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Feb 24-25th Severe Weather


Anti tornado

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GRR update...

000
FXUS63 KGRR 241610
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1110 AM EST Fri Feb 24 2017

LATEST UPDATE...
Update
.UPDATE...
Issued at 1109 AM EST Fri Feb 24 2017

Low pressure will track across the southern CWA this evening. This
will bring a warm front into the our area. The SPC outlook of
enhanced risk of severe storms lines up very well where this warm
front is expected to lift. This SE area of our CWA should see
CAPE values approach 1000 J/KG along with helicity values around
300 m2/s2. Concern for isolated tornadoes remains in this region.

Any storms going north of a Holland-St. Johns line could be
severe, but they will be entering the cooler and less unstable
air, so they should begin to weaken and become more elevated,
where hail becomes the main threat.

A conveyor belt of moisture is maintained over Western IN into SW
MI where a few showers exist late this morning. This should also
be the region of more development through the mid/late afternoon.
Convective allowing models suggest storms organizing after 21Z,
and then clearing the CWA by 04Z.

Temps are tough today with a large gradient across the CWA.
Expect highs around 40 north, to the lower 60s south. Nudged temps
upward across the central CWA. Most areas should see their max
temps in the early evening as the low comes through.

Have allowed the winter weather advisory to expire. An occasional
mix will still be possible across Highway 10, but impacts are no
longer expected.
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IWX update...

000
FXUS63 KIWX 241400
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
900 AM EST Fri Feb 24 2017

.UPDATE...
Issued at 831 AM EST Fri Feb 24 2017

Forecast updated to reflect continued mention of showers/isol
storms as nose of elevated instability works across the area. Few
higher reflectivity cores suggested a marginal severe hail risk
but thus far only pea to half inch diameter hail (lots of
lightning though). Once this passes by, vis sat shows at least
partial clearing if not a period of mostly sunny skies until
cloud cover begins to move back in with pre frontal trough.
Clearing should allow for a rapid warm up this morning into the
60s.

Lots of uncertainty with regards to severe potential this
afternoon/evening as a dynamically volatile, but moisture starved
environment will reside across the area. Main threat may end up on
the cold front itself late this afternoon into this evening with
mainly damaging winds (isolated tornado). Pre-frontal trough still
being shown as active on some of the hi res guidance so can`t let
our guard down this afternoon, especially seeing how vigorous
development has been in some areas this morning with elevated
storms. Strong capping should move in through much of the day
which may keep the pre frontal trough less active. 13Z SPC
outlook brought the slight and enhanced risks back to the west a
touch. Will continue to monitor the situation and update as
needed.
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.UPDATE...
Issued at 1125 AM EST Fri Feb 24 2017

Mesoscale Update...Initial showers/isol storms have either pushed
NE of the area or weakened as main warm front was now residing
across southern Lower Michigan. South of the front, much of the
forecast area was in a capped warm sector with temperatures in the
lower to middle 60s and dewpoints in the middle 50s (FWA already
shattered their record, now sitting at 68). Sufficient mixing has
been occuring of the higher low level wind fields to bring gusts
to 30 knots in several locations. Near the lake shore, combination
of lake shadow and proximity to front yields a much colder setup
with readings only in the mid 40s to near 50. Effective warm front
could pose a severe threat for locations mainly north of the toll
road with strongest shear expected to reside there. However, may
push just far enough north to push most impacts just north of the
forecast area.

Pre frontal trough has been agitated over the past few hours as
suggested by HRRR but capping in place has generally limited
development. Steepening mid level lapse rates may help to allow
more robust updrafts to punch what should be a slowly weakening
cap this afternoon (lightning strike now showing in Cass Co
Indiana). Can`t justify more than slgt chance to chance pops until
more expanded development occurs. 15Z HRRR suggests expansion of
convection along this trough and even more robust development
along the cold front, currently across Central Illinois as it
moves east. Effective shear in excess of 60 kts and expanding EML
should still make for pockets of damaging wind potential as well
as tornadic threat with any discrete cells. Situation will be
monitored closely. Only minor changes to SWODY1.
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Having a few meager elevated cells passing through a lot earlier than expected. Cloud bases well over 1K ft.  Looks like the cap is still holding firm.  Think we hit our hi of 70 a couple of hours ago now down to 65/53.  Not looking very promising around these parts unless we get some up tick with the front.

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Winds have largely veered to SW across IN/OH, with the exception being up in far northern IN. Southern MI looks okay too with better low level turning/SRH.

There are signs that some backing may take place by late afternoon a bit downstream, but for the next couple of hours, the setup looks relatively benign.

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Sun is back out after the cell that just went through 30 mins ago, temps and dew are recovering easily.

Also the SPC is still confident

    ..SOUTHERN LOWER MICHIGAN THROUGH THE OHIO AND TENNESSEE VALLEYS     ONLY MINOR ADJUSTMENTS HAVE BEEN MADE TO PREVIOUS OUTLOOK. STORMS   ARE EXPECTED TO UNDERGO A GRADUAL INCREASE THROUGH THE EVENING   HOURS. PRE-FRONTAL BAND OF STORMS ALONG WARM CONVEYOR BELT FROM   SOUTHERN IN TO SOUTHEAST LOWER MI HAS BEEN SLOW TO INTENSIFY. THIS   APPEARS TO BE DUE TO A RESIDUAL INVERSION AND MODEST CAPE WHICH ARE   LIMITING OVERALL UPDRAFT STRENGTH. AS DEEPER FORCING FOR ASCENT   CONTINUES TO ACT ON THE INVERSION LAYER, FURTHER INCREASE IN   CONVECTION WITHIN THIS BAND WILL PROBABLY OCCUR. ADDITIONAL STORMS   WILL LIKELY DEVELOP ALONG THE COLD FRONT THIS EVENING. INITIAL STORM   MODES WILL BE PRIMARILY DISCRETE, BUT EVOLUTION TO LINES SEGMENTS   MAY OCCUR, ESPECIALLY WITHIN ZONE OF STRONGER LINEAR FORCING ALONG   THE FRONT. WARM SECTOR WIND PROFILES ARE UNIDIRECTIONAL, BUT WITH   STRONG EFFECTIVE BULK SHEAR SUPPORTING POTENTIAL FOR ORGANIZED   STORMS INCLUDING A FEW SUPERCELLS AND BOWING SEGMENTS. THOUGH A FEW   TORNADOES REMAIN POSSIBLE, OVERALL TORNADO THREAT MAY BE MITIGATED   TO SOME EXTENT BY MODEST CAPE AND 0-1 KM HODOGRAPH SIZE. OTHERWISE   PRIMARY THREAT IS EXPECTED TO TREND TOWARD DAMAGING WIND, ESPECIALLY   AS STORMS DEVELOP AND ORGANIZE ALONG THE COLD FRONT.    


 
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IWX eyeing the next hour or two for good development with the shortwave

Convective event slowly unfolding in what is more of a typical 
March/April airmass with much of the area well rooted in the warm 
sector as low pressure tracks across far NW parts of the area this 
afternoon. Record already broke at Ft Wayne with a high of 69. Most 
areas seeing temps in the 60s with dewpoints in the mid 50s. 
Lakeshore areas have not gotten to enjoy the warm air thus far. Pre 
frontal trough has been attempting to light up and initially 
struggled as strong EML kept things capped and updraft strength 
limited. Shortwave trough now approaching and allowing for uptick in 
convective initiation and subsequent severe threat, especially 
into SE Michigan as well as portions of NW Ohio. Will need to 
watch these areas but main area of concern now highlighted by 
recent SWOMCD issued for convective threat along the cold front 
with radar showing very disorganized development from NW Indiana 
into portions of Illinois. To summarize, strong to severe storms 
still possible into the evening hours with high res models 
suggesting potential at least scattered reports of wind damage in 
any LEWP/QLSC signatures and a risk for large hail/isolated 
tornadoes in discrete cells or in notches on above mentioned 
convective lines. Severe threat should end rapidly by 3Z with 
colder air rapidly falling in behind the front. 

 

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