Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/08/20
Area Forecast Discussion
National Weather Service Duluth MN
911 PM CST Mon Dec 7 2020
.DISCUSSION...(This evening through Sunday)
Issued at 342 PM CST Mon Dec 7 2020
Our quiet weather pattern continues with a warm up through the week
and Wednesday looks like our next best shot at seeing some sun. We
are still examining this coming weekend for our next shot at some
snow and cooling temperatures.
Light snow this morning has largely tapered off other than some
brief lake effect snow showers along the North Shore of Lake
Superior. The stratus deck in place at the moment will likely
continue through this evening into tomorrow as the upper level
shortwave over the region slides to the east. The strong
inversion currently in place will also lend itself to areas of fog
across much of eastern Minnesota tonight. Southwest flow will build
tomorrow becoming gusty at times. This will begin to advect in both
clearer skies and warmer temperatures. Wednesday should see mostly
sunny skies and highs near 40, though daytime solar heating could
push those temperatures up a couple more degrees.
Cloudier skies look to come back by Thursday as northerly flow
returns and temperatures respond accordingly with temperatures
beginning to decrease. We are currently monitoring the possible
track of a system that will move through the upper Midwest this
weekend forced by a deep trough and associated jet stream in the
upper levels. Due to the nature of the snow bands associated with
this type of storm, a shift in the track by a hundred miles can
make the difference between 10 inches and a trace of snow, so we
are waiting until model ensembles come into better agreement before
making snowfall accumulation predictions. However due to the
northeast flow that will likely set up, we may be able to count on
Lake Superior to ramp up lake effect snow production through the
weekend for the South Shore of Lake Superior. We should also see a
rapid temperature decrease as this system passes and we settle into
more winter-like temperatures for at least a couple days.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 555 PM CST Mon Dec 7 2020
Widespread IFR/LIFR conditions covered most of the Northland this
evening. We expect most areas will see the visibility drop tonight
before some improvement late tonight into Tuesday morning. The RAP
is depicting the low ceilings well this evening and forecasts
clearing from west to east as 950-900MB winds veer and increase
with a passing low level trough. It`s always a challenge
determining if the models are too quick with the clearing and this
is especially true at night and in the cold months. We followed
the general trends of the RAP but didn`t clear as fast as it
Issued at 911 PM CST Mon Dec 7 2020
The pressure gradient will strengthen overnight into Tuesday as a
frontal boundary and trough move across Lake Superior. Southwest
winds will increase to 10 to 20 knots with gusts around 25 knots
and perhaps a couple to 30 knots. The wind will be strongest and
wave response highest along the Bayfield Peninsula and a portion
of the North Shore, mainly north and east of Taconite Harbor.
Expect the wind and waves to diminish Tuesday evening as they veer
to west. Winds will become west to northwest later Wednesday and
remain 15 knots or less into Thursday.
.PRELIMINARY POINT TEMPS/POPS...
DLH 28 39 26 39 / 0 0 0 0
INL 26 38 24 38 / 0 0 0 0
BRD 27 41 28 42 / 0 0 0 0
HYR 27 40 24 42 / 0 0 0 0
ASX 29 41 28 42 / 0 10 0 0
LS...Small Craft Advisory from 6 AM Tuesday to midnight CST Tuesday
night for LSZ121-140-146.
Small Craft Advisory from 6 AM to 6 PM CST Tuesday for LSZ141-
Area Forecast Discussion
National Weather Service Grand Forks ND
918 PM CST Mon Dec 7 2020
Issued at 916 PM CST Mon Dec 7 2020
With observations from Detroit Lakes to Fergus to Elbow Lake a
half mile or less this last hour went ahead an issued a dense fog
advisory through the overnight. Light winds will continue with a
saturated airmass in place.
UPDATE Issued at 545 PM CST Mon Dec 7 2020
Low cloud clearing is starting to get overrun by high clouds
spreading southeast. Low clouds remain Roseau to just east of
Mahnomen to just east of Fergus Falls. HRRR 925 mb RH maintains an
eastward clearing overnight but this evening it may halt as winds
sfc-925 mb remain very light until after midnight. Will monitor
for any fog development and also temperatures.
.SHORT TERM...(This evening through Tuesday night)
Issued at 338 PM CST Mon Dec 7 2020
Impacts this period limited to some fog redevelopment over west
central Minnesota lakes country this evening.
HRRR short term model handling the clearing of low clouds
eastward well and used for sky cover trends thru this evening. Low
clouds clearing from Roseau to Elbow Lake and it will clear
gradually eastward reaching far eastern fcst area by 06z. 925 mb
winds turning WSW and in the 20 kt range helping to bring in drier
air from the west. Brief period where fog may reform in west
central MN so included some patchy fog but not expected widespread
or dense fog at this time due to the pickup in 925 mb winds
allowing for a bit of mixing. West wind 5 to 10 kts tonight in E
ND with warmer air moving esp at 925 mb and will expect to see the
higher terrain west of the Red River valley remain near or a bit
above freezing tonight, esp Walhalla area.
Tuesday will see high clouds, thin some in the aftn. West wind 5
to 15 mph. Not a strong west wind, and some high clouds may affect
temperature rise. Still though anticipating highs in the 40s with
some low 50s psbl in parts of E ND. Fair Tuesday night.
.LONG TERM...(Wednesday through Monday)
Issued at 338 PM CST Mon Dec 7 2020
Highlights within in the later half of this week include
continued seasonably warm temperatures Wednesday into Thursday.
This is followed by a trend towards possibly seeing some
accumulating precipitation Thursday into Friday, and possibly this
weekend. Cooler temperatures closer to seasonal normal is also
expected beyond Thursday.
Large, anomalous ridging centers itself over the region Wednesday
into Thursday continuing our recent warmth and dry conditions.
Ridging breaks down as upper troughing develops into the western
CONUS late in the work week. Some guidance hints at a leading
shortwave trough Thu/Fri bringing the potential for some light
precipitation. This is followed by a potential Colorado low-type
system moving out of the Central Plains and into the Upper Midwest.
Details like track and strength of this system, as well as its
interaction with the leading wave still remains unclear. Variance in
QPF within ensemble guidance is markedly large, making it difficult
to make conclusions on the low/high end amounts, precipitation type,
and location of heaviest precip. Regardless, most guidance does
suggest in this overall pattern change with precip likely somewhere
within the Northern Plains and Upper Midwest. But given the impact
footprint Colorado lows typically bring to the aforementioned
regions, monitoring the forecast would be prudent.
With upper troughing expected late into the week, cooler temps are
expected bringing conditions closer to seasonally normal, ie highs
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 545 PM CST Mon Dec 7 2020
Bemidji clearing timing is uncertain...thinking still around
06z/07z but at night clearing of low clouds is uncertain. Thief
River Falls and west will see high clouds thru Tuesday. Light
winds this evening then more westerly late tonight into Tuesday 5
to 15kts, though locally higher in NE ND Tues aftn.
MN...Dense Fog Advisory until 6 AM CST Tuesday for MNZ027-028-030-031-
Area Forecast Discussion
National Weather Service Paducah KY
955 PM CST Mon Dec 7 2020
Issued at 955 PM CST Mon Dec 7 2020
Made some sky adjustments mainly to account for the progress of
the clearing line according to the most recent satellite imagery.
Still not sure if the clouds will surge southward through the
whole area overnight, so delayed it a bit more. With prolonged
clear skies and light winds, fog is going to be a concern
overnight until and if the low clouds return. Used the NBM
visibility grids as a guide as no other guidance is the least bit
bullish on fog tonight. Managed to get some patchy fog in the
grids as a first start, but it could become more widespread and
pretty thick, if/where the low clouds don`t make it.
UPDATE Issued at 656 PM CST Mon Dec 7 2020
We have reconsidered the cloud trends as discussed in the
Aviation section earlier. With little flow in the low-levels, the
slow eastward progression of the clearing line may continue at
least through the evening. It looks to be making better progress
over Kentucky. The Sky grids have been adjusted to this thinking
through the evening, and then blend to the original mostly cloudy
everywhere thinking by sunrise. Not completely sold on the clouds
increasing from the north overnight, but have plenty of time to
make further adjustments if necessary.
The latest HRRR data was used for temperature and dewpoint trends
through the night and into Tuesday morning, as they were the best
match for our thoughts on sky trends. This results in temperatures
holding nearly steady in the EVV Tri State through the night.
Lows are now only expected to reach the middle 30s, while much of
southeast Missouri and adjacent portions of southern Illinois and
the Purchase area of Kentucky will likely drop into the mid to
upper 20s with good radiational cooling expected.
UPDATE Issued at 526 PM CST Mon Dec 7 2020
The AVIATION section has been updated for the 00Z TAF issuance.
.SHORT TERM...(Tonight through Wednesday night)
Issued at 248 PM CST Mon Dec 7 2020
Rain-free conditions expected through mid week time frame. Much of
the region along/east of the MS River has been plagued by cloud
cover trapped beneath a low level temperature inversion today,
keeping things on the chilly side even for early December. A weak
and moisture starved upper mid level short wave will drop south
within the steep northerly flow pattern tonight, bringing more in
the way of cloud cover. This may help to hold temps up a bit, but
most locations will still fall to between 25 and 30 by daybreak
Hoping to break out into some sunshine during the day Tuesday as
mid/upper level ridging begins to take place. Should help readings
climb back close to normal during the afternoon. Will mark the start
of a warming trend that will continue into mid week and beyond.
.LONG TERM...(Thursday through Monday)
Issued at 248 PM CST Mon Dec 7 2020
Our primary impact during the long term looks to be tied to a system
moving through Friday into early Saturday.
We remain dry on Thursday, as we await shortwave energy over the
southwest U.S. that will lift northeast into the Great Lakes region
through Saturday. At the surface, low pressure is expected to
develop in the OK/KS vicinity Thursday night before migrating into
the Great Lakes on Saturday. As it does so, a cold front will be
pushed eastward across our area. Models are in decent agreement on
the frontal passage occurring Friday night into Saturday morning.
Our primary period of rain looks to begin in our western counties
Friday afternoon and exit our eastern counties Saturday afternoon.
12z model runs continue to struggle to generate much in the way of
instability, so have kept thunder mention out. However, wouldn`t be
surprised if we eventually needed an isolated mention. QPF amounts
at the moment look to average in the 0.75" to 1" range.
Model solutions differ over the weekend with regards to a secondary
wave lifting northeast across the TN/OH Valley regions. The Canadian
and several GEFS ensemble members indicate this 2nd system occurring
sometime in the Saturday night through Sunday period. However, there
is not good agreement and a good chunk of models indicate dry
conditions in the wake of the late week system. Went ahead and left
in the NBM PoPs which generated a slight PoP across portions of the
region Sunday into Sunday night given the uncertainty.
Temperatures begin the period well above normal, with many areas
reaching the 60s on Thursday and Friday. Sunshine will be plentiful
on Thursday, but the increased southwesterly low level flow will
help offset the lack of sun on Friday. Continued to side with
readings above NBM numbers and closer to the 75th to 90th percentile
given we tend to over perform in these types of situations.
Cooler conditions return for the weekend into early next week,
with highs only reaching the 40s again by Sunday and Monday.
Issued at 526 PM CST Mon Dec 7 2020
The back edge of the low clouds has pushed just east of the MS
River, but not sure how much further it is going to make it. Left
the ceiling in at KPAH. Looking upstream, it should eventually
spread back to the west over KCGI late this evening. It also looks
like ceilings should trend lower (into MVFR) through the night,
with KMVN, KCGI and KPAH seeing at least a few hours in the lower
half of MVFR in the morning. With the final in a series of upper
disturbances moving through tonight, some final clearing should
spread eastward over most of the region through the afternoon.
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
935 PM EST Mon Dec 7 2020
A series of shortwave lows aloft will swing through the mid-Atlantic
through Tuesday. High pressure will once again build into the area
from the west through the middle of the week as the sub-tropical
ridge builds through the Southeast US.
.NEAR TERM /THROUGH TONIGHT/...
As of 935 PM Monday...
Although some weak radar echoes remain across the eastern portions
of the forecast area, no precipitation is being reported at
automated stations as of 9pm. Have kept in the inherited slight
chance of rain/snow across the Triangle through early morning that
the HRRR was insistent on showing for several runs - although it has
started trending away from that, and do not have any accumulation in
the forecast anyway. Skies have been slow to start clearing, but as
the upper level trough axis moves east, this should allow clouds to
start clearing. Bridges may become a little icy overnight where
roads remain wet and temps fall into the 20s. Lingering
northwesterly winds behind the front may keep the atmosphere mixed
enough in some places to only lower temps to the low 30s overnight,
however sheltered areas should radiationally cool to the mid to
upper 20s as skies clear behind the front.
.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 330 PM Monday...
One last upper-level trough will move from the OH Valley Tuesday
morning across NC Tuesday afternoon, however the moisture and
dynamics will be lacking and the weather will be dry for the day.
Surface high pressure will build from the Mississippi Valley towards
the central Appalachians, creating mostly clear skies, northwesterly
surface flow and cold advection with highs limited to the mid to
upper 40s in the afternoon. High clouds will be on the increase
Tuesday night, however lows should still radiationally cool into the
mid to upper 20s.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
As of 305 PM Monday...
Surface high pressure initially centered over the Gulf of Mexico
will shift east to the western Atlantic from Wednesday through
Friday. Aloft, an upper trough will then give way to height rises
and an upper ridge over the Eastern US by late week, pumped up by
the next deep trough that will be moving across the central US. This
pattern will result in mostly sunny skies and dry conditions for
central NC through Friday, along with warming temperatures through
the week. Forecast highs are in the lower-to-mid-50s on Wednesday
and upper-50s to mid-60s (5-10 degrees above normal) on Thursday and
Friday. Lows in the 30s are expected on Wednesday and Thursday
nights. Clouds will be on the increase Friday night, with lows in
Both the GFS and ECMWF are in good agreement that a deep upper
trough and associated cold front will then approach from the west on
Saturday, with surface low pressure moving NE into the Great Lakes
region. A coastal front will also be moving inland into central NC
Friday night and Saturday. Thus it appears the area may be in a
relative dry slot on Saturday, with the best chance for showers in
far western zones (from the approaching upper trough) and far
eastern zones (from the coastal front), where the forecast has
slight chance POPs. The best chance for showers across the entire
region looks to be Saturday night into early Sunday. QPF looks light
at this time, around a tenth to a quarter inch at most, but that
could change. While the operational runs of the 12z GFS and ECMWF
continue to quickly bring through the cold front and end
precipitation chances by Sunday afternoon, most GFS ensembles are
much slower with the front, keeping precipitation across the area
into Monday. Thus continue slight chance POPs Sunday night into
Monday. Southerly flow ahead of the cold front will result in mild
temperatures with highs in the 60s on Saturday, before it starts to
cool down to near normal by Sunday night and Monday, depending on
the exact timing of the cold frontal passage.
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
As of 705 PM Monday...
24 hour TAF period: Precipitation has ended at INT/GSO. A line of
sprinkles/flurries is moving through RWI/FAY, while another small
area of precipitation may redevelop during the late evening in the
vicinity of RDU. GSO/INT are already VFR, the remaining sites should
see lifting ceilings by midnight and VFR conditions for the rest of
the TAF period. Northwest winds will be gusty at INT briefly this
evening, then some wind gusts up to 20 kt will be possible at
INT/GSO/RDU Tuesday afternoon.
Looking ahead: VFR conditions will prevail through end of the week.
The next disturbance will move across the region this weekend.