Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/25/23
Area Forecast Discussion
National Weather Service Denver/Boulder CO
332 PM MDT Thu Aug 24 2023
.SHORT TERM...(This evening through Friday)
Issued at 258 PM MDT Thu Aug 24 2023
... Multiple Rounds of Heavy Rain Likely through Friday Night...
Key Messages:
1. Several rounds of heavy rain appear likely over the next 24-48
hours across our forecast area.
2. Burn area and urban/rural flash flooding will be possible as
tropical-like rainfall develops
3. Considerable uncertainty remains in the exact axis of heaviest
precipitation.
Details:
A difficult, but potentially impactful forecast is on the agenda
for the next couple of days, as the remnants of Tropical Storm
Harold combined with a deep subtropical moisture plume and an
approaching cold front, provide a unique combination of
ingredients for a late August rainfall event.
Water vapor satellite shows the remnants of Harold centered just
northwest of the Four Corners this afternoon, with a broad area of
south-southwesterly flow across the area. This shortwave/ex-
tropical system should continue to drift north/northeastward over
the next day as it travels around the western periphery of the
upper ridge axis centered over the Southern Great Plains.
We`re already seeing some effects of the increased moisture
across the high country this afternoon. A slow moving storm near
Estes Park dropped over 3/4 of an inch of rain in less than an
hour earlier this afternoon in a marginal environment. With
instability increasing west of the divide, have opted for a Flood
Watch for most of Grand/Jackson counties, including the East
Troublesome Fire, for this afternoon... which will continue
through Saturday. The last several runs of the HRRR indicate a
wave of slow moving/training thunderstorms this evening... which
could produce rainfall rates in excess of an inch per hour at
times.
Meanwhile, the main show still looks on track for Friday into
Friday night across the Foothills and most of the northeast
plains. Moisture will increase even more tomorrow, with
precipitable water amounts increasing to around 1.5 inches by
midday (roughly 2-4 sigma standardized anomalies). Initial model
soundings depict a nearly saturated column with deep warm cloud
depths and skinny CAPE profiles, along with fairly slow mean storm
motions. Storms that do develop would be capable of heavy rain
during the day, with some training/redevelopment of storms
possible. The ECMWF Extreme Forecast Index shows EFI values near
0.8-0.9 Friday afternoon/Friday night, with a SOT >2 in some
locations, both indicative of potential higher-end event. Both CMC
and ECM ensemble mean values show widespread areas of 1-1.5
inches by Friday evening, with more falling overnight (see the
Long Term below).
There are many questions left to be resolved, however (as is
usually the case in heavy rain events here). Many of the CAM
solutions are drier and/or quicker to push convection out of the
region. This appears to be influenced somewhat by the development
of a stronger high pressure system in Wyoming by Friday evening -
where the non-global models are much colder/stronger with this
feature and have a much stronger frontal push, and shunt most of
the precipitation off earlier and wiping out most of the remaining
instability in the area. The GFS is somewhat of a middle ground
approach with precipitation becoming more stratiform in nature
fairly quickly. Some guidance (NAM) also hint at a strong MCV-like
feature developing by the evening, which would certainly have its
impacts.
The bottom line (or your TLDR summary) - heavy rain is likely
somewhere across north-central and northeast Colorado this evening
and again on Friday. While not every location will see heavy
rainfall amounts, there is certainly potential for some spots to
see several inches of rain over a short time period within our
Flood Watch area. We`ll need to closely watch trends over the next
12 to 24 hours to see how several key features evolve... with the
upcoming 00z (and tomorrow`s 12z) guidance hopefully offering
some clarity. Stay tuned.
.LONG TERM...(Friday night through Thursday)
Issued at 258 PM MDT Thu Aug 24 2023
Heavy rain and storms will be ongoing Friday evening as remnants
of a Tropical Storm are over Colorado. With such high precipitable
water values in the 1.4-1.5" range, there will be warm rain
processes occurring with an usually "tropical-like" rain falling.
There is some consensus in the models that an MCV will develop
within the widespread heavy rain and storms. This vortex would
lead to very heavy rainfall amounts possibly around 2" per hour.
The exact location of this MCV will be tough to forecast. The NAM
and NAM Nest keep this feature farther east and the heaviest rain
would fall east of a line from Fort Morgan to Limon. The ECMWF
keeps a more northeasterly low level flow over our forecast area
and keeps the heaviest rain further west and along the I-25
corridor. The ECMWF is usually better at these time ranges so the
forecast and highlights were trended toward the ECMWF forecast. As
discussed in yesterday`s AFD, the ECMWF Extreme Forecast Index is
still on track with a significant signal for record rainfall
across north-central and northeast Colorado. Friday and Saturday
have large areas of 0.8 or above signaling a good chance of record rainfall.
In addition, there is a large area of shift of tails values that
are at 2. This means rainfall could be well above the record
amounts. Some high resolution models are producing extreme
rainfall values in excess of 7 inches of rain within a 36 hour
period. These may be on the high side of what will actually occur
but it would not be completely shocking if a report or two came in
with these values. The forecast rainfall totals in the forecast
are for a widespread 1-3" with localized 4-5" totals. A Flood
Watch for flash flooding was issued from Friday morning through
midday Saturday. There is low confidence in the end time of the
rainfall so the Flood Watch may be allowed to be canceled early on
Saturday.
There will be low clouds and left over light showers during the late
morning and early afternoon on Saturday. This will keep temperatures
on the cool side with highs staying in the upper 60s to low 70s
across the plains. This will keep conditions mostly stable across
the northeast plains which would limit thunderstorm activity during
the afternoon and evening. There will be more sunshine across the
mountains and foothills which will allow for better instability to
build in there. As a result, there will be scattered showers and
storms that develop over the higher terrain with the heaviest
rainfall being to the south of I-70. If there is cooler
temperatures and more cloud cover on Saturday, the flash flood
risk during the second half of the day would be much lower. If
there is sunshine during that day with instability building in,
there could be a small flash flood threat especially over areas
that received heavy rain Friday and Friday night. The lower threat
of flash flooding seems more likely during this period.
The shortwave trough and moisture associated with the remnants of
the Tropical Storm will move out of the area on Sunday. A slight
shortwave aloft will move through the area within northwesterly
flow. A cold front at the surface will also move through our
forecast area during the afternoon which will help to generate
good coverage of showers and storms across the area. Some of these
storms may produce brief heavy rain.
Northwesterly flow aloft will continue on Monday with light
northeasterly flow at the surface. The weak upslope flow along
with lingering moisture will result in showers and storms forming
mainly over the mountains and foothills. Areas east of I-25 should
remain dry.
A ridge over the Four Corners area will strengthen and move over
Colorado on Tuesday and through the rest of next work week. This
will lead to warmer temperatures with mostly dry conditions.
There does not appear to be any weather hazards during this
period.
&&
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1142 AM MDT Thu Aug 24 2023
VFR conditions expected this afternoon and evening, with
deteriorating conditions through the rest of the period. Most
showers and storms should remain well west of the terminals during
the day today. A cold front is expected to push into the region
after 00z tonight with a few northerly gusts >20kt possible. There
may be just enough moisture for a few showers to develop with the
fropa this evening.
Behind the front, moisture should increase and ceilings will
slowly lower through the night. Initially ceilings will fall to
around 3000ft AGL early Friday morning. Ceilings should continue
to slowly lower through the day tomorrow. Showers will be possible
after about 15z with areas of heavier rain likely somewhere near
the terminals Friday afternoon and evening. Eventually there
should be a shift into MVFR/IFR cigs/visby with the arrival of
heavier precipitation.
&&
.HYDROLOGY...
Issued at 258 PM MDT Thu Aug 24 2023
A limited to elevated threat of burn area flash flooding is
expected through tonight, mainly for the East Troublesome burn
area. Models have trended toward a period of moderate to heavy
rain over Grand/Jackson/far W Larimer county overnight tonight.
Enough moisture and instability should be available initially this
evening with this first wave of convection, and have gone with a
Watch for this period.
Have gone with a broad Flood Watch for flash flooding on Friday,
with a significant burn area flash flood threat also accompanying
this. Ensemble guidance hammers a swath of Larimer/Weld/Morgan
counties and there appears to be a potential for as much as 3-5
inches of rain. The latest ECMWF ensemble shows as much as 2.5
(50th) to 5 inches (90th percentile) across Larimer county over a
24 hour period. While CAM guidance is a bit spottier with QPF, all
the ingredients are there for a heavy rain event.
The heavy rain will continue Friday night into Saturday morning.
It will begin to taper off from west to east late Friday night
through midday Saturday. As a result, the Flood Watch will expire
at noon Saturday. Showers and storms will form later in the day on
Saturday and will form on Sunday and Monday as well. These may
have heavy rainfall but the overall flash flood threat will be
lower.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late Friday night for COZ030-032-033.
Flood Watch from Friday morning through Saturday morning for
COZ035-036-038>046-048>051.
&&
$$
SHORT TERM...Hiris
LONG TERM...Danielson
AVIATION...Hiris
HYDROLOGY...Hiris/Danielson
Area Forecast Discussion
National Weather Service Boston/Norton MA
943 PM EDT Thu Aug 24 2023
.SYNOPSIS...
Showers overspread the region from west to east tonight, and
continue through much of Friday. Heavy downpours may lead to
localized flooding. A few thunderstorms on Friday could become
strong. Isolated to scattered showers and storms are possible
on Saturday, especially during the morning. Trending drier and
seasonable for Sunday and Monday, before shower chances return
for Tuesday and Wednesday. Distant Franklin could bring an
elevated risk for rip currents early to mid next week.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
10 PM Update...
As indicated in the previous update, rain showers have been a
bit more progressive this evening compared to earlier forecasts,
with a rather stratiform band of rain located across central MA,
eastern CT, and RI. While light, this band has dropped over 0.1"
of QPF in some locations. To account for the progressive nature
of the rain this evening, increased PoPs across the CWA, save
for the Cape and Islands where subsidence due to high pressure
over the Atlantic will stave off showers for a good part of the
overnight hours.
Otherwise, the bulk of the forecast is in good shape.
7PM Update...
Light rain is already starting to fall in western MA and CT and
is pushing east. Hi-Res guidance seems to be struggling on
picking up the quicker progression of the rain so the forecast
pops were manually increased this evening. Otherwise the
forecast remains on track.
Previous discussion...
Highlights
* Increasing clouds with rain showers spreading in from west to
east. Heavier showers and perhaps a few embedded thunderstorms
late/toward daybreak.
Stuck under quasi-zonal flow across the northern tier of the US.
A shortwave trough lifts from the eastern Great Lakes into
northern New England tonight. A low will slide from Lower
Michigan into the eastern Great Lakes and a warm front will
begin lifting across the Mid Atlantic.
Will see showers spreading in from west to east and becoming
increasingly likely as the night progresses. Should really see
an uptick with activity becoming more widespread after 06Z as
the 850/925 hPa 30-40+ kt southerly low level jet slides into
our area. This also coincides with PWATs increasing to roughly
1.5-2" with the column saturating. Not a whole lot of
instability to work with perhaps a few hundred J/kg of MUCAPE,
but given the LLJ there could be some embedded thunder. At this
point not thinking there is a severe risk as any activity should
be elevated given the warm front is still lifting across the Mid
Atlantic. However, there could be some localized heavy downpours
given the PWATs and warm cloud layer depths between 3-4 km.
Somewhat consistent amongst the CAMs, so have leaned toward them
for the forecast.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Highlights
* A washout for most with showers and embedded thunderstorms.
Localized urban and poor drainage street flooding may occur.
On top of this an isolated strong to severe thunderstorm is
possible.
* Showers/storms become more hit/miss during the interior Fri
night into early Sat.
Still under quasi-zonal cyclonic flow through this period. The
shortwave over the area lifts offshore on Fri. A deeper trough
will dig from western Ontario/northern MN into the central Great
Lakes by late Fri. This trough digs into the eastern Great
Lakes/western New England by early Sat. A warm front lifts into
and perhaps through parts of southern New England on Fri. The
warm front/low slides into the Gulf of Maine by Fri night and
the trailing cold front slides through parts of the region
heading into Sat.
Main concern during this timeframe is the risk for localized
flooding, especially across eastern CT, RI, and central/eastern
MA. Given that we`ve been dry for the past couple of days it
will take a bit for flash flooding with 1 and 3 hr RFC FFG being
roughly 2-4". At this point think that this is the highest risk
for impactful weather for our area as PWATs are around 1.5-2
inches for much of Fri with warm cloud layer depths between
4-4.5 km. Did bump up precip amounts toward the NERFC/WPC
guidance, which matches up well with the HREF 48 hr PMM
guidance. The result is widespread 1-3 inches of rainfall and
think that there could be localized amounts of 3+ inches
especially in any areas where thunderstorms develop. Think the
risk is highest across the aforementioned locations above as
this is also where the 30-40+ kt LLJ is moving through. Given
how localized this threat is anticipated to be, based on
embedded thunder activity we have held off from hoisting a Flood
Watch at this point in time.
As previous shift indicated the overall severe weather threat
remains low. Instability remains meager with MUCAPEs of a few
hundred J/kg. However, with the warm front lifting in and
potentially through there is a surface boundary to keep an eye
on as other environmental parameters highlight there could be a
risk for a strong/severe storm. Will have deep layer shear in
the 0-6 km range of 30-40+ kts. On top of this we will have 0-1
km SRH of 100-200 units. Fortunately the vast majority of guidance
does not realize this per UH tracks and the NCAR HRRR Neural
Network Convective Hazards. However, CSU severe ML probs still
indicating a low tornado risk. Given the environment think this
is feasible especially as the warm front is lifting through.
Will be something we need to monitor closely especially during
the morning hours on Fri.
Expecting the shower/storm activity to become more spotty later
on Fri into Fri night across the interior. Though think there
will be another uptick of activity across eastern areas heading
into Sat as the cold front slides in and the S/SSW LLJ
strengthens.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Saturday
Another shortwave trough will move across the region Saturday with
an associated surface low pressure system and cold front out ahead
of it. The cold front will be the focus for thunderstorm development
Saturday morning across eastern MA and RI. Given we are still a bit
out of the hi-resolution model window, finer details will need to be
worked out. instability looks limited for the most part but NBM has
probabilities of near 50% for SBCAPE to reach 1000 J/kg. A 80knot
jet streak sets up over the region contributing to 30 to 35 knots of
sfc to bulk shear. Timing of the cold front will be key to how much
instability we can build during the day. Overall, the threat for
thunderstorms looks to be more scattered then widespread, but we
will certainly need to keep any eye on the severe threat as more hi-
res guidance becomes available. CSU ML products currently highlight
eastern MA in a 5% risk for hail and wind. As for high temps
Saturday, it will feel quite warm and muggy until a secondary cold
front drops through Saturday night. Highs should top out in the
upper 70s to low 80s with dew points nearing 70F. Saturday night
lows will ultimately depend on the progression of the secondary cold
front with lows generally in the upper 50s to low 60s. The risk for
showers and thunderstorms looks to come to an end Saturday evening
with clearing skies.
Sunday
The short wave begins to retreat north and the secondary cold front
begins to shift offshore. With cooler air advecting in Sunday, highs
should only top out in the low to mid 70s. More clouds then sun look
likely with cyclonic flow aloft and NE winds bringing in moisutre
off the ocean. Mainly dry both Sunday and Sunday night outside of
some light drizzle especially for eastern MA due to low level
moisutre. Flow becomes more westerly Sunday night kicking out the
remaining moisture. This should allow for clearing skies and ideal
radiational cooling. because of this, brought lows down a few
decrees using MOS guidance. Lows should generally range in the low
50s inland, with upper 50s closer to the waters.
Next Week
The week starts off quiet with a brief shortwave ridge passing to
the north. A potent longwave trough ejects out of the Great Lakes
Tuesday or Wednesday. This will bring another round of showers and
thunderstorms to the region. The good news is that the trough should
push Franklin out to sea, but a close eye will still need to be kept
on the exact path. Franklin will at least bring moderate to high
surf and rip current into our waters mid week. Behind the
trough, A strong high pressure system looks to build in for the
remainder of the week bringing cooler fall like air to the
region.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight...High confidence in trends, but moderate in exact
timing.
Rain and MVFR ceilings have moved into western terminals a bit
earlier then model guidance had indicated so have pushed up
timing of showers and lower ceiling across all interior
terminals. showers should move in to eastern terminals between
05-09z with MVFR ceiling following shortly after. IFR ceilings
are possible towards day break and tomorrow afternoon for
interior terminals but confidence is low at this time. There may
be some embedded thunder with storms tonight, but confidence
was also to low to include in TAF`s. Winds out of the S/SE at
5-10 kts with some gusts up to 20 kts toward daybreak across
eastern terminals.
Friday...High confidence.
Widespread MVFR to IFR conditions with localized LIFR in any
heavier showers or thunderstorms. Still am not confident in the
thunderstorm coverage as will be dependent on the warm front
lifting through, which is uncertain at this time. Think the risk
is highest across the CT River Valley, but have held off from
mentioning for now in the TAF. Should see activity become more
hit/miss during the afternoon across the interior. Winds S/SE at
10-15 kts with gusts of 20-25 kts.
Friday Night...High confidence.
MVFR to IFR conditions with hit/miss showers and perhaps a few
thunderstorms across eastern areas especially heading toward the
Sat AM push. Winds out of the S at 5-15 kts shifting to the SW/W
from west to east late. May have some 20-25 kt gusts across the
Cape/Islands.
KBOS TAF...High confidence in trends, but moderate in exact
timing of rain.
Increasing mid/high clouds with MVFR ceilings and perhaps some
spotty showers pushing in roughly 06-08Z. Conditions may
lower to IFR with more widespread showers and perhaps a few
embedded thunderstorms on Fri. SE winds 10-15 kts with gusts of
20-25 kts.
KBDL TAF...High confidence in trends, but moderate in exact
timing of rain.
MVFR tonight with showers. Could see borderline IFR toward
daybreak on Fri as heavier showers move in and perhaps some
embedded thunderstorms. Confidence not high enough in coverage
to include in the TAF. Should see shower activity become more
hit/miss Fri afternoon, but may remain IFR until late. S/SE
winds around 5-10 kts.
Outlook /Saturday through Tuesday/...
Sunday through Monday: VFR.
Monday Night: VFR. Slight chance SHRA.
Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA.
Tuesday Night: VFR. Chance SHRA.
Wednesday: Breezy. Chance SHRA, isolated TSRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Through Friday Night...High confidence.
Rain showers spread into the waters late tonight, but will have
fairly widespread rains Fri and Fri night with embedded
thunderstorms possible. Winds tonight out of the S/SSE at 10-15
kts and gusts up to 20 toward daybreak. Winds continue to
increase on Fri/Fri night to 10-20 kts with gusts of 25-30 kts.
Seas 1-3 ft tonight, but increasing to 3-6 ft across the outer
waters on Fri. Should be solidly 4-7 ft Fri night across the
outer waters and 3-5 for the coastal waters near RI. Did extend
the SCA into Sat for portions of the waters. Please see the
Small Craft Advisory for more detailed information.
Outlook /Saturday through Tuesday/...
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Sunday Night through Monday: Winds less than 25 kt.
Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.
Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers.
Tuesday Night: Winds less than 25 kt. Local rough seas. Chance
of rain showers, isolated thunderstorms.
Wednesday: Winds less than 25 kt. Areas of rough seas. Chance
of rain showers, isolated thunderstorms.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Friday for
ANZ231>234-251.
Small Craft Advisory from 8 AM Friday to 2 PM EDT Saturday for
ANZ235-237.
Small Craft Advisory from 8 AM Friday to 8 PM EDT Saturday for
ANZ250-254>256.
&&
$$
SYNOPSIS...BL/KP
NEAR TERM...BL/KP/KS
SHORT TERM...BL
LONG TERM...KP
AVIATION...BL/KP
MARINE...BL/KP
Area Forecast Discussion...Updated
National Weather Service Billings MT
754 PM MDT Thu Aug 24 2023
.UPDATE...
Adjusted sky cover for a few hours this evening to better capture
the cumulus field W and S of KBIL. Visible satellite imagery also
showed smoke/haze moving south into the area from N MT and S
Canada wildfires. Based on HRRR, increased the haze over the area
through the night and into Friday. Arthur
&&
.DISCUSSION...
Through Saturday night...
The Northern Rockies will be under the periphery of an upper ridge
through Saturday night. In addition, surface high pressure will
move eastward across southern Canada on Friday. These patterns
will give quiet weather to most of the area most of the time.
However, beginning Friday afternoon, weak upper air disturbances
will move within the flow over the area. These disturbances will
bring isolated to scattered showers and thunderstorms (20-40%
chance) to the mountains and adjacent foothills Friday afternoon
into the evening, then to much of south central MT Saturday
afternoon into the evening (20-60% chance, greatest in mountains),
and to southeast MT Saturday night (20% chance). The hazard with
the thunderstorms will be strong, gusty winds across the area, and
heavy downpours over southeast MT where low-level southeasterly
winds will aid in moistening the lower atmosphere considerably.
Smoke: Smoke is in the air in our area this afternoon and likely
will persist through Friday. The 12z HRRR model shows smoke
dissipating Friday night.
Low temperatures will be in the 40s and 50s tonight then 50s to
lower 60s Friday night. High temperatures will generally be in the
70s and 80s Friday, as low-level winds bring in cooler air from
Canada to ND then MT, then 80s Saturday as low-level winds bring
in warmer air from the south and southwest. RMS
Sunday through Thursday...
High pressure ridging will build over the forecast area Sunday
continuing into Tuesday. This will result in rising heights and
warming temperatures. Conditions are expected to be dry but an
isolated shower/thunderstorm can`t be ruled out over the mountains
and adjacent foothills. However, no organized system is expected.
However, by Tuesday a large trough and upper low will move into
the Pacific northwest. This will shift the ridge axis east of
Montana allowing for a southwest flow aloft to return. The low
will move east along the Canadian border Wednesday and Thursday
flattening the ridge and sweeping a Pacific cold front across the
forecast area. Although some thunderstorm activity is possible as
the low moves east, the main impact as of now looks to be gusty
downslope west/northwest winds. Fire weather will be a concern
Wednesday as a result of the very warm temperatures and frontal
passage.
Afternoon highs will be above normal Sunday through Wednesday
with readings Sunday in the middle 80s warming into the 90s for
Monday into Wednesday. Temperatures will cool below normal behind
the front for Thursday with middle 70s to lower 80s. Hooley
&&
.AVIATION...
Scattered evening clouds will dissipate overnight, leaving VFR
conditions tonight into Friday. A layer of smoke may reduce
slantwise visibility late tonight through Friday. TWH
&&
.PRELIMINARY POINT TEMP/POPS...
Fri Sat Sun Mon Tue Wed Thu
-----------------------------------------------------------
BIL 056/083 060/089 062/086 058/087 058/092 062/093 058/082
00/U 12/W 21/U 00/U 00/U 11/U 21/U
LVM 051/080 054/086 055/084 051/086 054/090 056/086 050/077
02/W 22/T 13/T 00/U 01/U 22/T 21/B
HDN 053/084 057/090 058/086 053/088 054/093 059/094 054/082
00/H 11/U 20/U 00/U 00/U 00/U 21/U
MLS 056/080 060/091 062/085 056/085 056/091 062/094 060/082
00/U 01/U 10/U 00/U 00/U 01/U 21/U
4BQ 058/082 060/090 062/085 055/085 054/091 061/096 060/084
00/H 00/U 10/U 00/U 00/U 00/U 21/U
BHK 053/078 055/086 059/083 053/081 053/086 058/091 058/081
00/H 01/U 10/U 00/U 00/U 00/U 21/U
SHR 053/081 055/087 057/083 052/083 052/089 057/093 054/081
01/H 11/U 12/T 10/U 00/U 01/U 11/U
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.
&&
$$
weather.gov/billings
Area Forecast Discussion
National Weather Service Columbia SC
741 PM EDT Thu Aug 24 2023
.SYNOPSIS...
Heat Index values increase Friday and Saturday with near record
high temperatures and heat index values potentially exceeding
advisory criteria in some locations on Saturday. An unsettled
weather pattern sets up by the end of the forecast period, with
cooler temperatures and multiple chances for showers and
thunderstorms late this weekend into early next week.
&&
.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
As seen in visible satellite imagery, a distinct MCV and vort
max aloft is moving down the east flank of the Appalachians
into NC as of 7pm. Broad lift ahead of this shortwave helped
triggered convection across the Upstate of SC earlier, and is
now driving persistent strong convection across Central NC. RAP
analysis shows the available instability with more than 2000
J/kg ML CAPE and surface obs show more pervasive moisture with
dew points in the low mid 70`s in these areas, allowing for some
strong- severe storms to develop; dry aloft seen in the water
vapor imagery is contributing to the severity of these. As this
storms move south they are anticipated to weaken as we lose
diurnal heating and the storms will cross a fairly well defined
moisture gradient, moving into surface dew points in the mid
60`s across northern and central SC. Consequently, instability
available to these storms will quickly fall off after 8pm. ML
CAPE will fall from 2000+ J/kg in central NC to less than 500
J/kg in the Pee Dee of SC. Hi- res guidance broadly supports
this outcome and is generally in good agreement with current
obs. So while a widespread severe threat is not likely, a strong
cold pool is developing in central NC, so there will be a
window of potential damaging winds into Lancaster and
Chesterfield counties mainly between 9-11pm, before the
convection becomes outflow dominate and washes out.
&&
.SHORT TERM /7 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Hot and humid conditions dominate during the period as upper
ridging shifts east. The ridge combined with downslope flow will
promote warm air advection and high temperatures approaching
records with values in the upper 90s to around 100 degrees.
Confidence in locations exceeding the century mark is higher on
Friday as an approaching cold front could produce scattered
showers and thunderstorms Saturday afternoon which would limit
how warm we get. Heat index values may approach criteria in some
locations, especially in the Southeastern Midlands on Saturday
but confidence is not high enough to consider any products with
this forecast package. Overnight lows will be in the lower to
mid 70s.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
A significant pattern change is expected during the extended as
upper ridging retreats west in response to a developing trough
over the eastern CONUS. The surface cold front is expected to
approach from the north on Sunday and stall near or over the
region early next week serving as the lifting mechanism for
afternoon and evening convection each day. There will be the
potential for locally heavy rainfall, as tropical moisture is
drawn north out of the Gulf of Mexico. Some of the guidance,
most notably the Euro, attempts to develop a tropical cyclone
out of this moisture but confidence is low to moderate at best
for now. Regardless, improving weather conditions are expected
by Thursday as troughing lifts to the northeast. The silver
lining for the long term is that the expected clouds and
precipitation will put an end to the extreme heat with near to
below normal temperatures expected after starting on Monday.
&&
.AVIATION /23Z THURSDAY THROUGH TUESDAY/...
Ridging to our northwest will provide NW flow aloft over the
area which may drive convection into the forecast area this evening
from NC. We expect this convection to weaken as it moves toward
the area due to the dry air mass. The storms should remain
north of the TAF sites but there is a non zero chance of
thunderstorm restrictions late this evening. There will be some
convective debris clouds overnight keeping the threat of
widespread fog low. The fog threat should be limited to AGS
during the early morning hours, similar to the previous night.
Light west winds pick up Friday with no rain expected.
EXTENDED AVIATION OUTLOOK...Moisture increases this weekend
leading to potential for fog/stratus and periods of
showers/storms through Tuesday.
&&
.CLIMATE...
Daily Record High Temperatures for Columbia Metropolitan
Airport (CAE) and Augusta Bush Field (AGS):
August 25th - 100 at CAE (1975) and 99 at AGS (1968)
August 26th - 100 degrees for both CAE (1954) and AGS (1959)
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
Area Forecast Discussion
National Weather Service Corpus Christi TX
604 PM CDT Thu Aug 24 2023
...New AVIATION...
.SHORT TERM...
(Tonight through Friday night)
Issued at 347 PM CDT Thu Aug 24 2023
The sea breeze has been slow to develop today with radar showing a
slow drift inland forming at this time. Deeper mixing has occurred
with dewpoints falling into the 60s for inland areas while 70s are
holding over the Coastal Bend. May see brief period where heat
index values approach 110 once the sea breeze moves inland this
afternoon.
Satellite imagery shows a TUTT low just west of the Yucatan
peninsula over the Bay of Campeche. Higher moisture covers the
Gulf of Mexico from off the Louisiana coast to east of the Lower
Texas coast where scattered convection has developed. The TUTT
low will to move to the west-northwest and move inland over
northeast Mexico Friday afternoon. Chances for convection will
develop later tonight as the axis of higher moisture moves
northwest into the Gulf waters of the Middle Texas coast. Enough
moisture and instability will work its way inland on Friday to
provide isolated convection with the sea breeze in the afternoon.
Activity may even be scattered over the southern parts of the
inland Coastal Bend.
Will show slightly warmer temperatures for Friday. With a little
more humidity than today, afternoon heat index values could be
near advisory levels for the coastal plains. But confidence is not
high enough to go ahead with the advisory at this point. Will
leave it for the night shift to decide.
Winds will become light tonight. With recent rains, there should
be sufficient boundary layer moisture for patchy fog to form over
the inland coastal plains late tonight into early Friday morning.
&&
.LONG TERM...
(Saturday through next Wednesday)
Issued at 347 PM CDT Thu Aug 24 2023
Key Messages:
- Elevated heat indices return for the Coastal Bend and Coastal
Plains
Not much change from the previous forecast package. The upper-level
ridge over the Southern Plains will hold strong through the weekend
then slowly moves westward into the Desert Southwest early next
week. This will allow a weak cold front to push into Texas and
attempt to make its way into South Texas. Despite low confidence of
this actually happening, it if does happen it will only increase
rain chances and not provide a cool down. Other than that, our other
chance for rain in the long term will be Saturday as an inverted
trough moves across northern Mexico. Warm temperatures ranging
between 95-105 degrees are expected each day except for Saturday
and Wednesday where the possible added cloud cover and rain
chances could keep highs below 100 degrees. With the increased
moisture and warm temperatures, elevated heat indices are expected
to return to the Coastal Bend and Coastal Plains with indices
ranging from 109-114 degrees.
&&
.AVIATION...
(00Z TAFS)
Issued at 532 PM CDT Thu Aug 24 2023
Continued with a persistence forecast regarding fog potential for
the Coastal Plains tonight. The HRRR continues to be the only
model hinting at it; however, with the recent rain, there is
enough moisture in the low levels to keep from ruling fog out.
Expect MVFR visibility will develop sometime between 07Z and 09Z
then persist through 14-15Z Friday.
&&
.MARINE...
Issued at 347 PM CDT Thu Aug 24 2023
Weak onshore flow will develop behind the sea breeze for this
evening and then become light overnight. The winds will shift to
the northeast for Friday morning with the approach of a surface
trough over the western Gulf of Mexico. The winds will turn to the
east as the sea breeze forms Friday afternoon. Scattered showers
and thunderstorms will be possible over the Gulf waters Friday as
an upper level disturbance moves through the western Gulf of Mexico.
Weak to moderate onshore flow is expected each afternoon with light
and variable winds at night. Isolated to scattered showers and
thunderstorms will be possible Saturday, Tuesday and Wednesday
across the local waters.
&&
.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi 77 96 78 96 / 0 20 10 20
Victoria 75 101 75 100 / 10 20 0 20
Laredo 77 102 78 99 / 0 10 10 10
Alice 73 100 75 99 / 0 20 10 20
Rockport 79 95 79 92 / 10 20 10 30
Cotulla 74 101 78 98 / 0 10 10 10
Kingsville 74 98 77 99 / 0 20 10 20
Navy Corpus 79 93 81 95 / 10 30 20 30
&&
.CRP WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&
$$
SHORT TERM...TMT
LONG TERM....JCP
AVIATION...LS/77
Area Forecast Discussion
National Weather Service State College PA
1045 PM EDT Thu Aug 24 2023
.SYNOPSIS...
A line of storms over Lake Erie and southern Michigan is
expected to move southeast and across much of PA overnight. Some
storms could be severe with damaging winds the most likely
threat. Friday looks like a humid day with only isolated storms,
mainly in the afternoon. Saturday should be less humid and
cooler, but still hold scattered afternoon showers and
thunderstorms. Sunday and Monday look slightly cooler and mainly
dry.
&&
.NEAR TERM /UNTIL 8 AM FRIDAY MORNING/...
Storms over LE, now, but have no punch to them. The best
thermodynamics remain west of the CWA, even for the next 2 hrs
as the first storms should enter the NWrn couple counties of our
CWA. Latest SPC SVR Watch comes right up to the border, and that
seems reasonable looking at the most recent SPC mesoanalysis
graphics. Our area is certainly more stable in the low levels
than all of CLE`s and most of PBZ`s warning areas. Cells headed
for wrn NY are weaker, but deep layer shear is still progged to
be respectable at 30-35KT over our nrn/wrn counties in the next
few hours. We will continue to monitor the progression of the
huge complex over MI. The latest progs from RAP and HRRR pull
that complex mainly to the south and into the inflow where
70-75F dewpoints live (OH and far wrn PA). This seems like a
reasonable expectation, given our relatively low current
dewpoints (65-69F) in our wrn counties. A slight bulge in EHI is
seen over Warren Co at this point, so there is still a small chc
of a spinning storm. Will continue the course for this update,
as timing and intensity of precip are on track.
Prev...
First inklings of storms (some severe) back over central Lower
Michigan and near MKE. If those cells are the beginning of the
anticipated MCS, they are perhaps just 1-2hrs ahead of schedule
to make it into our nrn counties. Local radar is very quiet with
the heaviest of our showers (no TS) moving S out of the CWA at 7
PM. Due to nebulous and haphazard forcing for the next few
hours, we`ll maintain 20-30 PoPs for all of the area. But, most
places should stay dry or only see a sprinkle or two. Still very
interesting to watch how this potential event unfolds. Local
sfc/llvl stability is weak, but has been in place for quite a
while. Dewpoints have risen a few degs F over the last couple of
hours. Will hold onto all wording of poss svr and heavy
rain/flooding for the time being. The flooding threat may be
more across the N than W if some storms can line up and train
across the nrn mtns. The anticipated line/bow of storms trailing
south of the weak sfc low slated to move in from the W overnight
will be moving pretty fast to make any prolonged heavy rain
which could hold the potential for flooding. This is especially
true since we have had very little rain over the past several
days. It`s been since the 18th that we had more than a half of
an inch of rain anywhere in our CWA (a stripe from UNV to IPT
and to the NE).
Prev...
Convergence along nose of a weakening 850 mb speed max
is maintaining patchy light drizzle and isolated pockets of
light rain over eastern third of central PA early this
afternoon. Shortwave responsible for most of the forcing for
upward vertical motion is exiting to the southeast, with a lull
in the isolated shower activity expected for most into this
evening. Most of this time will be relatively rain free, but
given nearly saturated soundings in the 0-2km layer, combined
with an upsloping southeast flow, we can`t rule out some
occasional patchy drizzle across central and eastern areas.
Main concern remains convective potential late tonight into
early Friday and associated severe wx risk and heavy rain
potential. Model consensus tracks a fast- moving shortwave
from the GLAKS late tonight which may erode capping enough for
a possible MCS across Western PA tonight. Deep layer moisture
pools in this area, with PW in excess of 2"+ over the
Alleghenies overnight. CAMs remain rather divergent, but with
moisture pooling strongly over the Alleghenies, it appears the
main heavy rainfall threat will be focused there. Still some
indications of potentially strong to severe storms reaching
western and central PA counties mainly from midnight through 4AM
accompanying the MCS. If convection were to remain somewhat
surface based, updraft helicity fields even support the
possibility of a isolated tornado in the vicinity of the NY/PA
border (NW PA) where progged low level shear is highest at the
intersection of the low level jet and the surface warm front.
Elsewhere, the severe weather threat looks low in the stable air
across the eastern half of the state. However, ensemble plumes
support a good chance of elevated convection in this part of the
state tonight associated with strong warm advection at the nose
of the low level jet.
Ensemble plumes indicate most likely areal average rainfall
tonight in the 0.25 to 0.50 inch range. However, +2SD pwats
will likely support torrential downpours with any tstorms and
the latest HREF supports localized totals of 3+ inches over
northern PA, where WPC currently highlights a slight risk of
flash flooding.
&&
.SHORT TERM /8 AM FRIDAY MORNING THROUGH SATURDAY/...
Front exits my south/southeastern counties early Friday morning
with gradual deep layer drying throughout the morning and into
the afternoon. Still expect fairly considerable cloud cover on
Friday however, with sfc dewpoints slow to fall, waiting for
secondary boundary to drop across the region Friday night into
Saturday morning. Saturday should feature plenty of sunshine and
lower humidity as high pressure noses into the region from
Ontario.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
As the upper-level ridge continues to retrograde we can expect
to see slightly below average temperatures and somewhat wet
conditions across the Commonwealth for the extended period. By
sunday the 500mb ridge will be confined to the four corner
region of the western United States and allow for an amplifying
trough to progress through Pennsylvania from the north on
Tuesday into Wednesday.
Sunday is expected to be dry with max expected temperatures to
be in the low 70s to the north east and reach 80 in the
Susquehanna valley. A short-wave will pass overhead Monday and
bring a slight chance of rain to the area during the afternoon
hours before the main trough propagates through. Tuesday
into Wednesday may hold some heavier showers and thunderstorms,
but the flow of best moisture from the S/E will be meager and
may not line up with the approach/passage of the trough and cold
front moving down from the Upper Midwest/Great Lakes.
Additionally, some uncertainty remains in the guidance for what
temperatures will be like at the end of the extended period.
Temps will all depend on how quickly the ridge rebuilds over the
midwest. As a result, decided to stick with the NBM for
temperatures for the end of next week.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
A line of thunderstorms that is currently developing over
Michigan will impact the area overnight. Current thinking is
that the line should approach BFD around 05Z and then continue
pushing southeastward through the night, but the exact timing
is still somewhat uncertain. Gusty winds and heavy downpours
will be the main threats with these storms.
While VFR conditions will be possible for a few more hours, cigs
will lower ahead of the approaching thunderstorms to MVFR/IFR.
Ceilings will likely stay MVFR for most locations through the
morning with a few lingering showers, but southern sites could
see low VFR conditions return later in the day.
Outlook...
Sat...Showers/t-storms possible in the afternoon.
Sun-Tue...VFR conditions.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...DeVoir/Dangelo
NEAR TERM...DeVoir/Fitzgerald/Dangelo
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Bauco/Bowen
AVIATION...Bauco
Area Forecast Discussion
National Weather Service Cheyenne WY
527 PM MDT Thu Aug 24 2023
.SHORT TERM...(This evening through Saturday night)
Issued at 300 PM MDT Thu Aug 24 2023
Forecast concerns deal with location and timing of severe
thunderstorms this afternoon...followed by heavy rainfall tonight
through Saturday morning.
Currently...Upper low from Tropical Storm Harold now located near
the 4 corners area this afternoon. Upper ridge axis has shifted
eastward into western Nebraska. PWATS this afternoon range from
1.0 inch in Carbon County to 1.25 inch in the Panhandle. Surface
low over northeastern Wyoming this afternoon with a surface
boundary extending south into the northern Panhandle and then east
across central Nebraska. Across the northern Panhandle...SBCAPE
values are up near 1500 to 2000 J/KG up near Dawes and Box Butte
Counties this afternoon. A Marginal Risk for severe storms extends
from a line from Bridgeport to Lusk.
Latest HRRR and RAP simulated radar shows convection becoming
widespread across central Albany and southeastern Carbon Counties
this afternoon. Also shows a couple cells up near that Marginal
Risk area around 23Z this afternoon. Evening crew will need to
watch radar closely for a time. Attention turns to tonight into
Friday.
Frontal boundary shifts south into the southern CWA after
midnight tonight as the upper low from Harold moves into northern
Colorado just south of Carbon County. HRRR/RAP simulated radar
showing convection filling in across Albany and Laramie Counties
after 12Z. Pretty high 6 hour QPF seen on ECMWF/NAM/SREF and GFS
between 12Z and 18Z Friday...though do think the QPF maxima are
too far north. Kept the higher QPF down here near the I-80
Corridor. Mid shift will need to determine whether to expand the
Flood Watch further north as the event unfolds. Guidance continues
to show moderate to heavy rainfall continuing through the
afternoon Friday. Forecast storm motions for Cheyenne and Laramie
under 10kts through the day Friday...so storms are going to be
dumping a lot of rain. Precipitation becomes more stratiform
Saturday evening as frontal boundary continues to shift south and
we lose all instability.
.LONG TERM...(Sunday through Thursday)
Issued at 300 PM MDT Thu Aug 24 2023
A decent amount of uncertainty in the long term forecast, with a
possible wet start to the week, and continued hot and dry conditions
that are expected to soon follow.
By the early start to the week, shortwave energy is expected to dig
to the southeast across the Northern Rockies and Plains into the CWA
producing primarily northwesterly flow across north to north-central
CONUS. Combined with some lingering tropical moisture will aid in
the production of afternoon showers and thunderstorms along the I-25
corridor and further east in to the Nebraska Panhandle. All in all,
not too concerned with severe potentials as the thermodynamic
profiles remain on the low end. However, the GFS does try to bring
in some pockets of higher MUCAPE across KSNY with better low to mid
level lapse rates further east into Nebraska. With the latest GFS
model runs, will need to monitor through the early portion of the
weekend to determine if isolated showers and thunderstorms will be
the more likely scenario or if stronger storms might be able to
develop.
Main uncertainty with the long term forecast exists for Monday, with
the placement of the upper level ridge being the deciding factor for
either a dry or wet forecast. Current GFS and Euro deterministic
models vary slightly, with the Euro placing better moisture
advection into the region and kicking up diurnal convection. On the
opposite end, the GFS proposes a drier solution with primarily
northerly flow across southeast Wyoming and the Nebraska Panhandle
keeping PWATs below 0.65 inches and much better precipitation for
Colorado. At this time, went with Euro for having slightly better
handle on the lingering low-level moisture and the resultant higher
PWATs.
Tuesday through the early morning on Thursday, the upper level ridge
is progged to push eastward, with the ridge axis positioning
directly across the High Plains, keeping the area mostly hot and
dry. GFS 700mb model guidance have continued to indicate
temperatures climbing to around 15C to 18C for southeast Wyoming and
the Nebraska Panhandle, and gaining traction with the NAEFS mean
700mb temperatures in the climatological 99th percentile for much of
the region. Therefore, started blending in higher percentiles of the
NBM into the current forecast to account for this temperatures
increase. Hottest day expected is progged for Wednesday, with
daytime highs in the mid-80s to low-90s along the I-25 corridor and
mid-90s for the Nebraska Panhandle. However, if these trends in the
GFS continue, could see those temperatures continue to increase in
the next forecast update.
Chances for afternoon showers and thunderstorms increase by late
week, with an upper level closed low developing across the Pacific
Northwest and pushing its way eastward. Portions of this system are
possible to dig far enough south for some energy to kick up
precipitation along the way. Still a bit too far out to call, but
will need to be monitored throughout the week for any impacts
possible.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 509 PM MDT Thu Aug 24 2023
An active weather forecast will continue the next 24 hours for
terminals as VCTS, -SHRA, and -TSRA spread across the region the
next 12-24 hours. VFR is anticipated between 0Z and 12Z Friday,
but low CIGs and VIS are expected to increase across terminals in
the next 12 hours from 12Z to 0Z Friday/Friday evening. Localized
MVFR to IFR fluctuations as the showers and thunderstorms spread
across the area. Wind gusts up to 25 knots are possible in the
next 24 hours where the strongest thunderstorms occur.
&&
.FIRE WEATHER...
Issued at 300 PM MDT Thu Aug 24 2023
Minimal fire weather concerns through the weekend as area is going
to see widespread wetting rains beginning tonight and continuing
through Saturday. Remnants of Tropical Storm Harold will interact
with incoming monsoonal moisture to create widespread rain across
southeast Wyoming and Nebraska Panhandle. Widespread rain expected
to end from north to south Saturday morning...but still looking
at good chances for afternoon and evening showers and storms each
day through Tuesday. Hotter and drier after Tuesday.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Flood Watch from Friday morning through late Friday night for
WYZ115>119.
NE...Flood Watch from Friday morning through late Friday night for
NEZ054.
&&
$$
SHORT TERM...GCC
LONG TERM...MRD
AVIATION...BW
FIRE WEATHER...GCC
Area Forecast Discussion
National Weather Service Des Moines IA
1057 PM CDT Thu Aug 24 2023
...Updated for the 06z Aviation Discussion...
.DISCUSSION.../Tonight through Thursday/
Issued at 411 PM CDT Thu Aug 24 2023
Key Messages:
- Few storms possible in the north overnight
- Relief from the extreme heat for most tomorrow
- Excessive Heat Warning still in effect through tomorrow
afternoon for those south of I-80
- Cooler with sporadic precipitation chances this weekend
The hot and muggy conditions continue today for much of the state as
temperatures have climbed into the mid to upper 90s early this
afternoon. Fortunately, dewpoints are slightly lower today, although
still in the mid to upper 70s. This has resulted in heat index
values of 105 to 110+ this afternoon. Those in far northern Iowa
have remained a bit cooler with the northerly flow and weak cold air
advection behind a diffuse cool front, but lack of much cloud cover
and high dewpoints pooled along and behind the front has still
allowed temperatures to climb into the low 90s and heat indexes near
100F. Lows tonight will remain seasonably warm but slightly cooler
than previous nights, as temperatures fall into the low to mid 70s.
The cool front will slowly leak further south this afternoon and
evening, switching flow across the area to be more northerly. This
will bring relief from the extreme heat for most of the area by
tomorrow, although temperatures will still be seasonably warm. This
boundary will stall out in the south, resulting in another day of
hot temperatures for the far southern portions of the area. With
high dewpoints along the front, heat index values will again be
quite uncomfortable in the afternoon. Therefore, given the prolonged
period of heat in this area and high heat index values tomorrow,
have extended the Excessive Heat Warning through tomorrow afternoon
for counties south of I-80.
The much discussed upper level high pressure responsible for our hot
temperatures the last few days continues to break down through the
weekend. This change in the pattern will bring cooler temperatures,
as well as a few sporadic chances for showers and thunderstorms. The
first of these chances will be in northern Iowa early tomorrow
morning as precipitation develops along the northern edge of the
ridge. HRRR and RAP guidance show convection out in Nebraska and
South Dakota organizing into an MCS that would track into northwest
Iowa and across the northern portions of our CWA. The parameter
space along with this MCS isn`t overly robust but with effective
shear values near 30 kts, instability around 1500 J/kg, and a
relatively moist profile with PWATs of ~1.9 inches, organized
convection can`t be ruled out. Should this pan out, the primary
concern would be bursts of gusty winds resulting from evaporative
cooling in the drier low levels. Other short range guidance is less
organized with this convection, with only scattered showers and
storms developing in northern Iowa early tomorrow morning.
The next chance for storms wont be long after this, as more
development is possible Friday evening. This parameter space will
boast slightly more instability than the early morning convection
but will have a limited window out ahead of a boundary pushing south
through the state. Shear along the boundary will again be marginal,
with values around 30 kts. Most of the short range guidance doesn`t
key in on much convection Friday evening, with the NAM Nest and ARW
being the outliers along with a few global models producing sporadic
convection in southern Iowa. Therefore, widespread severe storms are
unlikely, but given the dry low levels and higher instability, gusty
winds and small hail are possible with stronger storms. This is
spelled out in the SPC marginal risk also in place for this area.
After the second boundary brings cooler air through again Friday
night, temperatures return back to normal for the weekend as highs
only reach the low 80s on Saturday and Sunday. This will make for a
fairly pleasant weekend with light wind and much cooler temperatures
than what Iowans have been enduring recently. Precipitation also
mostly holds off through the weekend, with only a slight chance of
showers and storms clipping the far southern edge of Iowa Sunday
morning. A wave then moves through late Sunday night and into
Monday, which looks to bring more precipitation chances to start
out the work week. Again, these chances are sporadic and likely
wont result in widespread rainfall, but will continue to monitor
through future forecast cycles. Next week, temperatures remain
mostly seasonal with no extreme heat in site for the rest of the 7
day period.
&&
.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1057 PM CDT Thu Aug 24 2023
There has been little change in thinking since 00z. VFR
conditions are expected for much of tonight with nothing beyond
patchy mid or high cloudiness. While VFR conditions still remain
most likely, stronger showers and storms may develop over
northern Iowa 11-18z Friday which have the potential to degrade
conditions, mainly due to visibility. Confidence in occurrence and
location is too low to mention beyond VCSH as of yet however.
Convection may also develop over southern Iowa late Friday
afternoon as well, possibly near KOTM, with any impactful
conditions omitted due to similar thinking.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 7 PM CDT Friday for IAZ070>075-
081>086-092>097.
&&
$$
DISCUSSION...Dodson
AVIATION...Small
Area Forecast Discussion
National Weather Service El Paso Tx/Santa Teresa NM
545 PM MDT Thu Aug 24 2023
...New AVIATION...
.SYNOPSIS...
Issued at 200 PM MDT Thu Aug 24 2023
Temperatures will be warming back into the 90s through the weekend
as upper high builds back over the region. Thunderstorm chances
will be areawide through Friday, but shift to the far west
Saturday, then to the east Sunday. A weak front will move in early
next week and bring the best chance for areawide storms Monday and
possibly Tuesday. Heat returns for the second half of next week.
&&
.DISCUSSION...
Issued at 200 PM MDT Thu Aug 24 2023
Thanks to the remnants of Harold moving through yesterday, we have
some low level moisture in place which will just spin around the
upper high over the next week. Models in good agreement with
pattern which starts out with high over OK and ends with the high
back over OK. In between, the high pushes west into AZ which
brings the heat back to the region. Currently there is a deep
southerly flow over the area and some isolated storms starting to
develop over higher elevations. Temps are slow to warm this
afternoon due to the moisture and clouds which is keeping things
capped over the lowlands. Models are picking up on storms
developing in Mexico and then pushing north into the Rio Grande
Valley overnight. GFS has been showing this for several runs while
the HRRR has been slow to catch on, but latest couple of runs are
increasing storm coverage after about 05Z. Went along with this
solution and focused highest coverage between Dona Ana, El Paso
and western Otero counties. Don`t expect severe weather, but PW`s
still over 1.3 inches, so locally heavy rain could be an issue.
Going into Fri and Sat, high pushes westward and ends up over
central NM into the TX Panhandle by 00Z Sun. This will push best
moisture to the western zones, possibly all the way into AZ by
late Sat. Should still see at least scattered storm coverage over
the Gila and west of the Divide, also over the Sacramento
Mountains. Then it will depend on outflows, but with the continued
heavy rain potential, think outflows will be fairly strong and Fri
evening could see storms down into the El Paso area. Saturday is a
little more questionable with storm coverage. GFS keeps almost all
activity out of the CWA while the EC is active over the Gila and
west of the Divide again. Looking at surface winds, both models
agree winds will be east to southeast all the way to the Gulf of
Mexico which would not support the GFS solution of dropping
surface dew points over the area into the low to mid 40s over most
of the lowlands. Kept chance pops out west and tapered off further
east closer to the high center. Looking at highs into the 90s over
the lowlands, think 100 will be tough to come by, but possibly in
the lowest elevations of the Rio Grande in TX.
The upper high shifts into AZ by late Sunday which allows the best
moisture to wrap around the east side and pick up storm activity
across the eastern zones. This does look like the most down day
for activity though. Highs will still be in the 90s. On Monday, an
upper trough moves through the Great Lakes and helps to push a
weak back door into the region which will be enough when combined
with an upper wave will increase storm coverage across the area.
Decent instability and moisture around, so locally heavy rain is
possible, not sure of severe threat since shear is not overly
impressive, but N to NE flow aloft can bring surprises. Storms
coverage looks to decrease Tue as upper high starts to elongate
eastward as Great Lakes system moves east. Still looks like storms
fire over the Sacs and then storms develop off the outflows over
the lowlands.
Moisture gets pushed out of the area for Wed/Thu with high moving
back over NM. Temperatures will warm back into the 90s after a few
semi-cooler days of Mon/Tue.
&&
.AVIATION...
(00Z TAFS)
Issued at 538 PM MDT Thu Aug 24 2023
P6SM FEW-SCT060-080 SCT-BKN150-200 for most areas, but with
increasing clouds from the south, as SHRA/TSRA moving in through
03Z...and track north across the VCTY of KELP/KLRU/KDMN. Thus have
TEMPO groups for PCPN/TSRA from 02-08Z. With these expect
potential for brief MVFR conditions with lowering CIG, averaging
050-070. Also areas of VSBY AOB 2-3SM in RA/+RA. Outflow winds
likely from the south at 20G35kts. Expect rain/storms to push
north away from the southern terminals aft 08Z with slowly
improving conditions...and possible impacts to KTCS.
&&
.FIRE WEATHER...
Issued at 200 PM MDT Thu Aug 24 2023
Low level moisture will remain around the region into early next
week with storm chances daily, placement will just move around as
the upper high shifts back over the region. Best chances for rain
Fri and Sat will be west of the Divide, although all the lowlands
could see storms Fri evening. Sunday the storm chances shift to
the east, but then become areawide for Mon as a weak back door
front moves in from the NE. Temperatures will be warming back into
the 90s for the lowlands, but RH`s should remain 20-25% and higher
with easterly low level flow continuing through the weekend.
Slightly cooler temperatures for early next week will result in
RH`s around 30% and higher. Winds will remain light except near
thunderstorms. Vent rates generally poor north to good south.
&&
.PRELIMINARY POINT TEMPS/POPS...
El Paso 72 94 72 98 / 40 20 20 10
Sierra Blanca 64 87 63 90 / 30 20 10 10
Las Cruces 68 92 68 94 / 50 30 30 20
Alamogordo 66 90 66 92 / 20 30 20 20
Cloudcroft 50 66 50 70 / 20 50 10 30
Truth or Consequences 68 89 67 91 / 40 50 30 40
Silver City 63 85 63 87 / 30 70 60 50
Deming 67 92 67 95 / 30 40 50 20
Lordsburg 66 92 66 93 / 30 60 50 50
West El Paso Metro 72 93 72 96 / 50 20 20 10
Dell City 68 91 66 95 / 10 20 0 10
Fort Hancock 68 95 67 95 / 30 10 10 10
Loma Linda 65 85 64 87 / 30 20 10 10
Fabens 69 93 68 97 / 30 20 10 10
Santa Teresa 68 90 68 94 / 50 20 20 10
White Sands HQ 70 91 70 93 / 40 30 20 20
Jornada Range 67 90 67 95 / 40 30 30 20
Hatch 67 93 67 94 / 50 30 40 30
Columbus 68 92 68 94 / 30 30 40 20
Orogrande 66 89 64 90 / 30 20 20 10
Mayhill 55 80 54 81 / 20 50 10 30
Mescalero 53 79 53 82 / 20 60 20 30
Timberon 53 77 53 78 / 20 50 10 20
Winston 58 79 58 81 / 30 70 40 50
Hillsboro 63 88 63 91 / 30 70 40 40
Spaceport 65 90 65 91 / 40 40 30 30
Lake Roberts 55 84 55 85 / 30 70 50 50
Hurley 65 89 65 89 / 30 70 50 50
Cliff 58 91 58 90 / 30 70 50 50
Mule Creek 61 88 61 88 / 30 60 60 50
Faywood 65 88 65 90 / 30 70 50 50
Animas 65 93 66 93 / 30 60 50 40
Hachita 65 92 65 93 / 20 50 50 30
Antelope Wells 64 92 65 93 / 20 50 50 30
Cloverdale 63 88 63 89 / 20 50 50 40
&&
.EPZ WATCHES/WARNINGS/ADVISORIES...
TX...None.
NM...None.
&&
$$
FORECASTER...14-Bird
Area Forecast Discussion
National Weather Service Goodland KS
524 PM MDT Thu Aug 24 2023
.SHORT TERM...(This evening through Sunday night)
Issued at 230 PM MDT Thu Aug 24 2023
Tonight...another mild night is in store for the area with low
temperatures in the lower 60s to lower 70s.
Friday-Friday night...the 500mb pattern features an upper level high
centered over northern Texas with southwest flow aloft over the
area. The remnants of what was hurricane Hilary are forecast to move
into the area during the afternoon and overnight hours. GFS/NAM/SREF
precipitable water values range from 1.3 to 1.8 inches across the
area. At the surface, a stationary cold front is front is forecast
to reside across the southern part of the forecast area by late in
the afternoon, then well south of the area during the night.
It appears that areas along north of the frontal boundary will have
higher pops in the afternoon compared to the rest of the area. This
trend continues during the night. The NAM and ECMWF 850-500mb
relative humidity and qpf forecasts also show higher pops and qpf
along and north of I-70 while the HRRR and GFS show higher pops and
qpf south of I-70. Hopefully these details get ironed out on the 00z
model cycle. Locally heavy rainfall and potentially some localized
flash flooding or flooding of low lying and poor drainage areas is
possible. Given how dry its been the past week or so and
disagreement on placement of the highest qpf we`ll be holding off on
any flood highlites at this time.
High temperatures are forecast to be in the lower 80s to near 100
degrees with low temperatures in the middle 50s to middle 60s.
Saturday-Saturday night...the 500mb high pressure area slowly
migrates west into New Mexico through the period as an upper level
trough approaches from the northwest.
We`ll continue with high chance and likely pops in the morning with
slowly decreasing pops in the afternoon and overnight hours as the
moisture associated with the remnants of Hilary slowly move away
from the area. PWAT values remain rather high during the day,
decreasing slowly during the night. The threat for locally heavy
rainfall will continue, primarily during the day.
Todays NBM high temperature guidance has come down several degrees
compared to 24 hours ago and doesnt look too bad. I`ve trended
temperatures toward the cooler NAM/SREF/ECMWF solutions which
support high temperatures generally in the upper 60s to middle 70s.
Still room to lower a bit more if the NAM verifies (its forecast
highs are in the middle 60s to upper 70s). Low temperatures are
forecast to be in the middle 50s to lower 60s.
Sunday-Sunday night...generally dry conditions return during the day
with perhaps a few showers/thunderstorms across far eastern Colorado
in the afternoon as mid level moisture increases ahead of an upper
level trough. During the overnight hours, most of the area has
slight chance to chance pops with the passage of the upper level
trough. High temperatures are forecast to rebound back into the
lower to middle 80s with low temperatures in the 55 to 60 degree
range.
.LONG TERM...(Monday through Thursday)
Issued at 230 PM MDT Thu Aug 24 2023
Monday...the 500mb pattern features a large trough to our east
and high pressure to our west/southwest, putting the area under
northerly flow aloft. There is a hint of moisture in the 700-500mb
layer, supporting slight chance to chance pops for much of far
eastern Colorado during the day. GFS/ECMWF/GEM 850mb temperatures
are very close to the current forecast highs in the middle 70s to
upper 80s. Low temperatures are forecast to be in the lower to
upper 50s.
Tuesday...todays 500mb forecasts from the GFS/ECMWF/GEM models show
the influence of the upper high spreading into our area from the
west as the east coast trough moves away. With very little moisture
available for precipitation, the dry forecast from the NBM looks
good. NBM forecast highs in the lower to middle 80s look reasonable
when compared to a blend of GFS/ECMWF/GEM 850mb temperatures. Low
temperatures are forecast to be in the 55 to 60 degree range.
Wednesday...the upper level flow becomes a bit more zonal with a
closed low traversing along the US/Canada border and upper ridge
center over New Mexico. Little moisture available once again for
rainfall so will maintain a dry forecast. GFS 850mb temperatures are
about 6C warmer than the ECMWF/GEM temperatures making it difficult
to pinpoint high temperatures. It appears that NBM high temperatures
in the 85 to 90 degree range favor the ECMWF/GEM 850mb temperatures.
Low temperatures are currently forecast to be in the middle 50s to
middle 60s.
Thursday...a monsoonal flow pattern redevelops with the upper level
ridge to our southwest and the above mentioned low bordering the
North Dakota/Canada border. There could be a few thunderstorms after
00z generally along and west of KS Highway 27. GFS 850mb
temperatures continue to be 4-5C higher when compared to the
ECMWF/GEM models. High temperatures are currently forecast to be in
the 90 to 95 degree range, closer to typical mixing from the
ECMWF/GEM models.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 521 PM MDT Thu Aug 24 2023
VFR expected to prevail at both KGLD and KMCK through the TAF
period. A cold front Friday morning will shift surface winds to
northeast. Scattered showers and thunderstorms will develop Friday
afternoon, but confidence is low in directly impacting either
terminal at this time.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
SHORT TERM...99
LONG TERM...99
AVIATION...024
Area Forecast Discussion
National Weather Service Green Bay WI
1016 PM CDT Thu Aug 24 2023
Updated aviation portion for 06Z TAF issuance
.SHORT TERM...Tonight and Friday
Issued at 315 PM CDT Thu Aug 24 2023
The latest RAP analysis and satellite/radar imagery show a weak
wave of low pressure located over southwest Wisconsin and an
associated warm front south of Wautoma and Fond Du Lac early this
afternoon. North of the front, north to northeast winds and a
stout inversion have kept the shallow, cool airmass and widespread
low stratus in place. Temperatures are really struggling to warm
beneath this cloud mass, with temps still in the upper 60s over
Vilas county. Although there are some breaks in the overcast
upstream, the clouds extend across Lake Superior to eastern
Dakotas. As the hot air dome retreats further south, forecast
concerns revolve around cloud/temp trends, and thunderstorm
potential on Friday afternoon.
Tonight...Weak high pressure will build toward the western Great
Lakes as the cold front drops south of the region. North winds
will continue to advect a shallow, cool airmass across northern
Wisconsin, with an inversion trapping the stratus in the boundary
layer. While some breaks in overcast will likely occur, think
mostly cloudy to overcast conditions will be most prevailing. Like
last night, think ceilings will fall with areas of fog and mist
developing late. Remained on the warmer side of guidance with lows
in the upper 50s to middle 60s.
Friday...The morning will start out cloudy, and looking upstream,
think will see partial clearing take place by midday. However, a
potent shortwave will dive southeast across Lake Superior and push
a weak cold front across the region in the afternoon. With strong
winds aloft, deep layer shear of 40 to 50 kts and a straight
hodograph would favor splitting storms and rotating updrafts.
Think dynamics will be sufficient to overcome a lack of low level
convergence and moisture to get widely scattered storms to
develop. However, instability is marginal (500-750 j/kg of cape)
for severe storms and there are doubts about cloud cover
inhibiting steep low level lapse rates from developing. So at this
point, will continue the wording as isolated strong storms
possible that could contain small hail and gusty straight line
winds to 50 mph. Remained colder than the NationalBlend with highs
ranging from the middle 70s to middle 80s.
.LONG TERM...Friday Night Through Thursday
Issued at 315 PM CDT Thu Aug 24 2023
The main highlights from this forecast period revolve around
showers and storms departing at the start of the period, cooler
and drier conditions for the weekend, and the next chance for
showers and storms Monday into Tuesday.
Friday night through the weekend...The departing cold front could
still produce a storm or two Friday evening, but as we get into
the early overnight hours, quiet conditions will move into the
region. CAA behind the cold front from Friday will bring a relief
to the heat, with highs dropping back into the 70s, and establish
a region of broad surface high pressure that will keep mostly
quiet conditions for the region. Winds will shift towards the
south again by Sunday as the surface high departs, bringing back
a slight rise in temperatures for the end of the weekend.
Rest of the extended...The next chance for precipitation will be a
fast moving shortwave that will cross the region early next week,
Monday into Monday evening. Showers and storms will accompany this
frontal passage, but the strength of the storms will largely
depend on the timing of the front as it enters the region. Quiet
conditions will quickly return for late Monday night and last
through the remainder of the extended.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 1005 PM CDT Thu Aug 24 2023
Widespread low stratus covered much of the forecast area late
this evening, and was slowly filling in over central and east
central WI. Partial clearing was noted over NW WI and parts of
the Upper Peninsula of MI, where high pressure was building in.
Expect low stratus to cover most of the forecast area overnight,
and light winds and lingering low-level moisture should allow
fog to develop. VSBYs should drop to IFR in most areas, but dense
fog and LIFR/VLIFR conditions are expected in NC WI, including the
RHI TAF site. The fog is expected to mix out between 13z-15z/Fri,
with the stratus deck gradually rising to MVFR, then VFR toward
midday. An upper level disturbance and associated cold front may
bring scattered thunderstorms to the RHI TAF late Friday
afternoon, but the strongest upper level forcing is expected to
pass by to the north. A scattered, weakening line of showers or
storms may briefly impact the southern TAF sites early in the
evening, so will mention showers for a few hours.
Another round of low clouds may also drop into northern WI during
the late evening on Friday.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM.....MPC
LONG TERM......Uhlmann
AVIATION.......Kieckbusch
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
902 PM CDT Thu Aug 24 2023
...New MESOSCALE UPDATE...
.MESOSCALE UPDATE...
Issued at 853 PM CDT Thu Aug 24 2023
Showers and storms have now dissipated so adjusted PoPs to
reflect current weather conditions. As storms rolled through,
there were gusts as high as 40mph offering instant relief from the
heat knocking temperatures down some 15 degrees. However it
didn`t last long and temperatures climbed back up once storms
cleared, but they did stay below 100 degrees. Low temperatures
tonight will be slow to fall and only drop to the mid to upper
70s. Clear to mostly clear skies can be expected. /JNE/
&&
.DISCUSSION...
Issued at 259 PM CDT Thu Aug 24 2023
Today and tonight: An upper ridge is finally showing signs of
weakening as denoted by observed heights of 595dm, down from 603dm
and some high cirrus has been observed across the area this
morning. ESE surface flow has allowed for deeper moisture, with
dewpoints in the mid 70s across the area. While these are slightly
mitigating factors compared to recent 100+ days, temperatures
should near record to record highs today. Record high potential is
largely dependent on how deeply mixed we can get this afternoon.
With recent observations and near term guidance, best mixing
should be south of I-20 along HWY 49. The development of CU fields
on visible satellite is evident of the greater moisture and may
also limit record potential. An excessive heat warning remains in
effect areawide through at least Friday, with likely extensions in
future forecasts.
Higher dewpoints should lead to much warmer nights, approaching or
exceeding record warm lows (upper 70s to near 80) across the area.
This will exacerbate heat stress conditions as little relief is
expected in the overnight hours.
Friday will see much of the same weather conditions with the
continuation of hot and mostly dry weather. However, there is some
hope for rain, especially in the southeast as CAMs depict low end
pops in the form of scattered showers and storms. HRRR depicts a
plume of greater moisture amid southerly flow. The upper ridge
begins to retreat west resulting in height falls, especially in the
south east. However, much of the north and western areas will still
be under the influence of the upper ridge, and hot and dry
conditions should still continue. /SAS/
Friday night through Wednesday: Although record high temperatures
are expected Saturday and near record high temperatures are expected
Sunday the unusually high mid level ridge that has brought the
record heat wave to our CWA will continue to gradually weaken over
our region through the weekend. The lower heights and thickness`
through the weekend will begin to allow for more diurnally driven
convection each day but until significant rainfall occurs, the
threat for wildfires will continue, especially across the southern
half of our CWA. In addition, the hot temperatures combined with
humidity will result in heat index values above 110F areawide
Saturday and then above 110F over all of our CWA except our
northeast Sunday where heat indices between 105-109F are expected.
The less oppressive conditions in our northeast Sunday will be the
result of a shortwave topping the mid level ridge and helping a weak
frontal boundary sag south across northeast Mississippi. This
frontal boundary will drop through our CWA Monday as another
shortwave drops through the region and deepens the upper level
trough developing over the eastern CONUS. For now, it looks like the
heat will continue across our southern zones Monday but an earlier
fropa with some decent rain amounts could mitigate any heat related
products for our CWA. By Tuesday, the heat stress related products
are expected to have ended but high fire danger will likely still be
a concern is significant rainfall doesn`t occur. Tuesday into
Wednesday the upper level trough will shift east and the mid level
ridge will begin shifting east again. Wl have a drier airmass in
place thanks to the cold front and no heat stress related products
are anticipated. /22/
&&
.AVIATION...
(00Z TAFS)
Issued at 607 PM CDT Thu Aug 24 2023
Rain and thunderstorms have finally crept back into the forecast
providing some gusty winds currently at a few sites. Though aftn
-SHRA and -TSRA have prevailed, VFR conditions will remain through
the period at all sites with an exception of PIB. As temperatures
cool down tonight, PIB could see some shallow BR around 12z and
briefly drop to MVFR, but will quickly return to VFR. Aftn
stratus will be possible tomorrow across MEI and HBG but no
impacts to flight categories are expected. Winds will vary in
direction through the period but speeds will be less than 10mph
with brief gusts as storms develop in the aftn. /JNE/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 78 103 75 102 / 10 30 20 30
Meridian 76 102 75 101 / 0 30 10 20
Vicksburg 78 102 75 102 / 10 30 10 30
Hattiesburg 76 103 75 103 / 10 20 10 30
Natchez 77 102 75 101 / 20 30 10 30
Greenville 78 101 76 101 / 0 10 10 20
Greenwood 78 102 75 102 / 0 20 10 20
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Excessive Heat Warning until 9 PM CDT Friday for MSZ018-019-
025>066-072>074.
Red Flag Warning from 9 AM to 8 PM CDT Friday for MSZ040-041-047-
053-054-059>064-072>074.
LA...Excessive Heat Warning until 9 PM CDT Friday for LAZ007>009-015-
016-023>026.
Red Flag Warning from 9 AM to 8 PM CDT Friday for LAZ007>009-015-
016-023>026.
AR...Excessive Heat Warning until 9 PM CDT Friday for ARZ074-075.
&&
$$
SAS20/22/JNE
Area Forecast Discussion
National Weather Service Pueblo CO
317 PM MDT Thu Aug 24 2023
.SHORT TERM...(This evening through Friday)
Issued at 313 PM MDT Thu Aug 24 2023
Key messages:
1) Slightly better coverage of showers and storms over and near the
higher terrain late this afternoon/this evening.
2) Widespread showers and thunderstorms expected on Friday, though
still some uncertainty about the location of the heaviest rainfall.
Currently, remnant circulation from Harold evident in satellite
imagery near the 4 corners, with associated convection beginning to
increase over swrn CO this afternoon. Still not much t-storm
activity in south central/sern CO as of 21z, with mainly isolated
storms spilling eastward into the San Juans/La Garitas, and some
weak activity over the eastern mountains, where some weak
instability has developed. For late afternoon and into the evening,
expect storm activity to ramp up along the Continental Divide as
moisture increases and remnant low drifts north, but only isolated
convection over most interior valleys and the eastern mountains,
where forcing remains weak. I-25 corridor could see some weakening
showers drift across this evening, but not expecting and significant
activity. Overnight, tropical nature of the air mass suggests storms
may linger well past sunset, and will keep pops going through the
night over the higher terrain. On the plains, cold front reaches the
Arkansas River by sunrise, with a period of gusty north winds behind
the boundary.
On Friday, HRRR/GFS suggest cold front sags southward toward the NM
border in the morning, while various other models hang the boundary
up in sern CO through the day. Remnant low drifts northward across
wrn CO during the day and PWAT values increase as modified tropical
air mass spreads over the state, with values above an inch over the
plains, and nearly 1.5 inches over nrn CO, north of I-70. Expect
widespread shower and thunderstorm activity to develop by early
afternoon and spread across most of srn CO by early evening, lowest
pops over the sern plains, highest pops farther north in the upper
Arkansas Valley. Still a good deal of spread amongst various model
solution as to where the heaviest rain will fall, though rough
consensus seems to point to areas north of I-70 for the greatest
potential for flooding rainfall. Over srn CO, several CAMs point
toward Pueblo County for heavier rainfall during the day Friday,
with perhaps some secondary development in Fremont County toward
00z, while holding off heavier rain for El Paso County until
evening. Considered a flash flood watch for Fremont/Teller/El
Paso/Pueblo for Friday afternoon, but held off as we would like a
little more consistency among the CAMs in both area/timing of
heavier rain and position of the frontal boundary before issuance.
Severe threat looks fairly low, though a marginal strong/severe
storm looks possible over the far east where air mass is slightly
more unstable. Max temps will finally be cooler, though eastern
plains will still reach the lower 90s with some sun early in the
day.
.LONG TERM...(Friday night through Thursday)
Issued at 313 PM MDT Thu Aug 24 2023
Key Messages:
1) Heavy rain continues into Friday night, with flash flooding
possible across portions of our area.
2) Another round of heavy rain will be possible Saturday afternoon
and Saturday evening.
3) Cooler temperatures and continued chances for showers and
thunderstorms persist into the beginning of next week, before drier
air arrives midweek.
Friday Night..
Tropical moisture and warm rain processes continue to spark
widespread showers and thunderstorms across the area well into
Friday night. Forecast soundings show "long, skinny" CAPE, high
freezing levels, and low LCLs, which all point the potential for
torrential rainfall that could persist well into the overnight
hours. Models continue to place highest forecast QPF values along
and north of Highway 50, where best chances to see heavy rain and
flooding look to exist for this initial round of precipitation.
Ensembles depict PWATs over 180% of normal well into Saturday
morning, with EC members dragging those near 200% values further and
further southeast across our plains with every update. Both the HRRR
and the NAM nest also depict some sort of MCV developing along the
Highway 50 corridor Friday night as well, depending on where the
front ends up. Current thinking is that heaviest rain will fall
along and north and highway 50, which aligns with the slight risk
outline from the WPC. That said, if current trends persist, this
risk could spread further south into our plains as the event draws
closer.
Saturday..
We`ll likely see continued upslope enhanced cloud cover and rain
showers throughout Saturday morning, with better chances for more
widespread showers and thunderstorms moving in once again by the
afternoon and evening hours. Given that PWATs decrease to around
150% of normal, and we will be more stable, chances for heavy rain
and flooding look to be less, though still non-zero, for Saturday
afternoon/evening. Antecedent conditions may still be enough to lead
to flooding on Saturday, especially for our urban areas and/or our
burn scars that receive significant rainfall on Friday night.
Daytime highs look to remain below normal, with most of our plains
topping out in the 70s.
Sunday Onwards..
We remain in northwesterly flow for Sunday and Monday, which will
likely keep daytime highs near or just below normal. We could also
see the potential for severe thunderstorms on our plains both
afternoons, given the possibility of residual moisture and shear
that looks to be around. Drier air arrives by midweek, with
temperatures gradually to warming back into normal ranges by the
Tuesday and Wednesday timeframe.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 313 PM MDT Thu Aug 24 2023
VFR at all taf sites the next 24 hrs, with scattered tsra over
mainly the mountains this evening and overnight. Will continue the
vcsh for KALS into the evening to account for weakening convection
drifting into the area, though stronger storms will likely stay
north and west of the terminal. Cold front early Friday morning will
bring a period of gusty north winds to KCOS and KPUB after 08z, then
Widespread tsra expected Fri afternoon/night, with impacts at all
terminals.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...PETERSEN
LONG TERM...EHR
AVIATION...PETERSEN