Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/27/19
Area Forecast Discussion
National Weather Service Columbia SC
1046 PM EDT Thu Sep 26 2019
A weak cold front will be near the forecast area tonight and
become stationary in the area Friday. The front will focus
scattered showers and thunderstorms mainly Friday afternoon and
evening. The front will dissipate late Friday night. High
pressure and above normal temperatures are forecast Saturday and
Sunday. There will be another chance for showers associated
with a diffuse cold front Monday.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Record heat occurred today with new record high temperatures
being set at Columbia (99) and Augusta (97). A cold front was
pushing southeast through central PA/WV into southeast KY and
central TN. This front will continue to push south into the
forecast area by Saturday morning before stalling.
Skies expected to be relatively clear through the night although
an increase in clouds is possible during the predawn hours in
the Pee Dee and eastern Midlands region due to potential stratus
cloud development. Overnight lows will again remain above normal
with lows in the upper 60s to lower 70s.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
The front is forecast to be stalled in the forecast area Friday.
There may be lingering fog associated with the front and nocturnal
cooling early. The SREF guidance supports higher probabilities of
early morning fog in the southeast section.
The models indicate general upper ridging but there may be a
shortwave trough in the ridging. The front along with a sea breeze
boundary which may push well inland along with the possible upper
support plus heating should result in thunderstorms. The ARW
suggested the greatest coverage in the southeast part likely because
of the sea breeze boundary. The guidance has been consistent with
chance pops and believe this is reasonable because coverage should
be limited with upper ridging plus little convergence into a weak
front. Moderate instability may occur as indicated by the NAM
supporting possible severe thunderstorms, but the weaker instability
indicated by the GFS is more likely because of cloudiness and
relatively high h5 temperatures of -6 to -7 C. The guidance has been
consistent with highs near 90.
Scattered thunderstorms may linger Friday evening but dissipate
overnight with the loss of heating and a more diffuse front along
with upper ridging. Fog may become an issue late because of high low-
level moisture associated with the remnants of the front and light
wind. The MAV and MET MOS indicated fog. The guidance was close with
lows near 70.
The models have been consistent with upper ridging and associated
mid-level capping more dominate Saturday and Sunday. Surface ridging
was also depicted in the region. The pattern supports above normal
temperatures and a diminished thunderstorm chance. We followed the
guidance consensus with lows mainly near 70 and highs in the middle
90s with pops less than 20 percent.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
The GFS and ECMWF indicate ridging at the surface and aloft
dominate. However, there may be increased moisture Monday
associated with a diffuse backdoor front. The GFS and ECMWF MOS
support continued above normal temperatures. We maintained pops
less than 20 percent through the period, except did keep about a
20 percent pop because of the possible backdoor front Monday.
Tropical system Karen may turn westward and get closer to the
Southeast Coast, but the impact chances are low for the forecast
area. The GFS and ECMWF do not indicate the system reaching the
forecast area. The timing would not be until the middle to late
part of next week if by chance the system were to affect the
local area. See the latest advisory on Karen from the National
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
A sea-breeze boundary continues pushing inland this evening
although has also not advanced as far inland as the previous
night. With drier air over the region we anticipate shorter
duration restrictions tonight. Fog-prone AGS is most likely to
have IFR or lower visibility restrictions. Model guidance is
more optimistic than the previous night. Recent runs of the HRRR
have suggested a brief period of IFR/LIFR stratus across the
central Midlands and CSRA early Friday morning.
Scattered showers and thunderstorms are expected Friday
afternoon. Associated reductions in visibility and strong wind
gusts will be possible. Otherwise, winds will be light and
generally out of the east or south.
EXTENDED AVIATION OUTLOOK...Daily restrictions possible in
early morning fog and stratus.
Area Forecast Discussion
National Weather Service Marquette MI
628 PM EDT Thu Sep 26 2019
.SHORT TERM...(This evening through Friday)
Issued at 330 PM EDT THU SEP 26 2019
RAP analysis and visible imagery show Upper Michigan under the
peripheral influence of sfc high pressure centered over IL. Earlier
lake effect rain showers mainly east of Marquette have diminished,
and though diurnal cumulus overperformed today skies are clearing
out from west to east this afternoon as drier air works in. Dew
points this afternoon are in the upper 30s over the interior, with
temperatures in the upper 50s to lower 60s.
As a shortwave digs out of Saskatchewan and Manitoba tonight,
surface cyclogenesis in the vicinity of ND will commence. This low
will trek across the Boundary Waters and then turn northeasterly
Friday morning, with a strong LLJ developing ahead of the low over
Upper Michigan late tonight. Scattered showers will develop and move
in from the WSW as well, mainly affecting the western and northern
UP overnight. As the associated cold front moves through the UP
during the day, better rain chances are expected over the central
and eastern UP, though there are some indications of a band of rain
setting up over the west around midday as the front moves in as
well. Rainfall totals should mainly be under a quarter inch though
locally approaching half an inch over the northern and especially
far eastern portions of the area by the end of the short term.
The pressure gradient will remain strong through Friday, and 850 mb
winds will approach 50+ kts for a brief period in the AM. Wind gusts
of 20-35 mph will be possible, highest over favored locations like
the Keweenaw, along the Lake Michigan shores, and downslope
locations in the northern UP. Pressure falls will maximize over NW/N
Lake Superior in the 08-14Z time frame, allowing for a strong
isallobaric component to the winds.
There is a slight chance for a small amount of instability to creep
into southern Menominee and Delta Counties and an isolated rumble of
thunder cannot be completely ruled out in the afternoon, but for the
most part it will just be a dreary, cool, and windy Friday. Showers
will gradually diminish and begin to exit eastward through the
evening and winds should start to lessen as well as high pressure
builds into MN.
.LONG TERM...(Friday night through Thursday)
Issued at 436 PM EDT THU SEP 26 2019
The long advertised (showed up in models more than a week ago)
pattern of an amplifying western CONUS trof this weekend is still on
track. This will result in a building eastern CONUS ridge. However,
at the same time, strong height rises over Greenland will occur,
resulting in a -NAO. This will tend to suppress heights over se
Canada, keeping the eastern CONUS ridge from building farther N.
Thus, what looked like a more prolonged warm spell for Upper MI days
ago will not develop out of this western trof/eastern ridge pattern.
In the end, there may only be one, possibly two, warm days (solidly
above normal temps) early next week as an ejecting shortwave from
the western trof sends associated sfc low on northeastward track
just nw of Upper MI, placing the fcst area briefly in the warm
sector. Thereafter, tendency for some degree of troffing in se
Canada will allow cooler conditions (probably a few days of blo
normal temps) to prevail until next weekend. As for pcpn, best
opportunity of shra will occur late Sun/Mon in association with the
aforementioned ejecting shortwave. After that wave passes, the
western CONUS trof will linger, allowing for the potential of
additional shortwaves to lift ne toward the area. However, pcpn
potential across the fcst area thru the midweek period will depend
on how far s the early week cold front moves, which is dependent on
the degree of height falls over se Canada. Right now, it appears
those height falls may be sufficient to push the cold front far
enough s so that the more persistent/heavier pcpn stays se of Upper
MI, but that`s not for certain. Even if it does slip well s, there
will be a continued risk of shra from time to time thru the midweek
period as energy ejects from the western trof. Obviously, better chc
of shra will be across the se part of the fcst area, closer to the
frontal boundary. Dry weather should set in late week as building
mid-level ridge shifting from western toward central Canada supports
strengthening sfc high pres settling into the Upper Lakes.
Beginning Fri night, cold front associated with shortwave crossing
the northern Great Lakes on Fri will be exiting to the se of the
fcst area during the evening. Showers vcnty of the front will depart
early. During the night, 850mb temps are fcst to fall to 0 to 2C,
marginally low enough to support potential of some light lake effect
shra. However, inversions falling to 3-4kft suggest pcpn potential
is minimal. So, no mention of pcpn will be included in this fcst
issuance. High pres ridge building into nw WI could lead to the
first widespread frost of the season over western Upper MI Fri night
as winds diminish toward calm. The one complication is whether there
may be stratocu hanging around thru the night due to low-level winds
off Lake Superior.
The sfc high pres ridge will shift across Upper MI during the day on
Sat. While skies will become mostly sunny across the area, there may
be a fair amount of cu/stratocu development for a time during the
morning. High temps will be near or slightly blo normal.
Sat night/Sun, NAM and ECMWF are quicker advancing pcpn ne into
Upper MI as waa regime develops/strengthens and lifts n and e across
the Plains in response to the amplifying western trof. Given the
broad nature of the waa which is not particularly focused toward the
fcst area in addition to the antecedant dry air mass over the area
and limited theta-e adv, seems the NAM/ECMWF are too quick spreading
shra ne. Shra may reach the counties bordering WI late Sat night
with some shra then continuing to spread ne across the area on Sun
under strengthening theta-e adv.
During Sun night, approach of sfc warm front, nose of 40kt low-level
jet aimed toward Upper MI and advection of elevated instability
toward the area should yield more widespread shra/sct tsra. With
precipitable water surging up to around 1.5 inches, 200-250pct of
normal, hvy rainfall will be possible.
Shra coverage will likely decrease on Mon as sfc warm front should
lift n of Upper MI. If the front does lift n, it will become a
warm/humid day with high temps in the 70s F and dwpts back into the
60s F again.
As alluded to above, fcst on Tue/Wed will depend on how far s cold
front moves in association with shortwave lifting across northern
Ontario. Placement of the front will be important as it will become
a focus for episodes of mdt/hvy rainfall. For now, fcst will depict
a gradient across the fcst area with lowest chc of shra nw and
highest potential se. High temps will fall back to the 60s Wed and
50s Wed as low-level cooler air steadily spreads se toward Upper MI.
Expect a drying trend Thu/Fri as front pushes farther s with
upstream sfc high pres approaching. Depending on how cool the air
mass becomes, some lake effect -shra may eventually develop. Some
higher terrain locations over the w and n central may see high temps
fail to reach 50F on Thu.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 627 PM EDT THU SEP 26 2019
VFR conditions will continue through Fri morning at all sites.
Showers move in overnight. MVFR conditions will set up by Fri
afternoon at all sites.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 330 PM EDT THU SEP 26 2019
Winds this afternoon are generally around and under 20 knots except
near Isle Royale where 25 kt gusts have persisted. South winds will
pick up quickly tonight ahead of the next strong system, with 30 kt
winds overspreading the lake from west to east and then some gale
force gusts looking likely on lake for about a 6 hour period Friday
morning. A few gusts as high as 40 mph seems possible at higher
platforms. A gale warning will be in effect for several zones to
cover this threat. Cold front clears the lake Friday evening and
winds shift to NW and relax back to around 20 kts. They subside
further on Saturday to around 15 kts as high pressure moves
overhead. The next strong system approaches Lake Superior Monday
with some strong E winds possible as early as Sunday evening over
the western lake, but models are spread out in their solutions so
confidence during this period remains low for now outside of the
expectation for 15-25kt winds early next week.
Beach Hazards Statement until 9 PM EDT this evening for MIZ006.
Gale Warning from 8 AM to 2 PM EDT Friday for LSZ249>251-266-267.
Gale Warning from 5 AM to 1 PM EDT Friday for LSZ263-264.
Gale Warning from 8 AM to 2 PM EDT Friday for LMZ248-250.
Area Forecast Discussion
National Weather Service Blacksburg VA
826 PM EDT Thu Sep 26 2019
A weak cold front moves south across the region tonight. High
pressure following the front to the north will drift off the
Mid-Atlantic coast Friday into Friday night in advance of
another cold front that approaches Saturday night. This front
pushes in from the north by Sunday.
.NEAR TERM /THROUGH FRIDAY/...
As of 826 PM EDT Thursday...
A weak cold front will drop south across southern portions of
forecast area this evening into tonight. An isolated shower is
possible along the boundary for the next couple of hours. The
HiRes-ARW-EAST and HRRR showed all convection ending by 03z.
KFCX radar loop showed showers diminishing quickly this evening
with weaker instability across the southern Appalachians. Cut
back pops for tonight. Adjusted temperatures utilizing the
latest surface obs, their trends, and shaped towards NBM for
this evening into tonight. Made some minor adjustments in clouds
tonight into Friday. High pressure builds into our area
Friday. Have a good night!
As of 230 PM EDT Thursday...
Small clusters of shallow pre-frontal convection now over the
west will gradually shift southeast and weaken upon crossing
the ridges while encountering strong westerly flow/dry air.
This also supported by lack of much instability across the
region this afternoon given such a well mixed environment per
latest analysis. However latest short term guidance suggests
that once winds diminish that some of these showers may make it
east of the Blue Ridge and perhaps redevelop in spots over the
far west where aided by westerly upslope convergence. Thus added
in a bit more pop in the east/southeast through early this
evening while keeping chance pops over the far southwest.
Otrw weak cold front to dip southeast through the region
tonight resulting in another surge of dry and somewhat cooler
air for later tonight into Friday as high pressure builds to the
north. May again see some low level moisture get banked up
against the western ridges with guidance depicting some residual
low clouds over the southwest as well. This may be overdone
given dry advection but leaving in enough clouds to maintain
partly cloudy in spots over the mountains but becoming mainly
clear elsewhere with some patchy fog around. Appears enough
cooling/decoupling to allow lows to fall into the 50s north
including valleys with lingering higher dewpoints holding the
south in the 60s.
Surface high quickly swings offshore to the northeast on Friday
under fast/flat flow aloft and ahead of the next upstream
shortwave trough/cold front. This to veer the low level flow
more around to the southeast in the afternoon with some degree
of gradual moisture return over the southwest late in the day.
However model soundings show a very dry column so running
without pops with perhaps a bit more cloudiness lingering as
well out east within the easterly flow. Kept highs on the warm
side of guidance over dry ground, similar to the 12z Euro mos,
despite the weak onshore trajectory. However still cooler than
today per highs mostly 70s to near 80 mountains and low/mid 80s
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 315 PM EDT Thursday...
High pressure should move off Cape Cod on Friday night, while a cold
front crosses over the Great Lakes. Upper level ridging should take
place over the Southeast during this weekend as the cold front
reaches the Northeast and begins to dive southward. The heat and
humidity should spark isolated afternoon showers and thunderstorms
in the mountains. The models continue to improve in agreement with
the coverage of convection, so this improving confidence has
resulted in nudging the POPs a little higher. The moderate drought
conditions and the capping aloft will likely prevent any significant
thunderstorms or heavy rainfall from occurring. Temperatures were
matched with the warmer ECMWF and the NBM, which continue to perform
well during this unseasonably warm and dry month.
As the cold front reaches the Mid Atlantic by Sunday evening into
Sunday night, it will transition to a backdoor cold front due to
high pressure from eastern Canada wedging southwestward against the
eastern slopes of the Appalachian Mountains. Cloud cover, POPs, and
temperatures have been altered to portray a cooler, cloudier, and
somewhat wetter trend as the cool wedge of high pressure arrives.
This pattern to start out the new week presents itself as the best
opportunity in a while to obtain any amount of needed moisture
across the CWA even if the rainfall rates will be light.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 330 PM EDT Thursday...
A backdoor cold front ahead of a developing cool wedge of high
pressure will push southwestward through the CWA on Monday. East
winds should advect moisture from the Atlantic Ocean along this
frontal boundary to provide some light rain, especially along the
eastern slopes of the Blue Ridge where upsloping would occur. Some
drizzle and fog may accompany the low clouds by Monday evening into
Monday night. Temperatures were pushed downward to more favorably
meet the cooler GFS guidance as the ECWMF and NBM are usually too
warm during a wedge pattern.
The moisture and clouds should progress west of the Blue Ridge on
Tuesday as drier air within the surface high arrives over the
Piedmont. The cool wedge may not erode as quickly during the
morning, which makes the confidence in the forecast for Tuesday
rather low. Skies over the Piedmont could clear out by midday to
allow temperatures to recover, but locations to the west may still
be dealing with low clouds and showers even into the afternoon.
Eventually, the cool wedge should erode completely by Wednesday as
surface high pressure gains control over the Mid Atlantic. Warmer
and drier weather will resume at this point. Another cold front may
arrive later in the week to bring a chance of rain, but details
remain rather murky as the ECMWF appears to be slower with the front
arriving and also shows less moisture than the GFS.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 734 PM EDT Thursday...
A cold front will continue to drop south this evening into
tonight. VFR conditions will prevail this evening into tonight.
An isolated MVFR shower is possible the next hour or two withe
the frontal boundary. Gusty westerly winds can occur ahead and
just behind the front this evening with gusts up to 25-30 kts
especially along the ridges.
VFR ceilings and isolated showers could linger over the
southeast this evening until the front clears tonight.
Otherwise, clearing skies and VFR conditions elsewhere until
midnight. Areas of fog are possible tonight in the valleys
especially at KBLF/KLWB and KBCB. Mainly MVFR to IFR conditions
depending on if any moisture occurs with any showers. Also,
there is the potential for low clouds including sub-VFR mainly
around KBLF where could drop down to LIFR late in stratus per
Weak high pressure builds in on Friday with widespread VFR
expected after early fog fades. However some residual VFR
level cloud canopy may persist within easterly flow at KLYH/KDAN
Friday afternoon as a weak wave passes to the south.
Medium to high confidence in ceilings, visibilities and winds
during the taf period.
.Extended Aviation Discussion...
Moisture returns again on Saturday as high pressure moves east with
isolated showers or thunderstorms possible along the Blue Ridge
and again across the mountains Sunday ahead of another weak
cold front. This boundary likely to linger into Monday with
added isolated showers possible. This may result in brief MVFR
in spots mainly over the mountains this weekend into early next
week. Drier air is expected Tuesday night into Wednesday.