Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/23/24
Area Forecast Discussion
National Weather Service Boston/Norton MA
1021 PM EDT Fri Mar 22 2024
.SYNOPSIS...
Active period of weather arrives late tonight through Saturday
night with heavy rain, flooding, wintry weather, and marine
hazards. Drying out Sunday into early next week but rather windy
along the coast, especially Cape and Islands. Below normal
temperatures will prevail. The next chance of rain will be
Wednesday and Thursday as another frontal system approaches.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Update: 10:25pm
No changes to the forecast at this point in time, have blended
in latest high-res guidance to better track the increasing
dewpoint temperature. Did toss in a mention of flurries, mainly
across central and western MA over the next two hours as a warm
front begins to lift north. Still, there is a good deal of dry
air at the lowest level of the boundary layer. As this saturates
we will start to see more of the precip reach the ground.
Did get a report of a snow flakes flying in central Worcester
County over the past hour. It is difficult to see on area web
cameras, but mPING reports are slowly coming in to support this.
As of 10:15pm there remains a large T/Td depression, but it is
worth nothing the dewpoint has climbed from -1F to +12F in the
last 75 minutes.
One note about the incoming rain. It is worth nothing the 00z
HRRR has shifted the axis of the heaviest rainfall to the west,
more inline with central and eastern CT. The 00z NAM 3KM does
show a slight shift west as well, but not to the extreme of the
HRRR. Will be evaluating the rainfall potential over the next
couple hours. Nevertheless, southern New England should expect
widespread 2-3 inches of rain between late tonight through early
Sunday morning. The part of the forecast with lower confidence
is the exact area the axis of the heaviest rain sets up. We will
continue to monitor this with the rest of the 00z suite of
guidance.
Previous Discussion...
Tonight/early tomorrow
First half of the night is quiet across the region with some
increasing cloud cover and light winds ahead of a robust low
pressure system that will move over the region tomorrow. Active
weather begins to settle over southern New England during the
early morning hours as a surface warm front associated with a
deepening low-pressure system begins to lift over the region.
Temperatures on the north side of the warm frontal boundary will
be well below freezing. As warmer air aloft overruns the cooler
air in place, we`ll begin to see precipitation develop in the
form of light snow showers across western MA and CT. As the warm
nose edges further north, a melting layer develops between
about 850 and 900 hPa. With surface temps remaining at or below
freezing, this will support a freezing rain profile for
north/northwest Hartford county, western MA, and northern
Worcester county. Based on latest suite of ensemble guidance,
freezing rain may begin as early as 5am across western MA/CT and
continue through 09 to 10 am when surface temps will begin to
rise above freezing and allow a changeover to rain. Prior to the
changeover, substantial ice accumulations from a few hundredths
of an inch to a tenth of an inch or more will be possible. For
this reason, a winter weather advisory remains in effect for the
aforementioned areas expected to experience freezing rain.
Winds increasing out of the southeast to 10 to 15 knots during
this period as well.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Tomorrow
By mid-morning tomorrow, surface temps will have increased to
above freezing across southern New England. This will result in
any remaining frozen precipitation changing over to rain. From
there on out, the rest of tomorrow is a complete wash out. A
coastal low develops and moves off the mid-Atlantic coast before
tracking over or just southeast of The Cape/Islands. An
impressive region of frontogenesis develops across southern New
England by early afternoon and will support a period of heavy
rainfall that may result in urban, small stream, or poor
drainage flooding. Latest HREF run paints a swath of 2 to 4
inches of rain across CT, RI, and southeastern MA with the
heaviest rainfall between roughly 2pm and 8pm. While confidence
in a significant rainfall event is higher than normal, even
subtle changes in the storm track could result in the axis of
heaviest rainfall lifting north or south, so there still remains
a bit of uncertainty at 24 hours out. Given the relatively wide
goal post for the axis of heaviest rainfall, a flood watch is
in effect for the southern and eastern forecast areas. Only
northern Worcester county, Franklin, and Hampshire counties are
excluded. In addition to small stream flooding, some larger area
rivers in southern RI are at risk for flooding as well (see
Hydro section). Temperatures range from upper 30s to low 40s
across the interior/northwest areas tomorrow, with more mild
temperatures in the upper 40s to low 50s across southeastern MA
and RI.
Tomorrow Night
Surface cold front associated with the low-pressure system
moving over southern New England pushes through the region
tomorrow evening. This brings precipitation to and end for most
of the region from west to east between about 8pm and 2am.
Clearing and strong northwest winds from 15 to 25 mph will
follow the cold front. Precip lasts a bit longer over The
Cape/Islands tapering off between roughly midnight and 4am.
Temps dive into the lower to mid 20s across the
interior/northwest areas and upper 20s to lower 30s across
southeastern MA/RI prior to sunrise on Sunday.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Highlights:
* Mostly dry Sun into Tue, but blustery with below normal
temperatures. Quite windy over the Cape/Islands
* Increasing risk of wet weather Wed into next Fri. Temperatures
trending back above normal late next week.
A broad mid level trough is expected to morph into a mid level
cutoff over the North Atlantic early next week. This should trap
the surface low pressure beneath it, and keep it lingering
offshore of southern New England. Still some uncertainty in just
how far offshore this low pressure will wind up being. At
present, thinking the latest NationalBlend (NBM) deterministic
solution is on the pessimistic side of the envelope. Maintained
a faster departure of clouds and rainfall Sunday.
High pressure over eastern Canada is expected to nudge into our
region for Monday and Tuesday, leading to mainly dry and partly
cloudy conditions across most of our region. The exception to
that will be across far eastern MA, and especially the Cape and
islands. Thinking clouds may linger longer there, along with a
few showers Sunday morning. Will possibly need a Wind Advisory
at some point Sunday into Sunday night into Monday. It`s
marginal still, so not very high confidence. With all the other
ongoing headlines, will wait until confidence increases before
issuing such a headline.
The weak high pressure should maintain dry weather MOnday and
Tuesday, but also bring in colder air with a persistent N to NE
wind. Eventually though, this high pressure should break down
and move farther offshore. That will open the door for a slow-
moving front to impact southern New England late next week, most
likely some time from late Wednesday into Friday. It should not
be a total washout, but looking at the prospect of a prolonged
period of unsettled weather. Will need to monitor the impact of
any additional rainfall on our creeks, streams and rivers, which
should still be recovering from the rainfall this weekend.
Temperatures should trend warmer mid week, and likely return to
above normal temperatures Thursday into Friday.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High- greater than 60 percent.
Tonight...High confidence in trends. Moderate in timing.
VFR through about 06Z with light southwesterly winds becoming
more south/southeasterly. Conditions begin to deteriorate after
06Z as precip associated with a surface warm front lifting over
southern New England begins to support MVFR ceilings and light
precip. Frozen precip will be an issue at the western terminals
(BDL/BAF/ORH). A brief period of -SN, followed by -FZRA, will
be possible beginning as early as 08Z. Elsewhere, any precip
will be limited to -RA, but likely will be closer to or after
12Z before precip reaches the eastern terminals.
Tomorrow...High confidence in trends. Moderate in timing.
Light FZRA may persist at BDL/BAF/ORH through as late as 14Z,
but will changeover to rain thereafter with surface temps rising
above freezing after sunrise. MVFR cigs/vsbys deteriorate to IFR
by 18Z as rain overspreads the region. Rain picks up in
intensity after 18Z and remains steady through 00Z. Southeast
winds gradually increase throughout the day ranging from 10 kt
across the interior to 15 to 20 kt over the coastal plain.
Tomorrow Night... High confidence in trends. Moderate in timing.
IFR/MVFR cigs improve to VFR returns as precip gradually ends
from west to east from 00 to 06Z. Rain lingers a bit longer over
The Cape/Island terminals likely tapering off between 06 and 09Z
with VFR returning to this area between 09 and 12Z. Winds
strengthen after 00Z behind a surface cold front. 15 to 25 knot
sustained northwest winds with gusts up to 35 knots.
Outlook /Sunday through Wednesday/...
Sunday: VFR. Strong winds with local gusts up to 40 kt.
Sunday Night through Monday: VFR. Strong winds with gusts up to
45 kt.
Monday Night: Mainly VFR, with local MVFR possible. Strong
winds with areas of gusts up to 45 kt.
Tuesday: Mainly VFR, with areas MVFR possible. Windy with gusts
up to 35 kt.
Tuesday Night: Mainly VFR, with areas IFR possible. Windy with
local gusts up to 30 kt. Chance SHRA.
Wednesday: MVFR/IFR conditions possible. Chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight
Quiet marine conditions through about midnight tonight.
Thereafter, winds begin to increase out of the southeast ahead
of robust low pressure system with sustained winds of 20 knots
and gusts up to 25 knots by sunrise.
Tomorrow
Conditions deteriorate rapidly tomorrow as a strong low pressure
moves over southern New England. Steady 20 knot southeast winds
persist with gusts up to 35 knots possible, especially over the
southern coastal waters. Seas gradually increase from 4 feet
early in the day to 6 to 9 feet by tomorrow evening. Nearshore
eastern zones stay a bit lower with 4 to 6 foot seas. A Gale
Watch is in effect through Monday morning.
Tomorrow Night
A cold front moves over the waters tomorrow night. Winds become
even stronger out of the north/northwest with 30 knot sustained
winds for most of the marine zones. Wind gusts from 30 to 40
knots. Seas increase to 10 to 13 feet over the outer coastal
waters, and 6 to 10 feet for the nearshore waters.
Outlook /Sunday through Wednesday/...
Sunday: Moderate risk for gale force winds with local gusts up
to 45 kt. Rough seas up to 15 ft.
Sunday Night through Monday: gale force winds with gusts up to
45 kt. Rough seas up to 15 ft. Slight chance of rain showers.
Monday Night: Moderate risk for gale force winds with gusts up
to 45 kt. Rough seas up to 15 ft.
Tuesday: Low risk for gale force winds with gusts up to 35 kt.
Rough seas up to 13 ft.
Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance
of rain showers.
Wednesday: Winds less than 25 kt. Areas of rough seas. Chance
of rain showers.
&&
.HYDROLOGY...
Heavy rainfall tomorrow afternoon and tomorrow evening is likely
to lead to minor, and perhaps moderate, river flooding across
southern Rhode Island. Greatest risk for minor flooding appears
to be along the Wood River at Hope Valley, where the MMEFS
indicates a 94 percent chance of minor flood stage being
reached, and a 54 percent chance of moderate flood stage being
reached.
Several other rivers across southern New England including the
Shawsheen, Charles, Assabet, Pawcatuck, and Pawtuxet Rivers are
at an elevated risk to reach at least minor flood stage due to
excessive rainfall.
The Pawtuxet River at Cranston is of particular concern given
latest ensemble forecast guidance paints a bullseye of 2 to 4
inches of rain over this basin in only a 3 to 6 hour time
period. MMEFS indicates a 63 percent chance of moderate flood
stage being reached, and even a 24 percent chance of major flood
stage being reached. Residents and businesses near this location
will want to keep a close eye on updates for potential River
Flood Warnings and take action accordingly.
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 2 AM to noon EDT Saturday for
CTZ002.
Flood Watch from Saturday morning through Sunday morning for
CTZ002>004.
MA...Winter Weather Advisory from 2 AM to noon EDT Saturday for
MAZ002>004-008>011-026.
Flood Watch from Saturday morning through Sunday morning for
MAZ005>007-009-011>024.
RI...Flood Watch from Saturday morning through Sunday morning for
RIZ001>008.
MARINE...Gale Watch from Saturday afternoon through Monday morning for
ANZ230>237-250-251-254>256.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 2 AM to noon EDT Saturday for
CTZ002.
Flood Watch from 8 AM EDT Saturday through Sunday morning for
CTZ002>004.
MA...Winter Weather Advisory from 2 AM to noon EDT Saturday for
MAZ002>004-008>011-026.
Flood Watch from 8 AM EDT Saturday through Sunday morning for
MAZ005>007-009-011>024.
RI...Flood Watch from 8 AM EDT Saturday through Sunday morning for
RIZ001>008.
MARINE...Gale Watch from Saturday afternoon through Monday morning for
ANZ230>237-250-251-254>256.
&&
$$
SYNOPSIS...Belk/RM
NEAR TERM...Belk/Dooley/RM
SHORT TERM...RM
LONG TERM...Belk
AVIATION...Belk/RM
MARINE...Belk/RM
HYDROLOGY...RM
Area Forecast Discussion
National Weather Service Columbia SC
858 PM EDT Fri Mar 22 2024
.SYNOPSIS...
Moisture will overspread the region tonight as a low pressure
system approaches from the Deep South. Widespread showers and a
few thunderstorms are expected tonight, becoming more scattered
on Saturday as the upper low moves over the area. Breezy
conditions are possible Saturday afternoon and evening as the
pressure gradient tightens. Upper ridging will build over the
area for Sunday and Monday. A slow-moving cold front will move
through the area during the mid-week period with the next
chance of showers. Temperatures will be below normal this
weekend, warming to near to above normal values for the mid-week.
&&
.NEAR TERM /UNTIL 8 AM SATURDAY MORNING/...
Waves of showers continue to overspread the area thanks to
strong 850-700mb warm advection and corresponding isentropic
lift ahead of the approaching low pressure system and upper
level trough. Heights will continue to fall overnight into
Saturday morning as the 500mb trough axis remains to our west,
but isentropic lift will weaken slightly with 850-700mb shifting
more southwesterly behind the primary axis of frontogenesis
that is currently pushing through. While widespread are expected
through roughly 03z, precip should become more scattered for
the rest of the overnight period as the overrunning flow
weakens slightly, with 40+ knot 850mb winds shifting into NC.
Heights falls aloft and continuing low level moisture advection
into the area will help develop a bit of instability across the
area just ahead of the 500mb trough axis. So combining some
enhanced synoptic forcing and the steepening mid-level lapse
rates will likely allow for a few thunderstorms to develop
overnight. The HRRR and much of the other hi-res guidance
suggests this as well, falling in line with ht previous
thinking, developing some deeper convection into the CSRA and
Midlands within a weakly unstable environment with modest low-
deep layer shear. So a few loosely organized clusters of strong
showers or weak thunderstorms are expected overnight; the
severe potential looks limited thanks to barely any surface
based instability and only marginal shear profiles anyhow.
&&
.SHORT TERM /8 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
Saturday and Saturday Night: The upper trough will be situated
over the Ohio and Tennessee Valleys at the start of the day
becoming negatively tilted as it slowly moves east, passing over
the CWA Saturday night. While the surface low will pull away
early in the day, the combination of lingering moisture and the
approaching upper trough will likely produce scattered showers
with a few thunderstorms possible, especially closer to the
coast. Breezy conditions are possible later in the day as the
pressure gradient tightens but confidence is not high enough at
this time to warrant a Lake Wind Advisory. A cooler and drier
air mass rushes in Saturday night with skies clearing out.
Temperatures will be below normal.
Sunday and Sunday Night: Upper ridging builds into the region
and will combine with surface high pressure passing to our
north to produce a sunny, cool, and dry day. Gusty conditions
may persist during the first half of the day but the pressure
gradient should relax allowing our winds to gradually diminish.
Clear skies and light winds at night could create a risk of
frost/freeze conditions, particularly over the Northern
Midlands. Temperatures continue to be below normal.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
The axis of the upper ridge moves overhead on Monday, passing
to our east on Tuesday in response to a developing trough over
the Central CONUS. Meanwhile, high pressure maintains dry
conditions over the FA on Monday before the next storm system
approaches on Tuesday. Unsettled weather is possible during the
mid-week period as it may take several days for this storm to
clear the region with high pressure arriving near the end of the
extended. Temperatures will likely be near to below normal on
Monday and near to above normal during the middle of next week.
&&
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
Deteriorating conditions tonight and into Saturday morning.
Widespread showers and a few embedded thunderstorms are expected
through the overnight, then becoming scattered Saturday morning
after 23/12z. Ceilings expected to lower to MVFR/IFR tonight
with periods of LIFR early Saturday morning. Expect some reduced
VSBYs in +RA and patchy fog. Ceilings may improve late Saturday
morning as showers scatter out and weaken. SFC winds will shift
from east to south tonight and may be gusty to 15-20 kts at
times. Winds then shift to north/northwest Saturday with rain
ending Saturday afternoon.
EXTENDED AVIATION OUTLOOK...Some restrictions possible
Saturday afternoon. No significant impacts to aviation expected
Sunday through Tuesday.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
SC...None.
GA...None.
&&
$$
Area Forecast Discussion
National Weather Service Lake Charles LA
1005 PM CDT Fri Mar 22 2024
...New UPDATE, MARINE...
.UPDATE...
Wx map shows broad surface low over the Southeast U.S. with weak
high pressure over Texas, and a stronger surface high further
north, building across the area. Aloft, the mid to upper low
centered over Northern Mississippi. Across our region, northwest
winds around 10 to 15 mph with gusts over 20 mph as the cold air
advection continues across the region. See marine discussion for
the expansion of the Small Craft Advisory. Wrap around clouds from
the mid to upper low will continue to be hit and miss overnight
across inland locations. Overall, expect morning lows near
50/lower 50s north of I-10, and lower/mid 50s further south.
Overall, forecast on track with no major changes made.
08/DML
&&
.SHORT TERM...
(Tonight through Monday night)
Issued at 331 PM CDT Fri Mar 22 2024
As mentioned above, a few showers or isolated storms will be
possible late this afternoon into early this evening as spotty
convection develops along the southwestern flank of the low aloft.
This convection should diminish as the system moves further away
and daytime heating wanes. Expect a gradual decrease in cloud
cover overnight, with the passage of a secondary front helping to
reinforce a drier airmass over the region. Temperatures are
expected to fall to around 50 across the northern zones with lower
50s across the southern zones, right close to mid to late March
climatological normals.
Dry and pleasant conditions are expected for the weekend as
ridging at the surface and aloft pass over the region. Under
mostly sunny to partly cloudy skies on Saturday, temperatures
should climb into the 70s areawide. An increase in high clouds is
expected Saturday night, with low clouds developing during the day
Sunday as low level winds become more southeasterly. Winds will
gradually strengthen and become gusty on Sunday as low pressure
develops over the plains, but are expected to remain below
advisory levels at this time. Temperatures will remain near
seasonal values through the weekend.
By Sunday night into Monday, southwesterly flow will develop
aloft as a large trough moves into the western US. A strengthening
LLJ will transport moisture across TX into the central plains as
surface low pressure deepens in response to a series of impulses
rotating through the trough and ejecting into the central and
southern plains. Strong southerly gradient winds will develop
over the area on Monday, and this may necessitate the issuance of
wind advisories for at least part of the area, especially with
winds gusts potentially reaching 35 to 40 KT as the LLJ translates
over the area. Moisture will quickly increase, with PWATs
climbing to near 1.6 inches, well above the 90th percentile for
mid to late March.
Convection is expected to initiate across NW TX Sunday night
along a cold front, gradually evolving into a line of storms as it
approaches the area on Monday. Forecast soundings continue to
show favorable wind profiles with strong deep layer shear and low
level SRH values peaking between 200-400 m2/s2. This, combined
with modest but sufficient instability, could support organized
convection with rotating updrafts. Given the linear nature of the
convection, this will likely result in a QLCS type system
progressing across the area during the day Monday, with embedded
bowing segments and isolated tornadoes. However, any discrete
cells that form in advance of the line would be capable of
developing supercellular characteristics with all modes of severe
weather possible. The latest SPC outlook for Day 4 (Monday)
depicts a 15% probability of severe weather across the entire
area. The southern plains impulse and its attendant cold front are
expected to move through the region Monday night into Tuesday,
and the main forcing and focus for severe weather will shift east
with time.
In addition to the risk for severe weather, there is also a
marginal risk for excessive rainfall per WPC Day 4 ERO, given the
ample moisture available. Ensemble based probabilities suggest at
least a 20 to 30 percent chance of rainfall amounts exceeding 2
inches across central LA, with lesser totals expected further
south and west. The heaviest rainfall amounts and higher rainfall
rates will be confined with the strongest cells along the line, as
well as any pre-line cells, and these will need to be monitored
for any training potential.
24
&&
.LONG TERM...
(Monday through next Thursday)
Issued at 331 PM CDT Fri Mar 22 2024
A cold front with a likely line of storms will be exiting to the
east of the forecast area when the period begins on Tuesday. High
pressure from the Plains will be building in behind the front
bringing some breezy northwest winds on Tuesday with drying
conditions.
This high pressure system at the surface will slowly move across the
forecast area during the mid week period, along with upper level
ridging. This will bring pleasant and seasonal conditions.
By the end of the week, the high will be moving off to the east with
a southerly flow off the Gulf helping to bring warmer and more humid
conditions.
07/Rua
&&
.AVIATION...
(00Z TAFS)
Issued at 611 PM CDT Fri Mar 22 2024
A dense cloud deck extends across central Louisiana and towards
the coast. MVFR ceilings are the main concern until sunset. At
that point VFR conditions will return. Overnight winds will be
from the NW at 10 to 15 knots. At the Acadiana terminals,
occasional gusts up to 25 knots will be possible after sunrise.
&&
.MARINE...
Northwest winds will strengthen tonight into Saturday morning,
then diminish during the day Saturday. Latest HRRR guidance, plus
observations from the wind sensor at at Cypremort Point, LA (VCPL1)
suggest slightly higher sustained winds near 20 kts, so have expanded
the Small Craft Advisory to include Vermilion & Atchafalaya Bays.
With the winds and seas staying elevated a few hours longer Saturday,
extended the Small Craft Advisory into the afternoon hours.
08/DML
&&
.PRELIMINARY POINT TEMPS/POPS...
AEX 50 71 45 73 / 10 0 0 0
LCH 53 74 49 73 / 10 0 0 0
LFT 54 72 50 75 / 10 0 0 0
BPT 54 77 54 76 / 10 0 0 0
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...None.
TX...None.
GM...Small Craft Advisory until 10 AM CDT Saturday for GMZ430-432-450-
470.
Small Craft Advisory until 1 PM CDT Saturday for GMZ435-436-452-
455-472.
Small Craft Advisory until 4 PM CDT Saturday for GMZ475.
&&
$$
SHORT TERM...08
LONG TERM....07
AVIATION...14
Area Forecast Discussion
National Weather Service Pendleton OR
729 PM PDT Fri Mar 22 2024
.EVENING UPDATE...Satellite imagery shows a well-developed closed
low slowly pushing into the Oregon coast this evening. The SW flow
leading this low has allowed for some shower activity and even
some convective development to occur across the Cascades and
eastern mountains over the last couple of hours, however rain
activity outside of the mountains thus far has been very light.
00z HRRR suggests more widespread activity will begin by 06z
(11pm) tonight, spreading to the rest of the forecast area
overnight. Confidence in convection outside of the mountains
remains low (<10%), however cannot completely rule out a stray
rumble of thunder, especially along the eastern foothills of the
Cascades. Guidance then has precip activity dwindling down by
daybreak tomorrow, before the low overhead leads to more potential
convective activity in the afternoon.
Changes to the forecast package this evening were focused
primarily on touching up PoPs based on latest trends. Did add
mention of thunder in the northern Blues, where lightning had been
detected on satellite earlier this evening. Evans/74
&&
.PREV DISCUSSION... /issued 502 PM PDT Fri Mar 22 2024/
AVIATION...00Z TAFS...Light precipitation is afoot during this
period as low to mid clouds start coming in (BKN to OVC 030-080) for
most sites through the overnight period. Breezy conditions are
expected for KRDM and KBDN this evening and again tomorrow morning,
bringing winds above 10kts. For others, winds will be around 10kts.
Feaster/97
SHORT TERM...Tonight through Sunday...Satellite and radar imagery
this afternoon shows a band of light precipitation pushing
northeast across WA, while light echoes over northeast OR and
southeast WA have only resulted in virga so far. Meanwhile, partly
cloudy skies have developed in areas behind this main band, though
current visible satellite shows little indication of vertical
cloud development in these areas. Through the rest of today and
tonight, a deep low offshore will gradually push a cold front east
across the eastern half of the PacNW while shortwave impulses
periodically pass overhead. During this afternoon and into the
evening, the arrival of the cold front/shortwave impulses as well
as weak instability at the surface is expected to result in
increasing shower activity. Increasing instability at the surface
(about 100-300 J/kg of CAPE) along the northern Blues and the east
slopes of the OR Cascades is expected to aid in the shower
development through the evening, with even an isolated clap of
thunder possible in these areas.
Tonight into tomorrow morning, the center of the low offshore
will continue to approach the PacNW while the cold front boundary
pushes east and north across the region. This will result in snow
showers developing across the higher mountain terrain, while rain
showers will be possible elsewhere overnight. The upper low will
transition into an open trough throughout tomorrow as it pushes
ashore near the OR/CA border, while the cooler airmass associated
with this low feature will filter into the region. There will be
another round of shower activity across the forecast area, and
with snow levels dropping to between 4kft to 4.5kft along the
Cascades, there will be snow chances at the pass levels tomorrow.
Also, modest low to mid-level lapse rates and increasing surface
based instability will allow for isolated thunderstorm development
from central OR to northeast OR and far southeast WA tomorrow
afternoon into the evening. Shower activity will retreat to the
mountains tomorrow night as the now upper trough continues to push
into the Desert Southwest.
Sunday, a quick moving shortwave will dive down the back of the
trough and bring another chance of mountain snow showers and light
rain showers to the lower elevations. Breezy westerly winds will
also develop in the lower elevations, with sustained winds
15-25mph expected through the Gorge and the Kittitas valley. The
shortwave is expected to exit by the afternoon, allowing a
transient ridge in the northeast Pacific to slide across the
PacNW, with only light snow flurries continuing along the Cascade
crest, northern Blues, and the Wallowas.
A cooling trend starting tomorrow will result in afternoon
temperatures dropping to near to below normal this weekend, with
afternoon temperatures mainly in the 50s. As for morning lows,
they will remain near normal, with upper 20s to lower 30s in the
mid elevation and mountain valleys, and mid to upper 30s across
the rest of the lower elevation zones. Lawhorn/82
LONG TERM...Monday through Friday...An active, progressive pattern
will dominate the region for the period, with persistent chances of
precip and largely cooler-than-average temps extending to even
beyond the long term.
Ensembles are largely in agreement on the spirit of the pattern,
being that of a train of systems largely W/NW in origin, however the
progressive nature of the pattern causes the ensembles to fall out
of sync by the midweek next week. As a result, can speak with good
confidence (60%) on the nature of the synoptic pattern, but as far
as the exact timing on when the axes of troughs/ridges lie over the
forecast area, confidence is low (30%).
The low expected to envelop the region for most of this weekend will
depart to the east by the start of next work week, leaving us under
relatively benign NW flow. GEFS and EPS produce light precip for
portions of our lower elevations, namely the foothills of the Blues
and Grande Ronde Valley, while the NBM largely keeps precip in our
high mountain zones. Even then, precip looks to be light, with even
the wetter LREF solution suggesting about a tenth to two tenths
during the day Monday over the mountains. Snow levels look to be
around 3000 to 4000 feet.
NW flow turns into transitory ridging by Tuesday, before a more
organized low arrives around the midweek. This low is the main
source of discrepancy across the ensembles, as some clusters, namely
from the GEFS, are much more progressive in arrival time, while the
EPS keeps ridging around for a bit longer before bringing the low in
closer to Thursday. The primary effect of this low, however, will be
widespread breezy winds, PoPs, and cool conditions, as ensembles do
agree that the low will stem from the WNW rather than a more mild
westerly or SW origin. Snow levels start to trend more towards 2500-
3000 feet, leaving pass-level impacts across the WA Cascades
uncertain, but confidence is moderate (40%) in the forecast area
seeing a wetting rain from this midweek system. Other specifics,
including potential convective threats and more precise snow levels,
are too difficult to determine at this time, considering how far out
into the long term this system will occur.
With this midweek low looking to envelop the PacNW beyond the long
term, expect cool and wet conditions to persist into next weekend, a
stark departure from the dry and warm conditions we saw under the
ridge earlier this week. Evans/74
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 42 58 38 53 / 40 40 30 70
ALW 44 60 41 53 / 40 70 40 80
PSC 47 64 42 60 / 40 30 30 50
YKM 42 60 37 60 / 80 60 20 20
HRI 45 64 41 58 / 50 40 30 60
ELN 38 55 35 57 / 80 80 20 20
RDM 35 54 33 50 / 80 30 30 20
LGD 39 53 34 48 / 50 80 50 70
GCD 38 55 33 50 / 60 60 50 60
DLS 43 60 41 58 / 100 40 30 30
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&
$$
SHORT TERM...74
LONG TERM....74
AVIATION...74