Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/23/24
Area Forecast Discussion
National Weather Service La Crosse WI
928 PM CST Sun Dec 22 2024
.KEY MESSAGES...
- Freezing drizzle and light snow will likely occur late tonight
into early Monday afternoon. While amounts will be light,
confidence has increased (60%) that freezing drizzle will
affect the morning commute along and northeast of I-94 and
along I-90 east of the Mississippi River.
- Warmer temperatures in the 30s and potentially even the 40s
return over the next 7 days.
&&
.UPDATE...
Issued at 927 PM CST Sun Dec 22 2024
Tricky forecast continues for overnight and early Monday. While
no headline changes are planned at the moment, confidence is
still wavering on how possible freezing drizzle may work out
overnight into Monday morning. Often a tough forecast to
determine, but we are certainly taking into account potential
for impacts Monday morning with holiday travelers and such. Good
thing is most schools are closed.
Temperatures continue to warm this evening with readings above
freezing up to I-90 already. With continued warm air advection
overnight, should not see any drop, especially as wet bulbs
continue to climb too. Still fighting some dry mid layers with
passing radar echoes rarely reaching the ground.
00z model guidance is delaying additional precipitation a bit,
and quick look at ensembles suggest maybe lower signals for
freezing precipitation, or at least lower confidence. Tricky
part is it does not take much to cause impacts. Latest RAP data
suggests there is some loss of ice advecting in overnight which
might favor drizzle and certainly the isentropic lift favors
eventual saturation. So, we will see how it all comes together.
Could still see a brief, light snow accumulation as system moves
through during the day Monday but not sure there will be much
impact.
&&
.DISCUSSION...
Issued at 302 PM CST Sun Dec 22 2024
Wintry precip overnight into Monday
Overnight into Monday, upper wave, located over MT as of 19z, will
advance east-southeast to the Great Lakes, passing over the CWA.
Ahead of this feature, expect low level WAA, currently ongoing, to
continue wit this also bringing some moisture to the area in the
low to mid-levels. With QG forcing helping to generate lift and low-
level upglide seen on the 280 and 285K surfaces, precip would
seemingly be a good bet across much of the area. However, issue with
the precip event continues to be trouble with a dry air intrusion
around 700mb, giving progged soundings, including much of the 22.12z
HREF, a bit of an onion shape with a saturated DGZ atop a dry layer
atop saturated low levels. In northeast Iowa and adjacent areas of
MN and WI, this dry air will likely eat into both the ice
introduction zone aloft and the near-surface moist layer to prevent
much precip from occurring, though if it were to occur, it would
mainly be freezing drizzle. For areas to the northeast - roughly
between a Rochester to Boscobel line and I-94 - ice crystals will
struggle to survive the fall while low level moisture depth may be
sufficient for freezing drizzle to occur more often compared to
areas to the southwest, with surface temps rising above freezing
during the day leading to a changeover to straight drizzle. For
areas in our far northeast, this intrusion will be weaker but still
strong enough to lead to an initial period with freezing drizzle
before snow becomes dominant after sunrise as ice slowly saturated
the mid-level dry layer.
Unfortunately, the timing of this freezing drizzle, if it occurs,
would affect the morning commute and areas along I-90 east of the
river and along I-94. Thus, while confidence in impactful freezing
drizzle is lower than would be comfortable, have issued a Winter
Weather Advisory covering north central WI, the I-94 corridor, and
Vernon and Richland Counties. Buffalo and Trempealeau may need to be
added but confidence in impacts there was too low to override
collaboration concerns with this update. This may change this
evening or overnight as the situation evolves.
Warming up next week
Next week brings a general trend toward rising heights aloft and
warmer temperatures with highs in the 40s and 50s. Christmas upper
trough continues to focus potential impacts to our southeast, so the
forecast remains free of precip for the 24th and 25th. Beyond
Christmas, confidence in details of the upper pattern becomes low,
particularly with a series of three upper disturbances during the
latter part of the week, where guidance spread remains large with
both timing and position, which will have implications for any
precip with these waves. That said, temperatures are warm enough
that LREF probs for snow are under 5 percent, so have gone with an
all rain forecast while sticking with NBM PoPs.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 549 PM CST Sun Dec 22 2024
An area of surface low pressure over northeast Nebraska is
forecast to track northeast toward southeast Minnesota into
central Wisconsin. Forecast soundings show VFR ceilings today
start, however with time, low level moisture increases enough
for patchy freezing drizzle as the surface low tracks through
the region...with mixing with and changing to snow. The hi-res
models show varying coverages of snow including parts of
southeast MN into central WI or just central WI. For now with the
with the precipitation being quite light, included a prob30 at
both RST/LSE Monday morning with IFR/LIFR ceilings. Brisk south
winds diminish as the surface low approaches, then shifts to
the west and northwest later monday Morning and Monday
afternoon.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 3 PM CST Monday for WIZ017-029.
Winter Weather Advisory from 3 AM to 3 PM CST Monday for
WIZ034-041>044-053-055.
MN...None.
IA...None.
&&
$$
UPDATE...Shea
DISCUSSION...Ferguson
AVIATION...Zapotocny
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
630 PM EST Sun Dec 22 2024
.KEY MESSAGES...
- Forecast confidence continues to increase for wintry weather on
Monday from midday into the early evening.
- Highest snowfall amounts will be north of M-46, with lighter
amounts and the increased chance a period of sleet and/or light
freezing rain across the Detroit Metro region.
- Warmer weather expected Christmas Day through the end of the week.
&&
.AVIATION...
Southeast Michigan is caught in a setup tonight that will favor both
midlevel moisture return with southerly gradient trajectories but
mid to upper level subsidence and stability due to confluence aloft.
The net result for the next 12 to 18 hours through midday Monday is
VFR conditions with midcloud based at approximately 8.0-10.0 kft
agl. Modest warm air/moisture advection in advance of Pacific
shortwave will then support precipitation chances Monday afternoon
and Monday evening. Latest trend has been to push back timing and
delayed the onset at all taf sites by an hour or two. Northern taf
sites will support all snow, whereas southern taf sites including
DTW may see a period of RAPLSN mix at the front end. Uncertainty
remains on when precipitation will begin and low confidence exists
on the duration of any mixed precipitation. When confidence
increases on location of higher precipitation rates, may need to
insert some LIFR flight categories due to visibility restrictions or
on ceiling heights.
For DTW...Pushed back timing of precipitation onset to 19Z Monday.
Will have the potential for mixed precipitation at the beginning of
the event before precipitation changes to snow. Total amounts will
be depended on the duration of snow which remains of low confidence.
DTW THRESHOLD PROBABILITIES...
* Low for ceiling at or below 5000 feet tonight, then high after 19Z
Monday.
* Low for precipitation type as light freezing rain and/or sleet
before 18Z Z Monday, then high for a changeover to snow by 19Z
Monday.
&&
.PREV DISCUSSION...
Issued at 300 PM EST Sun Dec 22 2024
DISCUSSION...
This is the coldest day of this young winter season thus far - with
many locations start from near, if not slightly below, 0F this
morning - and temperatures struggling to climb through the teens.
The early sun has giving way to the mid clouds staged over Western
Michigan. These clouds will thin and move out of the area only to
give way to more mid/high clouds by sunset as the upstream system
approaches.
A well defined shortwave trough over the Northern Plains within the
broader west-northwest flow will spin through the Great Lakes Region
on Monday. The system is currently moisture starved - with limited
precipitation coverage. Expectations are for the low-level moisture
poised over east Texas north into southern Missouri to get pulled
into the warm conveyor belt as the wave crosses the region.
Recent guidance trends on both translation and development sequence
is slower. This is especially noted with the RAP sequence slowing
slightly each cycle. The net impact is a weaker system with a shift
northward of the primary forcing. Furthermore, the NWP suite is now
collapsing on a common solution picture, with the CAM offerings more
muted with the precipitation production compared to prior cycles.
This slower solution timeline places the bulk of the precipitation in
the afternoon and early evening hours - with a little longer runout
time across the Thumb along the near surface track.
The column warms substantially over the next 24 hours with a nose of
above freezing air crawling in around 850-mb from around M-59 and
southward during the midday hours. The integrity of the warm air
will be rather tenuous with any higher precipitation rate quickly
cooling the layer. The vacillation of the thermal profile will be
enough to support a few rapid precip type transitions between light
freezing rain, sleet, and snow - depending on intensity. Only minor
glazing would occur with any light freezing rain, as surface
temperatures will be hovering around freezing. The boundary layer may
warm enough by late afternoon across Metro Detroit and south to
support rain.
There appears to be two to three waves of forcing with moisture
transport. The lack of continuous inflow of moisture will lead to
rather erratic coverage with initial saturation layers in the
isentropic ascent generating a frontogenetic response, only to quell
rather quickly due to lack of sustaining moisture. The net result
will be widely varying snowfall amounts north of I-69. Additionally,
the warming column will push the DGZ deep into the cloud layer -
removed from the peak forcing. Therefore, expecting near to slightly
lower than climatological snow ratios. The net result is a base of 1-
3 inches, with pockets of 4-5 inches where the forcing can maintain
longevity, most likely along and north of M-46.
The western flank of the cold dome will be somewhat resistant to
leave the Lakes Region on Christmas Day - offering another round of
clouds and a small chance of precipitation as another pulse in
moisture transport glides up the isentropic slope. The near surface
layer will be another couple clicks warmer - so rain appears to be
the dominant type for anything that falls.
The column then will continue to warm supporting above average
temperatures for the remainder of the week - probably with more low
clouds and fog again.
MARINE...
Southerly flow strengthens through the night as low pressure
approaches from the upper Midwest. Peak winds occur Monday morning
with gusts between 25-30kts possible across the bulk of Lake Huron
and 20-25kts possible over the rest of the region. Despite the
offshore flow, winds will be strong enough to support 3-5+ft waves
in the Thumb nearshore waters- small craft advisories are in effect
until Monday afternoon. Widespread snow tapers off by early Tuesday
as low pressure vacates to the east setting up northerly winds
(veering from NW to NE) in its wake. Gradient rapidly weakens on the
backside of the system as high pressure is quick to build in
resulting relatively light northerly flow (at or below 15kts). Weak
influence from this high persists through midweek maintaining
lighter flow.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 4 AM to 4 PM EST Monday for LHZ421-
441>443.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&
$$
AVIATION.....CB
DISCUSSION...Mann
MARINE.......KDK
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service Quad Cities IA IL
900 PM CST Sun Dec 22 2024
.KEY MESSAGES...
- The risk of freezing drizzle tonight into Monday morning has
gone down. The risk now looks to be a 20-30 percent chance
north of an Independence, IA to north of Sterling, IL line.
- Warmer temperatures along with several chances for rain will
finish out 2024 with very little sunshine.
&&
.UPDATE...
Issued at 852 PM CST Sun Dec 22 2024
Looking at 00z guidance coming in, and both the NAM and NAMnest
continue to support a lower end freezing drizzle in our northern
and / eastern CWA. However, both of these models have once again
incorrectly initialized and maintain a overly aggressive snow
depth over our entire northeast 1/2 of the CWA through the next
couple days, and that`s already wrong. Our current snow depth
generally runs 1+" from near Dubuque to Freeport, with much less
to the south and southwest. With temperatures already running
3+ degrees higher on 2M temperatures than both models, that
incorrect snow depth seems to be playing a factor.
The HRRR has less snow depth this far south, and not too
surprisingly, has little to no ice. Thus, our forecast with
lower end chances (15-25%) for light icing will remain until we
see short term trends take place late tonight.
The incoming low clouds are making the way northeast as
expected, but remain well southwest of the CWA, in southeastern
Kansas as of 845 PM. They are lifting northeast at 40kts, so we
do expect an increase in lower clouds towards morning.
&&
.SHORT TERM /THROUGH MONDAY/...
Issued at 237 PM CST Sun Dec 22 2024
Quiet conditions will be seen through midnight as a storm system
approaches the area.
After midnight and through Monday morning, the clipper system will
quickly move through the area. The trend from the models 24 hours
ago has been to move the track of the storm further north. The
further north track now raises questions regarding any impactful
weather late tonight into the Monday morning commute.
The better forcing is still from Minnesota into Wisconsin. Forecast
profiles of the atmosphere continue to suggest the potential for
drizzle and/or freezing drizzle for roughly a 6 hour time frame from
about 3 AM to 9 AM Monday morning. The further north track of the
low center now would confine any freezing drizzle to the deeper snow
field across the area; roughly Independence, IA to north of a
Sterling, IL line. Compared to yesterday, the overall risk for
freezing drizzle has gone down and now looks to be at a 20-30
percent chance.
The southerly winds pushing warm air and moisture into the area at
lower levels combined with cloud cover does have the potential (15-
20 percent) for keeping any precipitation in a liquid form late
tonight into Monday morning.
Clearing skies from west to east by late Monday morning and through
the afternoon and continued southerly winds will help boost
temperatures above normal.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 237 PM CST Sun Dec 22 2024
Monday night/Tuesday
Assessment...high confidence on dry conditions
Dry conditions with near seasonable temperatures will be seen as
high pressure quickly moves through the Midwest. Attention then
turns to the remainder of the week.
Tuesday night through Sunday
Assessment...high confidence on warmer than normal temperatures.
Several chances for rain with little sunshine expected.
The second half of the week and into the weekend will result in very
little if any sunshine being seen. The lack of sunshine can be
traced to an inversion aloft helping to trap moisture in the form of
clouds across the Midwest as each system moves through the Midwest.
It will not rain continuously the entire time period. There will be
periods of 6-12 hours where dry conditions will be seen.
There are differences between the global models in timing. However,
there is loose agreement of at least two and possibly three systems
moving through the Midwest.
The models agree that Monday night and Tuesday will be dry across
the area.
The models diverge slightly but still have fairly good agreement
that the first round of rain will occur Tuesday night into Wednesday
for areas along and east of the Mississippi. The model consensus
during this time frame has a 20 to 40 percent chance of rain.
The individual models begin to diverge after Wednesday but the
overall trend of the deterministic and ensemble members indicate
Wednesday night and Thursday looks to be dry.
The next time frame that looks favorable for rain is Thursday night
through Friday night as another storm system moves through the area.
Given the slight differences in timing and track, the model
consensus has a 35-50 percent chance of rain.
Saturday into Sunday has the highest uncertainty regarding rain
chances. Two scenarios are in play; 1) a second storm system will
arrive right on the heels of the late week system or 2) a separate
upper level disturbance traveling well behind the first system moves
in from the Plains.
Regardless of which scenario is correct, the models agree that
moisture will be trapped below an inversion aloft which will keep
clouds across the area. With a layer of saturated moisture already
in place, there will be a risk of rain when lift acts upon it. Right
now the model consensus has a 30-40 percent chance of rain Saturday
and Saturday night that decreases to a 20 percent chance of rain for
Sunday.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 532 PM CST Sun Dec 22 2024
VFR conditions are expected through early Monday morning, as
south winds at the surface and aloft continue to drawn in milder
air and eventually moisture. The onset of low clouds, with bases
of 2500 to 3500 ft are expected to arrive late tonight, with
some possible drizzle or freezing drizzle in northwest Illinois
and far northeast Iowa. These clouds are currently in Oklahoma,
and will need to travel and expand from a long ways away, but
this should spread into eastern Iowa and Illinois around the 09z
to 12z time frame. A fast moving clipper system moving north of
our area will switch winds to west Monday morning, and in cold
advection through the day, MVFR cigs may linger in northeast
Iowa all day.
Low level wind shear is expected overnight, with strong south
winds of 40 to 45 kts about 1400-1600 ft above the ground. This
LLWS should end around 12Z, as the low pressure system shifts
east into Wisconsin.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.
&&
$$
UPDATE...Ervin
SHORT TERM...08
LONG TERM...08
AVIATION...Ervin
Area Forecast Discussion
National Weather Service Peachtree City GA
830 PM EST Sun Dec 22 2024
...Evening Update...
.UPDATE...
Issued at 820 PM EST Sun Dec 22 2024
Small update this evening mostly to rain chances in eastern GA
Monday night. Not much change overall, just a small reduction in
rain chances in line with some of the most recent model updates.
Isentropic upglide still looks to be the primary mechanism by
which any rain will form, and discussion below still holds for
rain (and possibly brief light sleet chances).
&&
.SHORT TERM...
(This afternoon through Monday night)
Issued at 202 PM EST Sun Dec 22 2024
No forecast concerns or weather impacts expected. Dry and cool
conditions with only light east winds.
Humidity this afternoon did drop below NBM forecasts so again
lowered dewpoints for 15Z Mon-00Z Tues blending MOS and HRRR
with NBM and NBM 10th percentile. Still likely too cool for any
prescribed burning but will continue to monitor for possible fire
danger statement.
Any very light precip associated with weak wave over FL peninsula
should hold off until Monday night as it slides NE off SC/GA
coast. With relatively dry low levels, moisture aloft and a bit of
evaporative cooling from light precip falling into dry air, could
see some light sleet mixed in with sprinkles. No impacts expected.
SNELSON
&&
.LONG TERM...
(Tuesday morning through next Saturday)
Issued at 202 PM EST Sun Dec 22 2024
Polar express? More like shortwave express! As we move into the
longterm period, the jet pattern moves out of a NW flow into a more
split flow/divergent regime on Wednesday (Tuesday dry). The northern
polar jet generally troughs out, though intermittent constructive and
destructive amplification will mask the larger feature. These
shortwaves will be the main weather driver through the holiday week.
High pressure near the surface and ridging aloft over the east coast
will continue to drive surface E flow, supporting the wedge and the
thin layer of dry air near the surface. That said, flow quickly
become W and SW as you move upwards, meaning modestly warm moist air
overriding the surface feature. Low end PoPs (15-30%) move across
the CWA Wednesday onward. Conditions will likely be dreary with
consistent thick cloud cover, off and on rain/drizzle, and low
accumulations. Most areas will struggle to see much more than 0.30"
through Saturday. The probability of anywhere seeing more than 0.5"
of rain, according to ensembles, sits right around 25-30% north of
I85 and 15-20% to the south. Thunderstorms through the extended
outlook appear unlikely with a general lack of instability and weak
synoptic lift.
Temperatures through the long term will be slightly above normal,
even with the wedge. Highs each day will be in the mid 50s to even
mid 60s. The coolest temps will be closer to the beginning of the
week with Tuesday lows near 30 up north and closer to 40 down south.
Overnight temperatures increase through the week to the 40s and 50s.
SM
&&
.AVIATION...
(00Z TAFS)
Issued at 651 PM EST Sun Dec 22 2024
VFR through TAF period. Winds will remain on east side through
period, going light overnight then 7-12 kts tomorrow by the
afternoon. Some very elevated cloud may begin to impact metro TAF
sites by 00Z tomorrow night, but currently expecting conditions to
remain VFR.
//ATL Confidence...00Z Update...
High all elements.
Lusk
&&
.PRELIMINARY POINT TEMPS/POPS...
Athens 25 46 29 56 / 0 0 10 0
Atlanta 29 48 32 57 / 0 0 0 0
Blairsville 22 46 26 56 / 0 0 0 0
Cartersville 27 49 28 57 / 0 0 0 0
Columbus 30 54 35 61 / 0 0 0 0
Gainesville 26 46 30 57 / 0 0 0 0
Macon 28 51 34 58 / 0 0 10 0
Rome 26 50 28 57 / 0 0 0 0
Peachtree City 26 49 30 58 / 0 0 0 0
Vidalia 32 52 40 61 / 0 10 10 0
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...SNELSON
LONG TERM....SM
AVIATION...Lusk
Area Forecast Discussion
National Weather Service Grand Forks ND
951 PM CST Sun Dec 22 2024
.KEY MESSAGES...
- Wintry mix within southeast North Dakota into west-central
Minnesota after sunset into early Monday morning may impact
travel conditions from light icing. There is a 40% chance of a
glaze of ice through Monday morning.
- Warming up for the holiday week.
&&
.UPDATE...
Issued at 951 PM CST Sun Dec 22 2024
The reflectivities continue to take more of a SSE track, but the
winter weather advisory is still holding up. May need an
extension once we reevaluate conditions in the next few hours.
Forecast remains on track.
UPDATE Issued at 716 PM CST Sun Dec 22 2024
Starting to see the area of mixed precipitation make its way
into southeastern North Dakota. Use caution out and about as
things are expected to be slick where this mixed precip falls.
Forecast remains on track.
&&
.DISCUSSION...
Issued at 315 PM CST Sun Dec 22 2024
...Synopsis...
Water vapor satellite imagery this afternoon reveals an
elongated, low amplitude shortwave trough within ND/MT, with a
modest but present mid level jet helping force and propagate
this east- southeast. Radar and surface observations/reports
confirms an area of freezing rain within west and central ND.
Radar returns are showing up in eastern ND into MN, although a
notable dry layer rooted around 800 mb is preventing these
leading radar returns from reaching the ground.
Forecast guidance continues to suggest this dry layer should
saturate as the main wave moves through southeast ND into
central MN, allowing a wintry mix to reach the ground, including
freezing liquid. This continues the potential for light icing in
these locations tonight into Monday morning. Additionally,
recent guidance is suggesting the possibility of freezing
drizzle elsewhere through the morning on Monday. More on the
potential for light icing and associated uncertainty can be
found below.
Low level moisture trapped underneath an inversion will also
promote the development of fog within portions of our area,
including the possibility of dense fog. Latest guidance like
HRRR and HREF holds relatively highest chance (40%) for dense
fog within eastern North Dakota along and west of the Red River
Valley tonight into Monday morning. However, as is common with
fog, confidence is low on location and coverage of dense fog.
Getting into next week, ensemble guidance wants to propagate
upper ridging and split flow east into the central CONUS by
late next week. As it does this, some ensemble guidance favors
embedded weaker shortwave troughs within the flow to move
through the Northern Plains/Upper Midwest, which may bring brief
periods of light precipitation. This regime also favors warmer
than average temperatures, including temperatures near or just
above freezing. This will influence precipitation type, and
additional bouts of wintry mix or even plain rain will be
possible.
Ensemble guidance differs in exactly how split flow moves into
the central CONUS as well as how the upper ridge breaks down and
propagates eastward. But one cluster of guidance does reveal
broad southwest flow aloft over the Plains and Midwest by late
next week, with upper troughing now attempting to dig into the
western CONUS. This may promote a larger system to develop and
move through the central CONUS. Uncertainty in potential
impacts is large from this potential system late next week, not
only driven by differences in synoptic evolution within ensemble
guidance, but also with temperatures hovering around freezing
leading to uncertainty in precipitation type.
...Potential impacts from icing tonight into Monday morning..
Despite the shortwave and its associated precipitation already
within central ND, uncertainty lingers with respect to coverage
of light icing. As the wave moves into central MN, synoptic
forcing starts to weaken as the modest jet maintaining the wave
starts to lessen. This brings uncertainty in how much precip
may actually be able to punch through the dry 800 mb layer.
There is evidence of mid level conditional instability above 700
mb which introduces more showery-type precipitation, again
lowering confidence in coverage. In our area, we also have
deeper low level cold layer under warm nose aloft. This may
promote sleet in addition to freezing rain. Lastly, as the wave
moves east into Minnesota, cooler air filtering in behind the
departing mid level forcing will help keep the lowest 1 km
saturated.
The departing wave also takes away ice nuclei aloft,
introducing potential for freezing drizzle. Guidance differs in
how deep this lowest, supercooled liquid layer lingers over our
area, with some whisking moisture away by mid morning, while
others hold onto sufficiently deep moisture throughout the day
Monday.
Looking at the 12Z HREF specifically, neighborhood probability
of icing 0.01" or more is around 40% near the SD border/tri
state area tonight into Monday morning.
Thus, will continue to message potential for light icing within
southeast ND into west-central MN via the Special Weather
Statement, but if confidence increases in more widespread icing,
a Winter Weather Advisory may be warranted. Despite the
uncertainty, we are also messaging to be prepared for
potential of impacted travel conditions for the Monday morning
commute.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 528 PM CST Sun Dec 22 2024
Conditions will continue to deteriorate overnight into Monday.
Ceilings will decrease to IFR/LIFR at all TAF sites by around
12z Monday, with lower vsbys possible around DVL. Some freezing
precipitation expected tonight around FAR and south through 6z. Winds
will be out of the north, or variable, all under 10 knots.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Winter Weather Advisory until midnight CST tonight for NDZ038-
039-049-052-053.
MN...Winter Weather Advisory until midnight CST tonight for MNZ003-
024-027>032-040.
&&
$$
UPDATE...AH
DISCUSSION...CJ
AVIATION...AH
Area Forecast Discussion
National Weather Service Grand Rapids MI
957 PM EST Sun Dec 22 2024
.KEY MESSAGES...
- Wintry mix focused on Monday
- Milder with small precipitation chances Tuesday-Friday
- Much warmer with rain next weekend
&&
.UPDATE...
Issued at 957 PM EST Sun Dec 22 2024
Radar echoes approaching from the west are not reaching the
ground and there is some dry air to overcome before our precip
event gets going. Guidance still suggests the first snows will
develop over the nrn counties although that initial warm
advection wing up there looks like it will be a transient feature
and not produce much accumulation by daybreak. Most of the
measurable/impactful precip should hold off until after daybreak
then develop fairly quickly tomorrow morning. One notable trend in
the newer 00Z HRRR and NAM guidance is a farther south position
of deformation zone later in the day Monday and that may give
higher snow amounts to the U.S. 10 and M-20 corridors. No changes
to the Winter Weather Advisory.
&&
.DISCUSSION...
Issued at 249 PM EST Sun Dec 22 2024
- Wintry mix focused on Monday
We will be issuing a Winter Weather Advisory for the entire area
starting early Monday morning, and lingering into Monday evening.
The northern portion will be for 2-5 inches of snow, the middle
section will be for a wintry mix of sleet, snow, and a little
possible freezing rain, and the southern portion will be for mainly
freezing rain.
A weak area of low pressure across the Central Plains this afternoon
will move toward the area through tomorrow. This system does not
look to be one that would cause impacts. However, with increasing
moisture and warmth ahead of it, a mixed bag of precipitation types
will bring some impacts to the area, especially given the holiday
time frame.
We will see a wing of warm air advection snow develop after midnight
across almost the northern half of the forecast area. This looks to
be a 3 to 5 hour period of a band of light snow moving from West to
East. This will bring no more than a few tenths of an inch of snow
by 12z. Then, we will see additional precipitation develop between
10-12z Monday as the frontal system approaches, and better moisture
makes its way up over the area by then.
This will bring another batch of snow to the northern third to half
of the forecast area. Further south toward I-96, the snow will then
mix likely with some sleet and possibly freezing rain. This occurs
as temps aloft approach freezing, before those temps wet bulb down
some to change things back over to snow in the afternoon. This
mixture will cut down on snow amounts, but have the travel impacts
from sleet and freezing rain. Further south for the southern two
rows of counties, the melting layer will be warm enough, and the sfc
below freezing into early afternoon that the predominate p-type will
be freezing rain.
Once the moves through, the heavier precipitation will stop, but we
get into the dry slot for the southern two thirds of the forecast
area. The northern section will see snow continue expected to be
just north of the dry slot. The rest of the counties may go to more
drizzle or freezing drizzle for the afternoon, depending on where
the 32-33F isotherm ends up. The most likely scenario is that it
comes close to the I-96 corridor, and southern two rows warm enough
above freezing to end the threat. This is uncertain however, as it
is something very tricky to pinpoint. Some places will see impacts
continue most of the day.
Finally everything will move out by late Monday evening with the
system, allowing everyone to dry out.
- Milder with small precipitation chances Tuesday-Friday
The period from Tuesday through Friday has trended a bit drier, but
there will still be small chances for precipitation in this period.
The changes are a result of one more northern stream short wave that
will move by, just to the NE of the area. This wave does not look
close enough to bring precipitation to the area late Tuesday and
Wednesday. It will slow up the pattern change that will take place
to go to more of the SW flow aloft. Moisture return will be delayed,
as will organized short wave activity.
A short wave ridge moving through on Thursday should bring just dry
weather with somewhat milder temperatures starting to move in.
- Much warmer with rain next weekend
The expected pattern change that will bring the much warmer and wet
conditions to the area now looks like it will be centered over next
weekend.
The ridge on Thursday moves by, and the long wave pattern then
becomes from the SW at that time. We actually may miss out on the
leading wave as it looks to get shunted to the SE of the area with
the next long wave trough pushing in quickly.
It is at that time that we see the deep moisture and warmth from the
Gulf arrive ahead of the short waves lifting NE toward the area.
There is a potential that we see 50 degrees once again with the
amount of warmth coming this way.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 636 PM EST Sun Dec 22 2024
We`re still expecting mixed snow, sleet, freezing rain beginning
Monday morning across the terminals. Most of the sleet will be
along the I-96 terminals, while the I-94 terminals have a better
chance of seeing freezing rain.
As colder air works into Lower MI late in the period, the
precipitation should change over to light snow before ending
Monday evening.
We`ll see a corresponding decrease in cloud cover and visibilities
as the precipitation moves in.
Additionally, LLWS is expected Monday with a strong southwest wind
aloft.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 1 AM to 11 PM EST Monday for
MIZ037>040-043>046-051-052.
Winter Weather Advisory from 7 AM to 11 PM EST Monday for MIZ050-
056>059.
Winter Weather Advisory from 7 AM to 7 PM EST Monday for
MIZ064>067-071>074.
MARINE...Small Craft Advisory until 10 PM EST Monday for LMZ844>849.
&&
$$
UPDATE...Meade
DISCUSSION...NJJ
AVIATION...04
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
852 PM CST Sun Dec 22 2024
.KEY MESSAGES...
- Chance of snow and freezing drizzle late tonight and early
Monday across central MN and western WI. Any accumulation
would be light, but travel conditions could vary from area to
area Monday morning.
- A warming trend will occur this week with highs in the low to
mid 30s by Christmas and near 40 possible by later in the
week. Rain chances increase late week and next weekend.
&&
.UPDATE...
Issued at 823 PM CST Sun Dec 22 2024
Main changes made to the forecast were to delay the onset of
precipitation chances a few hours and reduce the amount of ice
(freezing rain/drizzle), with snow looking to play a more
predominate p-type roll.
Meso analysis at 8pm shows the h85 and h7 thermal ridge were
centered from the KC area up through the center of MN. 00z KMPX
sounding had a warm nose peaking at about 820mb with a
temperature of nearly +10C (had we completely mixed out that
warm nose, we would have had temperatures in the low to mid 70s,
which would have been an early Christmas miracle!). However,
the bigger issue with that sounding was the very dry wedge of
air observed between roughly 850mb and 600mb (about 4k to 12k
feet AGL). It`s this dry air that is the key culprit in the
delay to precipitation chances, with our precipitation chances tied
to the arrival of the main shortwave, which is still back out
near Bismark. Strong CVA out ahead of the vort max with this
shortwave should provide the spark for a narrow west to east
oriented band of precipitation to move into the Alexandria area
around 9z and the Twin Cities over to Eau Claire between 12z and
15z. As this forcing and precip is moving in, the warm nose
will be rapidly collapsing, with forecast soundings supporting a
scenario where there`s a brief window (up to 1 hour) where
precip starts as a sleet/snow mix before switching over to all
snow. 00z models have backed off a bit on the amount of QPF
(especially the NAM), so even less in the way of snow is
expected, with the later arrival of precip also greatly reducing
our icing threat. Given the diminished icing threat and low
snowfall amounts, we`ll continue to run with the Special Weather
Statement for the wintry precipitation, with no Winter Weather
Advisory headlines planned for now.
&&
.DISCUSSION...
Issued at 206 PM CST Sun Dec 22 2024
Morning clouds have cleared and most of the area has been
enjoying clear skies through early afternoon. High clouds are
returning, however, ahead of a shortwave evident on satellite
imagery over eastern MT and central ND. This shortwave will
dig and undergo some strengthening tonight as it propagates
east southeast across the southern half of MN. This would
normally be a strong signal for precipitation across the area,
but a dry warm layer between 850 and 700 mb will evaporate or
sublimate hydrometeors efficiently. The DGZ centered between 600
and 500 mb does remain sufficiently saturated for most of the
event. If stronger bursts of precipitation develop, then the
dry layer could temporarily be overcome. Forecast soundings
show this scenario quite well. As Omega spikes within the DGZ,
the profile is quick to saturate and precipitation reaches the
surface. After the Omega weakens, the dry layer returns. Given
the strength of the shortwave and the saturated DGZ, these
bursts appear likely to form at times, but will remain brief and
of low coverage across MN. In WI, the likelihood of formation
is higher given the fully matured shortwave by that time and an
ability to keep most of the profile saturated. Therefore,
hourly PoPs are low, except for areas closer to central WI, but
looking at the whole period late tonight and early Monday it
seems relatively likely most areas will experience some light
precipitation at some point however brief, whether from freezing
drizzle with saturation in the boundary layer or from bursts of
freezing rain or snow as outlined before. Regardless, any
accumulation of snow or ice would be pretty light. Travel
conditions may vary from area to area Monday morning, depending
on how prevalent the precip is in that location.
A zonal but a wavy shortwave-rich pattern will dominate the rest
of the month and keep mild air in place across much of North
America. The West Coast will be subject by a fire hose of
moisture for the next week and some of these systems will
survive the trek across the Rockies to emerge over the Plains as
weak, fairly compact systems. Given the magnitude of warm air
throughout the atmosphere, precipitation will fall as liquid.
Some freezing rain can`t be ruled out at night, but that would
be the exception with surface temps likely remaining above
freezing. The current snowpack is expected to make it to
Christmas, but probably not far beyond that.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 557 PM CST Sun Dec 22 2024
Tricky forecast with respect to shortwave currently over Bismark
that will track across southern MN late tonight and western WI
Monday morning. There`s still a wide range of solutions for the
degree of precip we will see locally, with the NAM definitely
the worst case scenario (a couple of inches of snow for
MSP/RNH/EAU) and and the GFS the best case scenario (maybe a
dusting at RNH/EAU). The HRRR leans toward a GFS solution, with
not much precipitation falling. Given the uncertainty, kept
precip mention in TAFs where we already had it, though delayed
that precip onset by a few hours, with lots of dry air needing
to be overcome before precip can make it to the ground. The warm
nose will be collapsing as the forcing for precip moves in, so
there may be a brief period of sleet in MN before changing over
to mostly snow. All snow looks to be the p-type for WI
terminals. What there is more confidence in is that Monday
morning, IFR cigs should become common area wide.
KMSP...Although a low probability outcome, what we`re seeing
from the 18z NAM and 21z RAP does provide a worst case scenario
for MSP, with about 2 inches of snow falling between roughly 7am
and 11am. It`s at about a 20% probability, so something to
watch, but we continued to favor more of a GFS/HRRR idea with
nothing more than a brief burst of snow possible Monday morning
as the upper wave moves overhead.
/OUTLOOK FOR KMSP/
TUE...MVFR cigs likely, chc IFR. Wind S 5-10kts.
WED...MVFR cigs likely, chc IFR. Wind SE 5-10kts.
THU...MVFR/IFR cigs/BR. Wind S 5-10kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
UPDATE...MPG
DISCUSSION...Borghoff
AVIATION...MPG
Area Forecast Discussion
National Weather Service Marquette MI
659 PM EST Sun Dec 22 2024
.KEY MESSAGES...
- Southerly wind lake effect snow into eastern Upper Michigan
will be followed by a clipper system moving in from the
west. Together these will bring wet snow to south-central and
eastern Upper Michigan through Monday.
- Lake effect may produce another inch or two in Luce and Schoolcraft
counties before the clipper brings another 1 to 3 inches.
Isolated higher amounts will be possible in the Luce and
Schoolcraft counties. Together this snow may result in minor
travel impacts through Monday.
- Drier and warmer conditions expected behind the early week
system for Christmas Eve and Christmas Day.
&&
.SHORT TERM /THROUGH MONDAY/...
Issued at 212 PM EST Sun Dec 22 2024
Upper Michigan continues to be caught between mid-upper level
troughing across the east coast with a ridge extending through the
northern Plains. Within this northwest flow, a weak shortwave
supported flurries here and there this morning thanks to some seeder
feeder action. Further upstream, a closed low with a shortwave
extending south just west of the ridge has supported the development
of a surface low over South Dakota, per RAP analysis. With Upper
Michigan being caught between the upstream surface low and a surface
high stretching from Quebec into the Ohio River Valley, in addition
to continued cold air aloft and the weak progressing shortwave, a
long axis lake effect snow band streaming northward into eastern
Upper Michigan has been observed on GOES satellite products and KAPX
radar. Webcams also show some occasional light snow in parts of
Schoolcraft, Luce, and Mackinac counties. From these noted
observations, impacts so far appear to be minimal.
Some CAMs, namely the RAP and HRRR have really dialed back the
intensity of these snow showers into eastern Upper Michigan in the
past 24 hours. This is also reflected in the recent HREF run, which
has dialed probabilities of snowfall rates exceeding an inch per hour
to <10%. A good bit of the 06z and 12z deterministic guidance
though, continues to suggest the potential for an inch or two of
snow in Schoolcraft and Luce counties through midnight. However, it
should be noted that most of these packages have lowered
accumulations and have a poor handle on the placement of the current
band. With all this being said though, generally believe snow
accumulations should amount to an inch or two, with higher amounts
being possible in a very narrow band. Current radar trends suggests
this would likely be from near or east of Manistique northeastward
into Luce County near McMillan. Any snow through the remainder of
today and through midnight will also become increasingly wetter,
with morning snow ratios estimated near 15:1 trending toward 10:1
this evening.
The upstream clipper low will continue organizing before shifting
east into Iowa/southern Minnesota this evening. Through Monday, the
low will track east-northeast through Wisconsin, across Lake
Michigan, and then into Lower Michigan. This will position Upper
Michigan along the low`s northern flank and under the influence of
continued warm air advection and a weak 850-500mb TROWAL before the
low`s inverted trough and a weak shortwave shifts through. The
effect will be a swath of wet snow moving through the Upper Great
Lakes after midnight tonight through early afternoon Monday, with
lake enhancement of this swath being possible into eastern Upper
Michigan. A majority of guidance packages stretch this swath from
near Iron Mountain through Menominee and Delta counties, into
Schoolcraft County where lake enhancement potential begins. This
said though, the northern extend of the band is up for some debate
thanks to the 12z NAMNest and HRRR keeping a majority of this south
of Watson. Despite these differences though, wet snow accumulations
should still amount to two inches or less through the event under
this swath. In Schoolcraft and Luce counties, lake enhancement in the
morning should end by afternoon thanks to mid-level winds shifting
with the transiting low. Additionally, surface temps potentially
climbing above freezing Monday make anything more than 3 inches
difficult to achieve. Current thinking is that 2 inches could be
widespread with amounts potentially approaching 4 inches being
localized through Monday evening. Given all this uncertainty and
that holiday travel is in full swing, opted to issue an SPS for
Luce/Schoolcraft for the time being. All solutions keep the west
dry, save for scattered snow shower potential developing by Monday
afternoon.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 343 PM EST Sun Dec 22 2024
High pressure over northern Ontario and MN at 1026 mb descends
southeast into the Great Lakes Monday night as a mid level shortwave
drops south over the UP early on. This decreasing cyclonic flow and
increasing dry air works against lingering LES. At the same time,
WAA increasing 850 mb temps closer to negative 1-2C diminishes the
Superior sfc-850 mb delta-Ts given that average water sfc temps are
around 4.5C. Any snowfall will yield negligible accumulations and no
impacts. Some cloud cover likely will continue, but dry weather
should return to the UP by Tuesday morning. Otherwise, under partly
to mostly cloudy skies, lows settle into the teens to mid 20s. Brief
mid level ridging returns for the day Tuesday as the sfc high
becomes centered over southern Quebec, but extends southwest over
the Great Lakes Basin. Dry weather continues with some more daytime
clearing likely, allowing for highs to peak between 28 to 33, warmer
by the lakeshores.
The mid level ridge gives way to a shortwave for Tuesday night into
Wednesday and the NAM/NHCandian/ECMWF try to squeeze out some light
snow out of that and some additional possible lake enhancement off
Lake MI. That said, the sfc high pressure mentioned earlier remains
pretty stagnant during this period, and lift is not strong with
significant dry layers noted above 900 mb. Thus the forecast
reflects dry weather persisting under cloudy skies. Otherwise,
expect another mild day with highs near freezing on Tuesday with
temps then falling mainly into the 20s overnight into Christmas Day.
After Christmas Day, another ridge moves over the Great Lakes,
continuing the dry weather through Thursday. With troughing over
Rockies/Plains, southerly flow brings well than normal temps (10-20F
above normal) by next weekend. Ensembles probabilities support
overnight lows remaining above freezing, especially the GFS with 0%
across the UP Thursday night through the day Sunday. The ECWMF and
Canadian ensembles show somewhere between 20-40% chances for below
freezing in the interior Friday night and Saturday night. Guidance
spreads on arrival time of troughs pivoting over the Great Lakes
late next week, but there is support for anomalous warmth and
moisture surging up from the Gulf of mexico over the weekend
accompanied by a sfc low. Primary p-type likely will be rain given
the airmass expected, but there are low chances (15-30%) of snow
mixing in return Sunday onward. Also, dew point temps reach into the
30s starting on Thursday with above freezing dew point temps over
much of the UP Friday night through Saturday night. This alongside
highs in the upper 30s to mid 40s will help melt snowpack and also
possibly result in some patchy fog. While it`s a ways out yet, will
continue to watch the fog potential in upcoming forecast packages as
this could have some impacts on holiday travel.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 658 PM EST Sun Dec 22 2024
Low-level dry air that is currently allowing for VFR at IWD/CMX/SAW
will give way to increasing low-level moisture tonight as a
disturbance approaches. As a result, MVFR cigs will develop
overnight at all terminals with further reduction to IFR at IWD/SAW
early Mon morning. A little -sn or -fzdz could develop late
tonight/Mon morning, but potential for occurrence is too low to
include mention in fcst. Passing sfc trof late morning or early aftn
may support ocnl -shsn/flurries. As for winds, low-level jet over
the area this evening is not quite strong enough to warrant
inclusion of LLWS. Southerly winds tonight will become light/vrbl
for a time Mon morning, then become northerly Mon aftn.
&&
.MARINE...
Issued at 343 PM EST Sun Dec 22 2024
South winds of 20-30 kts over the east and 15-25 kts over the west
continue into tonight. Winds fall below 20 kts by around midnight in
the west and by Monday morning in the east as a clipper system
begins to move over Wisconsin. There is a low chance (15-30%) of
gale force gusts to 35 kts this evening/early tonight over east,
mainly in a corridor between Marquette and Grand Marais northward.
As the clipper continues east over the Great Lakes, winds veer
northerly Monday morning, continuing around 20 kts through Monday
evening before falling back below 20 kts for Monday night. Southerly
winds, mainly 20 kts or less, are expected Tuesday through the week
and likely into next weekend for most of the lake.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...JTP
LONG TERM...Jablonski
AVIATION...Rolfson
MARINE...Jablonski
Area Forecast Discussion
National Weather Service San Francisco CA
341 PM PST Sun Dec 22 2024
...New AVIATION, MARINE...
.SYNOPSIS...
Issued at 233 PM PST Sun Dec 22 2024
An active weather pattern is still forecast over the next week as
several upper level storm systems move through the region. The
most impactful storm system appears to arrive late Monday and
through the day on Tuesday. Isolated to scattered thunderstorms,
some of which could be strong, are forecast across most of the Bay
Area and parts of the Central Coast. Rain-free conditions are
forecast on Christmas Day with additional rain chances through the
end of the week. Very hazardous marine and beach conditions are
also forecast through the first portion of the week.
&&
.SHORT TERM...
Issued at 233 PM PST Sun Dec 22 2024
(This evening through Monday)
A brief lull in widespread rain activity is anticipated to come
to an end as we head into this evening. Satellite imagery
indicates cooling cloud tops associated with shower and
thunderstorm activity due west of the Cape Mendocino. The
satellite fields also show the leading edge of 300mb flow starting
to nose into the area. Over the next 12-24 hours, I anticipate
that the ongoing band of showers and embedded thunderstorms to
continue to track south and east toward the Bay Area and Central
Coast. With stronger forcing for ascent (largely thanks to jet
exit forcing) and some limited instability (~50 J/kg), rainfall
amounts across the North Bay will average closer to 1/2" up to
around 1" (greatest values across far northern Sonoma, Marin, and
Napa counties). Instability is anticipated to wane closer to the
coastline and so I do believe that the thunderstorm potential
tonight into Monday morning will be on the limited side (higher
over the offshore zones), but we`ll monitor trends. As this next
round of showers and embedded thunderstorms marches eastward,
it`ll outpace some of its parent synoptic scale forcing. As such,
70-90% PoPs across the North Bay will taper downward quickly to
around 20% across the Monterey Bay region by sunrise Monday. A
conglomerate of the high-resolution short term guidance in
conjunction with time-lagged HRRR runs support the current PoP
configuration currently advertised in the grids.
From an impacts standpoint, we`ll see some rises on area creeks,
streams, and smaller rivers, but widespread significant flooding
is not anticipated during the overnight hours. Dangerous and
potentially life-threatening surf and marine conditions are
advertise with 30-40 ft breaking waves possible through the short
term forecast period. For more details, see the marine and beaches
section of the AFD below. Otherwise, after sunrise, a good
portion of Monday is anticipated to be rain-free, outside of
coastal drizzle.
&&
.LONG TERM...
Issued at 233 PM PST Sun Dec 22 2024
(Monday night through next Saturday)
Key Messages:
*Train of storm systems through next week
*Most impactful storm appears to be late Monday into Tuesday
*Rainfall totals between today and Sunday: North Bay: 6-10" | Bay
Area: 2-6" | Central Coast: 2-6" | Salinas Valley: Up to 1"
*Wind gusts up to 40 mph (isolated 45 mph in spots) on Tuesday
*Life-threatening beach and ocean conditions linger into next week
NWP continues to remain in good agreement through Christmas Day
regarding the evolution of our next big storm system slated to
arrive later Monday and into the day on Tuesday. The forcing for
ascent associated with a largely positively titled upper trough
will extend down into our area. This translates to high confidence
that most if not all areas will experience rainfall late Monday
and into Tuesday. PoPs range from 80% to near 100% across nearly
the entirety of the Bay Area and Central Coast. 12 hour 500mb
height falls are still on the order of +100 meters with mid- level
flow exceeding 70 knots. There`s likely to be a couple of rounds
of showers and isolated storms on Tuesday. The initial band of
precipitation will impact a good chunk of the Bay Area and
Central Coast during the morning hours on Tuesday, with perhaps a
break late morning. As the upper low advances eastward,
instability aloft will build thanks to the lower temperatures in
the mid- levels. CAPE values approach 200-400 J/kg over coastal
regions as well as the Bay Area beneath the core of the upper low.
0-6km shear values, however, are on the order of 10-15 knots,
which is a bit of a contrast to yesterday. The forecast upper
trough has amplified and as a result, the conveyor of stronger
mid-level winds has shifted southward. This yields a less
"sheared" environment which is a key ingredient to severe weather.
Instability may still foster some robust updrafts and thus a
gusty wind (up to 45-50 mph) and lapse rates on the order of 7-7.5
C/km per forecast sounding would support coin-sized hail (pennies
or smaller).
As it pertains to the QPF, there may still be a wet bias in some
of the NBM bias-corrected precip accumulation fields thanks to our
early season AR that impacted the area. Overall, the potential
for flooding doesn`t necessitate any flood headlines just yet as
the chances of exceeding 6 hour flood guidance (around 2-4 inches
of rain in a 6 hour time period), even in the slightly more wet
NBM, appears low. In fact, the probability of 6 hour QPF exceeding
1" is only around 60% across the North Bay---the area that saw
the highest rainfall totals over the last 30-60 days. We`ll
continue to advertise the potential for rapid rises on area
creeks, streams, and smaller rivers. If thunderstorms become more
widespread (due to higher instability or more lift), then the
flooding threat would ramp up and we`ll be mindful to monitor
trends over the next day or so.
Outside of rain and thunderstorms, chances for a peak gust or two
above 35 mph is around 60-80% mainly across the higher terrain of
the North Bay, East Bay, SF Peninsula, Santa Cruz Mountains, and
the Big Sur Coastline/Santa Lucia`s Tuesday morning and early
afternoon. Chances for 40 mph wind gusts across this areas drops
to around 20-50%. Even the higher end deterministic wind solutions
(NBM 90th percentile and MTR WRF) only indicate 40 mph wind gusts
across the higher terrain. As such, I don`t anticipate the need
for wind headlines (unless things change dramatically). Regardless,
those with outdoor decorations will want to make sure they are
secure so that they aren`t displaced by the wind.
Christmas Day still appears mostly rain-free with partly sunny
skies. Hazardous marine and beach conditions are still
anticipated, however.
Our lull in the rain will end Boxing Day (Thursday) and onward
with still a high degree of uncertainty. The overall synoptic
pattern appears that it`ll be governed by our Tuesday system
kicking eastward into the Great Plains with diffuse mid-level
troughing lingering across the Pacific Northwest. While the multi-
model ensemble paints QPF largely Bay Area and points northward,
individual model groupings offer some varying solutions. The model
groupings that consist of predominantly Canadian and GFS ensemble
members suggests more shortwave ridging and a "drier" solution,
while model groupings comprising largely of EPS members would
offer a "wetter" solution. For now, we`ll roll with the
deterministic NBM given that just about all individual model
solutions advertise some QPF, but additional refinements may be
needed as we venture through the week.
&&
.AVIATION...
(00Z TAFS)
Issued at 341 PM PST Sun Dec 22 2024
Conditions vary widely from VFR to LIFR this afternoon per surface
metar observations and satellite imagery. Thunderstorms are occuring
over the northern outer coastal waters with a 500 mb trough. Rain
will continue to spread over the Bay Area through this evening.
Surface visibilities and ceilings lowering in low clouds and fog
/VLIFR-IFR/ tonight and Monday morning. Gradual improvement to
MVFR-VFR expected by late Monday morning and afternoon, though there
still may be a few areas IFR conditions during the afternoon.
Vicinity of SFO...MVFR with rain developing this evening. Rain ending
late tonight with IFR developing and continuing much of Monday. Light
northeasterly to southeasterly wind.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...MVFR-IFR tonight and Monday morning. MVFR
for Monday afternoon. Light and variable winds, becoming light
southeasterly tonight and Monday morning.
&&
.MARINE...
(Tonight through next Friday)
Issued at 326 PM PST Sun Dec 22 2024
Large, building westerly swell continue through this morning with
a temporary decrease in swell later Sunday. Then, a large to very
large westerly swell is expected Monday into Tuesday. Wave
heights will remain elevated through late next week with 15 to 20
foot waves Monday through Wednesday. Expect dangerous conditions
for small crafts through the weekend and into midweek. Elevated
seas will continue to produce enhanced shoaling at harbor
entrances and bars.
&&
.BEACHES...
Issued at 107 PM PST Sun Dec 22 2024
A High Surf Warning will replace the High Surf Advisory later this
afternoon for elevated surf of 20 to 25 feet. Breaking waves near
30 feet are anticipated, with some of the favored spots such as
Mavericks potentially experiencing up to 40 foot breaking waves.
With the duration of this High Surf Warning, a Coastal Flood
Warning was also issued to address the potential for significant
impacts to coastal locations such as piers, wharfs, and other
structures along the coastline. Flooding/inundation of
roads, parking lots, and coastal trails can also be anticipated.These
conditions will result in dangerous and life-threatening bay,
ocean, and beach conditions through Tuesday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 4 PM PST this afternoon for CAZ006-505-
509-529-530.
Coastal Flood Warning until noon PST Tuesday for CAZ006-505-509-
529-530.
High Surf Warning until noon PST Tuesday for CAZ006-505-509-529-
530.
PZ...Small Craft Advisory until 3 AM PST Tuesday for Mry Bay-Pigeon
Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt
Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt
Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-
10 nm.
&&
$$
SHORT TERM...Bain
LONG TERM....Bain
AVIATION...Canepa
MARINE...Behringer
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