Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/14/21
Area Forecast Discussion
National Weather Service Boston/Norton MA
928 PM EST Sat Feb 13 2021
.SYNOPSIS...
Active weather starting tonight, with weather systems tonight and
every day except Wednesday. Each weather system will bring a mix of
weather types. Light amounts are expected tonight. Then another light
wintry mix is possible on Monday before a more potent storm
could bring significant ice accretion to much of Southern New
England on Tuesday. We dry out briefly on Wednesday before
another significant winter storm arrives late Thursday into
Friday with all precipitation types possible. Below normal
temperatures are expected through the end of the week.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
925 PM Update:
Expanded the Winter Weather Advisory northward to include all of
Rhode Island and the remainder of Bristol and Plymouth Counties.
Current radar shows the northern end of the precip shield from
roughly Willimantic CT to Pawtucket RI eastward into Marshfield
MA. Spotters and mPING reports indicate very light precip,
either as snow, "snizzle", or freezing rain across parts of RI,
with FZRA also being reported at TF Green Airport. Think the
HRRR is presently handling the precipitation shield the best,
which matches roughly where the Advisory was expanded into.
Following this, light precipitation should continue into a good
part of the overnight (about 08z). We do lose cloud ice after
midnight following NBM cloud-ice probs so transition from frozen
precipitating types (S/PL) to freezing drizzle appears on
track. Any icing will not amount to anything more the a light
glaze and on the whole be fairly spotty, but it doesn`t take
much to cause slick roads and sidewalks. Further north into
interior MA and into Greater Boston, precip may end up being
very spotty if any develops at all.
Previous discussion:
BOX radar shows the leading precip shield moving into southern
CT/RI with little making it to the surface thanks to a large
dewpoint depression. But, as we head into the overnight hours
that gab will close. We still anticipate that the majority of
southern New England sees less than an inch of snow. Coastal
areas are at the highest risk for ice accretion - up to a tenth
of an inch.
While it is still relatively quiet we only have to look just to
our neighbors on Long Island - there freezing rain is being
reported along the south central coast. Only changes that were
made were to bump up POPs along the coastal areas of CT/MA/RI.
Overall the messaging remains the same and you can read that in
the prior discussion below.
===============================================================
Low pressure along the Carolina coast moves northeast tonight to
a point well south of Nantucket. A 130-kt upper jet feeds
between the coastal system and the South Coast, providing some
support of lift during the night.
Snow and freezing rain observed over the DelMarVa area will move
into Srn New England tonight. Warm air moves northeast into at least
the coastal areas and possibly to the Mass Pike. This suggests a mix
of precip across the region. If anyone stays all-snow, it would be
Northern MA. Based on Bufkit GFS soundings northern CT/RI mix/change
to sleet but not freezing rain. The NAM soundings are a little
warmer with an hour or two of freezing rain at BDL. For now we will
hold the freezing rain to our South Coast with snow/sleet farther
north. Even this may be limited, as the soundings show dry air at
the ice nucleation level, which may result in freezing drizzle
rather than snow/sleet. Will add freezing drizzle to the list of
forecast p-types. Expect QPF of up to 0.10 inches, maybe 0.15 on
Cape/Islands. This suggests snow/sleet of a coating to an inch and
South Coast FZRA of a few hundredths.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Sunday...
The coastal system passes south of the 40N/70W benchmark and moves
off well south of Nova Scotia. Expect drying in upper parts of the
column, but lingering moisture in the low parts. This work against
any snow/sleet, but may allow drizzle/freezing drizzle during late
morning and early afternoon. Low level temps aloft suggest max sfc
temps in the 30s, therefore the potential for both forms of drizzle.
Sunday night...
High pressure in the Plains and across Eastern Canada will maintain
a north-to-south surface flow overnight. Plenty of moisture remains
in the column for clouds, but jet dynamics are not favorable and IVT
is still aimed over Georges Bank and farther offshore. Advection
ahead of the next system will start approaching late at night, but
remain offshore during the night. Expect min sfc temps ranging from
the upper teens northwest to the lower 30s southeast.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
Highlights...
* Light wintry mix possible on Monday, followed by a more potent
storm on Tuesday with significant ice accretion possible.
* Dry and cold on Wednesday and possibly first part of Thursday with
1040 mb high over New England.
* Another potent winter storm late Thursday into Friday with
all precipitation types on the table.
* Turning colder but dry on Saturday.
Overall pattern...
Overall, a very active weather pattern in the long term. The CPC 6-
10 day outlook gives a 30-40 percent chance of below normal
temperatures and 40-50 percent chance of above normal precipitation.
A deeply negative Arctic Oscillation (AO) is forecast to increase
sharply over the upcoming week, turning neutral or even slightly
positive. When a rapid change in the AO occurs, we typically get
into a very active weather pattern here in Southern New England.
Unfortunately, due to the thermal profiles, we will be dealing with
a variety of wintry precipitation, instead of straight rain and/or
snow. On the synoptic scale, we are in a persistent H5 ridge that
promotes SW flow aloft but at the low levels, we have E/NE flow from
an inverted trough axis which will result in considerable low level
cold air drainage and moisture. So while we get into +5 and even
+10C at 850 and 925mb, it remains sub-freezing near the surface. And
per the CIPS analog threat guidance, this is a classic setup for
freezing rain. If the sub-freezing layer near the surface is deeper,
then we may get more sleet than ice.
The details...
The two main windows for significant ice accretion appears to be
late Monday into Tuesday and late Thursday into Friday. It is also
possible that we have to deal with a light wintry mix on Monday and
all it takes is a glaze of ice to cause travel issues. But this will
probably be the appetizer ahead of the main course, that is, the
potential ice storm. It is quite concerning that both the NAEFS and
EC ENS Situational Awareness Table show 99.5 percentile for QPF,
PWAT and Integrated Water Vapor Transport (IVT) for our area on
Tuesday and Friday. In other words, we will have a lot of moisture
to deal. The timings are not set in stone at this time frame, but
the threat for significant icing and consequently, hazardous travel
conditions exist for this upcoming work week. People with travel
plans will want to monitor the forecast closely.
As for possible ice accretion amounts, that too is extremely
challenging given observed amounts and impacts could vary greatly on
the microscale level. The criteria for an Ice Storm Warning is half
an inch of ice accretion and the initial thinking is that we could
be pushing widespread quarter inch ice accretion with up to half
inch possible. Again, if the low level cold air is deeper, it could
be more sleet than ice especially for the interior. On the flip
side, if the surface temperature warms a bit quicker to above
freezing, then it could be a brief period of sleet and/or freezing
rain before a transition to plain rain. This would be possible for
areas along and near the South Coast.
Headlines wise, we are not issuing any headlines right now for the
long term due to the active weather in the near and short term.
However, an Winter Storm Watch is certainly a possibility for
these two events, which requires a 50 percent confidence of
hitting criteria, in this case, half an inch of ice accretion.
Of course, there is also the possibility of the warm nose aloft
being not as stout and if that happens, we could be looking at a
few inches of front-end thump snow. So we could also be
hoisting Winter Storm Watches for the possibility of 6 inches of
snow. Also of note is the risk for power outages due to a
combination of heavy, wet snow/sleet and/or ice accretion.
The good news is that Wednesday and Saturday look dry with surface
high pressure in control. But overall, this week looks like an utter
wintry mess with Wednesday and Saturday looking like windows of
opportunity for clean ups. The forecast is extremely challenging and
given the amount of uncertainty with timing and precipitation types,
have opted to keep the discussion not overly specific.
&&
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Overnight...
Ceilings lower from VFR evening to IFR late at night. Vsbys
lower as a mix of precipitation arrives...generally 1 to 3 miles
in NE CT, RI, SE MA and 4 to 6 miles farther north and west.
Precip types favor snow/sleet from northern CT through Metro
Boston, and snow changing to freezing rain along the south
coast/islands. Precip starts around 9PM-Midnight and continues
overnight. Amounts should be light.
Sunday...
Precipitation tapers off during the morning. Lingering drizzle or
freezing drizzle through midday. Ceilings at IFR in the
morning...improving to MVFR in the east and VFR in the west.
Sunday night...
Clouds linger, with VFR conditions most places and MVFR cigs over RI
and SE Mass.
KBOS TAF...High confidence in TAF.
KBDL TAF...High confidence in TAF.
Outlook /Monday through Thursday/...
Washingtons Birthday: Mainly IFR, with areas MVFR possible.
Chance RA, chance SN, chance PL, chance FZRA.
Monday Night: Mainly IFR, with areas MVFR possible. Breezy.
Chance RA, chance FZRA, chance SN, chance PL.
Tuesday: MVFR/IFR conditions possible. Breezy. PL, RA, FZRA,
chance SN.
Tuesday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance FZRA, slight chance SN.
Wednesday: VFR. Breezy.
Wednesday Night: VFR.
Thursday: Mainly IFR, with local VFR possible. Breezy. SN
likely, chance FZRA.
&&
.MARINE...
Short Term /Tonight through Sunday night/
East winds may become borderline for Small Craft Advisory on the
outer waters south of RI, while remaining waters will be 20 kt or
less. The steady east wind will build seas on the southern outer
waters, with heights of 5-6 feet. Will issue a SCA for our ANZ254 to
ANZ256 waters for Tonight through Sunday night. Periods of light
wintry precip overspread tonight, then move off during Sunday
morning. This could reduce visibilities down to 1-3 miles at times
tonight.
Outlook /Monday through Thursday/...
Washingtons Birthday: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain, slight chance of freezing
rain.
Monday Night: Winds less than 25 kt. Seas up to 5 ft. Rain,
freezing rain likely.
Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Rain, sleet, freezing
rain. Local visibility 1 to 3 nm.
Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 8 ft. Slight chance of
freezing rain, slight chance of snow. Local visibility 1 to
3 nm.
Wednesday: Winds less than 25 kt. Areas of rough seas.
Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.
Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of snow, rain likely, chance of freezing rain.
Visibility 1 to 3 nm.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Winter Weather Advisory until noon EST Sunday for MAZ017>024.
RI...Winter Weather Advisory until noon EST Sunday for RIZ001>008.
MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ254>256.
&&
$$
SYNOPSIS...WTB/Chai
NEAR TERM...WTB/Chai/Gaucher
SHORT TERM...WTB
LONG TERM...Chai
AVIATION...WTB/Chai/Gaucher
MARINE...WTB/Chai
Area Forecast Discussion
National Weather Service Caribou ME
931 PM EST Sat Feb 13 2021
.SYNOPSIS...
High pressure will move northeast of the region by Sunday,
as weak low pressure tracks well south of the region. Another
High is expected to cross the region Sunday night into early
Monday followed by an upper level disturbance crossing the area
later Monday into Monday night. Low pressure will approach from
the southwest Tuesday and move south of the region Tuesday
night. High pressure builds in on Wednesday and Wednesday night
before another low pressure approaches from the southwest late
Thursday.
&&
.NEAR TERM /THROUGH SUNDAY/...
930 PM Update: The arrival of thicker hi cld cvr have result in
temps not falling as fast into the late eve ovr Nrn areas as
prev thought, so fcst lows were ovr this area were raised a few
deg F, particularly ovr the colder vly areas. Otherwise, fcst
hrly temps/dwpts were updated to erly ovrngt lows posted arnd 1
to 2 am from trends seen from latest avbl sfc obs.
Prev Disc: High pres will ridge into the region tonight
allowing for light winds and mostly clear skies intially, before
clouds arrive later at night as low pres apchs from the sw. The
ridge axis from that high will lift out to the ne overnight.
High clouds were pressing ene per the latest satl imagery and
will continue to advance and gradually lower and thicken up
overnight. Temps will be allowed to drop off rather quickly
after sunset. The high clouds are still rather thin to allow for
some radiational cooling across the central and downeast areas
w/overnight temps hitting the single numbers before leveling off
after midnight. Across nrn and nwrn areas, clear skies will
hang on longer to allow for good radiational cooling and some
very cold temps. Inversion in place will allow for temps to hit
well below zero before clouds arrive by early Sunday morning,
especially in the low lying areas.
Low pres is forecast to develop off the mid Atlc coast tonight
and lift ne on Sunday passing well s of the region. As it does
so, an inverted trof extending out from the low is shown by the
model guidance to setup over western New England and push to the
east. Two areas of precip are forecast to set up w/one area
associated w/the low passing well s of the region and the other
associated w/the inverted trof. The main focus will shift toward
the inverted trof overnight into Sunday as some good llvl
convergence and some mid leveling forcing will generate a period
of light snow across the wrn and nnw areas by Sunday morning.
The latest runs of the HRRR/NAM, RAP and even the GFS support
this setup. Most of the forcing and weak advection associated
w/the ocean low remains well offshore. So, just a grazing of
some light snow by early Sunday morning. Confidence has
increased to raise pops to 60% across the w and n areas for
early Sunday as the best forcing pushes across those area. Given
the DGZ below 15k ft and decent moisture up through 700 mbs as
shown by the soundings, snow ratio could be 20:1 or higher
across the nrn 1/2 of the region. Despite low QPF(
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
836 PM CST Sat Feb 13 2021
.UPDATE...
Doppler radar is showing a series of light freezing bands moving
across the San Antonio areas and to the north and east. We have
gotten a few reports of sleet as expected with temperatures in the
lower 20s. This trend is expected to persist for the next several
hours. Then a break in the precipitation is forecast early Sunday
morning before an upper level pulse of energy pushes across central
Texas and aid the chances for more freezing rain and sleet over the
Hill County including the north part of Travis County. Went ahead and
adjusted ice accumulation amounts up to one tenth of an inch across
the Williamson and northern Travis Counties. It is a dangerous
situation and going to get worst on Sunday.
&&
.PREV DISCUSSION... /ISSUED 608 PM CST Sat Feb 13 2021/
AVIATION...
/00Z TAFS/
Doppler radar is showing light echoes across the San Antonio
airports and soon reaching the KAUS terminal. With temperatures
below freezing, expect freezing rain over the area if precipitation
does fall to the surface. An upper level disturbance moving across
the Rio Grande will provide the lift for precipitation to get going
this evening into Sunday morning. MVFR cigs are expected to prevail
overnight into Sunday morning. Can`t rule out a few hours of IFR
around 10Z to 15Z . Another upper level disturbance is forecast to
push across the area on Sunday afternoon and evening and continuing
through Monday. During this time frame, we are expecting freezing
rain and sleet first and then changing over to snow and MVFR and IFR
cigs. Strong winds from the north are expected with gusts up to 30
knots throughout the night Sunday into Monday.
PREV DISCUSSION... /ISSUED 233 PM CST Sat Feb 13 2021/
SHORT TERM (Tonight through Sunday Night)...
The area of drizzle from earlier today has mostly come to an end
across the area. The freezing line is currently located from a line
from just north of Del Rio to Uvalde to Kenedy. Not expecting much
more in the way of warming is anticipated across the area with the
freezing line staying fairly constant. Some of the hi-res model
guidance is progging another round of light drizzle or very light
rain to develop around 6-7 PM this evening and impact portions of
the I35 corridor through midnight or so before mostly ending with
some patchy activity likely continuing through the night. The ice
accumulation from the evening will be light, but as we have seen this
morning, it will take just trace amounts to cause additional
problems on the roadways this evening. Residents are urged to
continue to remain off the roadways if at all possible.
Temperatures will drop several degrees tonight with cold air
advection continuing and the loss of the indirect heat from the sun.
For tomorrow, most locations along and north of I10 will continue to
remain below freezing with the remainder of the CWA perhaps warming
into the middle 30s. A large trough axis will move into the Southern
Plains by the early evening hours tomorrow and will send a very
strong polar front into the region. Ahead of the front, models
remain in good agreement that light rain/freezing rain/sleet and
possible snow will develop in the mid to late afternoon across much
of the area. This will be just the initial setup for the main event
with the main forcing arriving overnight with a possible intense snow
band moving through the area. The initial round of icing will stick
immediately to all surfaces and the snow will likely be on top of
that creating very hazardous traveling conditions tomorrow night.
The deterministic runs of the ECMWF/GFS/Canadian remain consistent
with 3-5 inches of snow over a large area of the CWA with some decent
ice accumulations in the southeastern CWA. These totals may be
overdone slightly but very cold air temperatures could lead to better
rain to snow ratios. The NAM and some of the other high-res models
remain dry outliers with much lower snow totals. However, the
extended range of the HRRR shows similar totals to the global models.
While there is some hesitance because of the NAM, one would think
the setup of a long-wave trough and strong forcing would tend to
support the global models being more accurate. In additional there
is some signal of some frontogentical forcing that may lead to
banding issues for somewhere in our CWA. This is especially true in
the 18z HRRR. Our official forecast will for snow will show 3-4
inches with isolated higher amounts north of a Kerrville to Austin
line and 2-3 inches north of a Rocksprings to Boerne to LaGrange
Line. Less than 2 inches is expected for the remainder of the area.
For ice, greater than a tenth of an inch is possible along and east
of the I35/37 corridor. Have upgraded the watch to a warning for the
remainder of the CWA except for Maverick and Dimmit County where an
advisory is in effect with less accumulations expected there.
In addition to the wintry precip concerns, temperatures behind the
polar front will drop rapidly from already cold values. By Monday
morning temperatures will be in the single digits in the Hill Country
and in the teens for much of the remainder of the area. With strong
north winds, wind chill values will be below 0 for much of the area.
Any motorists that may become stranded, should be prepared for
prolonged exposure in these conditions with hypothermia likely.
Again, stay off the roadways if at all possible!!
LONG TERM (Monday through Saturday)...
Precipitation will end from west to east across the area Monday
morning with a cold day expected. Highs Monday will top out in the
teens and 20s for most of the area. Lows Tuesday night will likely be
the coldest weather this area has seen since 1989! Lows will range
from 3-9 degrees for locations north of Interstate 10 with teens
across the other locations. Wind chills will be as low as -4 to 10
degrees. With the prolonged cold conditions, pipes will become an
issue. Protect them as best as possible as bursts are almost all but
guaranteed.
A brief drying trend is expected Tuesday night, but our next system
arrives Tuesday night. Models are in fairly good agreement that this
will likely be mostly freezing rain with some possible sleet mixing
in across the Hill Country. With 850 temps warming rapidly with the
low-level lift ahead of a trough, surface temperatures will hopefully
warm as well. Global models show all but the northern counties above
freezing by noon and will show freezing rain transitioning to rain
for the southern counties. However, a cold front with some wrap
around moisture could transition the precipitation back to a
snow/sleet mixture Wednesday night. Will try to show all of this in
the grids, but confidence in the mid-week forecast remains low as we
are still 5 days out. Regardless, this historical cold weather
outbreak that will be talked about for years to come looks to give
us another round of frozen precipitation mid-week. The good news is
drier and slightly warmer weather look to return on Friday and
Saturday.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 27 29 13 21 6 / 30 60 90 20 0
Austin Bergstrom Intl Airport 27 30 12 22 5 / 30 60 90 20 0
New Braunfels Muni Airport 28 31 14 24 7 / 30 60 90 10 0
Burnet Muni Airport 23 25 8 18 5 / 30 60 90 10 0
Del Rio Intl Airport 31 37 16 29 17 / 10 30 80 - 0
Georgetown Muni Airport 25 27 9 19 3 / 30 60 90 20 0
Hondo Muni Airport 29 34 14 27 10 / 20 40 80 - 0
San Marcos Muni Airport 27 31 13 22 6 / 30 60 90 20 0
La Grange - Fayette Regional 30 34 15 22 9 / 30 50 90 30 0
San Antonio Intl Airport 29 32 15 24 10 / 30 50 90 10 0
Stinson Muni Airport 29 33 16 26 11 / 30 50 90 10 0
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until noon CST Monday for Atascosa-Bandera-
Bastrop-Bexar-Blanco-Burnet-Caldwell-Comal-De Witt-Edwards-Fayette-
Frio-Gillespie-Gonzales-Guadalupe-Hays-Karnes-Kendall-Kerr-Kinney-
Lavaca-Lee-Llano-Medina-Real-Travis-Uvalde-Val Verde-Williamson-
Wilson-Zavala.
Winter Weather Advisory from 3 PM Sunday to noon CST Monday for
Dimmit-Maverick.
&&
$$
Short-Term/Aviation...17
Long-Term...04
Area Forecast Discussion
National Weather Service Grand Rapids MI
1058 PM EST Sat Feb 13 2021
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 300 PM EST Sat Feb 13 2021
- Lingering showers along lakeshore tonight
- Snow showers and bitter cold for Monday Morning Commute
- Snow with coldest temperatures this winter through mid week
&&
.UPDATE...
Issued at 1058 PM EST Sat Feb 13 2021
Main concerns tonight are lake effect snows towards the Lake
Michigan shoreline and the threat of patchy dense fog across the
area.
As for the lake effect snow, a bit concerned that we may see
higher totals than forecast along the shoreline tonight. HRRR
surface wind fields show that convergence along the shoreline may
hold in place through the night and focus accumulations there.
This has already been going on this evening and it may continue
overnight. We have likely pops in the forecast with accumulations
of an inch or two. We will be keeping an eye on radar imagery
through the night.
Another concern is patchy dense fog that has been ephemeral here
at the GRR airport this evening. An hour or so ago, we dropped to
1/4 of a mile in dense fog. It has since lifted considerably. The
fog is radiational in nature due to some melting that went on
during the mid afternoon hours. That melting added moisture to the
boundary layer and when combined with clearing and a temperature
drop this evening led to almost instant fog in spots. We still
have some 1/4 mile fog being reported across the area. The
expansion of stratocumulus off of the lake and an increase in
winds in the lowest couple thousand feet should lead to the fog
becoming very patchy or even eliminated. We will be watching this
threat tonight as well.
&&
.DISCUSSION...(This evening through next Saturday)
Issued at 300 PM EST Sat Feb 13 2021
-- Lingering showers along lakeshore tonight --
Widespread light snow continues across the upper mid west with
locally heavy bands embedded. The heaviest line is moving through
the Ludington region and will continue to slowly drift eastward
as the afternoon progresses. So far one to two inches have fallen
out of these showers with another one to 3, mainly along the
lakeshore, expected.
These showers are stemming from moisture on the southern end of a
large quasi stationary upper level low north of Minnesota and is
slowly moving eastward. A short wave trough emanating from this
low will cycle northward and, along with an upper level jet, will
take the corresponding moisture with it. This will allow snow
showers to end in most places as high pressure builds into the
wake. Snow showers along the lakeshore will continue. Copious
amounts of mid level clouds will signal that cloudiness will
continue through Sunday.
-- Snow showers and bitter cold for Monday Morning Commute --
The break in snow will be short lived as another wave of snow will
move through Sunday night into Monday morning. The aforementioned
upper level low will tilt positively and be caught up by an
elongated long wave trough.
This interaction will along for a moisture flow and boundary to
form through the midwest and bring snow showers to Indiana, Ohio
and the southern end of Michigan. This will also be bringing
bitterly cold air. This cold air correlates with -15 at 850mb
which will bring lows of -2 to 6 F Monday morning. Widespread
subzero wind chills are expected Monday morning with temps
continue to be low through late in the work week.
-- Snow with coldest temperatures this winter through mid week --
Another round of snow showers will continue Tuesday as the cold
and snow weather continues. The heaviest snow is expected in the
southeastern counties. Have held off on an advisory for now but if
the signal moves northward or an intensification of the bands
then one may be needed. However, given latest guidance the
heaviest snow will be to the southeast.
The cold air will continue through mid week with wind chills near
criteria though currently they are just above. So that will need
to be monitored. The cold air mass will lift to the northeast
through the latter half of the week with more moderate
temperatures possible late in the week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 724 PM EST Sat Feb 13 2021
Tried to write the 00Z TAFs a bit more optimistic than what model
guidance would suggest. Model guidance would indicate we should
continue to have widespread MVFR and even IFR conditions the next
24 hours. Indications are that may not be the case as the system
related precipitation is peeling off to the east and dissipating
rapidly as of 00z. A look at aviation conditions as compared to an
hour or two ago shows a fairly big improvement from widespread
IFR up to MVFR. My feeling is that this trend will continue and
we will go VFR from KGRR and KAZO to the east overnight.
The pattern overnight and into Sunday is one of northwest flow
lake induced clouds, which tries to turn more northerly towards
Sunday evening. Also of note is the flow is light, generally less
than 20 knots below 10,000ft. Lake effect clouds/snow in a light
wind regime such as this normally features clouds trending towards
the shoreline of Lake Michigan with clearing inland. So, we have
gone optimistic inland (VFR) as we head through the evening. The
06z set of TAFs may be even more optimistic as lake effect towards
Lake Michigan looks light.
Winds will generally be light northwest through the period at
5-15 knots.
&&
.MARINE...
Issued at 1115 AM EST Sat Feb 13 2021
Small craft advisory criteria will be met tonight through
tomorrow. Winds will shift to the northwest and increase. With ice
covering the nearshore south of Grand Haven the value in issuing
a headline is very low. Waves will be 4 to 6 feet north of Grand
Haven and have issued an advisory. Freezing spray should increase
tonight and Sunday, further coating the piers and lighthouses
that are near open water.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 PM EST Sunday for LMZ847>849.
&&
$$
UPDATE...Duke
SYNOPSIS...Ceru
DISCUSSION...Ceru
AVIATION...Duke
MARINE...Ceru
Area Forecast Discussion
National Weather Service Gray ME
1032 PM EST Sat Feb 13 2021
.SYNOPSIS...
A weak weather system brings the chance for some light snow
or even patchy freezing drizzle Sunday morning. That will begin
what should be an active weather week...with another round of
light snow possible late Monday before a more substantial system
brings snow and possibly some mixed precipitation to the region
Tuesday. Another storm system is expected by the end of the
week.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
1030 PM Update...We continue to be dry this evening as we`re
in between two areas of relatively weak forcing for ascent.
Much of the night will be cloudy and dry with light winds.
However, it`s possible that we`ll see some very light snow or
flurries Sunday morning, with perhaps a few pockets of freezing
drizzle. Not big changes to the forecast at this hour except for
adjust temperatures a little bit.
630 PM Update...Little change to the going forecast other than
to lower PoPs a bit for tonight - more in line with the latest
HRRR guidance. Otherwise, just a few minor adjustments to
temperatures.
Previously...
Impacts: Very light snow possible early Sunday morning, especially
for NH and far western portions of western ME. Could make for slick
travel.
It`s quiet out there at this hour as mid and high clouds continue to
stream overhead. Conditions should remain quiet through the late
evening as well with clouds thickening and lowering as we head into
tonight.
Low pressure will slide off the mid-Atlantic coast tonight and a
shortwave will move across New England. These two features will
provide just enough forcing to generate a coating of snow before
sunrise, primarily in NH and portions of far western ME. Even a few
tenths will be enough to make roads slick for travelers on Sunday
morning, especially with temperatures in the single digits and
teens and road temperatures expected to be near or below
freezing.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Impacts: Very light snow continues into Sunday morning with slick
roads expected. Will continue assessing the potential for freezing
drizzle for late Sunday morning as the precipitation comes to an
end.
With the low pressure continuing to move east and the shortwave
pulling off to the north, forcing for ascent will quickly wane late
Sunday morning, but probably not before most of the region picks up
another tenth or two of snowfall.
Do want to mention the possibility of light freezing drizzle Sunday
morning as well. A look at forecast soundings around the area shows
a nearly saturated layer from the surface to between 700 and 800 mb,
some weak upward vertical motion and a deep dry layer collocated
with the DGZ above the saturated layer and inversion. Not confident
enough to put it in the grids with this package as temperatures in
the lower levels may still be just cold enough for snow to develop
instead. Even light freezing drizzle could be impactful, especially
on already lightly snow-covered roads, so will mention in the HWO
now and let subsequent shifts continue to assess.
Highs will range from the mid 20s north to the lower 30s south; some
locations in southern NH may make a push to get above freezing. Any
precipitation should be coming to an end by early afternoon, but
clouds will persist over southern and western areas into the evening.
Quiet conditions return Sunday night with partly to mostly cloudy
skies and lows ranging from the positive single digits north to the
upper teens south.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
An active week is in store as we deal with two winter systems,
one on Tuesday and another at the end of the week. This is
mainly the result of strong ridging over the Atlantic
colliding with remnant polar vortex cross Ontario and srn
Quebec. This will great strong temp/gradient across New
England, so any waves that pass thru at 500 MB will be able to
produce strong thermal advection. An temps fluctuate a bit
around these systems, although not too badly as low levels will
mostly stay cooler, thanks to NW-NE flow.
Monday could start off with some sun, but clouds will thicken as
we see some weak mid-level FG and tightening of the temp
gradient. Could see some SHSN or maybe some very light snow
associated with this FG, but mostly looks light, and may have a
tough time since it will likely falling from somewhere between
5-10k ft, and initially airmass near the sfc will be dry. Highs
Monday will be in the mid 20s to low 30s. May see a little
break before we start to see precip moving in from the coastal
low, likely after midnight and closer to daybreak in central ME.
P-type is one of the bigger questions, although it will all
start as snow. Models have not instilled a lot of confidence
regarding progression poleward of the warmer mid level, and the
12Z Euro has come in cooler, which would mean more snow. Still
I think there`s a possibility of seeing some PL or FZRA mixing
in on Tuesday across SE NH and the ME coast, but not confident
on how much or how that will affect snow amts. Overall QPF still
coming around 0.75." I don`t think anywhere will rise above
freezing but some coastal areas and the MHT-ASH corridor could
see temps of 30-32, with 20s elsewhere. Precip should wind down
late afternoon to early evening, with colder air moving in and
upslope SHSN Tue night.
The 500 MB trough tamps down the ridging on Wed, and some cooler
air will work in with high mainly in the 20s on Wed. Expect
mountain clouds and mainly sunny skies S of the mtns.
The next system approaches Thu and should impact the area Thu
night into Friday. This wave is a little weaker, with not as
cold air to the N than the Tuesday system, and should see the
ridge, and the surge of warm air aloft to have a snow to mix to
rain event in the srn areas. Of course this is day 6, so
confidence is low attm.
&&
.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
Short Term...VFR conditions expected at all terminals through this
evening. Ceilings will begin to lower after midnight but should
stay above MVFR levels until around 12Z. Chances for snow begin
to ramp up between 06Z and 12Z, but at this time, the only
places where confidence was high enough for me to put snow in
the TAF was at HIE and LEB. Do think that MHT/CON/PSM/PWM have
decent chances as well, but could also be FZDZ...and even if it
does snow, it will likely be brief and very light or could just
be flurries. Will let future TAF packages assess the possibility
at those sites with additional data this evening.
Long Term...Monday could start as mainly VFR, but should see
MVFR cigs become predominant during the afternoon, with possible
IFR vis in spotty -SN. Tuesday will likely be stuck in IFR or
lower all day in mostly SN, although there is some potential
for PL or FZRA at KMHT/KPSM/KPWM/KCON. Tue evening will start
to see improvement with VFR returning by late Tue night. VFR is
expected Wed-Thu.
&&
.MARINE...
Short Term...Seas will remain rather calm through the short
term. Winds will become more northeasterly tonight as low
pressure passes to the southeast of the waters, gusting to 15-20
kt at times. Winds then turn more northerly late Sunday into
Sunday night but remain well below SCA criteria.
Long Term...SCA will likely be needed late Mon night into Wed,
and initially E flow develops ahead of coastal storm, then
shifts to NW behind the storm Tue night and Wed.
&&
.CLIMATE...
We are in the midst of what is likely to be the longest
continuous freeze of the season. While the most intense of the
cold air is likely to remain well to our west, the sustained
period of subfreezing temperatures is likely to be the longest
observed in this region since the Great New Year`s Cold Snap of
2017-2018.
The first subfreezing day in our current stretch was on February
7 and is ongoing. Current forecasts project subfreezing
temperatures will last deep into next week, likely approaching
or exceeding 10 straight days at or below freezing.
At Portland, a stretch of 7+ days at or below 32 has occurred
118 times in 80 years of records. This averages out to about 3
times every two years. The last stretch of 7+ days at 32 or
colder occurred from December 15 thru 21, 2020. This stretch of
subfreezing temperatures is likely to be the longest since the
stretch of 15 days observed from December 25, 2017 thru January
8, 2018. The longest stretch of subfreezing days was 23 days and
occurred twice, from January 25 thru February 16, 2007 and from
December 8 thru December 30, 1989. Temperature records at
Portland began in 1940.
At Concord, a stretch of 7+ days at or below 32 has occurred 228
times in 133 years of records. This averages out to about 5
times every 3 years. The last stretch of 7+ days at 32 or colder
occurred from January 28 thru February 3, 2019. This stretch of
subfreezing temperatures is likely to be the longest since the
stretch of 15 days observed from December 25, 2017 thru January
8, 2018. The longest stretch of subfreezing days was 37 days
from December 22, 1976 thru January 27, 1977. Temperature
records at Concord began in 1868.
At Augusta, a stretch of 7+ days at or below 32 has occurred 173
times in 73 years of records. This averages out to more than
twice per year. The last stretch of 7+ days at 32 or colder
occurred from December 15 thru 21, 2020. This stretch of
subfreezing temperatures is expected to be the longest since the
stretch of 15 days observed from December 25, 2017 thru January
8, 2018. The longest stretch of subfreezing days was 33 days and
occurred twice, from January 20 thru February 21, 2015 and from
January 4 thru February 5, 1955. Temperature records at Augusta
began in 1948.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.
&&
$$
NEAR TERM...Ekster/Watson
SHORT TERM...Watson
LONG TERM...Cempa
Area Forecast Discussion
National Weather Service Jacksonville FL
903 PM EST Sat Feb 13 2021
.UPDATE...
A quasi-stationary frontal boundary is draped across northeast
Florida just south of I-10 and extends northeastward into the
Atlantic waters while a weak low is southeast of Apalachicola, FL.
The moist airmass over the area has mainly stabilized limiting
thunderstorm development over our area. Waves of showers will
continue to move northeastward up from the Gulf of Mexico and
spread across southeast Georgia and northeast Florida. Have
removed thunderstorm chances from our area except for our north-
central FL zones which remain south of the boundary. Current
thunderstorms off the coast of Tampa could move into our north-
central Florida zones by midnight. A large temperature gradient
continues with lows tonight ranging from the low 40s in southeast
Georgia to the mid 60s in north-central Florida.
&&
.PREV DISCUSSION [642 PM EST]...
.NEAR TERM [Through Tonight]...
18Z regional surface analysis places a weak low just SW of
Apalachicola, FL, with a quasi-stationary frontal boundary
extending ENEward from it toward Fernandina Beach, FL and then
curving NEward off into the Atlantic waters. Aloft, mostly SW
flow is in place over the southeastern CONUS with weak upper level
impulses periodically ejecting northeastward over us, bringing
upper level support for occasionally stronger storms.
Model guidance continues to be in general agreement that the
front will lift slowly northward as the Gulf low moves eastward
through tonight. This will keep most of NE FL in the warm sector,
with a gradual increase in instability this afternoon as clouds
from this morning continue to scatter out while SE GA stays in
the cool, more stable airmass. Decent bulk shear near 40 kt is
still in place. Clouds over N-central FL have just begun to
scatter out over the last couple hours, leading to increasing
instability in that region. HRRR is showing our next band moving
into that area from the SW in the next few hours, which is still
seeming plausible and could still bring a few heavier showers and
pose a threat for isolated damaging wind gusts. Instability will
wane again as we head into the overnight period, but we still
expect to see a few rounds of showers along/near the frontal
boundary overnight.
A large temperature gradient is in place on either side of that
stalled frontal boundary, with temperatures in the mid-upper 40s
in inland SE GA and in the upper 70s in N-central FL. Overnight,
temperatures won`t cool much under dense cloud cover, staying in
the mid 40s in SE GA and dipping into the mid 60s in N-central FL.
.SHORT TERM [Sunday Through Monday Night]...
At the low levels on Sunday, we`ll remain sandwiched between an
inverted coastal trough off SE GA`s Atlantic coastline and an area
of surface low pressure in the NErn Gulf Waters south of
Apalachicola, FL. A quasi-stationary frontal boundary will be
stretching between these two features, draped across NE FL roughly
along the I-10 corridor. At the upper levels, waves of energy
continue to parade northeastward over the front, enhancing upper
level divergence and leading to elevated instability along and S
of the boundary. Model guidance shows the SW-NE oriented frontal
boundary will pivot Sunday and become more SSW-NNE oriented,then
lift northeastward Sunday night as a stronger +PV anomaly pulls
that Gulf low away, then swing eastward late Monday night. The
boundary is expected to remain in place near the FL-GA border
Monday, but with less energy/enhancements aloft, not as much
widespread rain is forecast.
In terms of dynamics, we`ll have the greatest instability in the
warm sector along and S of the I-10 corridor, with MLCAPE peaking
around 400-600 J/kg on Sunday afternoon and 700-900 J/kg on Monday
afternoon. Adequate deep layer shear of 40-60 kts will be in place
across the region through the period. Juicy PWATs of 1.5-2" across
our area on Sunday will mean plenty of moisture is on tap for
storms through the day, but values will taper down to around
1.25-1.75" Monday after some of the energy aloft gets pulled away.
The low level jet will increase to around 40-45 kts along and S of
the boundary Sunday, then wane overnight only to surge to around
50 kts across SE GA on Monday afternoon/evening. Low level SRH
right along the frontal boundary will be around 100-150 m2/s2
through the period means a brief tornado or two can`t be rule out
for storms along or very near to the boundary, especially if
storm-scale pressure/vorticity perturbations occur. Overall, the
waves of energy will lead to on and off rounds of showers with
embedded thunderstorms capable of producing heavy rain and strong
to severe damaging wind gusts.
As for temperatures, we`ll continue to see that strong temperature
gradient across the area on Sunday with highs in the low 50s near
the Altamaha River and highs near 80 around the Ocala area.
Likewise, Sunday night temps will range from the upper 40s to mid
60s across the region. That gradient will shrink a little bit on
Monday, with highs in the mid 60s near the Altamaha River and
highs in the low 80s near Ocala and Flagler Beach. Lows Monday
night will fall to the mid-upper 50s in SE GA and the upper
Suwannee Valley, low-mid 60s in NE FL.
.LONG TERM [Tuesday Through Saturday]...
On Tuesday, the stalled frontal boundary should finally push
eastward, giving the area a little break from all this rainfall.
This break will be brief, however, with a much more potent +PV
anomaly digging into the Srn Plains Wednesday, bringing that
boundary back as a warm front by Wednesday night. A very energetic
frontal system will then find its way across the SErn CONUS
through the end of the work week. Some model disagreements on the
exact timing for when this one will reach us at this point, but
current thinking is Thursday night, with a much colder drier air
mass pushing in Friday-Saturday. In fact, SE GA may even see a
frost on Friday night/Saturday morning as this colder air mass
moves in.
.AVIATION...
[Through 00Z Monday]
Widespread IFR/LIFR ceilings persist over southeast Georgia and
have returned to some of the northeast Florida sites. IFR/LIFR
ceilings and visibilities will affect all sites overnight and
linger into tomorrow morning. Showers continue to move
northeastward from the Gulf of Mexico overnight affecting the TAF
sites. Showers continue tomorrow with chances for thunderstorms
for the northeast Florida sites.
.MARINE...
A stalled frontal boundary is draped across our coastal waters
from near Fernandina beach northeastward. Multiple rounds of heavy
rainfall and isolated thunderstorms are expected over the next
several days for our coastal waters as this front shifts back and
forth. Storms will be capable of producing damaging wind gusts.
When it`s not raining, sea fog will develop as winds will remain
relatively light, with the most dense fog developing in the
overnight hours and hanging in through the late morning as we`ve
seen the last several days.
Rip Currents: NE FL and SE GA- Moderate Risk through Sunday
.FIRE WEATHER...
A wet pattern will remain in place through Monday night, with a
brief break in the rain on Tuesday, then 20-30% chances for
showers return again by Wednesday. A strong cold front is expected
to move in towards the end of the work week. Transport and 20 ft
winds may be elevated in north-central FL as a series of low
pressure systems move through the area, but with such a wet
pattern in place, no red flag conditions will develop. Along and
north of the front, winds will be so light that daytime
dispersions will be around 20 or less this afternoon and again on
Sunday. Multiple rounds of heavy rain and isolated thunderstorms
producing damaging winds will continue throughout most of the
period. Fog is possible for the next few mornings.
.HYDROLOGY...
A flood watch is in effect for inland SE GA and the upper Suwannee
Valley through Sunday. In this region, 2-4" of rainfall is
forecast to occur over the 2 day period, with isolated higher
totals anticipated which could lead to localized flooding. Further
southeast, widespread rainfall totals should be around 1-2", but
again, localized higher totals are anticipated which could lead to
localized flooding. As for our rivers, minor flooding is already
occurring at points along the Santa Fe and Little Satilla Rivers
and additional rainfall this weekend is anticipated to further
aggravate these basins as well as bring portions of the Altamaha
River into minor flood stage early next week.
&&
.PRELIMINARY POINT TEMPS/POPS...
AMG 43 53 50 68 55 / 70 90 30 40 70
SSI 49 60 53 66 59 / 90 80 40 30 50
JAX 53 65 57 74 62 / 80 80 30 40 50
SGJ 57 70 60 76 63 / 60 60 30 40 40
GNV 60 73 61 78 62 / 80 80 30 40 60
OCF 63 77 63 81 63 / 50 80 20 40 60
&&
.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Flood Watch through Sunday evening for Hamilton-Suwannee.
GA...Flood Watch through Sunday evening for Appling-Atkinson-Bacon-
Clinch-Coffee-Echols-Jeff Davis-Northern Ware.
AM...None.
&&
Area Forecast Discussion
National Weather Service Key West FL
1045 PM EST Sat Feb 13 2021
.DISCUSSION...
The 00z KEY sounding showed deep southerly flow and a Precipitable
Water (PW) value well in excess of the 90th percentile for this
time of year. Water vapor imagery showed a nice shortwave lifting
northeast from the Yucatan into the southeast Gulf late this
afternoon. It continues to ride northeast this evening, to the
east of the strong but stationary front over the Central Gulf. The
upper disturbance is contributing to the unsettled convective
weather to our west and northwest this evening. Over our waters,
have recently seen the first lightning of the evening just
northeast of Dry Tortugas.
The strongest convection should remain out over the deeper Gulf
waters during the next few hours before lifting up toward
Southwest Florida even later tonight. After that, may see a few
stray showers develop over the Straits and lift north toward the
Keys.
&&
.MARINE...
Satan Shoal and Pulley Ridge buoys are respectively reporting 3-
and 4-foot seas this evening. Isolated thunder may be a concern
for a few more hours over the deep southeast Gulf waters. Fast
movement to the north could mean 30-knot gust potential.
Otherwise, southerly winds across the open Straits have likely
freshened to the point this evening for adding cautionary
headlines for the overnight hours. These winds will decrease on
Sunday morning.
From synopsis...A front stalled across the Gulf of Mexico will
dissipate Sunday and Sunday night. A new frontal zone will merge
with the old frontal boundary Monday and Monday night, then stall
over the extreme southeastern Gulf of Mexico on Tuesday. A potent
low pressure system will develop over the western Gulf of Mexico
on Wednesday, then race to the northeast to east Wednesday night
and Thursday. Southeast breezes will freshen Wednesday and
Wednesday night in advance of the deepening surface low in the
Gulf of Mexico. Our confidence is increasing for a cold front to
be nearing the Florida Keys late Thursday night or Friday morning.
&&
.AVIATION...
Recently added VCSH to the Marathon terminal due to a nearby
shower on radar, as well as recent HRRR solutions which show some
showers passing nearby overnight. EYW could miss out altogether,
despite being closer to the deeper convection lifting north
through the southeast Gulf waters. Deep southerly flow and
somewhat deeper moisture will lend itself to rounds of mid-level
clouds. All in all, VFR conditions will prevail for the next 24
hours.
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...Haner
Aviation/Nowcasts....Haner
Data Acquisition.....11
Visit us on the web at weather.gov/key
Follow us on Facebook and Twitter at:
www.facebook.com/nwskeywest
www.twitter.com/nwskeywest
...Updated Aviation Forecast Discussion...
.DISCUSSION...
Issued at 250 PM CST Sat Feb 13 2021
The main forecast concerns are snow amounts in southeast NE
tonight into Sunday and the very cold weather with wind chills of
20 below zero to 40 below zero tonight into Tuesday. We expect
the coldest wind chills to be after midnight Sunday night into
Monday morning, then again after midnight Monday night into
Tuesday morning.
Surface analysis this afternoon showed high pressure extending
from southern Canada all the way down into Texas. There were
variable amounts of cloud cover, and temperatures ranged mostly
from around zero to 5 above. The 500 mb pattern today features a
low with heights around 505 decameters over southwest Ontario and
a trough from British Columbia down to Arizona.
Expect that clouds will thicken over the area tonight as lift
moves in from the west. A band of snow should develop from the
west over western and southern NE tonight into Sunday morning,
then fade out with time in the afternoon. Added a few counties
and adjusted the end time of the Winter Weather Advisory for
southeast NE to 6 pm Sunday. Also started the Wind Chill Advisory
a bit earlier this evening in our northern and eastern counties.
Felt amounts that snow amounts could reach upwards of 3 inches in
the advisory. Inched the area with possible measurable snow
northward a bit to Columbus, Fremont, Omaha/Council Bluffs closer
to the northern edge shown by using a blend of 12Z runs of GFS,
RAP and ECMWF. Amounts on the northern edge should be an inch or
less. Look for lows tonight from about -5 to -12 or so, warmest
south and coldest north/northeast parts of the forecast area.
On Sunday, it now looks like the highest potential for measurable
snow is in the morning. For now let the advisory go longer, but we
may be able to end that earlier than 6 pm if trends continue. For
highs, well we currently do not expect anyone to get above zero.
Wind chill watch for Sunday night into Tuesday morning is still on
track and will probably be converted to a wind chill warning at
some point, for the times we expect the worst conditions. Very
cold temperatures are forecast for Sunday night and again Monday
night, so any wind at all will create a strong chill factor.
Some model guidance suggests a weak system moving through the
region for Tuesday afternoon into Tuesday night. For now will keep
close to the POPs suggested by NBM and keep it dry, but we may
need changes to that period as we get closer.
Cold high pressure will slowly move off to the east later in the
week, with a slow moderation of temperatures. The pattern will be
wet or snowy to our south and east. Highs could reach the lower
20s in our western and southern counties by Thursday, and we
should all see highs in the 20s to around 30 in eastern NE and
southwest IA by Friday. We should rise above freezing Saturday, if
the current forecast pattern holds.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 623 PM CST Sat Feb 13 2021
A few flurries have shown up in the area. Opted to include
potential MVFR conditions at OMA as TQE had some reduced
conditions with these flurries. Expect these flurries to die out
with sunset. After 06z, some snow showers will move in, mainly
affecting LNK and to much lesser extend OMA.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Wind Chill Watch from late Sunday night through Tuesday morning
for NEZ011-012-015>018-030>034-042>045-050>053-065>068-078-
088>093.
Wind Chill Advisory until midnight CST Sunday night for NEZ011-
012-015>018-031>034-045.
Winter Weather Advisory from midnight tonight to 6 PM CST Sunday
for NEZ065-066-068-078-088>093.
Wind Chill Advisory from midnight tonight to midnight CST Sunday
night for NEZ030-042>044-050>053-065>068-078-088>093.
IA...Wind Chill Watch from late Sunday night through Tuesday morning
for IAZ043-055-056-069-079-080-090-091.
Wind Chill Advisory until midnight CST Sunday night for IAZ043-
055-056-069-079-080-090-091.
&&
$$
DISCUSSION...Miller
AVIATION...Pearson
Area Forecast Discussion
National Weather Service Phoenix AZ
420 PM MST Sat Feb 13 2021
.UPDATE...Updated Aviation Discussion.
&&
.SYNOPSIS...
One weather system this weekend will bring showers mainly over higher
terrain areas north and east of Phoenix, while locally windy conditions
should provide the greatest impact this evening across the lower deserts.
The disturbance for Tuesday will again mainly bring breezy to locally
windy conditions with light precipitation over higher terrain areas.
Temperatures through much of next week will be a few degrees below
normal, before a warming trend looks likely by next weekend.
&&
.DISCUSSION
Latest streamline analysis depicts a well-defined shortwave
trough across southern Utah and northern Arizona. To its west, an
elongated swath of vorticity extends from central Arizona well
upstream into the Great Basin. Consequently, strong vorticity and
jet-forced ascent is resulting in thickening clouds across north-
central Arizona. Further west across southeastern California,
strong winds have persisted near Twenty-Nine Palms, which has
produced areas of blowing dust (now evident on GOES-17) and
reduced visibilities. Latest suite of model guidance continues to
indicate winds will gradually strengthen across the lower deserts
this afternoon, including the Phoenix area. Although gusts to 30
mph are most likely, latest HRRR and HREF ensemble max suggest an
isolated gust to 40 mph cannot be ruled out.
Consensus among the hi-res CAMs is that this system will pass
through with little chance for rain. However, a handful of members
including the NAM Nest do indicate a brief shower will be
possible in the Valley this evening between 8 and 10 pm. Best
chance for rain will be across the higher terrain north and east
of Phoenix, though even the highest amounts will be less than a
quarter of an inch, except across the highest peaks where lift
will be maximized. Bigger impact will be the wind, though speeds
will generally subside overnight behind the trough axis.
Cooler conditions are anticipated Sunday in the wake of the
trough. NBM continues to trend cooler with widespread high
temperatures in the mid 60s across the lower deserts. Meanwhile,
lingering moisture across Gila County will manage to squeeze out a
few snow showers above 4500 ft, though accumulations are not
expected. Further west, the pressure gradient will remain tight
enough to support breezy conditions, particularly across portions
of southeastern California and southwestern Arizona.
&&
.PREVIOUS DISCUSSION...
The deep trough situated across the central part of the country will
keep heights aloft over our region fairly stable through the
first half of next week, likely keeping temperatures near normal
through at least Wednesday. Yet another progressive shortwave
trough still looks to pass through our region on Tuesday, but it
looks to be rather weak and again may only result in mostly high
terrain showers. Gusty winds will likely again be the main impact
with this early next week system with gusts potentially reaching
near advisory level across our western deserts. An even drier air
mass seems to settle in for the middle of next week, potentially
helping to bring below normal overnight lows for a night or two
later next week. However, even the coldest lower desert spots
might struggle to get into the 30s given the air mass does not
look very cold. Ensemble cluster analysis then points toward a
high amplitude ridge well off the West Coast likely nudging more
into our region at some point by next weekend. If this scenario
were to play out, high temperatures over the lower deserts would
likely be pushing 80 degrees by next Saturday.
&&
.AVIATION...Updated at 2315Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Gusty westerly winds of 15-20 kts with gusts near 30 kts will
persist for 1-2 additional hours and then weaken. Speeds of near
10 kts will continue through much of the day tomorrow and remain
generally westerly or southwesterly. A few showers will be
possible around the terminals, with the best chance towards KSDL
and KDVT between 2 and 4Z this evening. SCT-BKN coverage will
develop near 7-8 kft, and potentially briefly drop lower under any
showers. A second cloud deck near 10 kft will thin out overnight
with just high clouds tomorrow.
Southeast California/Southwest Arizona including KIPL and KBLH:
Strong westerly winds are gusting 20-30 kts at KBLH and 30-40 kts
at KIPL. These strong winds will persist overnight and through
tomorrow at KBLH but will gradually become more northerly. At
KIPL winds will also gradually become northerly, but speeds will
drop to 10-15 kts. A few areas of blowing dust may reduce
visibility at times this evening, potentially down to a few miles
briefly. Otherwise, high clouds will continue through the forecast
period.
&&
.FIRE WEATHER...
Monday through Friday:
Fairly dry conditions are anticipated through much if not all of
the week with one weather system likely moving through on Tuesday,
but mainly bringing wetting rain chances across the high terrain.
Winds will also pick up again on Tuesday, lasting into Wednesday
with gusts likely approaching 35 mph over the western deserts.
Much lighter winds are expected for late in the period. Minimum
relative humidities through Tuesday will mostly fall between
15-25% over the deserts and 25-35% across the high terrain, while
beginning Wednesday falling mostly into the 10-15% range.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Blowing Dust Advisory until 10 PM MST this evening for AZZ530-
533.
CA...Wind Advisory until 10 PM PST this evening for CAZ560>562-566-
570.
Blowing Dust Advisory until 9 PM PST this evening for CAZ561-
568>570.
Wind Advisory until 8 PM PST this evening for CAZ567.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Hirsch
AVIATION...Hodges
FIRE WEATHER...Kuhlman
Area Forecast Discussion
National Weather Service Shreveport LA
1001 PM CST Sat Feb 13 2021
.UPDATE...
Lowered temps across the far north and loaded in NAM00Z winds.
&&
.SHORT TERM...
Mostly cloudy skies with a few breaks and already low 20s north of
I-30. So we did lower lows down into upper teens there.
Elsewhere, our air temps are in the mid to upper 20s north of I-20
and low to mid 30s south. The water vapor shows the lead short
wave energy now over S TX and moving our way. Mosaic radar
coverage is picking up a bit of an increase in coverage and
surface reports in S TX show a quite varied mix in progress.
We pushed back our initiation of precip from midnight to closer
to 2 to 3 am for parts of E TX. The new NAM has very spotty
coverage of a mix, so icy patches will become likely near
daybreak and keeps more of the coverage in E TX. The HRRR is
similar to the NAM to start, but goes area wide for the spotty
coverage by mid morning. The soil temp 4 inches down is 40 now in
Shreveport, so some melt water will soon be freezing as the heat
is used up, but roads should be good over one more night. A few
overpasses will bear the brunt of any icing overnight. The winds
seemed a little light and we have loaded in the new NAM for the
overnight hours. No changes to anything else at this time. /24/
&&
.PREV DISCUSSION... /issued 624 PM CST Sat Feb 13 2021/
AVIATION...
For the ArkLaTex terminals MVFR/VFR for much of the overnight
with a lead short wave to the big event early Monday on the way.
This little lead disturbance is moving over S TX attm and will
move ovhd early on Sun. MVFR with some reduction in vsby with
light fog as sn and/or frz ra will spread over the region after
daybreak. The initial snow falling from the middeck will become
more of a freezing ra to dz event during the aftn as warm air
advects over the arctic air in the lowest levels ahead of the big
trough. Sfc winds keep N/NE this cycle with SW flow aloft. /24/
PREV DISCUSSION... /issued 318 PM CST Sat Feb 13 2021/
SHORT TERM.../Tonight through Sunday/
Cloud cover across portions of the Ark-La-Tex is thinner today,
compared to yesterday, allowing more insolation to affect surfaces
and boosting afternoon highs in certain areas. A trend that hasn`t
changed as much is cold air advection from shallow northerly flow,
which still helps keeps the diurnal curve flatter regardless of any
extra sunshine. By tonight, cloud cover should thicken once again in
advance of our first round of wintry precipitation, which is
currently evident in a trough axis proceeding across West Texas,
gradually entering East Texas overnight into early Sunday.
Our Winter Storm Warning is set to begin at midnight tonight due
to the onset of wintry precipitation occurring in the forms of
light freezing rain and sleet first in Deep East Texas, with light
sleet and snow showers approaching the Red River Valley.
That band of a wintry mix quickly fans out across the entire Ark-La-
Tex by Sunday, evolving into snow showers for zones north of the I-
30 corridor, a mixture of sleet and freezing rain between the I-30
and I-20 corridors, and mainly a chance of more freezing rain south
of the I-20 corridor. In the wintry precipitation process,
evaporative cooling both keeps most afternoon highs below the
freezing mark and gradually enhances cooling aloft for the change
over to solid precipitation throughout the day. Accumulations and
accretions expected through the afternoon include a few tenths of
an inch in snow/sleet, and a few hundredths of an inch in ice
respectively, both producing travel hazards upon cold, and/or
elevated surfaces. /16/
LONG TERM.../Sunday Night through Friday Night/
Very little change in thinking for this first big wave of winter wx,
which will be getting underway at the start of the long-term.
Deep srn stream trof axis to push into the Southern Plains/W TX,
bringing additional lift and a very cold airmass swd Sunday night.
Wintry mix of precip is likely at the onset of the precip Sunday
night, as the airmass will still be shallow, transitioning to snow
from nw to se as temps aloft cool into Monday. Significant travel
impacts continue to be expected with this event, with snow amounts
generally in the 2-6 inch range, with isold higher amounts possible,
for all areas except N Central LA, and ice accums areawide around a
tenth to a quarter of an inch for all but our nwrn areas. Winter
Storm Warning remains in effect from late tonight through Monday
evening. In addition, wind chills will be very cold Sunday night
through Monday /below zero into the single digits/, so have also
issued a Wind Chill Advisory from midnight Sunday night through
Monday evening. Very cold air will continue to filter swd Monday
night, as the trof axis and precip shift ewd. Model output has
continued to trend colder, with single digits now encompassing our
entire region.
Temp trends through the remainder of the week continue to run below
NBM output as deterministic model output has trended colder. It is
unlikely for any portion of our region to get above freezing until
Wednesday and/or Thursday, and these "warmer" areas will likely be
confined to the ern and sern portions of the region.
Swly flow aloft will continue as another trof axis moves into TX
Tuesday night into early Wednesday. Isentropic lift associated with
this trof will again bring another significant winter wx episode.
The setup appears similar to the event earlier in the week, with
initial onset of precip mixed in nature, transitioning to snow as
the air aloft cools with the approach of the trof axis Wednesday
night. Highest snow/sleet accums will set up across the nwrn half of
the region, with the sern half seeing more in the way of ice accums,
likely similar to the early-week event. There continue to be some
differences in model timing, but precip looks to move e of the
region by Thursday evening/night.
We should see a warming trend take hold Friday and beyond, as nwly
flow aloft finally clears our clouds and the sun returns. /12/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 27 29 19 22 / 30 40 80 70
MLU 24 27 20 21 / 10 40 60 90
DEQ 19 26 12 20 / 10 70 90 40
TXK 24 27 17 20 / 20 60 80 50
ELD 22 24 16 21 / 10 60 80 80
TYR 25 28 11 16 / 40 50 90 50
GGG 27 28 16 19 / 30 50 90 60
LFK 29 33 18 23 / 30 20 90 70
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...Hard Freeze Warning from midnight Sunday night to 6 PM CST
Monday for ARZ050-051-059>061-070>073.
Winter Storm Warning until 6 PM CST Monday for ARZ050-051-
059>061-070>073.
Wind Chill Advisory from midnight Sunday night to 6 PM CST
Monday for ARZ050-051-059>061-070>073.
LA...Hard Freeze Warning from midnight Sunday night to 6 PM CST
Monday for LAZ001>006-010>014-017>022.
Winter Storm Warning until 6 PM CST Monday for LAZ001>006-
010>014-017>022.
Wind Chill Advisory from midnight Sunday night to 6 PM CST
Monday for LAZ001>006-010>014-017>022.
OK...Hard Freeze Warning from midnight Sunday night to 6 PM CST
Monday for OKZ077.
Winter Storm Warning until 6 PM CST Monday for OKZ077.
Wind Chill Advisory from midnight Sunday night to 6 PM CST
Monday for OKZ077.
TX...Hard Freeze Warning from midnight Sunday night to 6 PM CST
Monday for TXZ096-097-108>112-124>126-136>138-149>153-
165>167.
Winter Storm Warning until 6 PM CST Monday for TXZ096-097-
108>112-124>126-136>138-149>153-165>167.
Wind Chill Advisory from midnight Sunday night to 6 PM CST
Monday for TXZ096-097-108>112-124>126-136>138-149>153-
165>167.
&&
$$
24/16/12
Area Forecast Discussion
National Weather Service Tulsa OK
1004 PM CST Sat Feb 13 2021
.DISCUSSION...
Have updated snowfall amounts for tonight in areas to the
northwest of I-44, as most recent runs of the HRRR and HRW suite
have continued to focus the initial frontogenetic band of snow in
the 06-12z time frame more to the north. Mid-level radar echoes
have been gradually expanding across SW-central OK likely in
response to this increased forcing. An environment characterized
by steep lapse rates above the cold air at the sfc may be
supportive of CSI in the elevated front zone, and thus some heavy
banding of snow may occur late tonight into Sunday morning.
The overall message of the forecast remains the same tonight as a
significant winter storm is shaping up for a large part of
eastern OK and northwest AR. Dynamic upper level system located
near the Four Corners, which has produced numerous CG lightning
strikes across NM/AZ this evening, continues to move east, and
will provide a prolonged period of strong forcing over much of
the area.
North winds have begun to increase over the past couple of hours
in response to the approaching system, with gusts around 25 mph
becoming common across northeast OK. Wind chills have fallen below
-5 in parts of NE OK as a result and while this is technically
wind chill advisory criteria, this will be covered by the winter
storm warning beginning at midnight. Higher dew points
depressions seem to have cut off the lake effect snow across
eastern OK, however sfc reports indicate there is still some
ongoing in the FYV area...so have added flurries into the
forecast for the remainder of the evening. Per satellite this
appears to be mainly down wind from Beaver Lake.
&&
.PREV DISCUSSION... /Issued 554 PM CST Sat Feb 13 2021/
AVIATION...
CONCERNING TAF SITES KTUL/KRVS/KBVO/KMLC/KXNA/KFYV/KFSM/KROG.
Bands of light to moderate snow are expected to develop across
northeast Oklahoma late tonight with locally heavier bands possible
across aforementioned area into the morning hours. Areas of snow
will spread into southeast Oklahoma/northwest Arkansas by late
morning with snow expected to continue at all TAF sites through
the end of the forecast period. LIFR conditions will briefly be
possible in the heavier snow bands, otherwise IFR conditions will
likely prevail. Exact timing of the heavier bands will try to be
resolved on subsequent forecasts.
PREV DISCUSSION... /Issued 148 PM CST Sat Feb 13 2021/
DISCUSSION...
The deepening and drying arctic air mass has resulted in an end to
the flurries for the most part as well as the lake effect snow.
There are reported sightings of the star about 92 million miles
away from us. Some folks call it the sun. All I know is it`s nice
to see. This appearance will be brief.
We`re expecting the onset of the much talked about winter storm
to be after midnight tonight. CAM guidance is keying in on a
frontogenetic band setting up close to the I-44 corridor to the
north of the 850mb frontal zone, where locally heavy snows are
likely. The narrower and more intense nature of the band depicted
in the CAMs suggest some CSI and maybe a rumble of thunder. This
band will gradually shift east thru the day Sunday and weaken
while another band along the 700mb frontal zone advances WNW to
ESE across the entire region Sunday afternoon and night. The event
comes to a rather quick end Monday. The upper system is expected
to remain more of an open wave with the bulk of the forcing and
QPF with the upper system itself to stay just to the south and
east of the forecast area. This has resulted in an overall
reduction in snow amounts over portions of northwest Arkansas and
southeast Oklahoma. Nevertheless, expected amounts are at least
close to warning criteria, then you combine that with the high
impact to travel from blowing and drifting snow and the dangerous
wind chills.
The next system will follow quickly on its heels Tuesday night
into Wednesday. There is still quite a bit of uncertainty
regarding some important details. The GFS is painting the picture
of an epic snowstorm for our area, while the EC is not. There are
significant differences in the amount of QPF that will fall over
our area. Will continue the theme of the previous forecast with
the heavier snow potential south of I-40. Bottom line, this system
has the potential to be a high impact to travel, but
uncertainties in the details still exist so don`t get too hung up
on amounts at this point.
A warming trend will start in the wake of this system toward the
end of the week on into next weekend, slowed initially by snow
melt.
Lacy
&&
.PRELIMINARY POINT TEMPS/POPS...
TUL 5 9 -2 5 / 80 90 80 10
FSM 16 20 7 14 / 0 80 90 20
MLC 11 16 0 9 / 40 90 90 10
BVO 3 7 -5 4 / 80 90 70 0
FYV 6 14 0 10 / 20 80 90 10
BYV 5 12 -1 8 / 10 80 90 20
MKO 9 12 -1 7 / 50 90 90 10
MIO 2 7 -5 5 / 40 90 80 10
F10 6 11 -2 7 / 70 90 80 10
HHW 18 22 5 14 / 0 70 90 20
&&
.TSA WATCHES/WARNINGS/ADVISORIES...
OK...Winter Storm Warning until 6 PM CST Monday for OKZ049-053>076.
AR...Winter Storm Warning from 6 AM Sunday to 6 PM CST Monday for
ARZ001-002-010-011-019-020-029.
Wind Chill Advisory until 6 AM CST Sunday for ARZ001-002-010-011.
&&
$$
SHORT TERM...14