Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/20/18
Area Forecast Discussion
National Weather Service Charleston SC
1001 PM EST Wed Dec 19 2018
.SYNOPSIS...
A strong storm system will bring multiple impacts to our area
tonight into Friday. High pressure is forecast to return this
weekend and persist through early next week.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
The current forecast is on track and only required minor
adjustments.
Inland high pressure will hold firm as low- level jetting begins
to strengthen across the Southeast U.S. ahead a phased longwave
trough extending north to south across the central states.
Isentropic assent will rapidly intensity after midnight with
moisture gradually working from the top down reaching near
saturation for most areas by daybreak. Expect a good portion of
the forecast area will be seeing rain by sunrise Thursday and
pops reflect this trend with going to 90-100% by 20/12z. Lows
from the upper 40s inland to the mid 50s at the beaches look on
track.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday: The mid-levels will consists of a trough axis stretching
along the MS Valley in the morning. The trough will shift eastward
and continue to amplify as time progresses. A weak low may develop
at the base of the trough, roughly over the Southeast overnight. At
the surface, a storm system will be developing to our southwest in
the morning. Low pressure initially over or near the FL Panhandle in
the morning will move northeastward and split into two separate lows.
One will be located just to our west late at night while the other
will be located/developing over the Eastern Great Lakes region. A
complex series of fronts will be associated with these lows. Plenty
of moisture will be across our area. Models still hint at PWATs
peaking ~1.75", which is 2-3 standard deviations above normal per
NAEFS. With good moisture and lift in place, POPs are at 100%.
Moderate rain is expected during the daylight hours. Most locations
should expect 1.5-2.0" of rain through Thursday night. Though,
locally some >2" amounts are possible, especially across the
Charleston Tri- County area. Precipitation will begin to taper
off in the evening, with remnant showers persisting overnight.
Temperatures will remain a few degrees above normal within the
warm air mass.
Tides: Moderate rainfall with the Thursday morning and afternoon
high tides could cause drainage issues. However, the strongest
onshore winds in the afternoon are expected to be with the lower of
the two high tides, limiting the potential for flooding from
saltwater inundation. Winds parallel the coast with the daybreak
Friday high tide, so it`s still too early to determine the flood
potential with that tide.
Friday: The mid-levels will consist of a strong trough stretching
from the Great Lakes region into the Southeast during the morning
hours. The trough will move eastward with time and become negatively
tilted. At the surface, the strongest portion of the storm system
will be far to our northeast. However, the second low initially to
our west early in the morning will quickly move to the northeast
with time. Gulf Coast high pressure will begin building into the
Southeast overnight. Wrap around precipitation associated with the
departing low should gradually wind down during the daytime. QPF
shouldn`t add up to much. Dry conditions should prevail overnight.
Temperatures will be near normal.
Winds: Southwest winds should be gusty in the afternoon, especially
along the coast. A wind advisory may be needed, especially for the
Charleston County coastline. Impacts may be more noticeable with the
saturated ground. Winds will increase over Lake Moultrie Friday
and could reach Lake Wind Advisory criteria with 25 knot gusts.
Saturday: The mid-levels will consist of a negatively tilted trough
moving off the coast, allowing zonal flow to develop over the
Southeast into the afternoon. At the surface, broad high pressure
initially over the northeastern Gulf of Mexico will move towards the
Southeastern U.S. Dry conditions will prevail. Temperatures may
be a few degrees below normal.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Cooler and dry conditions expected to prevail this period with high
pressure generally dominating. Temperatures should be near to above
normal.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
VFR conditions will steadily deteriorate closer to daybreak and
continue through the day as widespread rains impact the region.
Expect widespread IFR vsbys and MVFR Cigs to prevail after
sunrise with gusty winds impacting both terminals. Gusts in
excess of 25 kts are possible. There is a potential for low-
level wind shear during the afternoon, but the situation looks
to marginal to include a mention for the 00z TAF cycle.
Extended Aviation Outlook: A storm system will bring flight
restrictions late Thursday through Friday. Gusty winds likely late
Thursday through Friday night. VFR Saturday through Monday.
&&
.MARINE...
Tonight: Fairly weak winds expected this evening, then rapidly
strengthening SE winds late tonight as surface low pressure
moves into south central GA. Winds and seas expected to be just
shy of Small Craft Advisory criteria in the GA waters around
daybreak Thursday.
Thursday through Monday: Both the NAM and GFS wind have
increased across the Charleston County waters to justify a Gale
Watch. Interestingly, the GFS shows several 50 kt wind barbs
over the Georgia offshore waters closer to the Gulf Stream.
Unclear if this will occur or not, but a nasty wind signature in
noted in both the GFS and NAM.
A storm system will bring impacts to our area Thursday into
Friday, causing high winds and seas. Models indicate a short
window of Gale Conditions are possible for the GA waters beyond
20 nm Thursday afternoon into evening. For simplicity with the
marine headlines, we opted to only go with a Gale Watch with
this zone. For all of the remaining waters within 20 nm, we have
Small Craft Advisories for winds and seas starting Thursday. A
second surge of winds/seas is expected Friday morning into
evening for all of the coastal waters. Gale conditions seem
likely, but it`s still too early to issue Gale Watches to cover
this time period. Very steep wind- driven seas could peak above
10 ft beyond 10 nm and around 15 ft across the outermost portion
of the outer GA waters. Additionally, the Charleston Harbor
will have periods of at least Small Craft Advisory wind gusts
Thursday evening into Friday. However, there is still enough
uncertainty in the start time to warrant holding off on an
advisory at this time. Winds and seas will trend downward Friday
night into Saturday as the storm system moves away.
&&
.HYDROLOGY...
High resolution guidance is coming into better agreement that a
period of heavy rain will impact mainly Southeast South Carolina
Thursday afternoon through mid-evening, clearing the Charleston
Tri-County area last. Both the RAP and H3R show what appears to
be a nasty line of highly forced convection moving northeast
across the Charleston Tri-County mid-late afternoon as high tide
is peaking. Although tides are expected to remain well below
advisory thresholds, heavy rains falling a few hours either side
of high tide usually causes problems, especially in wet regimes
such as the one the region is currently in. CPC soil mositure
analysis shows soil moisture values are running roughly 600% of
normal for this time of year across the quad-county area. 1-hr
and 3-hr flash flood guidance values are as low as 2.2 inches in
places, which could be easily overcome in pockets of heavier
rainfall. A Flash Flood Watch has been issued for Charleston,
Berkeley, Dorchester and Colleton Counties for Thursday from
noon until 11 PM EST.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Flash Flood Watch from Thursday afternoon through Thursday
evening for SCZ043>045-049-050-052.
MARINE...Small Craft Advisory from 10 AM Thursday to 1 PM EST Saturday
for AMZ352.
Gale Watch from Thursday afternoon through late Thursday night
for AMZ350.
Small Craft Advisory from 7 AM Thursday to 1 PM EST Saturday
for AMZ354.
Gale Watch from 7 AM EST Thursday through late Thursday night
for AMZ374.
&&
$$
Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
549 PM CST Wed Dec 19 2018
.UPDATE...
Issued at 537 PM CST Wed Dec 19 2018
Updated for the 00z Aviation Discussion below.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 308 PM CST Wed Dec 19 2018
Complex scenario in the short term with a wintry mix spreading in
tonight. Precipitation will taper off Thursday morning from west
to east, but lake effect snow will continue along the snowbelt
region of northwest Wisconsin.
A neutrally tilted trough will dig from the Northern Plains into
the Upper Mississippi River Valley tonight. A broad low will
deepen over northern Minnesota and Lake Superior. This will
gradually spread precipitation in from west to east. There is
still a lot of uncertainty in specific precipitation type as
forecast soundings are still all over the place. At the moment it
appears that a wintry mix will spread in from west to east. The
heaviest precipitation is expected late tonight under better
synoptic lift along the northwest side of the low. Expect more
snow than a wintry mix across the Minnesota Arrowhead where up to
an inch of snow accumulation is possible. Light ice accumulations
are expected across much of the region, which may make slick
roadways. If temperatures aloft cool quicker than currently
anticipated then precipitation may change over to more snow than a
mix. Flow aloft will become northwesterly and advect cold air
into the region. Lows range from the mid 20s to the low 30s.
The trough will slide into northern Wisconsin by Thursday
evening, while the surface low weakens over Ontario. This will
gradually bring precipitation an end from west to east. Expect
some wintry mix as precipitation winds down as ice is lost aloft.
Lake effect snow will continue across portions of the snowbelt
region of northwest Wisconsin. Expect cooler highs in comparison
to today due northerly cold air advection. Highs range from the
mid 20s to the mid 30s.
.LONG TERM...(Thursday night through Wednesday)
Issued at 308 PM CST Wed Dec 19 2018
The extended period of dry weather the region has seen is likely to
come to an end by next week.
A few minor systems plow their way through a continued dry air mass
mainly driven by short waves and residual Pacific moisture. The
first arrives Saturday into Sunday with only minor snowfall
accumulations. A second system may slide across on Christmas morning
bringing enough snow for a white Christmas according to the GFS and
ins ensembles. The Canadian also suggests this feature, but the Euro
does not. Temperatures trend towards a more normal range, but still
reading slightly on the high side.
The main story is the potential for a system after Christmas that
begins to brew finally tapping into both the Gulf and Pacific
moisture sources. Models are in fair agreement for day 7 and 8, but
still a lot, stressing a lot, of details to be ironed out with this.
Though the first potential heavier snow maker in over a month on the
horizon sure elicits some attention.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 549 PM CST Wed Dec 19 2018
A very messy forecast will continue through the evening hours
across the Northland, with mainly a mix of MVFR to LIFR
conditions. A mid-level trough and associated cold front will move
through the region, resulting in chances of a wintry mix. Very
moist low-levels, as seen in RAP and NAM model soundings, will
continue for the next several hours, with a very low stratus deck
and visibility reductions. The low visibilities in KDLH are
expected to continue as a combination of several models
indicate these low visibilities will remain through much of the
overnight hours. As the cold front passes through during the
overnight hours, the low stratus and vsbys will slowly scour out,
but strong northwest winds will move in behind the front. Some
MVFR ceilings are expected to linger despite the cold front
passage.
&&
.MARINE...
Issued at 308 PM CST Wed Dec 19 2018
There is some potential for winds to ramp up Thursday morning, but
only to small craft criteria. A second round of small craft winds
possible Sunday. A larger system may arrive after Christmas packing
gales, but still too early to tell where it will track and its
intensity.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 29 31 15 25 / 60 50 0 0
INL 24 26 8 21 / 50 10 0 0
BRD 27 30 16 28 / 30 20 0 0
HYR 31 34 20 27 / 40 50 10 0
ASX 32 35 21 28 / 50 60 20 10
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Dense Fog Advisory until 1 AM CST Thursday for MNZ037.
LS...None.
&&
$$
UPDATE...JTS
SHORT TERM...WL
LONG TERM...Wolfe
AVIATION...JTS
MARINE...Wolfe
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
618 PM CST Wed Dec 19 2018
.SHORT TERM...(This evening through Thursday night)
Issued at 230 PM CST Wed Dec 19 2018
A surface low skirts along the US-Canadian border tonight, dragging a
weak cold front across the upper Midwest tonight and tomorrow. There
has been quite a bit of moisture return this afternoon ahead of the
front, with dewpoints rising into the upper 30s across eastern
Minnesota and western Wisconsin. However, we`re still lacking in the
mid-level moisture department however as evidenced by the "dry"
echoes on radar this afternoon. Isentropic ascent will continue
through this evening and help to saturate more of the column but it
is still looking like deep moisture will be lacking by the time we
see the best deformation and ascent aloft later tonight into
tomorrow morning. Thus, only expecting a few hundredths of an inch of
precipitation out of this system tonight through tomorrow morning.
Precipitation will likely start off as drizzle later this evening,
with a change over to light snow or even a light wintry mix through
the overnight hours as cold air advection behind the front cools the
column enough to introduce ice. With low temperatures expected to
hover around freezing, and warm antecedent temperatures, widespread
freezing drizzle looks unlikely to develop tonight. However, can`t
rule out a few slick spots on elevated or low-lying surfaces in
areas that do manage to drop below freezing. Precipitation should
change completely over to snow by sunrise, with light snow looking
possible during the morning commute across eastern Minnesota and
western Wisconsin. Overall, little to no ice or snow accumulation is
expected so impacts should remain negligible. Snow departs off to
east by Thursday afternoon, with a gray and blustery day expected as
brisk northwest winds behind the front gust up to 30 mph. Dry
weather returns into Friday with cooler, but still above normal,
temperatures behind the front. Highs will range around 30 and lows
between the upper teens to low 20s.
.LONG TERM...(Friday through Wednesday)
Issued at 230 PM CST Wed Dec 19 2018
The longer term concerns remain chances for snow through Christmas
Day and trend of potential storm system late in period.
Starting out the long term, high pressure following the Thursday
trough should provide some sunshine and light winds. Highs will be
cooler, with lower 30s common. The next short wave trough moves
along the northern and will provide a chance of light snow,
mainly across the northern portion of the CWA. Moisture is meager
with the trough so we expect only light snow with minor impacts.
Temperatures cool a bit more into Tuesday with models diverging
once again on handling the short wave trough. The GFS has more of
a split flow with most of the jet energy riding across northern
MN Monday night into Tuesday. It does pull a frontal boundary
through the area put little in the way of QPF. The ECMWF is has
shifted its energy farther south and tracks it well south of the
area. If we do get any snow with this system, it will be light at
best and will limit any significant travel impacts. We did retain
some lower end blended PoPs for this system.
The GFS sets up a nice baroclinic zone to the south of the
CWA by late Tuesday. This should help intensify the developing
low pressure system forecast to move out into the
Colorado/Oklahoma panhandle region by Wednesday morning. The GFS
has trended more southeast with the surface low track as it
deepens and occludes into southern WI by Thursday morning. This
would leave most of our CWA in a more favorable snow outcome. It
also lifted large amounts of moisture into the region with over
an inch of QPF forecast for a large swath of the CWA. The ECMWF
has trended slower and a bit cooler as it did shift the low track
over southeast MN. This would favor a possible mix over the
southeast CWA with mainly snow again over the west and north. GEFS
probability plots haven`t focused on one particular area for more
significant snow/precipitation, with the GEFS plumes still
showing a rather large ensemble spread. However, both
deterministic models do show good potential for a higher impact
type event for travel after Christmas. Travelers should continue
to monitor the forecast concerning this potential storm system.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 617 PM CST Wed Dec 19 2018
Stratus that developed this morning over eastern MN/western WI has
stalled out over the last couple of hours. Still, as a stronger
push of west winds develops in the next couple of hours over MN,
both the HRRR and LAV say this stratus deck will begin moving
east, so continue to move stratus out at MSP/STC/MKT. Over
northeast NoDak, the next batch of post frontal status is
gathering steam as it heads this direction. The HRRR has a pretty
good handle on it, so followed its timing for bringing this
stratus in. By sunrise Thursday morning, this stratus will
encompass the entire MPX area with 600-1200 ft cigs. We are
seeing a good push of dry air at the low levels Thursday afternoon
and expect a good sized clearing to develop over central MN in
the afternoon that will spread south. Kept any precip out of the
forecast as moisture really looks to be lacking. May see an
occasional sprinkle/flurry, but nothing more than that.
KMSP...The halt in the eastward progress of the clearing line is a
little concerning and it is certainly possible it never gets here.
One thing to watch out for is that if it does start working east
again, conditions on the western edge of the stratus really
deteriorate to 1sm or less vis and sub 500 ft. cigs, so we`ll have
to watch for conditions to worsen before stronger NW winds arrive
to help mix things out a little bit better late tonight.
/OUTLOOK FOR KMSP/
Fri...VFR. Wind N at 5 kts.
Sat...Chance MVFR late. Wind lgt and vrb bcmg WNW 10 kts late.
Sun...Chc MVFR cigs. Wind NW 10G20 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&
$$
SHORT TERM...ETA
LONG TERM...DWE
AVIATION...MPG