Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/01/21
Area Forecast Discussion
National Weather Service Charleston SC
1038 PM EST Sun Jan 31 2021
A cold front will move offshore tonight. High pressure will
then steadily build into the region through the middle of the
week. Another front could reach the forecast area next weekend.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 1030 PM: KCLX indicated a broad band of light to moderate
rain off the coast. To the west, a small band of showers was
pushing east across the middle Savannah River valley. Latest run
of the HRRR indicates that the upstream convection will continue
to track east through the rest of the night, passing over
portions of the CWA tonight. I will keep mentionable PoPs
through most of the night. Temperatures may cool by 10 degrees
by day break Monday, with gradually cooling expected through
mid-morning. The forecast will feature adjustments to the hourly
temperatures through the rest of the night.
AS of 920 PM: The cold front and associated convection has
pushed off the GA and SC coast. The forecast will be updated to
remove mention of thunderstorms over land, shift winds from the
west, begin reducing PoPs from west to east.
As of 620 PM: KCLX detected a fine line of reflectivity over
inland GA/SC approaching the coastal counties. This feature
appeared associated with the position of the wedge front/cold
front. Based on radar trends, rainfall rates should increase
with the passage of the front. Deeper convection was detected
over southern GA, tracking to the NE. It is possible that this
activity could track over the coastal GA counties with thunder
later this evening. The forecast will continue to indicate
greater coverage this evening, with a mention of thunderstorms.
An upper level low/trough located over the MidWest will
deepen/dig tonight as mid-level jetting rounds its base,
eventually extending from the Great Lakes to the Gulf of Mexico
by late tonight. At the surface, its low pressure component will
move across the Ohio Valley, and a cold front with waves of low
pressure will develop along the front moving across the
forecast area tonight.
Light rain will continue through the evening, although it will
be patchy in coverage due to some areas stabilizing at the
surface with evaporative cooling occurring. Because of this,
winds/gusts have decreased slightly with some gusts up to 30
mph expected through the night, mainly along the coastal areas.
Heavier showers then look to consolidate into a band that rakes
through with the front between 6 and 11 pm. It is also during
this time when there could be a few t-storms, mainly south of
I-16 in Georgia where the best SBCAPE is situated, albeit no
more than 250 J/kg. Given that shear is around 50 kt, there is a
risk for a stronger storm or two. SPC has portions of Long,
Tattnall, Liberty, and McIntosh counties in a Marginal risk for
severe thunderstorms through tonight. Deep moisture wrapping
around the surface low will make its way into the area behind
the main line of showers. Isolated/scattered showers are
possible beyond midnight, especially inland as PWATS still cling
to close to 1". Cold air advection as well as a more stabilized
environment should limit these showers from progressing further
east, however. Rainfall totals are still on track to range from
1/2" to 1", with locally higher amounts targeting mainly the
Charleston Tri-County region, as well as in the extreme
southeast GA counties where a stronger thunderstorm is possible.
Cold air advection will strengthen late tonight/early morning,
dropping temperatures into the mid and upper 40s, perhaps near
40F in the extreme inland counties by dawn Monday.
.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Monday and Monday night: Aloft, an impressive upper low will
continue to deepen and sink southward along the Eastern Seaboard,
then begin to shift slightly eastward overnight. At the surface, the
forecast area will be caught in the cyclonic flow around the
deepening low centered just off the New England/Mid Atlantic coast.
Plenty of residual moisture will be in place up to around 10 kft,
helping to produce mostly cloudy to overcast skies through the
period. Also, with the cold air aloft under the trough/closed low we
will see isolated to scattered showers, mainly across southeast
South Carolina and the Tri-County region. The best gradient will be
aligned across southeast Georgia, supporting frequent west-northwest
gusts to around 25 mph. Conditions won`t be quite as breezy the
further northeast you go as the isn`t nearly as tight. Overall, it
will be a very chilly and cloudy day. Temperatures will likely
struggled to reach 50 for much of the forecast area thanks to the
persistent cloud cover. The best chance for low 50s will be along
the immediate coastal corridor. Overnight lows are forecast to range
from the low 30 inland to the mid 30s closer to the coast.
Tuesday through Wednesday: Lingering moisture will finally pull away
from the area on Tuesday and skies will steadily clear out, becoming
mostly clear for Tuesday night and Wednesday. Tuesday actually looks
like it will be accompanied by the strongest winds as the tightest
pressure gradient lines up right across the forecast area. Frequent
gusts to around 25 mph are expected, and we could even see some
gusts approach 30 mph. There will be plenty of sun by Tuesday
afternoon, but we will still see temperatures right around 50 just
about everywhere. Wednesday will only be a few degrees warmer, but
fortunately not as breezy. Tuesday night lows should result in a
widespread freeze with upper 20s inland and low to mid 30s right
along the coast.
Lake Winds: Winds will remain elevated across Lake Moultrie through
much of the early part of the week. The strongest winds are expected
Monday night when gusts could approach 25 knots.
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Models start out in good agreement. High pressure will be over the
region Wednesday night, moving offshore into Thursday. Expect dry
conditions with moderating temperatures on Thursday. Friday and
Saturday is when each model shows something completely different.
All have a front approaching our area, but they disagree on it`s
position and the resulting weather. The best we can do at this point
is slight chance to chance POPs Friday into Saturday. More changes
will be needed with this part of the forecast.
.AVIATION /04Z MONDAY THROUGH FRIDAY/...
Prior to the 0Z TAFs, KCLX detected a fine line of reflectivity
approaching the terminals from the west. This feature appeared
associated with the position of the wedge front. Based on
upstream observations near the wedge front, conditions should
gradually fall to MVFR early this evening. Based on MOS and
forecast soundings, ceilings should fall well within IFR range
to LIFR late this evening into the late night hours. A cold
front is expected to sweep west to east across KCHS/KSAV during
the pre-dawn hours, shifting winds from the NW. During the
daylight hours Monday, NW winds should gusts generally between
20-25 kts with MVFR ceilings lingering.
Sub-VFR ceilings could linger at KCHS through Monday afternoon, but
prevailing VFR should return Monday night. Winds will be breezy
Monday afternoon (especially at KSAV), and then again at both KCHS
and KSAV on Tuesday.
Today and tonight: A cold front is expected to pass over the
waters around midnight, which will allow winds to veer out of
the southwest and then out of the west by early morning, with
late night cold air advection to develop. Winds will remain
20-25 kt with gusts up to 20 kt throughout the night, hence
Small Craft Advisories are in effect across all waters,
including the Charleston Harbor. There will also be period of
Gales that will impact the outer Georgia waters tonight, where
we have a Gale Warning in effect through most of the night. A
Small Craft Advisory will be needed thereafter.
Seas will continue to build up to 6-8 feet in the nearshore
waters out 20 nm and up to 10 ft in the outer GA waters. After
the passage of the front, seas will gradually decrease by a
couple of feet. Mariners are also alerted to the potential for a
few t-storms tonight in advance of the cold front.
Monday through Friday: A tight pressure gradient and cold air
advection will support persistent and strong northwest winds Monday
through Tuesday night. Conditions will improve considerably on
Wednesday and then remain below advisory criteria through the end of
the week, though southerly flow could be close to criteria Thursday
night and Friday. For Monday, the best gradient and strongest winds
will be aligned across the Georgia waters with gusts up to around 30
knots. For the South Carolina waters, winds and seas could actually
end up falling below Small Craft Advisory criteria for a period of
time. However, we opted to just keep the advisory going for all
zones (outside of Charleston Harbor) as a solid surge is expected
Monday night. In fact, we could see another period of gales in the
outer Georgia waters Monday night and this will be added to the
Hazardous Weather Outlook. Solid advisory conditions will prevail
through Tuesday and much of Tuesday night. All advisories should
come down by midday Wednesday.
MARINE...Small Craft Advisory until 2 AM EST Monday for AMZ330.
Small Craft Advisory until 11 AM EST Wednesday for AMZ350-352.
Gale Warning until 4 AM EST Monday for AMZ374.
Small Craft Advisory until 5 AM EST Wednesday for AMZ354.
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
544 PM CST Sun Jan 31 2021
.DISCUSSION...(This evening through Sunday)
Issued at 108 PM CST Sun Jan 31 2021
The clearing line is slowly moving across the forecast area this
afternoon. The west is already sunny and the temperatures are a
little warmer than in the east. As a surface high builds into the
area, winds continue to decrease. The clouds in the east have kept
the temperatures from warming very much.
There are several things going on this forecast period. First will
be fog. The next round of fog is expected across the area tonight.
Temperatures warming to around or just above freezing have melted
a little snow and there is plenty of low level moisture. The low
clouds moving out will get out of the area this afternoon/evening,
but are near enough that fog could form. The surface high across
the area and light winds will allow for temperatures to cool below
the current dew points and all this leads to an increase in fog
chances for tonight. The HRRR and SREF both have fog across at
least portions of the area. The HRRR is mostly in the east while
the SREF is over the entire area with the best probabilities in
the central part of the forecast area. Already have areas of fog
in and that should be a good start, but may need to be increased.
The next question will be clearing out the fog on Monday. The HRRR
and SREF both have it moving out by mid morning or so, so will
keep that for now. During the day Monday, the surface high moves
to the east and by afternoon there is some warm advection,
especially in the western part of the forecast area. Even with
warm advection, the temperatures will struggle to warm
significantly because the winds are expected to be light enough
that mixing will be minimal. The east will still be cool since
there will be some clouds through much of the day.
The fog does not end there. Even with the surface high moving to
the east, winds are expected to be light. Fog is a possibility
again Monday night. There will be a little melting of snow, warm
advection over the cold snow and light winds. The fog could begin
during the evening and last into mid morning on Tuesday. Even
then, the fog chances are not over yet. Temperatures Tuesday
afternoon will be a little warmer and there will be more snow
melting during the day, combined with light winds Tuesday night
and the SREF has good probabilities for fog again. Since this is
still a few days away, have kept it just patchy for now.
Wednesday will be a little warmer. Winds will be from the south
and increase just a little. During the day Wednesday, another
system develops to the west and by Wednesday night there will be a
cold front that moves through the area. Behind the cold front,
there is a chance for some precipitation. It could start as rain
early in the evening, but is expected to mix with and change to
snow as the temperatures cool off during the evening and
overnight. Temperatures remain cool during the day Thursday and
most of the area will have snow with some of the southern parts of
the area having a rain/snow mix. By Thursday evening, this system
is departing and only a little light snow is possible.
This ushers in the last of the concerns for the forecast period.
Friday will continue to be cool, but by Friday night the next cold
front moves through and brings in the coldest air of the season so
far. Temperatures Saturday and Sunday will only reach the teens
and lower 20s for highs and that could be generous. Lows will be
in the single digits and even a little below zero in the north.
Along with the cold temperatures, there are some small chances for
some snow Friday night through Saturday night. It could mainly be
just squeezing out moisture out of the cold air, but with it being
so cold it would be fluffy and could accumulate. There is still
some uncertainty on the precipitation chances at this time.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 544 PM CST Sun Jan 31 2021
Significant wx: Beginning what could very well be prolonged
(48-72+ hrs) of mainly IFR/LIFR VSBYs and CIGs.
Tonight: VFR to LIFR. Have deteriorated TAFs for tonight fairly
significantly as fog appears likely to develop after 03Z. Exact
timing remains a bit uncertain, and some model data suggests EAR
could be more on the edge compared to GRI. Nonetheless, expect at
least IFR VSBYs, perhaps even LIFR (esp. at GRI), and LIFR CIGs of
200-400ft. Winds will be lgt and vrbl. Confidence: Medium.
Monday: LIFR or IFR. Expect LIFR/IFR fog and LIFR CIGs to start
the day. With lack of mixing, its very possible that conditions
will be slow to improve, even by late morning. Have a return to
MVFR VSBYs for aftn, but this could be generous. VSBYs like tank
again Mon eve. Lgt and vrbl winds during the morning, bec
primarily light out of the SE by aftn. Confidence: Medium.
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
745 PM EST Sun Jan 31 2021
Issued at 745 PM EST SUN JAN 31 2021
00z sfc analysis shows a slow moving area of relatively deep low
pressure passing by just to the northeast of the JKL CWA. This is
swinging the winds around to the northwest through the area and
bringing in colder air. This system is also starting to wrap its
commahead pcpn back into Kentucky - soon to be spreading into
eastern parts of the state. Combined, this means mainly light snow
developing for our western counties late this evening and
spreading east with time through the night. Staggered WWA have
been hoisted for this prolonged snow event. Temperatures (and
dewpoints) are currently running from the middle and upper 30s in
the west to the mid 40s east. Meanwhile, winds are blowing from
the west to northwest at 5 to 15 mph with gusts to between 20 and
25 mph at times. Have updated the forecast in the near term to
fine tune the PoPs and add in the latest obs and trends for the
T/Td grids. These updates have been sent to the NDFD and web
.SHORT TERM...(This evening through Monday night)
Issued at 530 PM EST SUN JAN 31 2021
Late this afternoon, an upper level low was centered near the IN
and OH border, northwest of east KY with an upper level trough
extending south through the MS Valley. Several vort maxes were
rotating around the upper level low, one of which is working into
East KY at present and likely partially responsible for the area
of showers across the southeastern portions of the area, another
upstream nearing the confluence of the OH and MS Valley sand
another further northwest near the IA/MO border. At the surface,
an occluded area of low pressure is centered near the OH River to
the east of KCVG with a trailing occluded front south into eastern
KY extending south from Fleming County to just east of the I 75
corridor. A sfc trough extends southwest from the low near the OH
River. Further to the east, a low pressure system is starting to
take shape along the eastern seaboard over the Carolinas.
Tonight and into Monday, the upper level low is expected to move
slowly east to and be centered near the mid OH Valley region
around dawn on Monday and then move to the piedmont region along
the eastern seaboard by Monday evening. The lead shortwave trough
will move east of the area this evening, with the next two approaching
the western portions of the area and merging overnight into early
on Monday as they track into the Appalachians. A sfc trough will
work across the area overnight to around dawn on Monday, with much
colder air working in aloft and at the sfc with this. The column
should cool sufficiently that around midnight if not 11 PM, rain
should begin to mix with or perhaps change to snow along the
western tier of counties and then gradually from west to east and
from the higher elevations above 2500 feet down to the southeastern
valleys through around dawn on Monday. Sfc temperatures should
fall to near if not a little below freezing as this passes. Cold
air advection continues through the day with another vort likely
rotating across the area during the afternoon. The low level flow
will also be upslope west to northwest behind the sfc trough,
initially enhancing snow a bit near the escarpment and perhaps
the Log Mtns of Bell County, and then as the winds become more
northwesterly through the morning into the afternoon, enhancing
snow in the southeastern counties generally along or southeast of
KY 80 and the Hal Rogers Parkway.
Even as the upper low moves further east of the area on Monday
night, an additional vort likely work across the area while the
low level flow remains upslope with moisture persisting,
especially over the southeast and east. Periods of snow or snow
showers should continue through Monday night as well, particularly
across the south and west, but gradually starting to taper off
from northwest to southeast.
This is going to be a long drawn out event with snowfall over 30
to 36 hours reaching the 4 to 6 inches range in some of the
higher elevations above 2000 feet and perhaps reaching the 4 inch
mark along the escarpment as well. HRRR and some of the HREF
guidance PMM Snowfall point toward this potential. Intensity will
be quite variable as well. However, every 6 hour period snowfall
should only average a half of an inch to one inch with locally
higher amounts, especially late tonight to early on Monday in the
escarpment and late Monday into Monday night in the southeast.
With that in mind, the Winter Weather Advisory headline category
still fits this scenario due to the long duration event. Some
adjustments have been made to the start times based on the latest
thinking and in coordination with surrounding offices. The end
time has been extended into Monday night or early Tuesday across
the south and east as the upslope event should persist during that
There will be travel impacts at times, with the Monday morning
and Monday evening commute likely impacted with the Tuesday
morning commute also possibly impacted in the southeast. The long
duration 30 to 36 hour totals should average 1 to 4 inches for
most locations, generally with higher amounts along the
escarpment and in the higher elevations in the southeast. Above
2000 feet, 4 to 6 inches may accumulate with locally higher
amounts above 3000 feet.
.LONG TERM...(Tuesday through Sunday)
Issued at 530 PM EST SUN JAN 31 2021
An active long-term period is in store for eastern Kentucky.
Lingering upslope snow showers and flurries will gradually be
coming to an end on Tuesday with just some minor accumulations
possible over Southeast Kentucky. High pressure brings a brief
reprieve on Wednesday before another late week storm system and a
potential arctic cold front bring more rain, snow, and colder air.
12z Tuesday-00z Thursday...
The period will start off Tuesday morning with a powerful
nor`easter centered south of Long Island and its supporting ~532
dam low located over the Delmarva Peninsula. A ridge of high
pressure will be located over the Plains and will be supporting a
surface ridge spanning from the Texas Gulf Coast to western
Ontario. The deep low will only gradually drift toward the
Canadian Maritimes through 0z Thursday while the next Pacific
trough pushes into the Rockies/Northern Plains and knocks down the
ridge over the Central US. This will shunt the surface ridge
across the Ohio Valley on Wednesday.
In sensible terms, look for lingering snow showers across those
higher elevations above 1,500 feet Tuesday morning while a few
flurries linger as far back as I-75 and I-64. This activity will
gradually diminish through the day and perhaps give way to partial
sunshine outside of the highest terrain by the afternoon.
Additional accumulations will be minimal, ranging from a dusting
north of Highway 80 up to around 1-1.5 inches above 3,000 feet.
Even though temperatures are expected to reach the low to mid 30s,
a brisk northwesterly breeze at around 8 to 15 mph will make it
feel several degrees colder. An upper level disturbance rotating
around the departing low is expected bring another uptick in cloud
cover and perhaps a few flurries Tuesday night. Tuesday night`s
low temperatures are tricky, as any clearing would allow for rapid
radiational cooling in the snow-covered valleys; but, if clouds
prevail, that cooling potential won`t be realized. Remained close
to NBM guidance for now and forecasted lows in the upper teens to
lower 20s. Skies should become mostly sunny on Wednesday as the
high pressure moves in. Even so, light northwest to westerly flow
and the snow cover will keep high temperatures on the chilly side,
likely mid to upper 30s for most.
The next upper level trough will initiate a low pressure system in
the lee of the Colorado Rockies as it descends onto the Plains
mid-to-late week. The models still differ on timing and many of
the specifics around this system, but they do bring in milder
temperatures for eastern Kentucky and a round of rainfall for
Thursday into Friday, along and ahead of the system`s cold front.
A brief changeover to snow can`t be ruled out on the tail end of
the system. Thereafter, the models and ensembles have latched onto
the the potential for an arctic cold front arriving over the
weekend with 850 mb temperatures plummeting toward -20C or colder.
The GFS keeps the arctic frontal passage rather tame with just
some blustery snow showers. The ECMWF and the Canadian show a low
pressure system riding along the front and leaving behind a
blanket of snow. This push of colder is also air well-supported by
the various ensemble means. While there is still plenty of
uncertainty, given the run-to-run and model-to-model differences,
early next week could be very wintry across eastern Kentucky.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 720 PM EST SUN JAN 31 2021
Conditions will continue to gradually deteriorate into the IFR
range everywhere this evening. IFR conditions should then
generally prevail through the end of the period with some periods
of LIFR possible in any heavier snow showers into the day Monday.
Ceilings could be down to near or below airport mins for some of
that time, as well. With the low pressure system working across
the area, periods of rain will occur this evening. Colder air
flows into the area from west to east through 12Z, and especially
between 06 and 12Z, changing any rain to snow during the night.
The snow will then continue through the rest of the period. Winds
will be basically locked into the northwest direction through the
forecast period at around 10 kts with some periods of lull and
occasional gusts to near 20 kts.
Winter Weather Advisory from 1 AM Monday to 7 AM EST Tuesday for
Winter Weather Advisory from 11 PM this evening to 7 PM EST
Monday for KYZ044-050-051-058-059-068-069-079-083.
Winter Weather Advisory from 1 AM Monday to 10 AM EST Tuesday
Winter Weather Advisory from 4 AM Monday to 10 AM EST Tuesday
Area Forecast Discussion
National Weather Service Pocatello ID
133 PM MST Sun Jan 31 2021
.SHORT TERM...Tonight through Tuesday night. Early afternoon
satellite imagery was showing a ridge over the region with lingering
low clouds along the Montana border near Monida Pass. Looking
upstream, a broad upper low was noted edging toward the NW coastal
waters. The numerical models show the ridge holding firm over CNTRL
Wyoming through Monday evening as short-waves eject from the low off
the coast into SW Canada. Starting early Tuesday morning and
continuing through Tuesday night, the weakened trough begins to move
onshore with increasing moisture impinging on the CNTRL mountains
through the day Tuesday and the remainder of SE Idaho Tuesday night.
The operational models favor a split in the trough with the NRN
branch impacting SE Idaho. With that said, there are some
interesting differences between the models with the GFS representing
the slowest solution, the NAM being the most progressive, and the
ECMWF falling in between. The speed of the solution has a direct
impact on the onset of precipitation across the SE mountains. With
that said, I have generally allowed the National Blend of Models to
drive the boat here as it would taken into account all the
variability. Temperatures are expected to run at or slightly above
normal through Tuesday and then much above normal Tuesday night due
to the incoming trough. Huston
.LONG TERM...Wednesday through next Sunday. Fairly widespread precip
should be ongoing Wed AM, likely predominantly snow or all snow by
that time as temps diurnally cool, shutting down from NW to SE Wed
afternoon/eve as a cold front crosses the region. Breezy conditions
are also possible, with perhaps some pockets of blowing snow. Our
storm total snowfall forecast has changed little, with higher-
elevation locales that normally benefit from a WSW flow potentially
picking up advisory-level totals over 5" (esp the Sawtooths and
Galena/Banner Summits), with generally an elevation-dependent 1-4"
across the srn/ern highlands and a bit more in the mntns surrounding
the Teton Valley. Totals are still coming in at generally less than
an inch for the Snake Plain, ern Magic Valley, and some srn highland
valleys where precip will be lighter and also fall partially as rain
prior to Wed AM. High temps Wed won`t really have a fair shot a
fully "topping out" and succeeding at life between the cloud cover
and the cold front, generally reaching the 30s.
Starting Thurs, SE ID will be positioned directly in an active storm
track sandwiched between a building ridge of high pressure over the
Pacific and a longwave trough over the cntrl/ern US, with both
synoptic features nearly stationary. This storm track will be
governed by a cool, moist, NW flow, with occasional disturbances
providing foci for precip chances. Temps will thus be near to below
normal into the weekend. The first disturbance riding this flow is
still forecast to drop SE across the area Thurs night and Fri,
bringing light snow that should favor the ern/srn mntns. This
disturbance remains pretty progressive, and has trended weaker/less
amplified in today`s 12z model suite, more of a ripple in the
pressure height field than a bonafide organized shortwave. (In fact,
this feature isn`t picked up at all by 500mb cluster analysis.)
Every QPF cluster DOES include over 0.10 inches QPF for at least
some portion of our ern highlands (if not greater real estate), so a
shot of more organized moisture is certainly there with a bit of a
mid-level vorticity max/jet embedded in the flow. A range of
solutions is noted in the GFS/EC ensemble members as we check snow
for various points across the forecast area, but even the highest
accums are light-moderate everywhere with that ern highland
preference evident for highest totals...some members are coming in
as high as 3-4" for Driggs (so likely more at higher elevations). We
may see a break on Sat, followed by a variety of potential model
solutions regarding the occurrence/timing of our next disturbance
Sun or Mon. By this time, 500mb cluster analysis has 2 clusters (55%
of the members, GFS-heavy) supporting an increasing eastward
influence of the Pacific ridge which may tend to nudge the active
storm track east of our area, while another 2 clusters (about 45% of
the members, EC/Canadian-heavy) maintain the status quo. Thus,
forecast confidence remains high in continued near to below normal
temps, but is low in sensible wx details Sat and beyond. High-impact
storms currently seem unlikely. Low temps may reach the single
digits above to single digits below zero by the weekend for some
areas, depending on cloud cover. - KSmith
.AVIATION...A ridge of high pressure will remain the dominant
synoptic wx feature across SE Idaho both today/Mon, with light winds
and a SLIGHT drying trend noted in the guidance over the period as
well. Fog/low stratus development last night/early this AM generally
followed the HREF flavor with KIDA remaining just south of the main
shield. Tonight/Mon AM, development is much more limited to non-
existent across ALL guidance with slightly wider sfc temp/dew point
depressions advertised. Given recent rain/snow, we can`t COMPLETELY
rule out some development, esp near water sources, but we have no
strong basis to include it in any TAFs at this time. The HRRR
suggests (unsurprisingly) KIDA/KDIJ would be the best candidates,
but both terminals fared well last night, and again we are trending
a bit drier. In other news, the HRRR suggests a southerly downslope
wind MAY develop at KPIH this afternoon at up to 10kts, but we`re
not really seeing signs of this just yet and all coarser guidance
maintains a NE down-plain flow, so will stay the course and monitor.
Also, high-res guidance tries to creep showers in toward KBYI/KSUN
by Mon AM (WELL in advance of the next system), but this is not
supported across deterministic models (little upper-level support/
lift) and has been dismissed for now. The result of all of this is
mostly one-liner TAFs (except KSUN/KDIJ for wind shifts) with no
widespread aviation impacts. Overall confidence is high, with again
lower confidence in patchy fog/low stratus. It still appears precip
with our next system should hold off until Tue night. - KSmith
Area Forecast Discussion
National Weather Service San Diego CA
110 PM PST Sun Jan 31 2021
High clouds will thicken tonight through Monday as moisture aloft
increases from the southwest. For Monday, it will be mostly cloudy
with sprinkles, or scattered light showers at times. The best chance
for anything measurable will be over the mountains. Meantime, low
pressure off the coast of western Canada will slowly sink south
along the West Coast, bringing a chance of showers on Wednesday. Dry
weather and offshore flow is forecast for the latter part of the
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Satellite imagery midday showed high clouds streaming NE across the
State. After numerous large breaks this morning, they were
consolidating early this afternoon, and look even more solid well
off to the SW, so look for more thickening overnight. Surface
pressure gradients have been moderately offshore all day, with the
offshore wind-prone areas of the mtns/passes reporting E-NE winds of
20-25 MPH with gusts 30-40 MPH. Temperatures were running some 7-12F
above values observed at midday yesterday.
A weak ridge over the Southwest will drift east today, as a longwave
trough sets up off the West Coast. At the same time, a little
farther to the west, a ridge will be amplifying over the EastPac
along 140W. The ridge is now forecast to drift east this week, which
will crimp the effects of the trough. Most deterministic model
solutions are now coming up dry over SW CA midweek, as the trough
gets squeezed by the ridge and comes inland farther south. Shower
chances remain in the forecast for Wednesday, but are lower, with a
downward trend. The GFS 12Z ensemble member solutions remain
predominantly wet, while the ECMWF is mostly dry and the NAM12
deterministic runs are mostly dry.
The forecast proximity of the ridge to the West Coast will now limit
chances for significant precipitation this week, however, a
considerable amount of subtropical moisture will still get entrained
in the SW flow aloft for the next 24-36 hours. This could still
bring us some light precipitation, especially on Monday. For now,
measurable precipitation, if any, is expected on the higher
mountains, while lower elevations will likely only see sprinkles at
times. This has been advertised by several HRRR runs and the WRFEMS
as well. Frequently, advecting moist airmasses from the SW of San
Diego are fraught with uncertainty, since we generally only have
satellite interpretations of the atmospheric structure. For now, we
will accept the current model depictions, keeping small measurable
amounts over the mountains and just sprinkles at lower elevations.
In any case, amounts will be very light, since there is little
forcing to act on this moisture.
Once we get the weakening trough out of the way midweek, the latter
half of the week looks dry with predominantly offshore flow and
seasonally mild temperatures. The block forming over the far EastPac
late this week may not be around too long though. The 12Z medium
range guidance from the EC/GFS both show it breaking down next week
with quite a bit of spread in ensemble solutions as well.
312100Z...SCT-BKN clouds with bases 10,000-15,000 feet MSL to
continue through Monday. Breezy east-northeast winds expected across
mountains and adjacent foothills through tonight, with gusts of 20-
30 kts. Winds will diminish overnight.
No hazardous marine conditions are expected through Tuesday.
Increasing northwest winds may develop on Wednesday with gusts near
20 kts and combined seas of 6-7 feet possible across the outer
Skywarn activation will not be needed today.
Area Forecast Discussion
National Weather Service Tulsa OK
951 PM CST Sun Jan 31 2021
Back edge of low clouds hasn`t made much eastward progress this
evening, and recent HRRR output suggests clearing may be a bit
slower than previously expected. Have tweaked sky cover some for
the remainder of the night.
.PRELIMINARY POINT TEMPS/POPS...
TUL 28 50 31 57 / 0 0 0 0
FSM 30 50 28 56 / 0 0 0 0
MLC 28 51 31 58 / 0 0 0 0
BVO 27 47 27 56 / 0 0 0 0
FYV 28 45 24 54 / 0 0 0 0
BYV 28 43 25 52 / 0 0 0 0
MKO 28 47 29 55 / 0 0 0 0
MIO 28 45 26 53 / 0 0 0 0
F10 28 50 31 58 / 0 0 0 0
HHW 29 53 32 56 / 0 0 0 0