Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/16/20
Area Forecast Discussion
National Weather Service Columbia SC
739 PM EDT Thu Oct 15 2020
Low level moisture will interact with a cold front moving
through the region with chances of showers this evening through
Friday. High pressure along with cool and dry conditions will be
over the region Friday night through the weekend. Dry weather
will continue through the middle of next week.
.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
Upper impulse in a SW flow aloft, with a weak surface trough over
the region enhanced by a sea breeze, with shallow moisture,
providing scattered showers and isolated thunderstorms this
evening. Overnight, as surface pressure falls across the region
in advance of an approaching 500 hPa trough digging into the OH
valley, a weak closed surface low is forecast to develop across
the upstate, with a weak surface front (manifested mainly as a
moisture gradient/wind shift) dragging to its south across the
CSRA. This then looks to move into the rest of the CWA between
06z and 10z overnight. Ahead of it, scattered showers will
develop within a decently moist environment (PWs 1.4-1.6") and
move through the region, exiting northeast around or after 12z.
Lows should stay in the mid 60s across the forecast area.
.SHORT TERM /7 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Upper trough will be moving through the eastern portions of the
U.S. on Friday. This will help to push an initial cold front
into the area early Friday morning, with lingering scattered
showers still possible across mainly central and northern
portions of the forecast area. Winds will turn from westerly to
more northwesterly through the day. A second stronger cold front
will then move through late in the day on Friday, finally drying
the entire forecast area out and ushering in the colder airmass
for the start of the weekend. Behind the second front, winds
turn more northerly with cold advection taking hold.
Temperatures through the day Friday will not be as warm in most
areas, especially the western cwa, but should still climb into
the low to middle 70s. Areas further east where the front will
be slower to get too will be able to climb into the lower 80s
before the fropa. Significant cool down will occur Friday night
through Saturday both Friday and Saturday nights in the mid 40s
to around 50.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Forecast will remain dry through the longer term period.
Moisture return across the eastern cwa late in the period could
lead to an isolated shower or two across the eastern counties,
but confidence remains low and have gone dry. Temperatures will
be slightly below normal Sunday then return to near normal for
Monday through Thursday.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Mid level short wave trough evident over south central Ga toward
the lower Savannah river area triggering showers near OGB early
this evening where instability has been moderate near surface
trough. Mid level capping has limited degree of convection
although locally heavy rain has fallen just east of the OGB
terminal. Conditions should improve at OGB over the next hour or
so with mainly mid level ceilings expected to persist.
Pressure ridge offshore overnight with weak surface extending
from southeast Ga into the Midlands SC. A cold front will be
approaching from the Upstate tonight and should be moving
through the area around daybreak. Showers currently near OGB
should lift to the northeast as short wave moves northeast.
Other showers in the Piedmont and east-central GA should remain
mainly west of the terminals. A few showers may develop ahead of
the front late tonight but CAM models suggest scattered and
mainly focused to the north of the CAE/CUB terminals. Expect
strato-cu as the front approaches possibly lowering to MVFR or
IFR but lamp and HRRR have trended higher. Visibility should
stay up with mixing in the boundary layer. Winds will shift to
northwest behind the front with mainly mid level ceilings after
18z. Winds may increase to around 10 knots.
EXTENDED AVIATION OUTLOOK...No restrictions expected ad dry air
advects into the area.
Area Forecast Discussion
National Weather Service Marquette MI
741 PM EDT Thu Oct 15 2020
.SHORT TERM...(This evening through Friday)
Issued at 330 PM EDT THU OCT 15 2020
Latest RAP analysis, and GOES Satellite show that closed surface low
of 991mb that moved through the UP last night is now south of the
James Bay, continuing to move east-northeast away from the region.
As tradition being on the back side of a deepening low pressure is
that blustery west-northwest winds will continue through the day but
slowly diminishing from west to east as the low continues to move
away. Lakeshore Flood Advisory will drop off this evening for Alger
and Luce Counties as wind and waves should be weaker than earlier
today. Mid to upper level analysis still shows an upper level low
over northern Canada, which will continue to be a nuisance as this
will continue to bring shortwaves to the region. Latest guidance is
now showing a weak shortwave moving through Friday, contradicting
previous runs of being dry Friday. Another chance for some lake-
effect rain or snow showers is possible again with caa taking
control heading into the weekend so for those looking for a warmup,
doesn`t look likely anytime soon.
As this surface low continues to move east-northeast away from Upper
Michigan, clouds will hang around thanks to upslope winds from Lake
Superior and with caa having a stronghold over the area, most Lake-
effect precip will fall in the form of snow over the west-northwest
wind belt zones later this afternoon and into tonight with
convergence from the land breeze will help aid this, especially east
of Marquette. Could end up with some light accumulations across the
higher terrain and over the Keweenaw as well. Any accumulations
should remain under an inch. Lake-effect looks to hang on, at least
according to the NAM and GFS. Drier air will continue to work into
the area with high pressure off to the west over the Northern
Plains. Heights won`t rise much and barely any waa will work in as
the caa hangs on. Hi-res guidance is trying to hint at a weak
shortwave for Friday which might trigger light precipitation. There
isn`t good forcing or fgen but since given this cooler pattern were
in, might be safe to add slight chance PoPs for the daytime. With
the winds continuing to decrease throughout today and tonight, will
hang onto the Lakeshore Flood Advisory out east since waves take a
little bit longer to subside. Winds will become more of a pure
westerly direction but will not be as breezy as previous days.
Temperatures this afternoon will not rise much, if not at all, just
with those northwest winds and lake-effect bands will keep highs
pretty much where they are now. Did tweak a few spots a degree or
two lower from fcst this morning. Lows tonight will be chilly with
mostly 30s with 20s in the interior with help from winds relaxing a
bit overnight. Not much rebound for Friday with 850mb temps around
-7C, resulting in upper 30s over the west and higher terrain and 40s
east and along Lake Michigan.
.LONG TERM...(Friday night through Thursday)
Issued at 338 PM EDT THU OCT 15 2020
An active weekend still looks to be in the works, as guidance
continues to highlight the northeast track of a fall storm through
the Upper Great Lakes Saturday afternoon into Sunday. This system
looks similar to other recent storms, with strong southerly winds
preceding strong northwesterly winds, with widespread precip. The
difference is that this storm will already have some cold air in
place ahead of it, so some snow is expected. On the backside of this
system, a period of lake effect is looking likely into the middle of
next week, with some shortwave support embedded within developing
Beginning Friday night, the tail end of a shortwave moving through
the base of long wave troughing will exit east, giving way to
clearing skies for much of the region. The exception looks to be the
west wind belts where some lake induced cloud cover and some showers
looks to linger through the night. Where skies clear up, light winds
will allow for overnight lows to sink into the 20s and the high
teens in the traditional cold spots.
Attention then turns to the approaching storm. Low pressure
developing in the lee of the Montana Rockies will sink southeast
into the Dakotas before pivoting toward the northeast through the
Upper Great Lakes Saturday night. Strong WAA/isentropic lift ahead
of this system will allow precip to spread over the region Saturday
afternoon into the evening. Model soundings and wetbulb zero height
values indicate precip early in the west half, particularly the higher
terrain, could start off as snow. As WAA increases though, all
precip should switch over to rain across the forecast area by late
afternoon. With high temps topping out in the upper 30s to low 40s,
it looks to be a sloppy and dreary kind of afternoon. Models are
consistent with a break in the precip, or transition to
drizzle/flurries overnight Sat/early Sun as the region dry slots
along the southern side of the low. Along the west side of the low,
strong CAA will surge cold air south into region, allowing for wrap
around precip to switch back over to snow overnight Saturday. Given
lake-850mb delta temps of ~16C, lake enhancement is likely within
the northwest wind belts of western Upper Michigan. In terms of snow
accumulations, an inch or two isn`t out of the question in the west
Saturday morning before the warmer air arrives. If this ends up
being the setup, I suspect a period in the west where some roads
could be sloppy as the snow melts through the day.
Another aspect of this storm are the winds. Tightening pressure
gradient looks to result in pressure drops of 3-5mb per 3 hours,
which will increase southerly winds on Saturday. As the system
transits through, increasing CAA and just as sharp pressure rises
are anticipated, resulting in strong northwesterly winds. To add to
this, some isallobaric wind increases could be realized as the wind
becomes perpendicular to the pressure gradient. Overall, expect a
blustery winds Saturday through early Sunday, especially by Lake
Michigan. The southerly winds off Lake Michigan and the Bay Saturday
night could exceed 40kts and a gale watch has been issued for the
nearshore waters and the open lake zones for Lake Michigan. These
winds will help build large waves and cause lakeshore flooding and
beach erosion concerns for the shorelines of Delta and Schoolcraft
Following this storm, 850mb temps look to bottom out in the -7 to -
10C range. With these delta Ts, along with low directional shear,
lake effect snow showers are looking likely for the northwest wind
belts early Sunday. The pattern looks to become more zonal by Sunday
afternoon, resulting in westerly flow generally through the early
part of next week. A few shortwaves embedded within this flow Sunday
night and on Monday could help reinforce any ongoing lake effect.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 737 PM EDT THU OCT 15 2020
VFR conditions should prevail at all terminals through the TAF
period. The only exception might be KCMX where an isolated lake
effect snow shower moving over the site late tonight/early Friday
could briefly lower conditions to MVFR.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 330 PM EDT THU OCT 15 2020
Winds will continue to diminish through the rest of the afternoon,
heading into Friday. Current Gales will drop off this afternoon but
still could have a few gale force gusts to 35 kts through early
evening before winds drop to under 20 kts by Friday morning. With a
weak shortwave moving through Friday, winds will be between 15-25
kts from the west then dropping back under 20 kts Friday night into
Saturday morning. Then attention turns to next system for Saturday
A strong fall storm is progged to transit Lake Superior Saturday
afternoon and evening. Current guidance consensus brings the low
northeast through the western half of Lake Superior. As the low
approaches, southerly gales to 40 knots are anticipated in the
eastern half of Lake Superior. Some higher platforms could
experience higher gusts given the 45-50knot LLJ that is progged to
coincidentally migrate through. These winds could build significant
waves upwards of 10ft on the north end of our US forecast zones and
into Canadian waters. As the low transits up Lake Superior, winds
will become northwesterly gales to 35 knots, mainly in the central
and eastern portions of the lake. For the time being, issued a gale
watch for the north-central and eastern portions of Lake Superior to
account for both the southeast and northwest gale events. Following
this event, winds will continue to trend downward beginning Sunday
and by Monday, return to westerlies near 20kts lake-wide.
Gale Watch from Saturday afternoon through late Saturday night
Gale Watch from Saturday morning through late Saturday night for
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
959 PM EDT Thu Oct 15 2020
A cold front will approach from the west tonight and cross central
NC early Friday. Canadian high pressure will follow and build across
the middle Atlantic later Friday through Saturday, then offshore on
.NEAR TERM /THROUGH TONIGHT/...
As of 955 PM Thursday...
Cntl NC will remain in swly flow aloft tonight, downstream of a
broad trough centered across cntl NOAM and anchored by a deep vortex
(516 dm at 500 mb) over srn NU. Within that broad trough, a
shortwave will amplify into the mid-South and mid MS Valley through
12Z fri, well upstream of cntl NC. More influential for cntl NC will
likely be a preceding mid level trough evident in 00Z/16th 500-700
mb upr air and regional VWP data over the Savannah Basin this
evening, which is forecast to lift newd across the Carolinas with
associated ~30 meter mid level height falls, forcing for ascent, and
mid level moist axis.
At the surface, a cold front was analyzed at 01Z from cntl PA swwd
near the WV/VA state line, far ern TN, n-cntl AL, the lwr MS Valley,
and and sern TX; and this boundary will cross the Appalachians and
move across the NC Foothills and nwrn Piedmont late tonight. East of
the Appalachians this evening, a surface trough and elongated area
of low pressure stretched from e-cntl GA, w-cntl SC, and wrn NC, in
a zone of related mass/moisture convergence. That pre-frontal low is
forecast to develop newd across w-cntl NC between 06-12Z Fri, the
last 2-3 hours of which will be characterized by a merger of the
approaching front with the pre-frontal trough/low over the nwrn NC
Although earlier convection over both the Upstate and e-cntl SC has
been weakening during the past few hours, the models continue to
suggest additional convection will re-develop along the pre-frontal
trough, across the srn and wrn NC Piedmont, by around 06Z. That
convection, amidst increasing but still weak instability, should
then become increasingly-influenced by low level frontogenesis and
mesoscale forcing for ascent as the cold front merges with the
low/trough Fri morning, beneath the larger scale ascent and
moistening provided by the mid level trough lifting out of the
Savannah Basin. The result will be scattered to numerous showers,
and isolated storms, overspreading the wrn half of cntl NC and
focused between the Triad and Triangle, Fri morning. Rainfall
amounts around a quarter inch may be locally maximized around one
half inch from near HFF to BUY and former IGX, if training of cells
occur where recent HRRR runs suggest.
It will otherwise remain mild in the 60s, in light sly to swly flow
overnight, with post-frontal CAA likely to send temps into the
mid-upr 50s late over the wrn Piedmont, including the Triad.
.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 225 PM Thursday...
A strong cold front will move into central NC early Friday morning
and quickly advance through the area by Friday afternoon. A low is
expected to develop along the front, over the Carolinas and then be
pushed east and offshore with the front. Meanwhile aloft, the upper
trough will become negatively tilted as a shortwave swings through
the base over the mid-Atlantic. There is still fairly high
confidence that a line of showers will move through the area ahead
of the front through early afternoon, with the possibility of some
thunder in the afternoon. The best PVA aloft will move over the area
later Friday eve/night. Also, 925mb and 850mb frontogenesis will be
maximized over central NC in the aft/eve immediately behind the
front. As a result, some post-frontal light rain will be possible
through the evening/midnight, before completely drying out Friday
night as the s/w lifts away from the area. Cool high pressure will
then build into central NC Friday night. For temperatures, given the
current timing of the front moving through the area by Friday
afternoon, expect a non-diurnal temperature trend during the day,
with temperatures falling behind the front. As a result, the "low"
temperature Friday morning may actually be higher than the
temperature during the afternoon, especially over the western and
northern Piedmont. Highs will range from upper 50s NW to around 70
degrees SE, but as mentioned previously, many of the "highs" will
occur during the morning hours. Lows Friday night will drop into the
upper 30s NW to mid 40s SE, with the potential for some mid 30s in
the usual cool spots. However, the extent of the cooling will hinge
on how quickly the skies clear out. Winds will generally remain 5-10
kts through the night with some lingering gusts in the possible in
the Coastal Plain.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 330 PM Thursday...
Cool surface high pressure will settle into the area from the north
on Saturday and Sunday, resulting in dry weather and a taste of
autumn. Saturday will be the chilliest day, with high temperatures
only in the upper-50s to mid-60s, or about 10 degrees below normal.
While thicknesses will be on the rise Saturday night, this should be
when the center of the high is most directly overhead, and winds
will be lighter. Thus Sunday morning should be slightly cooler than
Saturday morning for central NC as a whole, with lows in the upper-
30s NW to lower-40s SE. This could result in some patchy frost,
mainly in the northern Piedmont. Highs will increase on Sunday to
mid-60s to lower-70s as more easterly return flow results from the
high lifting away to the NE.
Confidence has increased for the weather pattern next week, with
both the GFS and ECMWF coming into much better agreement that an
upper ridge will be anchored over the Southeast US. This will keep
any fronts well NW of central NC, resulting in mostly sunny skies
and minimal precipitation. However, easterly/southeasterly return
flow will result in gradually increasing moisture through the week,
with dew points in the 60s by Tuesday through Thursday. This
combined with weak instability may still result in a slight chance
of showers during the afternoon and evening from Tuesday through
Thursday, with the best chance across the Coastal Plain. Highs will
be near normal through the week, in the 70s, with lows increasing
from mid-40s/lower-50s at the beginning of the week to the upper-
50s/lower-60s by the end of the period.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 800 PM Thursday...
Initially dry, VFR conditions this evening will yield to scattered
showers and the development of MVFR to IFR ceilings late tonight-
early Fri, ahead of and along a strong cold front, and abrupt wind
shift from swly to nnwly, that will cross cntl NC TAF sites from nw
to se; between 08-09Z at INT and GSO and 13-15Z at RWI and FAY.
While ceilings are expected to lift to low VFR at INT and GSO prior
to 18Z Fri, post-frontal light rain and MVFR-IFR ceilings will
linger through most of Fri at RDU, FAY, and particularly RWI,
before then clearing by around the end of the 00Z TAF period.
Outlook: VFR conditions are expected through early next week, as
Canadian high pressure builds across and offshore the middle
Atlantic through that time.