Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/30/21

Area Forecast Discussion

National Weather Service Bismarck ND

 921 PM CST Mon Nov 29 2021

.UPDATE...
Issued at 921 PM CST Mon Nov 29 2021

We did add patchy fog to the forecast over western ND from 09 to
15 UTC, as it appears boundary layer stability and saturation in
vicinity of a weak frontal zone may favor its formation, although
recent guidance hasn`t been especially consistent in that signal.
Otherwise, ongoing shower activity in central ND will continue to
diminish as supported by radar trends, and only minor changes
were made to the rest of the forecast with this update.

UPDATE Issued at 555 PM CST Mon Nov 29 2021

Only minor changes were made to the evening forecast per recent
observational and rapid-refresh guidance trends. Precipitation in
north central ND is occurring in the right entrance region of an
~120 kt jet streak and zone of weak midlevel frontogenesis, and
is likely being aided by steep midlevel lapse rates. Extrapolating
radar trends suggests that activity should move out of the area by
mid evening. Otherwise, there`s a signal in recent guidance such
as the HRRR and GLAMP for fog development late tonight and Tuesday
morning, so if that remains consistent we may need to add fog into
the forecast for parts of the area with a later update.

&&

.SHORT TERM...(This afternoon through Tuesday night)
Issued at 205 PM CST Mon Nov 29 2021

Early this afternoon, the synoptic pattern was characterized by
broad northwest flow across a majority of the CONUS, with
troughing centered over the northeast. At the surface, high
pressure was centered over northeastern Wyoming, with a weak cold
front moving through the southern half of the forecast area.
Breezy west- northwest winds will continue through the afternoon,
with mild afternoon highs ranging from the lower 40s in the Turtle
Mountains area to the upper 50s in the southwest.

High clouds have been streaming in due to a shortwave moving
through the northwest flow, bringing a chance of rain to the
southwest tonight, with the bulk of precipitation chances to the
south and west of the forecast area where the base of the vort max
is. There is also a slight chance of rain in the north central
early this evening, with a weak impulse that CAMs were picking up
on, but that should be pretty short lived. Otherwise, it will be
mostly cloudy, with overnight lows generally in the 20s.

We`ll have another relatively mild day on Tuesday for the last day
of November, with a warm front drifting east through the day.
Chances for rain and snow start in the north central in the early
afternoon, before expanding south and east through the James
River Valley by the evening. There could potentially be some
p-type issues, primarily in the Turtle Mountains region, if the
front and associated precip chances speed up or slow down. But for
now, just have rain, snow, or a rain-snow mix, with chances
diminishing late in the evening.

.LONG TERM...(Wednesday through Sunday)
Issued at 205 PM CST Mon Nov 29 2021

Warm and windy Wednesday, before a steady cooling trend through
the weekend to bring us back down to near normal temperatures.

Broad northwest flow aloft continues through the end of the work
week, in response to higher heights over the southwestern US and
downstream persistent troughing over the eastern seaboard. In
coordination with our neighbors, we went ahead and bumped up high
temperatures slightly on Wednesday in the wake of Tuesday`s warm
front, as the deterministic NBM was on the lower end of guidance.
This puts forecast highs for Wednesday from the mid 40s in the
Turtle Mountains to the low to mid 60s in the southwest, with
these forecast highs just a few degrees cooler than records at
Bismarck and Dickinson (60 and 63 with records of 62 and 66,
respectively) or higher than the record like at Minot (54 with a
record of 56). Of course, the winds will come with the warmth,
with westerly winds sustained around 20 to 25 mph through the day.

From here starts the steady cooling trend as upper flow slowly
becomes more zonal and cooler air filters into the region, along
with a few weaker waves moving through, bringing low and scattered
chances for precipitation. One of those chances is Thursday, and
then again on Saturday night into Sunday. There is high confidence
on highs on Saturday being generally in the mid 20s to mid 30s, so
much closer to normal for this time of year compared to what we`ve
seen lately.

Next week is where much more uncertainty emerges. Cluster analysis
shows significant differences between ensemble means of the EC,
GFS, and Canadian, with the EC favoring a pattern similar to this
week, the GFS building a strong ridge over the Northern Rockies,
and the Canadian developing a trough off the western CONUS. These
uncertainties are reflected in a large spread in NBM temperature
percentiles, so although the current forecast has temperatures
right around normal to start next work week, this could change
pretty significantly over the next few days as guidance comes into
better agreement.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 921 PM CST Mon Nov 29 2021

VFR conditions may generally prevail tonight and early Tuesday,
but there is a chance of fog or low stratus developing in western
ND after about 09 UTC with an accompanying risk of MVFR or IFR
conditions. In addition, a warm front will move eastward across
the area Tuesday, and ceilings will lower, likely into MVFR range
at KMOT by Tuesday afternoon.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...CJS
SHORT TERM...MJ
LONG TERM...MJ
AVIATION...CJS



Area Forecast Discussion

National Weather Service Cleveland OH

 943 PM EST Mon Nov 29 2021

.SYNOPSIS...
High pressure exits to the east through this evening. Meanwhile,
a weakening clipper-type low will move generally eastward from
the Upper Mississippi Valley this afternoon to the Great Lakes
region overnight tonight before dissipating in vicinity of Lake
Ontario Tuesday morning. In the wake of the low, a weak trough
lingers over our region before a weak ridge attempts to build
from the Ohio Valley Tuesday night.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
Update...
Will be watching the western zones as the banding of snow that
has set up has not been as progressive as originally thought, so
may need to up these snow totals slightly. RAP guidance
suggesting a couple more hours residence in the far SW zones.

Previous Discussion...
Cyclonic westerly to northwesterly flow aloft and embedded
shortwave disturbances affect our CWA tonight through Tuesday.
A relatively-strong shortwave disturbance over the Upper MS
Valley this afternoon should move generally east-southeastward
across the Great Lakes overnight tonight through Tuesday
morning. This disturbance should then reach New England by
nightfall Tuesday evening. At the surface, a ridge exits
eastward from our CWA this evening. Meanwhile, a clipper-type
low accompanying the aforementioned shortwave will track
generally eastward from the Upper Midwest this afternoon to the
Great Lakes region overnight tonight. This low should then
dissipate in vicinity of Lake Ontario Tuesday morning as the
low becomes vertically-stacked with its parent shortwave
trough. Of note, isolated and light lake-effect snow and/or
rain showers in far-northeast OH and northwest PA will continue
to shift northward and eastward across the primary snowbelt and
retreat over Lake Erie by this early evening as the mean low-
level flow backs from westerly toward southwesterly. A lowering
inversion will cause lake-induced CAPE to wane and the lake-
effect precip will weaken further. Little or no snow accumulation
is expected.

Moist isentropic ascent aloft, ahead of the shortwave trough,
will allow a swath of widespread light precip to overspread our
CWA from west to east between about 9 PM this evening and the
predawn hours of Tuesday morning. Despite weak low-level WAA
accompanying the low pressure system, the wet-bulb effect should
allow snow to be the predominant precip type. Precip should
last for about six hours at any one location before ending from
west to east during the course of Tuesday morning. Snow may mix
with rain just before precip ends due to a combination of
lighter precip rates and a slower rate of the wet-bulb effect
amidst the low-level WAA regime. Model soundings indicate the
potential for moderate to strong isentropic ascent to be
maximized in a cloudy DGZ and allow a burst of moderate to heavy
snow to occur for an hour or two from west to east. Still
expect snowfall totals of 1-3" across the CWA. Lows should reach
the 20`s to 30 degrees in northwest PA and the lower 30`s in
northern OH around midnight tonight before readings rise
slightly through daybreak via the aforementioned WAA. Behind the
widespread precip, fair weather and partly to mostly cloudy
conditions are expected through Tuesday afternoon as a surface
trough lingers over/near the Great Lakes and a surface ridge
attempts to build from the TN Valley. Daytime highs should reach
the mid 30`s to lower 40`s in northwest PA and the low to mid
40`s in northern OH. The coolest readings are expected in the
higher terrain of northwest PA.

Cyclonic westerly to northwesterly flow aloft prevails Tuesday
night as the surface ridge attempts to build further from the TN
and OH Valleys. Fair weather is expected for most of our CWA.
However, a westerly to west-northwesterly mean low-level flow
may be just cold enough to allow a mix of lake-effect snow and
rain showers to impact the primary snowbelt. Model soundings
suggest lake-induced CAPE of several hundred J/kg and lake-
induced equilibrium levels near 5kft AGL will only be
marginally supportive of light precip. Any snow accumulations
should be less than one inch. Overnight lows should reach the
upper 20`s to mid 30`s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
The period will start out fairly quiet as mid/upper shortwave
ridging over the OH Valley early Wednesday shifts to the E Coast
during the afternoon with a 1024 mb surface high moving east as
well. A fast moving northern stream mid/upper shortwave will
approach the lower Great Lakes by Wednesday evening reinforcing the
chilly northwest flow pattern. Moisture advection ahead of this
shortwave is limited, but strong upper support near the left exit of
a 100-130 knot 300 mb jet streak will lead to periods of light rain
late Wednesday afternoon into Wednesday night with the greatest
coverage over the lakeshore counties. As the shortwave progresses
East/Southeast across the Northeast CONUS Thursday, the associated
surface low will deepen to around 990 mb while moving across Ontario
and Quebec dragging a cold front through our region Thursday
afternoon. Weak cold air advection and cyclonic flow behind the
front with 850 mb temps cooling to 0 to -3 C will support scattered
lake-effect rain and snow showers late Thursday afternoon into
Thursday night, so kept chances for precip in Northeast Ohio and
Northwest Pennsylvania given a W to NW flow across Lake Erie.
Guidance indicates very dry 850-700 mb profiles for this event with
shear quickly increasing Thursday night as shortwave ridging builds
in from the SW, so expect lake-effect to be light and disorganized.
Elsewhere, dry conditions are expected over the north central,
northwest, and southern most counties since these areas avoid the
flow from the lake.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
An active long-term period is expected with a series of Alberta
clipper-type systems, but confidence on timing the periods with the
best precip potential is low given model differences. The
aforementioned shortwave ridge Friday morning will be short lived as
the next northern stream shortwave approaches from the Northwest.
Warm air advection/isentropic ascent will lead to some light showers
ahead of this feature, and with highs in the mid/upper 40`s, it will
be a chilly and damp Friday. Renewed longwave troughing over the
Great Lakes and Northeast behind this system and associated cold,
cyclonic flow could set up lake-effect rain/snow showers behind the
cold front late Friday night, with this activity potentially
persisting into early Sunday. It should be noted that there are
significant differences in the degree of the cold air among the
ECMWF, GFS, and CMC for Saturday into Sunday. These differences, as
well as questions on the amount of moisture and shear, make the
amount of lake-effect low confidence at this point. At this time,
westerly flow Friday night and Saturday veering to Northwest
Saturday night into Sunday morning points to the highest PoPs
starting over the primary snowbelt of Northeast Ohio and Northwest
Pennsylvania then shifting further inland. There should be a break
Sunday as shortwave ridging builds in before another clipper drops
Southeast late Sunday into Monday followed by renewed lake-effect
chances. We are definitely heading into the Christmas season!

&&

.AVIATION /00Z Tuesday THROUGH Saturday/...
Light snow to overspread the region and will see lowering
ceilings in fairly rapid order as the warm front approaches from
the west. IFR expected in the snow in visibilities, and at times
in ceilings, which could put down a quick 2 or so inches in just
a couple of hours. Snow exits to the east, and with it being a
warm front in nature, some rain mixing in with the snow upon
exit is possible even though this may be in the overnight hours.
Once the snow exits a terminal, should be a fairly quick
rebound to VFR conditions.

Outlook...Non-VFR with periods of rain and/or snow are possible
Tuesday afternoon through Saturday.

&&

.MARINE...
Southwest winds at 10-15 knots Wednesday will increase to 20-25
knots and veer more west-southwest Wednesday night and west Thursday
as a cold front moves through. This will lead to small craft
conditions. A lingering trough Thursday night will keep NW winds up
in the 10-20 knot range before diminishing to 5-10 knots during the
day Friday and backing more westerly due to shortwave ridging
building into the lower Ohio Valley. A series of fast moving
shortwave troughs and associated cold air advection will support
strong 15-25 knot westerly flow Friday night and Saturday decreasing
to 10-15 knots and becoming NW Saturday night and Sunday, so small
craft advisories could be needed again this weekend. Additional
small craft advisories are possible Sunday night into Monday as
southerly flow increases ahead of another front Sunday night veering
to NW Monday.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...None.

&&

$$
SYNOPSIS...Jaszka
NEAR TERM...Jaszka/26
SHORT TERM...
LONG TERM...
AVIATION...26
MARINE...



Area Forecast Discussion

National Weather Service Twin Cities/Chanhassen MN

 704 PM CST Mon Nov 29 2021

.DISCUSSION...(This evening through Sunday)
Issued at 310 PM CST Mon Nov 29 2021

Temperatures have overachieved and made it to the 60 degree mark
across far southern Minnesota with widespread upper 40s to mid 50s
across central Minnesota where a warm front has moved through. This
front hasn`t quite made it into western Wisconsin where temperatures
are still in the low 40s. Additionally, this area has been battling
cloud cover left over from this morning`s weak clipper system,
currently centered over northern Wisconsin. Winds have already
switched back around to the northwest across western Minnesota as of
the 2pm hour as the weak cold front on the heels of the
aforementioned warm front makes its way eastward. Winds are also a
bit breezy on the backside of this system with gusts of up to 30 MPH
possible into the evening hours.

Heading into tomorrow, we`ll be a bit cooler with another clipper
taking aim at region by tomorrow night. P-type becomes the main
concern as temperatures will start out above freezing and then hover
near freezing or just above mainly south of I-94. However, similar
to this morning, dry air aloft will likely greatly reduce the amount
of precip able to reach the ground, resulting in little to no
accumulation. But even if some areas of central Minnesota and
northwestern Wisconsin are able to pick up a few hundredths of an
inch of snow, another shot of warm air will quickly melt it. Went
ahead and bumped highs up for both Wednesday and Thursday as they
have been underdone lately. Another run at 60 is likely for
southwestern Minnesota and upper 40s and 50s to the north and east
for Wednesday with WAA working in from the west.

We see a cooling trend begin Friday with temperatures returning to
near normal into the weekend. Our next possible chance of some snow
looks to be late Sunday, but model agreement is still quite poor at
this point in time. So, have left NBM PoPs as is for now, which are
fairly unimpressive.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 622 PM CST Mon Nov 29 2021

Main concern this period is the stratus up in northwest Ontario that
is heading for the Arrowhead. There are some guidance members that
show these clouds possibly reaching as far west as MSP. Since its 18z
run, the HRRR has been trending toward a much less aggressive
approach with the stratus through the night, so kept TAFs VFR, with
EAU being the airport that has the greatest chances of seeing some
stratus Tuesday morning. Winds will remain out of the northwest, but
by late Tuesday afternoon, the approach of the next clipper for
Tuesday night/Wednesday morning will quickly switch winds back to the
southeast to end this period.

KMSP...The RAP/HRRR/NAM/GFS all show precip breaking out at MSP just
before 6z Wed, which is the end of this TAF period. It looks warm
enough to keep P-type as all rain, but given the number of models
producing light precip at MSP, did bring in some prevailing rain at
4z Wed to cover that threat. It looks unlikely this forcing/precip
will bring sub-VFR conditions with it.

/OUTLOOK FOR KMSP/
Wed...VFR. Wind W/SW 10-15 kts.
Thu...VFR. Wind NW 10G20 kts.
Fri...VFR. Wind lgt and vrb bcmg NW 15G25kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&

$$

DISCUSSION...Dye
AVIATION...MPG



Area Forecast Discussion

National Weather Service Portland OR

 223 PM PST Mon Nov 29 2021

.SYNOPSIS...Areas of drizzle and light rain will be possible to the
north late tonight into tomorrow, with high pressure keeping
conditions drier to the south of Salem. A weak cold front brings a
chance of light rain Wednesday night into Thursday for northern
zones, followed by a similar system Friday night or Saturday.
Temperatures will remain above normal through at least Thursday,
though confidence is increasing in temperatures returning closer to
seasonal normals as we head into the weekend.

&&

.SHORT TERM...This evening through Thursday...Radar, webcam, and
surface weather observations from early Monday afternoon showed areas
of drizzle occurring for locations to the north of Florence along the
coast and to the north of Salem inland. This was associated with a
stratus deck featuring cloud bases between 500-1500 feet. The latest
iteration of the HRRR appears to be handling the low stratus and
drizzle relatively well compared to other available model guidance.
HRRR BUFR soundings this evening show cloud bases lifting a bit
towards sunset while the stratus deck attempts to temporarily scatter
out. The HREF ensemble mean for low-level cloud cover also suggests
the stratus deck will begin breaking up a bit this evening. As a
result, there will be decreasing chances for drizzle this evening
until chances increase again later tonight as the stratus deck
solidifies and boundary layer moisture deepens. That said, not much
if any drizzle is expected to the south of Salem as the moist layer
will likely not be deep enough to support drizzle. This trend should
continue tomorrow, with locations south of Salem likely staying dry
while areas to the north deal with areas of drizzle and/or light
rain. It will also be another mild day for this time of year, with
forecast highs generally in the upper 50s to lower 60s, warmest to
the south.

Surface high pressure will expand northward across northwest OR and
southwest WA Tuesday night, which will bring calm winds and help set
the stage for areas of fog and/or low stratus to develop over the
interior lowlands. This makes for a difficult high temperature
forecast on Wednesday, which has the potential to be relatively warm
with highs around 60 degrees according to the NBM. That said, if fog
and/or low stratus hangs on through much of the day, then highs in
the upper 40s to mid 50s would be the more likely outcome. Forecast
soundings show very limited vertical mixing across the area on
Wednesday with nearly calm boundary layer winds, especially in the
southern Willamette Valley and Lane County Cascade foothills. This
should make it difficult for fog and low stratus to lift, so the NBM
25th percentile guidance was used for the high temperature forecast
on Wednesday. This decreased forecast high temperatures by a few
degrees. In reality, the NBM 10th percentile guidance may be even
more realistic, but confidence is not high enough to go with that at
this time. However, confidence is high that the poor vertical mixing
and weak boundary layer winds will result in a stagnant airmass over
the southern valley and Lane County Cascade foothills, including
Eugene and Oakridge. Therefore, an Air Stagnation Advisory has been
issued for these areas through Thursday morning due to a prolonged
period of light winds and reduced mixing. While air quality currently
remains good, there is the potential for air quality to gradually
deteriorate over the next couple of days. It appears conditions
should begin to improve on Thursday as the surface pressure gradient
strengthens over the forecast area and brings more mixing. -TK

&&

.LONG TERM...Thursday night through Sunday night...The 12z iteration
of the GFS/EURO both show offshore flow developing Thursday night
into Friday as surface high pressure strengthens east of the Cascades
and relatively lower pressure develops along the Oregon coastline.
This will set the stage for breezy east winds through the Columbia
Gorge into eastern portions of the Portland metro, with winds turning
to the north over the central and southern Willamette Valley. While
there is still some uncertainty regarding the strength of the
pressure gradient over the Columbia Gorge, it appears it will be a
fairly typical gap-driven east wind with gusts in the 20 to 30 mph
range at Troutdale. Slightly stronger gusts can be expected between
Troutdale and Corbett, with the strongest winds at Crown Point where
gusts could exceed 40 mph. As usual with our gap-driven east wind
events, northerly flow in the central and southern valley will be
considerably weaker with gusts only around 10-15 mph. Aside from the
wind, Thursday night and Friday should be dry and cooler with
temperatures falling down to seasonable normals for early December
(mid to upper 40s during the day, 30s at night).

Models and their ensembles are still showing a good deal of model
spread this weekend in regards to precipitation chances and the
overall synoptic scale pattern. The WPC`s cluster analysis displays
this uncertainty well, as some cluster solutions suggest upper level
ridging will continue across the western United States while others
suggest ridging will flatten and allow for shortwave troughs to
affect the Pacific Northwest. If ridging continues, then the ongoing
warmer and drier than normal conditions would most likely continue
this weekend. If the ridge flattens out, then more seasonable
temperatures and occasional chances for rain would be likely. That
said, the GFS ensemble and the EURO ensemble are now slightly
favoring warmer and drier than normal conditions this weekend with
upper level ridging continuing. Decided not to stray away from the
NBM given the uncertainty involved. -TK

&&

.AVIATION...00Z TAF preliminary thoughts: As expected, low clouds
have remained across much of the area. However, lift through
those clouds have brought drizzle and brief light rain which
dropped vsbys down to lower IFR ranges. As of 22Z, am starting to
see the low clouds begin to dissipate. Continue to think 23-00Z
will be the transition period to somewhat higher cloud bases.

For tonight, conditions will gradually deteriorate as mixing
ends and stable low level conditions develop as a warm front
approaches from the northwest. Expect low clouds and patchy fog
to return overnight and likely last through the Tuesday morning
hours. Additionally, the warm front will likely bring rain to
KAST after daybreak to further bring low cloud and visibility
concerns. Some rain may also spread as far east as KTTD and
south to KUAO. Flight conditions will again be slow to improve
tomorrow, perhaps returning to VFR inland near 30/22Z but stay
low end MVFR or IFR along the coast.

For detailed regional Pac NW aviation weather information, go online
to: https://weather.gov/zse

KPDX AND APPROACHES...Little immediate improvement with cigs
likely to remain below FL015 until closer to 30/00Z. Cigs will
then fall below FL040 again near midnight (08Z) and then closer
to FL010 a few hours later. Then, no improvement expected through
the Tuesday morning arrival push with the earliest return to VFR
not much sooner than 30/22Z. /JBonk

&&

.MARINE...No significant changes with the primary concerns
continuing around the approaching warm front tonight and Tuesday.
Main wind focus stays over the northern waters although winds
may be a bit slower to ease Tuesday evening with the latest trend
possibly warranting an extension of the SCA for a few hours
after Midnight Tuesday night into Wednesday. The initial wind
event will also bring combines seas above 10 feet for the
northern waters. However, today`s wave guidance now brings seas
in the central waters to 10-11 feet but not until Wednesday. Will
watch this trend as well to see if it necessitates bringing
those waters into the SCA any sooner than early Wednesday.

Then, high pressure well offshore will force a cold front across
the waters from north to south on Thursday for another round of
gusts 25-30 kt but from the northwest. Seas will also build
toward 10-12 feet under a northwesterly swell if they haven`t
dropped below prior to that.

Friday and Saturday bring weak pressure gradients across the
waters, however, low pressure located well offshore will bring
some form of easterly component winds. /JBonk


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until noon PST Thursday for Cascade
     Foothills in Lane County-Cascades in Lane County-South
     Willamette Valley.

WA...None.
PZ...Small Craft Advisory from 3 AM to 10 PM PST Tuesday for coastal
     waters from Cape Shoalwater WA to Cascade Head OR out 60
     nm.

     Small Craft Advisory until 3 PM PST this afternoon for Columbia
     River Bar.

     Small Craft Advisory from 11 PM this evening to 3 AM PST
     Tuesday for Columbia River Bar.

&&

$$

www.weather.gov/portland

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