March 2021 Weather Discussion

[tron777]

Day 2 SPC discussion for the OV has been updated below. Still a slight risk S of I-70 and a marginal risk for the I-70 corridor on north.


...Ohio Valley...
Fairly widespread precipitation should occur over a majority of the
lower OH Valley through the day. This should temper diurnal
destabilization to some degree, but weak instability will probably
still develop along/east of the surface low and northward-moving
warm front. At least an isolated severe threat may develop late
Thursday afternoon into the evening as the southerly low-level jet
strengthens over this region and low-level moisture increases. The
potential for a low-topped line of storms capable of producing
damaging wind gusts and tornadoes will exist given the strength of
the low-level flow and related shear. These storms will likely be
tied to a cold front as it tracks northeastward through the evening
and overnight hours.

[tron777]

12Z Euro has AM rain / convection ending during the mid afternoon period. Then we get a break before the evening convection moves in with the cold front. By 8pm, we have a 992 MB low over Eastern ILL that deepens to 982 over N Indiana at 1am Thurs night. Cold frontal passage will probably be in the 8-11pm range IMHO should this run be correct. From a severe standpoint, Dews get to 60+ S of I-70, basically where the slight risk area is. 10M wind gusts are showing 50-60 mph with CAPE values of 1000 J/kg from near Cincy and points south. Probably 500 for I-70. So all in all... if the instability is realized, expect winds to 60 mph in the stronger cells with a squall line coming thru in the evening hours at some point with embedded QCLS spin up's possible. If the GFS is correct and the instability isn't realized then gusts in excess of 40 mph will be likely by default anyway right ahead and immediately behind the cold front. So that is my latest thinking at this point.

[tron777]

Oh... forgot to give my rainfall forecast. 0.50" to 1" depending on if we get that break in the action or not.

[tron777]

72 degrees currently imby...

[cloudy72]

SigTor for tomorrow afternoon......quite large 75-90% area in MS/AL....just like last week.

sigtor.gif

[tpweather]

Last week ended up rather nice in terms of severe weather as I don't believe anybody was killed. Let's hope we have a similar outcome this week. I believe this week looks worse than last week for a few reasons. More folks will be involved with possible severe weather, low pressure that is getting stronger. A steady rain lasting into late afternoon is what we need in hopefully keeping the severe weather down but we will still have strong winds late in the evening and overnight.

[Bgoney]

Last week ended up rather nice in terms of severe weather as I don't believe anybody was killed. Let's hope we have a similar outcome this week. I believe this week looks worse than last week for a few reasons. More folks will be involved with possible severe weather, low pressure that is getting stronger. A steady rain lasting into late afternoon is what we need in hopefully keeping the severe weather down but we will still have strong winds late in the evening and overnight.

Agree Tim, not to concerned for tornadoes in our backyards, but if we do see a solid or broken line with the cold front probably between 10pm and 1am they'll be able to tap those 850 winds for severe criteria. Just the storm motion is expected to be between 50 and 60mph.

[tpweather]

What I have noticed is heavier rain forecasts for folks near the Ohio River and northward. What this tells me from the models is the warm front will only get so far north and areas just north of the front could get some decent rains. I still like the lower end but if the warm front sort of stalls then need to watch totals. Still not worried about flooding .

[tron777]

Outstanding AFD from the boys highlighting the uncertainty in surface low strength, track and degree of instability.

Quite a lot to unpack for the short term discussion, so let`s
get right to it.

During the morning hours, anticipate a fairly cohesive/large
band of rain with perhaps some embedded thunder to be tracking
northeast into and through the ILN FA into the afternoon. This
initial round of widespread pcpn will occur on the nose of an
impinging/strengthening H8 LLJ and in response to S/W energy
pivoting northeast through the increasing SW flow aloft. This
will yield a good deal of mass convergence/lift across the local
area during the late morning into early afternoon, supporting
the persistence of widespread rain to move through the region
during this time frame.

The initial band of rain will deliver between 0.50-0.75" of rain
to some spots before activity becomes much more
isolated/scattered in nature past mid afternoon into early
evening. This will occur as the warm front pivots north through
the area, with southeasterly sfc flow becoming established
region-wide.

By late afternoon, will see a neutrally-tilted H5 trof close
off across the mid Mississippi River Valley with sfc
cyclogenesis/deepening occurring along the spine of the lower
Mississippi River. The trof will gradually become more
negatively tilted during the evening, supporting rapid deepening
of the sfc low as it tracks northeast into the western Ohio
Valley. This will yield a rapid strengthening of the LL wind
fields during the evening, with still some uncertainty in the
exact track of the surface low itself. The hi-res CAMS continue
to show a much more muted solution, with a broader/less deep
surface low tracking a bit further to the south/east than what
many deterministic and ensemble solutions would suggest. The
general consensus seems to be a sfc low track from Paducah to
north of Indy to just west of Ft. Wayne, putting the ILN FA
squarely in the open warm sector of the strengthening system.
From the afternoon into the late evening, many solutions point
toward a fairly rapid deepening of the sfc cyclone from ~1000mb
to sub 990mb from 18z to 03z, which would result in a
corresponding uptick/strengthening of the LL wind fields in a
rather dramatic fashion.

With the strengthening LL wind fields and the arrival of better
lift and forcing, will see a second batch of showers, with more
widespread storm activity, track northeast into the ILN FA
around/past 00z. This will occur from SSW to NNE, with the main
question at this juncture being the degree of BL destabilization
that is able to occur, especially in the wake of widespread rain
during the late morning and afternoon hours. Model soundings
show a fairly saturated LL profile through early evening, with
very borderline lapse rates and marginal instability --
especially any that is SB in nature. The wind fields -- both in
magnitude and expanse -- are concerning. The LL directional and
speed shear is notable, yielding hodographs are long and
somewhat curved. The main limiting factor for severe potential
will be the lack of instability rooted near the surface, which
may be rather limited except /just/ along/immediately ahead of
and east of the actual sfc low track itself. This would support
an environment where the greatest severe threat would exist
immediately near/east of the sfc low track, which current model
consensus would place mainly near/west of the I-75 corridor.
This, of course, is entirely dependent on the track of that sfc
low and the degree to which we can attain SB destabilization in
the wake of afternoon activity. The profile will be very
saturated, but very energetic. If even a little bit of SB-instby
is realized, it would not take much at all for stronger cores
to translate down some /very/ strong wind to the sfc. The
positioning of the local area WRT the sfc low, which would
elicit sfc winds that are largely backed in nature, could
support a tornado or two if the ingredients come together in
such a manner. Again, feel that this would be favored
immediately near/east of the sfc low in the 01z-05z time frame,
which at this time appears it would set up in a narrow corridor
from south-central/SE IN through far west-central Ohio. Without
a narrow N-S ribbon of SB instby, even with the H8 LLJ of
70+kts, it would be a bit more difficult, although not
impossible, to translate stronger winds to the sfc until we get
into a post-frontal environment. Any activity east of the I-71
corridor may be slightly elevated in nature and therefore be a
bit less concerning than activity that develops immediately
along the front itself.

And with all of this being said -- once we get into a post-
frontal environment, on the backside of the sfc low after the
storms move away, the setup for strong synoptic-based winds
becomes much more favorable -- especially in a corridor
immediately to the south/west of the sfc low track. This will
occur with a steepening of the LL lapse rates coincident with
the robust LLJ, which will slowly peel away to the north/east
through the late nighttime period. Current momentum transfer
techniques suggest widespread potential for 40+kt gusts in a
several hour time window (esp. 04z-10z), with some potential for
50+ kt gusts in a small SW to NE corridor immediately trailing
the sfc low as the pressure rise/fall couplet tightens rather
dramatically. At this juncture, there continues to be good
support for 40+ kt gusts near/north of the Ohio River, with the
greatest potential for 50+ kts existing near the I-71 corridor
and points to the north/west in Ohio. There is enough
uncertainty in the track of the aforementioned sfc low, which
will have an impact on where the highest gusts will be favored,
that did not have enough confidence for an upgrade at this
juncture. This being said, do feel it is necessary to at least
mention the potential for some higher-end gusts on a small
spatial/temporal scale in the middle of the night. Would not be
surprised to see synoptic-based/non-tstorm related winds near/in
excess of 65 MPH in a few spots (with the favored area from EC
IN through parts of WC and central OH). This will depend
entirely on just how much deepening of the sfc system occurs and
whether it aligns in a manner with favorable mixing/transfer of
winds aloft to the sfc in the predawn hours. There is a /BIG/
difference in the wind gust/damage potential between a 985mb
low and a 995mb low. But nonetheless, current ensemble mean
probabilities suggest near/greater than a 50% probability of
50+kt gusts for much of the current watch areas, so will
maintain as is for now. Additionally, do think a Wind Advisory
will eventually be needed for areas even outside the current
watch areas, but feel we are still just outside the time window
to issue at this point. Will continue to highlight the potential
in the HWO.

Highs on Thursday will be dampened by the widespread rain during
peak diurnal heating hours. In fact, will expect to see warmest
temps in central Ohio where the rain will take the longest to
reach. Highs range from the lower 60s in the Tri-State to lower
70s in central Ohio into south-central Ohio. Drier conditions
evolve late Thursday night in the post-frontal environmen

[tron777]

74 for the high at CVG and IMBY... warmest of 2021 thus far.

[cloudy72]

Looks like MGY hit 75 and I actually made it to 76!

[Bgoney]

18z NAM ups the ante with the low further south , almost over Indianapolis. Its gone to now- casting and see how the day unfolds with much uncertainties at play and again agree with Tim that we need to see how far the warm front can make it north

[tron777]

The strength of the low is key. The stronger it becomes, the more NW the low tracks. The more NW the low tracks, the more northward the warm front goes. The more northward the warm front goes, the more unstable our airmass can become due to better dews and a stronger LLJ coming in by tomorrow evening. A lot of uncertainty and we're only 24 hours or so out.

[tron777]

18Z HRRR Sounding valid as of 8pm near CVG.

hrrr_2021032418_030_39.0--84.73.png

I like my thoughts from earlier. Rain / embedded storms move in mid to late morning tomorrow ending around 2pm or so tomorrow afternoon., We get a break then anytime after 8pm we are fair game with a line of storms to come in from SW to NE ahead of the low out in ILL which deepens as it moves into Northern IN after midnight. Isolated severe possible with a low end tornado risk with brief spin up's should we see any kinks in the line with any bowing segments. The bowing segments will be where the stronger winds are going to be found. If instability stays below 500 J/kg, the severe threat will be low. If we can manage 1000 J/kg or more, we'll have a legit shot at damaging winds and brief tornadoes.

[tpweather]

Great Posts guys and the nws did a wonderful job explaining what may happen on Thursday. Now cast is going to be the way to go and I will be keeping up from afar.

[tron777]

I also agree that it'll be nowcast. With most severe wx events that is the case. I think we've got a pretty good idea on the things to watch that most folks can agree on.

1 - How long of a break and can we see do we get tomorrow afternoon for instability purposes? Any sunshine???
2 - Strength and track of the surface low tomorrow evening which in turn will tell us how strong the LLJ will be as well as the strong wind potential pre as well as post frontal.

Should be interesting to see it all unfold. The Dixie States and TN Valley will be under the gun whether anything happens here or not. SPC was even thinking about upgrading a portion of the mod risk area to a high risk tonight. We shall see what they decide in the morning.

[MVWxObserver]

Sure am NOT looking forward to the 12 hour windstorm on Thurs night - early Fri morning!

Prayerfully no shingles damage i.e etc.

[MVWxObserver]

Prayers / thoughts with all today and tonight.

My nephew lives near Nashville, TN and currently is in the Moderate Risk i.e.

[Angelika]

Upgraded to a high wind warning.

[Bgoney]

day1probotlk_wind.gif

day1probotlk_torn.gif

[Bgoney]

We find ourselves in a familiar scenario for our area for late tonight, a textbook "high shear low cape "(HSLC) situation.

20210325_062504.jpg

[tron777]

Good morning all! High Wind warnings and advisories have been issued for all locations. Rain is to our SWE and we're waiting on it to push in later this morning. We'll see how the afternoon progresses as that will set us up for this evening. Winds 50-60 mph are likely behind the cold front tonight even without severe wx. I would make sure you have loose objects secured and what not while you can today.

Bgoney… I agree... straight line wind damage possible and a brief spin up possible.

[tpweather]

Good morning Les. What a busy day in the weather world. We can see on the radar a large area of rain to the southwest. Judging so far with the movement it looks to get into the local area before noon and then will that movement slow down or continue to move rather fast. Yes there are sort of two warm fronts and that is dealing with dew points. Once the first one moves through dews should go up to near 60 or so. The second one is much further south over the Tn valley and that will have dews getting really high and one reason the severe weather is much more likely there especially in terms of tornado's.

[tron777]

Good morning Les. What a busy day in the weather world. We can see on the radar a large area of rain to the southwest. Judging so far with the movement it looks to get into the local area before noon and then will that movement slow down or continue to move rather fast. Yes there are sort of two warm fronts and that is dealing with dew points. Once the first one moves through dews should go up to near 60 or so. The second one is much further south over the Tn valley and that will have dews getting really high and one reason the severe weather is much more likely there especially in terms of tornado's.

Good morning Tim! It should be a busy day down south and then this afternoon for the TN Valley and Dixie States. Our busyness will be this evening and tonight with the high winds. Even if we don't get severe wx, the high winds post frontal are still going to cause some problems with trees coming down and power outages in some areas occurring. The winds will continue tomorrow morning also and only slowly diminish into the afternoon.

[BookNerdCarp]

[url]]

From Storm Prediction Center