Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/04/16
Area Forecast Discussion
National Weather Service Columbia SC
939 PM EST Sat Dec 3 2016
Dry conditions will persist through this evening with surface
ridging across the region. A low pressure system in the western
Gulf Coast Region Sunday will move northeastward and into the Ohio
River Valley Tuesday. The associated warm front will likely remain
south of the forecast area through Monday then lift north near or
into the forecast area Tuesday ahead of a cold front. The cold
front will likely be off the coast Tuesday night. Another cold front
will bring unseasonably cold conditions for next weekend.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Surface high pressure will continue to ridge into the forecast
area through tonight. Satellite trends indicate mid and high
cloudiness streaming into the forecast area well ahead of the
southern stream system over the southwest part of the nation. The
moisture will continue to increase tonight. Radar trends suggest
light rain become more widespread in north Georgia...moving toward
Upstate SC. Low levels remain dry at the moment. HRRR and rap
suggest rain will move into the Piedmont and possibly the west
Midlands/CSRA earlier than Mos guidance suggests. Raised pops in
the west through the overnight into tomorrow morning as isentropic
lift/moisture flux increases. Rainfall amounts will be quite light
through at least 09z due to dry low levels. Cloudiness will help
hold up temperatures tonight. The temperature guidance was
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
The models indicate a surface wedge pattern along with increasing
isentropic lift developing Sunday and continuing into Monday
night. At the surface...high pressure will reside along the mid
Atlantic coast Sunday providing a northeast low-level wind flow. A
system will move across the Great Lakes Sunday night and
additional high pressure will build in across the Mid Atlantic/New
England region for Monday into early Tuesday. An initial
shortwave trough will move east across the country on Sunday
tapping Gulf of Mexico moisture as it tracks eastward and bring
rain to the region by late Sunday. A more significant closed upper
low over northwest Mexico will eject eastward into the southern
plains and western Gulf Coast region by late Monday and cross the
region on Tuesday keeping rain chances high over the area.
Have indicted likely to categorical pops Sunday afternoon into
Tuesday morning. Have kept maximum temperatures below the
guidance for both Sunday and Monday...in the upper 40s to mid
50s...because of wedge conditions. Used the local wedge equation
and blended it with guidance for temperatures. Should see little
diurnal cooling...with lows in the lower 40s to lower 50s.
The GFS...NAM and ECMWF hold the warm front south of the forecast
area through Monday night. The warm front may move into the
forecast area Tuesday but this is questionable because the cool
wedge may linger. The models often erode the cooler/wedge
conditions too quickly. Depending on where the boundary sets
up...isolated storms are possible Tuesday as the upper trough and
surface cold front crosses the region. Severe thunderstorms could
possibly occur if the warm front gets into the forecast area and
surface-based instability develops.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
The medium-range models show the cold front off the coast Tuesday
night with dry weather through Wednesday night. Another cold front
looks to cross the region in the Thursday/Friday time frame. Both
the GFS/ECMWF sweep the front through on Thursday. The GFS is a
little drier in the way of precipitation while the ECMWF
continues to be slower and wetter.
Seasonable temperatures Wednesday and Thursday are forecast to
cool dramatically for the end of next week as much colder air
pours into the eastern conus.
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Surface high pressure will continue to ridge into the forecast
area from the north through the TAF period. A warm front will
develop south of the forecast area well ahead of low pressure in
the western Gulf of Mexico. Cloudiness will be on the increase
during the TAF period but the initial dryness associated with the
surface ridging should help hold up ceilings. Latest radar
composite showing light showers moving into the western Midlands
this evening. Patchy light rain possible at all TAF sites during
the overnight. The GFS and NAM MOS and SREF guidance were
consistent will IFR or MVFR ceilings holding off until after 12z.
The MOS indicated light northeast wind. Expect periods of light
rain and possible MVFR fog across the area and during the
afternoon on Sunday.
EXTENDED AVIATION OUTLOOK...Expect widespread IFR conditions
associated with a warm front through Tuesday.
Area Forecast Discussion
National Weather Service Caribou ME
957 PM EST Sat Dec 3 2016
High pressure will build across the region late tonight through
Sunday. A weak trough of low pressure will cross the region Monday
into Monday night.
.NEAR TERM /THROUGH SUNDAY/...
935 PM Update: Latest radar ref imagery shows that most sn shwr
activity that was ovr E Cntrl ptns of the region has diminished.
In fact...initially skies became ptly cldy as far N as Caribou,
but bkn-ovc SC has filled back in from the St Lawrence seaway.
Latest HRRR sim model radar ref does not show much in the way of
additional sn shwr activity for the ovrngt, but does hint at lgt
St Lawrence seaway sn streamers, particularly for the NW where we
keep a mention of low chc sn shwr PoPs. Elsewhere across the N, we
keep a mention of isold sn shwrs. Any sn amounts from narrow sn
streamer bands should be lgt in the order of a half inch or less,
with most lctns receiving a dusting or less. Over E Cntrl and
Downeast ptns of the region, enough llvl drying with downslope NW
winds has allowed for some clrg, where we xpct to hold thru the
Otherwise, fcst hrly temps and dwpts have been updated based on
trends seen in latest mid eve sfc obs. At one point, we thought we
needed to lower fcst ovrngt lows, but with additional low SC cld
cvr movg back into Nrn ptns of the region, temps have acutually
rebounded by a deg or two F ovr the last hr or two. Lastly, we
made adjustments to hi trrn temps and winds for the ovrngt into
Orgnl Disc: An upper level disturbance will move east of the
region tonight, with surface high pressure starting to build
toward the region late. Skies will remain mostly cloudy across the
forecast area tonight. Scattered snow showers will occur across
the north and mountains early tonight, with isolated snow showers
late. Isolated to scattered snow showers will occur across the
Bangor and Downeast areas early tonight. Any snow accumulations
tonight are expected to be less than an inch. High pressure builds
across the region Sunday. Mostly cloudy skies along with isolated
snow showers are expected across the north and mountains early
Sunday, with decreasing clouds during the afternoon. Across the
remainder of the forecast area expect partly/mostly cloudy skies
early Sunday with decreasing clouds during the afternoon. Low
temperatures tonight will range from around 20 to the lower 20s
north, to the mid to upper 20s Downeast. High temperatures Sunday
will range from the mid to upper 20s north, to the mid 30s
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
Much colder weather is on the way for our new week. High pressure
cresting over the area Sunday night will bring clear and calm
conditions resulting in the coldest night so far this season.
Temperatures will range from the single digits north to the mid
20s Downeast. A very weak trough of low pressure will then
approach on Monday bringing a mostly cloudy sky and just a slight
chance for some snow showers Downeast. High pressure will return
on Tuesday with sunny and cold conditions followed by a clear to
partly cloudy and very cold night Tuesday night.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
A weak trough crossing the area on Wednesday will bring some
clouds, but will likely be too weak for anything more than
flurries. A more vigorous trough of low pressure will approach
Wednesday night thickening clouds across the area and bringing a
chance of light snow by Thursday morning. Forecast guidance has
been quite variable on the outlook for Thursday with the latest
GFS now forming a strong low in the Gulf of Maine on Thursday and
spreading significant snow across the central and northern part of
the region Thursday into Thursday night with rain Downeast. The
new ECMWF, however, has a much more open trough and produces a
weak system suggesting only light snow late Thursday into Thursday
night. Either way, Cold air and breezy conditions will follow
through the end of the week Friday into Saturday. With many of
the lakes and rivers still open and releasing water vapor into the
air, the chances for flurries and snow showers will likely persist
following the system through at least Saturday. High pressure
should return to the area on Sunday.
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
NEAR TERM: Occasional MVFR conditions are expected across the
north and mountains tonight, with local IFR conditions also
possible early. Occasional MVFR conditions are expected across the
Bangor and Downeast regions early tonight, with VFR conditions
developing overnight. Occasional MVFR conditions are possible
across the north and mountains though early Sunday afternoon, with
VFR conditions later Sunday afternoon. VFR conditions are expected
across the the Bangor and Downeast regions Sunday.
SHORT TERM: VFR conditions in high pressure are expected Sunday
night into Monday. Conditions may lower to MVFR Downeast Monday
afternoon. Generally VFR conditions are expected in high pressure
Monday night through Tuesday night. VFR to MVFR conditions are
likely on Wednesday, with MVFR/IFR conditions possible Thursday.
NEAR TERM: A Small Craft Advisory is in effect for much of the
waters, with the exception of the intracoastal waters, tonight
through Sunday afternoon. However, the intracoastal waters might
need to be included in the Small Craft Advisory.
SHORT TERM: Winds and seas should remain below SCA Sunday night
through Wednesday night. An SCA or Gale is possible late Thursday
or Thursday night depending on the development of a coastal low
late in the week.
MARINE...Small Craft Advisory until 4 PM EST Sunday for ANZ050-051.
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
949 PM CST Sat Dec 3 2016
The upper level pressure system currently over northwest Mexico is
forecast to push to the southeast while sending several short-
waves overnight across our area. Latest HRRR and NSSL-WFR models
show convective initiation overnight into Sunday morning with
storms starting across the southwest counties/coastal plains area
and then moving and expanding across the I-35 corridor. With this
newly round of moderate to heavy showers possible affecting same
areas that received 3 to 5 inches of rainfall last night through
late this morning, we opted to issue a Flash Flood Watch which is
in effect through late Sunday night. As the upper low pushes
across the Rio Grande Plains Sunday evening, yet another round of
moderate to heavy showers is expected along and east of I-35
Sunday evening into Monday morning. Weather conditions will
improve Monday west to east as the upper low moves into central
.PREV DISCUSSION... /ISSUED 543 PM CST Sat Dec 3 2016/
IFR/LIFR will be the most likely flying categories at all area
airports for the next 24 hours. There may be brief improvement,
but it is not likely to last for any extended period. There will
also likely be off and on rain in Austin and San Antonio overnight
and into the afternoon Sunday. It shouldn`t have much effect on
category. At DRT rain will begin overnight and continue through
the day Sunday.
PREV DISCUSSION... /ISSUED 342 PM CST Sat Dec 3 2016/
SHORT TERM (Tonight through Monday Night)...
Widespread light to moderate rain showers along with a few
thunderstorms continue across most of south central texas this
afternoon. Radar trends do show a slight decrease in this activity
across the Rio Grande plains and southern Edwards Plateau. We do
expect a slight decrease in rainfall this afternoon and evening,
with mainly light rain expected. However, another round of
moderate to locally heavy rainfall is expected beginning late this
evening into early Sunday morning as the upper low over the
central Baja peninsula nudges eastward. As deep layer forcing for
ascent spreads into the region, we expect an increase in coverage
of showers and thunderstorms. A brief lull in the activity is
expected Sunday afternoon before another round of lift moves
through with the main upper low. This should bring another round
of moderate to locally heavy rainfall to the region beginning
Sunday evening and continuing into early Monday morning. Given
saturated soils across the central portion of our area and
expected periods of heavy rainfall through Monday morning, we have
issued a Flash Flood Watch for portions of south central Texas.
The watch extends as far west as Bandera and Medina counties
eastward through the San Antonio metro area into the Highway 77
corridor. Total rainfall amounts of 1 to 2 inches with isolated
amounts up to 4 inches are possible in the watch area from late
tonight into early Monday morning. The main upper low will move
east of the region on Monday and we will see a quick end to the
precipitation from southwest to northeast by early evening.
LONG TERM (Tuesday through Saturday)...
Westerly flow aloft behind the departing upper low along with
sunny skies and northwesterly downslope winds will allow a brief
warming and drying trend to take place on Tuesday. On Wednesday,
we should see enough moisture return to warrant a slight chance
for showers generally along and east of I-35. A weak cold front
along with an increase in cloud cover will also work to knock
temperatures back closer to climatological normals. A much
stronger cold front will move through Wednesday night bringing
gusty north winds and much cooler air to the region. Daytime highs
on Thursday and Friday will likely remain in the 40s to near 50
for most areas. We also expect good potential for a widespread
freeze Thursday night and Friday night across a good portion of
south central Texas. High temperatures are expected to remain
below normal on Saturday.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 48 54 47 58 46 / 100 80 90 60 -
Austin Bergstrom Intl Airport 48 53 47 58 44 / 100 80 90 60 -
New Braunfels Muni Airport 49 53 48 60 45 / 80 90 90 50 -
Burnet Muni Airport 46 51 44 54 43 / 80 70 90 70 -
Del Rio Intl Airport 51 53 47 62 44 / 50 80 80 30 0
Georgetown Muni Airport 47 52 46 55 44 / 100 80 90 70 -
Hondo Muni Airport 50 55 47 62 43 / 40 90 90 30 -
San Marcos Muni Airport 48 54 48 59 45 / 90 90 90 50 -
La Grange - Fayette Regional 49 54 49 58 46 / 90 90 90 50 -
San Antonio Intl Airport 50 54 49 60 47 / 80 90 90 40 -
Stinson Muni Airport 51 55 49 61 46 / 80 90 90 40 -
Flash Flood Watch through late Sunday night for the following
Public Service/Data Collection...Williams
Area Forecast Discussion
National Weather Service Green Bay WI
636 PM CST Sat Dec 3 2016
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Sunday
Issued at 246 PM CST Sat Dec 3 2016
The latest rap analysis and satellite/radar imagery show high
pressure stretching from northern Ontario, across the Great Lakes to
the Gulf Coast early this afternoon. Low clouds have shown little
signs of dissipating so far today, due to a sharp inversion at 850mb
based off the 12z GRB sounding. Still some spotty flurries showing
up on radar, and will keep a mention of flurries to the end of the
afternoon. Looking upstream, light rain and snow is moving northeast
over Nebraska and Kansas early this afternoon ahead of the next
shortwave trough. As this trough moves into the western Great Lakes
on Sunday, snow accumulation potential and impacts are the main
Tonight...High pressure will be sliding to the east as height falls
occur over the northern Plains ahead of the next shortwave. Because
of thermal troughing and a sharp inversion across the state, the low
clouds are going to be tough to dislodge. Minor warm advection does
occur late and models do show low level moisture thinning out after
midnight, but think the low clouds will likely stick around through
the evening. But even if the low clouds break up, mid-clouds will be
arriving from the southwest ahead of the next trough. Moisture
looks to become deep enough for light snow to push into central
Wisconsin after about 3 am which could yield a tenth or two by
daybreak. With the ample cloud cover, increased min temps a couple
Sunday...Light snow will continue to spread northeast across the
region during the morning hours and then continue through the
afternoon. Forcing in the form of isentropic ascent and mid-level
fgen only looks modest, but the shortwave does become negatively
tilted as it swings through the region during the afternoon.
Moisture looks a little more robust over eastern WI than farther
west, but complications arise from having max temps projected to
rise above freezing, partially due to a southeast and south wind
through the day. Thinking is that wind speeds may not be strong
enough to have much of an impact over the Fox Valley, but will
likely have some influence on ptype along the Lakeshore where rain
could mix with snow from the late morning through the afternoon. But
with temps around 33 or 34 in the Fox Valley, think snow will
partially melt on roadways, and that could still create hazardous
travel. Given snow amounts of 2-3 inches from the Fox Valley to
central WI, will issue a winter weather advisory for snow. Amounts
will be less along the lakeshore and also over northern WI.
.LONG TERM...Sunday Night Through Saturday
Issued at 246 PM CST Sat Dec 3 2016
Winter like cold temperatures will arrive by the
middle of the week and continue through the remainder of the
Some light snow will be ending Sunday night as the upper trough
exits the area. The a flat upper ridge moves in for Monday and
Monday night with dry weather. Upper troughs passing by to our
north and south could produce some light snow Tuesday afternoon
or evening but there is not much moisture available, so snow
amounts should be a dusting to an inch.
A sharp upper trough drops south towards the region Wednesday and
moves slowly across the Great lakes Thursday and Friday. Arctic
high pressure builds in as the upper flow becomes northwest bringing
the coldest air of the season to Wisconsin. The air is not expected
to be super cold, just 5 to 10 degrees colder than normal. It will,
however, feel very cold to many people as the weather has been so
mild during the last two months. Snowfall of any significance seems
to be limited to the snowbelt areas in the far north Thursday
night and Friday.
.AVIATION...for 00Z TAF Issuance
Issued at 632 PM CST Sat Dec 3 2016
MVFR ceilings remained across the region early this evening, but
may tend to rise and break up as the evening progresses.
Regardless, conditions will deteriorate Sunday morning as light
snow overspreads the region. Expect the snow to arrive in the
AUW/CWA areas around 12z, and RHI/GRB/ATW/MTW between 14z-16z. The
heaviest snow should occur during the afternoon hours, when IFR
and localized LIFR conditions are likely. The snow should start to
taper off in central WI late Sunday afternoon.
Winter Weather Advisory from 9 AM to 6 PM CST Sunday FOR WIZ031-
Winter Weather Advisory from 6 AM to 6 PM CST Sunday FOR WIZ030-
Area Forecast Discussion
National Weather Service Houston/Galveston TX
707 PM CST Sat Dec 3 2016
Per radar and surface/marine observations, the frontal boundary
continues to sag farther offshore, and the heaviest rain is
currently over our Gulf waters, extending into Southwest
Louisiana. Over land, numerous light to moderate showers are still
falling across the entire area. These showers will continue
through the evening, but we should at least be looking at a brief
respite from the heavy rain this evening into at least the early
That said, multiple convection allowing models fill back in with
more precip over the area after midnight and towards Sunday
morning. Like Saturday, both the boundary near the coast and
(to a lesser extent) farther inland near the 850mb front will be
the foci for precipitation. There is general consensus that the
surface front/coastal trough will be forced back towards shore
some overnight, and if it sets up in a similar spot, we could see
a repeat rain performance. On the plus side, recent runs of the
HRRR seem to be trending to the heaviest rain setting up more
offshore than right on the coast, which would be very welcome.
Regardless, the heavy rain in coastal communities Saturday create
a saturated situation in which lesser rains Sunday still look to
pose flooding problems. And even if the axis of heaviest rain just
misses, rain will fall.
.PREV DISCUSSION... /ISSUED 549 PM CST Sat Dec 3 2016/
Still looking at periods of SHRA/TSRA and associated IFR ceilings and
visibilities overnight and on into tomorrow. Hard to pinpoint the spots
that will have the most impact, but current thinking is that the locations
closest to the coast (LBX and GLS) and offshore might be at the greatest
risk for periods of TSRA while the rest of the area has mostly SHRA.
In the stronger activity, LIFR conditions will be possible. Do not anticipate
significant improvement until Monday and Monday night when this storm
system finally moves off to the east. 42
PREV DISCUSSION... /ISSUED 332 PM CST Sat Dec 3 2016/
Note to users of HGX radar: Rainfall estimates are running 15-40%
too LOW so use w/caution.
Tonight through Monday...
Swath of significant rainfall along the coast today with 3-11"
fallen thru 3pm. Frontal boundary has sagged back offshore, but
just a gradual slope behind it is still allowing some training
heavy rain which will probably continue at the coast this evening.
The next disturbance will move in from the w/sw overnight
spreading another batch of precip across the area and into the
Will maintain the Flash Flood Watch that`s out across the CWA.
That being said, vast majority of folks will see just stratiform
light/moderate rain. Totals will gradually add up thru the weekend
and once grounds become saturated enough...any heavier downpours
will runoff to cause flooding. Highest concern for the next 12-24
hours is Brazoria, Galveston, Chambers and SE Liberty where we`re
already at and above the point of ground saturation. To complicate
things there, higher water/tide levels won`t allow for efficient
Upper trough kicks out of Mexico and across Texas Sun night-Mon
night. Coastal trof & gradient tightens back up near the coast,
and depending on eventual details, may produce a somewhat similar
scenario as we saw last night & this morning. Improving
conditions anticipated beginning Mon night. 47
Tuesday through Saturday night...
Tuesday should be pretty dry and sunny, but rain chances return
to the forecast Wednesday ahead of a cold front that should pass
through SE Texas overnight Wednesday night. Temps will cool off
significantly behind the front with highs on Thursday only
forecast in the 40s and 50s. The northern counties may experience
their first freeze so far this season on Friday morning, and these
freezing temperatures may extend southward into the Houston metro
area. Dry conditions and slowly rebounding temps are expected
through the rest of the period. 11
Areas of rain with embedded thunderstorms continued to occur over
most of the nearshore Gulf waters and Galveston Bay at mid
afternoon. The rain was occurring along a warm frontal boundary that
was nearly stationary just off the immediate coast. Isolated
stronger storms with wind gusts and waterspouts will continue to be
possible into this evening east of the warm frontal boundary.
Periods of rain and embedded thunderstorms will continue through
Sunday night into Monday and end late Monday as the storm system
moves east of the area.
Tidal flooding will continue to be a threat along low-lying areas
at the coast through tonight. Problems may persist into Sunday and
Other impacts expected are advisory conditions due to winds and seas
over the Gulf waters. The pressure gradient weakens slightly tonight
and may lead to diminishing winds; however, seas will probably stay
up at least over the offshore waters tonight. Winds may pick back up
later Sunday into Monday. 40
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 49 54 48 56 45 / 80 90 90 80 10
Houston (IAH) 53 56 50 59 48 / 80 80 90 90 10
Galveston (GLS) 59 61 57 64 56 / 90 90 100 90 10
TX...Flash Flood Watch through Sunday evening for the following
Coastal Flood Advisory until 6 AM CST Sunday for the following
GM...Small Craft Advisory until 7 PM CST this evening for the
following zones: Coastal waters from Freeport to the
Matagorda Ship Channel out 20 NM...Coastal waters from High
Island to Freeport out 20 NM.
Small Craft Advisory until midnight CST tonight for the
following zones: Waters from Freeport to the Matagorda Ship
Channel from 20 to 60 NM...Waters from High Island to
Freeport from 20 to 60 NM.
Area Forecast Discussion
National Weather Service Indianapolis IN
1000 PM EST Sat Dec 3 2016
The Near Term Section has been updated below.
Issued at 205 PM EST Sat Dec 3 2016
High pressure over Indiana will quickly move east exiting the
region but bringing generally quiet weather tonight. A quick
moving upper level weather disturbance will sweep into the Ohio
Valley on Sunday...ahead of a weak cold front. This may bring a
mix of precipitation initially to central Indiana on Sunday
morning...before changing over to all rain during the afternoon.
Another high pressure system will arrive on Sunday night and
Monday...brining a return to dry weather to start the work week.
However...active weather is expected in the week ahead as a pair
of weather systems will push across Indiana during the
week...brining chances for rain and Monday night and Tuesday and
some snow on Wednesday night into Thursday.
.NEAR TERM /Rest of Tonight/...
Issued at 1000 PM EST Sat Dec 3 2016
Radar mosaic and observations show an area of showers and some virga
moving into southwestern Kentucky and southern Illinois. The
northward advancement of anything reaching the ground has been very
slow and hi res models seem to have a pretty good handle on this.
Current runs of the RAP and HRRR don`t bring anything into the area
until 10-11z and then bring echoes slowly into the southwestern
counties. Forecast soundings continue to show some potential for a
rain snow mix at or shortly after onset. This matches nicely with
going forecast and thus will make no appreciable changes at this
time. Previous discussion follows...
Forecast soundings tonight and time height sections continue to
shows a top down type saturation occurring through the night as
the high pressure system departs and the trough and short wave to
the west approach. Thus will keep skies cloudy tonight...and stick
close to a blend on temps.
Forcing associated with the advancing wave may arrive in the
western parts of the forecast area by daybreak. This may result
light precip amounts near 12Z...thus some low chance pops may be
needed...although confidence in a pre 12Z measurement is low.
.SHORT TERM /Sunday through Tuesday/...
Issued at 205 PM EST Sat Dec 3 2016
Active weather is in store for Sunday as both the GFS and NAM
suggest a moderate negatively titled short wave to push into
Illinois and Indiana through the course of the day. Excellent
dynamics aloft appear in place ahead of this system. Additionally
the 295K isentropic surface shows good lift through the day with a
surge of Specific humidities to over 3 g/kg. Forecast soundings
and time height sections also show deep saturation. Thus hopefully
superblend will allow a near 100 pop. Forecast soundings show
lower levels starting the day below or near freezing...thus some
mix in precipitaion type will be possible with the onset as temps
warm through the day due to daytime heating and broad warm air
advection. Given the expected precipitation through the
day...will trend highs cooler than the MAVMOS.
GFS and NAM suggest the upper wave quickly departs on Sunday
evening...and isentropic forcing is shut off. Mid levels show good
subsidence arriving through the night as High pressure is
expected to build at the surface. Cannot rule out a stray
lingering shower across the eastern parts of the forecast area
around 00z-02z as the forcing departs...but for the most
part...precip will be ending and will trend pops toward dry.
High pressure is then expected to settle across the region on
Monday. Forecast soundings remain quite dry with an inversion
aloft and unreachable convective temps. Thus will trend toward a
partly cloudy sky and a blend on Highs.
Next up...the GFS and NAM once again suggest a strong low
pressure system and associated upper wave to sweep out of the
southern plains and push in to the ohio valley on late Monday
night into Tuesday. A similar set-up appears once again within the
forecast soundings...with a top down type saturation. Once again
the 295k Isentropic surface shows excellent lift with specific
humidities over 5 g/kg. Thus again will ramping pops higher than
guidance on Monday Night and Tuesday as these features arrive.
Fortunately the column appears a bit warmer with this second
system...thus precip type should remain all rain.
.LONG TERM /Tuesday night through Saturday night/...
Issued at 205 PM EST Sat Dec 3 2016
Conditions will become dry early in the extended as a system
traversing the Southeast moves farther east. The dry weather will
be short-lived though as a more potent system tracks through
Ontario. As moisture is drawn into this system, precipitation
chances will begin increasing across Central Indiana on Wednesday
night. A cold blast of air accompanying this system could result
in some of the first snow accumulations of the season across the
forecast area from Wednesday night into Thursday. Models continue
to differ on moisture amounts though with the GFS a bit drier than
the Euro. So, this will continue to be monitored over the next
several days for timing and snowfall totals.
.AVIATION /Discussion for 040300z TAF issuance/...
Issued at 905 PM EST Sat Dec 3 2016
Updated current conditions at KIND, and extended time of MVFR
ceilings at KLAF through 4z. Previous discussion follows...
MVFR ceiling at KLAF should rise to VFR over the next hour or two
and then all sites should be VFR through the overnight. Sunday
morning expect to see MVFR ceilings first move in from the west
and then conditions to deteriorate further within a few hours as
saturation occurs through the column and rain commences. There is
some chance of a wintry mix at onset, but the probability of
occurrence and potential amount of time of a mix before a
changeover to rain is low enough to leave out at this time. Began
the precip in the TAFs with VCSH, and this would likely be the
period where mixing could occur. After that strong forcing moves
in and ceilings should drop below IFR along with visibilities
around 1 1/2SM at their worst. Light and variable winds overnight
will remain fairly light Sunday at around 5 kts but will be mainly
out of the southwest during the day.
Area Forecast Discussion
National Weather Service New Orleans LA
959 PM CST Sat Dec 3 2016
Surface analysis indicated a warm front extended near the entire
southern Louisiana coast. A squall line of thunderstorms extended
from north of the boundary over southwest Louisiana, southwestward
into the northwest Gulf of Mexico just ahead of an inverted
trough/elongated surface low pressure system. As the parent upper
level storm system moves slowly east over northwest Mexico, the
squall line is expected to continue moving east towards the
southwest portion of the forecast area after midnight, probably
quite a bit slower than indicated by the convective allowing,
high-resolution HRRR based on current eastward movement of only
The warm front should move slowly inland and approach I-10
sometime late tonight or tomorrow morning. Any thunderstorms that
maintain integrity and exhibit bowing segments could produce a few
strong to severe wind gusts in the 40 to 60 mph range over areas
generally south of I-10 and west/southwest of metro New Orleans
between 2 and 7 am. Regarding heavy/excessive rainfall potential,
most areas of south central and southeast Louisiana and south
Mississippi are still coming out of a drought, and flash flood
guidance is on the high side ranging from 2.5 to 3 inches in 1
hour, 3 to 3.5 inches in 3 hours and 3.5 to 4 inches in 6 hours.
While locally high amounts in these ranges have a chance of
occurring, the risk is not great enough to warrant a flash flood
watch at this time. Since additional heavy rainfall potential is
forecast through Monday, it is possible a flash flood watch could
eventually be issued for portions of the forecast area. Updates
have been issued that now include mention of thunderstorms and
heavy rain potential tonight. 22/TD
Strong east winds in the 20 to 30 knots range have been occurring
on Lake Pontchartrain and Lake Borgne most of this evening, so
upgraded the "Small Craft Exercise Caution" to a "Small Craft
Advisory" with an update earlier, and that advisory is in effect
until midnight tonight. Otherwise, remainder of Coastal Waters
Forecast looked on track at this time. 22/TD
.PREV DISCUSSION... /issued 358 PM CST Sat Dec 3 2016/
Modest isentropic lift underway over a very dry low level column.
some light rain reaching surface with some slow saturation from
top-down taking place. meanwhile, mechanically enhanced baroclinic
zone noted along the texas coast, per radar presentation of very
thin surface base convective band along frontogenetic zone.
Satellite imagery shows large baroclinic leaf structure with jet
streak downstream of large cut-off low. 12Z chart analysis
indicated much stronger jet dynamics occurring on the upstream
side of the low, indicative of much deeper digging of the low to
still occur over the next 24 hours or so. As upper system begins
to eject, the warm sector is expected to surge northward to place
the forecast area squarely in the better surface based instability
region monday. There may some inhibition afforded due to cooler
marine layer, but high helicity storms may be deep enough to
penetrate higher wind gusts and a few funnels that may be capable
of reaching close to the surface immediately ahead of the front.
The ECMWF is faster with the evolution and passage of the surface
low in the late afternoon, whereas the GFS is about 6 hours later.
Best timing does appear to be in the Monday late afternoon and
early evening hours. Next issue will be heavy rain potential, with
storm total QPF amounts coming in generally between 2 to 4 inches
over the northwestern portions of the forecast area, 1 to 2 inches
elsewhere. Area rivers can handle some runoff, but will have to be
monitored over the next few days. Went close to model blends on
temperatures and PoPs, but held off mention of thunder until
Sunday as most weather tonight will be elevated isentropic until
convective instability can deepen much later tonight into sunday
Strong cold front swings through the area Monday night as surface
low lifts into the western Tennessee Valley. Tuesday should be
drier and considerably cooler though the much colder air rushing
into the region on arctic surge Wednesday night. Models showing a
band of precipitation accompanying the front, but the GFS is less
pronounced and faster at flushing out the moisture Thursday, while
the ECMWF actually shows a weak surface low over the northeast
gulf that may maintain wrap-around moisture over the area for much
of Thursday. At this time, will indicate chance PoPs for mainly
Thursday morning. Temperatures are expected to warm very little on
Thursday, perhaps remaining in the 40s most of the day, then
freeze conditions in the interior sections of the area for Friday
morning and again Saturday morning. Another surge of arctic cold
moves in Sunday with a very cold over-running rain anticipated.
Though not calling for it this far out, some patchy sleet may not
be out of the question next Sunday if low level temperatures fail
to modify between systems. More on this later. 24/RR
Most rain remaining just north and west of KMCB and KBTR, with other
terminals dry. Have started to see ceilings lower into the MVFR
category at most terminals in the last hour or so. Expect these
ceilings to continue to lower through the evening with IFR ceilings
possible at most terminals after about 08z. Mesoscale modeling
indicates rain spreading back into the remainder of the area after
about 04z, so could see visibilities reduced below what forecast
currently shows. Little, if any, thunder expected through 18z
Surface ridge located over the upper Mississippi River and low
pressure in northern Mexico will keep moderate persistent easterly
flow with a tight pressure gradient. Thus will keep small craft
advisory going in offshore waters and exercise caution headline over
tidal lakes and Lake Borgne. A gradual reduction in wind speeds will
take place late tonight and Sunday as the sfc low is finally
expected to lift toward the region. Winds will shift to the west and
increase to near small craft Monday night as a cold front associated
with that low pressure moves through. Expect this wind shift to be
brief as the pressure field breaks down before a very strong cold
front marches through Thursday morning. 35
DSS code: Blue.
Activities: Small Craft Advisory. Monitoring convective and heavy
rainfall trends through Monday night.
Decision Support Services (DSS) Code Legend
Green = No weather impacts that require action.
Blue = Long-fused watch, warning, or advisory in effect or
high visibility event.
Yellow = Heightened impacts with short-fused watch, warning or
advisory issuances; radar support.
Orange = High Impacts; Slight to Moderate risk severe; nearby
tropical events; HazMat or other large episodes.
Red = Full engagement for Moderate risk of severe and/or
direct tropical threats; Events of National Significance.
.PRELIMINARY POINT TEMPS/POPS...
MCB 52 62 54 66 / 90 90 70 80
BTR 58 67 57 68 / 80 90 70 80
ASD 61 71 60 70 / 70 70 60 80
MSY 64 73 63 72 / 70 70 60 80
GPT 61 72 61 70 / 70 70 60 80
PQL 59 72 62 71 / 60 80 60 80
GM...Small Craft Advisory until midnight CST tonight for GMZ530-532-
Small Craft Advisory until noon CST Sunday for GMZ555-557-570-
GM...Small Craft Advisory until midnight CST tonight for GMZ532-534-
Small Craft Advisory until noon CST Sunday for GMZ557-570-572-
Area Forecast Discussion
National Weather Service Marquette MI
700 PM EST Sat Dec 3 2016
.SHORT TERM...(This evening through Sunday)
Issued at 322 PM EST SAT DEC 3 2016
12Z raobs/latest wv imagery and RAP analysis show shrtwv rdging
moving e thru the wrn Great Lks and supporting a sfc hi pres rdg
axis stretching fm nw Ontario into WI. Although the larger scale
subsidence/mid lvl drying associated with these feature are
suppressing any larger scale pcpn, some lk effect snow showers
linger under h85 temps arnd -8C and primarily along a lk induced
trof stretching fm the ern cwa acrs scentral Lk Sup and the Keweenaw
into wrn Lk Sup. However, lo subsidence invrn base arnd h85 and near
absence of a dgz within the moist lyr under the invrn base are
limiting the sn intensity. Looking upstream, plenty of lo clds
linger thru MN despite presence of llvl acyc flow. Farther to the w,
there are a pair of shrtwvs of interest. The first is lifting enewd
thru SDakota while the second is out of the Rockies into the
Main fcst concerns in the short term wl focus on pops/qpf on Sun
associated with pair of upstream shrtwvs.
Tngt...As the shrtwv rdg/sfc hi pres rdg axis shift slowly to the
eand allow the gradient flow to shift to the s, expect only some sct
light snow showers to persist along the weak lk induced sfc trof
axis that wl become oriented fm near Isle Royale acrs ecentral Upr
MI and into nrn Lk MI. The wshft to the s in the presence of h85
temps still arnd -7C may result in some weak enhancement off Lk MI.
With considerable lo clds likely to linger thru the ngt over most of
the cwa, opted to raise fcst min temps a couple of degrees. Although
the incrsg downslope s wind later might cause the lo clds to break
up over the far w, the steadier wind and arrival of some waa mid/hi
clds ahead of the first shrtwv moving enewd fm the Plains would tend
to hold temps up there as well.
Sun...The first shrtwv lifting newd fm the Plains is fcst to shear
out and bring mainly just some thickening mid clds as the dynamic
support wl be inadequate to saturate the lingering dry lvls
associated with the rdg axis passing to the e. However, the s wind
btwn the departing sfc hi pres rdg axis and falling mslp to the w wl
still allow for some snow showers psbly mixed with rain to stream
into the ern cwa off Lk MI. During the aftn, the second shrtwv now
moving into the nrn Plains is progged to shift toward the Lower
Great Lks by 00Z Mon. The arrival of some dpva/deep lyr qvector
cnvgc/upr dvgc on the nrn flank of this feature wl allow for a some
steady light snow, primarily over the se half of the cwa closer to
the stronger forcing and where there wl be some lingering
enhancement of the pcpn off Lk MI. Although this pcpn wl fall mainly
as snow except perhaps right near the shore, warming of the sly flow
off the waters that lift temps above 32 wl tend to limit snow accums.
.LONG TERM...(Sunday night through Saturday)
Issued at 322 PM EST SAT DEC 3 2016
Shortwave trough becomes negatively tilted while crossing the Upper
Great Lakes Sun aftn into Sun evening. Sfc-h85 trough crosses Upper
Michigan through this time switching winds from S-SE to W and
providing low-level convergence and lift. Main area of deeper layer
q-vector convergence stays mainly south and that should keep
widespread snow with the system later Sun into Sun night limited to
an inch or two. One exception though as S winds ahead of trough with
h85 temps of -7c would support lake enhanced snow downstream of Lk
Michigan. Similar to what has occurred last couple days with the
lake effect off Lk Superior, sfc temps in the low to mid 30s likely
will lead to rain/snow mix or only rain near the immediate shoreline
of Lk Michigan including at locations such as Manistique and the
east shore of the Garden Peninsula. Just inland where lake enhanced
snow is more widespread, it should be cold enough for mainly snow.
Run total qpf is all over the place over northern Lk Michigan and
into eastern cwa. Higher outliers are the GEM and WRF-ARW which show
totals nearing 0.80 inch late Sun aftn through late Sun night. Low
end values are 0.25-0.35 inches from the GFS and SREF mean. Since
stronger forcing remains south of Upper Michigan and higher qpf
values are very high outliers compared to SREF plumes and NCAR
ensemble qpf, will go more middle of road for qpf on the order of
0.3 to 0.5 inches and go with idea that there could be a few inches
of fresh snow which could result in slippery travel Sun evening on
untreated roads. Think the marginal temps in the mid 30s will
ultimately limit snow accums than what would otherwise occur with
the expected qpf totals. For now will mention this snowfall and
slippery roads in the Hazardous weather outlook.
Snowfall over the east cwa should taper off quickly after midnight
as larger scale q-vector divergence/subsidence and drying moves in
and with sfc winds backing west once the sfc trough exits to east.
Sfc high brings dry weather on Monday though not sure how much
clearing occurs as there could be moisture blo 925mb trapped beneath
subsidence inversion. High temperatures should only rise into the
mid to upper 30s, coolest where southwest winds upslope to the
higher terrain of cntrl Upper Michigan.
Mon night into Tue rather strong shortwave trough slides across
northern Plains and lifts into south central Canada. Sfc low deepens
blo 1000mb. GFS most aggressive in bringing swath of moisture into
Upper Great Lakes ahead of the low and even those soundings look dry
above h85 over all but far west cwa. Soundings do hint at low level
moisture with weak lift which would result in drizzle or freezing
drizzle over the central and east with some added moistening off Lk
Michigan. GFS looks like cold outlier with cold front over central
Upper Michigan by 12z Tue and h85 temps down to -12c over western Lk
Superior while ECMWF and GEM are not even down to -5c. Overall
though the GFS is quicker in bringing colder air in Tue and Tue
night, ECMWF does catch up by Wed and they have similar solutions as
both models keep shortwave trough and strong sfc low over Manitoba
and northern Ontario completely separate and unphased with shortwave
trough and sfc low sliding across the Ohio Valley. Whenever the sfc-
h85 cold front moves through there is some weak deep layer q-vector
convergence shown and there is also hint of another weaker wave
lifting across area along the cold front on Tue night. Otherwise,
large scale subsidence and drying takes hold into Wed as stronger
trough aloft remains over Manitoba and northern Ontario and southern
stream shortwave trough crosses the southwest Conus. Lake effect
during this time will likely be confined mainly to Keweenaw with sfc
to h85 winds from the W or WSW and h85 temps blo -12c as Lk Superior
temps are still 5-6c. Inversion heights around 5kft should limit
intensity of lake effect but could have several inches of fluffy
snow accum since the dgz will be within the lake convective layer.
Deep trough aloft with widespread cold air will continue to occupy
much of the eastern half of the Conus later Wed into Thu. Southern
stream wave should stay far enough southeast of Upper Great Lakes to
prohibit stronger storm to affect the region, though the lower
Michigan could see widespread snow as sfc low lifts across Lower
Great Lakes toward New England. ECMWF more in line with that idea
while GFS keeps system too sheared out to cause much snow until it
reaches northern New England late this week. Back over the Great
Lakes, lake effect snow will be the main story. Areas favored by NW
winds will see the the most snow as h85 temps continue to fall to
around -15c by late Thu into Fri. Sometime late in the week there
will be a reinforcing sfc-h85 cold front that could bring winds to
more N so lake effect could shift around to north flow areas for a
time. Plenty of deep moisture to h7/10kft with large scale trough
overhead so lake effect may be moderate to even heavy depending on
when shortwaves work through to enhance the snow further. Stronger
low-level winds will push snow showers farther inland than normally
seen and since low-level temps will be sufficeiently cold for snow,
should see snow all areas, even near the Great Lakes shorelines.
Lake effect will continue into Sat for NW flow areas, especially
over eastern cwa. Certainly by late next week it will look and feel
more like winter across most of Upper Michigan.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 659 PM EST SAT DEC 3 2016
With sfc high pres ridge shifting e of the area and southerly winds
increasing, a strengthening downslope component to the wind should
allow VFR conditions to prevail at KCMX tonight with KIWD improving
from MVFR to VFR this evening. Meanwhile, at KSAW, VFR conditions
will likely fall back to MVFR overnight as the upsloping southerly
flow taps moisture off Lake Michigan. An approaching disturbance
will spread -sn across Upper MI Sun. Conditions will likely fall to
IFR at KCMX/KSAW in the aftn. At KIWD, while prevailing MVFR
conditions are expected with the -sn, there may be some periods of
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 322 PM EST SAT DEC 3 2016
Expect winds to remain 25 kts or less through Mon as the pres
gradient remains relatively weak. An approaching lo pres trof will
tighten the gradient Mon night/Tue, resulting in sw winds up to 30
kts. There could be some w gales to 35 kts over mainly the ncentral
on Tue night into Wed under the tighter pres gradient on the
southern flank of the deepening lo pres moving into nw Ontario and
with the arrival of colder air that will increase overwater
instability. Depending on how quickly the Ontario lo pres deepens
and how fast it moves away, there could be some nw gales late this
coming week as colder air surges into the Upper Lakes. There is
likely to be some freezing spray as waves build.
Area Forecast Discussion
National Weather Service San Diego CA
800 PM PST Sat Dec 3 2016
Gusty northeast winds will continue tonight near the mountains and
foothills but continue to decrease elsewhere. Under clear skies, it
will be another chilly night where winds stay light, with fair and
warmer weather on Sunday. Cooler with increasing clouds, higher
humidity, and onshore flow early next week. Offshore winds and
warming will follow for the latter half of next week.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Winds have diminished greatly this evening. A post-storm map was
issued recently to highlight the areas of high winds that occurred
over the past two days, as well as a storm summary report.
Hi-res HRRR model is showing brief resurgence of Santa Ana winds
later this evening due to a brief enhancement to the offshore
pressure gradient. These strong winds will again decrease before
daybreak Sunday morning.
Sunday will be a bit warmer with lighter winds region-wide. It will
also be abundantly sunny with high pressure still in control of the
No significant changes were made to the evening forecast update.
...Previous discussion, issued at 1252 PM PST...
Surface pressure gradients were relaxing to the deserts late this
morning, but remained at 6 MBS SW NV to KSAN. Weak onshore gradients
were in place to the lower deserts. Peak wind gust reports were all
under 45 MPH at midday.
It will be another chilly night as the dry air gives up what heat it
gathered today. In some of the sheltered valleys temperatures will
fall to near the freezing mark briefly with patchy frost possible.
Where some winds continue, it will be much more mild.
The wind warning/advisory is no longer in effect since winds have
decreased below advisory strength. The northeast winds are likely to
pick up again locally, later this evening over portions of the Santa
Ana and San Diego County Mountains, with some gusts near or above 45
Strong surface high pressure over the Great Basin will weaken
through Sunday as a cut-off, upper-level low pressure center slips
SE along the west coast of Mexico. This will relax the pressure
gradient across the southland allowing wind to drop off for those
areas that still have wind today. After a sunny and warmer day under
a weak upper-level ridge on Sunday, a broad trough will develop
south across the Rockies and Great Plains. This will turn flow back
onshore with cooler weather and more clouds as the marine layer
By midweek, the surface flow turns back offshore as high pressure
rebuilds over the Great Basin and Rocky Mountains. This will bring
Fair and warmer weather through Friday.
040400Z...Northeast wind gusts of 30 to 40 knots will continue
through early tonight over mountain crests and along coastal
mountain slopes. Local LLWS will occur in the area, along with
strong up/downdrafts. Winds will very slowly decrease tonight.
Otherwise, clear skies and unrestricted vis will prevail through
No hazardous marine weather is expected through Thursday.
Gusty north to northeast winds have continued to weaken this evening
across the region. A minor surge of Santa Ana winds is still likely
to occur later this evening over the Santa Ana Mountains, and
relative humidity will have very poor recovery once again, with near
critical conditions over the Santa Ana Mountains. Therefore the Red
Flag Warning remains in effect for the Santa Ana Mountains/foothills
until 3 AM PST. Conditions will improve Sunday with lighter winds
and slight RH recovery.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Red Flag Warning until 3 AM PST Sunday for Santa Ana Mountains-
Including The Trabuco Ranger District of the Cleveland