Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/06/17
Area Forecast Discussion
National Weather Service Billings MT
711 PM MST Sun Feb 5 2017
Main reason for update this evening is the Canadian cold front
which is pushing into our cwa ahead of schedule. Already seeing a
wind shift to N-NE winds at Judith Gap and Roundup, where temps
have fallen quickly to the teens. Latest HRRR is catching on to
this and suggests a wind shift to Billings before 06z. Have
updated wind grids to show this earlier shift, and have also
adjusted low temperatures down several degrees due to the cold
advection behind the fropa. We may also see some stratus or
perhaps even fog advect from the north during the overnight hours.
Will make no changes to wind advisories in effect for Livingston
and Nye, where gusts continue to exceed 50 mph. Will be
interesting to see how far west/south the Canadian front makes it
into tomorrow morning. Given our abundant snow cover and current
trends, am confident it will make it closer to the foothills than
models are suggesting, making for a difficult temperature forecast
tomorrow. Billings will likely stay on the cold side of the
surface boundary on Monday.
.SHORT TERM...valid for Mon and Tue...
Active period of weather for the short term. Early on, winds will
be an issue for the western valleys, later in the short term
(Monday night mainly), the potential for heavy snow showers draws
all the attention.
Winds have been gusting 50-55 mph at Livingston this afternoon
with gusts to 60 mph at Nye. Models were pointing to the strongest
winds being this evening, with winds gradually backing off
overnight into Monday morning. Reason for this is probably the
models were pointing to instability increasing from mountain top
level overnight. Models are notorious for not handling the cold
air in the western valleys, which will aid in the low level
stability and producing a stronger stable layer at mountain top
level than what the models think. Will keep the advisory going and
hit the wording hardest for tonight.
Attention then turns to the approaching trough for snow potential
Monday night into early Tuesday. The passing of the trough looks
a little farther north and not quite as sharp as previous runs.
The ECMWF was a little stronger with the shortwave, but the
farther north passage would mean less upslope potential and more
downslope at 700mb. Upslope does develop, but it was shallow and
very quick as it was mainly for a 6 hour period mid to late
evening. Instability was there with lapse rates 850-500mb at
7.5c/km. Frontogenesis was impressively strong and should provide
strong ascent. The EC hits the west hard during the evening and
then weakens ascent overnight as frontogenesis sinks south. The
GFS hits areas south of Billings hardest and drifts ascent south
out of the area quickly overnight. The EC does hang frontogenesis
up along the slopes overnight Monday which could lead to a longer
period of snow showers there. All this being said, the system
moves through very quickly and looks like a snow shower event and
not so much of a large and broad scale synoptic event. Will opt to
not issue any highlights at this time due to model differences,
speed of system and overall northward shift of the trough
providing downslope flow through mid levels.
Have lowered snow amounts slightly as models have come in
generally lighter on precipitation amounts with the speed of the
system. Will generally go with 1-3 inches, with the potential for
2-4 inches over the west and south. Future shifts may be able to
pin point the most likely location for 3-4 inch snow totals or
where the models hang up lift for a prolonged period of time. Will
keep messaging potential heavy snow showers Monday night. Will
linger snow showers potential during the morning and have raised
PoPs for Tuesday morning.
Temperatures Monday will be tricky as the GFS lifts the arctic off
the slopes and warms western and central zones into the 30s. The
EC keeps the arctic in place as it drops in tonight and keeps
highs in the lower 20s. Will lean toward the EC as believe the
arctic will stay in play. Also guidance has not been good at all
in handling temperatures during this latest pattern. Tuesday looks
chilly as well with the arctic firmly in place. TWH
.LONG TERM...valid for Wed...Thu...Fri...Sat...Sun...
Latest models for Wednesday have much less energy working across
the area, thus PoPs have been lowered accordingly. Through the
remainder of the forecast period, it will be a general drying
trend. However, there will is still energy moving through the
zonal flow, so still have some chance PoPs. With the zonal flow,
winds will be downsloping so still expect temperatures to warm
through the period. Winds continue to look gusty along the
foothills later in the week as some gap flows could increase.
High confidence that MVFR or possible IFR ceilings will
move into KBIL and KMLS late tonight through early Monday morning.
Patchy fog is also possible in these areas, but confidence is not
as high. Otherwise, VFR will prevail tonight. Snow will move into
areas mainly W of KBIL during Monday with MVFR/IFR conditions.
VFR to MVFR will prevail elsewhere. Areas of mountain obscuration
over the Beartooths, Absarokas and Crazys will become widespread
on Monday. Gusty SW surface winds to 50 kt over KLVM will become
lighter from the E sometime Mon. morning. A cold front with a band
of snow will affect the area Mon. evening. Arthur
.PRELIMINARY POINT TEMP/POPS...
Mon Tue Wed Thu Fri Sat Sun
BIL 011/028 012/018 001/019 016/044 037/048 026/037 021/038
02/J 84/J 33/S 21/E 22/R 11/B 11/N
LVM 036/041 017/028 013/034 026/051 042/050 028/039 020/038
16/W 93/J 34/S 32/R 33/R 22/O 21/N
HDN 014/026 009/018 907/017 009/044 033/046 024/037 015/036
01/E 74/J 33/S 21/E 12/R 11/B 11/B
MLS 011/019 004/011 912/010 004/039 033/045 025/034 017/034
01/E 73/J 22/S 21/B 12/O 11/B 11/B
4BQ 019/029 008/019 905/018 009/043 034/047 024/037 017/034
00/E 73/J 22/S 21/B 11/B 10/B 11/B
BHK 012/017 004/010 913/007 001/038 031/045 023/032 016/032
01/E 73/J 22/S 21/B 11/E 11/N 11/N
SHR 024/035 013/021 005/022 014/046 033/048 024/037 016/036
01/B 74/J 33/S 21/B 11/B 11/B 21/B
MT...Wind Advisory in effect until 1 PM MST Monday FOR ZONES
Area Forecast Discussion
National Weather Service Hastings NE
550 PM CST Sun Feb 5 2017
.SHORT TERM...(This evening through Monday)
Issued at 326 PM CST Sun Feb 5 2017
A few mid and high level clouds have been moving through the
forecast area this afternoon. The surface high over the area
overnight has been moving to the east but is a little slower and
winds have not turned to the south as much as was expected.
Temperatures have been slow to warm up without the mixing.
The surface high is expected to continue to move to the east and
winds should continue to come around to the south. That will bring
in additional moisture. There has been some persistent stratus
across southern Kansas and Oklahoma this afternoon and with the
south winds tonight, the stratus is supposed to redevelop and move
toward the north. The expectation is that the stratus will move into
the southeastern part of the forecast area and there will be a
little fog around the edges of the stratus. The SREF probs and HRRR
have some fog in the southeast but do not get it too far into the
forecast area. Have kept the patchy fog for much of the area and
tried to keep areas further to the southeast. The fog is expected to
linger into the morning hours and just get out of the area by mid
day. Skies will be partly to mostly cloudy during the day.
Temperatures will be a little warmer.
.LONG TERM...(Monday night through Sunday)
Issued at 326 PM CST Sun Feb 5 2017
A cold front moves through the forecast area Monday evening, but the
cold air does not move into the area until during the day on
Tuesday. Even then, the southern part of the area should warm up
pretty well since the cold air will not reach that area until late
Tuesday afternoon. Winds will be from the northwest and increase
some in the afternoon as the colder air moves into the area.
An upper level wave moves into the area Tuesday night and brings a
chance for precipitation to the area. Temperatures are cold enough
hat it will all be snow. The better chances for snow will be in the
northern part of the forecast area, mainly along and north of
Interstate 80, late Tuesday night into Wednesday morning. By
Wednesday afternoon and into Thursday, the PoPs are lower and more
sporadic, but mostly in the north. There will be some accumulation,
but at this point it does not look to be heavy. The problem is that
each run of the models has just a slightly different location.
From Thursday through Friday evening expect dry conditions and
temperatures will be warming back up again. It is short lived,
because another cold front moves through Friday night and brings
colder temperatures again on Saturday. There is also an upper level
wave that brings a chance for precipitation. This time the
temperatures start off warm enough to be mostly rain then mix with
or change to snow before coming to an end Saturday night. Dry and
cooler again for Sunday.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Monday evening)
Issued at 538 PM CST Sun Feb 5 2017
Low level stratus across Oklahoma this evening is expected to
creep northward overnight...eventually spreading into north
central Kansas and extreme south central Nebraska early Monday
morning. While the low level stratus and significantly reduced
visibilities are expected to remain to the south of the
terminals...cannot rule out a few hours of MVFR VSBYS at either
terminal around dawn...with VFR conditions returning during the
morning hours. Overall...light southerly winds are expected
through the period with CIGS expected to remain at or above 12KFT.
Area Forecast Discussion
National Weather Service Lincoln IL
914 PM CST Sun Feb 5 2017
Issued at 913 PM CST Sun Feb 5 2017
The rest of the night should be uneventful weather-wise, with mid
and high clouds drifting across Illinois in the westerly flow
aloft. Low temps have been dropping very close to forecast lows
already in some areas, so minor adjustments to low temps downward
The next concern will be the advance of fog and low clouds into
our forecast area from the south, as a warm front progresses north
into Illinois. While the depth of moisture will be very shallow,
it appears there will be enough lift for some drizzle to develop
south of I-72 after 9 am tomorrow. Forecast soundings indicate
that sufficient lift and moisture deep enough for rain showers
might be delayed until afternoon. Will be adding drizzle to the
morning forecast, and adjust timing of onset of rain showers.
Thunder chances look to remain mainly Monday night, and will keep
thunder out of the Monday forecast.
Updated forecast info will be available shortly.
.SHORT TERM...(This evening through Monday)
ISSUED AT 255 PM CST Sun Feb 5 2017
Mid/high clouds currently evident on visible satellite imagery
across Iowa/Missouri will stream eastward into central Illinois late
this afternoon and evening...resulting in a period of partly to
mostly cloudy skies. Based on satellite timing tools and HRRR RH
fields...it appears these clouds will tend to dissipate and push
into the Ohio River Valley overnight. Thanks to light winds and the
overall partly cloudy conditions, low temperatures will bottom out
in the upper 20s and lower 30s.
Clouds will once again begin to increase Monday morning as a
developing storm system approaches from the southwest. Current
satellite shows low clouds poised upstream across Oklahoma/Arkansas
and these will spread northward as the system takes shape. HRRR has
a good handle on the clouds right now and shows them reaching the
southeast KILX CWA south of I-70 between 10z and 12z...then
overspreading the entire area by late morning. While forecast
soundings show ample low-level moistening indicative of low clouds
and patchy fog, mid/upper levels remain dry throughout the day. As a
result, am not expecting much precip to develop and have therefore
kept Monday afternoon PoPs in the slight to low chance category.
With increasing southerly winds, high temperatures will climb into
the lower to middle 50s.
.LONG TERM...(Monday night through Sunday)
ISSUED AT 255 PM CST Sun Feb 5 2017
The weather system coming into the area Monday night will be
deepening as it moves in, which will lead to much higher pops than
during the day Monday. The cold front associated with this weather
system will start out well west of the area, but should quickly move
east during the night, reaching western IL by morning. Most models
agree on this timing, but the ECMWF is slightly slower with the
front. By noon on Tuesday, the front will be through most of the
area. Showers will increase and spread over the area Monday night
and then continue to the east and northeast during the morning hours
of Tuesday. Models continue to forecast sufficient instability over
the whole area Monday night and then over the eastern part of the
CWA Tuesday. So, chance to likely thunderstorms will remain included
in the forecast through Tuesday morning. With the system exiting the
area quickly on Tuesday, thunderstorm chances will drop by Tuesday
afternoon into the slight chance category, with the chance of
showers remaining the the eastern parts of the CWA. This system will
move northeast into the Great Lakes region very quickly, so Tuesday
night will now be dry and temps will begin to fall as the colder air
advects into the region.
Models then show a couple of weak impulses moving across the CWA on
Wed. One impulse moves across the southern part of the CWA, while
another one moves across the northern part of the CWA. Both impulses
move through Wed afternoon. However, not very confident in these
features given they both are producing precip underneath a large
area of cold high pressure. Will keep the pops at slight chance for
the northern one, but will maintain the chance pops for the impulse
moving across our south. Since models also struggle with the timing
of these small features, will have the southern impulse chances
during the whole day. Once these weak impulses move through the
area, high pressure will dominate the weather over the CWA with dry
weather through Friday night.
The next weather system to effect the area will arrive Sat. Based on
the model output, this system doesn`t begin to get active until it
reaches central IL. Precip will develop and increase over the CWA
with precip chances extending from Sat through Sunday. The precip
over most of the area will be in the form of rain. A mix of precip
and just snow will be possible early Sat morning and then again late
Sat night into Sunday morning. This mixed precip will remain over
the northern part of the CWA, roughly along and north of a Rushville
to Bloomington line.
Temps will remain quite warm Tue, but then drop once the front goes
through and be below normal for Wed and Thur. The rest of the week
and into next weekend will warm back up as the high pressure shifts
off to the east and southerly winds return to the area.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 550 PM CST Sun Feb 5 2017
A weak disturbance will pass across central Illinois this evening,
bringing mid-level clouds at 12K FT for several hours of the
overnight. RAP and NAM forecast soundings indicate the ceilings
will lower to around 12000ft during the 03z-06z time frame, the
improve toward sunrise as the band of clouds departs to the east.
Main aviation forecast concern continues to be the approach of a
stronger storm system and its subsequent lower clouds and precip
on Monday afternoon. The latest HRRR indicates IFR ceilings
spreading northward from Missouri/southern Illinois late tonight,
remaining south of the KILX terminals until after sunrise. Based
on HRRR forecast and NAM soundings, have introduced IFR ceilings
at KSPI by 15z...then further north to KBMI, KCMI and KPIA by
17z-19z. Ceilings are expected to lower to LIFR after 20z from
south to north, with visibility dropping to IFR during the same
Winds will initially be from the NW at around 5-6kt early this
evening, then will become light/variable by midnight. A southerly
wind of around 10kt will develop by 15z- 16z Monday morning and
continue through the afternoon.
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
908 PM CST Sun Feb 5 2017
Updated for evening discussion.
.DISCUSSION...Local radars had a band of showers and a few
thunderstorms moving east along the Highway 82 corridor. Latest
surface analysis had a warm front between Highway 84 and Interstate
20. This front will drift a little farther north tonight and shift
the band of convection a little farther north. Have added mention of
thunder in the north tonight with the update. Across the south patchy
dense fog development is possible toward morning. /22/
Prior discussion below:
Tonight and Monday...Satellite and surface data are indicating the
surface warm front has pushed to just south of the Interstate 20
corridor at 21Z. North of the boundary, cloudy, cool and showery
weather has been the rule through the day as isentropic ascent
continues overtop the cool airmass. To the south of the boundary,
clouds have decreased and temps have increased with readings as warm
as the mid 70s in the far south.
The warm front should continue to slowly lift northward overnight
and into Monday morning. The dense cloud cover and showery
conditions will continue to the north of the boundary overnight,
while areas to the south will see decreasing clouds during the
evening. Boundary layer cooling will lead to fog formation after
midnight over the south with some areas becoming dense, especially
over the far south where expected lows in the mid 50s surpass
current crossover temps in the upper 50s to near 60. The HRRR is
also showing dense fog formation possibilities, but presently looks
to remain patchy.
The fog will lift by mid morning with the majority of the remaining
showers lifting north of the area by noon. Monday will be quite warm
over the region with near record maximums in the mid and upper 70s,
and possibly approaching 80 over some of the southern portions. With
such heat this time of year would be concerned about convective
potential, but building cap above the boundary layer will put a lid
on that possibility./26/
Monday Night through Sunday...Our focus for Monday night and onward
continues to be on a passing shortwave and its potential to initiate
possibly severe thunderstorms Tuesday into Tuesday night. Model
guidance has trended toward an overall less amplified upper air
pattern over the last few cycles, with decent agreement from the NAM
as it has begun to cover the Tuesday period. A lead shortwave trough
is expected to be sliding from TX/OK into Arkansas on Monday night,
with a second shortwave displaced northwestward over the Northern
High Plains. This slightly slightly out-of-phase setup will result in
only weak cyclogenesis of a surface low moving from the Plains to the
Midwest Monday night into Tuesday. A cold front extending south from
this low should slowly advance toward a Shreveport-Memphis line by
Tuesday night. Southerly flow in advance of the cold front will bring
a warm and moist airmass northward along the Mississippi River, with
dewpoints reaching the low 60s in our northeast LA parishes and
southeast AR counties by early Tuesday morning.
As mid-level heights fall ahead of the approaching shortwave, the
combination of moistening low levels and cooling mid levels could
result in a weakly capped (10-20 J/kg of MLCIN) but unstable
atmosphere with 1000 J/kg MLCAPE or greater around the Delta region
Tuesday morning. A stronger cap to the south will limit the potential
for thunderstorm development closer to I-20 and areas south of
there. Especially with any lift from the passing shortwave, there is
a potential for severe thunderstorms to develop in the vicinity of
the frontal boundary. Expected 40 to 60 kts of 0-6 km shear is
sufficient to organize these thunderstorm updrafts into supercells.
Low-level shear values near 30 kts and effective SRH around 200-300
m2/s2 will be supportive of a tornado threat especially while morning
LCL heights are in the 500m range. The threat for severe weather
becomes a little more uncertain heading into Tuesday afternoon and
Tuesday night as the shortwave moves east of the front. Even with
weak mid-level height rises behind the shortwave additional storms
will be possible later into the day if strong enough daytime heating
or the added focus of outflow boundaries can help updrafts overcome
the cap. Damaging wind gusts and large hail would be the primary
threat from storms by Tuesday afternoon. Will keep a Limited threat
area for severe thunderstorms with possible tornadoes going across
the northern one-fourth of the forecast area on Tuesday where severe
chances are greatest.
Low end shower and thunderstorm chances continue into Wednesday
before the cold front finally clears the area Wednesday night. A
brief cool down for Thursday will be followed by a return to warm
weather as a broad ridge builds over the country. Rain chances return
the forecast over the weekend ahead of another deep shortwave sliding
across the U.S. /NF/
00Z TAF discussion: IFR/LIFR Cigs with -RA wl cont this evng north of
I-20 while VFR conds cont south of I-20. The -RA wl taper off by 06Z
but IFR/LIFR conds wl cont tonight in the north. IFR/LIFR cigs and
vsbys wl develop across the southern half of the area by 09Z. Conds
wl slowly improve areawide after 15Z to VFR by 18Z. VFR conds wl
prevail arewide Monday aftn through evng. /22/
.PRELIMINARY POINT TEMPS/POPS...
Jackson 55 78 60 76 / 23 9 9 47
Meridian 51 78 59 75 / 52 10 9 45
Vicksburg 54 76 61 78 / 20 14 20 39
Hattiesburg 54 76 59 76 / 10 5 7 38
Natchez 59 76 62 77 / 13 13 16 33
Greenville 51 72 60 75 / 82 32 41 48
Greenwood 52 74 60 74 / 90 27 34 60
Area Forecast Discussion
National Weather Service Memphis TN
829 PM CST Sun Feb 5 2017
.DISCUSSION...02Z Surface analysis places a warm front over
portions of Southern Mississippi, Northern Louisiana, and into the
Red River Valley of Texas and Oklahoma. Regional WSR-88D radar
trends have shown an increase in showers near the warm front.
Latest 00Z WRF and HRRR suggest best potential for showers and
perhaps an isolated elevated thunderstorm will be predominantly
overnight across the remainder of the Mid-South. Updated rain
chances to reflect these trends. Otherwise, the forecast overall
is in good shape.
.PREV DISCUSSION... /issued 525 PM CST Sun Feb 5 2017/
Updated to include the 00z aviation discussion.
PREV DISCUSSION... /issued 307 PM CST Sun Feb 5 2017/
The back edge of clouds continues to sit generally from a Forrest
City, Arkansas to Savannah, Tennessee line. Expect the clouds to
slowly begin to lift north over the next couple of hours as a
secondary warm front that remains over Southern Mississippi begins
to lift north. Clouds should cover the entire Mid-South by
midnight. Showers with a few embedded thunderstorms associated
with the front will spread into North Mississippi this evening
and increase in coverage during the overnight hours. Low
temperatures will likely occur this evening before holding steady
over even slightly rising.
The warm front will surge through the entire Mid-South by Monday
morning. Expect lingering showers and thunderstorms over portions
of Northwest Tennessee. Clouds should scatter out some over North
Mississippi, possibly into areas of West Tennessee. This should
allow temperatures to warm up into the lower 70s. Isolated shower
and thunderstorm development may occur over Eastern Arkansas
during the afternoon as the upper trof begins to swing east.
The upper trof will move into the area Monday Night. Showers and
thunderstorms will blossom over the Mid-South Monday Night ahead
of the upper trof. Some of these storms could become severe. Best
timing for severe weather will come Monday Evening into Tuesday
Morning across the Mid-South. Expect by mid-day Tuesday the
severe threat will diminish as the upper trof pushes east. Clouds
may actually begin to clear behind the morning activity and would
not be surprised to see temperatures surge into the mid 70s across
areas along and west of the Mississippi River during the
The trailing cold front will move into the area Tuesday Night.
However, it doesn`t look like the front will quickly pass through
the CWA like models have been showing. The 12Z runs of the NAM,
GFS, and ECMWF have the front stalling out over the Mid-South into
Wednesday before clearing the area Wednesday Night. As a result,
have added chances for rain to the forecast for Wednesday and
Cooler temperatures will filter into the area behind the front.
Both the GFS and ECMWF now have the next upper trof moving in
before the cold air gets in place. Thus, the chances of snow have
Temperatures will quickly rebound by Friday as surface high
pressure shifts east. Chances for showers will begin to occur on
Saturday ahead of the next cold front. The front is expected to
move into the area Saturday Night into Sunday. Thus next weekend
could be a wet one.
Low clouds are streaming back to the north rapidly this evening
and will overspread the remainder of the area over the next few
hours. IFR conditions are observed at KTUP and will persist
through much of the period. Farther north, initially MVFR ceilings
will eventually lower to IFR with scattered showers and patchy
drizzle expected later tonight into Monday. Ceilings are expected
to improve slightly Monday afternoon, but should still remain
below 2000 ft. Light south to southeast winds will prevail
overnight, becoming south at 10-15 kts by midday Monday.
Area Forecast Discussion
National Weather Service Melbourne FL
1030 PM EST Sun Feb 5 2017
Pressure gradient will slacken as the ridge builds overhead,
resulting in light and variable winds overnight. Minimal cloud cover
will couple with these winds to generate strong radiational cooling
conditions that will promote fog formation. Have increased fog
potential across north half of FA as both HRRR and local WRF models
show reduced visibilities expanding across the area overnight.
Lows in the mid to upper 50s, except lower 60s Martin coast. On
Monday, low level flow veers to the E/NE as the ridge builds over
the peninsula. Under partly/mostly sunny skies, max temps will be in
the M/U70s except L70s along the Volusia County coast due to the
cooler shelf waters.
Primary concern will be fog development across the northern
terminals mainly TIX-ISM northward. IFR VSBYs possible lifting by
No significant changes to current coastal waters forecast.
Tonight-Monday...Gentle to moderate N/NE breeze bcmg E/NE as a weak
frontal trof off the SE coast lifts up the east coast, allowing high
pres centered over the GOMex to drift over the SE coast. Diminishing
NE swell will continue to enhance lcl wind waves...nearshore seas 4-
5FT subsiding to 3-4FT...offshore seas 5-6FT subsiding to 4-5FT.
.PRELIMINARY POINT TEMPS/POPS...
DAB 53 73 60 80 / 0 0 0 10
MCO 54 79 59 81 / 0 0 0 10
MLB 55 76 62 79 / 0 0 0 10
VRB 54 77 63 80 / 0 0 0 10
LEE 52 77 59 81 / 0 0 0 10
SFB 53 78 59 81 / 0 0 0 10
ORL 54 79 60 81 / 0 0 0 10
FPR 55 78 62 79 / 0 0 0 10
Area Forecast Discussion
National Weather Service San Francisco Bay Area
349 PM PST Sun Feb 5 2017
...A Wet and Windy Week Ahead...
.SYNOPSIS...A Pacific storm system will bring the first round of
rain back to our region this evening through tonight. A moist
flow off the Pacific will then produce periods of rain from Monday
Night through Tuesday night with rain possibly continuing in the
North Bay into Wednesday. One final system will bring additional
rain and wind to the entire region Thursday and Thursday night.
Dry weather is expected to return by next weekend.
.DISCUSSION...As of 3:00 PM PST Sunday...Hard to believe with the
occasional breaks in the clouds today plus seasonably mild
temperatures that rainfall will rapidly return to the San
Francisco and Monterey Bay Region starting this evening. Satellite
nicely shows a fast moving cold front associated with a 995 MB low
well to our northwest quickly advancing to the coast. KMUX radar
is still mostly clear of echoes, although last half an hour we are
starting to see the leading edge being picked up.
Models are generally in good agreement and the last few runs of
the HRRR have mostly stayed consistent, so looking for rain to
get to the coast by early in the evening and then quickly move
through northwest-to-southeast generally by midnight. Rainfall
could be locally heavy at times as the band moves through although
rain rates are not forecast to reach levels that would trigger
many hydro concerns. As the front nears southerly winds will also
increase with local gusts over 30 mph likely (over 45 mph in
higher elevation spots). Looks like it will mostly stay below
advisory levels, so did not issue a product. Rain will then change
to showers behind the front. By Monday afternoon urban locations
are looking at between 1/4" and 3/4" with higher elevation
locations generally 1/2" to locally over 1". Due to an anticipated
higher than normal number of cars on the road this evening
compared to most Sundays, there could be a fair number of problems
especially since it should coincide with the highest rain amounts.
On wildcard is the remote possibility for thunder this evening
mainly near the coast, although lightning strikes well to our
west have been trending downward.
Active weather will then continue for the remainder of Monday
through at least Thursday night as multiple weak impulses combine
with a moist flow overhead. IVT values that will briefly peak
close to 500 tonight will have several more spikes (potentially
peaking around 750 kg/m/s late Monday into Tuesday) through the
week. widespread rainfall will return late on Monday and continue
through most of Tuesday. Rainfall from the second system will be
considerably higher -- urban locations 2/3" to 1.5" with 1.5" to
locally more than 3" for coastal ranges. Current forecast from
CNRFC keeps streams and rivers below flood stages, however all of
them are expected to have rapid rises. Will be keeping a close eye
on the latest numbers to see how they are adjusted after the first
round of rain tonight. Southerly winds will again be of concern
with speeds likely over 30 mph.
Rain will again change to showers for most locations by Tuesday
night and continue to the first half of Wednesday before generally tapering
off by late in the day. On Thursday the third, and likely last
major round of rain will move through with precipitation
anticipated going into Friday. Current estimates show similar
precipitation values for it compared to the system that will race
A ridge of high pressure will likely build back to the California
coast starting over the weekend with the first half of next week
looking mostly dry.
.AVIATION...As of 3:40 PM PST Sunday...Lowering cigs the rest of
the afternoon as a frontal system approaches. Gusty south to
southeast winds switching south to southwest sometime after 06Z
which is when we expect fropa. A period of moderate rain is
expected just ahead of fropa. Winds slowly decrease overnight.
Vicinity of KSFO...MVFR cigs with rain becoming widespread after
02Z. Vsby may drop to 4-6 miles in heavier rains. Southeast winds
gusting to 30 kt switching to southwest after 07Z. Rain turns to
showers after 07Z and lasts through midmorning Monday.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Cigs lowering to MVFR after 04Z with rain
spreading into the area. Fropa expected around 09Z with rain
becoming showers. Gusty southeast winds to 30 kt at KSNS with SE
wind just ahead of fropa.
.MARINE...as of 3:40 PM PST Sunday...A cold front will move
across the coastal waters this evening and tonight resulting in
increasing southerly winds and a slight chance of thunderstorms.
Gusty winds will produce small craft advisory conditions with
fresh swell. Winds will turn west to northwest and decrease on
monday but will increase again Tuesday as another system
approaches the area.
.Tngt...SCA...Mry Bay until 3 AM
SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
SCA...Pigeon Pt to Pt Pinos 0-10 nm until 3 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM
SCA...SF Bay from 9 PM until 3 AM
PUBLIC FORECAST: Bell
AVIATION: W Pi
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