Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/08/20
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
330 PM AKST Sat Nov 7 2020
.SHORT TERM...A low pressure system tracking NE along the
Aleutians has caused increasing high clouds over the region today,
keeping temperatures from warming as much as expected across the
north. The assoc warm front extending out across the NE gulf will
cause snow to move into Yakutat later Saturday night then become
mixed with and change over to rain by Sunday morning. The precip
will spread over the northern panhandle through Sunday morning,
then to the far SE corner of the panhandle later in the afternoon
or even early evening. Snow is expected initially, but strong
southerly winds will work quickly to change the snow to rain
through the day near sea level. Some accumulations of up to 2
inches are possible before the change over. For the Mendenhall
Valley, Haines, and Skagway closer to 4 inches are expected and
White Pass is expected to see 6-9 inches of snow.
Winds with the front increase to 35-50kt over the outside waters
on Sunday. Cross Sound increases to 35kt in the afternoon and
Clarence Strait to gale force as well Sunday evening. These strong
winds will work to raise snow levels above 1000ft across the
north and 2-5kft for the south Sunday evening. Heavy rain is
expected during this period.
The rain on top of a the snow pack across the north is going to
make for very poor roadway conditions. Additionally, storm drains
and culverts will likely clog with a mix or rainwater, slush, and
wet snow. Snow loading on roofs and sheds may become an issue as
well due to the very high water content of snow. Similar concerns
exist for aircraft stored outdoors and moored, unattended
vessels.
The low will track E-SE across the area through Monday. Expect
rain to transition to showers at that point and winds to shift
west behind the front, then northerly behind the low. CAA behind
the system will likely be enough for some snow to mix back in with
the showers Monday afternoon/evening, but the precip will also be
ending around that point and thus too short-lived for
accumulations.
.LONG TERM.../Monday through Saturday night/...As of Friday
evening. At the start of the extended forecast period, a low will
be sliding south along the coast. This low is expected to bring
heavy rain across the panhandle through Sunday. Rain chances will
begin to diminish through the day on Monday from North to South
with areas across the southern panhandle and along the coastal
mountains hanging onto the precipitation the longest. Winds
associated with the frontal band will be on the decreasing trend
Monday, diminishing from small craft through the southern inner
channels to 15 kts or less. Surface ridging quickly builds in
behind the exiting low pressure displacing it SSE of Haida Gwaii.
This will allow for a quick dry period Tuesday before the next
weather systems arrives late Tuesday night into early Wednesday.
By Wednesday, a parent low pressure system will be located in the
Bering Sea. Guidance supports an associated triple point low to
form along the Aleutians which will then slide east into the NE
Gulf coast. There is potential for this system to bring
significant QPF totals across the panhandle with periods of heavy
precipitation. By early Thursday morning, the parent low will
have moved into the Northern Gulf pushing onshore an additional
uniform frontal band. P-type is a concern with this system as
colder temperatures will be in place from Tuesdays CAA. Depending
on how strong the southerly WAA ahead of the approaching system
is, the northern panhandle could see significant snow
accumulations.
From Thursday through Saturday, a low looks to become locked in
on the central Gulf keeping precipitation chances elevated
through the remainder of the extended period as multiple vortices
approach the panhandle.
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory from 7 AM to 6 PM AKST Sunday for AKZ025.
Strong Wind Sunday afternoon for AKZ022.
Winter Weather Advisory from 7 AM Sunday to midnight AKST Sunday
night for AKZ019.
Winter Storm Warning from 9 AM Sunday to 6 AM AKST Monday for
AKZ018.
Strong Wind Sunday afternoon for AKZ017-018.
MARINE...Storm Warning for PKZ052.
Gale Warning for PKZ022-042-043-051.
Small Craft Advisory for PKZ011>013-021-031>034-041-053.
&&
$$
Ferrin/CC
Visit us at http://www.weather.gov/Juneau
Area Forecast Discussion
National Weather Service Great Falls MT
516 PM MST Sat Nov 7 2020
...Aviation Section Update...
...Major Winter Storm to Impact North-Central and Central Montana
Tonight Through Sunday with Blizzard Conditions Expected Across
Portions of North-Central Montana...
.SYNOPSIS...
A major winter storm will move into the area tonight with rain and
snow changing to snow for most areas this evening and all areas by
Sunday morning. Snow may be heavy at times with strengthening north
to northwest creating significant blowing and drifting snow late
tonight through Sunday over the plains before snow and winds
diminish Sunday night.
&&
.DISCUSSION...
Little change from previous forecasts with regard to snow amounts
and wind/visibility impacts expected with the storm tonight through
Sunday. Upper level low lifting out of the Great Basin will merge
with upper troughing and much colder air moving south from western
Canada tonight to create a significant winter storm across the
region. The resulting mid level circulation developing in ID/SW MT
this evening tracks east to eastern MT by Sunday morning and onward
to SK/MB Sunday night.
Snow associated with the Canadian trough and colder airmass moving
south along the Rockies will spread southward this evening while an
initial disturbances ejecting out of the Great Basin system spreads
widespread showers northward, evolving into an area of widespread
precipitation this evening as flow aloft turns SE then easterly ahead
of the mid-level circulation developing over ID. The cold air
surging southward, initially along the east slopes of the Rockies,
will trigger the change from rain to snow for western portions of
north-central and central MT early this evening with the colder air
and change to snow spreading south and eastward overnight. Areas
from Bozeman to Lewistown and Havre may not see the change-over to
snow until after midnight tonight with areas east of Lewistown
changing to snow early Sunday morning. Snow intensity peaks Sunday
morning for most areas but continues into the afternoon. Light
snow lingers into Sunday evening across north-central MT before
ending late Sunday night. Total snow accumulation forecasts have
changed little with greatest amounts expected across much of
north-central MT and lesser amounts across southwest MT.
Gusty N to NW winds will spread south and east across the area
tonight and across most of north-central and SW MT by Sunday
morning. Strongest winds with gusts as high as 40-50 mph are
likely across western portions of north-central MT late tonight
through Sunday morning where a Blizzard Warning remains in
effect. Gusts in the 35 to 45 mph rage are likely further east
across the remaining counties in north-central MT later Sunday
morning through the afternoon with these winds reaching eastern
portions of north-central MT late Sunday morning through the
afternoon and the Blizzard warning has been expanded to include
Judith Basin, Fergus and Blaine counties. Significant impacts are
expected in the areas under Winter Storm and Blizzard warnings
from the combination of wind and snow, peaking Sunday morning but
continuing through much of the day. Travel will be particularly
difficult in areas under the Blizzard warning, where blowing snow
and very low visibility impacts Sunday morning may transition to
greater impacts from blocked roadways and drifting snow Sunday
afternoon as snow intensity diminishes.
Snow and winds decrease Sunday night as the storm system lifts out
into central Canada. Most areas will see steady temperatures in the
teens and lower 20s Sunday with wind chill values as low as the
teens below zero by late Sunday afternoon. Temperatures fall to
the single digits and teens above zero Sunday night and
potentially colder in some areas near the Canadian border where
some clearing is possible by Monday morning.
Tuesday through next Saturday...A broad low pressure trough will
develop over much of North America during this time, which will keep
temperatures below normal. Weak shortwave troughs will pass over
Montana during this time, bringing periods of gusty winds and
generally light precipitation, and minor temperature fluctuations.
At this point, there is a chance for strong winds Friday and next
Saturday, but will continue to monitor the situation for now, as
confidence in the forecast is somewhat low that far out.
Coulston
&&
.AVIATION...
516 PM MST Sat Nov 7 2020 (08/00Z TAF period)
A major winter storm causes widespread aviation impacts throughout
this TAF period. Expect LIFR conditions to occur due to low
visibility and low ceiling at all airfields. Blizzard conditions are
forecast across north-central and central Montana. During periods of
gusty winds, expect reduced visibility in snow and blowing snow. In
areas of light winds, visibility will be reduced in snow and fog.
Low level wind shear is included in the following TAFs: KCTB, KHLN
and KWYS. Expect all associated turbulence. Widespread mountain
obscuration is forecast. Aircraft icing is to be expected.
- Fogleman
Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 16 22 10 27 / 100 100 90 10
CTB 14 19 3 25 / 100 100 80 0
HLN 17 24 9 27 / 90 100 70 10
BZN 20 28 5 23 / 90 90 40 10
WYS 22 30 3 23 / 100 80 20 0
DLN 17 25 2 23 / 80 100 30 0
HVR 19 28 8 23 / 100 100 100 30
LWT 18 25 8 26 / 90 100 60 30
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 8 PM this evening to 5 AM MST Monday
Broadwater...Central and Southern Lewis and Clark...Jefferson...
Meagher.
Blizzard Warning until 5 AM MST Monday Eastern Glacier...Eastern
Pondera...Eastern Teton...Liberty...Northern Rocky Mountain
Front...Southern Rocky Mountain Front...Toole.
Winter Weather Advisory from 11 PM this evening to 5 AM MST
Monday Beaverhead...Gallatin...Madison.
Blizzard Warning from 11 PM this evening to 8 AM MST Monday
Blaine...Fergus...Judith Basin.
Blizzard Warning from 8 PM this evening to 8 AM MST Monday
Cascade...Chouteau...Hill.
&&
$$
http://www.weather.gov/greatfalls