Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/08/18

Area Forecast Discussion

National Weather Service Bismarck ND

 949 PM CDT Sat Apr 7 2018

.UPDATE...
Issued at 942 PM CDT Sat Apr 7 2018

The only minor change we made to the late evening update was to
eliminate the mention of freezing drizzle on the leading edge of
precip as it moves into the southwest later tonight. A look at the
latest iterations of mesoscale models precip type indicate all
snow. We populated probIce grids with the latest RAP which
produced 100 percent ice over the southwest through 12 UTC. We do
lose ice on the back edge of precip and there was already a
mention of freezing drizzle Sunday morning in the far southwest.
This still looks possible. A mix of the latest RAP with previous
fcst did expand it east a little farther. However precip moves out
of the far southwest pretty quick in the morning so impacts appear
minimal at this time. Also no changes to snow amounts far
southwest as QPF amounts are negligible by this time.

Updated text products will be sent shortly.

UPDATE Issued at 639 PM CDT Sat Apr 7 2018

Surface low pressure continues to deepen over the northern high
plains in response to an upper level impulse moving through the
northern Rockies. Surface winds from the southeast continue to
increase over southwest North Dakota, which is depicted well with
the afternoon package. Radar reflectivities continue to propagate
quickly through central Montana. Latest iterations of short range
models are fairly consistent with the current PoP forecast but we
did delay the onset of higher pops just a bit in the southwest
late this evening. Otherwise, no significant updates. Populated
latest sensible weather elements and blended to mid-evening
values. Updated text products will be sent shortly.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 219 PM CDT Sat Apr 7 2018

Snowfall potential for tonight into Sunday highlights the short
term forecast.

As has been the trend with the past few late season snow events,
snow ratios have been too high from the consensus of a blended
snow ratio technique approach. Thus, lowered snow ratios
significantly from this consensus to around 9:1 southwest, and
10-12:1 elsewhere. Thus, expecting widespread snowfall amounts of
2-4 inches across the advisory area with the rapidly propagating
band of snow. The CAMS through their 18 UTC iterations support a
delayed onset of the band from west to east tonight into Sunday
morning. Thus, delayed the start time of the Winter Weather
Advisory to 09Z for the Missouri River Valley. The 12Z start time
may be too early across the James River Valley. Life threatening
conditions for newborn livestock are expected. There is a slight
chance of freezing drizzle before the onset of snow, however, any
ice accumulations are expected to be minimal. Precipitation
intensity will decline through the afternoon on Sunday.

.LONG TERM...(Sunday night through Saturday)
Issued at 219 PM CDT Sat Apr 7 2018

A brief and relative moderation in temperatures Tuesday into
Thursday, and a potential late season winter storm for the
Northern Plains late next week and weekend highlight the extended
forecast.

The 12 UTC global suite favors mean upper level ridging across
the Northern Plains Tuesday through Thursday. However, this will
likely result in temperatures still below normal, but, warmer
relative to the recent period of well below normal temperatures.
The warmest day may be Wednesday with mixing associated with a
clipper, where there is a chance of at least getting back to
average highs in the 50s across the southwest and south central.

Thereafter, the 12 UTC global suite continues to favor the
potential for a Colorado Low to possibly impact the Northern
Plains late next week and weekend. Much uncertainty remains as
depicted by the 12 UTC GEFS QPF plumes.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 942 PM CDT Sat Apr 7 2018

VFR conditions to begin the 00Z TAF period. Southeast winds with
gusts of 25-30kts are expected across southwest North Dakota this
evening. Snow with IFR/LIFR conditions will develop across
western North Dakota tonight after 06 UTC, and spread into most of
central North Dakota Sunday morning. Snow will continue, but, the
intensity will decrease Sunday afternoon.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 AM CDT /3 AM MDT/ to 7 PM CDT /6
PM MDT/ Sunday for NDZ009-010-017>021-034-035-046.

Winter Weather Advisory from 1 AM CDT /midnight MDT/ to 7 PM CDT
/6 PM MDT/ Sunday for NDZ031>033-040>045.

Winter Weather Advisory from 7 AM to 10 PM CDT Sunday for NDZ036-
037-047-048-050-051.

&&

$$

UPDATE...TWH
SHORT TERM...PA
LONG TERM...PA
AVIATION...TWH



Area Forecast Discussion

National Weather Service Boston/Norton MA

 1014 PM EDT Sat Apr 7 2018

.SYNOPSIS...
A coastal storm tracking well offshore may bring a brief period
of light snow late tonight and early Sunday to Nantucket.
Otherwise, dry and unseasonably cool weather persists into
Monday. Low pressure will develop off the Carolinas early
Tuesday. Some light rain or even a bit of snow may push across
the region early Tuesday, then a front will push across late
Tuesday or Tuesday night. Another low will quickly move across
Thursday into Thursday night with a chance for showers.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

1015 PM Update...

Latest runs of the HRRR and HRRRX continue to support previous
forecast with precip shield from developing low off NC coast to
just clip Nantucket between 09z-12z. Forecast reflects this
nicely with highest pops during this time period. Ptype appears
to start as rain and then if wet bulb temps are realized
changing over the snow. Duration is very brief along with
marginal temps so not expecting much if any impact. Latest runs
of HRRR and HRRRX keep Cape Cod dry overnight into Sunday
morning.

Otherwise a dry, tranquil night ahead but colder than normal
with temps running about 5-10 degs below avg.

Previous Discussion...

Consensus of global and hi-res guidance keeps frontal wave well
offshore with only impact to Nantucket and possibly the outer
Cape with a period of light snow late tonight and early Sunday.
Guidance supports up to an inch accum for Nantucket, mainly on
non paved surfaces as temps expected to remain just above
freezing. Otherwise, dry and cold conditions with mid/high
clouds moving back across the region this evening before
clearing from the north late tonight.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Sunday...

Light snow over Nantucket and possibly the outer Cape will end
by mid morning, then clearing in the afternoon. Elsewhere,
sunshine will give way to broken cloud cover in the afternoon as
low and mid level moisture increases ahead of approaching mid
level trough. Steep 925-700 mb lapse rates develop in the
afternoon, but moisture is limited. Still, can`t rule out a few
late day snow showers in the interior. Another day with well
below normal temps in the mid 40s, colder higher terrain. Gusty
north winds 20-30 mph will develop over Cape/Islands.

Sunday night...

Clouds and a few snow showers possible in the evening with mid
trough passage, then clearing skies expected. Another surge of
gusty winds will likely develop over Cape/Islands with the
trough passage. Unseasonably cold temps for the 2nd week of
April with lows upper teens to mid 20s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Overview...

The overall pattern does not change too much through most of
the long term period as cold H5 cutoff low pressure will spin
from Hudson Bay across Quebec through most of next week. Noting
the storm track remains across the northern tier states. Lowered
H5 heights forecast to remain across the region through at
least Wed night or Thu. 12Z model suite and ensembles signaling
cold pool/long wave trough sinking across the Rockies into the
western Plains states by around Friday, which could mean a
responding ridge building across the mid and upper Mississippi
valley into the Great Lakes.

Temperatures will remain well below seasonal normals through
Tuesday, then could see some gradual moderation around Thursday
or Friday though readings could still be a few degrees either
side of normal for mid April.

Details...

Monday...
High pressure will push off the mid Atlantic coast during
Monday, but W-NW wind flow will keep temperatures around 10
degrees below seasonal normals for early April. Clouds will push
into western areas during the afternoon.

Monday night through Tuesday night...
12Z guidance signal low pressure moving off the Carolina coast,
further S than depicted in previous model runs, and pushing it
NE well offshore. This will keep the bulk of the precip offshore
during this timeframe, though may see some of the northern
fringe push into S coastal areas during Tuesday.

A weak H5 short wave in the northern stream flow may bring some
light precip, possibly a mix of rain/snow mainly across the
higher inland terrain after midnight Monday night into early
Tuesday morning. The short wave is moisture starved, with less
than 0.1 inches of precip expected. The low then moves steadily
to the central Atlantic Tuesday night with improving conditions.

Wednesday and Thursday...
High pressure builds from New England southwestward across the
Ohio and Tennessee valleys to the lower Mississippi valley
Wednesday which will slowly sink S during the day. Another fast
moving system crosses southern Canada and the Great Lakes Wed
night/Thu, though noting widening model solution spread so
timing and track are in question. At this point, have the best
chance for showers, possibly some mixed rain/snow showers at the
onset late Wed night across the E slopes of the Berkshires and
CT valley, changing to all rain by mid morning Thu. Will
probably see 0.1 inches or less once again with this system.

Friday and Saturday...
Rather low confidence with sensible weather as fast flow aloft
continues. At this point, may see dry conditions during Friday
as temperatures may run close to or slightly below seasonal
normals. Strong low pressure may develop across the central or
northern Plains states Fri night or Sat, with a front trying to
extend to the mid Atlantic states. High pressure nosing out of
northern Quebec may keep dry conditions in place into Friday
night. With the fast flow, could see a few showers sneak in late
Fri night or Sat, but timing is uncertain.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Sunday Night/...High confidence.

1015 PM update...

Latest runs from HRRR and HRRRX support previous TAFs with
precip impacting ACK 09z-12z, likely beginning as rain and then
mixing with or changing to snow before ending around 12z. Given
fairly light precip intensity and marginal temps not expecting
much if any impact. Cape Cod may remain dry with precip shield
remaining just offshore.  Earlier discussion below.

===============================================================

Tonight...
VFR, except area of snow will likely clip ACK with MVFR and
possibly brief IFR conditions 09Z-12Z.

Sunday...
Brief MVFR/IFR in snow early over ACK, otherwise VFR. Cigs
around 5K ft developing in the afternoon. A few snow showers
possible late. North wind gusts to 25 kt developing over outer
Cape/Islands.

Sunday night...
Mainly VFR. A few evening snow showers possible.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...Moderate confidence.

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday: Mainly VFR, with areas MVFR possible. Slight chance
RA, slight chance SHRA.

Tuesday Night: Mainly VFR, with local MVFR possible. Slight
chance SHRA.

Wednesday: VFR.

Wednesday Night: Mainly VFR, with local MVFR possible.

Thursday: Mainly MVFR, with areas VFR possible. Breezy. Chance
SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Sunday Night/...

Through Sunday...
N winds increasing late tonight and especially Sunday behind
departing coastal storm. Gusts to 25 kt, strongest over waters
south and east of Cape Cod. SCA for outer waters and nearshore
waters around Cape Cod.

Sunday night...
Another surge of gusty NW winds to 25 kt expected behind mid
level trough passage.

Outlook /Monday through Thursday/...Moderate Confidence.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Tuesday: Winds less than 25 kt. Slight chance of rain, slight
chance of rain showers.

Tuesday Night: Winds less than 25 kt. Slight chance of rain
showers.

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft.

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM Sunday to 8 AM EDT Monday for
     ANZ231-232.
     Small Craft Advisory until 4 AM EDT Sunday for ANZ235.
     Small Craft Advisory from 6 AM Sunday to 8 AM EDT Monday for
     ANZ250.
     Small Craft Advisory until 8 AM EDT Monday for ANZ254>256.

&&

$$
SYNOPSIS...KJC/EVT
NEAR TERM...KJC/Nocera/EVT
SHORT TERM...KJC
LONG TERM...EVT
AVIATION...KJC/Nocera/EVT
MARINE...KJC/EVT



Area Forecast Discussion

National Weather Service State College PA

 1157 PM EDT Sat Apr 7 2018

.SYNOPSIS...
Unseasonably cold weather for early April will continue
through early in the upcoming week. Temperatures are projected
to trend upward to more seasonable, Spring levels during the
latter half of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Western edge of altostratus deck associated with coastal low continues
to skirt southeast Pa late this evening, while mostly clear
skies noted across most of the forecast area.

Skies should eventually become clear across the southeast
counties, while a shortwave diving across the lower Grt Lks
will spread increasing clouds into the Allegheny Plateau later
tonight, with perhaps a few snow showers/flurries over the
northwest counties toward dawn.

Mostly clear skies and a light wind will allow temperatures
to fall steadily late this evening, resulting in another very
cold night for early April. Lingering snow cover will likely
assist radiational cooling over the Allegheny Plateau, where
readings should dip to the mid and upper teens before leveling
off upon arrival of clouds late. Elsewhere, lows expected in the
low to mid 20s.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Scattered lake effect snow showers across the northwest
mountains during the morning hours should give way to scattered,
cellular type snow showers/flurries by afternoon, the result of
diurnal heating and cold temps aloft. Have placed the highest
POPS of around 40 pct across the northwest mountains, with a
diminishing chance of measurable precip southeast (downwind) of
the mountains. For most of the area, Sunday will be a dry and
unseasonably cold day with a good deal of cu/stratocu across
central and northern Pa and partly sunny skies over southeast
Pa.

Model 800mb temps support max temps no better than the low 30s
in the northwest, to the low and mid 40s across the southeast
counties.

A brief period of clearing is expected Sunday evening, as
cooling boundary layer results in diminishing cu/stratocu.
However, clouds will increase late Sunday night ahead of the
next weather system spreading light snow across the Upper
Midwest and an inverted sfc trough extending NE up the Ohio
River Valley. Some patchy light snow is possible across the
Laurel Highlands toward daybreak Monday.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Models still indicating some sort of boundary lingering across
PA with a weak short-wave bringing chance precipitation as snow
in the morning then changing to chance rain in the afternoon.
Likely pops for snow in the Laurels in the a.m. Very low chance
POPs in the far eastern counties. Precipitation amounts will be
very light.

Colder than normal air remains in place under a broad upper
level trough with short-waves (shots of energy) rotating through
every 18 hours or so. Hence a limited (coverage) light snow
potential lingering through the colder overnight hours changing
to chances of rain as temperatures warm into the afternoon. This
pattern breaks for a bit by Wednesday morning as a high pressure
surface ridge builds across. With some sun across south-central
PA temperatures will get into the mid 50s.

Model differences begin to increase with the handling of the
next storm system into Thursday regarding the timing and track
of the low to our north. This should eventually bring milder
more seasonable air into central PA but continue the chances
for showers right into the weekend.

&&

.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
VFR conditions continue across central Pennsylvania airfields
tonight. Expect VFR conditions to persist through the TAF
period in all areas except the Northwest Mountains, including
KBFD. There, a shortwave will dive down from the north and bring
MVFR ceilings and some light snow showers beginning between 10z
and 12z. Short range ensembles support the idea of ceilings
between 1k and 3k feet well into the afternoon. Latest HRRR also
suggests that light scattered snow showers will continue into
the afternoon across the far north.

Northwest winds will continue to slacken overnight, but are
expected to again pick up and become gusty Sunday afternoon,
beginning between 14z and 18z.

Next set of fast moving systems will spread some light snow to
the north, and a snow/rain mix to the south, beginning Monday
afternoon, and keep conditions unsettled into Tuesday.

Outlook...

Sun - early Monday...Mainly VFR. Breezy.

Mon afternoon - Tue...MVFR and IFR possible in snow (north) and
rain/snow showers (south).

Wed...VFR.

Thu...Restrictions in SHRA and SHSN.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Lambert
LONG TERM...Watson/Steinbugl
AVIATION...Jung




Area Forecast Discussion

National Weather Service Sioux Falls SD

 1037 PM CDT Sat Apr 7 2018

.UPDATE...
Issued at 919 PM CDT Sat Apr 7 2018

Updated PoPs and QPF for Sunday`s snow event. Latest guidance
suggests that snow should come in quickly by daybreak Sunday.
There is still a bit of dry air to overcome, initially, but once
that happens a progressive but intense band of moderate snow
should move northeast.

Latest RAP and 00Z NAM also have trended slightly deeper and
further south with the 500 mb wave as it pivots over eastern SD
later this afternoon. This in return may keep the 850mb low
slightly further southwest than initially thought, pulling snow a
bit further southwest as well.

Adjusting QPF and trimming back snow ratios to account for
temperatures and ground melting still results in a boost of about
an inch of snow along the southern periphery of the advisory. So
expanded the advisory to cover areas with the best potential for
3+ inches of snow.

Will need to monitor trends of the GFS/EC, but could see snow/QPF amounts
over the Buffalo Ridge areas boosted slightly further given
trends of a deeper and more dynamic system.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 354 PM CDT Sat Apr 7 2018

Main focus in the closer term is still the spring storm system
moving through late tonight through Sunday night. By late tonight, a
short wave will have entered the western Dakotas. This wave moves
rapidly eastward on Sunday, with 700-500mb QG forcing showing a bulk
of the wave moving across the northern half of the forecast area. At
the surface and lower levels, winds will become southerly tonight
with an increasing low level jet which will help to rapidly saturate
the lower levels. In fact, it still looks as though from the
humidity time sections and soundings that saturation occurs very
quickly, nothing subtle or gradual about it. The low level jet
increases to 40 to 45 knots late tonight and Sunday morning which is
coincident with a tight surface pressure gradient. Therefore
concerning winds, increased speeds in these locations a good 5 knots
over consensus winds producing 25 to 35 mph values before decreasing
through the afternoon on Sunday. The increasing wind will impact
lows tonight too, putting the break on falling temperatures after
midnight. Therefore mainly used consensus raw model values for lows
instead of MOS type values which keeps readings more mild than MOS.

Back to the system, mid level frontogenesis is initially quite strong
and moves eastward along the belt of QG forcing. Therefore a band of
snowfall will rapid develop first in our far western zones late
tonight, then moving eastward across the area on Sunday. Did slow
down the timing of when the precip begins east of I 29 a few hours
on Sunday based on the latest short range models and cams. After the
initial surge of deep saturation associated with the frontogenesis,
QG forcing and low level jet, the mid levels begin to dry out from
west to east on Sunday, except across our far northern and eastern
zones. For ice introduction probabilities to create snow, used a
consensus of the NAM and GFS relative humidity field from 700-600mb
and lowered the prob ice accordingly when this layer dried out.
Therefore mentioned freezing drizzle/drizzle mixed with the snow
whenever and where this layer dried out. Opted this time for the
drizzle mention instead of rain because most of the QPF with this
system is based on snowfall. Therefore any wintry mix that falls
will be extremely light. Concerning highs on Sunday, altered
previous readings very little. There is a chance that our southwest
zones toward south central SD may warm up more than forecast if they
clear out more than anticipated.

For Sunday night, the primary wave deepens a fair amount in our
eastern zones with another short wave on its heels moving into the
central Dakotas. Because of the deepening wave, saturation depth
remains stubbornly high during the evening hours for locations east
of I 29, arching back toward Brookings. Robust PV continues to
linger in the 700-600mb layer in our east and far north, so
therefore raised pops in these areas above superblend values, at
least early in the evening. All told, have 3 to 6 inches of snowfall
along and east of a Huron, to Sioux Falls, to Storm Lake IA line,
and thus put out a winter weather advisory for snow and windy
conditions for these locations. It was tempting to shorten up the
ending time of the headline for east of I 29 in our zones. However
light freezing drizzle could be a threat for those areas with
saturation still running through the lowest 3km. But this is
something to keep an eye on with future forecasts is the ending time
of the headline.

.LONG TERM...(Monday through Saturday)
Issued at 354 PM CDT Sat Apr 7 2018

On Monday, the GFS was a bit of an outlier in keeping some light
flurries in place east of the James River valley due to very cold
air aloft. However kept out of the grids for now since no other
solution was showing that potential. But something to keep an eye
on. In addition, cooled highs a little on Monday across the areas
where three or more inches of snow cover are expected on Sunday.

Then finally in the middle of the week we get more of a Pacific
dominated air mass. Raised highs across the southern half of our
forecast area on Wednesday given the GFS and ECMWF 850mb
temperatures. Would not rule out 60 to 65 in our far south. Also
raised highs a little bit for northwest IA and extreme southeast SD
on Thursday, but less so then we did on Wednesday. On Friday, there
is still one heck of a strong storm moving out into the plains, and
there is actually pretty good consensus between the deterministic
GFS and ECMWF in tracking the upper low northeastward from western
Nebraska to central and eastern SD Friday and Friday night. It will
be very windy on the backside of the surface low beginning Friday
night and into Saturday. Best precipitation chances are at this time
sketchy at best. Taken literally, our forecast area here would get a
healthy dose of a dry slot on Friday and Friday evening but of
course things will change.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1035 PM CDT Sat Apr 7 2018

Mid-level clouds gradually arrive after midnight as snow begins to
develop to our west. A burst of moderate snow will move through
the terminals during the morning hours, dropping visibilities and
ceilings to IFR levels.

The afternoon remains more uncertain however. Feel that FSD/HON
should remain with continued light snow or perhaps drizzle into
the early evening. Sioux City remains more uncertain with low
confidence in the TAF groupings beyond 18Z.

MVFR to IFR ceilings will persist into the evening hours.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 7 AM Sunday to 1 AM CDT Monday for
     SDZ038>040-053>056-061-062-067.

MN...Winter Weather Advisory from 7 AM Sunday to 7 AM CDT Monday for
     MNZ071-072-080-081-089-090-097-098.

IA...Winter Weather Advisory from 7 AM Sunday to 7 AM CDT Monday for
     IAZ001>003-012>014-021-022.

NE...None.
&&

$$

UPDATE...Dux
SHORT TERM...MJ
LONG TERM...MJ
AVIATION...Dux



Area Forecast Discussion

National Weather Service Wilmington NC

 958 PM EDT Sat Apr 7 2018

.SYNOPSIS...
Low pressure will move offshore overnight dragging a strong cold
front with it. Weak high pressure will follow, bringing chilly
temperatures to the area Sunday. Slowly developing low pressure
offshore will bring rain Monday and Monday night, possibly
lingering into Tuesday. Below normal temperatures are expected
for the first half of the week with dry weather returning by
Wednesday. Above normal temperatures are expected to develop
late in the week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 930 PM Saturday...Dual fronts across the area have merged
as weak low pressure moves offshore. Based off latest surface
obs, center of the low is likely right along the southern Grand
Strand, and will eject NE during the next few hours. As this
occurs, the primary cold front is sinking southward, and clearly
evident both via obs and on radar imagery. The weaker front,
which was responsible for the line of stronger showers earlier,
is being overtaken by this primary front and the undercutting
cold air is weakening the rain rates. This is expected to
continue, and the current area of rain along the SC coast is
expected to advect east and come to an end around midnight.

Two things will occur as this front moves offshore. The first is
the advection of cold dry air on gusty north winds. This is
occurring already across the northern half of the CWA, with
hourly temp drops of up to 10 degrees likely immediately behind
the front. This occurs as 850mb temps plummet as well, and are
forecast to fall to below 0C on Sunday. It is surprising that
MOS numbers are so warm tonight, the European the exception, and
this is likely due to forecast soundings predicting continued
cloud cover much of the overnight. Upstream obs already in the
low 30s near the VA/NC line, so have hedged mins downward a bit
from inherited, and am quite a bit cooler than most numerical
guidance, again the Euro excluded. Expect mins to fall into the
upper 30s NC, low 40s SC, with continued winds preventing any
frost, but producing wind chills around 30 degrees.

The aforementioned cloud cover may persist as the second item of
note occurs. High-res guidance, including the HRRR and SPC HREF
members depict a secondary area of showers currently across
upstate SC moving overhead between 1am and 5am. This occurs
beneath a strong vort impulse, and with soundings remaining
saturated expect renewed shower activity is likely. Despite
saturating, forcing is weak and instability is nil, so just some
very light rain is forecast overnight with a few hundredths of
an inch of QPF possible. Despite falling temps, no freezing or
frozen precip is forecast. Relevant portion of previous
discussion below:

As of 315 PM Saturday...Lingering morning clouds along the
coast should quickly move offshore Sunday morning with mostly
sunny skies expected during the day. Some warm advection cirrus
could appear in the sky late in the day ahead of the Monday-
Tuesday storm system, but not enough to spoil a nice day. The
incoming airmass is very chilly with 850 mb temps expected to
settle in the 0C to -2C range, not quite record values but
certainly among the coldest 10 percent of climatological values
for this time of year. Highs only 55-60.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
As of 315 PM Saturday...850mb winds veer sharply and increase in speed
Sunday night, going perpendicular to isotherms. The surge of
isentropic lift will yield rapidly increasing clouds. Low
temperature forecast is rather interesting: at the surface the flow
remains easterly making it difficult for warm advection to be
realized at the surface and so expect another night with lows near
40, roughly 10 degrees below climatology over northern zones.
Southern zones will be underneath the strong baroclinicity and
should tap into some of the milder air. Nighttime lows will be
closer to seasonable across a good part of SC counties. On Monday a
tight area of low pressure moves up the coast. It will remain
offshore preventing the area from seeing any of the warm sector and
thus likely precluding thunder. However the continued isentropic
lift atop the surface-based northeasterly wedge flow could lead to
an appreciable rainfall over much of the area (locales further east
more preferentially). This quick shot of heavy rain will end by
evening as the low passes by and the upglide and warm advection both
shut off. The cool advection is rather weak and plenty of clouds
appear to linger, both favoring a fairly seasonable night.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 315 PM Saturday...GFS has trended slower with progression
of the coastal low off the Carolinas. This trend puts the GFS
in a position similar to yesterday`s ECMWF, but is still faster
in the end. As a result opted to carry POPs through Tuesday.
Highest POPs and QPF will be found along the coast. High
pressure will move across the area during Wednesday and setup
off the coast for Thursday creating weak return flow. The GFS
had shown a boundary attempting to push southward into the area
before dissipating and lift north, but the latest run halts it
farther north. If this front does in fact stay farther north
then the warm temperatures for Thursday appear legit. Continued
return flow Friday into Saturday support above normal
temperatures. Rainfall chances increasing very late in the
period as the next front approaches.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
As of 00Z...Cold front dropping south, at the moment, extends
from Wilmington westward across Aynor to Effingham. The heaviest
pcpn is ahead of the front. Once the front drops thru, the
convective showery nature of the pcpn will become more
stratiform with light rain or drizzle dominating thru 08z
inland, and to 10Z at the coast. Also after FROPA, convective
type cloudiness will transition to a low stratus deck, sub 1k
feet. Between 10Z thru 14Z, the low stratus deck will break up
as drier air infiltrates at all levels of the atm. Will have
enough moisture in the low levels for a sct possibly bkn cold
air advection cu/sc deck in the 3500-5000 ft range.

Winds after the CFP will become NNE at 15g25 kt on average. This
the result of the low off the NC Coast intensifying while
accelerating off to the ENE, away from the U.S. East Coast. The
gustiness in the wind fields will drop off around 18Z Sun,
followed by the sustained winds dropping below 10 kt during Sun
aftn and possibly decoupling altogether by the end of this fcst
period as the center of the sfc high moves overhead.

Extended outlook...Sun Night VFR becoming MVFR by daybreak Mon.
For Mon into Mon night MVFR with possible IFR conditions due to
quick moving low pressure that passes south of the FA. For Tue
thru Thu Mainly VFR.

&&

.MARINE...
NEAR TERM /THROUGH SUNDAY/...
As of 930 PM Saturday...Cold front sagging southward across the
waters will stall briefly as an area of low pressure moves
overhead through midnight. Although the forecast surge of
northerly winds has begun across the northern waters, it will
still take several hours for all waters to experience the
rapidly increasing north winds, reaching 20-30 kts with gale
force gusts. As this occurs, seas will climb from current 2-4
ft, to 4-6 ft, and perhaps as high as 7 ft or more near the 20nm
boundary of AMZ250 and AMZ252. The current strong SCA remains in
effect for all waters through Sunday. Relevant portion of
previous discussion below:

As of 315 PM Saturday...High pressure should build in from the
west Sunday with diminishing winds and improving wave heights
during the day.

SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 315 PM Saturday...Some uncertainty for the short term as to
whether or not headlines will be needed again. Sunday night begins
with light onshore3 flow with high pressure over NY/PA and a weak
developing low over Florida/GOMEX. The latter is what will modulate
how much conditions deteriorate. Some guidance has the low quite
compact and close to shore and would hint that conditions could ramp
up to SCEC levels. However this solution is becoming an outlier and
the low may end up farther from shore (and weaker and slower)
precluding quite the gradient pinch implied by current forecast.
Monday night will bring NE winds on the backside of the departing
low and short period wind waves, and no headlines.

LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 315 PM Saturday...Low pressure is progged to be east of
the Carolinas Tuesday morning, helping to maintain a northerly
wind across the adjacent coastal waters. As the low lifts
farther northeast and east during the day winds will diminish
and seas begin to subside. Light/variable winds late Tuesday night
into Wed will eventually become southwesterly as high pressure
sets up farther offshore. Although speeds are expected to increase
during Thursday Small Craft conditions do not appear likely at this
time. Seas will be highest Tuesday morning in the northerly fetch,
then become quite benign Tuesday night into Wednesday. Seas will
build some in the southwest fetch during Thursday.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory until 2 PM EDT Sunday for AMZ250-252-254-
     256.

&&

$$
SYNOPSIS...JDW
NEAR TERM...TRA/JDW
SHORT TERM...MBB
LONG TERM...SRP
AVIATION...DCH
MARINE...



Area Forecast Discussion

National Weather Service Topeka KS

 1105 PM CDT Sat Apr 7 2018

...AVIATION UPDATE...

.SHORT TERM...(This evening through Sunday)
Issued at 223 PM CDT Sat Apr 7 2018

As of 20Z Saturday afternoon northwest mid-level flow remains
across the central Plains with troughing in the east and ridging
in the west. A mid-level low was encroaching the Pacific
northwest coast, west of the ridge. At a surface, a broad ridge
stretched from southern Canada to the US/Mexico border. As a
result light winds and sunny skies will continue through the
afternoon and evening. Transitioning into tonight, the surface
ridge will push east of the region after 06Z allowing southerly
flow and WAA to overspread central and western KS. The best WAA
and associated isentropic ascent look to hold off until after 12Z.
Precipitation onset times will be tricky as meager boundary layer
moisture and modest ascent will reside across the CWA. As the
aforementioned shortwave traverses the central Plains during the
late morning and afternoon, expect the precipitation field to
expand, especially along and north the KS/NE border where better
large scale ascent looks to reside. For precipitation types,
NAM/GFS forecast soundings suggest sufficient saturation within
the DGZ for ice to be introduced within the column. Max Tw aloft
values from the NAM and GFS look to remain at or below 0C,
limiting the potential for sleet. Therefore, expect predominately
rain and/or snow. As WAA continues to overspread the region from
southwest to northeast through the afternoon expect all
precipitation to transition to all rain as sfc temperatures warm
into the 40s to near 50. The trough will exit the region Sunday
evening, ending all precipitation from west to east late Sunday
afternoon and evening. QPF amounts look to remain light with only
a few hundredths. Snowfall amounts look to remain at a trace to
maybe as much as a 1/2 inch, with the highest amounts along the
KS/NE border.

.LONG TERM...(Sunday night through Saturday)
Issued at 223 PM CDT Sat Apr 7 2018

Transitioning into the extended period, a secondary weak shortwave
trough is progged to traverse the central Plains on Monday,
reinforcing the northwest mid-level flow. Precipitation chances
also return Monday with thermal profiles suggesting a
predominately rain solution, although a brief wintry mix is
possible in north central KS Monday morning. Spring-like
temperatures look to return by midweek next week as mid-level
ridging and southerly surface flow overspread the region. H85
temperatures are progged to approach 20C, yielding high
temperatures in the 70s to low 80s Wednesday/Thursday/Friday. We
then turn our attention to the next strong mid-level trough
progged to encroach the region by late next week. Shower and
thunderstorm chances are highly dependent on the timing of the
trough passage. Fire weather may become the biggest concern
Friday afternoon behind the dry line/differential mixing boundary
as the GFS and ECMWF both have the boundary within or east of the
CWA.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday)
Issued at 1105 PM CDT Sat Apr 7 2018

The 00Z NAM has trended more towards the RAP and GFS ideas of dry
air in the boundary layer into the mid morning hours. As a result,
precip initiation may hold off until the low level dry air is
overcome closer to noon or the early afternoon. By this time,
temps are forecast to be above freezing at the terminals. There is
some uncertainty in temps however as the NAM forecast soundings
remain cooler than the RAP or GFS and are suggestive of some wet
snowflakes. Think VFR conditions will persist through the night
with MVFR conditions more likely with the precip in the second
half of the forecast period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Baerg
LONG TERM...Baerg
AVIATION...Wolters