Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/04/22
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
357 PM AKST Thu Feb 3 2022
.SHORT TERM.../Through Saturday/
**Round 2 of Significant Wintry Precipitation and Heavy Rain**
Current satellite imagery Thursday afternoon shows an atmospheric
river aimed right over Southeast Alaska. CIMMS MIMIC Layer Rel
Humidity satellite imagery depicts a long plume of tropical
moisture being funneled northward into Southeast Alaska with
moisture values upwards of 400% of normal. All of this moisture
will continue stream into the area ahead of low pressure system in
the western gulf. Model guidance does not have a good handle on
the track of this low as it approaches the NE Gulf coast tonight.
Guidance today has trended further south and east with the track,
keeping the northern half of SE AK entrenched in cold air and
northerly flow. The trend in all of the guidance over the past
few days has been to keep the cold air around longer across the
north as the boundary separating the cold and "warm" airmasses
remains stationary across the Central Panhandle. While surface
temperatures remain below freezing across the north, warm air is
still being pumped in aloft as shown on model and MDCRS
soundings. 21Z MDCRS soundings from Juneau show a warm nose around
6,000 feet with temperatures approaching 32F. This warm nose is
expected to grow as southerly flow continues aloft today and
tonight. Expect sleet and freezing rain to mix in at times this
evening for the Icy Strait corridor and NE Gulf Coast. Confidence
remains low on the timing of the transition to plain rain and how
fast the rain/snow line moves northward. Despite guidance
continuing to trend colder, different models show various times
for a transition to rain. Due to all the uncertainty, went with
the colder guidance and extended the Winter Storm Warnings through
6 AM Friday. There is a chance some areas will transition to rain
before that; while other areas remain snow. It is likely areas
along the Outer Coast (Pelican, Elfin Cove, Yakutat) could change
over to rain first, while areas further inland remain snow longer.
For Juneau, expect downtown and the airport to change to rain
first while Mendenhall Valley and further out the road remain snow
Friday morning. Another area of low confidence is how much mixed
precip (sleet and freezing rain) will fall. Extended periods of
mixed precipitation will likely result in lower snowfall totals,
but much higher impacts due to ice accumulation. Expect the
rain/snow line to surge northward Friday as the low moves north
into Canada and the pressure gradient flips southerly everywhere,
even Upper Lynn Canal. After the low passes, expect scattered
rain showers to diminish until the next system approaches
Saturday.
Heavy Rain Threat: While the north receives heavy wintry
precipitation, the southern half of the Panhandle from Sitka to
Kake and southward (except Hyder) will remain all rain through the
weekend. Expect 2 to 4 additional inches of rainfall/liquid
through Saturday night. Heavy rainfall will continue through
Thursday as the atmospheric river remains over the area and dumps
an additional 1 to 2 inches of rain. The main low to the west
moves into Canada and pushes a front through the region on Friday
shutting off the main moisture plume. Diminishing showers expected
behind the front until the next system arrives on Saturday with
another round of heavy rain. This system on Saturday is expected
to push another front into the Panhandle with an additional 1 to 2
inches of rain expected across the entire region. Snow levels will
continue to rise with the Saturday system so expect an increase in
snow melt in the mountains, especially below 2,000 feet. River
rises and flooding potential will need to be monitored closely due
to the back to back round of heavy rainfall.
Wind and seas: Elevated winds and higher seas are expected to
continue through the weekend as multiple systems impact the
region. A gale force front pushes into the Panhandle tonight with
Gales developing in the Southern Inner Channels and Small Crafts
through the rest of the Inner Channels. SW flow behind the front
will be quite strong on Friday as SW Gales develop in the Gulf.
Expect strong SW winds with gusts of 40 to 50 mph along the Outer
Coast, POW Island, and the Southern Inner Channels Friday. A brief
break in winds occurs Friday night into Saturday before the next
Gale force front approaches the Outer Coast Saturday evening. This
next front will have more wind energy and better upper dynamics
than the previous front; therefore have added gusts upwards of 50
mph for the Outer Coast, POW Island and Southern Inner Channels
Saturday evening. Also expect low end Gales to develop through the
Central and Southern Inner Channels Saturday evening as the front
pushes in.
Forecast confidence remains around average for the winter storm
and is high for the heavy rain and wind potential. The main area
of concern in the short term is the northward progression of the
rain/snow line and the mixed precip potential across the north
tonight.
.LONG TERM.../Sunday into Tuesday morning/...A series of Gale-
force fronts will bring a warmup, ample liquid precipitation, and
gusty winds to the Panhandle and eastern Gulf for the weekend and
into early next week. The only locations that look to have wintry
precipitation will be the Klondike highway near White Pass and
Haines Highway near Haines Border Customs.
As for temperatures, highs look to stay near 40 to just shy of 50
degrees and lows look to remain between near freezing to right
around 40 degrees from north to south, respectively. This warmer
weather is brought to us by strong persistent southerly flow,
which will bring Warm Air Advection out ahead of the
aforementioned approaching frontal systems. This warmup is well
indicated via Warm Air Advection on the 850mb model forecast
temperature and pressure field.
As for winds, Gales up to around 40 knots are expected on
Saturday out ahead of the approaching Gale-force low and
associated front, which will diminish through Sunday morning.
During this timeframe, Gales will be experienced over the eastern
Gulf waters, just off the outer coast, over Clarence Strait,
Yakutat Bay, over the Inner Channels near ocean entrances, and all
the way to Five Finger. Elsewhere, over adjacent Inner Channels,
including Lynn Canal, expect winds up to Small Craft strength. A
weaker, but still Gale-force front looks to move into the Gulf and
approach the Panhandle Monday evening into Tuesday morning. Gales
could occur just off the Outer Coast from Sitka, northward for
that time period. The strongest winds up to 40 knots will be
associated with a couple of barrier jets located to the southeast
and the southwest of Yakutat Bay over the northeastern Gulf
waters. Strong winds up to 40 to 55 mph look to occur over Outer
Coast and southern Inner Channel land areas, as well.
These systems will have plenty of deep tropical moisture with a
fairly long fetch to work with. Model forecast IVT values of up to
around 800 kg/(ms) are aimed at the Panhandle for the weekend and
into early next week. Therefore, forecast Storm Total QPF values
of up to around 2 and up to 3 inches of liquid are forecast
throughout the period for many areas in the Panhandle. There may
be standing water in typical poor drainage areas and areas blocked
by snow.
Model agreement was good for the most part for the long-term
forecast period. Therefore, forecast confidence is average.
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from 9 PM AKST this evening through late tonight for
AKZ023-027-028.
Winter Weather Advisory until 9 PM AKST this evening for AKZ024.
Winter Storm Warning until 6 AM AKST Friday for AKZ017-020>022-
025.
Winter Storm Warning until 9 AM AKST Friday for AKZ029.
Winter Storm Warning until 6 PM AKST Friday for AKZ018-019.
MARINE...Gale Warning for PKZ022-036-041>043-051-052-310.
Small Craft Advisory for PKZ012-013-021-031>035-053.
&&
$$
CM/JLC
Visit us at http://www.weather.gov/Juneau
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
650 PM CST Thu Feb 3 2022
.UPDATE...
Issued at 650 PM CST Thu Feb 3 2022
An early evening update here to mainly note a conversion of the
Warning to a Winter Weather Advisory in the far southern CWA
(along/south of a Dwight IL to Demote IN line) for tonight. Law
enforcement across the affected counties unanimously reported
major issues on west-east roads due to blowing and drifting snow.
Some counties even have recommended no travel tonight besides main
roads due to the impassible nature of the drifting snow in some
of these locations. We collaborated a Winter Weather Advisory for
the far south through tonight based on this, running it through 3
A.M. with winds gradually easing late this evening through the
overnight. While there is some blowing snow from even gustier
winds north of this area (including at ORD and MDW airfields with
"DRSN" in their METARS), though the reports have all been that
this is more patchy. Did add blowing snow verbiage into the
forecast through tonight for a good portion of the CWA, with more
widespread coverage in the south. Did also bump up wind gusts
across the CWA, with regular 20-25 mph being observed and
occasional 30 mph gusts across the metro this evening.
Otherwise, lake effect flurries and at times light snow showers
continue across northeast Illinois. Even though the convergence
of the streamlines is a narrow zone, the actual flurries plume is
broader on radar with occasional snow showers. Some of these
showers in mainly DuPage County have appeared to be spawned from
aircraft exhaust with the added nuclei supporting snow crystal
formation. We see this at times when clouds are at the cold end of
the supercooled liquid zone (-7 to -11C) and that`s what AMDAR
soundings are indicating right now. These snow showers have
produced brief modest rates per social media reports, but last
for a very quick duration due to the rapid advection of the
showers in the north-northeast flow. Cannot rule out a dusting
under these though.
Also of note, if looking at our radar one will notice a plume
emanating from northwest DuPage County, and that is concentrated
smoke from a fire at a large records storage facility near
Bartlett, per reports from Emergency Management. Analyzing the
radar reflectivity and correlation coefficient, it is possible
some of this is also creating nuclei favorable for snow showers
as it rises into the cloud layer. This looks to be over southern
Kane and northern Kendall Counties. These showers also would not
last long in any one location but could produce quick
accumulations.
Will need to take a look some more this evening at the snow shower
potential mid-late afternoon into early evening on Friday with the
strong mid-level vorticity maximum passage. It is a question on
whether there will be sufficient moisture, as the thermal profile
is favorable lining up some of the steeper low-level lapse rates
and instability with the dendritic growth layer. A dusting to
several tenths of an inch of snow looks like it might be able to
occur in strips with any showers. This is primarily over far
northern into northeast Illinois and far northwest Indiana. Again
will look into more and overnight shift will further.
MTF
&&
.SHORT TERM...
Issued at 254 PM CST Thu Feb 3 2022
Through Friday night...
After dropping an inch or two of snow in far northeast Cook
county earlier today, the lake effect snow band has since shifted
west and is oriented into southeast Wisconsin with light snow
extending across Cook, Lake and DuPage counties in Illinois.
Additional accumulation of up to an inch will be possible in far
northeast Illinois with a dusting extending southwest into
northern Cook and DuPage counties. Meanwhile the advertised
"second round" of snow continues to ease in areas south and east
of a Paxton to Rensselaer line with additional totals of under a
half inch expected before it fully shifts east of the area by this
evening.
Temperatures today are in the teens and low to mid 20s across the
area this afternoon. We cool off into the single digits tonight
outside of the metro with lower teens in Chicago thanks to the
urban heat island and lingering low clouds.
Heading into tomorrow, temperatures only warm into the lower 20s
early afternoon before a quick moving weather system and
associated cold front sweeps across the area bringing a chance for
light snow and flurries mid afternoon. Moisture will be a
limiting factor but a quick dusting of snow is possible across
northeast Illinois. Light snow may linger near the lake into
Friday night but as the surface ridge moves overhead overnight
skies clear to the west allowing temperatures to dip near to below
zero.
Petr
&&
.LONG TERM...
Issued at 254 PM CST Thu Feb 3 2022
Saturday through Thursday...
The start of the weekend will feature quiet weather and much needed
sunshine as surface high pressure will slide into northern Illinois
ahead of an approaching mid-level ridge. The high will shift to the
Ohio River Valley on Sunday, a mid-level disturbance aims to push a
clipper system into the upper Great Lakes Saturday through Sunday.
Its associated cold front is progged to push through the Great Lakes
Monday morning, bringing a short lived cool down after a slightly
milder Sunday. The bulk of the precipitation will remain in
Wisconsin and the UP of Michigan as the better synoptic scale
forcing stays north of the area.
More quiet weather is expected midweek. Winds across the Midwest
will veer south/southwest in response to the northern stream storm
track across the upper Midwest. This will send temperatures back to
more seasonal levels in the 30s. The recent snowpack across the
state will likely keep temperatures on the lower side of guidance,
especially across our southern counties.
Ensembles depict a few additional clippers next week, a slightly
stronger one pegged to pass through Wisconsin in the later Thursday
time frame. The NBM has latched onto this wave, which would be our
next best chance for any light snow in the upcoming week.
BW/KMD
&&
.AVIATION...
For the 00Z TAFs...
Issued at 603 PM CST Thu Feb 3 2022
The concerns include:
* Lake effect flurries and temporary snow showers tonight, with
associated MVFR CIGs
* A burst of heavier snow showers/squalls Friday PM-evening
Lake effect flurries continue to stream into northeast Illinois,
with some heavier aircraft seeded showers southwest of ORD. The
lake effect showers have been a bit better organized into far
southeast Wisconsin and northern Lake County Illinois. Concern
this evening is that if these slightly better organized snow
showers pivot back eastward, could bring reduced VSBY and threat
for a dusting of snow to ORD. Current expectation is for any more
robust activity to remain west of MDW. Flurries should finally
wind down toward daybreak Friday. High MVFR CIGs will prevail at
Chicago area sites.
On Friday, west-southwest winds will develop ahead of an arctic
front and strong weather disturbance. CIGs will be low VFR or high
MVFR. As the strong disturbance approaches Friday afternoon,
expecting an uptick in light snow/snow showers with embedded
heavier snow showers/squalls into Friday evening. With steep lapse
rates and instability of the lower levels of forecast soundings,
concerned for temporary heavy rates and potential for a quick
coating (up to a few to several tenths) of snow on the runways. In
addition, winds will increase from the west during the burst of
snow. Given the steep lapse rates and decent shot of heavier snow
showers, these could also cause gusts up to 25 kt or higher. For
this issuance, introduced prevailing -SN and TEMPO 1SM IFR VSBY,
with threat there for LIFR VSBY in heaviest snow showers. The
disturbance will pivot off to the east by the late evening, with
flurries probably continuing as winds shift to northwest and gust
up to 20 kt.
Castro
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory...ILZ032-ILZ033-ILZ039 until 3 AM Friday.
IN...Winter Weather Advisory...INZ010-INZ011-INZ019 until 3 AM Friday.
LM...Small Craft Advisory...nearshore waters until 3 AM Friday.
&&
$$
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