Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/23/21
Area Forecast Discussion
National Weather Service Boston/Norton MA
1029 PM EDT Mon Mar 22 2021
High pressure remains in control. Dry weather prevails for much
of the upcoming week with mild days (inland from the coast) and
cool nights. The warmest day looks like Thursday. A cold front
will likely bring showers Friday, along with gusty winds.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
1020 PM Update...
Nighttime Microphysics satellite imagery shows an area of low
clouds pushing northwest towards the Cape and Islands as well as
the RI/MA South Coast. Falmouth is reporting 3000 ft stratus but
no impactful weather yet. Many locations in SE MA and RI have
seen dew point depressions falling to 5 degrees or less. With a
1030 mb surface high moving offshore and light southerly winds,
using pattern recognition, areas of fog that are locally dense
should develop later tonight into the pre-dawn hours. The
question remains timing and areal coverage. 01z HRRR has
somewhat less bullish on the northward extent of the dense fog
coverage, keeping it generally south of US Route 44 across
Bristol and Plymouth County. In addition, it has also delayed
the onset of the fog. For now, have opted to hold off on any fog
headlines and will reevaluate for the next update. Otherwise,
forecast remains largely on track.
8 PM Update...
The forecast remains largely on track this evening. The most
significant change to the forecast was increasing the reach of
the developing stratus layer further north to include the
Boston metro and I-95 corridor. Much of the short term guidance
supports the notion that the stratus layer will extend further
north than it did last evening. Fog may form as far north as
Providence, but will be fighting significant dewpoint
depressions around ~10F, suggesting it is likely that fog will
be limited to the south coast, Cape, and Islands. A dense fog
advisory is not out of the question across SE MA/Cape Cod
as visibilities may be reduced to 1/4 mi or less.
If the stratus does in fact develop across metro west and
Boston, radiational cooling may be limited, and temperatures may
not reach their forecasted lows, especially across SE MA and
RI. W MA and CT should remain relatively clear overnight.
Clear skies abound this afternoon under a
ridge of high pressure with light winds and temperatures well
into the 60s. The only exception is along the coast where sea
breezes are ongoing, holding temperatures in the 50s. Tonight
surface ridging continues with winds becoming light, beginning
turning E/NE. Radiational cooling should be rather efficient
overnight, especially further north where skies stay clear or
are slower to cloud over. We will once again be dealing with a
surge of low level moisture trapped beneath a low level
inversion, mainly along the south coasts and southeast MA. This
will bring the return of low stratus and fog, likely more
widespread than we saw this morning. Clouds advance as far north
as the MA pike before retreating Tuesday morning. Low
temperatures dip into the 20s for cold spots, but most will be
in the 30s. Again this will be a night where the inversion means
Worcester should be one of the warmest locations in the region,
around 40 degrees.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday high pressure ridging continues. Main change will be
boundary layer winds shifting out of the east. This will once again
hold east coastal locations in check temperature-wise, in the upper
50s (low 50s on the Cape and islands). Elsewhere most locations
rebound back into the mid 60s. Lingering stratus and fog south of
the MA pike in the morning should dissipate by mid to late morning
as the inversion is eroded. Nantucket and the outer Cape stand the
best chance of holding on to clouds into the early afternoon.
Tuesday night moisture advection returns to the low levels once
again from the east with low/mid clouds overspreading from east to
west, while in the upper levels W/SW flow brings scattered high
clouds as well. Warm air advection from the south brings warmer low
temps, in the upper 30s, perhaps low 40s, limited by surging
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
* East wind keeps things cooler Wednesday. Showers and spotty chance
of thunder on Wednesday night.
* Much warmer Thursday.
* Better chance for precipitation on Friday as low pressure passes
to our NW. Cold front passes through sometime Late Friday
or Early Saturday.
Wednesday through Thursday Night...
The high pressure that was dominant Monday and Tuesday moves well
northeast into the open Atlantic, but still suppresses low pressure
moving off the coast of the Carolinas to our south and east. East
wind off of the cold Atlantic will keep temperatures in the 50s
across E. MA and Rhode Island Wednesday; areas in the CT River
Valley, shadowed by the Worcester Hills, have the best shot at
approaching 60. A shortwave that passes through Wednesday afternoon
may bring a chance of spot showers, but a better chance of showers
occurs Wednesday night as a warm front pushes in from the southeast.
About 0.1" of QPF expected. K index values approaching 30,
especially along the south coast and Cape Cod suggest that we can`t
rule out an isolated rumble of thunder.
Significant warm air advection on southwest flow in store for
Thursday. Temperatures expected to reach into the upper 60s and low
70s. Some guidance suggests even warmer solutions, with the ECMWF
showing highs in the mid 70s. High temperatures will hinge on how
much sun breaks through the cloud deck. Southwest flow will keep
areas along the south coast much cooler.
Friday through Saturday...
A more significant chance of precipitation arrives on Friday as a
low pressure system slides to our NW across the Great Lakes and
Northern New England. The chance for thunder seems more likely
Friday afternoon along a cold front that moves from NW to SE across
our area. The exact timing of this front differs between guidance,
as the GFS favors a much faster progression compared to the ECMWF
and Canadian models. With CAPE values approaching 600 in some
guidance, namely the ECMWF, and the K index topping 30, isolated
chances for thunder were expanded across much of Southern New
A strong low level jet develops on Friday, as 925 mb winds gust 55-
60+ kts. Given that cold air will be ushered in behind the passing
front, mixing is expected, and gusts to 30 kts cannot be ruled out
sometime Friday afternoon through Saturday morning. Cooler and
sunnier behind the passage of the front on Saturday, most will
remain in the 50s.
Sunday and Beyond...
The GFS, ECMWF, and Canadian models all signal
the development of a low pressure system late next weekend/early
next week. The exact timing of this system, and p-type, differ
significantly between the guidance. Should the storm take a more
inland track, we would remain in the warm sector and should see
rain. If the storm takes a more coastal track, we could see a bit of
snow mix in. Given that we are heading into late March, confidence
in accumulating snow is low. More attention will be paid to this
system late week.
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00Z update...Moderate confidence.
VFR and light winds to start the night. At the time of this
writing, a stratus deck was beginning to develop southeast of
Nantucket and is expected to progress to the NW overnight.
Stratus and fog expected to develop along the south coast
tonight and may lift north across portions of northern CT, RI
and SE MA. Some guidance hints that stratus will make it`s way
all the way up into Boston, which would drop ceilings into
Conditions will improve to VFR after about 15Z tomorrow.
Easterly winds develop at this time and will extend through the
end of the TAF period. Stratus/fog may develop again on Tuesday
night across the south coast and SE MA, which would result in
MVFR and IFR ceilings.
KBOS TAF...Moderate confidence. Stratus may develop far enough
north to affect KBOS, but may stay just south of the airport.
Conditions will be highly influenced by the northern extend of
the stratus. Fog not expected at KBOS due to forecasted >10F
KBDL TAF...High confidence.
Outlook /Wednesday through Saturday/...
Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA.
Wednesday Night: Mainly MVFR, with areas IFR possible. Chance
Thursday Night: MVFR/IFR conditions possible. Chance SHRA.
Friday: Mainly MVFR, with local IFR possible. Breezy. Chance
SHRA, isolated TSRA.
Friday Night: Mainly VFR, with local MVFR possible. Windy with
local gusts up to 30 kt. Slight chance SHRA.
Saturday: VFR. Breezy.
Tranquil conditions through tonight with light winds and seas.
Looking at mainly light easterly flow Tuesday and Tuesday night,
but increasing SE swell will result in seas building to 5-6 ft
over outer southern and SE waters.
Outlook /Wednesday through Saturday/...
Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of
Wednesday Night: Winds less than 25 kt. Seas up to 5 ft. Rain
showers likely, isolated thunderstorms.
Thursday: Winds less than 25 kt. Seas up to 5 ft.
Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers.
Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas. Chance of rain showers,
Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 9 ft. Slight chance of rain
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas.
Area Forecast Discussion
National Weather Service Des Moines IA
645 PM CDT Mon Mar 22 2021
...Updated 00z Aviation...
.DISCUSSION.../Tonight through Monday/
Issued at 227 PM CDT Mon Mar 22 2021
-- Light scattered showers become widespread tonight into Tuesday
-- If there are breaks in the cloud cover Tuesday afternoon, there is
a risk of strong to perhaps severe storms over southern Iowa
-- Breezy on Wednesday as showers come to an end
-- Additional precipitation chances Thursday and then again this
weekend with near to slightly above normal temperatures
Details: GOES-East Day Cloud Phase Distinction shows plenty of
low clouds stretched from southwest to northeast over much of the
state with high clouds streaming well northeast of the state as
well. There are some peeks of sunshine over southeastern and far
northern Iowa. The steadiest rainfall this afternoon is over
western Iowa, but scattered showers also extend into parts of
central Iowa. Showers will become more widespread tonight as low
level thermal lift along with QG convergence increases over the
state ahead of the upper low. In addition, precipitable water
values around 1 inch will also be pulled into the state. The lift
will remain through Tuesday and with cloud cover and periods of
rain favored much of day, have trended temperatures downward from
initial blend of guidance, which was at the 75th percentile. A
conditional risk tomorrow is the possibility of a few strong or
severe storms ahead of the upper low and the matched surface low
along a wind shift if breaks in the cloud cover develop. There is
an area of 0-3km MLCAPE up to around 100 J/kg that develops over
southern Iowa with 15 to 20 knots of bulk shear in the same layer
in the GFS. The 12z HRRR and NAM have higher amounts of 0-3km
instability, though the NAM does not bring the instability as far
north. Forecast soundings at LWD (12z NAM/6z GFS) show good low
level turning in the first kilometer with helicity values over 100
m2/s2. The same can not be said about the 12z GFS, which does not
show a favorable environment for rotation. In coordination with
SPC, the midday update to the day 2 outlook has introduced a
marginal risk of severe weather into southern Iowa. Many of the
updraft helicity tracks from the 12z HREF are shown over northern
Missouri with the 12z HRRR showing one or two tracks into our far
southeast forecast area toward mid-afternoon Tuesday. Thus, a
non-zero tornado risk will remain for tomorrow, but is highly
contingent on some surface heating.
As the upper low moves overhead and continues northeastward away
from the state, the low level thermal lift will decrease Tuesday
night. As QG convergence becomes subsidence on Wednesday, will see
showers come to an end as winds turn breezy. Fortunately, the rain
will be spread out over time with within bank rises on rivers and
streams expected along with a beneficial boost to soil moisture.
Winds from the northwest with gusts of 25 to 35 mph should be
common over much of the forecast area as well. The next shortwave
will be approaching from the Four Corners region on Wednesday and
bring with it the next chance for precipitation. While the NAM,
GFS, and ECMWF all show some precipitation over the state at some
point Thursday -- namely the southeastern part -- there is still
a good number of ensemble members that show the precipitation
remaining southeast of Iowa. At this point, will keep low PoPs
with the highest chances over southeast Iowa and more so points
southeast of Iowa.
A final shortwave rotates through the region late this week into
this weekend. The GFS and ECMWF and a majority of their ensemble
members have some precipitation passing over the state with the CMC
and its ensembles on the drier side. At this time, a prolonged
period of low PoPs is into this upcoming weekend, which will likely
get parsed down to a shorter period. While much of the week will
have temperatures near seasonal levels, slightly warmer temperatures
are possible depending on timing of precipitation next weekend.
.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 641 PM CDT Mon Mar 22 2021
Widespread stratiform cloud cover blankets Iowa this evening. As
of the early evening CIGs were staying at MVFR. However, rain
showers will continue to spread Tuesday, and as this happens
expect CIGs to drop to IFR. Depending on localized areas of heavy
rainfall, visibility may drop to IFR as well. The next 24 hours
will not present the most favorable aviation conditions.
Area Forecast Discussion...UPDATED
National Weather Service Hanford CA
730 PM PDT Mon Mar 22 2021
.UPDATE...Have updated the Wind Advisory which had been in effect
for the Central Sierra and North Kings River areas to a High Wind
Warning from 100 pm PDT Tuesday until 500 am PDT Wednesday. HRRR
continues to show stronger wind gusts over these areas and is now
projecting gusts as high as 70 mph Tuesday evening and early
.SYNOPSIS...A trough moving through the Great Basin tonight
through Tuesday will lead to a chance of light precipitation,
primarily for the higher elevations of the Sierra, and higher
elevations of the Tehachapi and Fort Tejon areas. Gusty winds
will impact the Kern county mountains and desert into Tuesday
morning. Offshore flow then develops on Tuesday into Wednesday,
with strong northeasterly winds possible in the Sierra mountains
.DISCUSSION...An upper level trough currently over central Oregon
will dig southeastward through the Great Basin tonight, reaching
northern Arizona by Tuesday afternoon. The current pressure
gradient from SFO-LAS is 8mb, and will continue to increase
through the early morning hours. This will set the stage for
strong west to northwesterly winds through Tehachapi pass, and
into the surrounding desert area. Wind gusts up to 50 mph are
conceivable through Tuesday morning. As this system swings through
the region tonight, there is a 30% chance of light precipitation,
primarily for the highest elevations of the Sierra. Any amounts
will be negligible.
Northwest flow aloft will act to enhance upslope flow into the
Tehachapi mountains and Fort Tejon area this evening through
Tuesday morning. There is a 50% chance of light rain, drizzle, and
snow showers generally above 5000 feet. The latest guidance shows
up to 1/3 of an inch of QPF along the highest peaks, and up to
1/10 of an inch along the Grapevine and Frazier Park areas. The
highest peaks may see a trace to two inches of snow, with snow
levels around 5 to 6 thousand feet for most of the day.
As the aforementioned trough exits into northern Arizona,
northwesterly flow will turn to an offshore northeasterly flow.
Although not the best setup, a weak Mono wind event is becoming
more likely. The short-term ensembles are indicating wind gusts up
to 60 mph starting Tuesday afternoon, continuing into Wednesday
morning. Strong wind gusts up to 30 mph are also possible in the
southern San Joaquin Valley Tuesday, but the current NBM
probabilities of seeing winds greater than 35 mph are around 50%.
Thus I will hold off on any wind products in the valley.
Another trough of low pressure will swing through the Great Basin
on Thursday, bringing increasing winds into Kern County, and a
very slight (15%) chance of precipitation in the Yosemite area.
.AVIATION...Expect areas of MVFR with local IFR and terrain
obscurations along the west and north facing slopes of the Sierra
through at least 18Z Tuesday. Also, expect areas of MVFR with
local IFR and terrain obscurations along the west and north facing
slopes Kern County mountains from 06Z Tuesday through at least
20Z Tuesday. Strong sustained west to northwesterly winds of 25 to
35 mph with gusts up to 50 mph are likely in the Kern County
mountains through at least 18Z Tuesday. Gusty northeasterly winds
are then possible in the Sierra Nevada mountains and foothills
after 20Z. Otherwise...VFR conditions will prevail across Central
California through the next 24 hours.
.AIR QUALITY ISSUES...None.
The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
an/or to provide feedback.
High Wind Warning from 1 PM Tuesday to 5 AM PDT Wednesday for
Wind Advisory until 8 AM PDT Tuesday for CAZ196>199.
Area Forecast Discussion
National Weather Service Marquette MI
629 PM EDT Mon Mar 22 2021
.SHORT TERM...(This evening through Tuesday)
Issued at 403 PM EDT MON MAR 22 2021
WV imagery and RAP analysis indicated a broad mid/upper level
trough through the Rockies and a downstream ridge over the eastern
CONUS resulting in southwest flow toward the northern Great
Lakes. A shortwave trough from near James Bay to the MN arrowhead
was lifting off to the northeast. At the surface, a weak front
extended from eastern Upper Michigan into north central WI while
high presssure building from MN into western Upper Michigan was
bringing mostly clear skies.
Tonight, WAA and 285k-290k isentropic ascent will increase overnight
along and north of a slowly advancing 850 mb front and nearly
stationary surface frontal boundary over northern WI. Light
rainfall amounts of a tenth of an inch or less are expected given
the modest moisture inflow and availability. With min temps in the
mid to upper 30s, no freezing pcpn is expected.
Tuesday, the rain band into central Upper Michigan will lift
northward during the morning with a lull in the pcpn until rain
increases again toward the late afternoon as isentropic lift and
stronger moisture transport moves in as the mid level and sfc
advance toward southwest IA. Temps will remain above average with
highs in the lower 50s south and east. However, northeast winds will
keep readings in the lower 40s near Lake Superior.
.LONG TERM...(Tuesday night through Monday)
Issued at 325 PM EDT MON MAR 22 2021
The main focus of the this long term period will be a strong surface
low that will be tracking up from the central plains, across Upper
Michigan Wednesday into Thursday. This low will have quite a bit of
moisture associated with it, mainly in the form of rain which will
be a welcome sight for Upper Michigan as we are currently in an
abnormally dry time according to the latest drought monitor. Some
consistency from the overnight runs and this mornings runs show the
system occluding before reaching Upper Michigan with a surface low
of around 995-997mb by Wednesday morning. Rain should be falling by
Tuesday night and will mostly be widespread rain through Wednesday.
QPF amounts will range generally from 0.25 inches to 0.75 inches of
rain with possibly higher amounts near 1 inch over far western Upper
Michigan. As the system begins to move away from Upper Michigan late
Wednesday into Thursday, a cold front will move across Upper
Michigan from west to east and will change rain showers to more of a
rain/snow mix then light snow showers once the front passes, mainly
over the west and possibly north central too. System will be out of
the area by Thursday morning with some clearing and dry conditions
for most of Thursday.
Another shortwave will approach the Upper Great Lakes late Thursday
into Friday and models are starting to come into a general agreement
as to the track of the low. The GFS has trended further south to
align more with the ECMWF and Canadian across the Lower Peninsula of
Michigan which would keep the pcpn just to the southeast of Upper
Michigan. With the newer guidance in, will probably go towards more
of a drier solution for Thursday night and Friday. The NAM is the
current outlier with the track closer to the Mackinaw Straits. We`ll
see if the NAM will catch up to the others but will still lean
towards a bit drier solution with some slight chc PoPs for now.
That shortwave will move out late Friday before yet another
shortwave will be approaching on Saturday, which will bring another
chance of pcpn. This will be a mix light rain/snow showers Saturday
afternoon through Sunday. This shortwave will move out by early
Monday with high pressure building in for this time next week.
As for temperatures, it will still be above average on Wednesday
with highs in the 40s to low 50s before the cold front moves through
Wednesday night into Thursday with cooler temperatures for Thursday
and Friday. Friday will be the coldest day in the extended with
highs mainly in the low to mid 30s. Temps will rebound a bit for the
upcoming weekend with upper 30s to mid 40s.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 629 PM EDT MON MAR 22 2021
VFR conditions will prevail tonight for IWD and CMX before
deteriorating to IFR on Tue morning with some pcpn moving in.
Conditions will then stay IFR at IWD and CMX into Tue evening. VFR
conditions at SAW will fall to IFR by late tonight as rain moves in.
Conditions will fall further to LIFR on Tue with northeast upslope
flow with rain and fog at SAW.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 403 PM EDT MON MAR 22 2021
Light and variable winds of 15 knots or less expected across the
lake into this evening as weak high pressure builds into the
area. By Tuesday, a low pressure system moving northeast from the
Central Plains will result in winds veering around to NE and
increasing to 20-30 kts, greatest over the western third of the
lake. NE winds may even reach low-end gale force gusts over the
west end late Tuesday and Tuesday night before slowing diminishing
and backing northerly on Wed as the low lifts over the lake. N-NW
increase again to 25-30 knots on Wed night behind the low which
lifts ne of the lake. Winds become lighter and N-NE on Thu before
increasing NE to 25 knots Thu night into Friday as another system
tracks from the southern Plains into the Great Lakes.
Area Forecast Discussion
National Weather Service Pendleton OR
858 PM PDT Mon Mar 22 2021
Latest radar and ground truth observations show that organized
precipitation has either ended or moved out of the area. Short
range guidance does indicate that there could be some lingering
snow showers over the eastern Oregon mountains for the next few
hours, little accumulation is anticipated. As a result, the winter
weather advisories were allowed to expire at 800 PM/0300Z.
Dry northerly flow and slight ridging will begin to build in so an
lingering precipitation will come to an end by morning. For this
update, made adjustments to pops...mainly to lower them. Also,
updated temps where needed based on current obs and latest
06Z TAFS...VFR conditions are expected through the period under
dry northerly flow and slight upper level ridging.
Winds remain gusty at DLS and will likely remain elevated through
the night and into Tuesday, with gusts generally 20 to 25 kts.
Elsewhere, winds continue to decrease and will be 10 kts or less
by morning if not sooner and remain there for the remainder of the
.PREV DISCUSSION... /issued 426 PM PDT Mon Mar 22 2021/
00Z TAFS...VFR conditions expected. Mainly isolated -SHRA around
the region could pass over a TAF site through the evening, but
overall impacts will be limited. Gusty winds to around 30 kts will
continue through the evening hours before decreasing to around 10
kts or less overnight through Tuesday.
PREV DISCUSSION... /issued 1133 AM PDT Mon Mar 22 2021/
UPDATE...A warm front that is bringing moderate to heavy snow to
the Cascades and the northern Blue Mountain continues to impact
these areas. Winter weather advisories are in effect for the
Cascades and the Blues today. The lower elevations will receive
rain, with snow levels around 2500-3000 feet MSL. This weather
system will move out of the area tonight, but residual moisture
and a healthy northwest flow will continue to cause upslope snow
showers over the northern Blues, and may need to extend the
advisory for there. However, the Cascades are expected to see
snow decreasing today and will likely not need to extend the
advisory for there. The atmosphere is expected to become unstable
this afternoon from the John day highlands to Wallowa County.
These areas have a possibility of afternoon and early evening
thunderstorms. It will be windy over most of the forecast area
today and tonight, with wind speeds approaching advisory speeds
for the Kittitas Valley, but only for a short time. Therefore will
hold off on any wind highlights at this time. A cool northerly
flow will develop on Monday with still a possibility of a few snow
showers over the northeast mountains as an upper ridge builds off
AVIATION...18Z TAFs...Mountain snow continues today with rain
showers at possible at PDT/ALW. Can`t rule out a shower at RDM/BDN
as well. Mountain obscuration likely. Ceilings will be 4-7kft at the
terminals today. Improving conditions tonight with clearing skies at
the taf sites and mountain snow showers diminishing. Winds 14-24g24-
34kts today decreasing to less than 10kts tonight.
PREV DISCUSSION... /issued 524 AM PDT Mon Mar 22 2021/
SHORT TERM...Today through Wednesday night...Shortwave trough
will dig sewd across the region today exiting the region by
Tuesday morning. This will bring rain and mountain snow to the
area with rain shadowing east of the Cascades. There will be
moderate to heavy snow in the Blue Mountains and near the Cascade
crest today before tapering off. Latest SPC HREF is showing
borderline warning amounts over the northern Blues mainly over the
higher peaks. Thus places like Ski Bluewood, Tollgate, and the
higher snotels could see snow totals of around 10 inches. However
with the spring sun angle and borderline daytime temperatures plan
on leaving the advisories that are in effect as is for now and
not upgrade to warnings. Another concern for today are the winds.
Current LAMP guidance is showing winds approaching advisory levels
in the Kittitas Valley and the eastern Gorge but only for a short
window of time this afternoon and evening so will hold off on
issuing an advisory for these areas. Finally, very steep low to
mid level lapse rates over the eastern portion of the forecast
area may result in enough CAPE for an isolated thunderstorm or two
this afternoon...mainly Grant, Union, and Wallowa Counties.
Latest HRRR is showing some decent convective cells in this area
from 20-23Z. All precipitation will end this evening and Tuesday
looks to be a dry pleasant day with seasonable temperatures and
light winds. The next storm system will drop sewd across the area
late Wednesday and Wednesday night similar to the current one and
produce some lower elevation rain and mountain snow. As of now
QPF/snow amounts appear a bit lighter with this second storm. It
will also be breezy to windy in the lower elevations Wednesday
afternoon and evening. 78
LONG TERM...Thursday through Sunday. Models in good agreement
with the general pattern. Upper level trough will be moving east
of the region into Idaho on Thu. Lower elevation rain and mountain
snow decreasing in the morning and becoming more focused over
northeast Oregon mountains in the afternoon with upslope flow.
Ridge building in Thu night with precipitation over the Blues
ending by evening. Clearing skies overnight. The ridge will
strengthen Fri into Sat with a dry northwest flow. Expect mainly
clear skies and warm temperatures. Highs will be in the upper 50s
and 60s. A fairly strong upper level trough and jet will be
approaching the Pacific northwest on Sunday. Clouds and wind will
be increasing. Slight timing differences at this point in the
models. Light precipitation could overspread the Cascades during
the day. This system moves through Sunday night and Mon with rain
and mountain snow. Much cooler and windy Mon. 94
.PRELIMINARY POINT TEMPS/POPS...
PDT 31 52 31 54 / 10 0 0 30
ALW 33 54 34 56 / 10 0 0 40
PSC 30 59 36 58 / 0 0 0 10
YKM 28 59 32 56 / 0 0 0 30
HRI 33 58 35 57 / 0 0 0 20
ELN 31 55 33 53 / 0 0 0 30
RDM 21 50 26 52 / 0 0 0 20
LGD 29 45 24 47 / 30 0 0 40
GCD 29 48 25 51 / 20 0 0 20
DLS 36 57 36 53 / 0 0 0 50
Area Forecast Discussion
National Weather Service Reno NV
535 PM PDT Mon Mar 22 2021
No significant changes to the forecast of yet, but will be
monitoring. After reviewing the data for the slider, the potential
for accumulating snow on the valley floor is higher than it looked
this afternoon. Thunderstorms are forming behind the front in
Oregon, a signal increased instability. While snow levels are
higher right now, running around 5000 feet, almost all precip with
the main band will be post-frontal when snow levels and temps
fall rapidly. In addition, frontogenetical forcing and
modest instability will promote more intense snowfall for a 1-3
Latest HRRR runs show a fairly intense band moving through the
I-80 and Highway 50 corridors around midnight. As is typical for
sliders, the heaviest snow will be in western Nevada, with light
if any snow in the Sierra around Tahoe, with a better chance for
Mono County. At this point in time, the probability of the valley
floors in western Nevada seeing an inch of snow is 40% with a 10%
chance of 2 inches or more. X
.PREVIOUS DISCUSSION... /Issued 239 PM PDT Mon Mar 22 2021/
Winds increase through Tuesday as a cold front moves through the
region. Snow showers tonight will result in some slick roads
into the commute time Tuesday morning, especially in elevations
above 5000 feet. Another front is expected Thursday for a drop in
temperatures, breezy winds, and a chance for showers. Warmer
springlike conditions are likely this weekend.
The first part of our slider system came in a bit wetter than
expected with some light rain/snow showers moving southward
across the northern Sierra and western NV this morning. This has
moistened the atmosphere which should help precipitation
proficiency tonight (lack of dry layer), but also raised dewpoints
("warmed" the snow level potential) which will likely limit
snowfall potential on lowest valley floors below 4500-5000 feet.
As a result, we increased QPF but reduced snowfall amounts on the
lowest valley floors. Otherwise, timing of the front and
associated forcing are still in place to bring a short-lived
(1/2-1 hour) but moderate intensity band of showers tonight,
starting across northeast CA and northwest NV this evening,
sliding through the I-80/Hwy 50 corridors 10 pm - 2 am, and then
south of Highway 50 late tonight into daybreak Tuesday. Impact-
wise, expect an inch or two of wet snow in foothill areas which
may result in slick roads as temperatures fall below freezing
behind the band of precipitation. Warm road temperatures will
limit snowfall down on the lowest valley floors with conditions
remaining mostly wet. Being this is an slider type system,
snowfall amounts in the Sierra will be on the light side,
generally an inch or two, including the Tahoe Basin.
Winds will increase behind the front with a brisk, very cool day
Tuesday. Temperatures will struggle to hit 40 in the Sierra
valleys and likely reach only 40s in the lower elevations. Strong
northeast winds will develop across the Sierra ridges and continue
into Tuesday night (gusts could approach 100 mph). We have
hoisted lake wind advisories for both Lake Tahoe and Pyramid Lake
for rough lake conditions.
A brief break for Wednesday ahead of a second slider system to
drop in from the north Thursday. This will bring another round of
showers and gusty winds, although the track is slightly farther
east in the latest ensemble guidance. Based on the performance of
the current system against national blended guidance, we have
extended some low chance POPs back to the Sierra to include most
of western NV Thursday. Snow levels are a bit higher and any
showers are expected to move across during daylight hours. So
impacts right now are low.
High pressure will finally build into the region this weekend
which promises dry and warmer conditions. Temperatures will likely
push to 60 in the Sierra valleys and low-mid 70s across western
NV. These conditions may persist into next week although a weak
trough may brush our area to the north for a slight uptick in
A fast-moving storm system moves through the Great Basin tonight
with snow showers and increasing winds. There is a slight chance
of blowing dust over KHTH, KNFL, KWMC this afternoon.
Looks like another band of snow showers is expected overnight,
mainly between 06-09z with a quick burst of IFR snow to western
Nevada terminals including KRNO, KCXP, KMEV and into central Nevada
near KNFL as well. Snow accumulations for the valley floors will
be difficult tonight, as temperatures/snow levels will be right
near valley floors and may be too warm for accumulations.
Snow accumulations will be minimal, with about a 70% chance of
nothing, up to a dusting of snow--but only less than 20% chance
of seeing one inch of accumulations. There is a better chance of
seeing snow up to an inch or two around KTRK and KTVL tonight,
although with these slider-type storm systems, we tend to see
better accumulations in western Nevada than Tahoe.
Early Tuesday morning flights before 12z will be the most affected
by this snow with potential for deicing and snow removal, but the
biggest chance is that we see minimal accumulations. Snow should
move out of the area by 12z Tuesday, with gusty north to east winds
through the day on Tuesday. -Hoon
NV...Lake Wind Advisory from 8 AM to 7 PM PDT Tuesday for Pyramid
Lake in NVZ004.
Lake Wind Advisory from 8 AM Tuesday to 5 AM PDT Wednesday for
Lake Tahoe in NVZ002.
CA...Lake Wind Advisory from 8 AM Tuesday to 5 AM PDT Wednesday for
Lake Tahoe in CAZ072.
For more information from the National Weather Service visit...
Area Forecast Discussion
National Weather Service Sacramento CA
215 PM PDT Mon Mar 22 2021
Mostly dry weather this week with a slight chance of mountain
showers into tonight and again Thursday. Warmer temperatures
expected most of this week. Breezy to locally windy Tuesday into
A weak vort max ahead of the main short wave trough brought a few
light showers to the high Sierra this morning into the early
afternoon. This activity has diminished now but we will see the
main short wave trough track out of OR into NV this evening. This
will bring the return of light showers mainly over the mountains
with the best chances at the Sierra crest. HRRR runs along with
some of the other CAMs have been consistent on a few light showers
pushing into some of the lower elevations mainly along the
I-80/Hwy 50 corridor to the east of SAC around 11pm/6z. We do see
some weak mid-level instability and that is likely why we are
seeing these lower elevation showers on the CAMs. Overall should
remain dry with dry low levels but maybe a few sprinkles or a
light shower east of Roseville along I-80/Hwy 50 early tonight.
The trough will push to the south of us by tomorrow morning and
will begin to close off. This will bring breezy north and east
winds to the area. MFR-SAC gradient is forecast to tighten to
around 10 to 11 mb Tuesday through Tuesday evening which could
result in north wind gusts in the Valley up to 25 to 35 mph,
locally to 40 mph. SAC-RNO gradient forecast around 8 to 9 mb
Tuesday night which could result in easterly wind gusts in the
mountains up to 35 to 50 mph, locally higher in wind prone areas.
Valley winds are expected to be strong enough for a Wind Advisory
and went ahead and issued one with this package from Tuesday
8am/15z to 8pm/3z.
Winds will begin to diminish Wednesday morning and short wave
ridging will bring quiet conditions. Another short wave trough
will push into the PacNW and track into NV Wednesday into
Thursday. This trough looks to remain a bit further to the east
than the trough today. This will bring only a slight chance for
mountain showers Thursday mainly at the mountain crest south of
I-80. This trough will bring some clouds to the area as well.
Strong ridging will begin to build in Thursday night.
Temperatures this week will climb under the high pressure.
Temperatures will remain right around normal today and Tuesday
before rising a few degrees for midweek. Valley temperatures are
forecast right around 70 degrees on Wednesday.
.EXTENDED DISCUSSION (Friday THROUGH Monday)...
EPac high pressure moves into Northern California Friday into the
weekend bringing above average temperatures, lighter winds, and
mostly clear skies to the area. Highs will be around 10-15 degrees
above average this weekend, and the first 80 degree readings of
the season will be possible across the Central Valley this weekend
or Monday. A bit of spread is seen in the ensemble guidance via
the cluster 500mb heights with the possibility of a trough moving
across the PacNW on Monday. Main influence of the trough would be
moderating temperatures back towards normals for late March.
VFR cigs/visbys are expected for the next 24 hours. Light SHSN
may develop across high mountain elevations over the southern
Cascades and northern Sierra after 22Z with local MVFR conditions
possible with this activity. Surface winds under 12 knots thru 12Z
before breezy north winds in the Valley develop, becoming
stronger in the afternoon.
Wind Advisory from 8 AM to 8 PM PDT Tuesday for Carquinez Strait
and Delta-Central Sacramento Valley-Mountains Southwestern
Shasta County to Western Colusa County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Southern Sacramento Valley.