Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/30/20
Area Forecast Discussion
National Weather Service Boston/Norton MA
957 PM EDT Thu Oct 29 2020
The remnants of Zeta will bring a soaking rain into this evening
along with strong winds near the coast. Rain will change to snow
overnight into Friday morning from north to south, even across all
of RI into southeast Massachusetts. 1 to 3 inches of snowfall is
expected. The storm moves out Friday afternoon. High pressure
returns this weekend with dry but chilly weather Saturday, followed
by milder conditions Sunday. Early next week will feature dry but
colder than normal weather.
.NEAR TERM /UNTIL 10 AM FRIDAY MORNING/...
10 pm update...
Precipitation rates have come down a bit over western MA as a
slot of dry air has filtered in ahead of the next round of
precipitation. HRRR model which has a good handle on the current
rainfall is leaning towards less precipitation than expected for
the western half of MA through 06UTC. Thus, decided to bring
rainfall totals down by about half for this for the 00Z-06Z UTC
time frame. Otherwise the previous forecast remains on track.
Remnant of Zeta now over MD and continuing
to move rapidly ENE to south of New England this evening. Some
mid level dry air north of the system and as a result seeing the
rain shield becoming fragmented over NJ into NYC. Thus may see
rain intensity slacken here for a time. However tropical
moisture aloft and remnant mid level low associated with Zeta
will produce periods of moderate to heavy rain into this
evening, then slackening off 00z-03z west to east as remnant low
A chilly rain with temps in the 40s and NE winds increasing as Zeta
passes to the south and 1020+ high builds into Quebec, squeezing the
pressure gradient. NE winds increase noticeably after 00z with gusts
up to 50 mph across Cape Cod and the Islands. Included Block Island
in the wind advisory given G50 mph seems likely. Given trees remain
fully to partially leaved across this region, low risk for down
branches and isolated power outages.
.SHORT TERM /10 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
425 pm update...
*** Accumulating Snow Likely Inland & into the Boston-
Providence-Hartford corridor ***
Overnight and Friday morning...
As remnants of Zeta move offshore, cold air begins to advect on
backside across New England, with column cooling from top down.
Rainfall intensity decreases later this evening but then picks up
again overnight as vigorous closed low over the southern MS Valley
advects northeast toward the region. As the cold air deepens rain
changes to snow, first across north-northwest MA around midnight and
then the rain-snow advances southward into the Boston-Providence-
Hartford line toward daybreak.
This is when models show mid level banding developing as mid/upper
level jet approaches from the southwest. Model qpf has trended
upward a bit from previous run which seems reasonable given strong
jet dynamics. HREF now showing low prob of up to 1 inch per hour
snowfall rates from about 12z-16z across northern portions of CT/RI
and MA including the city of Boston. This seems reasonable given the
strong mid level banding signature.
Initially snow will melt especially on paved surface given current
ground temps are in the upper 40s and lower 50s across the area.
However impressive cold air advection Friday morning when snow is
falling, with all model guidance showing 925 mb temps down to -4C to
-5C across northern MA and quickly advecting southward into CT and
RI. This will also support a coastal front developing with good cold
air drainage down the coastal plain into eastern MA and RI with snow
eventually accumulating on all surfaces. The limiting factor for
snow accumulations is initially melting snow on the front end and a
short duration of moderate to heavy snow, mainly 11z-16z. So while
our snow forecast of 1-3" will likely fall short of advisory
threshold (widespread 3+"), the combination of roads becoming snow
covered during the morning commute, vsby lowering to 1/4 mile at
times in heavy snow and the season`s first snowfall, is sufficient
support for a winter weather advisory to increase public awareness.
In addition, wet roads initially combined with temps falling below
freezing Friday morning (interior MA, northern CT into NW RI) may
fall into the upper 20s), may yield icy spots as well. Thus likes
like a slippery and slow morning commute. Highest snow totals on non
Will have to watch if 3+ inch amounts become more likely, especially
on trees, as the heavy/wet quality of the snow combined with trees
partially to fully leaved, would increase the risk for down tree
branches and possibly isolated power outages. Also next shift may
have to expand winter weather advisory eastward into all of eastern
MA including Boston if confidence increases on accumulating snow.
For the Cape and Islands, precip likely remains all rain other than
perhaps ending as a brief period of light snow around midday.
Upper air pattern is progressive so precip ends west to east late
morning into the early afternoon. Breaks of sunshine possible late
from west to east as well. Although not much of a temp recover given
strong low level CAA. It remains very windy on Cape Cod and the
Islands with NNE winds gusting up to 50 mph.
Astronomical tides are rather low which will likely preclude any
flooding. A surge of 1-2 ft is expected Fri but likely need a
surge of 2 to 2.5 ft for minor flooding. Minor splashover is
the worst case scenario along east coastal MA.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
425 pm update...
* A bit of a roller coaster temperature wise in the extended. Much
colder than normal Friday night into Saturday morning.
Temperatures trend upward through the weekend. This is followed by
another shot of cold air early next week. Temperatures trend
upward again mid to late in the week.
* Light precipitation chances Sunday into Monday.
Friday night through Saturday...
A trough will initially be over southern New England Friday evening,
while a ridge is building over the Northern Plains/Upper Mississippi
River Valley. The trough will lift offshore into Saturday morning.
The ridge will build into the central Great Lakes/Ontario. The ridge
will build over New England on Saturday and offshore by Sunday
morning. High pressure will build into the eastern Great Lakes into
Saturday morning. The high remains over the region on Saturday
before building into the maritimes Saturday night into Sunday
High pressure will bring clear skies and really relax the pressure
gradient over the region heading into Saturday morning. Aloft -5 to
roughly -10 degree Celsius 850 hPa air will advect in due to
northerly flow aloft. This in combination with the light winds will
result in very strong radiational cooling. Have knocked down the low
temperatures toward the 10th percentile of guidance. This results in
lows in the teens to low 20s across much of the interior. The
coastal plain will see readings range from the mid 20s to the mid
30s. Some spots are still in the growing season, so may need Freeze
Warnings in future forecast updates.
Temperatures trending upward Saturday and Saturday night. The highs
shifts to the east of the region. This will shift winds aloft to a
southwesterly direction, which will advect milder air into the
region. Still will be colder than normal for this time of year, but
dry with highs generally in the 40s on Saturday.
Saturday night through Monday night...
The ridge builds offshore on Saturday night into Sunday morning,
while a trough digs into the central Great Lakes. The trough will
continue digging as it moves into the eastern Great Lakes/New
England late on Sunday through Monday. At the surface southern New
England will remain within the warm sector ahead of a deepening low
over Ontario/Quebec late on Saturday through Sunday. The cold front
associated with the low will swing through late on Sunday into
Monday ushering in another blast of cold air.
Throughout this window it appears there could be some light
precipitation across the region. Best chance of any appreciable
precipitation is over southeast MA late on Sunday into early Monday
associated with the cold front passage. This is a result of an
influx of PWATs increasing to around 1 due to southwesterly flow.
Ptype is expected to be all rain. Though there may be some light
snow on Monday into Monday night as things are winding down.
Much colder air coming in wake of the front. Will see 850 hPa
temperatures falling to roughly -8 to -13 degrees Celsius on Monday
into Monday night. High temperatures change from near seasonable
temperatures on Sunday (generally the 50s) into the 30s and 40s on
Monday. Low temperatures bottoming out on Monday night into Tuesday
with readings in the teens and 20s, but the coastal plain will see
readings in the upper 20s to low 30s.
Tuesday and Wednesday...
Drier weather returns Tuesday and Wednesday as high pressure builds
in. Still another cold day on tap for Tuesday with northwesterly
cold air advection aloft. Temperatures topping out in the 30s to mid
40s. Does appear there will be a significant warm up for mid to late
in the week as flow becomes southwesterly advecting much warmer air
in. Temperatures rebound into the 50s for Wednesday. May see
widespread low to mid 60 degree readings for highs on
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight... Widespread IFR with embedded LIFR conditions tonight
with periods of moderate to heavy rain. Changeover from rain to
snow overnight beginning around 9UTC for western terminals and
expanding to the eastern terminals and south coast by 12 UTC.
Snow may be heavy at times bringing visibilities down to 1/2
mile or less. All rain for the Cape and Islands where there will
be gusty winds up to 45 knots out of the northeast.
IFR conditions will gradually improve to MVFR during the early
to mid afternoon and eventually VFR by late afternoon as rain
and snow showers taper off. Gusty winds will wind down gradually
over the same time period before high pressure and light winds
settle over the region Friday night into Saturday.
KBOS TAF...High confidence in TAF trends. Uncertainty in exact
timing. Heavy snow at times possible 10z-16z. Snowfall 1-3 inches
possible, highest amounts non paved surfaces.
KBDL TAF...high confidence in TAF trends. Uncertainty in exact
timing. Heavy snow at times 09z-15z. Snowfall 1-3 inches possible,
highest amounts non paved surfaces.
Outlook /Friday Night through Tuesday/...
Friday Night: VFR. Breezy.
Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Sunday: Mainly VFR, with areas MVFR possible. Windy with local
gusts up to 30 kt. Chance SHRA.
Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Monday: VFR. Windy with local gusts up to 30 kt.
Monday Night: VFR. Windy with local gusts up to 30 kt. Slight
Tuesday: VFR. Breezy.
425 pm update...
Gale warnings for all waters. NE winds 25-35 kt tonight into Fri
morning, except G45 kt across the outer waters from Cape Cod to
Block Island. Winds slowly decrease Fri afternoon.
Outlook /Friday Night through Tuesday/...
Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 12 ft.
Saturday: Winds less than 25 kt. Areas of rough seas.
Saturday Night: Winds less than 25 kt. Seas up to 5 ft.
Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Seas up to 5 ft. Chance of rain showers.
Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft. Chance of rain
Monday: Strong winds with local gusts up to 30 kt. Rough seas
up to 10 ft. Slight chance of rain showers.
Monday Night: Moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain
showers, slight chance of snow showers.
Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft.
CT...Winter Weather Advisory from 4 AM to noon EDT Friday for
MA...Wind Advisory until 2 PM EDT Friday for MAZ022>024.
Winter Weather Advisory from 4 AM to noon EDT Friday for
RI...Wind Advisory until 2 PM EDT Friday for RIZ008.
Winter Weather Advisory from 4 AM to noon EDT Friday for
MARINE...Gale Warning until 4 PM EDT Friday for ANZ232.
Gale Warning until 2 PM EDT Friday for ANZ233>235-237.
Gale Warning until 11 AM EDT Friday for ANZ230-236.
Gale Warning until 2 PM EDT Friday for ANZ231-250-251.
Gale Warning until 6 PM EDT Friday for ANZ254>256.
Area Forecast Discussion
National Weather Service Des Moines IA
1001 PM CDT Thu Oct 29 2020
Issued at 1001 PM CDT Thu Oct 29 2020
Little change to forecast though have brought slight PoPs a bit
farther south across the far north. Subjective H850 analysis shows
weak wave digging southeast with warm air advection driven light
snow over the Dakotas now; some echoes showing up in southern MN
and far northern Iowa, but airmass remains dry. As the night
progresses, the column will saturate over the north. Cloud depth
not very deep and perhaps some light snow/flurries overnight. HRRR
soundings at KMCW continue to show small potential for light
freezing mist with loss of ice introduction, but with a small dry
layer near the surface, impacts should be limited if any. None the
less will pass along to overnight shift. /rev
.DISCUSSION.../Tonight through Thursday/
Issued at 259 PM CDT Thu Oct 29 2020
The primary weather themes include mainly dry conditions through
the entire period, gradual warming to end the week, somewhat windy
conditions this weekend, and above normal temperatures Tue-Thu.
There will be minimal hope of appreciable moisture return with
our weather influenced by dry northwest upper level flow through
tomorrow, and only a brief flip to southwest ahead of the weekend
long wave trough passage. This will be followed by a transition
back to dry northwest flow before either zonal flow or minor
ridging takes hold into the middle of next week.
The immediate concern overnight will be the fate of the current
stratus central and east, and possibly a very small area of light
precip toward the MN border. With the surface ridging
approaching, do not expect full clearing until the warm front
passes and/or washes out later Friday, and there may even be a few
patches of fog overnight in the meantime. Mainly thermodynamic
lift 3km and below may brush light precip across the far
northeast. Have kept type frozen/snow, but light freezing rain
cannot be ruled out as some soundings suggest insufficient
moisture depth for ice introduction. Moisture is so suspect that
it could very well remain dry this far south as well.
By Saturday, our attention will turn toward the long wave trough
passage with increasing warmth and southerly flow ahead. Temps
should be well through the 50s with breezy south winds. Phased
thermodynamic and kinematic lift peaks across our area Saturday
morning into midday, but there won`t be sufficient moisture for
precip at any level. Strong subsidence than follows into Sunday
morning with brisk NW winds expected overnight Saturday through at
least Sunday morning. Winds may gust to 30+kts at times on both
the warm and cool side of the frontal passage.
Looking ahead to next week, warming will commence in earnest with
highs back into the 50s Monday after the Sunday cool down. This
will be followed by either zonal flow, or weak ridging depending
on solution, but regardless will favor weak but prolonged
southerly low level flow, boosting highs in the 60s for
consecutive days to end the period. All models suggest at least a
central/southern Plains short wave passage by Thursday, but
deterministic and ensemble solutions differ with regard to the
degree of long wave phasing. The vast majority of solutions keep
things dry by Day 7 regardless of how things play out, either due
to the lack of moisture and/or forcing.
.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 619 PM CDT Thu Oct 29 2020
Main focus will be lingering MVFR cigs north this evening. Statocu
that developed southeast/east should slowly dissipate aft sunset
with MVFR becoming VFR north with time. Otherwise, light winds in
place thorugh period with gradual swing to southeast flow between
06 to 12z. Small risk of brief precipitation near KMCW around 12z,
otherwise dry entire period. /rev
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
949 PM EDT Thu Oct 29 2020
Drier air will begin to filter into the area behind Zeta starting
tonight. A couple shots of cool Canadian air will support below
normal temperatures with possible frost/freeze conditions this
weekend into early next week. Temperatures start to rebound by the
middle of next week, while most locations remain mostly dry through
the seven days.
.NEAR TERM /THROUGH FRIDAY/...
Evening Update...A line of showers has formed ahead of a llvl convg
zone across the ern zones. The line has slowed as it has become
parallel with the upper pattern. There are decent rainfall rates,
however, the line as a whole is weakening with loss of lift. Don/t
envision any hydro issues across the ern zones as that area received
the least precip with the remnants of TC Zeta...but will keep an eye
on area streams, esp arnd Meck Co over the next couple hrs. The wind
adv areas still look good as the LATEST RAP shows a h85 temp
gradient developing ahead of the upper trof axis. Decent CAA will
aide in bringing stg gusts to the sfc and a few trees may be downed
due to moist antecedent conds thru the overnight, mainly abv 3500
800 PM Update...Issued a wind advisory for NE GA and the wrn NC
mtns. Strong forcing from an upper low and some measure of llvl CAA
will enable gusts in the 35-40 kt range. Due to the recent heavy
rainfall, it/s possible a few trees may be blown down.
730 PM Update...Shower activity continues across the Upstate and srn
NC this evening. These cells are moving quickly NE in a strongly
sheared environ and have been mixing down winds on the order of 35
kts. Expect these showers to continue across the ern Piedmont over
the next few hrs and due to highly moist soils, a few weak trees and
limbs could be blown down underneath the stronger downdrafts.
500 PM Update...Starting to see a few cells pop up across NE GA and
the western Upstate. The activity is remaining fairly shallow and
short-lived for now, but with sfc convg increasing in moderate
sbCAPE and a deeply sheared environ...will watch for possible stg
development thru the next update.
As of 250 PM EDT Thursday: We are now in the calm after the storm so
to speak as Zeta has exited the area with breezy and warm conditions
in its wake. In fact, we are nearing daily record highs with
temperatures near 80 across much of the area. The unseasonably warm
and humid weather won`t last!
A closed upper low over the lower Mississippi River Valley will
merge with the polar jet over Appalachians tonight before pushing
offshore into Friday. A weakening front with the closed low will
pass through the region from the west this evening with little
fanfare other than to maintain some breezy westerly winds at times
and perhaps some isolated showers and a thunderstorm or two focused
southeast of I-85. A secondary, more pronounced cold front will wrap
in behind the departing trough, ushering in much colder air on gusty
northwest winds. In fact, strong cold air advection and a tightening
surface pressure gradient that becomes orientated more northwest to
southeast may support advisory level wind gusts across high mountain
elevations tonight. Given the recent rain there is at least some
potential for additional downed trees or powerlines for this area.
In collaboration with neighbors have held off on a wind advisory for
now, but will pass along the potential need to the next shift.
Upslope clouds and some shower activity is likely behind the front
near the TN border. Overnight lows in the mid 40s to mid 50s will be
a good 10 to 15 degree drop off this mornings lows with the dry and
gusty conditions making it feel even cooler. Cold air advection will
continue into Friday and support only about a 10 degree warm up over
the morning lows despite good insolation, with highs in the mid 50s
to mid 60s.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 2:30pm EDT Thursday: Saturday and Sunday will be notably
cooler with area well behind major cold front, with large dome of
high pressure over the eastern CONUS and northerly cold advection
just coming to an end Saturday morning. As high pressure moves
eastward on Saturday, winds become more northeasterly and brief
wedge flow conditions are expected for Saturday night/Sunday, with
consequent overcast skies and a slight chance for a little rain or
drizzle. Some areas of frost or freeze are possible Saturday morning
in higher terrain areas and the foothills, with more widespread
frost/freeze possible Sunday night. Temperatures look like they
will be 5 to 10 degrees below normal Saturday and Sunday, and this
will be a drop of 10 to 20 degrees from levels seen today
(Thursday). Currently, only a few of the highest elevation locations
are forecast to drop below freezing Saturday morning, and will hold
off on a Freeze Watch for the moment. Next front begins to affect
northwest parts of the CWA late on Sunday, which should disrupt the
CAD as winds become northwesterly.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 2:30pm EDT Thursday: Monday morning may be the coldest point
so far this season, with freezing temperatures forecast for all of
the higher elevations, and frost possible elsewhere, though frost
may be mitigated by wind. Tuesday morning may be slightly colder due
to lighter winds, with a better chance for frost all areas. Cold air
is courtesy of a synoptic front that passes through late
Sunday/early Monday which is associated with a progressive long wave
trough. This will usher in much dryer and cooler air for Monday and
Tuesday, with moisture beginning to recover on Wednesday. Dewpoints
Monday and Tuesday will be in the 20s. Dry air mass provides little
chance for any rain, with mostly clear skies through Thursday.
Temperatures slowly warm from Tuesday afternoon onward, but Monday
and Tuesday look to be 5 to 10 degrees below seasonal normal.
Strongest winds of the period are with the FROPA Sunday night/
Monday morning, with highest winds over higher elevations at 10 to
20 mph. These northerly winds combined with cold/dry advection will
produce some wind chill down into the teens at the highest
elevations in exposed locations.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: A few showers are crossing the SC and srn NC
areas this evening. These will approach CLT arnd 00z and may mix
down stg gusts and bring MVFR/IFR restrictions...have VCSH for now
as confidence is low on track and duration of these cells. After
this activity clears east arnd 03z...the fcst will become VFR all
TAF sites with winds remaining fairly stg and gusty at times
overnight and into the daytime period. Winds will veer...generally
going from sw/ly to nw/ly thru the period.
Outlook: General VFR conds will prevail through the next few days
although diurnal restrictive cigs/vsbys are possible across the mountains
and foothills each morning.
01-07Z 07-13Z 13-19Z 19-00Z
KCLT High 99% High 100% High 100% High 100%
KGSP High 92% High 100% High 100% High 100%
KAVL High 100% Med 72% Med 68% Med 61%
KHKY High 100% High 91% Med 76% High 100%
KGMU High 100% High 92% High 100% High 100%
KAND High 100% High 100% 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 are available at
the following link:
GA...Wind Advisory until 4 AM EDT Friday for GAZ010-017.
NC...Wind Advisory until noon EDT Friday for NCZ033-048>053-058-059-
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
840 PM CDT Thu Oct 29 2020
Updated for evening discussion.
Despite strong low level subsidence in the cold air advection
regime, sufficient overall ascent remains with the advancing thermal
trough to support the persistent low cloud cover in the shallow
moist layer near 850 mb this evening. RAP and HRRR show the low
level thermal trough moving through most of the area after midnight
and taking the majority of the cloud cover with it as subsidence
becomes dominant. Residual cloud cover will remain in the east
around sunrise, but clearing will ensue shortly thereafter./GG/
Prior discussion below:
Tonight into Tomorrow: A much cooler day has prevailed across the
region with temperatures 15 to 20 degrees cooler than this time
yesterday. This all comes as a front moved through the region
earlier today and an upper trough moved across the region. Cold
air advection has been in full swing today, and despite the
sunshine, temperatures have been in the upper 50s and lower 60s
today. A chilly night is expected, but some cloud cover moving
across the region may help keep conditions better than they
otherwise might be. Temperatures tonight will be in the lower 40s.
Another cool day is expected tomorrow with highs ranging from the
upper 50s in the north to the lower 60s in the south. Northerly
winds will continue tomorrow but overall wind gusts should not be
as strong as they were today. Dry weather will continue Friday./28/
Saturday through Thursday: Dry weather looks to persist this
weekend through the middle of next week, with generally high
agreement among model guidance for the overall pattern through
that time. Between departing high pressure and the next cold
front, max temps on Saturday should rebound to near 70 degrees
across the area. Then heading into Sunday, a digging upper-level
shortwave trough and attendant surface low over the Great Lakes
trough will usher a cold front through our forecast area. Timing
of the front`s arrival means cold air advection may not establish
fully until the afternoon - after temps have a chance to warm up
during the day. Stuck with a general consensus blend of guidance
for the day until the finer details come into focus.
In the wake of the front though, Sunday night through Monday
night especially will be cooler. As post- frontal surface high
pressure settles over the Deep South, nighttime cooling will have
a chance to overachieve with radiational cooling. While no
freezing temperatures are currently anticipated, frost development
across looks increasingly likely across much of the forecast area
Monday night into Tuesday morning. Added patchy frost to the
forecast for Monday night as lows fall into the lower to mid-30s
with light winds and clear skies. Did not include in the
Hazardous Weather Outlook text or graphics at this time, but will
likely need at least "Limited" threat area going forward to
capture the frost potential. /NF/
00Z TAF discussion: MVFR ceilings this evening, mainly north of
Interstate 20, will diminish from the west after midnight. VFR
conditions will prevail for the remainder of the period./GG/
.PRELIMINARY POINT TEMPS/POPS...
Jackson 43 60 41 69 / 3 0 0 0
Meridian 45 60 42 70 / 0 0 0 0
Vicksburg 43 61 41 69 / 1 0 0 0
Hattiesburg 44 63 42 71 / 0 0 0 0
Natchez 43 62 41 69 / 0 0 0 0
Greenville 40 57 39 65 / 3 0 0 0
Greenwood 40 59 40 68 / 7 0 0 0
Area Forecast Discussion
National Weather Service Marquette MI
633 PM EDT Thu Oct 29 2020
.SHORT TERM...(This evening through Friday)
Issued at 353 PM EDT THU OCT 29 2020
Latest RAP analysis and GOES Satellite show troughing that extends
from the Hudson Bay, down into the northern CONUS. With the cold
front passing last night, sfc ridging of 1025mb is currently over
the northern plains that will gradually shift towards the Upper
Great Lakes Region by later this evening. Until then, north to
northeast winds will be the driving force for some flurries or light
lake-effect snow showers this afternoon. There were some areas of
freezing drizzle from this morning. I don`t really expect to see
much in the way of freezing drizzle this afternoon cannot completely
rule it out but as a precaution, did include it in the grids with
temps not rebounding from this morning. Winds will continue to ease
and relax throughout the evening and overnight and any precip
chances should be ending as well. With latest guidance, did end up
penciling in some slight chc PoPs over the Keweenaw with a few
webcams from Copper Harbor to near Houghton were showing light
flurries. Clouds should be breaking up and clearing by Friday
morning, setting up for a dry Friday with a mix of sun and clouds.
Temperatures this afternoon have not really risen much since this
morning with the clouds wanting to hang around. Did not mess with
the temps for the rest of the day as I think the forecast is
relatively on track. Lows tonight will again be mostly in the 20s
with a few upper teens over the interior. If clouds do break earlier
than anticipated, then lows could fall further but not really
confident at this point as clouds and moisture look to keep
temperatures from dropping too much. Even with some sunshine Friday,
don`t think temperatures will warm too much as compared to today
with highs again in the 30s.
.LONG TERM...(Friday night through Thursday)
Issued at 350 PM EDT THU OCT 29 2020
Weak upper level ridging will begin to take place by Friday night
over the CWA allowing for moderated temperatures during the
overnight period into Saturday. 700mb temperatures warm close to the
0 degree Celsius mark by late Saturday, which should mix down to the
surface and allow afternoon highs to be near seasonal averages of
the mid to upper 40s, with the southernmost inland areas reaching
The main weather system to affect the region will approach from the
west Saturday night. This weather event looks to have multiple
impacts as strong winds and lake effect snow showers will take place
between Saturday night and Sunday afternoon. Medium range guidance
has been in good agreement on the location and placement of the lake
effect areas and strong winds the past few days. Gale force winds
will be likely across the waters of Lake Superior along with
shoreline erosion becoming possible during the strongest part of the
weather system evolution. 700mb temperatures will decrease rapidly
from near the 0 degree Celsius mark Saturday afternoon to near -15
to -18 degrees Celsius by Sunday evening.
Overall, snow showers will increase in coverage from west to east
early Sunday morning once the changeover in the lowest elevations
from rain to snow occurs. Initial thoughts are for the heaviest lake
effect snow to occur on the western half of the CWA, and then
transition to the eastern half of the CWA for midday Sunday through
the afternoon. The GFS has the slowest propagation of the weather
event, thus the higher snow totals are forecast based off that
model. The remaining medium range guidance has the weather event
being more progressive, and inhibiting snow accumulation totals.
Timing differences are still in place regarding an approaching
shortwave disturbance on Monday arriving on the northern borders of
the CWA potentially bringing a rain/snow mix to some of the areas.
This shortwave will not have all that much of an impact in
comparison to the weekend system.
Upper level ridging then begins to take hold over the area as
temperatures moderate nicely back to seasonal averages, with several
areas likely eclipsing 50 degrees by the mid to late portion of next
week before the next weather system approaches the area the
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 633 PM EDT THU OCT 29 2020
MVFR cigs are ongoing at all terminals and should remain at MVFR for
the rest of the evening. All sites will go VFR later tonight, first
at IWD and last at SAW.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 353 PM EDT THU OCT 29 2020
Winds will continue to ease through Friday with winds generally
below 20 knots. This will last through Saturday morning and then
attention will turn to Saturday afternoon into Sunday. Confidence
his high, regarding the potential for high-end gales Saturday
afternoon into Sunday. Winds will increase from the south with
speeds up to 40 knots over the east half while the west half has
winds up to 30 knots with some gale force gusts to 35 knots
possible. Winds will transition to the northwest gales across the
entire lake early Sunday morning through Sunday afternoon. Winds
will be between 40-45 knots across the west half with possible storm
force gusts between 50-55 knots across the east half. Waves will
reach between 14-20 ft on Sunday. With the high confidence in this
occurring, have posted a Gale Watch for west half and far east, and
a Storm Watch for north central and east. Winds will diminish below
20 knots by Monday morning and will continue under 20 knots into
Gale Watch from Saturday morning through Sunday afternoon for
Gale Watch from Saturday morning through Sunday morning for
Storm Watch from Sunday morning through Sunday afternoon for
Gale Watch from Saturday evening through Sunday afternoon for
Gale Watch from Saturday evening through Sunday morning for
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
930 PM EDT Thu Oct 29 2020
A surface area of low pressure and associated cold front will sweep
across the region tonight. Canadian high pressure will follow for
Friday and Saturday.
.NEAR TERM /THROUGH TONIGHT/...
As of 930 PM Thursday...
Winds continue to diminish with the departure of Zeta off the Mid
Atlantic coast, although a fairly tight MSLP gradient persists over
the region with surface low pressure centered over extreme NW NC /
SW VA, a frontal zone extending from this low ENE to Zeta, a cold
front extending south through GA, and large dense high pressure
covering the Central Plains, so the risk of periodic gusts to 15-30
mph will hold tonight. MLCAPE of 500-1000 J/kg persists within the
warm sector over the central and eastern Carolinas, and while the
loss of heating should allow this to trend down a bit over the next
few hours with rather low mid level lapse rates, the falling heights
aloft and strengthening DPVA should help support increasing
convection becoming more organized and growing upscale as it tracks
rapidly NE. Damaging straight line winds attending bowing segments
remain the primary threat given 40-45 kts at 925 mb, although some
rotating cells cannot be ruled out. Have largely followed the timing
of the last few HRRR runs, marching a convective line across the CWA
over the next several hours, with a lingering threat of scattered
showers and storms over the N and NE CWA overnight with the arrival
of the potent mid level shortwave trough and upper divergence max
within the associated right jet entrance region. Expect the surface
low to track roughly eastward along the NC/VA border tonight, with
weak surface troughing trailing back to the SW, and the actual
synoptic front not pushing through until shortly before daybreak.
Expect lows from the low 50s NW to low 60s far E. -GIH
Earlier discussion from 350 PM:
Wind gusts continue to diminish across cntl NC this afternoon; and
all wind headlines will be cancelled with the 4 PM forecast package.
A period of shortwave ridging aloft and subsident and stable
conditions has expanded across NC this afternoon, between Zeta and a
closed mid-upr level low over nwrn MS. That low will become an open
wave trough while lifting and accelerating newd across the srn
Appalachians and srn middle Atlantic through 12Z Fri, with preceding
50-100 meter 500 mb height falls and maximized QG forcing for ascent
centered over cntl NC at 06Z Fri.
At the surface, the remnants of Zeta, centered over srn MD at 19Z,
will continue rapidly enewd and offshore the middle Atlantic through
early this evening. A cold front was analyzed from Zeta wswwd across
wrn VA and cntl WV, to a 999 mb low over ern KY. A trailing cold
front was analyzed from that low sswwd across wrn GA and the cntl FL
panhandle. The low will develop slowly ewd across the frontal
segment across wrn and cntl VA through early tonight, while the
trailing cold front continues ewd across GA and the Carolinas,
including across cntl NC between approximately 03-07Z Fri.
While wind gusts will generally weaken with both nocturnal cooling
and the departure of the strongest flow accompanying Zeta, gusts
between 20-35 mph will be possible at least intermittently
overnight, in both swly flow ahead of, and nwly flow behind, the
aforementioned cold front.
Visible satellite imagery and regional radar data depict deepening
cumulus and widely scattered showers along the cold front from ern
TN swd across w-cntl GA this afternoon. The models indicate
continued deepening and development will occur across GA and the wrn
Carolinas through 00Z Fri. That convection will subsequently
overspread cntl NC, while probably organizing into a broken line
along the front. While the overall severe threat will remain only
marginal owing to weak lapse rates and instability, the latter
characterized by SBCAPE of generally less than 750 J/kg, the
presence of strong vertical wind shear supplied by a 100 kt, swly
500 mb jet will maintain a conditional risk of locally
strong/damaging surface wind gusts up to 45 kts or perhaps an
isolated tornado, mainly along and east of a line from AFP to RDU to
HNZ. Occasionally gusty surface winds will then continue behind the
cold front overnight-early Fri, as much cooler and drier air surges,
in nwly flow, across the region, with lows mostly in the 50s.
.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 205 PM Thursday...
The surface low will shift off the mid-Atlantic coast Friday morning
as the upper shortwave exits northeast of the area. A cold front
will be east of the area by early Friday in the wake of the
departing surface low off the mid-Atlantic coast. High temperatures
on Friday could be a bit tricky, but generally expect low 60s NW to
upper 60s SE. Strong northwesterly flow will advect some cooler,
drier air into the area, though the better CAA will occur Friday
night as high pressure builds into the northeast and ridges into NC.
With clear skies overnight but continued breezy conditions, expect
lows Friday night in the mid 30s NW to mid 40s SE.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 251 PM Thursday...
Surface high pressure moving across the Northeast on Saturday will
result in a cool and dry Halloween in Central NC. Highs will be
below average in the mid 50s to lower 60s with lows in the 40s. A
strong deep mid-level trough will move across the area Sunday
afternoon and evening bringing below average temperatures. Models
continue to show a slight chance of precipitation across the area
with QPF between a trace and hundredth of an inch. Before the front
moves across the region, temperatures will be warmer than Saturday
with highs in the low 60s in the NW and Low 70s in the SE. As the
high pressure builds across the southern central plains and moves
east, it will bring the coldest temperatures of the season so far
this season. Sunday night the NW Piedmont will see temperatures in
the low 30s while the Coastal Plain will see upper 30s/ low 40s. The
strong SW winds will keep frost from developing Sunday night/Monday
morning. Highs Monday will be in the low to mid 50s, which is 15-20
degrees below normal. Monday night winds will be calmer due to high
pressure overhead and clear skies will help make this the coldest
night of the forecast period. Monday night temperatures across the
entire area will be in the low to mid 30s resulting in some patchy
frost, especially in the NW Piedmont. As the high pressure moves NE
along the coast, temperatures will still be well below normal but
will be in the upper 50s and low 60s. Wednesday and Thursday high
temperatures will remain slightly below normal in the upper 60s and
low 70s, with lows 40s.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 740 PM Thursday...
A complex weather pattern remains for the 00z TAF period. Post-
tropical cyclone Zeta has already raced offshore into the Atlantic
Ocean. Winds have relaxed a tad, but are still between 10 and 20
knots out of the south and southwest. There is some uncertainty on
the direction and speed of the wind. In addition, expecting a period
of low-level wind shear overnight-early Friday as winds remain
strong around 35 knots. Currently, a weak area of low pressure
exists over far northeastern Tennessee, with a trailing cold front
extending into western NC and into Georgia. This cold front will
track through during the overnight hours. Ahead of the front,
expecting rain showers over the Triad, with a brief period of MVFR
ceilings. Further east, expecting a line of showers and
thunderstorms developing between 02-04Z at RDU, 04-06Z at FAY, and
05-07Z at RWI, with IFR/MVFR conditions. These storms should quickly
race east onto the Coastal Plain shortly after 08Z, with some
lingering showers at RWI till 09Z. Winds will shift to be out of the
northwest after 13Z and remain gusty between 20 and 25 knots during
the day with VFR taking over.
Outlook: A couple of areas of high pressure will maintain mainly VFR
conditions through early-mid next week, interrupted briefly by a
chance of showers and MVFR conditions along a passing cold front on