Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/26/21
Area Forecast Discussion
National Weather Service Boston/Norton MA
1046 PM EDT Sun Apr 25 2021
Gusty and drier conditions tonight and Monday. Turning milder
for Tuesday into Wednesday, with limited chances for showers or
thunderstorms across northern and western Massachusetts on
Wednesday. A cold front may bring more widespread rains to the
region on Thursday with a cooldown in temperatures. Late in the
week into the weekend features continued unsettled through
generally dry conditions, with temperatures trending near to
below average for late April.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
1030 PM Update...
No changes in the latest update. Forecast remains on track.
725 PM Update:
Coastal low well southeast of Nantucket continues to pull away
toward Georges Bank. Outside of very spotty back-end showers
across Cape Cod, drier NW flow is increasingly taking hold and
this is allowing for more substantial breaks in overcast
cloudiness. Expect more of the same thru late evening, with
clouds lifting and scattering out with most areas trending
mostly clear by midnight. Have reduced PoPs to sub-mentionable
levels/dry for the remainder of the tonight period.
Focus then turns to cold/dry advection and increasing
breezy to gusty conditions. On the winds, I incorporated a bit
more of the HRRR winds as it and the RAP guidance seem to have a
decent enough handle on the onset of gustiness. Expect NW gusts
to begin late evening/midnight across western MA/northern CT
and into the early overnight to pre-dawn Monday hrs across
central/eastern MA and RI. Though we are looking at cold
advection for the remainder of the night, going to have to keep
an eye on model consensus low-30s to near 40 degree low
temperatures. Though the overall idea of cooler temps west and
somewhat milder east makes sense, possible small upward
adjustments to temps could be needed in later updates as
guidance can sometimes trend too cold in well mixed/breezier
Low pressure passing south and east of Nantucket will move off
toward Nova Scotia tonight. Western edge of the rain was moving
through Eastern Massachusetts. Expect the rain to taper off by
Satellite shows breaks in the clouds over Western CT and Western
MA, more breaks over NY. These will work east, bringing clearing
Pressure gradient starts the night rather light although
favoring a north to northwest wind. As a northern stream
shortwave moves past, expect the surface pressure gradient to
tighten, bringing increasing northwest sustained wind. Cold
advection by this wind will generate mixing that will bring
stronger gusts to the surface. Winds aloft will increase to
around 25 kts overnight, so expect gusts of 25 to 30 mph
With clearing skies and cold advection, expect temperatures to
fall into the 30s and low 40s. Coldest temps will be along the
Berkshire East Slopes, which will be 30-32.
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Overview... Shortwave that passes overhead tonight digs and
closes off as it moves to the Maritimes Monday and Monday night.
Upper ridge approaches from the west Monday night.
A sharp pressure gradient continues into Monday. This along with
cold advection mixing from above will generate gusty northwest
winds. Winds in the mixed layer will reach 30 kt, so expect
gusts of 30 to 35 mph during daytime mixing. There is a chance
that winds aloft could reach 35 kt, which would support gusts to
Mixed layer to 850-mb would support max temps in the mid 50s,
and to 800-mb around 60. So the forecast range for max temps
will be mid 50s to low 60s, coolest in the hills.
It will be a dry airmass, as dew points are forecast to fall
into the 20s.
The pressure gradient diminishes at night as high pressure
builds in. Expect mainly clear skies at first, then some mid-
high clouds late at night. Temps should again fall into the 30s
and low 40s.
.LONG TERM /TUESDAY THROUGH SUNDAY/...
* Warming trend Tues into Wed. Possible 80 degree readings Wed for
interior western New Eng. Late-day/evening showers, possible t-
storms at least for northern MA on Wed.
* Still considerable uncertainty on rain chances Thurs, but trending
wetter than not with cooler temps.
* Unsettled Fri into Sat, with temps trending near to below-avg by
early into the weekend.
Tuesday and Tuesday Night:
Upper low from Monday night will continue to pull away, and with it
comes an anticipated warming trend starting Tuesday, with rising 500
mb heights and surface ridging to our south. Should see plenty of
sun, though rising temperatures through the 925-850 mb layer will
continue to support a shallower mixing depth. With westerly winds,
highs well into the 60s should be fairly common, even to the eastern
MA coast. In the interior, highs should reach the lower to mid 70s
with an additional boost from downsloping winds.
A bit more uncertainty specific to PoPs/rain chances for Tuesday
night, as a warm front approaches from the WSW. Models vary on the
exact placement and its NE advancement, but there is some elevated
instability evident rooted around 800 mb in NAM-based soundings. 12z
ECMWF also shows K-indices running around 30-33 units. Each of these
sources support a potential risk for showers with embedded thunder,
but warm-frontal lift appears better further SW than into Southern
New England. For now, have left the forecast dry with an increase in
clouds advertised, but it is possible that PoPs/thunder could be
introduced as confidence increases.
Wednesday into Wednesday Night:
Confidence in the forecast unfortunately continues to trend lower
than average into the mid to latter part of the workweek.
Warm front from Tuesday night looks to lift back northward early on
Wednesday, with warm-sector air mass overspreading much of Southern
New England. Despite a considerable amount of cloudiness, Wednesday
should be the mildest day in the period with high temperatures in
the interior reaching well into the 70s (to near 80 in the CT
While most of the first part of the day should be on the dry side,
the concern and uncertainty in the forecast comes later Wednesday
into the evening. While the GFS and Canadian GEM don`t necessarily
subscribe to this solution, the NAM and the 00/12z ECMWF depict a
weak/subtle surface low progressing ESE from Ontario into eastern
NY/western New England later Wednesday. Mid-level lapse rates are
still rather notable at values around 6-6.5 C/km, and K-indices
again rise into the 30-35 unit range. Especially in our northern
areas (thinking north of the Mass Pike and especially along/north of
Route 2), we could have a period of thunder associated with
strengthening 700-500 mb winds (effective shear ~45-50 kt) and about
500-800 J/kg of MUCAPE per NAM soundings at Orange, MA. After some
coordination with neighboring WFOs, did opt for slight chances for
thunder north of the Pike thru early evening, then trended towards
showers for most of the rest of the forecast area into the evening
hrs. For the evening, lows look quite mild for late-April with
values into the 50s, with similar dewpoints.
Thursday into Friday:
As mentioned, still a considerable level of uncertainty in the
details, but most of the global models are coming around to the
idea of wetter conditions for Thursday along a cold front, along
with cooler temperatures. The ECMWF is something of an outlier
in showing Thursday being largely dry in the wake of the
Wednesday/Wednesday night activity, with another wave then
arriving later Thursday into Thursday nite. Raised PoPs about
10% or so over NBM which brings solid Chance PoPs during the day
and at night on Thursday. Cooler highs in the 60s to near 70,
lows in the upper 40s to near 50.
Differences in model solutions then become even more apparent on
Friday. The more progressive Canadian GEM/GFS show a unsettled NW
flow regime with cooling thermal profiles; on the other hand the
slower ECMWF shows a cold frontal passage later Fri with onset of
cooler NW flow more into Fri. Sided closer to NBM given the
uncertainty with Chance PoPs initially, then trending lower (e.g.
drier) for late in the day and evening. Highs in the lower to middle
60s and lows in the mid 40s.
Despite the stated uncertainty in the middle to latter part of the
workweek, most of the global models actually show some consistency
in showing deep troughing on Saturday associated and a cool pocket
of air aloft. This sets up a potential for unsettled (partly to
mostly cloudy skies) but generally dry conditions at least for
Saturday, with temps trending near to below-avg. It does look to be
a brief shot of troughing aloft however, with pattern beginning to
transition back towards ridging and drier weather for Sunday.
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update:
Tonight: High confidence.
SCT-OVC VFR ceilings have already developed for most of the TAFs
as of the 00z TAF issuance. However residual MVFR-IFR ceilings
across SE MA and Cape Cod/Nantucket should trend to VFR thru
02z. Main focus will turn to increasingly gusty NW wind
conditions for the second half of the evening/overnight. Expect
NW gusts 20-25 kt developing around 03-05z western airports, and
around 05-07z for the central and eastern airports, remaining
gusty into Monday AM.
VFR with clear skies. Gusty winds out of the NW at 10-20 kts
with gusts 30 to 35 kts.
Monday night...High confidence.
VFR. Northwest winds continue gusty in the evening, then
diminish at night.
KBOS TAF...High confidence in TAF.
KBDL TAF...High confidence in TAF.
Outlook /Tuesday through Friday/...
Wednesday: VFR. Slight chance SHRA.
Wednesday Night: Mainly VFR, with local MVFR possible. Slight
Thursday: Mainly VFR, with local IFR possible. Chance SHRA.
Thursday Night: Mainly VFR, with areas MVFR possible. Chance
Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance
Friday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.
Saturday: VFR. Breezy. Slight chance SHRA.
Rain tapers off this evening as surface low exits to the
northeast. Winds shifting from the NW and increase to 20-25 kts
with gusts up to 30 kts late. Seas 5-9 feet for the southern
waters and build to 4-8 ft for eastern waters. Small Craft
Advisory continues for most waters.
Small Craft Advisory for all waters. Gusty NW winds with speeds
to 30 kt, possibly the lower 30s. Seas 4-7 ft.
Small Craft Advisory continues. Gusty northwest winds in the
evening with gusts to 25 kt, diminishing during the night. Seas
4 to 7 feet, especially on the outer waters.
Outlook /Tuesday through Friday/...
Wednesday through Wednesday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Slight chance of rain showers.
Thursday through Friday: Winds less than 25 kt. Seas up to
5 ft. Chance of rain showers.
Friday Night through Saturday: Low risk for Small Craft
Advisory winds with gusts up to 25 kt. Areas of rough seas.
Slight chance of rain showers.
Strong gusty northwest winds are expected across southern New
England on Monday as high pressure nudges in from the west and
with a deep low near Nova Scotia/New Brunswick. This will
promote deep boundary layer mixing and dry relative humidities.
Given this setup the forecast has gusts of 30-35 mph with
minimum relative humidities of 20-35 percent during the
Observed rain amounts through 2 PM today... 0.50 to 0.60 inches
in Srn RI and SE Mass, 0.25 to 0.50 in Nrn CT, Nrn RI, and
parts of Ern Mass south of Boston, 0.25 inch or less across
extreme northern CT and much of Western/Central/Northeast Mass.
MARINE...Small Craft Advisory until 10 PM EDT Monday for ANZ232>235-237.
Small Craft Advisory from 2 AM to 8 PM EDT Monday for ANZ230-
Small Craft Advisory from 2 AM Monday to 6 AM EDT Tuesday for
Small Craft Advisory until 6 AM EDT Tuesday for ANZ250-254>256.
Area Forecast Discussion
National Weather Service Caribou ME
916 PM EDT Sun Apr 25 2021
Low pressure will exit across the Maritimes overnight through
Monday. High pressure builds into the area Tuesday into
Wednesday. Low pressure and a frontal boundary are expected to
approach Wednesday night and clear the region Thursday
afternoon. A frontal boundary is expected to move into the
region on Friday.
.NEAR TERM /THROUGH MONDAY/...
9:16 PM Update: Low pressure is visible on satellite pictures
in the Atlantic to the south of the Gulf of Maine. The low will
pass east of Halifax by Monday morning with a trough extending
back into eastern New Brunswick and northern Maine and into
Quebec. The precipitation this evening has been more showery
across the north with steadier light rain across Washington
County. Overnight, a mid level low and pool of colder air aloft
will begin to move in from the west and precipitation will
transition to wet snow across the western Saint John Valley and
North woods. As the cold air comes in from the southwest snow
showers will become possible across the central highlands,
although precipitation in this area is more likely to be showers
and not a steady precipitation. Further to the east,
precipitation should remain in the form of rain/showers
overnight. Made some slight adjustments based on the current and
expected conditions, but overall the changes were minor.
Scattered showers occurring attm across the northern and western
areas in response to the warm front lifting n. Decent llvl
convergence in place along the front and steep lapse rates
leading to an area of enhanced activity across the northern
border late this afternoon into the evening. The RAP soundings
indicated some CAPE around 200 joules this afternoon, but best
instability shifts ene by early evening. The latest run of the
HRRR hints at some instability as does the NAMNEST, but cloud
cover has kept a lid on any convective development. After
further investigation into the RAP soundings, decided to
include a small area across the northern border and nw areas for
a tstm and gusty winds given the inverted V-sounding. Low pres
will get organized off the southern New England coast and lift
up toward the Gulf of Maine tonight. This low will become the
primary low as the upper trof becomes negative tilt w/strong PVA
coming around the base of the trof aiding in further
development. Precip will become more stratiform in the form of
rain later in the evening as that low lifts ne. Not expecting a
heavy precip event as the best energy w/this system will remain
to the east. Temps will start off mild tonight, but the trend of
the guidance continues to show that a cooldown is expected
overnight into early Monday morning across the western areas as
colder air wraps in behind the sharpening upper trof. This will
lead to temps dropping down to 0c or lower at 925mbs leading to
the potential for rain to mix w/or changeover to snow. The areas
to see this potential changeover to snow will be across the NW
Woods down into Moosehead Lake region w/maybe around 0.5" of
snow by 8 AM Monday morning. Further east, temps will stay warm
enough for rain.
Upper low closes off across northern New Brunswick on Monday
w/cold air swinging further east, and rain mix w/or changing
over to a period of snow. The areas to see the changeover will
be across Northern Maine into the Maine Central Highlands.
Further s, just some rain showers. Not expecting any significant
snowfall accumulation w/the potential of around an inch or two
across the higher terrain of Northern Maine the Maine Central
Highlands. NW winds will be picking up during the day on Monday
w/potential for some gusts to hit 30 to 35 mph, w/some sites
such as GNR and FVE seeing gusts hitting 40+ mph. Daytime temps
will be below normal.
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Vertically stacked closed low pressure over the Canadian
Maritimes will slowly drift eastward Monday night into Tuesday.
Blocking high pressure upstream with cause the slow movement.
The result will be rain and snow showers in the northeast corner
of the forecast area Monday night into early Tuesday morning
with no more than an inch of snowfall in the high terrain of
the North Woods. Most of the area will have lows in the mid to
upper 30s under mostly cloudy skies and gusty NW winds. The
clouds will move very slowly eastward on Tuesday such that NE
Aroostook will stay in the clouds all day with highs only in the
lower 50s, but Bangor will see sunshine and highs popping into
the mid 60s. This raises some concerns about fire weather given
the continuing gusty NW winds and low relative humidity. Weak
high pressure builds Tuesday night with clearing spreading
across the area and lows mostly in the mid to upper 30s. The
high pressure system appears to stay in place most of the day on
Wednesday with increasing clouds and chances of showers
increasing late day. Highs will move up towards the low to mid
60s for the whole area and this will probably be the warmest day
of the week.
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
The period continues to be unsettled and generally mild with a
lot of uncertainty in the exact timing and details. There is a
decent shot for a few days of beneficial rainfall. Using a
blend of models, PoPs remained at the chance level or higher
most of the period until Sunday. Thursday has the best shot at
being dry and Thursday night to Friday night are most likely to
be the wettest. The basic scenario involves a rich flow of deep
moisture in the southern stream from a cut off low in the
southwestern states, a building upper ridge along the
southeastern US coast, a series of weak shortwaves in the
northern stream and the block in the Atlantic. A warm front
will try to push warmer and more humid air into the area, but
the details on its arrival vary from Wednesday night per the GFS
to Thursday night for other models. That depends on the
strength of the upper level ridging in the SE US and how fast
the cut off low moves out of the Maritimes. Guidance generally
agrees on low pressure crossing the area later Friday, followed
by a northwesterly flow and scattered showers for Saturday and
Saturday night. High pressure builds by Sunday.
.AVIATION /01Z MONDAY THROUGH FRIDAY/...
NEAR TERM: As of 9 pm, MVFR at KBHB and VFR at the terminals
from KBGR north to KFVE. Expect conditions to lower to MVFR at
all of the terminals tonight with IFR likely by daybreak Monday
at the Aroostook County terminals in rain. The rain could mix
with, or change to snow by Monday morning across KFVE and then
KCAR/KPQI by late morning. Wind variable, but mostly E-SE 5 to
10 knots late this evening, becoming NNW 10 to 15 kts with gusts
up to 20 kt late at night into Monday morning. For Monday, IFR
north becoming MVFR by late morning for all terminals and then
VFR by the early afternoon for KBGR and KBHB. MVFR holding
across the northern terminals through the remainder of the
afternoon. NW winds 15-20 kt w/gusts 30 kt w/KFVE seeing 35+ kts
during the afternoon.
Monday night into Tuesday morning...MVFR tempo IFR in snow
showers north of GNR and HUL. Otherwise VFR. NW winds gusting to
Tuesday afternoon through Wednesday evening...VFR with light
Wednesday night into Friday....MVFR tempo IFR due to rain and
low cigs. Light winds.
NEAR TERM: Winds/seas will remain below small craft advisory
levels through tonight. SSE winds 10-15 kt becoming NNW 15-20
kt by early Mon morning w/gusts to 25 kt. Seas building to 4-6
ft. Vsbys will lower in rain tonight.
Mon...NW winds 15-20 kt w/gusts 25-30 kts. The highest gusts
will be across the outer zones. Seas 5-7 ft. Rain transitioning
SHORT TERM: SCA conditions continue into Tuesday morning and the
next weather event is the threat of fog Thursday and Thursday
night. A weak SCA for the outer waters is possible Friday night.
Higher astronomical tides through early week. There is storm
surge expected late tonight, but the high tide is expected near
1015 PM. As a result, coastal flooding is not likely. Tuesday
night around midnight is a much higher astronomical tide, but no
storm surge expected.
MARINE...Small Craft Advisory from 5 AM Monday to 10 AM EDT Tuesday for
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1031 PM CDT Sun Apr 25 2021
.SHORT TERM...(This Evening through Monday)
Issued at 231 PM CDT Sun Apr 25 2021
1. A few showers and isolated storms into Monday morning.
2. Near record highs possible on Monday, with some fire danger.
3. Potential for isolated strong storms Tuesday morning.
4. Cooler mid-week followed by strong warmup by May 1.
Today: Warm front just beginning to enter the southern CWA at mid-
afternoon. Temperatures south of the boundary are mixing well into
the 70s, with temperatures on the cooler side of the boundary still
climbing into the 60s. Further northeast, stratus is slowly
retreating away from the area, but highs may fail to reach the mid
40s until the very end of the day in Southwest Minnesota.
Tonight: The surface warm front will continue to slowly edge
northward through the night. Continued low-lvl mixing should
prevent any large scale fall in temperatures tonight, and will hold
overnight lows in the upper 40s to lower 50s. Short term guidance
continues to show enhancement of the low level jet after dark
tonight, in response to a series of shortwaves crossing the Central
Rockies. Increasing low-lvl convergence across portions of central
South Dakota into the northeastern third of the state should lead to
the development of showers late this evening and overnight. MUCAPE
values do climb into the 100-400 J/KG range, but remain very tall
and thin the sounding profile. So would anticipate a bit of
isolated thunder, but no severe weather. Stratus may try to build
southward late tonight, as boundary layer moisture begins to
increase. A lot of uncertainty in this development, which could
slow the rise in temperatures a bit Monday morning.
Monday: Surface low pressure developing in the Nebraska Panhandle
should begin to slide east and then north through the day. Strong
warm advection with 850 mb temperatures pushing into the lower 20s
across northern Nebraska should result in temperatures approaching
the top 10 percent of warmest days on record for the 26th. Have
generally followed the better mixing shown by the HRRR and RAP,
given dry ground conditions and dry low level temperature profile.
This combination could lead to falling dewpoints, especially across
the MO river valley where RAP/HRRR guidance mix dew points towards
the lower 20s to teens. Winds are a bit more uncertain as the
stronger surface flow should result across portions of Iowa and
Minnesota in the afternoon as the surface low edges into south
central South Dakota. The mismatch in winds and lowest RH may
preclude any fire weather headlines at this time, but these trends
will need to be monitored.
.LONG TERM...(Monday Night through Sunday)
Issued at 231 PM CDT Sun Apr 25 2021
Monday Night: A cold front will begin to sink southward Monday
evening and stall across northwest Iowa by Tuesday morning.
Soundings indicate that SFC based convection should be capped along
the advancing boundary. However, HREF MUCAPE values approaching
1500 J/KG are projected to advance north of the boundary by
midnight. Increasing dPVA and 850 frontogenesis may be enough to
develop scattered convection towards the 3am Tuesday hour with this
convection continuing into mid-morning Tuesday. Given reasonable
speed shear in the effective column, can`t argue with the potential
for an isolated stronger hailer Tuesday morning. This is also
hinted at in HREF probabilities, and I wouldn`t be surprised to
see convective outlook risks increased.
Tuesday: Shower and isolated thunderstorm chances may continue
through the day on Tuesday. Depending on the positioning of the
frontal boundary, areas of Northwest Iowa could see highs climb
towards the lower 70s. Further northwest, highs will be much
cooler towards the 50s.
Wednesday: Shower chances may hold on into Wednesday as mid-lvl
troughing will be slow to slide east of the region. Temperatures
will remain below normal through Wednesday with a generally north
Thursday-Friday: Temperatures will begin to warm up nicely through
the end of the week as mid-lvl heights begin to rise and winds turn
back southerly. Highs in the 60s are likely Thursday with highs
rising into the 70s on Friday.
Saturday-Sunday: Strong southwesterly flow aloft arrives for the
weekend and this puts the region in a good position to see well
above normal temperatures to start the weekend. Gusty southwest
winds should push highs well into the 80s Saturday with some
uncertainty on passing showers and temperatures a shade cooler by
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1028 PM CDT Sun Apr 25 2021
A somewhat low confidence forecast for late tonight into Monday
morning in regard to the potential for MVFR and IFR ceilings.
Currently the higher resolution models indicating very little
lower stratus while the Nam and GFS are much more widespread. Will
lean a little more heavily on the high resolution models and keep
the stratus in check a little more. Would think that the better
chance would be along and north of roughly I-90 which is also
along and north of the surface warm front. Tough call with
decou;ling winds washing out this front a bit as well. Otherwise
any lower ceilings that do develop should lift north pretty
quickly in the morning. Scattered showers and an isolated
lightnring strike will also be possible overnight with the better
chances north of I-90.
Area Forecast Discussion
National Weather Service Louisville KY
1025 PM EDT Sun Apr 25 2021
Issued at 1025 PM EDT Sun Apr 25 2021
Current temps across the region are sitting in the low-mid 50s, with
dewpoints in the 40s and calm winds. 00z sfc analysis reveals a
1023mb high located over the Great Lakes and building into our
region. This will lead to a clear and cool night with ridge/valley
splits and potential fog development. Hi-res guidance has backed off
a bit through this evening on fog development for the overnight, but
still question the overall extent of it. Believe we`ll see at least
patchy fog within the river valleys, but could expand a bit more
beyond the valleys in the Bluegrass region.
While crossover method indicates the best region to see locally
dense fog would be LEX and surrounding areas, one inhibiting factor
that could limit overall extent of fog will be soil temps. With 4"
soil temps around 9F warmer than the crossover temp, that would
suggest more of a scenario with patchy fog with variable
visibilities instead of an expansive dense fog scenario. All fog
potential is east of I-65 and should only last for a few hours
during the pre-dawn Monday hours. Have slightly increased coverage
of fog in wx grids, as well as updated the near term grids with
latest obs/trends. Updated products coming shortly.
.Short Term...(This evening through Monday)
Issued at 225 PM EDT Sun Apr 25 2021
In the near term, clouds will continue to clear out across the CWA
this afternoon as a weak cold front pushes southeastward. Satellite
imagery shows most locations partly to mostly sunny with the
exception of the Bluegrass where low stratus continues to hold.
Thanks to the cloud cover, the KY Mesonet shows a nice gradient of
temperatures from the west-southwest where temperatures are in the
low 60s to the east-northeast where temperatures are in the low/mid
50s thanks to lingering cloudcover.
Clouds will clear out overnight as a sfc high continues to build in
over the eastern and southeastern US tonight into tomorrow. Winds
will become light to calm overnight allowing for good radiational
cooling. Once again, areas of patchy fog could form tomorrow
morning, especially east of I-65 and along south of the parkways.
The best chance of fog is likely across the Bluegrass where clouds
were slowest to clear this afernoon and max heating wasn`t reached.
Lows will be mostly in the low/mid 40s with some upper 30s across
our eastern counties.
Upper level ridging will continue to increase heights over the area
tomorrow with the axis of the ridging being over the Ohio Valley by
tomorrow afternoon. With a 1020mb sfc high off to our east, we will
have a good return flow allowing temperatures to warm into the upper
70s with some isolated 80s possible.
.Long Term...(Monday night through Sunday)
Issued at 228 PM EDT Sun Apr 25 2021
Monday Night through Tuesday Night...
Notable upper ridging takes hold over the eastern CONUS through the
early to mid week time frame. Meanwhile, steady S/SW surface flow
will also develop thanks to the pressure gradient between low
pressure over the high Plains, and high pressure centered off the
mid Atlantic Coast. Ultimately, this setup will lead to a
temperature surge as values reach well above normal by Tuesday
afternoon. Soundings show good vertical mixing up into H85 temps
around 15C in addition to the steady warm advection at the surface
and good solar insolation. All indications are to go on the high
side of guidance with those factors in mind. As a result, will look
for low to mid 80s just about everywhere. Think we`ll fall short of
records that range in the upper 80s to touching 90 degrees for that
day, but a good 10 to 12 degrees above normal seems like a safe bet.
Also worth noting that Tuesday night lows will be quite mild in the
low to mid 60s given steady southerly flow and increasing upper sky
Wednesday through Thursday Night...
The upper ridge axis will be pushed off the SE CONUS by mid week as
a northern stream shortwave moves from the northern Plains into the
Great Lakes, and a cutoff low hangs up over the SW CONUS. A
baroclinic zone is expected to set up from the Rio Grande River
Valley up through our region and into New England between the
western trough/cutoff lows and the eastern upper ridge axis through
mid week. Expect Wednesday will still be mostly dry and warm with
precipitation chances starting to creep in from the NW later in the
day. Better chances arrive later Wednesday into Thursday as the
upper features mentioned above push eastward and drag the front
through our area. Highest pops look to be Thursday, along with some
thunderstorm chances. At this point there doesn`t appear to be a
whole lot of instability and that is current limiting factor to any
severe potential. However, soundings do take on a more tall/skinny
profile to the point where some heavier rainfall rates may be
possible. Some training may also occur as flow will be nearly
parallel to the slow moving boundary for a while. PWATs also appear
to peak around 1.5" through the column through mid week. Right now,
the heaviest axis of rain looks NW of our CWA, but will be something
to watch as over 1" of rain is currently forecast for areas along
and west of I-65.
Friday - Sunday...
By late week, the northern stream shortwave will be the driving
factor in pushing the cold front through our area. Meanwhile, the
aforementioned cutoff low will slowly meander eastward across TX.
We`ll see a dry NW flow aloft and surface high pressure pattern over
the Ohio River Valley into the weekend which will bring a return to
dry conditions. Highs in the low 70s on Friday are expected to
gradually warm to the upper 70s by Sunday.
.Aviation...(00Z TAF Issuance)
Issued at 720 PM EDT Sun Apr 25 2021
IMPACTS: Potential fog development overnight for LEX/BWG.
DISCUSSION: Latest sfc analysis continues to place a weak
stationary/cold frontal feature along and parallel to the Ohio River
this evening. VFR conditions across the region at this time will
continue for most through the forecast period. Still believe the
weak cold front will sag south overnight, leaving a clear sky zone
in its wake. RAP model soundings suggest that radiative cooling will
be sufficient enough to develop a low level inversion strong enough
to prevent turbulent mixing. Additionally, using the crossover
method, the highest potential for fog appears to be at LEX, but
could also see some patchy BR at BWG as well. Will keep BWG at low-
end VFR, but will bring LEX down to MVFR for a few hours for Monday
morning. Winds are already pretty light across the region, and
expect these calm conditions to continue thanks to a sfc high
located to our north and helping with the development of overnight
Other than the fog chances VFR ceilings will remain the rest of the
forecast with winds turning out of the south tomorrow.
CONFIDENCE: Medium on visibility/fog for LEX/BWG.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
848 PM PDT Sun Apr 25 2021
.SYNOPSIS...Isolated light showers will continue from about San
Jose southward through the remainder of the evening. Otherwise,
expect clearing overnight from north to south, with cool
temperatures and patchy late night fog. Continued cool, but dry
conditions are forecast for Monday. A warming trend begins
on Tuesday, with above normal temperatures expected in most areas
from Wednesday through Friday. Cooling is forecast for next
.DISCUSSION...As of 8:45 PM PDT Sunday...A cold front that
brought showers to much of our forecast area today continues to
weaken as it pushes south through the southern Santa Clara Valley
and Monterey Bay Area. Rain totals today were highest in the North
Bay where some locations in the coastal hills picked up about a
half inch. Otherwise, rain totals were generally less than a
quarter inch, with most urban areas accumulating less than a
tenth of an inch. Isolated light showers will continue across the
southern portion of our forecast area through the remainder of the
evening, otherwise expect clearing from north to south overnight.
The airmass behind the front is quite chilly with the 00Z OAK
sounding reporting an 850 mb temp of 1.4 deg C, and models
indicate further cooling to about 0 deg C overnight. Thus, we
could see some upper 30s for lows in some of our cooler inland
valleys by daybreak Monday, especially in the North Bay Valleys.
Also, patchy fog is possible in the valleys late tonight and early
on Monday, most likely in the North Bay.
Mostly sunny skies are forecast for Monday as the weather system
moves well off to our southeast. However, some clouds will likely
develop in the afternoon, especially over the hills, as a
shortwave trough drops in from the northwest and maintains
unstable conditions. Models develop isolated afternoon showers
tomorrow, mainly to the north and east of our area. However, the
latest HRRR develops a few showers over the hills of Napa and
eastern Sonoma County in the late afternoon, and the 00Z NAM
develops isolated late afternoon showers along far eastern Santa
Clara County as well as the southeastern portions of San Benito
and Monterey Counties. Thus a few showers over our inland hills
late tomorrow afternoon can`t be ruled out. But for most of our
area, expect dry conditions tomorrow. The shortwave trough will
bring a reinforcing shot of cool air into our area and so
temperatures will remain cooler than normal. However, with more
sun tomorrow, afternoon highs should be close to what they were
today, or a few degrees warmer in some locations.
From Previous Discussion...Tuesday we`ll see the start of a
warming trend as the trough digs deeper into the Inter-mountain
west and a ridge builds off the Pacific Coast. This will result in
closer to normal temps - mid to upper 60s around the Bay, and low
to mid 70s inland. Wednesday the ridge shifts over the west
coast, bringing some light offshore flow and above normal temps -
more widespread 70s and some low 80s. Further warming will occur
inland Thursday as the ridge strengthens. Warmest spots will see
upper 80s and perhaps 90, which is pretty similar to our last heat
event. Temps near the coast will remain seasonably warm, so there
will not be much concern in terms of heat impacts. Friday will be
the final day of this heat stretch, before weak troughing cools
the area back to near normal over the weekend.
.AVIATION...As of 5:22 PM PDT Sunday.....For the 00Z TAFs. It`s
VFR-MVFR with showers over the South Bay, the East Bay and north
Central Coast. MVFR ceilings tonight and Monday morning. Low level
moisture resulting in patchy fog overnight, especially across the
Vicinity of KSFO...VFR, west wind 10 to 15 knots diminishing to 5
to 10 knots tonight. MVFR ceiling tonight and Monday morning until
16z then VFR through Monday afternoon and evening.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR, southwest to northwest winds at 10
knots diminishing to light and variable tonight and Monday morning.
MVFR ceilings tonight and Monday morning then VFR Monday afternoon
.MARINE...as of 5:08 PM PDT Sunday...A weak front continues to
move through the waters this afternoon bringing light to moderate
showers. Winds will shift out of the west to northwest behind the
front from north to south the rest of today with northwest winds
expected to prevail by tonight. Brief locally breezy conditions
possible along the boundary as it passes by. Winds will increase
tomorrow afternoon and evening particularly along the inner
coastal waters north of Point Reyes, between Pigeon Point and
Point Pinos, and south of Point Sur. Mixed seas to persist with a
shorter period northwest swell and a longer period southerly
PUBLIC FORECAST: Dykema/Lorber
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Area Forecast Discussion
National Weather Service Pocatello ID
910 PM MDT Sun Apr 25 2021
.UPDATE...Quick update this evening to adjust PoP and QPF for
ongoing precipitation event across East Idaho. Tweaks were slight.
Region is in a relative break with bulk of the rainfall occurring
in the southeast highlands overnight as upper low continues to
sag southeast through Oregon/northern California. DMH
.PREV DISCUSSION... /issued 144 PM MDT Sun Apr 25 2021/
SHORT TERM...Tonight through Tue night. A closed low is making
its way on shore tonight and by Mon afternoon should be centered
in northern Nevada. This puts eastern Idaho in a consistent period
of moist southwesterly flow that is pumping quite a bit of
precipitation into portions of the forecast area, mainly the
souther tier along the UT-ID border, including the Badger wildfire
incident area, and the eastern highlands along the WY-ID border.
Closed lows move slowly, and the precipitation is heaviest Mon
with a tapering off of precipitation production for Mon night--but
no real end in eastern Idaho until the extended forecast period
below. By Mon, cold air will have moved in and threatens to
produce snow even in the higher elevations of the Snake River
plain. There is a lot of freeze-thaw, with even Stanley in the
central Idaho mountains getting into the 40s for at least some
partial melting. It is difficult to say how much will stick during
the period starting tonight and ending Tuesday morning, but
nearly 6 inches should fall over Galena Summit between Stanley and
Ketchum, 2 inches for Monida pass on Interstate 15, and around an
inch for Pine Creek Pass into Wyoming. Raynolds Pass should be
the standout for U S Route 20 with nearly 9 inches falling during
that same time.
Instability of the atmosphere is going up and there is a threat of
thunderstorms for Mon afternoon over the entire forecast area and
Tue afternoon over the eastern half. Do not expect severity issues with
less upper level support compared to yesterday (Sat) and
extensive cloud cover suppressing surface heating. Out flow could
still approach 45 to 50 mph.
Wind is expected to be in the breezy range with a wind shift Mon
night from south and west to the northwest. Do not expect Lake
Wind Advisory conditions at this time, although thunderstorms may
produce poor boating conditions. Messick
LONG TERM...WEDNESDAY THROUGH NEXT SUNDAY...
Not thrilled with the cool, wet, dreary wx in the short-term portion
of the forecast? Allow us to spread some spring cheer! All long-
range models and model ensemble clusters support a solid ridge of
high pressure building across the Great Basin/nrn Rockies for
Wed/Thurs/Fri with high forecast confidence, supporting mostly
clear/sunny skies and a warming trend with highs in the upper 50s/
upper 60s Wed surging into mid 70s/mid 80s by Fri. That`s 15-20
degrees above climatological normals for late April, putting record
high temps in jeopardy at all of our climate sites Fri. Sure enough,
ECMWF EFI (Extreme Forecast Index) values are topping out at 0.6-0.7
for MaxT, suggesting that an unusually warm event is likely compared
to the model climate period. That said, a comparison of our NBM-led
forecast to GFS/EC ensemble meteograms for MaxT suggest we`re right
where we should be with strong ensemble clustering 4 degrees either
side of our current forecast, so we didn`t make any nudges. On the
fire wx front, the warming trend will be accompanied by a drying
trend in afternoon MinRH values (potentially as low as 14-20% by
Thurs/Fri) along with diurnally breezy conditions, but depending on
how fuels respond to the current/ongoing wet period, we MAY be a
little more definitively entering our spring "green-up" by that time
which MIGHT take the edge off the early start to fire season we
have been dealing with this year. Still, something to be mindful of.
Next weekend, all 500mb height ensemble clusters support the ridge
breaking down to some degree, and a possible shortwave trough moving
across the nrn Rockies. EOF patterns suggest the current greatest
source of forecast uncertainty is how strong/amplified the trough
will be (which is reflected by a variety of solutions in the
deterministic models), with a secondary source of uncertainty tied
to exact timing of the trough. The 500mb height clusters reflect a
range in potential amplification as well, but they all currently
keep the trough axis west of our CWA Sat. SO, while an introduction
of clouds/potential precip ahead of the trough may take the edge off
of high temps, the generally warm pattern should continue.
Unsurprisingly, the clusters with a stronger/more amplified trough
yield solutions that are wetter than the mean, and given the heat
and overall synoptic picture, t-storms would be possible. Sun, high
temps and t-storm potential both revolve around timing of the
trough axis/associated cold front, with cluster analysis offering
roughly a 50/50 chance of our SE Idaho CWA spending most of the day
on the warmer pre-frontal side vs. the cooler post-frontal side of
this system, so stay tuned. All things considered, the NBM did a
great job of capturing all of these themes and trends, and very few
edits were made. - KSmith
AVIATION...Cool, dreary, moist, showery wx is the order of the
day across SE Idaho as a trough of low pressure continues to
slowly push east into the nrn Rockies, and while we may see a
SLIGHT overall lull in shower activity and a SLIGHT cig
improvement this afternoon for most terminals, clouds will hold on
at close to the VFR/MVFR threshold for most locales. Instability
(fuel) should remain too low for t- storms. This eve, all model
guidance supports a SW to NE oriented swath of more organized
precip returning for KBYI/KPIH/KIDA/KDIJ, starting as early as
01z/7pm at KBYI and 03-04z/9-10pm elsewhere (albeit with some
timing differences between the high-res guidance sources). This
should be followed in short order by cigs trending into MVFR
territory and staying there for the rest of the TAF period...while
confidence on start-time of this next round is a bit low because
of the model differences, timing confidence on the 06- 08z "cig
crash" FM groups for KPIH/KIDA/KDIJ in the 18z TAF package are a
bit more solid. HRRR guidance wants to go even lower into IFR
territory, but held closer to the MOS consensus for now and just
used the HRRR for timing...will see how things trend as NAM time-
heights somewhat follow the HRRR idea. Didn`t get too aggressive
with dropping vsbys for most sites as temps/dew points should be
just warm enough to support rain, but gosh...it`s going to be
CLOSE at KDIJ. If precip manages to switch to snow tonight, expect
vsbys to crash to 1-2 SM, which is not currently reflected in the
TAF. Meanwhile, KSUN may pull off quieter, VFR conditions tonight
and Mon AM. Mon afternoon/eve, the heart of the low pressure
system responsible for this wx rides the nrn NV border, with
continued unsettled and showery conditions expected (potentially
into at least Tue AM). A few t-storms will be possible Mon
afternoon. - KSmith