Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/06/21
Area Forecast Discussion
National Weather Service Duluth MN
532 PM CST Fri Feb 5 2021
.DISCUSSION...(This evening through Thursday)
Issued at 337 PM CST Fri Feb 5 2021
A prolonged relatively dry but very cold period is in store across
the Northland with Wind Chill Advisories and Warnings needed
through much of the forecast period.
Cold air will continue to move into the region tonight with 850MB
temperatures dropping to around 30 below zero Saturday. High
pressure will remain off to the west keeping a decent gradient in
place which will keep the wind up tonight into Saturday, from 8
to 15 mph with higher gusts. Cloud cover hasn`t been too
widespread this afternoon and we expect some decrease tonight
which will help allow temperatures to drop. There may be some
stronger katabatic winds again tonight along the North Shore as
seen in the HRRR and RAP. We went into the 75th percentile for
winds there which gave gusts 35 to 40 mph. There could be some
locally higher values as well. We kept Wind Chill Advisories for
all areas tonight, a few spots in far northern Minnesota will
touch 40 below and if it appears to be more widespread, a Wind
Chill Warning may be needed. We have POPs along portions of the
South Shore tonight due to the cold west/northwest low level flow.
The airmass is dry but very cold and at least some flurries
shouldn`t be too hard to produce. We don`t expect much for
accumulation and the HREF agrees with only light amounts from the
Bayfield Peninsula through Hurley and Gile.
A shortwave will aid in bringing in the colder air Saturday and
may produce some clouds and flurries, mainly over northern
Minnesota. The cold will be the main story through most of the
period and we extended the Wind Chill Advisory through Sunday for
northern Wisconsin and Pine County in Minnesota. However, values
may rise above advisory thresholds for a time during the afternoon
but it will remain quite cold. For portions of northern Minnesota
the advisory was extended into next Tuesday. Far northern
Minnesota will see the coldest temperatures and enough wind to
produce wind chills lower than 40 below. We issued a Wind Chill
Watch there from Saturday evening into Tuesday. We expect that
period to feature wind chills lower than 40 below at night with
them rising during the day but remaining at least at advisory
thresholds. The cold looks to stick around well into next week,
and Wind Chill Advisories/Warnings may be needed beyond Tuesday.
Monday night will have to be watched for some very cold lows, 30
below to around 40 below, over far northern Minnesota. The high
noses further into the region which will weaken the gradient some
and may allow for more areas to decouple. However, the guidance is
mixed at best in forecasting this with the GFS/Canadian showing a
stronger gradient than the ECMWF. There also may be some cloud
issues to deal with.
Despite the very cold temperatures and high delta-T values, lake
effect snow will not be a big threat over the next several days.
This is due to the low level winds remaining too west of north
limiting fetch. We did increase POPs along the Bayfield Peninsula
toward Hurley/Gile tonight into Saturday but only have light
accumulation each period over the next few days.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 532 PM CST Fri Feb 5 2021
Very cold air will continue to move into the Northland tonight into
Saturday. A mix of MVFR and VFR clouds will occur through the
period, with the MVFR ceilings most likely over far northern
Minnesota and along the South Sore. There still will be some
flurries or light snow as well as drifting/blowing snow this
evening. Winds will diminish tonight but won`t become light as a
stronger gradient remains in place. Overall, we expect clouds to
decrease for most areas tonight but as often is the case in these
cold airmasses, some MVFR or even isolated IFR ceilings will be
possible in spots. The clouds will hang around the longest in far
northern Minnesota and along the South Shore. Strong wind gusts will
be possible along the North Shore tonight as well due to katabatic
winds.
A shortwave may bring some flurries/light snow on Saturday to
portions of the Northland but little accumulation is expected.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH -14 -5 -21 -6 / 10 10 10 0
INL -18 -10 -25 -10 / 10 10 10 0
BRD -11 -4 -20 -5 / 10 0 0 0
HYR -10 1 -21 -3 / 10 0 0 0
ASX -8 0 -15 -2 / 40 30 20 10
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Wind Chill Advisory from midnight tonight to noon CST Sunday for
WIZ001>004-006>009.
MN...Wind Chill Watch from Saturday evening through Tuesday morning
for MNZ010>012-018>021-026.
Wind Chill Advisory until 8 PM CST Saturday for MNZ010>012-
018>021-026.
Wind Chill Advisory until noon CST Tuesday for MNZ025-033>037.
Wind Chill Advisory from midnight tonight to noon CST Sunday for
MNZ038.
LS...None.
&&
$$
DISCUSSION...Melde
AVIATION...Melde
Area Forecast Discussion
National Weather Service Fort Worth TX
704 PM CST Fri Feb 5 2021
...New Short Term, Aviation...
.SHORT TERM... /NEW/
Update:
Only adjustments from the midday short-term discussion below was
to increase west and northwest winds by Saturday afternoon. Deep
mixing initially in behind the exiting surface low and prefrontal
trough will promote increasing westerly winds 15 to 20 mph.
Increasing low level CAA behind the mid afternoon cold front and
a strengthening pressure gradient will drive even stronger
northwest winds 15 to 25 mph with gusts 30 to 35 mph. We may reach
borderline Wind Advisory Saturday afternoon, so this will need to
be monitored closely. Look for winds to veer northerly and
decrease to between 10 to 15 mph after nightfall Saturday evening.
Regarding precipitation with the next mid level impulse Saturday,
it still appears the best lift and moisture will be confined to
East Texas and the Ark-La-Tex. Instability looks marginal at best,
so kept any isolated potential for lightning strikes out of the
forecast and kept best rain chances confined to our northeast
counties. A rogue shower or two can`t be ruled out across the
eastern counties as far back west as the eastern DFW Metroplex.
05/
Previous Discussion:
/This afternoon through Saturday/
Large scale subsidence will increase behind a departing shortwave
this afternoon, resulting in decreasing clouds and an end to rain
chances.
After a cold start to the morning with lows in the 30s and lower
40s, temperatures will slowly warm through the afternoon,
reaching highs in the 50s and lower 60s. The return of low level
moisture tonight in response to a deepening lee trough across the
Central and Southern High Plains will result in the return of low
clouds along with slightly warmer temperatures. Lows tonight will
range from the upper 30s to the lower 40s.
Another cold front will move across the region on Saturday,
bringing a reinforcement of dry and cool air along with a breezy
west to northwest wind Saturday afternoon. The breezy and dry
weather will result in an elevated threat for grass fires,
especially across the far western zones. A few locations in the
west could also briefly touch Wind Advisory criteria behind the
front, but the windy conditions will be brief and on the low end
of criteria.
Cold air advection Saturday afternoon will be offset but ample
sun and some adiabatic warming, therefore, highs should still
manage to reach th upper 50s and 60s in most locations. The only
exception will be the northeast zones where clouds will linger the
longest.
79
&&
.LONG TERM... /Issued 323 PM CST Fri Feb 5 2021/
/Saturday night through Next Friday/
The main story of the long-term forecast is to continue to monitor
the arctic cold airmass that will expand southward next week. But
first...let`s enjoy the nice/mild temperatures Sunday and Monday.
A surface ridge will move over the region Saturday night,
shifting our winds to the southeast by Sunday morning. The
combination of light winds and clear skies will result in
overnight temps in the 30s. Many locations across North TX will
see temps below freezing Sunday morning. Temperatures will warm
into the mid 50s and 60s in the afternoon, with a few locations
reaching low 70s across the far western counties. Expect another
mild/warm day on Monday with some areas across Central TX warming
into the low-to-mid 70s ahead of the next system.
The next front is set to arrive Monday evening or Tuesday
morning, bringing the first round of cold air to the region.
There`s a low chance for a few light showers Monday afternoon and
night mainly across the northeast where the best convergence of
moisture and lift will exist. The high temperatures on Tuesday
will stay in the 40s and low 50s across North TX, to 50s and 60s
across Central TX.
Another shot of arctic cold air will push southward mid-to-late
week. Despite the large uncertainties on how much moisture will be
available for any winter precipitation, this pattern will definitely
support some very cold temperatures. Most of the medium and long
range guidance continue to support a negative phase of the North
Atlantic Oscillations (NAO) during this time period, which will
allow the Canadian and arctic cold air to move south. If this
forecast verifies, we will be looking at temps 20+ deg below
normal with highs in the 30s to low 40s and overnight lows in the
teens and 20s on Thursday/Thursday night and Friday.
What we all want to know is...will we get any wintry
precipitation? The way things look right now it appears that this
system will bring a chance of a wintry mix across most of North &
Central TX on Thursday-Friday. The deterministic GFS continues to
be more aggressive in bringing some wintry precipitation, as it
keeps showing the highest overrunning moisture over our area.
While the ECMWF keeps most of the activity north and west of us,
many of the ensemble members do show a southern track of the
shortwave. When compared to our climatology, this type of pattern
(North American Trough) has been associated with very cold
temperatures, but limited moisture. Still, there has been cases
where just the right amount of moisture was available to produce
wintry precipitation. All we can do now is keep monitoring the
trends as the forecast will definitely change as we get close to
this time period.
Sanchez
&&
.AVIATION... /NEW/
/00Z TAFs/
Challenges: Arrival of MVFR cigs below 020 and potential
southwesterly LLWS within the PBL.
VFR conditions and southeast winds 10 to 15 knots will be the
rule, as lee-side cyclogenesis deepens across E NM and slowly
moves east-southeast into the TX Panhandles/NW TX region
overnight. S-SW flow within the PBL is expected to increase to
between 30 to 40 knots during the pre-dawn hours. These strong
southerly winds just above the surface will help draw rich
moisture from the Gulf of Mexico northward and into the area
between 08z-12z Saturday morning.
MVFR cigs mostly between 1300-2000 feet are expected to impact
Waco by 08z-09z Saturday before arriving at D10 terminals in the
DFW Metro by 12z Saturday. Moisture progged by RUC soundings looks
fairly deep (~ 1500 feet deep), thus MVFR cigs will likely hold
over all terminals until late Saturday morning. The strong S/SW
PBL winds and less intense SE surface winds during the predawn
hours may present a brief period of LLWS just before 12z. Confidence
is too low at this point to insert into the forecast.
A surface low tracks east across the D10 area with veering low
level flow and drier low level air by 18z and should help scatter
any MVFR cigs out. Though a stray shower or two is possible near
eastern DFW Metro terminals, I will maintain no mention VCSH in
the forecast.
Surface winds will veer W/SW 13-17 knots before going NW 15-20
knots with gusts between 25-30 knots with cold FROPA by 21z with
the surface low moving east away from the area during the
afternoon. Crosswinds may present some impacts at DFW International
for mid morning through early afternoon, with earlier impacts on
any diagonal runways being used due to ongoing construction main
runways at the airport.
05/
&&
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 40 59 34 61 46 / 0 5 0 0 0
Waco 40 66 34 64 46 / 0 0 0 0 0
Paris 37 50 31 54 38 / 0 40 0 0 0
Denton 37 58 30 61 43 / 0 10 0 0 0
McKinney 37 57 31 60 43 / 0 10 0 0 0
Dallas 42 60 35 63 47 / 0 5 0 0 0
Terrell 38 58 32 60 43 / 0 10 0 0 0
Corsicana 41 63 35 63 46 / 0 5 0 0 0
Temple 40 68 34 66 47 / 0 0 0 0 0
Mineral Wells 37 61 31 67 44 / 0 5 0 0 0
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
922 PM CST Fri Feb 5 2021
...Short Term Update...
.UPDATE...
Issued at 917 PM CST Fri Feb 5 2021
QPF and the resulting snow totals for tonight and Saturday
morning were nudged down slightly to match trends on the latest
runs of the HRRR and RAP. This takes the peak snowfall totals down
closer to the 4-6" range.
Otherwise, things appear to be mostly on-track. Radar returns are
starting to blossom over western portions of the area, and these
areas should start seeing snowflakes shortly. It appears that the
heaviest snow will occur roughly between 2am and 9am, and
accumulating snow should end by noon on Saturday.
&&
.DISCUSSION...(This evening through Friday)
Issued at 416 PM CST Fri Feb 5 2021
So far this season we have generally been blessed with rather mild
winter weather, but thats all about to change this week. This week
could potentially be the harshest winter weather we have had thus
far this season! There have been quite a few changes over the last
couple of forecast packages, but thankfully that has been due to
models coming in to better agreement. So as of right now there are
really 4 main topics to cover:
1. First round of snow tonight and into tomorrow
2. Second round of snow tomorrow night and into Sunday
3. Third round of snow Sunday night
4. The Arctic blast and our dangerous wind chills
So starting from the top with the first round of snow that is
expected tonight. A broad upper level trof has been digging its way
south over the Northern and Central Plains with a parent low
situated over Ontario. This low and the short waves that move around
it, are the start of our intense weekend and week ahead. Snow
ratios, QPF, and snow totals have all been trending up over the last
2 forecast packages. Models have come in to better agreement as
recently as this morning, with a nearly unanimous southward shift in
the main snowband. The most difficult aspect currently is being able
to nail down the location of this band. There is also likely to be a
sharp gradient in snowfall totals due to this band, even one county
apart could mean the difference between 2" and 5" for example. This
is also expected to be a very fluffy snow, with the highest snow
ratios being around 18:1 and 19:1. Nearly all of the short term
models have been trending up in their pwat values and therefore
their QPF as well. So even though it`s tempting to think that the
current QPF estimates might be too high given how cold this system
is, there seems to be enough evidence and model support to
justify the current forecast. With the high SLRs and QPF, 5-7" of
snow is expected to fall within the band and 1-5" is expected
elsewhere. Winds will also create the issue of blowing snow and
reduced visibilities with gusts expected to be around 25-30 mph.
The second round of snow is expected tomorrow night and into Sunday
morning. A quick little short wave dives south over our area while
we remain in NW flow aloft. As cold Arctic air is funneled south
snow ratios will remain high and it`s possible to get at least
flurries out of nearly every perturbation that passes through. With
this set up it really doesn`t take much to get some sort of
snowfall. This second round (and the third round) are not expected
to be nearly as intense as the first one tonight. However, even
limited moisture can still produce several inches of snow due to the
higher SLRs. With this second wave snow amounts look to be mainly
between a Trace to 3" and mostly north of the NE-KS border. The
areas that could see above an inch are mainly north of the I-80
corridor at this point, though that could change between now and
then.
The third round of snow comes Sunday overnight and is even less
still. Once again being in NW flow aloft allows for even the
smallest of waves to affect us, as is the case here. The coldest air
really begins to settle in around Sunday night and so we could
squeeze out an additional T-1" of snow with this little perturbation
Sunday night. This particular one is probably the most uncertain of
the three and a lot is still subject to change. But the main point
is that over the next several days it will be very easy to have even
just a little bit of snowfall.
Now on to the fourth point, the real winter kicker...the blast of
Arctic air that is being funneled south by this entire system.
Temperatures will start to plunge tonight and tomorrow but continue
to drop through Sunday and bottom out with highs in the low teens
and single digits on Monday. Lows are expected to drop below zero
starting Sunday night and will drop even further in the coming days.
Unfortunately this air mass looks to stay in place for a while as
the upper low oscillates over Ontario. Wind chills will be
dangerously cold Sunday night onward, with the lowest values
generally being around -15 to -25 degrees. The single digit and
lower teens daily highs continue through the end of the 7-day
forecast. This means our temps will be a good 20+ degrees below
average for this time of year.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday)
Issued at 523 PM CST Fri Feb 5 2021
Snow will begin to move into the area after 06Z, becoming fairly
widespread after 08-09Z. Ceilings are expected to be MVFR, with
visibility below a mile at times.
Snow will begin to let up in the 12-14Z timeframe, with ceilings
likely eventually rising back to VFR in the afternoon.
Winds will turn northerly early Saturday morning, with gusts to
around 20kts. This will also lead to some minor blowing snow
before winds taper off again in the afternoon.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Storm Warning until noon CST Saturday for NEZ046>048-
061>064-075>077.
Winter Weather Advisory until noon CST Saturday for NEZ039>041-
049-060-073-074-084>087.
KS...Winter Weather Advisory until noon CST Saturday for KSZ007-019.
&&
$$
UPDATE...Mangels
DISCUSSION...Shawkey
AVIATION...Mangels
Area Forecast Discussion
National Weather Service Goodland KS
900 PM MST Fri Feb 5 2021
.SHORT TERM...(This evening through Saturday night)
Issued at 140 PM MST Fri Feb 5 2021
Satellite imagery and 500mb RAP analysis early this afternoon
showed northwest flow prevailing above the High Plains on the
western side of a large upper trough. A disturbance was moving
through the northwest flow and into the central Rockies,
generating cloud cover and light snow in the mountains. At 1:00
PM MT, temperatures ranged in the 40s across our area with
northwest winds turning west at 10 to 20 mph. Cloud cover began
sliding into the region from the west off of the Rockies.
For tonight and early Saturday, the disturbance embedded in the
northwest flow aloft advances southeast towards the High Plains and
produces a northwest to southeast oriented band of snow over central
Nebraska and northeastern Kansas. The heart of this band will be
well off to our northeast, but areas east of a line from Wray,
Colorado to Gove, Kansas could get clipped by some light snow. The
main timeframe to watch will be after midnight tonight into Saturday
morning. At this time, the forecast calls for around one inch of
snow near McCook, NE and Norton, KS with amounts quickly decreasing
to the south and west. Otherwise, expect low temperatures in the
upper teens to low 20s. A surface low crosses the region overnight,
shifting winds to the north with the potential for gusts near 35
mph on its backside.
Snow tapers off to the east Saturday morning, with breezy winds
carrying on behind. Winds should go light during the afternoon hours
as the low pushes further away from the region. The frigid air
filtering in behind the disturbance and lingering cloud cover will
make for a wide range in high temperatures and a difficult
temperature forecast. Current thinking is for highs ranging from the
low 20s in the northeast portion of the region to the low 40s in the
southwest.
On Saturday night, another round of snow looks to develop across
central Nebraska as the next disturbance passes through the
continued northwest flow. Again the majority of the snow will stay
north of the region, but light amounts (less than a half inch)
cannot be ruled out north of the Nebraska border. Temperatures fall
into the single digits and teens for most of the area, with a few
locations staying up in the low 20s in eastern Colorado. Will need
to monitor the potential for fog development as winds turn
southerly overnight.
.LONG TERM...(Sunday through Thursday)
Issued at 144 PM MST Fri Feb 5 2021
Much colder in the long term period with the potential for light
snow as well.
Sunday will be the last of the "warmer" days as the western portion
of the area will see temperatures that are near the climatological
average while locales further northeast will likely be cooler due to
cloud cover. Another reason those locales will be cooler is that the
colder air mass will move in from the Central Plains during the day
which will cap highs as it moves through. It is worth noting that
the upper level pattern is fairly stagnant with 500mb flow out of
the northwest during most of the period as a broad trough sits
across the CONUS. Snow looks to be unlikely as the surface low is
currently forecasted to be too far west and south to affect the
region. However, it would not be unreasonable for flurries at
different points during the entire period given the colder air that
is expected and potential for higher RHs aloft.
Monday through Wednesday look to be fairly similar in conditions as
the large scale pattern is stagnant with that upper trough across
the CONUS and the arctic air mass set up over the Central Plains.
High temperatures are currently forecasted to be in the 20`s during
these days with lows in the single digits or just below zero. Given
such cold lows, will need to watch wind chills as the forecast has
them approaching negative 15 to 20 degrees F. Model guidance does
hint at on and off cloud cover through these days though precip
remains unlikely given the high pressure across the area.
Thursday on is uncertain as guidance begins to differ on how the
upper pattern will evolve starting late Wednesday. The ECMWF and GFS
largely disagree on the prevailing conditions with the ECMWF
bringing in moisture from aloft while the GFS is drier. Both
guidance and ensembles agree that the center of the upper trough
will begin to push off to the east, though both deterministic models
suggest it will also dig further south. There is disagreement though
on how that will happen and how far south it will dig. Either way,
this will need to be watched as both NAEFS and ECMWF anomaly tables
have a 2.5 percentile 850mb temperature Thursday into Friday in
regards to 30 year climatology. They both also have a minimum value
in comparison to 20 years of forecasts for this time period.
However, this is still too far out to determine if this would happen
and if it would even lead to cooler temperatures given that the area
is already below average and there are hints of snow moving through.
Will continue to monitor how the pattern evolves and if the
suggested anomaly remains.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 900 PM MST Fri Feb 5 2021
A stationary front bisects the KGLD and KMCK terminals late this
evening with sub VFR cigs on the cold side of the front (KMCK) and
VFR cigs on the west (KGLD). From taf issuance through 12z KMCK is
expected to remain in sub VFR cigs with a chance for light snow.
Stratus is expected to get close to KGLD but for now should be
just east/northeast of the terminal. Winds at KGLD begin from the
south under 10kts veering to the northwest up to 10kts by 12z
while KMCK remains from the east and northeast at speeds up to
10kts.
From 12z-00z winds at both terminals become north to northeasterly
in the morning with gusts up to 30kts expected then shifting to
the east and southeast at speeds up to 10kts in the afternoon as a
cold front pushes west and strong high pressure drops into the
central plains. KGLD is currently expected to remain VFR while
KMCK remains under sub VFR cigs.
From 00z-06z winds at KGLD increase from the south-southeast
around 15kts with higher gusts, 11kts or so from the east-
southeast at KMCK. Cigs are expected to lower sub VFR at KGLD
toward the end of the period as stratus moves west toward the
terminal. KMCK remains under sub VFR cloud cover.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
SHORT TERM...JBH
LONG TERM...KAK
AVIATION...99
Area Forecast Discussion
National Weather Service Jackson MS
926 PM CST Fri Feb 5 2021
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
The forecast thinking is generally the same with showers expected
to increase later tonight and shift northward as we go through
Saturday. Have just made minor adjustments to the overnight and
early morning forecast to account for latest observational and
near term guidance trends. /EC/
Prior discussion below:
Tonight and tomorrow: Scattered showers continue south of I-20
into the evening...though should start to drift southward/have a
few breaks before 05/06z when another quick disturbance will
stretch that precip slightly northward again. Going into
tomorrow...the rain across the region remains the main issue. HRRR
was far more conservative with the northern extent of the
showers. Whereas the 12Z NAM was far more aggressive with lifting
that stalled front back to the north a bit... having more precip
across the entire area by 12Z. The 18Z NAM came in and eliminated
the pops north of I-20 before noon tomorrow, far closer to the
HRRR. Trended the forecast in this direction. And although the
pops may remain conservative, the increasing cloud cover in the
east and north...will result in cooler highs, particularly east of
I-55, by at least a couple of degrees. /HJS/
Tomorrow night through Tuesday:
The forecast period starts off tomorrow night with a longwave trough
draped across the CONUS with an embedded shortwave trough rounding
the base of the longwave over the Lower Mississippi Valley. Surface
cyclogenesis will be underway along a coastal baroclinic zone with
the surface low lifting through the Florida Panhandle and along the
Carolina coast by Sunday morning. Associated showers will continue
along the Hwy 82 corridor through the overnight hours with dry
conditions returning to the area by Sunday morning. A surface cold
front over northern Arkansas and Tennessee will make little
southward progression as it becomes oriented parallel to upper flow
aloft. As such, no airmass change is expected with the coldest air
bottled up over the Northern Plains and Midwest. Temperatures will
moderate heading into the beginning of next week with afternoon
highs climbing into the low to mid 60s by Monday with upper 60s to
near 70 possible on Tuesday, especially south of I-20. A shortwave
ejecting through northern Mexico will bring another round of rain to
the area Monday night into Tuesday. Global guidance differs with
respect to the strength of the wave with the ECMWF depicting a
stronger wave and wetter solution while the GFS remains weaker and
drier. Kept the forecast in line with the national model blend and
will continue to advertise rain chances.
Wednesday into next weekend:
The main focus for the long term forecast period will be the
potential for winter weather along with dangerously cold
temperatures late next week into the weekend. Ensemble guidance
continues to depict a pronounced signal for an intrusion of very
cold arctic air beneath active southwesterly flow aloft. This
synoptic setup, along with top analogs, supports a multi-day period
of dangerous cold with several chances for winter weather. Strong
cross polar flow will allow a frigid arctic airmass to spill into
the Northern Plains on Wednesday. This airmass will be anomalously
cold with an associated 1050mb surface high (2-2.5 sigmas above
normal). Meanwhile, further aloft, persistent southwest flow will
remain in place over the Lower Mississippi Valley with embedded
perturbations ahead of a potent shortwave trough forecast to dive
into northern Mexico by Thursday morning.
The arctic cold front will move through the area during the
Wednesday night to Thursday timeframe and will establish a shallow
sub-freezing layer beneath warm temperatures aloft. This will set
the stage for potential winter weather as aforementioned
perturbations swing through aloft followed by the main shortwave
trough ejection. While confidence is increasing that at least some
portion of the area will see accumulating winter weather, exact
timing and placement remain more uncertain and will hold off on
mention in the HWO/graphics for now. Predominate precipitation type
looks to be a mixed bag of rain, freezing rain, sleet and
potentially some snow if enough moisture becomes juxtaposed with
deeper cold air.
The center of the arctic high is progged to slide into the Southern
Plains and Mississippi Valley by the weekend and will usher in a
dangerously cold airmass characterized by temperatures anomalies 15-
22 degrees below normal. This will yield overnight low temperatures
dropping in the low 20s to teens and afternoon highs struggling to
climb into the low 30s. Furthermore, wind chill values are forecast
to drop into the single digits across much of the area. While the
signal for dangerous cold remains strong, drastic run-to-run model
variability continues to make pinpointing a focused timeframe very
difficult this far out, thus will keep the HWO/graphics clear for
now.
It is worth noting that this potential winter weather and dangerous
cold event has a high ceiling and potentially high impacts due to
the combination of ice/sleet/snow followed by arctic air. However,
the magnitude will be dependent on several moving parts coming
together just right and exact details remain unclear at this point
in time. The forecast will continue to evolve over the upcoming
week and as such, the reader is strongly encouraged to stay
abreast of the latest forecast throughout the week as details are
ironed out and model guidance comes into better agreement. /TW/
&&
.AVIATION...
00Z TAF discussion:
Expect rain to diminish early this evening in the Pine Belt area,
but a significant trough approaching Saturday will bring moist
ascent with rain and IFR ceilings redeveloping across much of the
area by afternoon. Light surface winds will pick up from the east
Saturday and could be gusty at times. /EC/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 36 49 39 56 / 29 66 23 0
Meridian 37 47 38 54 / 28 64 26 0
Vicksburg 38 51 39 55 / 21 57 18 0
Hattiesburg 41 51 41 59 / 68 82 12 0
Natchez 40 53 40 58 / 45 79 11 0
Greenville 35 48 35 49 / 1 32 38 0
Greenwood 35 49 36 52 / 1 28 48 0
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.
&&
$$
Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
852 PM CST Fri Feb 5 2021
.UPDATE...
Issued at 852 PM CST Fri Feb 5 2021
A forecast update is in place for temperatures using hourly
forecast temperatures derived from the short term model blend plus
bias correction, the RAP model plus bias correction and the HRRR
model without bias correction. This lowers highs Saturday a few
degrees and attempts to capture the arctic air progressing south
through nrn Nebraska this evening. The rest of the forecast is on
track. The evening models appear to be tracking the highest
snowfall amounts through the Sandhills as predicted.
&&
.SHORT TERM...(This evening through Saturday night)
Issued at 309 PM CST Fri Feb 5 2021
The primary forecast challenge centers on the threat for multiple
rounds of accumulating snow this weekend, and temperatures through
next week. Winter Weather Advisories remain in effect overnight
tonight with the addition of a Winter Storm Warning for Custer
County.
Not much has changed with respect to the overall pattern across much
of the CONUS with a large-scale trough pivoting across the northern
Great Lakes and highly amplified flow upstream of this feature with
a building ridge off the West Coast. Caught in between these
features, the local area is seeing the influence of an upper-level
jet as it slides just to the south. At the surface, the Arctic cold
front bisects the area in half oriented northwest to southeast with
highs only in the 20s and clouds as of 20z to the northeast with
upper 30s to low 40s across the southwest. This front will continue
to stall this afternoon but should see a renewed southward push as a
quick diving clipper system approaches the area late this evening.
As this moves south, mid-level fgen will increase quickly from 03z
to 09z which will tap into PWAT values which climb to the 0.25-0.35"
range. While this isn`t overly impressive, the forecast forcing for
ascent is expected to be rather strong which will allow forecast QPF
values to overachieve. Indeed, numerical guidance has started to
hone in on a consensus that paints a stripe of liquid precipitation
exceeding 0.3". This is in good alignment with the latest NAM and
Canadian output, SREF/HREF probabilities, as well as latest high res
guidance. While the GFS remains the furthest south with its output
and therefore is considered the outlier, the ECMWF has trended
upwards with its QPF output and aligns with the aforementioned list
in terms of location. Greatest uncertainty with snow amounts will
exist along the southern edge of the snow gradient with increasing
confidence north across the Sandhills. Subsequent shifts will have
to monitor closely for any southward shift towards the fairly
resolute GFS output. As for snow amounts...given the magnitude of
cold air in place, expecting SLR ratios to exceed climatological
values and will likely climb above the 75th percentile. This puts
much of the area in the 16:1 to 18:1 range with some guidance even
suggesting making a run at 20:1. This is plausible given a deep DGZ
and strong lift originating in this zone. Will not go this
aggressive, however. Even with the lower SLR values, snow amounts
should lead to widespread 2-5" total accumulations with a small area
approaching 4-7" limited to Custer County. As a result, opted to
continue the Winter Weather Advisory across the area with the lone
change being to upgrade Custer County to Winter Storm Warning after
coordination with eastern offices. Winds aren`t likely to be overly
strong with this event, peaking around the 10 to 20 mph range
overnight which should limit the blowing snow potential. Snow will
wind down through the late morning hours as the focus shifts to the
east and fgen rapidly diminishes. Morning lows Saturday will fall
into the single digits to teens across the area with wind chills as
cold as 5 to 15 below zero possible with the coldest values expected
across far north central Nebraska.
Expect a break from the snow during the bulk of the daytime on
Saturday. Highs should only reach the low teens to low 30s northeast
to southwest. Snow will renew late Saturday evening as a second mid-
level disturbance moves overhead. Similar to the first round,
forcing will largely come from increasing fgen and warm air
advection. Moisture will be a little more limited and focus for this
lift will be further north than the previous round. New snow
accumulations will generally fall in the 2-4" range therefore will
have to monitor this for additional winter weather headlines but
will forego any issuance at this time to not mix messaging with the
first round. Snow will linger into early Sunday morning with lows
dropping a further 5 degrees across the board. Snow will diminish
slowly through the day Sunday, with the last of the potential ending
for areas north of Highway 92 by early evening. Can`t rule out some
light snow persisting later, but confidence is low at this time.
Highs Sunday will be similar to what was seen Saturday, ranging from
around 10 in the northeast to around 30 in the southwest which will
likely be the last day of seeing temperatures approach the freezing
mark for an appreciable amount of time.
.LONG TERM...(Sunday through Friday)
Issued at 309 PM CST Fri Feb 5 2021
Beginning 00z Monday. The region remains entrenched in northwesterly
flow for Monday through the middle part of next week. Strong surface
high pressure will settle into the area from eastern Montana which
will only reinforce the cold air expected to move in. Sunday night
into Monday, will be watching for some light snow to develop on the
leading edge of the surface high pressure system. Moisture will be
fairly limited so any snow amounts are expected to remain fairly
light. Daytime highs will top out in the single digits to low teens
Monday through Wednesday, which is 25 to 35 degrees below normal
each day. Morning lows will fall below zero across the area, even
approach the negative teens. This alone is enough to cause concern
for extreme cold across the area. Though no one day appears to be
overly windy, any wind developing will only exacerbate the cold by
introducing wind chill values falling into the -20s. At this moment,
no one day appears to be overly breezy given persistent high
pressure in place across the local area and eastward. In
summary...while cold temperatures are confident at this time the
precise wind chill values remain in flux somewhat and are lower
confidence. Either way, prolonged exposure to the expected air
temperatures alone will be enough to cause problems to anyone not
properly prepared so plan on limiting outdoor exposure and layering
up each morning through the extended period.
Reinforcing cold air arrives on Thursday with the approach of
another surface high in the 1035-1045 hPa range. As a result,
expecting the coldest day of the week on Thursday. We could see
additional light snow across our southwest zones Thursday into
Friday, but differences between the main model outputs remain and
ensemble guidance isn`t highlighting any one particular period as a
slam dunk so will keep inherited PoPs of less than 20% as they
are.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 534 PM CST Fri Feb 5 2021
The area of IFR/LIFR in snow and low ceilings near KIBM will move
east and expand north and south across wrn Nebraska by 06z, and
ncntl Nebraska by 08z. This area of snow and low ceilings/vsby
will exit wrn and ncntl Nebraska by 12z Saturday.
Areas of MVFR/local IFR ceilings are expected across wrn and ncntl
Nebraska throughout day Saturday.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM CST /8 AM MST/ Saturday for
NEZ005-008>010-023>029-035>037-057-059-094.
Winter Storm Warning until 9 AM CST Saturday for NEZ038.
&&
$$
UPDATE...CDC
SHORT TERM...NMJ
LONG TERM...NMJ
AVIATION...CDC
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
909 PM CST Fri Feb 5 2021
.UPDATE...
Issued at 900 PM CST Fri Feb 5 2021
New model data is trickling in this evening. The 00Z NAM is
already out through Sunday into Monday, and it seems to compare
well with the 18Z NAM for our snow tomorrow. Both runs of the NAM
are drier than our going forecast, and would therefore produce
less snow. All of the thermodynamic forcing still looks strong,
but it`s slightly displaced from the moisture. The latest run is
also a little slower bringing precipitation into our area during
the afternoon, perhaps due to the very dry low levels that the
snow will have to overcome. While we don`t yet have a new run of
the GFS, the 18Z run was similarly slower than the current
forecast, but made up for some of the slower onset of precip with
more QPF on Saturday evening to yield similar snowfall amounts to
our forecast.
With the latest deterministic NAM showing the possibility of
lesser snowfall amounts than previously expected, and no other
updated guidance at the moment, I do not have high enough
confidence to make changes to our current forecast and Winter
Weather Advisory.
Carney
&&
.SHORT TERM... (Through Late Saturday Night)
Issued at 324 PM CST Fri Feb 5 2021
Main takeaways in the short term forecast:
-Snowfall totals for Saturday afternoon were increased to reflect
growing confidence in higher QPF and measurable snow across the CWA.
-A Winter Weather Advisory will take effect at 9am Saturday and last
through 9pm Saturday for northern/central MO and west-central IL.
-Behind the system, the most bitter cold we`ve seen so far this
season will bring wind chill values between -5F and -10F across the
CWA.
A longwave trough is now squarely in place across the CONUS, which
will set the stage for the cold, unsettled pattern through the
forecast period. Other than a chance of light snow tonight along the
I-70 corridor, which is depicted among a few of the short-range
deterministic guidance and CAMs, an uneventful night is expected.
Winds will stay out of the west/northwest this evening, and while
the coldest temperatures stay away from the northern CWA, the entire
area should end up well-below-freezing tonight. If winds were a bit
more northerly, temperatures would likely sink much lower with
colder air atop a snowpack north of MO being advected south.
A notable difference from the previous forecast is the organization
of the shortwave trough that makes it way through the CWA along the
periphery of the longwave on Saturday. Previously, two areas of
forcing in the northern and southern streams did not seem to phase
well-enough to result in any robust snowfall. However, nearly all
deterministic and ensemble guidance is now in fairly good agreement
that the two maxima of PVA will be closer together and phase/amplify
over MO. The latest HREF mean snowfall totals suggests a broad swath
of 2-4" of across the CWA, with locally-higher amounts. Taking a
closer look at the constituent members of the 12Z HREF, the HRRR
seems to have influenced those significantly-inflated numbers. That
being said, all guidance is trending upward in terms of QPF in
conjunction with the better forcing organization. The National Blend
of Models is now suggesting higher snowfall totals in the northern
portion of the CWA, approaching 4" when all is said and done
tomorrow night. Differing from the HREF, however, it does have lower
totals (1-2") along and south of I-70.
Looking closer to the surface, guidance agrees on a fairly robust
axis of 850-700mb frontogenesis across the central third of
Missouri. Model soundings also show a deep DGZ with at least modest
lift in that layer, further solidifying the notion of not only
higher snowfall totals, but periods of time where snowfall rates
could reach 1" per hour. In these bands, visibility would certainly
be restricted and hazardous travel would be a concern. After taking
into account the consensus on higher snowfall totals, and also
considering higher SLRs where temperatures aloft will be much
colder, snow totals were increased to 2-4" of snow across
north/central MO and west-central IL, 1-3" along I-70, and up to 2"
south of that. A Winter Weather Advisory will take effect at 9am
Saturday and last through 9pm Saturday for northern/central MO and
west-central IL, where snow totals will be highest. I will caution
that, given the trend in guidance and the potential for mesoscale
banding, locally-higher amounts are possible.
The truly-cold air rushes into the region associated with an arctic
air mass behind this system tomorrow afternoon through tomorrow
night. Not helping to moderate temperatures, winds will be more
northerly tomorrow evening. As mentioned earlier, this wind
direction will advect even-colder air off of the snowpack in
southern Iowa into our CWA. Wind chills knock on the door of Wind
Chill Advisory Criteria (-15F) in far northeast MO/west-central IL,
but confidence in winds being strong enough to drop the wind chills
further precluded me from issuing a product at this time.
Regardless, the coldest (both in terms of true temperatures and wind
chills) night of the season is expected Saturday night.
MRB
.LONG TERM... (Sunday through Next Friday)
Issued at 324 PM CST Fri Feb 5 2021
Attention was given to the active weather in the short term, but the
main points of concern through the extended period:
-Well-below-average temperatures continue through the end of the
period overall, but brief periods of "less-cold" air remain
a possibility.
-Confidence in another round of snow on Monday continues to increase
across the northern half of the CWA, but timing/position
uncertainties abound amidst the near-zonal mid-level flow.
-A period of relatively-dry weather takes hold by mid-week, but the
bitter cold remains in place.
Sunday will be the first full day of the true bitter cold, and
locations in northeast MO and west-central IL may break low maximum
temperature records. The record "low-high" temperature at KUIN
(Quincy Regional Airport) is 13F, and the latest forecast tops out
just around 12F. Northerly winds will aid colder air to advect off
of the snowpack to our north in addition to the cold air associated
with strong surface ridging. Short term guidance and CIPS Analogs
from Saint Louis University stay true to the bitter cold, as they
have in the recent past.
Another shortwave appears poised to translate east across the base
of the longwave trough Monday. While there seems to be more
agreement among deterministic and ensemble solutions than in
previous forecasts, timing and position differences regarding the
strongest forcing still exists. The pattern of nearly zonal flow
typically results in these events that are difficult to nail down
until about 48 hours prior, but the signal for precipitation is
consistent from the last several guidance suites. WPC Cluster
Analysis is supportive of precipitation in the northern CWA: every
cluster has a swath of precipitation for Monday in that area. With
attention being paid to the near-term concerns, the NBM PoPs were
left in, but are likely too low. Temperatures will certainly be cold
enough for snow where it precipitates, and the very cold air aloft
will likely lead to higher SLRs. Right now, the best chances for
snow are north of I-70, where the forcing will pass through.
After Monday/Monday night, the main story remains the very cold air,
but no robust signals for precipitation exist. Again, zonal flow
will rarely show its hand for precipitation until the event gets
closer, but there are some signals at some more amplification of the
upper-level pattern that may break us free of the longwave trough
late next week. While PoPs after Monday night remain low, quick
rounds of precipitation are not off the table through Friday.
MRB
&&
.AVIATION... (For the 00z TAFs through 00z Saturday Evening)
Issued at 544 PM CST Fri Feb 5 2021
VFR flight conditions are expected to prevail across the forecast
area through Saturday morning. Some very light snow/flurries have
developed over a small part of eastern Missouri, north of the St.
Louis Metro area, and stretching into south central Illinois. Air
near the surface is very dry, so this light precipitation may not
even reach the ground. The next round of precipitation to affect
the region will move in to central Missouri during the late
morning or early afternoon, and spread east over the entire area
by mid to late afternoon. Snow will bring MVFR ceilings and MVFR
to IFR visibilities which will persist through the end of the
forecast period.
Carney
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory from 9 AM to 9 PM CST Saturday for
Audrain MO-Boone MO-Callaway MO-Cole MO-Gasconade MO-Knox
MO-Lewis MO-Lincoln MO-Marion MO-Moniteau MO-Monroe MO-
Montgomery MO-Osage MO-Pike MO-Ralls MO-Shelby MO-Warren MO.
IL...Winter Weather Advisory from 9 AM to 9 PM CST Saturday for Adams
IL-Brown IL-Calhoun IL-Greene IL-Jersey IL-Macoupin IL-
Montgomery IL-Pike IL.
&&
$$
WFO LSX