portion of Sunday.
Colder air rotating around the departing upper low moving through
North Dakota will lead to the potential for a few flurries or snow
showers into Sunday.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from midnight CST tonight to 10 AM CDT Sunday for
SDZ038-050-052-053-057>060-063>065-068-069.
MN...None.
IA...None.
NE...None.
&&
$$
SHORT TERM...JH
LONG TERM...JH
AVIATION...Dux
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
855 PM CST Sat Mar 11 2023
.UPDATE...
Issued at 849 PM CST Sat Mar 11 2023
Light to moderate snow has just about filled in across the
northern part of the CWA, namely areas north of I-80. Webcams
across the Rockford metro and vicinity show snow accumulating on
cooler surfaces and even a few roads are beginning to gather a
dusting. Further south, we`re seeing light rain and rain/snow mix
filling in where there`s just enough positive energy above the
surface to melt the snow on its way down. As we continue to cool
both diurnally and dynamically with still a little bit of room
between temps and wet bulbs, we should see the rain/snow line drop
south through the remainder of the evening and into the
overnight. Additionally, many areas across the metro have been
struggling with some dry air through roughly the 800-900mb layer
inhibiting precip aloft from reaching the ground over the past
couple of hours. However, ACARS soundings out of MDW show that
we`ve recently managed to overcome that thanks to modest, albeit
ample, low level warm advection, a tad earlier than RAP and HRRR
soundings were suggesting we would. RAP mesoanalysis places a
notable swath of 700mb f-gen over the central and western CWA on
the leeward side of the encroaching trough which lines up well
with where we`ve been seeing the more moderate snowfall which has
been pulling visibilities down as low as one mile here and there.
This f-gen is expected to continue pushing to the northeast with
the trough through the rest of this evening. The better synoptic
forcing will also eject to the northeast as the trough axis
approaches meaning we`ll likely see the heaviest of the snow over
the next few hours. Snow is still expected to continue through
the night but will lighten up as forcing lets up and we maybe see
little bit of dry advection near 925mb, or so the RAP and HRRR say
though it`s tough to nail down where that`s coming from. All in
all, the forecast through the night looks to be on track.
Doom
&&
.SHORT TERM...
Issued at 308 PM CST Sat Mar 11 2023
Through Sunday night...
A pair of upper level disturbances are noted in the water vapor
imagery across the Plains early this afternoon. The first of
these is currently shifting eastward into the Lower to Mid-
Missouri Valley, while a more pronounced northern stream upper
low is moving eastward into western North Dakota. These features
will play a large role in our sensible weather tonight through
early Monday.
While cloud cover has been, and will continue to be persistent
through the day, warm air advection in advance of the approaching
Mid-Missouri Valley disturbance is helping drive temperatures
well into the 30s (with some low 40s south) as of this writing.
Expect these readings to hold steady in the 30s to around 40 into
early this evening. Precipitation is expected to hold off across
the area through late this afternoon. Thereafter, we should see
the warm air advection driven precipitation shield across IA
steadily translate eastward across the area through the evening
in concert with the parent mid-level disturbance.
While the entire area looks to see precipitation from this event
tonight, overall amounts will be much lower than they were with
Thursdays weather system. However, precipitation types do look to
be a bit tricky again with this event, especially for areas south
of I-80, where warmer boundary layer conditions will reside into
early this evening. These slightly warmer conditions will likely
result in areas south of I-80 onsetting as a period of rain for a
few hours this evening before potentially mixing with a bit of wet
snow later in the evening. Farther to the north, a brief rain
snow mix is possible at onset, but slight cooler conditions should
support primarily wet snow shortly after onset. While some wet
snow accumulations still appear likely tonight, especially for
northern areas, light precipitation rates and marginal surface
temperatures should keep total amounts mainly under 2". In fact,
many areas are likely to see less than an inch, and mainly on
grassy and elevated surfaces!
The main mid-level disturbance (the primary forcing mechanism) is
expected to shift east of the area a bit after midnight tonight.
As it does so, a much drier mid-level airmass is expected to shift
overhead atop a lingering low-level moist layer. In spite of this,
light precipitation is likely to continue across the area overnight
as low-level isentropic upglide continues in this moist layer in
response to the northern stream system shifting into the Upper
Midwest. While precipitation type may continue to support some
light snow overnight, there is concern that the snow quality will
become rather poor overnight, possibly even mixing with (or
changing to) drizzle at times as the much drier mid-level airmass
shifts overhead. This suggests that any additional snow
accumulations late tonight into early Sunday morning may become
minimal.
The lower level moist layer should become deep enough across far
northern IL to support a continued period of snow showers mid to
late Sunday morning as low-level warm air advection
continues. While this is the case, marginal surface temperatures
during the daylight hours will once again limit any minor slushy
accumulations to grassy areas and elevated surfaces. Temperatures
should warm close to 40 early Sunday afternoon, so any lingering
precipitation there will likely fall as light rain. Late in the
day and into the early evening hours, the northern stream system
is expected to drive a cold front eastward across the area. This
may result in a quick moving area of rain and snow showers as the
front interacts with a corridor of steep low-level lapse rates.
Certainly cannot rule out some minor accumulations with this
across parts of northeastern IL, especially if a brief period of
heavy rates materialize, but the main limiting factor for much in
the way of accumulation will be the warm surface temperatures
preceding the front.
Another period of possibly more robust snow showers looks
possible either very late Sunday night, or early Monday morning as
a secondary cold front and an attendant mid level disturbance
drops southward across the area. This potential will have to be
monitored as it could occur during the early Monday morning rush.
KJB
&&
.LONG TERM...
Issued at 221 PM CST Sat Mar 11 2023
Monday through Saturday...
Highlights for the long term forecast period:
* Lingering isolated/scattered snow showers and flurries on Monday
* Unseasonably chilly for the first half of the upcoming workweek;
milder heading into the latter half of the week
* Precipitation likely to return to the area Thursday and/or Friday
The vort max responsible for our late Sunday afternoon and Sunday
night precipitation chances will likely be centered over or near the
southern half of Lake Michigan come Monday morning. This feature
will continue to wander off to the southeast throughout the day on
Monday, and our forecast area will spend the day entrenched within a
cold cyclonic flow regime as the associated low pressure centers at
the surface and aloft remain east of our longitude. The ensuing cold
air advection should ensure that skies remain overcast or mostly
cloudy throughout the day and that high temperatures won`t make it
out of the 30s. Low-level lapse rates will also steepen in response
and should bring about some blusterier conditions for the morning
and afternoon hours on Monday with regular north-northwesterly
gusts into the 20-30 mph range appearing to be likely.
The main question forecast question for Monday is whether there will
be any additional snow showers lingering around and what the nature
of those showers would be like, in terms of both coverage and
intensity. The present thinking is that the residual forcing
associated with the mid/upper-level trough and the steepening low-
level lapse rates should be just enough to support isolated to
scattered snow shower activity in our forecast area on Monday, but
that the relative absence of quality moisture and the overall
magnitude of the forcing at play should limit impacts to just
occasional brief visibility reductions beneath the more coherent
snow showers and perhaps some streaky dustings or coatings of snow
occurring on colder surfaces. The exception to this could be in
portions of northwest Indiana, where marginally favorable lake
effect parameters may be able to support a longer duration snow band
or two that could leave behind a narrow corridor of 1+" of snow on
the ground when all is said and done. However, this is a low
confidence scenario at this vantage point. Considering everything
altogether, maintaining slight chance and chance PoPs across most of
our CWA in lieu of the lower NBM PoPs seemed warranted at this time.
Even if true snow showers didn`t materialize, think that some
flurries may still be wrung out of the overhead stratocumulus deck
over at least a portion of our forecast area on Monday.
The magnitude of cold air advection should wane Monday night, but
there appears to be a decent chance that the low cloud cover
overhead will scatter out to some extent. Low temperatures appear
likely to at least dip into the 20s either way, and if skies do
clear out, then lows in the teens appear very attainable, at least
across interior northern Illinois. High pressure will build into the
region on Tuesday, and while clear skies should allow temperatures
to bounce back a bit, the relatively cold starting point and
marginally cold to neutral thermal advection should still keep
Tuesday`s highs below normal for this time of year. Return flow on
Wednesday will then kickstart the return of warm air advection,
which will be further prolonged into Thursday as a developing
surface low over the Great Plains maintains poleward low-level
thermal and moisture trajectories to its east. A return of 50+
degree temperatures thus appears likely for most or all of our
forecast area on Wednesday and/or Thursday, and it would not be
surprising for some 60+ degree readings to be seen on Thursday as
well if the aforementioned low pressure system is not as progressive
as the fastest ensemble solutions currently suggest (most 12Z
guidance was not that progressive with this system).
The aforementioned developing low pressure system will be spawned as
northern stream and southern stream waves embedded within western
CONUS longwave troughing interact with one another Wednesday into
Thursday. Some forecast guidance is suggesting that these two waves
will phase nicely, culminating in a closed-off upper-level low that
will spiral over the Great Lakes as we head into next weekend. Other
guidance suggests that there won`t be much of any phasing between
these two waves, and whatever low pressure system develops won`t
hang around very long after passing through our area. Either way,
the odds of rain occurring here sometime in the Thursday through
Friday time frame look fairly good for a system that`s still 5-6
days away. Snow can`t be ruled out on the backside of this system,
especially if a closed low does come to fruition over the Great
Lakes, but this is still a lower confidence forecast item that,
along with the finer details of the earlier rainfall, will become
clearer in the coming days as additional forecast guidance continues
to come in.
Ogorek
&&
.AVIATION...
For the 00Z TAFs...
Aviation Forecast Concerns:
* Snow develops this evening, with a period of IFR vis and minor
accumulations overnight. IFR ceilings linger at least into
Sunday morning before improvement to MVFR.
* Snow tapers off by morning and likely becomes a mix of snow and
drizzle. Period of heavier convective rain/snow showers possible
in the afternoon.
* East winds tonight become southeast Sunday morning, then south
briefly Sunday afternoon ahead of a cold front. Winds shift west
behind that front Sunday evening, with some gusts around 20 kt.
Light snow will spread across the area this evening as a mid-
level disturbance currently over IA approaches. There could be a
very brief rain/snow mix as precipitation begins, but should
change to all snow fairly quickly as intensity picks up. The
strongest forcing looks to be from late evening to past midnight,
when IFR visibility and minor accumulations are likely. Weakening
ascent and decreasing saturation in favored snow-growth
temperature levels suggests snow will weaken in intensity by the
pre-dawn hours, with visibilities improving to MVFR. Moist low
levels will likely maintain IFR ceilings into Sunday morning
however.
A second upper trough over the upper Midwest will maintain weaker
forcing across the region through the day Sunday, with lighter
intermittent light snow/flurries. Several models indicate loss of
saturation in the ice-bearing thermals range and thus may see a
mix of light snow and drizzle especially during the midday and
afternoon hours. A period of heavier snow/rain showers is possible
during the mid-late afternoon hours, as low-level lapse rates
steepen ahead of an approaching cold front. Scattered snow showers
may persist behind the front Sunday evening, though with low
confidence in coverage, as somewhat drier air spreads in.
Easterly winds tonight will turn southeast Sunday morning, then
light southerly ahead of the cold front during the afternoon.
Behind the front, winds will shift to the west-northwest, and
will become somewhat blustery with gusts around 20 kts.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Lubbock TX
514 PM CST Sat Mar 11 2023
...New AVIATION...
.SHORT TERM...
(This evening through Sunday)
Issued at 216 PM CST Sat Mar 11 2023
Current RAP analysis has the surface low over eastern Kansas with
west winds across the forecast area this morning and afternoon.
Winds have already begun to increase this morning with 30 to 40 mph
sustained winds and gusts up to 50 mph, especially across the far
southern Texas Panhandle and northern South and Rolling Plains.
Elsewhere winds will be breezy at 15 to 25 mph with some gusts up to
35 mph possible. A Wind Advisory remains in effect until 7 PM CST
across the southwest and south central Texas Panhandle and much of
the South Plains. Temperatures off the Caprock are warming quite
nicely this afternoon into the 80s, with areas along the Caprock
slightly cooler in the 70s.
As of 1 PM CST, the cold front associated with the surface low is
located in the Southern Texas Panhandle over Amarillo. The front is
expected to approach the far southern Texas Panhandle in the next
few hours where the boundary will stall across the northeast zones
as the surface low moves farther east. Temperatures immediately
behind the front across the Texas Panhandle this afternoon are in
the upper 50s to 60s. Therefore, temperatures in the next few hours
may be halted across the far southern Texas Panhandle behind the
fast approaching cold front. Tonight, mostly clear skies and light
northeast to east winds as the front continues to push southward
will give way to brisk temperatures in the 30s to lower 40s. A few
areas across the far southwest Texas Panhandle may approach near
freezing low temperatures by tomorrow morning. Heading into
tomorrow, zonal flow will continue aloft with a few high clouds
possible. The cold front is expected to stall again near the
southwest to western South Plains with west winds and temperatures
in the upper 60s to lower 70s ahead of the frontal boundary.
Otherwise, east to southeast surface winds are expected across much
of the forecast area which will contribute to cooler temperatures in
the upper 50s to lower 60s. A few models have a slight chance for
some light rain showers to generate across the west starting in the
late afternoon hours, mainly along that surface boundary.
&&
.LONG TERM...
(Sunday night through next Friday)
Issued at 216 PM CST Sat Mar 11 2023
A cold front will continue pushing westward across the FA late
tomorrow evening and will reach central New Mexico by Monday
morning. Guidance continues to show the possibility of rain showers
late tomorrow night/early Monday behind the front as a weak upper
short wave moves over the region. Some precip does look to be
possible, but if it occurs it would likely be lighter than portrayed
by the models as the main forcing will be from isentropic lift.
Precip chances will be better late Monday through late Tuesday
morning as a more defined upper shortwave develops near the Four
Corners and pushes southeastward towards the FA. Moisture should
still be in place across the region as surface winds continue to be
out of the southeast. Rain chances will push to our east by midday
Tuesday following the exit of the shortwave.
We will begin a warming trend into the upper 70s/low 80s by
Wednesday as upper ridging sets up over the region. This will
quickly change by Thursday. An upper trough is progged to move into
northern California early Wednesday, amplify, and push eastward
towards New Mexico by late Wednesday evening. A developing surface
low ahead of the upper trough would allow for a windy Wednesday
evening. While models are in agreement with the development and
passing of the upper trough, they disagree on the tilt which, in
this case, would determine the validity of forecasted precip. The
GFS keeps the trough more positively tilted as it approaches the
region and the ECMWF has a neutral to slightly negative tilt. The
positive tilt would result in a dry forecast where as the ECWMF`s
solution would allow for better precip chances. These systems tend
to be more positively tilted and dry, but there is still plenty of
time for the models to smooth out the details. Regardless of the
outcome, the setup would allow for windy conditions on Thursday
morning ahead of a cold front, and windy conditions behind the cold
front Thursday afternoon and evening.
&&
.AVIATION...
(00Z TAFS)
Issued at 514 PM CST Sat Mar 11 2023
VFR prevails for the TAF period. Cold front has crossed KCDS and
will continue to move southward throughout the remainder of the
evening, with winds shifting to the north at KPVW and KPVW prior
to 06Z tonight. Winds will continue to veer during the overnight
hours and into tomorrow with speeds generally around 10 kt.
Sincavage
&&
.LUB WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 PM CST this evening for TXZ021>024-027>030-
033>036.
&&
$$
SHORT TERM...11
LONG TERM....51
AVIATION...09
Area Forecast Discussion
National Weather Service Memphis TN
826 PM CST Sat Mar 11 2023
...New UPDATE...
.UPDATE...
Issued at 819 PM CST Sat Mar 11 2023
Showers and storms have developed this evening across the Mid
South. Strong to severe storms will move into north Mississippi
later tonight with large hail and damaging winds being the main
threat. Following the passage of the cold front, cooler and dry
weather will prevail through midweek. Freezing temperatures will
are expected Monday morning over parts of northern West Tennessee.
&&
.SYNOPSIS...
Issued at 238 PM CST Sat Mar 11 2023
Showers and thunderstorms will move through the Midsouth tonight,
along a fast-moving cold front. A few of these thunderstorms will
be capable of producing large hail, damaging winds and localized
flash flooding, mainly during late evening and early overnight
hours. Showers and isolated thunderstorms may linger over north
Mississippi Sunday morning.
Following the passage of the Sunday`s cold front, cooler and dry
weather will prevail through midweek. Freezing temperatures will
are expected Monday morning over parts of northern West Tennessee.
Freezing temperatures are forecast over most of the Midsouth
Tuesday and Wednesday mornings, with a hard freeze likely over
much of West Tennessee early Tuesday and Wednesday.
PWB
&&
.DISCUSSION...
(This evening through next Friday)
Issued at 238 PM CST Sat Mar 11 2023
Early afternoon GOES water vapor imagery showed a low amplitude
upper level ridge over the lower MS River valley, downstream of
trough axis lifting through the Great Plains. Warm advection
downstream of the trough axis is contributing to modest elevated
instability over the Ozarks, into western portions of the
Midsouth. Convection may be additionally aided by the right
entrance region of a 90kt 250mb jet streak over the lower Ohio
River Valley. Early afternoon SPC Mesoanalysis page showed 60kt
of 0-6km bulk shear over the Midsouth, likely aiding in the
organization and maintenance of showers and thunderstorms.
The midlevel trof will lift into the MS River valley this evening
and early overnight, as diffluent flow flow aloft overspreads the
Midsouth. Showers and thunderstorms will focus along a southeast-
moving surface cold front and attendant frontal wave. 18Z HRRR
depicts modest prefrontal mixed layer CAPE of 500 to 800 J/kg.
Midlevel lapse rates prevail near 6.7 C/km late this evening,
decreasing to around 5.5 C/km overnight. This is about the time
the HRRR depicts a 60kt 700mb speed max arrival, more bowing
structures and tendency for forward-propagating storms. The
implication: A marginal large hail threat over the MS River delta
this evening will likely transition to a marginal damaging wind
threat over north MS overnight. Overnight flooding rain threat may
lessen with the more progressive storm evolution depicted by the
HRRR.
Dry and cooler conditions will prevail from Sunday afternoon
through the middle of next week, as a continental polar airmass
prevails. With dewpoints in the upper 20s to lower 30s, nighttime
freezing temps will be possible as soon as the pressure gradient
relaxes and winds go light. This appears most likely to occur
Tuesday and Wednesday mornings, with hard freezes over West TN,
and at least a light freeze over most of the Midsouth. In the
interim, Monday morning could see temps drop to around freezing
over northwest TN. With strong mixing and winds Monday morning, it
likely feel the coldest morning of the week, with wind chills
dipping to the low 20s from far northeast AR through the MO boot
heel and and far northern West TN. Monday morning wind chills will
drop to the lower 30s over north MS. A Freeze Watch will likely
be issued in a subsequent forecast package.
The next rain event will arrive late Thursday into Friday,
associated with a progressive longwave trough. Severe thunderstorm
threat with this system will likely remain limited, given the
limited time for a robust low level instability axis to develop.
PWB
&&
.AVIATION...
(00Z TAFS)
Issued at 538 PM CST Sat Mar 11 2023
Spotty shower and thunderstorm development is currently ongoing
across the Mid-South and is expected to continue through the
overnight hours, becoming more widespread by midnight. An
approaching cold front will allow for winds to become northerly
at 10-12kts by sunrise. As this front moves through, IFR ceilings
are possible across all sites, but this will only last a few hours
before returning to MVFR by Sunday afternoon.
ANS
&&
.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&
$$
PUBLIC FORECAST...MJH
AVIATION...ANS
Area Forecast Discussion
National Weather Service Pocatello ID
123 PM MST Sat Mar 11 2023
.SHORT TERM...Tonight through Sunday night. Early afternoon
satellite imagery was showing a weak to modest west flow across the
WRN states in the wake of yesterdays storm system. Looking upstream,
a low pressure system was centered off the WRN Canadian coast.
Numerical models show a weak disturbance cycling through the base of
the low into NRN California Sunday morning with attending clouds and
moisture spreading into the region during the day for a chance of
snow showers across the southern and central mountains during the
day. As this disturbance lifts NE Sunday night, the low off the WRN
Canadian coast begins to amplify ingesting more Pacific moisture
into the strengthening SW flow across the region. This should result
in a better chance of seeing snow showers across a broader area of
SE Idaho Sunday night, particularly the CNTRL mountains where 1 to 2
inches of additional snowfall may be realized. Temperatures remain
below normal for this time of year. Huston
.LONG TERM...MONDAY THROUGH NEXT SATURDAY. Active wx remains on tap
for the Mon-Wed timeframe next week, with consensus growing in the
most significant rain/snow falling in a roughly 48 hour period from
Mon eve through Wed eve, courtesy of 2 shortwave troughs ejecting
inland off the Pacific loaded with moisture. This event will remind
us spring is coming, as snowfall accumulations will be HIGHLY
elevation-dependent. Tue, except windy conditions from the SSW, with
the ern Magic Valley and lower Snake Plain downsloped and thus warm
and relatively drier (light showers), with significant snow falling
in the mntns, especially surrounding the Wood River Valley. Most
accumulations will occur above about 6,000 feet. Wed, expect a cold
front shifting strong/gusty winds into the west, and the most
significant snowfall gradually shifting into the ern highlands,
again with most accumulation above about 6,000 feet, with everything
ending Wed night. Storm totals will likely reach 1-2 feet in the
mntns, but an inch or less from the lower Wood River Valley down
across the Magic Valley, Snake Plain, and srn highland valleys as
temps will support mostly rain there. Highs in the 40s, and lows
perhaps not dropping below freezing Mon/Tue nights across the ern
Magic Valley, lower Snake Plain, and srn valleys, combined with
rain, means we will need to closely watch for localized flooding,
likely to a greater extent than what we started to see with
yesterday`s event in a few spots. The ECMWF EFI continues to
highlight climatologically high rain/snow for this event with a more
modest overall response for wind, and our snowfall forecast
currently sits comfortably near the NBM 50th percentile with minor
adjustments made in valley bottoms. Keep in mind the rain/snow line
will fluctuate diurnally between about 5,500 feet and 6,500 feet.
500mb cluster analysis continues to show a hint of uncertainty as to
exactly how quickly the second shortwave will clear out Thu
(currently we are forecasting a mostly dry day), but stronger
consensus in the ensembles by Fri at which point an amplified
(although progressive) ridge will give us a break. 01
&&
.AVIATION...The next 24 hours will be characterized by a break in
impactful wx for southeast Idaho terminals under shortwave ridging,
with moderate to high confidence in VFR cigs/vsbys just about
everywhere along with light winds less than 10kts. Model guidance
does suggest the sfc will be quite moist tonight (supported by
yesterday`s widespread rain and snow), yet most models are not
developing fog/low stratus issues. A hint of low stratus appears in
MOS guidance near KIDA along with some development on the HRRR
between about 08z and 17z Sun AM (especially just west of the
terminal), so while confidence is very low in this occurring
(perhaps a 10% chance), we`ll be keeping an eye on it. Sun, expect
increasing mid-level clouds from SW to NE throughout the day. Precip
will be moving our way associated with the next approaching
shortwave trough, but the HREF suite "washes out" model-simulated
radar echoes as they try to penetrate into the forecast area, with
little consensus on organized rain/snow at any given location
through Sun eve. At this time, confidence is at least moderate in
dry conditions at KPIH, KIDA, and KDIJ, but lower for KSUN and
especially KBYI (where we have gone ahead and introduced VCSH after
13z Sun). Beyond, expect a period of wet, windy, and more impactful
wx for aviation Mon through Wed. 01
&&
.HYDROLOGY...Avalanche debris continues to partially block the Big
Wood River near Hailey threatening a number of homes in the Della
Vista subdivision. Thus the Flood Warning was extended for another
24hrs.
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Portland OR
249 PM PST Sat Mar 11 2023
.SYNOPSIS...A weak atmospheric river and associated frontal system
will impact the region with widespread rain Sunday through Monday,
but river levels are not expected to reach flood stage. Snow levels
will increase to over 5000 feet Sunday morning and afternoon as a
warm front lifts northward across the area. Snow levels will then
fall behind a cold front on Monday, lowering to around 2000 feet
Monday evening. Precipitation should be more disorganized and showery
Monday night through Wednesday before drier and warmer weather
arrives on Thursday due to a transient shortwave ridge passing over
the Pacific Northwest. Chances for light rain return on Friday as a
weak front sweeps eastward across western OR/WA.
&&
.SHORT TERM...Saturday night through Tuesday...Models and their
ensembles remain in agreement for moist southwesterly flow aloft
Saturday night through at least Monday afternoon. It appears moisture
will peak Sunday night into Monday as the polar jet to the north
buckles southward and merges with the sub-tropical jet to the south
and sends a 120-130 kt jet right over Oregon on Monday. This will
help bring a plume of sub-tropical moisture into the region, and the
GEFS/EPS remain in good agreement that IVT values will peak somewhere
between 250-500 kg/ms as a weak atmospheric river impacts
northwest OR and southwest WA. At and near the surface, the
deterministic NAM/GFS/EURO are all showing a warm front lifting
northward across the forecast area Sunday morning with a weak AR
pushing into the area behind the warm front as PWAT values increase
to 0.7-0.8 inches. Overall forcing looks very weak during that time,
suggesting rain will generally be light in intensity rather than
heavy. Hourly rain rates from the HRRR and UWWRF on Sunday only peak
around 0.1-0.15 inches per hour. This is nowhere near enough to
prompt concerns for flash flooding, river flooding, and/or debris
flows. The NBM continues to show snow levels rapidly increasing to
over 5000 feet behind the warm front, thus limiting winter weather
impacts to the high Cascades above pass level. This is good news for
anyone who is planning on driving over the Cascade passes on Sunday,
as precipitation will be in the form of rain or a rain/snow mix
rather than all snow.
However, snow levels will begin to decrease late Monday into Tuesday
morning behind a cold front that is set to push eastward across the
area Monday morning and afternoon. Both the GFS and the EURO depict
much stronger Q-vector convergence and mid-level frontogenesis with
the cold front when compared to the warm front, and the latest CAM
guidance is simulating a large swath of light to moderate stratiform
rain over the area along and ahead of the cold front. This round
of rain looks to be heavier compared to the warm frontal
precipitation, but hourly rain rates are still nowhere near our
thresholds to prompt concern for debris flows over our recent burn
areas in the Cascades. Precipitation should quickly transition to
scattered showers behind the cold front Monday evening. Given the
showery nature of precipitation behind the front when snow levels are
set to decrease to 1500-2000 ft Monday night, not expecting overly
significant snow amounts as pass level (generally just an inch or
two, however 3-5 inches is possible for Willamette Pass where
precipitation appears heavier). Below the snow level, forecast rain
amounts have not changed much. Still expecting 1-1.5 inches of rain
from 5 AM Sunday through 5 AM Tuesday across the interior lowlands
and 1.5-2.0 inches at the coast. Generally expecting 2-3 inches over
the mountains, but locally higher amounts up to 4 inches are
possible. Fortunately, these rain amounts are not high enough to
prompt river flooding concerns. Tuesday currently looks drier as the
AR shifts further south and focuses mainly on southwest OR and CA.
That being said, some model guidance (including the 12z deterministic
EURO) does shift an area of heavier precipitation into northwest OR,
especially south of Salem. Meanwhile, the deterministic GFS keeps our
area dry on Tuesday except for the Lane County Cascades and
foothills. Will leave NBM PoPs for Tuesday given the uncertainty,
which shows a 30-50% chance of rain, except 60-70% in the Cascades.
-TK
.LONG TERM...Tuesday night through Saturday...The GEFS/EPS/CMC
ensemble mean for 500 mb heights are all showing a transient upper
level trough pushing eastward across western OR/WA Tuesday night with
an attendant cold front at the surface. The EURO depicts a slightly
stronger front compared to the GFS. In fact, the GFS suggests the
front will quickly decay after moving inland, resulting in only light
showers for the mountains with mainly dry conditions for the lowlands
Tuesday night and Wednesday. The EURO brings decent rain amounts
even to the lowlands, around 0.25 inches or higher. Regardless of the
outcome, overall impacts look low and snow amounts in the Cascades
look too low to prompt winter headlines.
Models and their ensembles are still in excellent agreement on
Thursday, showing a shortwave ridge passing over the region. This
will bring dry weather and warmer temperatures with highs at least in
the mid to upper 50s. The NBM 1D Viewer is still showing a 15-20%
chance for high temperatures of 60 degrees or warmer Thursday
afternoon across the Willamette Valley and a 5-15% chance along the
coast, highest over the central coast and southern Willamette Valley.
The outcome will ultimately come down to cloud cover conditions; if
skies wind up mostly sunny then highs near 60 would most likely
materialize. It appears Thursday`s pleasant weather will be
short-lived, as rain returns to the forecast Friday with temperatures
cooling slightly at the surface and aloft. -TK
&&
.AVIATION...00Z TAFs: At 22Z satellite imagery showed a weak warm
front over southwest Washington lifting to the north. Flight
conditions have improved to VFR across the area, with cigs
generally 060 to 080. Expect VFR to prevail across the area
through at least 06Z Sunday. Cigs begin to lower across the south
half of the area after 06Z Sunday as a warm-frontal boundary draped
across northern California drifts north. Increasing -RA across the
south after 10Z will result in MVFR conditions. The frontal boundary
reaches the Columbia River around 15Z Sunday. Expect predominant
MVFR conditions after 15Z Sunday, with areas of IFR possible along
the coast.
For detailed Pac NW aviation weather information, go online to:
http://weather.gov/zse
KPDX AND APPROACHES...At 22Z cigs 060-070 were noted at the terminal
and vicinity, except 035-045 in the Tualatin River Valley. Cigs
AOA 080 to prevail Saturday evening. Cigs expected to lower to around
070 by midnight. Light rain develops between 12Z and 15Z, with a
greater than 70 percent chance of MVFR starting at 15Z. Expect
predominant MVFR after 15Z. Weishaar
&&
.MARINE...At 1 PM, satellite imagery showed an upper level low
over the northeast Pacific west of Hadai Gwaii and a moist frontal
boundary along 40N streaming into northern California. Wind speeds
were generally 15 to 20 kt.
Little change through Sunday morning. Models show a 1000 mb surface
low centered near 45N 128W by 11 AM Sunday. Expect increasing
southerly wind over the southern waters around midday and then
spreading north through the afternoon. The surface low is forecast
to move onshore near the southern tip of Vancouver Island early
Sunday evening. Model guidance shows 30 to 35 kt boundary layer
wind speeds (used as a proxy for gusts) developing over the waters
around 5 PM Sunday. The National Blend of Models (NBM) shows a
65-70 percent chance of gale force gusts at buoy 46050 Sunday
night. The high resolution ensemble mean model output indicates 35
kt gusts over a majority of the area 5 PM Sunday. Based on the
above, will upgrade the Gale Watch to a Gale Warning valid 5 PM
Sunday to 2 AM Monday, except starting at 7 PM for PZZ251 and
PZZ271, including the Columbia River Bar. This looks to be a
marginal, low-end gale event. The wind shifts to westerly late
Sunday night, with wind speeds decreasing to around 15 kt by 7 AM
Monday.
Another rapidly-developing low pressure well west of the north
California waters early Tuesday, is forecast to remain south of
the forecast area. This results in general northerly wind over the
waters. Longer range models show a fairly strong frontal system
impacting the waters late next week.
Mixed swell continues over the area through early next week.
However, overall wave heights will be 7 ft or less through early
Sunday afternoon. Combined seas peak 10 to 11 ft late Sunday
night, with a substantial wind wave component. Wave heights settle
to around 6 ft Monday. Spectral model guidance suggests wave
heights approach 20 ft late next week. Not sold on this outcome
just yet, as the NBM guidance shows 12-15 ft. The 90th percentile
NBM wave heights valid 11 PM next Saturday are 15-19 ft. Weishaar
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 2 PM to 7 PM PDT Sunday for Coastal
waters from Cape Shoalwater WA to Cape Falcon OR out 10 NM-
Columbia River Bar-Waters from Cape Shoalwater WA to Cape
Falcon OR from 10 to 60 NM.
Gale Warning from 7 PM Sunday to 2 AM PDT Monday for Coastal
waters from Cape Shoalwater WA to Cape Falcon OR out 10 NM-
Columbia River Bar-Waters from Cape Shoalwater WA to Cape
Falcon OR from 10 to 60 NM.
Small Craft Advisory from 11 AM to 5 PM PDT Sunday for Coastal
waters from Cape Falcon OR to Cape Foulweather OR out 60 NM.
Gale Warning from 5 PM Sunday to 2 AM PDT Monday for Coastal
waters from Cape Foulweather OR to Florence OR out 10
NM.Coastal waters from Cape Foulweather OR to Florence OR
from 10 to 60 NM.
Small Craft Advisory from 8 AM to 5 PM PDT Sunday for Coastal
waters from Cape Foulweather to Florence OR out 10 NM-
Waters from Cape Foulweather to Florence OR from 10 to 60
NM.
&&
$$
www.weather.gov/portland
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Area Forecast Discussion
National Weather Service Raleigh NC
955 PM EST Sat Mar 11 2023
.SYNOPSIS...
Weak high pressure will build east into the region through tonight.
Cold air damming will develop across central NC Sunday, north of an
area of low pressure and associated frontal zone that`s forecast to
track east across GA, SC, and southern coastal sections of NC
through Sunday night.
&&
.NEAR TERM /TONIGHT THROUGH SUNDAY NIGHT/...
As of 950 PM Saturday...
Only minor changes were made with the evening update. Widespread
high clouds across the region that had been in place earlier are
largely dissipating, and some spots have begun to radiationally cool
particularly in the NE as current temperatures are 36F at KTDF,
KHNZ, and KIXA. Widespread clouds will begin to move in from the
west in a few hours, but they should arrive late enough in the NE
for low temperatures of about 33-35F there, where some patchy frost
will be possible. Still not expecting any subfreezing temperatures,
and ensemble probabilities of this occurring are quite low. In the
west, temperatures should stop falling once the clouds arrive and
until precipitation moves in. Dew points are in the mid-to-upper-20s
across the northern Piedmont as expected with the surface high
pressure wedging down, but did raise them a bit in the south and
east as they are in the 30s there.
As for precipitation, delayed its arrival slightly based on the 00z
high-res guidance (including the HRRR, RAP, and NAMNest). Also
slightly cut back the area of forecast 0.1-0.2" snowfall amounts
tomorrow morning across the northern Piedmont, as a later arrival of
precipitation would tend to favor less frozen, and snow depth
forecasts in the latest HRRR and RAP are now essentially zero. Still
expecting very minimal to no impacts especially given the very warm
soil temperatures. Otherwise, the previous discussion is below:
As of 400 PM Saturday...
Patchy frost possible over the nrn Coastal Plain tonight.
A wintry mix of rain and snow will develop late tonight-Sunday
morning over the nrn NC Piedmont, which may briefly change to all
snow for a few hours near the VA border Sun morning, but with little
to no accumulation as it mostly melts as it falls.
Shortwave ridging will build from the Great Lakes east to the mid
Atlantic tonight, then offshore through Sunday night, through which
time and downstream of a closed mid-level cyclone in the nrn stream
that will move from the nrn Plains to the upr Great Lakes.
Meanwhile, and more importantly for cntl NC, a lwr amplitude
perturbation in the exit region of an energetic/active srn stream
will stream from the cntl Plains this afternoon to the OH Valley and
cntl Appalachians through early Sunday. A strong mid-level WAA
regime and nw to se-oriented band of 700 mb frontogenesis will
precede and accompany that feature and spread from the mid MS
Valley/mid-South this afternoon to the srn mid Atlantic by 09-12Z
Sun. Lwr-level WAA and isentropic lift will follow and overspread
cntl NC through the day and early nighttime hours Sun.
At the surface, the center of weak (~1018 mb) high pressure will
ridge across the mid Atlantic tonight, then offshore, but with
associated surface dewpoints in the 20s that will have been
deposited over VA/NC and favor hybrid to in-situ cold air damming
Sun-Sun night. Around the srn periphery of that damming regime, a
lead low will migrate newd into the TN Valley/srn Appalachians
Sunday, then yield to a secondary/coastal low forecast to develop
along and offshore the NC coast, along the wedge front, Sunday night-
early Monday.
Considerable cirrus/cirrostratus has already overspread SC and srn
NC this afternoon; and this high-level moisture will continue to
overspread the remainder of the Carolinas overnight - slowest and
thinnest over nern NC, including the nrn/cntl Coastal Plain. Those
areas may radiationally-cool into the lwr-mid 30s and favor the
development of patchy frost. Otherwise and elsewhere, temperatures
will cool into the upr 30s to mid 40s this evening, steady as clouds
thicken and lower overnight, then diabatically cool into the mid 30s
where and when precipitation overspreads the Piedmont through Sun
morning. The trend in model guidance since last evening has been for
a faster arrival of that precipitation band late tonight-early
Sunday.
A combination of top-down and forecast partial thickness/TRENDS
nomogram favor the presence of a deep/near freezing isothermal layer
aloft and melting of snow in a shallow, above freezing surface layer
that will likely support a larger and more prolonged area of
rain/snow mix or even all snow across the nrn NC Piedmont Sunday
morning. That appears to be the case after an initial period of
light rain incompletely saturating/cooling the sub-cloud layer at
onset, then both warming and drying aloft, and insolation from a mid-
March sun angle, during the afternoon, which would favor a
changeover to rain/drizzle that will continue through Sunday night.
***However, most/all snow should melt as it falls*** owing to 1)
very warm soil temperatures that have ranged from mid 40s to lwr 50s
F the past couple of mornings to 50s to near 60 F this afternoon, 2)
above freezing air temperatures except for perhaps a 2-3 hr period
when heavier precip rates would favor "melting out"/ diabatically-
cooling to 32-33F an otherwise ~750-1000 ft AGL above freezing
surface layer, and 3) a mid-March/late winter sun angle through the
morning-midday hours. Any accumulation of perhaps a tenth to two
would be limited to any period of all snow and confined to elevated
surfaces near the VA border.
Otherwise it will be a chilly and raw/wet end to the weekend, with
periods of rain and drizzle lingering through much of Sun night, and
with a small diurnal range of highs in the upr 30s north to low-mid
40s south, and lows just a degree or three cooler Sun night.
Rainfall amounts are expected to range around one half inch,
slightly lower across the nrn Piedmont and higher across the srn
tier.
&&
.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As of 218 PM Saturday...
Monday: The sfc low will quickly exit offshore early Monday morning
leaving behind just lingering stratiform rain across our far eastern
zones. Behind the system, low-level stratus will likely linger into
Monday afternoon, before another sfc cold front finally clears cloud
cover late Monday night. Given the extensive cloud cover expected
for much of Monday, max temperatures will struggle to reach above
the mid to upper 50s for much of our area. Low-level thicknesses are
expected to plummet into the 1280 to 1290m range overnight Monday.
However, given that residual stirring of winds expected, don`t
believe we`ll see strong radiational cooling as a result. As such,
the current forecast calls for sub freezing lows across the NW
(upper 20s) to slightly above freezing lows elsewhere (lower 30s).
Thus, future shifts may need to issue a freeze warning for those in
the northwest Piedmont Monday night.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 218 PM Saturday...
Upper pattern through the extended: An anomalous upper low will move
across the upper Midwest and through the New England Monday through
Wednesday morning promoting wnwly flow aloft over central NC. Mid-
level riding will then build across the central US promoting nwly
flow aloft over our area Wednesday/Thursday. Flow will then turn
more swly Friday through Saturday as the next upper trough
approaches our area.
Tuesday through Thursday: Strong CAA is expected to develop across
our area as chilly sfc high pressure over the central US eases
eastward. Increasing nwly flow through the depth of the atmosphere
will promote anomalously dry conditions (PWAT ~20 to 25% of normal)
Tuesday through much of Thursday. Additionally, good mixing should
promote gusty conditions Tuesday and Wednesday afternoons. Tuesday
in particular will likely see frequent gusts of 25 to 35 mph
especially across northern areas. Given the anomalously dry air
expected during this period, the pattern will favor increased fire
weather danger concerns especially Tuesday afternoon. Sub-freezing
conditions appear increasingly likely across most of central NC
Tuesday night into Wednesday morning as low-level thicknesses drop
to near record lows for mid-March. Additionally, ensemble
probabilities for sub-freezing temperatures range from 100 % in the
Triad to 55% in the southern Coastal Plain Wednesday morning. Thus,
a freeze warning will likely be needed for much of central NC
Tuesday night/early Wednesday morning. Winds decouple Wednesday
night promoting another round of chilly overnight lows in upper
20s/lower 30s. Daytime highs Tuesday/Wednesday will remain chilly
in the upper 40s to upper 50s (~10 degrees below normal). Near to
just above normal highs return Thursday afternoon in the lower to
mid 60s.
Friday through Saturday: The chilly sfc high will move offshore by
Friday morning promoting sswly low-level flow and warmer
temperatures across our area. Daytime highs will reach well above
normal into the upper 60s/mid 70s Friday (overnight lows in the mid
40s). Rain associated with an approaching sfc cold front is expected
to approach and push through central NC sometime late Friday through
Sunday morning. Latest 12Z deterministic guidance (as well as
ensemble probabilities for measurable precip) has slowed down the
arrival of precip compared to previous runs. Thus, have trended the
POPs down for Friday compared to the inherited previous forecast,
but with highest POPs currently still forecasted on Saturday. This
will likely need to be altered, however, as uncertainty decreases
closer to next weekend. Highs on Saturday will depend on cloud/cover
precipitation, but as of now the forecast calls for upper 50s in the
NW to upper 60s in the SE. Overnight lows follow a similar gradient
in the mid 30s (NW) to around 40 in the far SE.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 640 PM Saturday...
24 hour TAF period: High confidence VFR conditions will prevail
through about midnight at all terminals. Cigs will thicken and lower
quickly between 06Z and 12Z Sun, with sub-VFR conditions earliest
(08Z-10Z) at KINT and KGSO, then subsequently at KRDU, KRWI and
KFAY. Cigs will likely drop into the IFR/LIFR range everywhere by
15Z at all terminals and remain there through the end of the TAF
period. Visbys will also drop to between 1SM and 4SM everywhere.
Additionally, there could be a brief period of some SN mixed with
the RA from onset through about 15Z, most likely at KINT, KGSO and
possibly KRDU, then change over to and remain all liquid through the
end of the period. Finally, there continues to be a signal for LLWS
potential owing to the presence of a 35-40 kt LLJ late Sun aft
through Sun eve, primarily at KFAY, KRDU, and KRWI, as the low
tracks northeast along the Carolina coast.
Looking ahead: Light rain/drizzle could linger into Sun night, while
LIFR/IFR conditions will persist through Sun night/Mon morning. VFR
conditions should return by Mon afternoon and prevail through mid-
week.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...CBL
NEAR TERM...Danco/MWS
SHORT TERM...Luchetti
LONG TERM...Luchetti
AVIATION...KC