Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/01/17
Area Forecast Discussion
National Weather Service Wakefield VA
912 PM EST Sat Dec 31 2016
A weakening cold front will approach the region from the
northwest overnight...as high pressure slides offshore. The front
will drop across the area Sunday morning, becoming stalled over
North Carolina Sunday afternoon. Developing low pressure over the
southeast will push the stalled front back north as a warm front
Monday and Monday night, followed by an upper level trough
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Early evening wx analysis reveals 1024+mb surface high pressure
centered offshore. To the northwest, ~998mb sfc low pressure
continues to slide across southern Ontario, with the associated
sfc boundary extending from the eastern Great Lakes back into the
middle Mississippi River Valley. Aloft, parent northern stream
upper trough is traversing east across the interior northeast
toward New England. Meanwhile, light S-SW flow aloft is allowing
numerous weak perturbations to push across the deep south,
resulting in sct to numerous showers across the southeast this
Moisture streaming ahead of the troughs to the west has resulted
in mostly cloudy to overcast conditions across the local area.
Noting some light returns on KDOX/KAKQ radars over the VA Northern
Neck and Lower Eastern Shore. However, with dry antecedent
airmass in place (Dewpoint depressions of 15-20 deg F), this is
doing little more than contribute to persistent BKN-OVC cloud
deck ~8-10kft this evening. The nrn stream wave will continue to
push ewd overnight, with the associated cold front approaching
from the nw. Hi-res models suggest that the nrn stream
wave/associated cold front could tap into some srn stream moisture
to produce some light rain later tonight. HRRR and most of CAMs
show some sct showers mainly along the US-58 corridor or mainly
along the VA/NC border into SE VA. Confidence with respect to
measurable rainfall is low, so forecast PoPs are only ~20% over
this same area. QPF would be minimal, only a few hundredths of an
inch at most. Otherwise, most of the local area will ring in the
new year on a mostly cloudy to overcast note. Low temperatures
will be realized within the next few hours for the southern half
of the area...with temperatures remaining steady to slowly rising
into the low to mid 40s after midnight. Farther north, look for
early morning lows to range from the upper 30s to low 40s from the
NW piedmont counties over toward the Northern Neck and Lower
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
The front stalls across NC Sunday while surface high
pressure builds from the Ohio Valley into ern PA/NJ as a shortwave
trough pushes offshore. Meanwhile, another shortwave trough will
lift newd from the Southeast Conus by aftn. PoPs of 20-30% are
forecast for far srn VA/ne NC Sunday morning in vicinity of the
front, with 40-50% PoPs for sw portions after 18z as some weak lift
arrives ahead of the shortwave trough approaching from the sw.
Farther n/ne, dry conditions are expected under a partly to mostly
sunny sky as high pressure prevails. Maintained continuity with
respect to high temperatures. Forecast highs are expected to be in
the upper 40s over s/sw portions with thicker cloud cover and the
potential for some light rain, with 50-55F for most other locations.
Moisture and shortwave energy aloft will continue to arrive from the
sw Sunday night as moist low-level se flow develops. This will
result in overrunning conditions as the coastal/warm front remains
immediately s of the local area through 12z Monday. The best lift
arrives after midnight and will be confined mainly to se portions
where 70% PoPs are forecast. Forecast soundings/cross-sections do
depict saturated conditions below 800mb, so there is rather high
confidence (60%) for light rain, mainly after 06z. Forecast lows
range from around 40 n to to the mid 40s s/se under an overcast sky.
A decent CAD set-up is expected by Monday as the coastal/warm front
gradually pushes inland through the day, with nw portions remaining
in the wedge. 12z data continues to show a wave of low pressure
tracking along the front. As a result, categorical PoPs are forecast
from srn/se portions in the morning to the coast by aftn, with
likely PoPs (60-70%) across the nw. Pw values rise to ~1.2-1.4" (+2
st dev) and this combined with modest ascent could result in
rainfall amounts of 1-2" across portions of se VA/ne NC, with lesser
amounts expected to the nw. Forecast highs range from the upper 40s
nw to the lower 60s for coastal se VA/ne NC.
The warm front lifts through the region Monday night. The latest
data supports a lull in shortwave energy aloft. However, low-level
WAA and moisture should result in stratus/fog and the potential for
areas of light rain and/or drizzle. Temperatures will not fall much
Monday night with lows ranging from the mid/upper 40s over the
Piedmont to the low/mid 50s se. A more substantial trough pushes
from the Tennessee Valley Monday night to the Mid-Atlantic Tuesday.
There will still be enough moisture to support 60-80% PoPs Tuesday
morning, with a dry slot pushing into the region during the aftn, so
PoPs taper to chc. The area will be fully within the warm sector
with highs well into the 60s, and some 70s possible se if there is
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Secondary cold front pushes across the region late Tuesday night
as an anomalous upper low tracks into eastern Canada. Thanks to
westerly flow aloft, expect conditions to dry out quickly Tuesday
night, with only lingering slight chance POPs for the Maryland
Eastern Shore. A broad, upper level trough is forecast from the
Northern Plains to the Northeast Wednesday with west to southwest
flow over the Mid-Atlantic region. Colder and drier air mass will
lag behind the system briefly as the high is slow to build into
the Midwest due to the broad upper trough. The result will be
temperatures in the mid to upper 50`s Wednesday under a partly
cloudy sky. The trend beyond Wednesday is for cooler and drier
conditions as the Canadian high slowly builds into the Midwest and
Southeast under a potent shortwave tracking across the Great Lakes
and into the Mid-Atlantic. The wave drops into region Thursday
night into Friday morning. While the air mass will be quite dry,
will keep mention of slight chance to low end chance POPs Thursday
night due to a weak boundary remaining over the region.
Temperatures forecast to be cold enough for frozen precipitation,
but due to the dry air mass, qpf will be rather meager. Highs
Thursday in the upper 30`s north to mid 40`s south. Lows Thursday
night generally in the 20`s. Dry Friday as the Canadian high
builds into the region. Highs in the mid/upper 30`s inland to low
Attention then turns to shortwave energy tracking across the
Southern Plains Saturday, which could produce a wave of low
pressure along the Southeast coast. Latest guidance has trended
the system farther southward, but will keep a slight chance of
precipitation into southeast Virginia/northeast North Carolina.
Highs Saturday back into the mid/upper 30`s after morning lows in
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
For the most part, VFR conditions will prevail through the 00Z
TAF period. Mid/High clouds have increased through the afternoon,
with high clouds now covering all terminals, as an upper trof to
the west approaches. A southwest breeze will continue overnight
with ceilings lowering to 5 to 7 Kft. There will be a slight
chance for rain at KORF/KECG Sunday morning. Have left TAFs dry at
this time, as there is uncertainty how far north precip will get.
NAM is quite aggressive in bringing a period of light rain to
especially KECG in the 09Z-14Z time frame. A weak cold front
moves through during the day Sunday, with a drying trend that
will raise ceilings across northern portions, possibly allowing
breaks in the mid or high level cloud deck. Deeper moisture will
be on the increase from the southwest by late Sunday afternoon,
especially across southern areas, with the potential for rain to
arrive just after the 00Z TAF period ends.
OUTLOOK...Widespread rain and sub VFR conditions are expected
Sunday night through Monday night. Some improvement is expected on
Tuesday with precipitation expected to become less widespread and
perhaps more showery. Building High pressure and fair weather
return for Wednesday. Overrunning moisture will bring an increase
in cloud cover Thursday but the forecast remains mostly dry.
Latest surface analysis centers high pressure off the Southeast
coast with low pressure over the eastern Great Lakes region. The
attendant cold front stretches southwestward into the Southern
Plains. The resultant pressure gradient has produced southerly SCA
conditions over the Bay and Atlantic waters north of Cape Charles
Light with speeds generally 15-25 knots. Few gusts around 30 knots
observed north of Parramore Island. Seas generally 4-6 feet north
of Cape Charles Light and 3-4 feet south. Waves 2-3 feet, with 4
feet possible in the upper Bay. The low tracks along the Saint
Lawrence River Valley tonight as flow becomes southwest and
diminishes. Have extended headlines for the Bay through 1am, but
kept the northern coastal waters through 7am. Seas subside to 3-4
feet early Sunday morning. Cold front pushes across the waters
Sunday but is quickly replaced by weak high pressure late Sunday
and Sunday night. Flow becomes north to northwest at or below 10
knots. The high builds into New England Sunday night and Monday as
flow becomes onshore at 10-20 knots. Seas build to 2-4 feet, with
5 feet possible across the northern coastal waters. A wave of low
pressure then lifts over the waters late Monday into Monday night,
which could push seas in the northern waters slightly higher. The
low lifts north of the region Tuesday as the next cold front
approaches from the west. Southwest flow increases to 10-20 knots
late Tuesday and Tuesday evening. Front pushes across the waters
Tuesday night. High pressure slowly builds into the region through
South to southwest winds have resulted in tidal departures around
-0.5 to -1.0 foot MLLW during low tide late this afternoon.
Another period of below average tides are expected tonight, with
departures forecast between -0.5 and -1.5 feet MLLW. As a result,
low water advisories have been issued for the Atlantic coastal
waters, the lower Chesapeake Bay, and the lower James River.
MARINE...Low Water Advisory from 2 AM to 7 AM EST Sunday for ANZ632-634-
Small Craft Advisory until 1 AM EST Sunday for ANZ630>632-634.
Low Water Advisory from midnight tonight to 4 AM EST Sunday
Small Craft Advisory until 6 AM EST Sunday for ANZ650-652-654.
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
652 PM EST Sat Dec 31 2016
Two items to speak to in this edition of the aviation discussion.
Very late cold air advection behind a weak cold front feature has
led a minor resurgence in wind speeds the past hour. Seeing wind
gusts bump up into the 25 to 30 knot range across all of
southeastern Michigan. Some gradient flow will hold on, but given
the overall weak pressure gradient the thinking is that increasing
nocturnal stabilization will cause winds to weaken substantially as
the evening wears on. Subsidence in the wake of the front does not
appear strong enough to completely wipe out stratocumulus for
tonight. Latest satellite trends show solid VFR to potential MVFR
deck filling in south of the I 69 corridor. Back edge clearing is
definitely pushing across Lake Michigan so feel a clearing trend
will emerge tonight. The problem is the guidance is somewhat noisy
on timing and given the trends it should wait until after 06Z. Moved
fairly aggressively in lockstep with the RAP output with the
clearing late due to a strongly backing wind in the low levels.
For DTW...Currently witnessing west northwest wind trajectories
which is significantly at odds with the guidance probs (which is
more WSW). See no reason to move away from this W or WNW trajectory
at least for the first 6 hours of the TAF period. The forecast is
calling for a very aggressive backing of the wind to the south by
Sunday morning. Expecting clouds right at 5000 ft agl for the first
6 hours of the period, scattering out after 06z tonight.
//DTW Threshold Probabilities...
* High for ceiling 5000 ft or less through the evening then low
the latter half of the night. Low on Sunday.
Issued at 315 PM EST Sat Dec 31 2016
Light snow and rain, will continue to work east across the Saginaw
Valley and northern Thumb through the early evening as moisture
spreads into the area ahead of a cold front. Weak lift and moisture
have had to first overcome dry air, resulting in only limited
precipitation so far despite an earlier boost of moisture off Lake
Michigan. Potential for precipitation to fall as all snow will
increase through the very late afternoon and evening as surface
temperatures cool just ahead of and along the front. Drier air
pushing in behind the front will strip moisture out of the dendritic
growth zone this evening, as forcing also exits. This will end the
chance for snow. Snow accumulations will be very light, if any.
Gusty winds have been the other concern today, as modest southwest
gradient mixes down higher winds aloft. Cold air advection will
deepen the mixed layer as we head into the evening, but this will be
coincident with low-level jet exiting the area to the east.
Strongest gusts of 35 to 40 mph should stay south of I-94 where
higher winds aloft are located and where clearing allowed temps to
warm into the 40s. Winds will decrease this evening as the low pulls
away and the gradient relaxes. We will keep some wind overnight for
most locations however as westerly gradient is maintained between
surface high pressure centered over the Ohio Valley and low pressure
tracking across northern Ontario. Locations south of M-59, closer to
the high center, should go calm to nearly calm very late however.
Surface high pressure over the Central Plains and Ohio Valley will
expand into Lower Michigan tonight, keeping the area dry. Post-
frontal cold air advection and westerly flow across Lake Michigan
will help keep some clouds over the area through much of the night
however, until warmer air advecting over the lake tempers response
and allows skies to clear late. South to southwest flow tomorrow and
subsidence from high pressure at the surface and aloft should
promote mostly clear skies aside from some higher clouds working in
late. Sunshine and southerly flow will help to boost temperatures
into the upper 30s to near 40 tomorrow.
Pattern will then turn warmer and wetter by Monday as the upper wave
now over the Desert Southwest lifts up into Michigan along a warm
front, and is followed by the arrival of a trough that results from
some degree of phasing between the upper low off the California
coast and upper energy ejecting out of the Pacific Northwest. Models
still show some differences with how these two systems interact, and
forecast may need some adjustment through the first part of the
week. General idea is for light precipitation to occur along an
initial warm front Monday morning/afternoon while the upper wave
works across. Precipitation should remain light as ascent must first
overcome dry air in place. Concern will be for early-day cold
temperatures at the surface to become overrun by warmer air aloft,
providing a chance for freezing rain before the better surge of warm
air and moisture arrives ahead of the larger trough axis during the
late afternoon and evening. This will immediately end concern for
any p-type but rain for the second half of the day and overnight as
surface temperatures rise. Any freezing rain that occurs initially
looks light, and should have only a small impact as temperatures
quickly warm through the low 30s. Passage of the upper trough axis
combined with coupled jet structure aloft and surge of gulf moisture
should then provide widespread rain during the evening and overnight.
A weak low pushing from Lake Superior into the Hudson bay will drag
with it a strong cold front on Tuesday, which will quickly put an
end to the above normal temperatures that are expected for the early
half of the week. Daytime highs will stayed capped throughout the
20s on Wednesday, as a strong pressure gradient brings breezy
conditions. A shift in wind from the SW to W will also bring in the
chance for lake effect snow showers. Winds are expected to hold
steady from the west, allowing the chance for lake effect snow to
persist into the early morning hours on Friday, as surface
temperatures struggle to break the lower 20s for a daytime high. A
large surface high pressure is then expected to build into the
region late Friday into Saturday and will diminish any lingering
lake effect snow showers as we head into the weekend.
Southwest wind up to low end gales will be possible for a few more
hours over the south third of Lake Huron prior to the passage of a
cold front. A gale warning remains in effect there with small craft
advisories farther south. The Lake Erie nearshore was added as
updated ice analysis indicated the water now mostly open through
that zone. The front will shift wind to the west followed by a
diminishing trend through the evening as high pressure slides into
the Ohio Valley. Gradient wind will remain elevated Sunday but more
firmly below headline criteria as high pressure moves toward the mid
Atlantic states while a weaker low moves through northern Ontario.
Marine wind and wave conditions will then transition to influence by
a large low pressure system developing over the Plains states by
Monday. This system is expected to track through the Midwest during
Tuesday and bring a warmer and more stable temperature pattern over
the water. The system will be deepening with time and is expected to
pull a strong cold front through the region Tuesday night into
Wednesday when the next round of gales are outlooked.
Lake Huron...Gale Warning until 7 PM EST this evening FOR LHZ363-462>464.
Small Craft Advisory until 11 PM EST this evening FOR LHZ421-
Lake St Clair...Small Craft Advisory until 7 PM EST this evening FOR LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 7 PM EST this evening FOR LEZ444.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Wilmington OH
959 PM EST Sat Dec 31 2016
A weak cold front and showers will move east tonight. High
pressure is forecast to provide mainly dry weather on Sunday. A
potent area of low pressure will bring showers back into the
forecast Sunday night into Tuesday.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Frontal boundary now entering NW forecast area, with clearing
skies to push into areas from Dayton and northwest through the
next few hours. HRRR still hanging on to a solution developing a
very narrow snow shower band to push through the area, but all
precipitation still remaining to the NE of the forecast area at
this time. Can`t rule out some very light and brief development,
but have kept it out for now.
With North/NW forecast area to partially clear and winds
diminishing and the southern forecast area to remain under low
clouds, a decent temperature gradient overnight with mid 20s
north and mid 30s south.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
Weak high pressure stretching from the mid Atlantic Coast back
into Ohio should keep dry conditions over the FA through most of
Sunday. However, a few showers may affect southern locations in
increasing moisture and lift well ahead of extensive low pressure
forming over the High Plains.
As the low winds up and tracks east, loosely organized chunks of
moisture and lift are shown by models Sunday night and Monday,
keeping a chance of showers in the picture.
Forcing and moisture circulating around the low will become more
organized as the low moves to southern Indiana Monday night, when
the bulk of showers are expected. Went with categorical pops as
per latest model blends. Look for a half inch to one inch of rain,
giving a precip surplus to start 2017.
Temperatures will be boosted above normal by warm advection in the
southerly flow ahead of the low. Highs Sunday in the 40s will be
followed Monday by well above normal readings in the 50s.
.LONG TERM /TUESDAY THROUGH SATURDAY/...
Mild and wet scenario for beginning of forecast period. Cold
front pushing out during the day Tuesday. Some differences in
handling of short wave/upper low skirting across the area. GFS
wants to dry out fcst area quicker with some linger moisture with
ECMWF. Will trend toward GFS but keep rain chances into the
afternoon tapering off from west to east. Should be mainly dry all
areas by Tuesday night. Models in good agreement now of arctic air
surging in through Wednesday and Thursday. High pressure will
build in and remain in control through end of fcst period with
models taking any chance of snow out of the picture except perhaps
for some lake effect flurries or scattered light snow showers.
While no significant snow accumulation on the ground, still a good
bet to see some upper single digit low temperatures by Friday or
Saturday, but will compromise with surrounding office fcst and
keep lows out of this territory for now. Highs should be mainly
20s to around 30 for Thursday to Saturday time frame.
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
As the prefrontal precipitation makes its departure, MVFR ceilings
settling in, and wind gusts diminishing and to become westerly
with the frontal passage from 02z-06z. While stratus will give way
to some clearing at KCMH/KLCK/KDAY in the 07-12z timeframe, this
could allow some MVFR BR to develop in the 10-13z window. KILN
less certain for the clearing/BR vs. lingering stratus in this
window, whereas confidence is higher for clearing in the north.
Ceilings lift during the daytime hours on Sunday, but moisture
return in the form of scatter showers near the end of the period
OUTLOOK...MVFR ceilings and visibilities are possible at times
Area Forecast Discussion
National Weather Service Lincoln IL
859 PM CST Sat Dec 31 2016
Issued at 859 PM CST Sat Dec 31 2016
The center of the surface high pressure will pass directly across
Illinois tonight, providing clear skies with light and variable
winds. There is some concern about fog formation in low lying
areas, but forecast soundings and bufkit analysis are indicating
only marginal chances of fog. Will leave out of the forecast
grids for now. HRRR and RAP analysis show visibility reduction
only to 5-6 miles, which is hardly enough to warrant a mention in
the forecast. The current forecast is handling the expected
conditions well, and no formal update will be needed this evening.
.SHORT TERM...(This evening through Sunday)
ISSUED AT 246 PM CST Sat Dec 31 2016
Cold front is sweeping through Central Illinois this afternoon, with
winds coming around to more northwesterly and tempering the diurnal
swing for the Midwest. Low clouds moving in behind the front slowly
eroded this afternoon as they run into a drier airmass. Overnight
and tomorrow...the weather should remain quiet and cooler, with lows
dropping into the 20s. RH not saturating...and have left fog out of
the forecast for now. Models continue to mix in enough dry air to
further erode the clouds as the high pressure ridge axis drifts
across the region overnight. Winds lighten and become somewhat
variable before taking on a more easterly component early tomorrow.
Easterly flow will remain somewhat weak through the first part of
the day...and temper any significant warm up for Sunday. Max temps
will remain in the upper 30s and lower 40s.
.LONG TERM...(Sunday night through Saturday)
ISSUED AT 246 PM CST Sat Dec 31 2016
Models are in good agreement that a weather system will be moving
northeast into the CWA for the beginning of the New Year. However,
models differ on timing of said precip. NAM and Canadian are
quickest and bring precip in after midnight Sun night. GFS does not
have precip in CWA til Mon morning, while ECMWF is not til
afternoon. Earlier forecast had chance precip after midnight in the
CWA and based on model blend, will back off and just have slight
chance late Sun night. P-type will be dependent on when it starts in
northern part of CWA so we still will carry a slight chance of light
fzra in northwest parts of CWA late Sun night, but then changing to
rain as temps warm during the early morning hours. The front will be
moving through the CWA Monday and southwesterly winds will bring
moisture back into the area. Instability ahead of this front looks
to be low and the system does not look all that dynamic at this
time, but could be just enough instability in the east and southeast
during the afternoon and evening hours, that a rumble of thunder or
two is possible. So have included an isolated threat of thunder in
the forecast for this time period...though it probably will not get
mentioned in the worded forecast yet. Chance of precip will diminish
late Monday night into Tue, with only a chance of precip remaining
in the eastern part of the CWA during Tue. As colder air advects
into the area from the northwest, some of the lingering precip could
be in the form of snow, but chances will be in the slight category
and only in the northwest parts of the CWA. Any precip remainder of
the CWA Tue will be rain. Then dry weather will advect into the CWA
for Tue night through Wed night.
At the same time, the upper level pattern will be one of a flat
trough/zonal type pattern over most of the US. This pattern will
allow the very cold air to advect into the area and remain over a
good portion of the US through the week. In this zonal type flow the
models have become inconsistent with some showing chances of weak
snow systems moving through the area, and other models showing
nothing. Models themselves have also become inconsistent from run to
run. So confidence in any precip is very low. However, model blend
has a slight chance of precip now for Thur and Thur night, and then
again Sat in the southeast. Will not make any adjustments here and
let the models work themselves out of their issues over the next
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 548 PM CST Sat Dec 31 2016
The cold front has pushed east of all the terminal sites, and
winds have shifted to the NW and started diminishing. Sustained
winds should diminish below 10kt at all TAF sites by 02z, before
becoming light and variable under the surface ridge axis. The
center of the surface high will push east of Illinois already by
sunrise tomorrow, so a southeast wind is expected to develop at
all sites in the morning. Wind speeds should remain less than
10kt, under a weak pressure gradient.
Clouds will be of little concern, with the only clouds of note at
15K feet altitude or higher.
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1035 PM EST Sat Dec 31 2016
Issued at 1035 PM EST SAT DEC 31 2016
Had to drop overnight lows just a bit for this evening`s update.
Otherwise adjusted PoPs to reflect decreasing coverage of showers
across the north. At least scattered showers will continue to
affect our southern zones through the overnight as the frontal
boundary stalls/washes out across the region. The H850 trough
never makes it further south than the Ohio River and shears out.
With loss of support aloft the actual sfc boundary becomes
increasingly difficult to pick out. But with showers decreasing
in the north and winds backing to the east later tonight across
the heart of the CWA, the sfc front may just be making it through
most of our area. Updated forecast package has been issued.
UPDATE Issued at 715 PM EST SAT DEC 31 2016
Forecast is in pretty good shape this evening. Cold frontal
boundary continues to push closer to our area. A broken band of
showers is also pushing eastward and is currently overspreading
the area. No major alterations to the forecast package early this
evening. Did make some adjustments to the grids for hourly trends.
No zone update at this time.
.SHORT TERM...(This evening through Sunday night)
Issued at 300 PM EST SAT DEC 31 2016
19z sfc analysis shows a cold front approaching Kentucky from the
west as low pressure moves through the Great Lakes and high
pressure holds on to the southeast. This front has pushed more
moisture into the area today raising dewpoints from the teens up
into the 30s through the afternoon. This also brought with it a
batch of light pcpn where wetbulbing led to a mixed bag of wx
types on the leading edge. With the wetbulbing temperatures, in
many places, fell back from the mid 40s into the upper 30s. The
pressure gradient between the system and ahead of the front
contributed to breezy conditions as well with sustained winds from
the south to southwest at 10 to 20 mph and gusts up to 30 mph.
Across the northwest parts of the area winds have been enhanced by
a passing low level jet with speeds of up to 35 mph noted. Winds
have also been gusty on the highest peaks along the Virginia
border with gusts to 40 mph observed.
The models are in good agreement aloft through the short term
portion of the forecast. They all depict a shallow trough
crossing the Great Lakes in the northern stream loosely connected
to a weak southern stream wave coming out of the Four Corner`s
Region. The energy with this will pass through Kentucky this
evening followed by small height rises as the pattern evens out
and ridging builds a bit across the Southeast. However, the
pattern keeps amplifying through Sunday as a diving and deepening
southern stream trough heads into the Big Bend area of Texas. This
will prompt heights to peak over Kentucky Sunday night with bits
of energy moving northeast into the area on deep layer southwest
flow. Given the model agreement have favored a blended solution
along with a hard lean toward the HRRR and NAM12 for specifics.
Sensible weather will feature light pcpn around through the
evening along with the development of patchy fog. Temperatures
will not drop off much through the night in the face of continued
WAA as the cold front stretches out just to the northwest of the
area. Spotty light rain continues through the night with the
southeast seeing the best chances for any accumulations of note -
most of the rest of the area will see trace to a few hundredths of
accumulation. Likewise, on Sunday mild conditions will prevail as
south winds continue and more spotty light showers pass through
eastern Kentucky. The mild wx rolls into Sunday night with the
better chances for soaking rains contained over the southeast
parts of the area while damp wx - light rain and patchy fog -
continues elsewhere across the forecast area.
For most of the forecast elements started with the CONSShort and
ShortBlend with only minor adjustments in the near term for
current conditions and then lows on Sunday night allowing for some
ridge and valley distinctions. Did also tighten up PoPs through
the period with more of a drop off in measurement chances to the
north and west of the area and the reverse in the southeast.
.LONG TERM...(Monday through Saturday)
Issued at 250 PM EST SAT DEC 31 2016
A mild start to the new year is expected with highs into the 60s on
Monday and Tuesday. However, despite the mild conditions, lots of
moisture will remain trapped over the region, leading to periods of
light rain from Monday night through Tuesday. The best chances for
rain will come late Monday into Monday night as a potent shortwave
trough pushes northeast across the area. Good forcing and moisture
will accompany this system and thus, have gone with high pops. The
rain will linger through Tuesday night, but will gradually taper off
and should be out of the area by around dawn on Wednesday. Dry
weather will be in store as we head into the middle of the week.
A cold front will sweep southward Tuesday night and usher in much
colder weather for the rest of the week. Highs by Thursday and
Friday may not get past the freezing mark for most locations.
Despite decent confidence in the temperature forecast, the same
cannot be said of the precipitation forecast. The 12Z ECMWF run has
reversed course yet again and is now trying to bring a swath of snow
across our region Thursday and Thursday night. The 12Z GFS, on the
other hand, is now establishing ridging across the area on Thursday,
with no precipitation at all for our area to end the week. That
being said, went with only a slight chance of precipitation Thursday
afternoon through early Thursday night, with no precipitation at all
across the area from late Thursday night through Saturday morning.
Any snow accumulations that do occur should be very light at best.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 715 PM EST SAT DEC 31 2016
Active weather this evening. based on current conditions and
trends, model guidance seemed reasonable. Thus tended to stay
close to it for the forecast. Main forecast challenge will be
VSBYS and CIGS. A band of showers associated with a cold frontal
boundary is pushing eastward this evening and will overspread the
area through the evening and overnight period. In general VSBYS
are expected to drop into the MVFR range and remain there through
much of the forecast. Low CIGS will be the major flight hazard
tonight, dropping down into IFR/LIFR territory for much of the
overnight. The low stratus is expected to rise for a period of
time Sunday, with our more northern terminals such as SYM and JKL
being the most likely to see MVFR CIGS. Winds will continue to
decrease this evening and remain generally light through the
period, gradually backing out of the southeast.
Area Forecast Discussion
National Weather Service Marquette MI
919 PM EST Sat Dec 31 2016
Issued at 919 PM EST SAT DEC 31 2016
Looks like quiet weather for any New Years Eve activities late this
evening into the very early morning hours of 1 Jan 2017. Snow
showers that affected much of the eastern cwa this evening are moving
out over Lk Superior. Temps have bottomed out over western interior
with single digits showing up over Gobebic county. Temps over
interior central will slip rest of this evening possibly into the
single digits before thickening mid clouds overnight bring temps back
into the teens. Those clouds are tied to isentropic ascent south of
shortwave and sfc cold front over Manitoba that should bring some
light snow overnight (after 1 or 2 am ET) to northwest Upper Michigan
then refocusing late tonight (after 4 am ET) for the northeast cwa.
Any snow accumulations should be minor with a couple inches possible
from Ontonagon to L`Anse and across the rest of the Keweenaw
Peninsula and also over the far northeast cwa, including Grand
Marais. Increased pops, qpf and snow for the expected trends.
Expect lingering lake effect in W to NW flow on Sun over the
Keweenaw in the morning with h85 temps down to -11c or -12c and
inversions at 4-5kft. Increased pops for the morning across the
Keweenaw. Could see additional inch or two of fluffy snow in the
morning where the snow showers persist, then inversions lowering blo
3kft will diminish the lake effect snow in the aftn. Elsewhere,
skies should be mostly cloudy with minimal weather concerns. Happy
.SHORT TERM...(This evening through Sunday)
Issued at 358 PM EST SAT DEC 31 2016
WV imagery and RAP analysis indicated a broad mid/upper level trough
from Hudson bay into the north central CONUS resulting in wnw flow
from wrn Canada through the nrn plains into the nrn Great Lakes. A
weak upstream shortwave trough was located over srn Manitoba. At the
surface, a trough extended into ern Lake Superior from low pressure
near the Sault. Upstream, a ridge extended from the central plains
into MN. Radar and vis satellite loops indicated a weak meso-low
north of Munising, and other bands of lake enhanced snow showers into
north central Upper Michigan.
Tonight, 850 mb temps around -10C along with low level troughing and
lingering deep moisture over the area will continue to support sct
shsn into this evening mainly from Marquette eastward. Although
there may be a brief burst of heavier snow, any accumulations should
remain minimal, less than an inch given the marginal instability.
Backing winds to sw as the ridge slides by to the south late this
evening will push the LES offshore. However, an area of 280k-290k
isentropic lift ahead of the Manitoba shrtwv will bring another area
of light sn/shsn into wrn Lake Superior and then into the Keweenaw as
winds veer to the wsw. LES potential remains marginal with 850 mb
temps around -10C.
Sunday, sct -shsn over the Keweenaw will linger into the morning but
diminish into the afternoon as drier 900-700 mb air moves in with
inversion heights dropping to around 3k ft. Otherwise, under partly
to mostly cloudy skies temps will again climb above normal with
highs in the upper 20s to around 30.
.LONG TERM...(Sunday night through Saturday)
Issued at 254 PM EST SAT DEC 31 2016
A mid/upper level ridge building from the northeast Pacific into
Alaska will result in pattern amplification across the CONUS with a
broad trough forming over the western CONUS and expanding eastward
through the week. The pattern will also favor the intrusion of an
Arctic airmass by midweek that may linger through next weekend.
Temperatures near or above normal into Tuesday will drop below
normal with LES increasing for nw to wnw snowbelts.
Sun through Sun night, Broad mid-level ridging will keep conditions
mainly dry through the period. 850mb temps climbing to -4C south and
-8c north on Sun will bring moderating temps after a cold early
morning. Although the sfc high pres is fcst to build into New
England Sun night, enough low level dry air will persist under the
sfc ridge axis extending back into the Upper Lakes to maintain dry
conditions through the night. More mid/high clouds will result in a
warmer night, generally in the upper teens and low 20s.
Monday-Tuesday, The models suggest that a low pressure wave will
lift northeast from the Southern Plains into the Great Lakes.
Operational models still indicating a lot of uncertainty regarding
track/strength of developing sfc low. Both the 12z ECMWF and 12z
Canadian are trending farther se with a 1005 mb sfc low tracking
through the Ohio Valley late Mon night and Tue morning then
deepening the low to 984 mb as it moves into New England late Tue
night. The 12z GFS on the other hand shows a 994 mb low tracking
farther north into central MN Monday night then across western Upper
Mi on Tuesday. Differences in the forecast track will obviously
impact ptype and the more western track of the GFS will result in
more mixed pcpn Mon night into Tuesday. Given that the GFS appears
to be more of an outlier from ensemble tracks and SREF members will
side more with the non NCEP models. But even the non-NCEP solutions
bring enough of a warm layer into the se cwa to support mixed pcpn,
including sleet and freezing rain along with the snow. Model QPF of
.3 to .6 inch suggest the potential for moderate to possibly heavy
snow at times over the western to north central cwa. As the low
departs significant lake effect or lake enhanced snow for n to nw
flow favored areas will also be possible Tue afternoon into Tue
night with 850 mb temps falling to -18C to -20C and a shortwave
trough moving through the region.
Wednesday-Friday, Once the low moves farther e on Wed, long duration
les off Lake Superior will persist with 850 mb temps dropping to -20
to -25C late in the week. Locations affected each day will depend on
daily wind directions with nw winds only gradually backing to wnw or
w by Thursday afternoon into Friday. The Keweenaw Peninsula will
again see the heavier and more persistent LES and greater impacts
from blowing snow. Eastern shoreline areas may also get into some of
the heavier LES accumulation. Would not surprised if long duration
LES warnings will be needed over the Keweenaw and possibly far
eastern shoreline areas.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 658 PM EST SAT DEC 31 2016
As one low pressure system exits Upper Michigan to the east this
evening another will pass across northern Ontario overnight bringing
possible light snow after midnight to CMX. Cooler air behind the
Ontario low arriving late tonight will lead to lake effect snow at
CMX through midday Sun. No significant weather is expected at IWD or
SAW through late Sun aftn. Mainly VFR conditions until overnight at
IWD and CMX when MVFR cigs return. MVFR cigs wont move back into SAW
until Sun morning. Only vsby reduction will be at CMX late tonight
through Sun morning with IFR vsby at times during the lake effect
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 358 PM EST SAT DEC 31 2016
Southwest winds will increase to around 30 knots as the pres
gradient increases between a ridge south of Lake Superior and low
pressure into nw Ontario. Winds will then diminish by Sunday
afternoon. Another periods of winds to 30 knots and possibly a
northerly gale will develop by late Monday night into Tuesday as a
low pressure deepens near the northern Great Lakes and moves off to
the east. However, there is still uncertainty with the track and
strength of the low. Northwest winds to around 30 knots will then
linger from Wednesday into Wed night with potential for heavy
freezing spray as arctic air moves in.
Area Forecast Discussion
National Weather Service Norman OK
603 PM CST Sat Dec 31 2016
We made some minor adjustments to the overnight forecast based on
observation trends and latest short term model guidance. The first
adjustment was precipitation type in the northwest. Bufkit
soundings are marginal for exclusively snow with the wet bulb
temperature near or just above 0C through a fairly deep layer, so
we went with rain and snow. The second was to add slight chance
probabilities of rain showers in western north Texas and a portion
of southwest and south central Oklahoma later tonight. Ascent from
approaching shortwave trough and moistening, albeit meager but
probably sufficient, may result in some brief showers there. The
third was to try and convey a little more certainty in
occurrence/coverage with fog in the southeast portion of the area
later tonight and so we transitioned wording from "patchy" to
"areas". Locally dense fog seems possible and mentioned of this
was added to the Hazardous Weather Outlook.
Minor adjustments may be needed to tomorrow`s forecast,
specifically with spatial coverage of fog/drizzle (may need to
expand further westward and northward). We will also need to
reevaluate for the possibility of light precipitation early in the
morning across the northeast and east central portion of the area.
Right now we have snow flurries mentioned, but NAM thermal
profiles show a warm advection regime probably favoring more
light drizzle or sprinkles. NAM and RAP differ in the amount of
low level moistening/saturation so confidence is low now but we
will monitor trends.
.PREV DISCUSSION... /issued 515 PM CST Sat Dec 31 2016/
Light north/northeast winds this evening will gradually shift to
the east and then to the south during the day on Sunday. Mid
clouds will increase overnight with an outside possibility of some
light rain showers near the Red River and far northwest Oklahoma.
Some light snow may mix in at times in the northwest. Otherwise,
lower level moisture will result in development of MVFR ceilings
across southeast into central Oklahoma toward morning, impacting
OUN/OKC and eventually PNC. MVFR conditions then are expected to
linger through much of the day at those sites.
PREV DISCUSSION... /ISSUED 237 PM CST Sat Dec 31 2016/
A cold front continues to slowly progress southward across western
and central OK this afternoon. SE OK will not be influenced by
this front through tonight with a sfc low remaining near this
region/front stalling. As a result, expect some fog to develop late
tonight thru tomorrow morning over SE OK within easterly moist
flow. A mid level vort max, currently moving into northern NM, is
still expected to lift over the panhandles late tonight through
early morning. Some brief, light snow will be possible with this
feature though moisture appears limited. Do not expect any
accumulation at the current time, but can`t rule out a dusting
across NW OK. Light rain/showers will then be possible by mid day
across SE OK.
Expect more widespread fog late Sun thru early Mon east of I35 as
southerly flow returns and dewpoints climb back into the 50s ahead
of a deeper mid to upper low moving over west TX. This feature is
expected to pass over central TX Sun night and Mon morning.
Widespread showers and isolated storms will be possible with it,
especially along and south of the Red River. A few strong to
severe storms could develop initially over portions of western
north TX late Mon, and then across extreme S/SE OK thru the early
morning hours as mid level lapse rates steepen with the mid to
upper trough. As the trough passes overhead mid day Mon and winds
veer, cloud cover will diminish and temps will climb well above
average Mon afternoon.
The next modified arctic cold front will move into OK early Tue
AM, and then dive southward during the day into TX. Precipitation
is not expected behind the front, although some stratus may
briefly accompany it. The depth of the cold air will continue to
deepen through mid to late next week as several mid to upper
shortwave troughs move over the northern plains and upper midwest.
Expect temps to remain well below normal after Tue. In addition,
mid level moisture will increase along a baroclinic zone Thu AM
along and north of I40. A couple of mid to upper level
perturbations within WNW flow, subtle mid level WAA, and
divergence aloft associated with the RRQ of an upper jet may
support light snow across the northern half of OK by Thu. Better
lift will likely accompany a mid level shortwave trough Fri, and
based on fairly decent moisture agreement between the ECMWF and
GFS decided to increase PoPs (snow) into low chances.
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 56 32 58 47 / 0 10 10 30
Hobart OK 51 31 57 42 / 0 10 10 30
Wichita Falls TX 61 34 63 51 / 0 20 10 50
Gage OK 47 27 57 37 / 0 20 10 0
Ponca City OK 50 27 53 45 / 0 10 10 20
Durant OK 65 43 61 56 / 0 10 30 50
Area Forecast Discussion
National Weather Service Mount Holly NJ
942 PM EST Sat Dec 31 2016
High pressure south and east of the Mid-Atlantic will continue to
drift offshore as a cold front approaches from the west and passes
through the region tonight. Weak high pressure will build across
the Northeast on Sunday before moving into New England Sunday
night. A warm front will lift north towards the Mid-Atlantic and
Northeast Sunday night and Monday as weak low pressure develops
over the Southeast and lifts to the north and east. Another area
of low pressure will move into the region on Tuesday. A strong
cold front will pass through the Eastern Seaboard on Wednesday,
and then a series of upper level disturbances will pass through
the region through the end of the week as high pressure drops from
Canada and into the central United States.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Isolated sprinkles and flurries continue this evening, associated
with a weak short wave/vorticity impulse moving into the area. As
we go through rest of the evening and early part of the overnight,
a stronger short wave/vorticity impulse is forecast to approach
the area from the west, ahead of a weak cold front. There is not a
lot of moisture associated with these second impulse. However,
latest hires guidance like the HRRR and RUC continue to spread
some QPF across the area this evening and into the early morning
hours. With there being large temperature/dew point depressions,
it may be more sprinkles or flurries. But we`ve still kept isolated
rain or snow showers across the area, although any showers will
likely only produce trace amounts of precipitation.
Otherwise, cloudy skies will continue through much of the night to
ring in the new year. This cloud cover, combined with initially
plenty of wind above the surface should keep temperatures from
dropping all that quickly for much of the night. The better chance
of radiational cooling may not occur until just prior to sunrise
when some clearing should occur along with less wind. We favored a
MOS/continuity blend for the low temperatures and indicated a
slower temperature drop for awhile at most places. The breeze is
expected to diminish through early this evening as mixing should
weaken and the low-level jet eventually shifts more offshore.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
As a weakening trough shifts to our northeast to start Sunday,
the new year, some ridging begins to arrive from the west and
southwest. This will drive surface high pressure right over our
area as we go through the afternoon hours. There should be plenty
of drying along with subsidence during Sunday to prevent much in
the way of clouds. However there could be lingering stratocumulus
in the morning especially across the northwestern areas before
increased subsidence occurs. A northwest breeze may turn a bit
gusty in the morning, however overall less wind as high pressure
High temperatures were mostly a MOS blend with some local tweaks.
The airmass is forecast to modify some through the day, therefore
a milder afternoon is anticipated for much of the area (especially
the I-95 corridor on south and east with a downslope wind
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Overview...A prolonged period of unsettled weather on tap for much
of the upcoming week, with a return to below normal temperatures for
the end of the week.
Low pressure develops over the Southeast U.S. on Sunday and a warm
front developing out ahead of that low will lift north towards the
Mid-Atlantic and Northeast Sunday night and Monday morning. With
abundant low level cold air in place, and rising temps aloft, can
expect a period of freezing rain to develop sometime after midnight
Sunday night and the pre-dawn hours Monday morning. Surface temps
across the Delmarva and southern and coastal NJ should be warm
enough to support all rain, and areas that look to be most impacted
by a period of freezing rain will be along and north of I-95 first.
The rain/freezing rain line will lift north through Monday morning,
with freezing rain becoming plain rain, first to areas north of I-
78, and then to areas north of I-80 by Monday afternoon.
Based on latest model trends, the heaviest of the precip should stay
south of the Delmarva, and only expecting light amounts of QPF
Sunday night and Monday. As a result, currently not expecting much
more than a few hundredths of an inch of ice, mainly along and north
Meanwhile, an upper trough will into the Western U.S. as a weak
shortwave passes through the southern U.S. early in the week.
Surface low pressure will develop associated with that shortwave
over the Great Lakes Monday night, and then that low tracks east on
Tuesday and moves offshore Tuesday night. No ptype issues expected
with this system, as a lack of cold air aloft and at the surface
will mean precip should start out as and stay as rain through the
duration of the event Monday night through Tuesday night. With
southerly flow, temps will be well above normal on Tuesday,
generally in the 40s to low 50s across the Delmarva.
Pattern change then expected for the middle to the end of next week.
H5 low will move into the Pacific Northwest on Monday and slowly
track east through the week. By Tuesday night, this upper low will
rapidly intensify over the Great Lakes, and as it deepens, will pull
cold, Arctic air into the Northern and Central Plains. A deep upper
trough will encompass much of the northern U.S. by Wednesday, with
850 MB temps as low as -22C.
Strong cold front will pass through the region on Wednesday.
Depending on the timing of the front, could have a case where high
temps are reached Wednesday morning, and then temps fall through the
afternoon. Not confident enough yet to include something like this
in the forecast, as it is too far out to be certain. But by
Wednesday night, can expect low temps almost 20 degrees colder than
Tuesday night. Highs on Thursday will be about 10-20 degrees colder
than Wednesday, and then the coldest air arrives for Friday and
Saturday. Highs on Thursday will generally range from the low to mid
20s across the Poconos, to the low 30s north of I-95, and in the
upper 30s to around 40 for central/southern NJ and the Delmarva.
Highs will be a few degrees colder than that on Friday and Saturday.
Lows will range from the teens and 20s.
In terms of sensible weather, with trough setting up over the
Northeast, can expect several shortwaves to rotate around the trough
and into the region. Isolated snow showers possible. For now, will
generally keep PoPs capped at slight chance, though may have some
chance PoPs for the Poconos.
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Tonight...VFR conditions expected across the TAF sites. Clouds
will lower from 10/12,000 feet to around 5,000 feet through this
evening and overnight. Clouds are expected to begin to scatter out
late in the night and toward daybreak Sunday.
Isolated showers or flurries/sprinkles are possible this evening
into the early morning hours. Any precipitation is expected to
end by 06z/07z.
Southwesterly winds 10-15 knots with gusts around 20 knots early,
diminishing 5 to 10 knots overnight, then becoming west-northwest
A southwesterly low-level jet of 50 knots arrives later this
evening (especially from the TTN-PHL-ILG area south and east).
However the strongest winds should remain above 2000 feet.
Therefore, low- level wind shear was not included in the TAFs.
Sunday...VFR. Northwest winds around 5 to 10 knots Gusts in the
mid/upper teens late morning through midday, then becoming lighter
by late afternoon.
Sunday night and Monday Morning...generally MVFR CIGs/VSBYs, with
local IFR conditions possible. Chance for freezing rain at
KABE/KRDG and possibly KTTN, and then freezing rain changes to
plain rain through Monday morning. For all other terminals, rain.
Monday afternoon...MVFR/IFR conditions in rain.
Monday night through Tuesday night...IFR/LIFR conditions in rain.
Wednesday...Generally VFR, but some light rain/snow showers
possible in the afternoon. Gusty W/NW winds developing in the
Thursday...VFR. Gusty W/NW winds.
The Gale Warning has been extended for a few hours through 4 am
for our far northern marine zone of ANZ450 through midnight.
Winds at buoy 44065 have been gusting 35-37 knots the last couple
of hours, and could continue gusting over the next several hours.
Farther south, winds have not been gusting that high, and the low
level lapse rates diminish over the next few hours. A 50-knot
southwesterly low-level jet moves across the area through about
the first half of tonight then it shifts offshore. This is ahead
of a weak cold front and while some warming is taking place, there
is a window of opportunity for an occasional gale force gust (to
35 knots), but we do not think the duration will be as long
farther south. The forecast soundings generally indicate that
this may mostly be confined to this evening. Given the
southwesterly flow and the potential shorter duration, we will
continue to run with a strong Small Craft Advisory for the rest of
the waters. The winds should start to settle overnight as the
front moves through and the low- level jet moves offshore. High
pressure then builds in during Sunday with less wind and subsiding
seas. We trimmed back the advisory to 09z Sunday for Delaware Bay,
and kept the end time of 15z Sunday for the ocean zones.
Sunday night through Monday morning...Rain developing. Sub-SCA
Monday afternoon through Monday night...SCA conditions possible on
the ocean. VSBY restrictions in rain.
Tuesday through Tuesday night...Sub-SCA conditions. VSBY
restrictions in rain.
Wednesday through Wednesday night...SCA conditions on the waters
in developing NW flow. Gales possible Wednesday afternoon.
Thursday...SCA conds possible in 25-30 KT wind gusts.
MARINE...Small Craft Advisory until 10 AM EST Sunday for ANZ451>455.
Gale Warning until 4 AM EST Sunday for ANZ450.
Small Craft Advisory until 4 AM EST Sunday for ANZ430-431.
Area Forecast Discussion
National Weather Service Phoenix AZ
805 PM MST Sat Dec 31 2016
Another low pressure system will move into the Desert Southwest
tonight and early Sunday. Widespread rain will spread across the
region with lingering showers persisting in eastern Arizona Sunday
afternoon. Mostly dry, but continued cool and somewhat unsettled
conditions are likely for much of next week.
As one weaker PV anomaly lifts into northern NM, a secondary deeper
system continues to dig along the southern CA coast. Light showers
have persisted in the upslope region east of the Phoenix metro, but
otherwise some measure of weak sinking motion covers much of the CWA
early this evening. However, this will change abruptly as marked
difluent flow aloft and strong cyclonic vorticity advection has
already begun moving into SE CA. Regional radar images shows banded
rain covering much of San Diego County poised to move into Imperial
and eastern Riverside counties. Despite minimal instability, a few
lightning strikes have also been sampled upstream owing to the
intense dynamical nature of this weather system. All indications
still point towards rain moving into areas west of the Colorado
River through midnight, then enveloping the remainder of the
forecast area through Sunday morning. Just made some minor revisions
to the short term forecast based on immediate observational and
early 00Z model trends, but otherwise still looks like a near
certainty just about everyone gets wet over the next 24 hours.
/242 PM MST Sat Dec 31 2016/
Latest model guidance has trended somewhat slower, but also stronger
with regard to the onset and intensity of the precipitation. This is
most evident in the latest runs of the HRRR which indicate that a
line of storms containing moderate to heavy rain will march steadily
through southeastern California/southwestern Arizona between
midnight and 6am. Although CAPE will be neglible, model-based
reflectivities and strong vorticity forced ascent in the vicinity of
the mid-level cold pool suggest some potential for lightning and
even small hail. Ahead of the main batch of precipitation, hi-res
guidance also suggests that conditions will be moist enough in the
warm sector for isolated to scattered showers to develop as far east
as the Phoenix area. However, most likely period for rainfall in
south-central Arizona will be a few hours later in a 6-hour window
centered around 8am.
Latest ensemble-based SREF and GEFS QPF estimates indicate rain
totals around 0.4 inches for the Phoenix area, though some
variability is expected across Maricopa County. Highest rain amounts
may actually occur to the west in portions of La Paz and Yuma
Counties, where between 0.5 and 0.75 inches is probable. Although
strong subsidence will build in behind the low late Sunday morning,
persistent moisture will again support additional isolated to
scattered shower activity during the afternoon, mainly across the
foothills and favored upslope areas of Maricopa and Gila Counties.
On Monday, as the low tracks off to the east, there will still be a
lingering slight chance of showers over the lower southwest and
central deserts deserts; the showers will primarily be instability
based as the QG forcing will be mostly over and the boundary layer
will stay very humid.
From Tuesday through the end of the week, the forecast will remain
rather cool and unsettled. Initially a large area of low pressure is
forecast to develop across the western CONUS centered north of
Arizona. However, how this low evolves with time is not being
handled well at all by operational model guidance and ensemble
members from the GEFS are all over the map. Run to run consistency
from the GFS and ECMWF is still very low. As a result we have not
really changed the extended forecast; we will keep slight chances in
the forecast most every day with best threats over south central
Arizona. POP trends will continue to follow the NAEFS POPs. High
temperatures will stay near or slightly below seasonal normals
during the period. Overall the forecast is rather broad brushed for
next Tuesday through Friday.
South-Central Arizona including KPHX, KIWA, and KSDL:
A prolonged period of lower cigs and rain showers will be a major
problem for Phoenix terminals late tonight through Sunday. 7K-9K ft
cigs will begin to lower below 6K ft well after midnight with sct
showers breaking out sometime in the 09Z-10Z time frame. Light
easterly sfc winds will prevail until the rainfall arrives.
Lower end MVFR conditions with frequent showers are a near certainty
from around sunrise through much of Sunday morning. Some periods of
IFR are also possible. Confidence is moderate that MVFR cigs and
widespread mountain obscuration will persist through the afternoon
hours Sunday as well. Southeast sfc winds will gradually become
westerly by the afternoon, though timing of this wind shifts carries
Southeast California/Southwest Arizona including KIPL and KBLH:
Lowering cigs and widespread rain will be quite problematic for SE
CA terminal sites late this evening through Sunday morning. Cigs
will gradually lower below 6K ft this evening with rain showers
starting over the area in a 05X-07Z time frame. A period of MVFR
conditions are likely at KIPL, though improving conditions should
arrive later Sunday morning. KBLH will likely experience much lower
cigs and more prolonged rain with IFR conditions likely late
tonight. MVFR conditions may persist into the daytime hours before
improving Sunday afternoon. Otherwise, sfc winds may become
gusty from the W/NW for a period Sunday morning.
Aviation discussion not updated for amended TAFs.
Monday through Friday:
In the wake of a very wet weather system, much cooler temperatures
will prevail for much of the week, closer to or below seasonal
normals for a change. Unsettled storm pattern will remain over the
western U.S., allowing for cool temperatures and only modest drying
to settle into the districts by midweek. Winds speeds overall will
follow typical drainage and diurnal patterns while remaining rather
light and generally under 10mph.
.SPOTTER INFORMATION STATEMENT...
Skywarn Radio Net activation is not expected this week.
Visit us on Facebook...Twitter...and at weather.gov/phoenix
Area Forecast Discussion
National Weather Service Raleigh NC
820 PM EST Sat Dec 31 2016
Unsettled weather will develop across central North Carolina Sunday
through early next week as a series of weather disturbances move
across the region.
.NEAR TERM /TONIGHT/...
As of 820 PM Saturday...
Radar and surface observations indicated nothing more than a few
sprinkles have reached the ground with the patchy, light showers.
Most of these sprinkles have been confined to the southern third of
the region. The lower levels remain very dry with surface dew points
in the teens across the north and west, ranging into the 20s SE.
Winds had become SW at 5-10 mph as the parent high pressure become
centered offshore. However, the moistening from the top down will
take quite a while to occur in the NW where no POP is forecast. In
the south, the latest HRRR and other High-Res near term models still
indicate the highest probability (only 20-30 percent) of light rain
(0.01) will be possible across the Southern Piedmont eastward into
the Southern Coastal Plain later tonight. Otherwise, cloudy with
lows in upper 30s to lower 40s.
.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
As of 245 PM Saturday...
There should be some ongoing light rain over the western and
southern portions of the CWA by 12Z Sunday, driven mainly by weak
isentropic lift and upper divergence in the right entrance region
of a 130kt jet over the Mid-Atlantic States. The forcing isn`t
terribly strong, as the two primary shortwaves over the southern
Plain and Southwest US are rapidly deamplifying today, and the local
airmass (dewpoints in the 20s) will take some time to moisten. In-
situ cold air damming will develop by Sunday in response to the
evaporative cooling, and temps will only reach the mid 40s in the
Piedmont to lower 50s (which may be too high if precip is
persistent) in the southern Coastal Plain.
A more expansive rain shield should spread back in Sunday night as
warm advection begins to strengthen ahead of a shortwave currently
off the central California coast that gets kicked east by a
positively tilted trough over the western US. Widespread rain early
Monday may be heavy as PW rises to 1.5 inches (over 200% of normal)
and the coastal/warm front tries to retreat inland. However the CAD
should hold, keeping temps in the upper 40s and 50s for most of the
area. The aforementioned West Coast shortwave is forecast to
maintain its amplification and swing across the region Monday night,
bringing another round of showers that could be locally heavy.
especially across southern areas as the coastal front continues to
eek slowly northward. models are likely overdone in its progression
until Tuesday when drier air aloft spreads across the area and
insolation aids in erosion. Storm total QPF from WPC ranges from
0.5" to a little over 1", which is at or just below NAEFS and EPS
means. Convection over the Gulf Coast and Southeast States could
impact the total qpf, something tough to discern this far out. If
the shortwave does maintain its character, isolated lightning
strikes may be possible despite the lack of an intrusion of higher
dewpoint air and instability. Not including thunder at this point
given the uncertainty.
The CAD should break from southwest to northeast on Tuesday,
allowing temps to climb into the 60s and lower 60s, with the main
arctic front trailing and crossing the area early Wednesday.
.LONG TERM /Wednesday through Saturday/...
As of 335 PM Saturday...
Broad cyclonic mid and upper flow will be established across much of
the region on Wednesday, with a sfc cold front exiting the east
coast. This pattern will begin a slow cooling trend across our area
that will last through the end of the week, as depicted by forecast
low level thicknesses falling from around 1350m at 12z Wed to around
1270m by 06z Sat. While arctic high pressure will gradually build
across our area through the end of the week and weekend, a couple of
disturbances embedded within the aforementioned cyclonic flow are
worth noting. The first such disturbance is forecast by both the GFS
and ECMWF, originating in the northern stream over the Northern
Rockies Tuesday night, that will pass by to our north early on
Friday. Robust jet energy assoc with this feature and assoc lift is
progged to support some very light precip across our area as early
as Thursday evening, perhaps through Friday morning. Forecast
soundings suggest enough cold air may be in place (given the
aforementioned cooling trend) to support light rain at the onset
perhaps mixing with or changing to light snow before precip ends
Friday morning. Since QPF amounts are very light, right now this
system doesn`t appear to be a major concern, but worth watching.
The other disturbance of concern is a short wave that the models
break off from the closed low over the Pac NW and move in the
aforementioned flow across the country and across the SE by Saturday.
Given the evolution of this wave, it`s no surprise that the models
have been struggling with the details for our sensible weather next
weekend. The bottom line is that the models have been depicting a
Miller A type sfc low developing over the NE GOM by late Friday (in
response to the aforementioned short wave in the broad cyclonic
flow) which moves NE and off the SE coast by Sunday. While the past
few days we`ve seen model runs spread moisture across our area from
the south over the weekend (coupled with a cold sfc high to our
north which would suggest p-type concerns), more recent runs of both
the GFS and ECMWF have shifted/suppressed both the sfc low and bulk
of the moisture more to our south and southeast. While these recent
models trends support a much lower-impact forecast (perhaps even a
dry forecast), it`s worth pointing out that the 12Z GFS still
suggests some precip across SE zones on Saturday, and there`s still
a sniffy amount of spread in both the GFS and ECMWF ensemble
members. This system also worth watching, but trending toward a
Regardless of the precip forecast, arctic high pressure will mean
high temps struggling to reach the lower 40s by weeks end, but
clouds keeping low temps not too far from freezing during that same
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 700 PM Saturday...
24-Hour TAF period: Clouds will gradually thicken and lower from
west to east across central NC this evening into early Sunday
morning, with even some light rain or sprinkles possible by early
Sunday morning (mainly at KFAY). Cigs are expected to lower into the
MVFR range on Sunday morning, then possibly lower Sunday afternoon
along with some light rain spreading across the area in association
with disturbances moving through the southwesterly flow aloft.
Outlook: Expect conditions to deteriorate further on Sunday evening,
with sub-VFR conditions persisting through Tuesday in assoc/w a
series of upper level disturbances in SW flow aloft. VFR conditions
are expected for Wednesday and Thursday.