Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/21/24
AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
948 PM EDT Fri Sep 20 2024
.SYNOPSIS...
High pressure looks to linger across the Southeast with a series of
shortwaves passing through our area ahead of a developing area of
low pressure. Off and on rain chances will persist through the
forecast period. Cooler temperatures are expected to start next
week.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 945 PM EDT Friday...
Key Messages:
- Dry weather with patchy fog possible overnight.
Late this evening, low pressure was centered just off the srn
New England coast. Also, a potent area of high pressure was
centered over srn Texas and extends out towards the Gulf Coast
states. Under a clear to partly cloudy sky across the region,
temps were ranging from the lower 60s to the lower 70s.
Expect dry weather overnight, under a mostly clear to partly
cloudy sky. Patchy fog will be possible toward Sat morning.
Lows will range from the upper 50s to mid 60s.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
As of 245 PM EDT Friday...
Key Messages:
- Showers and storms expected Saturday evening into the overnight
hours.
- Becoming mostly dry and cooler to start the new week.
The ridge of high pressure will move a bit eastward along the Gulf
Coast this weekend while weakening. Shortwaves will ride along the
northern edge of the ridge into our neck of the woods. The first is
expected to move in later Saturday afternoon with increasing rain
and storm chances. Hi-res model guidance continues to keep the best
chances of rain/storms along and west of I-95 Saturday evening into
the early overnight hours. The Storm Prediction Center does have our
northwest CWA corner in a Marginal Risk for severe weather on
Saturday. The primary threat would be localized gusty winds,
especially where more daytime heating occurs and the storms move in
first. The HRRR tries to have a second round of activity move down
from the north during the early morning hours of Sunday and affect
areas east of I-95, but the NAM Nest and RAP aren`t as excited about
it. Did include a slight chance of rain for coastal locations
before sunrise on Sunday. Kept PoPs low for Sunday evening
aside from isolated showers across NE NC as we should
temporarily dry out.
Moisture lingers along the top of the ridge ahead of another
shortwave on Monday. The shortwave doesn`t move much through the
day, so any rain chances will likely be focused across the far
western edge of the CWA. High temperatures will be in the lower 80s
on Saturday, then cooling into the mid 70s by Monday.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 245 PM EDT Friday...
Key Messages:
- Low-end precipitation chances linger.
The area of high pressure looks to be traversing the far southeast
coast on Tuesday before sliding just offshore midweek. An initial
shortwave will cross the middle Mississippi River valley on Tuesday
before ejecting into the Great Lakes ahead of a developing cut-off
low further west. Here locally, we will be in southwesterly flow in
between the high pressure and low pressure, allowing moisture to
continue to slide in around the edge of the ridge. Rain chances
will try to nudge back in on Tuesday, but may get held up to
the western corner of the CWA depending on the position of the
high. Beyond that, models disagree on the position of the broad
area of low pressure, thus confidence in the forecast for
midweek and after is low. Generally, would expect low-end rain
chances to persist for now. Temperatures will gradually warm a
bit as thicknesses rise with the ridge pushing up the coastline.
Highs are forecast to be in the upper 70s to around 80 degrees.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
As of 805 PM EDT Friday...
Could see another round of fog overnight resulting in patchy
IFR or MVFR conditions near terminals. Kept it as a mention of
3SM at RIC, SBY and PHF for now where confidence is a little
higher. Conditions improve after 12-14z Sat morning.
Generally VFR conditions expected for most of the day on Sat.
However, shower and storm chances will return to the area late
Sat aftn through Sun morning, possibly affecting the TAF sites.
Outlook: Lower CIGs (mostly MVFR) will be likely in most areas
Sun into Sun evening, due to more moist NE or E flow. Isolated
showers will be possible also.
&&
.MARINE...
As of 340 PM EDT Friday...
Key Messages:
- Small Craft Advisories remain in effect for all coastal waters through
Sunday night.
- Confidence in potential Small Craft Advisory conditions across
the Chesapeake Bay/lower James River Sunday has decreased.
- Winds increase Sunday with persistent long period swells
keeping seas elevated into the middle of next week.
Sfc low pressure (~1003mb) lingers well off the NJ coast, with high
pressure centered across NewFoundland/Labrador. The stronger
pressure gradient remains offshore this afternoon, with NE winds
remaining around 10-15 kt with gusts up to 20 kt across the
coastal waters through tonight. Winds become variable 5-10 kt
Sat morning into Sat afternoon before becoming SE 10-15 kt Sat
evening. Cannot rule out a few gusts up to 20 kt across the
upper bay and rivers Sat evening, however, confidence is low.
The low off the Mid Atlantic coast gradually moves south Sun
into early next week. However, models continue to trend lower
with respect to NE winds Sun. There is still a decent surge of
NE winds expected on Sunday, but winds have trended towards 15
kt with occasional gusts up to 20 kt across the lower bay as
opposed to sustained 15-20 kt. As such, confidence is too low
for any headlines (outside of 3-4 ft waves at the mouth of the
bay) for the Ches Bay at the moment. A slow improvement is
expected by mid week, though SCAs for seas are still probable
into at least early Wed given the long period easterly swell.
Waves and seas were 1-2 ft (2-3 ft at the mouth of the bay) and 4-6
ft respectively this afternoon. Seas build to 5-7 ft by Mon before
subsiding by mid week. As such SCAs are now in effect for the
coastal waters this afternoon through Sun night. However, there may
be a period Sat night into early Sun morning where seas drop below 5
ft across the southern coastal waters. That being said, it appears
to be brief lull with seas building later Sun.
&&
.TIDES/COASTAL FLOODING...
As of 340 PM EDT Friday...
Tidal departures are fairly uniform across the entire area,
generally from +1.0 to +1.5 ft above astro tide levels. With rather
high astro tides given the full moon cycle as well as the typical
higher autumn tides, these departures have been enough to lead to
widespread minor flooding over the past few days. Over the next 24-
48 hrs, the onshore flow will persist with sfc low pressure
lingering well offshore and high pressure over eastern Canada nosing
a bit to the south into the weekend. Indications are for tidal
departures to increase into the +1.5 to up to +2.0 ft range by later
Saturday through Sunday (potentially continuing through the middle
of next week). Confidence has increased in reaching near or into
moderate flood stage across the Chesapeake Bay, Virginia Beach,
Currituck, and Accomack/Northampton for at least the high tide Sun
afternoon (potentially several high tide cycles in spots). As such,
have expanded the Coastal Flood Watch to included all of these areas.
In addition, a High rip current risk is in effect through
Saturday and will likely be extended into Sunday as well.
&&
.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...Coastal Flood Advisory until 10 AM EDT Saturday for MDZ021>023.
Coastal Flood Watch from Saturday afternoon through Sunday
evening for MDZ021>023.
Coastal Flood Advisory until 4 PM EDT Sunday for MDZ024-025.
NC...Coastal Flood Advisory until 6 AM EDT Saturday for NCZ102.
Coastal Flood Watch from 8 AM EDT Saturday through Sunday
afternoon for NCZ102.
VA...Coastal Flood Advisory until 6 AM EDT Saturday for VAZ076-078-
085-098-521-522.
Coastal Flood Watch from 8 AM EDT Saturday through Sunday
afternoon for VAZ098.
Coastal Flood Advisory until 8 AM EDT Saturday for VAZ075-077.
Coastal Flood Watch from Saturday afternoon through Sunday
evening for VAZ075-077.
Coastal Flood Watch from Saturday morning through Sunday
evening for VAZ076-078-085-099-100-521-522.
Coastal Flood Advisory until 6 PM EDT Saturday for VAZ083-084-
086-089-090-093-095>097-518-520-523>525.
Coastal Flood Watch from Sunday morning through Sunday
afternoon for VAZ084-086-523>525.
Coastal Flood Watch from Sunday morning through Sunday evening
for VAZ089-090-093-095>097.
Coastal Flood Advisory until 5 AM EDT Saturday for VAZ099-100.
MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ650-652-654-
656-658.
&&
$$
SYNOPSIS...JKP
NEAR TERM...TMG
SHORT TERM...JKP
LONG TERM...JKP
AVIATION...TMG
MARINE...RHR/RMM
TIDES/COASTAL FLOODING...AKQ
Area Forecast Discussion
National Weather Service La Crosse WI
1044 PM CDT Fri Sep 20 2024
.KEY MESSAGES...
- Showers and storms return for Saturday afternoon and evening
(50- 80% chance). An isolated strong to severe storm or two
cannot be ruled out with gusty winds and hail.
- Shower and thunderstorm probabilities linger into Sunday and
Monday, but are decreasing north of I90.
- More seasonal temperatures Sunday into early next week.
&&
.DISCUSSION...
Issued at 150 PM CDT Fri Sep 20 2024
Rest of Today - Saturday: More Showers and Storms For Saturday
Currently, water vapor imagery and 20.15z RAP 500mb heights show the
overall synoptic pattern with quasi-zonal flow over the local area.
To our west, a descending wave can be noted moving into portions of
Montana with an upper-level ridge to our south. Consequently,
temperatures today are relatively consistent with previous days with
high temperatures in the upper 70s to middle 80s. As we head into
tomorrow, the aforementioned upper-level wave pushes southeast with
an attendant surface cold front pushing eastbound. Ahead of this
front, weak warm air advection pushes northward into our local area
with some of the CAMs (mainly the FV3 and HRRR) have some showers
during the morning, however kept lower precipitation chances (10-
15%) for now with the weaker forcing regime.
The more substantial chance for any precipitation comes later into
the afternoon and evening as 850mb moisture transport increases,
aiding in advecting instability northward ahead of the cold front.
As a result, seeing many of the CAMs developing showers and storms
during the later afternoon hours. Overall the current thinking with
the 20.15z RAP/HRRR guidance keeps the better instability (2000-2500
J/kg of MLCAPE) across northeast IA where the strong moisture
advection is present. Shear profiles in model soundings are a bit
more questionable with 700mb winds being on the weaker side. This
can be noted with the 20.12z HREF ensemble with the soundings
showing weak effective inflow shear with median values around 15
kts. However, stronger synoptic flow at and above 500mb and
equilibrium levels eclipsing 200mb, storms could have some effective
shear to work with the inter-quartile spread in the 20.12z HREF
ensemble soundings varying between 30 to 35 kts which is on the
marginal side but could support some near-severe hail with
respectable mid-level lapse rates of 7 to 8 C/km in the 20.15z RAP.
Additionally with hints of some DCAPE (up to 1000 J/kg) along the
front during the afternoon, could see some gusty winds initially. As
a result, the SPC has our region in a Marginal Risk (threat level 1
of 5) for this lower-end potential.
Parts of the area received heavier rainfall of 1 to 3" Thursday
evening. Rainfall totals are mostly forecast to be 0.10 to 0.6"
through the weekend and the 3hr flash flood guidance is 2 to
3.5" for most spots. Some of the HREF guidance shows the potential
for localized higher amounts, thus will need to watch out for
those areas that are a little more primed and experience
stronger storms or storms repeating over the same area.
Sunday into Early Next Week:
Sunday morning, the 500mb pattern is progged to have an area
of closed low pressure over Ontario and another closed low over
northeast Colorado. The surface front is forecast to push
through the forecast area with surface high pressure building
into the the Dakotas. Drying is occurring from the northwest
with precipitation chances decreasing from the northwest.
However, the 850mb frontal boundary is still pushing through
parts of central and southern Wisconsin with deep moisture
nearby. The trend is southeastward during the day, then
returning northward Sunday night into Monday as the closed low
over Colorado tracks into Nebraska and pushes east as an open
wave Monday. Due to the latitudinal differences in the
deterministic models, the solutions vary from it being a washout
over parts of the forecast area south of I90 to being
completely dry Monday. Sunday morning to Monday morning, the
EC/GEFS/Canadian ensemble probability of 0.10" or more of
rainfall varies from 10% to nearly 80% near DBQ with the 20.00Z
run. Compared to the 19.12Z run, the northern gradient had
tightened and pushed southward slightly with it being drier
north of I90. Similarly, the trend from Monday morning to
Tuesday morning from the 12Z run yesterday to the 20.00Z run is
in the 20 to 40% range, but also trended southward of I90 with a
tightening gradient toward DBQ. We`ll see how this trends
through the weekend.
Our seasonal highs are in the lower 70s and we have highs in the
60s to lower 70s forecast Sunday through Tuesday. So, even
though it will be much cooler that recent days, it will be
closer to normal.
Mid to late-week:
The models diverge for again for mid-late week on where a
trough will evolve into a closed low over the Mid-Mississippi
River Valley or over the eastern Great Lakes. this will play
into the precipitation chances/cloud cover/winds/temperatures
for then. Temperatures are currently forecast to warm somewhat
with highs in the 70s to end the week.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1041 PM CDT Fri Sep 20 2024
Skies will be mainly clear tonight and then high and mid clouds
will move into the area on Saturday morning and early afternoon.
As a cold front moves toward the area during the mid- and late
afternoon, the CAMs are showing scattered showers and
thunderstorms possibly impacting the TAF sites. Since confidence
is not overly high, just introduced a PROB30 at KRST starting
at 21.21z and ending at 22.01z and at KLSE starting at 21.22z
and ending at 22.02z.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Naylor/Zapotocny
AVIATION...Boyne
Area Forecast Discussion
National Weather Service Billings MT
205 PM MDT Fri Sep 20 2024
.DISCUSSION...
Through Saturday night...
A few showers had developed N of the forecast area, ahead of the
approaching cold front this afternoon. Also, GLM and echo strength
supported isolated thunder. Added a small PoP across the northern
tier from 18Z-21Z, then kept the rest of the afternoon and
evening PoPs as they were from the earlier update. A few snow
showers are possible in the high elevations of the Beartooths.
Front still forecast to dive through the area from 21Z-00Z,
accompanied by gusty winds that will continue into tonight. Nudged
the gusts up toward the NBM 90th percentile based on what the
ECMWF meteograms were showing. Had localized patchy fog in the
forecast tonight through early Saturday. Cyclonic flow aloft on
Sat. will push E during the day. PWAT`s were low, so kept the
forecast dry. It will be cooler behind the front with highs in the
60s. Winds will be gusty E of KBIL under the stronger flow aloft.
Weak ridging will keep dry weather over the area Sat. night. HRRR
had some patchy fog over KSHR. Arthur
Sunday through Thursday...
Main forecast concerns next week are on precipitation chances Sunday
night into Monday then drying out with warming temperatures next
week.
The next weather system to pass through the region will be Sunday
night into Monday as a trough and cold front sweep through the area.
This system will bring medium chances for rain to the region along
with some snow for higher elevations. This system quickly exits the
area Monday afternoon then ridging builds in. WPC clusters continue
to indicate high confidence in ridging building over portions of the
western CONUS producing warmer and drier conditions for the region.
There is a 67 percent chance that highs will reach or exceed 75
degrees at Billings on Thursday with probabilities increasing to 78
percent on Friday. The ridge looks to break down later on Thursday
so will have to keep an on this period for timing of the frontal
passage.
&&
.AVIATION...
VFR conditions are expected through the TAF period. A cold front
sweeps through the region late this afternoon into tonight bringing
sct-bkn clouds with bases in the 4kft-7kft range. Isolated rain
showers are also possible. Surface high pressure returns by
Saturday morning with quiet weather expected the remainder of the
TAF period.
&&
.PRELIMINARY POINT TEMP/POPS...
Sat Sun Mon Tue Wed Thu Fri
-----------------------------------------------------------
BIL 043/061 040/073 051/068 045/072 048/080 052/081 052/080
20/U 00/U 13/W 10/U 00/U 00/U 00/U
LVM 034/063 034/075 043/067 040/074 044/081 047/080 047/079
00/U 00/U 24/W 10/U 00/U 00/U 01/U
HDN 041/062 036/074 045/069 042/073 044/082 048/082 047/081
20/U 00/U 03/W 10/U 00/U 00/U 00/U
MLS 044/062 039/072 046/071 045/071 046/080 051/081 050/081
20/U 00/U 01/B 00/U 00/U 00/U 00/U
4BQ 044/061 038/073 045/070 045/071 046/080 052/082 051/083
20/U 00/U 02/W 10/B 00/U 00/U 00/U
BHK 042/061 036/071 043/071 042/071 044/079 049/080 048/080
20/B 00/U 01/B 00/B 00/U 00/U 00/U
SHR 039/063 034/075 042/068 040/073 042/083 046/083 047/082
20/U 00/U 03/W 10/U 00/U 00/U 00/U
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.
&&
$$
weather.gov/billings
Area Forecast Discussion
National Weather Service Quad Cities IA IL
833 PM CDT Fri Sep 20 2024
.KEY MESSAGES...
- Highs in the mid 80s to near 90, or 8 to 15 degrees above
normal, are expected Saturday
- Marginal Risk for severe storms late Saturday afternoon into
the evening for the far NW CWA.
- Rainy and much cooler for Sunday and Monday with highs in the
mid 60s to lower 70s, which is slightly below normal.
- Dry conditions are expected to prevail Tuesday through Thursday
with temperatures in the low to mid 70s.
&&
.UPDATE...
Issued at 833 PM CDT Fri Sep 20 2024
Latest CAMs have become more robust with convection in the
afternoon as daytime heating destabilizes the the warm sector.
The 00z HRRR depicts a supercell that rides the sfc boundary SE
along the Mississippi River into NW Illinois in the
mid-afternoon, before bowing it out. Wind gust forecasts in the
HRRR suggests severe winds are possible with this cell. Then
later in the afternoon a wave moving across the warm sector
should lead to more strong to severe storms. Right now large
hail and damaging winds are the main threats. If we get that
supercell, then a tornado risk would exist as well. Another
wrench in the forecast are the storms out west right now. Where
do they end up and what kind of anvil shield could we see in the
AM. Regardless, environment is supportive of severe weather.
&&
.SHORT TERM /THROUGH SATURDAY/...
Issued at 224 PM CDT Fri Sep 20 2024
Tonight, high pressure will drift east of the area as a warm front
lifts northeast into SE IA and NE MO towards daybreak bringing
clouds and shower and storm chances to that area. In the meantime, a
pleasant night is expected, with evening temps slipping into the
upper 60s and 70s, nearly calm winds, and moonlit skies.
Temperatures will eventually settle into the upper 50s to mid 60s by
daybreak, with areas around Keokuk possibly only seeing upper 60s.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 224 PM CDT Fri Sep 20 2024
Saturday through Monday night, an upper level low will slowly be
moving from northern AZ, across the plains, and into the mid MS
Valley while a surface low moves across Canada with a trailing cold
front moving across the area. Some upper level waves will be drawn
up along this boundary during this time, bringing periods of better
rain chances to the region. This appears to be a good widespread
rainfall period of good wetting rains. Currently the WPC rainfall
forecast for the 3 days has amounts roughly of a half to 1 inch
forecast north of I-80 with 1 to 2 plus inches possible to the
south. There will be some dry periods, especially across the north
half of the CWA. The most likely chances are for late Saturday night
into Sunday morning and across the far south from Sunday evening and
overnight into Monday. SPC has a Marginal Risk area for the NW
quarter or so of the CWA. This is dependent on whether any
morning convection and debris clouds can clear out early enough
to help destabilize the atmosphere. Thunderstorms are forecast
to develop in the late afternoon into the evening with the focus
locally north of I-80, with the better potential off to the NW
where SPC has the Marginal Risk area. The main threats are hail
and damaging winds. Based on the last couple of HRRR runs, the
best timing is roughly from 5pm to 9pm.
Tuesday through Thursday, the forecast blend continues dry
conditions as high pressure builds into the region. Temperatures
will inch upwards from the upper 60s and low 70s Tuesday to the low
to mid 70s by Thursday. The GFS drops an upper low over MO and
IA mid to late week, which may result in some introduction in
POPs and cooler temperatures.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 615 PM CDT Fri Sep 20 2024
VFR conditions are expected through the period as high clouds
move into the area. Winds are expected to remain at or below 10
kts through the period. In the AM there is a 30% chance for SHRA
at BRL. CID may need showers/storms added to 06z TAF if better
agreement on timing of showers/storms can be attained.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.
&&
$$
UPDATE...Gibbs
SHORT TERM...14
LONG TERM...14
AVIATION...Gibbs
Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
648 PM CDT Fri Sep 20 2024
.KEY MESSAGES...
- Warm and Humid
- Storms Overnight into Saturday Morning
- Stronger Storms Possible Sunday
- Cooler Temperatures Next Week
&&
.DISCUSSION...
Issued at 250 PM CDT Fri Sep 20 2024
There are three primary H5 features that will contribute to active
weather through the remainder of this weekend. A 592dam high is
centered over Texas, that has been amplified toward the lower
Mississippi River Valley due to a deeper trough starting to come
ashore the southwestern CONUS. Meanwhile, another trough is moving
across the Canadian Prairie Provinces. The surface cyclone with the
Canadian system is starting to move toward Hudson Bay, with the cold
front stretching across much of the CONUS, and is currently moving
across Central Missouri as of the late morning and afternoon hours.
A brief period of H5 height rises has provided weak subsidence on
the backside of this cold front, which has been keeping conditions
dry through much of this afternoon across the forecast area. A weak
vort max is expected to eject ahead the deeper mid-level trough over
the southwestern CONUS later this evening, providing modest H5
height falls across our area and may interact with the cold front
that will be parked somewhere in the southeastern third of our
forecast area. The surface cyclone associated with this wave likely
stays over the High Plains, but surface southerly flow south of the
cold front should increase instability overnight for the
southeastern third of the forecast area, and we may see some
elevated instability develop further northwest. Current CAMs depict
thunderstorm development after 04z this evening and entering our
western counties around the 06z-07z timeframe. MUCAPE values off the
12z HREF are progged around 1500-2000 J/kg, with 0-6km bulk shear
values in the ball park of 25-30 kts. This may be enough to support
a few isolated severe storms producing wind gusts around 60 MPH and
hail around quarter size early Saturday morning. Steeper lapse-rates
between 700mb-500mb may foster a few stronger updrafts. However,
current HRRR and RAP soundings are very dry in middle portions of
the troposphere, which may be detrimental to deep convection
initiation as the forcing is moving through. This may even be a
potential source of later initiation time then what current CAMs are
depicting in simulated reflectivity fields. This first wave pushes
east by late morning. For the remainder of Saturday afternoon,
another short-wave trough and vort max eject out of the southwestern
CONUS and continue to develop a broad surface cyclone across the
Plains. This enhances low-level southerly flow as far east as the
Mississippi River Valley, and will start to push the cold front back
northward as a warm front. Along the warm front, expecting
isentropic ascent to promote additional shower development. If there
is any lingering elevated instability, a few thunderstorms may
become possible, though current CAM guidance suggest this travels
further north, impacting only far northwestern portions of the
forecast area. Regardless of storm mode, heavier rain showers are
expected most of the day as ensemble probabilities for measurable
rainfall are above 80 percent for most of the forecast area, and for
a threshold of .50 inches of QPF is nearly 50 to 60 percent.
Temperatures Saturday afternoon are expected to be generally in the
80s, with cloud cover keeping conditions slightly cooler, but WAA
will prevent a drastic cool down through most of the day.
Sunday, H5 trough lifts out of the southwestern CONUS into the High
Plains. Stronger dCVA occurs in the southern Plains as this moves
eastward, but mid-level height falls expand further eastward and
inverted surface troughing should extend into eastern Kansas through
Central Missouri. Stronger AVA over the Northern Rockies develops a
surface anticyclone that will push southward out of the Northern
Plains, and should set the stage for a stronger cold front to
develop across the Missouri River Valley heading into Sunday
afternoon. Amongst deterministic guidance, there is still discrepancy
in how far north the primary H5 kinematic forcing travels, and this
also impacts how far northward favorable surface pressure falls
occur with the surface cyclone, and how quickly the front moves
through the area. Overall ensemble probabilities for rainfall remain
high, with over 80 percent probabilities for any measurable
rainfall, and continued 50-60 percent probabilities for at least
0.50 inches of rainfall. Between Saturday and Sunday activity, some
areas may see as much as 2-3 inches of rainfall by the end of this
active pattern, which will be welcomed due to current drought
conditions across the region. The main uncertainty is with how
strong storms will be, and what the severe threat could look like.
Instability should not be an issue to come by, with high
probabilities for exceeding 1000 J/kg of MUCAPE. However, if the
cold front and forcing sink further south, stronger updrafts could
initiate closer to the Interstate 44 corridor Sunday afternoon into
evening. If the system takes track that is further north, areas up
to Interstate 70 or even Hwy. 36 could experience stronger deep
layer shear as well as better surface convergence that could
generate a few storms. Hail and wind would be the primary threat. If
the surface cyclone ends up in a spot where surface winds back
considerably, could see a concentrated corridor of enhanced SRH that
presents a brief tornado threat if storms were to be discrete.
However, uncertainty remains too high to confidently pinpoint any of
these mesoscale details at this time. In addition, instability
recovery from Saturday activity and cloud cover could also play a
large role in boundary strength and differential heating. Again,
even if severe storms fail to go, there should be enough forcing and
moisture around to still provide rain showers across much of the
area. With respect to any flooding concerns, most areas will be able
to handle 2-3 inches of rainfall, especially if it is spaced out
over 36 hours. Will only need to monitor a few urban areas for fast
responding creeks, but even these will be able to handle a decent
amount of rainfall given the dry conditions over the past few weeks
across the region.
Heading into next week, our area will be under prominent troughing,
with potential for a closed-low to remain directly overhead. This
will keep temperatures substantially cooler. Most points in the
forecast area next week have an inner-quartile temperature range
between the upper 60s and mid 70s. While there will be some lift in
the presence of the troughing overhead, the front from the weekend
likely pushes most of the moisture out of the area. Ensemble
probabilities for measurable rainfall through most of next week
remains lower. If we see long periods of cloud cover, we may see
multiple periods of light sprinkles move through. Overall
probabilities for any measurable rainfall after Monday are between
10 and 15 percent.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 630 PM CDT Fri Sep 20 2024
VFR conditions will likely prevail through much of this TAF
cycle, but a threat of thunderstorms will be present for much of
that time also. The nocturnal low level jet is expected to push
storms in Kansas east into Missouri this evening, arriving in
the vicinity of Kansas City between 03Z and 04Z. The storms are
rather high based, so VFR conditions will prevail expect if a
storm directly impacts a terminal. Additionally, once the storms
get in the vicinity the same LLJ might keep storms bubbling
across the region late tonight and again in the morning.
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...None.
KS...None.
&&
$$
DISCUSSION...Krull
AVIATION...Cutter
Area Forecast Discussion
National Weather Service Sioux Falls SD
1021 PM CDT Fri Sep 20 2024
.KEY MESSAGES...
- Rainfall amounts continue to trend down for the weekend,
though moderate chances (20-30%) for a tenth of an inch of
rain remain across portions of NW Iowa and NE Nebraska.
- With the passage of a cold front on Saturday, temperatures trend
downward to below normal levels for Sunday and Monday.
- Temperatures trend back to near normal levels for next week,
with a limited chance of precipitation through the period.
&&
.DISCUSSION...
Issued at 249 PM CDT Fri Sep 20 2024
With a weak high pressure system now well off to our southeast and a
cold front beginning to move into far western North Dakota, our warm
and semi-breezy conditions continue into the evening hours.
Observations show current temperatures in the lower to mid 80s,
possibly cresting the upper 80s in south-central South Dakota, with
breezy winds west of I-29 gusting into the 20s. While it does make
for rather pleasant conditions outside, given the low relative
humidity values in the 20s and 30s there is an elevated fire danger
risk. Heading into the overnight hours, a small quick moving surface
low pressure begins to moves through from west to east. Global
models and ensembles suggest scattered showers and tstorms may be
possible, though hi-resolution guidance is not convinced...so have
kept the overnight period dry, though a non-zero chance for
an isolated shower does exist.
As a closed off upper level low remains in the desert SW, an upper
level trough off to our north with the aforementioned cold front
will be moving through the area from northwest to southeast during
the day. The front will abruptly be swinging winds around to become
out of the north-northwest, with a few hours of stronger wind gusts
into the 30s and lower 40s possible behind the front, especially
along and west of I-29 into the mid-morning hours. While the timing
and location still needs to be better agreed upon, high-resolution
convection allowing models (CAMs) do show the potential for post-
frontal convection developing along the slightly lagging elevated
cold front. The HRRR is most aggressive with this possibility,
but it does have support from both the NAMnest and ARW, all of
which put down between a tenth and a quarter of an inch
sporadically. With 500- 1000J/kg of CAPE, depending which model
and layer one lifts from, along with 30-40 knots of wind shear,
marginally severe thunderstorms can`t be ruled out. However,
will need to monitor the convection that is expected to form
well south of the region (Nebraska/Iowa/Missouri/Kansas border),
as that could keep moisture from reaching up into the
region...SPC carries a marginal risk (level 1 out of 5) for
portions of the area along and east of a line from Sioux City to
Spencer, IA.
As the front continues to slide southeastwards, wind gusts into the
20s are expected throughout the afternoon hours. Given the cold
frontal passage throughout the day, daytime highs range from lower
70s near Huron, SD to lower/mid 80s by Storm Lake, IA. Heading into
the evening hours with the front well south/east of the area, models
continue to hold onto low (20-30%) chances for precipitation
generally along and south of the highway 20 corridor. Overall, for
the 24 hour period starting Saturday morning into Sunday morning,
the NBM and ensemble systems give a roughly 20-40% chance for a
tenth of an inch, highest in our southernmost counties
(Woodbury/Ida/Buena Vista) in Iowa.
Sunday will see the arrival of a surface high pressure, which will
continue to advect cooler and drier air across the region, keeping
precipitation chances low. NBM continues to hold onto 20-30% chances
for light rain south of I-90, but given the trends to push QPF
further south I would imagine pops will continue to lower over the
next model runs. However, Sunday will actually feel like fall across
the region with afternoon highs in the mid to upper 60s, along with
decreasing sky coverage throughout the day. Probabilities for
afternoon highs greater than 70 deg F are rather low in the 10-20%
range, outside of the warm-biased GFS, so these cooler temperatures
do have good ensemble support leading to higher confidence in these
cooler than normal temperatures.
While Monday warms up slightly into the upper 60s to lower 70s, the
below normal temperatures continue with mostly dry conditions. Model
uncertainty rises into the middle of the week as they disagree on
how the upper level pattern evolves, though they do all agree on
keeping the forecast mostly dry into the end of the week.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1018 PM CDT Fri Sep 20 2024
Mid-lvl moisture continues to slowly arrive late this evening.
As the LLJ and a weak wave approach from the southwest, some
isolated elevated convection will be possible over eastern
SODAK after 3am. This aforementioned LLJ may also bring a period
of LLWS through daybreak.
At the same time, a surface front will plunge southeast in the
morning, likely reaching KSUX/KOTG by mid-day, and then exiting
the CWA by 3pm. Behind the front, lingering mid-lvl clouds may
be possible, but more impactful is the gusty northwest winds
over 25 mph at times.
Most of the area will stay dry on Saturday, with some elevated
post frontal shower development near Highway 20 after dark.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&
$$
DISCUSSION...APT
AVIATION...Dux
Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1052 PM CDT Fri Sep 20 2024
.KEY MESSAGES...
- There is a marginal risk (5-15% chance) for severe weather along
and southeast of a Champaign to Taylorville line through 8pm
this evening. The primary concerns will be isolated damaging
wind gusts and large hail.
- Greater rain chances materialize Saturday night through Monday.
There is a 50-60% chance of 1-2 inches of rain across central
Illinois during that time period.
&&
.UPDATE...
Issued at 819 PM CDT Fri Sep 20 2024
This evening, a weak cold front is located roughly along a
Taylorville to Danville line. North of the front, dew points have
dropped into the 50s and skies have cleared except for a few
patches of cirrus. South of the front, warm and humid conditions
persist with dew points near 70 degrees. Scattered showers and
storms continue along and south of I-70 but have weakened in
intensity compared to a few hours ago. Storms should continue to
diminish as the boundary layer stabilizes with loss of daytime
heating. The severe threat has ended across this area and expect
the lingering showers and storms to end altogether by 10-11pm this
evening.
Deubelbeiss
&&
.SHORT TERM...(Tonight through Saturday)
Issued at 316 PM CDT Fri Sep 20 2024
19z/2pm surface analysis shows a weak cold front just east of the
I-55 corridor. Convective clouds have been slow to develop
along/ahead of the boundary due to synoptic subsidence in the wake
of the early morning showers: however, clouds have begun to get
organized over the past hour from Danville southwestward to near
Taylorville. This will be the zone to watch for widely scattered
thunderstorm development over the next few hours. The HRRR has
consistently delayed convection until after 22z/5pm, and this
looks reasonable given recent satellite/radar trends. Any storms
that fire will have moderate instability to work with as characterized
by MLCAPEs in excess of 2000J/kg. However, the strongest deep-layer
wind shear remains displaced well to the west and convergence
along the slow-moving boundary is meager. As a result, am only
anticipating widely scattered convection (20-30% chance)
along/southeast of a Champaign to Taylorville line through mid-
evening. A couple of the cells may be capable of damaging wind
gusts and/or large hail, but the overall severe risk will remain
low. After the evening showers/storms fade away, several CAMs are
suggesting fog development along/ahead of the front overnight. The
most consistent signal for widespread low visibilities and
potential dense fog has remained across northern Indiana, but
given high dewpoint air (65F+) think patchy fog is a good bet
across the E/SE KILX CWA after midnight. Will need to keep a
close eye on observations and latest model trends this evening, as
a Dense Fog Advisory may eventually be needed...particularly east
of the I-57 corridor.
Morning fog will quickly dissipate, leading to another partly
sunny and hot day with highs once again reaching the upper 80s and
lower 90s. A few showers may graze the far W/SW CWA during the
morning, with a few showers potentially re-developing west of the
I-55 corridor during the afternoon: however, most locations will
remain dry.
Barnes
.LONG TERM...(Sunday through Next Friday)
Issued at 316 PM CDT Fri Sep 20 2024
A vigorous short-wave trough evident on latest water vapor imagery
over Manitoba/Saskatchewan will dig southeastward into the Great
Lakes, pushing a stronger cold front toward central Illinois late
this weekend. 12z Sep 20 models are all in good agreement that the
front will push into west-central Illinois late Saturday night,
then linger across the region until Monday night when a second
wave across the Plains finally pushes the boundary further east.
Given copious deep-layer moisture from the Gulf of Mexico with NAM
precipitable water values climbing into the 1.75-2.00 inch range
and strong upper dynamics, the stage will be set for beneficial
rainfall across much of central Illinois. The latest projections
suggest widespread amounts of 1.50-2.50...with isolated higher
amounts where stronger storms materialize.
Once the system departs, cooler/drier weather will arrive across
the Midwest for the middle and end of next week. High temperatures
will drop into the lower to middle 70s and overnight lows will dip
into the lower to middle 50s Tuesday through Friday.
Barnes
&&
.AVIATION... (For the 06z TAFs through 06z Saturday Night)
Issued at 1052 PM CDT Fri Sep 20 2024
A weak cold front has settled south of the terminals with drier
air slowly filtering in from the north. Where the dew points
linger in the mid to upper 60s, there will be some fog potential
overnight into Saturday morning. This chance is greatest at CMI
and DEC and cannot be ruled out at SPI. Light and variable winds
and mostly clear skies are expected overnight. Winds will set up
out of the SE Saturday morning, then shift to the S/SSE around
10-12kt during the afternoon. Winds will diminish back below 10 kt
again with sunset Saturday evening. Another round of showers and
thunderstorms are expected across central Illinois, but beyond the
current TAF valid period ending 06Z Sunday.
Deubelbeiss
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Indianapolis IN
1133 PM EDT Fri Sep 20 2024
.KEY MESSAGES...
- One more hot day Saturday
- Isolated to scattered thunderstorms this evening into early
overnight
- Turning cooler and more active with greater rain chances Sunday
through early next week
&&
.FORECAST UPDATE...
Issued at 1003 PM EDT Fri Sep 20 2024
Convection coverage continues to decrease as the atmosphere over
parts of the area have been worked over already and as convective
inhibition builds with loss of heating elsewhere. Isolated strong
storms remain across the southern forecast area.
Expect convection coverage to gradually diminish into the early
overnight as inhibition strengthens. Will keep slight chance to
chance category PoPs through the early overnight, with PoPs
gradually diminishing from north to south. A strong storm remains
possible through about midnight across the far southern forecast
area, with gusty winds and small hail the primary threats.
Later tonight, as an inversion strengthens behind a cold front, low
level moisture will become trapped. Fog is likely to develop,
especially across the northern half of central Indiana. The latest
HRRR shows the potential for low visibility over much of that area.
For now, have upped wording to areas of fog in the northwest where
odds are highest for more widespread fog. Will keep a close eye on
it tonight for later updates.
Low temperatures look good, so just adjusted hourly forecasts to
account for areas that have experienced rain cooled conditions this
evening.
&&
.MESOSCALE UPDATE...
Issued at 1050 PM EDT Fri Sep 20 2024
Radar loop was showing the bulk of the convection and all of the
lightning strikes have moved into far south central Indiana, late
this evening. The heaviest cell was moving southeast across Knox
county where PWATS were above the 75th percentile, around 1.6 inches
per SPC mesoanalysis. The CAPE axis extended from around St. Louis
to Kokomo with 200 J/kg still over the upper Wabash Valley. A few
additional weak cells have popped up across areas north of
Indianapolis late this evening as well, and the cold front has
slowed down, so will add low chance PoPs back across northern
sections for the next few hours. Otherwise, with light winds and
clear skies away from convection, fog will be a concern, especially
over northern sections and the Wabash Valley per Hi-res guidance.
&&
.SHORT TERM (This Evening through Saturday)...
Issued at 146 PM EDT Fri Sep 20 2024
A broken line of convection continues to develop along a weak
frontal boundary across the lower Great Lakes. To this point...
development southwestward along the boundary back into northwest
Indiana and northeast Illinois has been a struggle...with warm air
aloft and a capping inversion between 850 and 700mb serving as
deterrents. Despite clouds moving across the forecast area from
earlier showers...18Z temperatures had warmed into the mid and upper
80s over much of the region.
It has been two weeks since there has been any sort of convective
threat to talk about...and the aforementioned frontal boundary to
our north will provide at least the opportunity for some locations
across central Indiana to see some much needed rain later this
afternoon into the evening. Remain a bit pessimistic on how
extensive the convective coverage will look and will discuss this in
greater detail below.
This Afternoon and Evening
Short range trends through the rest of the afternoon will be
critical in determining how convection evolves into the forecast
area through the evening. While the signal is there in most of the
model suite for scattered convection later...the CAMs have not been
overly helpful in the details so far today. While the presence of a
narrow axis of deeper low level moisture and an overall increase in
BL shear support convective development...the negative factors also
present are likely the main reason for the struggles from the
individual CAMs in addition to the mishandling of low level
moisture. These negative factors...
1) An abundance of dry air in the mid levels and a lingering cap in
the 850-700mb layer
2) poor lapse rates
3) impacts from dry antecedent surface conditions
In a nutshell...still feel the overall model suite is overdoing
convective coverage for late afternoon into the evening. The
available instability and shear alone is suggestive of convective
development...but anticipate that storms will be in a messy...
chaotic multicellular mode that likely remain scattered at best due
to the dry air aloft and the poor lapse rates. A rise in pops late
this afternoon into the evening is warranted but have a hard time
justifying much higher than 30-40 pops at this point and focused
primarily across the northern half of the forecast area. Lightning
and brief heavy rainfall will be the primary impacts to Friday
evening activities but there remains the possibility for locally
gusty winds with any collapsing cells.
Late Tonight through Saturday
The frontal boundary will migrate south tonight and eventually wash
out across the southern part of the state by Saturday morning.
Cannot rule out a few showers accompanying the boundary south
overnight but dry conditions are expected across the forecast area
prior to daybreak Saturday. Model soundings are supportive of a
sharp nocturnal inversion developing in the predawn hours and with
light flow and the potential for an infusion of moisture from any
rain later today in the near surface layer...the fog potential is
elevated towards daybreak Saturday and focused especially across
northern parts of the forecast area.
Any fog will burn off quickly Saturday morning with ridging aloft
and a weak surface high reestablishing over the region. Expect yet
another hot day with dry conditions and mostly sunny skies in tandem
with light E/SE flow. Mid and high level cloud coverage may increase
subtly late day Saturday...signaling a welcome transition to a more
unsettled and cooler regime Sunday into the first half of next week.
More on this in the Long Term discussion below.
Temps...lows will slip down into the lower 60s over northern
counties where a light northerly flow will develop in wake of the
front. Further south expect mid and upper 60s. Low level thermals
support upper 80s and lower 90s on Saturday but this will put a wrap
on the recent stretch of hot weather with cooler temps to follow
into early next week.
&&
.LONG TERM (Saturday Night through Friday)...
Issued at 146 PM EDT Fri Sep 20 2024
Saturday Night Through Monday.
The pattern continues to trend more active for late this weekend
into early next week as a frontal system associated with a broad
trough across southern Canada pushes through the Midwest. Latest
model runs and ensemble guidance suggests that the frontal passage
is likely late Sunday into Sunday night with scattered to numerous
showers out ahead of the front. A secondary wave just behind the
main wave then looks to move through on Monday with the potential
for heavier showers. The QPF for the initial event is likely a bit
overdone with the very dry antecedent conditions but with saturation
from the first event, some appreciable rainfall looks likely by
Tuesday but there remains quite a bit of uncertainty as to where the
higher axis of rain will fall.
There is high confidence in much cooler air behind the front with
highs in the upper 70s to 80 on Monday followed by the low to mid
70s through the rest of the week.
Tuesday Through Friday.
Forecast confidence begins to fall off by Tuesday as models struggle
on how quickly to push the Monday system through with at least a
decent chance for wet conditions to continue into Tuesday before
conditions begin to dry out for the middle of the week. There will
remain some low chances with weak impulses within the northwesterly
flow aloft, but the best forcing will be well gone by late Tuesday
into Wednesday.
Focus then shifts to the low potential for more appreciable rainfall
towards the end of the work week with models showing there may be a
seasonably strong closed low to the west of Indiana which would
advect significant amounts of Gulf moisture into the Ohio Valley.
This scenario looks unlikely based on how ensembles are handling the
low, but there is a decent number of individual members that show
the heavy rain outcome and will need to be monitored going forward.
Looking beyond Friday into the weekend, tropical moisture looks to
continue to advect northward which could keep the active pattern
going into the following week.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1132 PM EDT Fri Sep 20 2024
Impacts:
- IFR and worse fog is expected to develop toward daybreak,
especially at the smaller airports that received the most
rain
Discussion:
Would not completely rule out brief convection at KBMG early in
the TAF period. Otherwise, could also see a shower or thunderstorm
after 06z Sunday at KIND as another cold front approaches from the
west and interacts with a very warm, moist and unstable atmosphere.
Otherwise, IFR and possibly worse fog and or stratus will be the
main concern overnight, especially at the smaller airports.
Winds will be most very light to calm through the TAF period.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
MESOSCALE...MK
UPDATE...50
SHORT TERM...Ryan
LONG TERM...White
AVIATION...MK
Area Forecast Discussion
National Weather Service Louisville KY
941 PM EDT Fri Sep 20 2024
.KEY MESSAGES...
* Above normal temperatures continue this weekend
* Slight chance (20 percent) for showers and storms this evening
and overnight for southern Indiana and the Ohio River vicinity
* Slight chance continues for central Kentucky during the day
Saturday as a weak frontal boundary stalls over that region
* More widespread precipitation chances arrive early next week
ahead of a cold front.
&&
.UPDATE...
Issued at 941 PM EDT Fri Sep 20 2024
Weak frontal boundary to our north continues to serve as a focus for
convective development this evening. Much of the activity has
remained well north of the the CWA. Have been monitoring a couple
of clusters of storms. The first is in the Bloomington, IN area
with a secondary cluster out west of Vincennes, IN. This activity
is moving southeast and may hold together over the next few hours
and eventually get into perhaps portions of Dubois/Orange county
after midnight.
The boundary to the north is forecast to drop southeastward tonight
and may produce some additional convection across southern IN and
into portions of north-central KY after midnight. Latest HRRR runs
continue to suggest this scenario, though overall coverage still
looks to be 20% or less. Severe weather is not expected with this
activity as the boundary layer will continue to stabilize. However,
PWATs ware up above 1.5 inches to around 1.75 inches so locally
heavy rainfall will be the main weather hazard. Given the dry
conditions, this should not cause any hydro issues, in fact, this
would be quite welcome rainfall. Current forecast has all of this
well in hand.
&&
.SHORT TERM /THROUGH SATURDAY/...
Issued at 323 PM EDT Fri Sep 20 2024
Weak cold front is generating shower/storm activity over northern
Indiana this hour, with a notable gap of surface-based cloud cover
over central Indiana. This front will accelerate some southward this
evening, as storm-generated cooler air pushes it. However, as those
storms weaken approaching the Ohio Valley, that push will end and
expect a stalled boundary to set up somewhere along the Ohio River
Valley late tonight and through Saturday. This boundary should serve
as the focus for isolated to widely scattered convection.
Precipitable waters will be well above normal, in the 1.5-1.7" range
in this vicinity. Given potential for slower motions along the
boundary, heavy rain is a concern, but falling over short-range
drought stricken areas will alleviate that concern somewhat.
Added cloud cover should help out with temperatures tomorrow, but
still expecting above normal readings, both for morning lows thanks
to that moist airmass and afternoon highs, still in the upper 80s to
around 90. Given the added moisture, heat indices actually may end
up a few degrees warmer than today...so something to be mindful of
with any outdoor weekend activities.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 323 PM EDT Fri Sep 20 2024
Saturday Night - Tuesday...
As we head into the second half of this weekend, a pattern shift
will begin to take place that will bring more active weather to the
Ohio Valley for the first half of next week. A northern stream upper
trough ejecting from Manitoba toward Hudson Bay will bring a surface
cold front into the upper Midwest, with the front expected to hang
north and west of the region at least through the day on Sunday.
Increasing low-level moisture ahead of the front will aid in the
development of showers and thunderstorms Saturday night into Sunday
over central IL and IN, with some of this activity spilling into our
area on Sunday. Confidence in temperatures will decrease as the
front approaches, as uncertainty related to the existence of rain
and clouds leads to increased spread in guidance. Expect a general
northwest-southeast gradient in temperatures on Sunday, as more
cloud cover/rain will limit warming along and north of the Ohio
River. Across eastern and south central KY, another day of well-
above normal temperatures is likely, with highs in the upper 80s and
low 90s.
For the beginning of next week, a southern stream open-wave trough
over the central Rockies is expected to eject eastward toward the
Mississippi Valley. As the system pushes eastward, another sfc wave
is expected to develop along an elongated baroclinic zone located
just northwest of the region. This second wave will bring more
widespread shower and storm chances Monday into Tuesday as the front
and upper wave gradually push east. Low-level moisture just ahead of
the front will increase instability, with 12Z GFS showing 1000-1500
J/kg SBCAPE across southern IN and north central KY Monday
afternoon. Mid-level flow will be modestly strong, allowing for wind
shear that will be marginally supportive for organized convection.
Can`t rule out a few strong storms Monday afternoon and evening,
though machine learning and other severe proxy guidance are not
particularly concerning at this time.
The unsettled pattern will continue into Tuesday as the front
lingers in the area. Temperatures should continue a downward trend,
though ensemble members and NBM probabilistic guidance continue to
show higher levels of spread, likely due to uncertainty in
prevalence of clouds and precipitation.
Mid-to-Late Next Week...
Model divergence in the synoptic pattern increases considerably from
Tuesday through the end of next week, leading to a wide range in
potential impacts. WPC ensemble cluster analysis shows two general
families of solutions late next week.
The first solution, represented in general by the 00Z (and to a
lesser extent, the 12Z) operational ECMWF, has a farther eastward
progression of the aforementioned upper trough by the middle of next
week, with the trough axis centered near the lee of the Appalachians
for the second half of next week. This solution brings the drier
post-frontal air mass all the way into the region, leading to
seasonable temperatures and relatively uneventful weather for mid-
late next week.
The second solution, represented by the 12Z operational GFS, has the
upper trough hang back to the west of the Mississippi Valley,
keeping our area in a humid and unsettled air mass on the east side
of the trough. This solution would lead to continued rain chances
through most if not all of next week, and would be much more
beneficial for ameliorating local drought concerns. Unfortunately,
this solution would increase the potential for tropical activity as
a disturbance which is expected to develop near the Yucatan
Peninsula early next week gets pulled into the central Gulf of
Mexico (and potentially farther north toward our area).
These two solutions have roughly equal percentages of ensemble
support (the first solution is slightly greater) in the 00Z ensemble
guidance, and forecast confidence in any one solution remains low,
with the current forecast sort of splitting the difference between
the two. Stay tuned as significant changes to the forecast for next
week may be required as subsequent model guidance comes in later
this weekend.
&&
.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 714 PM EDT Fri Sep 20 2024
VFR conditions are expected through the upcoming TAF period. Look
for southwest to west-southwest winds this evening and these should
slacken off after sunset. Will continue to watch storms to the
northwest of the region to see if they can make it down into
KHNB/KSDF by late evening. Current indications suggest this is a
low probability scenario, so will continue to leave TAF`s dry with
this package.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Air Quality Alert until midnight EDT tonight for KYZ029>031.
IN...Air Quality Alert until midnight EDT tonight for INZ077>079-
090>092.
&&
$$
UPDATE.......MJ
SHORT TERM...RJS
LONG TERM....CSG
AVIATION.....MJ
Area Forecast Discussion
National Weather Service Marquette MI
629 PM EDT Fri Sep 20 2024
.KEY MESSAGES...
- Isolated showers and maybe a thunderstorm possible this evening
east half. Patchy fog forming late tonight/early Saturday mainly
central and east.
- Extended stretch of well above normal temperatures continues
through Saturday with highs mainly in the upper 70s and 80s.
- Multiple rounds of precipitation possible through the first half
of next week. Thunderstorms that do form are not expected to be
severe at this time.
- Temperatures around normal are expected to return next week.
&&
.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 356 PM EDT Fri Sep 20 2024
Latest water vapor imagery and RAP analysis shows shortwave trough
slowly progressing east through the east half of Upper Mi with the
visible satellite imagery showing widespread diurnal cu across the
U.P. Subsidence/mid-level drying behind this shortwave feature has
resulted in dry conditions today over western Upper Mi. Central and
eastern sections of the U.P. have seen a few isolated showers pop up
in the vicinity of the mid-level trough axis and focused along
outflow boundaries/lake breezes especially east of MQT in the past
hour. This environment has also been more favorable for convection
as lower to mid 60s dew points have led to MLCAPE values approaching
1000 j/kg central and east. However, build up of convection over the
central and eastern U.P. has been largely inhibited by strong mid-
level drying as noted on fcst soundings. Afternoon temperatures have
been mostly in the 70s although a few lower 80s readings have been
observed over the interior west.
Other than some lingering isolated showers/t-storms over the east
mainly early this evening, expect dry conditions to prevail as
shortwave ridging and associated subsidence builds across the area
from the west. Moist dew points in the upper 50s and lower 60s along
with clearing of diurnal cu and light winds will likely lead again
to patchy fog forming overnight into portions of central and eastern
Upper Mi. Fog could become locally dense over eastern portions.
Expect min temps generally lowering into the 50s with a few upper
40s readings possible over the typical cool spots of the interior
west.
&&
.LONG TERM /SATURDAY THROUGH FRIDAY/...
Issued at 415 PM EDT Fri Sep 20 2024
Active weather pattern to begin the long term forecast as the
sensible weather will be dictated by the evolution of multiple
shortwaves passing in the vicinity of the Upper Great Lakes through
early next week. Following Saturday`s well above normal
temperatures, more seasonal temperatures return Sunday and beyond
with highs in the 60s. While there is enough spread in the ensembles
in the back half of the week to keep slight-chance (~20%) PoPs in
the forecast for the eastern portions of the UP through the week,
ensembles have continued to trend more dry with each ensemble suite
run. Beyond next week, ensembles still favor ridging over the
central CONUS, potentially leading to downstream high pressure over
the Upper Great Lakes, which aligns with the CPC 8-14 day and 3-4
week precip outlooks which put the UP in a below normal precip
pattern.
Saturday will begin dry as weak surface ridging fills in behind the
departed cold front. Mostly clear skies will allow highs to climb
back to around 80. While this is unseasonably warm, the NBM gives
less than a 5% chance of breaking a record high at the MQT WFO.
However, if the WFO does break 80, it would be the most 80 degree
days in any September, showing how unusually warm this stretch has
been. The break in the clouds and precip will be brief however as a
~1005mb low will quickly jet along just east of the Manitoba/Ontario
line, bringing showers and non-severe thunderstorms to the UP for
overnight Saturday through Sunday along the low`s cold front. Recent
runs have brought this low closer to the UP, which means that
dynamic support for rainfall and thunderstorms should be better. No
severe weather is expected though as HREF mean SBCAPE Saturday
evening is only around 500 J/kg at most, though 0-6km shear at least
looks modest at around 30 kt. Precip totals for this system look to
be around a quarter of an inch, so nothing extreme, but welcome
rainfall for a lot of areas that have struggled to get precipitation
this month.
Once the front departs Sunday night, the next feature to watch will
be a 500mb trough that will exit the Four Corners region Saturday
night. Ensemble spread is still high as to the impacts of this
system as the trough could potentially interact with a Alberta
Clipper-style trough that will be approaching the Upper Great Lakes
at approximately the same time and there is disagreement as to the
strength of each system and the track of the resulting surface
features. Regardless of the exact solution, the NBM continues to
trend more dry, with the western UP now strongly unlikely to see
precip (PoPs less than 15%) and the eastern portions only have PoPs
around 30%. If clear skies can verify Monday and Tuesday morning,
interior low temperatures could get a bit cold, with bias-corrected
MOS guidance suggesting lows in the upper to mid-30s in the interior
west Monday and the widespread interior on Tuesday. Should mid-30s
verify, there is a chance for patchy frost (~20%) those mornings.
Moving into the second half of the work week, the 12Z GEFS shows
anomalous ridging building over the Northern Plains and Canadian
Prairie with 500mb height anomaly reaching +20 dam over Manitoba by
Thursday morning. Downstream high pressure of that ridge would tend
to have the UP rather dry moving into late September, and with the
GEFS showing preference for anomalous ridging over the central CONUS
throughout the run, the CPC outlooks of less than normal
precipitation will be on-track.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 628 PM EDT Fri Sep 20 2024
Expect VFR to prevail at all terminals through the period.
&&
.MARINE...
Issued at 415 PM EDT Fri Sep 20 2024
Westerly wind gusts to 25 knots over the western portions of Lake
Superior will gradually diminish tonight now that the cold front has
completely passed over the lake. Localized surface ridging will keep
wind gusts under 20 kt until Saturday evening, where another passing
cold front will allow westerly and northwesterly wind gusts to 25
knots over the western half of the lake Sunday morning and up to 30
kt over the eastern portions of the lake during the day Sunday. This
will force waves up to 4 feet along the shores of the Keweenaw
Peninsula Sunday morning and waves of 4-6 feet over the east half of
the lake throughout Sunday. Thunderstorms are possible with this
front, but are not expected to be severe. Winds are currently
forecast to be below 20 kt next week, but a couple of shortwave
troughs approaching the Upper Great Lakes in the first half of the
week could force a few gusts to 25 kt, but uncertainty is too high
at this time to say exactly where, when, and how those gusts may
occur.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Voss
LONG TERM...GS
AVIATION...07
MARINE...GS
Area Forecast Discussion
National Weather Service San Diego CA
205 PM PDT Fri Sep 20 2024
.SYNOPSIS...
A low pressure system moving across southern California will
continue to bring scattered thunderstorms for this afternoon and
early evening in southwestern San Bernardino and western
Riverside Counties, with the greatest potential for heavier
rainfall in the San Bernardino Mountains and the Mojave desert.
For Saturday through Monday, dry with a warming trend with high
temperatures warming to around 5 degrees above average for inland
areas on Monday. Generally fair weather with seasonal temperatures
will continue for Tuesday through Thursday, but with greater
spread in the temperature guidance for the coast and valleys.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
This afternoon...The low pressure system over SoCal is moving
quickly eastward and should be over the lower Colorado River
valley by late this evening. It`s producing scattered showers and
tstms over much of the region. Tstms cover much of southwestern
San Bernardino County and western Riverside County. Currently,
there are no storms in Orange or San Diego Counties but the storm
cells are moving to the southwest in the flow around the upper low
and could reach those counties later this afternoon and evening.
At least for a relatively brief period before the low and
associated dynamics moves too far to the east.
From previous forecast...
Temperatures today will remain well-below seasonal averages, as much
as 15 to 20 degrees below average for the mountains and inland valleys,
with high temperatures for the Inland Empire mostly in the 70s.
Dry and warmer conditions are expected this weekend. On Saturday,
greater warming is expected for the mountains and deserts with
slower warming for the coast and valleys. Warming will continue on
Sunday with the greater warming for the coast and valleys. High
temperatures on Sunday will return to around seasonal averages,
with high temperatures in the mid 80s to mid 90s for the Inland
Empire and around 100 for the lower deserts.
The warming is expected to continue into Monday, with high
temperatures for inland areas around 5 degrees above average,
mostly in the 90s for the Inland Empire and around 105 for the
lower deserts.
The marine layer will persist and low clouds will cover much of
the area west of the mtns tonight. each night and morning.
Generally fair weather with seasonal temperatures will continue
for Tuesday through Thursday, but with greater spread in the
temperature guidance for the coast and valleys.
&&
.AVIATION...
202030Z...SCT to locally BKN low clouds based at 2500-3500 ft MSL
present along the coast into inland San Diego County.
Meanwhile, BKN cumulus/CB and thunderstorms based at 7-10k ft MSL
extend from the San Bernardino and Riverside mtns into the northern
Coachella Valley and the Inland Empire. These are moving CCW around
a low pressure system, which is currently over northern SD/south-
central Riverside counties but moving east rapidly. Thunderstorm
chances continue for the aforementioned areas as well as the eastern
Santa Ana mtns, most likely through 00Z this evening as the low
pressure moves off to the east but isolated storms could continue
through 02Z. Lightning, erratic and gusty winds, local moderate
up/downdrafts, and reduced vis in locally heavy rain expected near
thunderstorms.
Mid-level clouds will clear late this evening into the overnight
inland, but low stratus clouds rebuild again along the coast between
03-06z this evening, with bases around 2000-2500 ft MSL lowering to
around 1500-2200 ft MSL early Sat AM. These will move inland to
cover the entire coastal basin overnight. Clouds clearing to the
coast 17-19Z Sat, with otherwise clear skies Sat.
&&
.MARINE...No hazardous marine conditions are expected through
Wednesday.
&&
.HYDROLOGY...
A low pressure system moving across southern California will
continue to bring scattered, mostly light showers and thunderstorms
for this afternoon and early evening. The low will move
southeastward across southwestern San Bernardino and western
Riverside Counties this evening. The greatest potential for any
heavier rainfall is in the San Bernardino and Riverside County
Mountains. Hourly rainfall rates of up to four-tenths of an inch
will be possible, with totals of up to one-half in the San
Bernardino Mountains by about 8 pm.
The most likely location for any mud and debris flows from recent
fires would be with the Line Fire in San Bernardino County. While
much of the higher resolution guidance shows peak hourly rainfall
rates to around four-tenths inch, there is greater uncertainty in
the timing of any heavier rainfall during the afternoon. Some of
the guidance has the peak earlier in the afternoon while some of
the more recent HRRR model guidance is later in the afternoon,
between about 4 and 7 pm.
The current local NAM-bounded WRF model solution is showing an
overall slight slowing of this low pressure system. Indications
are now for showers/tstms persisting in extreme southwestern San
Bernardino County and western Riverside County until 7-8 pm today.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
PUBLIC...PG
AVIATION/MARINE...CSP
Area Forecast Discussion
National Weather Service Las Vegas NV
146 PM PDT Fri Sep 20 2024
.SYNOPSIS...A low pressure system moving through southern
California will continue to produce scattered to numerous showers
and thunderstorms through tonight. Heavy rainfall is possible with
the stronger storms along with gusty winds. Drier conditions will
resume Saturday onward with a warming trend commencing.
&&
.DISCUSSION...Through next Friday.
Impacts in the way of locally heavy rain(flooding), gusty winds and
hail from thunderstorms associated with the slow moving upper low
will stay with us through tonight.
Upper low presently east of Los Angles will continue to slowly
trudge east through southern California into early this evening. The
low will then start to accelerate east across western Arizona late
tonight/Saturday. Several stronger cells that passed over rain
gauges have produced between 0.50"/hr to 1"/hr. On such storm did
close Highway 127 north of Baker.
Storm coverage has already started to diminish across the western
Mojave Desert, but new showers and thunderstorms will continue to
develop and expand in coverage over southern Nevada and northwest
Arizona the rest of this afternoon through tonight. As for gusty
winds, HRRR has been somewhat consistent run-to-run suggesting a
period of gusty north-northeast winds (35-45 mph) impacting the Las
Vegas Valley, northern Clark and southern Nye Counties in a window
between 5 pm and 9 pm this evening.
There may be a few showers lingering in eastern Clark and southeast
Lincoln County tomorrow morning through 8 am PDT, otherwise any
shower coverage will be confined to northwest Arizona tomorrow.
Intermountain West will be under a dry northwest flow early in the
week with GEFS/EPS both showing a weak open trough dropping
southeast across Utah/Colorado. This will usher in some locally
gusty north winds Tuesday, as well as produce a slight dip in our
temperatures. The rest of the week looks dry with high pressure over
the Great Basin and Desert Southwest.
&&
.AVIATION...For Harry Reid...Showers and thunderstorms will be in
the forecast through tonight as an area of low pressure moves east
across southern CA/NV. Expect mainly vicinity showers through 00z
with a general southeast to northwest movement. Winds are expected
to be easterly with speeds around 8 kts, but southeast winds around
8 knots can`t be ruled out as showers and storms develop. It is also
possible that we could see more a more variable wind direction at
times due to showers and thunderstorms in the vicinity. Storm
chances will continue after 03z, but are expected to move from a
northeast to southwest direction. Gusty and variable outflow winds
are also possible through the evening with gusts up to 25 knots are
times. Sky conditions will range from scattered to broken today with
bases AOA 8kft AGL, followed by improving skies overnight with bases
lifting to around 12kft AGL by daybreak Saturday.
For the rest of southern Nevada, northwest Arizona and southeast
California...Low pressure moving across southern California today
and northwest Arizona overnight will bring the threat of showers and
thunderstorms to the region. KDAG will see the threat of showers
and storms through this afternoon before diminishing this evening.
The Colorado River TAF sites will see chances increase late this
afternoon and early evening and have included VCTS in both EED and
IFP TAFs. Conditions will improve by Saturday morning, with all but
the far eastern sections of the region seeing precipitation chances
end. Aside from gusty winds near thunderstorms, winds will be from
the east to southeast in most areas, with sustained speeds of 12
knots or less. Winds at KBIH will be primarily from the north
through the TAF period. Sky conditions will range from scattered to
broken today with bases AOA 8kft to 10kft AGL, followed by improving
skies west to east overnight with bases lifting to around 12kft AGL
by daybreak Saturday.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
DISCUSSION...Pierce
AVIATION...Gorelow
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