Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/30/21
Area Forecast Discussion
National Weather Service La Crosse WI
1056 PM CDT Thu Jul 29 2021
.SHORT TERM...(This evening through Friday)
Issued at 240 PM CDT Thu Jul 29 2021
Canadian wildfire smoke is being shuttled southward across the
area in northerly upper level flow downstream of Rockies to High
Plains upper ridge. The smoke is rather dense and is making it
down near surface in areas of WI, IA and especially across MN
where visibilities are being restricted to 1-5 miles. Air Quality
Alerts are in place for MN and recently issued for IA as well.
Satellite shows a marked decrease in smoke upstream over portions
of southern Canada and the Arrowhead of MN, and HRRR Vertically
Integrated Smoke suggests we could see some diminishing late
tonight before another infusion of smoke on Friday with point
source primarily fires near the Manitoba and Ontario border.
Aside from the smoke, the only other forecast item of note is
chance of rain, primarily Friday afternoon into Friday night.
Better moisture, instability and lift is depicted to our south,
thus any unfortunately rainfall amounts look to be light for some
of our south/southwest counties in moderate to severe drought. The
rain could limit highs Friday into the lower 70s in some areas south.
.LONG TERM...(Friday night through Wednesday)
Issued at 240 PM CDT Thu Jul 29 2021
Flow pattern aloft looks to remain stagnant with ridging entrenched
out west and broad troughing east. This will lead to a continuation
of northwest flow and generally a drier and cooler regime.
Embedded within the northwest flow will be a couple of stronger
shortwaves and rain chances. The first one still slated for
Saturday PM/eve with an attendant cold front. Bulk shear has
trended weaker from yesterday to around 20-25 kts 0-6km, while
instability fairly unchanged with around 1000-1500 j/kg CAPE, but
still sufficient to perhaps foster a few stronger storms
potentially. The cold front will then usher in a cooler and drier
airmass for the end of the weekend into the start of next week,
with very pleasant highs in the 70s to near 80 and lows in the
50s. There is a signal for another stronger shortwave and cold
front heading toward the middle of next week accompanied by rain
chances.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1057 PM CDT Thu Jul 29 2021
The main concern for aviation is whether the wildfire smoke is
going to remain in the area to produce additional visibility
reductions Friday. Base on surface observations, most of this has
been pushed west of the Mississippi River with the MVFR reductions
confined to areas west of Interstate 35. The HRRR suggests the
smoke will start to return to the area later Friday as the surface
ride slips to the south allowing the winds to come back around to
the southwest. This could bring some visibility reductions back
into the area, but confidence on how quickly this may occur is not
high enough to include in the last part of the forecast.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...McClure
LONG TERM...McClure
AVIATION...04
Area Forecast Discussion
National Weather Service Cheyenne WY
530 PM MDT Thu Jul 29 2021
.SHORT TERM...(This evening through Sunday)
Issued at 405 PM MDT Thu Jul 29 2021
Forecast challenges deal with heavy rainfall and possible severe
weather through Saturday in the short term.
Currently...Frontal boundary lays across far northeastern Colorado
to a surface low near Cheyenne and then from Laramie to just west
of Casper this afternoon. SPC surface based CAPE on the order of
3000 J/KG down here near Cheyenne to around 2000 J/KG out by the
storm ongoing just south of Arlington. Have been getting reports
of heavy rain/flash flooding in a pretty data sparse area west of
Laramie.
Latest short term guidance showing storms developing west of the
Laramie Range through the late afternoon, HRRR showing storms
developing east of the Laramie Range across southern Platte and
southern Goshen Counties around 02Z and continuing through at
least 06Z tonight. Cheyenne and CFD may be spared thunderstorms
this evening as we have been down in stratus all day. Any outflow
boundaries from the north would really throw a wrench in the
forecast...so kept fairly high chance PoPs in the forecast for
here.
Best surge of monsoon moisture Friday with PWATS up near 1.3
inches at Laramie and Rawlins. Long skinny CAPE profiles on
forecast sounding with little in the way of CAPE...so looking at
heavy rain producers. WPC has a SLight Risk area identified for
flash flooding...so went ahead and issued a Flash Flood Watch for
parts of Albany and eastern Carbon County. Will need to watch the
Mullen burn scar area closely as they are right in the bullseye
of this heavier precip Friday afternoon.
.LONG TERM...(Sunday night through Thursday)
Issued at 405 PM MDT Thu Jul 29 2021
Trends for next week have been on track for a gradual decrease in
moisture across the southeastern CONUS, with a slight increase in
temperatures through Thursday as an upper level ridge begins push
eastward. Guidance has been a bit bullish with POPs, especially on
Tuesday afternoon. PW anomalies have indicated a stronger decrease
in moisture across with a lowering to 0.4 to 0.75 inches, with the
GFS drastically reducing areal coverage of showers and
thunderstorms. Went ahead and started trending POPs down 10% to
account for this uncertainty. Can still see a chance for afternoon
thunderstorms with brief northwesterly flow on Tuesday and several
embedded shortwave throughout the week. Daytime highs are expected
to increase, relative to the cooler weekend, with highs in the low
90s east of I-25 and in the mid to low 80s to the west. Overall, not
too many fire weather concerns through the end of next week as
minimum RH values remain above 20 percent and winds remain below
criteria.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 523 PM MDT Thu Jul 29 2021
VFR conditions will continue for all TAF sites until 09Z for
southeastern Wyoming and until 12Z for the western Nebraska
Panhandle due to possible fog conditions. Thunderstorms will push
eastward across the region starting at KLAR until 03Z and KCYS
until 04Z. Light rainfall is possible for KCYS until 07Z and skies
will remain BKN along with low cloud bases for all sites. Low
visibility and MVFR conditions are possible for KRWL until 15Z and
KCDR until 18Z.
&&
.FIRE WEATHER...
Issued at 405 PM MDT Thu Jul 29 2021
Minimal fire weather conditions over the next few days as
monsoonal moisture surges into the area from the south. Expect
widespread wetting rains Friday and Saturday across southern
areas. Areas further north will see lesser amounts of rain...but
humidity expected to remain high. Afternoon showers and storms
expected on a daily basis through the weekend before monsoonal
moisture shifts south back into Colorado.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Flash Flood Watch from Friday morning through Friday evening for
WYZ105-110-114>116.
NE...None.
&&
$$
SHORT TERM...GCC
LONG TERM...MD
AVIATION...AW
FIRE WEATHER...GCC
Area Forecast Discussion
National Weather Service Des Moines IA
648 PM CDT Thu Jul 29 2021
.DISCUSSION.../Tonight through Thursday/
Issued at 305 PM CDT Thu Jul 29 2021
Forecast Highlights:
-- Sultry southern Iowa with a chance of storms into this evening
-- Smoke sinking southward into Iowa this afternoon and tonight
causing visibility reduction; lessening on Friday
-- Showers and storms re-enter the state, particularly later
Friday into Saturday morning
-- Lower humidity, around seasonal temperatures Sunday into middle
of next week
Details: There are three main concerns in the near term forecast
with heat (1) and storm chances (2) over southern Iowa and reduced
visibility due to smoke from Canadian wildfires (3). Temperatures
are well into the 80s if not the low 90s with high dewpoints in the
upper 70s or low 80s over southern Iowa this afternoon. This is
where the current heat index values are in the 105 to 110 degree
range and will let the heat advisory continue until early this
evening.
The front that caused isolated showers and storms along I-80 and
just south shortly after sunrise this morning and has continued to
caused storms over southeastern Iowa and points southeast now
resides near the Iowa/Missouri border. The front will serve as an
area of convergence for possible scattered storm development back
into central Iowa this afternoon and evening. The moisture rich
airmass over southern Iowa has created a high instability
environment with MLCAPE values eclipsing 4000 if not 5000 J/kg, but
deep layer shear is marginal around or less then 25 knots at
present. Still, storms that are able to form could become become
severe. Forecast soundings show that as the boundary layer has
warmed through the day, the moisture has remained fairly steady
resulting in inverted v soundings with downburst gusty wind
potential. In addition, given the high instability within the hail
growth zone, severe hail is also possible. It does remain uncertain
if storms will develop over our far southern counties or over
northern Missouri. SPC mesoanalysis shows and forecast 700mb also
indicate there is an area of 12C+ temperatures north of the front
that will move over southern Iowa. Where 700mb temperatures are
lower, like the RAP and HRRR forecast show now around 11 to 11.5C at
KLWD, this may allow with convergence along the front to get storms
to start around the 20z to 22z period. Will be monitoring the 1
minute imagery from GOES-East to see if any initial anvils orphan
giving an indication to a cap that is weakening. Storms that do
develop in Iowa will slowly move southeastward, but with the front
stalling and lingering over southwestern Iowa activity may remain to
some degree overnight over this area.
Other concern today into tomorrow morning will be haze and near
surface smoke from Canadian wildfires. 6z/12z HRRR smoke has been
showing an extensive area of high smoke concentration not just
aloft, but at the surface. This shows up best in the CIRA GeoColor
RGB and particularly looking at the nadir view. The smoke is even
visible easily at midday in the GOES-East visible channel, denoting
just how high the concentrations are in the atmosphere. While we
have typically added sky cover for the upper level smoke that causes
an opaqueness to an otherwise blue sky, there have been surface
visibility reductions over Minnesota. Those even moved into our
far northwestern forecast area this morning with Estherville
dropping down to 3 miles in haze, which there are at once again
this afternoon. As the smoke moves down this afternoon into
tonight, have haze and smoke in the forecast to account for the
surface visibility impact. In addition, the Iowa DNR, which
monitors air quality over Iowa, has decided to issue an air
quality alert, which our office has relayed for the Iowa DNR.
There should be a minimum in scattered shower and storm activity
along the boundary south and west of Iowa Friday morning. As the mid-
level ridge over the central US is gradually pushed back to the
southwest of the area due to troughing pushing down over
northeastern North America, this will allow for a shortwave trough
to move over the state. This shortwave will help to invigorate
convection along the surface front, which compared to 24 hours ago
is farther northeast. Still, the highest chances for rainfall will
be from northwest into southeast Iowa later Friday into Saturday.
There could be a short window for a few strong storm with moderate
instability Friday afternoon and higher deep layer shear over
southwestern Iowa. On the heavy rainfall side, precipitable water
values will top 2 inches over southwest Iowa with warm cloud depths
over around 4500m. Forecast guidance shows that a swath of 1 to near
3 inches is possible from western into south central Iowa.
Mitigating water issue concerns is the recent dry stretch with
crops able to take quite a bit of rain in addition to 850-300mb
flow that does strengthen overnight Friday.
As a shortwave trough drops into the Great Lakes with surface low
pressure moving through Ontario, a secondary cold front stretched
back into our region will finally push through Saturday night. At
this time, eastern Iowa and points eastward would be favored for
scattered storms as this drops through the region. Sunday into the
middle of next week, a large area of high pressure settles over the
region. This will bring lower humidity and dewpoints and more
seasonal temperatures through this period. As the high begins to
move off to the east late in the week, moisture will begin to return
to the region.
&&
.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 647 PM CDT Thu Jul 29 2021
Main aviation impacts are going to be visbilility restrictions due
to the wildfire smoke moving south behind frontal passage earlier
today. MVFR visibilities will be most likely, but there will be
periods dipping into IFR. Greatest threat being across
northernmost terminals. Confidence decreases somewhat further
south, but did add some visibility reductions into KDSM and KOTM
for a time after 05z or so. Conditions should improve somewhat as
the air mass mixes after 13-15z tomorrow. Also added VCSH to KFOD
tomorrow afternoon as convection chances begin increasing. May
need to expand to other sites as well, but will await 00z data to
add confidence to the where and when.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT this evening for IAZ070>075-081>086-
092>097.
&&
$$
DISCUSSION...Ansorge
AVIATION...Hahn
Area Forecast Discussion
National Weather Service Grand Forks ND
748 PM CDT Thu Jul 29 2021
.UPDATE...
Issued at 748 PM CDT Thu Jul 29 2021
Surface high pressure will pushing across the area overnight and
continue to move some of the lower level smoke from the area.
Increasing westerly flow aloft will bring additional smoke into
the area aloft in its stead. Expect northerly winds to turn light
and variable overnight, and then increase form the south on
Friday. An update Aviation Discussion is attached below.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 250 PM CDT Thu Jul 29 2021
Poor air quality due to smoke continues at least into the evening,
with localized visibility restrictions under 1 mile in the thickest
areas of smoke.
Regarding smoke/air quality: Northerly flow remains in place through
this evening. Later this evening/overnight a mid level shortwave and
associated surface low pass through SD and this will allow for low
level flow to shift to the west-southwest and may bring a few light
showers to our far southwest near the SD state line. Surface winds
may remain light and variable, so while there will be some
improvement (as already see in the northern RRV) smoke may become
trapped below the nighttime inversion. HRRR smoke model is more
optimistic as the night goes on, but past events we saw smoke
impacts linger until breezier west-southwest winds developed and
mixed out what smoke was trapped within the RRV. This would not be
expected until after daytime mixing gets underway Friday morning.
Friday-Friday night: A weak shortwave within NW flow passes main
northeast, with weaker PVA during the afternoon/evening over our
CWA. Westerly flow/WAA ahead of the associated cold front will allow
for warmer temps and highs may reach the mid/upper 80s (cloud/smoke
dependent). There isn`t a lot of moisture advection, but there may
be enough instability/forcing for showers and thunderstorms to
develop upstream and move southward into northeast ND and northwest
MN before weakening/falling apart further south. Severe doesn`t
appear to be favored, however there is some indication of pockets of
MUCAPE 1500-2000 J/KG near the International Border during peak
heating that may support isolated strong storms as the front passes.
These are likely dependent on lapse rates/clearing and confidence
isn`t high as moisture advection in the BL and aloft will be minimal.
One unfortunate result of the cold front and building Canadian high
pressure will be a return to long-fetch northerly flow from the
Canadian wildfires in Manitoba/Ontario which will likely carry thick
wildfire smoke back into our region late Friday night into Saturday
morning.
.LONG TERM...(Saturday through Thursday)
Issued at 250 PM CDT Thu Jul 29 2021
Not much to talk about starting August. The last day of July will
feature breezy northerly winds, keeping the more northerly locations
along the international border in the 70s for highs.
A ridge continues to dominate the upper levels. As the week begins,
this ridge will shift back to our west. Unfortunately, the heat of
the summer will continue for the foreseeable future with this
pattern, as hot and dry conditions will continue.
There is some hinting in the guidance that we could
see some precipitation mid week next week, however, it will not be a
drought buster. Confidence is low in terms of amounts and locations,
so not much else can be said except we are seeing some signals for
precipitation in the first week of August.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 748 PM CDT Thu Jul 29 2021
Expect generally VFR conditions across eastern ND and the Red
River Valley corridor with variable visibility in smokey skies at
low to mid levels aloft. Areas of MVFR vsbys in smoke will
stretch across northwest and west central MN this evening and
overnight... with conditions slowly improving from west to east by
early morning. Winds will be light out of the north, becoming
light and variable overnight, and turning from the south through
the morning from the south.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...Gust
SHORT TERM...DJR
LONG TERM...AK
AVIATION...Gust
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
658 PM CDT Thu Jul 29 2021
.DISCUSSION...(This evening through Thursday)
Issued at 344 PM CDT Thu Jul 29 2021
Overall scenario is a weak boundary that has stalled and
bifurcated our CWA. This boundary is somewhat detectable using
streamlines, and using dew point/heat index data to detect
moisture pooling along the boundary. Deep layer shear is weak, but
MLCAPE is moderate to high, and quite high along a very narrow
corridor adjacent to the boundary that has all but stalled. Not
much of a cap to bust today, and the past few runs of the HREF
have indicated that a narrow corridor of 30-50 percent coverage of
convection may occur, with quite efficient rainers in store. With
the combination of high instability and low shear along the
stalled boundary could actually spin up a couple of landspout
tornadoes if cells last long enough in this pulsey environment.
And of course a couple of strong to marginally severe storms are
quite possible as well. This development will closely correlate to
daytime heating, so when the sun sets this evening, it is only a
matter of a couple of hours that the storms will lose their punch
and decrease in coverage (if they develop). Already see CU fields
near I-80, slightly north of the axis of highest POPS in the
forecast. I did include 20 POPs as far south as parts of north
central KS as HREF has stubbornly included this area to be
watched, and sure enough, some CU have developed there as well.
This boundary should eventually move north overnight a bit and
will set us up for higher dew points on the Nebraska side, with
dew points with more moisture pooling, but actually mixing out a
bit farther south in KS. More storms could fire along the boundary
tomorrow, with storms firing again near the boundary in a similar
environment as today, but just focused a tad more into our
north/northeast CWA. More strong to severe storms will be
possible in the late afternoon and evening. A heat advisory has
been issued for parts of south central NE and north central KS for
the heat index.
The HRRR smoke model strongly indicates we will have some smoke
mix down tonight into Friday, focusing most of the smoke and
smokey haze in our north.
Finally cooling down Saturday behind the long awaited push south
of the boundary as the upper ridge shifts a bit west and surface
high pressure builds in from the north. Dew points will take an
extra day to dry out, and for Sunday we will be noticeably drier
and the more comfortable conditions will stick around for a good
few days. Could see some storms firing in our south for Saturday
as the front takes time to completely clear the CWA, and would not
be out of the question for a strong storm to develop in our far
south for Saturday afternoon as well.
After the dry Sunday/Monday, small POPs return by late Monday
night into Tuesday into mid week with return flow.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 648 PM CDT Thu Jul 29 2021
Fairly difficult forecast regarding ceilings and visibility. First
for ceilings, we have MVFR ceilings that are irregularly shaped
and have been quite stubborn in the vicinity all day, especially
to the north and have at least temporarily set up in the KGRI
area. Movement of this stratus is rather erratic and shape
shifting, so predicting development is quite difficult as models
do not seem to have a very good grasp. This does have the
hallmarks of persisting for at least a few hours, judging by
stratus history all day to the north. Also, we have a wildfire
smoke problem with smoke mixing down to the surface originating
from fires in Canada. HRRR smoke model indicates a lowering of
visibility to MVFR for KGRI, and may be a touch earlier than what
is indicated in the forecast if latest observations to the north
are an indicator. Any shot at 1SM should remain north of both
terminals. Wind should remain relatively light as flow near the
surface boundary will be weak and flow aloft is weak as well.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory until 9 PM CDT this evening for NEZ046>049-060>064-
072>077-082>087.
Heat Advisory from noon to 9 PM CDT Friday for NEZ062>064-
075>077-085>087.
KS...Heat Advisory until 9 PM CDT this evening for KSZ005>007-017>019.
Heat Advisory from noon to 9 PM CDT Friday for KSZ006-007-018-
019.
&&
$$
DISCUSSION...Heinlein
AVIATION...Heinlein
Area Forecast Discussion
National Weather Service Goodland KS
543 PM MDT Thu Jul 29 2021
.SHORT TERM...(This evening through Friday night)
Issued at 327 PM MDT Thu Jul 29 2021
Short term forecast concerns are going to remain hot temperatures
with dry conditions and the possibility of smoke from forest
fires over the western U.S. moving through the area.
High pressure aloft remains centered over the central High Plains
region during the day on Friday with a surface low consolidating
over eastern Colorado that moves across the forecast area Friday
night along with a cold front. Cooler temperatures are expected
behind that cold front. Also concentrated behind that cold front,
some of the smoke from fires over the western U.S. and Canada is
being shown by the HRRR to be concentrated near the surface on the
northern side of the cold front. The area of concentrated smoke
near the surface may be enough for some folks to smell, create air
quality issues, and produce areas of haze and reduced visibility
in smoke if concentrations end up being high enough. Have decided
to go ahead and bring smoke and haze into the area overnight
Friday night into early Saturday morning.
.LONG TERM...(Saturday through Thursday)
Issued at 327 PM MDT Thu Jul 29 2021
The forecast focus shifts from hot temperatures to the possibility
of additional haze and smoke from forest fires during the first
part of the weekend, to the chances of showers and thunderstorms
each day from Saturday through the middle of next week.
Saturday and Sunday, the high pressure area that had been located
over the Rockies and central High Plains retrogrades westward as a
large ridge amplifies over the Intermountain region northward into
western Canada. That amplified pattern breaks down through the
upcoming work week as short wave troughs initially top the ridge
on Monday and Tuesday and then end up plowing through the ridge by
late in the week.
Showers and a few storms are depicted by guidance as following the
surface front across mainly the northern part of the forecast area
Friday night into early Saturday with additional more numerous
storms moving off the Front Range and developing along the frontal
boundary as it moves south of the area Saturday late afternoon and
evening. A similar setup is expected Sunday and Monday with storms
developing mainly over the Rockies and moving eastward over the
plains late each day as they dissipate, with storms being more
numerous over the southern plains in closer proximity to the
remnants of the frontal boundary.
For Tuesday through Thursday, it looks like a northwest flow
pattern sets up with several short waves moving through the flow
that will help contribute to the development of mainly diurnal
storms. Model consistency lessens through the week with the timing
and locations of individual short waves.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 542 PM MDT Thu Jul 29 2021
KGLD expects to see VFR conditions during the 00Z TAF period.
Winds at KGLD start south-southeasterly around 12 kts with
occasional gusts up to 20 kts before winds decrease to around 8
kts at 02Z. By 07Z, KGLD winds look to turn southerly then
increase to 12 kts at 15Z. At 17Z, the southerly winds at KGLD
become 12G20 kts then decrease to around 11 kts by 22Z.
KMCK also sees VFR conditions throughout the 00Z TAF period
starting with southeasterly winds at 12 kts. At 02Z, winds at KMCK
turn easterly around 8 kts then slow to 5 kts by 11Z. At 14Z, KMCK
winds become southerly around 9 kts before increasing to 10G15 kts
at 20Z.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
SHORT TERM...LOCKHART
LONG TERM...LOCKHART
AVIATION...076
Area Forecast Discussion
National Weather Service North Platte NE
619 PM CDT Thu Jul 29 2021
.SHORT TERM...(This evening through Friday night)
Issued at 323 PM CDT Thu Jul 29 2021
Satellite shows two fairly potent UA disturbances moving through
MT and WY this afternoon. The disturbances are the basis for
likely thunderstorm chances Friday afternoon and Friday night. The
disturbances will lift north and east through wrn SD tonight and
move through ncntl Nebraska Friday and Friday night. The models
suggest the first disturbance moving SD tonight would set off
scattered thunderstorms across nrn Nebraska late tonight and
Friday morning and the second disturbance arrives Friday afternoon
or evening producing the best thunderstorm chance.
h500mb-300mb winds aloft increase to 25 to 40 kts across ncntl
Nebraska and a warm front will lift north Friday providing focus for
storm development. Given the strong winds aloft and the excellent
upper level support shown by the models, some amount of severe storm
development appears likely. The only limiter might be lapse rates;
temperatures at h500mb remain fairly warm, -7C or warmer.
Storm hazards are primarily wind damage and perhaps isolated tornado
development. Given the warm air aloft, large hail would seem to be a
lesser concern. The models are in very good agreement opening up a
warm sector across ncntl Nebraska Friday afternoon. The strong winds
aloft, deep moisture and attendant warm front are the basis for the
tornado concern.
Precipitable water increases to over 1.5 inches ahead of storm
development and this is the basis for WPC`s marginal excessive
rainfall outlook.
All of this storm activity should be south and east of ncntl Nebraska
Saturday morning.
Isolated to scattered thunderstorm coverage is in place this evening
and overnight for the ongoing thunderstorms across across wrn and
ncntl Nebraska. The 12z KLBF UA sounding suggested a high based or
elevated thunderstorm chance. Given the very weak winds aloft- 15-
20kts at h500-h300mb, these storms have the potential to produce
wind gusts and this is the basis for SPC`s day one marginal severe
weather risk.
The temperature forecast leans on the short term model blend plus
bias correction. The produced lows mostly in the 60s and highs in
the 80s north and 90s to near 100 south Friday. A surge of warm air
and deeper mixing across srn Nebraska supports the very warm
temperature forecast. Dew points are expected to fall somewhat in
the afternoon and a check on heat indices suggest upper 90s. No Heat
Advisory will be issued for this forecast but it will be close.
Later forecasts could include a Heat Advisory along and south of
Interstate 80 if dew points can remain in the mid 60s or higher
throughout the afternoon.
.LONG TERM...(Saturday through Thursday)
Issued at 323 PM CDT Thu Jul 29 2021
Western and north central Nebraska will remain post-frontal Saturday
and beyond. The robust area of thunderstorms across ncntl Nebraska
Friday should send an outflow driven cold front through wrn
Nebraska Saturday.
Sunday and beyond, a fairly strong upper low will form near Hudson
Bay and this will place wrn and ncntl Nebraska in a strong northwest
flow aloft as strong subtropical high pressure aloft becomes
centered over the cntl and srn Rockies. A reinforcing Canadian cold
front will move through Nebraska Sunday. This back door cold front
will push through the region and become stationary across ern WY and
nern Colorado. The result will be several days of highs in the 80s
and thunderstorm chances will be confined to wrn Nebraska where,
presumably, storm activity firing across WY or the Black Hills will
move south-southeast through wrn Nebraska at times.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 619 PM CDT Thu Jul 29 2021
A couple aviation weather concerns arise over the next 24 hours or
so, including reduced visibility from haze/smoke and
thunderstorms. The brunt of the smoke will likely stay over the
northern terminals (KVTN to KONL) with visby improving overnight
but falling again around sunrise. Isolated thunderstorms may
affect southern terminals (KOGA to KLBF to KBBW) with tempo gusty
erratic winds. Thunderstorm coverage will increase tomorrow
morning and afternoon, mainly in the north. Some storms could be
severe after 30/21z with large hail and wind gusts 50+ kts.
&&
.FIRE WEATHER...
Issued at 323 PM CDT Thu Jul 29 2021
A check on the 18z RAP and HRRR model near surface smoke
forecasts suggests the thick plume of trapped near sfc smoke
across ern SD this afternoon will drop south into northern
Nebraska tonight and possibly remain in place during the day
Friday. The models provide a 48 hour forecast and suggest the
smoke will partially mix out Friday. The smoke is trapped in an
inversion layer below 700mb.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Snively
FIRE WEATHER...CDC
Area Forecast Discussion
National Weather Service Louisville KY
1113 PM EDT Thu Jul 29 2021
.Mesoscale Update...
Issued at 1111 PM EDT Thu Jul 29 2021
Isolated to scattered thunderstorms have filtered into our southern
Indiana and Kentucky Bluegrass counties and are approaching the Ohio
River. Activity thus far has remained sub-severe, though one storm
currently along the Orange/Harrison (IN) county line has shown
supercellular characteristics and has been watched closely.
Activity over the next hour or so will likely remain isolated to
scattered, but we could see some additional storms drift in from the
north overnight along the cold front. The overall strength of the
convection overnight still has the potential to become severe given
some favorable instability and modest shear in place, but at least
up to this point weak capping in the low levels has kept things from
getting too out of control.
Issued at 920 PM EDT Thu Jul 29 2021
Isolated to scattered storms are starting to develop or enter into
our southern Indiana counties. Most of this activity has been non-
severe, but toward Crawford County, Illinois, there was a supercell
that produced a TDS via KVWX. The environment across our southern
Indiana counties remains very unstable above a weak inversion (>4000
J/KG MUCAPE), so if/when storms can overcome it and tap into the
unstable air, they could quickly become strong or severe.
Earlier in the day, models hinted at broken lines of strong to
severe storms pushing into our region during the overnight hours.
The latest HRRR runs indicate much of this activity may stay
isolated to scattered in nature for the majority of the night, and
given the latest radar trends, think this could be a viable
solution. Severe potential also looks like it could persist a bit
longer than originally thought and affect portions of south-central
Kentucky through 08z-09z. One concern with more discrete activity
overnight would be a lesser threat for severe wind potential and a
higher threat for large hail and isolated tornadoes in supercells.
Thankfully, deep layer and low level shear weaken as you go toward
southern Kentucky, so the highest threats for severe potential
continue to be across southern Indiana and northern/central Kentucky.
Issued at 658 PM EDT Thu Jul 29 2021
AMDAR soundings within the past hour have indicated a weakening of
the cap in the 900-800mb layer with winds now taking on a more
northwesterly component. KLVX has also detected a couple of rogue
cells that developed, though they have struggled to strengthen given
the weak capping still in place. This activity is not anticipated to
become strong or severe.
Over the next hour or so, we may continue to see an occasional rogue
cell go up across southern Indiana and central Kentucky. Activity
currently in central Illinois and Indiana along a weak surface
boundary will begin drifting into our southern Indiana CWA counties
between 00-01z. Additional activity along a cold front just to its
north will filter into the region around or after 03z. Strong to
severe storms will be possible with that activity as it drifts
southward.
Issued at 515 PM EDT Thu Jul 29 2021
Recent AMDAR soundings from SDF indicate a fairly impressive cap
remains in place (~23C near 800mb). A look at SPC mesoanalysis pages
and high-res model guidance of 900-800mb fields indicate a warm
`nose` of temperatures stretching from the central Plains into the
lower Ohio Valley resulting in the strong cap. Winds currently at
these levels are generally out of the west or west-northwest, so
temperatures in these levels should not change much in the very near
term, which means the cap should stay in place and prohibit storm
development.
It`s not until we get closer to 00z that we begin to see winds in
these levels shift more northwesterly as a trough sinks in from the
north. Cooler temperatures aloft associated with the trough will
advect in and help to break down and weaken the cap. Convection
currently in central Indiana and Illinois will drift close or toward
our area over the next several hours, and depending on how organized
it is and if there are any outflow boundaries or cold pools
associated with convection, it could be enough to overcome a
weakened cap. Threat for strong to severe storms will likely occur
after 00z and persist into the early morning hours.
&&
.Short Term...(This evening through Friday)
Issued at 320 PM EDT Thu Jul 29 2021
...Strong to Severe Storms Possible this Evening...
So far this afternoon temperatures have warmed into the upper 80s
and low 90s as of 2 pm EDT. Dew points were just oppressive in the
mid/upper 70s. This was producing heat indices around 100 degrees,
mostly west and along I-65 where we have the higher dew point
values. This heat and moisture has created a very unstable
atmosphere which will remain in place as we go into the evening
setting the stage for the development of strong to severe storms.
The Storm Prediction Center continues to keep the northern third of
our CWA (county warning area) in a slight risk for severe
thunderstorms. The main threat being gusty damaging winds and
torrential heavy rain.
Afternoon mesoanalysis shows sfc cold front stretching across
northern MO into northern IN over Lake Erie. Radar was showing
scattered development just south and along the boundary. South of the
front was strong to moderate instability with CAPE values across
central KY and southern IN ranging from 2500-3500 J/kg east of I-65
to 3500-4500 J/kg to the west. Model soundings were showing dry air
aloft keeping our DCAPE between 800-1000 J/kg keeping the main
threat gusty damaging winds in the strongest storms this evening.
Current hi-res model guidance is showing a slower solution in the
development of scattered to broken convection this evening. Updated
timing looks to drop a broken to scattered line of storms southward
into our southern Indiana and north-central Kentucky counties
between 9 PM- Midnight EDT and pushing southward into southern KY in
the early morning hours. As the storms work to along and south of
the Parkway, guidance has been consistent in showing the activity to
diminish as it reaches the TN/KY border by day break.
Tomorrow will feature cooler and less humid weather for the end of
the week. Dew points will fall into the low/mid 60s by the afternoon
with afternoon temperatures in the low to mid 80s north of the
parkways and mid/upper 80s south.
.Long Term...(Friday night through Thursday)
Issued at 315 PM EDT Thu Jul 29 2021
The long term forecast will see only minor changes.
On Saturday, as a shortwave/cold front drops south, trying to
amplify the trough over the eastern CONUS, a few showers and
thunderstorms will be possible. With most of the available moisture
towards the CWA`s southwest, believe the best chances of
precipitation will be on the southwestern side of the CWA Saturday
night before fading Sunday. Rainfall totals are expected to range
from a hundreth of an inch in our southeastern Indiana and
northeastern Kentucky counties to around three quarters of an inch
near Bowling Green. Some isolated areas could see higher
amounts under heavy downpours.
Moving into early next week, northwest flow with surface high
pressure remains over the CWA. This will suppress moisture to the
south and drop dew points into the 50s across the CWA by Tuesday.
With this pattern and lack of available moisture, believe mostly dry
conditions will prevail through the end of the work week.
However, the GFS does try to form an upper closed low over the
region on Wednesday. This would increase precipitation chances
towards the end of the week, but for now, don`t believe this is
likely. Plans should be based on a mostly dry comfortable week with
highs in the 80s and low dew points.
&&
.Aviation...(00Z TAF Issuance)
Issued at 659 PM EDT Thu Jul 29 2021
A broken line of showers and thunderstorms are may develop tonight
ahead of a cold front and push through southern Indiana and central
Kentucky. If a storm impacts a terminal site, expect gusty winds and
briefly reduced visibilities and ceilings. Drier air will filter in
behind the front and winds will turn to the north. VFR conditions
are anticipated in the wake of the storms for the remainder of the
forecast period.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Mesoscale...DM
Short Term...BTN
Long Term...KDW
Aviation...DM
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
652 PM CDT Thu Jul 29 2021
.UPDATED for 00Z Aviation Discussion...
Issued at 627 PM CDT Thu Jul 29 2021
&&
.SHORT TERM...(This evening through Friday night)
Issued at 302 PM CDT Thu Jul 29 2021
The main impact today into tomorrow will be the continued smoke
across Minnesota and Wisconsin. Smoke is present across all of the
forecast area, but the smoke has not been going to the surface
equally across all areas. For much of Wisconsin this smoke has
remained aloft, but for much of Minnesota this smoke has made it down
to the surface. This has resulted in the MPCA issuing an AQA for most
of the state of Minnesota. North winds will continue to move the
smoke across Minnesota today. HRRR smoke runs suggest that there will
be some clearing of near surface smoke late this evening into tonight
across parts of the state. The best chances for this clearing will be
in the eastern parts of Minnesota, but the air flow could keep the
smoke around for longer farther west.
Outside of the smoke high pressure will limit chances for much wet
weather today and tomorrow. A system passing off to our southwest
could provide some rain showers in parts of southern and southwest
Minnesota on Friday, but little QPF is expected. The good news in
this forecast is that it does look like we will get a break from the
heat and humidity today and tomorrow.
.LONG TERM...(Saturday through Thursday)
Issued at 302 PM CDT Thu Jul 29 2021
Northwest flow over this period will provide for a few chance for
some active weather with shortwaves along the flow, but overall no
widespread rain events on the horizon as Minnesota moves farther into
drought. None of these shortwaves at the moment look to arrive with
the necessary moisture to provide us much chance for rain. The best
chances in this period are on Saturday, but these chances are mostly
confined to western Wisconsin so they will provide little relief for
the drought stricken areas. Smoke will remain a concern as well over
the next week as fires continue in Canada and the western US. The
main feature to watch for will be how much can make it to the
surface. If it remains aloft than impacts will be limited to reddish
suns and cooler temperatures. If it makes it the surface than the air
quality will be poor like it is today across much of Minnesota.
Finally temperatures look to be near to below normal through the
weekend, but look to rise back into the near to above normal range by
the middle of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 627 PM CDT Thu Jul 29 2021
Areas of smoke will continue this evening. The latest HRRR guidance
shows the lowest visbys moving to the southwest and exiting the
region overnight. Otherwise expect some high clouds and northeast
surface winds becoming more southerly on Friday.
KMSP...
Look for a few hours of MVFR visby due to the smoke this evening.
Then expect VFR conditions to return overnight and last through
Friday.
/OUTLOOK FOR KMSP/
Fri...VFR. Winds SE 5-10 kts becoming SW.
Sat...VFR. Winds NW 10-20 kts.
Sun...VFR. Winds N 10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
SHORT TERM...NDC
LONG TERM...NDC
AVIATION...JRB
...Updated Aviation Forecast Discussion...
.DISCUSSION...
Issued at 333 PM CDT Thu Jul 29 2021
Plenty of moving parts in the forecast.
Two different airmasses in place.
Smoke from northern wildfires.
Chance of severe weather.
Heat advisory for southwestern CWA.
Visibility in parts of South Dakota and especially Minnesota is
down to under three miles due to the wildfire smoke working in
with the cooler air from Canada. HRRR has been consistently
suggesting it will envelop the area this evening and overnight and
may reduce visibility as low as 2 miles in parts of northeastern
Nebraska.
Heat indices this afternoon have been pushing well over 105 for
much of the area and have meandered into excessive heat warning
territory at times. Dewpoints have sneaked over 80F in parts of
western Iowa.
The front has been... well... stationary through much of the day
but will sag south this evening and may produce some thunderstorms
just north of the Kansas state line after 5pm. With the heat and
humidity as high as it is, would be hard pressed to believe large
hail would be any real threat, but PWAT values are in the 90th
percentile for parts of the CWA and wet downbursts seem
reasonable.
The threat for severe weather is greater on Friday when an MCV
over Wyoming will ride the ridge and help produce plentiful shear
and quite the hodographs as revealed in guidance. Expecting
storms to work northwest to southeast in the evening and overnight just
north of the front. Hail and damaging winds are possible.
Have foisted a heat advisory across Otoe, Saline, Seward,
Lancaster, Gage, Jefferson, Gage, Pawnee, Johnson, Nemaha, and
Richardson counties for Friday afternoon where heat indices will
be improved versus today, but still peak near or just above 105F.
Parts of northern Kansas will be warmer and an EXCESSIVE HEAT
WARNING borders our southern counties. At the same time, some
locations along our northern edge may fall shy of 80F for a temp.
QPF for Friday night and Saturday morning will run between 1-3"
for some areas and flash flooding due to training could be an
issue... at least in localized areas. The drought conditions will
help prevent widespread flooding concerns. The heaviest rain may
fall along a line from O`Neil, NE to Omaha, NE to Lamoni, IA.
Dry conditions and sub-seasonal high temps settle in for the
remainder of the weekend after the showers and storms wrap up
mid- day Saturday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 611 PM CDT Thu Jul 29 2021
Convection had developed in southeast Nebraska, but is expected to
remain well south of TAF sites. More convection is possible around
12Z as low level jet rides over frontal boundary, so have included
at least a mention at all TAF sites. Low confidence and expected
limited coverage precludes a stronger mention in TAFs. Otherwise
areas of smoke spilling into northeast Nebraska could cause
visibility restrictions at KOFK as per sites upstream Thursday
afternoon. Fog is also possible at KLNK and KOMA as low level
moisture lingers through mid morning.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory until 9 PM CDT this evening for NEZ050>053-065>068-
078-088>093.
Heat Advisory from noon to 9 PM CDT Friday for NEZ065-066-068-
078-088>093.
IA...Heat Advisory until 9 PM CDT this evening for IAZ069-079-080-090-
091.
&&
$$
DISCUSSION...Nicolaisen
AVIATION...Dergan
Area Forecast Discussion
National Weather Service Phoenix AZ
532 PM MST Thu Jul 29 2021
.UPDATE...
Updated 00Z aviation discussion.
&&
.SYNOPSIS...
Storm chances will increase from east to west across Arizona today
with chances expanding into southeast California on Friday and
persisting through Saturday. Main storm threats will be strong
winds, blowing dust, and locally heavy rainfall. After near normal
temperatures today, readings will dip to below normal through the
upcoming weekend. Drying conditions starting Sunday will push
storm chances back to only the eastern Arizona high terrain, with
much of the area staying dry during the first half of next week.
&&
.DISCUSSION...
Monsoon activity will quickly increase today with multiple
weather disturbances poised to affect the region. Current radar
loops is already showing convective activity breaking out along
the Rim/White Mountains with additional scattered storms now
occurring across the lower deserts and over some the Gila County
Burn Scars. The main driving force behind thus increase in
monsoon storm activity is an westward advancing upper level
trough currently moving across northern Mexico. This upper level
trough is quite expansive in size and is analyzed as a closed low
at 300mb and mostly as an open trough at 500mb. As it continues to
track west northwest today into Friday it is forecast to weaken,
but much if not all of Arizona is seen coming under broad difluent
flow aloft as early as this afternoon.
latest HRRR high-res model runs are showing storms spreading
across SW AZ over the next few hours along with more activity
moving into southern Gila County. As far as the greater PHX area,
this morning`s clouds/virga seems to be limiting activity across
that region at this hour, but latest SPC HREF model output does
indicate storms attempting to move into that region from the east
this evening. Storms will be capable of strong gusty winds with
multiple outflows expected to form and locally heavy rainfall.
With PWATs ranging from 1.3-1.6" and a modest 10 kt east
southeasterly steering flow, this should keep storms fairly
progressive likely minimizing the potential flood threat over the
lower deserts. The biggest threats this afternoon and evening
should be strong winds and localized blowing dust with the 12Z
HREF highlighting a large area of 70-90% probability of greater
than 35 mph winds across the majority of Arizona. Although the
HREF shows a greater chance for this to happen across southern
Maricopa and Pinal Counties, it could happen anywhere this evening
as several outflows are expected. One large westward advancing
outflow is likely to reach the Colorado River by late evening with
additional showers and weak storms likely across southwest
Arizona into southeast California during the early overnight hours
tonight.
Friday still looks to be another active monsoon storm day, but
with less activity across eastern Arizona as some drier air works
in from New Mexico. The weakening upper level trough slowly
lifting northwestward through the Desert Southwest should still
provide some upper level support, while a trough off the West
Coast also provides additional ascent across southern California.
Moisture levels Friday will improve over today in most locations
with PWATs upwards of 2" across the western deserts, to 1.5-1.75"
across much of south-central Arizona, but lowering closer to 1.25"
in eastern Arizona. MUCAPEs Friday should also be higher likely
ranging from 1000-1500 J/kg from Phoenix westward through
southeast California. The storm threats Friday and Friday night is
expected to transition more toward heavy rainfall and localized
flooding, but southeasterly steering flow of 10-15 kts should keep
storms from remaining stationary over one area for very long.
Strong winds will continue to be a threat, but mostly in the form
of storm downdrafts instead of outflows. Bulk shear also increases
by Friday afternoon/evening across southwest Arizona and parts of
southeast California, so a few longer lasting severe storms may
be possible, along with a greater threat for flash flooding across
that area, thus a Flash Flood Watch has been issued for that
region.
For Saturday, the inverted trough will become a non-factor as it
lifts north, but the lingering trough off the West is forecast to
send up another upper jet max out of the south. This jet should
again provide broad ascent over much of the area on Saturday, but
we begin losing moisture especially across the western deserts.
Storm chances for Saturday are still quite uncertain, but NBM PoPs
are mostly in a 30-40% range. The drier air working in from the
southwest should overtake much of Arizona on Sunday likely
limiting storm chances Sunday to the high terrain north and east
of Phoenix. The first half of next week also looks to be quite dry
and may only involve a few daily afternoon showers and storms
across far eastern Arizona. Boundary layer moisture should also
gradually lower with each day early next week as the subtropical
high reforms initially just to our southwest before slowly
drifting over southern California into Arizona by Tuesday or
Wednesday. Although NBM high temperatures increase back to around
normal readings early next week, would not be surprised if we will
have to worry about some areas near excessive heat. If we do dry
out the boundary layer next week and a 594dm 500mb ridge is
overhead, excessive heat will be a possibility.
&&
.AVIATION...Updated at 0030Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Convective impacts due to strong outflow winds and the potential
for isolated to scattered showers and thunderstorms to develop
along them over the next few hours will be the main impacts for
the Phoenix terminals. A strong northeast outflow with 20-30 knot
winds is currently moving through KSDL and should clear KDVT by
0030Z and PHX between 0045-0100Z. A slightly weaker, more easterly
outflow is expected through KIWA, with a southerly outflow
currently moving through the West Valley in this time frame as
well. Given the uncapped environment and thus unstable airmass, we
have at least 50% confidence that storms will develop along
colliding outflows, with 30% confidence in TSRA at all TAF sites
except KIWA where colliding outflows are a bit less likely. Thus,
we have VCTS generally between 01-03Z for most of the TAF sites
except KIWA where VCSH is in place. Confidence in thunderstorm
development is highest in the West Valley due to the greatest
potential for colliding outflows. Brief gusts in excess of 35
knots and blowing dust with MVFR visibilities will be possible
with the northeast outflow, with isolated 40-50 knots possible
with the strongest individual storm cells. SCT-BKN cloud bases
down to 7-8 kft will be possible with these storms.
Assuming storms develop early this evening, the overnight hours
should be relatively inactive. Winds should retain easterly
headings through early afternoon before veering to the west at
5-10 knots. Another round of isolated to scattered convection is
possible late tomorrow afternoon into the early evening hours,
though confidence only warrants VCSH at this time.
Southeast California/Southwest Arizona including KIPL and KBLH:
Convective impacts over the next few hours will be the main
aviation impacts tonight. Shower and thunderstorm chances at KIPL
and KBLH are around 20% through 02-03Z, with slightly better
chances of VCTS at KBLH given ongoing convective activity. Wind
gusts in excess of 40 knots will be possible with the strongest
storm cells, though most should produce gusts closer to 25-35
knots. Another round of showers and thunderstorms is possible
along E-NE outflows later tonight in southwest Arizona into the
Colorado River Valley including KBLH, where another round of VCSH
is included from 06-10Z. However, confidence is too low to include
convection at KBLH at this time. Patchy blowing dust briefly
reducing visibilities will be possible with any storms. Otherwise,
winds will generally be southerly to westerly at KIPL and S-SE at
KBLH. Winds will generally be around 10-15 knots with gusts to
20-25 knots possible overnight with showers at KBLH. Cloud bases
should generally remain at or above 8-10 kft.
&&
.FIRE WEATHER...
Sunday through Thursday:
Unsettled conditions are likely through Sunday with the last of
the weather disturbances moving through the region. This should
bring fairly widespread shower and storm chances on Saturday
before more limited storms on Sunday. Shower and storm chances for
Mon-Thu will be limited to a few storms during the daytime hours
over the eastern Arizona high terrain. Main threats on Sunday will
be strong thunderstorm winds, heavy rainfall and possible
localized flooding. Temperatures will range from near to slightly
below normals the bulk of the period. Minimum afternoon humidity
values will range from 25-45% through the weekend before falling
back to 15-30% early next week. Overnight recovery will be mostly
good to excellent in a 40-80% range. Apart from thunderstorms,
winds will favor typical daily upslope/drainage patterns.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch from Friday afternoon through late Friday
night for AZZ530>533-535-536-538-539-559.
CA...Flash Flood Watch from Friday afternoon through late Friday
night for CAZ569-570.
&&
$$
DISCUSSION...Kuhlman
AVIATION...Hopper
FIRE WEATHER...Percha/Kuhlman
Area Forecast Discussion...CORRECTED
National Weather Service Pueblo CO
345 PM MDT Thu Jul 29 2021
.SHORT TERM...(This evening through Friday)
Issued at 340 PM MDT Thu Jul 29 2021
Hot and mostly dry conditions continue with thunderstorm activity
focused across the valleys and Continental Divide this afternoon.
Highest precipitable waters continue to reside to the west with best
chance for locally heavy rain across the Continental Divide through
this evening. Activity will wind down tonight with loss of heating.
Friday looks fairly similar to today, with perhaps a slight increase
in precipitable waters out west. Thunderstorms will develop over
the mountains around noon with northeasterly steering currents
keeping activity mainly over the mountains and valleys. Best
thunderstorm chances will be across the Continental Divide where
potential for locally heavy rainfall on the Chalk Cliffs will have
to be monitored for a localized flash flood potential. Overall
confidence is too low to issue a flash flood watch just yet. Will
let later shifts assess CAMS models as event nears and hoist any
necessary watches. Otherwise another hot day on tap for the plains
with temperatures around 100 degrees for the lower Arkansas River
valley. -KT
.LONG TERM...(Friday night through Thursday)
Issued at 340 PM MDT Thu Jul 29 2021
...Flash Flooding may be an issue for Saturday and Sunday for the
burn scar areas, and a slight chance that the urban areas could be
impacted as well...
For Friday...there will be a chance of afternoon and early evening
thunderstorms over the central mountains. A few storms will be
possible over the eastern mountains and a very slight chance over
the I-25 corridor as well, but much more isolated in nature.
For Saturday through Sunday...scattered to numerous thunderstorms
will develop over much of the mountainous terrain, and showers or
thunderstorms could develop during the early hours of the morning on
Saturday over the plains and possibly later in the afternoon, with
the I-25 corridor receiving the best chance. There could be
localized flooding over the burn scar areas, and possibly over the
urbanized areas during the later in the day on Saturday. On Sunday
most of the shower and thunderstorm development will be confined to
the mountains and southern areas of the CWA, especially during the
afternoon and evening hours.
For Monday through Tuesday...Scattered showers and thunderstorms
will develop across much of the region during the afternoon and
evening hours, some storms could become severe. Flash flooding will
be possible over the burn scar and urbanized areas. Storms will be
more likely over the plains on Tuesday.
Detailed discussion:
Friday...
The ridge is continuing slightly retrograde back to the west with
the axis becoming more negatively tilted by Friday. The center of
the surface high positioned over northeastern Colorado. This
feature, coupled with an upper level low over northern Mexico that
is also propagating towards the west and is allowing drier air on
the subsident side will keep most areas of our CWA warm and dry
throughout Friday evening, as the brunt of the monsoonal moisture
plume remains further to the west. There will be the enough moisture
to allow for orographically induced convection over the central
mountains and there could be enough residual moisture as well to
cause a few storms to develop over the eastern mountains and over
the I-25 corridor as well, however, these will be much more isolated
in nature. With a strong ridge overhead and southerly flow over most
areas, temperatures will be very hot, with triple digit heat likely
over the lower Arkansas River Valley.
Saturday and Sunday...
As the negatively tilted ridge axis becomes more elongated over the
northwestern CONUS, a longwave trough downstream over the northern
plains is going to deepen and allow for some of the monsoonal
moisture plume to be advected in from the northwest. This, along
with an associated cold frontal boundary extending over the central
plains with a developing surface low over the Great Lakes region,
will help to produce forcing and help to induce convection over our
area by the early morning and throughout the afternoon and evening
on Saturday. The models are differing quite significantly now with
the timing of the front, as well as the amount of moisture available
over the plains. The HRRR and NAM have been much drier and quicker
with frontal passage and not much in the way of precip over the
central and eastern plains as the GFS and SREF. The timing could be
crucial as to which areas will experience the most rainfall and if
there is enough cooler air moving in behind the front, it could help
to stabilize the lower levels too much and minimize the threat for
much in the way of thunderstorms over the plains. Right now, the
general consensus of frontal passage will now be much earlier than
shown in previous model runs for the past few days, and have FROPA
occuring for the northern areas of the CWA around 09Z to 12Z with a
weak lee side meso-low developing over the central plains. Then
the front will pass over the southern portion of the CWA by around
12Z to 15Z. The thunderstorms over the mountains could contain
localized flash flooding in and around burn scars and some of the
heavier showers and thunderstorms could cause flash flooding for
urbanized areas, especially over the I-25 corridor. There doesn`t
appear to be enough mid level shear showing up in the models,
therefore the severe thunderstorms. For Sunday, the cooler air
could cause most precip to more stratiform in nature as the lower
levels remain too capped and stable for many locations. Winds will
be primarily from the southwest ahead of the front and switch to
the northeast. Along with the increase chance of measurable precip
over most of the CWA, the frontal passage will also create a
cooldown, with temperatures falling into the evening hours and max
temperatures will be closer to around the seasonal average for
most locations. -PS
Monday through Wednesday...
The monsoonal moisture plume will shift back towards the east as the
axis over the Four Corners repositions itself over Colorado as the
surface plateau high strengthens. This will allow for more showers
and thunderstorms to develop over most areas, with the best chance
being in the afternoon and evening hours over the mountains, and as
the axis slowly shifts more to the east on Tuesday, this will give
the plains a better chance of seeing convection further east towards
the Kansas border. As the ridge also continues to slightly build
back with a strengthening surface high pressure, expect max
temperatures to gradually warm going into the middle part of next
week with the best chance of thunderstorms over the plains by
Wednesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 340 PM MDT Thu Jul 29 2021
KALS: VFR conditions are expected over the next 24 hours. Isolated
rain showers and thunderstorms are possible tomorrow afternoon, but
confidence is low in development. If a thunderstorm were to develop,
the main impacts would be brief heavy downpours and erratic outflow
winds. Otherwise at KALS, expect light and variable winds overnight,
before increasing in magnitude tomorrow.
KCOS and KPUB: VFR conditions are expected over the next 24 hours.
Winds will become light and variable overnight and into tomorrow
morning, before increasing early tomorrow afternoon. Skies will
remain mostly clear through tonight and into tomorrow afternoon as
well.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...KT
LONG TERM...STEWARD
AVIATION...SIMCOE