Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/22/24
Area Forecast Discussion
National Weather Service Grand Junction CO
536 PM MDT Sat Sep 21 2024
.KEY MESSAGES...
- An early fall storm will bring showers and storms through
tonight with mountain snow, mainly above pass level, though
Vail, Monarch and Red Mountain passes are likely to experience
wet, slushy snow tonight.
- Unsettled conditions remain in place through Monday, with
afternoon thunderstorms possible, mainly over higher terrain,
before drier conditions move in Tuesday through the end of the
week.
- Temperatures rebound to near normal Monday and Tuesday
followed by a warming trend during the latter part of the week
as high pressure builds over the region.
&&
.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 314 PM MDT Sat Sep 21 2024
Showers and thunderstorms came this morning across southeast
Utah and spread into southwest Colorado as advertised with these
storms starting off fairly robust on the leading edge of the
wraparound precipitation on the eastern and northern sides of
the low. Also hinted by the models, a dry slot has wrapped up in
the center of the closed low over the Four Corners this
afternoon, shutting down convection in that region. CAPE values
were fairly decent in the 500 J/kg range this morning across
southeast Utah and southwest Colorado, with that region in the
left exit region of the upper level jet, so forcing was
sufficient for thunderstorms. However, the latest HRRR indicates
CAPE reducing to less than 100 J/kg later this afternoon and we
are seeing a reduction in the strength of convection this
afternoon as showers are becoming more stratiformed with
embedded thunderstorms here and there. Gusty outflow winds of 30
to 40 mph have been observed and expect this to remain the case
through this evening as the wraparound moisture continues around
the closed low. Small hail was detected earlier in the day but
thinking this concern is waning as top down saturation begins to
occur with the advection of cooler air associated with the low. The
closed low will track through southwest to central Colorado
this evening, staying around central Colorado overnight before
exiting to the east Sunday morning.
Speaking of cooler air, snow levels look to lower to around
10kft this evening, which is the period that some snow will
accumulate at elevations above 10kft, focused on the central
Colorado mountains where the closed low appears to stall
overnight before moving out. Models were quicker with the
progression of this closed low today and this is seen on
satellite and radar trends. Snow accumulations look to be
around 2 to 4 inches with the best chances overnight but pass
level should remain wet to slushy in spots with limited impacts
if any. Some light snow will linger over the high terrain
through Sunday morning and models are indicating some isolated
to scattered shower and storm development over the western
Colorado divide mountains Sunday afternoon, but overall drier
northwest flow should be pushing in by Sunday afternoon with
little additional accumulation. Sunday night is expected to be
quiet with breezy northwest flow ahead of a quick moving
disturbance set to move through Monday. Temperatures on Sunday
will be markedly cooler with highs 5 to 10 degrees below normal
in the wake of this fall storm, right on cue with the official
first day of Autumn!
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 314 PM MDT Sat Sep 21 2024
Monday afternoon, a quick moving shortwave trough will pass
through the area from the northwest, leading to some isolated
showers and storms over the western Colorado mountains. Other
than that, should be a relatively quiet day as lower valleys
look to remain dry with the mountains picking up some convection
but probability and PoP chances seem to remain on the lower end.
Blended guidance is finally starting to fall in line with the
overall drying trend that was seen in the deterministic models
since Friday`s morning run with a strong ridge of high pressure
building across the western half of the CONUS Monday, shifting
overhead by mid week. Despite a weak shortwave trying to disrupt
the ridge next Thursday across the Northern Rockies, this really
has a minimal impact as the ridge rebounds and remains in place
through next weekend. So, confidence is higher that Tuesday
through the end of the coming week will remain dry with
temperatures warming back to near to slightly above seasonable
levels by Wednesday and perhaps as much as 10 degrees above
normal by the latter half of the coming week.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 533 PM MDT Sat Sep 21 2024
An area of low pressure continues to lift northeastward through
the area this evening, bringing scattered showers and
thunderstorms, as well as a concentrated area of light to
moderate stratiform rain. VFR conditions should prevail, but
occasional drops into MVFR will be possible over the next 6
hours. Higher elevation terminals, such as KTEX and KASE, may
see some snow mix in with rain showers. Gusty and erratic winds
remain a threat, although lightning is dwindling with the loss
of daylight. Clearing will begin across the south around 06z
tonight and gradually work northward, with all terminals seeing
clearing between 12-15z tomorrow morning. Winds will be
primarily easterly to southeasterly through the period.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&
$$
SHORT TERM...MDA
LONG TERM...MDA
AVIATION...TGJT
Area Forecast Discussion...Updated
National Weather Service Lincoln IL
742 PM CDT Sat Sep 21 2024
.KEY MESSAGES...
- Beneficial rainfall is on tap late tonight through Monday
night.
- The axis of heaviest rainfall has shifted southward from
previous forecasts...with 1 to 3 inches anticipated everywhere
along and south of I-72. Points further north will pick up 0.5
to 1 inch.
- Cooler and drier conditions will prevail for the middle and end
of next week.
&&
.UPDATE...
Issued at 742 PM CDT Sat Sep 21 2024
Earlier convection lingered through about 5 pm over south central
Illinois, tracking southeast along a CAPE gradient associated with
the stationary front. Forecast area remains dry now, with regional
radar mosaics showing some showers and a few storms moving east
across central and north central Missouri. Our current balloon
sounding is showing quite a bit of dry air below 650 mb, so
despite surface dewpoints near 70 over a good part of the
forecast area, some moistening will need to take place to get
additional showers in here.
The main cold front shows up on surface obs and radar mosaics from
the SW to NE corners of Iowa, and should be near the Illinois
border toward mid morning Sunday. Latest HRRR runs continue to
show convection filling in along the boundary, though overall
remaining fairly disorganized. Main surge of showers/storms is
expected to be moving into western Illinois toward midnight and
reaching the I-57 corridor before sunrise.
Main forecast updates were to adjust the rain trends, especially
this evening.
Geelhart
&&
.SHORT TERM...(Tonight through Sunday)
Issued at 322 PM CDT Sat Sep 21 2024
19z/2pm surface analysis shows a nearly stationary frontal boundary
extending from Keokuk, Iowa southeastward to just north of
Evansville, Indiana. To the north of the front, much lower
dewpoint air has settled into the N/NE KILX CWA where readings are
currently in the upper 40s and lower 50s. Further W/SW closer to
the boundary, moisture is considerably richer as evidenced by
dewpoints in the upper 60s and lower 70s along/southwest of a
Galesburg...to Lincoln...to Effingham line. A line of convection
that formed along the primary instability axis near the
Mississippi River around midday has largely dissipated...with
lingering light showers noted from Peoria to Taylorville. Further
south where MLCAPEs are analyzed at greater than 2000J/kg, the
line has re-intensified from Litchfield to Mount Vernon. This
activity will track eastward and spill into the SE KILX CWA south
of I-70 over the next couple of hours. Further north, only
isolated showers are anticipated in the more stable environment
for the remainder of the afternoon and through the evening.
As a cold front approaches from the west and the low-level jet
energizes from Texas into Missouri, a large area of showers and
thunderstorms will develop west of the Mississippi River...then
push eastward into central Illinois late tonight into Sunday
morning. Given copious deep-layer moisture and favorable dynamics
ahead of the cold front, have carried likely to categorical PoPs
late tonight and categorical across the board Sunday morning. The
cold front will sink south of the I-70 corridor by Sunday evening,
resulting in decreasing rain chances across the northern half of
the CWA at that time.
Barnes
.LONG TERM...(Monday through Next Saturday)
Issued at 322 PM CDT Sat Sep 21 2024
The frontal boundary is progged to become nearly stationary in the
Ohio River Valley Sunday night through early Tuesday: however, as
a closed upper low evident on the latest water vapor imagery over
the Desert Southwest shifts eastward, it will interact with the
front and bring overrunning showers/thunder to much of central
Illinois. Given the expected position of the boundary, the axis
of heaviest rainfall has shifted southward from previous
forecasts. The latest projections suggest widespread rainfall
totals of 1 to 2 inches along/south of I-72...with isolated
amounts approaching 3 inches south of I-70. Further north from
I-72 northward, amounts have been decreased into the 0.50 to 1
inch range.
Once the upper low departs, the front will get nudged further S/SE
and the rain chances will come to an end by Tuesday evening. After
that, dry and cooler weather is anticipated for the remainder of
the extended as highs drop into the lower to middle 70s and
overnight lows dip into the lower to middle 50s Tuesday through
Saturday.
Barnes
&&
.AVIATION... (For the 00z TAFs through 00z Sunday Evening)
Issued at 620 PM CDT Sat Sep 21 2024
Main TAF concerns will begin after 06Z, with the approach of a
cold front from the northwest. A large area of showers will move
from west to east, impacting all TAF sites between 07-12Z. While
isolated thunder will be possible over a large part of central
Illinois, only the area from KSPI-KCMI has a high enough
confidence of thunder to include a mention at this time, focusing
on a 3-hour window at each site. Will need to watch for some
additional thunder potential as the cold front sweeps across
central Illinois early Sunday afternoon, though confidence is low
at this point.
Ceilings should hold around 10kft through the evening, then
steadily lower as the rain approaches. Ceilings should lower to
below 3,000 feet shortly after the rain begins, and remain below
2,000 feet the remainder of the forecast period.
Geelhart
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Northern Indiana
921 PM EDT Sat Sep 21 2024
.KEY MESSAGES...
- Chances for showers and storms increase Sunday into Sunday
night, bringing at least some rainfall to the area.
- A break in the rain is expected Monday into Monday evening
before another chance arrives late Monday night into Tuesday.
- Cooler temperatures will prevail through much of the period
with highs in the 70s.
&&
.UPDATE...
Issued at 914 PM EDT Sat Sep 21 2024
No notable changes to previous forecast are warranted at this
time. Ongoing convection this evening is confined to areas well
to the west across southwest/south central Wisconsin at the nose
of instability ridge. Stable bubble and dry low level air will
persist locally through the early overnight hours. During the
overnight, a series of convectively enhanced short waves from
this upstream convection will begin to enter confluent
mid/upper level flow eventually allowing the strong low-mid
level theta-e gradient to push aggressively back across the area
into Sunday morning. Near term isentropic progs would suggest
best isentropic ascent shifting north of the local area Sunday
morning, with a few showers possible toward daybreak feeding off
this increase in elevated moisture and northward lifting
isentropic forcing. More widespread showers/iso storms may work
across the area from from west to east from mid morning through
mid afternoon Sunday in association with pocket of pre-frontal
moisture convergence and upper level short wave forcing,
followed by larger scale frontal response. Timing of precip
onset still a bit uncertain given multiple forcing mechanisms
and highly advective moisture profiles, but general theme of
previous forecast left intact at this time.
&&
.DISCUSSION...
Issued at 253 PM EDT Sat Sep 21 2024
Strong subsidence, well depicted on satellite, over the area
will hold strong until towards 12Z Sun as the next wave edges
into the region. Narrow area of showers/storms in western IL
should quickly meet its demise as it runs into the western edge
of the subsidence. Re-development will take place overnight
across northern MO into western IL, and then tracking towards
the region. Several models seem to suggest the bulk of this
initial shot may pass near/south of US-24 as noted by the last
shift. Despite this, models do agree on a better influx of
moisture (PWATs 1.75" or higher) and instability to set the
stage for development during the afternoon and evening hours
with the 15Z RAP looking the most reasonable at this point.
Overall severe threat quite low, but locally heavy rainfall
would be the main concern, something that is welcome if it
doesn`t runoff too fast. Will maintain likely pops through the
day. Showers/storms are likely to linger in eastern areas into
the evening and possibly overnight hours as the sfc boundary
takes its time working east.
Drier air will advect in Monday on N/NE winds as the upper level
trough digs in. The increasing flow getting things stirred up
beach wise with increasing waves and swim risk from Mi City to
Bridgman. Yet another wave moves towards the area Tuesday, but
models vary on potential impacts on the area partially due to
differences in available moisture and sfc low development that
will be starting to the west as a deeper wave resides somewhere
in eastern KS/W MO. System could bring another good shot of rain
to the area, but confidence is low on the evolution. Have kept
pops in the chc to low end likely for now. Thereafter, models
agree on the stronger wave cutting off but vary on how far west
and south. Some minor moderation in temps could occur, but most
likely we will stay below normal.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 700 PM EDT Sat Sep 21 2024
A strong instability gradient sprawled across the Mid MS valley
and lingering mid level subsidence across northern Indiana
should limit any eastward expansion of shower activity across
northern Illinois into this evening. By late this evening and
especially into the overnight, broad mid/upper level upstream
confluent flow will allow for more active short wave pattern to
influence western Great Lakes, allowing for an eastward shift to
strong low-mid level theta-e gradient. This should allow for
uptick in rain shower potential, particularly late Sunday
morning into Sunday afternoon as low level frontogenesis forcing
also becomes more prevalent. Weak mid level lapse rates and
moistening low/mid levels should temper overall instability.
While some isolated-scattered thunder is possible Sunday, will
continue to omit mention due to these limiting factors. Light
and variable to light southeast winds will veer southwest 5 to
10 knots on Sunday in pre-frontal environment, before shifting
west toward end of this forecast valid period with frontal
passage.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
UPDATE...Marsili
DISCUSSION...Fisher
AVIATION...Marsili
Area Forecast Discussion
National Weather Service Marquette MI
829 PM EDT Sat Sep 21 2024
.KEY MESSAGES...
- The prolonged stretch of above normal temperatures ends today,
with temperatures cooling near normal Sunday.
- A round of showers and storms accompany a cold front tonight
through Sunday. Severe weather is not anticipated, but some
small hail are possible with stronger storms.
- Showers end from west to east through Sunday as the cold front
exits the UP. Gusty NW winds behind the front, with the
highest gusts along the eastern shores of Lake Superior up to
30 mph.
- Other than a slight chance (15-20%) of showers associated
with a low pressure passing through Lower Michigan Tuesday,
dry weather is expected this week.
- Patchy frost potential (~20%) for typical cold spots of
interior western Upper Michigan Monday and Tuesday morning.
- Supportive setup for patchy fog (~20%) each morning next
week.
&&
.UPDATE...
Issued at 829 PM EDT Sat Sep 21 2024
As of 0015z, the upstream dry cold front, apparent on KDLH, had
pressed east of the Duluth and is now pressing through northeastern
Wisconsin, the Arrowhead, and far western Lake Superior. To the
south, convection in central Wisconsin has struggled to inch into
the UP so far. This cluster of showers and thunderstorms is
currently pressing east through northeastern Wisconsin. Current
trajectories have these moving into Menominee County in the next
hour or two. Recent hourly RAP and HRRR guidance packages reflect
these trends fairly well and suggest some elevated destabilization
ahead of the front will support additional shower/storm development
across Central Upper Michigan after midnight.
&&
.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 321 PM EDT Sat Sep 21 2024
Latest water vapor imagery shows a well-defined shortwave trough
lifting northeast into northern Ontario and northern MN this
afternoon. This shortwave trough will move into the Upper Great
Lakes later tonight and Sunday, sending a sfc cold front across
Upper Mi tonight into Sunday morning. WAA and a 40+ kt LLJ max ahead
of the cold front have already supported showers and scattered t-
storms early this afternoon into north central WI and portions of
western Lake Superior. A few showers may have made it into far
western Upper Mi but showers have generally dissipated moving into
into ridging and the associated dry and stable air mass across Upper
Mi. While it`s been more cloudy into western Upper Mi due the
convection drifting into that area, ridging has supported more
sunshine into central and eastern areas of the U.P. this afternoon.
Afternoon temperatures have generally been in the 70s to lower 80s,
warmest inland east and coolest west under the clouds.
Heading into this evening and tonight, the vort max/shortwave will
continue to lift northeast through northern Ontario which will send
the mid-level trough axis across Upper Mi later tonight into Sunday.
As the system`s associated cold front moves across Upper Mi tonight
into Sunday morning, showers along the cold front will most likely
move into far western Upper Mi early this evening and then spread
into central Upper Mi late evening and eastern Upper Mi overnight.
Instability along the front is not particularly impressive,
generally 500 j/kg MUCAPE, with the best of that south along the WI
border. Effective shear along the front when showers will be
occurring also generally looks like it will be 30 knots or less, so
not really expecting any severe storms, but maybe a stronger storm
with some dime-sized hail could develop south central along the WI
border where marginal instability and shear appear to be maximized.
Look for min temps lowering into the 50s behind the cold front
tonight. Northwest winds behind the front could gust near 30 mph
late tonight/early Sunday along the tip of the Keweenaw.
&&
.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 404 PM EDT Sat Sep 21 2024
A cold front exiting the UP to the east Sunday will signal the
departure of the best chances of precipitation for the next week
ahead. A Colorado Low-style shortwave will phase with an Alberta
Clipper-style shortwave over the southwestern extent of the Midwest
Monday into Tuesday and the resulting surface low will pass through
the Lower Peninsula of Michigan Tuesday, resulting in most of the UP
staying high and dry. 500mb ridging then builds in behind the
departing trough Wednesday into the weekend and while the details
are uncertain (and could be complicated by any potential tropical
development), another blocking pattern could bring up to 50% chances
of an extended period of drier than normal weather into October.
For Sunday, showers and thunderstorms will be ongoing in the morning
hours across central to eastern Upper Michigan. Showers should exit
the CWA by 02Z Monday, though not before bringing an additional
quarter to half inch of rain to the eastern third of the UP. Despite
meager surface instability, HREF reflectivity paintball plots still
show some isolated to scattered thunderstorm potential with the
showers, so slight chance to chance thunder (15-30%) has been kept
in the forecast, though no severe weather is forecast. Winds look to
be gusty behind the front especially over Lake Superior, with some
shoreline locations seeing up to 30 mph gusts out of the NW, though
the gusts will not penetrate too far inland with HREF mean gusts in
the interior around 20 mph at most.
Monday will be a dry day as 1019mb surface high pressure (12Z GEFS
clusters) will reside overhead. Monday and Tuesday morning both have
the potential (~20%) for morning patchy radiation fog. MOS guidance
suggests lows in the upper to mid 30s in the interior west both
mornings, which could lead to some patchy frost for elevated flat
surfaces and typical cold spots. Will hold off on any products as
the temperatures look borderline and there`s some disagreement
between the NBM deterministic and its own ensemble 50th percentile
that leads to decreased confidence. If the percentiles are to be
believed, there is around a 25% chance of some sub-freezing lows
around the Houghton/Baraga/Iron County triple point on Monday
morning and across more interior locations on Tuesday.
As the pair of troughs coalesces on Tuesday morning, the resulting
surface low around 1010mb looks to pass through Indiana/southern
Lower Michigan on Tuesday. PoPs have all but trended completely out
of the UP now, though there is still ~15% chances for the farthest
south and east portions of the UP to just get brushed by the
precipitation shield of this system. Ridging behind the system will
bring mainly clear skies and a slight warming trend of highs from
around the mid 60s on Monday to the mid 70s by the weekend. The
pattern gets a bit unclear by the weekend as the global
deterministic models struggle to resolve whether a rex block
sets up or if there is interference from a potential tropical
system in the late week, but the CPC still has the UP in a up to
50% contour of lower than normal precipitation through the end
of September regardless of exact solution.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 725 PM EDT Sat Sep 21 2024
Cold front will move through Upper Michigan overnight, supporting
MVFR ceilings developing, mainly at KSAW. Recent model and
observational trends of ongoing convection and prefrontal
environment highlight stability and dry air winning out, which is
reflected in this TAF with the drier trend at KCMX and KIWD. With
that being said though, cloud bases will lower as the front
approaches and MVFR ceilings may develop, most likely at KIWD. As
the front continues eastward, guidance continues to highlight
additional showers and some thunderstorms developing and potentially
impacting KSAW overnight. Expect improving conditions at KSAW by
morning as most shower activity presses east of the terminal. Post
frontal winds will become north to northwest with some gust
potential upwards of 20-25kts, mainly at KCMX and KSAW.
&&
.MARINE...
Issued at 404 PM EDT Sat Sep 21 2024
Winds will remain at 20 knots or below this afternoon and early
evening. As a cold front sweeps across Lake Superior tonight, winds
behind the front will gust to near 25 knots out of the west and
northwest, first over the western portions of the lake around
midnight and then over the east around 8 AM Sunday morning. Winds
fall below 20 knots in the west through Sunday morning with winds
relaxing in the east throughout the overnight period into Monday
morning. Winds then look to remain below 20 knots as major low
pressure systems remain far from Lake Superior. As the cold front
passes tonight and Sunday, there is a chance (~30%) of
thunderstorms, though severe weather is not expected. Waves behind
the front will peak between 4 and 5 feet along the Keweenaw
Peninsula shores Sunday morning and over the east half of the lake
between 6 and 7 feet during the day Sunday, falling below 4 feet
lakewide by Monday morning.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
UPDATE...JTP
SHORT TERM...Voss
LONG TERM...GS
AVIATION...JTP
MARINE...GS
Area Forecast Discussion
National Weather Service Pueblo CO
526 PM MDT Sat Sep 21 2024
.KEY MESSAGES...
- Widespread showers/scattered thunderstorms across most of
southern Colorado this evening and overnight, then
precipitation intensity/coverage begin to fade early Sunday
morning.
- Snow levels drop down to around 9000 feet early Sunday
morning, though most accumulating snow (5-10 inches) will stay
across the higher peaks at/above 10kft.
- Below average temperatures throughout the majority of the
week, returning to normal by the end of the week.
- Dry conditions are expected throughout the week.
&&
.SHORT TERM /THROUGH SUNDAY/...
Issued at 352 PM MDT Sat Sep 21 2024
Currently, upper low over nern AZ at mid-afternoon, with expanding
area of showers and thunderstorms over much of the region as upward
vertical motion increases across srn CO. Strongest storms so far
today have been over the San Luis Valley, where weak instability
(CAPE around 500 J/KG) and strong wind shear/upward motion were
generating some fast moving convection. Hail threat with these
storms will be limited by weak instability, but will need to watch
for at least a low end severe wind threat across the Valley through
00z given storm motions of 50-60 mph.
For the remainder of the afternoon into the evening, shower and
thunderstorm coverage will expand across the area as low approaches,
with HRRR suggesting a rather robust band of thunderstorms crossing
the mountains 23z-03z, then impacting the I-25 corridor and eastern
plains 02z-07z. Will continue with high pops and a mention of
thunderstorms all areas, as strong forcing will overcome weak
instability and keep tsra chance going until at least midnight. Snow
levels hangs out between 9-10k feet through the evening, though
wouldn`t be surprised to see stronger convection drive it lower
toward 8k feet at least briefly, though accums should remain mainly
over the peaks. After midnight, low passes overhead with vertical
motion gradually diminishing from sw to ne as main deformation zone
shifts into nrn CO. Overnight QPF, starting at 00z, will range from
a half inch to slightly over an inch over much of the higher
terrain, while valleys and I-25 corridor see numbers around a half
inch. Plains should see a quarter to half inch overnight, perhaps a
little heavier far southeast corner if stronger convection over ern
NM/wrn TX can hold together as it comes north this evening. Overall,
made only a few minor changes to ongoing forecast, as previous set of
grids appear to have a good handle on things.
Sunday, upper low gradually shifts out of Colorado into nwrn KS by
late afternoon, though moisture and instability will linger across
the area. Still a good deal of showers early in the morning over the
eastern mountains and plains, with most activity then weakening/
ending by noon. A few showers/weak storms could re-fire over mainly
the mountains in the afternoon as mid-level lapse rates remain
rather steep, though not expecting anything particularly strong or
widespread. It will definitely fell like fall across all the area
temperature-wise, with max temps only in the 50s/60s at lower
elevations, 40s/50s mountains.
&&
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 352 PM MDT Sat Sep 21 2024
The closed that has been impacting the short term forecast continues
its journey towards the northeast, but a lingering trough will still
be overhead at the beginning of the long term forecast period, which
will bring some light rain below 12kft and light snow above 12kft
over the easter San Juan Mountains. The strong low pressure system
brought cold air over the region and that will continue during the
overnight where low temperatures will be in the 30s and 40s over the
mountain valleys and the plains. Currently it doesn`t seem that any
frost products will be needed, but it is close, so we`ll need to
keep monitoring.
Below average temperatures are expected throughout the majority of
the week over the plains and mountain valleys. On Monday the high
temperatures will be in the upper 60s to low 70s over the plains and
mountain valleys. A weak shortwaves will begin to pass over
Colorado, once again bringing light snow over 12kft and rain below
12kft over the eastern San Juan Mountains. Otherwise dry conditions
and light winds everywhere else.
Tuesday through Saturday:
The rest of the will have some influence from a tropical system that
will be impacting the U.S. South, therefore there is some uncertain,
depending on the tropical system`s path. Overall, the flow over
Colorado is expected to be fairly weak with ridging aloft
developing over the western half of Colorado with northerly
winds over the eastern half. There isn`t precipitation being
resolved for the rest of the forecast period, just dry
conditions with temperatures reaching closer to seasonal by the
end of the week.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 522 PM MDT Sat Sep 21 2024
An upper 500 mb low will track across the region tonight. This
system will bring an area of lift over the region at the
beginning of this fcst and bring a threat of enhanced showers
and isold thunder to the 3 taf sites, KPUB, KALS and KCOS. After
this lift goes by, precip will be more showery in nature and
thunder threat will be negligible. However, with plenty of
moisture around, MVFR cigs are likely, and they will last
through about 16-18Z tomorrow. Then expect VFR conditions
thereafter.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MDT Sunday for COZ058-060-
082.
&&
$$
SHORT TERM...PETERSEN
LONG TERM...SKELLY
AVIATION...HODANISH
Area Forecast Discussion
National Weather Service Raleigh NC
852 PM EDT Sat Sep 21 2024
.SYNOPSIS...
An upper level disturbance will track southeast through the Mid
Atlantic region tonight. A back-door cold front will move south
through the area late Sunday followed by surface high pressure
extending south into the area through much of the upcoming work
week.
&&
.NEAR TERM /TONIGHT/...
As of 852 PM tonight...
Cluster of thunderstorms approaching northern NC for late evening...
The cluster of showers and thunderstorms over central and southern
VA continues to move southward toward northern NC. Satellite data
suggests the weak short wave diving SE through VA. The latest
data analysis indicates a weak low pressure over southern VA, with
the best moisture convergence just to the west of the clustering of
storms near Roanoke. However, lingering MLCape values were
around 1000-1500 J/kg over NW into north-central NC, with some CINH
showing up as well as temperatures cool with sunset. The latest RAP
and most CAMS indicate the showers/storms entering northern NC
between 930 and 1030 PM, then weakening as they move toward/into the
eastern portions of the Triad, Triangle, and Rocky Mount areas
between 1100 PM and 200 AM. Radar currently depicts some cores of
the storms with 60+ dbz up above 20k feet with a Severe Thunderstorm
Warning 25 miles north of Granville and Vance Counties. It is
possible a warning will be needed, but we expect most if not all
storms will weaken into the "garden variety" or below severe limits
in the next hour.
Previous discussion as of 203 PM Saturday...
A line of scattered showers and thunderstorms is progged by all of
the HREF members to develop to our north this evening then drift S
and SE across our CWA between 04-10Z tonight... all in response to
the weak short wave trough that is currently crossing the Ohio
Valley, which is forecast to move ESE across the Mid Atlantic region
tonight and move off the coast by Sunday morning. In the meantime,
we`ll see intervals of sct-bkn shallow cu the remainder of the
daytime hours today, esp west of US-1 where currently the best
moisture and instability is located... then high clouds moving in
this evening out ahead of the upstream shower/tstm activity. Then
during the hours right before daybreak, there could be a couple
hours of patchy fog, esp locations the see the greatest coverage of
showers/tstms overnight. Lows tonight in the low-mid 60s.
&&
.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 115 PM Saturday...
Aloft, the sub-tropical ridge will progress eastward through the
srn/ctl Appalachians and into the Carolinas through Sun night.
Central NC should be under nwly flow on the northeast periphery of
the ridge. At the surface, a low will continue sliding sewd through
central NC Sun morn/aft. A backdoor cold front should slide south
through the area Sun aft/eve, with high pressure ridging in behind
it. There could be some lingering showers across the east Sun
morning. Additional showers/storms could slide swd through the
Coastal Plain/far ern Piedmont Sun eve/night as the backdoor front
slides southward through the area. There could be about a 10 degree
spread in highs from SW to NE due to the front, around 90 degrees SW
to low 80s NE. Lows could drop to around 60 degrees in the northeast
Sun night, with generally mid 60s expected elsewhere.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 230 PM Saturday...
* Near to slightly above normal temperatures into midweek, followed
by seasonal to slightly below average late week and weekend
* Shower and storm chances highest Tue into Thu
* Forecast confidence decreases mid to late week as ensemble systems
continue to differ on the overall synoptic pattern and possible
tropical influences
We will start the week with ridging building into the area at mid-
levels from the north and northeastern Gulf. High pressure will
build into the area from the Eastern Seaboard and Canada. Models
still show a lingering backdoor front to our southwest in northern
SC, though it appears models have trended further south with its
location. As such, rain/storm chances are lessened Mon aftn/eve, but
still cannot rule out a 20-30 percent chance over the western and
southern Piedmont. Temperatures will be near normal in upper 70s to
low 80s.
Ridging will continue into midweek, though we should get increasing
influence from a trough over the MS/OH valleys and Great Lakes late
Tue through early Thu. Model and ensemble solutions start to diverge
on how the trough evolves as it moves east, but there does appear to
be a general consensus that a cold front will try to move through
sometime Thu morning. It`s still unclear whether it will actually
move through or stall out and linger NW of us. Ahead of that front,
shower and storm chances should increase (30-60 percent), primarily
in the late Tue through Wed night period. Temperatures should rise
above normal ahead of the front to above average in the low to mid
80s.
Probabilistic and ensemble solutions continue to vary widely in the
Thu to Sat timeframe with respect to the synoptic pattern. Some
ensemble cluster solutions indicate troughing over the MS valley and
ridging off the western Atlantic (aka latest GFS/CMC), which would
favor warmer highs and help draw northward any disturbance in the
Gulf later in the week. Where it tracks though is widely varied.
Other solutions show troughing nearby with the aforementioned cold
front, keeping rain chances elevated. And still a third solution
shows a rex/omega ridge pattern near the OH valley and troughing on
either side, which could favor drier conditions to start but also
advect any tropical system in the Gulf over the weekend. This is
seen in the prior 00z ECMWF. Speaking of the Gulf, NHC now has a 60-
percent chance of tropical development late next week over the south-
central Gulf. Where the system would move is highly dependent on the
pattern discussed above, which is too uncertain, but certainly bears
watching, given a wide range of potential impacts. As a result, have
kept rain chances low Thu to Sat, with temperatures near to slightly
below normal in the upper 70s to near 80.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 735 PM Saturday...
VFR conditions will persist at all terminals for much of the 24 hr
TAF period. However, upstream convection over central VA may hold
together as it approaches KRDU/KRWI. As such, these terminals may
experience brief sub-VFR conditions between ~03 and 07Z tonight.
Otherwise, some patchy fog may develop at the northern terminals
early Sunday morning (confidence highest at KINT/KGSO/KRWI). VFR
conditions will return after 13Z Sunday. Additional showers may be
possible Sunday afternoon along a backdoor cold front, but
widespread sub-VFR conditions are not expected.
After 00Z Monday: Mainly VFR conditions expected each day, with the
exception of sub-VFR fog/stratus each morning. There is a chance for
mainly afternoon/evening showers/tstms each day, which could also
briefly reduce flt conditions at times.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...np
NEAR TERM...Badgett/np
SHORT TERM...KC
LONG TERM...Kren
AVIATION...Luchetti/np