TPW in a convective environment

Below is a comparison of two different TPW products (AllSkyLAP layer Precipitable water and Merged TPW Composite Sat Sfc Merged Total Precipitation Water) compared to RAP Analysis from the SPC Mesoanalyst page.

Control group: SPC Mesoanalysis Precipitable Water

The AllSkyLAP product (below) seems to do a better job at "painting the picture," however, it's reliance on the GFS model often leads to a delay in PWAT drops in areas of convection. This is highlighted the best across central IL, where RAP Analysis shows PWATs in the 1 - 1.25 inch range while the AllSkyLAP product shows values closer to the 1.5 inch range straight from GFS output.

AllSkyLAP

TPW (below) does a better job at accounting for this, at least across the central IL study area, resulting in more realistic 1.1 to 1.3 inch values.

TPW

Precipitable Water Comparisons

The Blended TPW product (top left) shows promise in creating an all-observations precipitable water product in AWIPS. The polar-orbiter PW data in cloudy areas produces artificial gradients and inaccurate values compared to modeled fields (GFS top right and HRRR bottom left), but its attempt to generate an all-observational PW product is successful. I am unsure of how to suggest improvements in the cloudy areas but would encourage these model-free fields continue to be developed.

The AllSky PW product (bottom right) looks really good. The inclusion of GFS data in cloudy areas is a neat idea and the partly cloudy areas seem to be well-computed. This is a tool I will definitely use for situational awareness. -Atlanta Braves

Allsky, TPW, and NUCAPS Moisture and Instability Profiles

Radar image of a severe QLCS in NW Arkansas at 1923Z.  This line has been producing wind damage and a few spin up tornadoes. Next I'm going to diagnose column moisture and instability downstream, across north-central Arkansas using satellite and satellite-model merged products.



The GOES-16 AllskyLAP showed a deep plume of moisture extending from the Gulf of Mexico northward into Arkansas and Missouri.  Specifically, in north-central Arkansas, sampled PWATs were around 1.60 inches and MUCAPE was near 700-800 J/kg. Skies were mainly clear in this area, which resulted in a relatively smooth appearance in the PWAT and CAPE plots. Interestingly, and not plotted here, the 700-300mb AllskyLAP PWAT had a lower values or drier conditions to the east of the approaching QLCS. This presence of mid-level dry air may be conducive for severe weather over north-central and northeast Arkansas over the next 1-3 hours -- especially for damaging winds.



Merged TPW data at 19Z estimated PWATs near 1.50 inches into north-central Arkansas. However, there was a sharp discontinuity from 1.50 to 1.00 into the northwest part of the state where widespread cloud cover was present and the data is from polar orbiting satellites (some of which could have been advected in). The SPC mesoanalysis did not display a sharp gradient in PWATs in this area, but rather had a gradually decrease to 1.30 inches.



Not the best satellite pass with my area of concern on the far western fringe of the NUCAPS data. Surprisingly, the sounding data on the edge in northern Arkansas was nearly identical to the SPC mesoanalysis data with values near 1200 J/kg! It likely helped that skies were mainly clear at the time of the pass. The GOES-16 AllskyLAP data was underdone in comparison.  As mentioned, only up to 700-800 J/kg.



NUCAPS 700-500mb lapse rates in northern Arkansas are close to model forecasts. The NUCAPS in this pass was indicating lapse rates around 6.2 C/km. Model data was generally a little bit lower aroudn 5.8 C/km.  The SPC mesoanalysis was on the high end near 6.5 C/km. Roy

Merged Advanced TPW Too Low in Cloudy Areas this Afternoon

The Merged Advanced TPW is underdoing PWAT values in cloudy areas over central Oklahoma. There are discontinuities where it goes from clear to cloudy skies.



The 18z KOUN RAOB sampled 1.52" PWATs, while the Advanced TPW is showing only around 1.00".

Meanwhile, the All Sky LAP PWAT appears to be better representing reality, with PWATs around 1.70"



Ron Dayne

Merged TPW Composite Values running low

A quick comparison at 21Z reveals that Merged TPW Composite is running about .3 inches lower than Blended Total PW.

Four Views of TPW

After making some adjustments to the color scaling, we're able to mix model and analysis products of TPW.   The GOM was mostly clear, while clouds covered most of the land.  A very moist airmass was onshore, the Hammond LA GPS site measured 2.25" of TPW.
The GFS and HRRR forecasts both indicated this maximum.  The All-Sky LAP also did well, although it's field is a reflection of the good GFS forecast.  The Merged TPW did not generate these very large purple values (> 2" of TPW) except in a very small area.  The polar orbiter TPW retrievals used in Merged TPW must not have sampled these large values to advect in.  The operational blended TPW (which relies heavily on GPS sites for the analysis over land) also showed a maximum.  This points to the possibility that including the surface GPS network into Merged TPW and All-Sky LAP might be a way to increase the precision of these analyses.

Cloud Mask from CIRA Merged TPW (blue = clear; yellow = cloudy)

[caption id="attachment_16647" align="alignnone" width="1422"]
Four Views of TPW along the Gulf Coast at 19 UTC 09 May 2019: Upper Left: CIRA Merged TPW: Upper Right: All-Sky LAP. Lower Left: GFS 6 hour forecast @ 18 Z, Lower Right: HRRR 1 hour forecast @ 19 Z.

Analyses and forecasts all agreed well on the drier air over the central GOM.

JohnF

Comparison of ATPW and Blended TPW

I was finally able to take a look the ATPW (top left) and compare it with the operational blended TPW (top right). My first impression was that both products show similar large scale patterns with a large plume of moisture extending from the Gulf of Mexico into the Ohio River Valley. The ATPW also tends to show a little more detail in the moisture field compared to the blended TPW.

At 15Z ATPW shows an area of lower moisture over the Texas Gulf coast which is sort of fills in by 17Z, likely due to upstream moisture being advected into the area. In contrast, this moisture is continuously present in the blended TPW. ATPW generally had PWATs around 1.5 in, while the blended TPW had PWATs around 1.7-1.8 in. In contrast, 12Z RAOBs along the coast had PWATs that ranged from 1.6 inches at KBRO to around 1.8 at KLCH. These values seems to match better with the blended TPW product. I suspect that the upstream convection over Louisiana and lingering clouds over the coast impacted the ATPW that was corrected in the blended TPW.

TPW Differences Along Dryline

The CIRA Merged TPW and All Sky LAP in the TX panhandle show some differences in the vicinity of the dryline at 19 UTC on 7 May.  This is a cloudy region so the retrievals are either GFS (All Sky LAP) or advected polar microwave (Merged TPW),  The All Sky LAP TPW shows a moist panhandle, with values in green / yellow (1" or above).  The Merged TPW indicates lower values in green / purple, or about 0.7".  Surface dewpoints range from 59-65 F, indicating moist air ahead of the dryline.

Surface GPS observations from Suominet at three TX stations in the panhandle (Amarillo - 1.0", Borger - 1.0", and Canadian - 1.1") lean closer to the All Sky LAP analysis.  An hypothesis for the Merged TPW being low is dry retrievals from higher terrain to the west being advected into the moist sector.







JohnF

GOES All Sky LAP TPW and CIRA Merged TPW Cloud Mask Differences

At 22 UTC on 6 May 2019, the All Sky LAP and CIRA Merged TPW Data type products show differences in the cloud mask.  A shallow Cu field over NC / SC is indicated in GOES visible imagery,.  The data type masks of the two products (blue = clear; yellow / gray = clouds) show some clouds in the All Sky LAP mask, while the CIRA Merged TPW mask does not have these Cu detected.  This is likely due to the lower resolution (~ 15 km) of the GOES-16 TPW data used in Merged TPW versus the All Sky LAP resolution.







GOES-R TPW has a nominal resolution of 10 km.

JohnF

All-Sky LAP PW vs. Merged TPW

There has been considerable examination of the All-Sky LAP products (PW and CAPE) this week, and for good reason - they're quite good. I wanted to take a quick look at how the All-Sky LAP total PW compared with the merged TPW product. The All-Sky product is on the left and TPW on the right. I overlaid the 20z 1 hour RAP PW forecast for comparison. Ignoring the higher resolution of the All-Sky, the very broad distribution of enhanced and depressed values are similar in location between the two products. However, the TPW values are considerably lower than both the All-Sky and the RAP forecast. Further, pulling the 21z SPC mesoanalysis PW shows that the All-Sky tends to be the better of the two satellite products.

The TPW seems good for very broad generalizations, but if given a choice between the two in operations, I'll take the All-Sky, All-Day Every-Day.

--Stanley Cupp

Merged-TPW compared to Sfc obs

The merged-TPW product compared well to the surface obs with 1) the strong gradient along the dryline 2) the lower PWAT values behind the MCS and 3) axis of greater PWAT along the immediate Gulf Coast. Actual values however were too high in the dry air (MAF/DFW) and too low in the moist air (DRT/CRP). Values compared to 12Z soundings at BRO the best.



-- SCoulomb

PW Options

The AllSkyLAP Precipitable Water Product continues to be my favorite of the two options. There are too many unrealistic gradients that form within the composite merge. In this case notice how Texas seems to be especially prone to the errors where numerous sharp & and unrealistic gradients exist east of the dryline.


Top is the Blended PW & Bottom is the AllskyLAP

South Beach

All Sky Total PW vs CIRA Merged PW

Figure A (CIRA Merged PW)


Figure B (All Sky Total PW)


Figure C (All Sky Sfc-900mb PW)

Notice the big difference in Figure A compared to Figure B from DFW to OUN coverage area, Figure B with All Sky Total PW was handling the plume of moisture streaming northward much better.  This also correlates well to area of deep convection in Figure C in the deeper moisture region. 

-Jake Johnson