Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/22/21
Area Forecast Discussion
National Weather Service Gaylord MI
1025 PM EST Sun Nov 21 2021
.UPDATE...
Issued at 1025 PM EST Sun Nov 21 2021
Cold front has pushed east of Northern Michigan late this
evening. CAA has begun in earnest...quickly activating over-lake
instability. Last vestiges of synoptic precip has exited east of
our CWA with the front...transitioning our ongoing precip event to
a multi-band W/NW flow lake effect snow event. Tight pressure
gradient behind the front has resulted in a rapid strengthening of
winds...gusting as high as 40-50 mph at times with the highest
winds along our Lake Michigan shoreline areas. PLN gusted as high
as 46 kts just before 8 pm. Strong winds are pushing lake snow
bands further inland as expected...with at least some snow falling
across almost all of our CWA. Reduction to vsbys due to falling
and blowing snow has modest so far...with most surface obs
reporting vsbys at or above 1SM even within some of the heavier
snow showers. Still expect Eastern Upper Michigan will see the
development of heavier snow bands overnight thanks to high
inversion heights (around 13 kft) and better low level moisture
availability. Inversion heights are much lower across Northern
Lower Michigan...in the 5-7 kft range...which should translate to
significantly less potential for accumulating snow.
See no reason to deviate from expected snow amounts and ongoing
headlines. Will maintain the Winter Storm Warning/Winter Wx
Advisory for Chippewa county where some locations could see up to
a foot of new snow overnight into Monday as a result of deep lake
convection... targeting far Northern Chippewa county for highest
snow amounts. Will also maintain the Wind Advisory for all of our
Lake Michigan shoreline counties thru the balance of the night.
&&
.NEAR TERM...(Through Tonight)
Issued at 351 PM EST Sun Nov 21 2021
...Major blast of winter on the way for eastern upper MI...
High Impact Weather Potential: Locally very high. Heavy lake effect
snow with near blizzard conditions in parts of eastern upper MI
tonight. Gusty winds, strongest this evening. A quick burst of snow
this evening in spots and/or icy roads developing.
1000mb surface low is just w of James Bay. A sharp and well-defined
cold front extends south across eastern Superior and down the long
axis of Lake MI. Gusty winds usher in strong cold advection
immediately behind the front. This November gale has a large number
of forecast concerns, centering on wind, lingering synoptic precip
that goes from rain to snow, and lake effect.
Presently, warm advection ahead of the cold front has boosted temps
into the upper 30s to mid 40s across northern MI. Developing precip
shield is all liquid, with some shallow convective elements emerging
recently over northern lower MI. This warm air and liquid precip
is not long for this world, with the cold front entering nw lower
MI and western Chip/Mack now, and exiting over Lk Huron by 7 pm. A
number of wind gusts to circa 40kt/45mph have been seen over WI,
though diurnal mixing (aided by some outright sunshine) is aiding
wind production there. A solid isallobaric component will be
present for us to aid wind production, as will mixing over the
increasing unstable lakes. Nam BUFR soundings still support circa
45mph gusts in susceptible coastal areas near Lake MI. No
significant changes made to wind headlines (at least since
Mackinac Co was added earlier).
Strong cold advection will allow precip to transition to snow before
transitioning further to lake effect. A quick burst of snow squall-
type activity is expected between 5 and 9 pm, where synoptic forcing
best intercepts increasing overlake instability. This is of greatest
concern over far northern lower MI, between roughly PLN and GLR
inclusive. A quick inch of wind-blown snow, along with strong winds,
will produce a brief period of potentially hazardous travel
conditions. Elsewhere, wet roads will become icy this evening.
By 11pm, we will transition to pure lake effect snow. 850mb temps
are presently circa -4C, but we will drop about 10C by morning.
Inversion heights on Lk Superior start out near 12k ft mid/late
evening, then lower closer to 8k ft overnight. A potent 500mb
shortwave trof will close off as it passes north of the Sault
tonight. That will keep more synoptic moisture available over
Superior, much more so than even over northern Lks MI/Huron. Hi-res
guidance is near unanimous in developing a dominant band over
central/eastern Superior, with a slightly wobbly wnw to nw fetch
sending it into the vicinity of the twin Saults overnight. Lake-
induced CAPE values are in high triple digits, and the DGZ is very
well-placed in the layer of max ascent to maximize dendrite
production and snow-liquid ratios. (Though we will have enough
wind, and associated fracturing/compaction of snowflakes, to
hinder ratios.) Initial guidance from WPC gave just about an inch
of liquid QPF in the 6hr window ending at 12Z/7am Monday, in a
band over ne Chippewa Co. Have toned that down, just to give some
snowfall accums that I can sort of live with. Have also adjusted
the position of the band ne-ward a touch, to give the HRRR at
least a bit of credence. Recent runs of that model clobber
northern Sugar Isl tonight, while allowing the Sault to escape the
worst of it. But that said, there are still some very large
accums in the forecast for tonight (and into Mon morning), over
the Sault and the north half of Sugar Isl. Someone is getting a
foot of snow (at least) tonight, though it could conceivably end
up being mostly Canadians. There is also a very tight snowfall
gradient toward lesser amounts as you head sw from the Sault.
Upgrading central Chippewa Co to a warning is obvious. The dominant
band expected overnight will produce very high accums and near-
blizzard conditions. Note that (thankfully) the strongest winds will
occur this evening, before the best lake effect gets set. Adding se
Chippewa to an advisory is also reasonable, with the stronger winds
allowing the lake effect snow bands to penetrate more easily into
the Drummond Isl area. Western Chippewa was a tougher call, with
weaker but still reasonably impressive banding expected to poke into
Hulbert/Strongs. But still figure that there are enough snow and
winds to produce winter storm-level impacts there. So upgraded that
zone to a warning as well.
Lake effect snow should be far, far less potent for northern lower
MI. Deeper moisture is not available, and inversion heights (8k
dropping to 5k ft) and lake-induced CAPE (mid triple-digits) are
sharply lower. Localized 1-3" accums expected.
Min temps tonight mainly low-mid 20s. Wind chills will drop well
into the teens.
&&
.SHORT TERM...(Monday through Wednesday)
Issued at 351 PM EST Sun Nov 21 2021
...Lake effect continues through Monday...
High Impact Weather Potential...Moderate. Accumulating snow
continues through Monday, possibly lingering into Tuesday morning.
Pattern/Synopsis...The upper level pattern begins the week with
anomalously strong troughing stretching from Hudson Bay down through
the Tennessee Valley...and strong ridging over the western half of
the CONUS. A strong jet 120-140kt exists between these...with cold
air driving southeast across the lakes. The pattern remains
progressive however, with troughing moving off the east coast and
ridging moving into the Great Lakes by late Tuesday. The next
system, a positively tilted trough, moves across the Rockies heading
into mid-week...set to bring more showers just before/heading into
Thanksgiving.
Forecast/Details...We remain in cold cyclonic flow with lake effect
ongoing through the day Monday. DeltaT`s remain aoa 20C with
inversion heights 8-9 kft and plenty of low level moisture to be had
across Ern Upper. Snow (likely banded per hi-res guidance) will
still be going strong, with a dominant band expected to still be
chugging along from lake Superior, across Ern Upper into Nrn Lake
Huron. With boundary layer winds expected to be 290-300 deg believe
Nrn Chippewa county, including the SOO, will see the heaviest
accumulations with the snow band wavering over them the longest...
Nrn Lower will still have ongoing lake effect snow, just to a lesser
extent in intensity, with inversion heights up around 7 kft and
drier mid-levels above the lake convection. Overall expect
additional accumulations of 3-5" across portions of western
Chippewa/Mackinac counties, with the SOO receiving more, upwards
of 6 or 7 inches through the day, with lower amounts (1-2") across
portions of Nrn Lower. Although winds will start the day gusty
they will be slowly diminishing with the slackening gradient
through the day. Regardless, blowing snow is still possible,
especially closer to the Lake Michigan shore.
As we head through the night the environment becomes increasingly
less-favorable for robust LES, with inversion heights lowering,
rapidly loosing saturation through the DGZ, and winds weakening and
backing slightly through the night. Surface ridging moves overhead
early Tuesday and we get into southwest return flow with 850mb
temperatures rising through the day. Overall a quiet period with
temperatures moderating into the upper 30`s/lower 40`s.
Shortwave ridging pushes east of us Wednesday with an elongated
positively tilted trough approaching from the west. A weakening
surface low will be trekking into Ontario across western Lake
Superior through the day, keeping us in gusty southerly flow. WAA
and moisture advection occur throughout the day (PWAT`s get up to
around 0.70" which is at least 1 St. Dev above normal for late
November.) However, believe rain chances will hold off until the
afternoon and possibly even even as the columns takes a bit to
saturate, and relatively little forcing is expected ahead of the
incoming system. Forecast afternoon highs are expected to be milder
(in the mid to upper 40`s) but the gusty winds will make it feel a
bit brisk.
.LONG TERM...(Wednesday night through Sunday)
Issued at 351 PM EST Sun Nov 21 2021
High Impact Weather Potential...Minimal for now. Watching Wed/Thurs
system
Pattern Synopsis/Forecast...Heading into Thanksgiving the
aformentioned western trough crosses the upper Great Lakes...with
its associated surface low following suit into southeast Ontario.
This will bring a period of rain/snow showers Wednesday night,
changing over to snow through Thanksgiving Day as colder air filters
in on northwest winds behind the system. Additional precipitation
chances are expected late week through the weekend, as a series of
waves rotate down through the Great Lakes. The best snow potential
looks to be associated with a clipper dropping through the Great
Lakes on Sunday. Overall no huge accumulating snow events expected
late week/through the weekend with highs generally ranging through
the 30`s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 611 PM EST Sun Nov 21 2021
A period of synoptic snow along a fast-moving cold front will drop
conditions to IFR this evening...with the lowest vsbys and cigs
across far Northern Lower Michigan and the interior/higher
elevations of Northern Lower Michigan where precip will switch
over to snow first. Strong CAA behind the cold front will produce
lake effect snow showers later this evening into Monday...
targeting our typical snowbelt areas of Northern Lower Michigan
directed by W/NW flow. Greatest snow chances and worst conditions
(IFR) will generally be between PLN and TVC as lake snow banding
develops tonight and persists into Monday. Strong W/NW surface
winds of 20 to 30 kts will occasionally gust to 35 kts...
especially along the Lake Michigan shoreline areas of NW Lower
Michigan.
&&
.MARINE...
Issued at 351 PM EST Sun Nov 21 2021
Strong cold front is crossing northern Lake MI, with very gusty w
to nw winds behind it. Gales expected on all waters tonight and
into Monday morning. Only gradual improvement after that.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until noon EST Monday for MIZ088.
WINTER STORM WARNING until 7 PM EST Monday for MIZ086-087.
WIND ADVISORY until 5 AM EST Monday for MIZ016-020-021-025-031-
095>099.
LH...GALE WARNING until 10 AM EST Monday for LHZ345>349.
LM...GALE WARNING until 10 AM EST Monday for LMZ323-341-342-344>346.
LS...GALE WARNING until 10 AM EST Monday for LSZ321-322.
&&
$$
UPDATE...MR
NEAR TERM...JZ
SHORT TERM...STJ
LONG TERM...STJ
AVIATION...MR
MARINE...JZ
Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
549 PM CST Sun Nov 21 2021
.DISCUSSION...Updated for latest aviation discussion below.
&&
.AVIATION...The TAFs have been simplified a bit to reflect the
overnight passage of a cold front. The timing of the showers in
the TAFs are based on the HRRR model. Overall, VFR is expected
at the aerodromes through the next 24 hours.
&&
.PREV DISCUSSION... /issued 308 PM CST Sun Nov 21 2021/
SHORT TERM (Tonight through Monday Night): The main story in the short
term revolves around the cold front expected to pass through Deep
South Texas late tonight into early Monday morning and the potential
for flooding with the showers and thunderstorms expected ahead of
and along the frontal boundary.
Ahead of the front, southeasterly winds will continue to advect low
to mid level moisture across the area, increasing precipitable water
to 1.4 to 1.7 inches. With ample moisture and moderate instability
(CAPE near 1000 to 1500 J/kg) some of these showers and
thunderstorms could be efficient rain producers and lead to the
threat of flash flooding. On top of this, soils are still relatively
saturated due to recent rains, increasing the flooding potential for
areas that receive storms with higher rainfall rates. Most of the
models have the higher rainfall amounts west of I-69E with totals
between 1.5 to 2 inches, but locally heavier rainfall will possible.
As such, a Flood Watch is out from 6 PM tonight to 6 AM Monday
morning. Then most of the rain will clear out by mid to late morning
as the front pushes south of the Rio Grande and ushers in a drier,
more stable airmass.
Decent cold air advection behind this front will cause high
temperatures to drop 10 to 15 degrees from today to Monday, with
highs near 70 degrees. With the front passing through early Monday
morning, cold air advection behind the front will compete with weak
diurnal heating across areas that will see more sun...maintaining a
small temperature variation during the day tomorrow. Some locations
may even see their high temperature early in the morning before the
colder air moving in drops/maintains near stable temperatures for
the rest of the day. Overnight Monday night, the cloud cover will
begin to dissipate and temperatures will drop into the upper 40s for
the ranchlands, mid to upper 50s in the Valley, and the 60s along
the immediate coast.
LONG TERM (Tuesday through Sunday): As the front exits the area for
Tuesday, a large mid-level ridge moves over the central United
States and Texas for Tuesday and Wednesday. This ridge will bring
southeasterly flow to the CWA, warm air advection, and give us a
break from the rain for a couple of days. Beginning Wednesday
morning, a couple of positively tilted trough formations begin to
strenghtens across the western portion of the country. Wednesday will
be the warmest day of the week with high temperatures in the mid 80s
and will also be breezy as the troughs move into western Texas and
strengthen the surface pressure gradient over the CWA.
By Thursday morning, a cut-off low begins to form over the Baja
Peninsula separating itself from the stronger low over the northern
Midwest. This cut-off low pulls 500mb vorticity completely across
the central United States. The energy being pulled further south
will help bring the cold front all the way down to Deep South Texas
for Thanksgiving Day.
As far as precipitation goes, the models still haven`t quite agreed
on the location or exact timing, but Deep South Texas can expect to
see rain before the actual front moves through. However, they both
still currently show the eastern CWA receiving the best chance for
rain during the day Thursday. Looking at forecast GFS soundings for
12z-00z Thursday/Friday, PWATs are still staying steady around 1.5
to 1.8 inches. The GFS/ECMWF are in slight disagreement regarding
the initial timing of the front. The GFS has the winds shifting
north Thursday evening while the ECMWF has the front coming through
a little later around midnight instead. The low over Mexico
eventually closes itself off by Saturday leaving a coastal trough
positioned over the Gulf Waters into the weekend. This trough will
give us a slight chance of rain over the coastal counties and gulf
waters for Saturday and Sunday. The WPC QPF forecast also has their
24-hour Day 5 QPF outlook showing 1.25 to 2.00 inches expected
especially for the Rio Grande Valley valid for 00z Friday to 00z
Saturday.
Thursday`s high temperatures will still be near seasonal but once
the front moves through, we can expect highs in the low 70s and lows
in the lower 50s with a northerly wind for the rest of the long term
period.
MARINE (Tonight through Monday Night): Marine conditions will remain
favorable through this evening, but will then quickly deteriorate
behind the cold front expected to pass through early Monday morning.
Showers and thunderstorms will form ahead of and along the frontal
boundary, leading to additional hazards with the potential for
lightning, strong wind gusts, and reduced visibility. Small Craft
Advisories are in effect from early Monday morning into Monday
evening. Then winds and seas will gradually subside Monday night.
Tuesday through Sunday: Winds and seas will still be elevated
following the front on Monday. As a ridge moves into the area on
Tuesday, seas will begin to improve but then are elevated once
again as the troughs develop over the Plains and breezy
southeasterly flow returns. Southeasterly flow dominates until
Thanksgiving Day when a front pushes through the area. This front
will increase our seas to 5 to 8 feet overnight Thursday into
Friday and stay elevated through the long term period. Small Craft
Advisories may be needed as early as Wednesday morning.
&&
.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL 64 71 60 76 / 60 40 0 0
BROWNSVILLE 64 72 58 79 / 60 50 0 0
HARLINGEN 61 70 54 78 / 70 40 0 0
MCALLEN 61 70 54 78 / 80 50 0 0
RIO GRANDE CITY 59 71 52 78 / 90 30 0 0
SOUTH PADRE ISLAND 68 72 67 74 / 60 50 10 0
&&
.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Flood Watch through late tonight for TXZ248>250-252-253-353.
GM...Small Craft Advisory from 6 AM to noon CST Monday for GMZ130-132-
135.
Small Craft Advisory from 3 AM to 6 PM CST Monday for GMZ150-155-
170-175.
&&
$$
This product is also available on the web at:
https://weather.gov/rgv
Area Forecast Discussion
National Weather Service State College PA
953 PM EST Sun Nov 21 2021
.SYNOPSIS...
A sharp cold front will cross the Commonwealth overnight,
ushering in a couple of days of lake effect snow showers lasting
Monday into Tuesday. Conditions will greatly improve by midweek.
Wednesday and Thanksgiving Day both look dry. However, another
strong cold front looks like it will blast through PA on Friday
with rain arriving Thursday night. More blustery weather is then
expected for the rest of the long weekend.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Broken band of light to moderate rain showers extends from the
Pocono Plateau through the South Central Mountains late this
evening, along and ahead of the first of two cold fronts to
cross the area overnight. Front #1 tracks to the east of the
Lower Susq by or shortly past midnight. Front #2 delivers a
real cold punch in the predawn hours, and despite the lowering
inversion overnight, there`s sufficient lift and a ribbon of
instability along it to produce a line of snow showers as it
passes between 05z to 08z across NW and NC Mountains.
Instability and moisture wane as one moves farther south along
the Allegheny front, so we think generally weakened snow showers
and flurries will accompany the front in the predawn hours of the
morning over the Central Mountains. A snow squall can`t be
ruled out farther N and W, but instability is somewhat lacking
and inversion is generally below 5kft at BFD per latest RAP
soundings. We`ll still need to keep an eye on the development of
convection along the arctic front as robust moisture flux off
of the warmer lakes this time of year can produce hybrid events.
Any snow accumulations should stay below an inch over the NW
third of the area, and little to no snow accums elsewhere as the
temps will still be a little too mild at sunrise for anything
to stick. Mins in the upper 20s N and around 40F in Lancaster
and Harrisburg. The wind could gust into the 20s along and
behind the second front.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
Snow showers associated with the arctic front should be gone
around sunrise, but it could take until 13-14Z to pass thru LNS.
The wind then picks up everywhere as we mix thru the day. Gusts
inn the 20s will be widespread with a 30+ gust here and there.
LES is a certainty with the temps at the top of mixed flow off
the lakes dropping into the perfect -12C to -17C dendritic snow
growth zone. The fetch is not the longest fetch for much of the
time. Will continue to play the climo card and paint the highest
snow totals over NW Warren Co and along the NY border toward
Potter and Tioga Counties. The eventual totals through Tuesday
morning will get between 3-6 inches. But, it looks unlikely that
any 12-hr period will go AOA 3" for accums. The best conditions
look to be Monday afternoon and Mon night. Will hold off on an
advy for the time being, but could certainly see one being
hoisted for Warren/McKean Cos by later shifts.
Temps will only rise 3-5F thru the day Mon. We`ll drop to 20-26F
for most of the area Mon Night.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Little change with evening update. Blustery and colder
conditions will continue for Monday night and Tuesday, as very
cold air plummets south across the region with passage of a deep
upper trough and H85 temperatures cooling to around negative
10C by late Monday night/early Tuesday morning.
Snow squall potential looks to have backed off overall over the
past day or two as moisture aloft quickly dries out, but will
nonetheless see some snow showers continue across portions of
the Alleghenies.
Lake effect snow showers look to kick up in this regime,
especially later Monday into early Tuesday as the coldest of the
air arrives and lapse rates steepen downwind (southeast) of Lake
Erie. Several inches of accumulation are likely in the favored
snowbelt of northwest Warren County, with lesser amounts farther
southeast, mainly across the Alleghenies into the Laurel
Highlands. Northwest winds will gust up to 35 mph at times.
All medium range guidance lifts the aforementioned upper trough
out by later Tuesday, with surface high pressure building in
for midweek. Thus, expect lingering lake effect snow showers to
taper off over the Alleghenies Tuesday afternoon, with clearer
and milder conditions by Wednesday. However, the setup could be
favorable for a very cold Tuesday night with the surface ridge
over the state.
After a dry period of weather Wed and Thanksgiving Day, focus
then shifts to the trailing cold front which could approach
Thursday night. So far it looks like this front will bring
mostly rain showers Thu night.
Post frontal cold temperatures, gusty winds, and snow showers
appear in the offing for Friday, with lake effect snow showers
possibly lingering into the weekend.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Another round of showers will move across central PA this
evening as a cold front moves in from the west. Generally seeing
VFR conditions in the east with brief periods of MVFR due to
lower cigs across the central airspace. IFR cigs however over
the north (BFD) and west (JST) will likely persist through the
night. Cold front will diminish precip tonight, but lower cigs
persist into early Mon, especially over the west. Pattern will
transition to gusty westerly flow with colder air bringing lake
effect snow showers and lingering MVFR/IFR conditions across
western/northwestern airspace Monday into Tuesday.
Outlook...
Mon-Tue...MVFR/IFR west with -shsn. VFR central/east. Gusty
winds 20-25kt from 280-320 degrees. -shsn and winds fade Tue.
night.
Wed-Thu...VFR. No sig wx
Thu night...Showers/restrictions possible with next frontal
system.
Fri...Breezy NW flow, snow showers mainly NW.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Lambert/DeVoir/Dangelo
NEAR TERM...DeVoir/Dangelo
SHORT TERM...DeVoir/Dangelo
LONG TERM...DeVoir/Fitzgerald/Colbert
AVIATION...RXR/Travis
Area Forecast Discussion
National Weather Service Des Moines IA
1139 PM CST Sat Nov 20 2021
...Updated for the 06z Aviation Discussion...
.DISCUSSION.../Tonight through Saturday/
Issued at 259 PM CST Sat Nov 20 2021
Key Messages:
- Light Precip Far Northern Iowa This Evening
- Gusty Winds Sunday; Considerable Cool Down
- Cold Monday, Warmer Tuesday into Wednesday
Tonight and Sunday:
A few short-wave perturbations have been moving across the area
through the general zonal mid-level flow pattern across the region.
There has been enough moisture in the mid-levels to result in cloud
cover, especially north of U.S. Hwy. 30. Slight chance POPs with
sprinkles/flurries have been left in the forecast through the middle
part of this evening for northern portions of the forecast area,
mainly where the clouds are expected to persist to with stream of
mid-level moisture. The HRRR along with other CAM solutions continue
to depict weak precipitation across this area. The main challenge
that hydrometeors will face is a dry layer present in the lowest 1
km of the troposphere. While radar has been showing weak reflectivity
along and north of U.S. Hwy. 20 this afternoon, there have not been
any reports thus far at the surface of rain or light snow. Most
hydrometeors appear to be evaporating. With the weak forcing and
some moisture though, a few may be able to survive, especially if
saturation is able to sneak down below 700mb. If any light
precipitation is observed, accumulations are not expected to be
much, if any at all. There is a weak boundary that has been analyzed
from north of Omaha to around Mason City at of 18z, mainly denoted
by a northerly wind shift. The cloud cover in the area has kept
temperatures across the north slightly cooler when compared to
southern Iowa temperatures, not so much the boundary influence.
There is a slightly stronger short-wave trough currently moving into
the eastern Plains that is quickly pushing the surface high pressure
over Minnesota eastward. A strong trough further north in Canada
associated with a surface cyclone is also present, and is quickly
catching up with southern short-wave. As the first, more southern
short-wave moves across Iowa, CAA will begin in the 925-700mb layer,
and will also drastically increase flow. This will assist in
creating a deeper mixed layer across the region, with winds at the
top of it around 40-45 MPH. As a result, Sunday afternoon is
expected to be windy, with gusts 35 to 40 MPH likely across the
north. A few spots may see 45 MPH gusts. The current forecast is for
winds to mostly remain below headline criteria, thus no wind
headline has been issued for Sunday afternoon. Later in the day on
Sunday, the short-wave trough digging out of Canada will catch up
with the southern wave, and will result in a trough a low pressure
at the surface as well. This will accelerate a stronger cold front
across the area Sunday afternoon and into evening. This will
drastically decrease temperatures, especially after 00z. This may
start to hit northern reaches of the forecast earlier in the
afternoon. If the front slows down by a few hours, southeastern and
eastern Iowa may be able reach mid 50s temperatures again Sunday
afternoon. The arrival of the surface trough will maintain a
stronger pressure gradient, especially with a strong high pressure
behind the front, thus maintaining gusty winds into evening.
Temperatures Sunday Night into Monday morning should hit well below
freezing. Despite the strong convergence with this system, dry air
will quickly move in behind it, and will limit precipitation
potential as it moves through the area. Flurries may develop in some
areas, but for now are not in the official forecast.
Monday and Beyond:
As the trough propagates and deepens across the Great Lakes Region,
the pattern becomes further amplified by a mid-level ridge over the
western third of the CONUS. On Monday this will leave Iowa in an
area of strong northwesterly flow and plenty of AVA. This will
promote subsidence and continue strengthen the surface high pressure
across the area, and will continue to push cold air into the region.
Temperatures will struggle to make it out of the upper 30s on Monday
in this pattern. The propagation of the ridge axis though will make
steady progress though, as another trough makes landfall along the
western CONUS. By Tuesday, this will shift surface to 850mb flow
south-southwesterly, and create a WAA regime across and east of the
Missouri River Valley. This ridge axis should then push eastward of
the Mississippi River Valley by late evening on Tuesday, as the
short-wave digs into the Rockies. This will result in cyclogenesis
in the Front Range, and quickly pushes the cyclone into the Central
Plains. In response, low-level flow will remain southerly for much
of Tuesday and into Wednesday. The center of this cyclone is still
looking to track northwest of the forecast area, keeping most
locations in the warm-sector at least through Tuesday Night.
Wednesday high temperatures will depend on the propagation speed of
the cold front. Beyond Tuesday Night/ Wednesday morning, there are
now some discrepancies between GFS/ECWMF deterministic solutions, as
well as the respective ensemble members. The deterministic GFS has
started to expand the Gulf Moisture a bit further west and arriving
in southeast portions of the forecast area, compared to runs from
yesterday that kept it away. However, the GEFS members remain split,
with most members still keeping the higher QPF southeast of the
forecast area. Deterministic ECMWF brings a little bit more moisture
westward, but not as drastic as the GFS. NBM has introduced some
POPs for southeast and eastern Iowa Wednesday into Thursday, and
have not been substantially changed from that in the official
forecast. Currently, temperatures appear to be warm enough for an
all rain precipitation type for southeastern and eastern Iowa should
precipitation actually occur. Overall, Holiday Travel impacts across
Iowa look minimal at this time. Areas east of the Mississippi River
Valley may have some, as this is where the higher moisture is still
favored. Beyond Thursday, northwesterly flow once again arrives and
will provide cooler air across the area and into next weekend.
&&
.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1138 PM CST Sat Nov 20 2021
Sprinkles/flurries are expected overnight in central Iowa mostly
from VFR ceilings. Winds remain light and variable overnight. Cold
front moves through the state in the morning with mostly VFR
conditions during the day. There is an outside chance of MVFR
ceilings in northeast portions of the forecast area late
morning/early afternoon where some higher RH values cross the
area. Otherwise surface wind gusts of 25+kts are likely behind the
front.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
DISCUSSION...Krull
AVIATION...Cogil
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1259 AM EST Sun Nov 21 2021
.AVIATION...
Mid clouds around 10kft will continue to stream into the area
tonight ahead of the next system to impact the region Sunday. The
strong parent low will be well to the north while a weaker surface
low will track through the Ohio Valley. This low will result in
increasing moisture streaming into the area, lowering CIGS this
afternoon and bringing a period of light rain to the region. Best
chance for rain will be across the Detroit area while chances lessen
farther north. CIGS and possibly VSBYs will drop to MVFR this
afternoon with the rain and deeper moisture.
A cold front will then sweep across the area around 00Z tonight,
bringing strong westerly winds to the area. Winds will be strongest
between 00-06Z with gusts nearing 35 knots. Winds will then weaken
slightly the rest of the night maxing out closer to 25 knots.
.DTW THRESHOLD PROBABILITIES...
* Moderate confidence in cigs aob 5000 Sunday afternoon
* High confidence in precip type as rain Sunday afternoon
&&
.PREV DISCUSSION...
Issued at 358 PM EST Sat Nov 20 2021
DISCUSSION...
The plume of mid level moisture and elevated instability proved
worthy of the challenge posed by a formidable layer of dry air in
the low levels. This resulted in pockets of light rain and brief
flurries after impressive work was done from the starting point
shown in the 12Z DTX sounding. The mid level moisture axis now moves
eastward this evening. Low level dry air is reinforced by westerly
flow from the IA/MO/IL vicinity tonight while mid and high clouds
thin enough for partly cloudy conditions at times. A late return of
thicker high clouds, along with light but persistent south wind,
helps keep temperatures above freezing through sunrise Sunday.
High clouds late tonight precede the next low pressure system that
remains set to bring a stronger surge of moisture for rain during
Sunday. Forcing for vertical motion is mainly tied to the southern
stream shortwave initially which backs and strengthens the wind
field below 700 mb. Moisture transport that was lacking closer to the
surface today becomes strong enough to better saturate the low
levels by Sunday afternoon, especially from the Ohio border through
metro Detroit where likely/numerous POPs remain warranted. A trend to
monitor is from longer projections of hi-res runs like the RAP and
ARW which suggest light rain mostly misses SE MI. These solutions do
not back the wind as much in the low to mid levels apparently due to
earlier influence from the northern stream trough digging in from
central Canada by afternoon. This weakens and deflects isentropic
lift/moisture transport eastward before saturation in SE MI. The plan
is to buy another forecast cycle and look for additional support of
these hi-res runs from the remainder of the model suite. In the
meantime, a higher POP/low QPF scenario is maintained with entry
level likely POPs near the Ohio border tapering to chance toward the
Tri Cities and northern Thumb through Sunday afternoon. All rain
precipitation type is favored by a comfortable margin in QPF-
producing solutions.
The northern stream 500 mb trough takes over Sunday night beginning
with the strong cold front that it whips through Lower MI during the
evening. The frontal passage immediately transitions any remaining
precip to snow, although with coverage being surprisingly low given
the strength of cold advection over the Great Lakes. Model RH plan
views and soundings show the dry slot around the south flank of the
trough overwhelming any potential for significant lake effect snow
showers this far SE during Sunday night. The primary impact becomes
the surge of colder air driven in on initial wind NW gusts of 30 to
40 mph. The peak gusts diminish toward midnight while colder air
continues to arrive with temperatures down into the 20s and wind
chill into the teens by sunrise Monday.
The low level thermal trough becomes entrenched for Monday and
limits temperatures to a struggle for mid 30s across Lower MI, which
feels more like mid 20s when factoring in 20 mph NW wind gusts for
much of the day. Model boundary layer RH fields remain dry and a 300
wind direction less favorable for extension of lake effect snow
showers this far east. Some flurries from higher based diurnal
stratocu is about all the potential supported during the day and
then just stratocu Monday night as the wind backs with the passage
of high pressure through the Ohio valley.
Ridge will slide through the area Tuesday and Wednesday keeping the
weather fairly quiet with a slight warm up as winds turn back to the
SW. There is a weak shortwave lifting NE ahead of the next trough
which could drum up a few light showers Wednesday. Otherwise, next
chances of showers will come later in the week Thursday and Friday
as the next longwave trough passes east through the Great Lakes.
MARINE...
Moderate southwest flow will temporarily slacken the remainder of
the day and through tonight as the pressure gradient briefly weakens
across the central Great Lakes. Existing Small Craft Advisories
along portions of the Lake Huron nearshore waters and outer Saginaw
Bay will thus be allowed to expire. Southwest winds will then
quickly ramp up again Sunday afternoon and especially Sunday night
and into early Monday morning as low pressure developing over the
upper Midwest rapidly deepens and tracks northeast towards the
northern Great Lakes. This system will pull a strong cold front
across the region flipping winds to the northwest along with a surge
of cold air. Winds to gale force across the Lake Huron basin will be
likely during this time, and Gale Warnings have been issued for all
of the Lake Huron waters. The potential will exist for a few gusts
to strong gales Sunday night across the northern Lake Huron waters.
Small Craft Advisories will also be in effect during this time for
Lake St. Clair and western Lake Erie, where it is anticipated that
gusts will remain just below gale force. Moderate northwest flow
remains in place through the middle of next week as high pressure
slides eastward across the Ohio Valley.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 7 PM this evening to 10 AM EST Monday for LHZ421-
422-441>443-462>464.
Gale Warning from 4 PM this afternoon to 10 AM EST Monday for
LHZ361>363.
Lake St Clair...Small Craft Advisory from 7 PM this evening to 10 AM EST Monday for
LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory from 7 PM this evening to 10 AM EST Monday for
LEZ444.
&&
$$
AVIATION.....DRK
DISCUSSION...BT
MARINE.......IRL
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service Marquette MI
546 PM EST Sun Nov 21 2021
.SHORT TERM...(This evening through Monday)
Issued at 324 PM EST SUN NOV 21 2021
Radar and satellite imagery, as well as local obs show a cold front
passing through the UP this afternoon. As the cold front is moving
through, obs and webcams show areas across the UP seeing light
snowfall, with some bursts of heavy snowfall seen at times too.
Therefore, expecting most of the area to maybe get a quick inch from
this cold frontal passage, with some spots outside the NW wind lake-
effect belts seeing up to 2 inches locally. The western NW wind lake-
effect belts could see up to 4 inches, with locally an inch or two
more in the higher elevations, this afternoon into tonight as lake-
effect snow starts after the front passes (we are starting to see
the lake-effect begin now from Ironwood to the Keweenaw). Given the
strong post-frontal winds, could also see some patches of blowing
snow too. In the eastern NW wind lake-effect belts, models are
showing a good agreement whereby lake-effect snow behind the cold
front develops this evening and continues on through tonight into
Monday. This lake-effect snow is expected to drop a significant
amount of snowfall in the snowbands; thinking there is going to be
about 6 to 8 inches this evening into early Monday morning where the
snowbands set up, with locally up to 10 inches possible at spots.
Areas of blowing snow are also expected tonight into tomorrow,
particularly along the Lake Superior shoreline as gusty winds up to
50 mph could greatly reduce visibilities. Therefore, a Winter
Weather Advisory is in effect for Alger, Luce, and Northern
Schoolcraft counties from 5pm this evening to 10am tomorrow.
Snowfall rates should begin to ease up, and eventually end, from
west to east Monday as a ridge begins to build in from the Northern
Plains.
Another hazard that is expected this afternoon into tonight is gusty
winds. Winds up to around 45 to 50 mph are possible across Upper MI
this afternoon into early tonight as the cold front brings a strong
temp and pressure gradient across the UP. Behind the cold front,
impressive vertical mixing up to around 5 kft is expected this
afternoon. We could see this impressive mixing continue into tonight
as well. Some obs at KCMX this afternoon have shown peak wind gusts
up to 59 mph, so it does seem possible that winds will overachieve
what is already forecasted (as well as the max of model guidance).
However, I also have my doubts for having the Wind Advisories
continue into the overnight hours as the latest HRRR and RAP model
soundings do show some areas not supporting strong mixing of the
winds early tonight. If this were to occur, then Wind Advisory level
gusts would not be realized. However, I`m not fully convinced to cut
short the Wind Advisories yet, as the NAM3km is still showing strong
mixing, and the HRRR at other places is still showing strong mixing
throughout the overnight hours. Therefore, keeping all but Gogebic
County under a Wind Advisory until the overnight hours. (Did not
include Alger, Northern Schoolcraft, and Luce Counties either, but
that was because the high winds are included in the Winter Weather
Advisory.)
Another threat we could see this afternoon into Monday is lakeshore
flooding, particularly in the east in Alger and Luce Counties. Due
to the strong NW winds behind the cold front this afternoon and
tonight, we could see some minor beach erosion and lakeshore
flooding from the Porkies up to the tip of the Keweenaw as waves get
up to 10 to 14 feet in height. However, over in Alger and Luce
Counties, expect waves to reach up to 14 to 20 feet; therefore, a
Lakeshore Flood Advisory has been issued for Alger and Luce Counties
from 7pm tonight to 10am Monday morning, as some beach erosion and
minor damage to docks and property is possible. The lakeshore
flooding is expected to end Monday as the winds over Lake Superior
begin to die-down.
On Monday, expect the lake-effect snow and breezy conditions to end
from west to east throughout the day as ridging builds into the
area. However, given that cold air aloft is still expected to be
above us, thinking the high temps will struggle to get above
freezing Monday.
.LONG TERM...(Monday night through Sunday)
Issued at 415 PM EST SUN NOV 21 2021
Medium range models are in good agreement in showing a -NAO
developing this week, but it may only be short-lived with
indications of the NAO trending neutral by the start of Dec. During
the long term part of the fcst, there will be one main shortwave
trof of concern, and the -NAO will work to drive this shortwave to
amplify se thru the Great Lakes into the ne U.S. late week. Just
beyond this fcst period toward the middle of next week, another
shortwave may be forced on a similar amplifying trajectory, but with
the NAO trending neutral, it may not amplify as far to the se as its
predecessor unless a transitory building western N America ridge
becomes sufficiently amplified. As for pcpn, pcpn over the next 7
days may end up being exclusively lake effect driven. Developing LES
this aftn/tonight will linger into Mon night over the e, and then
we`ll await the next amplifying trof in the late Wed to Fri time
frame. Similar to the system affecting the area today, this wave
will likely have limited synoptic pcpn for Upper MI. Push of colder
air on the backside will then bring another bout of nw flow LES,
beginning Wed night, continuing thru Thanksgiving day and winding
down on Fri. At this point, it looks like dry weather should mostly
prevail over the weekend. As for temps, seasonably cool conditions
early this week will trend warmer (above normal) by midweek ahead of
the next amplifying trof. Temps will then trend down (blo normal)
Thanksgiving Day thru Sat on the backside of the amplifying trof.
Warming to above normal will then get underway again late
weekend/early next week as the late week trof departs and the next
potential amplifying trof approaches.
Beginning Mon night, lingering light nw flow LES off eastern Lake
Superior will continue to diminish and should end around sunrise as
sfc high pres ridge passes across the area, shifting winds offshore.
There may yet be a few flurries over the w in the evening. With
winds becoming light and skies becoming clear to partly cloudy,
expect a chilly night. Traditional interior cold spots across the w
half may slip blo 10F, especially in areas where some snow cover
exists. Otherwise, teens and 20s will be the rule, warmest east
along Lake Superior.
Mid-level ridging will then build eastward from the Northern Plains
to the Upper Great Lakes by Tue evening and then to the Lower Great
Lakes by Wed aftn. To the w, a trof moving across the Pacific NW Tue
morning will move out across the Plains on Wed. As a result, pres
gradient will tighten across the area Tue/Tue night btwn the
departing sfc high pres ridge and the sfc trof moving out over the
Northern Plains. This will translate to a 40-50kt low-level jet
developing into the Upper Lakes later Tue into early Wed. Peak low-
level jet speeds could reach 50-60kt Tue night. The resulting strong
waa (850mb temps surge to 5-10C Tue night) will serve to strengthen
inversion which will then work to inhibit increasing winds at the
sfc, especially Tue night. While wind gusts will reach up to 25-
30mph Tue aftn, the increasing stability Tue night will keep winds
in check. Possible exceptions will be near Lake MI and in the s to
sw wind downslope areas near Lake Superior. Won`t know for sure
until we get to Tue, but right now, GFS fcst soundings more so than
NAM fcst soundings suggest potential of advy level wind gusts in
those areas Tue night. Despite the strong waa/isentropic ascent,
there is too much dry air across Upper MI for pcpn. Pcpn Tue would
be more likely to occur to the n, deeper into the retreating cold
air where moistening of the lower levels would be easier to achieve.
With the surge of warmer air into the area Tue night, high temps on
Wed should push solidly into the 40s F across the board.
The mid-level trof moving across the Plains on Wed will amplify thru
the Great Lakes on Thanksgiving Day and into the ne states on Fri.
Associated cold front will move across the area Wed night, setting
the stage for nw flow LES and blustery conditions (not nearly as
windy as the current system over the area) to develop from w to e
Wed night/Thanksgiving Day as 850mb temps tumble back to the
-12 to -16C range. At this point, it doesn`t look like a major lake
effect event, but advy amounts are probably a good bet, especially
btwn Marquette and Newberry. If you have travel plans for the
Thanksgiving holiday, continue to monitor the forcast in the coming
days. LES will then diminish into Fri. There are some hints that a
shortwave may drop se on the backside of the trof over the ne states
over the weekend, so a dry weekend across the entire fcst area is
not certain.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 545 PM EST SUN NOV 21 2021
Behind a cold front, MVFR conditions will continue as lake-effect sn
sets up in the NW lake effect snow belts. Expect gusty NW winds
across all TAF sites until around Mon afternoon. As the lake-effect
sn begins to wind down in the west, could see improvement to VFR
conditions at KIWD and KCMX late Mon. Given that KSAW is outside the
typical NW lake-effect snow belts, it will stay VFR through the
period.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 415 PM EST SUN NOV 21 2021
NW winds are gusting up to 40-45 kts across Lake Superior this
afternoon, including a few storm force gusts up to 50-55 kts, as a
cold front passes. Expect the winds to slowly diminish tonight and
Monday, getting below gale force gusts by late Monday. Winds should
decrease to 20 kts or less by Monday night. Expect the winds to
increase quickly again from the south/southwest Tuesday, with gusts
up to 30 kt Tuesday night. Gale gusts up to 35 to 40 kt are possible
Tuesday night and Wednesday across the east half of Lake Superior.
Winds are expected to decrease to around 25 kts for a short time
Wednesday evening, before another cold front moves across the lake
Wednesday night and Thanksgiving Day, bringing with it northwesterly
winds up to 30 kts across the lake. Expect the winds to become
north/northwesterly Thursday night, with winds to diminish to around
20 kts or less from west to east Thursday night into Friday.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Wind Advisory until 11 PM EST this evening for MIZ001>003-084.
Winter Weather Advisory until 10 AM EST Monday for MIZ006-007-
085.
Lakeshore Flood Advisory until 11 AM EST Monday for MIZ006-007.
Wind Advisory until midnight EST /11 PM CST/ tonight for MIZ004-
005-010-011.
Wind Advisory until 1 AM EST /midnight CST/ Monday for
MIZ012>014.
Lake Superior...
Gale Warning until 10 AM EST Monday for LSZ249>251-266-267.
Gale Warning until 7 AM EST Monday for LSZ243>248-264-265.
Gale Warning until 3 AM EST /2 AM CST/ Monday for LSZ162-240>242-
263.
Lake Michigan...
Gale Warning until 10 AM EST Monday for LMZ221-248-250.
&&
$$
SHORT TERM...TAP
LONG TERM...Rolfson
AVIATION...07
MARINE...TAP/Rolfson
Area Forecast Discussion
National Weather Service Paducah KY
1104 PM CST Sat Nov 20 2021
.SHORT TERM...(Tonight through Sunday night)
Issued at 128 PM CST Sat Nov 20 2021
Southerly surface winds and southwesterly low level flow will
continue across the PAH forecast area through tonight. Meanwhile,
with an approaching mid level shortwave, warm advection rain is
possible after midnight in the northern half of the region,
especially north of I-64.
As the surface cold front approaches from the west, deeper
moisture and dynamics will combine for development of widespread
rain across most of the region, with the highest PoPs over
easternmost MO, western KY, and southwestern IN during the day Sun
as the front continues to move eastward. A clap of thunder or two
is possible near the AR/TN line. Otherwise, the column appears
too stable for tstms at this time. A half inch or less QPF is
expected. Pcpn should be out of even the southern Pennyrile
region of KY by Sun night as winds will be out of the northwest
by then, gusting above 20 mph at times after midnight.
After a mild night tonight in the lower half of the 40s, and
highs in the 50s Sun, lows Sun night will be at or below freezing.
.LONG TERM...(Tuesday through Saturday)
Issued at 128 PM CST Sat Nov 20 2021
Strong high pressure will move across the area Monday through
Tuesday, as a deep longwave forms over the east 1/3 of the nation.
This airmass with the high will bring us our coldest and driest air
of the season so far.
Return flow is forecast to get underway Tuesday night on the
backside of the high, and as a mid level ridge passes across the
region. It will be warmer Wednesday but continued dry as we sit
between a high over the Mid Atlantic and a surface cold front that
should extend from the Great Lakes southward into the southern
Plains.
The front will continue east Wednesday night as a positive tilt
longwave takes shape over the nation`s mid section. We expect rain
will expand in coverage and move into the area especially after
midnight.
The signal is becoming more persistent for our peak rain chances to
be on Thanksgiving day in conjunction with the front moving across
the area. There is a growing consensus as well that the activity
will end more quickly than what the models depicted over the past 2-
3 days, a trend that was recognized by the previous shift, and
continues to be supported by the latest ensemble and deterministic
output from the GFS/GEFS and EC/ECENS. There is still some wavering
with timing, so adjustments will continue. The rapid end will likely
mute or eliminate any concern for a brief change over to a light
rain/light snow mix. Still way out there, but impacts are not
anticipated at this time. Friday will be dry and colder, with dry
weather continuing into the first half of the weekend.
&&
.AVIATION...
Issued at 1104 PM CST Sat Nov 20 2021
With the 06z Sunday WFO PAH TAF issuance, the trend for VFR to
MVFR ceilings and visibilities will initially take place in the
12z-16z Sunday time frame across the TAF sites. A trend from MVFR
to IFR during the 14z to 20z Sunday for KPAH, KEVV, and KOWB just
ahead of the cold frontal passage.
Behind the frontal passage, a return from MVFR to VFR ceiling and
visibility conditions should occur within two to five hours.
The current HRRR simulated reflectivity forecast seems to do well
on the timing and impact of rain on the WFO PAH TAF sites,
depicting the warm conveyor belt and isentropically lift zone for
precipitation overnight and through the day on Sunday.
&&
.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&
$$
SHORT TERM...DB
LONG TERM...08
AVIATION...Smith
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
1000 PM EST Sun Nov 21 2021
.SYNOPSIS...
High pressure will move offshore tonight as an upper level
disturbance approaches the region from the west. A cold front will
move across the area on Monday, bringing a chance of rain to the
area along with much cooler temperatures and breezy conditions. Well
below normal temperatures will remain in place across the area
through the middle of the week, then moderate closer to normal by
Thursday.
&&
.NEAR TERM /TONIGHT/...
As of 1000 PM Sunday...
A surface cold front has made its way to the spine of the
Appalachian Mountains. High overcast skies cover North Carolina,
while low to mid clouds extend across the western half of the state.
Despite some dry air that is present, this still appears to be a
high pop/low QPF scenario. Increased pops to categorical overnight
primarily northwest of US-1 as synoptic and high-resolution models
have good run-to-run consistency in showing showers in all
locations. The latest runs of the HRRR have continued to slow down
the arrival of the precipitation, and this trend has been blended
into the forecast. This keeps the Triad dry through at least
midnight, and still have the bulk of the rainfall waiting until just
before sunrise to reach the Triangle. Cloud cover will keep
temperatures warmer than they have been, in the mid to upper 40s.
&&
.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 1000 PM Sunday...
The one tweak to Monday`s forecast this evening is that showers will
be slightly delayed in clearing the region. Rain should end in the
Triad around noon, across the Triangle in the early afternoon, and
across the Coastal Plain by mid/late afternoon. The previous Sunday
2:13pm discussion follows.
The surface cold front and associated band of showers will make
rapid progress through the area on Monday. An additional few
hundredths of an inch of rain are possible area-wide as the front
moves through, for a grand total of a tenth to a quarter of an inch
by the time all is said and done. Again, given abundant dry air
ahead of this system, not to mention that the best forcing will be
located across the Great Lakes vs central NC, this will not be a
significant rain event. Rain will end in the Triad by mid morning,
across the Triangle around noon, and across the Coastal Plain by mid
afternoon.
Despite the lack of noteworthy rainfall, the front will usher in
colder temperatures and breezy conditions. Some degree of cold
advection should begin by late morning in the west and as skies
clear out and low level lapse rates steepen, breezy winds in the 15-
20mph range can be expected. From the Triangle eastward, clearing
skies and breezy winds will likely hold off until after noon. At
least some degree of breeziness will continue into the evening hours
coincident with the arrival of much colder air aloft and lower
thicknesses as the base of the upper trough moves through the area.
Temperatures tomorrow will remain somewhat mild, but slightly cooler
than today`s highs. Given the delay in arrival of much cooler air
until later in the afternoon/early evening, highs should still
manage to reach the mid/upper 50s. However once the cooler air
settles in tomorrow night, look for overnight lows to drop into the
upper 20s/around 30 area-wide.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
As of 400 PM Sunday...
As the mid/upper trough moves offshore and cool ~1030 mb Canadian
surface high pressure slowly moves across the TN Valley and
Appalachians on Tuesday, height rises and subsidence will result in
sunny skies over central NC. However, continued NW flow and strong
CAA will result in highs only reaching the mid-to-upper-40s, which
is 10-15 degrees below normal. As the high slightly strengthens and
moves overhead on Wednesday morning, clear skies and light winds
will result in ideal radiational cooling conditions. Lows will only
be in the lower-to-mid-20s, and a few upper teens in the usual
coldest spots can`t be entirely ruled out. These will be the coldest
temperatures our region as seen since the spring.
Shortwave ridging will move across the area on Wednesday and
Thursday as surface high pressure weakens and pushes south. As the
flow turns southerly, warmer temperatures on Wednesday (highs in the
lower-to-mid-50s) and Wednesday night (lows in the upper-20s to
lower-30s) will give way to even warmer temperatures on Thursday
when highs will reach the lower-60s. The GFS and ECMWF continue to
be in good agreement that a shortwave trough and cold front will
then move across central NC Thursday night into Friday morning. Both
the 12z ECMWF and 12z GFS now have precipitation with it, as the GFS
has trended toward the sharper trough solution seen on the ECMWF.
More than a third of GEFS have some precipitation, as do the
majority of ECMWF ensembles. Forcing looks decent with the
shortwave, and the GFS has PW values up to and even exceeding an
inch. Thus bumped POPs a bit above NBM once more, to low chance
across the area on Thursday night in the west and Friday morning in
the east. Dry weather and below-normal temperatures will move back
in behind the front for the rest of Friday into Saturday, before the
high may move offshore and temperatures warm a bit on Sunday.
Another shortwave trough looks to move across the area on Sunday,
but the air will be much drier and confidence is too low for even
slight chance POPs at this time.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
As of 700 PM Sunday...
24 hour TAF period: VFR conditions will begin the TAF period, but
MVFR ceilings are expected at all TAF sites tonight with IFR
possible at KFAY and KRWI as a cold front moves through central NC
tonight into Monday morning. Skies will clear behind the front
rather quickly and allow for VFR conditions to return, but gusty
winds will follow out of the NW with highest gusts expected at
GSO/INT. A strong pressure gradient at the surface will allow the
gusty winds to persist into the overnight hours, likely not
subsiding until sometime Tuesday morning.
Outlook: High pressure will settle in over the southeast Tuesday
through Thursday maintaining VFR conditions across the area. The
next chance for sub-VFR conditions looks to be Friday morning as
another cold front is forecast to push through central NC.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Leins
NEAR TERM...Green
SHORT TERM...Green/Leins
LONG TERM...Danco
AVIATION...Swiggett/Luchetti