Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/18/23
Area Forecast Discussion
National Weather Service Boston/Norton MA
1019 PM EST Sun Dec 17 2023
.SYNOPSIS...
A strong storm moving up the eastern seaboard will bring very
strong winds, heavy rain and coastal flooding along the south
coast later tonight into Monday. High elevation snow and rain
showers possible Tuesday before a prolonged dry period sets up
from Wednesday through the weekend. Temperatures will be
seasonable to slightly above normal by late next weekend. Those
hoping for a white Christmas will need to wait for another
chance in 2024, with little to no precipitation expected after
Tuesday.
&&
.NEAR TERM /THROUGH MONDAY/...
1010 PM Update:
Conditions continue to deteriorate with bands of rain spiraling
northward as strong low pressure is still located over the
Carolinas. There has been some enhanced rain with even some
instances of observed lightning in these warm frontal/moist
advection surge rain bands. 00z OKX RAOB shows some elevated
instability that may be responsible for these convective-
elements. Expect these embedded heavier downpours to continue
to shift northward into NH/VT by thru midnight. But the real
crux of heavier rains arrives around the pre-dawn into the
Monday morning period. Pretty remarkable multi-model agreement
in placement of QPF bullseyes into western MA and northern CT
into western RI during the 09-12z timeframe, this rain being
forced by extremely strong moisture transport now taking shape
over the mid-Atlc region. There are some model solutions which
show warm cloud depths around 10 to 11,000 ft into these same
areas as well. I opted to increase QPF for our western and
central MA and northern CT areas by a quarter to third of an
inch, and further upward adjustments could be needed. We do
have the Flood Watch in effect for these areas, so there`s
really not a big change to the messaging, but will stress that
Monday morning commuters will need to be aware of the potential
for urban and poor drainage street flooding as that seems to be
a growing risk, along with potentially rapid responses on
smaller creeks and streams.
No significant change needed on the wind and coastal flooding
concerns. Did notice maybe a small decrease in the low level jet
strength on the 00z NAM but not enough for any changes there.
Previous discussion:
Key Points...
* Strong to damaging wind gusts late tonight and Monday, especially
near the coast
* Heavy rainfall will result in areas of urban and poor drainage
street flooding and minor to moderate river and stream
flooding
* Minor to moderate coastal flooding along portions of the south
coast
Evening update...
The first initially overrunning wave of precip has fully
established itself across SNE with the warm front just now
approaching the S coast. We should begin to see winds take on a
more southerly component over the next couple hours, as VAD
profiles are showing the nose of the southerly LLJ already
approaching from the south with roughly 40 kt at 2kft. Adjusted
POPs and wind timings slightly, but based on latest short-fused
guidance, the forecast looks to remain on track.
Previous discussion follows...
A rather dynamic system will be impacting SNE later tonight into
Monday as a southern stream negative tilt trough lifts north into
the region. Highly anomalous low level jet ahead of the trough will
transport high PWATs northward. Low level wind anomalies are 5-6SD
above normal which is maxed out relative to climatology for this
time of year, and PWAT anomalies are 4-5SD above normal. This is a
very strong signal for an anomalous wind and rain event. No changes
to Flood watches and High Wind warnings/advisories. The Coastal
Flood watch for Narragansett Bay and RI south coast was upgraded to
a Coastal Flood warning, Coastal Flood advisories were issued for
the Bristol county MA coast and for the north shore.
Winds...
The S/SE low level jet is quite impressive and encompasses a wide
area as it lifts northward along the coast late tonight into Monday.
The NAM remains the strongest of the guidance with 850 mb winds
peaking at 100+ kts across eastern New Eng and 925 mb winds 90+ kts
over Cape/Islands. The HRRR and HiResW-ARW are also indicating 90
kts at 925 mb. Timing of peak jet is about 09-15z near the south
coast and 12-18z for Cape/Islands. As is always the case with these
southerly low level jets, the uncertainty is how much of this wind
will mix down given soundings do show a low level inversion in
place. Typically about 50 percent of the 925 mb wind offers a
reasonable first guess with an inverted temp profile. However, in
this event we have very impressive pressure falls moving to the
north and west, up to 10-12 mb in 3 hours. This is quite impressive
and will enhance winds due to the isallobaric acceleration so we
should achieve at least 60 percent of the 925 mb wind. Could get
up to 70 percent of the 925 mb wind where temps exceed 60
degrees, with best chance across eastern MA/RI and portions of
CT valley. This supports gusts 60-70 mph over the Cape/Islands
and 50-60 mph in the coastal plain from PVD to BOS. These winds
will be capable of tree damage and power outages, especially
given increasingly saturated soils. Winds will taper off further
inland as there is a strong 925 mb wind gradient, but should
see 40-50 mph gusts across interior MA/CT, but probably less
wind across NW MA.
In addition, there is some elevated instability so any thunder would
help to bring stronger gusts down. Hi-res CAMs do show convective
elements so will have to monitor radar closely as SPC placed
portions of SNE in a marginal risk. Will be dependent on
instability. Little to no surface based instability is forecast,
with just a few hundred J/kg of MUCAPE.
Rain/Flooding Potential...
QPF was derived from a blend of NBM and WPC. Wind and PWAT anomalies
indicate a strong signal for an excessive rainfall event as strong
low level jet combines with a coupled upper level jet and acts on
anomalous PWAT plume. EFI values are near 1 across western New Eng
indicating all EPS members are forecasting QPF that exceeds the max
of the model climate for this time of year. Rainfall amounts of 2-4
inches expected west of I-95 corridor with localized 5+ inch amounts
along the east slopes of the Berkshires due to orographic
enhancement from SE upslope flow. The HREF PMM actually indicating
localized 7 inch amounts. Rainfall amounts should be less across SE
MA and Cape Cod with generally 1-2 inches. Heaviest rainfall will be
late tonight and Monday morning, with rainfall intensity gradually
lessening through the afternoon as mid level dry slot lifts
northward.
MMEFS from the NAEFS and GEFS suggesting several rivers in RI and
eastern MA reaching minor flood, with several rivers in the CT basin
reaching moderate flood. In addition, expect areas of urban and poor
drainage street flooding.
Coastal Flooding...
See coastal flood section below.
&&
.SHORT TERM /MONDAY NIGHT/...
See Long Term section below.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Highlights...
* Snow and rain showers possible Tuesday
* Prolonged dry period sets up by Wednesday, extending through
the Christmas Holiday. Seasonable to slightly above normal
temperatures expected
Low pressure that impacts southern New England on Monday moves to
our northeast with a dryslot developing behind the departing low
late Monday afternoon and early evening as a strong cold front
traverses across southern New England.
Deep digging trough, with the 540mb line extending as far south as
the Carolinas, associated with the cold front is very slow to
move east of southern New England Tuesday. High temperatures are
likely to be experienced very early in the day as cold pool
aloft of 925mb temps of minus 6C to minus 9C center about SNE by
Tuesday evening. As this trough/front crosses southern New
England, it will tap into what little moisture is left, PWATs
~0.3-0.4", to generate some snow showers across the high terrain
and rain showers elsewhere through early Tuesday night. The
forecast currently calls for between a trace and a half inch of
snow above 1000Ft in the Berkshires, consistent with ensemble
probabilities of >1" of snow between 10-40% GEFS) and 0% (ECMWF
and CMC).
Trough axis finally aligns with southern New England by Tuesday
evening as strong ridging develops across the central CONUS/Great
Plains on Wednesday. We remain on the right edge of the ridge for
much of the next week, so while precipitation chances will be
suppressed, temperatures and flow will be rather stagnant. With
ridging to our west, we remain sandwiched between that and low
pressure that remains nearly stationary well east of the benchmark.
Several days of northerly/northwest flow given the position of the
low will yield near to slightly above normal temperatures from
Wednesday through the weekend, temps building a degree or two each
day.
For those hoping for a white Christmas, odds are favoring that
you`ll have to wait for another chance in 2024, with dismal
precipitation chances through the holiday.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00Z TAF Update:
Sunday Night: High Confidence...
Already noting LLWS across much of Southern New England this
evening with about 40-50kt at 2000ft. Therefore, latest TAF
update will reflect increasing LLWS into the early morning
hours. Otherwise, mix of predominantly IFR, with occasional MVFR
where RA mixes out the low clouds.
Winds continue to increase, strongest surface gusts out of the
southeast generally 09Z-18Z. where 40-50kt expected along the
east coast with 50+ Cape/Island terminals.
Monday: High Confidence...
IFR for all terminals with moderate to heavy rain in the
morning. Winds should peak between 12-18z with gusts
40-60knots. Wind shear will also peak during this time with
925mb winds approaching 70-90 knots. Winds in the morning remain
SE, but shift to the S then SW by afternoon. After 18z, winds
and heavy rain should begin to lighten up. Ceilings begin to
lift slowly after 18z to MVFR levels by 00z
Monday Night: Moderate Confidence
Continuing to see improvements Monday night. Ceilings should
improve from low end MVFR to MVFR/VFR. Winds continue to
diminish out of the SW and wind shear should no longer be an
issue.
KBOS TAF...High confidence in TAF.
VFR with pockets of MVFR this afternoon. Becoming MVFR then IFR
tonight with pockets of light rain. Moderate to heavy rain
begins late overnight and lasts through tomorrow morning. Wind
shear of 40-60 knots is possible starting this evening through
tomorrow afternoon. Surface winds gradually increase tonight
peaking between 12-18z with gusts up to 50 knots. After 18z
tomorrow, winds begin to diminish and ceilings improve to MVFR.
KBDL TAF...High confidence in TAF.
MVFR/IFR this afternoon becoming IFR this evening. Light rain
this evening becoming moderate to heavy overnight. Heavy rain
and gusty winds to 40 knots through 18z tomorrow. After
18z,should see improvements to MVFR and gusty winds.
Outlook /Tuesday through Friday/...
Tuesday: Mainly VFR, with local MVFR possible. Breezy. Chance
RA.
Tuesday Night: VFR. Breezy. Slight chance RA.
Wednesday: VFR. Breezy.
Wednesday Night: VFR. Windy with gusts up to 30 kt.
Thursday through Thursday Night: VFR. Windy with gusts up to
35 kt.
Friday: VFR. Windy with areas of gusts up to 30 kt.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Overall high confidence.
** Dangerous Marine Conditions overnight and Monday
Highly anomalous low level jet will bring dangerous marine
conditions with strong winds and high seas late tonight and
especially Monday. Storm warnings remain in effect for all waters
for southerly gusts 50-55 kt, up to 60 kt over outer waters. Seas
will build up to 25 ft over southern outer waters and 20 ft over
eastern outer waters. Rain will become heavy at times late tonight
into Monday and reduce visibility.
Outlook /Tuesday through Friday/...
Tuesday: Winds less than 25 kt. Rough seas up to 16 ft. Chance
of rain.
Tuesday Night: Winds less than 25 kt. Rough seas up to 12 ft.
Slight chance of rain.
Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Rough seas up to 10 ft.
Wednesday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 10 ft. Slight chance of rain.
Thursday: Moderate risk for gale force winds with gusts up to
35 kt. Rough seas up to 11 ft. Slight chance of rain.
Thursday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 12 ft.
Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 11 ft.
&&
.TIDES/COASTAL FLOODING...
Coastal Flood watches were upgraded to a warning for Narragansett
Bay and the RI south coast. Stevens institute and PETSS
guidance indicating a peak surge of 4+ ft at Providence. This
may occur a few hours before high tide, but nonetheless there is
a high probability of widespread minor flooding in Narragansett
Bay with storm tides of 8 to 8.5 ft at Providence. There is a
lower risk of reaching or exceeding 9 ft (moderate flooding
threshold) if the peak surge coincides with high tide. We are
also concerned with the ocean exposed south coast for localized
moderate flooding. While surge values will be a bit less, seas
just offshore expected to peak at 20- 25 ft and this wave action
will be enough to produce more significant impacts than the
storm tide would otherwise indicate.
Coastal flood advisories were issued for the south coast of MA in
Bristol county for Fall River, Westport and New Bedford where a 2-3
ft surge will result in minor flooding.
Finally, we may also see areas of minor flooding along the north
shore, especially at Gloucester during the mid afternoon high tide.
This area is more exposed to S/SE flow so we issued a coastal flood
advisory. A surge up to 2 ft is forecast which is enough for minor
flooding given wave action. Less of a risk for Boston and the south
shore but can`t rule out minor splashover in a worst case scenario.
Would need a 2 ft surge for minor flooding which may be tough to get
with a S wind.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch through Monday evening for CTZ002>004.
Wind Advisory from 1 AM to 4 PM EST Monday for CTZ002>004.
MA...Flood Watch through Monday evening for MAZ002>005-008>013-017-
026.
Wind Advisory from 1 AM to 4 PM EST Monday for MAZ002-003-
008>011.
Wind Advisory from 5 AM to 7 PM EST Monday for MAZ004>006-012-
026.
High Wind Warning from 5 AM to 7 PM EST Monday for MAZ007-
013>024.
Coastal Flood Advisory from 1 PM to 5 PM EST Monday for MAZ007.
Coastal Flood Advisory from 10 AM to 2 PM EST Monday for
MAZ020.
RI...Flood Watch through Monday evening for RIZ001>004.
High Wind Warning from 5 AM to 7 PM EST Monday for RIZ001>008.
Coastal Flood Warning from 10 AM to 2 PM EST Monday for RIZ002-
004>007.
MARINE...Storm Warning from 1 AM to 7 PM EST Monday for ANZ230>237-250-
251-254>256.
&&
$$
SYNOPSIS...KJC/KS
NEAR TERM...KJC/Loconto/Guest
SHORT TERM...KJC
LONG TERM...KS
AVIATION...Loconto/KS/Guest
MARINE...KJC/Loconto/KS
TIDES/COASTAL FLOODING...KJC
Area Forecast Discussion
National Weather Service Burlington VT
926 PM EST Sun Dec 17 2023
.SYNOPSIS...
A significant storm will bring a period of moderate to heavy
rainfall and gusty to possibly strong winds, primarily Monday
morning. Minor to moderate river flooding is forecast due to
snowmelt runoff and rainfall. After a period of warm conditions,
temperatures will become much cooler, supporting snow showers
on Tuesday. Dry and uneventful weather is expected for the rest
of the week.
&&
.NEAR TERM /THROUGH MONDAY NIGHT/...
As of 916 PM EST Sunday...Water vapor shows a maturing cyclone
with deep warm moist conveyor along the eastern seaboard. Sfc
analysis places 988mb low pres just of the central SC coast with
greatest 3hr pres falls toward eastern NC. Radar shows large
areal coverage of precip along the eastern seaboard, extending
from northern VT/NY into eastern NC with axis of heaviest precip
approaching eastern PA/central NJ. This will continue to advect
northward and be into our cwa by Monday morning with periods of
moderate to heavy rainfall. Going fcst of 1.5 to 2.5 inches
looks very good with locally amounts near 3.0 possible acrs
Essex County NY. Crnt obs indicate between 0.10 and 0.20 most
locations, with amounts already approaching 0.50 in Essex
County, NY, so Ausable will need to be watched closely overnight
into Monday, along with other rivers as heavier precip
develops. Meanwhile, winds have been a bit frisky over Rutland
County with Danby gusting to 44 mph, 38 mph at Mendon and 33 mph
at Rut. These winds will continue overnight as 850mb jet
strengthens associated with deepening sfc low pres. Based on
00z data, wind advisory looks good, as still some uncertainty
lingers with amount of mixing, given moist adiabatic soundings.
I did tweak winds a bit to match crnt trends. Also, placed pops
at 100% for most of the area for the entire night, as its going
to rain and measure everywhere in our cwa. Final tweak was to
bump temps up into the mid/upper 50s for most of the CPV on
Monday and increase sfc dwpts to near 50F, based on latest 00z
guidance and progged 925mb temps with warming downslope
east/southeast flow.
Previous discussion below:
* High Wind Watches have been converted to Wind Advisories
across the western slopes of the Greens.
* Flood Watches remain in place with minor to moderate river
flooding still anticipated due to a combination of rainfall
and snowmelt runoff.
After a dry afternoon, precipitation chances will be on the rise as
a dynamic storm system approaches our area from the south. The area
of convection currently over the Carolinas would have to watched
closely heading into this evening because it could have downstream
impacts on the surface low development. RAP currently has the
coastal low pressure off South Carolina at 993 mb. More robust
thunderstorm development has shown to have the ability to result in
a further eastward shift in downstream surface low pressure
development. Despite the calendar saying mid December,
unfortunately, we are once again dealing with a warm rain event for
North Country. The exact surface low pressure track, its forward
motion and extent of deepening will all have an impact on how much
terrain shadowing we get, the westward extent and duration of the
higher dew points (40s and 50s), as well as the potential for
downslope winds off the mountains.
At this time, we are fairly confident in the low tracking right over
the Champlain Valley. This is now supported by both the global
ensemble guidance as well as the Convection-Allowing Models (CAMs).
This means the wind threat has decreased for the western slopes of
the Greens. With less terrain shadowing, the coverage of moderate to
heavy rainfall has also increased. Rainfall amounts are now in the
1.5 to 2.75 inches range, with the eastern upslope regions of the
Adirondacks and Greens expected to receive over 3 inches. However,
as explained in the hydrology section, that is not expected to
result in a significant deterioration in the river flooding
potential.
Steady rainfall arrives after sundown this evening, becoming heavy
at times especially during the latter half of the overnight hours as
a potent 70-80 kt 850mb jet overspreads the area. Forecast soundings
show deep saturated profiles up to 15000 ft, indicative of efficient
warm rain processes. PWATs rise to over an inch by the pre-dawn
hours on Monday, so Monday morning commute could be difficult with
steady rainfall, hydroplaning issues and localized urban poor
drainage ponding. Nonetheless, the flash flooding threat is nil to
minimal with overall manageable rainfall rates expected.
Temperatures overnight tonight into Monday morning will not fall all
that much if not rise a few degrees so a few record maximum
overnight lows could be challenged. On Monday, dew points surge into
the 40s with low 50s not out of the question. With widespread highs
in the 50s (near 60 across southern VT), a few daily record high
temperatures are likely to be broken. Nonetheless, it would not be
exactly a pleasant day with wind driven rain. This would lead to
melting of the snowpack, which would result in sharp river rises
when combined with the rainfall contribution. Looking at the NOHRSC
analysis, there is widespread 1-2 inches of snow water equivalent
along and east of the Greens. However, that appears to be an
overestimate compared to our network of observations, which suggests
that the liquid equivalent of snowmelt is closer to 1 inch. More
details can be found in the Hydrology section.
With regards to the wind threat, it has trended downwards due to the
eastward shift in the surface low pressure track. As a result, the
best low-level jet dynamics will be further east. While there can
still be localized 50-55 mph gusts across parts of the western
slopes of the Greens, most of the wind speeds are now expected to be
in the 30 to 40 mph range. Therefore, the High Wind Watches have
been converted into Wind Advisories.
Then overnight Monday, colder air gets advected into the region from
the southwest. This means that the colder air will be lagging the
main precipitation shield. So we do expect a few hours of dry
weather before snow showers increase in coverage from the west.
Little to no accumulations are expected through early Tuesday
morning outside of the Adirondacks.
&&
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 317 PM EST Sunday...An upper level low swings through on
Tuesday and brings some snow showers to the region. Snow totals will
be relatively light with the highest amounts in the Adirondacks,
Greens, and St. Lawrence Valley. Here, totals look to be around 1-3
inches with isolated areas up to 4 inches. The rest of the region
should see totals mostly under an inch. The precipitation might
briefly start as rain in the broad valleys of Vermont but it will
quickly change to snow. Ground temperatures will still be pretty
warm at the onset due to the prior warm and rainy conditions on
Monday, so that might limit accumulations. Another possible
limitation will be that precipitation rates should be relatively
light during the entirety of the storm. This will combine with
temperatures at or above freezing in the broad valleys and likely
limit accumulation efficiency. The St. Lawrence valley will be an
exception the colder air should be in place before the precipitation
arrives and the precipitation rates might be a little higher than
the other valleys. The snow showers will slowly move out overnight
and temperatures will fall below freezing everywhere. There will be
a non-diurnal temperature trend on Tuesday with highs at midnight
and temperatures falling throughout the day.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 317 PM EST Sunday...A quiet weather pattern will dominate the
forecast period with only a few snow showers possible over the
weekend and no major storms. A large area of high pressure will move
into the region on Wednesday and it will generally remain in place
into the start of next week. Temperatures will be close to normal
with highs in the upper 20s and 30s and lows in the teens and lower
20s. There should be a decent amount of sun during the period as
well. Over the weekend, there will be a weak shortwave swinging
through the region that may bring some showers. However, there will
be scarce moisture and weak forcing so any precipitation would be
light. The models are trending drier so its becoming more likely
that the weekend will just be dry. For anyone who wants a White
Christmas, they are going to have to hope that some snowpack can
survive the rain tomorrow and the light snow that falls on Tuesday
will stay around. The next chance of significant precipitation is
not until past the end of the forecast period.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Through 00Z Tuesday...Multiple hazards expected to impact
our aviation sites over the next 12 to 24 hours. First is the
strengthening 2500 to 4000 feet above ground level jet of 60 to
80 knots, producing areas of moderate to severe turbulence,
especially near the terrain. Localized wind gusts up to 35
knots possible at Rutland toward 12z Monday. Next hazard is
lowering cigs from VFR to MVFR and areas of IFR at MPV this
evening into Monday morning. As heavier rain overspreads our taf
sites, expect mostly MVFR with periods of IFR vis/cigs likely,
especially after 06z. As moisture continues to deep widespread
IFR/LIFR cigs with IFR vis can be expected to develop acrs many
of our taf sites by Monday morning. Southeast/south winds will
eventually shift to the southwest/northwest on Monday aftn with
some improving conditions possible at PBG. Bottom line expect
changeable conditions over the next 12 to 24 hours with multiple
aviation hazards anticipated.
Outlook...
Monday Night: Mainly MVFR, with local IFR possible. Likely SHRA,
Chance SHSN.
Tuesday: Mainly MVFR and IFR, with areas VFR possible. Likely
SHSN.
Tuesday Night: VFR. Chance SHSN.
Wednesday: VFR. NO SIG WX.
Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.
&&
.HYDROLOGY...
* Minor to moderate river flooding is expected, with water levels
cresting Tuesday morning.
As of 315 PM EST Sunday...A strong low pressure system will
bring widespread rainfall to the North Country late tonight
through Monday before rain transitions over to snow showers.
Widespread rainfall amounts between 1.5 and 2.75 inches with
locally 3+ inches amounts possible on eastern upslope locations
of the Green and Adirondack Mountains. However, where we expect
the 3+ inches amounts are lesser of a concern. Firstly, the
Adirondacks have a colder snowpack than the Greens. For this
system, they will also be in the window of higher/warmer dew
points for a shorter duration. So there will be less snowmelt
contribution to river rises for Ausable Forks (ASFN6).
Nonetheless, given the flashy nature of ASFN6, we are currently
forecasting it to go briefly into low-end moderate flood stage.
The second area of 3+ inches concern is along the eastern
upslope areas of the Greens, which go into the Connecticut River
basin rather than the Winooski River basin. Having said that,
we do expect Winooski River at Essex Junction (ESSV1) to go into
moderate flood stage, given that it is further downstream and
drains a larger surface area of the basin. In other words, the
rain and snowmelt along the course of the river and its
tributaries will all likely add up.
Using our network of observations, including CoCoRaHS and Co-op
data, we concluded that the liquid equivalent of the snowmelt
contribution to area rivers would be no more than 1 inch, which is
quite a bit lower than the NOHRSC remote sensing/model output
estimate. Through coordination with NERFC, most gages are expected
to reach minor flood stage with the exception of ASFN6 and ESSV1.
For the latest official river forecasts, please visit
https:/water.weather.gov/ahps2/forecasts.php?wfo=btv
&&
.CLIMATE...
Unseasonably warm air will arrive Sunday night, leading to high
likelihood of record daily temperatures at most climate sites.
In addition, heavy rainfall will lead to likely daily record
precipitation. Here are the current records (and forecast values)
for Monday 12/18.
Max Temp Records
KBTV KMPV KMSS KPBG KSLK
57|1921 (55) 50|1949 (54) 44|1949 (46) 51|1966 (51) 49|1984 (47)
High Min Temp Records
KBTV KMPV KMSS KPBG KSLK
39|1996 (43) 35|1996 (40) 34|2015 (34) 36|2012 (40) 35|1996 (32)
Precipitation
KBTV KMPV KMSS KPBG KSLK
0.85|1954 (1.09) 0.86|1954 (1.46) 0.70|1951 (1.78) 0.62|1990 (1.35) 0.50|1954 (1.05)
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Flood Watch from 1 AM EST Monday through Tuesday morning for
VTZ001>011-016>021.
Wind Advisory from 1 AM to 4 PM EST Monday for VTZ011-016>019.
NY...Flood Watch from 1 AM EST Monday through Tuesday morning for
NYZ028>031-034-035.
&&
$$
SYNOPSIS...Chai
NEAR TERM...Chai/Taber
SHORT TERM...Myskowski
LONG TERM...Myskowski
AVIATION...Taber
HYDROLOGY...Chai
CLIMATE...WFO BTV
Area Forecast Discussion
National Weather Service State College PA
1046 PM EST Sun Dec 17 2023
.SYNOPSIS...
A strong coastal storm will move north along the Carolina coast
overnight and bring a widespread soaking to heavy rainfall
across all of Central and Eastern Pennsylvania into Monday
morning. The soaking rain will be followed by strong blustery
northwest winds and accumulating snowfall/heavy snow showers
Monday into Tuesday. In the wake of the storm, expect much
improved weather conditions by Wednesday with moderating
temperatures into late week.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Moderate to locally heavy rainfall rates have reached into the
Lower Susq and parts of the SC Mountains this evening, with QPE
exceeding 1.25" thus far in parts of these areas. Rainfall
totals thus far through 1030 PM range from 1.25"+ at KMDT and
1.00+" at KTHV to .67"+ from the SC Mountains northward to the
Ridge and Valley region. Regional radar mosaic indicates
heaviest rain band setting back up from northern Adams County
through Dauphin and Schuylkill County at this hour. Inst rafl
rates do exceed 1.5 to 2" but with no training anywhere. FFMP
indicates heaviest hourly rates of 0.8" to 1"+ within the
aforementioned area.
Overall model trend of the past 24 hours has continued into
this evening with hi res runs of the HRRR and NAM12 simulating
the heaviest rainfall of 2.5-3"+ farther east, now straddling
the eastern borders of Schuylkill and Lancaster Counties.
Correspondingly we`ve nudged our rainfall totals in that
direction with generall half to three quarter inch reductions in
storm totals into the central mountains, but still a very solid
2"+ across the eastern third of central PA. Best chances to see
3" or more remains eastern Lancaster and Schuylkill County at
this time. Heaviest rainfall of the storm over the Lower Susq
River Valley will be from now through 06-07z.
Sfc low northeast of Charleston SC this evening will deepen by
7-8 mb by the time it reaches the Delmarva region during the
predawn hours Monday, then reach NYC by midday Monday. Tonight`s
rainfall is only the first part of a multi- faceted storm
system that will eventually bring a "triple threat" of heavy
rain, wind, and snow to central PA over the next 24 to 48 hours.
Flood Watch remains in effect for the eastern half of central
PA, where 2" or more would at least cause minor flooding of poor
drainage areas and significant rises on flashier creeks. Lower
QPF may eventually keep they usual suspects (Swatara, Harper`s
Tavern, etc) just under flood stage (and also just below the 6
hourly Flash Flood Guidance values of 2 - 2.5 inches). We`ll
continue to watch upstream rainfall estimates and gage readings
into the overnight.
Locally higher amounts over 3" remain possible in the favored
higher terrain of east-central PA where upslope lift will be
enhanced/maximized with southeast exposure. However, with a band
of deeper convection possible near the I-95 corridor some of
the deeper moisture could be robbed from our eastern CWA. Period
of heaviest rainfall wraps up by 12z Monday from south to
north.
As for gusty winds, although an anomalous low-level jet will
overrun eastern PA later this afternoon and evening, model
sounding profiles also show the existence of an inversion above
the boundary layer, which should prevent the strongest winds
from mixing to the surface, save for perhaps the highest
elevations. Colder air wrapping into the backside of the storm
behind a blustery NW flow could begin to change rain to snow
over the Laurel ridges by the end of the period as we transition
into the next phase of the storm.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Good, in depth collaboration with surrounding WFOs to maintain
Winter Storm Watch for Warren County for a combination of
Synoptic and LES (and a Winter Weather Advisory for the Wrn
Mtns), and a Winter Storm Warning remains in effect for Somerset
County where the track of the deepening nrn stream trough and
long fetch off the upstream Glakes and orographic lift will
combine to bring a favorable setup for significant snow.
Potential for heavy lake enhanced and upslope driven snow
accums has increased since this morning (NBM 55-60% percent
chance of >=6" along Laurel Mtn west of US219). The strong
gusty NW wind could enhance winter/travel impacts with blowing
snow and significantly reduced visibility. Model instability
appears to be lacking for widespread squalls as the cold air
arrives, with robust instability tracking well south of the
Mason Dixon line, but some moderate snow bursts are possible
by Monday evening as 5H trough axis slices across the region.
Peak wind gusts (out of the NW) just below advisory category
thresholds (35-45 mph) should develop from later Monday into
early Tuesday as cold advection steepens lapse rates and
improves downward momentum transfer. Best wind gusts should
impact the area Monday evening as the upper trough axis passes
the area and boundary layer mixing and channeled flow is
maximized. This will continue to highlighted in our HWO and
contained in the wording of the WSWs. The wind shift from
southeast to northwest amidst saturated soils could support an
elevated risk of localized power outages as trees sway and water
logged limbs fall in the blustery conditions.
Snow showers likely last through Tuesday morning before
diminishing as high pressure over the Plains shifts to the east
over WV Tuesday night. Temps on Monday likely exhibit a non-
diurnal trend with Tuesday being the seasonably coldest day of
the week with highs in the upper 20s to upper 30s.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Continuation of enhanced NW`ly flow in the wake of the sfc low
will promote lake-enhanced precipitation through Tuesday
morning. Plowable snowfall Monday night into Tuesday over the
NW and along the Laurel Highlands remains likely with the NW
flow providing enhanced fetch off lake Erie and a continuous
upslope flow along the Allegheny mountains. The limiting factor
will be the deep layer flow becoming more anticyclonic as this
will cut into the residence time for the increased moisture and
limit overall snow amounts. If given trends are maintained we`d
expect some additional winter headlines to be needed for the
Monday night- Tuesday timeframe.
High pressure will begin building to the south after Tuesday
morning and encourage a similar trend to what we have seen the
last couple weeks. A slight warming in temps towards the end of
the week and dry conditions expected until the next low pressure
system approaches from the west during the weekend.
Deterministic guidance does suggest a return of precipitation
towards the end of the extended period as a sfc low approaches
from the west. Timing and coverage remains uncertain at this
time, especially with the last couple runs not being consistent,
so we have capped PoPs at Chc/SChc for Friday night with higher
chances coming in closer to the Saturday morning timeframe.
&&
.AVIATION /04Z MONDAY THROUGH FRIDAY/...
LIFR to IFR conds across central PA will continue Sunday evening
into Monday morning with high (70-80%) confidence as the surge
of Atlantic moisture continues progressing northward. Conds will
deteriorate further within the axis of heaviest rainfall, with
LIFR thresholds on vsby and cigs likely based on RAP model
soundings with saturated profiles at the lowest levels. At this
time, have timed out this rainfall to impact MDT/LNS between
03-05Z and IPT/UNV between 04Z-06Z given the progressive
movement of this feature. There is some possibility that
restrictions come an hour sooner, but have kept closer to
guidance which has been fairly consistent run-to-run wrt timing
of impacts at these airfields. Further to the west, timing of
heaviest rainfall becomes slightly less certain, but moderate
(50-60%) confidence on impacts at JST/AOO/BFD in the 05-08Z
timeframe with similar thinking on +1hr and restriction onset.
IFR/LIFR conds at daybreak expected (90+% confidence) to
continue into the day at BFD/JST with snow mixing in late in the
TAF period (~17-18Z) and becoming the more dominant
precipitation type in the 21-22Z timeframe. For all other
terminals, some improvement is possible later on in the TAF
period after an initial period of LIFR/IFR conds. Some
relatively drier air has potential to curb off precipitation
west of the Alleghenies, with MVFR cigs possible closer to the
16Z timeframe. There is moderate (40-50%) confidence on this
gradual improvement and have kept some lower clouds in the fcst
to outline slightly lower confidence on the lower cloud deck
scattering out until there is more model consistency.
NW`ly winds (at 300-330) will prevail Monday morning with
sustained 15-20 kts (lower elevations) to 20-25 kts (higher
elevations) and gusts pushing towards 35 kts at the highest
elevations of southern PA and along the Allegheny Front. Winds
will continue into the end of the TAF period and likely beyond
with high (80-90%) confidence.
Outlook...
Tue...Snow persists at BFD/JST, w/ variable conds (VFR much of
the time, occasional restrictions in flurries/SNSH) elsewhere.
Wed and Thu...Predominantly VFR.
Fri...Rain moves in from the west late, restrictions possible.
&&
.CLIMATE...
It has been 325 days since the last measurable snowfall
(>=0.1") at Harrisburg. This currently ranks as the 3rd longest
run on record. There is a low probability for measurable snow
Monday night into Tuesday; otherwise the longest run looks very
much in jeopardy based on the forecast into next weekend.
1. 330 days ending 12/13/2020
2. 328 days ending 01/21/2007
3. 325 days ending 12/16/2023
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Monday afternoon through Tuesday
morning for PAZ004.
Winter Weather Advisory from 1 PM Monday to 10 AM EST Tuesday
for PAZ005-010-017-024.
Flood Watch through Monday evening for PAZ028-037-041-042-046-
049>053-056>059-063>066.
Winter Storm Warning from 1 PM Monday to 10 AM EST Tuesday for
PAZ033.
&&
$$
SYNOPSIS...Lambert/DeVoir/Steinbugl
NEAR TERM...Lambert/DeVoir/Steinbugl
SHORT TERM...Lambert/DeVoir/Steinbugl
LONG TERM...DeVoir/NPB/Bowen
AVIATION...NPB
CLIMATE...Dangelo/Steinbugl
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
549 PM EST Sun Dec 17 2023
.AVIATION...
While main rain from earlier today has ended, scattered showers will
work back through the area this evening within southwesterly flow in
advance of approaching cold front with a continuation of MVFR cigs.
This cold front will sweep through the area early Monday morning and
bring a wind shift to the northwest with gusts into the 25-30 knot
range by midday. A mix of rain/snow showers along the front will
change to all snow showers with a peak intensity period immediately
along and behind the front in the late morning to early afternoon.
However, widely scattered snow showers will persist on into Monday
evening as well. Ceilings should remain generally MVFR with vsbys in
snow MVFR to occasional IFR.
For DTW...After a few showers sweep through the area this evening,
additional rain/snow showers will be possible along the cold front
around 08-10z Monday, with falling temperatures supporting scattered
to numerous snow showers after 12z. Peak coverage still looks to
occur between 16z and 19z. Temperatures in the mid 30s should limit
accumulations in this window, but falling temps the rest of the day
may allow for a dusting through the evening. Wind direction Monday
will be centered around 320 degrees with peak gusts of up to 30
knots during the afternoon.
.DTW THRESHOLD PROBABILITIES...
* High for ceiling at or below 5000 ft on through Monday.
* Medium for rain/snow precipitation mix overnight, high for all
snow after 12z Monday.
&&
.PREV DISCUSSION...
Issued at 340 PM EST Sun Dec 17 2023
1000-850 mb convergence associated with meridional deep moisture
transport axis was the primary forcing responsible for rainfall over
Southeast Michigan this morning. A dry slot has since arrived and
has provided enough erosion of lower level stability to allow for a
robust convective shower response within a shorter wavelength
deformation axis. The dry air and dynamic subsidence within the dry
slot is shown to lower down through approximately 3.5 kft agl this
afternoon which will shut down the organized widespread
precipitation. However, cooling within the 1.5 to 3.5 kft agl layer
will keep saturation and cloud overhead. Occasional drizzle will be
possible particularly in the higher elevated areas across northern
Metro Detroit. Quiet weather is anticipated this evening with
temperatures in the lower 40s.
Dynamic northern Plains potential vorticity anomaly and deep trough
will dig through the western Great Lakes tonight and across Lower
Michigan on Monday. Thermal progs will be relatively mild to begin
the day, then cool steadily after 15Z. There are two time window for
relatively modest synoptic scale forcing Monday. The first will be
between 15-20Z for all of the cwa associated with the vorticity
maximum push, while the second will be 00-03Z timeframe as an
enhanced area of 700-500mb moisture advects over Saginaw Bay and the
Thumb brings the prospects for some lake enhancement..
Thermal progs suggest relatively warmer near surface temperatures
between 11-14Z Monday which will support initial precipitation as a
mix of rain and snow. Steady cooling will then allow for all
precipitation type to changeover to snow quickly by mid to late
morning. Best forcing passes well south of Lower Michigan with the
1000-500mb height fall max, so duration along the front during the
late morning should be fairly quick. HRRR and NAM have slightly
shifted times but this early window could favor sometime between 15-
18Z. Air temps in the middle lower to middle 30s with a warm ground
off of a mild weekend precludes much accumulation potential other
than grass/vegetation. The second time window for precipitation is
expected to favor the Thumb region with lake enhancement as synoptic
scale moisture aloft spreads overhead and there is some onshore flow
from Lake Huron. There is a lot of uncertainty with how far south
(away from the Thumb) snow will exist into the cwa given the
reliance at the mesoscale. At this time, not expecting much impact
on the Metro area during the evening hours with dynamic subsidence
being progged for 2.5 to 7.0 kft agl. Snowfall of 2 inches or less
is expected in the Thumb with Huron County down into northern
Sanilac counties standing the best chance for accumulation.
The model trend for strong winds Monday has been to push the best
gusts into the noon to 10 pm time window. Cold air advection is
shown in the model soundings to support mixing depths at greater
than 4000 ft agl. Distributing of time lagged ensemble wind gusts
exemplifies a signal for a single mode in the 27 to 33 knot range. A
little more uncertainty exists in the Thumb with a much broader
distribution. Suspect that greatest wind gust will be right along
the immediate shoreline areas of Lake Huron reaching and exceeding
40 knots, with wind gusts falling off quickly inland, but still
remaining in that 27 to 33 knot range. Will not be issuing any Wind
headlines with this package, but may need Wind Advisories in Huron
and Tuscola counties.
Deferential anticyclonic vorticity advection will lead to
increasing surface high pressure on Tuesday. Developing southwest
flow will then lead to an extremely dry air mass for the middle and
end of the week. Highs Tuesday will be around the freezing mark with
readings in the 40s Wednesday through Sunday.
MARINE...
The main wave of rainfall has pushed east of the central Great Lakes
this afternoon with southerly flow in place this afternoon while a
strengthening low pressure system moves northward along the Carolina
coastline. The combination of this low pressure system`s arrival
into the New England region and inbound Canadian trough with an
associated strong cold front will bring a high confidence gale event
starting tomorrow morning. Post frontal northwest winds with
unstable conditions will bring sustained winds of 30-35 knots and
gusts to around 40 knots across Lake Huron. Winds arrive slightly
later in the morning for Lake St Clair and Lake Erie where will be
slightly less, but should still reach gales for a period of time.
Occasional waves across central and southern Lake Huron will also
reach or exceed 20 feet by late Monday afternoon and evening. Gale
Warnings have been issued with this forecast package. A transition
from rain to snow will also occur with the cold advection. Winds
decrease below gales Tuesday morning as high pressure ridge arrives.
Lighter winds and more stable marine conditions hold into mid-week
with the return of more mild air.
PREV DISCUSSION...
Issued at 322 PM EST Sun Dec 17 2023
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Gale Warning from 7 AM Monday to 1 AM EST Tuesday for LHZ361-422.
Gale Warning from 7 AM Monday to 7 AM EST Tuesday for LHZ362-363-
421-441>443-462>464.
Lake St Clair...Gale Warning from 10 AM Monday to 1 AM EST Tuesday for LCZ460.
Michigan waters of Lake Erie...Gale Warning from 10 AM Monday to 1 AM EST Tuesday for LEZ444.
&&
$$
AVIATION.....DG
DISCUSSION...CB
MARINE.......AA
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
559 PM CST Sun Dec 17 2023
.KEY MESSAGES...
- Wind Advisory in effect for portions of the outlook area
tonight into Monday morning for NW gusts up to 45 mph.
- A cold, windy surge is on the way tonight into Monday, with
flurries or isolated snow showers possible at times.
- After Monday, temperatures will then trend back to above
average. Another liquid precip system currently looks on track
for Thursday night into Friday.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 230 PM CST Sun Dec 17 2023
A strong cold front will bring a surge of NW winds into the
region tonight with gusts of 40 - 45 mph expected. Model
soundings are showing steep low-level lapse rates, near dry
adiabatic up to ~850mb, with unidirectional flow in the
boundary layer. The HRRR develops streamers or horizontal
convective rolls as shown in its wind gust field, which is a
testament to the convective overturning expected in the boundary
layer and this increases confidence for peak gusts hitting
advisory criteria. RAP 925mb and 850mb winds are impressive too
at 45 kts and 50 kts, respectfully.
Issued the Wind Advisory for counties roughly along and
northwest of a line from Fairfield to the Quad Cities to
Dubuque. Confidence in this area is the highest for several
hours with peak gusts around 45 mph. With that said, there is
potential for near advisory level gusts further to the east and
southeast which later shifts will have to re-evaluate. For now,
opted to go with the advisory where confidence is a bit higher
and the open terrain is more favorable for maximizing wind
gusts. There also could be some brief snow showers and flurries
late tonight into early Monday morning that could lead to brief
visibility reductions.
Although it`s mid to late December and cold wind chills should
be expected, since it has been so mild lately Monday AM wind
chills in the single digits and teens will feel like quite the
shock! Make sure to bundle up!
Winds will gradually decrease through the late morning and early
afternoon as the surface pressure gradient weakens. For the
afternoon, expect NW gusts to hold between 30 - 35 mph with
wind chills in the teens.
&&
.LONG TERM /MONDAY THROUGH SUNDAY/...
Issued at 230 PM CST Sun Dec 17 2023
Following Monday`s windy cold highs in the 20s to lower 30s, a
cold winter night is expected, though no added affect from snow
cover. The end result should be a low temperature in the 10 to
15 range north of Interstate 80 and in the 15 to 18 range to the
south. Wind chills should not be much of a factor after
midnight, as winds will trend toward light and variable
overnight.
As advertised, this cold blast will be short lived, as the passing
upper trof will already be on its way out by Tuesday. The cold
start should provide a breezy cold day, with south winds
Tuesday, as highs reach the lower 30s north to upper 30s south.
These south winds will continue to draw in milder air for the
mid week, as highs on Wednesday reach the 40s, followed by 50s
for Thursday through the Christmas Weekend ahead. This
incredible warmth for late December will include rain chances,
especially in southern areas for Thursday night through Friday.
This chance has been present in ensemble runs for the past few
days, with the main deviation in whether it tracks this far
north or not. For now, this is supportive of 30-60% NBM pops for
rain.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 533 PM CST Sun Dec 17 2023
LATEST 2311Z IR SATELLITE HAS FIRST POCKET OF MVFR CLOUDS MOVING
ACROSS THE REGION AND EXPECTED TO BE FOR A FEW MORE HOURS.
SMALLER AREA OF IFR CLOUDS WERE ACROSS KDBQ REGION. THESE CLOUDS
WILL BREAK AWAY FROM THE AREA IN A SHORT PERIOD AT THE BEGINNING
OF TAF PD. POCKETS OF MVFR AND VFR CLOUDS WILL COME BACK LATER
TONIGHT WITH THE COLD FRONT. EXPECT BRIEF SNOW SHOWERS POSSIBLE
FOR A FEW HOURS AS THE FRONT PASSES THROUGH. PLACED A BRIEF TEMPO
GROUP TO HIGHLIGHT THIS FEATURE. BETTER SNOW SHOWER REGION
IN KDBQ AND KMLI REGIONS AND PLACED SOME VISIBILITY RESTRICTION
TO ACCOUNT FOR THIS BASED ON THE DATA. CLOUDS WILL DECREASE
NORTHWEST TO SOUTHEAST DURING THE PERIOD FROM 18/10Z TO 18/15Z.
OTHERWISE WIND IS A SIGNIFICANT FACTOR TONIGHT AND TOMORROW
ACROSS THE REGION. EXPECT MAINLY NORTHWEST WINDS TO CONTINUE
STRONG AND INCREASING OVERNIGHT. CURRENTLY HAVE WIND GUSTS UP
TO 38KTS ACROSS SITES DURING A PERIOD IN THE TAFS. FURTHER TAFS
MAY NEED TO SLIGHTLY UP THE WIND GUSTS AS THE SITUATION
DEVELOPS. EXPECT WINDS TO DECREASE SLIGHTLY BY THE END OF THE
TAF PD.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Wind Advisory from 11 PM this evening to 9 AM CST Monday for
IAZ040>042-051>054-063>068-076>078-087>089.
IL...Wind Advisory from 11 PM this evening to 9 AM CST Monday for
ILZ015-024.
MO...None.
&&
$$
SHORT TERM...Uttech
LONG TERM...Ervin/Uttech
AVIATION...Holicky/Uttech
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
511 PM CST Sun Dec 17 2023
...New AVIATION...
.SHORT TERM...
(Tonight through Monday night)
Issued at 102 PM CST Sun Dec 17 2023
Surface high pressure is in place, centered near the TX Coast today
per RAP analysis. A weak surface low near the Panhandle is helping
to drive very light SW winds between these two features. With ample
sunshine, we`ve already warmed well into the 60s by noon and should
see many locations reach the low 70s. Tonight, look for warmer
temperatures than this morning mainly bottoming out in the mid 30s
to mid 40s.
As upper ridging gradually crosses the Four Corners and begins to
flatten over the Plains by Monday night, a broader area of surface
high pressure will spread across the central CONUS. It will push a
weak cold front and northerly wind shift across the region during
the day, and so high temperatures will be cooler than today over
northern portions of the region, mainly in the low to mid 60s. Highs
will still reach the upper 60s and lower 70s south.
As the surface high shifts eastward and becomes centered to our NE
tomorrow night, winds should quickly go calm after sunset.
Temperatures will quickly fall into the 30s and lower 40s, and there
is a chance for some low-lying Hill Country/I-35 areas to dip below
freezing again. Meanwhile, a high stratus deck will overspread the
region from west to east overnight. It could do a little to help
prevent additional radiative cooling, but high cirrus aren`t the
best insulators as far as clouds go. Right now, we think
temperatures will probably remain at or above freezing in most
locations, but portions of Llano, Burnet, Williamson, Gillespie,
Kendall and Blanco Counties do have 30-50% freeze probabilities at
this time per the NBM.
&&
.LONG TERM...
(Tuesday through Sunday)
Issued at 102 PM CST Sun Dec 17 2023
Dry weather conditions persist through the middle of the week with
warmer lows and highs temperatures. By Thursday morning, cloudy
skies are forecast across the local area with possible light
drizzle/rain and patchy to areas of fog across the coastal Plains,
portions of the I-35 corridor and the Hill Country. Increased
moisture and a southerly wind flow from the surface to the middle
level of the atmosphere are forecast to combine forces to keep the
local area under chances for rain the rest of Thursday into Friday.
Chances for rain and even an isolated thunderstorm or two could be
possible on Friday into Saturday as an upper level disturbance pushes
across the Rio Grande and southern Edwards Plateau and then an upper
level storm pressure system moves across the SW conus into the
southern Plains. The shower activity comes to an end from west to
east around mid to late Saturday morning and spread across the I-35
and coastal Plains area on Saturday afternoon. However, rain chances
return on Saturday evening into Sunday as a cold front pushes across
the local area. There are good chances for rain for the latter part
of the week into next weekend, however, qpf values are relatively low
with the Hill Country having the highest probability (40-50 %) to
get rainfall amounts of three quarter to one inch through this wet
period.
&&
.AVIATION...
(00Z TAFS)
Issued at 511 PM CST Sun Dec 17 2023
VFR conditions will exist through the period, with a slight increase
in upper level cloud cover through the day Monday. Winds will be
mainly light and variable ahead of a reinforcing cold front that
will move through the region Monday morning, bringing northerly to
northeasterly winds up to 10-12 kts. Winds will then diminish again
Monday evening.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 44 65 39 63 / 0 0 0 0
Austin Bergstrom Intl Airport 41 65 35 63 / 0 0 0 0
New Braunfels Muni Airport 42 67 39 66 / 0 0 0 0
Burnet Muni Airport 41 63 34 61 / 0 0 0 0
Del Rio Intl Airport 43 69 44 66 / 0 0 0 0
Georgetown Muni Airport 41 63 35 62 / 0 0 0 0
Hondo Muni Airport 39 70 39 65 / 0 0 0 0
San Marcos Muni Airport 40 66 37 64 / 0 0 0 0
La Grange - Fayette Regional 41 66 38 63 / 0 0 0 0
San Antonio Intl Airport 44 68 41 65 / 0 0 0 0
Stinson Muni Airport 42 70 42 67 / 0 0 0 0
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Short-Term...KCW
Long-Term...17
Aviation...Gale
Area Forecast Discussion
National Weather Service Grand Forks ND
707 PM CST Sun Dec 17 2023
.KEY MESSAGES...
- Possibility for snow squalls exists this afternoon and evening
in the area. Continuing to monitor.
- Gusty winds and snowfall this afternoon and tonight. Amounts
less than an inch expected.
- Warm and quiet weather through Friday.
- Uncertainty increases over the weekend as we approach
Christmas.
&&
.UPDATE...
Issued at 703 PM CST Sun Dec 17 2023
Snow showers are moving through portions of the Red River Valley
on the MN side this evening. This continues for the next several
hours, with slight reductions to visibilities down to a couple
miles at times. Up to an inch will be possible where the snow
showers occur. Winds are diminishing below wind advisory
criteria, thus the advisory will be allowed to expire at 02z.
&&
.DISCUSSION...
Issued at 232 PM CST Sun Dec 17 2023
Today through Tomorrow: Satellite shows clearing behind this
area of light snow this afternoon. This clearing affects us two
fold: 1) Mixing higher winds down to the surface from aloft in
the Devils Lake Basin and southern valley this evening, and 2)
possibly providing some instability for the potential of snow
squall development.
Guidance is showing the environment is right for snow squalls to
develop tonight in the northern valley and move SE across the area,
but whether this prediction comes to fruition is the question. Steep
lapse rates, decent frontogenesis at the 700 - 925 layer, and
moderate synoptic forcing support the flagging of the northern Red
River Valley all the way to the southern Valley in the RAP Snow
Squall Parameter. We will continue to monitor the forecast as it
shows its cards, but something to be aware of if you had travel
plans this evening.
On the wind front, gusts up to 45 MPH are possible into tonight as
the winds pick up with this shortwave and attending cold front.
Sustained winds in the Devils Lake Basin and southern valley will
range from 25 - 30 MPH. This will be removed from the area of
greatest snowfall, so a wind advisory was issued over a winter
weather advisory. Still, reduced visibility will be a concern in
falling snow in these areas. In terms of snowfall, probabilities for
accumulations greater than or equal to an inch are in the 15 - 30%
range in the Red River Valley. Most amounts across the area are
expected to be around half an inch today and tonight.
As we start the work week, Monday will be quiet on the weather
front. Today`s cold front will drop temperatures, so more seasonal
highs in the 20s are expected for tomorrow.
Tuesday through Saturday: Zonal flow is expected from Tuesday
through late this week, as a large upper level ridge parks
itself over the central US. Our area will be on the northern
edge of this ridge, so another period of warm and quiet weather
is expected. Temperatures will rise steadily each day from
Tuesday through Saturday. Average temperatures are in the upper
teens to low 20s for this time of year, but we will see highs a
good 10 to even 20 degrees above average. This is shown well by
the NBM, as it has probabilities of exceeding 40 degrees at
greater then 50% across southeastern ND starting Thursday,
lasting into the weekend.
A weak wave will cross the region on Friday. However, nearly all
ensemble guidance keeps the moisture associated with it to the south
of us. Precipitation, if any, is favored to fall as a few flurries
or even sprinkles due to the warm temperatures that are expected.
Ensemble consistency breaks down on Saturday, as models are having a
hard time determining what happens as a cutoff low over the
southwestern US kicks out over the central plains. Guidance has a
wide range of potential scenarios on how this unfolds. Cluster
analysis is split over a more southern vs northern track of the low
as we approach the Christmas holiday. It is something to watch at
this point considering it is a busy travel period, but too early for
much in regards to details.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 521 PM CST Sun Dec 17 2023
Chances for snow continue for TVF, FAR, and GFK for the next
several hours as we see radar returns moving SSE along the Red
River Valley. Reduced visibilities are possible at times due to
the mixture of winds and falling snow. BJI will have chances for
snow through the evening hours. DVL remains dry, with SCT cloud
coverage. MVFR to VFR conditions through the rest of the evening.
Potential IFR around any snow showers. Winds continue to be
strong this evening, but are showing signs of diminishing. Gusts
up to 45kts are possible on an isolated basis, but 30-35kts is
more common in coverage. Winds diminish further around 06z for
all sites, with light and variable around 12z for DVL, TVF, GFK,
and FAR through 18-20z. Light and variable winds for BJI around
18z-23z. After, winds turn toward the south, with VFR
conditions.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Wind Advisory until 8 PM CST this evening for NDZ006-007-014-
015-024-026>030-038-039-049-052>054.
MN...Wind Advisory until 8 PM CST this evening for MNZ001>003-029.
&&
$$
UPDATE...Spender
DISCUSSION...AK
AVIATION...Spender
Area Forecast Discussion
National Weather Service Glasgow MT
209 PM MST Sun Dec 17 2023
.DISCUSSION...
AFTERNOON DISCUSSION:
The area of 30-40 kt 850 hPa winds mixing down is pushing east as
seen from the latest RAP mesoanalysis. Mixing will shut down with
the loss of daytime heating this evening, bringing winds back to
more light and variable around midnight with a switch to more
southerly flow for Monday. Aloft, a ridge builds in from the west
tonight, become more of a zonal flow by Tuesday, with a cutoff 500
hPa low moving off the California coast through Friday. This
keeps temperature 10 to 20 degrees above normal through Saturday
with dry conditions.
We keep monitoring the trends with the ensembles hinting at a
pattern change for Christmas weekend and into Christmas Day. The 12Z
initialization of the GEFS shows the aforementioned cutoff low
moving to the Southwest US while a trough off the British Columbia
coastline moves to the east, extending its axis down to the
cutoff low moving through the Southern Rockies on Christmas Eve.
The 06Z initialization had a similar pattern outlook, however had
not that quite of a strong trough moving into the Northern
Rockies. The latest runs of the ECMWF ensemble has this pattern
change, however, the trough axis merging with the cutoff low
sooner over the West Coast resulting in diminishing synoptic
upper-air divergence over Montana. Latest NBM long-range guidance
hints that any QPF resulting from this pattern change remains
south and east of northeast Montana. Altogether, it continues to
be important to monitor this trend given the travel importance of
the Christmas weekend.
-Enriquez
&&
.AVIATION...
LAST UPDATED: 2100Z
FLIGHT CATEGORY: VFR
DISCUSSION: Mostly clear overnight, with high clouds building over
eastern Montana late Monday morning and into the afternoon.
WIND: Northwest 10-20 kts winds subsiding this evening, briefly
becoming light and variable near midnight, then switching more
southwesterly at 5-10kts through Monday.
-Enriquez
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
weather.gov/glasgow
Area Forecast Discussion
National Weather Service Gray ME
811 PM EST Sun Dec 17 2023
.SYNOPSIS...
Low pressure off the Carolina coastline will deepen as it tracks
northward tonight and passes west of the area during the day
Monday. This strong storm system will bring widespread moderate
to heavy rainfall rainfall, which combined with snowmelt will
bring several rivers to moderate flood stage along with poor
drainage flooding. In addition to rainfall impacts, this system
will bring strong to damaging southeast winds along with large
waves and minor coastal flooding impacts. This system exits
Monday night followed by scattered rain and snow showers
Tuesday. Mostly dry weather is expected from Wednesday into the
weekend.
&&
.NEAR TERM /UNTIL 7 AM MONDAY MORNING/...
Update...Mostly minor changes to the near term to adjust PoP to
match latest radar trends.
The largest change was the expansion of wind headlines this
evening. 18.00z raobs are trickling in...and observed winds at
925 mb are matching quite well around MHX and WAL with the
latest RAP guidance. The NAM however appears to be overdone by
about 10 kt. With the NAM forecasting a 925 mb LLJ in excess of
100 kt in the Gulf of ME by Mon afternoon this is a good thing
to see that it is running hot to start. However the RAP being on
target early on is concerning because it also cranks the LLJ up
to around 100 kt by midday Mon. While it will be far less
expansive and slightly weaker in magnitude...it is still strong
enough to warrant some expanded headlines in magnitude and
area. Add in that Bufkit forecasts show a good chunk of the I-95
corridor mixing to 60-65 kt...I feel like 50 kt gusts are more
likely than not from PWM north. I have expanded the high wind
warning to include that I-95 corridor...and then pushed the wind
advisory westward to include southern NH and the foothills.
Previous discussion...Infrared and water vapor satellite
imagery this afternoon continues to show increasing moisture
across the region with a few ASOS reports across southern
locations of drizzle and fog along with lowering cloud decks.
Northeast radar mosaic shows some very light returns now
approaching southern NH and this will eventually become the
leading edge of the rain once the column fully saturates later
this afternoon and evening. Current temperatures are primarily
into the 40s, although a few 30s remain across the interior
where a weak CAD remains.
Shortwave ridging will move offshore tonight as closed low
pressure within a negatively tilted trough axis quickly begins
to move northward along the Eastern Seaboard. This area of low
pressure will begin interacting with another shortwave trough
within the northern stream, which will allow a large rain shield
to develop well displaced from the parent low. This will result
in widespread rain to overspread the entire region tonight with
rainfall rates gradually increasing overnight as precipitable
water values and IVT increase to around +5 standard deviations.
Areas of fog can also be expected along with a non- diurnal
temperature trend as onshore flow gradually increases.
&&
.SHORT TERM /7 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
The aforementioned area of low pressure will cross over western
New England on Monday as another sfc low moves northeastward
offshore of our coastline. The combination of strong forcing for
ascent and the presence of the very moist airmass will continue
to allow for periods of moderate to locally heavy rainfall. The
rainfall forecast has increased a bit based on latest mesoscale
guidance with 4-6" now expected across southern facing mountains
with locally higher amounts possible across the highest terrain.
Elsewhere, generally between 2-3" is likely with locally higher
amounts, especially if any convection or training occurs. The
one notable exception will likely be across the downslope
locations where some spots may receive less than 1" of rain.
For more information regarding the flooding threat please see
the hydrology section below.
The second greatest threat that this system will bring is strong
to locally damaging southeasterly winds. Latest model guidance
continues to advertise the presence of a ~100 kt 850 mb jet
moving across the coast the coastal plain on Monday afternoon.
This combined with a sharp pressure fall/rise couplet and heavy
rainfall rates will likely result in power outages areawide. As
a result, went ahead and issued a High Wind Warning for the
coastline along with a Wind Advisory for the coastal plain.
There is some potential that portions of this wind advisory may
eventually need to be upgraded to a high wind warning should
confidence in sufficient mixing of the LLJ increase.
Nevertheless, gusts up to 65 mph are possible within the warning
with 50-55 mph gusts within the advisory. Downsloping winds
also continues to look likely and therefore issued a Wind
Advisory for the usual downslope areas of the north. Thankfully,
it does not look too cold behind this system, thereby limiting
the threat some for those who won`t have electricity.
Minor to pockets of moderate coastal flooding and wave runup
actions including significant beach erosion and damage to some
vulnerable structures also can be expected. A Coastal Flood
Warning has been issued for the entire coastline. For more
information please see the coastal flooding section below.
Record highs are also possible, please see the climatology
section below.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
An upper trough will slide southeast of the area Tuesday
bringing some snow showers in the mountains and rain showers
south of the mountains. A zonal flow pattern sets up across the
northern tier of the US Wednesday and Thursday while an upper
low remains near stationary south of Nova Scotia. Northern New
England looks to remain mostly dry through the second half of
the week while the proximity of the upper low could spread some
showers into the Mid Coast. Surface high pressure then builds in
from the west next weekend. Temperatures will be several
degrees above normal Tuesday with some cooling through the
second half of the week, while overall temperatures average
above normal.
A compact upper low over the eastern Great Lakes Tuesday night will
transition to an open wave as it slides south of area Tuesday. This
wave will trigger mainly snow showers in the mountains with low
chances for some rain showers south of the mountains. QPF will be
light with this feature so not expecting much in the way of impacts.
A strong blocking ridge in the northern Atlantic will lead to this
wave to consolidate into an upper low that spins nearly stationary
south of Nova Scotia Wednesday and Thursday. The 12Z model suite is
in good agreement this upper low will remain too far east to
spread much in the way of precipitation into the area.
The blocking in the North Atlantic starts to break down late in the
week while ensembles favor building heights over Hudson Bay with
these positive height anomalies building into New England over the
weekend. This signals a continuation of mostly dry conditions into
next weekend.
&&
.AVIATION /01Z MONDAY THROUGH FRIDAY/...
Short Term...MVFR ceilings will continue to lower to IFR and
eventually LIFR tonight into Monday as widespread RA arrives.
Pockets of +RA are also possible, especially during the day on
Monday. Southeasterly winds will gradually increase tonight
along the coast before becoming gusty to strong areawide Monday.
Gusts up to 45-50 kts are likely at KPWM, KPSM, and KRKD with
40 kts elsewhere. Winds will gradually become southwesterly late
Monday night into early Tuesday while weakening. LLWS can be
expected for much of the day on Monday as a strong LLJ moves
across the region.
Long Term... Snow showers in the mountains and western NH could
bring periods of MVFR to IFR conditions Tuesday. VFR likely
prevails Wednesday through Friday.
&&
.MARINE...
Short Term...Strong low pressure will cross to the west of the
waters on Monday, bringing a period of storm force southeasterly
winds and seas of 15-25 ft across the outer waters. A Storm
Warning has been issued for all area waters.
Long Term...Large waves start to subside Tuesday while they
remain above SCA thresholds through the end of the week. Winds
stay below SCA thresholds Tuesday into Wednesday. An area of low
pressure will become nearly stationary south of Nova Scotia
during the second half of the week and could bring some
northerly wind gusts in excess of 25 kts.
&&
.HYDROLOGY...
Widespread minor to moderate river flooding, flash flooding with
road washouts, and widespread overland flooding possible late
tonight through Monday night. Rain will overspread the region
tonight with increasing intensity on Monday. The initial rain and
snowmelt will serve to prime the system, then the additional rounds
of heavy rainfall on Monday will result in flash flooding and
widespread small stream flooding. The combined runoff is projected
to reach between 3 to 5 inches stretching from the Pemigewasset
watershed in NH to the Carrabassett watershed in ME. The river
response in these watersheds and those in-between will be quick with
the potential for moderate levels. Road washouts are anticipated as
frozen/partially frozen ground is unable to absorb any runoff. Some
locally significant streamflows are possible on un-gaged small
streams in the White Mountains and ME Mountains/Lakes region. Travel
disruptions are likely, particularly Monday afternoon into
Monday night. The most impactful flooding is likely to occur
along south/southeast facing slopes. Flooding could be
comparable, though not exact in footprint, to the widespread
impacts felt on May 1 for this region.
Rainfall south of the foothills is expected to be impactful, but
less significant with amounts between 1.5 to 2.5 inches. Any
frozen ground will quickly thaw, however the saturated soils
will support little peculation. The streamflows across the area
are above normal, which means several small streams are likely
to reach bankfull with localized flooding. Low lying and urban
flooding is also possible. Flood warnings could continue Monday
night into Tuesday if flood waters are slow to recede. Routed
river flows from the headwaters will cause main stem rivers to
rise with the potential for minor flooding along most, with
isolated chances for moderate.
&&
.TIDES/COASTAL FLOODING...
Astronomical tides are not particularly high on Monday, but
maximum storm surge values of 2-3 ft will likely line up with
the time of high tide to bring minor to possibly moderate
coastal flooding impacts. Additionally, large nearshore waves of
15-20 ft will also bring impacts during the Monday afternoon
high tide including splash over and significant beach erosion.
A coastal Flood Warning has been issued for the coastline for
minor inundation and moderate wave runup impacts.
&&
.CLIMATE...
Temperatures will soar well into the 50s on Monday, December
18th. The daily record high temperature for Portland is 53
degrees, Concord is 59 degrees, and Augusta is 52 degrees on
this date. All of these could be potentially challenged.
Record warm low temperatures are also possible on both Sunday
and Monday night at these locations.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flood Watch from 5 AM EST Monday through late Monday night for
MEZ007>009-012>014-020>022-033.
Wind Advisory from 7 AM Monday to 1 AM EST Tuesday for
MEZ007>009-012>014-018-033.
High Wind Warning from 7 AM Monday to 1 AM EST Tuesday for
MEZ019>028.
Coastal Flood Warning from 2 PM to 6 PM EST Monday for
MEZ023>028.
NH...Flood Watch from 5 AM EST Monday through late Monday night for
NHZ002>009-011-012-015.
Wind Advisory from 7 AM Monday to 1 AM EST Tuesday for NHZ001-
002-010>013-015.
High Wind Warning from 7 AM Monday to 1 AM EST Tuesday for
NHZ014.
Coastal Flood Warning from 2 PM to 6 PM EST Monday for NHZ014.
MARINE...Storm Warning from 7 AM Monday to 1 AM EST Tuesday for
ANZ150>154.
&&
$$
NEAR TERM...Legro
Area Forecast Discussion
National Weather Service Louisville KY
1000 PM EST Sun Dec 17 2023
.Forecast Update...
Issued at 1000 PM EST Sun Dec 17 2023
Evening satellite imagery shows mostly cloudy skies across the
forecast area. Some clearing has worked into far western KY this
evening which has allowed temps to fall into the lower 30s out that
way. Across our region, temperatures were largely in the lower 40s
west of US 27/127. East of US 27/127, temps were in the middle 40s.
KLVX 88-D was picking up some light returns over the region. The
low stratus deck may be producing a little drizzle which may persist
for a few hours. However, with temperatures above freezing, this
will not be impactful. Will continue to keep an eye on the back
edge of the clearing line. This may creep as far east as the I-165
corridor. Overnight lows in the low-mid 30s continue to look on
track.
As for Monday, the early runs of the 17/00Z suite are now rolling
in. So far, not much change from the earlier runs, other than
perhaps the overall threat of snow showers/squalls probably will be
more concentrated across our eastern/northeastern areas with a
sharper cut off back toward the I-65 corridor. Strong cold front
and associated synoptic scale forcing will arrive by mid-late
morning with scattered snow showers moving into
southern/southeastern IN by 9-11 AM and then rolling into north-
central and east-central KY during the afternoon. Model soundings
show very steep lapse rates associated with colder pocket of air
overspreading the region. In fact, some model soundings actually
generate some surface based CAPE during the afternoon. While the
HRRR is usually a little too aggressive with precipitation generation
in steep lapse rate environments, the synoptic scale forcing and jet
streak placement aloft looks to support the overall convective
development as depicted by the HRRR/NAM runs. Given the instability
noted in the soundings, I wouldn`t be surprised to see a few
lightning strikes tomorrow afternoon across our far NE Bluegrass
counties. Snow squall parameter continues to be more concentrated
over SW OH and northeastern KY with a more pronounced gradient as
you head back toward the I-65 corridor. In general, scattered snow
showers with embedded heavier snow showers and possibly some snow
squalls will be possible in our NE quarter of the forecast area
tomorrow afternoon.
As of this writing, no changes are going to be made to headlines at
this time. However, based on some of the early 17/00Z rolling in,
the trends in the data suggest that the current winter weather
advisory in our NE sections remains in good shape. However, I have
concerns about how much impact we`ll see back toward the I-65
corridor. One concern I have is that the moisture in the DGZ really
falls off the further west you go. So while we`ll have snow showers
in the I-65 corridor, they may not be intense or as widespread as
we`ll see out east. We will carefully evaluate the 17/00Z data
suite tonight and some refinements to the western edge of the
advisory may be required in the overnight forecast package.
&&
.Short Term...(This evening through Monday)
Issued at 336 PM EST Sun Dec 17 2023
=====================================================================
Key Messages:
- Falling temperatures and gusty winds (20-30mph) Monday
- Scattered to numerous snow showers and possible snow squalls
during the day could cause travel impacts Monday afternoon and
evening.
- Wind chills in the mid teens Monday night.
=====================================================================
Sfc boundary has worked off to our east and have noticed winds
shifting more out of the west. Just behind the front, we`ve seen a
narrow break in the clouds but expect cloud cover to fill back in
overnight. Slight surface ridging extending from the Mid-Mississippi
Valley into the Ohio Valley, along with drier air aloft will keep
low-level moisture trapped below an 800mb inversion. This should
help keep temperatures in the upper 30s/low 40s through the
overnight. While a weak lobe of vorticity is expected to push
through overnight across the Ohio Valley, there doesn`t look to be
enough to produce much if any in precipitation so kept things
overnight.
The main event will be associated with the arrival of a strong
Arctic cold front and the axis of a deepening upper trough diving
southward out of the Great Lakes into the Ohio Valley during the day
Monday. A strong anomalous area of PV will work in across the Ohio
Valley with the trough axis as cold air advection works in behind
the cold front. Scattered rain and snow showers will spread from the
northwest to the southeast during the morning and become more
numerous and scattered towards the afternoon as the showers
transition over to all snow. As colder air advects in over the area,
low-level lapse rates begin to steepen and model soundings continue
to show ample saturation in the lowest part of the DGZ or snow
growth zone. Model soundings also continue to advertise SBCAPE of
around 50-100J/kg instability, most notably from Louisville over to
Lexington and northward through the Bluegrass into Cincinnati.
Cyclonic flow aloft along with the left exit region of the 500mb jet
over the Ohio Valley, we will have enough instability to develop
scattered to numerous snow showers during the afternoon. Snow squall
parameters continue to advertise values over 1 to as high as 3-4
over our northeastern CWA. Factor in the gradually falling
temperatures behind the front, strong gusty winds of 20-30mph and
snow showers potentially leading to the development of snow squalls
across parts of the area. With all this in mind, and after talking
with our surrounding forecast office, decided that the societal
impacts of the following: The first significant snow threat of the
winter. We`re one week out from Christmas and there will be plenty
of holiday travel on area highways. And the best chance for snow
showers appears to be from the afternoon into the evening commute.
Decided to issue a Winter Weather Advisory due to impacts rather
than the usual criteria for an advisory.
Main area of concern looks to be along and east of I-65 and along
and north of the Bluegrass Parkway. This includes the Louisville
Metro, the I-64 and I-71 corridors east of I-65 as well as the
Lexington Metro and the I-75 corridor, especially tomorrow afternoon
and evening.
While temperatures look to remain above freezing for most of the day
Monday along with our currently warm surface and road temperatures,
one very intense burst of heavy snow on an area highway could
quickly negate any benefit from those above freezing temperatures.
Then factor in near whiteout conditions from gusty 25-30mph winds
and you can quickly have significant travel hazards over a very
short time. While any snow that falls tomorrow looks to only put
down a coating on mainly elevated and grassy surface, a more intense
burst of snow could put down around a quarter of an inch or more
depending the intensity. Likely most of the area will not see any
accumulating snow but given the societal impacts on area highways
this time of year still feel very confident in the decision to
highlight the snow squall threat with a winter weather advisory.
Trough axis and associated upper-level dynamics quickly push off to
the east tomorrow night into Tuesday morning. Skies will clear from
west to east and winds will gradually diminish but with lows falling
into the upper teens by Tuesday morning. Wind chills Monday night
will be in the low to mid teens.
.Long Term...(Monday night through Sunday)
Issued at 300 PM EST Sun Dec 17 2023
================================================================
Key Messages
- Chance of windchill readings in the low teens/single digits
Tuesday morning.
- Gradual warming back into the low to mid 50s by the end of the
week.
- Next chances for rain return Thursday through the end of the week.
================================================================
Tuesday through Thursday: High pressure continues to build across
the region for fairly quiet weather heading into the middle of the
week. The dry Canadian air mass will have a low moisture content,
and with light wind, expecting wind chills as low as 10-15 degrees
for much of the area Tuesday morning. Temperatures will slowly
increase as the high pressure moves eastward and warm air returns
with southerly flow Tuesday night into Wednesday. The average highs
this time of year is in the upper 40s, which is expected on
Wednesday. Temperatures warm back into the low to mid 50s by
Thursday.
Friday - Sunday...Look for increasing rain chances by the end of the
workweek and next weekend. There is substantial model spread during
this period, so low confidence exists for precipitation timing and
intensity. A small perturbation ahead of Pacific troughing will lift
across the Mid Mississippi Valley and stretch a cold front to the
south/southwest. This pattern will favor warm advection showers
spreading over the lower Ohio Valley.
&&
.Aviation...(00Z TAF Issuance)
Issued at 628 PM EST Sun Dec 17 2023
IMPACTS:
* MVFR cigs overnight
* Very gusty NW Winds Monday
* Snow showers and possible snow squalls Monday afternoon
DISCUSSION:
Cigs this evening are likely to drop into the MVFR range and stay
there overnight with northwest winds of 5-10 knots. Winds will
pickup toward sunrise Monday as a strong upper level disturbance
moves into the region. Look for gusty northwest winds of 15-20kts
and gusts to 30kts at times at HNB/SDF/LEX, slightly lesser gusts
are expected at BWG. As upper level system pushes into the region,
lapse rates will steepen significantly and snow showers are expected
to develop across the region. A few snow squalls will be possible
with the highest chance over at LEX. For now, plan on keeping SHSN
in the TAFs as timing snow squalls at the terminals at this time
range is not possible. Within the snow showers, reduced vsbys and
cigs are possible as they move through. Weather conditions will
improve after 18/23Z as the upper level system pulls off to the
east. However, gusty northwest winds will continue into the
evening hours before diminishing late.
CONFIDENCE:
Cigs : Medium-High
Wx : Medium-High
Winds: High
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update.......MJ
Short Term...BTN
Long Term....MCK
Aviation.....MJ
Area Forecast Discussion
National Weather Service Pendleton OR
248 PM PST Sun Dec 17 2023
.SHORT TERM...Tonight through Tuesday...Satellite and surface
observations this afternoon show the stratus layer has lifted in
height slightly over the region, with patchy dense fog having
dissipated along the Blue Mountain foothills. However, dense
freezing fog continues to impact areas from north central OR to
areas just north of Redmond. The cooler airmass under the stratus
layer has moderated temperatures across impacted areas, including
the Redmond area which has seen the stratus layer just to it`s
north. Otherwise, areas outside of the stratus layer have seen
plenty of warming into the 40s to low 50s in some areas.
Tonight into tomorrow morning, an upper ridge over the region will
continue to support the stratus layer across the lower elevations
with the expectation of this layer extending across the rest of
central OR. Patchy dense fog and freezing fog is expected to
redevelop across the lower elevations tonight, especially in the
Columbia Basin, north central OR, and the Yakima/Kittitas valleys.
Temperatures underneath the stratus layer will drop 3 to 5 degrees
tonight, though the Wallowa valley may see a more significant drop
into the lower to mid 20s tonight.
By tomorrow morning, a shortwave trough off the coast of northern
CA will begin to lift northeast across the PacNW and produce
precipitation impacts area-wide through Tuesday. Ahead of the
system passage, mid to upper level cloud cover will increase from
the southwest, while a mild Pacific airmass begins pushing into
the intermountain PacNW. Snow levels will be on the rise early
tomorrow, with snow levels above 6kft to 7kft across most
locations outside of the central WA Cascade east slopes (4.5kft
to 5.5kft) and far northeast OR (5kft to 6kft). In most mountain
areas, a rain/snow mix Monday is expected to transition to mostly
rain by Tuesday morning. However, in the WA Cascade east slope
valleys, near to below freezing air trapped near the surface and
warm air aloft will result in patchy freezing rain, with at least
a few hundreths of an inch in ice accumulations. Tuesday morning,
the warm air aloft is expected to mix down in these valley areas
and have light freezing rain turn over to just rain. As for
mountain snow, accumulations will be very light to just a trace
outside of the Cascade and Wallowa peaks/high ridges, and only an
inch or two along those peaks and high ridges. All told,
liquid equivalent precipitation amounts in the mountains will be
between 0.2 to 0.4 inches, and up to 0.15 inches in the lower
elevations. A weak warming trend will take place over the course
of Monday and Tuesday, with high temperatures expected to warm
into the 40s and lower 50s by Tuesday afternoon.
One thing to note through the short-term period will be the breezy
to windy conditions through the southern Grande Ronde valley.
Expect gusts between 45-50mph at the mouth of Ladd and Pyles
canyons through Tuesday morning. Lawhorn/82
.LONG TERM...Wednesday through Sunday...Models are in good agreement
on the evolution of the longwave pattern through the extended
period. An upper level low will drop southward along the California
coast Wednesday through Thursday. This will lead to a split flow
regime with the Pacific Northwest experiencing weak SW-W winds
aloft. This pattern looks favorable for at least patchy valley fog
and stratus Wednesday and Thursday morning. On Wednesday and
Thursday the ECMWF EFI is indicating a high potential for above
climatological normal temperatures in the mountains and high
plateaus of Oregon and SE Washington. The current NBM forecast
maximum temperatures for Wednesday are 7-13 degrees above normal in
these areas and only slightly less Thursday. Precipitation
associated with the CA upper low will stay south of the region
Wednesday and Thursday.
On Thursday night an upper level trough in the northern stream will
dig southeastward and move across the PACNW Friday into Saturday.
The GEFS is a bit shallower and faster than the EPS which brings a
bit stronger and slower trough across the area. In either case this
system appears like it will be no stronger than moderate intensity
and the threat for high impact weather is low (30%). POPS Friday and
Saturday will be highest in the mountains (30-60%)and 15-30% in the
lower elevations. The 50 percentile QPF amounts for the 48 hour
period ending 12Z Sunday ranges from .20-40 inches in the mountains
and .01-.10 inches in the lower elevations. Snow levels will start
out at around 5000 feet Friday morning and gradually lower to 2000
feet by 12Z Sunday.
Winds in the lower elevations could be somewhat of a concern on
Friday afternoon and evening if the deterministic GFS pans out. The
GFS shows a cold frontal passage with 30 meter west winds of 25-35
mph. The GFS and ECMWF ensembles as well as the NBM are weaker with
the winds. Went with the NBM winds for this forecast since even with
the GFS solution the odds of needing wind highlights are low (20-
30%).
Ensemble data is showing the return of an upper level ridge for
Sunday with decreasing chances (10-15%) for precipitation. 78
&&
.AVIATION...00Z TAFS...VFR conditions are forecast at KBDN though
there is a chance (30-40%)that the stratus to the north may filter
into the TAF site tonight. The stratus layer has recently made it to
KRDM with LIFR CIGS. LIFR conditions in FG and stratus are expected
to return to KPDT early this evening and persist through the night.
The guidance for KALW is somewhat conflicting. All guidance shows
LIFR CIGS in stratus tonight but VSBYS vary from less than 1/2SM to
6SM. The HRRR and HREF are showing LIFR vsbys with probabilities of
less than 1/2SM of 60-70%. Will lean toward the HREF and HRRR
guidance for the this TAF package for KALW. Elsewhere MFR/IFR CIGS
in low stratus will affect the remainder of the TAF Sites through
the period. Winds will be light at all TAF sites at 7 kt or less.
78
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 29 37 33 44 / 0 20 30 50
ALW 31 38 34 45 / 0 20 30 60
PSC 33 37 34 43 / 0 10 30 40
YKM 31 39 33 42 / 0 20 50 60
HRI 32 38 34 44 / 0 20 40 50
ELN 28 38 31 40 / 0 20 40 60
RDM 27 45 41 51 / 10 30 40 40
LGD 31 41 35 43 / 0 20 40 70
GCD 31 45 36 48 / 10 40 60 70
DLS 36 41 37 43 / 10 40 80 80
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 10 AM PST Monday for ORZ044-050-
505-507-508-510-511.
Wind Advisory until 3 PM PST Tuesday for ORZ049.
Freezing Fog Advisory until 10 AM PST Monday for ORZ510.
Freezing Fog Advisory until 7 PM PST this evening for ORZ511.
WA...Air Stagnation Advisory until 10 AM PST Monday for WAZ026>029-
521.
Winter Weather Advisory from 1 PM Monday to 1 PM PST Tuesday for
WAZ522-523.
&&
$$
SHORT TERM...82
LONG TERM....78
AVIATION...78
Area Forecast Discussion
National Weather Service Phoenix AZ
504 PM MST Sun Dec 17 2023
.UPDATE...Updated Aviation Discussion.
&&
.SYNOPSIS...
Unseasonably strong high pressure over the region will continue to
bring well above normal temperatures through Tuesday with dry
conditions. This will allow highs to flirt with daily records
mainly in the Phoenix area. A significant pattern change will then
take place during the latter half of the week bringing an
abundance of moisture and clouds into the region initially
followed by very good chances for rain at some point from late
Thursday through Saturday. Temperatures will also cool back to
around normal by late week.
&&
.DISCUSSION...
Latest RAP streamline analysis depicts a high-amplitude upper-
level ridge extending northward from the Desert Southwest into the
Pacific Northwest. Temperatures are consequently running well
above normal for this time of year. Slightly warmer conditions are
likely across the Phoenix area Monday as the ridge migrates
eastward into the Rockies and the latest NBM indicates a 50
percent chance of breaking the record high of 79 degrees set in
1950. This will translate into a minor heat risk, which could
affect those individuals extremely sensitive to the heat.
Meanwhile, further west across southeastern California, somewhat
cooler conditions are anticipated as a storm system affects the
west coast.
Latest model ensembles are in good agreement PWATs will steadily
increase to 200 percent of normal Tuesday and Wednesday. The
moisture, combined with height falls and forced ascent associated
with a jet streak near Puerto Penasco will translate into a chance
of precipitation late Tuesday night and early Wednesday,
particularly from Phoenix eastward. However, latest model trends
are less bullish and indicate an eastward shift in the strongest
IVT, so any rain that does fall will likely only amount to a few
hundredths of an inch.
A weak short-wave ridge is expected to briefly develop across
Arizona Wednesday afternoon, which will spell a short break in the
potential for rainfall. Further west, however, a closed low in
the eastern Pacific will continue to deepen as it wobbles and
meanders southward off the California coast. There is considerable
uncertainty in exactly when deeper moisture and ascent with this
system will spread eastward, though the general consensus points
towards increasing rain chances in a window from Wednesday night
through Saturday. The most likely period for widespread rainfall
at this point appears to be Friday, especially if the low moves
into a favorable position off the Baja Peninsula, as suggested by
the two dominant model clusters mainly comprised of GEFS and ECMWF
ensemble members.
Behind the aforementioned closed low, uncertainty increases
dramatically as the models are generally divided into two camps.
The ECMWF ensemble members generally indicate a reinforcing
colder, closed low with the potential for additional
precipitation, whereas only a few GEFS members show this scenario.
During the Wednesday night through Sunday time frame, most likely
QPF from WPC paints a widespread area of 1+ inch precipitation
across the lower deserts, with even higher amounts across portions
of the higher terrain where orographic lift is maximized.
Meanwhile, with the clouds and precipitation, temperatures at or
below normal are also anticipated beginning Friday.
&&
.AVIATION...Updated at 0004Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light diurnal tendencies will prevail through the TAF period with
extended periods of calm to very light and variable, especially
around the timing of the directional shifts. There is potential
for winds to not shift fully west Monday, especially with
increased cloud cover. An brief uptick in wind speeds, up to 7-10
kts, is anticipated around late morning Monday, primarily at KIWA,
and gusts could reach the mid to upper teens. Cloud coverage
increases through tonight and cloud bases are expected to lower as
far as 13-14K ft.
Southeast California/Southwest Arizona including KIPL and KBLH:
Light winds, mainly < 7 kts, will prevail at both terminals with
extended periods of calm to very light variability. SCT-BKN cloud
bases will gradually decrease over the next 24 hours with the the
lowest bases reaching 15-18K ft.
&&
.FIRE WEATHER...
Unseasonably warm temperatures along with dry conditions will
continue over the next couple days. Winds will overall remain
light and somewhat follow diurnal patterns, but winds across
eastern Arizona are likely stay predominately out of the east with
breeziness at times. MinRHs will remain steady through Monday,
ranging between 10-20% before increasing substantially through the
middle part of the week. An unsettled weather pattern will take
place during the latter half of the week resulting in chances for
precipitation and cooler temperatures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hirsch
AVIATION...Benedict
FIRE WEATHER...Kuhlman