Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/30/24
Area Forecast Discussion
National Weather Service Boston/Norton MA
647 PM EST Sun Dec 29 2024
.SYNOPSIS...
A warm front moves across the region tonight, with temperatures
rising into the 50s. A cold front will bring windswept showers
Monday morning into midday, with brief downpours. Then a drying
trend begins Monday afternoon from west to east, with dry and
mild weather lingering into Tuesday. Another low pressure system
should bring rain New Years Day. Then colder and drier weather
should follow into the first weekend of 2025.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
645 PM Update:
Key Messages:
* Warm front struggles to lift northward but will eventually do
so as temps/dew points rise into the 50s.
* Timing has sped up on fast moving band of showers.
Warm front is struggling to lift through SNE this evening,
having stalled out across the CT River Valley and north
central/northeast MA to near Boston. Weak gradient and having
surface low well to our west means front will make a slow crawl
northward tonight, but eventually the warmer air will win the
battle as gradient begins to tighten. Bottom line is patchy
dense fog will persist in those areas north of warm front
tonight, but coverage will be much less than it was this morning
so we don`t see a need for Dense Fog Advisories at this point.
Latest few runs of the HRRR have sped up timing of band of heavy
rain showers through region, and may have more of an impact on
the Monday morning commute, even into Boston and Providence if
this trend proves to be correct. We do think band of showers
will fragment somewhat as it heads east, so the greater impact
will be for the Hartford/Springfield area and perhaps Worcester
as well. Still looks like a 1-3 hour period of downpours with
reduced visibility and poor drainage flooding, so plan on
allowing some extra time if driving Monday morning.
As for the winds, 925 mb southerly jet increases to almost 60
kt as it approaches, but model soundings remain inverted. Thus,
only expecting south winds gusting up to 25 kt or so late
tonight into daybreak Monday.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
249 PM Update:
Monday...
Key Messages:
* Narrow band of windswept downpours moves through CT/RI/MA in
the morning to noontime off the coast. Flooding not
anticipated, impacts limited to a slow AM commute
* Southerly breezes to 25-35 mph, strongest Cape and Islands.
* Rapid clearing during the afternoon with peeks of sunshine
developing late-day.
Fine line of low top convection associated with a cold front
sweeps across the region Monday morning, then exiting eastern MA
coastline between 16z-18z. These windswept heavy showers will
slow down the AM commute with lots of standing water on area
roadways, but will be very progressive and short lived. Activity
will exit CT and western-central MA between 8am-10am, then off
the eastern MA coast by 11am-12pm. Given its low top convection,
not expecting any thunderstorms, with probs only 5-10% chance.
Nonetheless, 3 hr rainfall of 0.75 to 1.25 inches is possible
given strong forcing and moisture advection. This will likely
yield minor poor drainage/urban flooding. Low level southerly
jet increases to 70-75kt at 925 mb before exiting off the
eastern MA coast midday. However, model soundings continue to
show a stout low level inversion, precluding strong winds from
mixing to the surface. This should limit wind gusts to 30-40
mph, strongest in heavy downpours. Although, HREF ensemble min
gusts does support G40-50 mph gusts. As previous forecaster
noted, given the absence of a strong isallobaric rise/fall
pressure couplet, these higher HREF wind gusts are a very low
prob. Something we will have to watch for trends in the 00z
guidance and see how fine line evolves tomorrow morning.
Behind the front, strong column drying should support partial
sunshine developing Mon afternoon from west to east. Post
frontal airmass is initially mild with 925 mb temps still +8C
over SNE 18z Mon. Therefore, highs of 55-60 are likely and well
above normal for late Dec. Behind the front, winds shift from
south to southwest with speeds 15-25 mph.
Monday night...tranquil with rising heights/subsidence advecting
across SNE. Not very cold with lows in the 30s. Gusty SW winds
at sunset diminish overnight with weakening pressure gradient.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
249 PM update...
Key Messages
* Dry most of New Year`s Eve with temps in upper 30s-lower 40s.
* Rain arrives overnight into New Year`s Day.
* Turning colder but dry as we head into the weekend.
Mild weather pattern lasts into New Year`s Day as upper ridge
remains offshore, but eventually gives way to colder and dry weather
by weekend as ridge shifts toward Greenland and broad upper trough
encompasses much of southeast Canada, Great Lakes, and New England.
Airmass is not unusually cold for early January but rather closer to
normal. On the MA/RI coastal waters, the colder air should produce
bands of snow or rain showers, and we may see light freezing spray
over the weekend closer to shore.
Not much change regarding the low pressure system that will impact
our area on New Year`s Day. Onset of rain has slowed a bit, now
expected to arrive after midnight and exit during the morning on New
Year`s Day, and ensemble probabilities still favor rainfall totals
averaging 0.5 to 1.0". System is progressive so we do not anticipate
any flooding issues. It`s still possible we see a brief change to
wet snow across higher elevations of western and north central MA as
low departs but any accumulation would be minimal.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00Z TAF Update: High confidence, except moderate confidence from
BDL/BAF into northern MA.
Warm front was struggling to lift north across region this
evening, especially near BDL/BAF and north of BOS where LIFR
persists with calm or light N winds. Front will eventually make
it north of these areas tonight bringing a wind shift to S but
expecting it to take until 03-06z to do so, which caused us to
be more pessimistic at those airports. Farther south, it`s VFR
with light S winds, and it should stay that way tonight.
LLWS is the main concern through the night as 2000 ft winds from
S increase to 40-60kt, with strongest winds near Cape Cod.
Coastal areas will see surface winds increase overnight with
20-30kt gusts.
Fast-moving band of showers with brief downpours will cross SNE
Mon morning, roughly 10-13z near BAF/BDL, 12-15z BOS/PVD. and
13-16z Cape Cod. Expect lowering to IFR cigs/vsbys as showers
move through and winds will drop off quickly as showers begin
but remain from S. Once band moves through, ceilings slowly
lift but we probably won`t scatter out to VFR until Mon
afternoon. VFR Mon night with SW winds.
KBOS TAF...High confidence. Front is near airport at 23z and
will edge slowly north, but despite remaining VFR winds will
take a few hours to shift to S. Higher confidence on trends Mon.
KBDL TAF...Moderate confidence. Cooler air is holding tough in
CT Valley and it`s possible that conditions will not improve
much tonight, but we should finally see warm front lift N after
03z.
Outlook /Tuesday through Friday/...
Tuesday: VFR.
Tuesday Night: MVFR/IFR conditions possible. Breezy. RA.
New Years Day: Mainly MVFR, with local IFR possible. Breezy.
RA.
Wednesday Night: Mainly VFR, with local MVFR possible. Windy
with gusts up to 35 kt. Chance RA, chance SN.
Thursday: VFR. Windy with gusts up to 35 kt.
Thursday Night: VFR. Windy with local gusts up to 30 kt.
Friday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High- greater than 60 percent.
249 PM update...
High confidence through Monday night.
Tonight...warm front lifts north into NH/ME waters, with
southerly winds increasing to 15-25 kt late. Drizzle in the
evening is replaced by heavy showers toward morning. Areas of
fog will limit vsby to 1-3 miles.
Monday...Continued the SCAs although latest guidance suggests
potential for a few gusts to 35 kt over the eastern waters
despite poor mixing. This is due to a stronger low-level
jetstreak. Windswept rains may reduce visby to 3 SM during the
late morning to early afternoon, then winds shift to SW and
decrease late. Improving vsbys with the wind shift from S to SW.
Monday night...dry weather and good vsby, with gusty SW winds
15-25 kt in the evening diminishing overnight.
Outlook /Tuesday through Friday/...
Tuesday: Winds less than 25 kt. Local rough seas.
Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Rain.
New Years Day: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 10 ft. Rain likely.
Wednesday Night: Strong winds with gusts up to 35 kt. Rough
seas up to 12 ft. Chance of rain.
Thursday: Strong winds with gusts up to 35 kt. Rough seas up to
12 ft.
Thursday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 10 ft.
Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from midnight tonight to 4 PM EST Monday
for ANZ230-231-250-251-254.
Small Craft Advisory until 1 PM EST Monday for ANZ232>237-255-
256.
&&
$$
SYNOPSIS...JWD/Nocera
NEAR TERM...JWD
SHORT TERM...Nocera
LONG TERM...JWD
AVIATION...JWD/Nocera
MARINE...JWD/Nocera
Area Forecast Discussion
National Weather Service Burlington VT
930 PM EST Sun Dec 29 2024
.SYNOPSIS...
A winter thaw will continue across Vermont and northern New
York over the next few days. Widespread rain will resume late
tonight and into early Monday ahead of a strong front; the
combination of snowmelt and storm total rainfall of a third to
two thirds of an inch will result in some river rises and flush
out river ice. Following another system for New Years Day with
elevation dependent rain and snow, colder air will return with
below normal temperatures expected late this week.
&&
.NEAR TERM /THROUGH TUESDAY/...
As of 922 PM EST Sunday...Winds have been overperforming across
northern New York this evening with wind gusts up to 45 mph
already reported in multiple locations. The low level jet will
be peaking in strength over the next few hours which should
allow for a few gusts up to 50 mph to be possible during the
overnight hours. Wind gusts are expected to be quite variable
meaning some gusts will be 30-35 mph but will occasionally
reach or exceed 45 mph. A special weather statement has been
issued given the potential for some damaging winds but shouldn`t
be super widespread or long-lived at any one location. Winds
are still expected to abate by daybreak.
Previous Discussion...A seasonably strong low pressure
system over the central Great Lakes region will deepen tonight
and begin its occluding phase near Lake Huron. Strongly
meridional flow out ahead of the system has been bringing an
influx of unseasonably moist and mild air across our region with
southerly winds bringing in temperatures reaching into the
lower 50s into northern New York, especially where downsloping
south- southeasterly winds are helping boost temperatures in the
western Adirondacks. This environment should expand eastward
across Vermont overnight. However, the storm track is a bit
farther west than what is needed to sustain a strong low level
jet across our forecast area, with strongest winds aloft staying
just to our west. That being said, its a close call on seeing
wave breaking action that can generate damaging wind gusts
associated with southeast winds in the northern Adirondacks. For
now, have leaned towards the HRRR depiction of wind gusts than
the predicted maximum gusts of several other high-resolution
models that show 55 - 65 MPH wind gusts tonight. Generally peak
winds associated with a 60 to 65 knot 850 millibar knot 850
millibar jet between 7 PM and midnight, then trending a bit
weaker overnight across Vermont. The strongest winds aloft look
to coincide with saturated forecast soundings that keep these
winds from mixing at all, and we won`t see convection that can
aid in transporting these winds down.
Widespread rain is expected primarily across the Adirondacks
and Vermont during the morning hours. Precipitation will be
heavy at times with some elevated instability, and will gradually
expand northward and eastward with time ahead of a fairly sharp
surface cold front. Extensive ponding on roads with continued
snow melt and soaking rainfall can be expected, and substantial
river and stream rises should result through tomorrow into
tomorrow night. Some nuisance flooding cannot be ruled out, but
rainfall amounts look to average under an inch across river
basins. Winds following the frontal passage will taper off aloft
but be able to mix as slightly drier air and cooling aloft
supports some modest gusts. Stronger gusts are favored in
western portions of northern New York for a period of time
during the day. However, an influx of moisture on southwesterly
flow will promote a return of precipitation, which will likely
be elevationally dependent snow. So some very wet, light snow
amounts are forecast for the western Adirondacks and cold rain
showers will fall in the St. Lawrence Valley, with perhaps a mix
of rain and snow in heavier showers. Some light rain/snow also
could graze northern Vermont, but the better moisture and
forcing looks to lift into southern Canada tomorrow night.
With still relatively mild air aloft (near -5 degrees Celsius at
850 millibars) and continued breezy conditions, temperatures
across the area will remain mild and mainly well above freezing.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
As of 335 PM EST Sunday...Tuesday will be a relatively quiet with
weak ridging across the region and increasing clouds ahead of the
next system arriving Tuesday night. Daytime highs on Tuesday will
climb into the upper 30s to mid 40s across the region, which is
nearly 15 degrees above normal for late December, but several
degrees cooler compared to the high temperatures on Monday.
Our next system will arrive Tuesday night, with precipitation
primarily starting out as widespread rain with some higher elevation
snow mixing in. There continues to be some uncertainty as to how
quickly precipitation transitions to snow during the day Wednesday
as colder air moves into the region, with the latest 12Z
deterministic guidance showing a faster transition to snowfall
compared to the previous forecast. Snow levels will gradually lower
towards the valley floors, but snow accumulations look to be minor
during this period.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
As of 335 PM EST Sunday...Broad upper level trough looks to develop
across much of the eastern United States later this week, which will
support the below normal temperatures for the beginning of 2025.
Precipitation will turn more showery by Wednesday evening. This
broad cyclonic flow will continue through the week, continuing to
bring some additional upslope showers as well as a response from
Lake Ontario. Westerly winds will keep the bulk of the lake effect
snow south of our forecast areas, but some additional snow
accumulation will be possible across St. Lawrence County and the
western Adirondacks. Despite starting off quite low, snow ratios
will gradually increase, which will likely lead to a few inches of
accumulating snowfall across the higher terrain. After a period of
well above normal temperatures, temperatures will trend much colder,
with high temperatures likely in the teens to lower 20s by the
weekend.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Through 00Z Monday...VFR conditions exist at many of our sites,
but we also have low ceilings at MSS and MPV currently. Some FG
has settled in at MSS with cooler temperatures and northeasterly
flow in place. Very complicated aviation forecast tonight, with
changeable conditions expected, and low level wind shear
areawide. A 55+ kt LLJ will bring increasing S winds, which is
already resulting in probable LLWS at SLK where light terrain
driven winds at the surface exist with near 40 knots of
southwest winds aloft. Due to strong surface inversions and
unfavorable wind directions for our terminals, surface gusts
will tend to be sporadic, but could gust 25-30 knots at times
overnight. Between mainly 07Z and 14Z, additional showers
associated with a cold front will spread across the region with
visibilities 3-5 SM possible. Behind the front, gusts will
become more likely and persistent in the 20 to 30 knot range,
with a few higher gusts possible at MSS, largely developing
between 12Z and 18Z. Ceilings and visibilities should trend VFR
behind the showers.
Outlook...
Monday Night: Mainly VFR, with local MVFR possible. Windy with
gusts to 30 kt. Chance SHRA.
Tuesday: Mainly VFR, with local MVFR possible. NO SIG WX.
Tuesday Night: Mainly VFR, with local MVFR possible. Definite RA.
New Years Day: Mainly MVFR, with areas IFR possible. Definite RA,
Definite SN.
Wednesday Night: Mainly MVFR, with areas IFR possible. Definite
SHSN.
Thursday: Mainly MVFR, with areas VFR possible. Chance SHSN.
Thursday Night: Mainly VFR, with areas MVFR possible. Slight
chance SHSN.
Friday: Mainly VFR, with local MVFR possible. Slight chance SHSN.
&&
.MARINE...
South-southeast winds near 20 knots will increase tonight and
peak overnight with steady 25-30 knot winds expected with some
higher gusts possible, especially on the broad waters. Wave
heights should build into the 2 to 4 foot range. After a lull
near a frontal passage midday Monday, winds will increase out of
the south by Monday evening with sustained 25 knot winds
possible again on Lake Champlain.
&&
.CLIMATE...
Record warm low temperatures and record warm high temperatures
will be possible. Temperatures will follow non-diurnal trends
today and tomorrow, so the ultimate highs and/or lows will
likely depend on temperatures near midnight each day. See below
for more information.
Record High Temperatures:
December 30:
KPBG: 51/2022
Record Warm Minimum Temperatures:
December 30:
KBTV: 45/2022
KPBG: 35/2022
KSLK: 35/2022
December 31:
KPBG: 38/1965
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.
&&
$$
SYNOPSIS...Kutikoff
NEAR TERM...Clay/Kutikoff
SHORT TERM...Kremer
LONG TERM...Kremer
AVIATION...Kutikoff/Neiles
MARINE...Team BTV
CLIMATE...Team BTV
Area Forecast Discussion
National Weather Service Des Moines IA
547 PM CST Sun Dec 29 2024
...Updated for the 00z Aviation Discussion...
.KEY MESSAGES...
- Fog redevelops tonight - patchy dense fog possible
- Upstream wave arrives Monday afternoon/night with rain snow
mix to snow prior to ending. Complicated snow forecast.
- Colder start to New Year with weak system Thursday.
- More significant storm (low confidence) next weekend?
&&
.DISCUSSION...
Issued at 234 PM CST Sun Dec 29 2024
.Short Term /Tonight through Monday Night/...
Confidence: Low to Medium
About the only high confidence element to the forecast is fog. Low
stratus and fog have begun to lift around the noon hour and some
improvement will remain through afternoon. Clouds will likely hang
on, so afternoon temperatures have been slow to catch up to highs.
Trimmed back highs a touch central to east today. Weather pattern
rather complex with stronger Ohio River low affecting much of the
Great Lakes to eastern seaboard. Aloft at H850 and at the sfc as
well this morning, a weak low has been tracking over Iowa with light
winds, a few sprinkles and remaining low clouds and fog. There
remains a ridge of high pressure from the upper Great Lakes west to
the High Plains at the surface, but aloft we still have a lingering
trough. This should result in more fog risk overnight tonight. Hires
models suggest the west and north are most at risk with central to
southeast Iowa having a lesser risk of dense fog. For now, will pass
details along to evening shift and let them evaluate for the
overnight hours, as areal coverage will be more difficult to predict
at this hour. Lows tonight will slide back to the lower 30s
northwest to the mid 30s southeast. Monday will begin with areas of
fog, but the approaching stronger wave currently over the Pacific
northwest will result in rapid cyclogenesis in the lee of the
Rockies by 06z to 12z Monday morning. Initially with that we will
see milder air sneak into the south/southeast with highs reaching
the lower 40s along and south of US30. Across the north, upper 30s
should be common. By late morning and early afternoon, isentropic
lift will commence over northwest Iowa, where precipitation will
initially fall as light rain through mid afternoon. Farther
northwest, stronger lift and more rapid cooling will result in
mainly snow over South Dakota. Various models are advertising
differing solutions with the Monday event. For starters, the GFS is
still lower on overall qpf amounts for our forecast area compared to
the EC. Another difference is the amount of cooling aloft as the low
deepens just to the south of the state Monday evening. The HRRR is
trending toward several inches of snow with instability possibly
playing a role in locally higher amounts. The EC is overall a bit
cooler with more rapid cooling aloft than the GFS. Both the GEFs and
EPS offer little comfort with little if any snow in the southeast to
maybe an inch or more in the central to west. Our probability
forecasts for snowfall accumulations show a 30 to 60% chance of 2
inches generally along and south of US30; and a 40 to 70% chance of
1 inch in the same area. Probability QPF ensembles suggest a 70
to 100% chance of 0.25 inches in the same area with a 40 to 70%
chance of 0.35 inches and a 0 to 40% chance of 0.50 inches of
water equivalent. Given the trends to have a quicker changeover
to snow sometime between 00 and 03z Monday evening, we have
bumped up our snow totals to up to an inch in spotty areas in
the south. This will bring a probability range higher over the
region, but may still fall short of the actual amounts. Current
HREF SPC forecasts have a mean and probability match mean (~50th
percentile)forecast of between 1 and 2 inches, while the max
forecast (90th or higher) leans toward 2 to 4 inches with
locally higher amounts southwest. This is an on the fence
forecast both at the surface and aloft; any quicker dynamic
cooling will favor the higher amounts and any slower cooling
aloft or at the surface will favor the lower amounts. It may
take until sometime tomorrow afternoon to project the trends in
the critical 6 hour period from 00 to 06z, when most of the
precipitation falls. The good news is that this is 24 hour ahead
of New Year`s Eve and hopefully will have less impacts to
travelers. Lows tomorrow night will fall to the lower to mid 20s
north and in the lower 30s southeast.
.Long Term /Tuesday through Sunday/...
Confidence: Medium
The system will be exiting Tuesday morning with lingering clouds
through the period as cold air advection settles into our forecast
area. Stronger winds and a second cold front will drive south
Tuesday night into Wednesday. Highs Tuesday will reach 20s and 30s
while overnight mins Tuesday night will fall to the 10s to lower
20s. Another weak wave will arrive by Thursday and prior to that the
pattern would suggest less sun than clouds. Highs Wednesday should
be in the 20s to lower 30s. Thursday will see the weak wave tracking
south of our area with some chances for light snow. Depending on the
available moisture, a dusting to inch of snow will occur. The
remainder of the forecast is rather uncertain with both the medium
range model bringing in a large pool of Arctic air south through the
weekend. The past several runs of each medium range deterministic
models have been chasing each other with a significant snow event
over southern Iowa Sunday into Monday. Today the EC has backed down
and the GFS has ramped up. If ensemble guidance is considered,
neither model favors any major system far enough north to bring the
snowfall amounts seen in some of the deterministic runs the past 2
days. In fact the ensemble mean of the low tracks in both the EC/GFS
push the system into the Southern Plains with little impact on our
area. Will need to monitor later trends, but for now will not be
leaning toward any big events and impacts. The only consistent
signal is the colder temperatures with more January like weather
from Friday through Sunday with highs in the teens/20s and mins in
the single digits and teens.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 547 PM CST Sun Dec 29 2024
While there are a few breaks in the clouds over northern and
western Iowa with VFR conditions at just MCW presently, clouds
will fill back in and ceilings will lower into LIFR quickly this
evening. Further, fog will develop and become dense with LIFR
or VLIFR restrictions. These restrictions will last into Monday
morning with improvement mid to late morning, particularly in
visibility as the fog dissipates. However, rain is expected to
slide in from the west with confidence highest at FOD and DSM
for prevailing groups. Elsewhere, PROB30 groups for the rain`s
arrival.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...REV
AVIATION...Ansorge
Area Forecast Discussion
National Weather Service Quad Cities IA IL
703 PM CST Sun Dec 29 2024
.KEY MESSAGES...
- Areas of fog, possibly becoming dense tonight for portions of
the area.
- Rain likely for most Monday afternoon through early Tuesday. A
transition to snow will be possible during the
evening/overnight, with some light accumulation and minor
impacts.
- Fast moving clipper system Thursday may bring dry, light
accumulating snow.
- Active weather returns this weekend into next week, with much
colder temperatures and a possible winter storm.
&&
.UPDATE...
Issued at 704 PM CST Sun Dec 29 2024
Another night of dense fog and have issued a dense fog advisory
for portions of eastern IA along and north of Hwy 30 through
noon on Monday. Visibilities have already dropped to 1/4 mile
at a few locations. The NBM indicates this dense fog to spread
east and south over much of the remainder of the forecast area.
Will continue to monitor trends and expand the advisory later
this evening if needed.
&&
.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 155 PM CST Sun Dec 29 2024
Morning satellite loops, observations, and webcams showed areas
of dense fog developed early this morning. While there was some
improvement at times today especially in urban areas, the fog
persisted into the late morning due to light convergent flow and
abundant low level moisture. Just above the surface, a rather
strong inversion sampled on the 12z DVN sounding at 930mb, kept
sub 1kft stratus over the entire area. As a result, temperatures
have only risen 4-8 degrees through the day. At 1 pm,
temperatures were in the upper 30s to mid 40s. Area radar
mosaics showed some returns of light rain/drizzle over portions
of northern and southeast IA ahead of a weak shortwave
upstream.
This Afternoon-Tonight...some light rain/drizzle may occur across
the southwest third of the CWA and have maintained slight
chance PoPs. This area may also see some patchy dense fog
persisting for another hour and I have issued an SPS to account
for this. Otherwise, damp and dreary conditions from recent fog
will continue. A deepening surface low to our east in IN will
lift northeast towards Lake Erie, with a surface ridge sliding
east over Iowa. This will set the stage for more fog
development. Forecast soundings and 12z HREF vsby progs show at
least patchy dense fog will be possible for areas along and
north of a line from Marengo through the Quad Cities. Decided to
hold off an issuing a dense fog advisory for now until
confidence increases on timing and placement.
Monday...any lingering fog should lift a few hours after sunrise. A
rather potent shortwave will move across the Plains, with rain
breaking out initially across Iowa. Forecast soundings suggest
top down saturation will take place rather quickly and cool the
entire column below freezing. There is a concern with recent
hi-res model solutions that rain will quickly change to snow as
early as 22z in central IA. The latest RAP shows strong omega
in the DGZ and a narrow fgen band developing and moving east
along I-80 during the late evening hours. The 12z HREF 1-hr 90th
percentile snowfall progs suggest 1"/hr snowfall rates may
occur in this band, which may overwhelm the marginal pavement
temps allowing for slushy 0.5"-2" snow accumulations. This is
something to be watched by later shifts and an SPS may be needed
if this comes to fruition. In addition, PWs rising near 0.7
tenths (above the 90th percentile for late December) combined
with strong forcing will bring some more beneficial and
widespread rainfall totals over a quarter of an inch. Some half
inch totals will not be out of the question across the southern
forecast area.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 155 PM CST Sun Dec 29 2024
Northwest flow aloft to bring more seasonable temperatures to start
the New Year, with even colder air expected this upcoming weekend.
850mb temps will remain in the -8 to -12C range through Friday,
resulting in highs in the upper 20s/low 30s and lows in the
teens/low 20s. Models continue to suggest a subtle and fast moving
clipper system moving through the flow Thursday, bringing a chance
of snow. Confidence on moisture availability and location remain low
and will continue to mention slight chance PoPs for now for areas
south of I-80.
This Weekend Into Next Week...confidence is increasing of a stronger
system moving over the Colorado Rockies and into the central Plains
Saturday and Sunday. Impacts from accumulating snow and gusty winds
are likely somewhere across the Midwest. While there is considerable
uncertainty on ensemble and deterministic low tracks this far out,
it does appear that our area will be on the cold side of system and
thus snow will be the main ptype. The surface low also will be
strengthening as it passes into the Ohio river valley, which may
bring gusty north winds on the back side. Beyond this, very cold
arctic air will drop south into the Midwest, with high confidence
(>70%) of below normal temperatures per CPC 6-10 day and 8-14 day
temperature outlooks. Sub-zero lows will be possible. Winter weather
fans rejoice!
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 545 PM CST Sun Dec 29 2024
Latest 2256Z satellite has plenty of clouds across the region.
Satellite data does show some breaks in the clouds. Current 23Z
observations have visibilities at 7 miles or more, however with
LIFR and IFR clouds. KDBQ currently only has scattered 400ft
clouds, but current data and thinking is that it will become
broken shortly. Latest data has northern and eastern sections
more likely with the fog and lower ceilings. Based on data and
trends went with lower visibilities and ceilings at KDBQ and
KCID during the TAF period. Maintained previous more pessimistic
TAF trends based on the past several days. Expecting LIFR
conditions at all TAF locations for a period of time. Otherwise
winds will become light and variable. Winds will pick up a
little to around 5 to 10 kts at a few locations later in the
TAF period. Focus then shifts to the next system which will
impact the region. It is currently just beyond this TAF period,
but may impact the next 30/06z TAF issuance.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Dense Fog Advisory until noon CST Monday for IAZ040>042-
051>054.
IL...None.
MO...None.
&&
$$
UPDATE...Haase
SHORT TERM...Gross
LONG TERM...Gross
AVIATION...Holicky
Area Forecast Discussion
National Weather Service Grand Forks ND
707 PM CST Sun Dec 29 2024
.KEY MESSAGES...
- Dense fog will expand across the area this evening through
Monday morning. Travel conditions will be impacted tonight
into the Monday morning commute.
- Colder conditions are forecast this week, with 30% chance of
hazardous wind chills around -30F by Friday within the Devils
Lake basin.
&&
.UPDATE...
Issued at 705 PM CST Sun Dec 29 2024
Keeping a close eye on webcams, satellite and observations as
monitoring the fog. The big area of fog from west central MN
continues to expand slowly NNW. It is moving into Fargo area at
01z as evidence by the Fargo NDSU NDAWN cam showing fog arriving
at the airport. Other fog area Baudette to Hallock back to
Grafton is less solid but is building or filling in to the
southeast toward TRF and slowly toward GFK. So idea of
widespread dense fog is correct. Devils Lake area will be
watched as fog is likely there though HRRR doesnt quite have as
extensive in that area.
&&
.DISCUSSION...
Issued at 247 PM CST Sun Dec 29 2024
...Synopsis...
Synoptically, water vapor imagery reveals weak troughing aloft
over the eastern Dakotas into Minnesota, although upper ridging
from the High Plains is encroaching upon the area, helping
promote low level ridging. At the surface, subtle high pressure/col
is being noted. This is helping trap low level moisture perhaps
aided by melting snowpack amid mid 30s to low 40s, particularly
in southeast North Dakota into Minnesota. Within this low level
moisture, dense fog has been persistent throughout the day, and
will continue to do so. In fact, expansion of dense fog will
occur starting early this evening, lasting through Monday
morning. More details on dense fog and associated potential
impacts can be found below.
A notable shortwave trough within Pacific Northwest will
propagate into the Central Plains. While its precipitation will
bypass our area to the south, this will help draw in colder air
currently in the western Canadian Prairie Provinces into the
Northern Plains starting Monday. This is partly helped by upper
troughing setting up around the Hudson Bay region by mid week.
As the nose of the cold air/cold front moves through late
Monday, weak but persistent cold air advection will help squeeze
out low level moisture bringing a chance for light
snow/flurries late Monday through Tuesday. At this time,
potential accumulations will remain on the lighter side, with
only a 10% chance to exceed 1 inch currently forecast within
this timeframe, although mesoscale enhancement from HCR
development may help local amounts between 1-2 inches by Tuesday
night. Brief freezing drizzle may also occur near the initial
cold front before temperatures cool enough.
Increasing high pressure sliding into the High Plains and
deepening low pressure within Ontario will increase the
pressure gradient over our area for an extended period of time,
generating breezy winds late Monday through Thursday. This
combined with temperatures trending colder with make for
blustery, brisk conditions this week. By late week, cold enough
temperatures and lingering wind may help push wind chill values
into the hazardous category (i.e. -30F or colder). More on this
can be found below.
Ensemble guidance still shows potential clipper late this week
around Friday/Saturday riding along a zone of baroclinicity on
the western fringes of polar air mass extending out of the
northern High Plains into the Midwest. There are still notable
synoptic differences within ensemble guidance regarding
strength, timing, and track of the clipper which would influence
location and severity of hazards like accumulating and blowing
snow. However, there remains a potential scenario that brings
winter impacts into the eastern Dakotas to western Minnesota
from such hazards.
...Dense fog through Monday morning...
Breaks between higher altitude clouds reveal extent of dense fog
nicely this afternoon. One area resides within west-central
Minnesota, with another in northwest Minnesota into adjacent
northeast North Dakota in the northern Red River Valley. HREF
probabilities associated with these areas are around 70%. These
probabilities expand in coverage across all of northwest and
west-central Minnesota as well as into the Red River Valley by
early evening, lasting through Monday morning, particularly
within west-central Minnesota. Conceptually, fog is driven by
subtle increase in low level moisture, as well as radiational
cooling, nudged by a melting snowpack. This along with weak
winds amid the surface high pressure/col lends high confidence
in dense fog within these areas. As such a Dense Fog Advisory
will remain in effect through Monday morning, although some
locations may see fog diminish prior to Noon as winds increase
with the approach of the passage of the low pressure system to
our south.
Elsewhere within eastern North Dakota, dense fog remains
possible given radiational cooling, calm winds, and melting
snowpack. However, confidence isn`t high in its location or
duration with the anticipation of winds increasing here first
sometime tonight.
While significantly reduced visibilities will impact travel
conditions, temperatures are forecast to dip below freezing
within fog. This as well as frost deposition onto surfaces may
make for slick surfaces tonight into Monday morning. This could
further make for hazardous travel conditions tonight into Monday
morning, including the Monday morning commute.
...Potentially hazardous wind chills late week...
Polar air mass combine with lingering breezy winds to bring
potential for hazardous wind chills around -30F Thursday night
into Friday. There are still some questions on whether or not
this occurs or where these hazardous wind chills occur. Things
lowering confidence include influence of a limited snowpack on
air temperatures, questions on coverage/amount of newly felled
snow from light snow late Monday-Tuesday bringing a fresh
snowcover, as well as how uncertain air temperatures mingle with
uncertain winds. As of now, the Devils Lake basin hold
relatively greatest chance of seeing wind chills -30F or colder.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 541 PM CST Sun Dec 29 2024
The issue for aviation tonight into Monday is fog, dense fog,
which is likely to expand and cover much of the area. The fog is
dense, so the change from VFR to IFR can be sudden. The exact
timing of when this occurs is uncertain at KGFK and KTVF. Fargo
airport is on the edge and should get into the fog 01-02z.
Devils Lake most uncertain but see no reason why some fog will
not get into that area overnight. Fog likely to persist into
Monday daytime.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Dense Fog Advisory until noon CST Monday for NDZ008-016-027-
030-039-053.
MN...Dense Fog Advisory until noon CST Monday for MNZ001>009-
013>017-022>024-027>032-040.
&&
$$
UPDATE...Riddle
DISCUSSION...CJ
AVIATION...Riddle
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
542 PM CST Sun Dec 29 2024
.KEY MESSAGES...
- The next round of widespread rain comes late Monday into
Tuesday,with areas along and north of I-70 having the best
chance (90-100%) for rainfall.
- Temperatures will become gradually colder into next weekend.
&&
.SHORT TERM... (Through Late Tuesday Night)
Issued at 238 PM CST Sun Dec 29 2024
Water vapor imagery currently shows the axis of an upper-level
trough swinging through the Middle Mississippi Valley. This feature
is helping cool temperatures aloft, and were skies have cleared
across far southeastern Missouri and southwestern Illinois, 100-200
J/kg of SBCAPE has developed leading to a low chance for
thunderstorms through this afternoon. However, current RAP analysis
shows an inversion across much of the area, which should keep this
activity isolated at most, if it even occurs. Further north across
the remainder of the CWA, a shortwave on the backside of the trough
and the left exit region of an upper-level jet is providing weak
lift and is responsible for the scattered rain seen along and north
of the I-70 corridor. The focus for this rain will gradually shift
east-southeastward through early this evening before exiting the CWA
to the east.
Given the abundance of low-level moisture still remaining in the CWA
and the inversion, another night of patchy fog is expected,
especially along and north of I-70. Fog may be dense at times across
northeastern Missouri and west-central Illinois, but any headline
decisions will be made this evening once details on the occurrence of
such conditions become clearer.
In the wake of the upper-level trough tomorrow, subtle ridging will
quickly build into the region. Southerly low to mid-level flow will
support temperatures topping out during the afternoon similar to
those we`re experiencing today. This warmth will come to and end,
though, as a shortwave digs into the region from the west-northwest
Monday afternoon and evening. Guidance has trended northward with
the passage of this wave`s surface low, with the consensus
supporting it tracking just north of I-70. While there is a 60%
chance that the entire CWA will receive measurable rainfall Monday
evening through Tuesday morning, the best chances (90-100%) exist
along and north of I-70 given the low`s track and clipper-like
nature. Here, rainfall amounts will range from 0.1-0.5" just north
of I-70, to 0.75-1" across far northeastern Missouri and west-
central Illinois. Some snow flakes could mix in as rainfall ends
across northeastern Missouri and west-central Illinois Tuesday
morning, but above freezing near-surface and ground temperatures
will mitigate accumulation and impacts.
In the wake of the shortwave, deep northwesterly flow will begin
ushering in colder air, with Tuesday`s highs being about 10 degrees
colder than Monday`s. Temperatures will still be just above normal,
but this will mark the beginning of a prolonged stretch of wintry
temperatures.
Elmore
&&
.LONG TERM... (Wednesday through Next Sunday)
Issued at 238 PM CST Sun Dec 29 2024
Though there are subtle variations, guidance consensus points to
that the Middle Mississippi Valley will be beneath northwesterly
flow through this portion of the period as a prolonged period of
troughing commences across the eastern CONUS. This will support a
stretch of near normal (highs in the upper 30s to low 40s, lows in
the 20s) to below normal temperatures through the long-term forecast
period, with ensemble means struggling to get out of the 30s for
highs across much of the CWA.
With cold air expected, our attention turns to precipitation
chances. Northwesterly flow aloft opens the door for clipper systems,
and deterministic guidance shows such a system quickly passing
through the Midwest late Thursday into early Friday. The subtlety of
these systems makes them difficult to forecast at these lead times,
and finer details are uncertain. However, recent guidance trends and
solutions show that I-70 and northward has the greatest chance of
seeing precipitation in the form of snow given forecasted
subfreezing temperatures. There, ensemble-based probabilities are
around 50-60% for measurable snowfall over a 24-hour period; though,
the lower values in the current forecast/NBM are due to differences
in timing.
The next clear chance for precipitation comes late next weekend, as
guidance consensus shows a more potent shortwave moving through the
region. Differences in amplitude and timing of this wave among
deterministic solutions and ensemble clusters lead to uncertainty in
precipitation and temperatures. If ridging can build into the region
ahead of the wave as some guidance suggests, temperatures will rise
to some degree, supporting a greater chance for liquid precipitation
especially if it occurs during the daylight hours. If temperatures
are not able to warm enough and precipitation occurs mostly at
night, then a greater chance of frozen precipitation can be
expected.
Elmore
&&
.AVIATION... (For the 00z TAFs through 00z Monday Evening)
Issued at 533 PM CST Sun Dec 29 2024
A deck of MVFR to IFR stratus is slowly moving east across
northern and eastern Missouri tonight. This will cause flight
conditions to deteriorate overnight. Fog will likely develop again
tonight, impacting portions of central Missouri, northeast
Missouri, and west-central Illinois. How dense the fog becomes is
still uncertain, but trends over the past several days lead me to
lean pessimistically. Any fog that develops is expected to
dissipate by late morning, with VFR conditions expected at most
terminals sometime in the afternoon as the stratus deck lifts.
This will be a brief shot at VFR, however, as the next system will
bring another shot of widespread light rain and low MVFR to IFR
ceilings tomorrow evening.
Jaja
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX