Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/11/18
Area Forecast Discussion
National Weather Service Charleston SC
915 PM EST Mon Dec 10 2018
.SYNOPSIS...
A trough will move offshore tonight. High pressure will prevail
Tuesday through Thursday. A storm system will affect the area
Thursday night into Saturday, followed by another area of high
pressure.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Previous thinking has not changed much with respect to p-type.
Opted to nudge pops up about 10-20% for many areas far north and
western areas where observations show drizzle still putting
down a few hundedths. Various AWOS/ASOS sensors, including KCHS,
have been periodically detecting UP (unknown precip). It is
unclear whether this is sleet or if the sensors are having a
hard time resolving the drizzle. Obserations up near KFLO have
recently reported light snow.
Early evening GOES-E water vapor imagery shows a strung out H5
trough extending across the Deep South into the Mid-Atlantic
with an H7 vorticity center near Augusta, GA. The trough
continues to produce modest upward vertical motion as it
interacts with a pronounced polar jet stretching from the
northeast Gulf of Mexico to a position well northeast of the
North Carolina Outer Banks. Bands of light to occasionally
moderate rainfall continue to blossom ahead of the trough per
KCAE and KJGX reflectivity trends with surface observations
showing vsbys ranging from 2-4SM in the rain.
High resolution guidance members are similar in dropping the
area of light rain currently over the South Carolina Midlands
back into central Georgia east/southeast into portions of
Southeast South Carolina and Southeast Georgia after midnight.
Pops to 20-30% were maintained across the western, central and
and northern zones with rain-free conditions persisting across
the far south. There are signals that the rain could mix with
some frozen precipitation after midnight as low-level dry air
works south and diabatic cooling begins to cool the lowest
layers of the atmosphere. Although considerable dry air remains
in place in the mid-levels, significant moisture remains in
place from roughly the surface to about 6 kft. The moisture
depth is forecast to increase to about 8 kft with the approach
of the H5 trough with temperatures in the top of the cloud
layer forecast to cool to about -10C. This yields about a 70%
chance of ice nucleation in the cloud and should be sufficient
for a good percentage of the cloud`s super-cooled water
droplets to crystallize. RAP soundings at KCHS, KRBW, KMKS and
KTBR suggest the column will be cold enough to support some
degree of rain, sleet and snow mixture, but how warm the region
remains below 1500 ft is still unclear, especially as dewpoints
begin to fall as low-level dry air works south. With
precipitation rates expected to remain quite light, suspect
diabatic cooling will not be fully maximized, thus anticipate
the main hydrometeor phase to remain liquid with only occasional
bouts of sleet and snow mixing in at times. If pockets of
heavier precipitation rates can be obtained, then a brief change
over to all snow or sleet could occur. However, confidence on
this scenario is quite low. For now, maintained a mention of a
slight chance of snow and sleet in the grids for the western,
central and northern zones, including parts of the Charleston
Metro Area.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday and Wednesday: The mid-levels will consist of a trough axis
spread along the Southeast coast Tuesday morning. The trough will
quickly move offshore Tuesday afternoon. Zonal flow will develop
overhead late Tuesday night and prevail into Wednesday. The flow
will start to turn to the southwest Wednesday night as a strong
trough moves over the Central U.S. At the surface, a trough will be
just offshore Tuesday morning, while high pressure is centered over
the Lower MS Valley. The trough will quickly move away Tuesday
afternoon. The center of the high will gradually move over the
Southeast into Wednesday, then start shifting offshore Wednesday
night. Strong subsidence and a lack of moisture will keep the
forecast dry for this entire time period. Despite plenty of sun, a
chilly airmass will keep highs Tuesday about ten degrees below
normal. This temperature trend will continue into Tuesday night,
with many locations away from the immediate coast reaching freezing.
Temperatures moderate a few degrees on Wednesday as the winds
gradually shift to the SW. Though, temperatures will remain several
degrees below normal.
Thursday: The mid-levels will consist of southwest flow overhead as
a trough strengthens over the Central U.S. At the surface, a trough
will start developing off the coast in the morning, strengthening
into the afternoon. Meanwhile, a strengthening storm system will
approach from the Lower MS Valley. Moisture will gradually increase
throughout the day. Though, models seem to keep the highest values
just off the coast or near the Altamaha River. Some precipitation
could develop across the GA coastal waters late in the day and maybe
near the Altamaha River. Hence, we have slight chance POPs there.
QPF will be minimal, if any. Despite increasing clouds, warm air
advection should allow temperatures to reach normal values for this
time of year.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A deep-layered low pressure system will affect the southeast US
Thursday night through Friday night, bringing fairly widespread
showers and perhaps some thunderstorms. Mainly dry weather
expected behind the storm system with temperatures at or
slightly below normal.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Cigs will remain near IFR/MVFR thresholds for much of the night
with KCHS expected to trend closer at or below upper-end IFR.
Could see a brief period of a rain/sleet mix at KCHS as a band
of light precipitation approaches from the west around 08z, but
no impacts are anticipated. VFR will return closer to daybreak
and continue for the remainder of the 00z TAF cycle.
Extended Aviation Outlook: MVFR or lower conditions could
return late Thursday through Friday night as a storm system
affects the area.
&&
.MARINE...
Tonight: A trough will move south through the waters with winds
shifting more solidly out of the northwest in the GA waters and
north-northwest in the SC waters. Speeds should stay below
Advisory levels, mainly in the 15-20 knot range, although some
25 knot gusts are possible can`t completely be ruled out
especially in the outer Georgia waters. Seas will build a bit,
mainly becoming 3-5 feet in the nearshore waters and 4-6 feet
in the outer waters where the Small Craft Advisory remains in
effect.
Tuesday through Saturday: A Small Craft Advisory should remain
in effect for the GA waters beyond 20 nm through Tuesday
evening, mainly due to seas. High pressure will build across the
Southeast Tuesday and Wednesday, allowing both winds and seas
to trend downwards. The next round of marine headlines is
expected Thursday night through Saturday night as a strong low
pressure system moves through the Southeast U.S.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until midnight EST Tuesday night for
AMZ374.
&&
$$
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1024 PM EST Mon Dec 10 2018
.SYNOPSIS...
High pressure spreads back over our region from the west and
then moves off the East Coast on Thursday. Another significant low
pressure system will develop to our west and bring more widespread
precipitation to the region by the end of the work week and into the
weekend.
&&
.NEAR TERM /THROUGH TUESDAY/...
As of 1015 PM: A 500mb shortwave trough traversing the area
continues to drive an area of light rain and/or drizzle across the
lower Piedmont of GA/SC. The deep moisture will be driven south
with time as drier high pressure expands from the Mississippi
Valley across the southern Appalachians. Updated PoPs are lower
as much of the returns on radar are not reported as reaching the
ground. Temps remain several degrees above freezing where this
precip is occurring. Significant cooling is not expected there
until cloud cover is forced out late tonight. Profiles suggest that
some snow may mix in where temps are coldest, but no direct wintry
impacts are expected from the precip. However, this will keep roads
wet and areas of black ice are thus expected wherever temps fall
below freezing late tonight. The extent will be somewhat limited
with temps not staying below freezing for very long before they
warm again after daybreak. For now we will maintain a mention of
the threat in a Special Weather Statement.
Further north, though temps are largely still above freezing,
cloud cover is beginning to break up. Dewpoints are already
several degrees lower than those in the precip area. On these
notes, over the northern zones temps should begin to fall sooner
and faster. With several inches or more of snow cover still
remaining min temps will be particularly cold, though hi-res models
seem to continue to struggle to adequately resolve them. Temps
eventually are expected to fall into the mid 20s. With such low
morning temps...it will take a while before sfc readings rise
abv freezing...making for an extended period of black ice into
mid to late morning...while the nrn NC mtns will likely remain
below freezing until the early afternoon. A winter weather advisory
remains in effect for the northern two-thirds of the CWFA for black
ice. While prog profiles look unfavorable to maintain a deep fog
layer, dewpoint depressions will shrink, permitting some patchy
fog to form. The dense fog depicted on e.g. the HRRR still seems
overdone, possibly resulting from the aforementioned unrealistic
surface cooling over the snow--HRRR min temp fcst at KCLT is 19
tonight. At any rate, wherever sfc temps fall below freezing,
any fog would be freezing fog, possibly making surfaces slippery
where not otherwise icy.
Another cold day on tap for Tue...yet it will be warmer than Monday
was. Skies will clear out...but with temps beginning the day so
cold and a reinforcing cP high building in...maxes will be held
abt 10 degrees below normal.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 200 PM EST Monday: The short term begins at 00z Wednesday with
NW flow aloft in the wake of the exiting wave, and weak ridging
beginning to build in from the west. Surface high pressure over the
northern Gulf Coast will work its way east, but troughing will
remain in the Piedmont and adjacent foothills, resulting in another
very cold night Tuesday night and chilly day on Wednesday. A
shortwave embedded in the flow will pass to our north Wednesday
night and Thursday, but should remain mostly dry, though cannot
rule out some isolated sprinkles or flurries especially the upslope
areas of the SW mountains. As the shortwave passes, weak ridging
will begin to build in ahead of a trough deepening down the Plains.
Southwest flow aloft will begin bringing a little more WAA into the
area toward the end of the short term, but with warm frontal precip
ahead this way of the deepening surface low over the Red River (of
the south) Valley.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 215 PM EST Monday: As we move into the extended, precip will
be overspreading the area from the west as the upper low cuts off
and digs in to the Lower MS Valley. Significant gulf moisture will
lift into the Deep South as the surface low occludes and the cold
front starts pushing east. Meanwhile, high pressure will move off
the Atlantic to our north, and as the precipitation starts falling
into the low-level dry layer, insitu damming will develop. Luckily
the incoming moisture will keep overnight lows Thursday night a
little warmer, because with a substantial warm nose in the low-level
WAA, if surface temperatures drop below freezing, could see some
freezing rain at onset. For now, since the warm nose is less
substantial further north, have kept ptype as a rain/snow mix, but
will need to continue reevaluating. Anything that falls will be
brief as temperatures warm during the day on Friday, though as a
note there is definite bust potential with highs depending on the
strength of the high. The insitu damming does look like it will keep
us pretty stable, and although the system is highly dynamic with an
impressive LLJ and deep-layer shear, instability is minimal to
nonexistent. Have continued trend of no thunder in the grids for
now. Other concern is the QPF, and we could see some storm total
amounts upwards of 3-4" Friday through Saturday, maximized (of
course) along the escarpment and especially the upslope areas of the
SW mountains. Still some disagreement in the track of the upper low
as it passes near (overhead or just to our north), but we should get
some flavor of NW flow snow across the mountains on the back edge,
some accumulation would be possible. Good thing though is that
temperatures trend closer to normal through the weekend.
&&
.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Light rain will occur over the SC sites
this evening as an upper level disturbance provides lift in
the nearly saturated low levels. Except for some spotty MVFR
cigs, no restrictions are expected with the precip. Drier high
pressure centered over the Mississippi Valley will filter over
the Appalachians over the course of the nightas this disturbance
exits the region, promoting drying. Skies will gradually begin to
clear from NW to SE in the early morning. A few hi-res determinstic
guidance sources suggest IFR to LIFR fog will form over parts of
the Upstate as skies clear. This is being discounted attm, as it
seems these same models are poorly modeling the effects of the
remaining snowpack. Fog mention has been reduced to a TEMPO. VFR
is expected after daybreak with light winds backing to SW in the
Piedmont, but remaining NW at KAVL.
Outlook: Cold and dry high pressure remains across the area
through Wednesday. Deeper moisture will return, with associated
restrictions, Thursday through Friday.
Confidence Table...
03-09Z 09-15Z 15-21Z 21-00Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 83% High 100% High 100% High 100%
KAVL High 96% High 98% High 100% High 100%
KHKY High 100% High 100% High 100% High 100%
KGMU Low 47% Low 50% High 100% High 100%
KAND High 100% Med 65% High 100% High 100%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
www.weather.gov/gsp/aviation
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Winter Weather Advisory until 10 AM EST Tuesday for GAZ010-017.
NC...Winter Weather Advisory until 10 AM EST Tuesday for NCZ068>072-
082-507>510.
Winter Weather Advisory until 11 AM EST Tuesday for NCZ035>037-
051>053-056>059-062>065-501>506.
Winter Weather Advisory until noon EST Tuesday for NCZ033-
048>050.
SC...Winter Weather Advisory until 10 AM EST Tuesday for SCZ001>009.
&&
$$
SYNOPSIS...DEO
NEAR TERM...SBK/Wimberley
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...Wimberley
Area Forecast Discussion
National Weather Service Wilmington NC
909 PM EST Mon Dec 10 2018
.SYNOPSIS...
Patchy light rain, possibly sleet, and a few snow flurries will
finish off a complex storm system tonight, but no accumulations
are expected. Temperatures will remain below normal Tuesday
through Thursday as high pressure moves across the Carolinas.
Another low pressure system will bring additional rain Friday
and Saturday, however much milder temperatures are expected.
&&
.NEAR TERM /THROUGH TUESDAY/...
As of 909 PM Monday...Based on a few -sn/-ip reports, and an
expanding but light radar signature, have placed mixed pcpn into
the zone forecasts a little earlier than previously advertised.
There is room for cooling with cold air advection and in the
evaporative processes, supporting cold enough temps with
lingering moisture content for a `light` rain/snow/sleet mix
through 8-9z before drying takes a foothold before daybreak.
As of 715 PM monday...Patches of T/.01 pcpn cannot be ruled out
overnight, and it still appears enough of a moisture and cold
air overlap will lend to light snow and flurries in a few spots,
but given that grounds will hold above freezing much of tonight,
and light nature of the pcpn, lasting accumulations of snow are
improbable in any one spot. No significant changes were made,
did add drizzle for the overnight period, as cold air advection
keep low level RH elevated until drying more in earnest Tuesday.
As of 330 PM Monday...Deformation/frontogenesis band is under
performing from a QPF standpoint today, not that we were
expecting a lot of rain but most areas are only receiving
drizzle or very light rain with just a couple of hundredths (if
that) being measured. The mostly drizzle will continue to drift
south and east in time tonight and with drizzle and surface
observations to the north showing no ice nuclei in the clouds,
wintry precipitation is all but out of the question. It really
comes down to surface temperatures, and even though guidance is
showing lows at or below freezing at most sites, my feeling (and
experience) is that temperatures will move little until we
clear out which of course means there will be no precip.
remaining. Tuesday looks to be sunny and cool. The temperature
forecast could be troublesome as surface wind trajectories will
be traversing snow cover to the northwest but guidance "should"
have this figured in. Overall expect upper 40s to lower 50s.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 330 PM Monday...Quiet time of wx expected for this
period. Ridging aloft and at the sfc will dominate across the
FA. A mid-level s/w trof will bypass the area to the NW and N
this period. Could see some cirrus making it across the
Appalachians and portions of the FA Wed. In general, low mean
rhs spell sunny Wed and mainly clear Tue and Wed nights. Cold
Wed morning with 20s...to low 30s at the coast that will warm
to widespread 50s for Wed highs. Stayed closer to the cooler
NAM/European MOS Guidance for Wed highs. Wed night will see lows
about 5 to 8 degrees milder than what occurs on Tue night.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 330 PM Monday...Thursday will see the sfc high and source
of the cold air move off the Mid-Atlantic coast. At the same
time, upper s/w and sfc low will result with intensifying low
pressure taking shape over the NW-N Gulf Coast states by Fri
morning. Models indicate a rather large swath of deep moisture
to advect across the FA during Fri with the WFP occur during
Fri. The wedge preceding this WFP will not be as strong due to
the cold air source no longer over land. With plenty of dynamics
avbl but questionable instability, needless to say will go ahead
and include possible thunder over land and adjacent waters for
Fri aftn and night. The 1st cold front pushes thru Sat morning
otherwise known as the dry slot. The true cold air advection will
occur late Sat night thru Sun as winds veer to an offshore
or downslope trajectory. Highs Fri and Sat will be well into the
60s with some MOS guidance breaking portions of the FA into the
70s. The CAA Sun into Mon not all that impressive with Sun and
Mon fcst temps at or category above normal.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
As of 00Z...Precipitation has been forming between LBT and ILM. The
HRRR takes this feature slowly southward overnight. Look for
deteriorating conditions at ILM and LBT in a couple of hours. The
Myrtles are already IFR and probably will stay there through the
overnight hours. Tuesday, conditions improving to VFR by mid morning
with that beautiful ball of light coming out to grace our afternoon.
Extended Outlook...MVFR into early Tuesday morning. VFR
developing on Tue and continuing through Thu before a return to
MVFR Fri potentially due to another coastal low.
&&
.MARINE...
NEAR TERM /THROUGH TUESDAY/...
As of 330 PM Monday...Northerly winds of 20-25 knots are in
place over the waters and will be for most of the evening and
overnight hours. There may even be a slight uptick in speeds
briefly as the gradient increases. Expect more of a
northwesterly flow Tuesday as speeds drop to 15-20 knots late in
the day. The latest wave guidance has small craft seas
persisting for a few more hours later Tuesday and if another run
or two shows this a bit of an adjustment on the expiration of
the advisory Will be warranted. Otherwise expect the current 5-8
feet to persist most of the period until late.
SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 330 PM Monday...Improving winds and sea conditions
expected this period. The last of the low`s will be accelerating
well offshore and away from the area waters at the start of this
period with offshore winds in it`s wake. Sfc high pressure
centered along the Gulf Coast States Tue night will ridge across
the area waters Wed with the High`s elongated center nearly
overhead Wed night. As a result, look for diminishing winds as
the center of the high moves closer with speeds dropping below
10 kt and possibly 5 kt or less during late Wed thru Wed night.
Seas will be in a subsiding trend especially with an offshore
wind trajectory and diminishing wind speeds aiding it`s
decrease.
LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 345 PM Monday...High pressure will slide off the Mid-
Atlantic coast Thu with increasing onshore NE-E flow. Models
indicate a WFP early Fri with modest onshore flow quickly
developing. Significant seas initially will be docile but
quickly build especially after the WFP as the sfc pg tightens
resulting in strong SE-S winds reaching SCA levels. Wavewatch3
builds seas to double digits by late Fri, at less than 10 second
periods indicative of the choppiness. The CFP will follow
during Sat as the sfc low moves up the Appalachian spine. Winds
will again veer and become offshore from the west to northwest
at SCA speeds. Seas will drop below double digits Sat with
continued 7 to 9 second periods. Isolated thunder will
be advertised possible Fri thru Fri night.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory until noon EST Tuesday for AMZ254-256.
Small Craft Advisory until 9 PM EST Tuesday for AMZ250-252.
&&
$$
SYNOPSIS...8
NEAR TERM...SHK/8
SHORT TERM...DCH
LONG TERM...DCH
AVIATION...43
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
622 PM CST Mon Dec 10 2018
.UPDATE...
622 PM CST
Doing the dense freezing fog a bit earlier this evening. Area of
very low stratus appears to be building back to the surface as
dense freezing fog again early this evening over east central IL.
GOES-16 nighttime microphysics RGB shows this very low stratus and
dense fog beginning to advect north into southern Ford and
southern Iroquois counties.
While off an hour or two on the timing, the RAP is depicting this
scenario and then shows the same dense freeze fog moving east
into northern IN and clearing out southeastern CWA in a few hours.
This scenario is quite plausible and strongly considered waiting a
bit and watching trends before issuing a dense fog advisory, but
thus far GOES 1-min imagery shows area expanding and back edge not
moving much, so think the course of least regret is to issue the
dense fog advisory now and if things clear out, cancel the
advisory early. Given how dense the fog is and the freezing/icy
potential (KCMI down to M1/4SM with an RVR of 1200ft plus 0.01"
of ice accretion) feel the best course of action is to get
headline out now.
Updated forecast products and the advisory will be out shortly.
- Izzi
&&
.SHORT TERM...
239 PM CST
Through Tuesday...
Tonight and tomorrow appear to bring a continued stretch of quiet
conditions with southwest flow between a surface low moving across
the Great Lakes and a ridge stretching from the western Gulf across
most of the eastern CONUS. The only question and concern would be
possible redevelopment of fog and low stratus. The most favorable
areas for this would appear to be in the some locations that took so
long to clear today. This would be especially true farther south
nearer the ridge axis where winds are lighter, high temperatures did
not get as warm today, and remnant boundary layer moisture is more
abundant. Opted not to include mention of this in the afternoon
update but this potential will continue to be monitored.
If conditions manage to stay clear, most locations should reach the
30s tomorrow with southern portions of the forecast area approaching
40 degrees.
Lenning
&&
.LONG TERM...
205 PM CST
Tuesday night through Monday...
Tuesday night into Wednesday, an elongated shortwave trough is
progged to move from the northern Great Plains across the Upper
Midwest. Models have come into better agreement with the wave
closing off at 500mb by Wednesday morning and tracking across far
southern Wisconsin. Models indicate the axis of highest QPF will
occur north of I-80, if not north of the IL/WI state line.
Forecast soundings continue to indicate additional concerns that
will need to be worked out. Anticipate a nearly isothermal layer
right around the 0C isotherm from the surface to around 925mb
early in the day Wednesday which will result in some p-type
concerns and uncertainty. In addition, there are several periods
during the event where saturation is not sufficiently deep to
introduce ice crystals into the column and may result in drizzle.
Will continue to mention the possibility of a wintry mix on
Wednesday. Some areas may see a dusting of snow, and will have to
keep a close eye on pavement temps during any periods of liquid
precipitation.
Further out, guidance continues to advertise a deep upper low
developing across the southern Great Plains late Thursday, though
models continue to have very large differences in how this low
evolves heading into the weekend. By late Friday evening, for
example, guidance ranges from New Orleans to Cleveland with
respect to the 500mb closed low position. The ECMWF has had a
consistent southerly track for several days now, however, both
the GFS and ECMWF have trended towards each other as of the latest
12Z cycle. Regardless of continued tracks differences, it appears
there will be a decent chance for warm advection driven rainfall
later in the day Thursday into Friday. Warm air wraps around the
low and is cut off from the colder air over Canada, so event may
stay primarily rainfall throughout. There remains uncertainty in
how far north precip will continue through the remainder of the
day Friday into Saturday, and much of that precip may stay to our
south if the southerly tracks verify. Expansive area of high
pressure is expected to build in behind the low early through the
middle of next week bringing a stretch of more quiet weather to
the region.
BMD
&&
.AVIATION...
For the 00Z TAFs...
Stratus and fog is once again present this evening, however, is
mainly to the southeast of most of the terminals and should
remain that way tonight into Tuesday morning. Am monitoring a
small area of IFR ceilings though, which may briefly impact GYY
over the next couple of hours. At this time, don`t anticipate this
area to expand and impact the other terminals but should mainly
continue to drift to the northeast. The steady southwest winds in
place this evening will persist through the period.
Rodriguez
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
612 PM CST Mon Dec 10 2018
.SHORT TERM...(This evening through Tuesday)
Issued at 254 PM CST Mon Dec 10 2018
Stratus continues to clear from west to east and the clearing line
has now reached I-35. It should continue eastward into the
evening hours. Just some thin high clouds are moving into western
MN from the Dakotas late this afternoon, but they are expected to
thicken some later tonight. This could hamper robust fog formation,
but there are still decent probs (35-60%) on the SREF and HREF
for low stratus and visibilities around 1 mile redeveloping area
wide after midnight. Increased cloud cover from the previous
forecast after this evening and continued the mention of fog
through Tuesday morning.
.LONG TERM...(Tuesday night through Monday)
Issued at 254 PM CST Mon Dec 10 2018
The long term period features multiple shortwave troughs passing
over the area, as a strong jet comes onshore off the Pacific
coast. The first of these approaches the area late Tuesday night
into Wednesday with strong vorticity advection resulting in a
cutoff low forming east of the area over the Great Lakes. Given
the better forcing holding off until the wave is east of the area,
not expecting much in the way of precipitation out of this
system. Forecasts soundings continue to show little ice in the
column, so light freezing drizzle continues to look possible along
with periods of flurries when/if ice can get introduced to the
cloud layer. With temperatures in the low-mid 20s Wednesday
morning there could be some slick areas on untreated roads during
the morning commute, primarily across southern Minnesota and west-
central Wisconsin.
Right on this system`s heels comes another, more organized, trough
Thursday as the northern and southern jets interact over the
Mississippi Valley. However, the best forcing with this trough
remains tied to the southern jet over the lower-Mississippi valley
so expecting little in the way of precip over our area again as
moisture remains scant across the upper Midwest. Forecast soundings
continue to show a mid-level dry layer around 700 mb, but think
enough ice will be introduced by a seeder cloud layer above to
result in light snow/flurries. Only a dusting of accumulation is
expected.
Beyond Thursday, benign and milder weather looks to prevail as the
jet remains well north of the area. Broad ridging builds over the
central US over the weekend which will keep temperatures mild into
the middle of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 612 PM CST Mon Dec 10 2018
It`s yet another night with a shallow near surface moisture layer
trapped beneath a strong and very dry inversion. The last couple
of nights, the HRRR has done a good job at capturing the main idea
for the evolution of the stratus and fog, so stayed close to it`s
idea tonight for these TAFs. Expect the stratus over WI now to
clear RNH/EAU shortly, but will stall out over central WI and
start to creep back west. It is looking likely that EAU will have
another FZFG/stratus event Tue morning, with RNH possibly having
issues as well. It is looking like MN terminals will have
nothing worse than an MVFR vis. Cirrus streaming in from the
Dakotas should help in keeping stratus/fog from becoming
problematic in MN. For Tuesday, mid/upper clouds will thicken as a
trough works across the Dakotas, but no precip or MVFR conditions
are expected during this period.
KMSP...Looking at forecast soundings, moisture is forecast to be
more shallow Tuesday morning than it was Monday morning, so agree
with the HRRRs idea that it`s likely going to be a VFR night.
Still, we have some reduced vis at 00z at FCM and LVN, so can`t
rule out some vis restrictions through the night as the temps
cool to near the dewpoint, so maintained MVFR vis mention from
previous TAFs. Clouds will thicken and lower through the afternoon
Tuesday, but not expecting any sub VFR cigs or any sort of precip
chance until after this TAF period.
/OUTLOOK FOR KMSP/
Wed...MVFR/IFR ceilings. Wind SE 5 kts.
Thu...MVFR ceilings. Wind lgt and vrb.
Fri...VFR. Winds W 5 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&
$$
SHORT TERM...BORGHOFF
LONG TERM...ETA
AVIATION...MPG