Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/29/18
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
857 PM EST Sun Jan 28 2018
Radar returns have slowly been increasing across SW Lower Mi over the
last hour. There is still a good deal of dry air in the column, thus
there have been no reports of snow in the sfc obs over the west side
of the state just yet. As the larger scale forcing increases tonight,
there will be a notable increase in ascent along the 280-290 deg
isentropic surfaces, focused across Se Mi between 08Z and 16Z Mon. A
narrow plume of moisture (2-3 g/kg specific humidities) will be
transported into the mid level frontal feature. This combined with
steepening mid level lapse rates and ascent focused within the
dendritic growth layer will support accumulating snow late tonight
Recent hi res solutions are suggesting the forcing will be a littler
farther up the frontal slope late tonight into early Mon morning,
impacting locations from the far northern Detroit suburbs possibly up
to Saginaw. Will therefore update to increase pops and snowfall
accums across the north. Model solutions are also trending stronger
with the trailing mid level deformation as the system exits east on
Monday. This suggests a little better snowfall across the eastern
half of the forecast area, possibly into Monday afternoon. For this
reason, an update will be issued to increase pops on Monday and bump
snow accums upward slightly from metro Detroit up through Port Huron.
Overall, snowfall totals from midnight tonight through early Mon
afternoon are still expected to fall in the 1 to 2 inch range, with
lessor amounts across the Saginaw Valley and northern thumb. There is
some concern for some locally higher amounts wherever a pivot point
in the mid level frontal forcing sets up. At this point, this looks
to be somewhere between Pontiac/Howell and Flint/Owosso.
Issued at 549 PM EST Sun Jan 28 2018
The region of light snow now over southeast Wisconsin will track
into Se Mi late this evening and persist through a good portion of
Monday morning. There will be an intensification in the larger scale
forcing driving this snow late tonight (after 07 or 08Z), with the
forcing persisting through daybreak. The snow is then forecast to
slowly decrease as it slides off to the east late Mon morning/early
Mon afternoon. Recent model guidance with some support by current
radar trends are suggesting the forcing may extend a little farther
north toward FNT. Total snow for the 12-hour period from midnight
through noon Monday may reach 2 inches at PTK and FNT, with lessor
amounts north toward MBS.
For DTW...Current indications suggest the higher intensity snow will
develop north of metro tonight, possibly not extending across the
airport until 10 or 11Z. The snow will then persist through the
morning before gradually tapering off during the afternoon. Peak
intensity of the snow is expected in the 11 to 15Z time period. Up
to an inch total accumulation is forecast.
/DTW THRESHOLD PROBABILITIES...
* High in ceilings below 5000 ft overnight through Mon afternoon.
* High in precip type being all snow tonight and Monday.
Issued at 246 PM EST Sun Jan 28 2018
Weak mid level low pressure associated with shortwave shearing out
across the central Great Lakes will basically provide a pivot point
for stronger dynamics sweeping into the area with strong shortwave
that came onshore over British Columbia late Saturday and has since
dug sharply into the central Great Plains into base of mean upper
trough over the eastern CONUS. This feature, and its interaction
with the aforementioned lead shortwave, is depicted very well on low
and mid level GOES16 water vapor imagery. It is also most pronounced
near the 400 mb level in model forecasts.
Most notable is the 80-100 knot jet streak around this lower level
that will be reaching the base of mean upper trough this afternoon
and evening and then lift up its east side into Monday. Height falls
associated with this system will lead to weak cyclogenesis over the
Ohio Valley with a well defined inverted low level trough extending
back to weakness associated with lead system over Lake Michigan and
SW lower Michigan.
The interaction of these systems basically leads to notably stronger
low-mid level forcing than what previous model solutions suggested
which will extend from this evening into Monday morning. As noted in
the previous discussion, forecast soundings remain strong in the
depiction of supersaturation with respect to ice up to the low level
(now nearer 10kft -vs- 8kft from 00z model cycle). This encompasses
a majority of the -10C to -20C layer, and with lift in this region
also notably stronger, anticipate slightly higher snowfall totals
over parts of the region (on the order of an inch or two).
Recent HRRR runs suggest best forcing, and most widespread light
snow accumulation, will set up between I-96/I-696 and I-69 with RAP
focused just a bit further north than that. Will adjust snowfall
forecast to this basic idea with sub-inch totals on either side. At
this time, upper level pattern appears progressive enough to shift
this deepening system east of area by midday Monday and allow area
to dodge a period of deformation snowfall as central plains wave
lifts up east side of upper trough. If there remains a wild card in
this scenario, deformation positioned a bit further west/northwest
into area would be something to watch.
Much colder weather settled back into area in the wake of this
system as NOAM upper trough amplifies and the first in a series of
arctic air masses dives south/southeast into the region. This colder
airmass will lead to high temperatures in the 20s early next this
upcoming week with lows in the teens (and perhaps down to around 10
above for some locations early Tuesday morning).
An approaching upper-level trough with embedded shortwaves and an
associated surface low pressure clipper system will bring the chance
for precipitation throughout Wednesday afternoon and evening. The
center of the clipper system will stay well north of SE MI,
traveling east across the southern Canadian provinces throughout
Wednesday, however, the low will transport enough moisture from the
south and will produce enough forcing to bring precipitation chances
to MI. The GFS/NAM/GEM produce a swath of precipitation that moves
NW to SE through the Wed 18Z to Thu 06Z time frame, while the ECMWF
run continues to restrict precipitation chances north of the CWA,
with slight chances to see snow across the thumb. If precipitation
does pan out, precipitation type remains to be the second
forecasting challenge. Top-down methodology produce a rain to wintry
mix solution for the Metro region, with a wintry mix to snow
solution possible closer to Flint and Tri-Cities, with the thumb
having the best chance to see purely snow.
Upper-level troughing will amplify Thursday into Friday as a strong
cold front starts to move in across Michigan. This will cause winds
to shift from the west to the northwest and in turn take Thursday
forecasted highs in the lower 30s down to the low to mid 20s for a
high by Friday. Holding off on putting lake-effect chances across SE
MI for now, but it is certainly possible with the colder W/NW air
funneling over the relatively warm lake that we will be able to
produce lake effect snow bands that reach the CWA. Lastly, long
range models are starting to resolve a low pressure system that will
bring the potential to see snow late Saturday through Sunday across
Light northerly winds becoming northeast 10 to 15 knots over Lake
Huron tonight will persist tomorrow, generating waves of 4 feet or
greater over the southern lake Huron basin. There higher waves will
persist into Tuesday, as northerly winds around 15 knots persist. A
quick flip of winds from northerly to southerly will then occur
Tuesday night into Wednesday ahead of the next low pressure system.
This strong low passing through Ontario will bring the potential for
Gale force winds over much of the open waters of Lake Huron on
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Green Bay WI
546 PM CST Sun Jan 28 2018
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Monday
Issued at 258 PM CST Sun Jan 28 2018
The latest RAP analysis and satellite/radar imagery show a compact
shortwave exiting southeast WI early this afternoon. Light snow
showers should also depart east-central WI over the next hour or
two. Meanwhile, cold advection is occurring behind a diffuse cold
front positioned over northern WI. Scattered snow showers have
been falling for most of the day north of highway 8, and flurries
elsewhere. Think these flurries will persist through around
sunset. Though there are some breaks, mostly cloudy conditions
prevail from northern Minnesota to northern Illinois. As high
pressure over the northern Plains moves towards the region over
the next 24 hours, light snow and cloud trends are the main the
Tonight...Flattened upper troughing will remain in place across
the western Great Lakes. Enhanced moisture along low level trough
will gradually shift southeast through the evening and exit
overnight. With light north flow off Lake Superior, will therefore
expect mostly cloudy/overcast conditions to persist through the
evening, before some breaks open up overnight. Some lake effect
snow showers will also graze the NE WI shoreline into the
overnight. Trajectories do not favor much accumulations, as bands
should remain mostly offshore. Temps will be colder tonight, and
range from near zero at Land O Lakes to the middle teens over the
southern Fox Valley.
Monday...Surface high pressure will be gradually building across
the northern Mississippi Valley and into the western Great Lakes.
Slow clearing will continue to take place during the morning with
more clouds lingering over central and north-central WI than
further east. May see a secondary surge of low clouds southeast in
the afternoon as weak shortwave energy arrives from southeast
Saskatchewan. But progged soundings suggest that clouds will not
be deep enough for snow. Colder highs in the mid teens north to
mid 20s south.
.LONG TERM...Monday Night Through Sunday
Issued at 258 PM CST Sun Jan 28 2018
Northwest upper flow will produce dry and seasonable
weather Monday night through Tuesday. An upper trough swings
through the Great Lakes Tuesday night and early Wednesday. Very
little moisture is available, but strong low level warm advection
and decent upper dynamics suggest that an inch or two of snow may
fall across the north with an inch or less elsewhere.
Much colder air will follow for the remainder of the week, with
the potential for wind chill advisories Thursday and Friday
nights across at least central and northcentral Wisconsin.
An inverted trough is forecast to form from eastern Colorado to
the northern Ohio Valley Friday night and Saturday. Some light
snow is likely north of the trough, but the latest model runs are
further south with this feature, so snowfall here should be light.
.AVIATION...for 00Z TAF Issuance
Issued at 536 PM CST Sun Jan 28 2018
Light snow in east central WI and flurries elsewhere will taper
off this evening. MVFR to low end VFR ceilings will likely
persist through late tonight, followed by partial clearing as
weak high pressure arrives. Most of the region will see BKN mid
to high level clouds on Monday, through stratocumulus may linger
over parts of northern WI.
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
908 PM CST Sun Jan 28 2018
Issued at 907 PM CST Sun Jan 28 2018
Regional radars are showing light precipitation moving east across
northern Missouri associated with weak shortwave trough. 00Z upper
air analysis indicated that this system is working with limited
moisture, so there will be some sublimation as the snow falls
through the atmosphere. In addition, the RAP is showing weakening
ascent as the shortwave trough moves east across Missouri and
Illinois tonight. So will maintain low PoPs through the overnight
hours with any snow accumulations staying below a half inch. Low
temperatures still look on track to fall into the 20s by morning.
.SHORT TERM... (Through Late Monday Afternoon)
Issued at 259 PM CST Sun Jan 28 2018
Upper level shortwave to drop southeast through region. So clipper
system to bring in a chance of light snow tonight. Each successive
model run has been a bit drier. For now kept low chance pops and
accumulations still will be hit and miss. So anywhere from a dusting
to a couple of tenths of an inch of snow is possible before daybreak
With colder air filtering in behind arctic cold front, highs will
struggle to rise on Monday despite clearing skies. Will have highs
only in the 30s.
.LONG TERM... (Monday Night through Next Sunday)
Issued at 259 PM CST Sun Jan 28 2018
Surface ridge to build in Monday night with clear skies and light
winds. So lows will dip down into the 15 to 20 degree range.
By Tuesday, surface ridge begins to move off to the east allowing
southerly winds to return once again. Temps to moderate through mid
week with highs by Wednesday back in the upper 40s to upper 50s.
Beyond that, extended models still have a cold front slide through
region beginning late Wednesday afternoon and into Wednesday night.
Low level moisture and dynamics will be limited, so it will be a dry
Broad based upper TROF still to setup over region for last half of
work week, but with a stronger ridge at surface building in. The
chances of precipitation with an upper level shortwave moving
through on Thursday is looking less and less likely, with better
chances further south, closer to frontal boundary that will have moved
through our area Wednesday night. 12z GFS is now completely dry
for our area, while 12z ECMWF still has some qpf for areas south
of I70. Even the ensembles only have a few members with pcpn over
area during this period. Blend came in trending lower with pops
which looks reasonable. So backed off mention in social media
products as it is looking less and less likely to snow
Beyond Thursday, surface ridge in place through Friday before moving
off to our east for the weekend. Extended models hinting at another
system moving through region Saturday night/Sunday, but definite
differences in timing and strength among the models. So will need to
keep eye on future model runs. For now have just rain changing to
snow for the last half of next weekend.
.AVIATION... (For the 00z TAFs through 00z Monday Evening)
Issued at 606 PM CST Sun Jan 28 2018
A weak storm system will move across the area tonight bringing a
chance of light rain or snow. Visibilities in the snow are expected
to stay VFR or MVFR. Any snow accumulations are expected to be
less than half of an inch. Some MVFR ceilings are expected late
tonight into Monday morning. Then dry and VFR conditions are
expected at the terminals after 18Z. Winds will remain out of the
north to northwest.
SPECIFICS FOR KSTL:
A weak storm system will move across the terminal tonight bringing
a chance of light snow between 06-10Z. Visibilities in the snow
are expected to stay VFR or MVFR. Any snow accumulations are
expected to be less than half of an inch. MVFR ceilings are
expected late tonight into midday Monday. Then dry and VFR
conditions are expected at the terminal after 18Z. Winds will
remain out of the north to northwest.
Area Forecast Discussion
National Weather Service Blacksburg VA
715 PM EST Sun Jan 28 2018
A cold front will move slowly east across the area this
evening, exiting the piedmont overnight. An Arctic front will
cross the area later Monday into Monday night. Cold high
pressure builds in with drier weather for the middle of next
.NEAR TERM /THROUGH MONDAY/...
As of 215 PM EST Sunday...
Surface front still remains on the northwest fringe of the area but
should begin to edge east across the region this evening as shortwave
energy to the southwest shears across ahead of the upstream Arctic
front. This upstream boundary with the digging 5h trough looks to
finally boot the axis of deep moisture ahead of the initial front east
of the region late tonight or Monday morning. However low pressure
developing off the southeast coast by early Monday may again tend to
slow up exodus as models hint at a residual leftover deformation zone
to the northwest lingering along the back of this surface wave.
Otherwise appears another several hours of steadier showers/rain
to persist through the evening with the heaviest along/east of
the Blue Ridge as the wave aloft currently to the southwest
shears through. Gradual drying to then take shape over the northwest
this evening as the front starts to edge east. Thus keeping likelys
northwest to categorical southeast half before seeing better
drying at least aloft head east of the mountains after midnight
per latest HRRR. This could spell another half inch of rain
south and a tenth to a third north/west before tapering to spotty
drizzle late. Cold advection filtering in may also catch some
of the exiting moisture far northwest toward daybreak, but since
slower only left in a mention. Kept lows on the warmer side of
Mos given current trends and slowness of the boundary to head
Lots of uncertainty on Monday as the area slides in between the low
offshore and ahead of the Arctic front still west of the mountains.
Some solutions continue to try and hang back a lobe of shallow moisture
across the region with low level moisture perhaps getting trapped in a
leftover weakness across the far west as deepening north/northeast
flow develops out east in the wake of the low. This could result
in spotty light snow/rain west of the Blue Ridge into early afternoon
with some patchy rain lingering east, but quite iffy and light
if it occurs at all. Otherwise looks like mainly cloudy despite
good drying aloft and even a drier boundary layer in the afternoon
before precip ahead of the Arctic boundary arrives late with a
rain/snow mix western ridges after sunset. Under weak cold
advection, keeping highs in the middle of guidance which results
in mostly 40s, except perhaps around 50 far south, and only in
the 30s on the western ridges.
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 200 PM EST Sunday...
The arctic front with its surge of cold air will barrel into the region
early Monday night. Good dynamic support from the upper jet and
vigorous short wave energy will combine with good low level moisture
with some influence from the Great Lakes to develop snow showers west
of the Blue Ridge. Expect a couple of inches of accumulation at the
preferred higher elevation locations along with some snow bands
bringing localized accumulations a bit further to the east. There are
also hints that the front will be able to couple with some lingering
synoptic deformation to produce some snow east of the Ridge, possibly
with some embedded mesoscale banding. All of this would impact the
morning commute Tuesday east of the Ridge so a winter weather advisory
may be needed if the situations continues as advertised in later model
Winds will be increasing significantly Monday night into Tuesday as the
low level wind field amplifies and a well mixed boundary layer allows
for good downward momentum transfer. Bufkit soundings also show a
lowering inversion that will help squeeze the flow and generate strong,
gusty winds. These winds will combine with the cold temperatures in the
advancing arctic airmass to create single digit wind chill values west
of the Blue Ridge by Tuesday morning. With the combination of strong
gusty winds and a couple inches of snow, will issue a winter weather
advisory for the higher elevations west of the Blue Ridge Monday
evening into Tuesday morning. A more widespread wind advisory may also
be needed for other locations with strong winds but less snow. Will see
how the situation develops and allow later shifts flexibility to issue
the necessary headlines.
Snow showers will gradually diminish to lingering flurries west of the
Ridge during the day on Tuesday as a large area of high pressure
settles over the region and brings fair but chilly weather to the
region through Wednesday. Wednesday morning looks to be the coldest
point during this cold spell with temperatures generally in the teens
with some single digits west of the Blue Ridge.
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 200 PM EST Sunday...
The progressive upper pattern will keep systems zipping along and allow
for a brief break in the action through midweek with a trend for
temperatures retuning at or above normal levels by Thursday. The next
frontal system with developing low pressure will then begin to affect
the region late Thursday into Friday.
The latest guidance is not as enthusiastic with QPF as previous runs,
but, there still appears to be enough associated cold air and
precipitation to allow for some accumulating snow to develop later
Thursday through Friday, though timing and location of any snow remains
uncertain. Will be watching upcoming model runs closely to see how the
High pressure will then bring fair weather with below normal
temperatures into next weekend before the next frontal system pushes
precipitation into the region from the west on Sunday.
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
As of 700 PM EST Sunday...
Poor aviation conditions expected through the TAF valid period,
with potential for improvement across the Piedmont during the
later portion of the TAF valid period, mainly after 16Z Monday.
Ceilings and visibilities will remain mostly IFR-LIFR throughout
the night in low clouds, fog, light rain, and drizzle. While the
main synoptic wave is moving east of the area this evening, low
pressure moving through the Southeast U.S. will spread rain
back into the area during the night. A deformation zone will
also bring rain back from the north/northeast later in the night
across the New/Roanoke/and Shenandoah Valleys. When not raining,
feel that drizzle and fog will be an issue, per most BUFKIT
soundings from most models. HRRR really hits fog concerns early
and continues throughout the night, which so do the NAM and GFS.
A Dense Fog Advisory may be needed later. For now will issue an
SPS concerning such. Worst conditions are along the Blue Ridge
and western mountains where the ceilings are down on the ridge
tops with 1/2SM or less visibility common in those areas. As
drier air continues to work into the region from the
north/northwest Monday afternoon, look for some improvement east
of the Blue Ridge with MVFR-VFR possibly by mid or late
afternoon. IFR improving to MVFR conditions will likely evolve
across the western upslope areas.
Winds will be mostly light and variable overnight, favoring a
north to northeast direction in most areas with speeds 5kts or
less at most sites. Winds will tend to back to the north-
northwest with time Monday, but speeds will remain mostly 7kts
Medium confidence in ceilings and visibilities throughout the
TAF valid period.
Medium confidence in wind direction, high confidence in wind
speed throughout the TAF valid period.
Lingering upslope northwest flow in the mountains brings more
MVFR/IFR clouds and scattered to numerous snow showers Monday
night into Tuesday. Northwest winds will also increase behind
the front Monday night and Tuesday with strong gusts possible.
VFR then returns to all sites mid- week as high pressure builds
in from the west.
Increasing amounts of polar air will spread into the eastern
U.S. during the later half of the week. Moisture will be
limited, but a reinforcing surge of Arctic air will arrive late
in the week and by next weekend. Each of these systems will be
accompanied by some potential for winter precipitation, mainly
in the form of snow as it appears right now. Periods of sub-VFR
ceilings will certainly be possible throughout the week, with
more lengthy periods of such across the western mountain and
VA...Winter Weather Advisory from 7 PM Monday to 10 AM EST Tuesday
NC...Winter Weather Advisory from 7 PM Monday to 10 AM EST Tuesday
WV...Winter Weather Advisory from 7 PM Monday to 10 AM EST Tuesday
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
814 PM EST Sun Jan 28 2018
Things have shaped up to be a very wet day across west central and
southwest Florida. The area of low pressure is now located just off
the west coast of Florida and will continue to track east over
Florida for the next 12 hours. Some reporting stations and radar
rainfall estimates are reporting anywhere from an inch of rain south
of Tampa Bay to 1.5 - 2.5 inches of rain with some local areas
approaching 3 inches. Rainfall amounts from Tampa Bay northward will
begin to taper off in the next 2-3 hours, while over southwest
Florida from Sarasota County southward will see increasing amounts
of rain over the next 2-3 hours. As the area of low pressure and
associated front moves off the east coast later tonight into early
Monday morning, rain chances will continue to decrease by mid-
morning on Monday, with all rain clearing the area by Monday
afternoon. Even with the rainfall moving out, cloudy skies will be
slow to clear out until late Monday into early Tuesday morning. I
have made some adjustments to the POPs based on latest radar and
HRRR guidance through the early morning hours. Will send out updated
Moderate to heavy showers are streaming in from the gulf producing
region wide MVFR conditions at all terminals. Over the next 6-9
hours, brief periods of IFR and LIFR can be expected in the heavier
showers. A stray thunderstorm may be possible over the next hour,
but will be so sporadic that I did not mention them in the TAF.
Winds will remain generally less than 10 knots with some gusts near
15 knots in heavier showers. The majority of the inclement weather
will have moved through the terminals by 14-16Z, but some lingering
low clouds and BR will be possible through late morning.
The area of low pressure is continuing to push through the gulf
coast waters with showers and a stray storm possible for the
overnight hours. Sea fog will also continue to be possible over the
coastal waters through the night as well. As the low moves eastward
out of the area on Monday, gradual clearing conditions can be
expected. High pressure behind the front settles into the
southeastern states by midweek. Winds will be veering around to the
north on Monday with likely small craft conditions possible by late
Monday into early Tuesday morning and continuing until Wednesday. At
that time, high pressure moves off the east coast allowing for the
winds to veer easterly and decrease below advisory level. No other
marine hazards expected through the period.
.Preliminary Point Temps/PoPs...
TPA 65 72 49 63 / 80 40 0 0
FMY 66 76 53 68 / 70 50 10 0
GIF 65 74 48 64 / 90 50 10 0
SRQ 64 71 51 64 / 90 40 0 0
BKV 64 71 43 62 / 90 50 0 0
SPG 64 70 50 62 / 80 40 0 0