Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/21/17
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
709 PM CDT Thu Jul 20 2017
.UPDATE...
Issued at 708 PM CDT Thu Jul 20 2017
Monitoring the current line of storms in northwest SD and
southwest ND as the push to the east towards the CWA (Corson
County). The storms are currently in an area of favorable
environmental conditions: steep mid level lapse rates, MLCAPE
values exceeding 1000-1500 J/kg, and effective shear values
around 60kts. In addition, dry low levels and a favorable
inverted-v RAP soundings have led to DCAPE values to exceed 1600
J/kg west of the Missouri River. Latest trends in the storms show
the southern cores weakening some what and the outflow on Bowman
radar out running the main storms to the east of Hettinger, so may
see some weakening before they reach the CWA. That being said, do
expect at least strong storms and continued the mention of a
severe threat in the grids. Still some uncertainty in how far east
things will track, as models strengthen the low-level jet and in
turn increase instability across the area through the night.
Followed existing forecast thought for slight to low chance PoPs
spreading east through the night.
&&
.SHORT TERM...(This Evening through Friday Afternoon)
Issued at 319 PM CDT Thu Jul 20 2017
Forecast challenges surround convective potential tonight and then
again Friday afternoon.
Currently, temperatures are warming through the 80s and 90s on light
southeast winds under a mostly sunny sky.
The synoptic scale setup tonight favors convective development out
west (across the northern high plains). The HRRR today begin to
latch on to a solution that bring convection all the way east into
portions of north central South Dakota late this evening (at or
after 10 PM CDT) and then similar to the other day begins to dig the
southern-most end of convective cells southward into portions of
central and south central South Dakota during the late night hours
tonight. Although, it has become consistent in producing a solution
like this, it does not have much support from any of the other CAM
solutions or 12Z non-CAM solutions today. Left in a small pop across
the southwestern zones late tonight transitioning over into
northeast South Dakota/wc MN toward Friday morning where all the
best forcing/lift seems to re-focus some potential for elevated
convection. Temperatures tonight on southerly winds, advecting
moisture northward into the cwa, and potentially maintaining a
partly to mostly cloudy sky should remain up, with readings
generally in the 60s and 70s.
On Friday, a cold frontal boundary will begin a slow push east
through the region, and by early afternoon there could be some
isolated to scattered thunderstorms developing along that boundary
(and any leftover OFB`s from overnight convection). Mid-level
thermal capping temps are not overly strong in today`s 12Z
solutions, so it`s seems reasonable to expect at least isolated to
scattered thunderstorms developing by mid to late afternoon on
Friday. The concern here is that deep layer shear and mixed layer
CAPE Friday afternoon over the James River valley eastward into wc
MN favor severe convective development. LCL`s may be a little bit on
the high side (2500ft to 3500ft agl) for tornado potential, but for
sure in the ball park. High temperatures tomorrow are going to warm
into the upper 80s to low 90s from the James River valley eastward
into MN, while readings climb nearly to 100 degrees over into the
Missouri River valley. Hot temperatures and high dewpoints will
result in Heat Indices ranging from 99F to 104F across portions of
central, south central and northeast South Dakota. A Heat Advisory
has been issued as such.
.LONG TERM...(Friday Evening through Thursday)
Issued at 319 PM CDT Thu Jul 20 2017
Thunderstorms may be ongoing across eastern SD Friday evening. A
trough will be overhead, extending from the parent lows across
southern Saskatchewan and southeastern SD to eastern NE. The trough
will exit east by 06Z (possibly lingering over our west central MN
counties for another couple of hours). Otherwise, dry high pressure
will slowly build into the region. Dry weather should be the rule
through at least Monday evening. At 500mb, the low over southern
Saskatchewan at 00Z Saturday will just shift east into Ontario by
Saturday night, keeping a trough overhead into Monday.
Fire weather concerns increase for Saturday, as temperatures rise
into the 90s for most locations. The main difference will the the
loss of moisture. Instead of dewpoints hovering near 70F like Friday
afternoon, they will be in the low 40s as dry high pressure builds
in from the west. RH values fall to 14 to 20 percent across most
areas west of the James River Valley. Winds our of the northwest may
end up being stronger then forecast, so will need to continue to
keep an eye on Saturday afternoon.
The sfc high will be across ND Sunday afternoon, and slowly move
across Minnesota Sunday night into Monday, with a ridge remaining
across the forecast area. The next lee trough will near SD Tuesday
morning, with unsettled weather making a return. Low pressure will
likely remain across the Central Plains Tuesday night through at
least Thursday, with the best chance of precipitation for now
looking like late Wednesday afternoon through Wednesday night. Lot
of time for change though between now and then.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 640 PM CDT Thu Jul 20 2017
Expect primarily VFR conditions at the TAF sites through the
period. There are two areas of concern for thunderstorms, first
for later this evening over central and north central SD and
again tomorrow afternoon over eastern SD. First for this
evening, think KMBG has the best opportunity for thunderstorms,
but didn`t have enough confidence on timing to include in the
TAFs. Based off latest trends and expected motions of the storms
in far northeast SD and western ND, would expect storms to be
there around 330-4Z. These storms will continue eastward through
the night while weakening, so only included VCSH at PIR/ABR until
there is a better idea of eastward extent. For tomorrow`s
thunderstorm potential, think development will occur along or east
of the Missouri River, but with the weakening surface low moving
through central SD during the day, confidence is low on exact
location/timing of development in the afternoon.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from noon CDT /11 AM MDT/ to 8 PM CDT /7 PM MDT/
Friday for SDZ016>018-033>037-045-048-051.
MN...None.
&&
$$
UPDATE...SRF
SHORT TERM...Dorn
LONG TERM...KF
AVIATION...SRF
Area Forecast Discussion...Updated
National Weather Service Billings MT
922 PM MDT Thu Jul 20 2017
.UPDATE...
Made some minor adjustments to PoPs to push isolated evening
activity just a little farther north off the foothills. Shower
activity over south central zones will be very limited as
strongest shortwave energy was moving into northeast Wyoming at
this time. Also adjusted PoPs a bit over southeast Montana to
focus the higher PoPs over the far southeast. Convection was
stubborn over northeast Wyoming and was trying to creep back into
the far southeast corner of the state. Also adjusted temperatures
down a couple of degrees over the east as current conditions were
a little ahead of guidance. TWH
&&
.SHORT TERM...valid for Fri and Sat...
Convection has been forming off the Beartooth Mountains and have
already begun pushing into Big Horn County as of 230 PM. This has
been the trend that the CAMs have been advertising. Meso-analysis
shows that CAPE values along the Dakota borders are getting to
around 2000 J/kg, and shear values are 40 to 50 knots through 6
km. Recent runs of the HRRR are still pointing towards stronger
convection developing later this afternoon in eastern Montana then
moving into the Dakotas. The convection currently in Big Horn
County will increase as it moves into the better environment.
A cold front will move through overnight and should be to around
Miles City by 6 AM tomorrow. This has will keep winds breezy
across Musselshell, Treasure, and northern Rosebud counties.
Tomorrow 850mb winds remain strong out of the northwest. With
mixing tomorrow afternoon, areas from Roundup to Broadus are
going to gusty winds with relative humidity values in the teens.
Have extended the current Red Flag to until 9 PM tomorrow for
Musselshell and Northern Rosebud, and have added Custer, the rest
of Rosebud, and Powder River Counties. Saturday will be dry, as
ridging builds back into the area. Reimer
.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...
No significant changes. The riding continues Sunday and most of
Monday keeping conditions dry. A low in southern Canada will bring
a weak cold front across the area. This will shift the ridge to
the east. This put the area in southwesterly flow. This will
result in some scattered PoPs each afternoon. The GFS ensemble is
not showing much in the line of moisture with any of this
activity. With the increase flow of monsoonal moisture,
temperatures will be slightly cooler. Reimer
&&
.AVIATION...
Isolated showers and thunderstorms will continue to weaken
through the night and be confined to areas south of a KBIL to
KBHK. Otherwise, clouds will decrease. A cold front will push
through southern Montana and northern Wyoming tonight and switch
winds to the northwest. Some gusts to 25 mph are possible with the
frontal passage. TWH
&&
.PRELIMINARY POINT TEMP/POPS...
Fri Sat Sun Mon Tue Wed Thu
-----------------------------------------------------------
BIL 064/090 059/090 061/095 065/095 065/092 066/090 065/092
20/U 00/U 00/U 11/U 21/B 22/T 11/U
LVM 054/086 049/088 051/092 056/093 056/089 058/087 055/089
20/U 00/U 00/U 01/U 21/B 22/T 22/T
HDN 064/091 058/092 058/097 062/098 063/095 064/092 062/095
20/U 00/U 00/U 11/U 11/B 22/T 22/T
MLS 068/091 060/091 062/096 068/099 067/094 067/093 066/095
10/U 00/U 00/U 01/U 11/B 12/T 21/U
4BQ 065/090 059/091 060/094 066/098 066/095 065/091 064/093
30/U 00/U 00/U 01/U 11/B 12/T 22/T
BHK 066/091 056/089 056/091 063/096 062/092 062/089 061/091
31/U 00/U 00/U 01/U 11/B 12/T 22/T
SHR 062/086 054/089 054/093 058/095 058/092 059/090 058/090
30/U 00/U 00/U 11/U 11/B 22/T 22/T
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Red Flag Warning in effect until 9 PM MDT Friday FOR ZONES
117-127-130.
Red Flag Warning in effect from 9 AM to 9 PM MDT Friday FOR
ZONES 131-132.
WY...None.
&&
$$
weather.gov/billings
Area Forecast Discussion
National Weather Service El Paso Tx/Santa Teresa NM
339 PM MDT Thu Jul 20 2017
.SYNOPSIS...
Moisture will continue to stream over the Borderland from the
south as an upper high moves over the lower Mississippi Valley
Friday and Saturday. With the moist airmass, heavy rain and
flooding will be a threat. As this upper high continues to drift
east, a new high center will form over the Great Basin. This will
turn our upper flow out of the north on Sunday into the first part
of next week. Abundant moisture will remain in place through about
Tuesday, with heavy rain and flood potential continuing. The upper
flow begins to draw in a bit drier air for Wednesday and Thursday,
with thunderstorms becoming more isolated.
&&
.DISCUSSION...
Monsoon pattern continues today as upper high slowly drifts east,
to near Arkansas/Missouri area this afternoon. Southerly flow
aloft will increase, along with moisture transport, over the area
tonight and Friday. PWs currently ranging from 1.5 inches NM
Bootheel to 1.2 inches over the Sacs. First thunderstorms today
formed over mountains as usual, and now are starting to form over
lowlands of the Bootheel and Otero County. Expect the CWA to
increase in thunderstorm coverage tonight, perhaps with best
evening action west of the Rio Grande Valley, shifting to the east
toward midnight. Several HRRR runs have been showing this pattern.
This large scale pattern will continue again Friday with heavy
rain/flood threat continuing.
Saturday through Tuesday...upper pattern continues to change, as
original high weakens and consolidates further east with Bermuda
high. A new high center will begin forming over the Great Basin
and turn our upper flow to the north. This does not initially
flush out much moisture at all, as recycled moisture aloft will
keep moist conditions over the area. Look for scattered/numerous
thunderstorms through this entire period. PWs continue around 1.4
to 1.6 inches, so heavy rain/flood threat expected to continue.
Wednesday and Thursday...both GFS/ECMWF showing recycled moisture
decreasing and getting pushed west in the NE-E flow aloft, with
deepest moisture from about Deming west. Will keep higher POPs in
this area with lower POPs to the east. GFS shows PWs falling to
1.2 inches east and north, to 1.4 inches southwest. Perhaps some
easing of flood potential.
&&
.AVIATION...Valid 21/00Z-22/00Z...
With monsoon flow established expect P6SM SCT-BKN050-070 BKN-OVC150-
200 through much of the period. However, periods of scattered
VRB25G40KT 1-3SM TSRA BKN030-050 will occur thru 06Z. Periods of
VCSH overnight with VCTS returning most terminals after 18z.
&&
.FIRE WEATHER...
Deep monsoonal flow will prevail over the region for most of the
week to come. This will result in increased chances for wetting
precip, especially Friday through Sunday. The threat of flash
flooding will increase as we head into the weekend as parts of the
region become saturated by repeat storms. In addition, frequent
lightning strikes along with gusty and erratic winds associated with
storms will be a concern for fire weather interests. Temps will tend
to run a bit below normal through the period resulting in elevated
Min RH values. Meanwhile vent categories will likely remain in the
fair to occasionally good categories into the weekend.
&&
.PRELIMINARY POINT TEMPS/POPS...
El Paso 72 92 71 93 / 20 20 30 20
Sierra Blanca 68 90 67 90 / 20 20 30 20
Las Cruces 67 91 66 92 / 20 20 30 20
Alamogordo 68 93 67 93 / 20 20 30 20
Cloudcroft 51 70 50 69 / 20 40 40 50
Truth or Consequences 68 95 67 93 / 30 20 40 40
Silver City 58 87 60 87 / 50 50 40 60
Deming 66 91 66 91 / 30 30 30 40
Lordsburg 65 90 65 91 / 40 40 40 40
West El Paso Metro 71 90 71 92 / 20 20 30 20
Dell City 70 95 69 95 / 20 20 30 20
Fort Hancock 74 92 71 94 / 20 20 30 20
Loma Linda 63 84 66 89 / 20 20 30 20
Fabens 71 91 70 93 / 20 20 30 20
Santa Teresa 68 91 69 92 / 20 20 30 20
White Sands HQ 69 92 68 91 / 20 20 30 20
Jornada Range 67 95 66 92 / 20 20 30 20
Hatch 66 93 66 94 / 30 20 30 30
Columbus 67 91 67 92 / 30 20 30 40
Orogrande 67 92 69 93 / 20 20 30 20
Mayhill 54 81 54 78 / 20 40 30 50
Mescalero 55 81 54 81 / 20 40 30 50
Timberon 53 79 54 79 / 20 20 40 50
Winston 55 86 58 87 / 40 50 50 70
Hillsboro 62 91 62 92 / 40 40 40 60
Spaceport 66 95 66 93 / 20 20 30 20
Lake Roberts 51 85 53 86 / 50 70 50 70
Hurley 59 87 61 88 / 40 40 30 60
Cliff 59 88 59 90 / 50 60 40 50
Mule Creek 58 88 58 88 / 50 60 50 60
Faywood 60 88 61 89 / 40 30 30 60
Animas 65 90 65 92 / 40 50 40 50
Hachita 64 90 65 90 / 40 40 40 60
Antelope Wells 63 86 64 88 / 40 60 50 70
Cloverdale 60 82 61 87 / 50 60 50 70
&&
.EPZ WATCHES/WARNINGS/ADVISORIES...
NM...None.
TX...None.
&&
$$
Hefner/Laney
Area Forecast Discussion
National Weather Service Lincoln IL
907 PM CDT Thu Jul 20 2017
.UPDATE...
Issued at 907 PM CDT Thu Jul 20 2017
Convection that developed in southeast IA is either backbuilding
or quasi-stationary. However, a frontal boundary is located near
I-74 and one shower has developed in Mclean county. isolated
showers/storms are still possible along this boundary this evening
and into the overnight hours. So will be keeping some form of pops
in this area though need to make some adjustments to pops to
match current radar trends/situation. Will also be updating cloud
cover to account for large cirrus shield that has spread into
central IL.
Update out shortly.
&&
.SHORT TERM...(This evening through Friday)
ISSUED AT 309 PM CDT Thu Jul 20 2017
Subsidence in the wake of a morning MCS that skirted central
Illinois to the northeast has prevented convective re-development
thus far this afternoon. However, latest LAPs analysis shows an
extremely unstable airmass in place...with peak CAPE values in
excess of 5000J/kg along and north of I-74. In addition, an area
of deep-layer moisture convergence is noted across the far
northern KILX CWA from near Galesburg E/SE to Chenoa. This is
likely in proximity to a residual outflow/differential heating
boundary left behind by the morning convection. Think this will be
the area to watch over the next few hours for widely scattered
thunderstorm development. HRRR has been consistently showing a few
cells firing across the N/NE late this afternoon into the evening,
so have included low chance PoPs along/north of I-74 accordingly.
Think any storms that develop will dissipate toward midnight, with
largely dry conditions noted overnight.
A cold front currently extending from southern Lake Michigan
to central Iowa will sag southward late tonight...eventually
stalling across north-central Illinois Friday morning. With a weak
boundary in the vicinity, have included low chance PoPs across the
entire CWA on Friday. While most locations will remain dry, a few
spots may pick up locally heavy rainfall with slow-moving storms.
The main story for Friday however, will be the continuation of the
oppressive heat and humidity. High temperatures will once again
top out in the lower to middle 90s, with peak afternoon heat index
values reaching the 105 to 110 degree range.
.LONG TERM...(Friday night through Thursday)
ISSUED AT 309 PM CDT Thu Jul 20 2017
Low pressure will develop over the Dakotas on Friday, then will
track slowly eastward into Wisconsin by early Saturday. Favorable
dynamics will exist ahead of the low to trigger the development of
an MCS across Minnesota/Wisconsin Friday night. This system will
track E/SE into southern Wisconsin and far northern Illinois late
Friday night into Saturday morning. All indications suggest the
storms will remain mostly N/NE of the KILX CWA: however, have
included low chance PoPs along/north of I-74 as the system brushes
by the north. Once the low moves into the Great Lakes, it will
drag a stronger cold front southward into central Illinois by late
Saturday. Most models suggests scattered thunderstorms will
develop along/ahead of the front across the northern two-thirds of
the CWA late Saturday afternoon and evening. With CAPES once again
exceeding 4000J/kg and 0-6km bulk shear increasing to around 30kt,
a few strong to severe thunderstorms with gusty winds, large hail,
and torrential rainfall will be possible. The storms will settle
into the southern CWA by Saturday night as the front sinks toward
the I-70 corridor.
Despite FROPA Saturday night, a trailing trough axis may trigger
isolated convection Sunday/Sunday evening. After that, deep-layer
northwesterly flow will bring a cooler and less humid airmass into
the region early next week...with highs dropping into the lower to
middle 80s for Monday and Tuesday. The next chance for widespread
precipitation will likely hold off until Thursday at the earliest
as another cold front approaches from the northwest.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 701 PM CDT Thu Jul 20 2017
One storm already developed over southeast IA and will slowly move
east into the area. Possibility is there that it will effect PIA
and BMI taf sites so have added VCTS for those two sites this
evening. Other sites should remain mostly clear with some high
cirrus blow off from the evening convection. Skies should be
mostly clear overnight with CU developing tomorrow...like today.
Winds will become light and variable at all sites this evening
with southwest winds returning tomorrow.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT Saturday for ILZ027>029-
036-037-040>042-047>054-061-062-066>068-071>073.
Heat Advisory until 8 PM CDT Saturday for ILZ030-031-038-043>046-
055>057-063.
&&
$$
UPDATE...Auten
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Auten
Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
819 PM CDT Thu Jul 20 2017
.UPDATE...
Issued at 813 PM CDT Thu Jul 20 2017
Updated forecast to let todays heat advisory go.
&&
.SHORT TERM...(This evening through Friday)
Issued at 304 PM CDT Thu Jul 20 2017
The HRRR models, RAP, GFS and NAM were the basis for isolated to
perhaps scattered coverage tonight. Satellite suggests a weak
disturbance across the Tetons will spark MCS activity this
afternoon. This storm activity should translate through the Black
Hills this evening and perhaps affect nrn Neb overnight.
The situation Friday afternoon is more certain as ML-CAPE increases
to 3000-4000 J/KG. Winds aloft at 500mb are weak at 15kt initially
but a localized speed max near 40kt develops from maturing
convection east of highway 83. All indications are heavy convection
will fire and severe weather would soon follow.
A heat advisory is in place for most of the area Friday. The GFS,
HRRR exp and NAM models plus bias correction were the basis for
highs in the upper 90s to mid 100s. Blended guidance plus bias
correction indicates dew points in the 60s to lower 70s which would
support heat indices 100+. The 16C h700mb thermal ridge will move
overhead, ahead of a cold front during the afternoon, and this
should present deep vertical mixing and super adiabatic lapse rates
near the SFC. There just one problem. The models forecast midlevel
clouds which will take a few degrees off the high temperature
forecast. Given that the forecast heat waves have been too cool this
summer, the forecast for 100s will stand for now.
The 16C thermal ridge should move in late tonight and hold up lows
to the upper 60s to lower 70s for a warm start Friday morning. The
12z HRRR exp model indicates North Platte warms to 90F by 10 am and
100F by 1 pm.
.LONG TERM...(Friday night through Thursday)
Issued at 304 PM CDT Thu Jul 20 2017
Whatever convection develops Friday afternoon is expected to grow
upscale Friday night as a significant cold front moves through Swrn
Neb. All models show this except for the ECM. Temperatures at 700mb
fall back to around 10C with precipitable water around 1.5 inches
which should support upscale growth. The models show a series of
weak disturbances crossing the Cntl Rockies Saturday with moisture
still in place across Srn Neb. Precipitable water decreases to an
inch or less Saturday night marking the end of rain chances.
Dry weather is expected Sunday through Tuesday as the subtropical
upper level ridge builds back into the Wrn U.S. Hot weather may
redevelop Wednesday and Thursday as this ridge begins to move east
again. The basis of the temperature forecast a model blend of bias
corrected GFS, ECM and GEM. This produced temperatures close to the
national blended data set.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 658 PM CDT Thu Jul 20 2017
Thunderstorms over the eastern plains of Wyoming and Colorado will
bring mid and high clouds to western Nebraska later tonight. Some
thunderstorms are possible over northern Nebraska Friday morning.
Have carried VCTS in the KVTN taf.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon CDT /11 AM MDT/ to 8 PM CDT /7 PM MDT/
Friday for NEZ005>010-022-024>029-035>038-056>059-069>071.
&&
$$
UPDATE...Power
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Power
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
725 PM CDT Thu Jul 20 2017
.SHORT TERM...
315 PM CDT
Through Friday...
Isolated light rain showers persist over northern IL, but the main
focus for convection will be along an advancing lake breeze and
south of I-80 near a weak boundary. I have low to medium confidence
in how many storms will form along these boundaries and how long
storms will persist into this afternoon/evening. The more agitated
clouds are associated with the lake breeze pushing across Lake and
Cook counties in IL so thinking a few showers/storms are possible
over the next couple of hours.
The boundary further south is near the southern forecast area
boundary over McLean, Champaign, and Vermilion counties. This
boundary is not as strong and satellite is not showing as much CU.
Therefore the general idea is isolated to widely scattered
showers/storms form along the lake breeze and near the southern
boundary through the early evening hours. Storms will then
concentrate along a Rochelle, IL to Rensselaer, IN line around
midnight. Models have not been handling convection well today so I
have low confidence in the forecast this evening and tonight.
As far as the severity of the storms, my main concern is torrential
downpours as PWATs are around 2 inches. The latest RAP analysis has
CAPE values over 3000 J/kg, but shear is lacking. The highest shear
values are 35-40 kt north of a Pontiac to Benton County Indiana
line. Therefore, all storms will produce torrential downpours that
may result in localized flooding, but only a few stronger storms may
produce large hail or damaging winds.
Outside of convection, dewpoints are very high in the mid 70s to
around 80 at some locations. Expecting fog to develop after midnight
especially where there isn`t nocturnal convection. Dense fog is
possible, but didn`t have the confidence to put dense fog in the
forecast just yet.
Low confidence continues into Friday`s forecast. Models have very
different timing and paths for a decaying complex sliding southeast
across the forecast area. Kept precip chances in the chance range
due to my low confidence even though I do expect a complex to impact
the region. Main impacts from this complex will be heavy rain and
gusty winds. Convective parameters look similar to today with CAPE
values over 3000 J/kg, but shear values of only 30 kt.
I made minimal changes to high temps Friday as I`m not sure how the
decaying system will impact temps. If the system rolls through
earlier than currently forecast, we could be seeing 90s like today.
However, if it comes through later, temps may only reach the upper
80s before the storms cool the environment. Either way, hot and
muggy conditions continue Friday.
JEE
&&
.LONG TERM...
243 PM CDT
Friday afternoon through Thursday...
Main forecast concerns/challenges are with continued rounds of
thunderstorms Friday evening through Saturday night, with severe
weather and heavy rainfall once again appearing likely throughout
this period. A Flash Flood Watch has been issued for portions of
north central and northeast Illinois Friday afternoon through
Saturday morning.
Friday Afternoon into Friday Evening...
Period begins active with guidance indicating progressive MCS to
likely move southeast through the region by either late Friday
afternoon or very early Friday evening. Given that there is no
real big change expected in the overall pattern, this appears to
be a highly probable scenario. Instability axis will still be
situated into northern Illinois and northwest Indiana, supporting
the idea that any upstream development will have a high chance to
move into northern Illinois in the late afternoon and early
evening hours. Still some uncertainty on exact track through
northern Illinois before shifting into northwest Indiana later in
the evening. A more focused impacted area may be realized during
the day Friday, but at this time, most locations along and north
of I-80 will have a high chance of observing this next complex of
storms. With this complex of storms, a damaging wind threat will
likely be the main hazard and given the likely progressive nature
of these storms, thinking any widespread flash flooding would be
low during this time. However, high PWATS around 2 inches and
strong instability in place will support torrential rainfall with
any storm. So can`t rule out minor flooding, especially as a quick
1-2 inches of rainfall will be possible.
Friday Night into Saturday morning...
This MCS will continue to shift to the east southeast through the
mid to late evening, still posing a damaging wind threat for
areas in northeast Illinois and northwest Indiana. At this time,
don`t see a large difference in the environment across these
locations, with these storms maintaining the same intensity and
damaging wind threat. As this complex of storms exits late in the
evening, should begin to already observe additional thunderstorm
development across areas from northeast Iowa and southwest
Wisconsin. Frontal zone position, additional upstream mid level
energy, and strengthening LLJ will likely support continued
thunderstorm develop along this axis throughout the night.
Instability/moisture axis and steering flow will once again
support any upstream development to move into areas in northern
Illinois and northwest Indiana with most locations observing these
additional storms. This situation becomes very concerning as
although there will remain a severe threat, the threat of flash
flooding increases during the overnight hours into early Saturday
morning. There is the potential for areas to receive a quick
additional amount of 2-3 inches given the possible training and
high likelihood of high rainfall rates/torrential rainfall. These
additional thunderstorms along with the area already observing
multiple rounds of thunderstorms with heavy rainfall and very wet
conditions in place, will provide a flash flood threat. Have
issued a Flash Flood Watch for portions of northern Illinois. Have
left out areas further to the south in Illinois and the counties
in northwest Indiana give some lower confidence in these
locations. Also, observed rainfall has not been quite as high
recently. Nonetheless, will continue to monitor possibly including
these areas with later forecasts.
Saturday and Saturday Night..
Confidence does lower with convective trends on Saturday and
Saturday night given some model variability with the synoptic
pattern. However, additional thunderstorm chances Saturday and
Saturday night still appear reasonable. Large scale forcing will
likely be in place along with a moist and unstable atmosphere,
supporting at least scattered development. Although the likely
pattern on Saturday does not appear favorable for widespread heavy
rainfall, the very moist conditions will still support heavy
downpours. With the possible pattern and the likely instability,
severe weather will also be a concern area wide.
Rodriguez
&&
.HYDROLOGY...
320 PM CDT
With the Flash Flood Watch out and additional river flood
products issued today, have allowed the ESF to expire. Previously
observed rainfall and expected multiple rounds of thunderstorms
beginning late Friday afternoon through early Saturday morning
likely to bring renewed rises to many area rivers. Of particular
concerns are the Fox, Des Plaines, and Rock river basins. Concerns
remain heightened on Friday and Friday night, where the
environment will be even more favorable for very efficient rain-
producing storms (training storms, possible backbuilding, deep
moisture, etc). While there is uncertainty on exact location, in
collaboration with WPC, adjacent WFOs, and the RFC, the focus is
presently most favored in southern Wisconsin and far northern
Illinois. WPC has continued the moderate risk of excessive
rainfall for this period.
Rodriguez
&&
.AVIATION...
For the 00Z TAFs...
Concerns:
- Thunderstorms across S-SW Tracon tonight
- Fog development
- Possible storms Friday PM
There is a developing complex of thunderstorms across west central
Iowa associated with a shortwave. This wave will move slowly ESE
and bring some showers and storms, but likely will follow the
instability gradient just off to the south and west of the Chicago
terminals. These storms would be slow moving and likely have quite
a bit of rain and lightning. Low confidence on these storms
getting to ORD/MDW/DPA and therefore kept the TAFs dry. Winds wil
slacken and it is very moist in the low levels, so will need to
watch for fog development. Did not hit things too hard yet as
there will be some passing clouds, but any gaps could see some
localize dense fog.
We also have low confidence on any redevelopment on Friday, at
least for this TAF period. There are several waves to our west
that will pivot northeastward around the expansive upper ridge
across the south central USA. Have maintained a low mention of
storm chances in the afternoon but timing very well could change.
KMD
&&
.MARINE...
315 PM CDT
Strong winds from a wake low this morning have dissipated. The baggy
pressure gradient has allowed a lake breeze to form. Despite gusty
southwest winds, the lake breeze is finally moving ashore over the
southwest end of the lake. Variable wind directions are expected
across the lake through tonight.
Winds become southerly tomorrow as high pressure shifts over the
eastern Great Lakes. One to two additional convective systems are
possible through Friday night. Any of these may produce a wake low
that briefly increases winds and waves to values higher than
currently forecast.
A weak low will pass over the lake Saturday night and winds
will become northerly behind it. A second and possibly stronger
surge of north winds will push down the lake Sunday night into
Monday morning. North winds 15-25 kt are possible. High pressure
moves over the lake Tuesday.
JEE
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flash Flood Watch...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...4
PM Friday to 9 AM Saturday.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Pueblo CO
352 PM MDT Thu Jul 20 2017
.SHORT TERM...(This evening through Friday)
Issued at 352 PM MDT Thu Jul 20 2017
Drier air has pushed in under the high which has shifted the focus
for thunderstorm development across the western and northern
portions of the forecast area. The eastern San Juans and La Garita
mountains as well as Chaffee, Lake and Teller/El Paso counties will
have the best chance for showers and thunderstorms. H7-H5 specific
humidities are still running around +6 to +8 g/kg...so locally heavy
rainfall will be the primary threats and flash flooding will be
possible on vulnerable burn scars, areas with susceptible soils
(like the chalk cliffs) and urban areas. Activity winds down after
04z, though some isolated showers will be possible over the
mountains through the early morning. Most of the southeast plains
will remain dry this evening...though high res models send an
outflow boundary southward into the highway 50 corridor which could
spark an isolated storm or two. Kept pops mainly confined to the I-
25 corridor counties for now as HRRR keeps majority of the activity
just north of the area through the late evening hours.
Friday will be a more active day across the district as the upper
high nudges eastward a bit allowing the monsoon plume to shift over
more of the mountains. Front drops through the southeast plains
during the late afternoon and evening...likely reinforced by outflow
from thunderstorms that develop along the Palmer Divide. Once
again... El Paso county should see an uptick in thunderstorm
coverage given forcing from the front. Threats from thunderstorms
will continue to be locally heavy rainfall capable of producing
flash flooding, wind gusts up to 50 mph and lightning. However
given some pooling of CAPE along the Palmer Divide in the afternoon
in vcnty of the front, we could see one or two strong storms with
hail to near the size of quarters. -KT
.LONG TERM...(Friday night through Thursday)
Issued at 352 PM MDT Thu Jul 20 2017
Relatively active meteorological conditions are anticipated over
many portions of the forecast district at times...especially from
Friday night into this weekend and then again from Wednesday into
at least next Thursday.
Primary meteorological concerns include but are not limited to
temperatures, increased precipitation potential(including locally
heavy rain and localized flash flooding potential favoring this
weekend and then again from Wednesday into at least next
Thursday). The potential also exists that intense thunderstorms at
times may also be observed from Friday night into this weekend
and then again by later next week.
Recent longer term computer simulations, PV analysis and forecast
model soundings indicate that precipitable water values over many
portions of the Interstate 25 corridor should run around 1 inch
or slightly higher at times from Friday night into this weekend
and then again from Wednesday into next Thursday. In addition,
northerly surge moves across eastern sections Friday night,
helping to enhance precipitation potential from Friday night into
this weekend.
The combination of adequate atmospheric moisture, surface
boundaries, the daily orographic heating cycle and subtle upper
disturbances will be capable of producing enhanced precipitation
chances(including flash flooding potential at times) from Friday
night into this weekend.
Also, projected localized capes and LI`s nearing/exceeding 1000
J/KG and -5C respectively at times from Friday night into this
weekend will be capable of generating some intense thunderstorms
with a limiting factor once again being projected low-grade mean-
layer wind shears. As always, WFO Pueblo will monitor closely and
issue hydro/severe products as needed.
Finally, in addition to generally low-grade gradient winds during
the longer term, anticipate that near to slightly below seasonal
later July maximum temperatures should be experienced over many
locations from Saturday into Monday with near to above seasonal
maximum temperatures then expected from Tuesday into Thursday.
Also, projected minimum temperatures during the longer term should
remain above late July climatological averages over the majority
of the forecast district.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 352 PM MDT Thu Jul 20 2017
Best chance for -TSRA will be at the KCOS airport late this
afternoon through this evening. Will carry VCTS for now given more
isolated coverage to thunderstorms, however a tempo group may become
necessary should radar trends support. Erratic gusty winds to 50
mph, VFR cigs and brief MVFR VIS with +RA will be possible under the
stronger storms. Winds will shift out of the north between 22z-23z
for KCOS and closer to 00z at KPUB as outflow from thunderstorms
pushes southward through the region. Thunderstorm outflows may also
affect the KALS airport late this afternoon through this evening but
looks like main activity should stay confined to the mountain areas.
A slight uptick in thunderstorms can be expected for Friday as the
monsoon plume shifts over the region. -KT
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$