Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/06/19
Area Forecast Discussion
National Weather Service Denver/Boulder CO
954 PM MDT Fri Jul 5 2019
.UPDATE...
Issued at 933 PM MDT Fri Jul 5 2019
Storms are rather persistent this evening likely due to sufficient
instability and moisture to go along with ascent from being under
the right entrance region of a jet over the central Great Plains.
We will let the Severe Thunderstorm Watch expire at 10pm although
a couple severe storms could continue near the Wyoming and
Nebraska borders. The threat for the heaviest storms will be over
the northeast corner of the state throughout the night tonight.
Changes were mostly made to POPs to account for what is currently
going on and what will happen late tonight and into tomorrow
morning.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 229 PM MDT Fri Jul 5 2019
Similar to yesterday afternoon, towering cumulus and storms have
initiated over the mountain terrain and west Palmer and these storms
should take more of an east to northeasterly track as they work
toward better moisture on the plains. Stratus across the plains
and foothills from this morning has nearly eroded with a cumulus
field developing in it`s place. Current ACARS soundings are still
showing the mid-level warmth cap near 700-650mb. This will take
awhile to break through on the plains, however any developed
storms from the higher terrain moving eastward into this
environment may survive and push out onto the far eastern plains
earlier before 00Z. With plenty of CAPE energy in the 1500-3000
J/kg range, along with forecast SFC-6K shear approx 40-45kts and
relatively drier air above 500mb, large hail will be the main
threat. Can`t rule out potential hydro issues from slow moving
storms, or even stalled or backbuilding storms. Areas of concern
with flooding would be burn scars, urban areas and foothill
valleys.
Storm activity should be active through late evening. Strongest
storms should push out of the area by midnight, however a few of
the short term models hint at persistent weaker thunderstorms
regenerating under southwesterly flow aloft for overnight into
early Saturday. Meanwhile, the NAM indicates convection up in SE
WY exiting into Nebraska and extreme NE CO while sending down
another surge of cool and moist northeasterly flow late tonight.
Will keep higher pops and QPF going for this into the overnight
period. With the likelihood of northeast surface flow overnight,
yet another round of low clouds and potential fog may be possible
for Saturday morning.
For early Saturday, starting to see subtropical moisture drawing
northward into the southern and central Rockies. With a deep
trough of low pressure spinning over the Pacific northwest, a
subtle shortwave trough will pass over the northern section of CO
by Saturday afternoon and evening. Therefore, ingredients again
coming together for another diurnal round of strong to potentially
severe storms for Saturday afternoon and evening. Due to cooler
high temps Saturday, ML CAPEs are about half of what the past two
afternoons have provided, however with ample moisture and a
triggering wave aloft, showers and thunderstorms will be likely.
With south to southeasterly surface flow developing across the
plains Saturday afternoon, the likelihood for a Denver cyclone
comes into play as a focus for storm initiation. A weak tornado or
two will again be a possibility with decent turning and
ventilation to the storms. With precipitable water values at this
time around 1.00", heavy rain and potential flash flooding issues
will be the main threats.
.LONG TERM...(Saturday night through Friday)
Issued at 229 PM MDT Fri Jul 5 2019
Saturday night, the models show a weak upper level disturbance
brushing across northern Colorado in the evening. Severe potential
will carryover into the evening hours. Best chance of
precipitation will be in the evening and should see the showers
decrease quickly after midnight. Sunday and Sunday night, the
upper ridge will remain centered over TX with subtropical moisture
continuing to advect northeastward across the cwa. Lower levels a
little drier, with ML 100 mb CAPES 500-1000 j/kg. PW values 0.75
to 0.95 inches, locally heavy rainfall but the overall severe
potential for thunderstorms should be decreasing. Expect
scattered coverage in the mountains, with scattered to likely pops
across the northeast plains late Sunday afternoon and evening.
Early next week, it will be warmer with slightly less convective
coverage in the afternoon and evening. The center of the upper
ridge does shift westward by early next week then builds over the
central Rockies. This will result in temperatures near seasonal
normals with decreasing coverage of thunderstorms in the
afternoon and evening. By the middle of the week, the ridge is
forecast to be centered near the Four Corners Region, with a weak
and drier northwesterly flow aloft over the forecast area.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 933 PM MDT Fri Jul 5 2019
Thunderstorms are developing over the foothills this evening and
weakening as they move over the plains. They could produce light
showers over DEN and APA with possible gusty winds. Storms are
more likely over BJC through the next few hours.
The chance for showers will fade after midnight. Winds will trend
toward drainage at all airports. During the early morning, low
clouds are possible at all airports due to the good moisture in
place. Another round of showers and storms will form tomorrow
afternoon and evening.
&&
.HYDROLOGY...
Issued at 229 PM MDT Fri Jul 5 2019
No significant changes to original thoughts on heavy rain and
flood potential this evening and also again for Saturday
afternoon. A few of the storms which have slow movement or get
stuck back- building could produce up to 3 inches of rain in 2
hours. Faster moving training storms would also produce flash
flooding issues. The more likely scenario is still single storms
producing an inch of rain in under an hour with minor flooding
possible, mainly in susceptible areas or places that got heavy
rain over the last couple of days.
Some mountain streams remain high due to snowmelt, with localized
minor flooding. These are generally not expected to be affected
by heavy rain today, as there is much less moisture west of the
foothills.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Danielson
SHORT TERM...Fredin
LONG TERM...Cooper
AVIATION...Danielson
HYDROLOGY...Fredin
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
834 PM CDT Fri Jul 5 2019
.UPDATE...
830 PM CDT
Watching a couple areas of convection and continued potential
convective growth through the rest of this evening. The severe
threat remains low, but spotty gusty winds to 35+ mph remain
probable under/near any deeper storms, as well as a localized
flooding threat especially under any slow-moving storm cluster,
such as in Winnebago County as of 830 p.m.
Early evening surface analysis indicates a persistent yet subtle
convergent boundary across far southern Wisconsin. A very minor
mid to upper level disturbance is also likely moving over the
state border area, with a 300 mb speed max of 40 kt (yes that`s a
speed max in this pattern over our area!). While the 00Z DVN
sounding was convectively contaminated, at least moderate
instability (1,500+ J/kg of MLCAPE) likely speaks for along the
surface confluence, as well as ample moisture. Together these
forcing features and environmental attributes should continue
scattered, to at times clustered, convection moving southeast
through 11 p.m. with probably isolated activity lingering into the
overnight. Think any convection may struggle as it gets south of
I-88/I-290 into the overnight, part diurnally and part getting
away from the aforementioned sources of focus.
Further south, basically east of I-55, isolated storms will remain
possible along old outflows and with only weakly stable
conditions.
For hazards, locally heavy rainfall will occur, especially with
any merged storms and it will not take much to get 1.5+ inches in
an hour over a small footprint. If that happens to be over an
urban area, that would result in a localized flash flood risk. The
downburst potential is lessening with the low-level lapse rates
not as steep, shown already by some recent AMDAR data. Still, with
precipitation loading some downdraft acceleration will remain
likely under any taller storms, and a spotty gust or two of 35-50
mph will remain possible.
MTF
&&
.SHORT TERM...
138 PM CDT
Through tonight...
Convection is starting to initiate in two defined areas,
consistent with our earlier thinking. The first is near and north
of a Mendota to Waukegan line ahead of a weak surface boundary
which is dropping into southern Wisconsin at this time. The other
is across our far southern counties, from near Chatsworth to
Fowler within a zone of increasingly agitated cumulus. Expect that
things will continue to slowly fill in through 4 PM in these areas
with individual storms moving towards the east-northeast around
15 mph. Given the lack of more appreciable mid-level flow, storms
will once again be of the pulse variety with individual life
cycles under about one hour, but exhausted outflows will be
capable of initiating new storms in this moist and unstable
environment. In addition, the environment appears a bit more
supportive of a strong downburst potential into the early evening
hours, mainly near and north of I-80. Can`t rule out a stray gust
to near severe limits (50-60 mph), but widespread severe weather
is NOT anticipated. Localized bouts of heavy rainfall will also be
possible through this evening in this very moist environment, with
hourly rainfall rates approaching 1-2" in spots not out of the
question. Thankfully, storm motions may be just quick enough to
limit the overall flood potential, however.
Towards 4-5 PM, we may also begin to see attempts at initiation
closer to the lakeshore in the vicinity of a strengthening lake
breeze circulation. If isolated storms initiate here, they would
drift out over the lake pretty quickly.
Current thinking is that the activity across our southern counties
may begin to clear out shortly after sunset and the loss of
daytime heating, although an isolated shower or storm will remain
possible there through 9-10 PM. Farther to the north, the approach
of a mid-level shortwave may help keep convection (at least
isolated to scattered in nature) going through 9-10 PM.
After about 2 AM or so, this aforementioned shortwave may get
close enough to initiate another round of isolated to scattered
storms, mainly north of I-88, so we`ll be holding onto some chance
PoPs through the overnight period to account for this as a
result. Finally, a cold front will push into the region late
tonight and into Saturday morning. As this occurs, shower and
isolated storm chances may increase briefly once again before the
front clears the area from north to south through the day on
Saturday. Doesn`t look like much of a dense fog threat with the
front (instead perhaps just an expansive stratus deck across the
lake), but we`ll keep an eye on upstream observations and trends
this evening.
Carlaw
&&
.LONG TERM...
320 PM CDT
Saturday Through Friday...
Latest guidance continues to suggest that a weak, diffuse cold
front, on the leading edge of a large, sprawling area of high
pressure, should push through the region early Saturday as the high
spreads across the Northern Plains through the Upper Great Lakes. A
gradual trend of diminishing low-level moisture will follow the
passage of the front, but will likely take some time for the
modified continental polar air mass to spread south, shunting the
more tropical-like air mass that has been in place for the past
several days. to the south. Weak convergence along the front should
keep chances for thunderstorms across much of the area through the
morning. The drier air should spread into nrn IL/IN in the
afternoon, ending the pcpn chances for locations north of I-80 in
the afternoon, but the front may slow or stall out as it moves into
the srn portions of the CWA, keeping greater chances for shra/tsra
into the afternoon. As sfc winds trend to nely, synoptically, on
Saturday, lake front locations should trend back to cooler than
inland areas, with highs Saturday only in the lower to middle 70s
along the lake front to the middle to upper 80s well inland.
Conditions should be dry for the remainder of the weekend into early
next week, though a weak system tracking through the Middle
Mississippi Valley on sunday could bring a slight chance for some
pcpn to the far southern portions of the CWA Sunday afternoon. A
return flow of warmer/more humid air will set up by mid-week as the
large sfc high slides through the Eastern Great Lakes and Upper Ohio
Valley. This will bring the next significant chance for showers and
thunderstorms and a return of temperatures back into the middle to
upper 80s.
&&
.AVIATION...
For the 00Z TAFs...
Main concern for the early evening will be continued chances for
scattered showers and isolated thunderstorms. Overnight, forecast
concern will shift to details of a weak cold frontal passage and
chances for some trailing stratus.
At issuance time, convective activity has subsided somewhat, but a
well defined outflow boundary is moving north through southern
Will County and northern Lake County, IN. Also, a small storm over
eastern Will is pushing out an outflow boundary as well. The
environment around the terminals has been convectively worked
over, but is still warm/moist/unstable and the area south of the
terminals, where the outflow boundary is moving north, has not
been convectively altered, so there will still be a chance for
additional showers and thunderstorms, at least through sunset. So,
will maintain a vcsh at ORD/MDW/DPA and a vcts at GYY, which is
still in closer proximity to active convection. Thunder potential
should diminish with sunset.
Winds will trend to nely overnight tonight following the passage
of a weak cold front. There may be a few lingering showers or
isolated thunderstorms into early Saturday along the cold front.
However, given the unfavorable diurnal timing, will only maintain
the vcsh mention and monitor for thunderstorm potential. Also,
much of the guidance has been advertising that some lower stratus
will push inland from Lake Michigan following the frontal
passage. Given a relatively consistent signal in the models for
mvfr cigs in stratus, have maintained the mvfr cigs. Confidence is
lower in and vis restrictions. There is a chance that some mvfr
vis could develop in the cooler air mass moving in from the lake,
but confidence is relatively low. While there may still be a
chance for some showers along the front as it pushes to the south,
expect that any associated pcpn will be well south of the
terminals by late morning and into the afternoon when daytime
warming should help renewed shra/tsra development.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO