Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/19/20
AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
714 PM EST Tue Feb 18 2020
A cold front crosses the area late tonight, then stalls along
the Gulf coast Thursday. Low pressure tracks northeast along
this boundary Thursday night into Friday as arctic high pressure
plunges into the nations mid section.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 710 PM EST Tuesday...
Early evening analysis reveals sfc low pressure over SErn
Quebec/nrn NY. The associated sfc cold front extends SSW across
east-central PA, wrn VA into the eastern TN Valley and the
western Gulf coast.
Forecast generally on track this evening. Did make minor changes
to PoP to reflect CAMs, with HRRR and NMM handling scattered
showers ahead of the front a bit better this evening. Front will
push across the region late tonight/overnight, and will be south
of the area into the Carolinas by sunrise. Scattered showers
(NW) with a dry start across the coastal plain early this
evening, with likely to categorical PoP overnight as moisture
streams NE along and ahead of the advancing cool front. Nudged
temps up a bit to reflect slightly slower timing, but overnight
lows in the 40s for most still looking good.
As of 245 PM EST Tuesday...
Has turned out to be a pretty decent day wx wise over the FA.
Clouds will lower and thicken early this evening then rather
large area of SHRAs will be moving into/across the FA (beginning
by mid eve W/central areas then at the coast mainly after
00Z/19. QPF to avg one tenth to one quarter N and NW to 1/2 to
3/4 of an inch S and SE. Limited or no clearing before 12Z/18. A
mild night w/ lows 40-45F (except u30s far NW).
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
As of 310 PM EST Tuesday...
SHRAs may linger far SE VA-NE NC in the morning (esp early)...otw
the front continues to push S to the gulf coast. Clearing is
expected through the day from NW to SE (late) as large cold sfc
hi pres pushes SSE across the nrn Plains. N winds will remain a
bit gusty...Mainly at the coast (before diminishing in the
afternoon/evening). Highs from the u40s-l50s.
Clear-partly cloudy and near seasonable wx Wed night w/ lows from
the u20s N and NW to the m-u30s far SE.
Yet another system will begin spreading moisture quickly into
the region from the WSW Thu. Weak lo pres will be tracking E
along the stalled frontal boundary INVOF gulf coast. Upper level
confluence right over the FA and that will likely become the nrn
fringe to any pcpn late Thu-Thu night. While lo pres tracks off
the SE CONUS coast Thu...hi pres will continue to settle/spread
out gradually from the Midwest to the nrn mid-Atlantic region.
This is one of only a very few storms to track by to our S this
Winter (so far) and offers the best chc at winter pcpn (SN) here
(since Nov). Highs Thu in the l-m40s.
Of course...there remain model differences. The NAM/GFS
continue to be farther N (and aggressive w/ QPF) into the cold
while the ECMWF remains consistent in keeping much of the
system`s moisture S of most of the FA (outside of mainly NE NC).
Would be more inclined to be more aggressive w/ pcpn (farther
N) if the NAM/ECMWF were in sync. They are not (and have not
been). Will the middle ground GFS win this battle? For now...its
a RA to wet SN scenario from late Thu afternoon into Thu night.
Have nudged/increased QPF (and corresponding SN accums) a bit N
of the previous fcst (more in line w/ WPC)...but will let the
models fight it out over the next 12-24 hrs before committing to
a wetter or drier soln. So...accums aob 2" (little or nothing N
of a FVX-RIC-WAL line)...highest across NE NC (by after
midnight Thu night). Becoming breezy/windy...esp at the coast.
Pcpn expected to end in SE VA-NE NC very late Thu night/early
Fri. Lows in the l-m20s inland to the l30s right at the coast in
SE VA-NE NC.
Hi pres and clearing out for Fri...though chilly w/ highs in the
u30s-l40s. Remaining breezy at the coast.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 230 PM EST Tuesday...
After a chilly night Fri night w/ the center of sfc hi pres
arriving late...Sat will be dry w/ seasonable conditions. Hi
pres moves off the coast Sat night-Sun as lo pres develops/tracks
into the mid MS Valley. Return S flow behind the depart high
will lead to milder wx Sun and expecting mainly high clouds to
arrive from the W (esp in the afternoon). Lo pres tracks from
near the OH river on to the ENE Mon then through the nrn mid-
Atlantic region (late Mon night) and off the coast Tue. 12Z/20
GFS slightly slower than the 12Z/20 ECMWF w/ its movement E.
Will have PoPs increase sharply by Mon afternoon/evening then
begin to taper off (W-E early) Tue.
Lows Fri night from the l-m20s inland to the u20s-around 30F at
the coast. Highs Sat in the u40s-l50s. Lows Sat night in the
u20s inland to the l-m30s at the coast. Highs Sun mainly in the
m-u50s. Lows Sun night in the m-u30s inland to 40-45F at the
coast. Highs Mon the m-u50s. Highs Tue from the m50s on the ern
shore to the u50s-l60s elsewhere.
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 710 PM EST Tuesday...
VFR conditions across area terminals this evening will give way
to thickening/lowering CIGs overnight ahead of a cold front.
That front will approach and move through the area late tonight,
quickly bringing widespread rain and IFR conditions for the
area, with best rain chances between 02-10z across terminals.
A period of IFR conditions is expected across all sites
generally from 05z- 10z (expect until after 12z at ECG).
However, after the cold frontal passage overnight, expect VFR
conditions to rapidly return from NW to SE Wed morning.
High pressure returns Wednesday aftn into Thursday morning. Low
pressure tracks across the Sern Conus Thurs night. This will bring
a chc of a brief rain/snow mix then all snow for far srn VA and
NE NC along with degraded flight conditions. High pressure
returns Friday into Saturday.
As of 350 PM EST Tuesday...
High pressure over the area is moving offshore in advance of an
approaching cold front associated with low pressure over southern
Ontario. Winds are out of the south at 5-10 knots on the western
periphery of the surface high. Waves in the bay are around 1 foot
while seas offshore are running 2-4 ft.
The aforementioned cold front crosses the region after 06Z tonight
from north to south. Decent pressure rises coupled with CAA and dry
continental air behind the cold front will lead to a period of
enhanced NNW flow through early Wednesday afternoon. Winds increase
to 20-25 knots with gusts to 30 knots for the Ches Bay, Currituck
Sound and offshore zones. Opted to raise headlines for the Lower
James River with this forecast package due to winds increasing to 20
knots with a gusts to 25 knots tonight. Winds will be a little
slower to subside across the southern bay Wednesday morning so the
SCA flags there are now in effect through 18Z. Left offshore
headlines untouched with the region south of Parramore Island
included in the SCA for seas building to 5 ft through Wednesday
The extended portion of the marine forecast remains uncertain
with increasing potential for low pressure to form off the
Southeast coast on Thursday as arctic high pressure over the
central Plains builds southeast. How far north the low comes
will have significant impacts on the wind/wave/seas forecast.
Consensus of the models this afternoon suggests SCA conditions
for all waters from late Thursday night through Friday with some
potential for low-end Gale conditions across the southern
MARINE...Small Craft Advisory from 4 AM to 1 PM EST Wednesday for
Small Craft Advisory from 4 AM to 6 PM EST Wednesday for
Small Craft Advisory from 4 AM to 10 AM EST Wednesday for
Small Craft Advisory from 4 AM to 10 PM EST Wednesday for
Area Forecast Discussion
National Weather Service Amarillo TX
525 PM CST Tue Feb 18 2020
For the 00z TAFs:
VFR conditions to prevail throughout the majority of the TAF
cycle, especially through the first half. Tomorrow afternoon we
should see conditions deteriorate (approaching MVFR) as cloud
cover increases through the afternoon and evening hours ahead of
a cold front. Have not included any precipitation just yet, but
KDHT and KGUY may see those chances increase in the next cycle as
we are anticipating snowfall Wednesday night. Wind speeds will
generally be light and go around the dial. Southerly winds will
prevail tomorrow ahead of the front, but a wind shift will be
expected in the next cycle as well.
.PREV DISCUSSION... /Issued 320 PM CST Tue Feb 18 2020/
SHORT TERM...Today through Tomorrow...
Overcast skies today are keeping temperatures from rising above
the 40s across the area. However, clouds are beginning to break
across the southeast and west central Texas Panhandle with the
chance for temperatures to rise up into the lower 50s. Winds
remain out of the north today, but will begin to turn clockwise
towards the south through tonight as a surface high pushes
southeast across the Oklahoma and Texas Panhandle. Winds will
remain from the south through tomorrow with gusty winds of 15-25
mph possible across the far northwest. Temperatures will drop into
the 20s across the area tonight and cloud cover tomorrow will
keep high temperatures similar to today in the mid 40s to lower
There is a small window early tomorrow morning for a slight chance
of snow flurries in the far northern part of the eastern Oklahoma
Panhandle with little accumulation expected. RAP soundings are
showing a saturated layer through the DGZ; however, the surface to
800mb remains dry. Therefore, the chance for moisture to reach
the surface is minimal with recent guidance and will be short
lived with little dynamical forcing. The next chance for moisture
will tomorrow night and mentioned in detail in the long term
LONG TERM...Tomorrow Night through Monday...
Main story in the long term forecast occurs right at the beginning
with the potential for snow Wednesday night into Thursday.
Wednesday, as surface ridging builds across the Upper Midwest into
the mid-Mississippi Valley and a weak southern stream disturbance
translates over the big bend, resulting low level winds across the
CWA will become southeasterly, moistening the low levels via upslope
flow. Wednesday night, highly positively tilted trough will slide
southeast from UT/WY, pushing a front south through the CWA and
leading to large scale ascent, particularly across our northern
zones. Given the decent low level moisture, this should lead to at
least a little light precipitation for a large portion of the
forecast area. Additionally, most guidance suggests an 850mb
frontogenetic band may set up somewhere across our northwest,
allowing for enhanced snowfall rates there. It should be noted that
peak ascent associated with these potential frontogenetic zones
looks to be displaced vertically from the dendritic growth zone -
progged to be located in the 500-650mb layer - which would hold back
peak snowfall rates despite the stronger ascent.
Main forecast questions remaining are: 1) How quickly will cold air
filter in and change the dominant precipitation type to snow? 2)
Where exactly will transient areas of 850mb frontogenesis set up?
and 3) Will ascent occur within a saturated dendritic growth zone?
Trends in guidance continue to suggest that only an hour or two of
rain will occur before a change over to snow, so confidence is high
that snow will indeed be the dominant precipitation type. On the
subject of frontogenetic banding, guidance is giving the usual
discrepancies in exact placement, with the best chance for this
setting up over our CWA across the western OK Panhandle. Finally,
efficient snow production from the dendritic growth zone looks to be
the major limiting factor for this snow event. For the southern half
of the CWA, the DGZ looks to only be saturated for an hour or two.
Across the northern half of the CWA, while broad ascent ahead of the
wave and a few more hours of saturation should occur, stronger
ascent associated with the previously discussed frontogenetic
forcing looks to be displaced vertically from the DGZ, limiting
snow production efficiency.
For the reasons stated above, this looks to be a typical weak snow
event for the Panhandles across all but potentially the western OK
Panhandle. Have gone with minor snow amounts across the TX Panhandle
and around 1-3 inches across the OK Panhandle, with highest totals
across Cimarron County.
Moving on in the extended to Friday, as elongated surface ridge
builds from S TX into the OH Valley, winds at the surface across the
Panhandles look to turn southwesterly. Have thus bumped highs up a
bit over consensus blend, with a return into the upper 40s and lower
50s expected after a frigid Thursday. As a weak disturbance
approaches the Sangre de Cristos Friday night, expect surface
pressure gradient to be maintained overnight due to lee pressure
falls. Have thus bumped lows up a bit over consensus as well in
deference to continued southwesterly winds during the overnight
For Saturday and Sunday, fast moving upper low approaches from the
west. Lead disturbances in the west-southwesterly flow aloft may
lead to some rain Saturday afternoon and evening. Lee cyclogenesis
looks to occur roughly overhead Saturday night with precipitation
possible across the northwest quadrant of the resulting low Sunday
as the upper low departs to our east. At this time, GFS/EC and all
available GEFS members depict 850mb temperatures above freezing
Sunday. Will thus keep all mentions of precipitation rain but, given
potential for breezy conditions, will need to remain vigilant as
even a small amount of snow may lead to deleterious visibility
Next Monday looks to be relatively uneventful. With many different
depictions of surface winds seen across operational guidance and
ensembles, have stuck with blended guidance for all elements during
VFR conditions are expected at all three TAF sites through the
period. Skies are overcast across all sites, but will begin to
break at AMA/GUY later this afternoon with high clouds still
possible. DHT will likely hold the overcast skies through tomorrow
morning before lifting. Winds are out of the north northeast for
all three sites before turning clockwise overnight and becoming
southerly by 12z tomorrow at DHT/GUY and 16z for AMA.
Area Forecast Discussion
National Weather Service Gray ME
934 PM EST Tue Feb 18 2020
Low pressure will pass north and east of the region tonight...
bringing snow and rain to an end. After a relatively mild day
Wednesday...much colder air will arrive Wednesday night through
the end of the week. Dry weather will continue through this
weekend with temperatures rebounding above seasonal norms. The
next chance for widespread precipitation is not expected until
at least early next week.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
930 PM... Extended the WWA where it is in place through,
midnight. The HRRR continues to show the precip just
disintegrating across all but the mtns over the next hour so,
There`s still a pretty decent cluster of precip to our west,
and not sure it`ll all end in the next hour, but the trend will
be downward through midnight. I so still think temps will surge
a bit after midnight, as the flow shifts W, and there`s a deep
enough mixing lyr to warm things up before the colder air moves
in. Also temps in upstate NY in the upper 30s to around 40 right
now, so there`s some support for this upstream.
8 PM...The atmosphere is keeping the mets busy tonight as
several surges of precip have occurred and coastal front, which
had pushed a little inland, got pushed back back the cold air,
not all the way to the coast, but some places went abv freezing
and then below. P-type continues to fluctuate, but the good news
is that all precip should begin to wind down in the next few
hours, at least according to HRRR. As drier air moves in, and
when sfc wind shifts to W, will likely see temps rise in many
spots for a few hours during the overnight, as the warmer mid-
lvl air mixes down.
525 PM...Based on looks at current temps and obs, updated the
forecast to try to time p-type changes a little better, although
in some areas, especially closer to the coast, where temps have
gone abv freezing p-type is fluctuating between rain and snow,
as marine got a push from strong onshore flow, but surge backed
off a bit and cold wedge between marine air just above the sfc
and warmer coming from the S at and abv 850 MB is hanging on.
Think by ~00Z these coastal areas should go to just rain. Across
srn NH, the warm is progressing NWD, and seeing a short period
of PL or FZRA before it warms up a bit there, and this zone will
shift north thru the area as well. Timing of precip and amts
were only tweaked a little and no change to advisories in
Previously...Moderate to heavy snow continues for much of the
forecast area at this time. These next few hours will be the
window for best snowfall accumulation. KBOX 88D shows a well
defined melting layer rapidly moving into Srn NH this hour as
well. This is well timed to latest RAP guidance...which I leaned
on for ptype forecast. So snow will mix with sleet...freezing
rain...or rain across Srn NH over the next hour depending on
surface temps. Above freezing surface air is moving inland from
the Gulf of ME...along with creeping Nwd into NH. This will turn
any precip to all rain once the warm air gets deep enough. That
being said the main precip shield is becoming ragged on the SW
side and so any mixed precip is expected to be very light. That
may fill in somewhat...as the main trof axis has yet to cross
our longitude...but again accumulation of any precip after about
7 pm should be light.
What is clear is that model guidance...as usual...was too quick
to warm the boundary layer. Our forecast was on the colder side
but was still too warm in many locations...especially interior.
While it remains in the teens at IZG...LEW...AUG...and
WVL...model guidance would have had them all well into the 20s
by now on their way to freezing. This is going to limit the
amount of straight rain likely tonight...but given that our
forecast was already fairly snowy across Wrn ME I see no need
for additional headlines. High temps are likely to be around
midnight for most locations. Needless to say a non-diurnal temp
trend was used for this period.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Wed will be a bit of a tricky temp forecast...with highs perhaps
early and temps falling or steady during the day. CAA will be
increasing thru the period...so I blended in mixed down temps to
capture that trend. Regardless the colder air moving in will
help to mix down some gusty winds. With gusts reaching 30 to 35
mph at times it will feel colder than the thermometer readings.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Summary: A cold start...but then moderating temperatures with an
extended period of generally dry weather expected through at least
Monday of next week.
High Impact Weather Potential:
* At this time...winds appear too light for wind chill
headlines Wednesday and Thursday nights...but both nights will
feature very cold temperatures.
--Pattern and Implications--
A look at early afternoon water vapor imagery over and
surrounding North America reveals a progressive flow with no
downstream blocking over the western Atlantic /+NAO/ and a
robust jet across the central Pacific /+EPO/ with a strong
vortex near the pole /+AO/. Overall this pattern would favor
ample Pacific /ie mild/ influence across the lower 48...with the
progressive flow yielding only brief bouts of cold air. This is
what we have experienced recently...and will continue through
the long term forecast period. The only bit of amplification in
the flow at the moment is a trough/ridge pair over the Gulf of
Alaska that will initially help drive another bout of cold air
into the northeast to begin the forecast period. Beyond
this...deterministic and ensemble guidance is in good agreement
that a relatively zonal flow pattern will continue through the
remainder of the long term forecast. After the initial cold
surge...this spells an extended period of generally dry weather
with temperatures moderating to warmer than normal values for
this time of year /in agreement with CPC 6-10 day outlook/.
Wednesday night - Friday: Very large high pressure center will
reside across the central United States through this period...
pushing a -2 to -3 sigma airmass /T8s/ into the northeast.
Thus...another relatively dry and cold period is expected with
temperatures below normal. Outside of some mountain snow showers to
open the period Wednesday...no precipitation is expected. T9s in the
mid minus teens Thursday will moderate a few degrees on Friday. This
will result in highs on Thursday only in the single digits in the
mountains with teens and lower 20s to the south...with highs
warming 5-8F on Friday. Undercut model consensus temperatures
both Wednesday and Thursday nights...following closer to colder
statistical guidance values. On Thursday night this will result
in lows falling well below -10 in the mountains /likely a few
readings below -20/...with single digits above and below zero
to the south of this.
Saturday - Monday: High pressure settles into the southeastern
United States during this period...with return flow bringing
moderating temperatures aloft with a resulting moderating trend in
our temperatures. Given the sprawling high to our south...and little
in the way of shortwave energy to our north...the quiet weather will
continue...with temperatures moving back above seasonal norms. The
only precipitation potential will come in the form of snow showers
in the mountains given upslope westerly flow...but significant
accumulations are not expected. By Sunday...the moderating
temperature trend will equate to highs in the upper 30s in the
mountains with 40s to the south.
Tuesday: By the end of this forecast period next Monday Night-
Tuesday there is modest guidance agreement that a cutoff low over
the southwestern states will eject north and east with the potential
for a precipitation event in our area. Too early to think about
details at this range...but the warm antecedent temperatures
suggests that PTYPE may very well be in question. Ensemble
precipitation probabilities at this range also suggest that
significant precipitation amounts />0.5" liquid/ are unlikely...but
we/ll watch this period as this forecast period becomes clearer.
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Short Term...Widespread LIFR in SN this hour...with some IFR
where precip has changed to RASN. That will continue into the
evening when rapid scattering out low clouds is expected from SW
to NE as a front moves in. I do not expect MVFR CIGs to linger
long before things go VFR late tonight. HIE will be the
exception where downsloping winds will keep mainly MVFR
conditions thru this evening...then upsloping winds do the same
Mountain snow showers may bring restrictions to HIE Wednesday night.
Otherwise, VFR conditions should dominate the Thursday-Sunday
Short Term...Winds will continue to increase ahead of low
pressure lifting thru this evening. Gale warning remain for the
outer waters and SCAs in the bays. CAA Wed will allow stronger
wind gusts to mix down during the afternoon. A period of
offshore gales is possible...again outside the bays.
Lingering SCA winds/waves through Thursday with quiet conditions
Thursday night into Friday before strengthening westerly winds bring
the potential for renewed SCAs Friday night into Saturday.
ME...Winter Weather Advisory until midnight EST tonight for
NH...Winter Weather Advisory until midnight EST tonight for NHZ001.
MARINE...Small Craft Advisory until 11 AM EST Wednesday for ANZ150>154.
Area Forecast Discussion
National Weather Service Medford OR
800 PM PST Tue Feb 18 2020
.DISCUSSION...19/00Z NAM in. 19/00Z GFS in through 69hr.
Clear skies prevail across the Medford CWA this evening with dry
easterly low level flow. The dry air and relatively cold air mass
in place will make for a cold night, and a freeze warning is in
effect along the north coast. The area will warm up quite a bit
after the cold morning, and afternoon temperatures will be cool
This is a typical pattern for low level offshore flow over the
area, with a long wave ridge offshore flopping over an upper
trough to the south. It will end tomorrow as the trough moves out
and the ridge axis moves onshore, bringing southerly flow aloft to
the area ahead of the upstream trough.
So, expect clear skies to continue through tonight, but sometime
later tonight into Wednesday, winds near the coast will turn
southerly, and this will eventually allow low clouds to surge
north along the coast. It will take a while for them to get to the
CWA as there is nothing out there now...usually they lurk around
Cape Mendocino before making the northward dash.
The 19/00Z NAM boundary layer RH fields suggest that the stratus
surge will reach the Brookings area sometime Wednesday evening.
The RAP doesn`t go out far enough, but extrapolating that output
also suggests a Wednesday evening arrival.
Inland areas will remain clear for the next several days, except
for scattered high clouds and patchy late night into early
morning low clouds.
Extended discussion from the Tuesday afternoon AFD...Fri 21 Feb
through Tue 25 Feb 2020. A fairly weak upper trough will move
through our forecast area Friday with a closed low moving into
southern California Friday night and then Arizona by Saturday.
Since the air mass preceding this trough is very dry, and the
closed low is expected to move in far enough to our south, we are
not expecting any precipitation during this time period. We`ll see
varying amounts of mid and high clouds, but also some sunshine
and temperatures near or a little above normal levels. Mornings
will still be chilly, though less so compared to earlier in the
week, especially east of the Cascades.
The next system we`re watching is a short wave expected to move
quickly east-southeastward from the Gulf of Alaska and then move
onshore into the PacNW late Saturday night into Sunday. The
latest trend in the guidance has been for less digging of this
trough. The GFS and GEFS ensemble members have been deeper and
colder, while the ECMWF and its ensembles have been more progressive
and not as cold. If the trend is correct, it would ultimately result
in a less cold, wet solution. But, since it`s still pretty far out,
we`ll still need to iron out the details. Still expect a pretty good
cold front to move through with snow levels rapidly lowering
from around 5000 feet down to 1500-2500 feet behind it by Monday
morning. By that time, however, most of the precipitation will have
ended or only remain in the mountains. An upper ridge will build
offshore Monday, so coverage of showers should diminish/end
with drier air moving in Monday night/Tuesday. -Spilde
.AVIATION...For the 19/00Z TAF Cycle...VFR is expected to prevail
nearly everywhere for the TAF Cycle across southern Oregon and
northern California. The exceptions to this are in the Umpqua Valley
as well as the northern portion of the Illinois Valley this morning.
The low clouds will dissipate by late afternoon bringing VFR to
these areas for a few hours. Freezing Fog and low CIGS will return
to the Umpqua Basin tonight including at KRBG before lifting
tomorrow. Additionally, guidance is suggesting reduced VSBYS and
lower CIGS with a coastally trapped wind reversal developing
overnight along the Northern California Coast and spreading
northward up to Gold Beach by the end of the TAF period. -Schaaf
.MARINE...Updated 730 PM PST Tuesday, 18 Feb 2020...Gusty north
winds and steep wind driven seas will gradually subside from north
to south across the waters tonight through Wednesday morning.
Relatively calm conditions under high pressure are expected
Wednesday through the remainder of the week. More active weather is
possible over the weekend in the form of a frontal system and larger
long-period swell arriving Sunday. Latest forecast models have
trended later and somewhat weaker with the arrival of the front.
Swell is still expected to be large though, at 18 to 20 feet with 15
second period. -BPN/Keene
OR...Freeze Warning from 11 PM this evening to 9 AM PST Wednesday
Pacific Coastal Waters...Small Craft Advisory until 4 AM PST
Wednesday for PZZ356-376.
Small Craft Advisory until 10 PM PST this evening for
Area Forecast Discussion
National Weather Service Marquette MI
647 PM EST Tue Feb 18 2020
.SHORT TERM...(This evening through Wednesday)
Issued at 308 PM EST TUE FEB 18 2020
MSAS analysis shows a 1000 mb surface low near the Ontario/Quebec
border this afternoon continuing to deepen as it moves away from the
area. NW wind behind it has been gusty at times due to the
combination of isallobaric winds from pressure rises as high as 6
mb/3 hr at times as steep surface lapse rates due to CAA aloft. Have
seen gusts into the 30+ mph range even well inland with 40+ mph
gusts along the Lake Superior shoreline. Expect these winds to
subside slightly in the next few hours before picking back up in the
about 00z-04z time frame when the next mid-level short wave on the
leading edge of the Arctic air aloft drops southeastward across Lake
Superior. The NAM and RAP indicate pressure rises once again
approaching 6 mb/3 hr in this time period and with 30-35 kt winds as
low as 900 mb in model soundings, should have no problem mixing down
30+ mph gusts again this evening. Therefore, manually inflated winds
and gusts in the grids during this period before trending back
towards the CONSRaw after 06z.
With this cold NW flow the other main story will be lake-effect
snow. LES is already ongoing over much of the NW wind snow belts but
currently is mostly light - except for some heavier bands over the
Keweenaw that have reduced vis at CMX to around 1/2 mile at times.
Expect that these Keweenaw/western U.P. bands will relax a bit after
midnight once moisture becomes shallower in the subsidence region
behind the aforementioned short wave. Additional snow amounts out
west of about 1-3" did not warrant a headline but the snow and
blowing snow combination justified an SPS that runs through 05z to
capture the period of strongest snow and gustiest winds.
For the eastern half of the NW wind snow belts, the longer fetch
will allow heavier snow bands to persist longer. Models continue to
focus on one or two long axis convergence bands developing over
eastern Lake Superior and pushing onshore near Grand Marais this
evening before gradually shifting east through Luce County overnight
and into Wednesday morning. This big band looks fairly transient,
which will cut down on snow totals somewhat, but with such deep
moisture and impressive lake-based instability we`ll still be
looking at several inches of snow in these areas. Therefore have
issued a Winter Weather Advisory for the normal cluster of Alger,
Luce, and northern Schoolcraft counties through 00z Thursday. In
addition to the new snowfall, blowing and drifting snow will
continue to be a concern in these areas, especially this evening
during the window of peak winds but really all the way through the
Wednesday morning temps should be nice and frosty with subzero
reading likely over the interior west, but hedged towards the
CONSRaw over anything statistical since temps are usually handled
better by raw models when there are lake-effect clouds and gusty
winds keeping the PBL mixed. Therefore wind chills only drop to as
low as -20, and only briefly, so despite the cold no wind chill
headlines will be needed. Temps tomorrow really won`t climb much
over their morning lows, with highs only expected to reach the upper
single digits west and mid teens east.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 212 PM EST TUE FEB 18 2020
Upper air pattern consists of a 500 mb ridge in the western U.S.
with a broad trough from the plains across the eastern U.S. 00z Thu.
The ridge moves into the Rockies 00z Fri and into the plains 00z
Sat. Fairly quiet weather this forecast period with lake effect snow
ending Wed night. Overall, did not make too many changes to the
In the extended, the GFS and ECMWF show a broad 500 mb ridge across
the southern plains with a trough off the east coast and another
over southern CA and Baja CA 12z Sat. Upper flow along the
Canadian/U.S. border is zonal on Sat. Upper troughing moves into the
upper Great Lakes 12z Sun. Troughing then moves into the northern
Rockies 12z Mon and into the central plains 12z Tue. Above normal
temperatures will occur for this forecast period.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 638 PM EST TUE FEB 18 2020
LES ongoing this evening within the WNW wind belt regions will
continue overnight, with some signs of partial clearing tomorrow.
KCMX will bear the brunt of the worst of the snow bands that have
set up, with improvement expected as the night progresses. Blowing
snow will also hinder visibilities, with winds slackening slightly
late tonight through the remainder of this TAF period.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 429 PM EST TUE FEB 18 2020
Two gale events will occur for this forecast period. The first is
happening into this evening across eastern Lake Superior with a low
pressure system off to the east. Heavy freezing spray will also
continue across the lake through Thu. Next gale event with southwest
gales up to 40 knots looks likely Thu afternoon into Fri.
Winter Weather Advisory until 7 PM EST Wednesday for MIZ006-007-
Heavy Freezing Spray Warning until 7 AM EST /6 AM CST/ Thursday
Gale Warning until 1 AM EST Wednesday for LSZ249>251-266-267.
Area Forecast Discussion
National Weather Service Pueblo CO
817 PM MST Tue Feb 18 2020
Issued at 759 PM MST Tue Feb 18 2020
Updated forecast based on current trends. Areas of dense fog
continue up in El Paso county per obs and CDOT cams. Also we have
had light continuous freezing drizzle down here in Pueblo for the
last few hours and have added freezing precip to the gridds for
most of the greater I-25 corridor region.
Quick glimpse of the new NAM and 36 hour HRRR shows brunt of
precip tomorrow evening will be from the EL Paso/Pueblo county
lines southward. Likewise see no need to change current hilites.
UPDATE Issued at 553 PM MST Tue Feb 18 2020
Based on CDOT web cams and obs, along with fcst soundings, have
issued a dense fog advisory for all of El Paso county. /Hodanish
UPDATE Issued at 503 PM MST Tue Feb 18 2020
Based on fcst soundings, there is probably a good chance we are
going to see areas of dense fog up in El Paso county this evening
into tomorrow morning, especially in N El Paso county. KCOS has
already dropped to 1/2sm FZFG for a short period, and are now up
to 2sm. KFLY and KCWM are currently at or below 1/4 sm FZFG. If
these trends continue, will issue a Dense Fog Advisory for the
region in later updates. /Hodanish
.SHORT TERM...(This evening through Wednesday)
Issued at 246 PM MST Tue Feb 18 2020
...Cool and Unsettled Weather Continues...
Current water vapor imagery and upper air analysis is indicating
moderate to strong westerly flow continuing across the Rockies, with
at broad upper trough digging across the Intermountain West at this
time. Water vapor imagery is also indicating tail end of and
embedded shortwave lifting out across the High Plains with another
embedded wave translating across the Northern Great Basin and yet
another translating across the Desert Southwest at this time.
Tonight...Some lingering light snow/flurries can be expected tonight
across the southeast Plains, especially in the Pikes Peak region,
with continued mid level waa/upglide and moist southerly low level
upslope impinging along the higher terrain. This will keep flurries
ongoing across the Pikes Peak region with areas of fog expected to
develop this evening and persist through through early Thursday
morning. Model soundings are indicating moisture aloft shallowing
out through the overnight hours, leading to the potential for light
freezing drizzle, though will let the evening shift continue to
evaluate the need for any winter weather highlights if light icing
develops. Any additional snowfall is expected to be light and less
than an inch.
For tomorrow...Embedded energy continues to translate across the
Rockies, with moisture and lift increasing across area through the
day. In addition, another surge of cool air will move across eastern
Colorado through the morning, with breezy north to northeast winds
of 15-25 mph developing through the late morning and afternoon. With
that said, there looks to be a brief break in precipitation across
the area early Wednesday, though will see snow developing across the
higher terrain through the late morning and afternoon, especially
the along the Palmer Dvd and Southern mountains and immediate
adjacent plains, with favored northeast low level flow. Snow
accumulations through late tomorrow afternoon will be generally
light, 1 to 3 inches, though with widespread snow continuing through
the the evening, the Wednesday afternoon/evening commute will likely
.LONG TERM...(Wednesday night through Tuesday)
Issued at 246 PM MST Tue Feb 18 2020
Snowfall will spread eastward from the mountains and I-25 corridor
onto the plains Wed evening, as post frontal upslope flow deepens
and upper wave drops into northern Colorado. East slopes of the
Sangres/Wets look most favored for heavier snow given moderate
low/mid level upslope component, and with lack of strong nly
downslope initially, Arkansas Valley in Fremont/Pueblo counties
could see a window for heavier snow Wed evening. Forcing is
slightly weaker farther east on the plains, though longer
duration of snowfall will lead to at least modest accums by Wed
morning. Snow ends quickly Thu morning as low/mid level flow
weaken and upper trough slides east. Overall, expect 4-9 inches
eastern mountains, 3-6 srn I-25 corridor and through Fremont
county, perhaps slightly higher Walsenburg/Colorado City areas.
Two to five inch range should catch most of the plains, with
highest amounts likely south of the Arkansas River. Will hoist
winter weather advisory for all the above areas beginning Wed
afternoon along and west of I-25, then spreading east onto the
plains after 00z. Mountains and interior valleys will see snow,
but only light accumulations, while Colorado Springs will see an
inch or two, with 2-4 in Teller County.
Clearing but still cold weather expected Thu, then warmer Friday
as brief upper ridge builds. Southern stream system then lifts out
of the swrn U.S. Saturday and across Colorado Saturday night,
bringing another round of moderate to heavy snow to the mountains
before ending Sunday morning. Lower elevations will see precip as
well, though rather warm low levels may lead to at least some rain
initially Sat evening, especially across the eastern plains.
System lifts out into the plains Sun, with rather mild and dry
conditions Sun into Mon, before cold front races through the area
late Mon and next upper trough slides southward through the
Rockies. This system looks colder than the one over the weekend,
though impacts still uncertain as upper low may close off too far
north and east to bring heavy snow to the region.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 246 PM MST Tue Feb 18 2020
IFR/LIFR conditions expected at COS through at least 14Z with moist
southerly low level upslope flow keeping flurries ongoing, as well
as developing fog at the terminal through the evening and overnight
hours. Low level flow goes more north to northeast aft 14Z, with
MVFR and VFR conditions expected through the late morning and early
afternoon. Another surge of cool air will move across the area, with
breezy north to northeast winds of 15-20kts expected to develop aft
18Z, with showers in the VC of the terminal through the late
MVFR and IFR conditions expected at PUB with moist easterly flow
keeping cigs low with patchy fog possible through at least 14Z.
Low level flow goes more north to northeast aft 14Z, with MVFR and
VFR conditions expected through the late morning and early
afternoon. Another surge of cool air will move across the area,
with breezy north to northeast winds of 15-20kts expected to
develop aft 18Z, with showers in the VC of the terminal through
the late afternoon.
ALS will remain VFR over the next 24 hours with breezy westerly
winds of 10-20kts developing tomorrow afternoon.
Winter Weather Advisory from 5 PM Wednesday to 5 AM MST Thursday
Winter Weather Advisory from 2 PM Wednesday to 5 AM MST Thursday
Dense Fog Advisory until 8 AM MST Wednesday for COZ084-085.