Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/07/20
Area Forecast Discussion
National Weather Service Caribou ME
911 PM EST Sun Dec 6 2020
.SYNOPSIS...
Strong low pressure will slowly exit across the Maritimes
through Monday. High pressure will cross the region Tuesday,
then exit across the Maritimes Wednesday. A cold front is
expected to cross the region Wednesday night into Thursday
morning. High pressure is expected for Friday.
&&
.NEAR TERM /THROUGH MONDAY/...
9:11 PM Update: Low pressure is near the western tip of PEI and
it will remain quasi-stationary overnight before beginning to
pull away during the day Monday. Moisture continues to wrap
around the low and will produce light snow across northern and
eastern sections of the FA late this evening and into the
overnight hours. The light snow will transition to scattered
snow shower and flurries by morning. At this point,the vast
majority of the accumulating snow is over with any add`l
accumulations under an inch. A gusty northwest wind and slowly
falling temperatures will allow for areas of blowing and
drifting snow, especially in areas that received more
significant snowfall from our recent storm that is winding down.
Made some adjustments to the PoPs and weather to hold on to
more stratiform light snow until around 3 am. Otherwise, just
very minor adjustments to the other forecast elements based on
the current conditions and expected forecast trends overnight.
Previous discussion:
The wrapped up low in New Brunswick will still have influence on the
region`s wx into tonight w/periods of snow, especially across
northern and eastern areas. Still some good convergence across
portions of the northern and eastern areas to keep steady snow going
w/bands of enhanced snow at times into early evening. This can be
seen on the latest NAM as well as HRRR streamline analysis. So, an
additional 1-3 inches is possible into the evening before
convergence weakens as the low slowly pulls away. Given this,
decided to drop the Winter Warnings and Advisories s of Aroostook,
Nrn Somerset, Nrn Piscataquis and Nrn Penobscot County. The Winter
Storm warning for the northern areas is in place through 7 pm.
The steady snow is expected to transition to snow
showers/flurries overnight w/the loss of the convergence and
sufficient forcing. Gusty NW winds will lead to blowing and
drifting of snow through at least midnight as temps have cooled
down to allow for more lighter snow which should be able to be
lofted quite easily. The winds are expected to let up by early
Monday morning w/a reduction in the blowing and drifting
expected. Temps will be dropping back slowly overnight as clouds
will hang on overnight.
Monday will see some improvement as the low pulls even further
away. There is still some risk of scattered snow
shower/streamers that will be coming off the open St. Lawrence.
Used a blend of the guidance for the pops which show 20-30%
across the northern and western areas. Any snow accumulation
will be light and less than an inch. Temps will warm some
w/upper 20s across the n and w, while central and downeast areas
are expected be in the lower 30s. NW winds will be much lighter
than they were today.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Maine will remain in a quite compact pressure gradient between
the exiting low and incoming high pres ridge into Tuesday. Much
of the low level moisture will have moved out of the region, but
clouds and some breezy conditions will remain. The NW winds
will keep cool air channeling into Maine, with temps falling
into the teens across the north Tues night, and lower 20s across
Downeast. Clouds may prevent a greater rad cooling effect, but
snow will still be on the ground for many central and northern
locations.
Gradient winds will finally slacken on Wednesday with a calmer
day. Clouds will remain overhead, but it should remain dry as
the brief sfc ridge passes overhead. The next chance of precip
arrives Wednesday evening and overnight as a weak shortwave
dives across New England north of a 500mb jet. The jet core is
forecast to remain south and west towards the central Great
Lakes, which keeps best divergence aloft in the exit region away
from any deeper source of moisture. Thus, have kept only a
slight chance of snow showers across the CWA overnight.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
For the second half of the week, temperatures will seasonable
with little in the way of precip during the work week. The item
to watch will be a large storm system developing across the
central CONUS around next weekend.
The aforementioned shortwave washes out on Thursday ahead of an
elongated upstream jet. The movement of this jet across the
northern tier of the US will help amplify a incoming longwave
trough along the western US. With the troughs arrival in the
lee of the Rockies, guidance suggests the formation of a strong
surface low across the Great Plains through Thurs night and
Friday. The footprint of the occluded low expands, bringing the
jet along the base of the trough and leaving much of the eastern
US in SW WAA beginning Friday afternoon through the late
weekend. EPS solutions take the low center into the Great Lakes
and Southern Quebec. This space and duration of the WAA will
trend daily sfc temperatures above normal. This is possible not
only for Maine but a bulk of the Northeast as indicated by
CPCs 6-10 day temp outlook. An anomalous surge of PWATs will
also be possible into the warm region, meaning the chance for
another rain event.
Most long range guidance shows the development of the system
across the nations midsection, but further confidence is
needed before considering QPF amts, timing, and potential hydro
impacts. The CWA has recently experienced a few heavy precip
events, and snowpack will likely remain across locations that
received significant snowfall over the past 24 hours, especially
in the deep woods. Thankfully, headwaters and soil moisture
Downeast will get a break during the week ahead.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
NEAR TERM: MVFR late this evening for all sites, w/tempo IFR
from KHUL northward. KBGR-KBHB should see VFR late this evening
and holding that way into Monday. Northern TAF sites should
hang on to MVFR for Monday. NW winds tonight at 10 to 20 mph
w/gusts to 25-30 mph especially this evening. This will lead to
areas of blowing and drifting snow, which will reduce
visibilities. Improvement on the wind for Monday for all sites
w/NW winds dropping back to 10-15 mph.
SHORT TERM:
Monday night: VFR. Light N wind.
Tuesday: VFR, a brief period of MVFR possible across the north.
N wind gusting up to 15 kt at BGR and BHB.
Tuesday night: VFR. Light NW wind.
Wednesday: VFR dropping to MVFR north, Light SW wind.
Wednesday night: MVFR to VFR north, a chance of snow showers.
VFR Downeast. Light SW wind.
Thursday: MVFR north, VFR Downeast. Light W wind.
&&
.MARINE...
NEAR TERM: A small craft advisory is in effect through early
Monday morning. Still expecting some gusts to 30 kts overnight
with a brief gust or two to 35 knots, mainly over the outer
zones. Seas are expected to slowly subside overnight. Winds are
forecast to drop below 20 kts w/seas subsiding to 3-4 ft by
midday Monday.
SHORT TERM: Conditions will predominantly be below SCA
criteria. The exception being Tuesday afternoon when N coastal
gusts increase to around 25 kt as low pressure passes outside
the Gulf of Maine, subsiding towards midnight. Winds become W
through Wednesday and into Thursday.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...Small Craft Advisory until 4 AM EST Monday for ANZ050>052.
&&
$$
Near Term...CB/Hewitt
Short Term...Cornwell
Long Term...Cornwell
Aviation...CB/Hewitt/Cornwell
Marine...CB/Hewitt/Cornwell
Area Forecast Discussion
National Weather Service Quad Cities IA IL
453 PM CST Sun Dec 6 2020
...00z AVIATION UPDATE...
.SYNOPSIS...
Issued at 310 PM CST Sun Dec 6 2020
A mix of sunshine, patches of lingering stratocu and afternoon
instability cumulus acrs the area, while the next upstream upper
level low was noted on water vapor imagery dropping south acrs LK
Superior. Northerly steering flow to lee of upper blocking pattern
acrs the western CONUS will continue to shuttle short waves down
acrs the upper Midwest and GRT LKS into early this week, before the
ridge flattens and presses eastward acrs the mid CONUS for a mid
week warm up. Following that, there still appears eastern Pacific
upper trof energy will stride inland and possibly induce a storm
system somewhere acrs the Midwest by late week.
&&
.SHORT TERM...(This Evening through Monday)
ISSUED AT 310 PM CST Sun Dec 6 2020
Tonight...Some of the banded instability CU should decay after
sunset but then a more extensive stratocu deck currently extending
from far southeast NE, eastern MN and NW WI/LK Superior, will look
to get dragged southeastward as the above mentioned closed low to the
north drops toward western lower MI by midnight, and toward IN/
northwest OH by Monday morning. This a bit further east track than
indicated by model runs at this time yesterday. But this system will
still utilize some higher cloud deck patches as seeder feeders to
the low stratocu deck that will slide acrs the local area after mid
evening. This will produce some flurries spreading in from the north
as the deck approaches along with lift from the wave aloft. There
may even be some bands more characterized as light snow as opposed
to flurries and produce a dusting like what occurred Sat night-early
Sunday morning.
Bulk of model solutions including HiRes suggest most of this flurry
or light snow activity to occur mainly along and east of the MS RVR
and spread in from the north after 10 PM, prime window then mid nigh
through 5 am from north-to-south. But higher band of seeder feeder
clouds seen on the current Vis satellite loop currently acrs
northwest into north central WI was pushing south-southwest. If this
trend maintains, the entire CWA will be at risk for flurries later
tonight. Extrapolating the ongoing band of light snow this process
is producing acrs north central WI ATTM, this band would almost miss
the CWA to the west or clip areas west of a Dubuque to Cedar Rapids
line. No model is handling this band at all. That`s if it can
maintain, and another evening of watching upstream trends so as to
adjust POPs for light snow and the need to spread flurry wording
further west. Lows tonight generally in the mid to upper 20s, but a
mix of cloud cover and clear holes will make for quite a temperature
variation.
Monday...Will be stubborn with lingering cloud cover with looks like
it may get trapped under post-wave ridging aloft/subsidence
inversion. But the subsidence may also act as a cloud scouring agent
like it did today, thus some holes or breaks also likely especially
by afternoon. Then the active northerlies will look to shuttle down
a weaker short wave trof down toward the area by evening. Thus more
clouds/stratocu may be on the increase again from the north by late
day. Will go with 75 percentile high temp potential making for
widespread upper 30s to low 40s, but more insolation tomorrow than
currently expected may make these values be a degree or two on the
cool side. ..12..
.LONG TERM...(Monday Night through next Sunday)
ISSUED AT 310 PM CST Sun Dec 6 2020
Key Messages:
1. Warmer temps to highlight most of the work week.
2. Next chance for precip will be the end of the week where
differences in guidance make for a difficult forecast.
Discussion:
Ridging aloft begins to move into the area at the beginning of the
period as WWA begins to bring in above 0 H85 temps. This will in
turn lead to a few days with temperatures in the 50s, well above
normal and even possibly reaching the 60s by midweek. We will get
close to potential record highs. With the shift in polar temps,
this set up will feature strong baroclinicity across the region and
thus at the end of the week we have the potential for strong storm
system.
At the current time, the GFS is the strongest of the models,
bringing a left entrance region into the area along with an upper
level wave shifting negative across the area. This is likely
currently overdone, yet is a perfect example of the potential
dynamically driven system for the end of the week. All guidance has
the majority of our area in the warm sector and rain for the area.
Wrap around snow is possible in most guidance and looking at the
ensembles the signal is for light snow. The main question is how
warm do we get Friday and whether or not we see storms. The GFS
would lead to quite amount of shear and potential for strong storms.
The GEM and ECM would be wet rain for the area. Also there are
timing differences in these systems which causes a longer period of
POPs in the extended. As we get closer to the event, expect this
window to get smaller as confidence increases.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 452 PM CST Sun Dec 6 2020
Challenging TAF for this period as a stratus deck builds across the
area from the north this evening. Guidance is in agreement of MVFR
conditions for all terminals, with some high-end IFR ceilings even
possible mainly for CID/DBQ. It becomes complex for tomorrow as some
CAMs show the deck mixing out, while other models like the RAP and
NAMnest keep MVFR conditions through the day. Have more confidence
in the later, as those forecast soundings maintain a strong low-
level inversion which is tough to mix out and often traps moisture
fairly well this time of year. Therefore, will maintain MVFR
ceilings through the period. Winds will be light and variable thanks
to broad surface high pressure to the west.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
SYNOPSIS...12
SHORT TERM...12
LONG TERM...Gibbs
AVIATION...Speck
Area Forecast Discussion
National Weather Service Green Bay WI
803 PM CST Sun Dec 6 2020
New Information added to update section
.UPDATE...
Issued at 803 PM CST Sun Dec 6 2020
A little more active evening than initially anticipated with
freezing drizzle developing across portions of central/north-
central Wisconsin. This is due to a fairly shallow layer of
moisture, along with upsloping/light northwest winds into Vilas
and Oneida County. This is also a result of shortwave energy
passing through the area this evening. RAP soundings indicate some
weak cooling of the thermal profile along with a bit deeper
moisture layer toward midnight into the overnight hours, which
would introduce more ice crystals into the cloud. This should
effectively transition/mix any precipitation to flurries or light
snow showers. In fact, have already seen this happening on webcams
and surface observations in Vilas County. Have extended the
Special Weather Statement farther south into Marathon County as
observations continue to show some southward advancement of very
light freezing drizzle or mist.
&&
.SHORT TERM...Tonight and Monday
Issued at 219 PM CST Sun Dec 6 2020
A fairly vigorous shortwave will drop through northeast Wisconsin
across Lake Michigan tonight, bringing with it overcast skies and
a chance for some light flurries and drizzle. Kept the mention of
patchy drizzle/flurries in through the approximate timing of the
shortwave, as they will likely dissipate without the upper level
forcing. Areas across central and north- central Wisconsin may
also see the development of patchy fog in the evening through late
tonight. With the low clouds in place, temperatures tonight are
not expected to drop as much as the past couple nights, with lows
in the lower to middle 20s.
Monday will continue the trend of cloud cover dependent
temperature forecasts. At this time, expect mostly cloudy skies
to remain in place over the area, which will keep highs a touch
cooler than previously forecast. Highs will likely still range
from the lower to middle 30s.
.LONG TERM...Monday Night Through Sunday
Issued at 219 PM CST Sun Dec 6 2020
Quiet and mild weather is anticipated through Thursday night,
followed by a potentially significant low pressure system next
weekend.
Dry conditions with a return to much above normal temperatures is
expected for the middle of the week. By Wednesday, highs should
be in the 40s to around 50 range, which is around 15 degrees above
normal. A weak cold front will move through on Wednesday, but is
not expected to bring much cooling into Thursday.
Although details are significantly different, medium-range models
show a potentially strong low pressure system moving through the
western Great Lakes region over the weekend. WAA/isentropic lift
should generate some precipitation on Friday, followed by cyclogenesis
as a deep upper trough/upper low moves into the region over the
weekend. The ECMWF has an open upper trough that is more progressive,
and tracks a deepening surface low through southeast WI and Lake
Michigan late Friday night into Saturday. The GFS initially tracks
a strong low to near the MN/IA border Friday and Friday night,
then shifts the vertically stacked system east through WI Saturday
into Saturday night. The Canadian is slower and farther west.
Regardless, it appears a significant system will impact the region
during days 5-7. The timing and track are very uncertain, and
will ultimately determine how much rain/snow occurs, and whether
winds will be a big concern. Will start to highlight the potential
for possible snow accumulations in the Hazardous Weather Outlook,
but refrain from making any significant changes to the blended
guidance pops at this time. If similar trends continue tomorrow,
will ramp up the pops and messaging accordingly.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 521 PM CST Sun Dec 6 2020
MVFR and IFR conditions are expected to push into each TAF site
this evening and then linger through at least Monday morning. The
lowest ceilings and perhaps some fog will generally be confined to
the central TAF sites, RHI/CWA/AUW. Some light flurries/snow
showers are also possible, especially at RHI. Otherwise, slowly
improving conditions can be expected toward Monday afternoon.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE.........Cooley
SHORT TERM.....Uhlmann
LONG TERM......Kieckbusch
AVIATION.......Cooley
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1043 PM EST Sun Dec 6 2020
.UPDATE...
Issued at 1041 PM EST SUN DEC 6 2020
Rain showers have spread into eastern KY near the Mtn Parkway
corridor from Central KY. Measureable rain has fallen in Central
KY per KY Mesonet stations and KLEX and KFFT ASOS stations
upstream. With clouds in place, temperatures generally remain
mild with temperatures above freezing at this point even in the
high terrain. However, as an upper level disturbance drops across
the region overnight, showers are expected to increase in coverage
over the southeastern portions of the area and as cold air moves
into the area and wetbulbing occurs, this should change to snow on
the ridgetops first not long after midnight. Some light
accumulationsare still anticipated with the SPS wording of a
dusting to a quarter of an inch for lower elevations and upwards
of an inch on the higher ridges in the southeast still on target.
Minor adjustments have been made to bring in chance and slight
chance pops a bit earlier and account for recent observations.
UPDATE Issued at 650 PM EST SUN DEC 6 2020
Other than minor adjustments based on hourly temperature trends
no changes were needed at this time. Recent guidance including the
HRRR continues to support the previous forecast.
&&
.SHORT TERM...(This evening through Monday night)
Issued at 521 PM EST SUN DEC 6 2020
The current upper level pattern features ridging stretched from
the Eastern Pacific through Southern California, before stretched
northward across the Rockies and into south central Canada.
Troughing remains positioned from the Great Lakes/New England down
through the Mississippi Valley, with embedded vorticity centers
noted across the Upper Great Lakes, Ohio Valley, and Lower
Mississippi Valley. At the surface, high pressure generally
controls for most west of the Mississippi River. Weaker high
pressure is seen across portions of the Great Lakes/Ohio Valley,
with broad low pressure stretched from the Central Appalachians
down through the Tennessee Valley. Despite the foggy start to the
day, and clouds on the increase across Eastern Kentucky into this
afternoon, temperatures managed to make into the mid to upper 40s
across the northern half of the area, with upper 40s to lower 50s
having occurred in the south.
A more decisive cool down will take place across the Ohio and
Tennessee valleys through the short term. This will be accompanied
by some light snow that will move in late tonight and through the
day on Monday, before gradually tapering to flurries Monday night.
The models are in good agreement through the short term, with the
trough becoming more amplified across the Eastern CONUS. This
occurs in response to the Great Lakes upper level vorticity lobe
dropping south, while the Ohio Valley vort max shifts east with
time. By Monday night, a deeper upper level low will be established
across the Delmarva region, before shifting towards the Western
Atlantic by early Tuesday morning. At the surface, low pressure
will deepen as it heads towards the Carolinas tonight, before
bombing out as it moves out over the Western Atlantic Monday into
Monday night.
For Eastern Kentucky, clouds will increase and lower tonight, as
moisture deepens with the approach of the short wave trough axis
from the eastward progressing upper level low across the Ohio
Valley. The models have trended up on the moisture associated with
this feature, with a mix of sprinkles/flurries initially later
this evening across the area, before column cooling allows for a
changeover to some snow showers overnight tonight and into early
Monday morning. The highest PoPs will be more focused across the
southeastern half of our area. Given the warm ground temperatures
in place, snow impacts will be more limited to elevations above
1500 feet, and especially along the typically favored highest
elevations along Pine and Black Mountains, where temperatures will
cool off much quicker, given the colder start. The snow showers
will gradually become more confined to far southeastern Kentucky
during the day on Monday, as deeper moisture exits. Snow amounts
will range from a dusting to a quarter of a an inch for elevations
near and below 1500 feet, mainly on grassy and elevated surfaces.
For elevations above 1500 feet, snow amounts of up to an inch are
expected. As such, have hoisted a Special Weather Statement for
the southeastern half of our area. Temperatures will trend below
normal through the period. Lows tonight will range from the mid to
upper 20s north, and the upper 20s to lower 30s south. Mostly
cloudy skies, cold air advection, and ongoing flurries/light snow
showers will keep temperatures from moving much on Monday, with
highs generally in the low to mid 30s. Skies may be a bit more
stubborn to clear Monday night, given the upslope flow in place at
the low levels. Lows will range from the low to mid 20s.
.LONG TERM...(Tuesday through Sunday)
Issued at 505 PM EST SUN DEC 6 2020
The long-term starts off chilly on Tuesday, but a pleasant
warming trend will send our temperatures to near the 60 degree
mark for Thursday and Friday. Unsettled weather and more
seasonable temps follow by the weekend.
Upper level troughing will initially be in place over the eastern
CONUS Tuesday morning with upper level ridging over most of the
west. An ~556 dam low will also be found west of Baja California.
Closer to eastern Kentucky, some weak northwest upslope flow and
an upper level vort max will likely keep low-level clouds over
the area through at least the first half of the day Tuesday. By
late in day, southwest flow develops along the northern fringes
of a surface high passing over the Deep South/Gulf of Mexico.
This should cause the cloud deck to erode and gradually move out
of the area. Given the widespread cloud cover through much of the
day, highs are only expected to reach the upper 30s to lower 40s
for most locales. Clear skies and light winds Tuesday night should
allow for a ridge-valley temperature split with lower 20s in the
valleys and upper 20s over the ridgetops.
An upper level trough and surface cold front drops into Great
Lakes on Wednesday. The trough will be deflected back to the
north on Thursday as a sharpening trough digs into the western
CONUS, captures the cutoff low near California, and pumps up a
compensating ridge over the Ohio Valley. Clouds will increase over
northern Kentucky on Wednesday ahead of the front but will later
retreat as heights rise and surface high pressure becomes well
established over the area by Thursday. Temperatures will warm into
the lower 50s for most areas Wednesday afternoon and then near
the 60 degree mark under mostly sunny skies on Thursday. The
nighttime ridge-valley temperature split will redevelop each
night, ranging from the upper 20 to mid 30s Wednesday night and
into the lower 30s to near 40 Thursday night.
Meanwhile, a lee cyclone will develop over along the eastern
Rockies Thursday and then lift toward the Great Lakes Friday into
Sunday, sweeping a cold front through the Commonwealth in the
process. The front and its associated precip are expected to
cross eastern Kentucky sometime between Friday night and Saturday
night, but plenty of uncertainty remains as the models struggle
with the storm system`s evolution. Clouds will increase and
thicken ahead of the front on Friday, but mild southerly flow,
early day sunshine, and continued dry weather should still allow
temps to near 60 degrees. The front will bring a good chance for
rain during the early part of the weekend. Behind the boundary,
temperatures will only reach the 40s at best Sunday while some
wraparound moisture and westerly flow could lead to some upslope
precipitation.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 710 PM EST SUN DEC 6 2020
Mid level clouds and stratocu are spreading southeast across the
region with VFR reported at present across East KY though some
MVFR is reported in portions of central KY. Overall, clouds
are still expected to generally thicken and lower from northwest
to southeast between 0Z and 6Z, as an upper level disturbance
currently over IN moves through the area followed closely by
another disturbance. This system to LOZ will bring some light
snow to the area, with most locations along and southeast of a
line from KSJS to KJKL to KLOZ to KSME seeing a period of IFR
ceilings and perhaps visibilities for a period between 06 and 15z.
Light snow showers/flurries will continue to linger across
southeastern into the last 12 hours of the period. Most of the IFR
visibility restrictions should generally be more confined to the
higher elevations towards the Virginia border, or south of a KSJS
to KJKL line by the 12Z to 18Z period. Winds will average around
5 kts or less through the period out of the northeast to
northwest.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...JP
SHORT TERM...GEOGERIAN
LONG TERM...GEERTSON
AVIATION...JP
Area Forecast Discussion
National Weather Service Miami FL
640 PM EST Sun Dec 6 2020
.Aviation...
Generally VFR conditions will prevail throughout the early evening
hours. Sub VFR conditions are possible during the overnight hours
as shower and thunderstorm activity increases out ahead of an
approaching cold front. Short fused amendments will likely be
needed as periods of IFR or LIFR are possible. Conditions will
begin to improve on Monday afternoon as a breezy northwest wind
moves in behind the front.
&&
.Update...
The shower and thunderstorms chances will begin to increase from
west to east later this evening and into the overnight hours out
ahead of an approaching cold front. The latest short range hi res
model guidance continues to suggest there will be enough
instability to support a couple of stronger thunderstorms during
the overnight hours. Because of this, the Storm Prediction Center
keeps most of South Florida in a marginal risk for severe
thunderstorms during this time frame. With the chance of heavy
downpours, as well as training thunderstorms over the same areas,
there is a risk for localized flooding during the overnight hours
with the highest chances along the east coast metro areas. The
strongest thunderstorms could also contain gusty winds. Showers
and thunderstorms will continue through Monday morning as the
front moves through the region. Conditions should start to improve
on Monday afternoon as drier air works in behind the front.
&&
.Prev Discussion... /issued 330 PM EST Sun Dec 6 2020/
..Concerns for localized flooding and tornados with strong storms
overnight...
..Chilly days ahead behind an early week cold front...
Discussion...
Short Term (Today through Monday):
The retreat of the surface warm front back into the region has
allowed for a recovery of area dewpoints with most of South Florida
in the 60s and even some lower 70s sneaking back in. Some portions
of Southwest Florida did briefly experience some enhanced mixing
which allowed dewpoints to drop into the 50s late this morning. The
mid-level trough will continue to progress eastward across the Gulf
today and tonight, pushing the associated surface cold front through
the region on Monday. Ahead of the cold front, we continue to have
concern for the development of a surface low or vigorous trough
which could enhance convection. The question of available
instability remains a crucial determinant for the quality and
quantity of convection for tonight. For a more in- depth look at the
mesoscale environment for tonight`s potential strong to severe storm
concern, please see the previous mesoscale and hydrology discussions
included below for your convenience. The Weather Prediction Center
has much of the east coast metro in the marginal risk for excessive
rainfall and the Storm Prediction Center has most of South Florida
in the marginal risk of severe weather tonight.
As the front pushes through the region on Monday, convection will
begin to clear out from west to east. The majority of the moist air
should be out into the Atlantic by Monday afternoon. Drier, colder
air will settle into the region for the late afternoon and evening
with the cloud cover eventually eroding which will allow the first
of several chilly nights on Monday night/Tuesday morning.
Temperatures dropping into the 60s across most of the region except
around the western portions of the Lake Okeechobee region where
upper 50s are possible. 10 to 15 mph winds could create wind chills
in the upper 30s and lower 40s in Glades and Hendry with 40s
sneaking as far as the Palm Beaches and the Alligator Alley
corridor.
Long Term (Monday night - Saturday):
Models depict the onset of a robust cold air advection event
starting Monday night in the wake of a FROPA, as high pressure
establishes over the SE CONUS. Expect morning lows to dip into the
40s over interior areas, and even into the upper 30s over areas west
of Lake Okeechobee. Coastal areas will likely remain in the upper
40s to lower 50s through Thursday. The afternoon highs should not
surpass the mid-upper 60s Tuesday and Wednesday, and climbing into
the low 70s by Thursday. With relatively dry air aloft and dominant
subsidence in place, very little to no rain is expected during the
long term with POPs remaining in single digits each day.
Models gradually migrate the aforementioned high towards the
Atlantic seaboard, which will veer the winds across SoFlo to a more
easterly flow by Friday afternoon. No significant moisture rebounds
should take place, keeping PoPs below 10 percent. Main changes will
be warmer temperatures for the end of the period. Temperatures
Friday morning rise to the low-mid 50s for interior areas, and into
the low 60s near the coast. Afternoon highs should climb back into
the upper 70s to low 80s for the upcoming weekend as the easterly
flow modifies the air mass.
Marine...
Strong northwesterly flow behind a vigorous cold front will create
hazardous marine conditions in the Atlantic and Gulf for small craft
early this week. A Small Craft Advisory is already in effect for the
offshore waters off Palm Beach County which will likely need to be
expanded to include all of the Atlantic waters off South Florida
along with the Gulf waters. Conditions should begin to improve by
mid-week in the Gulf though some lingering swell in the Atlantic
could cause improvement of conditions to be slightly slower.
Beach Forecast...
Improving conditions along the area beaches will be short-lived as
the vigorous cold front will bring strong northwesterly wind which
could cause an elevated rip current threat to develop along the Gulf
beaches early to mid week. Swell from an Atlantic low pressure
system could allow an elevated rip current risk to return to some of
the Palm Beaches this week as well, which could persist for several
days.
Prev Discussion... /issued 1020 AM EST Sun Dec 6 2020/
Mesoscale Discussion...
A mid/upper-level low over TX will deamplify into an open wave
today, as it phases with an additional mid-level impulse diving
southward into the middle Mississippi Valley. This evolution of the
mid/upper-level flow pattern will support the development of a long-
wave trough over the eastern states, and broad/enhanced mid-level
cyclonic flow increasing across the South Florida CWA into the
evening/overnight hours.
As the large-scale pattern continues to consolidate today, an upper-
level jet streak will develop over the SE CONUS -- providing upper-
level divergence and weak forcing for ascent across the region. At
the surface, a remnant quasi-stationary frontal boundary is evident
via the latest RAP mesoscale analysis -- extending from the southern
Gulf of Mexico eastward across portions of South Florida. South of
this surface boundary, rich boundary layer moisture is evident
(characterized by dewpoints in the upper 60s to lower 70s). As the
above mentioned enhanced mid/upper-level cyclonic flow increases
over the area, a weak frontal wave/surface low should develop over
the eastern Gulf of Mexico (along the quasi-stationary surface
boundary).
As the frontal wave develops, the aforementioned rich boundary layer
moisture will gradually spread northward across South Florida,
coincident with weak WAA and associated isentropic ascent over the
boundary. In addition, the latest high resolution model guidance
depicts the development of a southwesterly low-level jet across
South Florida, further enhancing mesoscale ascent, moisture
advection, and vertical shear profiles across South Florida.
All of the above mentioned factors will introduce a risk of
excessive rainfall and localized flooding during the overnight hours
-- supported by regenerative convection amid rich moisture/weak
persistent ascent. Thermodynamic profiles will be supportive of
locally heavy rainfall, though training/backbuilding of convective
cells will exacerbate the flooding risk.
There will also be a conditional risk of brief tornadic activity, as
enhanced deep-layer shear (near 45 knots) overspreads the CWA amid
rich surface moisture and elongating/veering hodographs. The primary
factor regarding tornadic potential will be the ability for
convection to become rooted at/near the surface -- where the rich
moisture will be located. We will be closely monitoring the
evolution of the aforementioned surface boundary and rich boundary
layer moisture.
There is currently plenty of uncertainty regarding storm
mode/evolution/intensity -- owing to the weak large-scale forcing
regime in place and anticipated marginal buoyancy over land areas. A
reasonable-worst case scenario involves the development of a few
rotating discrete cells amongst a larger area of rain, in addition
to locally heavy rain and flooding. Present indications are that the
greatest risk will be focused across the southern and eastern
portions of South Florida, including the Gulf Coast metro areas.
Keep up with the latest information from NWS Miami.
Hydrology...
South Florida has experienced little in the way of wetting rainfall
since the departure of Eta in early November. This will help with
the mitigation of flooding at the immediate surface over areas which
have drained or are not lower-lying. However, the ground water
levels across South Florida continue to be elevated due to the wet
year so far and Lake Okeechobee continues to sit well over a foot
above normal for this time of year. Releases from Lake Okeechobee
have allowed the lake level to slowly drop but that has kept area
canals and water conservation areas holding excess levels of water
which could make drainage of excessive rainfall more difficult.
&&
.Preliminary Point Temps/PoPs...
West Palm Beach 64 75 49 65 / 80 70 0 0
Fort Lauderdale 67 78 52 67 / 80 70 0 0
Miami 69 78 53 67 / 80 70 0 0
Naples 64 74 52 65 / 90 60 0 0
&&
.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory from 7 PM Monday to 10 AM EST Tuesday for
AMZ670.
GM...None.
&&
Update...55/CWC
Aviation...55/CWC