Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/01/20
Area Forecast Discussion
National Weather Service Des Moines IA
638 PM CDT Tue Jun 30 2020
...Updated for 00z Aviation Discussion...
.DISCUSSION.../Tonight through Tuesday/
Issued at 301 PM CDT Tue Jun 30 2020
Synoptic Overview:
Main features of interest over the next 36 hours are the short-wave
perturbation moving up the Mississippi River Valley and deep trough
becoming negatively titled over the Rockies. At the surface there is
a broad low pressure system centered over Kansas and Nebraska.
Influence of the pressure gradient from this does extend into Iowa,
leaving most of the upper Midwest in a southerly flow regime. There
is not a pronounced warm front with this system, but there is a
stronger cold front trailing it that can be seen in the temperature
and dewpoint analysis. Overnight an MCS developed in front of the
nose of the low-level jet in conjunction with the short-wave
producing torrential rainfall over eastern Missouri and wester
Illinois. Now that the low-level jet has weakened, this feature has
stalled but still continues to produce the torrential rainfall.
Today and Tomorrow:
With relatively weak H5 flow over the mid and upper Mississippi
River Valley this morning and afternoon, the short-wave perturbation
will stall and behave like a closed-low, which will leave stagnant
rain shower activity over western Illinois and eastern Missouri, and
parts of southeast Iowa. A few CAM solutions do depict some back
building of the convection into the Davis and Wapello counties, the
extreme southeast portion of the forecast area. The heaviest
rainfall for Iowa will look to be in the Keokuk and Burlington area.
Rainfall rates in our southeast area will need to be monitored
closely if more convection develops and stalls in our southeast
counties. However, radar trends over the past few hours have not
been showing an increase convection, and actually has dwindled
considerably in our southeast. Most guidance solutions do not bring
the precipitation associated with this short-wave and MCS much
further west of U.S. Highway 63. However, interaction with the
larger trough out west has complicated the forecast for the rest of
the day, late this evening and overnight. The trough is what will
eventually help to increase the flow across the upper Midwest and
eventually progress the MCS north and east, but not before it causes
problems in areas surrounding the Mississippi River.
Strong PV anomaly that has been sitting over the western CONUS the
past few days is now starting to propagate across the Rocky Mountain
region. The deep H5 trough has developed a negative tilt in the past
12-18 hours, and has sent a stronger shot of CVA into the High
Plains and Central Plains late this morning and has allowed for
further deepening of the surface cyclone. As the the 50-60 kt jet at
H5 rounds the base, the vort max and bulk of the CVA will eject into
the northern Plains this afternoon and evening, lifting the trough
northward into the southern Canadian Provinces. However, the height
falls from this propagation now appear to be extending further
eastward, and will clip far western and northwestern portions of the
forecast area late this evening. As a result, the convection
potential that yesterday looked to remain in eastern Nebraska and
Dakotas will now have potential to work its way through Iowa late
tonight. As the trough lifts, the associated surface low develops a
bifurcation point, with a secondary surface low developing in the
Dakotas and lifting northward with the parent trough, as the
southern end of slides eastward and breaks away from it. While it
will not be as stagnant as this morning`s short-wave and subsequent
MCS, the surface low propagation will slow. Convergence will
increase as it crosses into Iowa along with the trailing cold front.
CAM guidance has convection entering Iowa after 06z this evening.
The HRRR appears to to be depicting the most robust convection,
concentrating a stronger convective cluster moving eastward from
Sioux City toward Fort Dodge, and then diving southeastward. Other
CAM solutions are bit weaker and more widespread with convection
along the cold front. Instability will not be hard to come by. HREF
mean during the afternoon ahead of the convergent zone characterizes
the warm moist airmass with SBCAPE values between 3500 and 4500
J/kg, and maintains MUCAPE values in western Iowa over 2000 J/kg
late into the evening and overnight hours. For surface parcels
though will have over -150 J/kg of CIN that it will need battle, MU
will only have to battle -50 to -70 J/kg of CIN. There may some
struggle to initiate new updrafts at times, but the surface low and
cold front likely will provide extra forcing needed to beat this.
The wind shear, or lack there of, will be the main component that
largely hinders the severe potential. 0-6 km bulk shear values in
most model solutions struggle to reach 20 kts this afternoon and
evening ahead of the boundary. With the weak shear environment, it
is interesting how this morning`s HRRR cycles depicted a somewhat
organized convective cluster. Perhaps if a stronger cold pool
develops this may provide better support to a convective cluster.
But, the overall parameter space of the environment does not support
a highly organized system. Model soundings this evening do depict
DCAPE values in excess of 1000 J/kg, which certainly could foster
the development of a few downbursts with convection that perhaps
produce isolated severe wind gusts.
The bigger concern this evening could perhaps be heavy rainfall,
especially with any convection coming from the west that meets up
with stagnant MCS. Overnight and through Wednesday morning, GFS and
NAM depict warm cloud depths between 3500-4000m, with PWATs pushing
1.75 to 1.90 across most of central Iowa. While this system is
expected to move at a faster speed than the MCS over the mid
Mississippi River Valley, a new convective complex may still not be
overly progressive. HREF mean QPF is about 1-1.75 inches across
western, southwestern, and southern Iowa in the next 12-18 hours. A
few individual CAM members of the HREF have 2-3 inches on the high
side. In this environment, amounts this high are possible in
localized areas. However, as mentioned above regarding concerns
about thunderstorm potential, there will be CIN that updrafts will
have to fight. If robust convection fails to initiate, and storms
quickly become stratiform on the backside of the low and cold front,
rainfall amounts could be less. For rainfall totals, this is
currently the source of greatest uncertainty. Flash Flood guidance
across most of the area with high QPF is 2.75 - 3.00 inches in 6
hours. Given HREF mean QPF and uncertainty associated with
convection, have decided to hold off from issuing a Flash Flood
Watch for counties in our area. If flash flooding does occur, it
will likely be very localized. If there is an upward trend in the
precipitation forecast in the next few hours, a short fused watch
may be needed. Overall, the bulk of the area in the highest QPF will
be able to handle a decent amount of rain. Should robust rain
showers and thunderstorms hold up to the southeastern extent of the
forecast area (Wapello and Davis Counties), there could be
additional issues there. Over the last few hours though, Davis and
Wapello Counties have not had any rain accumulations, which is
helpful in reducing the flooding threat.
Extended:
Beginning Thursday afternoon, amplified thermal ridge develops across
the central Plains and into the mid Mississippi River Valley. Low-
level flow will remain southerly, brining in hot humid gulf air.
This will likely make for oppressive heat over the holiday weekend,
with heat indices pushing the mid to upper 90s. There will not be
any major forcing through the weekend, but air mass thundershowers
are certainly possible given the theta-e rich air that will be in
place across the region. At this time, it looks like the heat will
stay just below headline criteria through the weekend. Beyond the
official forecast period, more heat is in the forecast and could
become problematic.
&&
.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 638 PM CDT Tue Jun 30 2020
Primary concerns this TAF cycle will be thunderstorms and
associated restrictions. Plenty of high level clouds remain over
Iowa with FEW/SCT ceilings below FL030 in some places. There
could be intermittent MVFR at the central Iowa airports this
evening, but went prevailing VFR. Thunderstorms are just
beginning to develop over central Nebraska and will move into
central Iowa after midnight into Wednesday morning. Highest
chances of impacts would be at DSM and OTM with storms perhaps
just brushing FOD. For MCW and ALO, thunderstorms may end up
missing these terminals and removed from ALO this cycle and may do
the same for MCW next cycle. After storms pass through,
conditions should improve from north to south through the day back
into VFR.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Krull
AVIATION...Ansorge
AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
641 PM CDT Tue Jun 30 2020
.Discussion...
Issued at 326 PM CDT TUE JUN 30 2020
The MCV that moved through Missouri overnight is now centered over
northwest Illinois this afternoon and is slowly weakening as it
moves into northern Illinois towards the southern tip of Lake
Michigan. Scattered showers and thunderstorms have accompanied
this MCV and the cold pool has helped to reinforce an outflow
boundary that is generally bisecting Missouri from northwest to
southeast. Convergence along this boundary, CAPE values of ~3500
J/kg, and a weaker secondary shortwave moving out of the Ozark
Plateau has resulted in storms firing along portions of this
convergence zone over Central Missouri as well as across southwest
Missouri. Initial thinking was that this boundary may drift back
to the west but boundary looks pretty steady this afternoon with
no real push westward. The weaker secondary shortwave trough has
kicked up some showers with isolated thunder over portions of
southeast Kansas and southwest Missouri. As we head into the
overnight hours, we could see this activity perk up as the LLJ
starts to increase over eastern Kansas and far western Missouri.
Further to the north...an elongated trough over the northwestern
states rotating northward and its associated cold front will kick
off storms across central Nebraska later this evening. The resulting
MCS will push eastward before dropping southward. The first question
of the day will be just where the MCS will drop south and how long
it will hang together before weakening. CAM models are coming more
in line with this complex dropping southward into Missouri, but
discrepancies on timing and the general location of the line are
still a concern. Current thinking is that the MCS will follow the
1000-500 mb thickness which matches up well with the aforementioned
outflow boundary, generally from northwest Missouri southeastward to
southeast Missouri. The main question is how far west will this line
extend as some models such as the HRRR keep the western edge clipped
and eastern Kansas and far western Missouri would not see much, if
anything, overnight. The NAM Nest is a little more aggressive and
develops convection along the outflow boundary ahead of the incoming
MCS. After they merge the MCS takes a more southern route and the
western edge of the line would go through eastern Kansas and western
Missouri.
The second question of the day will be how this overnight system
will impact temperatures and the resulting heat indices tomorrow
afternoon. Lingering showers and thunderstorms tomorrow morning will
allow for a cooler start to the day with clouds possibly lingering
into late morning to early afternoon. As clouds scour out,
temperatures should recover fairly rapidly and we could see heat
indices quickly climb into the lower 100s. The longer the clouds
linger, the less likelihood we will see heat indices near heat
advisory criteria. For now have gone with a Special Weather
Statement to highlight the possible heat indices of 100-105 degrees
tomorrow afternoon and will hold off on issuing a Heat Advisory
given the uncertainty. However, future forecast updates may warrant
issuing an Advisory if confidence builds.
As a broad upper ridge builds over the central conus the rest of
this week, heat and humidity will remain a concern, especially
headed into the holiday weekend.
&&
.Aviation...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 640 PM CDT TUE JUN 30 2020
Mostly VFR with some MVFR conditions possible during the overnight
hours. Model trends indicate the possibility of showers and
thunderstorms rolling through the area during the early AM hours
Wednesday. Storms are expected to traverse the area from north to
south.
Vertical profiles and forecast models continue the trend
of a shallow moist layer favorable for nocturnal low level cloud
development. Also continuing is the trend of diurnal cumulus
development over the area during the late morning and early
afternoon which may bring MVFR ceilings. Finally, during the
second half of the forecast period a low pressure center
slowly traverses the area from east to west. This results in
winds shifting from southeasterly to easterly.
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
KS...Heat Advisory until 8 PM CDT this evening for KSZ057-060.
MO...Heat Advisory until 8 PM CDT this evening for MOZ053.
&&
$$
Discussion...Pietrycha
Aviation...CDB/Pesel
Area Forecast Discussion
National Weather Service Lincoln IL
855 PM CDT Tue Jun 30 2020
.SYNOPSIS...
Issued at 309 PM CDT Tue Jun 30 2020
Periods of showers and thunderstorms will continue across central
and southeast Illinois through Wednesday evening, some of which
may be strong and produce heavy rain. After that, we will be in a
pattern that favors only isolated afternoon storms, as well as
hot and humid weather, through the holiday weekend.
&&
.UPDATE...
Issued at 854 PM CDT Tue Jun 30 2020
Trends in nearly all of the high resolution models are looking
drier overnight in our forecast area. An MCV centered over eastern
Iowa is expected to shear out and drift to the NW away from
Illinois later tonight. The vortex is still triggering an axis of
showers/storms in west-central IL near Schuyler County, and the SW
flank of the MCV may remain active with rain/storms along the
Mississippi River Valley, per the NAM4K and HRRR. Despite the
models dry trends, spurious showers could bubble up at times, as
indicated by channels of cooler cloud tops across central IL.
Therefore, have not completely removed PoPs for now, but did
reduce them to slight chance 15-20% in most of the area. The best
chances of any measurable rain overnight will reside in our SW row
of counties, closest to where the Hi Res guidance has an axis of
precip overnight, so have kept a corridor of Chance PoPs (30-50%)
there. A late night/early morning storm complex could come into
western Illinois, per older runs of the HRRR and NAM4K, but more
recent output has that wave dissipating as it arrives near our
western counties. We had a larger area of likely PoPs in our W CWA
to account for that complex, but we have reduced that area with
the evening update, with further reductions possible if the models
continue their dry trends.
No other noticeable changes were made to the forecast, with muggy
lows in the upper 60s to low 70s likely.
&&
.SHORT TERM...(This evening through Wednesday night)
ISSUED AT 309 PM CDT Tue Jun 30 2020
Flash flood watch has been extended for a few more hours, now
through 10 am Wednesday.
Radar loops continue to show a well defined MCV spinning just
south of Macomb this afternoon. Northern portion of the rain
shield has diminished to scattered activity rotating around this
MCV, while more widespread heavy rain and thunderstorms have been
tracking from eastern Missouri into south central Illinois.
Infrared satellite imagery showing colder cloud tops with these
areas about to merge with a separate convective cluster over far
southern Illinois. With the focus shifting down there, rain
chances in our area for this evening have been cut back some.
Main period of concern begins around midnight, as redevelopment
begins in west central Illinois. As this occurs, an MCS that is
expected to develop Nebraska and South Dakota this evening will
track southeast. High-res models are a mixed bag as to how much
this MCS will play a factor in our area, with the NAM Nest most
likely to bring it this far northeast. A good chunk of the watch
area has already been hammered by the earlier convection, though
mainly on the fringes of our forecast area, so it would not take
much more rain to cause issues. MRMS estimates have shown 2-3
inches across Scott and western Morgan Counties, as well as south
of Springfield and west of Flora. With the timing uncertainty, it
was decided to extend the watch a bit longer, until 10 am.
Temperatures today have been significantly held down with the
rain, struggling to get out of the upper 60s/lower 70s in the
southern CWA. With an earlier stop to the rain on Wednesday, we
should have enough time to recover into the mid-upper 80s, though
that was lowered a few degrees from the previous forecast.
.LONG TERM...(Thursday through Tuesday)
ISSUED AT 309 PM CDT Tue Jun 30 2020
A rather stagnant pattern will remain in place late this week and
early next week. The upper level ridge over the central U.S. will
become more of a broad west-east configuration, favoring mainly
dry conditions with only a few afternoon pop-up storms through the
weekend. As the ridge flattens, longer range models show an upper
wave sliding along top. This will lead to a slightly better chance
of storms Monday and Tuesday.
Temperatures through the period will be fairly uniform: Highs in
the lower 90s, lows near 70, and afternoon heat index 95 to 100.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 659 PM CDT Tue Jun 30 2020
An MCV rotation remains centered in SE Iowa with storms
redeveloping on the southern flank advancing into Schuyler County
headed to the SE toward SPI. While IR satellite images indicate
some cooling of the cloud tops, no strong storm threat is
anticipated in the next 3-6 hours. The only MVFR ceilings
remaining are at CMI, closer to the stationary front draped from
NW Illinois to NE Vermilion County. High resolution models
indicate SPI will have the best chance for periodic rain/storm
threat tonight, with more isolated chances at the other TAF sites.
The eventual track of the MCV will control where additional
thunder potential with concentrate later tonight and Wed morning.
There is some indication in the forecast soundings that IFR clouds
may develop later tonight through just after sunrise. Added that
to SPI, but only went down to MVFR at the other terminals for now.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Wednesday morning for ILZ040-047>052-
061-066-067-071-072.
&&
$$
UPDATE...Shimon
SYNOPSIS...Geelhart
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Shimon
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
935 PM CDT Tue Jun 30 2020
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
The convection for the day has ended. Regional radars showed an
outflow boundary dropping south through western Tennessee that a
few hi-res models suggest will spawn some convection in our
northeast most zones around sunrise. Wl maintain pops there toward
sunrise but elsewhere no additional development is expected and
pops have been removed the remainder of tonight. Temperatures were
on track to bottom out a couple of degrees warmer than normal
again in the middle 70s. /22/
Prior discussion below:
Rest of this afternoon - Wednesday: Rest of this afternoon-
tonight: Convection has been been slow transpire this afternoon
due to morning stratus/rain showers that persisted into the
afternoon. Any convection that does develop will likely be more in
the northern areas that have warmed into the low 90s & a better
thermodynamic/microburst environment reside. However, to the
south, these areas have been cooler, outside of the Pine Belt &
less potential. Due to that, any organized stronger storms will
have the best potential in the ArkLaMiss Delta. Expect any showers
& storms to wind down by early evening. However, synoptic flow
will become more out of the northwest & perturbed flow will help
an MCS develop across the Ozark/Tennessee Valleys. For now, this
looks like most of the convection or any type of overnight MCS
will be more into the Mid-South into northern Alabama. However, it
is possible it might sneak in across north Mississippi & Golden
Triangle, generally after midnight to just before daybreak . Also
can`t rule out some morning showers across the south but likely
less coverage than this morning across central & southwest
Mississippi before daybreak.
Wednesday: The region will become entrenched in northwest flow
with synoptic ridging developing further to the west over the
central Plains. The subtropical ridge over the Gulf of Mexico will
begin to weaken, which will only help better northwest flow regime
to setup. This pattern will bring in a juxtaposition of copious
lapse rates/thermodynamics & microburst potential. High moisture
laden air, with PWs approaching 2 inches & dewpoints in the mid
70s, will support a warm & muggy environment. Thermal profiles
will be similar with heat & humidity reaching in the low-mid 90s &
heat indices climbing into the lower 100s & approaching 105
degrees along & west of Interstate 55. Due to that, kept the
combined "Limited" for heat stress in the HWO/graphics Wednesday
& into Thursday. With high warmth & humidity, a very favorable
thermodynamic setup will favor N-NW flow MCS potential (i.e.
7-7.5 deg. mid- level lapse rates, widespread 7-10+ microburst
composite parameters & SBCAPE/DCAPE upwards of 5000+ J/kg & 1500+
J/kg). This setup favors scattered isolated to severe organized
downdrafts/cold pools/line segments into late afternoon. HREF
guidance continue to prog a MCS diving down out of the
Ozarks/Tennessee Valley & potentially making it down into the Mid-
South & north Mississippi before early Wednesday evening. The new
12Z HRRR continues to trend in that direction & the 12Z Euro
shows consensus with the HRRR/ARW/NMM. Due to that, mentioned
this area in the HWO text/graphics for late Wednesday afternoon,
generally after 4PM, for "Marginal" severe for isolated severe
storms, with most potential into the evening hours & through
Thursday. Even though the 12Z HRRR has most convection into the
evening, wanted to account for faster convective cold pool motion
& extremely favorable MCS environment. /DC/
Wednesday night through Monday: Mid level ridge from the Southern
Plains into the mid MS valley will put much of the area in an active
northerly flow by Wednesday night. Shortwave dropping out of the
Midsouth will likely be already fueling strong convection over north
MS/west TN/north AL late Wednesday afternoon. 30-40 knots of deep
layer shear with continued instability (1500-2500 J/kg CAPE, 7C/km
and upper 20s vertical totals) during the evening should lead to
upscale growth/MCS development over north into eastern MS Wednesday
night with primarily a damaging wind threat. Will continue the
marginal severe threat, similar to the area outlooked by SPC, but
continue into Thursday as the parameter space continues to support
this sort of activity.
While the majority of the convection will remain in the east,
proximity to mid level ridge over western sections will help max
temperatures rise into the mid 90s Thursday. This with dewpoints in
the mid 70s will result in heat indices around 105, so will continue
limited dangerous heat risk in the HWO for these areas.
The mid level flow will gradually weaken moving into the weekend,
but the continued cyclonic nature will support higher than average
rainfall chances, mainly during the afternoon/evening. The heat
should not be as much of a problem as maximums stay around 90. /GG/
&&
.AVIATION...
00Z TAF discussion:
Radars showed very little convection in our area at 2330Z. HBG-PIB
may see a brief TSRA/SHRA before 02Z. Otherwise, some guidance
suggests early activity over our ne affecting GTR by 12Z Wed with
no additional development elsewhere until Wed aftn. VFR conditions
are expected to prevail away from TSRA activity through Wed aftn.
A possible exception is in cntrl MS 12-15Z when MVFR cigs may
develop before lifting above 3kft. /22/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 75 93 75 90 / 10 25 29 68
Meridian 75 93 74 89 / 14 40 48 81
Vicksburg 76 93 76 92 / 11 15 16 51
Hattiesburg 76 93 75 90 / 10 31 18 64
Natchez 75 92 74 91 / 13 13 6 32
Greenville 76 92 75 91 / 9 17 35 62
Greenwood 76 92 75 90 / 13 34 51 72
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.
&&
$$
22/DC/GG
Area Forecast Discussion
National Weather Service North Platte NE
610 PM CDT Tue Jun 30 2020
.SHORT TERM...(This evening through Wednesday night)
Issued at 321 PM CDT Tue Jun 30 2020
The forecast is following the short term model blend for likely
thunderstorm chances this evening east of highway 83 throughout
ncntl Nebraska. This is a little west of the previous forecast and
is based on post frontal thunderstorms forming in addition to
storms developing along a cold front which is slowing up across
cntl Nebraska this afternoon. Storm activity should last about 6
hours and exit ncntl Nebraska to the east around midnight tonight.
The rest of the forecast Wednesday and Wednesday night is dry as
a result of Pacific high pressure building through the region.
The models and latest SPC analysis indicate 4000-5000J/KG of MLCAPE
across ncntl Nebraska this afternoon. A belt of increasing winds
aloft across ern WY/Colo will move in this evening supporting
deep storm development but the directional shear appears limited.
This would seem to support splitting storms and competing
updrafts. SPC suggested supercells at the onset of storm
development evolving into a more linear mode as the MCS shifts
east later this evening. Both the NAM and RAP model soundings show
moisture deepening along the nearly stationary front. The
deepening moisture should weaken the cap by 22z-00z this
aftn/evening.
.LONG TERM...(Thursday through Tuesday)
Issued at 321 PM CDT Tue Jun 30 2020
An upper level ridge of subtropical high pressure centered over
the nrn Gulf of Mexico this morning will build north through Texas
and into Nebraska this week. The GFS and ECM both show an
attendant plume of subtropical moisture moving north with the
ridge. The result is a more moist environment supporting what
appears to be ordinary thunderstorm development across Nebraska.
The new forecast has more scattered thunderstorm chances Thursday
through Tuesday. Winds aloft should remain fairly weak at less
than 15kt. A modest increase in winds aloft is possible next
Tuesday as the ridge weakens with the approach of a nrn stream
disturbance.
The temperature forecast is for highs in the 90s Thursday and
beyond. This is consistent with h700mb around 11C. Steady south
winds are in place associated with a broad area of weak low pressure
forming across the cntl and nrn Plains.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 610 PM CDT Tue Jun 30 2020
Scattered thunderstorms will move through north central Nebraska
this evening (mainly from KBBW to KONL), resulting in tempo visby
and cig drops, along with gusty erratic winds. Otherwise, VFR
will continue through the forecast period. Gusty winds are the
main aviation weather concern, primarily through sunset tonight
(northwesterly) and again tomorrow afternoon (southerly).
&&
.HYDROLOGY...
Issued at 321 PM CDT Tue Jun 30 2020
Radar shows the cold front slowing up across ncntl Nebraska and
the rapid refresh models are pooling moisture behind this front.
Precipitable water will exceed 1.5 inches at the onset of
scattered thunderstorms early this evening. Storm cover should
expand throughout ncntl Nebraska this evening.
The deep southerly flow aloft and elevated CAPE of 2500J/KG shown in
the RAP and NAM models should support splitting storms and perhaps
some HP echo training. The RAP and HRRR are showing signs of a
expansive area significant rainfall with locally heavy rainfall
totals of 1.5 and 2.5 inches. The locally heavy rainfall would
probably lead to flooding in some areas. The Flood Watch in effect
across Holt and Boyd counties has been expanded south and west to
include Custer county and areas north to the South Dakota border.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 5 AM CDT Wednesday for NEZ006>010-026>029-038.
&&
$$
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Snively
HYDROLOGY...CDC
...Updated Mesoscale Forecast Discussion...
.MESOSCALE DISCUSSION...
Issued at 847 PM CDT Tue Jun 30 2020
Thunderstorms have slowly intensified and increased in coverage
over the past hour with a few severe hail reports in central NE.
The surface front is well-defined as a fine-line in radar imagery
from KUEX and at this time (just prior to 9 PM) is just nosing
into Knox county, extending south to near the western Boone county
line, and then south southwest from there. Low pressure over
Kansas has helped to back surface winds ahead of the front and
increase low-level convergence along the boundary. At the same
time, water vapor imagery shows a well-defined cooler/drier mid-
level airmass has been lifting northeast and has helped to
destabilize near the front. The front will continue moving east
for the next several hours, and expect a continued increase in
storm coverage and intensity through 11 PM. At some point, the
question becomes whether an organized cold pool will develop and
push east out of these storms, and the current belief is that this
will happen over the next 2 hours or so. As the cold pool and cold
front propagate east and southeast, they will interact with a pool
of deep boundary layer moisture and ample instability. Most model
guidance maintains greater than 3000 J/kg of MLCAPE into the early
morning hours. Forecast soundings indicate that it should be quite
easy for a cold pool to lift parcels to the LFC within the very
moist environment, and thus expect a forward propagating MCS to
organize and move initially east and then southeast across the
area. Severe potential will exist despite a general lack of deep
layer shear ahead of the front...owing mainly to the favorable
thermodynamics, and while some large hail will be possible it
appears that the greatest hail threat will be early this evening
with a transition to more of a damaging wind potential. Much of
this echoes earlier forecast thoughts, and for the most part the
forecast is largely unchanged. The main change would be an
increased potential for the MCS to impact a good chunk of
southwest Iowa and southeast Nebraska.
&&
.DISCUSSION...
Issued at 342 PM CDT Tue Jun 30 2020
Forecast Summary:
There is a fairly decent shot of thunderstorms tonight as a potent
shortwave rotates around upper low in the northern Rockies. Strong,
damaging winds will be the main threat, especially in the northern
half of eastern Nebraska and western Iowa. Then a trend toward
warmer temperatures will take us through the weekend with mid level
ridging building into the region.
Tonight and Wednesday:
Widespread low clouds have persisted across eastern Nebraska and
western Iowa this afternoon, holding temperatures to the middle and
upper 80s for the most part. However a soupy environment
characterized by dew points in the mid and upper 70s made it feel
more like the middle 90s in many areas. It also contributed to
instability as SBCAPE values over 5000 J/kg were noted on RAP
analysis. The atmosphere remains capped this afternoon, and should
remain that way until system approaches from the west.
Shortwave was noted on water vapor imagery rotating northeast
through eastern Wyoming at mid afternoon. Diffluent flow and cooler
mid level air was spreading into western sections of South Dakota
and Nebraska, and was approaching surface front extending from
persistent MCV in western North Dakota into central Nebraska. MLCAPE
was maximized along this boundary where 5000 J/kg was noted over top
of increasing moisture convergence. Effective shear was maximized
near and west of frontal zone, and is forecast to migrate east with
boundary this afternoon and evening.
Continued low level warming under cooling mid levels should lead to
scattered convection along frontal boundary shortly. Models have
been fairly consistent in this scenario. How things progress this
evening is still somewhat in question as solutions vary by a
couple of hours on timing of southeast movement into our area. The
HRRR has been consistent in development of storms, but has
trended slower in regards to advancement into northeast Nebraska.
Have followed this somewhat slower progression of storms into our
area.
Expect convection to begin shortly well west of our area where it
will percolate for several hours into the early evening before nudged
eastward by advancing shortwave and developing cold pool. It appears
supercellular storms with the threat of large hail and possibly
tornadoes will remain generally west of our area before storms
congeal into a line and advance east and southeast. The main
threat then will be damaging winds as instability remains high and
low level jet increases. Storms will likely enter western parts
of Knox through Boone counties by 7 or 8 PM, then race east and
southeast to reach the Omaha and Lincoln areas somewhere in the 10
PM to 2 AM timeframe, and western Iowa Midnight and later.
Damaging winds will be possible much of the night.
Expect main activity to be east of our CWA before 12Z, however
latest trend of HRRR suggests lingering instability behind this line
will be tapped for additional development near and northwest of
Interstate 80, which may linger through the morning.
Additional development Wednesday afternoon is a concern for
southeast Nebraska and southwest Iowa where models indicate frontal
boundary will set up during peak heating. Strong instability will be
available, but only modest shear and low level convergence. Will
introduce a chance for storms there for Wednesday afternoon.
Thursday through Tuesday:
Mid level ridging builds into the Plains from West Texas area on
Thursday and holds through much of the weekend. This pattern will
promote warming of mid and low levels which should squash most
convective attempts. However, low level moisture streaming into the
High Plains will fuel occasional rounds of convection there which
may hold together as they march east during the overnight hours to
affect at least our western CWA. And with 70s dew points remaining
in eastern Nebraska and western Iowa, instability will be high
each afternoon, so can`t rule out a pop-up storm from time to
time.
Otherwise expect highs to average the lower 90s each afternoon right
through Tuesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 707 PM CDT Tue Jun 30 2020
Primary forecast concern through this TAF is thunderstorms as a
large line of storms is likely to impact all TAF sites at some
point in the next 10 hours. There is a good likelihood that the
storms will produce strong wind gusts as they arrive, with some
potential for strong thunderstorm outflow to precede the storms
themselves. Gusts greater than 50 kts and some hail are possible.
Otherwise, confidence is low, but could see some low-end MVFR
cigs or perhaps even IFR around sunrise through mid morning before
scattering out.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&
$$
MESOSCALE...Barjenbruch
DISCUSSION...Dergan
AVIATION...Barjenbruch
Area Forecast Discussion
National Weather Service Nashville TN
637 PM CDT Tue Jun 30 2020
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
A few pre-Independence Day fireworks across the south already late
this afternoon with several spots seeing trees down and torrential
rainfall. We`re not quite done, however. Latest radar trends, as
well as hi-res guidance, suggest the storms in west KY will
continue to push southward into Middle TN over the next several
hours. The good news is that most of the atmospheric energy that
could be used to fuel these storms has been expended. For this
reason, we`re only expecting these storms to be `general` in
nature and sub-severe. Doesn`t mean a gust of 40 mph or so isn`t
out of the question, but that should be the exception rather than
the rule. If you have evening plans along and west of I-65, bring
an umbrella.
Forecast update out shortly.
&&
.AVIATION...
00Z TAF DISCUSSION.
BNA/MQY/CKV/CSV...Surface ridge is now situated to the immediate
east of Middle Tennessee this evening while an upper trough
approaches from the west. Most of the earlier storms have
diminished so that there is a dearth of echoes in the vicinity of
the terminals. Scattered POP`s remain in the forecast this evening
and overnight, and the HRRR does suggest some additional activity
forming and moving across the mid state. Expect stronger
convection late tomorrow morning through the afternoon as the
upper trough slides down the NW flow aloft into Middle Tennessee
and we add some daytime heating. The best time for storms appears
to be Wednesday afternoon, so we`ll focus our energies there,
although scattered cells may affect the terminals outside peak-
heating hours. Also, look for MVFR ceilings to develop overnight
and last into the morning owing to this moisture-laden air mass.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION......Unger
AVIATION........08
...Update to aviation forecast discussion...
.SHORT TERM...(This evening through Wednesday)
Issued at 354 PM CDT Tue Jun 30 2020
Surface obs at 20Z showed temperatures in the upper 90s across parts
of central KS and a very moist air mass in place with dew points in
the low and mid 70s area-wide. Heat index values continue to climb
this afternoon so an advisory will remain in place until 8 PM. Water
vapor imagery this afternoon continues to show a large upper trough
to our northwest, which is expected to trigger convection in the
Dakotas and Nebraska this evening as it pivots northward. Model
guidance on the probability of precipitation in northeastern
Kansas tonight remains varied with some convective allowing models
(CAMS) extending the tail end of the convection to our north all
the way to I-70, while others (including the HRRR) keep storms
north and east of the area. Our environment overnight will remain
very unstable aloft with the RAP showing near 4000 J/kg of
elevated CAPE. Shear will increase slightly as the LLJ gets going
so thunderstorms should survive if they move in. However, a stout
low level inversion should help to limit severe potential unless
the MCS becomes well organized, at which time we would need to
watch for a damaging wind risk. In terms of POPs for tonight, I
decided to go with 40 percent chances in far northeastern Kansas
to account for the possibility of storms making it this far south,
and slightly lesser chances closer to I-70. Either way, increased
cloud cover is expected tomorrow morning due to the complex of
storms traversing the region.
An area of surface low pressure will be in place over the CWA
tomorrow and will gradually weaken with time. Models continue to
show and hot and very humid air mass remaining in place and our
current forecast heat index values again approach advisory criteria,
especially in east-central KS. Thus, we have issued another Heat
Advisory tomorrow afternoon for east-central counties.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 354 PM CDT Tue Jun 30 2020
The upper level pattern in the long-term will be dominated by
expansive ridging aloft. This generally points toward a very hot
forecast this time of the year. In addition to the heat, there will
be nearly daily chances for isolated to scattered storms if enough
lift from instability can be realized. With the lack of a more
potent forcing mechanism late this week and this weekend, will keep
chances for storms low at this time with many locations likely to be
dry most days.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 619 PM CDT Tue Jun 30 2020
VFR conditions are expected through much of the evening and
overnight hours. Southeasterly winds will decrease to around 10
kts within the next hour. Main challenge for the forecast period
is a complex of thunderstorms progged to move across southern NE
overnight which may push a frontal boundary into the terminals
around 10Z, shifting winds to the east/northeast. Furthermore,
MVFR stratus and isolated storms may accompany the frontal
passage. Confidence is too low to introduce any thunderstorm
mention. Marginal LLWS is possible from 04-09Z. Diurnal Cu around
1.5-2.5 kft is expected by mid-morning, especially at the Topeka
sites.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for KSZ008>012-020>024-
026-034>040-054>056-058-059.
Heat Advisory from 1 PM to 7 PM CDT Wednesday for KSZ040-054>056-
058-059.
&&
$$
SHORT TERM...Teefey
LONG TERM...Teefey
AVIATION...Baerg