Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/17/19
AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
625 PM CDT Fri Aug 16 2019
.Discussion...
Issued at 252 PM CDT FRI AUG 16 2019
Main concerns heading into this evening involve redeveloping
severe weather chances along with the threat for heavy rain and
possible flash flooding. Out of the gate this afternoon, regional
radar imagery shows non-severe storms south of the CWA, with
mostly dry conditions further north across northeastern Kansas
and much of northern & western Missouri. This is likely the result
of a residual capping inversion that remains in place this
afternoon, as evidenced on latest available ACARS soundings out of
KCI. Meanwhile along the surface, latest available WPC surface
analysis and supporting observations indicates a stationary
boundary over southern Kansas earlier today is beginning to lift
north as a warm front, with upper 80s now being reported down
towards the Wichita area. With time, this boundary is expected to
eventually stall directly over the area this evening, with all
models in excellent agreement that this feature will be the focus
for new thunderstorm develop later tonight as a low-level jet of
50+ kts impinges upon the feature, and additional forcing for
ascent arrives from the northwest in the form of several pieces of
shortwave energy now seen over the central Plains and northern
Rockies.
Let`s address the severe weather potential first...
Storms are expected to develop after the 04z time frame over
northeast Kansas and northern Missouri along the north of the
aformentioned boundary. Based on this afternoon`s model
solutions, the bulk of this activity will likely be elevated in
nature with much of this activity likely remaining north of the
front. This suggests large hail will be the greatest threats,
however as storms that are initially discrete morph into clusters,
we cannot rule out the potential for strong wind gusts if enough
downward momentum is realized to penetrate into the boundary layer.
While we cannot rule out a possible tornado as well, the current
thinking suggests the tornado potential will be fairly low given
the elevated nature of expected activity. With ample amounts of
instability present due to the lingering EML airmass aloft, hail
in excess of 2" will be possible with the strongest cores,
especially early on as activity largely remains discrete in
nature.
Heavy rain potential...
Forecast guidance suggests all ingredients will be present for
heavy rain and possible flash flooding during the predawn hours.
Given some of our areas received in upwards of 3 inches from last
night`s rainfall, additional rainfall from training storms north
of the boundary will lead to additional flash flooding concerns
overnight. Quick look at available anomaly data suggests PWAT
values in excess of 2" overnight will be 2-3 standard deviations
above normal. In addition, 850 moisture flux divergence will be
maximized north of the boundary as well, with the NAM suggesting
values will also be 2-3 standard deviations above normal.
Furthermore, the synoptic set-up seems to agree with favorable
patterns for heavy rain over the lower Missouri Vly, with much of
our region residing squarely in the right entrance region of a
strong upper jet over Nebraska and Iowa. Considering mean 850-300
layered winds will be parallel to the stalled boundary, it seems
plausible that cell training will be possible with elevated storm
activity across northeast Kansas and northern Missouri overnight.
Due to these concerns, have hoisted a flash flood watch for much
of the area overnight, with the idea that if cell training does
develop, additional rainfall totals of 2-4" will be possible in
spots. This headline will run from 10 PM tonight through 1 PM
Saturday.
Storms should be exiting off to the east between 12-15z Saturday
morning, with dry conditions then expected through a good portion
of the afternoon hours. Fcst models show redeveloping shwrs/storms
during the evening hours as convection redevelops along the
lingering boundary. There is some severe weather potential with
this activity as well, but will address those concerns more in
detail after tonight`s activity. Unfortunately this boundary will
stick around through Sunday with additional shwr/storm activity
expected. Looks like we`ll finally see drier conditions move into
the region on Monday as the front finally clears the area.
&&
.Aviation...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 621 PM CDT FRI AUG 16 2019
The main threat tonight is going to be scattered thunderstorms
that will be forming up after midnight over eastern KS and western
MO. These storms will likely form over the top of the terminal and
will continue to redevelop over the area through the overnight
hours. There could be times of IFR visibility in heavy rain and
towards the early morning the chances of higher wind gusts will be
possible as the last line of storms pushes through. There is some
uncertainty as to how far south these storms will form with the
highest likelihood being along and north of the Missouri River.
MVFR ceilings may stick around through the morning before finally
scattering out in the afternoon.
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
KS...Flash Flood Watch from 10 PM CDT this evening through Saturday
afternoon for KSZ025-057-102>105.
MO...Flash Flood Watch from 10 PM CDT this evening through Saturday
afternoon for MOZ001>008-011>017-020>025-028>033-037>040-
043>046.
&&
$$
Discussion...32
Aviation...Barham
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
730 PM CDT Fri Aug 16 2019
.MESOSCALE DISCUSSION...
718 PM CDT
Isolated to scattered thunderstorm development should continue over
the next couple hours before winding down with the loss of afternoon
heating and the passage of a weak but supportive midlevel shortwave.
Local AMDAR soundings and the SPC mesoanalysis show a well mixed
boundary layer, meaning low level lapse rates have become favorable
for convection, though modest midlevel lapse rates and very marginal
deep layer shear have not been allowing most cells to sustain their
growth for an extended period. The exception would be farther to our
south where the SPC mesoanalysis suggests midlevel lapse rates are
more favorable. One cell has actually sustained itself after
splitting in the generally unidirectional westerlies, with the
northerly segment presently working its way through La Salle
County. Hail to nickel and perhaps quarter size will be possible
with the strongest cells, along with heavy rain and gusty winds.
Lenning
&&
.SHORT TERM...
239 PM CDT
Through Tonight...
We continue to monitor isolated to scattered thunderstorm
potential through early evening, and then the chance for more
scattered thunderstorms overnight mainly along and south of I-80.
A 1008 mb surface low across central Wisconsin this afternoon is
moving eastward with an attendant surface trough draped to the
south-southwest over north central and northwest Illinois. Ahead
of this feature are a couple confluence axes that have clumped
and agitated cumulus updrafts on visible satellite imagery. There
also is a weak MCV, or MCV-like feature, that had emanated from
Nebraska convection early this morning and is now drifting
eastward in north central Illinois. This does not have satellite
characteristics typical with an MCV to be concerned about during
peak heating, but nonetheless could be enough to help trigger
convective initiation in north central to northeast Illinois
through the rest of the afternoon and in northwest Indiana into
early this evening.
Mixed-layer CAPE is objectively analyzed around 1000 J/kg, though
in the vertical profile looks to be fairly narrow thanks to once
again marginal mid-level lapse rates. The DVN VAD wind profiler
does show 50 kt of mid-level flow, possibly enhanced just a bit
with the earlier mentioned MCV, so if a few taller storms can
develop, the deep layer shear is supportive of a stronger,
gustier storm or two. But that ability to have more sustained
updrafts is conditional that the full instability can be
realized. Given the look of the congested cumulus outside and on
satellite, not very confident in that occurring for stronger
storms.
As the low-level focus for any convective activity shifts
southeast it will stall, with a weak convergent boundary draped
across the southern CWA later this evening. As a 15-20 kt low-
level jet overrides this boundary, with assistance of a mid-level
speed maximum and sheared wave currently over the South
Dakota/Nebraska border, scattered convection may develop by early
overnight into parts of the western and southern CWA. More
organized, robust convection is expected by overnight in northern
Missouri and into central Illinois early Saturday morning. This
will serve as a focus and potential rob of moisture transport
further north into our area. Nonetheless, for areas mainly
along/south of I-80 the potential is there for scattered storms
throughout the overnight.
To the north of I-80 tonight, mostly clear skies at least this
evening and moist conditions will allow for potential fog
development, with low temperatures forecast around 5 degrees below
the current dew point. If skies were to remain clear through the
overnight, could envision some dense fog threat.
MTF
&&
.LONG TERM...
239 PM CDT
Saturday through Friday...
Broad/weak longwave troughing is anticipated across the western two-
thirds of the CONUS this weekend before a more amplified large scale
pattern returns for the early and middle portions of next week.
Several upper level shortwaves are anticipated to trek through the
region locally this weekend with the primary forecast focus
revolving around shower/thunderstorm timing and coverage, along with
the potential for stronger storms.
Any showers/storms that develop across central IL into the southern
CWA tonight are expected to still be in place come Saturday morning;
however, trends certainly support activity to be on a weakening/
diminishing trend through midday. Can`t entirely rule out a stronger
storm through this time frame, but expect that to be the exception
rather than the rule. Beyond midday Saturday, still can`t entirely
rule out an isolated shower/storm redeveloping given increasing
instability and weak surface troughing remaining in place, but
expecting any redevelopment to be few and far between. High
temperatures in the low-mid 80s area-wide.
An active pattern continues through the remainder of the weekend
with additional thunderstorms expected across much of the area,
especially Saturday night into early Sunday coinciding well with the
arrival of a more stout mid-level wave and a stronger LLJ focusing
across the region. Latest trends suggest convection blossoms to our
west across far northern MO/southern IA before trekking eastward
toward northwest IL and eventually into NE Illinois/NW Indiana.
Highest chances look to be after midnight through early/mid Sunday
morning, some of which will have the potential to be strong/severe
given plenty of bulk shear (~35-45 kts). A little concerned that
convection may outrun the best support aloft and greatest
instability...ultimately resulting in a weakening trend as it
crosses the forecast area, but worth monitoring this time frame over
the next 24-36 hours or so. Primary threat with any strong/severe
storms will be gusty winds and locally heavy rain given plenty of
deep layer moisture in place (PWATs progged to approach nearly 2.00
inches) across the area.
Additional periodic chances for showers and storms continue Sunday
afternoon into Monday, although expected to be less numerous. Timing
and intensity confidence becomes a little more muddled as we head
through this time frame, but none the less looks to remain somewhat
active.
Trends continue to support ridging building across the midsection of
the country by as early as Tuesday/Wednesday of next week...
potentially leading to a pattern reminiscent of a ring of fire
across sections of the middle and upper Mississippi Valley.
Certainly appears MCS development will be probable across or near
the forecast area at various times into the middle of next week
before a frontal boundary swings through midweek and brings a
stretch of cooler and likely drier conditions to wrap up the week.
Heat and humidity will be building Sunday through the middle of next
week with heat indices reaching the low 90s Sunday and varying from
the low-upper 90s across the forecast area Monday & Tuesday (of
course there`s the potential for this to be hampered a bit by
timing/coverage of convection).
Gillen
&&
.AVIATION...
For the 00Z TAFs...
730 PM...Forecast concerns including...
Isolated thunderstorms early this evening.
Chance of showers Saturday morning/early afternoon.
Patchy fog Saturday morning.
Wind directions Saturday.
Isolated thunderstorms continue to move generally east across the
Chicago terminals as well as central IL as a weak cold front moves
into the area. This activity is expected to end at the terminals
with sunset but the frontal boundary is expected to stall across
central IL with isolated/scattered activity possibly festering on
it through late evening.
Another round of thunderstorms is expected across northern MO
later tonight which may move into west central IL by daybreak
Saturday morning. Some of this activity may lift as far north as
the I-80 corridor by mid morning and some of the high-res guidance
brings showers into the Chicago terminals during the mid/late
morning. Confidence is low but opted to add vicinity mention with
this forecast. Its also possible that additional activity develops
during Saturday afternoon. Uncertainty with coverage increases
the further out into the the taf period and for now opted to stay
dry as much of the guidance is dry for Saturday afternoon/evening
at the terminals.
Patchy fog is possible across parts of the area Saturday
morning...especially northern IL where some clearing is possible
along with light winds. Have tempo mvfr vis at rfd/dpa but trends
will need to be monitored overnight and its possible some lower
vis may develop and some mvfr vis may be possible at ord/mdw.
Westerly winds will diminish this evening and likely become light
and variable overnight in many locations. Wind directions on
Saturday may start southerly or southeasterly then should turn
south/southwest during the afternoon with a possible lake breeze
by late afternoon...but confidence is low. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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