Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/23/21
Area Forecast Discussion
National Weather Service Charleston SC
911 PM EST Mon Feb 22 2021
.SYNOPSIS...
A weak cold front will move through late tonight, followed by
high pressure. A weak, backdoor cold front may move into the
area Thursday followed by a quick moving storm system that
could impact the area Friday and Friday night.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
The forecast is on track. 23/02z surface analysis placed the
southwest-northeast oriented cold front roughly along a Loris,SC-
Manning,SC-North,SC-Augusta,GA-Sandersville,GA-Warner Robins GA
line. The front is still on target to push offshore an hour or
two after midnight with drier/cooler air advecting in behind it.
The H3R and to some degree the RAP still suggest isolated
showers could redevelop right along the front has it pushes to
the coast. Although skies are clearing in the wake of the pre-
frontal trough that moved through earlier with the rain, GOES-E
fog imagery has recently shown an expansion of cloud cover in
the vicinity of the front. It could very well be that some of
the CAMs are over-developing this cloud cover similar to what
they do with the marine-based stratocumulus over the Atlantic.
Either way, impacts will be minimal if any showers were to
occur. Low pops around 5% were maintained with the front to
account for any possible showers that develop. Rain-free
conditions will certainly occur after FROPA.
Satellite and surface observations as well as a very useful
twitter post out of Hampton County, SC, show some localized fog
has recently developed across the interior with a few AWOS
sites reporting vsbys below 1/2SM. This fog is likely pretty
shallow with the wet grounds still in place, but these low
vsbys are not representative of prevailing conditions. Still,
motorists should be alert for rapidly changing conditions over
very short distances until the risk fog ends with the passage of
the cold front. A Special Weather Statement has been issued for
the interior through midnight to address these rapidly changing
driving conditions. Lows ranging from the lower 40s well inland
to the upper 40s at the beaches still look good.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Surface high pressure will build from the Louisiana Gulf Coast
Tuesday eastward into north Florida and the western Atlantic by
late Thursday. Mainly zonal west-northwesterly flow aloft will
gradually become west-southwesterly by Thursday. Dry air
filtering in behind the departing cold front will result in
mainly clear skies through Wednesday night with a bit of an
increase in cloud cover expected Thursday. Models have trended a
bit faster with dropping a backdoor cold front into the area
Thursday with the 12Z/22 GFS operational run on the slower side
of the solutions. Downslope flow will help offset cooler low
level temperatures and thickness values on Tuesday. Have trended
high temperatures up a bit on Tuesday and Wednesday, but not as
high as the quite warm MAV and MET guidance. Expect highs in
the mid to upper 60s on Tuesday and near 70 on Wednesday.
Thursday looks to be just a touch cooler than Wednesday in the
north behind the backdoor cold front, but a bit warmer in the
south. For all three days high near the cool coastal waters will
be no more than the lower 60s. Lows Tuesday night in lower to
mid 40s will moderate into mid to upper 40s for Wednesday night.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The back door cold front will move south through the area Thursday
night and into Friday, stalling out and dissipating south of our
area this weekend. Friday should remain relatively dry with showers
developing mainly to our north. Moisture associated with the system
affecting the Midwest will push into the area, which combined with
weak isentropic ascent could produce isolated to scattered showers
Saturday into Sunday. POPs remain fairly low considering much will
depend on moisture content, considering only weak isentropic ascent.
Another system looks to approach Monday into Tuesday with another
round of showers associated with a cold front. Temperatures should
sit right around normal for this time of year. Highs in the 60s/70s
and lows in the 50s seem to be persistent, with Monday being the
warmest day as WAA strengthens prior to a cooler air mass
encroaching the Southeast.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
VFR through the period at both KCHS and KSAV.
Extended Aviation Outlook: Flight restrictions should ease late
Monday after the passage of a cold front. VFR conditions should
prevail thereafter.
&&
.MARINE...
Tonight: Southwest winds 10-15 kt will become west to northwest
overnight. Seas will average 2-4 ft nearshore with 4-5 ft over
the Georgia offshore waters.
Tuesday through Saturday: Expect decreasing winds and subsiding seas
Tuesday into Wednesday night. By Thursday winds should be at or
below 10 knots, but will shift to northerly to northeasterly across
the northern waters Thursday. As the backdoor cold front sags south
Thursday night and into Friday, winds will tick up a bit. Seas will
subside Tuesday and Tuesday night in response to the weakening winds
with seas by Wednesday in the 1 to 3 foot range. As the high
pressure slides east, winds will become easterly to southeasterly
Friday night and Saturday with an increasing fetch. Seas will
increase later Friday and into Saturday and should reach 3 to 5 to
perhaps 6 feet. This results in some potential for Small Craft
Advisory conditions to be reached on Saturday across at least
portions of the waters.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
923 PM EST Mon Feb 22 2021
.UPDATE...
Ongoing mid level ascent in advance of the approaching wave has
been allowing snow to develop across northern Wisconsin and portions
of the western UP. The ascent will overspread Se Mi, although
focused more across the northern half of the CWA, during the
overnight. In light of recent hi res guidance and upstream returns,
overnight pops will be lowered slightly for metro Detroit and points
south. Otherwise, categorical pops still look reasonable across the
north. Southwest flow in advance of this system has been driving
warmer boundary layer air northward. Portions of nrn Illinois and Se
Wisconsin are already approaching 40 deg, several degrees higher than
most model solutions suggest. This will warrant an update to nudge
overnight temps upward a few degrees and mention a mix with rain over
at least the south half of the forecast area. Forecast snowfall
amounts across the Saginaw Valley and thumb region of an inch or less
seems reasonable as this region will have more prolonged forcing and
a little cooler boundary layer. Farther south, the warmer boundary
layer temps suggest minimal if any overnight snow accumulations.
&&
.PREV DISCUSSION...
Issued at 603 PM EST Mon Feb 22 2021
AVIATION...
The low level flow has backed southwest across Lower Mi. There is a
notable clearing of the MVFR stratus deck ongoing across far SW
Lower Mi as low level warming is shutting off the moisture flux from
Lake Mi. Although model soundings stubbornly hold onto a stratus
deck through the evening, the RAP RH plan views, which have the
support of upstream observations, suggest a clearing of these clouds
will occur at the Se Mi terminals in the 02Z to 03Z time frame this
evening. VFR conditions will however likely be brief as ascent
associated with a mid level short wave will overspread Se Mi after
06Z. Redevelopment of MVFR based clouds with some wet snow is then
expected after 07Z. Limited ascent will keep any accumulations under
an inch. The passage of the system to the east Tues morning will
result in a wind shift to the west, with increasing mixing depths
supporting frequent gusts just over 25 knots by late Tues morning.
For DTW...Boundary layer temps have warmed well into the 30s in
advance of the approaching short wave across Wisconsin. This
supports some of the model solutions that drive enough warm boundary
layer air into metro Detroit to result in a rain/snow mix or perhaps
a period of all light rain. This of course will limit any snow
accums.
DTW THRESHOLD PROBABILITIES...
* High in ceilings below 5000 feet overnight and on Tuesday.
* Moderate in precipitation type tonight being a mix of rain/snow.
PREV DISCUSSION...
Issued at 241 PM EST Mon Feb 22 2021
DISCUSSION...
Fast moving shortwave progressing through the Dakotas on the nose of
a large 150+ knot upper jet will bring a quick round of light snow
to the area tonight, especially north of M-59. Given the progressive
nature of this system and lack of decent moisture over the area, do
not expect much in the way of accumulation with a dusting to perhaps
an inch possible overnight. Jet dynamics are not very supportive as
this incoming jet is anti-cyclonic which will limit the left exit
region lift. Areas north of I-69 (and especially the Thumb) will have
the best chance of receiving that inch given the best lift from the
system remains north of the region.
A similar system will race into the region already by Tuesday night
and Wednesday morning. This system will benefit from the right
entrance region of this jet by that time which will be enhanced
given the continued anti-cyclonic structure. This will set up a
rather decent period of fgen forcing, but this will be well north of
the forecast area. A broad area of weak upper lift as vorticity max
shifts into the area will do little more that provide a chance of
light snow (perhaps a dusting to half an inch) over northern portions
of the forecast area generally north of I-69.
Temperatures will be mild into the middle of the week as compared to
the past few weeks with highs nearing 40 degrees both Tuesday and
Wednesday as westerly flow around the base of this second passing
shortwave maintains a flow of Pacific air into the region. Even the
colder air mass that settles into the area behind the Tuesday wave
will only bring high temperatures back to around freezing with low
in the teens to lower 20s and the core of this arctic air mass shift
east through Canada and remains north of the Great Lakes for the
most part.
A return of mild conditions is expected by the weekend as upper
ridging generally expands over the region as several significant
shortwaves dig into western CONUS from the Pacific ocean. Expect
highs back to around 40 for Saturday/Sunday. The chance of any
significant storm system during this period is pretty low. However,
would suspect that shortwave energy will likely eject into the area
within developing southwest upper flow as this Pacific energy
funnels onto the coast. This will renew a chance of precipitation by
the Saturday time frame with temperatures suggesting some mix of
snow and rain.
MARINE...
Winds shift to SW this evening due to the influence of a large low
tracking across the southern shores of the Hudson Bay. This Hudson
low will prevent any significant relaxation of the pressure gradient
locally allowing winds to maintain their strength, and combined with
the long fetch under a SW flow regime, another period of strong
winds capable of gusting up to around 30kts will be likely tonight
across central Lake Huron. While a stray gust to gale-force can`t be
ruled out early tonight, conditions are not favorable to create any
prolonged period of gales that would warrant a headline. Another
weak disturbance rounds this Canadian low and swings through the
central Great Lakes Tuesday bringing another shot of snow showers
and shifting winds back to W. This increases the fetch over northern
Lake Huron, and in combination with a still tightened gradient, will
allow for gusts up to around 30kts daytime Tuesday across that
portion of Huron. Similar to the SW flow, conditions under this W
flow are looking very marginal for gusts to reach and stay at gale
strength for a long enough duration. So, have held off issuing any
kind of headline.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
UPDATE.......SC
AVIATION.....SC
DISCUSSION...DG
MARINE.......KDK
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service New Orleans LA
403 PM CST Mon Feb 22 2021
.SHORT TERM (This evening through Wednesday Night)...
A bit of a tricky forecasted today, mostly in regards to a recent
frontal passage. A few targets of opportunity existed against
blended guidance earlier this afternoon, including a significant
lag of much lower Td`s in the post-frontal airmass. Observations
along and west of I-59 averaged 8-10 degrees lower in dewpoints,
and have opted to use short-range HRRR guidance to capture a much
sharper moisture boundary and drier air deep behind the front. The
CAA in the low-levels lagged significantly and weakened with
time, which without any low-level clouds from a post-frontal
thermal trough, did not have any impact to drive temperatures down
(typical with a sunny, daytime FROPA at this latitude and this
time of the year). But, who`s complaining? Almost all areas
experienced a beautiful spring-like afternoon. High pressure will
build in from the west this evening and settle in tonight, with
clear skies and calm winds expected. Expect maximized radiative
cooling processes by later tonight/early Tuesday with short-range
model soundings strongly supporting plenty of subsidence leading
to a prominent radiation inversion in the low/mid-levels. Dropped
temperatures a few degrees for many areas due to this, with focus
on typical drainage locations across the northshore and coastal
MS. Many will settle into roughly in the mid 30`s from BTR east
across the MS coast. A few spotty colder locations may see
freezing temperatures for an hour or two, with low to mid 40`s for
the southshore. Conditional probabilities of radiational fog
varies from 50-70% along the I-10/12 corridor between 10 and 13Z.
Some (not all) guidance supports this idea. Going to ride the
fence with patchy areas of fog come daybreak Tuesday for a large
portion of SE LA and maybe as far east as parts of coastal MS,
with dense fog potential being low confidence (cant rule it out,
but stay tuned for subsequent updates if necessary).
Main focus in the short term beyond Tuesday morning is staying
firm on a warmer bias. Will be averaging 2-3 degrees above blended
guidance both Tuesday and Wednesday as we have began to enter the
time of the year where guidance struggles on a higher sun angle
come peak afternoon temperatures. Not to mention clear skies
during the afternoon owing to plenty of afternoon mixing. The
surface high pulls east of the area late Tuesday and into
Wednesday, dragging slightly higher surface Td`s back to the area
from southerly winds. Only difference on Wednesday will be the
chance for some puffy low-level Cu thanks to a more moist PBL, but
still will be a beautiful and pleasant warm day. KLG
.LONG TERM (Thursday through Sunday)...
By early Thursday, noticing long-range guidance trying to push a
weak front into the area supported by an area of low pressure and
fast moving low-amplitude shortwave trough across the Great
Lakes/NE area. Can`t rule out some isolated showers as this
boundary eventually slows down becoming perpendicular to the
vertical wind profile aloft (unidirectional from surface to the
tropopause). With a stationary front draped across the area, it
will not take much to get atleast some light showers going with
just enough low-level convergence at work. Model soundings
illustrate a moist adiabatic thermal profile completely saturated
in the low-levels, which hints at the lack of any prominent low-
level conditional instability to work with. However, with surface
Td`s in the 60`s, any low-level lift would may lead to few
isolated thunderstorms. Going above blended guidance with PoP`s
from 12Z THU through 00Z FRI. (Primarily during the day on
Thursday). The front will pull back north again as a warm front,
out ahead of the next approaching shortwave trough from the west.
At this time, the fast/eastward progression of the shortwave
trough in the vicinity of strengthening ridging to the north
across the Great Lakes will support eventual weakening/stretching
of the trough axis. Regardless, this system will be a big rain
maker for areas to our north and west later this week. Just how
far south any of this rain will pull down from the north remains
in question, but seeing a wetter trend with the GFS as of today,
but not buying in on this just yet as model solutions are much
more inconsistent this far out. Either way, long-range
temperature trends are looking very warm for the upcoming weekend,
as a nice looking 588dm ridge builds in the Gulf of Mexico. The
strength of this ridge will try to keep most active weather well
to our north, leading to a warm/dry start to the early parts of
next week. KLG
&&
.AVIATION...
.18Z TAF PACKAGE...
Expect VFR conditions for all area terminals through the afternoon
and early overnight hours. A recent FROPA will deliver gusty
post-frontal surface winds, bearing 310 to 340 and gusting 12 to
15kts at times. Otherwise, clouds will clear out this afternoon
with only a few patchy low-level CU across coastal SE LA and MS.
Winds calm after sunset this evening, with continued clear skies.
Radiational cooling near the surface will help develop some patchy
areas of fog come daybreak Tuesday. At this time, the best
chances for morning fog will generally range across central
sections of SE LA and possibly across parts of coastal MS. Due to
lower confidence, have refrained from dropping visibility lower
than 1/2 mile. Time frame will generally be from around 10 to 13Z
tomorrow morning which may drop flight categories temporarily into
MVFR/IFR or periodically less in this time frame window. Any fog
that develops will quickly dissipate shortly after sunrise or
around 13Z revealing VFR conditions thereafter. KLG
&&
.MARINE...
Expect a weak cold front to continue swinging through marine
areas later this evening and tonight, leading to gusty
northwesterly winds to build in. Not anticipating any marine
highlights at this time, as winds will likely continue to diminish
into tonight as high pressure builds in. Look for clear and calm
conditions to continue through Thursday, as the next cold front
will likely stall across coastal inland areas right along the
northern Gulf coast on Thursday. Southerly winds will prevail at
this time through late-week and into the weekend, with calm seas
expected and no hazardous weather expected. KLG
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 35 72 40 72 / 0 0 0 0
BTR 37 72 42 75 / 0 0 0 0
ASD 34 72 41 74 / 0 0 0 0
MSY 45 72 48 75 / 0 0 0 0
GPT 36 69 43 70 / 0 0 0 0
PQL 34 70 41 70 / 0 0 0 0
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&
$$
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
539 PM CST Mon Feb 22 2021
.SHORT TERM...(This evening through Tuesday night)
Issued at 319 PM CST Mon Feb 22 2021
Extensive mid level cloud cover has moved in today as several weak
disturbances ride southeast within fast northwest flow. A few
showers are possible late this afternoon north of I-94 with one
disturbance, then another few showers are possible this evening
along I-94 again with a second wave. None of it will amount to
anything beyond a hundredth or two and temperatures will be warm
enough for mostly rain.
An eastward moving clipper will generate a band of precipitation to
the north of its track this evening over MT and ND. It will shift
eastward to central MN Tuesday afternoon and northern WI Tuesday
night as the surface low tracks across the northern CWA. The majority
of this precipitation (mainly in the form of snow) will remain north
of the CWA, but the northernmost counties from Douglas to Rusk will
likely be on the southern fringes of it. One to three inches of snow
could fall in those counties, but 3 to 5 inches are likely just
to the north. The position of this band will be critically important
for accumulations and a small shift north or south could have big
implications.
As the system heads east into WI Tuesday evening, wrap around rain
and snow showers could dip as far south as southern MN before ending
early Wednesday morning. Little or no accumulation is expected, but
did increase PoPs to 40s and 50s area wide.
.LONG TERM...(Wednesday through Monday)
Issued at 319 PM CST Mon Feb 22 2021
The tail end of Tuesday`s disturbance should be exiting the region
by Wednesday morning with dry conditions prevailing under clearing
skies. High pressure building in from the northwest will allow
temperatures to fall a few degrees from the relative warmth of the
beginning of the week, but increasing sun should help keep highs
above freezing. Thursday will be much of the same with high pressure
still in place. Change is on the horizon as we near the end of the
week with two potential weather makers. Southerly winds will
increase overnight Thursday into Friday ahead of the first system. A
500 mb trough moving across northern Minnesota will allow for
increased precip chances for much of the area by Friday afternoon
into the overnight hours. A rain mixing with snow is still possible,
particularly across southern Minnesota into western Wisconsin given
surface temperatures will be on the warmer side of freezing. However,
QPF amounts still appear to be light at this point.
Attention then turns to the second system, which still has a high
degree of uncertainty. The first point of uncertainty is what will
happen to temperatures behind the Friday system. General thinking is
that temperatures Saturday will be at least a few degrees cooler and
still by Sunday, but just how much is the question. The NBM has a
nearly 10 degree spread for both days, and the Euro and GFS differ on
Saturday by over 10 degrees. The GFS is more aggressive in both
southern extent and speed with bringing a weak clipper type system
down from Canada before deepening well off to the east of the
forecast area. The Euro depicts a more delayed movement of this
system and the cooler temperatures hold off until late in the
weekend. These differences in evolution of a surface feature across
the Central Plains make it difficult to pinpoint what this will mean
for us in terms of precip chances. Because of this, will stick with
low PoPs for Sunday/Sunday night until model consistency improves.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 539 PM CST Mon Feb 22 2021
Extensive returns across MN and WI on radar have produced few, if any
precipitation reports, so removed any precip mention from TAFs this
evening. Skies look to become mostly clear tonight into Tuesday
morning, before cloud cover increases ahead of BC shortwave that will
be approaching NW MN by the end of the period. By the afternoon,
snow will be spreading across northern MN, but looks to remain mostly
north of MPX terminals. Have not been as aggressive as models with
bringing MVFR cigs and -SN into AXN/STC until we get better
confidence on just how far south this band will reach.
KMSP...There is a batch of showers up by STC that may lead to a brief
hit of -RA around 1z, but it does not look worthy of including in the
TAF. For the end of the TAF, there will be snow moving across central
MN, but expect that precip to remain north of MSP. RAP doesn`t show
MVFR cigs moving into MSP until 9z Tue, so don`t have MVFR cigs
moving in as fast as the MAV/MET/LAV suggest.
/OUTLOOK FOR KMSP/
Wed...VFR. Wind NW 5-10 kts.
Thu...VFR. Wind NW 5-15 kts becoming SW.
Fri...Chc MVFR/IFR with -SN in evening. Wind SW 15G25 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
SHORT TERM...Borghoff
LONG TERM...Dye
AVIATION...MPG