An Overview of Precipitation Type Forecasting Using NAM and SREF Data

1
An Overview of Precipitation Type Forecasting
Using NAM and SREF Data
Geoff Manikin Mesoscale Modeling Branch NCEP/EMC
Thanks to
Jun Du SAIC/GSO _at_ EMC Keith Brill
NOAA/NCEP/HPC Brad Ferrier SAIC/GSO _at_ EMC Pete
Manousos NOAA/NCEP/HPC
2
12 km
80 km
40 km
3

• Operational NCEP Precip Type Algorithm
• Based on Baldwin and Contorno (1994)
• Examines a vertical thermodynamic structure
  that a falling hydrometeor encounters as it falls
  to the ground
• first determines if precip is generated as
  supercooled water or ice and then uses decision
  tree approach
• identifies warm (gt 0ºC) and cold (lt 0ºC)
  layers
• Computes area between 0 and Tw to identify layers
• Diagnoses snow if
• Coldest T at any level with p gt 500 mb is ? -4C
  and
• Area between Tw and 4C lt 3000 deg m
• Diagnoses freezing rain if
• coldest T in saturated layer is gt -4C and Tsfc
  lt 0C OR
• area between 4C and Tw gt 3000 deg m

4

• One Significant Issue with the operational
  scheme
• it intentionally over-
• predicts ZR/IP to
• have high POD
• area in this sounding
• between Tw and 4 C
• is gt 3000
• The algorithm would
• predict ZR for this
• sounding

5
The goal offer alternative precipitation type
forecasts from the single operational NAM model
run.
The alternate solutions 1) revise the NCEP
scheme perform check on warm area
between Tw and OC 2) Ramer algorithm based
on the ice fraction of precip reaching
the ground 3) explicit frozen precipitation
variable from the model microphysics
6

• Percentage of Frozen Precipitation
• Explicit Field from the NAM Microphysics
  (upgrade 11/01)
• Gives of precip reaching the ground that is
  frozen not a probability!
• Ranges 0 (liquid) to 100 (frozen)
• High values indicate snow or sleet
• Low values indicate rain or freezing rain

7
- Web Page contains nine geographical regions
- Page is updated for 00/12z NAM cycles
8
Data available for all 1300 Eta BUFR locations
Click on a star (bypass option available on main
page)
9
Sample Precip Type Meteogram
2-m T, Td
10-m wind precip
Ramer
Alt. NCEP
of frozen pcp
NCEP
950-700mb temps
10
Philadelphia Verification
fcst
obs
11
Syracuse Meteograms and Verification
fcst
obs
12
Need to Offer Alternate Algorithms in Gridded Form
13
Run Multiple Algorithms on Single Run
14
Account for Initial Condition Uncertainty in
Addition to Algorithm Uncertainty w/ the SREF
15
How to Tally the Dominant Type for Entire
Ensemble?
Consider 5-member ensemble with all 5 algorithms
predicting rain or snow
Member Rain Snow
1 3 2
RAIN SNOW SNOW SNOW RAIN 3-2 SNOW!
2 2 3
3 2 3
4 2 3
5 5 0
14 11 RAIN!
16
SREF Mean Dominant P-Type
New Product
Current Product
17
Issues to be Resolved
Require 0.01 of mean precip to give a type?
18
Explicit Method Often Gives More ZR
Use 2-m T instead of skin T ?
19
Summary

• NCEP p-type scheme performs well but has biases
  that invite an approach using multiple algorithms
• Precip type meteograms are available at
• http//www.emc.ncep.noaa.gov/mmb/precip_typ
  e
• Dominant p-type field will be available from
  operational NAM this winter provide NCEP and
  Ramer algorithm output as well?
• Dominant p-type will also be available in the
  SREF mean file