Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/12/19
Area Forecast Discussion
National Weather Service Hastings NE
649 PM CDT Thu Apr 11 2019
.SHORT TERM...(This evening through Friday)
Issued at 336 PM CDT Thu Apr 11 2019
Aloft: WV imagery/RAP tropopause analyses and aircraft obs
indicated moderately-amplified flow...with a longwave trof was
over the Wrn/Cntrl USA...and a ridge over the E Pac. The low that
affected the CWA last night and today was along the SD-NEB border
near YKN. This low will slowly lift into MN by 12Z/Fri and head to
near DLH by 00Z/Sat. In its wake...cyclonic W flow will remain
over NEB/KS. Meanwhile...a shrtwv trof will dive down the back
side of longwave trof and into the Desert SW.
Surface: Filling low pres was over NW IA. This low will cont to
fill as it occludes further tonight on its way into Srn MN. This
low will weaken into a trof over MN/WI tomorrow. The pres grad
here will gradually relax with weak high pres moving in late in
the day.
Post Mortem: This system definitely fell short of expectations...
good from an impacts standpoint...but not from a fcst viewpoint.
The performance of the EC was espcly disappointing...track of sfc
low...QPF etc. Its low was too deep and too far W. One aspect
that over-performed was the amt of hail that occurred with last
night`s tstms.
See LSR`s for hail/snow. The hail 4" deep btwn Kearney-Gibbon was
espcly impressive.
After viewing snowplow cams...trimmed most of the counties from
the Winter Wx Advy. Left the advy just for where winds were
gusting to 45 mph and producing some BLSN.
Rest of this afternoon: M/cldy and windy. There are some pockets
of -SN lingering here and there. Clds are breaking up over the SW
1/3 of the CWA from Cambridge-Plainville-Osborne. NW winds will
cont gusting 30-40 mph with and ocnl G45.
Tonight: M/cldy N of I-80 but decreasing clds S of I-80. There is
quite a difference btwn the 06Z/12Z NAM vs the 06Z/12Z GFS and
RAP regarding the extend of low clds vs clearing. The GFS and RAP
are more pessimistic while the NAM runs are more aggressive with
the dcrsg clds.
Still windy. NW winds 20-30G45.
Lows are a blend of the NBM with a little nudge up using the
blend of mdl 2m temps.
Fri: P-M/cldy along and N of Hwy 6. M/sunny S of Hwy 6. The cold
thermal trof will be over the CWA and fcst sndgs show quite a bit
of deep CU/SC will form with a sliver of CAPE. These clds will be
within the DGZ so expect sct snow shwrs in the morning...changing
to rain shwrs in the afternoon where temps will be just warm
enough.
Still windy as NW winds will be 15-25G35.
Temps much cooler than normal with highs in the 30s/40s...coldest
along and N of the Platte Rvr.
.LONG TERM...(Friday night through Thursday)
Issued at 336 PM CDT Thu Apr 11 2019
Aloft: The last 2 runs of the EC/GEM/GFS/GFS-FV3/UKMET mdls cont
to fcst the longwave trof to remain over the W thru next Wed. This
remains consistent with the 00Z EC ensemble mean. Two more
substantial shrtwv trofs will rotate thru the larger trof. The 1st
thru the Srn Plns Sat-Sat night and the 2nd next Wed. As this
latter trof moves E of the Plns...this will initiate a pattern chg
a Wrn rdg/Ern trof and NW flow here.
As for the shorter wavelengths...troffiness will remain over the
Cntrl Plns Sat...but a shrtwv rdg will arrive Sun with the flow
temporarily deamplifying. Heights will then begin falling again
Mon- Tue as the trof deepens over the W. That flow will re-
amplify. There is considerable uncertainty in what the trof will
look like when it ejects into the Plns Tue night into Wed. The
06Z/12Z GFS-FV3 and 00Z/12Z GEM runs are the strongest. NW flow
will develop here next Thu as that sys moves into the Ern USA.
Surface: Anticyclogenesis will occur over the Plns Fri night-Sat
as the high overhead strengthens. This high will weaken Sun. A lee
low will form over CO Mon ahead of a cool front fcst to be making
its way thru the Wrn USA. Return flow will strengthen with a
substantial warm-up...but it will be short-lived as the cool front
will cross NEB/KS Mon night. Another low will form on the tail
end of that front Tue over the TX panhandle. As that low lifts up
the front... that could spread some rain into the CWA Tue night
into Wed. The CWA will remain in the cool sector Thu behind a
deepening low well to the E.
Temps: Much cooler than normal Sat-Sun. A big warm-up Mon-
Tue...to a little warmer than normal. Then dropping back close to
or a little cooler than normal next Wed-Thu.
Precip: Currently the fcst has nothing Mon night...but there
could be sprinkles N of I-80. Tue night into Wed there is
potential for some substantial stratiform rain...mainly S of Hwy
6...but gvn the uncertainty aloft...wouldn`t bet on it just yet.
For now left thunder out of the fcst. While the 12Z GFS is close
to its ensemble mean with the position of the sfc low...it is the
further N of the last 2 runs of all the global mdls...suggesting
that it`s too far N with its instability. Spaghetti plots 12Z/Wed
show the GFS low near SLN while all other mdls are over OK or the
TX panhandle.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday)
Issued at 633 PM CDT Thu Apr 11 2019
Lower clouds will break up overnight. During the day tomorrow,
there will be some cold air cumulus that form. Northwest winds
will remain breezy through the period.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until 7 PM CDT this evening for NEZ039-
040-046-060-061.
KS...None.
&&
$$
SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...JCB
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
757 PM CDT Thu Apr 11 2019
.UPDATE...
756 PM CDT
Expect an uptick in rain showers and scattered thunderstorms this
evening along and ahead of the cold front as forcing increases
ahead of the incoming upper level low. Moderate to briefly heavy
rainfall may accompany this narrow axis with SPC analyzed PWATs of
1.1". Afternoon 18z from ILX was fairly dry, and now even the
evening soundings which are fairly moist still feature limited
instability and even some lingering capping south of the warm
front. Lapse rates aloft are still enough for lightning especially
as the upper low shifts closer to northeast Illinois and northwest
Indiana, and we are seeing an uptick in lightning across northwest
Illinois (though still scattered at this point).
SPC has lowered to a marginal risk given the aforementioned issues
with instability which is our main limiting factor, but given the
strength of the wind fields above the surface, a conditional/marginal
threat for damaging winds does still exist in any stronger
showers and storms, but expect coverage to be isolated.
KMD
&&
.SHORT TERM...
330 PM CDT
Through Friday...
Concerns include the risk for isolated to perhaps widely scattered
severe weather late this afternoon through part of this evening,
heavy rain/minor flooding risk, and strong winds for parts of the
area into the evening and area wide on Friday. Main message for
the severe risk is that it appears fairly low and a bit lesser
than previous thinking.
There are no major changes to forecast thinking for timing of
thunderstorms later today into this evening, gradually spreading
eastward from 4-6pm west to 10pm-12am east. Wind Advisory
headline remains in effect for areas mainly south of I-80 south of
the advancing warm front. Seeing gusts into the 40-45 mph range
just south of the CWA, so these should spread northward within
next few hours. Gusts up to 45 mph will remain possible through
just after sunset, so no changes were made to the advisory. Severe
threat remains rather uncertain/conditional, however, with timing
of any severe storms still appearing similar to previous forecast
thinking. Recent AMDAR soundings from MDW and RFD show a pretty
stout capping inversion to surface based convection based at 800
mb, with temperatures at +12 to +14 Celsius. ILX 18z sounding
showed even warmer temps around +15 Celsius close to 800 mb, so
this stout capping will need to be overcome and looks to be a
limiting factor.
There are steep lapse rates and modest elevated instability above
this capping inversion. With steep mid-level lapse rates
continuing to be advected northward and strong deep layer south-
southwest flow, the capping will be slow to erode. Areas in the
far west/northwest CWA closer to better forcing could get some
showers and possibly a thunderstorm after 21z, as some lightning
is noted in area of showers near the MS River slowly working
eastward. Elevated convection here is able to tap into the
instability above the capping inversion and this should gradually
increase as better forcing arrives from the west.
Continued red flags with respect to the potential surface based
severe threat include: expansive mid and high clouds limiting
insolation and warm sector dew points generally running below
guidance thus far in mid to locally high 50s serving to limit
SB/MLCAPE as warm front lifts northward (SPC mesoanalysis shows 0
MLCAPE as of about 3pm); and the deep layer shear vector parallel
to the cold front orientation. Limited instability combined with
extreme deep shear magnitude will likely prevent widespread
intense updrafts due to lack of balance of these elements. The
unfavorable deep shear vector orientation could also preclude
noteworthy forward propagation of line segments. Both of these
could prevent a more widespread risk for damaging winds, so
message will be potential still existing of isolated to widely
scattered severe instances. For perhaps a locally greater severe
risk, the warm front continues to lift north at a steady pace
(near IL/Kankakee River as of this writing) and the evolving
triple point of secondary low pressure lifting northward near MS
River could be area to watch over parts of central/north central
IL late afternoon/early evening up until about sunset. Cannot
completely rule out an isolated tornado in this area despite the
generally meager low level moisture. For more details, see the
recently issued SPC Mesoscale Discussion.
Any severe threat should wane after midnight as available
unstable wanes. Overall parallel orientation of shear to boundary
and convection ahead of it could tend to yield a transition to
more of a heavy downpour/isolated minor flooding risk (for more
details see WPC Day 1 Marginal Excessive Rainfall Outlook). If
deep moist convection repeatedly trains across the same areas as
appears possible with deep layer SSW flow causing slow eastward
movement of the convection, there could be isolated 1-1.5"
rainfall amounts in a fairly short duration. Showers/some embedded
storms will gradually end west to east after midnight into early
Friday with cold frontal passage.
In the wake of the cold front passage, the occluding and
weakening but still seasonably deep surface low will lift north
toward Lake Superior on Friday. This will keep the pressure
gradient tight across the region between the departing low and
weak surface ridging to our south. Cold advection aloft will
steepen low level lapse rates and make for more efficient low
level mixing. Forecast soundings suggest that advisory criteria
(gusts to 45+ mph) will certainly be possible depending on exactly
how deep mixing is and efficiency of transporting stronger near
to above 40 kt speeds from 900 mb and upwards down to the surface.
Another Wind Advisory may be needed, however since there is one in
effect for today I-80 south, opted to let midnight shift handle
this decision. Friday will otherwise be a quieter day weather
wise. Cold advection driven stratocu will fill in across at least
the NW 1/2 to 2/3 of the area, keeping temps in the upper 40s to
mid 50s under the increasing cloud cover. East central IL counties
into northwest Indiana has best chance of reaching the upper 50s.
Castro
&&
.LONG TERM...
206 PM CDT
Friday Night through Thursday...
Main concern in the extended continues to be with a rain/snow mix
on Sunday into Sunday evening, with some potential for a period
of all snow in some locations across north central IL.
Late Saturday night through Sunday night looks to have another
strong system impact the area. This will find us more in the cool
sector portion of the storm, or at least that continues to be the
trend in solutions. This gives concerns for the possibility of
numerous hours of wet snow or a wet snow/rain mix in places with
even potential for light slushy accumulation.
After high pressure brings us a pleasant weather Saturday, this
next closed upper low will move northeastward from the Southern
Plains. The current forecast track continues to favor the
deformation area over the CWA, which along with a stiff northeast
wind should support enough precipitation to help offset any
daytime warming on Sunday. Still too far in time to say if it is
enough to keep a wet snow mix going on Sunday, but enough of a
signal to continue this mention in the forecast through the day
and into Sunday evening. Highs look to remain below 40 for much of
the CWA with this regime, with the exception of areas south of
the Kankakee river valley where temps will rise well into the 40s.
Again strong wind gusts and potentially lakeside flooding
concerns could be raised with this system.
Rodriguez/MTF
&&
.AVIATION...
For the 00Z TAFs...
Main concerns in the latest TAF cycle are:
-Near term wind trends with an approaching warm front
-Timing a period of VCTS/TSRA
-Strong and gusty southwesterly winds on Friday
A warm front currently arcs roughly from a VYS to LOT to GYY line
and has not made much northward progress over the last few hours.
Expect this feature will eventually move through MDW and perhaps
right up to ORD before precipitation chances increase this
evening. Overall, the TSRA timing has not changed much with the
anticipation that overall convective vigor will gradually increase
this evening with the approaching of better forcing for ascent.
Extended the mention of -SHRA VCTS a bit to account for some
trailing stratiform strikes once the main band of convection
passes but conditions will steadily improve from west-to-east late
this evening and overnight.
The other concern will be the increasingly strong and gusty
southwesterly winds on Friday. Latest guidance suggests pretty
deep mixing up to about 800-750 mb Friday afternoon with
unidirectional wind profiles in the cold advective regime. Will
indicate 25G35kt in the area TAFs but note that occasional gusts
to 40 kts or higher will be possible during afternoon hours.
Gustiness will subside Friday evening as the boundary layer begins
to decouple
Carlaw
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...IN nearshore waters until 3 AM Friday.
Small Craft Advisory...IL nearshore waters until 9 PM Thursday.
&&
$$
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