Jump to content
  • Member Statistics

    17,609
    Total Members
    7,904
    Most Online
    NH8550
    Newest Member
    NH8550
    Joined

March 15/16 Severe Wx


kystormspotter

Recommended Posts

  • Replies 649
  • Created
  • Last Reply

Have to say that model verification with dewpoints today isn't exactly giving me confidence in the moister solutions for Tuesday.

 

 

You talking about what's going on where the current severe storms are happening?  How far off are the models?

Link to comment
Share on other sites

Some models at least 4-5 degrees. Were forecasting 62-65 and they are struggling to get out of the upper 50s.

 

 

Ouch

 

As far as Tuesday, not having the extra evapotranspiration boost at this time of year doesn't help, but I think if we can manage upper 50s dews then it should be enough for a pretty decent threat with the relatively steep mid level lapse rates.  If anything more than that occurs, then would obviously even have a bigger threat.

Link to comment
Share on other sites

ILX has a really good discussion... answers some questions I've had

 

All models continue to show deep layer shear associated with the
upper wave as it becomes negatively tilted late in the day Tuesday
with strong low level turning of the winds seen on the hodographs,
especially off the NAM. 850 mb winds depicted on the ECMWF were
southeasterly at 40-45 kts in the 21z-00z time frame across our
north. SREF forecasts of surface dew points were a bit more
conservative on Tuesday afternoon, compared with the NAM, with
mostly middle 50s forecast across our area, while the NAM near
60 degree dew points which pushed SB cape values above 2500 J/KG
over the eastern half of the forecast area Tuesday afternoon.
Forecast soundings off the NAM and GFS continue to show a capping
inversion in place at least into the early afternoon hours before
low level convergence starts to increase in the 925-850 mb layer
just ahead of the front, which should allow convection to
develop. The 4km NAM-WRF reflectivity simulations suggest the
development of storms off to our east after 21z just ahead of the
increasing low level moisture convergence. However, if the timing
off the ECMWF is correct, storms will develop by mid afternoon
further west, along or just west of Interstate 55 and streak east-
northeast through the rest of the forecast area by 02z.

Based off the low level wind profiles seen on the ECMWF, discrete
supercells capable of large
hail (with 700-500 mb lapse rates over
7.0
C/KM) damaging winds and isolated tornadoes will be possible
for a few hours, especially if the high
dew points seen on the NAM
verify, before cells consolidate into a fast moving line with
mainly a damaging wind threat through late afternoon into early
evening.
If the GFS verifies, storms will develop in areas east of
I-55 and be out of our area by 00z. Still quite a bit of uncertainty
with the timing of the shortwave and attendant cold front for late
Tuesday afternoon and evening. For now, will continue to mention
the higher probabilities for damaging straight line winds and hail
in the HWO for Tuesday, but as mentioned above, if the low level
moisture increases more than what is advertised in most models,
the
tornado threat will start to become a concern as well Tuesday
afternoon.

 

Link to comment
Share on other sites

Frontal position on the 00z NAM looks a tad east at 18z Tuesday...closer to the MS River.  So possible we may see something of a compromise on timing between the 12z and 18z run.

 

Looks further south. Stronger low level shear is kind of close to outrunning the better instability axis this run.

 

There's also a big weakness in 700 mb flow across E IL thanks to the shortwave ridging out ahead. That certainly would cause problems with storm mode/organization.

Link to comment
Share on other sites

Looks further south. Stronger low level shear is kind of close to outrunning the better instability axis this run.

 

There's also a big weakness in 700 mb flow across E IL thanks to the shortwave ridging out ahead. That certainly would cause problems with storm mode/organization.

 

 

Yeah, not a fan of that.  On the plus side, still trying to get 60 degree dewpoints up to around I-80.

Link to comment
Share on other sites

Yeah, not a fan of that.  On the plus side, still trying to get 60 degree dewpoints up to around I-80.

 

Seeing the same thing on the 4 km NAM. Instability axis displaced west of the best shear due to the lead shortwave ejecting NE early.

Link to comment
Share on other sites

This is an RC / Stebo question - during days where severe weather is forecasted such as what Tuesday is looking to be, how many mets are in the office during an outbreak like that? Are your shifts longer than usual? And does the SPC advise on watches/warnings?

In my case, I am an observer at an airport so it is just me on shift and a normal hour shift. RC would know more about the NWS office, I do know from my experience of interning though, they are staffed by several extra mets if possible for a potential severe weather day.

Link to comment
Share on other sites

This is an RC / Stebo question - during days where severe weather is forecasted such as what Tuesday is looking to be, how many mets are in the office during an outbreak like that? Are your shifts longer than usual? And does the SPC advise on watches/warnings?

I think the SPC decides all severe weather watches.

Where as warnings come out of he local office.

I'd think there would be coordination on warnings between the local office and spc and probably even coordination from nearby local offices helping track the severe storms.

Sometimes you have upwards of a dozen active severe thunderstorm cells in one CWA constantly moving.

In most cases where there is many cells whether on a linear line or clusters of supercells or discrete supercells they are typically moving very fast.

I'd think a lot of time is wasted coordinating information to local emergency authorities.

Which would inhibit actual tracking/forecasting of the storms.

Getting your eye off the radar for even 5 minutes you can miss the formative stages of a tornadic look.

Meaning that is missing crucial warning lead time.

So yeah I'd guess coordinating is high on expected severe days

Link to comment
Share on other sites

Interesting thing showing up on SREF. There's 2 concurrent maximums where severe storms are possible during the early evening. I'd imagine this suggests warm sector supercells near Louisville and a squall tracking from Des Moines to Chicago to extreme N IN 

 

Uji9uMF.gif

 

what does calibrated conditional probability of severe thunderstorm even mean, exactly? Why are you even posting this?

Link to comment
Share on other sites

They kept off the Enhanced Risk due to the thermodynamic differences among the models. Most prone area mentioned for surface based convection was Illinois, however, storm mode is in question because of the new NAM had weakened wind fields at 850-700mb.

If newer guidance were to ramp up the winds at lower levels, area of PVA over an uncapped warm sector could get nasty. Even with the weaker wind field, SPC mentioned a mix of semi-discrete cells and linear clusters. Moisture and storm morphology is what will define Tuesday.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.

×
×
  • Create New...