Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/22/18
Area Forecast Discussion
National Weather Service Albany NY
1040 PM EDT Wed Mar 21 2018
.SYNOPSIS...
A coastal storm will bring some snow south and east of the Capital
Region tonight. Generally fair but chilly conditions will return for
Thursday into Friday, although a passing upper level disturbance
could bring some snow showers for Friday.
&&
.NEAR TERM /THROUGH THURSDAY NIGHT/...
...Winter Weather Advisory for Dutchess and Litchfield Counties
until 8 AM Thursday...
As of 1040 PM EDT...The latest radar and observational trends
combined with the most recent 3-km HRRR and NAM nest guidance
support dropping the advisories in Ulster, eastern Columbia, and
southern Berkshire Counties. We also collaborated with WFO BOX
and OKX about converting the Winter Storm Warning for Litchfield
County to an advisory. The low-level dry air with the north to
northeast flow from high pressure over Hudson Bay continues to
keep the pcpn echoes suppressed south and east of the I-90
corridor.
The 00Z KALY sounding continues to show a slow and gradual
moistening of the column with clouds near H700 or about 10 kft
AGL. The PWAT has only risen to 0.28". The column finally
moistened between 9-10 pm for snow at KPOU. A few light snow
amounts have come in in southern Litchfield County in the 1-2"
range. Please see our latest PNS. An additional 2-5" is possible
with the heaviest amounts from Poughkeepsie-Torrington south
and east. Further north, a coating to a few inches is possible.
Some retooling of the PoPs and temps was done based on
observational trends. Portions of the Capital Region north and
west will received a few flakes or no snow at all.
Lows tonight mainly in the upper teens to mid 20s northern
areas, and mid/upper 20s central and southern areas. North to
northeast winds will remain brisk, esp across southern areas
where some gusts up to 25 mph could occur.
For Thursday, some lingering snow showers may be ongoing through
the morning across the Taconics, Berkshires, Litchfield Hills,
and even the Capital Region, before decreasing in the afternoon.
Some breaks in the clouds are expected to develop in the
afternoon. It will remain quite breezy, with northwest winds
gusting up to 25-30 mph at times. Highs should reach the upper
30s to lower 40s in valleys, with mainly lower/mid 30s across
higher terrain.
Weak shortwave ridging should build across Thursday night,
allowing for some clearing to occur. Temps may fall off more
than currently forecast due to decoupling, with current
forecast lows in the teens to mid/upper 20s, although again,
may be quite a bit lower in some areas.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
An upper tropospheric shortwave trough will remain over the
Northeast Friday through Sunday morning with multiple pieces of
shortwave energy slipping southward over the region. Limited moisture
and lift will inhibit precipitation beyond snow flurries or a few
passing showers over the weekend. The Adirondacks and higher terrain
in southern Vermont could see up to a few tenths of an inch of snow
accumulation over the weekend. High temperatures on Friday and
Saturday will be in the low 30s to low 40s with low temperatures in
the upper teens to mid 20s.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
The mean longwave trough over the Northeast will begin to weaken by
the end of the weekend, as a high amplitude ridge builds into the
Northeast from the west/southwest with temperatures moderating
closer to late March seasonal normal readings.
Sunday...A large sfc Canadian anticyclone /1040 hPa/ attempts to
ridge in from north-central Quebec, as an upper level trough moves
across the region with some isolated rain and snow showers
especially over the higher terrain south and east of the Capital
Region. The cold pool with the upper low will focus some
instability showers tied to the diurnal heating based on the latest
12Z GFS/ECMWF/GEFS/CMC. H850 temps will be in the -8C to -10C range.
Highs will run below normal by 10 degrees or so with upper 30s to
lower 40s in the valley areas, and upper 20s to mid 30s over the
higher terrain.
Sunday night into Monday Night...A high amplitude ridge builds in
from the Southeast through the Great lakes Region and into eastern
Canada. The H500 ridge folds over into the Northeast and the
Canadian Maritimes early in the week with a big cutoff cyclone off
the New England Coast. H500 heights increase to 570 decameters over
southeast Ontario and southern Quebec. Fair and cold or cool weather
will persist with lows in the teens and 20s, and highs on Monday
getting into mid 30s to mid 40s.
Tuesday will be the transition day where temperatures get closer to
normal readings with the sfc anticyclone anchored over northern New
England and the East Coast. A cold front will be approaching from
the northern Plains and western Great Lakes Region. Highs reach the
upper 40s to around 50F in the valleys with abundant sunshine, and
upper 30s to mid 40s in the mtns.
Tuesday night into Wednesday...Some differences with the medium
range guidance and the ensembles on the timing of the break down of
the ridge over the Northeast. A cold front, and a sfc low will be
approaching from the Midwest and Great Lakes Region. We slowly
increased a slight chance to chance of rain/snow showers late
Tue night into Wednesday with seasonable temps for the forecast
area.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Coastal storm continues to spin offshore, sending snow bands
north and west across southern New England and southern New
York. Moisture associated with the storm is battling a stout
feed of dry air from the north, and currently the dry air is
winning out. Snow potential at KALB/KGFL is little to none with
VFR conditions prevailing under a midlevel stratus deck. Snow
potential remains uncertain at KPOU/KPSF. Current thinking is
that the column will eventually saturate enough to support
snowfall at KPOU, but the timing was pushed back a few hours.
Once snowfall begins, visibility will likely deteriorate quickly
to IFR within an hour or two. The timing of the onset of
snowfall remains uncertain, making this a highly challenging
forecast. Even less confidence for snow potential at KPSF, but
enough evidence to maintain a mention of MVFR snow showers with
a TEMPO for IFR.
Conditions improve at KPSF/KPOU late tonight as the coastal
storm pulls away, with drier air raising ceilings to VFR late
tonight or early Thursday morning.
Winds will remain mainly northerly tonight at around 10 kt.
Winds will become north-northwesterly at around 10 to 15 kt late
Thursday morning into the afternoon, with some gusts of 20 to 25
kt possible.
Outlook...
Thursday Night: No Operational Impact. NO SIG WX.
Friday: Low Operational Impact. Slight Chance of SHRA...SHSN.
Friday Night: No Operational Impact. NO SIG WX.
Saturday: Slight Chance of SHRA.
Saturday Night: Low Operational Impact. Slight Chance of SHSN.
Sunday: No Operational Impact. NO SIG WX.
Sunday Night: No Operational Impact. NO SIG WX.
Monday: No Operational Impact. NO SIG WX.
&&
.FIRE WEATHER...
The Fire Weather season has officially begun across eastern New
York and western New England. Despite this, snow cover is in
place across much of the region, which will mitigate any
potential fire weather hazards for the time being. Additional
snowfall is expected today into tonight for southeastern parts
of the area which will continue to prevent issues in the near
future as well.
A coastal storm will brush far southeastern parts of the region with
some snow for tonight. Generally fair but chilly conditions will
return for Thursday into Friday, although a passing upper level
disturbance could bring some snow showers for Friday.
&&
.HYDROLOGY...
No hydrologic issues are anticipated through the week.
Although northern areas will stay dry today into tonight, areas
south and east of the Capital Region will see some snow for
tonight, with the heaviest amounts across Dutchess and
Litchfield counties. Total liquid equivalent in these areas will
be up to one half of an inch, although areas outside Dutchess
and Litchfield Counties will generally see less than a quarter
of an inch. This snowfall won`t have any immediate impact on
area rivers and streams.
Behind this storm system, mainly dry weather is then expected
for the remainder of the week and into the weekend. There could
be a few passing snow showers or flurries for Friday through
Sunday, but this will produce little to no measurable
precipitation.
A slow diurnal snowmelt is expected over the next several days,
with temperatures above freezing during the day, and below
freezing at night. There will be little impact on the waterways
with minimal, if any, rises.
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...Winter Weather Advisory until 8 AM EDT Thursday for CTZ001-013.
NY...Winter Weather Advisory until 8 AM EDT Thursday for NYZ065-066.
MA...None.
VT...None.
&&
$$
SYNOPSIS...KL/Wasula
NEAR TERM...KL/Wasula
SHORT TERM...Cebulko
LONG TERM...Wasula
AVIATION...Thompson
FIRE WEATHER...Frugis/KL
HYDROLOGY...Frugis/KL
Area Forecast Discussion
National Weather Service Bismarck ND
955 PM CDT Wed Mar 21 2018
.UPDATE...
Issued at 940 PM CDT Wed Mar 21 2018
For the late evening update the only significant change was to
delay the onset of fog.
Currently, there is an area of stratus/fog along the Canadian
border from Columbus and Portal eat to Kenmare and then more
patchy in nature from westhope to Rugby and Bottineau. Weather
Cameras in this area do not show much in the way of reductions in
visibility, with the exception of Kenmare. Also a quarter mile
visibility at Estevan so there is likely some patchy dense fog
along the Canadian border.
Elsewhere dense fog has yet to form, but we do see some
visibilities dropping down under 10SM. Too many factors pointing
to fog to back off, but we did delay the onset most areas and
limited fog to just patchy in nature over the southwest.
UPDATE Issued at 646 PM CDT Wed Mar 21 2018
For the early evening update we lowered sky cover across the CWA
this evening. Fog and stratus that lingered into the afternoon
finally dissipated except for a few areas remaining over the north
central and into the Turtle Mountains. Otherwise skies were clear.
This will likely set the stage for another round of fog/stratus
developing later this evening and overnight across northwest and
central ND.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 146 PM CDT Wed Mar 21 2018
Short term highlights include patchy fog overnight and the
oncoming winter storm beginning Thursday night.
Synoptically a ridge axis was centered over the northern Rockies
with northwesterly flow over the northern Plains. A surface high
remains in place under anticyclonic flow aloft. Light winds
associated with the high pressure and continuing snowpack
sublimation were enough to continue patchy fog in the forecast for
tonight.
Thursday mid-level winds turn southerly in response to an upstream
trough approaching from the west. Warm air advection, focused to
the southwest, will bring surface highs into the low to mid 40s
across our west/southwest.
.LONG TERM...(Thursday night through Wednesday)
Issued at 146 PM CDT Wed Mar 21 2018
Overnight Thursday a potent shortwave ejects out of the deep
Pacific trough. Strong mid-level southerly winds reaching 50 kts
will amplify moisture transport ahead of the wave as NAEFS
guidance has been consistent on anomalous precipitable water
values reaching the 99th percentile with this system. Strong lift
associated with deep frontogenesis under broad synoptic ascent
above will create a swath of moderate to at times heavy precipitation
across northwest to south-central and southeast ND.
Precipitation type will be heavily dependent on the surface
temperature and ice presence within the atmospheric profile. A
thermal gradient oriented along the band of precipitation will
cause rain to be the dominant precipitation in the southwest with
a transition to snow towards the Missouri River and eastward.
Uncertainty in accumulation totals along and west of the Missouri
River through Lake Sakakawea exist with surface temperatures
around or above freezing early Friday morning.
The greatest snowfall accumulations continue to be favored across
north central North Dakota through the James River Valley where
thermal profiles will be coolest under the coupling of intense
synoptic/mesoscale forcing. As this band of snow passes to our
east late Friday the threat for freezing drizzle on the back end
arises with ice loss aloft.
The 12Z global model suite continues to indicate additional
opportunities for accumulating snow Saturday night into early next
week under an active southwesterly flow pattern, with uncertainty
in intensity and exact location of precipitation.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 940 PM CDT Wed Mar 21 2018
VFR conditions to begin the 00Z TAF period. It appears KDIK will
have the best chance of remaining VFR through the night, although
some of the mesoscale models indicate KDIK could be near the low
stratus/fog late tonight into Thursday morning. Otherwise KISN,
KBIS and especially KMOT and KJMS are expected to develop
fog/stratus late this evening or overnight. Once fog does develop
IFR to LIFR ceilings and visibilities would be expected to linger
through mid to late morning on Thursday, before slowly improving
to MVFR Thursday afternoon. A light east to southeast flow is
expected tonight and Thursday morning, with an increasing
southeast flow Thursday afternoon.
Looking at latest RAP BUFkit soundings and GFS lamp guidance there
are some indications of more stratus than fog. Will continue to
look over this for issuance of the 06 UTC TAFS. Latest mesoscale
models continue to indicate low ceilings and visibilities
expanding from north central and east central ND westward to areas
mainly north and east of Lake Sakakawea and the Missouri River.
Tough call, but they have backed off a bit on the expansion into
the southwest, including KDIK.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday morning through Saturday morning
for NDZ002>005-010>013-021>023-025-035>037-047-048-050-051.
&&
$$
UPDATE...TWH
SHORT TERM...AE
LONG TERM...AE
AVIATION...TWH
Area Forecast Discussion
National Weather Service State College PA
1147 PM EDT Wed Mar 21 2018
.SYNOPSIS...
Long-duration, early spring snow storm will begin to finally
loosen its grip on the region this evening. The rest of the
week will feature cooler than average temperatures and
occasional flurries. The weekend now looks to be dry as the next
weather system passes to the south of PA.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
The snow is pretty much confined to about the SERN 1/3 of my
CWA and the HRRR continues to show it melting away over the
next several hours. There is good consensus that any measurable
precip will be over by midnight with little more than a few
lingering flurries into the wee hours.
Final storm totals will range from 10 to 20 inches and will
make this the biggest snow event for the 2017-18 winter season.
A check of snowfall records at Harrisburg indicates a 2-day
snowfall over 1 foot would crack the top-10 2-day March
snowfalls, with the benchmark of course being the 1993
"superstorm."
As temperatures fall overnight, slick spots could form on
untreated roads, sidewalks and elevated surfaces as areas of
slush and standing water from melted snow refreeze.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Models showing a trailing shortwave diving southeast across the
region on Thursday. Upper level diffluence ahead of this feature
should result in a fair amount of cirrus. Low PWATS and temps
aloft not cold enough to generate moisture flux from the Grt
Lks, so not anticipating anything more than scattered flurries
across the Laurel Highlands.
NBM/Superblend indicating max temps Thursday ranging from the
low 30s over the highest terrain of the Alleghenies, to the low
40s in the Susq Valley. However, a tight pressure gradient west
of coastal low will produce gusty winds, making it feel even
chillier. Bukfit soundings support frequent gusts between
20-25kts.
&&
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
All models tracking closed upper level low southeast across Pa
on Friday, likely supporting scattered, diurnally-driven snow
showers and flurries, mainly over the northern and western
mountains.
After that, focus will shift toward low pressure lifting out of
the Miss Valley next weekend. NAEFS/ECENS indicate this system
will likely pass too far south to affect central Pa, but will
maintain the slight chance for a period of snow.
After that, all med range guidance is showing upper level
ridging building into the region, supporting a high confidence
forecast of fair weather and warming temperatures early next
week. A dying cold front could approach the area late Tuesday,
potentially spreading showers into the state.
Temperatures should remain below seasonal normals through most
of the long term forecast, as upper trough remains over the
northeast conus. However, moderation is anticipated by Tue/Wed,
as upper trough lifts out.
&&
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
Improving conditions to drop down from the north and work in
from the west as storm pulls away with VFR conditions at most
airfields save for the far southeast....KMDT and KLNS where
a band of light to moderate snow continues. Increasing
northerly flow should bring back ceiling restrictions in the
higher elevations of the west and possibly parts of the southern
mountains overnight.
Outlook...
Thu...No sig wx expected.
Fri...Cig restrictions poss NW.
Sat-Mon...No sig wx expected.
&&
.CLIMATE...
RECORD DAILY MAXIMUM SNOWFALL SET AT HARRISBURG PA...
A RECORD SNOWFALL OF 8.1 INCH(ES) WAS SET AT HARRISBURG PA TODAY.
THIS BREAKS THE OLD RECORD OF 7.5 SET IN 1964.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...La Corte
NEAR TERM...La Corte
SHORT TERM...Fitzgerald/RXR
LONG TERM...RXR
AVIATION...Gartner/RXR
CLIMATE...
Area Forecast Discussion
National Weather Service Wilmington OH
939 PM EDT Wed Mar 21 2018
.SYNOPSIS...
Low pressure is moving east tonight, allowing high pressure and
a drier airmass to build into the region Thursday and Friday.
Low pressure will bring a mix of rain and snow to the region
for Saturday. High pressure and dry air are forecast to return
Sunday and Monday.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Surface analysis suggests a surface trough is currently over the
ILN CWA, extending from ESE-to-WNW, with a slight veering of
winds behind the southward-moving axis. Precipitation has
largely ended across the ILN CWA, with surface observations
showing that clouds remaining over the area are generally in the
mid-levels. The only exception, for the next hour or two, is the
chance for some light flurries or freezing drizzle in southern
Ohio / northeastern Kentucky, where a few pockets of low-level
moisture still exist. RAP projections (mainly at 900mb and
below) and a few light radar returns suggest this is the case,
and also suggest that it will come to an end soon.
A Special Weather Statement is in effect to highlight the
potential for refreezing tonight, as any wet roads will become
prone to becoming icy as temperatures fall into the 20s. The
main change for this evening forecast update was to drop
temperatures overnight, especially where the heaviest snow fell
earlier -- mainly in the western half of the ILN forecast area.
Temperatures were lowered by several degrees, especially as
clearing is beginning to work into the region from the west. In
fact, current HRRR/RAP runs suggest temperatures may fall even
lower than even in this updated forecast -- possibly well into
the teens. That is not out of the question given the
aforementioned conditions.
Previous discussion >
Surface analysis shows low pressure to the east and high
pressure to the west. ILN area is under a chilly northerly flow
between these systems. Moisture and forcing associated with the
low are diminishing and snow is ending. Still will see light
snow for a few more hours especially in eastern locations, but
little to no additional accumulation is expected. Clouds will
linger this evening until clearing from the west arrives
overnight with the high moving in. Temperatures will fall below
guidance to the lower 20s, with these cold readings aided by
snow cover.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Surface high pressure developing under a northwest upper flow
will extend across the area Thursday and Thursday night. This
will provide dry weather conditions and mostly clear skies
through the period.
Sunshine and modest warm advection will allow high temperatures
in the low to mid 40s, still close to 10 degrees below normal.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
In a northwest flow aloft, our region will be between weak systems
to our northeast and southwest on Friday. Surface high pressure will
remain in place, and with sunshine, temperatures will warm into the
40s.
Focus then turns to a low pressure system forecast to pass southeast
through the lower Ohio Valley and the Tennessee Valley Friday night
into Saturday night. Strong ascent in the form of a moist low level
jet will spread precipitation east/northeast into the region Friday
night into Saturday. There is an increasing signal for an
accumulating snow event, perhaps significant, for locations along
and north of the Ohio River. Many factors will play in how much snow
will fall such as surface temperatures, thermal profiles, time of
day, exact track of the low, and whether some locations along and
north of the Ohio never mix with or change over to rain. We
currently have a mix developing north of the Ohio with rain/snow
changing to rain south of the Ohio. However, strong lift/dynamic
cooling, along with a prolonged easterly flow in the low levels, may
keep sounding profiles saturated near or below the 0 degree isotherm
for points along and north of the Ohio River. Also, the strong
vertical motion will likely occur in the favorable dendritic growth
zone which will result in aggregate snowflakes. These types of
snowflakes can result in heavy snow with rapid accumulation. So,
until confidence increases in ptype and duration, have initially
went with conservative in amounts, with the caveats mentioned above
that could result in a heavier, more significant snow. This has been
placed in the HWO.
By Saturday night, the low pressure system will be pulling away to
the southeast, allowing surface high pressure to build back into the
region for Sunday. After lows between 25 and 30, highs will warm
back into the 40s on Sunday.
High pressure at the surface and aloft will remain over the region
on Monday. Temperatures will continue to moderate with highs in the
upper 40s to the lower 50s.
For the remainder of the extended, an increasing moist, southwesterly
flow will develop around the mid level ridge axis passing to the
east. This will bring clouds and the potential for showers as we
head into Tuesday. A frontal boundary will try to make inroads into
the area by mid week, keeping the threat for rain in the forecast.
Temperatures will continue to warm with 50s and perhaps 60s possible
by next Wednesday.
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
With any remaining light snow departing the area early this
evening, VFR conditions are expected through the rest of the TAF
period. Ceilings have shifted to VFR, mainly with mid-level
clouds, which should persist into the overnight hours before
clearing out entirely. Clouds tomorrow will generally just be
cirrus and some fair weather cumulus -- remaining VFR through
the day.
Winds will remain out of the northwest through the period,
diminishing some this evening, but increasing to around 8-12
knots tomorrow afternoon.
OUTLOOK...MVFR/IFR ceilings and visibilities are possible
Saturday and Saturday night. MVFR ceilings are possible again on
Monday.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...Coniglio
NEAR TERM...Coniglio/Hatzos
SHORT TERM...Coniglio
LONG TERM...Hickman
AVIATION...Hatzos
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
858 PM EDT Wed Mar 21 2018
.UPDATE...
Issued at 845 PM EDT WED MAR 21 2018
Snow showers generally continue to become lighter and more
scattered in nature. Since around 5 PM, we picked up about 0.3"
here at WFO JKL so several higher elevation locations near the VA
border will likely pick up more over the next few hours. The snow
showers should gradually diminish to flurries with loss of
daytime heating and as the upper level low gradually pulls
further away. The upslope flow will hang on for a couple more
hours near the VA border in the higher elevations and with some
accumulating snow still possible there over the next couple of
hours. With that in mind, we have transitioned over to an SPS for
most of the area, though the Winter Weather Advisory has been
extended through 11 PM for the VA border counties.
Since 8 PM, an NWS employee reported an icy overpass at MM 43 on
the Mtn Parkway. As temperatures cool into an through the 20s
tonight, more black ice is anticipated. The above mentioned SPS
was initially ran through around 8 AM.
&&
.SHORT TERM...(This evening through Thursday night)
Issued at 350 PM EDT WED MAR 21 2018
19z sfc analysis shows deep low pressure exiting the area with
healthy cyclonic flow continuing through eastern Kentucky. These
winds are upslope and as a result are helping to sustaining snow
shower activity even as the low`s center is in the process of
jumping to the East Coast. Visibilities with these showers
remain between 1 and 2 miles - still impacting the area and likely
accumulating a bit. Currently brisk northwest winds are running
at 10 to 15 mph with gusts to 25 mph. The CAA on those winds,
along with overcast conditions and snow showers, have kept
temperatures from climbing too far out of the lower 30s across
the area today. Meanwhile, dewpoints are similar to temperatures -
generally in the upper 20s to lower 30s. Wrap around snow showers
associated with the now coastal low are being enhanced by the
upslope flow in the far east supporting some light accumulations
this afternoon. Accordingly, will keep the WSWs running through
00z for the entire area, though we may be able to clear the
southwest before too long.
The models are in good agreement aloft through the short term
portion of the forecast. They all depict the deep trough that will
run up the East Coast tonight. Trailing energy will exit Kentucky
in northwest flow by Thursday morning. Height rises will follow
as strong ridging starts to work east out of the Rockies and into
the Plains. However, before this can influence the weather over
Kentucky much, another short wave will ride southeast out of the
northern Great Lakes region and brush by the area to the northeast
early Friday morning - maintaining the strong northwest flow at
mid levels. Given the good model agreement have favored a general
blend with a lean toward the higher resolution HRRR and NAM12 for
specifics.
Sensible weather will feature snow showers gradually winding down
this evening from west to east with accumulating snow expected to
be done toward 00z when the WSWs will likely be allowed to drop.
Following the snow showers dissipating, clouds will break up from
west to east late. CAA and radiative cooling tonight should send
readings down into the lower and mid 20s by dawn Thursday. Any
left over wet patches or slush on the roads tonight will likely
refreeze and create localized black ice conditions. Have messaged
this in the HWO and will make sure it is highlighted in the
evening weather story, as well. Sunshine and high pressure will
bring warmer temperatures to the area on Thursday drying us out
and taking care of most of the snow on the ground. For Thursday
night, the high will shift far enough east to allow some lower
clouds to return to the southwest parts of the area in the form
of a developing warm front. Otherwise, expect mostly clear skies
to also support a decent ridge to valley temp split overnight
outside of the Cumberland Valley.
Did make minor adjustments to temperatures tonight to go colder
in the places that have deeper snow cover and also due to CAA
affects on terrain. Likewise, adjusted temperatures Thursday
night for relative elevation differences away from the southwest
parts of the area. As for PoPs, lingered them a bit longer and
higher in magnitude through the evening and into the early
overnight hours in the east.
.LONG TERM...(Friday through Wednesday)
Issued at 305 PM EDT WED MAR 21 2018
The extended period will feature a mix of rain and snow to start
things off, as a couple of low pressure systems move across the
region over the weekend. The better chance of accumulating snow at
this time looks to be for the period Friday night into Saturday
morning. The latest model data indicates that the best chances for
accumulating snow will occur north of Highway 80. The second chance
for any snow will be Saturday night into Sunday morning, although
this shot of snow looks like it will be marginal at best with little
if any accumulations expected. Once the second weather system
departs the area late Sunday, we should see a period of dry weather
to begin the new work week. A ridge of high pressure should keep
precipitation associated out of most of the area until Tuesday
night. The ridge is then forecast to break down just enough to allow
an area of low pressure and its surface front to move across the
area on Wednesday. This system could potentially bring a good
soaking rain to eastern Kentucky.
Temperatures around the area should start off below normal, with
highs in the 40s and 50s expected Friday through Sunday. We should
see a return to normal temperatures on Monday, with highs that day
expected to max out in the mid to upper 50s. Next Tuesday and
Wednesday could see a return to well above normal temperatures, with
highs on both those days possibly topping out in the 60s. Nightly
lows should start off near or slightly above normal Friday and
Saturday nights, with above normal nightly lows on tap after that.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 835 PM EDT WED MAR 21 2018
Generally MVFR ceilings with MVFR and some areas of IFR vis in
snow showers was occurring across the region. Snow showers should
continue gradually diminishing to flurries and ending from
northwest to southeast over the next 6 hours or so. As drier air
moves into the region, improvement to VFR is expected at the TAF
sites through around 6Z. MVFR may hang on for a few hours after
that in far southeast KY. Once improvements to VFR occur, VFR
should persist through the end of the period as high pressure
builds into the area. Winds will average out of the west to
northwest at generally 10KT or less through 15Z and then become
more northwest at near 10KT.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 PM EDT this evening for KYZ087-
088-118-120.
&&
$$
UPDATE...JP
SHORT TERM...GREIF
LONG TERM...AR
AVIATION...JP
Area Forecast Discussion
National Weather Service Spokane WA
442 PM PDT Wed Mar 21 2018
.SYNOPSIS...
A change in the weather is expected as a deep upper level low
digs offshore tonight. This will pool moisture into the region
from the south resulting in an increasing chance of precipitation
beginning this evening and continuing at times through Thursday.
Most of this precipitation will fall as rain however snow will be
possible over the higher mountains. A cold front late Thursday
will bring gusty winds and deliver significantly cooler conditions
from Friday through the weekend with the threat of rain and snow
showers each day.
&&
.DISCUSSION...
Tonight and Thursday: The warm front will continue to move north
across the Inland northwest this afternoon and evening. It will
provide some light rain across the region. The last several runs
of the HRRR has shown heavier periods of rain moving up the
Okanogan Valley, and across the Palouse early this evening. That
is a result of the precip that is currently occurring down in
Portland and along the WA/OR border. The upper level trough moving
out of the Gulf of Alaska will push south through the night and
pick up the moisture that is streaming into California. Our
heavier stratiform precipitation will move into the Cascades
between 10pm and midnight and then spread east through the night
across eastern WA and north ID. The models have been consistent
for days of the heaviest precipitation occurring overnight into
early Thur morning across the eastern Cascades. There is a period
in the morning when precipitation intensity will decrease, and
then models show heavy precip again in the afternoon as the cold
front begins to push over the Cascades. The heaviest precip in the
afternoon will be across the eastern Cascades and stretch across
the northern tier of WA.
Liquid Precipitation Amounts: Precip amounts will vary. The
highest accumulations will be in the northern Cascades north of
Lake Chelan where they could see an inch to an inch and a half in
the mountains. They valleys will see over three quarters of an
inch. The Columbia Basin will see the least precip with a few
hundredths up to a quarter of an inch possible. Most of the Basin
will see about a tenth of an inch. All other locations will see
0.30 to 0.50 in the valleys with 0.50 to 0.75 in the mountains.
The Okanogan Highlands higher terrain could see up to an inch.
Snow Levels: Snow levels tonight will be above 5k ft. It isn`t
until Thursday afternoon that snow levels will start to fall as
the cold front pushes over the Cascades. The heaviest
precipitation will occur while snow levels are high. By late Thur
afternoon snow levels in the Cascades will drop down to about 3k
ft.
Snow Amounts: In the Cascades above 5k ft will see the heaviest
snow amounts. 7 to 14 inches is possible with amounts 20-22 inches
possible as you approach the Canadian border. In the 3-5k ft
range they could see a dusting up to 3 or 4 inches, locally up to
5 along the Canadian border. No snow is expected down to the
valley floors in the Methow, Lake Chelan, Leavenworth areas. North
Id Panhandle will also see some snow accumulation in the
mountains...about 1-3 inches, which would fall either early Thur
morning, or Thur evening.
Winds: Winds will increase ahead of the cold front Thursday
morning across the Palouse and into the Columbia Basin. In the
afternoon the winds will push into the Spokane area. Southeast
winds 10 to 15 mph in the morning becoming southwest 15 to 25 with
gusts up to 30 mph. As the front goes through after 3pm, there
could be local gusts up to 40 mph.
Thunder: Both the GFS and NAM are showing some instability in the
afternoon across the Columbia Basin (north and east of Moses Lake)
and moving north and east through the afternoon ahead of the cold
front. Have added a slight chance of thunder to these locations.
/Nisbet
Thursday night through Sunday...A vigorous cold front will move
from west to east Thursday night and drag an upper level low into
the region. The upper level low will dominate the weather through
the weekend. The result will be cool and unstable conditions
which will support isolated to scattered rain and snow showers
across the region from Thursday afternoon through Sunday. One
thing in our favor is that model guidance is very similar in
showing very dry air moving into the region behind the front. This
would mean localized brief moderate rain and snow showers, but
overall not widespread moderate to heavy precipitation.
Snow levels will drop down to near valley floors Friday then
rebound slightly Friday and Saturday to 2000-3000 feet. Some of
the higher terrain in the mountains could see some decent
accumulations through Friday. The passes will see measurable snow
with Sherman Pass and Lookout Pass getting 4-8 inches Friday and
Saturday. This will likely come in the form of brief heavy snow
showers. The northern valleys down towards the Spokane-Coeur
D`Alene metro and south to Pullman-Moscow could see localized
heavy snow/graupel showers that could result in a quick quarter to
half inch of snow. Both of these will have the potential to make
driving conditions quite dicey in a short period of time.
Temperatures will drop 7-10 degrees on Friday behind the front and
another 3-5 degrees Saturday dropping temperatures in the mid to
upper 40s, before rebounding a little Sunday. Gusty winds will
continue through early Friday with gusts through the Basin,
Pa;louse and ridges 30-40 mph.
Monday through Wednesday...High pressure will build into the
region Sunday night with a flat ridge over the region that will
slowly strengthen through the week. This will bring a drying trend
with temperatures warming back to normal through the week with
spring like conditions. Tobin
&&
.AVIATION...
00Z TAFs: A storm system will move into the region tonight and
linger over the region for several days. Several waves of
moisture will move from south to north through the night. Timing
these waves out past a few hours will be tough, but expect that
cigs will lower and rain chances will increase with each
successful wave. Precipitaiton will be stratiform and moderate at
times. A cold front will move across the Cascades after 18z
Thursday, move quickly through the area and be along the ID/MT
border by 00-03z. This period...18-00z will be when the area will
receive the heaviest rain and also gusty winds to 25 kts. VFR
conditions can be expected through 18z, followed by VFR/MVFR
conditons 18-00z. Tobin
&&
.PRELIMINARY POINT TEMPS/POPS...
Spokane 43 52 31 46 30 41 / 50 90 80 30 50 60
Coeur d`Alene 41 51 30 44 29 39 / 50 90 90 40 50 60
Pullman 45 52 32 45 31 42 / 50 90 80 40 60 60
Lewiston 47 59 36 53 36 48 / 30 70 60 30 40 50
Colville 41 53 31 47 28 45 / 70 100 100 50 50 60
Sandpoint 38 47 31 43 29 39 / 70 90 100 40 50 70
Kellogg 38 49 29 42 28 38 / 60 80 100 50 50 70
Moses Lake 43 56 31 53 29 51 / 50 60 10 20 30 30
Wenatchee 39 49 31 48 29 50 / 90 80 0 40 20 20
Omak 42 51 31 48 28 48 / 90 100 20 60 30 40
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch from 8 PM PDT this evening through Thursday evening
for Northern Panhandle.
WA...Flood Watch from 8 PM PDT this evening through Thursday evening
for East Slopes Northern Cascades-Northeast Mountains-
Okanogan Highlands-Okanogan Valley-Wenatchee Area.
&&
$$
Area Forecast Discussion
National Weather Service Charleston WV
1106 PM EDT Wed Mar 21 2018
.SYNOPSIS...
Upper low departs and snow gradually ends. High pressure takes
control late week, followed by another low pressure system next
weekend.
&&
.NEAR TERM /THROUGH THURSDAY/...
As of 11 PM Wednesday...Allowed the remainder of winter
headlines to expire.
As of 555 PM Wednesday...
Updated package to cancel winter weather advisory for the
lowlands including southeast OH. Radar and sfc obs indicate that
the wet snowfall has became light and not sticking on the
ground.
Winter weather advisory remains in effect for the western slopes
and a Winter storm warning remains in effect for the higher
elevations. Rest of forecast remains on track.
As of 215 PM Wednesday...
Temperatures across the lowlands are largely at or just above
freezing, so accumulating snow from anything falling after the
early morning hours have been difficult to come by in this
particular area. In the mountains, however, snow continues to
accumulate, and have this continuing well into the evening. HRRR
and RAP are showing a gradual dissipation of coverage and
intensity going forward as the upper level closed low
accelerates up the Atlantic Coast.
High pressure moves in later tonight, scouring out the mountain
low level moisture, but hold low end POPs until the thermal
trough shows signs of degradation. 850mb temperatures will not
recover very much during the day on Thursday. Skies clear
southwest to northeast.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 320 PM Wednesday...
The period begins dry and cold under the influence of broad
troughing across the eastern CONUS and surface high pressure.
The resulting temperatures will be around 10 degrees below
normal for mid-late March. Ridging in the central Plains is
interrupted by a rather wound-up short wave aloft ejecting out
of the Rockies with lee-cyclogenesis occurring on the surface by
Friday afternoon. As the low tracks across toward our area, it
will intensify as it enters the right entrance region of a Great
Lakes jet aloft.
Precipitation along the system`s warm front will enter the Tug
Fork/Big Sandy basin by Saturday morning. Depending on the
timing of onset relative to solar insulation, snow will fall
upon precipitation onset with a brief period of sleet and
freezing rain before a switch to all-rain with warm air
advection Saturday. Models agree that the center of low pressure
will pass to the south of us, limiting convective potential and
thus heavy rainfall potential with PWAT barely reaching 0.75" in
the Tristate area. As the system exits and cold air advection
kicks in with trough passage, temperatures will again drop and
switch rain back to a wintry mix/snow overnight.
Snowfall accumulations look to be up to 2 inches in the
lowlands with widespread amounts generally under an inch. The
mountains will likely see more as 850 temperatures begin to drop
and support accumulation, especially as the system exits
Saturday night into early Sunday, on the order of 2-4" and
locally up to 6" total. A light coating of ice is also possible
upon onset in the coal fields and sheltered valleys with a warm
nose aloft.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 350 PM Wednesday...
High pressure and ridging returns Sunday night through early
Tuesday with southwest flow finally bringing some much-deserved
warmer temperatures into the region. Look for Tuesday high
temperatures near 60 in the lowlands with deep southerly flow
and strong warm air advection. Positively tilted troughing over
the central Plains approaches mid-week, placing us at the end of
the fire house yet again - looking a another wet pattern to set
up with PoPs rising in the Mid-Ohio Valley Tuesday into
Wednesday. Did not deviate much from a consensus blend through
the long term.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
As of 145 PM Wednesday...
A saturated atmosphere continues over the area.
IFR ceilings and visibilities will continue at least through
04Z at HTS and BKW, and through 06Z or beyond at CRW, EKN under
IFR/LIFR conditions. PKB must be in the back edge of pcpn with
very light snow but MVFR conditions as well as CKB.
Snowfall will gradually diminish in intensity and coverage by
midnight. Upslope snow showers will be possible to last through
Thursday morning along the eastern mountains with IFR
conditions.
Conditions should begin to improve to MVFR and then ultimately
VFR by mid morning Thursday. Upper level storm system will make
its exit, with the lower level moisture eroding west to east.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z FRIDAY...
FORECAST CONFIDENCE: Medium.
ALTERNATE SCENARIOS: Timing of improvement late tonight may
vary from forecast.
EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
DATE THU 03/22/18
UTC 1HRLY 03 04 05 06 07 08 09 10 11 12 13 14
EDT 1HRLY 23 00 01 02 03 04 05 06 07 08 09 10
CRW CONSISTENCY L L M M M M M M M M M L
HTS CONSISTENCY M M M M M M H H H H H M
BKW CONSISTENCY L L L L L L L L L M M L
EKN CONSISTENCY L L L M L L L L M M L L
PKB CONSISTENCY H H H H H H H H H H H M
CKB CONSISTENCY M H M M M M M M M M M L
AFTER 00Z FRIDAY...
IFR in precipitation with the next system on Saturday.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...None.
OH...None.
KY...None.
VA...None.
&&
$$
SYNOPSIS...26/MC
NEAR TERM...ARJ/26
SHORT TERM...MC
LONG TERM...MC
AVIATION...ARJ
Area Forecast Discussion
National Weather Service Blacksburg VA
1134 PM EDT Wed Mar 21 2018
.SYNOPSIS...
Low pressure will lift northeast to the New England coast
Thursday. High pressure briefly returns to the region on Friday
followed by another potential winter weather system over the
weekend.
&&
.NEAR TERM /THROUGH THURSDAY/...
As of 1130 PM EDT Wednesday...
Forecast updated to cancel winter storm warning in the
mountains, as snow showers are abating and main support from
upper levels has exited along with limited trajectory for
upslope. Still should see a few snow showers/flurries early
overnight especially in the NC mountains, but no more than an
inch or less expected.
For those areas that were in the winter storm warning, they have
now been placed in a wind advisory for stronger winds gusting 35
to 50 mph. Namely, higher ridges and more concerned with any
lingering snow on limbs/trees plus wet ground from the snow
causing trees to fall.
No other major adjustments were made to the forecast, and have a
special weather statement out for black ice due to refreeze
further east.
Previous discussion from early evening...
Adjustments made to PoPs to account for a snow squall currently
moving through the New River Valley. While currently not
producing any accumulating snow, rates are high enough to
suggest that minor accumulations are possible, but not likely.
Once this squall dissipates, should be on track that only
significant PoPs will be in upslope areas. Also, adjusted
overnight winds up slightly per short range HRRR and LAMP
guidance. Adjusted current temps to obs but little to no low
change required to overnight lows.
As of 330 PM EDT Wednesday...
995 mb surface low centered well off the Delmarva coast trails an
inverted surface trough westward from its center across central VA
into the Alleghany Front. Most significant accumulating snow per
radar trends and spotter reports has been mostly in southeast West
Virginia. We`re steadily losing the influence of the synoptic-scale
significant accumulating snowfall, and in some locations has already
since ended. Current temperatures in the upper 20s to mid 30s across
the Blacksburg forecast area.
Wintry weather and wind will continue to be the focal point in terms
of sensible weather. Have made several changes to headlines. The
first was to remove the winter weather advisory areas and to clear
out a large portion of the Winter Storm Warning. The winter storm
warning remains in effect for western Greenbrier, Summers, Mercer,
Tazewell, Smyth, Grayson into Alleghany, Ashe and Watauga Counties
where the potential exists for significant upslope snow
accumulations along with blowing snow. I`ve also issued a impact-
based Wind Advisory from the New River Valley to the Blue Ridge,
northeast into the southern Shenandoah Valley, Alleghany Mountains
and eastern Greenbrier Counties. Though expected winds will likely
be either marginal Advisory or sub-Advisory, significant amounts of
snow have fallen across this area, and with an expectation of winds
increasing tonight into Thursday, the potential for downed trees and
powerlines in these areas is elevated. The Wind Advisory runs
through noon Thursday.
As mentioned, we are quickly losing influence of the primary winter
storm. As such, significant snow accumulations in many areas may
only linger until early evening at the latest and/or have largely
ended. I`ve kept the winter storm warnings going for the upslope
areas, as snowfall coverage and renewed intensity to light to at
times moderate levels should result. Admittedly, portions of the
winter storm warning have largely underwhelmed in terms of
accumulations to this point, especially in Watauga and Ashe Counties
in NC and into the Mountain Empire region. Did think about
downgrading to Advisories for these areas, but after collaboration
with surrounding offices, decided to opt for consistency and will
maintain the warnings. Upslope snow should really occur this
evening through about midnight, and snow will tend to taper from
south to north thereafter. Still looking at an additional 2 to
4 inches, with as much as 5 inches along higher ridges in the
winter storm warning area. Have also included mention of black
ice in the HWO as temperatures cool into the 20s tonight.
Specific to the winds, northwest winds will begin to increase
tonight. Admittedly, northwest wind gusts peaking between
midnight and mid-morning Thursday probably will be quite
marginal. However, much of the Wind Advisory area has
accumulated significant amounts of snow (between 4 and 10
inches, see public information statement). We had already heard
of trees being downed in parts of Summers County due to the
weight of snow in the Talcott area. That potential will be
greater in the Wind Advisory area with snow-weighted trees and
power lines. Threat may also exist in the winter storm warning
area, but for now have mentioned potential for downed trees and
power lines in the winter storm warning text statement. Peak
northwest wind gusts should be between 35 and 50 mph.
Clearing conditions expected on Thursday as high pressure builds
back into the region. Northwest wind gusts will still be rather
strong in the morning hours, but 850 mb wind max begins to decrease
and pressure rises begin to drop as the coastal low continues to
move away. Mostly sunny skies should also allow for some snowmelt to
occur. Highs mid/upper 30s to the low 40s west of the Blue Ridge,
into the 40s and near 50 across the Piedmont and Southside.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 330 PM EDT Wednesday...
High pressure in the Ohio Valley will build east across our region
Thursday night. The upper trof along the East Coast will slide east
into the Atlantic ocean. Low temperatures Thursday night will range
from the upper teens in the mountains with snow pack to the lower
30s in the piedmont.
Temperatures will moderate on Friday with the warm advection just in
advance of the next upstream system that may bring back high clouds
during the day. High temperatures on Friday will vary from around 30
degrees in the northwest mountains in Greenbrier county to the mid
50s in the Piedmont.
Clouds will continue to increase and lower from northwest to
southeast Friday night. Low pressure and its associated war front
will lift north Friday into Friday night. Some spotty light rain or
snow could also work in far western sections late. Low temperatures
will generally be from the upper teens in the mountains to the lower
30s along the southern Blue ridge.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 330 PM EDT Wednesday...
Low pressure tracks from Tennessee Saturday afternoon, across the
Tennessee Valley and Carolinas to the western Atlantic by Sunday
afternoon. All the energy will transfer to the coastal low by Sunday
night which move northeast in the Atlantic ocean on Monday.
Some differences in the guidance how far south this low will move,
which in turn will impact where the winter weather will be on the
northern side of the baroclinic zone. Timing has been fairly
consistent, keeping the best probability of precipitation from
Saturday afternoon into Sunday morning. The GFS is faster than ECMWF
with spreading of the moisture east. The axis of the heaviest QPF is
Variable depending on Model choice. Will mention winter storm
potential in HWO. While too early to pin point exact details,
looks like the heaviest snow potential will occur in the northwest
mountains especially western Greenbrier.
Surface high pressure wedges down the east slopes of the
Appalachians Monday and Tuesday. Will hold on to isolated pops in
case precipitation over the Tennessee and Ohio Valley spills east
into the mountains. Another cold front approaches from the west
Wednesday and drop south through our region Wednesday night into
Thursday.
Temperatures will remain below normal through the period, especially
daytime highs.
&&
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
As of 713 PM EDT Wednesday...
Snow showers continue through the region and should begin to
taper off in the next few hours in all but the typical upslope
areas. Conditions have become VFR for areas east of the blue
ridge and should remain as such outside of any remaining snow as
the Low responsible for them continues to move away from the
area. BLF and LWB will continue to see MVFR to IFR ceilings and
vis under northwest flow. Expect snow in these upslope areas to
begin to diminish during the overnight and early morning hours
as high pressure begins to move in from the west. Conditions
should improve to VFR for these locations if not before, then
soon after sunrise.
Gusty winds are expected during the TAF period as the pressure
gradient between the approaching high and the strengthening
Noreaster becomes stronger.
Extended Aviation Discussion...
Mainly VFR conditions are expected by Thursday night through
Friday night under weak high pressure.
Saturday into Sunday, a return to sub-VFR conditions is expected
as our next potential winter weather system crosses the area.
&&
.EQUIPMENT...
As of 1021 AM EDT Wednesday...
The Mount Jefferson NWR remains off the air. The radio unit
needed to repair the system is expected to arrive tomorrow
(Thursday). The earliest this system will again be operational
will be Thursday afternoon.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory until noon EDT Thursday for VAZ007-009>020-
022>024-035.
NC...Wind Advisory until noon EDT Thursday for NCZ001-002-018.
WV...Wind Advisory until noon EDT Thursday for WVZ042>044-507-508.
&&
$$
SYNOPSIS...JH/WP
NEAR TERM...AL/JR/WP
SHORT TERM...KK
LONG TERM...KK
AVIATION...AL/JR
EQUIPMENT...AL/AMS
Area Forecast Discussion
National Weather Service Sacramento CA
348 PM PDT Wed Mar 21 2018
.SYNOPSIS...
Wet weather continues into the weekend. Snow will remain above
pass levels through the evening, then lower with significant
accumulations at the higher elevations into the weekend.
&&
.DISCUSSION...
Brief break in widespread precip early this afternoon with a few
cloud breaks adding to increased instability. Breezy south winds
have developed and will last into early Thursday with a few gusts
to 40 mph. Short term mesoscale models including HRRR are
indicating scattered thunderstorm development around 4 pm lasting
to as late as midnight. A strong shear environment is in place
with helicity values 300-400. Instability will be conditional and
dependent on cloud breaks, but Bufkit shows values 200-600 j/kg.
Dewpoints have soared into the lower 60`s over the srn Sacramento
valley with plenty of fuel for destabilization. High shear
environment could lead to rotation and a brief funnel cloud or
isolated tornado in stronger cells, as outlined in latest SPC
thunderstorm discussion. High freezing levels will likely lower
the threat of hail except in the tallest/strongest storms.
Decided to upgrade winter storm watch to warning, although snow
level forecast remains a bit uncertain. NBM/Nam both bring snow
levels down to 6800 feet around 11 pm tonight and down to 6000
feet by late Thursday afternoon. In this scenario just a 500 foot
change in snow level could drastically change snow amounts along
I80 from Soda Springs to Donner pass where current forecast is
for 1 to 2 feet of snow through Thursday afternoon, as snow is
forecast to just barely make it down to pass level.
Thunderstorms with small hail will also be possible Thursday, as
a very unstable airmass moves over NorCal. Additional valley
rainfall amounts up to 1.50 inches are possible with mountain
values 2.00-4.00 inches are possible during the next 24 hours.
This will increase the threat for minor small stream and poor
drainage area flooding.
A brief break in the wet weather looks likely Late Thursday night
and Friday morning, before a colder system brings potentially
heavier and lower snow Friday night. Exact details of this system
remain a bit uncertain, but decided to issue Winter storm watch
for mountain areas above 3000 feet of the srn Cascades and Sierra
including I80 and Highway 50. At this time the heaviest snow
should move over the Sierra after 8 pm with 1 to 2 feet possible
through Sunday morning. Timing and amounts with this system could
still change, as confidence is just moderate.
&&
.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)
Main upper trough shifts east of the state during the day on
Sunday bringing the last of the precipitation for a while as upper
ridging builds over the eastern Pacific. Precipitation chances
will mainly be restricted to east of the central valley.
Precipitation amounts will be quite light but snow levels will be
abnormally low at around 1500 to 2500 feet. A few lingering
showers may still be possible Sunday night but building high
pressure will bring an end to any precipitation threat by Monday.
Temperatures warm by several degrees on Monday but are still
forecast to run slightly below normal. Upper level and surface
gradients indicate breezy north winds which will help to start
drying things out. Temperatures continue to warm on Tuesday as
upper ridge pushes inland with highs expected to warm to several
degrees above normal. Even more warming is expected on Wednesday
with highs throughout the valley expected to reach the mid 70s in
the northern Sacramento valley. Breezy north winds will continue
through the period between an upper low over the southwest U.S and
building high pressure over the eastern Pacific.
&&
.AVIATION...
Mainly MVFR/IFR conditions next 24 hours TAF sites as a Pacific
storm system pushes through the region, with isolated
thunderstorms through 06z in the Valley. Mainly IFR over
mountains. Snow levels dropping from around 8000 feet this
afternoon to around 6500 feet after 06z. Wind gusts 20-30 kt
through this evening in the Valley, locally stronger in
thunderstorms. Southerly winds into Thursday with gusts 20 to 30
knots northern in the Central Valley, 40-50 knots over the higher
Sierra.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 11 PM this evening to 11 PM PDT
Thursday for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.
Winter Storm Watch from Friday morning through late Saturday
night for Burney Basin / Eastern Shasta County-Shasta Lake Area
/ Northern Shasta County-West Slope Northern Sierra Nevada-
Western Plumas County/Lassen Park.
&&
$$