Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/07/23
Area Forecast Discussion
National Weather Service Denver/Boulder CO
847 PM MDT Sun Aug 6 2023
.UPDATE...
Issued at 844 PM MDT Sun Aug 6 2023
No significant updates to the forecast this evening. Most of the
remaining convection is south of I-70, with a couple of stronger
storms in South Park, the Palmer Divide, and Lincoln county.
Haven`t gotten many reports from storms these days, but I`d
imagine small hail and heavy rain is still falling out of the
stronger convection, and will continue to do so over the next
couple of hours. We should wrap up most of the stronger convection
by midnight, though the nearby upper jet streak might provide
enough support to maintain a few showers across the plains
through most of the overnight hours.
Have tried to make a few adjustments to the PoPs to better
capture where the more organized activity is this evening, with
only some minor updates to the foundational grids otherwise.
&&
.SHORT TERM...(This evening through Monday)
Issued at 245 PM MDT Sun Aug 6 2023
Convection is developing this afternoon with isolated coverage at
present, more so over the northern half of the CWA. The cells
were moving due easterly at 35-40 knots. The persistent Stratus
deck is still over the Greater Denver/central CWA area and down
into the the Palmer Ridge as this time. The weak upslope is
certainly aiding in its survival.
Models keep flat upper ridging over the CWA tonight and Monday.
Pretty strong zonal flow aloft is progged overnight. This becomes
northwesterly by Monday afternoon and decreases somewhat is speed.
The synoptic scale energy is benign for the first two periods.
Weak normal diurnal wind trends are progged for the first two
periods.
Currently, there is about 400-900 J/kg of MLCAPE over the mountains,
foothills and Palmer Ridge. CAPE is very low over the plains. On
Monday, the better CAPE is over the plains, especially the eastern
half. The precipitable water values increase over the plains for
Monday with 1.0-1.5 inches over the far east. The best pops for
this evening will be over the mountains and foothills. On Monday
afternoon, decent pops will cover the plains and foothills. For
temperatures, Monday`s highs should be about 10-12 F higher than
today`s current readings without a Stratus deck in place.
.LONG TERM...(Monday night through Sunday)
Issued at 230 PM MDT Sun Aug 6 2023
Scattered storms and even a couple severe storms will likely be
ongoing Monday evening over the far eastern plains, while weaker
showers and a couple storms will be decreasing closer to the Front
Range.
On Tuesday, the main concern is for severe storms. Models have
indeed trended toward a stronger and slower disturbance arriving
from the west/northwest. Low level moisture and a theta-e ridge
will build over the northeast plains, while there`s still
agreement that the I-25 Corridor and points west will see lower
dewpoints and higher storm bases. MLCAPE could build to 2000-3000
J/kg over the northeast plains, and with the amount of bulk shear
(35-45 kts), severe storms with very large hail and damaging
winds will be possible. The main question revolves around the cap,
which is more pronounced on Tuesday. That said, conceptual model
would suggest weakening of the cap late in the day or especially
evening with the arrival of the upper level trough. So while the
severe threat is conditional on the cap breaking, we do think the
synoptic setup would favor that to occur late in the day/evening,
unless the disturbance slows even more than currently advertised.
For Wednesday, the upper level disturbance will pass to the east,
with drying and slight ridging occurring. As long as the
disturbance fully passes by early in the day, we`ll see a weakly
subsident, drier, and capped airmass build over the forecast area.
Temperatures will be warming through Thursday with further warming
aloft and continuation of downslope flow. Mostly dry conditions
will prevail, with high temperatures reaching 90F or slightly
higher across the plains and I-25 Corridor. If we do see any
storms, it will be just high based and weaker convection with
gusty winds and mainly light rain.
There`s reasonable agreement that afternoon/evening shower and
storm coverage will increase by next weekend, as at least some
monsoonal moisture builds under the ridge. Temperatures will be
close to normal for this time of year.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 530 PM MDT Sun Aug 6 2023
Uncertain first few hours of the TAFs this evening. Two clear
bands of convection at the moment, with one extending from Grand
into Larimer county (north of the terminals) and one across the
Palmer Divide to the south. Guidance tries to eventually drop the
convection to the north and west into the area over the next few
hours, though there is very little instability to work with based
off the latest DEN ACARS soundings. Main impacts from any TS this
evening would be a brief period of variable/gusty winds along with
the chance of a drop into MVFR/ILS cigs.
Drainage flow should take over after 03-04z with VFR conditions
prevailing overnight. Expecting a wind shift back to the west or
west-northwest by Monday morning, then a shift back to north or
northeast by the afternoon. Another conditional threat of
thunderstorms Monday afternoon, with enough of a threat to justify
a PROB30 for now.
&&
.HYDROLOGY...
Issued at 245 PM MDT Sun Aug 6 2023
Scattered showers and thunderstorms will be moving swiftly
eastward this evening, which should preclude any flooding. The
storms will not be moving as fast on Monday afternoon and there
will be a limited threat of burn area flooding.
The flash flood threat remains limited at most on Tuesday as
scattered showers and storms will occur. However, these will be
fast moving and produce only brief moderate rainfall. Few if any
storms are expected Wednesday and Thursday.
Storm coverage and intensity will likely increase again toward
next weekend.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Hiris
SHORT TERM...RJK
LONG TERM...Barjenbruch
AVIATION...Hiris
HYDROLOGY...Barjenbruch
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
658 PM EDT Sun Aug 6 2023
.AVIATION...
Restrictive flight conditions will persist through the night and
much of Monday. The cyclone responsible for today`s widespread
rainfall with embedded intense showers is slowly trundling northeast
across southern Lower Michigan. An expansive area of low clouds,
light fog, and drizzle just upstream is expected to replace the rain
shield this evening. Meanwhile farther upstream over the Mid-
Mississippi Valley, another circulation is quickly approaching. The
resident cyclone will absorb the incoming wave early Monday -
keeping the region unsettled with continued low-clouds and scattered
showers.
Winds will veer around to west/northwest with passage of the first
circulation and then firmly establish northwesterly as the two
systems merge later on Monday. As drier air starts to filter in
later on Monday, the surface flow will also freshen and introduce a
gust component in the 20-25kt range.
.DTW THRESHOLD PROBABILITIES...
* High for ceilings aob 5kft through TAF period.
&&
.PREV DISCUSSION...
Issued at 321 PM EDT Sun Aug 6 2023
DISCUSSION...
Regional satellite shows the mid level short wave impulse now over
SW Lower Mi while a longer wavelength trough is rotating over Iowa.
There is currently enough phase separation between these two waves
to keep the lead wave somewhat progressive. The 12Z guidance
suggests the lead wave will weaken during the night as the upstream
wave advances across the Ohio Valley, with these two features then
phasing across the eastern Great Lakes on Monday. While the mid
level wave now over SW Lower Mi will weaken, there is strong
agreement that the 925mb to 850mb low will remain in tack and rather
compact. In fact, the sfc to 850mb low is forecast to deepen during
the night as more favorable upper level forcing comes into play
associated with the upper jet core rounding the base of the larger
scale trough axis.
Robust mid level deformation has developed this afternoon across
central Michigan, the Saginaw Valley and northern thumb. Given that
the lower tropospheric circulation is expected to maintain its
compact nature, system relative isentropic ascent into this TROWAL
feature will persist through the night. Some possible disruption to
the theta e plume feeding the TROWAL may occur late this afternoon
evening due to the potential for a convective release along the
associated sfc low/occluded front as it lifts across Ann Arbor and
metro Detroit this afternoon and evening. The latest meso analyses
is showing ongoing destabilization within the narrow warm sector
across NW Ohio. Most recent ACARS soundings out of both FNT and DTW
have precipitable water values at 1.9 inches. So locally heavy
rainfall and flooding will be a concern with any thunderstorms.
Given the slow movement of this mid level wave and persistent low-
mid level frontogenesis, much of the forecast area will see ample
rainfall tonight. Aside from the heavy convective rainfall potential
across the south today, probabilistic guidance trends suggest an
increased potential for 1 to 2 inch type rainfall amounts across the
tri cites and thumb, with locally higher amounts possible. Given the
much weaker convection across the far north and with some
indications that the better mid level deformation may shift into NE
Lower, a flood watch will be held off on in favor of a longer fused
flood advisory across the Tri Cities.
There is stronger agreement among the 12Z model suite that the main
dynamics and instability reservoir associated with the upper wave
sliding across the Ohio Valley on Monday will remain south and east
of the forecast area. Some lingering mid level deformation
associated with the lead short wave impulse and lingering deep layer
moisture overhead will at least support a chance of showers.
Residual low level moisture may also sustain some drizzle during the
day. Cloud cover is likely to hold through much of the day and will
keep forecast highs generally from the upper 60s to low 70s. Mid
level subsidence will expand across the area late Monday into
Tuesday as the phased system departs to the east. The
amplitude/timing of numerous convectively generated/enhanced short
waves forecast to traverse the mid Mississippi and Ohio Valley late
the week and northern stream troughs forecasts across the northern
tier us continues to carry a high degree of uncertainty for the Wed
to Friday time frame. There has been some growing clustering around
a more amplified wave to impact the region Friday.
MARINE...
Elevated winds and waves across marine zones along with showers and
possible thunderstorms can be expected over the next few days. The
first of two low pressure systems is moving over the southern Great
Lakes this afternoon with ascent on the northern end bringing
widespread rainfall into southern Lake Huron and scattered showers
and possible thunderstorms to the south. Elevated east to northeast
winds across Lake Erie this afternoon will arrive over Lake Huron
this evening as the low moves northeast. Northeast winds gusting to
around 20 knots overnight tonight will lead to increasing waves
across the nearshores of the northern Thumb into Saginaw Bay. A
Small Craft Advisory is in effect beginning tonight. The progression
of the low pressure tomorrow will back winds more northerly and draw
the higher waves and Small Craft Advisory conditions across the
remainder of the nearshore zones down to Port Huron by tomorrow
afternoon as gust potential increases to 30 knots. Showers and
thunderstorms will remain over the central Great Lakes tomorrow as
well. Winds turn out of the northwest on Tuesday as a trailing low
pressure moves across the northern Ohio Valley and the lead low
pressure is slow to move into Quebec. Winds and waves gradually
decrease throughout the day Tuesday as a high pressure builds into
the region.
HYDROLOGY...
A slow moving and compact low pressure system will traverse
Southeast Michigan from Southwest to northeast tonight, exiting to
the east early Monday morning. There is a very high moisture content
overhead within this low pressure system. More widespread rain will
occur along and north of the low track tonight, impacting the
Saginaw Valley and thumb region. Rainfall totals in the 1 to 3 inch
range are expected, with some locally higher amounts possible.
Farther south, along and south of I-69, precipitation this evening
will be more convective in nature. While widespread rainfall totals
over an inch are less likely, due to the convective nature of the
precipitation, locally heavy rainfall totals are certainly
plausible. This raises a concern for localized flash flooding with
any slow moving thunderstorm this evening. Given the more steady
nature of the rain across the Saginaw Valley and thumb region and
lack of widespread convective potential, the rainfall will occur
over a much longer period. While this will mitigate flash flooding,
low lying areas and urban areas are likely to see some minor
flooding. Rises on area creeks and rivers are also likely.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 2 AM Monday to 11 AM EDT Tuesday for
LHZ421-422-441.
Small Craft Advisory from 4 PM Monday to 2 PM EDT Tuesday for
LHZ442-443.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&
$$
AVIATION.....Mann
DISCUSSION...SC
MARINE.......AA
HYDROLOGY....SC
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.