Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/03/19
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1022 PM EDT Tue Apr 2 2019
A storm system traveling offshore the Eastern Seaboard will bring
some clouds tonight, along with spotty light rain or snow across
portions of western New England. Windy conditions will develop
behind the departing storm for Wednesday afternoon and evening. The
next chance of widespread precipitation looks to be on Friday, as a
frontal boundary brings some rain and snow to the area.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 1015 PM EDT...Regional radar depicts bands of
precipitation, mainly rain, extending from southwest to
northeast just off the mid-Atlantic seaboard. Another smaller
and weaker band was across Long Island and southern Connecticut.
Per the 00Z model hires model suite, question just how far west
this light precip shield gets as trends are now a little further
eastward. We will ever so slightly nudge the PoP/Wx grids a bit
further east as we will continue to monitor trends closely
overnight. Under considerable cloud coverage, temperatures have
been slow to decline as we will slow down the nocturnal descent
but keep overnight lows in place per latest runs of the
LAV/LAMP. Otherwise, minor tweaks to the hourly grids per
Prev Disc...High pressure is now located well southeast
of Nova Scotia and continues to depart away from the area.
Meanwhile, low pressure off the coast of eastern North Carolina
continues to intensity and deepen. Although the bulk of the
clouds ahead of this strengthening storm are still over the mid-
Atlantic states, mid and high level clouds are steadily
increasing over the area. Most locations should be mostly
cloudy by later this evening with overcast skies expected
through the duration of the overnight hours.
With the developing gradient and fairly decent mixing in place
(as usual this time of year thanks to the strong solar
insolation and lack of moist vegetation), southerly winds have
been gusty this afternoon, especially in north- south oriented
valleys, such as the Hudson Valley. Winds have been gusts 20-30
mph at times. These winds will start to diminish this evening
as nocturnal effects takes over and winds should be fairly light
for the overnight hours.
The low pressure looks to track northward offshore the mid-
Atlantic states for tonight and should be just southeast of
southern New England by daybreak Wednesday. Latest model
guidance, including the 3km HRRR show this storm being a bit too
far south/east to have much of an impact on our weather. Will
continue slight to low chc POPs across western New England, but
it looks like only far southeastern Litchfield County could be
brushed with a few hour period of light rain for late tonight.
If the storm does track a little further west than anticipated,
then perhaps some light rain (mixed with wet snowflakes at the
highest terrain) could also impact the Berkshires and southern
VT, but any amounts look very light.
With the clouds, temps won`t be as chilly for tonight. Overnight
lows look to fall into the mid 20s to mid 30s, with the
coldest temps over the Adirondacks.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
Coastal storm offshore of eastern New England will be departing
during the day on Wednesday as it continues to deepen.
Meanwhile, a northern stream shortwave and associated surface
frontal boundary will be moving from the Great Lakes towards the
Northeast for Wednesday as well. There won`t be much moisture
with this feature, but cannot rule out a few sprinkles or light
rain showers across the Adirondacks as it passes through the
areas during the late morning through early afternoon hours,
but any rainfall looks just a few hundredths at best.
Behind this frontal boundary, westerly winds will strengthen
aloft and colder air aloft will quickly move into the region.
12z model soundings suggest this could allow for a period of
deep mixing on Wednesday, with mixing as deep as 700-750 hpa.
This will allow for very gusty winds to reach the surface,
especially across areas that channel westerly flow such as the
Mohawk Valley, Capital Region and Berkshires. Winds also look
strong across high terrain areas of southern Vermont, the
Adirondacks and Catskills. Winds will be 15 to 25 mph with gusts
of 30 to 50 mph at times for the mid-afternoon through the
evening hours. Based on this, have issued a Wind Advisory for
much of the area from 2 PM through 10 PM Wednesday. High temps
should reach the 40s across the higher terrain and 50s for
Strong winds should start to diminish late Wednesday evening,
especially after midnight. Still, enough of a surface gradient
will remain in place to keep winds breezy through the overnight
hours. Overnight lows will fall into the 20s to mid 30s for the
area with skies becoming fairly clear.
On Thursday into Thursday night, high pressure will be building
towards the area from the Great Lakes. The high still will be
far enough away that during peak heating on Thursday, some
breezy conditions (gusts up to 25 mph) will still be possible.
Otherwise, it will remain dry and fairly sunny on Thursday. Some
clouds may start to return towards the area by Thursday night as
the next storm system rapidly approaches from the southwest.
Temps look seasonable with highs in the 40s to low 50s for
Thursday and lows in the 20s and 30s for Thursday night.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
After a system brings rain and rain/snow to the higher terrain
during the day Friday into Friday night, uncertainty increases
heading into the new week. While the pattern turns more active and
chances for precipitation increases, the timing, track and intensity
of various shortwaves remains uncertain. Users should continue to
check back for updates as we fine tune the forecast over the coming
We start the long term on Friday with a near 1035hPa high sliding
eastward into New England with a weak, open shortwave progressing
northeastward out of the Ohio Valley. Strong subsidence and abundant
mid-level dry air from our departing high pressure suggests that
precipitation should be slow to push into eastern NY/western New
England. Therefore, we continue to favor the ECMWF solution which
has consistently shown a slower start the past fews runs. A slower
onset also means that our chances for any wintry mix during the
cooler morning hours has lowered. The ridge axis gradually crosses
through our region during the day Friday resulting in thickening
clouds and eventually warm air advection driven precipitation,
especially by the afternoon. Despite warming aloft, we favored the
cooler temperature guidance for Friday. With our high anchored off
the coast of New England, southeasterly winds should lead to a
cooler/marine influenced air mass over region. Plus, low dew points
in the 20s to low 30s combined with increasing showers should cool
the column down adiabatically via wet-bulbing processes. Expect
highs to only reach into the upper 30s to mid 40s which is about 10
degrees below normal for early April.
As our system`s warm front reaches into the mid-Hudson Valley and
southern New England Friday night, a 45-50kt low-mid level jet in
its warm sector should result in increased moisture transport and
better chances for widespread and steadier periods of rain over our
region. We also notice hints in the latest model guidance of a
secondary low developing along the boundary which also would provide
focus for enhanced precipitation. Total QPF by 12z Saturday looks to
range 0.25 - 0.75" with localized higher amounts in the southern
Adirondacks and Greens which we commonly see in these southwest flow
regimes. The northern extent of our warm front remains uncertain but
if it only reaches into the Capital District which the GFS and ECMWF
both suggest, then the Adirondacks, Upper Hudson Valley and Greens
could change to rain/snow or even all wet snow overnight. The
current forecast reflects this thinking.
Our system exits by Saturday morning with high pressure from the
Great Lakes taking control of the region. For now, the ECMWF and GFS
both favor a mostly pleasant weekend as upper level ridging
increases (more so on the ECMWF than the GFS) for eastern NY and
western New England with seasonable temperatures in the 50s to
possible nearing 60 on Sunday. However, we will be monitoring a
few shortwaves in the Central Plains which look to head
eastward as we start the new work week. Lots of uncertainty in
exact timing and placement but the pattern does look to turn
more active so we followed suite from the previous forecast and
showed chance POPs starting Sunday night through Wednesday.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Intensifying coastal storm just off the outer banks of North
Carolina will continue to track northeast. Expansive cloud
shield, VFR, will persist through the overnight period. Winds
will generally be around 10kts or less overnight.
As this storm tracks quickly northeast, increasing pressure
gradient will result with wind magnitude increases during the
daylight hours Wednesday. Frequent gusts at or above 30kts are
expected from the west-northwest direction. Otherwise, VFR with
respect to CIGS/VIS.
Wednesday Night: Moderate Operational Impact. Windy. NO SIG WX.
Thursday: Low Operational Impact. Breezy. NO SIG WX.
Thursday Night: No Operational Impact. NO SIG WX.
Friday: High Operational Impact. Likely RA.
Friday Night: High Operational Impact. Likely SHRA...RA.
Saturday: No Operational Impact. NO SIG WX.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: Moderate Operational Impact. Chance of SHRA.
Gusty Winds and Low RH over the Next Few Days...
A storm system will track off the eastern seaboard tonight and
early Wednesday. Most of the precipitation with this storm will
remain east of the area. A cold front will then pass through
the region Wednesday afternoon bringing windy conditions into
Wednesday evening. Breezy conditions will also be in place for
Thursday with continued dry weather.
After a dry afternoon today, the RH will recover to 70-90
percent tonight, highest across the SW Adirondacks and across
western New England. RH values will lower to 20 to 30 percent on
Wednesday afternoon and again on Thursday afternoon.
Southerly winds will be 10 to 20 mph with some gusts up to 25
mph through this evening. Winds will become light/variable
tonight through mid morning Wednesday. Winds will then become
west to northwest, and rapidly increase Wednesday afternoon to
15-30 mph, with gusts of 35-55 mph. Winds will diminish somewhat
after midnight Wednesday night, but some gusts up to 25 mph will
continue through the day on Thursday.
Some light rain or wet snow is possible tonight across portions
of western New England, but amounts will be fairly negligible.
Also, a few sprinkles are possible with a cold front for
Wednesday afternoon, mainly impacting northern areas, but
amounts will generally be only a few hundredths at most. Dry
weather is then anticipated for Wednesday night through
The next chance for widespread precipitation will be Friday (as
rain or a rain/snow mix) as a frontal boundary approaches from
Other than some possible light rain/snow across western New
England tonight, generally dry weather is expected through
Thursday. Although daytime temperatures will be a little milder
than recent days, overnight lows still looks to below freezing
for much of the area for the next few nights. This should allow
for a diurnal melting pattern of the snowpack that continues to
be in place over the high terrain.
The next chance for widespread precipitation looks to be Friday,
with some rain and snow thanks to a frontal boundary. Some
rises are possible due to the expected precipitation, but at
this point, runoff looks limited enough to keep rivers and
streams within their banks.
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.
NY...Wind Advisory from 2 PM to 10 PM EDT Wednesday for NYZ032-033-
MA...Wind Advisory from 2 PM to 10 PM EDT Wednesday for MAZ001-025.
VT...Wind Advisory from 2 PM to 10 PM EDT Wednesday for VTZ013>015.
Area Forecast Discussion
National Weather Service Grand Forks ND
1002 PM CDT Tue Apr 2 2019
Issued at 1001 PM CDT Tue Apr 2 2019
Area radars show the one remaining area of showers is moving thru
central ND headed for SE ND. Observations reveal mostly snow
showers. This area of precipitation is moving SE and will need to
adjust pops for this into SE ND. Eventually they should fall
apart...but water vapor shows they be part of a weak short wave
with the center in north central ND moving into NE ND.
.SHORT TERM...(This afternoon through Wednesday)
Issued at 327 PM CDT Tue Apr 2 2019
Cold front has passed through our CWA, however steep low level lapse
rates combined with lingering forcing aloft has supported isolated
to scattered shower development. Better mid level lapse rates are
shown on RAP analysis in northwest MN, where moderate to heavy
pockets are quickly passing. Most snow is melting on contact, and
duration is brief enough that only a dusting or 0.5" at the most
would be anticipated. Stronger pressure rises and good mixing (with
localized enhancement from showers) is resulting in win gusts around
40 mph and we couldn`t rule out a few gusts to 50 mph before
stabilization/decoupling around sunset. These winds and more intense
showers are resulting in visibilities being reduced as low as 1/4
mile for brief periods, but considering short duration only Special
Weather Statement was issued. Most activity should end with loss of
Quieter weather tonight through Wednesday as Canadian high pressure
passes over our CWA. There could be a few lingering flurries through
early Wednesday morning in our far northeast (Lake of the Woods
county) where guidance holds onto a light precip signal. Lows will
be in the upper teens/lower 20s, while highs Wed should get to the
mid-upper 30s most locations (lower 40s south).
.LONG TERM...(Wednesday night through Tuesday)
Issued at 327 PM CDT Tue Apr 2 2019
Thursday-Sunday night: Westerly flow followed by shortwave ridging
Friday, followed by deeper southwest flow late Friday into
Saturday will result in increasing WAA. Overnight lows are
likely to be above freezing during these periods for most of our
area , especially Friday night and Saturday night. Highs will
increase substantially with many locations possibly into the 50s
or even 60s in the southern Red River Valley Saturday.
Regarding precipitation in these periods: Shortwave trough passage
Thursday-Thursday night may bring brief light precip, but most
forcing splits around our CWA and there is a limited window for
moisture advection. Much less confidence in system Saturday-Sunday
night ands there is large spread run-run between
deterministic/ensemble guidance on evolution of system. Latest
runs of ECMWF and GFS have completely flipped from previous runs
with ECMWF strong strong upper low causing issues in our area,
while GFS will well south. Previous two runs were the complete
opposite. There is still potential for instability building north
Friday night-Saturday night with LLJ/WAA possibly supporting
isolated thunderstorms in our south, but even then if southerly
track happens showers become less likely (much less thunder). Will
need to monitor as this could be a stronger system, but no
confidence in if this will be a problem for us.
Monday-Tuesday: Progressive pattern is depicted with consensus
favoring temps above normal (highs upper 40s-50s, lows near to
above freezing). Quick moving shortwaves may bring precip chances,
but probably similar to events today or Thursday this week (fast
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 705 PM CDT Tue Apr 2 2019
Expecting the gusty NW winds to diminish quickly early evening and
be much lower thru the night into Wednesday as high pressure moves
overhead. Scattered high based CU still around but less coverage
after dark and into Wednesday.
Issued at 327 PM CDT Tue Apr 2 2019
Snow melt and runoff continue to drive a general increase in water
levels for most locations along the mainstem Red River and its
tributaries across the southern Red River Valley. The only
exceptions to this are Wahpeton and Sabin which are seeing gradual
declines in water levels. However, both of these locations are
expected to remain in Moderate flood stage through much of this
Ice jamming continues to impact the Sheyenne river, especially in
the Mapleton area where an ice jam was reported just north of town.
This is causing rapid water level rise into Minor flood stage and
could lead to Moderate flooding if the ice jamming persists into
All other river forecast points forecasts generally remain unchanged
with Major flooding still expected in the Fargo area by the
weekend/early next week. Ice jamming in the tributaries and in area
ditches is slowing down run off for now, but with increasing
temperatures forecast for the second half of the week snow melt and
run off is expected to accelerate.
As mentioned, the ice jamming in the smaller tributaries and ditches
continues to cause areas of overland flooding in the southern
Valley. Overall conditions have not changed much in the past 24
hours with the exception of parts of far southeast North Dakota
where a few county roads have been impacted from minor overland
flooding. These conditions will likely linger through the rest of
the week before prolonged above-freezing temperatures help alleviate
ice jamming/plugging and allow for better runoff.
Area Forecast Discussion
National Weather Service Gray ME
1126 PM EDT Tue Apr 2 2019
Low pressure tracking offshore will bring some light snow and
rain mainly to coastal areas tonight. This will end tomorrow
with many areas warming into the 50s before a cold front blows
in Wednesday afternoon. Gusty winds can be expected behind the
front Wednesday afternoon. Cool temperatures can be expected
Thursday and Friday with the next wave bringing some light
precipitation Friday night.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
1120 PM Update...Backed off a little bit more on snow amounts late
tonight based on trends in latest guidance. Otherwise no
significant changes. Could be some decent windy rain/snow
squalls later Wed afternoon to keep an eye on with the northern
stream wave and associated cold front as well.
940 PM Update...Little change to the going forecast other than
to incorporate the last 3 runs of the HRRR into the PoP/QPF
forecast for later tonight through Wedensday morning. The HRRR
has shown very good run to run consistency late this afternoon
and evening with the western edge of precip shield basically
just brushing southeastern NH and the coast of ME. Have
continued with forecast of 1.5" snow or less most areas on
coastal plain, with a little more (2-3") on the Midcoast. Have
also sharpened up the western edge and pushed it a bit further
east. Western zones should remain dry overnight.
650 PM Update...High clouds continue to filter into the region
as coastal storm strengthens off the NC coast. No major
forecast changes at this time. Continue to watch trends in
mesoscale model guidance for any significant shifts in the
western edge of precip shield later tonight and tomorrow
morning. So far, the HRRR has been pretty steady run after run
with solutions that closely resemble our current forecast. Not
buying into the 18z 3KM NAM at this time with it`s western
solution being on the western edge of the guidance envelope.
Will certainly watch trends throughout the evening, however.
The only change to the forecast was to tighten up the PoP/QPF
gradient across interior zones late tonight and tomorrow morning
as the western edge should be pretty sharp.
Sfc low coming together off the coast of N Carolina this
afternoon as srn steam 500 MB wave interacts with convection
along stalled from in the area. This system will shift NE along
the coast tonight and phase with nrn stream late tonight early
Wed. This will occur too far to our S and E to avoid any major
impacts, but one concern will some snow or mixed rain/snow
around the morning commute. thinking is that intense snow
banding will stay offshore, which will allow a warmer boundary
lyr, and only occnl moderate intensity snow, to produce a mix
or some short periods of snow, with mostly accums of an inch or
less, which will likely not accumulate on the roads as well as
grassy or snow-covered areas. Up to two inches is possible at
elevations above 1000 feet, but mainly where QPF is over 0.2"
which will likely limit these areas to the ME coastal plain and
srn foothills as well as interior parts of srn NH. Lows range
from 25-30 in the N, to the low 30s in the south.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Wed will start off with that snow or rain, or mix, but temps
will warm quickly after sunrise, so much of any precip will turn
to rain by 8-9 AM or so, and will likely end during the morning
The second impact of this storm will be strong gust winds in the
afternoon, as low pressure deepens over er the maritimes, and
sfc high builds in on its helps from the west, creating strong
pressure gradient from the sfc up through about 700 MB. While
sustained will be closer to 20 mph, strong gusts in the 40-50
mph are possible, especially across the southern half of NH and
SW ME, and a briefly lining of the sfc to mid-lvl flow will
allow deep mixing. The downslope will help push afternoon temps
in the 50s across a large part of the area, and this quickly
melt any snow in the area. The mtns will see highs in the 40s.
The winds diminish around or after sunset, but it will still be
breezy Wed night with lows ranging from the low 20s in the N to
around 30 near the coast. Some upslope SHSN will be possible as
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Expect cool conditions Thursday and Friday in the post-frontal
air mass with high pressure building into the area. The next
wave will arrive from the southwest Friday night and will be our
next chance of precipitation. It`s still unclear how much
precipitation will fall with this, as this will be dependent on
how much moisture can get pulled into the wave before it moves
by as well as the evolution of the low level features. It could
begin as some light snow for much of the northern half of the
area, though temperatures will be borderline for accumulation
outside the mountains.
Beyond this expect high pressure to again build through the area
this weekend with near normal becoming slightly above normal.
Models not in great agreement on the broader pattern evolution
for next week yet. General consensus is a northern stream ridge
over central Canada with a southern stream trough crossing the
US toward New England. The degree to which some of this trough
gets cut off over the southern United States will play a big
role in determining the timing of any shots of precipitation for
our area. At this point, we are looking at a chance of rain
Monday through Wednesday. Although it is unlikely to rain that
entire time, it`s just too early to be able to narrow down when
the best chances will be as there remains considerable
disagreement on those finer details within the models.
.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
Short Term...Expect MVFR, with some tempo IFR late tonight into
Wed morning in RA or SN, with improvement to VFR midday. West
winds will gust to around 40 KT at times Wed afternoon, at all
but KHIE. Winds subside Wed evening with VFR thru the night.
Long Term...VFR expected through Friday. Rain and
interior/mountain snow move in Friday night with IFR conditions
likely. Clearing begins again on Saturday.
Short Term...Gales have been issued for Wed afternoon into Wed
night as strong W flow develops behind a departing low moving
thru the maritimes.
Long Term...Post frontal winds continue through Thursday before
finally dropping below advisory levels Thursday night. It will
be relatively tranquil through the rest of the week as high
pressure moves in. The frontal system arriving on Friday will
briefly increase winds, but should remain below advisory levels.
ME...Wind Advisory from noon to 7 PM EDT Wednesday for MEZ018-019-
NH...Wind Advisory from noon to 7 PM EDT Wednesday for NHZ005>015.
MARINE...Gale Warning from noon to 10 PM EDT Wednesday for ANZ151-153.
Gale Warning from noon Wednesday to 10 AM EDT Thursday for
Area Forecast Discussion
National Weather Service San Francisco Bay Area
432 PM PDT Tue Apr 2 2019
.SYNOPSIS...Lingering light rain showers may persist into early
Wednesday morning. Unsettled weather conditions are then likely to
persist through the remainder of the week with renewed chances of
rainfall likely by Thursday becoming more widespread Friday and
Friday night. Temperatures are likely to remain near seasonal
averages through the forecast period.
.DISCUSSION...as of 02:28 PM PDT Tuesday...A mix of clouds, rain
showers, and sun this afternoon as a weak frontal boundary moved
inland across the region. Rainfall amounts during the past 12
hours or so have ranged from trace amounts to a few hundredths of
an inch for most locations while portions of the Santa Cruz
Mountains reported upwards of around 0.50". Look for a few
lingering showers to persist into the evening and even into early
Wednesday morning. However, rain showers will again be light and
not amount to much more than a few hundredths to a tenth of an
inch through the night.
A week ridge will shift over the region on Wednesday with a brief
break in precipitation possible during the afternoon and evening
hours. By Thursday, the next round of rain will begin to move in
from the west as another frontal boundary approaches. A more
robust frontal system is forecast to tap into a deeper plume of
moisture and advect into the central California coast Friday into
Saturday. This system will bring widespread rainfall to the
region, first beginning in the North Bay sometime on Friday and
then across the remainder of the region Friday night into
Saturday. PWAT values are forecast to exceed 1.00" as the system
advects inland which would potentially result in a weak
atmospheric river at landfall. However, this system will move
rather quickly across the region and limit overall impacts (such
as flooding concerns). While the models do differ on timing and
exact trajectory, the ensemble members suggest a decent rainfall
event across much of the region from Friday into Saturday. Thus,
look for adjustments to the forecast in the coming days. Overall,
rainfall will be greatest in the North Bay with the potential for
1.00"-2.50", 1.00"-1.50" for Santa Cruz County, and 0.25"-0.75"
for most other areas. Cannot rule out higher totals in some of the
coastal ranges and lesser amounts in the rain shadowed valleys.
Showers may linger into Saturday in wake of the exiting system.
Drying conditions are then expected to develop south of San
Francisco by Sunday with the potential for ongoing precipitation
across the northern portion of the state into early next week.
Overall, temperatures through the forecast period will remain near
seasonal averages with a moist, zonal flow.
.AVIATION...As of 04:32 PM PDT Tuesday...for 00Z TAFs. MVFR cigs
to prevail through much of the period with patchy IFR cigs
possible overnight. The HRRR and the WRF show scattered showers
in the vicinity through tomorrow afternoon, although by then
shower chances will be minimal. Cigs should begin to lift back to
VFR by tomorrow afternoon. SW to W winds into tonight before winds
turn back out of the SE overnight.
Vicinity of KSFO...MVFR cigs to continue through tomorrow morning
with brief periods of borderline VFR conditions possible late
this afternoon. Cigs right now between 1500-3500 ft AGL. Guidance
shows MVFR cigs prevailing overnight. VFR conditions expected by
tomorrow afternoon. SW to W winds becoming SE to variable tonight.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Borderline MVFR/VFR ceilings to continue
into this evening before MVFR conditions are expected to settle in
overnight. W to SW winds becoming more southerly overnight.
.MARINE...as of 02:15 PM PDT Tuesday...Light southwest to west
winds overnight will become more southerly during the day on
Wednesday. Winds will then gradually strengthen on Thursday and
Friday ahead of the next approaching system, becoming gusty at
times. A new northwest swell will arrive on Friday and build into
PUBLIC FORECAST: RGass
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Area Forecast Discussion
National Weather Service Sacramento CA
312 PM PDT Tue Apr 2 2019
Unsettled weather this week as several weather systems impact
Northern California. The late-week system will likely be the
strongest with periods of heavy precipitation, gusty winds, and
lower snow levels.
A weakly negative-tilted trough is currently swinging through the
region which has fostered the development of widely scattered
showers. Most of these have fired within an axis of instability
over the northern San Joaquin Valley eastward toward the terrain.
The 21Z RAP objective analysis indicates some residual instability
exists along I-5 up toward Redding. However, there have been
fewer breaks in the clouds which has tempered the convective
potential. Any of these cells should quickly weaken after dark
given the loss of heating. Toward the Sierra, a Winter Weather
Advisory remains in effect through midnight for elevations 6,500
feet and above. The S-band radar shows snow levels have generally
meandered between 6,500 and 7,000 feet today. Any residual snow
showers should wind down overnight.
On Wednesday, while most of the region will be dry, the northern
mountains can expect passing showers throughout the day. One
limiting factor is the mid/upper-level ridge building across the
state which should keep the activity disorganized. Gradually the
focus will shift to the early Thursday system which is likely a
quick hitter. Total precipitation amounts will be light across the
region with highest Valley numbers near Redding where 0.25 to 0.50
inches is possible. Local terrain effects will bolster numbers to
near an inch in foothill and mountain locales. Not expecting any
travel concerns with 2 to 4 inches of snow in the forecast with
snow levels around 6,000 to 6,500 feet.
In advance of the high-end "Weak" Atmospheric River slated to push
onshore Friday morning, southerly winds will really begin to pick
up the prior afternoon. This is particularly the case over the
northern Sacramento Valley with wind gusts potentially reaching 35
to 40 mph in the evening to overnight hours. On Friday morning,
the initial bands of warm advection rainfall moves inland with
activity really picking up around the early afternoon over
mountain and foothill locations. Models currently advertise the
heaviest snowfall from the just after noon into the overnight
hours with snow levels roughly around 6,000 feet. This will likely
lead to hazardous mountain travel. Snowfall amounts of 1 to 2 feet
are possible during the duration of the late season winter storm.
Activity should turn more showery by Saturday morning. ~BRO
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)
The weekend forecast remains up in the air given continued
differences among deterministic and ensemble guidance. Run-to-run
differences remain an issue for the more reliable models which
diminishes confidence in the forecast. At this point, expect
scattered showers on Saturday with the better focus across the
interior mountain ranges. While Sunday initially appeared dry, the
GFS and ECMWF vary in evolving pattern. The upper ridge shown by
the 12Z GFS is stronger and forces the storm track closer to the
California/Oregon border for Sunday into early next week.
Meanwhile, the 12Z ECMWF depicts an offshore system strong enough
to flatten the ridge supporting an increase in precipitation to
conclude the weekend and into Monday. Details will likely
continue to waver given the fluctuating model guidance. At this
point, favored precipitation over the northern zones during this
period while keeping the I-80 corridor mostly dry. ~BRO
Line of showers/scattered storms with numerous cloud
flashes/pulses and isolated cloud-to-ground strikes will be moving
across the Nrn San Joaquin and Srn Sac Vly and into the Sierra
foothills and lower mountain elevations through 00z. Widespread
MVFR-IFR conditions expected along this line.
Elsewhere, widespread MVFR with areas IFR, especially over
mountains, through Wed morning. Freezing level near 7000-8000 ft
AMSL with snow level down to around 6500 ft AMSL. Areas of Sly
wind gusts up to 25 kts in the Central Vly til 03z Wed, and gusts
up to 35 kts over mountains into Wed morning.
Winter Weather Advisory until midnight PDT tonight for West
Slope Northern Sierra Nevada.