Tag: NUCAPS

the California convection that could actually convect

Posted in Live Blogs, NUCAPS on by Kristin C.

A late season trof moving onto the west coast has everyone east of the Rockies excited for tomorrow and the weekend. It is associated with an unusually late season and significant rain event throughout CA with afternoon storms scattered about in the central valley, deserts, and Sierra Nevada. The GLM was able to detect lightning in several storms in CA and NV. NOAA-20 made an overpass around 21Z and provided several viable soundings in the San Joaquin Valley and near the CA coast.

The NUCAPS sounding centered in Tulare County is shown below. MUCAPE values on the order of 563 J/kg were supportive of low-topped thunderstorms.  Neighboring soundings indicated similar or slightly reduced values of instability. With the focus on severe convection east of the Rockies, it is nice to see NUCAPS perform so well in a completely different region and dynamical regime (namely post-frontal open cellular convection).

Brian Kahn

IND TVS

Posted in Live Blogs, NUCAPS, ProbSevere on by Tiffany.

15 min prior to 1.75″ hail and 20 min prior to baseball-size hail, a supercell tracked NNW-SSE through Vermillion Co, IL …the Probsvr nailed the values for ProbHail at 96%, VILD 4.3, and a well defined TVS (100kt G-G) and strong MESO on NEXRAD ~ 7k’NUCAPS SVR TS values kinda nailed it in Ern IL :

East Central IL  (green dot) MU and FCST SFC CAPE were > 4000, LIs were > 12, DCAPE > 1000 (~50KT Gusts), SHIP > 1 and LR H8 – H5 ~8SRM showed Storm Top Div > 130kt 12 min prior to the Baseball Sized hailThis storm is not diminishing, with Storm Top DIV remaining well over 100ktEastern end of MCS continues to chug thru central IN (2130-2300z), ProbSVR ~ 23z looking good, more warnings on the way

Were there indications there could be large hail in eastern IL?

Posted in NUCAPS on by Tiffany.

Short answer: Yep.

NUCAPS Modified Sounding near Champaign/Urbana, IL from 18Z pass.

Since there were no 18-19Z special soundings from the IL/IN area, I looked to the AllSkyLAP CAPE which was only getting GFS retrievals in the ILX area. Those values were around 2300 J/KG or so.  The NUCAPS modified sounding near Champaign/Urbana, IL (shown above; the closest green dot to the storm that produced the severe hail), suggested more than 3500 J/KG of MLCAPE. Yesterday’s NUCAPS soundings suggested that the NUCAPS CAPE values were a bit high, but the ProbSevere MLCAPE values at the time of the baseball size hail in Westville (2105Z) were near 2773 J/KG.  So, yes, plenty of sources suggested high CAPE and thus there could be large hail in the area.

Also of note: The operational GOES 16 CAPE did not show any values because of clouds across the area.

-Tempest Sooner

A Day to Compare

Posted in HWT, NUCAPS on by Kristin C.

I initially wanted to compare model data, especially skew-t’s, that I usually use, to the NUCAPS products. My purpose was to  ascertain the feasibility of replacing or supplementing  point based model products with NUCAPS. As I was unable to access the model data I use daily I decided to compare NUCAPS with NAM and GFS.

First the comparisons in the rapidly changing thunderstorm environment in which I interrogated a large MCS over the Illinois/Indiana border.

I compared NUCAPS 18z skew-t (from clear air area) to NAM and GFS skew-t’s, at the same time and location.

NUCAPS presents a much more stable and dry environment than the model skew-t shows, and also much more stable than the actual current environment considering this storm has already produced hail, tornadoes and heavy rain.

Next, I compared an AllSkyLAP CAPE img at 18z (point J on the above picture),  to a NAM CAPE map over the same area/time. AllSkyLAP seems to be about 500J/kg higher than the NAM CAPE map.

Finally, I compared a NUCAPS CAPE img and the NUCAPS Skew-T at 18z over the same area and there was a huge variance. The skew-t was higher than the CAPE img by over 1300J/kg.

Lastly I decided to compare NUCAPS and model data from a stable area, non changing area.

I compared an observed skew-t from the KS/OK boarder to a NUCAPS skew-t. There is a one hour difference in the data but for the sake of this comparison I think this will work. 

The observed skew-t is a relatively dry column with .87pw and a T/D of 31/20C  at the surface and 10/-20C at 700mb. The CAPE is at a ridiculous 3746 J/kg. But with no moisture, lifting mechanism nor shear I wouldn’t expect development. When compared to the NUCAPS skew-t one can see a definitive difference. CAPE on the NUCAPS is at 0 with T/D at 24/11C at the surface and 7.9/-9.3C at 700MB which is a huge departure from what the observed skew-t showed…but how would the observed skew-t hold up to a model skew-t?

NAM 18Z model skew-t compared to the 17Z observed skew-t from the same area shows 28/17C SFC temps, only 3C off from the observed skew-t and at 700MB NAM shows 9.5/-8C only .5C off the temperature and 11 off the DP. Also, CAPE was much closer than when compared to the NUCAPS where SFC CAPE on the NAM is 3246J/kg and 3746J/kg on the observed.

Overall, after this small sample size of data, both severe weather and in clear weather, I believe that I would continue to use NAM/GFS over NUCAPS for my point based forecast needs.

 

***DESMOND***

messing around with NUCAPS in the volume browser

Posted in HWT, Live Blogs on by Tiffany.

A first cut at depicting the added value of the volume browser in AWIPS for NUCAPS soundings is shown below. I messed around with vertical cross-sections and time series of NUCAPS soundings in the upwind area of the MCS in northern IL that is expected to contain some potential for new convective initiation. Below is  the transect of the cross-section.

Here is the cross-section of equivalent potential temperature from NUCAPS at 18Z, NAM-12 at 18Z, and the HRRR at 18Z.

The two models and satellite soundings are in very good agreement at altitudes above 700 hPa, in less agreement between 700 and 850 hPa, and in poor agreement between 850 hPa and the surface. NAM12 is the highest with theta-e values between 336 and 344K, with HRRR about 5-10K colder, and NUCAPS still colder in the SW portion of the cross-section, and slightly warmer in the NE portion of the cross-section than HRRR.  Is it because of temperature or moisture differences?  It appears dominated by moisture discrepancies as shown below:

I can’t quite figure out how to plot additional (or fewer) contours (AWIPS newbie here) but its quite clear that NAM12 is the moistest and NUCAPS is much drier near the surface. The 12Z Quad Cities RAOB had 7-8 g/kg for water vapor mixing ratio but with the six-hour discrepancy it is challenging to establish ground truth.

The volume browser is capable of making time series plots too.  Here is a ring of points depicting time series of 850 hPa temperature lapse rates over the last few days of soundings:

The time series plot is shown below.  A two-day time series of sparse satellite soundings  isn’t all that insightful, but using this for 0-6 hour NUCAPS-FCST products (in comparison to model output) might be quite valuable for forecasters.

Brian Kahn

Pinwheel Fronts In The Dakotas

Posted in News on by Justin.

Mid afternoon into early evening saw a bretty good bloom of supercells along a SSW-NNE Cold Fronf in North Dakota…

Thru the period the SVRProb and SVRtor seemed to regularly over warn during this outbreak, BUT SVRHail was spot on, a little False Alarm-y, but it sure didn’t miss the Large Hail reports, with %s >90 both instances.  The RGB Day Convection GOES product seemed to respond pretty well with the hail instances as well.

Afternoon NUCAPS over forecast the CAPEs by ~ 500, PW by 0.2″, did well with the Downrush temp and DCAPE tho.

NUCAPS and AllSky Helpful in BIS

Posted in HWT on by Justin.

NUCAPS and AllSky both were helpful in tracking the afternoon destabilization over North Dakota today. Both data sources provided what seemed to be fairly accurate assessments of CAPE values. Clear sky and GFS retrievals in AllSky were similar, with the clear sky retrievals very closely matching the NUCAPS retrievals. Having a plan view depiction in AllSky was very helpful when combined with RAP shear vectors in accessing afternoon storm potential.

NUCAPS Sounding:

 

— warmbias —

 

Differences between Observed Sounding and NUCAPS

Posted in News on by Justin.

Compared KBIS observed 19z Skew-T to NUCAPS 20z Skew-T

Key points:
Lapse rate differences: Between 1-1.5C/km difference through all levels
SFC and MU CAPE was 500J/kg higher on the NUCAPS

Vertical profile is markedly different and is a much more saturated on the observed Skew-T

To further confuse matters the NUCAPS forecasted SFC CAPE values for the same location and time is 400J/kg…which is closer to the observed sounding than to the NUCAPS sounding.

—Desmond—

NUCAPS Gradients of CAPE

Posted in News on by Justin.

The 12Z Bismarck sounding was quite dry and and the surface observation at Bismarck was around 32F. Low level moisture has quickly rebounded this afternoon across central and western ND, however it remains dry across eastern ND. Dewpoints have come up into the upper 40s to near 50F and temperatures have climbed into the upper 70s. The AllSkyLAP CAPE loop clearly shows that instability is increasing across portions of ND with values topping out around 900 J/KG at 1930z, though most of the retrievals are GFS based because of cloud cover lingering in the area.

AllSkyLAP CAPE Loop

I decided to look at the NUCAPS soundings across the area to see if the CAPE values were similar. What I found was in the areas of low level moisture, the NUCAPS modified and unmodified sounding had similar MLCAPE values. However, as I checked NUCAPS soundings further east into the drier air, the un-modified soundings showed MLCAPE values that were far to high (should be near zero based on other observations), but the modified soundings were pretty spot on regarding the surface observations (especially Td, T may be slightly low), and thus MLCAPE values appeared to be more reasonable.

NUCAPS Swath. Soundings in quesiton are located just northwest of Bismarck, just northeast of Bismarck, and 2 dots east of Bismarck.

The next six images are the comparisons between the non-modified and modified NUCAPS soundings at three different locations. The first is near the peak in instability northwest of Bismarck, the second is east-northeast of Bismarck near the gradient, and the third is farther east into the drier air.

NOAA 20 Non-Modified NUCAPS Sounding just northwest of Bismarck
NOAA 20 RTMA Modified NUCAPS Sounding just northwest of Bismarck

 

 

 

 

 

 

 

 

 

NOAA 20 Non-Modified NUCAPS Sounding just ENE of Bismarck.
NOAA 20 RTMA Modified NUCAPS Sounding just ENE of Bismarck.

 

 

 

 

 

 

 

 

 

NOAA 20 Non-Modified NUCAPS Sounding 2 Dots East of Bismarck.
NOAA 20 RTMA Modified NUCAPS Sounding 2 Dots East of Bismarck.

 

 

 

 

 

 

 

 

 

With that said, the modified soundings seemed to do a decent job capturing the gradient in CAPE. The values appear to be a bit high compared to the AllSkyLAP CAPE (1183 vs 750 J/KG around the same time), and high also compared to the SPC Meso Analysis Page (around 500 J/KG).

Quick update…..

The Bismarck office fortunately did a 19Z sounding, which showed very weak MLCAPE, only 22 J/KG! So both the AllSkyLAP CAPE and the NUCAPS were overdone.

KBIS 19Z Sounding

-Tempest Boomer

Area Discussion Prior to Severe Wx Kickoff

Posted in Area Forecast Discussion (AFD), Forecaster Thoughts, General on by Justin.

Area discussion for the Dakotas: Lower heights area located over western S Dakota and stacks from 700-500mb and will make its way easterly throughout the day. 850mb winds from the south at 30Kts.

METSAT shows low/mid clouds moving into ND from the west with clearing over the center of the states where wx is expected. Upstream surface observations support this clearing as they show dry air advecting into the area from the south.

Radar shows weak convective activity to the north moving into Canada. Models and the SREF are in agreement that the majority of thunderstorm development happen around 1-3z.

Merged TPW Composite total PW values over the center of the N/S Dakota states where convection is expected according to SPC outlook is less than 1” with values between .80-.95” and AllSkyLAP 900mb PW is even lower at .30”.

NUCAPS fcst Sfc CAPE overlay CAPE values range between 400-500/kg but there are quite a few gaps in coverage.

Meanwhile AllskyLAP CAPE shows 900-1500J/kg, and NAM models show extremely high CAPE values of 3000-4500J/kg.

Local TAFs show no thunderstorms or even rain while the SPC continues to carry SLGT over the Dakotas. It’ll be interesting to see how this scenario plays out as the day progresses.

–DESMOND–