Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/13/18
Area Forecast Discussion
National Weather Service Bismarck ND
954 PM CDT Thu Apr 12 2018
Issued at 948 PM CDT Thu Apr 12 2018
Will maintain the current winter weather headlines across
southwest and south central North Dakota without changes.
Did add a mention of fog across the southwest per NDDOT webcam
trends through 0240 UTC depicting areas of dense fog with easterly
upslope flow prior to the onset of moderate to heavy snowfall.
Patchy freezing drizzle is possible.
UPDATE Issued at 715 PM CDT Thu Apr 12 2018
No changes to ongoing headlines at this time. Light to moderate
snowfall will continue this evening across southwest North Dakota
with easterly upslope flow and a shortwave across southeast
Montana. Precipitation intensity will increase late tonight into
Friday morning with increasing upper level diffluence and the
impacts of a jet streak. With near freezing surface temperatures
and strong easterly winds, compaction of snowfall will likely play
a significant role impacting snow ratios. Widespread 4-6 inch
totals across the Winter Storm Warning area are reasonable by
late Friday morning, with pockets around 8 inches. This is
generally depicted by the Cobb snowfall technique applied to the
RAP and HRRR through their 23 UTC iterations, but, lower than a
The most likely upgrade would be Dunn county from an Advisory to
a Winter Storm Warning. This will continue to be evaluated
through the evening.
.SHORT TERM...(This evening through Friday)
Issued at 305 PM CDT Thu Apr 12 2018
Current headlines look reasonable with no changes to current
warnings and advisories from previous forecast.
The snow amount forecasts continue to show a sharp delineation
due primarily to the forecast qpf which generally follows the
H700 mb flow/low. We continue to expect 6 to 8 inches of snowfall
across the southwest with 1 to 2 inches east of the Missouri
Strong winds continue to be a concern Friday as the storm wraps up
and moves east. Went with CONSMOS for wind guidance tonight
through Friday. Without much snowfall there appears to be a
limited blowing snow potential, although this was considered for
the southern James River Valley.
Rain will change to a rain/snow mix late this afternoon
southwest, then to all snow tonight. Looks like there will be a
potential for freezing rain/drizzle across the south central,
east of the Missouri River Valley late tonight and Friday as
there appears to be a lack of ice crystals in the soundings across
.LONG TERM...(Friday night through Thursday)
Issued at 305 PM CDT Thu Apr 12 2018
By Friday evening the stacked storm system is forecast to be
centered over NE/KS/IA area, with the precipitation envelope
surrounding the storm system essentially south of our area, still
affecting central and eastern South Dakota, southern Minnesota and
southward. Gusty north winds will linger across south central North
Dakota Friday night, with some drifting snow lingering in southwest
and far south central North Dakota.
Saturday through Monday:
Upper level ridging builds into the Dakotas in the wake of the
departing storm system. Mainly dry weather, with a slow warm-up.
Highs Saturday in the 30s rising to highs Monday in mainly in the
Monday night through Tuesday night:
The next storm system moves into the Pacific Northwest Sunday,
strengthening as it progresses across the Rockies, and emerging into
the Front Range and western Plains Monday. The models then split
this system: The northern stream lifts northeastward into
Alberta/Saskatchewan Monday night/Tuesday and into northern Manitoba
Wednesday...and the southern portion of the system emerges out of
the base of the main trough near the 4-corners, moving east across
the central Plains around Nebraska before lifting northeastward
towards the Great Lakes on Wednesday. For North Dakota, the
consensus of the models suggests mainly a glancing blow, with
chances of rain or snow Monday night through Tuesday night. The best
CAPE with this system remains associated with the southern stream,
but the GFS is depicting a short window Monday night over western
North Dakota, and we will continue to monitor this for thunderstorm
potential. Still below average temperatures with highs in the 40s
with lows in the 20s and 30s.
Wednesday and Thursday:
Broad upper level ridging builds into the region, allowing mainly
dry conditions. Below average temperatures remain with highs in
the 40s to lower 50s...and lows in the 20s to lower 30s.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 948 PM CDT Thu Apr 12 2018
Widespread IFR/LIFR conditions this evening in fog, stratus, and
snow across southwest North Dakota becoming LIFR/VLIFR tonight
into Friday morning in snow and blowing snow. MVFR/IFR stratus
northwest and south central will continue through the night, with
increasing ceilings possible northwest by Friday morning. Strong
northeast winds gusting around 35 kts across the James River
Valley and far south central North Dakota Friday. Improving
ceilings and visibility area wide Friday afternoon and evening.
Winter Weather Advisory until 7 PM CDT /6 PM MDT/ Friday for
Winter Storm Warning until 6 PM MDT Friday for NDZ031>033-040-
Area Forecast Discussion...Updated
National Weather Service Billings MT
911 PM MDT Thu Apr 12 2018
Drier air working into the area from the south at the mid levels
and low level moisture transport from the east is beginning to get
tapped out a bit as thunderstorm activity develops over the
Western Dakotas and northeast Wyoming. Net result is best band of
precipitation is currently over the northern tier of the region
and circulation which had been over the area is beginning to shear
apart and window for heavy snowfall is beginning to taper off.
Latest run total snow from RAP model shows an inch or less
accumulation along and south of the Yellowstone until one gets
east into Treasure county. Along with this temperatures are
remaining steady in the mid to upper 30s tonight in the Billings
area which will have a limiting effect on snow ratios. Have
dropped some of the advisories including Yellowstone County.
.SHORT TERM...valid for Fri and Sat...
Upper trough moving through Idaho this afternoon. There is a good
deal of induced forcing due to height falls, upper diffluence and
isentropic lift out ahead of it. This is producing widespread
moderate precipitation across portions of the CWA this afternoon.
The mountains and foothills have seen a mix of rain and snow turn
to mostly snow already. Models agree the upper low will track east
into southern Montana tonight before shifting southeast into the
central plains on Friday. This will result in a relative dry slot
over the southeast zones of our CWA tonight (mainly easter
Sheridan County to Powder River) before it fills in early Friday
morning. Our central and western zones will be the focus of the
main wrap around moisture and isentropic lift as the surface low
develops right over the southeast corner of Montana overnight. The
position of the surface low along with a weak trowal feature will
create very brisk northerly winds over the northern and central
sections of our forecast area. Despite the wet nature of the snow
overnight, this will probably result in blowing snow and some
drifting. As such, we will increase the areal coverage of blowing
Road surface temps drop after sunset of course so the chance of
accumulations on the roads increase after 8 PM. Some areas though
may not see much accumulate on roads until after midnight. Look
for a slick and/or slushy morning commute Friday for many
Precipitation will gradually wind down on Friday, with little if
any additional accumulations for most areas in the afternoon.
Highs will be in the 30s to lower 40s, except for the southeast
corner where 20s will prevail as clouds and precip linger there
most of the day. Models suggest road temps in most areas will warm
into the 50s and 60s Friday, so we do expect most snow/slush
covered roads to melt off through the day.
Some modest ridge building is progged for Saturday, but there is
a weak perturbation in the flow that may produce a few showers
over the mountains and nearby areas. BT
.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...
Models are in fairly good agreement this weekend into the middle
of next week. High pressure ridging will be in place early Sunday
then gets shifted east into the northern high plains in response
to a large upper low and trough that will move onto the Pacific
northwest coast. A southwest flow aloft will prevail from late
Sunday into Monday. The trough moves across the forecast area
Monday and Tuesday with both the GFS and ECMWF keeping the upper
low north of our forecast area across Southern Canada. At this
time, this scenario will result in scattered showers and no major
precipitation event. However, this upper low may bring some very
strong west/northwest winds across the forecast area on Tuesday.
Ridging then builds across the forecast area Wednesday. Models
bring another low onto the west coast Thursday but this one drops
southeast into the Four Corners region keeping a split flow aloft
across our area. Overall, no major storm systems at this time
with temperatures seasonal Sunday, above normal Monday and
possibly Tuesday, before cooling below normal Wednesday into
Most of the rain showers have switched to snow at this point.
Most locations, even if they don`t see snow, well see stubborn
MVFR/IFR cigs through the night. LIFR conditions possible in the
heavier snow showers generally north and east of KBIL. Conditions
slowly improve late Friday as the storm system moves out of the
region, but mountain obscurations are likely through the TAF
.PRELIMINARY POINT TEMP/POPS...
Fri Sat Sun Mon Tue Wed Thu
BIL 029/039 026/051 033/059 035/059 036/048 030/049 028/050
78/O 01/B 11/B 11/B 42/W 11/N 11/B
LVM 028/042 025/051 032/061 035/060 032/047 026/048 025/049
74/O 02/W 22/W 13/W 64/W 22/W 12/W
HDN 029/039 023/052 030/058 033/060 034/048 027/047 025/050
79/O 00/B 11/B 10/B 32/W 11/B 11/B
MLS 027/035 019/045 029/055 032/055 035/046 029/044 026/049
+9/S 01/B 10/U 10/U 22/W 11/N 11/B
4BQ 027/034 019/046 028/057 033/058 036/047 027/045 026/049
79/S 00/U 00/U 00/U 12/W 11/N 01/B
BHK 024/032 012/039 023/045 027/045 031/045 027/041 023/044
98/S 00/U 10/U 00/N 12/W 11/N 01/B
SHR 028/036 022/051 029/063 032/063 035/050 027/049 025/051
78/S 20/B 11/B 00/U 22/W 10/B 01/B
MT...Winter Storm Warning in effect until 6 PM MDT Friday FOR
Winter Weather Advisory in effect until 6 PM MDT Friday FOR
WY...Winter Weather Advisory in effect until 6 PM MDT Friday FOR
Area Forecast Discussion
National Weather Service Columbia SC
743 PM EDT Thu Apr 12 2018
High pressure centered off the coast will continue ridging into
the southeastern states through Saturday. This will produce
southerly flow over the region along with a warming trend. A
cold front will cross the area Sunday into Sunday night bringing
showers and thunderstorms. Dry weather and cooler temperatures
will arrive Monday with moderating temperatures through the
middle of next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Fair. The center of surface high pressure will remain just to
our east. Low level air still fairly dry, but some patchy fog
possible around sunrise mainly in fog prone locations. Overnight
lows will be low to mid 50s.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
An upper ridge and increasing southerly flow ahead of an
approaching storm system and associated cold front will yield
generally dry and warm weather during this period. Increasing
low level moisture from southerly flow around the surface high
centered offshore will support the possibility of some morning
stratus or fog (though stratus is favored with a 30 knot low
level jet). However, any low clouds should dissipate quickly
with surface heating and mixing and transition to a diurnal
induced cumulus field as temperatures rise into the lower 80s.
Continued southerly winds through the overnight hours Friday
night along with general airmass modification will result in
above normal lows in the upper 50s.
Atmospheric moisture will continue to increase over the area
with persistent southerly flow off the Gulf of Mexico as
precipitable water values rise over an inch by Saturday
afternoon with some weak instability developing due to solar
insolation. Forecast soundings show a substantial subsidence
capping inversion around 700mb that may inhibit any convection
that may try to develop so will continue with our current
forecast of only slight chance pops in the western Midlands and
upper CSRA where moisture is a bit better. Temperatures on
Saturday will again be warm in the 80s but how warm will depend
on amount of cloud cover that is present. The approaching cold
front will stall to our west over the TN/MS Valleys briefly late
Saturday into Saturday night as the upper trough amplifies a
bit more and this will keep most of the precipitation to our
west. Will continue to carry chance pops in the western portion
of the forecast area after 06z Sunday though as the system
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Active weather with the threat of severe weather and heavy rain
expected on Sunday to start the extended forecast period but
then a return to seasonable temperatures and relatively quiet
weather expected for the remainder of the forecast period.
Strong upper low over the Upper Midwest will move into the Ohio
Valley on Sunday pushing a cold front into the forecast area
late Sunday into Sunday evening. Ahead of the front, several
ingredients for possible severe weather or heavy rainfall will
come together. Strong moisture transport off the Gulf of Mexico
will support precipitable water values rising to over 1.5 inches
with dewpoints pushing into 60s. Increasing shear with a
southerly 850mb low level jet of 50-60 knots will allow for
organized convection to develop and the region will fall in the
favorable right entrance region of the upper jet during peak
heating while the upper trough also becomes negatively tilted.
SPC has outlooked the area in a 15% risk for severe weather and
we have been mentioning this threat for a few days now. Late
afternoon into early evening still appears to be the timing for
most significant weather and possible severe storms but
instability remains one of the ingredients that may or may not
develop depending on cloud cover. Will continue categorical pops
across the region on Sunday with a decrease in pops Sunday
night as the front crosses and a dry slot beneath the upper low
Generally fair weather expected the remainder of the forecast
period with surface high pressure over the region and
northwesterly 500mb flow on Monday supporting below normal
temperatures followed by a transition to more zonal flow and
temperatures warming back to near normal. Breezy conditions will
exist on Monday due to an increased pressure gradient and may
linger into Tuesday.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
VFR conditions most of the period although patchy fog expected
late tonight at fog prone terminals...AGS/OGB.
High pressure will remain off the Carolina coast through the
period with resulting increasing south flow. The air mass at the
present time is quite dry. The models suggest a shallow low-
level jet overnight which may limit fog potential. Will
continue forecast of a brief period of MVFR fog around dawn at
AGS and OGB due to model blend suggesting a threat in the CSRA.
However there is little support from the latest HRRR and lamp
guidance. South to southwest winds increasing to around 10 knots
mid morning Friday with scattered cumulus in the afternoon.
EXTENDED AVIATION OUTLOOK...Restrictions expected Sunday and
Sunday night as a cold front crosses the region along with
showers and thunderstorms. Strong and gusty winds expected
Sunday through Monday.
Area Forecast Discussion
National Weather Service Caribou ME
1021 PM EDT Thu Apr 12 2018
Low pressure will track eastward from the Great Lakes region
overnight. A cold front from northern Canada will approach
Friday and cross the region Friday night.
.NEAR TERM /THROUGH FRIDAY/...
1010 PM Update...
Rain is moving in from the sw per the latest radar loop with
either some sleet or snow in the southern sections of
Piscataquis County such as Greenville. Temperatures in that
region were in the low to mid 30s. Elsewhere, temps were in the
40s but were slowly cooling down. Given the low dewpoints across
the northern areas, expecting the rain to go to snow w/some
accumulation. Decided to stay close withe current forecast for
1-2 inches of wet snow by morning mainly across northern
Aroostook County. Attm, the radar does show some enhanced
returns across southern Maine. Ltg detection did show some
strikes moving across eastern NYS. This activity looks like it
will dampen as it moves east overnight. 00z ua showed upper jet
of 100+ kts moving out of western NYS and is shown by the RAP
and NAM12 to move across the southern portion of the region
overnight. This feature is helping to fuel the tstms in eastern
NYS and could very will enhance precip for a few hrs overnight.
Decided to adjust the QPF to account for terrain and this
Low pressure will track out of Quebec into northern Maine
tonight. The expected path is from Somerset County towards
southern Aroostook County. This track will be conducive to snow
north of the low...after evaporative cooling of the boundary
layer...and rain to the south. The surface low will line up with
a compact H500 shortwave and the LFQ of a strong upper jet.
There is some elevated instability coinciding with this
jet...currently in Ontario. This instability will weaken, but
still poses a risk towards coastal Hancock later tonight and
will have to be watched. QPF with the system looks to be mostly
in the quarter to half inch range. Snow is a threat north of a
line Greenville eastward towards Houlton. The snow will be
dependent on elevation, evaporative cooling, and intensity. In
general, most of the lower elevations under 1000ft will see one
to two inches and a lot of that will come within a couple of
hours when snowfall rates could hit an inch an hour...wiping out
the warm boundary layer. This could pose some brief travel
difficulty in the northern zones, but with lows around 33F, it
should be short-lived. There will be a strong LLJ to help
enhance this heavier burst of precip.
By late tonight, this fast-moving low will already be in New
Brunswick. In general, the air behind the low will be milder and
moister with highs tomorrow another couple of degrees warmer
than today. Dew points will also be considerably higher.
However, there will be sufficient H850 for a lot of cumulus
fields on Friday...and higher clouds will increase with
overrunning later in the day.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
Expect strong high pressure to build to the north of the region
across Canada Saturday and Sunday. At the same time a front will
remain stationary across to the south. Expect the front to
start to move to the north later Sunday along with
precipitation. Expect the precipitation to start as snow and
mixed in the north and central areas Sunday Night then change
to all rain by Early Monday. Have used the thickness tool run on
a 50/50 blend of the Nam and Gfs for precipitation type. Used
snow ratio for snow amounts.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Intensifying low pressure will track to the west of New England
Monday. Expect heavy QPF amounts Monday and Monday Night as it
does so. Rapid snow melt is possible. The upper level low
pressure system is expected to move across the region Tuesday
bring showers Tuesday into Wednesday. Showers are expected to
continue Thursday as upper level low pressure remains over the
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
NEAR TERM: All sites will deteriorate from VFR towards IFR or
LIFR tonight. The LIFR will occur in snow north of a line from
GNR to HUL. South of that line, rain will be accompanied by IFR
cigs. There is a slight chance of an embedded thunderstorm
towards BHB later tonight. LLWS will be an issue late this
evening into the overnight hours for all sites. Conditions
improve quickly towards VFR Friday morning.
SHORT TERM: Expect VFR/MVFR conditions Saturday. MVFR/IFR
conditions are expected Sunday. IFR conditions are expected
Monday and Tuesday.
NEAR TERM: Winds and seas will increase quickly tonight with
some gusts over 35 kts after midnight...especially further from
the coast. There is a slight risk of a thunderstorm tonight.
The rain ends later tonight and winds will decrease for Friday,
but seas will continue to build Friday morning in a southerly
swell up to 10 feet. Seas gradually decrease in the afternoon,
but the SCA will remain in place.
SHORT TERM: Have used a 50/50 blend of the Nam and Gfs for
sustained winds. For Waves: Expect southerly long period swell
3-4 feet/8 seconds to be the primary wave system Saturday and
Sunday with a secondary northeasterly wind wave 2-3 feet/4-5
seconds. A strong east to southeasterly fetch will develop
across the Gulf of Maine Sunday Night into early Tuesday with
waves build to around 9 feet/9 seconds by late Monday Night.
Will use NWPS for wave heights.
MARINE...Small Craft Advisory until 2 AM EDT Saturday for ANZ050>052.
Area Forecast Discussion
National Weather Service Charleston SC
1011 PM EDT Thu Apr 12 2018
High pressure will prevail through Saturday. A strong cold
front will affect the area Sunday, followed by dry high
pressure Sunday night through mid week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
On average our temperatures are running about 3-6F warmer than
24 hours ago, and this trend will persist through the overnight
as it provides us with our "warmest" night of the past several.
We`ll continue to keep watch on the development of patchy
stratocumulus from off the ocean late as weak isentropic ascent
and low level moisture advection occurs. Still no indications of
significant fog formation as per the bulk of the Hi-Res model
guidance since condensation pressure deficits are more than 10
or 20 mb and geostrophic winds are 10-15 kt. We`ll maintain
mention of "patchy" fog late, generally in the form of ground
For the early evening update we have adjusted sky cover to
reduce coverage early tonight based on satellite trends, but
also to increase it a little late due to some isentropic ascent
and an increase in boundary layer moisture from off the
Atlantic. This will lead to some late night stratocumulus, as
skies transition from clear/mostly clear to partly cloudy closer
Meanwhile, the fog potential is not extremely high, with the
NARRE-TL, SREF and HRRR all showing little if any chance.
However, since dew points are higher and since "patchy" fog is
already mentioned in the forecast, we will leave it there.
Suspect that most of it will be shallow ground fog though.
Weak warm air advection within a southerly low level flow and
the dew points in the 40s and 50s will prevent temps from
getting as cool as last night. We did lower some places in the
Francis Marion and along our NW tier for minimum temps, but
elsewhere we maintained the previous forecast of lows from
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Overview: A relatively quite pattern will hold on for Friday and
most of Saturday, but then more active weather is expected to return
ahead of a strong cold front on Sunday.
Friday and Saturday: A deep layer ridge, centered over the Atlantic
waters, will gradually push eastward through the period. Low level
southeast flow will prevail with only a slight chance for showers by
Saturday/Saturday afternoon, mainly extreme coastal/eastern
locations. Temperatures will be above normal, with highs both days
in the upper 70s to around 80, and lows Friday night in the upper
50s to lower 60s. Given the prevailing low level southeast flow,
temperatures will be cooler each afternoon closer to the coast.
Saturday night and Sunday: The pattern becomes more active as a
deep, full latitude upper trough approaches from the west. Moisture
will continue to increase from west to east, with a slight/low end
chance for showers after midnight Saturday night into early Sunday
morning. All models are in close agreement with the timing of the
deepest moisture, upper forcing and highest chances for
showers/thunderstorms for generally 18z Sunday to 00z Monday. Have
gone likely to categorical PoPs by Sunday afternoon. This would
coincide with peak heating, which could maximize CAPE. As has been
typical, instability/CAPE seems to be the limiting factor, with more
than sufficient deep layer shear/winds. However, latest global
models now nudge CAPE values near 1000 J/Kg, which would likely be
enough to support isolated severe storms. Given the unidirectional
wind profiles in the model soundings, if there are any strong/severe
storms, the main threat would likely be strong, straight line wind
gusts. It`s too soon to mention severe potential in the
grids/forecast, but will continue to highlight in the HWO. All
models also indicating breezy to windy low level conditions Sunday,
and have continued breezy mention in the forecast. Sustained
southerly winds of 15-25 mph with gusts 30-35 mph would not be out
of the question. High temperatures will be very mild/warm, in the
mid to upper 70s. With surface dewpoint temperatures expected to be
the mid to upper 60s, it will also feel more humid.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Precip associated with the cold front should be offshore by
midnight Sunday night. A brief cooldown will occur Monday into
Tuesday before the surface high shifts offshore with a quick
warm-up by mid to late week. It will be breezy during the
daytime hours each day due to a relatively strong gradient.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Ground fog is expected overnight into Friday morning, and
although there could be occasional flight restrictions, most of
the 00Z TAF cycle will be VFR at both KCHS and KSAV. SE to S
winds will become gusty Friday late morning and afternoon,
possibly stronger than now in the forecast, since we are showing
more in the way of average conditions.
Extended Aviation Outlook:
Friday through Saturday: VFR expected to prevail.
Saturday night: Brief flight restrictions/lower ceilings will be
possible late ahead of an approaching cold front and increasing
chances for showers.
Sunday: All models continue to show an increasing threat for severe
storms as a deep upper trough and associated surface cold front move
in from the west. Timing for the highest chances for
showers/thunderstorms and the potential for isolated severe storms
looks to be 18z Sunday to 00z Monday. Therefore, periods of flight
restrictions will be possible much of the day and into early evening
Sunday. Breezy southerly winds also look likely Sunday and into
Monday at both sites.
Sunday night through Tuesday: VFR expected.
Tonight: Sprawling high pressure that covers much of the
western Atlantic and Gulf of Mexico will persist, with its
associated ridge axis to extend over or just south of the local
waters. This will produce veering winds around to the SE and S
at speeds generally 10 kt or less, except for 10-15 kt on the
outermost Georgia waters. Seas will hold steady around 2-3 ft
within 20 nm, and 3-4 ft further out.
Friday and Saturday: No highlights as high pressure centered just
east of the waters continues to slowly push further east into the
Atlantic. Expect southeast winds of 15 knots or less and seas 3 to 4
Saturday night: Winds increase from the southeast then south ahead
of an approaching strong cold front and deep upper level trough.
Expect winds of 15 to 20 knots with gusts near 25 knots by late
night. Seas building to 4 to 6 feet, highest offshore GA waters.
Therefore, marginal Small Craft Conditions possible, especially
offshore waters by late night.
Sunday through Monday: A strong cold front and the potential for
strong to severe storms will move across the waters later Sunday
afternoon and Sunday evening. Winds and seas are expected to
increase into the Small Craft Advisory level, with sustained winds
of 20-25 knots and gusts near/around 30 knots possible, especially
ahead of the front Sunday and Sunday evening. Seas could build as
high as 7 to 9 feet offshore/beyond 20 nm offshore, and 5 to 7 feet
within 20 nm. Small Craft conditions could linger through much of
Monday behind the cold front, before gradually decreasing as high
pressure builds into the area from the west. By Tuesday, High
pressure is expected to be over the region with lighter winds/lower
seas below highlight levels.
Rip Currents...Increasing southerly flow late Saturday night
and through Sunday ahead of a strong cold front is expected to
increase the threat for rip currents. A moderate to possibly
high risk for rip currents will be possible by Sunday.
Area Forecast Discussion
National Weather Service Gray ME
900 PM EDT Thu Apr 12 2018
Fast-moving low pressure will move eastward across northern New
England overnight, spreading mainly light rain across the area.
Thereafter, a frontal boundary will remain nearly stationary to
the south of the forecast area and bring the threat for mixed
precipitation to NH and ME late Saturday through Sunday night. A
more substantial rain event may arrive Monday and Tuesday.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
900 PM...at 01z a 1002 millibar low was vicinity of Kingston, ON
/CYGK/ with a trailing cold front through the lower Great Lakes
and a warm front through eastern New York state. NWS Doppler
Radar mosaic showed an area of precipitation in advance of the
surface low and occluding warm sector. Precipitation was largely
falling as rain with some snow across the higher terrain. For
this ESTF update...I made minor adjustments to near term grids
that reflect radar trends as well as the latest mesonet.
Clouds continue to increase across the forecast area this
afternoon as low pressure approaches from the west. This low
will bring a widespread light rain to the region this evening
into the overnight hours. Followed an ensemble of the latest
several HRRR runs for PoPs as it appears to have a good handle
on the timing and coverage of rain. Portions of the western ME
mountains may pick up a little bit of snow tonight as it should
be just cold enough at higher elevations for some wet snow.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Much of Friday should end up being a partly sunny to variably
cloudy as we will be between two fast-moving systems. This will
likely be the last warm-ish day in awhile with highs in the 50s
and 60s...except for those in the far north. However, some light
rain may begin to fall late in the afternoon - mainly across
southern and western zones as the next burst of WAA approaches.
Mainly light rain is expected Friday night across most of the
forecast area as we will be right in or near the stationary
frontal zone. Across far northern zones, we expect a transition
to sleet/snow later Friday night as the depth of cold air
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Highly amplified flow will impact the region throughout the long
term period. At the surface, low pressure system over the
central Plains will be in the process of filling by Saturday. An
associated warm front will try to push warm and moist air in
from the southwest over the weekend. strong high pressure in
Canada (1045+ mb) will push a backdoor front into the region
from the north. These two air masses will interact and bring a
wintry mix of precipitation for most of NH and Maine through the
Models and model members disagree on the timing of the backdoor
front, which will be crucial as far as to how far south the
cold air gets during this event. Dense high pressure will help
in this case, so we are expecting a chance of freezing rain, at
least in pockets, across the area. Precipitation will start as
rain and gradually change to a wintry mix late Saturday night
into Sunday morning. Amounts of snow will be higher in the north
and may touch advisory range in certain areas. Roads at this
time of year are generally warm enough to handle light freezing
rain, but trees and walkways will accrete ice and become
slippery. Freezing/frozen precipitation could reach as far south
as the coasts. QPF amounts with this system will range from
0.5" in the north to and inch or more for central and southern
sections. This is about 150-200% of normal for this time of
year. Runoff will mix with snowmelt and will likely cause
flooding at multiple points on area rivers. Finally, winds will
whip up Sunday night into Monday with a strong LLJ in place.
Early next week the large trough axis will swing negatively as
it moves towards New England, with secondary cyclogenesis
occurring along the coast. Colder air will retreat north from
the mountains and foothills by Monday as warm air advection
begins. This looks like a straight rain/snow event in the
Tuesday/Wednesday time frame. Again QPF amounts look elevated.
Cyclonic flow remains in the region through midweek with
scattered showers in the forecast.
.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
Short Term...Low pressure moving across the forecast area
tonight will bring a period of light rain and MVFR cigs/vsbys at
most terminals - except perhaps KMHT. VFR conditions are
expected to return late tonight and last through much of Friday
before lowering to IFR Friday evening and night.
Long Term...MVFR ceilings and lower are expected Saturday into
Sunday in mixed precipitation. Freezing/frozen precip will being
across northern terminals and will gradually shift south,
changing rain into SN/-IP/-FZRA at times. Also expecting gusty
winds in the late Saturday to early Sunday time frame, with a
period of LLWS before the LLJ mixes down.
Freezing precip will change over to -SHRA most sites Monday into
Short Term...SCA remains in effect for all waters for tonight
and Friday. There will likely be some gusts around 35 kt...
especially off the mid coast but we are thinking widespread
gales will remain aloft and not likely mix down to the water for
a prolonged period of time.
Long Term...Small craft conditions continue Saturday into Sunday
with gales developing Sunday night into Monday.
MARINE...Small Craft Advisory until 8 PM EDT Friday for ANZ150>154.
Area Forecast Discussion
National Weather Service Spokane WA
446 PM PDT Thu Apr 12 2018
Breezy and gusty conditions along with some potential for
thunderstorms will linger this afternoon and early evening.
Periods of showers will continue Friday into Saturday with another
wet front bringing valley rain and mountain snow on Sunday into
Monday. Temperatures will remain generally cooler than normal
through the next week with showery and occasionally breezy
Tonight and tomorrow: Cold conditionally unstable airmass coupled
with abundant low level moisture left from recent and ongoing
rainfall as a negatively tilted disturbance rounds through the
outer edges/base of the trof pushing through Eastern Washington and
North Idaho will keep a portion of the evening unsettled with the
potential for some thunderstorms. If they do form they would be the
weak pulse variety moving with a storm motion to the east/northeast
at 15 to 20 mph. Infrequent lightning, gusty wind, and brief
downpours would be the primary nuisances associated with any
thunderstorms that develop. Otherwise decreasing
precipitation segue to a generally dry forecast marks most of the
remainder of the overnight into tomorrow morning period. Clouds
invade sky from the west and thicken and lower tomorrow morning
signaling the approach of the next weather system to bring rain to
most locations tomorrow. The breezy/gusty winds will linger into the
early evening then decrease. /Pelatti
Friday night through Thursday...
Another weather system begins to set up position off the west
coast. There will be flat shortwave ridging but a slow moving cold
front will keep baroclinic band precipitation active over the flat
ridge. Generally light precipitation will be in the forecast for
Friday night into Saturday with best chances Cascades, northern
mountains of Washington and the Idaho Panhandle.
As the low slowly digs off the west coast Saturday and Saturday
night the flow will turn more southerly ahead of the cold front
but surges of moisture continue as the warm sector establishes
itself over the eastern third of WA and ID Panhandle. During this
time precipitation moves away from the Panhandle and continues
over the Cascades. Being in the warm sector, much of the region
will enjoy warmer temperatures even into Sunday but moist
southerly flow continues so light precipitation or sprinkles in
overcast sky will still be possible as well as the slight
potential for thunderstorms northeast mountains Saturday.
Sunday afternoon and night the cold front begins it`s slow trek
inward. We will need to look out for isolated thunderstorm
activity in this potentially active frontal passage. There will
also be widespread showers moving across the region persisting
Monday, expect cooler temperatures after the cold front with
lingering rain and snow showers as convective showers will
artificially lower snow levels and some valley locations will see
the white stuff. However this time of year snow does not stick
around long even if it accumulates a little in the lower valleys.
There are some impressive precipitation totals for this storm
system especially for northeast mountains and north Idaho
Panhandle. This will continue to help swell creeks, streams and
rivers however no flooding is forecast. Debris/Rock slides are
still a concern as several have been reported this Spring during
and after heavy precipitation events like this.
With yet more minor disturbances in the overall weak westerly
flow we can expect on an off again showers Tuesday into Thursday
especially in the mountains. However temperatures will be on the
rebound to more normal values in the 50s (near 60 south) during
the day Wednesday and Thursday. TC
00Z TAFS: Upper trough pivots through the region while satellite
shows a weak circulation over the Columbia Basin. Convection is
blooming east of the circulation over Adams, Lincoln and Whitman
counties with showers, some of which with graupel and a threat of
lightning. The HRRR shows the convective activity skirting pass
the KGEG-KCOE corridor and toward KPUW through 03z with gusty
winds, and then dissipating through the evening. KMWH-KEAT should
stay dry and windy this evening. Clearing anticipated overnight
with lighter winds. Clouds increase 16-18z as winds become
southeast. Light rain anticipated after 18-21z with an approaching
front with local MVFR cigs possible. /rfox.
.PRELIMINARY POINT TEMPS/POPS...
Spokane 31 49 40 55 40 56 / 20 40 50 30 30 60
Coeur d`Alene 30 48 39 53 39 55 / 20 30 70 40 30 60
Pullman 32 49 40 55 40 57 / 20 30 60 20 20 60
Lewiston 35 57 44 62 44 63 / 20 10 40 20 20 50
Colville 30 51 40 55 39 54 / 20 40 60 60 60 60
Sandpoint 30 45 38 49 37 51 / 30 30 80 60 40 70
Kellogg 29 45 35 50 36 53 / 20 20 70 40 30 70
Moses Lake 33 57 42 62 41 60 / 20 30 20 20 30 60
Wenatchee 36 56 41 58 41 54 / 10 40 20 40 50 60
Omak 34 55 41 58 41 55 / 0 50 30 50 40 80