Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/18/21
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
643 PM CDT Sat Apr 17 2021
.DISCUSSION...(This evening through Saturday)
Issued at 307 PM CDT Sat Apr 17 2021
Biggest forecast concern is the chance of snow coming Monday night.
Ongoing sprinkles/showers, focused more west, should diminish by
evening as deep layer moisture wanes and shortwave trough axis
within a mean synoptic trough shifts south/southeast of the area
tonight. A particularly shallow and steep inversion is forecast by
model soundings for tonight.
Shortwave ridging within the mean synoptic trough in place over the
central/eastern United States should stave off any precipitation and
help boost temperatures a bit, although probably still a tad below
normal as we continue to be under the influence of the cool synoptic
A surface cold front is forecast is widely forecast to come through
Sunday night, passing through the tri-city area shortly after
midnight give or take a few hours. Some minor timing differences
among models, with the HRRR and GFS being a bit faster than the NAM
solution, but effectively bringing in cold air advection late Sunday
night, in time to make Monday exceptionally cold for this time of
year, topping out only in the lower 40s at best for the tri-cities,
with somewhat cooler temps to the north and a tad warmer to the
There will be a chance of post-frontal precipitation to develop
during the day on Monday, mainly on the Nebraska side as a band of
enhanced 700 mb frontogenetic forcing is expected to develop
within a 700 mb trough as there is widespread agreement in the
model world of this development. Temperatures during the day
should keep precipitation primarily as rain.
The 700 mb frontogenetic forcing gathers strength by Monday night as
it slips to the south across north central Kansas. This is also
widely accepted among model solutions. Models and ensembles are also
in decent agreement that as temperatures cool, snow amounts will
probably top out in the 1-3 inch range for north central Kansas,
given the relatively small window to work with. Ensembles indicate
that precip may hold over a bit into early morning Tuesday
compared to a bit of an earlier shutoff by operational runs, but
besides this, models and ensembles seem to be in decent agreement
with the upcoming scenario and the associated snow amounts.
Although GFS has shifted a bit farther north with heavier qpf, the
ECMWF has shifted south and backing off qpf. The NAM indicates a
tighter band, with qpf closer to the ECMWF. Forecast has backed
off a bit into the 1-2 inch range, and given the time of year, I
am not inclined to hold on to very high amounts, especially this
far out, given overall ensemble and operational model solutions.
The upper wave does not completely clear until after Tuesday, so I
did put in some sprinkles for Tuesday afternoon with increasing
low-level lapse rates.
Overall upper air ridging into mid-late week next week finally
returns us to near normal for temperatures by next weekend.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Monday)
Issued at 638 PM CDT Sat Apr 17 2021
We have a few showers primarily around Kearney at forecast
issuance time. These showers will quickly die off after sunset
with a dry night expected. Ceilings have been rising and we expect
VFR conditions throughout the remainder of the TAF valid period.
The wind will shift from northerly at TAF issuance time to
westerly winds by late tonight into tomorrow morning.
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
955 PM EDT Sat Apr 17 2021
High pressure builds back into the area through this weekend.
An area of low pressure will move through on Monday. A strong
cold front moves through the area late Wednesday.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 955 PM Saturday...Fast zonal flow aloft leading to a
decent amount of mid and high level clouds across eastern NC.
While the layers below 700 mb remain fairly dry, the combination
of some mid-level energy moving east through the zonal flow
aloft and a weak frontal trough over the area could kick up some
very light showers or sprinkles overnight. The HRRR and 3km NAM
continue to some isolated light showers or sprinkles over the
central and northern tiers of the CWA primarily and will leave
the very low PoPs in those areas overnight. With cloud cover
will help hold low temperatures in the 50 to 55 degree range
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
As of 340 PM Sat...Upper heights build slightly over the region
with skies clearing on the backside of the shortwave. Main
challenge for tomorrow is the possibility of a few isolated
shallow showers along the seabreeze. More hi-res guidance has
latched onto this idea and held an isolated shower mention for
the afternoon, predominantly along and east of Highway 17.
Raised forecast highs a couple degrees tomorrow with plenty of
sun around during the day, and also considering 12z forecast
low-level thicknesses initialized a bit lower than this
morning`s sounding observation. Low to mid 70s expected, with
mid 60s for OBX.
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
As of 245 AM Sat...A cold front will remain stalled to the south
through the middle of next week, with weak areas of low
pressure strengthening along it. A strong front will push
through the area Wednesday afternoon, with much cooler air
Sunday night through Tuesday...Front will remain stalled to the
south through mid week as waves continue to develop along it.
Weak low pressure and shortwave energy aloft will be enough to
support scattered showers and iso tstms Monday, and increased
pops a bit. High pressure will build in briefly Monday night and
Tuesday, then pushing offshore late Tue ahead of the next
front. Increased pops Tue slightly from previous forecast.
Gradual warm up through early next week, with highs back into
the 70s inland and upper 60s for the Outer Banks Mon and Tue.
Wednesday through Friday...Stronger front is progged to push
through late Wednesday, as waves of low pressure continue to
move along the stalled front offshore. 00z guidance in better
agreement with respect to timing, pushing the front offshore by
early Wed evening. Increased pops a bit from previous forecast
but still looks like it becomes a bit moisture starved moving
east of the Appalachians. Will keep sc tstm mention Wed
afternoon with modest instability and strong shear (50+ kt bulk
shear). Much cooler and drier airmass expected behind the front
with high pressure building in from the WSW and upper
troughing. We could have some Frost/Freeze concerns inland
Thursday morning. EC/GFS mos guidance show lows falling into the
low to mid 30s. Lowered temps a few degrees, but not quite that
low yet. Highs Thu generally in the 60s with dewpoints falling
into the 30s. Another cool night Thu night, with highs warming
into the mid 60s to low 70s Fri. EC and CMC have a strong storm
system impacting the area next weekend, but still 7 days out.
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Short Term /through 00Z Monday/...
As of 715 PM Saturday...VFR conditions expected at all the TAF
sites through this cycle. Some mid and high level cloudiness
associated with some mid-level shortwave energy channeled in a
zonal flow will persist overnight. This energy along with a weak
frontal trough over the area will lead to a small chance of some
isolated showers or sprinkles, but not enough to include in the
TAFs. Scattered to broken mostly mid clouds will persist on
Long Term /Sunday night through Wednesday/...
As of 245 AM Sat...Pred VFR conditions expected through the
period. Scattered showers and isolated tstms are possible each
day, mainly diurnally driven, which could briefly reduce
conditions to sub- VFR.
Short Term /Tonight and Sunday/...
As of 955 PM Saturday...Little change needed to the marine
forecast on this update. Winds at late evening as SE at 5 to 10
knots for the most part, with a few gusts to around 15 knots
over the northern tier. Seas are checking in at 2-3 feet with
11-12 second swells. Winds veer southwesterly overnight at 5-10
kts and then back to the north as another weak front drops
across the waters overnight. Bit of divergence in the intensity
(or even existence) of a post- frontal surge and shot the
forecast down the middle of guidance, favoring northerly winds
at around 10 kt. Sea breeze regime seen today will be in place
again tomorrow. With such little impactful wind, seas remain at
2-3 feet through the short term with periods of 10-12 seconds.
Long Term /Sunday night through Wednesday/...
As of 245 AM Sat...Front will remain stalled to the south
through the period as weak waves of low pressure move along it.
Fairly quiet wx expected across the waters the next few days,
but expect many wind shifts with stalled front and weak lows in
the vicinity. Winds generally 5-15 kt through Tue with seas 2-4
ft. A strong cold front will approach the waters Wednesday,
pushing through Wednesday afternoon and early evening. SCA
conditions likely to develop Wed afternoon with gusty SW flow
ahead of the front, then stronger NNW winds 20-25 kt and seas
4-7 ft developing behind it.
Area Forecast Discussion...updated
National Weather Service Portland OR
835 PM PDT Sat Apr 17 2021
...Updated aviation discussion...
.SYNOPSIS...An unusually warm and dry stretch of weather for April
will likely continue for much of the upcoming week, but there is a
decent chance cooler and wetter weather will return towards next
.SHORT TERM...Tonight through Monday night...Water vapor satellite
imagery this afternoon reveals an area of upper level high pressure
centered over the far northeast Pacific near western Washington and
Vancouver Island. A broad shortwave trough encompasses much of the
eastern Pacific while another shortwave trough is currently cresting
the upper level ridge across northern British Columbia and will slide
southward down the east side of the Rockies over the coming days.
Surface observations indicate temperatures have climbed to near 80F
along much of the north Oregon and south Washington coastline and
across much of the lowlands of interior northwest Oregon and
southwest Washington. Expect an additional couple degrees of warming
this afternoon with several record high temperatures for April 17th
in jeopardy including those at Portland, Hillsboro, Troutdale, Salem
Relative humidities have once again plummeted into the teens and
twenties across many interior valley and foothill locations this
afternoon. However, pressure gradients have decreased substantially
across the area, and as a result, winds have generally remained 10
kt or less. Nonetheless, fire danger will remain elevated through
Sunday, particularly for the time of the year as fuels remain
unusually dry for this time of the year and relative humidities
remain low during the afternoon hours.
Visible satellite imagery or just looking out the window reveals a
beautiful, not a cloud in the sky kind of day across most of
northwest Oregon and southwest Washington this afternoon. The main
exception to this remains along the central coast of Oregon between
Florence and Depoe Bay where fog and low clouds continue to hug the
coastline. Expect these clouds to spread back onshore between 3-5 PM
before gradually spreading northward along the coast overnight.
Latest HREF, RAP and NAM guidance suggests the fog and low clouds
tied to this southerly wind reversal should reach the mouth of the
Columbia River by daybreak and likely spread northward along the
Washington coast Sunday morning. Meanwhile, the GFS and UW-WRF are
generally much more pessimistic with regards to clouds and keep our
coastal areas clear into Sunday morning. Given the former guidance
is handling the current fog and low clouds vastly better than the
GFS and UW-WRF, opted to trend the cloud cover forecast towards more
clouds for the coast through Monday.
Models are in good agreement the area of upper level high pressure
currently over the region will weaken this weekend as a lobe of the
aforementioned shortwave trough in the eastern Pacific slides
eastward towards the Pacific Northwest on Monday. Several members of
the GEFS and EPS ensemble systems produce measurable rain across
portions of our CWA late Monday into Monday night, particularly our
southwestern zones around Lane, Lincoln and Benton Counties. This
appears to be in response to these models developing an area of
elevated convection due to negative thetae lapse rates between 700-
500mb and large scale lift occurring along the leading edge of a PV
anomaly. NBM PoPs are still generally 10% or less across these zones
late Monday, but opted to at least put in a slight chance mention of
sprinkles given the pattern. The latest operational model soundings
do not appear terribly favorable for measurable precipitation
reaching the ground so do not see a big reason to argue with the
current NBM PoPs. /Neuman
.LONG TERM...Tuesday through Friday...Mostly dry and warm weather
through the middle of next week as high pressure dominates west of
the Rockies. Temperatures will slowly lower around 10-15 degrees
through Friday. Within the flow around the high pressure, a shortwave
with a weak upper level low will pass over the area Tuesday morning.
Some models are showing a brief period of showers but ultimately not
expecting a lot of accumulation. This system has eroded over time as
well so confidence with it`s manifestation is marginal as it easily
could be impacted by the dry airmass. The stubborn high pressure and
dry air mass looks to start shifting east and being eaten away by a
broad area of low pressure dropping down from the north Pacific.
The low has quite a bit of consistency among models even this far
out. The main impact this low may bring some long waited
precipitation towards the end of the week. The main challenge is the
timing and whether or not the incoming low pressure will be deep
enough to "push" the high pressure out of the area. -Muessle
.AVIATION...A dry air mass will keep inland areas of northwest
Oregon and southwest Washington with VFR flight conditions through
the next 24 hours. Along the coast winds are expected to switch
around to a light south-southwest wind tonight and Sunday, which
will result in marine air with low clouds and fog spreading north up
the coast. KONP is likely to see IFR conditions developing early
tonight by 06Z, then a good chance of IFR conditions persisting
through the day Sunday. Further north the chances for IFR conditions
in low clouds and fog begin as early as late tonight, but the best
chances for IFR conditions reaching KAST don`t come until daylight
hours Sunday after 16Z.
For detailed regional Pac NW aviation weather information, go
online to: https://weather.gov/zse
KPDX AND APPROACHES...VFR conditions for the next 24 hours.
.MARINE...Rather benign conditions will continue through the
weekend with generally light northwesterly winds across the
waters and seas 4 to 5 feet into Sun morning. Near the Oregon
coast there is a good chance of a southerly wind reversal as
marine stratus and areas of fog push northward Sun morning.
Onshore westerly winds are likely Sun afternoon up to 10 kt
before turning northwest again late.
Surface high pressure builds northward Monday while thermally
induced low pressure returns over northern California early next
week. The increased pressure gradient across the coastal waters
will result in increasing northerly winds with low end Small
Craft Advisory gusts of 25 to 30 kt most likely late Monday
through Tuesday. Seas are also likely to climb into the 6 to 8
ft range Tue into Wed and be somewhat choppy. Seas will likely
fall to below 5 ft and winds decrease during the latter part of
next week. Some weather models suggest that by next weekend a
storm system could bring increasing southerly winds and seas next
weekend, but confidence in the details, is relatively low at
this time. /DDH
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