Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/25/19
Area Forecast Discussion...UPDATED
National Weather Service Lubbock TX
529 PM CST Sun Nov 24 2019
.AVIATION...
VFR conditions to continue through this period. May be a brief
period of LLWS tonight at LBB as winds aloft increase to about
35kts with a 30 degree difference from surface winds. Due to the
marginal nature did not include it within the TAF. /WCI
&&
.PREV DISCUSSION... /issued 317 PM CST Sun Nov 24 2019/
DISCUSSION...
BLUF: Wind on Tuesday follow by messy weather for the
Thanksgiving Holiday...some potential for frozen precipitation.
This afternoon, we have a fetch of Pacific moisture streaming into
the region thanks to an upper low well west of the Baja. In advance
of an approaching shortwave, high-level clouds have developed across
much of the forecast area. A weak cold front was sagging south
through the Central Plains. We`ll see the shortwave pass over our
area overnight, clearing skies and pulling the front closer to our
forecast area. By midday Monday, it should advance through the
northeast third to half of the FA before washing out, so we don`t
expect a major impact on highs tomorrow.
RAP IR analysis this afternoon shows the first ripple in the flow
across the Pac-NW of what will become our wind-maker for Tuesday. As
this deepens into an open low over the Rockies by Tuesday morning,
it will start to become somewhat negatively tilted, closing off as
it moves into KS by midday. The GFS and Euro have come into much
better agreement on the track and strength of this feature, with the
NAM being somewhat of an outlier. Soundings show mixing may not be
as deep as previously advertised, keeping us from tapping the higher
winds at H7; however, the gradient at lower levels will be tight
enough to keep winds likely at advisory or higher for much of the
area Tuesday afternoon. We have ramped up our advertising of this
event, and we`ll be evaluating the need for an advisory or watch
in the next shift or two.
Then we come to the messy Thanksgiving Holiday. As our wind machine
pulls away, a cold air will be pushed in behind it overnight
Tuesday. All the while, a large upper low will be deepening over
northern CA, pushing Pacific moisture back into our area during the
day on Wednesday. We`ll be looking at a chance for precip starting
late Wednesday through Friday night. This is a tricky forecast for
the first 24 hours of precip, though. Current thinking keeps most of
the area all liquid Wednesday afternoon, save for the southwestern
TX Panhandle, where a rain/snow mix may develop without
accumulation. Wednesday night, temperatures are debatable. With
profiles nearing saturation, cloud cover to consider and flow
starting to turn more out of the south, temperatures could have a
difficult time cooling...which could negate the frozen precip all
together. The likely scenario with this setup still leans towards
a rain/freezing rain mix for much of the FA, with only very light
snow mixed in. As the flow turns more southerly and southwesterly
Thursday, pulling in warm moisture, a transition back to all rain
and staying rain is expected. We`ll then be focusing on the
arrival of the famous dry slot, which models currently introduce
early Friday evening. From there on out, dry and breezy will be
prevalent before the next front late weekend. So, we are able to
better hone in on the time period for precip, but the exact precip
type is still to be foreseen.
&&
.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
58/99/99
Area Forecast Discussion
National Weather Service Marquette MI
639 PM EST Sun Nov 24 2019
.SHORT TERM...(This evening through Monday)
Issued at 420 PM EST SUN NOV 24 2019
WV imagery and RAP analysis indicated quasi-zonal mid/upper level
flow across the northern CONUS. The next significant upstream
shortwave trough was moving into western North Dakota. At the
surface, gusty westerly winds prevailed between a ridge through the
Upper Mississippi Valley and 991 mb low pressure near James Bay. Vis
loop indicated mostly sunny skies across Upper Michigan in the
relatively dry airmass. Mid and high clouds were increasing across
MN with the developing WAA pattern ahead of the shrtwv.
Tonight, short range models suggest that light snow will develop
over northern MN and expand eastward into western Upper Michigan
this evening as 285k-295k increases. However, little or no
accumulation is expected given the relatively modest dynamics and
dry low levels. Thickening cloud cover will also help keep min temps
mainly in the upper 20s inland to around 30 along the Great Lakes.
Monday, moderate to strong 700-300 vector conv associated with the
shrtwv should be able to squeeze out additional light pcpn mainly
over the north. With temps climbing through the 30s, any light snow
early will change over to rain. Rain chances will increase over the
west late as the sfc trough approaches and the deeper moisture and
with the shrtwv moves in.
.LONG TERM...(Monday night through Sunday)
Issued at 454 PM EST SUN NOV 24 2019
...Accumulating wet, heavy snow becoming likely late Tuesday night
into Wednesday...
Models suggest a building ridge over the N Pacific will drive a
trough downstream across the western CONUS on Monday. By Tuesday,
this ridge will begin to amplify as an area of low pressure develops
on the leeside of the Rockies Tuesday evening. This low pressure is
progged to lift northeast, reaching Lake Michigan by Wednesday
morning as a shield of precipitation will accompany it. This will be
the main focus of the period as it brings a chance for widespread 6
to 12 inches of system snow. Models solutions have come closer over
the last 24 hours, but the impacts from Colorado Lows are still
highly sensitive to the exact track of the low. A strong ridge of
high pressure moves in behind this low on Thursday that should keep
the UP dry through Friday as models suggest the development of
another low pressure system across the Central Plains into the
weekend.
Starting off on Monday night, models show a shortwave trough exiting
Upper Michigan to the east with scattered mixed precip coming to an
end. Some models suggest lake-effect precip to continue in the WNW
wind belts, however 850mb temps will only range from -4C to -6C.
Model soundings show inversion heights near 4-5kft, but limited
moisture throughout the DGZ. This would limit precip to be -SHSN, or
perhaps some -DZ/FZDZ.
Tuesday, brief ridging will help winds relax ahead of the next wave
of precipitation. Models have come into a good agreement for the
last 24 hours worth of runs. This low pressure system is expected to
deepen as it moves through Lower Michigan at roughly 988mb. Winds
were increased late Tuesday into Wednesday as NBM seemed to be too
low over land and marine. This increase in winds will bring an
increased chance at lakeshore flooding and erosion concerns for
areas affected by NE winds. It will also be blustery across Upper
Michigan with NE winds gusting up to 35 mph at times, especially
along Lake Superior which will bring some concerns for blowing snow.
As far as snow totals go, models are in decent agreement for QPF,
leading to increased confidence in snow totals at or above 6 inches
across the majority of the UP. This confidence in increased as SREF,
GEFS, and various deterministic models show mean snow totals at or
above 6 inches across portions of Upper Michigan. Snow totals in
these situations are highly sensitive to the exact track of the low,
so expect some shifting as we get closer to Tuesday night into
Wednesday. As it stands, have increased QPF slightly along the NE
winds lake-effect belts due to some lake-enhancement concerns as
850mb temps fall to -7C to -10C by Wednesday afternoon. This brings
the chance at up to a foot of snow across the higher terrain of
Marquette County. Of course, slight changes in low track and wind
direction will change the expected totals. Lowest snow totals are
expected along Lake Michigan as higher temperatures will create some
rain early on Wednesday as the warm sector of the low pressure
grazes Upper Michigan. If the low tracks further north, expect some
decrease in snow totals as rain coverage increases across Upper
Michigan.
Behind this system, troughing along the Pacific Coast will create a
period of ridging across the central CONUS. This ridging should cut
off any residual lake-effect early on Thursday as models suggest
another shortwave moving across the Rockies on Friday morning. This
shortwave is then progged to develop into another leeside low
pressure system. The GFS and EC have this low taking a similar path
across Lower Michigan which would bring another round of widespread
snow across Upper Michigan Saturday night into Sunday. The GEM shows
a similar solution to the GFS and EC, however, the GEM is roughly 24
hours behind with the low passing to the south on Monday. Overall,
the potential is there for another shot at widespread snow this
weekend, but additional details still need to be worked out as we
get through this first blast of snow Tuesday night into Wednesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 639 PM EST SUN NOV 24 2019
Snow showers moving in from the west later this evening into the
overnight hours will bring MVFR ceilings and possible visibility
restrictions to KIWD/KCMX. KSAW will see VFR ceilings prevail
tonight. Low pressure moving across northern parts of Lake Michigan
will push a cold front across the region during the day tomorrow,
leading to veering winds at all TAF sites and the return of MVFR
ceilings area-wide. A few models show the potential for ceilings to
get even lower, but for now have opted to maintain MVFR ceilings.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 420 PM EST SUN NOV 24 2019
Westerly winds to 30 knots across Lake Superior will diminish
tonight. Wind then increase back to 20-30 kts on Monday with broad
low pressure moving through Ontario and clipping Lake Superior. A
strong low pressure system will approach the area on Tue and will
bring northeast gales to 40-45 knots on Wed. The track of this low
is still uncertain and will have an impact on the wind speeds.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...JLB
LONG TERM...JAW
AVIATION...Ritzman
MARINE...JLB
Area Forecast Discussion
National Weather Service Seattle WA
222 PM PST Sun Nov 24 2019
.SYNOPSIS...Colder air will continue to filter into the region for
much of this week. Lingering showers will continue through
Tuesday before diminishing Wednesday. Snow levels may drop low
enough for some isolated snow or a rain-snow mix in some of the
lowland areas Monday night through Tuesday night. Conditions will
dry out Wednesday through late this week. The next chance for any
precipitation looks to be during the second half of next weekend.
&&
.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...A few showers have
developed this afternoon as expected. However, a PSCZ that earlier
was progged to develop during the early afternoon has yet to
form. However, short range guidance does still indicate the
potential for enhanced convection with this feature (also of note
is that the HRRR has trended a bit further north with this feature
now placing it along I-90). We will continue to monitor this
potential.
Shower activity is expected to increase somewhat overnight then
gradually diminish Monday through Tuesday night. Snow levels in
the central Cascades/central Puget Sound will drop below 3000
feet late this afternoon or early evening, reaching around 2000
feet Monday morning, around 1000 feet Monday night, and hovering
between sea level and 1000 feet Tuesday and beyond. Note that
areas to the north may see snow levels ~500 feet lower and areas
to the north ~500 feet higher. Some of the headlines:
* Widespread, significant snow accumulation is NOT expected in the
lowlands - in fact most areas will likely see no snow.
* However, we cannot rule out that any Puget Sound lowland area
could see a rain/snow mix or even a brief, light snow
accumulation (generally less than 1 inch) by the end of this
event.
* Pinpointing exactly where and when those accumulations will
occur is extremely difficult due to the hit/miss nature of the
showers. However, the best odds will be Monday afternoon through
Tuesday morning across the north Interior (Island, Skagit,
Snohomish, southern Whatcom, northern King, northern Jefferson,
and northern Clallam counties) where precipitation may be
enhanced by convergence at times, leading to temporarily lowered
snow levels and very isolated accumulations of 1-3 inches.
* The mountain passes will also see hit/miss snow showers through
Tuesday night - leading to quick bursts of snow accumulation
followed by periods of no snow. The best estimates place total
additional accumulation in the 4-8 inch range between now
through Tuesday night - though again convergence zones could
lead to significantly higher totals over narrow areas.
Obviously, with the lowering snow levels, temperatures are also
expected to fall over the next few days with lowland high
temperatures around 50 today, in the mid-40s Monday, and the low
40`s Tuesday. Overnight lows will fall to below freezing in most
lowland locations by Wednesday morning - so any residual moisture
on the roadways may turn to ice.
-Wolcott-
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Synoptically, a strong
mid level closed low will barrel down from Canada into the Pacific
NW Tuesday night into Wednesday. Current track of deep layer
moisture spares Washington and takes aim at southern OR and
northern CA. This leads ultimately to a dry forecast for the area,
however, could see a few wrap-around snow showers across the
Cascades during the first half of the day. Little additional
accumulation is expected. Still worth keeping an eye on the track
and progress of the closed low in case wrap-around lingers longer
than expected.
Thursday still looks mostly dry and cold for the Thanksgiving
holiday. High temps now looking to stay in the mid-upper 30s with
lows Thursday night in the low-mid 20s. An omega block tries to
develop across the eastern north Pacific & west coast Thursday
into Friday, keeping the cold dry pattern in place through the end
of the week and into the weekend.
The next chance for precipitation looks to hold off until late
Saturday or Sunday and even that is unclear at this time. With
cold air in place, cannot rule out precipitation starting as snow
or a rain/snow mix in the lowlands then turning to rain as snow
levels rise with an incoming system. We will continue to monitor
that potential this week.
Kovacik/Wolcott
&&
.AVIATION...Onshore flow will prevail tonight with NW winds
aloft. The air mass remains moist and slightly unstable for
scatted showers across the region. Ceilings are a mixed bag but
MVFR conditions are possible with showers. Most areas will see IFR
to MVFR conditions overnight. 33
KSEA...Expect showers in the vicinity tonight with possible MVFR
conditions. S winds at the surface to 10 kt. 33
&&
.MARINE...Onshore flow will continue tonight. Meanwhile, seas
will remain within 10 to 14 feet. A second system will drop down
from the northwest tonight and Monday for Small Craft Advisory
winds. Strong offshore flow will develop on Tuesday and continue
through Thursday. 33
&&
.HYDROLOGY...Snow levels will drop this week and significant QPF
accumulation is not expected, therefore, river flooding is not
expected during the next 7 days.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 10 PM PST Monday for Coastal Waters
From Cape Flattery To James Island 10 To 60 Nm-Coastal
Waters From James Island To Point Grenville 10 To 60 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater 10
To 60 Nm.
Small Craft Advisory for rough bar until 4 AM PST Tuesday for
Grays Harbor Bar.
Small Craft Advisory until 4 AM PST Monday for Coastal Waters
From Cape Flattery To James Island Out 10 Nm-Coastal Waters
From James Island To Point Grenville Out 10 Nm-Coastal
Waters From Point Grenville To Cape Shoalwater Out 10 Nm.
Small Craft Advisory until midnight PST tonight for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca.
Small Craft Advisory for hazardous seas until 4 PM PST Monday
for West Entrance U.S. Waters Strait Of Juan De Fuca.
&&
$$
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