Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/27/21
AREA FORECAST DISCUSSION
National Weather Service Albany NY
933 PM EST Fri Feb 26 2021
.SYNOPSIS...
High pressure will shift off the New England Coast tonight. A
low pressure system moving across the Great Lakes Region and a
warm front will bring some snow and light mixed precipitation
transitioning to rain on Saturday. Milder weather is expected on
the weekend, as another disturbance will bring some light
precipitation back into the region to close the weekend.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 933 PM EST....IR satellite imagery and surface
observations show high clouds have most of the area. There has
even been some breaks (especially for the western Adirondacks
and Mohawk Valley) at times as well. With the fairly thin high
cloud cover and light/calm winds, temps have been falling rather
quickly this evening. Most of the region has already fallen
below freezing, with only the mid Hudson valley still remaining
in the 30s. Temps have already fallen into the teens for parts
of the Adirondacks thanks to the breaks in the clouds as well.
Temps will continue to fall over the next few hours, as clouds
remain thin and winds stay light. All areas will be falling
below freezing, with mins ranging from the mid teens to the
upper 20s. Clouds will start increasing in thickness and
coverage after about 2 or 3 AM.
Although most of the overnight should be precip free, 3km HRRR
suggest some light steady snow should reach most areas by
daybreak with some dustings possible in the Mohawk and Hudson
Valleys to Berkshires and NW CT. Up to an inch is possible
across the higher terrain of the southern Adirondacks, eastern
Catskills and southern Green Mountains. While the main batch of
precip looks to continue up from the south towards the
Catskills, Mid Hudson Valley and Taconics, there should be
another area of precip that lifts towards the Mohawk Valley and
Adirondacks from central NY.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Precipitation transitions to rain through Saturday morning but
an additional inch or two of snow is possible along with a brief
mix with sleet in the southern Adirondacks before changing to
rain there. Strong warm advection and isentropic lift will bring
widespread rain to the region, exiting later Saturday
afternoon. Highs Saturday in the 40s with around 40 southern
Adirondacks and southern Green Mountains.
Cold advection quite weak behind the system and the next upper
energy will begin its approach from the west southwest later
Saturday night. There should be considerable cloud cover through
the night but some breaks in the clouds are possible at times,
not enough to help temperatures fall much. Although,
temperatures should fall to around or below freezing by Sunday
morning.
The next upper impulse and shot of enhanced warm advection and
isentropic lift arrives after daybreak Sunday with mixed
precipitation in the eastern Catskills, Schoharie Valley and
southern Adirondacks. Once again, any mixed precipitation
changes to rain as rain expands over the entire region. Highs in
the 40s with around 40 higher terrain.
Precipitation decreases in coverage to just showers Sunday
night, then a strong northern stream upper impulse tracks east
and southeast brushing northern parts of the region and northern
New England. Rapid cooling aloft ahead of a strong low level
thermal gradient along a low level cold front will result in
some convective instability. There could be some snow
shower/squall activity as the snow squall parameter in sources
of guidance suggests that possibility. Highs Monday in the
lower to mid 40s but 30s in higher terrain.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Potent upper level shortwave will be moving across Upstate New York
and into New England on Monday evening. A band of snow showers and
embedded squalls are expected with the passage of this Arctic
boundary, especially for areas north of the Mohawk Valley and I-90.
Best chance will be during the evening hours, with skies expected to
clear out after midnight.
Behind this strong cold front, much colder air will work into the
region, along with gusty northwest winds. Temps will fall into the
single digits and teens for Monday night and only rise into the 20s
for Tuesday. With the gusty winds over 30 mph at times, this will
result in low wind chills, especially for the higher elevations,
where wind chills around -5 to -15 are possible. Otherwise, it
should be dry with a mostly sunny sky for Tuesday, although the
gusty winds will mitigate any benefit of the early March sunshine.
The winds should start to diminish for Tuesday night into Wednesday
as high pressure builds towards the area. Some models do show a
southern stream storm around the mid-week, but most guidance shows
this storm (if at all) remaining south of the region. As a result,
it should be dry for the mid to latter portion of the week, with
daytime temps in the mid 30s to mid 40s and overnight lows in the
teens and 20s along with a partly cloudy sky.
&&
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Flying conditions are currently VFR with light/calm winds and
bkn-ovc high level clouds in place. These high clouds will be in
place for most of the night, with ceilings finally lowering for
the late night hours (after 3 AM). Some light snow will start to
spread south to north across the area around daybreak, although
snow should be brief (only a few hours in duration), as a strong
southerly flow will allow precip to mix with and changeover to
plain rain as temps rise above freezing. Within snowfall, flying
conditions should be IFR for visibility, but will improve to
MVFR as precip mix with and changes over to rain.
Although winds should be light for the overnight, southerly
winds will pick up around sunrise and be 10 to 15 kts through
the morning hours, with a few higher gusts possible. LLWS will
be possible, as 2 kft winds will be around 40 kts from a
southeasterly direction for the morning hours.
After precip changes to plain rain, it will start to taper off
for the early afternoon hours from south to north. However,
lingering low level moisture will keep MVFR cigs in place for
most of the day. Southerly winds may start to become more w-sw
by late in the day, but will continue to generally be around 10
kts for all sites.
Outlook...
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: Moderate Operational Impact. Chance of RA.
Sunday Night: Moderate Operational Impact. Chance of RA.
Monday: Low Operational Impact. Slight Chance of SHRA.
Monday Night: Moderate Operational Impact. Windy With Gusts To 33 kts. Chance of SHSN.
Tuesday: Low Operational Impact. Breezy. NO SIG WX.
Tuesday Night: No Operational Impact. NO SIG WX.
Wednesday: Low Operational Impact. Slight Chance of SHRA...SHSN.
&&
.HYDROLOGY...
No major hydrologic issues are foreseen through the middle of
next week.
Some melting and sublimation of the snowpack in the valleys is
expected during the day time over the next several days.
NERFC forecasts show minor up and down changes in river flows
due to the diurnal freeze/thaw cycle. River ice is not expected
to break up over the next several days.
Mainly light snow showers are expected this morning across the
southern Adirondacks and the western Mohawk Valley. Additional
light snow and rain is possible Saturday with temperatures
rising above normal to close the weekend. Some snow melt and
ripening of the snow pack is possible. Total QPF from the
Saturday system will range from a tenth to third of an inch with
some locally higher amounts over the southern Adirondacks,
eastern Catskills, and the western New England higher terrain.
Another system will bring light precipitation to close the
weekend mainly in the form of rain.
A strong cold front with snow showers is expected to move
through on Mon-Mon night with below normal temperatures
possible Tuesday before rising to near normal levels for the mid
week.
For details on specific area rivers and lakes, including observed
and forecast river stages and lake elevations, please visit the
Advanced Hydrologic Prediction Service /AHPS/ graphs on our
website.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.
&&
$$
SYNOPSIS...NAS
NEAR TERM...Frugis/NAS
SHORT TERM...NAS
LONG TERM...Frugis
AVIATION...Frugis
HYDROLOGY...NAS
Area Forecast Discussion
National Weather Service Binghamton NY
958 PM EST Fri Feb 26 2021
.SYNOPSIS...
An area of low pressure will track through the region tomorrow
bringing a mix of rain and snow showers. Another system follows
on it`s heels Sunday with another chance for precipitation.
Cooler with high pressure building in early next week.
&&
.NEAR TERM /THROUGH SATURDAY NIGHT/...
955 PM Update...
Added the mention of freezing rain as it is looking a little
more likely based on latest RAP forecast soundings. Will still
hold off on an advisory for now, but there is some concern that
a short fuse winter weather advisory may be needed for a few
hours tomorrow morning until temperatures climb above freezing.
Dew points are still well into the mid teens across the area, so
some evaporational cooling should occur at the onset of
precipitation. Also, road surface temperatures are just below
freezing, and if some light snow is to occur first, as is
currently forecast, the freezing rain will have less of an
impact on road conditions. Will add mention into the HWO for now
about the possibility of slick travel conditions for tomorrow
morning.
Previous Discussion...
Low pressure moves into our area overnight. Enough moisture and
lift look present to develop some precipitation. However, the
most abundant QPF over 1/10th of an inch looks to be confined
to the higher elevations in the western Catskills, Wyoming
valley and northern Oneida county where the terrain can enhance
precipitation. In these locations snow of an inch or two is
possible.
Soundings look fairly uniform throughout warming
fairly quickly through the morning hours Saturday. So while
precipitation should start as snow showers or light snow a
transition to rain should occur. Some sleet may mix in during
the transition but this or any freezing rain looks rather brief
at this time. Temperatures look to fall to around or just below
freezing but rise into the 40`s tomorrow. Once the low pressure
system passes to the east most of the rain showers should come
to an end in the afternoon hours.
Our region will be in between low pressure systems so while
a break in the precipitation is expected clouds will linger.
Temperatures only fall back to around 30 due to the cloud cover.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Main concerns in the short term are focused on the potential for a
wintry mix Sunday morning then rain in the afternoon through Sunday
night before the cold air sweeps back in on Monday with more
scattered snow showers through the day.
Upper level ridge across much of the Northeast US will allow for
early morning quiet weather on Sunday, but a passing upper low in
the Great Lakes moving to the e/ne will combine with a weak surface
inflection over the Appalachians moving newd into the mid Atlantic
region through most of the day Sunday. These two features will usher
in a broad area of large scale lift over the region amidst an
initially dry air mass, which may allow the precipitation to take a
little bit longer to reach the ground. However, a faint ribbon of
deep moisture will advect in later in the day and act to increase
the potential for precipitation in the afternoon.
The type of precipitation will be a challenge early in the day
Sunday with surface temperatures initially below freezing but
quickly warming into the mid to upper 30s by the late morning hours.
There will likely be some light snow mixing with sleet around or
just after sunrise moving in from south to north, but amounts should
be limited to less than a half inch. The precipitation will change
to all rain before noon, and the rain showers will likely persist
through the afternoon. Rainfall amounts will likely be limited to a
third of an inch or less in ne PA, the souther tier of NY and into
the Catskills. Even lesser amounts are expected further north into
the Finger Lakes.
As the upper low and surface feature to the south lift off to the
northeast, they slowly phase together and a colder air mass wraps
around the back side of the system, eventually pushing into wrn NY
by late Sunday night into Monday morning. Most of the guidance is
hinting at an initial cold front moving through Monday morning which
will be quite dry and relatively mild with the thermal gradient.
This may kick off a few snow showers through the morning, but the
secondary cold front...of an Arctic nature...winds up and starts to
push from the central Great Lakes into wrn NY/ern Great Lakes by
late Monday afternoon. There is expected to be a short wave
associated with this very cold air mass, and may generate some snow
squalls and eventually a period of lake effect showers downstream of
Lake Ontario. The axis of the coldest air will not arrive until
later Monday night, but the effects will begin to be felt just
before sunset.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
There is expected to be a period of very cold air and potentially
significant lake effect snow Monday night through Tuesday afternoon.
The LES will get kick started by a short wave embedded within a
very cold air mass, with 850mb temperatures -18 to -14 deg C. A
fairly steady northwest flow and favorable temperatures, along
with an open Lake Ontario will allow for the potential of lake
effect snow southeast of Lake Ontario into central NY Monday
evening through Tuesday morning. The 850mb ridge axis will shift
through the area Tuesday afternoon and should allow the winds
to back to the w/sw and bring any lingering lake snow showers to
an end.
A few days/nights of cold temperatures are expected early this week
with morning lows in the single digits and teens Monday and Tuesday
and afternoon highs in the 20s to near 30 on Tuesday.
Ridge of high pressure builds in briefly Tuesday night into Wed
morning, which will allow for a period of quiet but cold conditions.
However, this ridge will also advect in a slightly warmer air mass
on Wednesday with highs topping out in the upper 30s and lower 40s.
The pattern becomes a little more quiet and temperatures are more
seasonal into the latter half of the week with highs in the 30s near
40 and overnight lows in the 20s.
&&
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
VFR through the evening. However, ceilings and visibilities
drop around overnight with the arrival of light snow/rain and
possibly some brief freezing rain. The steadier precipitation
arrives during the early morning and could see some IFR
restrictions toward sunrise at most TAF sites. Exact timing of
when and how fast the restrictions move in are still somewhat
uncertain.
High probability of LLWS forming overnight as well at all
terminals and persisting until at least late Saturday morning.
Temperatures warm tomorrow afternoon and the warm/moist airmass
over the snow on the ground may lead to fog and and drizzle with
further restrictions into the evening possible.
Outlook...
Saturday night... Lingering restrictions possible.
Sunday...Occasional restrictions possible in scattered rain
showers.
Monday...Restrictions possible in rain and snow showers,
especially the Central NY terminals.
Tuesday and Wednesday... Brief restrictions can`t be ruled out
with a few rain and snow showers.
&&
.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...None.
&&
$$
SYNOPSIS...MWG
NEAR TERM...MPK/MWG
SHORT TERM...BJT
LONG TERM...BJT
AVIATION...MPK
Area Forecast Discussion
National Weather Service Green Bay WI
511 PM CST Fri Feb 26 2021
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Saturday
Issued at 238 PM CST Fri Feb 26 2021
The latest RAP analysis and satellite/radar imagery show high
pressure centered off the east coast of the U.S., and a cold front
positioned over the eastern Dakotas early this afternoon. The cold
front is tracking east with cloud bases mostly above 9kft and
little to no precip along it. 12z soundings from MPX and GRB tell
the story, with very dry air through large portions of the column.
Pwats range from near normal at MPX and around the 10 percentile
at GRB. Richer Gulf moisture is heading north but still a ways
away over southern Illinois and Indiana. Forecast concerns mostly
revolve around the potential for light wintry precip tonight.
Tonight...Clouds will be on the increase tonight as a period of
ascent arrives ahead of shortwave energy and the weak cold front.
Forecast soundings indicate that most of the ascent goes towards
saturating the atmosphere, and ascent exits before the column has
a chance to fully saturate. As a result, have backed off precip
chances significantly across north-central WI, but left a slight
chance in case spotty light snow develops. Chances are a little
higher over east-central WI around or shortly after midnight
where the northwest fringe of the deeper Gulf moisture grazes part
of the area. Temps look warm enough for spotty rain/freezing
rain/light snow but can`t see much in the way of accumulations.
Stayed on the warmer side of guidance compared to the national
blend, with lows ranging from the middle 20s to low 30s.
Saturday...Trailing shortwave energy will pass overhead during the
morning, but moisture looks even less than overnight and no
additional precip chances are expected. But clouds will likely
hang around for part of the morning before an influx of dry air
and subsidence leads to clearing skies for the afternoon. Temps
will remain warm and range from the lower to middle 40s.
.LONG TERM...Saturday Night Through Friday
Issued at 238 PM CST Fri Feb 26 2021
The main focus for the extended forecast will be the fast moving
shortwave trough accompanied by a fairly vigorous surface low
Sunday morning.
Saturday night through Sunday...A fairly robust and fast moving
system remains set to pass through the region late Saturday night
through Sunday morning. P-type will vary across the area with this
system. For the north, temperatures at the surface and aloft
should suffice to keep all precipitation as snow. Further south
and east, a wintry mix becomes possible as surface temps dip below
freezing but the 925-850mb layers remain just above freezing. How
much icing and sleet develop in these areas will vary depending
on if we can keep ice crystals in the clouds aloft. the mixed and
icing areas will likely be fairly narrow between the areas of snow
and rain. Some areas near the Fox Valley and lakeshore may also
just see rain with this system. As far as snow goes, most areas
will still have a shot of seeing some snow, but accumulations
across the north may be heavier as the shortwave provides a good
amount of lift through the dendritic growth zone. Brought up
amounts to around 2-4 inches for this forecast period for the
heaviest band of snow. In short, we`re set for a fairly sharp
gradient of snowfall from heavy to light to none across our area,
with a small window in there for some wintry mix and light icing.
Much will depend on the exact track of the system in the next
couple days. Behind this, winds will pick up Sunday afternoon, but
given the wet nature of the snow that morning, it`s unlikely
we`ll see any blowing/drifting snow concerns.
Rest of the forecast...There will be another shot at some light
snow for the far north as another shortwave comes southwards from
Canada early on Monday. Intensity will likely be somewhat
limited, as winds will not be conducive to much lake enhancement.
Still, there will be a window to accumulate up to an inch of snow
with this system. Winds will remain gusty during this period,
which may create a few areas of drifting snow on Monday. behind
this, a fairly broad but shallow upper ridge will move in to the
region, keeping us dry through the midweek. Another vigorous
system is possible towards the end of next week, but is currently
projected to pass south of the area.
Temperatures will dip briefly after the weekend, as CAA behind
the surface low on Sunday drops highs back into the upper teens to
upper 20s. Temperatures then recover for the middle of next week,
with highs pushing back into the lower to middle 40s as Pacific
air arrives from the west.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 511 PM CST Fri Feb 26 2021
An upper level disturbance will move across the area tonight and
produce middle clouds and maybe some sprinkles or snow flurries at
MTW and SBM. VFR conditions will continue Saturday.
A low pressure system will bring increasing clouds and some snow
or rain to the region late Saturday night into Sunday. Several
inches of wet snow and IFR conditions are likely north of a AUW to
AIG to IMT line.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM.....MPC
LONG TERM......Uhlmann
AVIATION.......RDM
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
558 PM CST Fri Feb 26 2021
.UPDATE...
Issued at 534 PM CST Fri Feb 26 2021
Updated to include 00z aviation discussion below.
&&
.SHORT TERM...(This evening through Sunday)
Issued at 253 PM CST Fri Feb 26 2021
Primary concern is the system which will move through the region
Saturday night into Sunday, bringing a band of accumulating snow
through as it does so. Until then things look fairly benign and mild.
There is the possibility of a few sprinkles with the surface and
upper level shortwave trough currently moving across the area.
Otherwise, look for decreasing clouds later tonight with winds
decreasing from now through that time frame. Saturday looks to be
mild across the area, with some increase in clouds during the
afternoon. Things get much more interesting Saturday night as a quick
moving shortwave trough and upper level jet streak move northeast
from the central Plains across our area. Guidance is in good
agreement on the development of a narrow axis of moderate to strong
frontogenesis beneath an area of upper level divergence with this
feature. Cross sections suggest that the frontogenesis will be
steeply tilted, which underscores why the axis of heavier
precipitation will be quite narrow (on the order of a county or two).
Above the frontogenesis zone the theta-e lapse rates look to be near
zero with an area of negative EPV (suggesting that although there
may not be upright instability some symmetric instability will be
present). The reduced stability will significantly enhance vertical
motion, helping to squeeze out as much precipitation as will be
possible in the 3-6 hour window of good forcing. The guidance
continues to show some differences in exactly where the frontogenesis
will setup, making it tough to forecast explicit snowfall amounts.
The HRRR extensions from 12Z and 18Z are farther north with things
than most of the other guidance (including the GEFS and EPS ensemble
systems), and have more precipitation (max at around 1" QPF) than
other guidance. However, as more CAMs become available, it will
certainly be worth watching how they handle this system. At this
point the forecast is likely less than what will eventually be the
maximum values, and instead has somewhat lower values spread over a
larger area to account for the uncertainty. Subsequent forecasts
should be able to better refine the maximum amounts and tighten the
forecast gradients to the north and south of that. The southern
gradient in snowfall looks to be particularly tight due to both lower
precipitation amounts and some rain mixing in with the snow for a
longer period (for most locations, any initial rain should change to
snow fairly quickly). The northern gradient in snowfall will be a bit
more baggy with some frontogenesis higher up (600-500 mb) extending
farther to the north/west (but the stability will be greater there
and the precipitation will be less, hence lower totals).
.LONG TERM...(Sunday night through Friday)
Issued at 253 PM CST Fri Feb 26 2021
During Sunday night, a second cold frontal passage is expected as a
northwesterly upper-level jetstreak moves from the Canadian Prairie
to the Northern Plains. This feature will be embedded within the
backside of the trough that brought precipitation earlier this
weekend. Guidance squeezes out enough QPF along the front (from the
marginal post-trough moisture) that a dusting to an inch of snow is
possible across northern MN into northwest WI. Lift and low-level
saturation decrease to the south, however some snowflakes cannot be
ruled out across our northern to eastern CWA. Thus, have introduced
slight chance PoPs in these regions Sunday night. Temperatures Sunday
night into Monday night will also decrease as a brief shot of cold,
arctic air follows the cold front. How cold temperatures get is
another question. The ECMWF and EPS mean show lows Monday morning
around 10 near Brainerd to mid teens south. Meanwhile, the GFS is
much colder (well below the 25th percentile of the EPS) with single
digits for most of the CWA and below zero temperatures in western MN.
Regarding Mondays highs, spread within the guidance only
increases. Overall, highs have been trending colder with the ECMWF,
EPS, and GEFS showing MSP only reaching the mid-20s. Meanwhile, the
GFS has been a steady cold outlier with single digits to mid-teens
forecast. It seems less likely that we get as cold as the GFS
suggests, however, it is concerning that other models are trending
that direction. Have opted to keep current NBM highs and lows Sunday
night through Monday night, as current forecast temperatures are
between the 25th and 50th percentile of the ensemble guidance. This
combined with model trends supports that leaning towards colder
temperatures are likely a safer bet. A split, zonal flow regime will
take over the CONUS after Monday, resulting in dry conditions for the
MPX CWA the rest of the period. On Tuesday morning, enhanced,
southwesterly 850 mb flow shifts eastward into the Northern Plains.
This will allow for strong WAA, building slight ridging over the
central US. Highs Tuesday are forecast in the low 40s, with upper 40s
possible in southwest MN. Winds Tuesday afternoon could also be
breezy from the enhanced low-level flow. Thus, have increased
sustained winds and gusts Tuesday to highlight this possibility. The
upper-level ridging will shift east Tuesday night but the warmer air
remains. Temperatures are forecast to slowly climb into the mid 40s
area wide (with slightly warmer temperatures on the Buffalo Ridge) by
Thursday. Looking ahead, it appears even warmer weather is possible
by late next week, as the Climate Prediction Center highlights a good
chance of above normal temperatures across the central US in their
6-10 and 8-14 Day Outlooks.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 534 PM CST Fri Feb 26 2021
Winds will settle down this evening, dropping to under 10kt by
roughly 03z-04z. Winds will then remain under 10kt throughout this
TAF set but undergo a directional change, eventually ending up N to
NE 24 hours from this time. VFR ceilings to start, generally in the
070-120 range, overnight through much of tomorrow. Lower ceilings
into the MVFR range will start to be a problem late afternoon into
the evening for sites along and north of I-94. No precipitation
expected through this TAF duration, but chances for -SN in southern
MN increase after 28/00z.
KMSP...No weather concerns through Saturday afternoon. Going into
Saturday evening, ceilings are likely to drop into the MVFR range,
and potentially sub-1700ft but not until after the evening rush.
Chances for -SN are too low for inclusion at this point but chances
increase significantly after 28/06z.
/OUTLOOK FOR KMSP/
Sun...MVFR/SN early, then VFR. Wind NW 10-15kts.
Mon...VFR. Wind NW 5-10kts becoming SW late.
Tue...VFR. Wind S 15G25kt.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
UPDATE...JPC
SHORT TERM...
LONG TERM...CTG
AVIATION...JPC
Area Forecast Discussion
National Weather Service Pueblo CO
314 PM MST Fri Feb 26 2021
.SHORT TERM...(This evening through Saturday)
Issued at 239 PM MST Fri Feb 26 2021
...Increasing Fire Danger on the Plains Saturday Afternoon...
Currently...windy over the higher terrain today, with occasional
gusts over 40 kts through the passes of the central mountains, and
30-40 kts over the upper Arkansas Valley. Winds on the plains have
gusted 20-30 kts at times this afternoon, though areas around
Colorado Springs have seen some periods of light ely flow as a weak
rotor circulation has apparently developed downstream of the high
terrain. Winds lessen overnight at lower elevations, though higher
exposed terrain will remain breezy into Sat morning. Upper wave
passes quickly through the nrn Rockies into the nrn Plains tonight
and Saturday, pushing a cold front south through the area Sat
afternoon. Just enough moisture and forcing for some snow showers
over mainly the Continental Divide from late tonight through Sat,
with some light (1-3 inch) accums likely. While snow will be light,
fairly strong winds accompanying the snowfall may produce some
periods of low visibility and difficult travel across high mountain
passes from Monarch Pass northward through the day. Over lower
elevations, strong wly winds will develop quickly in the morning,
then gradually turn more N-NW while remaining gusty in the
afternoon. RH falls off enough over the far sern plains to produce
Red Flag Conditions near the KS border for few hrs, so will hoist a
highlight essentially east of a La Junta to Kim line. Winds will be
strong farther west as well, though RH may stay just high enough to
avoid a warning as temps cool slightly behind the front, however
fire danger will still be high. Max temps tricky tomorrow with cold
front and cold advection in the afternoon, though NBM looked
slightly too cool given good mixing, and nudged maxes up a few degf
toward warmer MOS guidance.
.LONG TERM...(Saturday night through Friday)
Issued at 239 PM MST Fri Feb 26 2021
Current model guidance is in decent agreement through Monday, but
beyond that solutions diverge greatly, lowering forecast confidence
and making ensembles much less useful.
Saturday night through Monday...The upper trough over the area is
expected to send a low south of the area, likely too south to really
impact our area as far as precipitation goes. A brief, light dusting
over the mountains cannot be ruled out entirely, but any meaningful
accumulation is very unlikely at this time. High temperatures will
cool down a bit from the previous few days, but should still be near
seasonal norms, with high 30s-40s expected over the plains and 20s-
30s over the higher terrain. As the low continues to translate
eastward, Monday is expected to remain dry, with high temperatures
expected to rebound into the 40s-50s.
Tuesday and beyond...The GFS and ECMWF have completely different
forecasts through the rest of the extended period. The GFS does
things a little more dramatically, showing a brief period of upper
ridging on Tuesday and Wednesday followed by a potent upper low that
impacts the area into Thursday, which would give us a healthy dose
of snowfall before another dry period leading into next weekend. The
low was also shown to be wrapped up, with very strong northerly
winds (70 plus knots at 700mb) over the plains. The EC shows mainly
calm, zonal flow over the area Wednesday before sending a closed-off
low into Texas Thursday and Friday. This would bring some
precipitation to the southern part of our area, but it is unclear
how much.
While the models have begun to agree slightly more as we have moved
forward in time, the differences in the speed and structure of these
potential systems still leaves too much difference to decide on one
over the other. As a result, have mainly stuck with the blended
forecast for that time period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 239 PM MST Fri Feb 26 2021
VFR conditions expected the next 24 hrs at all taf sites. W-NW winds
have been slow to increase this afternoon at KCOS and KALS, though
latest HRRR suggests at least a couple hrs of 15g25kts possible into
early evening before speeds lessen after sunset. On Sat, W-SW winds
pick up quickly in the morning, with gusts 25-30 kts into the
afternoon at all sites. Cold front passes through KCOS and KPUB
after 21z, with flow becoming more N-NW into Sat evening.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 5 PM MST Saturday for COZ233>237.
&&
$$
SHORT TERM...PETERSEN
LONG TERM...GARBEROGLIO
AVIATION...PETERSEN
Area Forecast Discussion
National Weather Service Shreveport LA
959 PM CST Fri Feb 26 2021
.UPDATE...
To add patchy fog to the overnight forecast and into mid morning.
&&
.SHORT TERM...
Cloudy and cool in the north with mostly lower 50s and a tight
T/Td spread, giving way to light fog in many locales at 10pm.
Half mile now in Idabel is the worse so far with quarter mile in
the past. The cool air will hang in place and with temps easing
down toward daybreak, thus it is a given that the fog will grow
thicker. Perhaps even requiring an advisory in the predawn to
daybreak hours.
So expect some fog, but any rainfall which is a good chance over
top of this frontal boundary, that would help mix the air a bit
and could hold visibilites above criteria, so we will defer for
another few hours at least if possible. The HRRR does show
enhancement in the coverage of light showers during the next 6-12
hours as this boundary lifts to our N during midday on Saturday.
This could push the mercury toward 65 or so for even DeQueen which
will scour last in the valley. Highs near 80 in our southern tier
are reasonable considering we are still near 70 down there now
with the best shot at some free vitamin D via the sun. /24/
&&
.PREV DISCUSSION... /issued 611 PM CST Fri Feb 26 2021/
AVIATION...
For the ArkLaTex terminals, a stationary front lies along I-20
from KTYR to KSHV to KELD. Current obs IFR for KTXK and all
guidance indicating LIFR will dvlp on cold side soon and warm
side before daybreak. L/V winds to N will keep overnight, while
gusts from KLFK to KMLU are subsiding now will prevail S5-10KT
overnight. This boundary will lift out to N as a warm front on
Sat with some DZ and -RA 06-15Z along with fog. Gradient ahead of
next impulse improves late day with ra early on Sun from NW. /24/
PREV DISCUSSION... /issued 335 PM CST Fri Feb 26 2021/
SHORT TERM.../Tonight through Saturday Night/
Across the CONUS, a shortwave trough over the Northern Rockies
continues to dive ESE towards the Central Plains. Ahead of the
trough, most of the country remains in southwest flow aloft,
including our region. Last night`s shortwave that produced heavy
rain and severe hail across the northern half of the region,
continues to push eastward into the SE CONUS, with some lingering
shower activity between the I-20 and I-30 corridor in wake of the
system near a theta-e ridge. At the same time, the frontal boundary
that moved through the region a couple days ago continues to slowly
lift northward as a warm front. Its currently located along a line
from near Rusk Texas to Mansfield Louisiana to near Monroe
Louisiana. In wake of this boundary, clouds have thinned out and
warm air advection has allowed temps to climb into the mid to upper
70s. North of the boundary, a broad stratus deck remains across the
region, with some fog just north of the advancing boundary. Temps
in this region have remained steady in the low to mid 50s.
Not expecting much change for the remainder of the afternoon as
short-term progs only advance the warm front a little to the north
through the overnight period. However, showers look to continue near
the theta-e boundary along with some possible isolated
shower/thunderstorm development along the warm front. Expect
overnight lows in the upper 50s to lower 60s south of the front,
with mid 40s to low 50s across the remainder of the region.
By Saturday, the shortwave in the northern Rockies will kick out
into the Central Plains with another strengthening upper trough on
its heels diving southward into the Great Basin Region. In
response, southerly winds across the south-central CONUS will
increase, and the warm front will start to advance northward
during the day. Impulses will move across the region along the
flow, providing enough lift for precip to develop. The best chance
for convection will likely be north of the I-20 corridor near the
advancing frontal boundary. Expect much warmer temperatures, as
highs in wake of the front will climb into the 70s to near 80
degrees in some locations. /20/
LONG TERM.../Sunday through Friday/
Longwave troughing will dive SE through the Great Basin and into the
Desert SW Sunday, before eventually closing off Sunday night over
Srn NM. This troughing pattern will maintain deep SW flow over the
region late this weekend through at least the first half of the new
work week, and thus the elevated subtropical moisture feed will
continue from Cntrl TX through the Lower/Mid MS Valley into the OH
Valley. At the sfc, a shallow cold front remains progged to drift SE
into the region by midday Sunday/Sunday afternoon, with PVA embedded
in the dirty SW flow contributing to an increase in convection
development along/ahead of the front along a SW to NE oriented theta-
e axis ahead of the front. Have maintained consistency with t he
previous forecast with pops increasing to categorical Sunday
afternoon across much of NE TX/SW AR/NW LA, but did taper pops back
a bit across the Srn zones which will be farther removed from the
axis of greater large scale ascent and near and just ahead of the
front. With the deep lyr flow fairly unidirectional along the
frontal sfc, convergence isn`t progged to be particularly deep, even
as SBCapes rise to near 1000 J/Kg across the warm sector ahead of
the front. Lapse rates aloft are not impressive either, but rather
am expecting convection to remain along and behind the front, with
the potential for additional heavy rains to fall across the already
saturated areas of NE TX/SW AR Sunday afternoon/evening, before
eventually spreading SE into the Lower E TX/N LA/SCntrl AR from the
late afternoon through the overnight hours. Attm, minor flooding of
low lying, poor drainage areas is possible across NE TX/SW AR where
widespread rainfall amounts of 1.5-3.00+ inches fell since Thursday
afternoon/evening, although areas to the S should be able to take
the rainfall. Very warm/humid conditions are expected Sunday
afternoon ahead of the front over Lower E TX/N LA, where max temps
were bumped up a couple degrees over the cooler NBM, with the front
expected to shift S through the region Sunday night, exiting the
area before daybreak Monday.
The post-frontal rains will continue over much of the area Monday as
elevated isentropic ascent in the SW flow persists. However, the
aforementioned closed low over the Desert SW remains progged to
slowly shift E into the Srn Plains through Monday night, although
considerable timing discrepancies still exist with the slow
ECMWF/Canadian slower than the more progressive GFS entering the Red
River Valley Monday afternoon, with the latter two progs about 9-12
hrs slower. Prefer the slower more consistent solutions, with likely
pops maintained over much of the area Monday night, before dry
slotting undercutting the opening trough tapering the SHRA off from
W to E Tuesday, while drier low level air advects S ahead of sfc
ridging from the Ozarks into the Mid MS Valley. Temps should return
back to near seasonal norms by Wednesday with increased insolation,
with the outlier GFS still suggesting another developing closed low
entering the TX/OK panhandles Thursday, nearly 24 hrs earlier than
the ECMWF/Canadian. The NBM continues to trend closer to the GFS,
with slight chance pops over much of the area Wednesday night
through Friday, but did delay the reintroduction of pops a bit until
Wednesday night, but confidence remains low with this solution as we
round out the work week. /15/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 55 75 65 75 / 30 40 20 80
MLU 60 76 67 77 / 40 50 20 50
DEQ 46 65 57 68 / 20 80 70 80
TXK 51 68 62 70 / 30 60 50 80
ELD 51 70 61 74 / 50 50 40 80
TYR 54 73 64 73 / 20 60 20 80
GGG 54 73 64 75 / 30 50 20 80
LFK 62 78 65 77 / 20 30 10 50
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
24/20/15
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
844 PM MST Fri Feb 26 2021
.UPDATE...
Issued at 834 PM MST Fri Feb 26 2021
00z KUNR sounding showed boundary layer mixed to 512mb with a bit
of MUCAPE and thus, the isolated virga/-SHRASN early this
afternoon/evening. Looking at water vapour presentation, main
shortwave of interest over east central ID and it looks well-
defined.
00z guidance indicates system has slowed even more and thus,
onset of betters snows will likely be later in the afternoon.
Compact closed 700-500mb circulation will track across central WY
and then move along the SD/NE border Saturday night. Composite of
forcing/QPF placement suggests best chance of moderate snow
along/just south of I-90 corridor. Headlines for the Black Hills
looks good with possible extension needed to west and then
east/southeast into south central SD. If narrow deformation zone
links up with 800-600mb frontogenesis, steep lapse rates, and
upslope flow, a stripe of heavy snow could develop Saturday night.
Will allow all 00z guidance, especially the probabilistic
guidance, to come in before making impactful forecast changes.
Stay tuned overnight.
&&
.DISCUSSION...(This Evening Through Friday)
Issued at 200 PM MST Fri Feb 26 2021
Upper level analysis shows a trough over the western/central
CONUS, with ridging over the east. Weak shortwave energy crossing
over the Rockies, along with some midlevel moisture, is helping to
produce a few rain/snow showers across portions of the CWA.
Surface map depicts a trough over the northern plains. Under
partly cloudy skies, winds are westerly 10-20 kts, and
temperatures are in the 30s and 40s.
Today`s shortwave will exit the region tonight, and with mostly
clear skies, temperatures will dip into the teens.
The next, stronger, shortwave will approach the region early
Saturday. Deterministic models are still not in full agreement on
this system; RAP/NAM/GFS develop a closed 700 mb low that slides
across the CWA (RAP farthest north), while the ECMWF/Canadian keep
the wave open. Models are in agreement of a band of precipitation
developing somewhere across western SD. Wet-bulb zero heights
suggest mainly snow can be expected with this system, although some
rain could mix in across the warmer south central SD area. Surface
temperatures near to above freezing could decrease initial snow
accumulation, but evaporative cooling once precip begins could
negate that, along with the high snowfall rates. With deep
frontogenesis, strong positive vorticity advection, prolific lift
within the dendritic growth zone, steep lapse rates, and plentiful
moisture associated with this low, the potential exists for a band
with high snowfall rates and moderate to heavy snowfall. Most
solutions, including most of the hi-res models, place the band
across the southern half of our CWA. The previous runs of the
RAP/EC/HRRR had a more northerly track, but the 12Z RAP/EC and 18Z
HRRR runs have shifted south a bit, aligning more with the other
models. Another consideration is the possibility of upslope-
enhanced snow. Some upslope-enhancement will be possible over the
typical northern Black Hills area, and also across the
northern/eastern foothills, depending on the track of the low and
the extent to which northeasterly winds develop across the
western SD plains. Froude number is near to above one for the
northern and eastern Black Hills Saturday afternoon during the
period of peak moisture.
Main changes to the forecast include delaying the onset of
precipitation Saturday, according to model guidance. Also adjusted
winds to have a slightly more easterly component, consistent with
the upslope possibility along the eastern foothills, and increased
QPF a tad there accordingly. Bumped up wind speeds Saturday evening
on the backside of the low. Thinking the highest snow amounts will
be over the northern Black Hills and northern/northeastern
foothills, with 3-5 inches expected there. Will issue an advisory
for these areas, leaving out the Rapid City zone for now. Generally
1 to 3 inches of snow is expected from southwest to south central
SD, with locally higher amounts possible in banding. Models indicate
a local maximum around the Pine Ridge area, but accumulation will
depend on temperatures. Northeastern WY could see up to 2 inches
with this system, and northwestern SD should stay mostly dry.
Upper wave will shift out of the region Sunday, and strong upper
ridging builds over the west coast. Dry weather and a warming trend
can be expected at least through early next week, with highs
reaching the 50s by Monday. A weak midweek shortwave could bring a
pause in the warming trend, but warming resumes later next week as
the upper ridge rebuilds. Current deterministic NBM cold bias keeps
highs in the 50s through the week, but wouldn`t be surprised if
temperatures warm above current forecast.
&&
.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 428 PM MST Fri Feb 26 2021
Isolated -SHRASN with local MVFR conditions will end this evening.
VFR conditions then expected through early Saturday. Snow chances
increase across northeast WY mid-morning Saturday, spreading into
southern SD Saturday afternoon with widespread IFR conditions.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 11 AM to 11 PM MST Saturday for
SDZ024-025-072.
WY...Winter Weather Advisory from 11 AM to 11 PM MST Saturday for
WYZ057.
&&
$$
Update...Helgeson
DISCUSSION...Pojorlie
AVIATION...Helgeson