# Presentation: 606983

## IMPACT OF TAMDAR ONRUC FORECASTS: CASE STUDIES 

-  Ed Szoke,*  Brian Jamison*, Bill Moninger, Stan Benjamin,
- Barry Schwartz, and Tracy Smith*
- NOAA/ESRL Global Systems Division
- *Joint collaboration with the Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO

## Overview

-  Purpose of this work: Assess the impact of TAMDAR data on RUC forecasts
- Subjective evaluation concentrating on short-range precipitation forecasts
- Case studies are important as it can be difficult to demonstrate impact with statistics alone
-  Models used
- Compare forecasts from identical RUC-20 km runs with and without TAMDAR
-  Procedure
- Focus on 6-h accumulated precipitation forecasts ending at 0000 and 0600 UTC (but other fields also examined)
- Can easily compare to 6-h NPVU precipitation estimates
- For 1800 UTC runs compare forecast soundings with observed soundings

##                  Overview of cases presented

-  Looked for systems moving across the main TAMDAR area
-  Case 1 - 4-5 October 2005
-  Heavy rains WI-MN with sharp southern boundary – 2 parts
-  Case 2 - 21 October 2005
-  Weak system moving across the Ohio Valley
-  Emphasis on ceiling and visibility forecasts
-  Case 3 - 8-9 December 2005
-  Snowstorm bringing heavy snow to much of Illinois; night of the aircraft accident at Midway
-  Case 4 – 20-21 January 2006
-  Band of heavy snow across northern Illinois extending into se Wisconsin

## Case 1: 4 Oct 05

- Heavy rain event
- over portions of MN
- and WI near a quasi-
- stationary front
- (focus on area within
- the oval).
- Shown is surface
- map with radar at
- 2100 UTC 4 Oct.

## Case 1: 4 Oct 05.  Observed 6h precipitation ending 0000 UTC 5 Oct

- Note the very sharp
- southern cutoff to the
- rainfall across WI.

## Case 1: 4 Oct 05

- Display of the TAMDAR flights that would have gone into the RUC
- 1800 UTC forecast – flights shown for the 1h period ending 18 UTC

## Case 1: 4 Oct 05.  Comparison of 6-h RUC precipitation forecasts with and without TAMDAR for runs initialized at 1800 UTC. 

- The forecast using TAMDAR produces heavier rains over northern WI in better
- agreement with the observed rainfall.  For this period both runs err in having some
- precipitation farther south across all of WI.

- Without TAMDAR

- With TAMDAR

- >0.25”

- >0.5”

- >1.0”

- >0.10”

##                   Case 1: Comparison of 6h forecast soundings 

- For both ILX (Lincoln/Peoria, IL) and DTW (Detroit, MI) the RUC forecast using TAMDAR is a much closer match to the observed sounding, especially at and below 700 mb.

- -RAOB (observed sounding) is in green
- -RUC run with TAMDAR is labeled “dev2” and is in magenta
- -RUC run that does not use TAMDAR is in black

**ILX (Lincoln, IL)**

**Detroit**

## Case 1-part 2:              5 Oct 05

- 6 h later the
- situation is much the
- same with heavy
- rains near and north
- of the stalled front.
- 0300 UTC 5 Oct
- time is shown.

## Case 1: 5 Oct 05.  Observed 6h precipitation ending 0600 UTC 5 Oct

- The very sharp
- southern edge
- to the rain is
- still present.
- Areas of 1.5 to
- 2 inches of
- rain in this 6-h
- period in
- northern WI.

## Case 1-part 2: 5 Oct 05.  Comparison of 6-h RUC precipitation forecasts with and without TAMDAR for runs initialized at 0000 UTC/5 Oct. 

- For this period an even better forecast by the RUC run using TAMDAR as the forecast
- captures both the heavy rain over nw WI as well as the sharp southern cutoff of rainfall in WI.

- Without TAMDAR

- With TAMDAR

- >0.10”

- >0.25”

- >0.5”

- >1.0”

- >2.0”

## Case 2- 21 Oct 05

- Weak storm system
- moving into the Ohio
- Valley with most of
- the rain north of an
- east-west warm front.
- The emphasis in this
- case will be on the
- forecasts of ceiling
- and visibility
- (expressed as a RUC
- field called “FAA
- rules”).

##  21 Oct 05 case

- 6-h forecasts from the 1800 UTC RUC runs with and
- without TAMDAR,
- valid 0000 UTC on
- 21 Oct 05 for FAA
- rules.
- The run that uses TAMDAR tended to have smaller forecast areas of poor ceiling and visibility (LIFR
- and IFR), in closer agreement to the 0000 UTC analyses.

**6h forecast without TAMDAR**

**Analysis without TAMDAR**

**Analysis with TAMDAR**

**6h forecast with TAMDAR**

**LIFR**

**IFR**

**MVFR**

**VFR**

## Case 2- 21 Oct 05

- 6-h sounding forecasts from the RUC
- 1800 UTC runs.  The colors are the
- same as earlier (black for w/o
- TAMDAR, magenta-with TAMDAR,
- green-observed sounding).

- BNA-Nashville

- DTW-Detroit

- The most dramatic forecast difference is at Detroit where the run with TAMDAR is much closer to the observed dewpoint below 800 mb.

## 6

- An area of around 6”
- to as much as 8” of
- snow fell in the
- Chicago area mainly
- between 1800 UTC/8
- Dec and 0600 UTC
- on 9 Dec 2005.

**6**

**6**

**6**

**4**

**6**

**4**

**5**

## Case 3- 8 Dec 05 Evening of the Chicago aircraft accident

- Maximum precipitation
- amounts for this period
- were generally around
- 0.50” in central IL to
- 0.50-0.60” in the
- Chicago area.

**0.35**

**0.35**

**0.35**

**0.35**

**0.42**

**0.42**

**0.28**

**0.28**

**0.28**

**0.21**

**0.21**

**0.14**

**0.14**

## 12-h RUC accumulated precipitation forecasts with and w/o TAMDAR  

- 12-h RUC accumulated precipitation forecasts with and w/o TAMDAR

- with TAMDAR

- without TAMDAR

- >0.10” >0.25”  >0.50”

- For this 12-h period ending at
- 0600 UTC there is little
- difference between the two
- forecasts, both being fairly
- accurate across IL.

## Detroit

- And not a lot of differences were
- found in the 6-h RUC sounding
- forecasts valid at 0000 UTC 9 Dec
- for this case.

- Peoria, IL

- Green Bay, WI

## Wisconsin

- Most of the snow fell between 18-06 UTC/20-21 Jan

**Illinois**

**6**

**3**

**3**

**3**

- 12

- 6

- 6

- 6

**3**

- RUC 1800 UTC run without TAMDAR:
- 12-h total snowfall ending 0600 UTC

- RUC 1800 UTC run with TAMDAR:
- 12-h total snowfall ending 0600 UTC

- >3

- >4

- >6

*better forecast*
*of 6”+ snow *
*area*

*snowfall*
*extends *
*into WI*

## Case 4-20-21 Jan 06: 6-h accumulated precip forecasts from 0000 UTC RUC runs

- The RUC runs initialized at 0000
- UTC also had better forecasts for
- the run that used TAMDAR.
- Note, for example, the better
- forecast for the heavy area of
- precipitation (mostly rain) in the
- highlighted area (oval) south of
- Chicago.

- Observed 6-h precipitation

- RUC run without TAMDAR

- RUC run with TAMDAR

##          Case 4- sounding comparisons for the 1800 UTC 6-h forecasts

-          Case 4- sounding comparisons for the 1800 UTC 6-h forecasts

- Green Bay, WI

- Peoria, IL

- black-without TAMDAR
- magenta-with TAMDAR
- green-observed sounding

- At Green Bay the RUC run using TAMDAR
- had a much better forecast of moisture in the
- 700-900 mb layer.  At other locations the
- forecasts from the two RUC runs were not
- that different.

## observations

- There are some differences in the forecasts between
- the RUC run that used TAMDAR and the run without
- TAMDAR (for example, in the two areas highlighted).
- Verification is mixed as to which forecast overall is
- better, though in these two areas a lean towards the
- run using TAMDAR.

**RUC with TAMDAR**

**RUC without TAMDAR**

- IFR

- LIFR

- MVFR

- VFR

- LIFR

- IFR

- MVFR

- VFR

## Summary

-  RUC forecasts comparing runs that used TAMDAR with runs that did not have TAMDAR were analyzed for several cases
*** ***With an emphasis on short term (6-h) forecasts that have impact on aviation concerns (precipitation and visibility and ceiling)
-  Principal findings
-  Clear differences were often seen between the two RUC forecasts
-  Examples were found of substantially better precipitation forecasts, both in amount and in not forecasting rain where it did not occur
-  Differences were often seen in the forecast soundings
-  For example, for the 4-5 October event comparison of forecast soundings with verifying soundings showed much better forecasts of humidity
-  Since the only difference between the runs was the TAMDAR data that adds humidity measurements, this is strong evidence of the value of TAMDAR
-  Interestingly, for a case where the forecasts were not that different, we did not see much difference in the forecast soundings
-  The better forecasts from the RUC runs with TAMDAR appear to also extend to other fields such as ceiling and visibility